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  • On the correlation between telomere shortening rate and life span [Letters (Online Only)]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Ion Udroiu

    Whittemore et al. (1) find significant correlations between maximum life span (MLS) and telomere shortening rate (TSR) in mammalian and avian species. This interesting study comes to the conclusion that “critical telomere shortening and the consequent onset of telomeric DNA damage and cellular senescence are a general determinant of species life span.” An important issue, however, has not been dealt with by the authors. The use of linear regressions (those used by the authors) assumes that samples are independent, but this is not the case in interspecies studies. In fact, the samples (i.e., the values for each species) have different grades of dependency, which derive from their phylogenetic relationship (2). This is why all tests should be performed using phylogenetic corrections, like phylogenetic-independent contrast (3 …

    更新日期:2020-01-26
  • Reply to Udroiu: Interesting mathematical analysis of telomere shortening rate and life span [Letters (Online Only)]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Kurt Whittemore, Maria A. Blasco

    We appreciate Udroiu’s letter titled “On the correlation between telomere shortening rate and life span” (1). We acknowledge that our conclusion that “critical telomere shortening and the consequent onset of telomeric DNA damage and cellular senescence are a general determinant of species life span” in our recent publication (2) may not be the full story, but this conclusion does appear to be a fairly straightforward and logical explanation for our observations. We also understand that the same data can be analyzed using many different methods. We thought it was important to keep …

    更新日期:2020-01-26
  • An ancestral anatomical and spatial bias for visually guided behavior [Letters (Online Only)]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Patrick Friedrich, Michel Thiebaut de Schotten, Stephanie J. Forkel, Martin Stacho, Henrietta Howells

    Human behavioral asymmetries are commonly studied in the context of structural cortical and connectional asymmetries. Within this framework, Sreenivasan and Sridharan (1) provide intriguing evidence of a relationship between visual asymmetries and the lateralization of superior colliculi connections—a phylogenetically older mesencephalic structure. Specifically, response facilitation for cued locations (i.e., choice bias) in the contralateral hemifield was associated with differences in the connectivity of the superior colliculus. Given that the superior colliculus has a structural homolog—the optic tectum—which can be traced across all Vertebrata, these results may have meaningful evolutionary ramifications.

    更新日期:2020-01-26
  • Reply to Friedrich et al.: Both genetic and environmental factors may contribute to laterality in mesencephalic connectivity and bias [Letters (Online Only)]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Varsha Sreenivasan, Devarajan Sridharan

    We thank Friedrich et al. (1) for their keen interest in our study (2) and for highlighting additional examples of asymmetries in visually guided behavior and brain connectivity across several vertebrate classes.

    更新日期:2020-01-26
  • Evolutionary dynamics of recent selection on cognitive abilities [Evolution]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Sara E. Miller, Andrew W. Legan, Michael T. Henshaw, Katherine L. Ostevik, Kieran Samuk, Floria M. K. Uy, Michael J. Sheehan

    Cognitive abilities can vary dramatically among species. The relative importance of social and ecological challenges in shaping cognitive evolution has been the subject of a long-running and recently renewed debate, but little work has sought to understand the selective dynamics underlying the evolution of cognitive abilities. Here, we investigate recent selection related to cognition in the paper wasp Polistes fuscatus—a wasp that has uniquely evolved visual individual recognition abilities. We generate high quality de novo genome assemblies and population genomic resources for multiple species of paper wasps and use a population genomic framework to interrogate the probable mode and tempo of cognitive evolution. Recent, strong, hard selective sweeps in P. fuscatus contain loci annotated with functions in long-term memory formation, mushroom body development, and visual processing, traits which have recently evolved in association with individual recognition. The homologous pathways are not under selection in closely related wasps that lack individual recognition. Indeed, the prevalence of candidate cognition loci within the strongest selective sweeps suggests that the evolution of cognitive abilities has been among the strongest selection pressures in P. fuscatus’ recent evolutionary history. Detailed analyses of selective sweeps containing candidate cognition loci reveal multiple cases of hard selective sweeps within the last few thousand years on de novo mutations, mainly in noncoding regions. These data provide unprecedented insight into some of the processes by which cognition evolves.

    更新日期:2020-01-26
  • ECM1 is an essential factor for the determination of M1 macrophage polarization in IBD in response to LPS stimulation [Immunology and Inflammation]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Yaguang Zhang, Xuezhen Li, Zhongguang Luo, Liyan Ma, Songling Zhu, Zhishuo Wang, Jing Wen, Shipeng Cheng, Wangpeng Gu, Qiaoshi Lian, Xinhao Zhao, Weiguo Fan, Zhiyang Ling, Jing Ye, Songguo Zheng, Dangsheng Li, Hongyan Wang, Jie Liu, Bing Sun

    Inflammatory bowel disease (IBD) comprises chronic relapsing disorders of the gastrointestinal tract characterized pathologically by intestinal inflammation and epithelial injury. Here, we uncover a function of extracellular matrix protein 1 (ECM1) in promoting the pathogenesis of human and mouse IBD. ECM1 was highly expressed in macrophages, particularly tissue-infiltrated macrophages under inflammatory conditions, and ECM1 expression was significantly induced during IBD progression. The macrophage-specific knockout of ECM1 resulted in increased arginase 1 (ARG1) expression and impaired polarization into the M1 macrophage phenotype after lipopolysaccharide (LPS) treatment. A mechanistic study showed that ECM1 can regulate M1 macrophage polarization through the granulocyte-macrophage colony-stimulating factor/STAT5 signaling pathway. Pathological changes in mice with dextran sodium sulfate-induced IBD were alleviated by the specific knockout of the ECM1 gene in macrophages. Taken together, our findings show that ECM1 has an important function in promoting M1 macrophage polarization, which is critical for controlling inflammation and tissue repair in the intestine.

    更新日期:2020-01-26
  • QnAs with Roger J. Davis
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Sandeep Ravindran

    The human body’s response to stress can contribute to metabolic dysfunction, inflammation, and cancer. Roger J. Davis has spent his career elucidating the mechanisms underlying such stress responses. A professor of molecular medicine at the University of Massachusetts Medical School at Worcester, Davis was elected to the National Academy of Sciences in 2018. His landmark work on stress-activated signaling includes deciphering the mechanisms of action and function of the first human stress-activated MAP kinase, the cJun NH2-terminal kinase (JNK), which is implicated in various disease processes. In his Inaugural Article (1), Davis and his colleagues investigated the role of IL-6–mediated signaling in chronic low-grade inflammation, which can lead to metabolic syndrome. He recently spoke to PNAS about his findings.

    更新日期:2020-01-26
  • Pseudomonas aeruginosa lasR mutant fitness in microoxia is supported by an Anr-regulated oxygen-binding hemerythrin [Microbiology]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Michelle E. Clay, John H. Hammond, Fangfang Zhong, Xiaolei Chen, Caitlin H. Kowalski, Alexandra J. Lee, Monique S. Porter, Thomas H. Hampton, Casey S. Greene, Ekaterina V. Pletneva, Deborah A. Hogan

    Pseudomonas aeruginosa strains with loss-of-function mutations in the transcription factor LasR are frequently encountered in the clinic and the environment. Among the characteristics common to LasR-defective (LasR−) strains is increased activity of the transcription factor Anr, relative to their LasR+ counterparts, in low-oxygen conditions. One of the Anr-regulated genes found to be highly induced in LasR− strains was PA14_42860 (PA1673), which we named mhr for microoxic hemerythrin. Purified P. aeruginosa Mhr protein contained the predicted di-iron center and bound molecular oxygen with an apparent Kd of ∼1 µM. Both Anr and Mhr were necessary for fitness in lasR+ and lasR mutant strains in colony biofilms grown in microoxic conditions, and the effects were more striking in the lasR mutant. Among genes in the Anr regulon, mhr was most closely coregulated with the Anr-controlled high-affinity cytochrome c oxidase genes. In the absence of high-affinity cytochrome c oxidases, deletion of mhr no longer caused a fitness disadvantage, suggesting that Mhr works in concert with microoxic respiration. We demonstrate that Anr and Mhr contribute to LasR− strain fitness even in biofilms grown in normoxic conditions. Furthermore, metabolomics data indicate that, in a lasR mutant, expression of Anr-regulated mhr leads to differences in metabolism in cells grown on lysogeny broth or artificial sputum medium. We propose that increased Anr activity leads to higher levels of the oxygen-binding protein Mhr, which confers an advantage to lasR mutants in microoxic conditions.

    更新日期:2020-01-26
  • EPA’s proposed transparency rule: Factors to consider, many; planets to live on, one [Editorials]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    David B. Allison, Harvey V. Fineberg

    So reads a T-shirt sold by the American Statistical Association. This pithy quip encapsulates a fundamental principle of science: Scientists rely on evidence rather than authority. Indeed, “doubt has been considered essential to science since long before the scientific method was established in the 17th century” (1). Scientists seek reasons for why something should be believed as true, and those reasons involve data, the methods used to collect those data, and the logic connecting those data to conclusions. All other things being equal, absent the opportunity to fully inspect the data, methods, and logical connections of a study, scientists are less able to judge the validity of conclusions or the truth of propositions drawn from a study. As many of us heard from our middle school mathematics teachers, it is important to “show all your work.” Generating and evaluating the scientific evidence to form conclusions about the truth of a proposition is fundamental to the work of science.

    更新日期:2020-01-26
  • Dysregulation of TLR9 in neonates leads to fatal inflammatory disease driven by IFN-{gamma} [Immunology and Inflammation]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Alison G. Stanbery, Zachary R. Newman, Gregory M. Barton

    Recognition of self-nucleic acids by innate immune receptors can lead to the development of autoimmune and/or autoinflammatory diseases. Elucidating mechanisms associated with dysregulated activation of specific receptors may identify new disease correlates and enable more effective therapies. Here we describe an aggressive in vivo model of Toll-like receptor (TLR) 9 dysregulation, based on bypassing the compartmentalized activation of TLR9 in endosomes, and use it to uncover unique aspects of TLR9-driven disease. By inducing TLR9 dysregulation at different stages of life, we show that while dysregulation in adult mice causes a mild systemic autoinflammatory disease, dysregulation of TLR9 early in life drives a severe inflammatory disease resulting in neonatal fatality. The neonatal disease includes some hallmarks of macrophage activation syndrome but is much more severe than previously described models. Unlike TLR7-mediated disease, which requires type I interferon (IFN) receptor signaling, TLR9-driven fatality is dependent on IFN-γ receptor signaling. NK cells are likely key sources of IFN-γ in this model. We identify populations of macrophages and Ly6Chi monocytes in neonates that express high levels of TLR9 and low levels of TLR7, which may explain why TLR9 dysregulation is particularly consequential early in life, while symptoms of TLR7 dysregulation take longer to manifest. Overall, this study demonstrates that inappropriate TLR9 responses can drive a severe autoinflammatory disease under homeostatic conditions and highlights differences in the diseases resulting from inappropriate activation of TLR9 and TLR7.

    更新日期:2020-01-26
  • Uncertainty in learning, choice, and visual fixation [Psychological and Cognitive Sciences]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Hrvoje Stojić, Jacob L. Orquin, Peter Dayan, Raymond J. Dolan, Maarten Speekenbrink

    Uncertainty plays a critical role in reinforcement learning and decision making. However, exactly how it influences behavior remains unclear. Multiarmed-bandit tasks offer an ideal test bed, since computational tools such as approximate Kalman filters can closely characterize the interplay between trial-by-trial values, uncertainty, learning, and choice. To gain additional insight into learning and choice processes, we obtained data from subjects’ overt allocation of gaze. The estimated value and estimation uncertainty of options influenced what subjects looked at before choosing; these same quantities also influenced choice, as additionally did fixation itself. A momentary measure of uncertainty in the form of absolute prediction errors determined how long participants looked at the obtained outcomes. These findings affirm the importance of uncertainty in multiple facets of behavior and help delineate its effects on decision making.

    更新日期:2020-01-26
  • Theory of the strange metal Sr3Ru2O7 [Physics]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Connie H. Mousatov, Erez Berg, Sean A. Hartnoll

    The bilayer perovskite Sr3Ru2O7 has been widely studied as a canonical strange metal. It exhibits T-linear resistivity and a T log(1/T) electronic specific heat in a field-tuned quantum critical fan. Criticality is known to occur in “hot” Fermi pockets with a high density of states close to the Fermi energy. We show that while these hot pockets occupy a small fraction of the Brillouin zone, they are responsible for the anomalous transport and thermodynamics of the material. Specifically, a scattering process in which two electrons from the large, “cold” Fermi surfaces scatter into one hot and one cold electron renders the ostensibly noncritical cold fermions a marginal Fermi liquid. From this fact the transport and thermodynamic phase diagram is reproduced in detail. Finally, we show that the same scattering mechanism into hot electrons that are instead localized near a 2D van Hove singularity explains the anomalous transport observed in strained Sr2RuO4.

    更新日期:2020-01-26
  • Combinatorial protein-protein interactions on a polymerizing scaffold [Biophysics and Computational Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Andrés Ortiz-Muñoz, Héctor F. Medina-Abarca, Walter Fontana

    Scaffold proteins organize cellular processes by bringing signaling molecules into interaction, sometimes by forming large signalosomes. Several of these scaffolds are known to polymerize. Their assemblies should therefore not be understood as stoichiometric aggregates, but as combinatorial ensembles. We analyze the combinatorial interaction of ligands loaded on polymeric scaffolds, in both a continuum and discrete setting, and compare it with multivalent scaffolds with fixed number of binding sites. The quantity of interest is the abundance of ligand interaction possibilities—the catalytic potential Q—in a configurational mixture. Upon increasing scaffold abundance, scaffolding systems are known to first increase opportunities for ligand interaction and then to shut them down as ligands become isolated on distinct scaffolds. The polymerizing system stands out in that the dependency of Q on protomer concentration switches from being dominated by a first order to a second order term within a range determined by the polymerization affinity. This behavior boosts Q beyond that of any multivalent scaffold system. In addition, the subsequent drop-off is considerably mitigated in that Q decreases with half the power in protomer concentration than for any multivalent scaffold. We explain this behavior in terms of how the concentration profile of the polymer-length distribution adjusts to changes in protomer concentration and affinity. The discrete case turns out to be similar, but the behavior can be exaggerated at small protomer numbers because of a maximal polymer size, analogous to finite-size effects in bond percolation on a lattice.

    更新日期:2020-01-26
  • Selectivity filter modalities and rapid inactivation of the hERG1 channel [Chemistry]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Williams E. Miranda, Kevin R. DeMarco, Jiqing Guo, Henry J. Duff, Igor Vorobyov, Colleen E. Clancy, Sergei Yu. Noskov

    The human ether-á-go-go–related gene (hERG1) channel conducts small outward K+ currents that are critical for cardiomyocyte membrane repolarization. The gain-of-function mutation N629D at the outer mouth of the selectivity filter (SF) disrupts inactivation and K+-selective transport in hERG1, leading to arrhythmogenic phenotypes associated with long-QT syndrome. Here, we combined computational electrophysiology with Markov state model analysis to investigate how SF-level gating modalities control selective cation transport in wild-type (WT) and mutant (N629D) hERG1 variants. Starting from the recently reported cryogenic electron microscopy (cryo-EM) open-state channel structure, multiple microseconds-long molecular-dynamics (MD) trajectories were generated using different cation configurations at the filter, voltages, electrolyte concentrations, and force-field parameters. Most of the K+ permeation events observed in hERG1-WT simulations occurred at microsecond timescales, influenced by the spontaneous dehydration/rehydration dynamics at the filter. The SF region displayed conductive, constricted, occluded, and dilated states, in qualitative agreement with the well-documented flickering conductance of hERG1. In line with mutagenesis studies, these gating modalities resulted from dynamic interaction networks involving residues from the SF, outer-mouth vestibule, P-helices, and S5–P segments. We found that N629D mutation significantly stabilizes the SF in a state that is permeable to both K+ and Na+, which is reminiscent of the SF in the nonselective bacterial NaK channel. Increasing the external K+ concentration induced “WT-like” SF dynamics in N629D, in qualitative agreement with the recovery of flickering currents in experiments. Overall, our findings provide an understanding of the molecular mechanisms controlling selective transport in K+ channels with a nonconventional SF sequence.

    更新日期:2020-01-26
  • Allosteric activation of MALT1 by its ubiquitin-binding Ig3 domain [Immunology and Inflammation]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Rebekka Schairer, Gareth Hall, Ming Zhang, Richard Cowan, Roberta Baravalle, Frederick W. Muskett, Peter J. Coombs, Chido Mpamhanga, Lisa R. Hale, Barbara Saxty, Justyna Iwaszkiewicz, Chantal Décaillet, Mai Perroud, Mark D. Carr, Margot Thome

    The catalytic activity of the protease MALT1 is required for adaptive immune responses and regulatory T (Treg)-cell development, while dysregulated MALT1 activity can lead to lymphoma. MALT1 activation requires its monoubiquitination on lysine 644 (K644) within the Ig3 domain, localized adjacent to the protease domain. The molecular requirements for MALT1 monoubiquitination and the mechanism by which monoubiquitination activates MALT1 had remained elusive. Here, we show that the Ig3 domain interacts directly with ubiquitin and that an intact Ig3-ubiquitin interaction surface is required for the conjugation of ubiquitin to K644. Moreover, by generating constitutively active MALT1 mutants that overcome the need for monoubiquitination, we reveal an allosteric communication between the ubiquitination site K644, the Ig3-protease interaction surface, and the active site of the protease domain. Finally, we show that MALT1 mutants that alter the Ig3-ubiquitin interface impact the biological response of T cells. Thus, ubiquitin binding by the Ig3 domain promotes MALT1 activation by an allosteric mechanism that is essential for its biological function.

    更新日期:2020-01-26
  • Precision medicine integrating whole-genome sequencing, comprehensive metabolomics, and advanced imaging [Genetics]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Ying-Chen Claire Hou, Hung-Chun Yu, Rick Martin, Elizabeth T. Cirulli, Natalie M. Schenker-Ahmed, Michael Hicks, Isaac V. Cohen, Thomas J. Jönsson, Robyn Heister, Lori Napier, Christine Leon Swisher, Saints Dominguez, Haibao Tang, Weizhong Li, Bradley A. Perkins, Jaime Barea, Christina Rybak, Emily Smith, Keegan Duchicela, Michael Doney, Pamila Brar, Nathaniel Hernandez, Ewen F. Kirkness, Andrew M. Kahn, J. Craig Venter, David S. Karow, C. Thomas Caskey

    Genome sequencing has established clinical utility for rare disease diagnosis. While increasing numbers of individuals have undergone elective genome sequencing, a comprehensive study surveying genome-wide disease-associated genes in adults with deep phenotyping has not been reported. Here we report the results of a 3-y precision medicine study with a goal to integrate whole-genome sequencing with deep phenotyping. A cohort of 1,190 adult participants (402 female [33.8%]; mean age, 54 y [range 20 to 89+]; 70.6% European) had whole-genome sequencing, and were deeply phenotyped using metabolomics, advanced imaging, and clinical laboratory tests in addition to family/medical history. Of 1,190 adults, 206 (17.3%) had at least 1 genetic variant with pathogenic (P) or likely pathogenic (LP) assessment that suggests a predisposition of genetic risk. A multidisciplinary clinical team reviewed all reportable findings for the assessment of genotype and phenotype associations, and 137 (11.5%) had genotype and phenotype associations. A high percentage of genotype and phenotype associations (>75%) was observed for dyslipidemia (n = 24), cardiomyopathy, arrhythmia, and other cardiac diseases (n = 42), and diabetes and endocrine diseases (n = 17). A lack of genotype and phenotype associations, a potential burden for patient care, was observed in 69 (5.8%) individuals with P/LP variants. Genomics and metabolomics associations identified 61 (5.1%) heterozygotes with phenotype manifestations affecting serum metabolite levels in amino acid, lipid and cofactor, and vitamin pathways. Our descriptive analysis provides results on the integration of whole-genome sequencing and deep phenotyping for clinical assessments in adults.

    更新日期:2020-01-26
  • Reassessing enzyme kinetics: Considering protease-as-substrate interactions in proteolytic networks [Systems Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Meghan C. Ferrall-Fairbanks, Chris A. Kieslich, Manu O. Platt

    Enzymes are catalysts in biochemical reactions that, by definition, increase rates of reactions without being altered or destroyed. However, when that enzyme is a protease, a subclass of enzymes that hydrolyze other proteins, and that protease is in a multiprotease system, protease-as-substrate dynamics must be included, challenging assumptions of enzyme inertness, shifting kinetic predictions of that system. Protease-on-protease inactivating hydrolysis can alter predicted protease concentrations used to determine pharmaceutical dosing strategies. Cysteine cathepsins are proteases capable of cathepsin cannibalism, where one cathepsin hydrolyzes another with substrate present, and misunderstanding of these dynamics may cause miscalculations of multiple proteases working in one proteolytic network of interactions occurring in a defined compartment. Once rates for individual protease-on-protease binding and catalysis are determined, proteolytic network dynamics can be explored using computational models of cooperative/competitive degradation by multiple proteases in one system, while simultaneously incorporating substrate cleavage. During parameter optimization, it was revealed that additional distraction reactions, where inactivated proteases become competitive inhibitors to remaining, active proteases, occurred, introducing another network reaction node. Taken together, improved predictions of substrate degradation in a multiple protease network were achieved after including reaction terms of autodigestion, inactivation, cannibalism, and distraction, altering kinetic considerations from other enzymatic systems, since enzyme can be lost to proteolytic degradation. We compiled and encoded these dynamics into an online platform (https://plattlab.shinyapps.io/catKLS/) for individual users to test hypotheses of specific perturbations to multiple cathepsins, substrates, and inhibitors, and predict shifts in proteolytic network reactions and system dynamics.

    更新日期:2020-01-26
  • Regulation of adipose tissue inflammation by interleukin 6 [Immunology and Inflammation]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Myoung Sook Han, Alexis White, Rachel J. Perry, Joao-Paulo Camporez, Juan Hidalgo, Gerald I. Shulman, Roger J. Davis

    Obesity is associated with a chronic state of low-grade inflammation and progressive tissue infiltration by immune cells and increased expression of inflammatory cytokines. It is established that interleukin 6 (IL6) regulates multiple aspects of metabolism, including glucose disposal, lipolysis, oxidative metabolism, and energy expenditure. IL6 is secreted by many tissues, but the role of individual cell types is unclear. We tested the role of specific cells using a mouse model with conditional expression of the Il6 gene. We found that IL6 derived from adipocytes increased, while IL6 derived from myeloid cells and muscle suppressed, macrophage infiltration of adipose tissue. These opposite actions were associated with a switch of IL6 signaling from a canonical mode (myeloid cells) to a noncanonical trans-signaling mode (adipocytes and muscle) with increased expression of the ADAM10/17 metalloprotease that promotes trans-signaling by the soluble IL6 receptor α. Collectively, these data demonstrate that the source of IL6 production plays a major role in the physiological regulation of metabolism.

    更新日期:2020-01-26
  • Conformational changes upon gating of KirBac1.1 into an open-activated state revealed by solid-state NMR and functional assays [Biophysics and Computational Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Reza Amani, Collin G. Borcik, Nazmul H. Khan, Derek B. Versteeg, Maryam Yekefallah, Hoa Q. Do, Heather R. Coats, Benjamin J. Wylie

    The conformational changes required for activation and K+ conduction in inward-rectifier K+ (Kir) channels are still debated. These structural changes are brought about by lipid binding. It is unclear how this process relates to fast gating or if the intracellular and extracellular regions of the protein are coupled. Here, we examine the structural details of KirBac1.1 reconstituted into both POPC and an activating lipid mixture of 3:2 POPC:POPG (wt/wt). KirBac1.1 is a prokaryotic Kir channel that shares homology with human Kir channels. We establish that KirBac1.1 is in a constitutively active state in POPC:POPG bilayers through the use of real-time fluorescence quenching assays and Förster resonance energy transfer (FRET) distance measurements. Multidimensional solid-state NMR (SSNMR) spectroscopy experiments reveal two different conformers within the transmembrane regions of the protein in this activating lipid environment, which are distinct from the conformation of the channel in POPC bilayers. The differences between these three distinct channel states highlight conformational changes associated with an open activation gate and suggest a unique allosteric pathway that ties the selectivity filter to the activation gate through interactions between both transmembrane helices, the turret, selectivity filter loop, and the pore helix. We also identify specific residues involved in this conformational exchange that are highly conserved among human Kir channels.

    更新日期:2020-01-26
  • Fast-freezing kinetics inside a droplet impacting on a cold surface [Applied Physical Sciences]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Pallav Kant, Robin B. J. Koldeweij, Kirsten Harth, Michiel A. J. van Limbeek, Detlef Lohse

    Freezing or solidification of impacting droplets is omnipresent in nature and technology, be it a rain droplet falling on a supercooled surface; in inkjet printing, where often molten wax is used; in additive manufacturing or metal-production processes; or in extreme ultraviolet lithography (EUV) for the chip production, where molten tin is used to generate the EUV radiation. For many of these industrial applications, a detailed understanding of the solidification process is essential. Here, by adopting an optical technique in the context of freezing—namely, total-internal reflection (TIR)—we elucidate the freezing kinetics during the solidification of a droplet while it impacts on an undercooled surface. We show that at sufficiently high undercooling, a peculiar freezing morphology exists that involves sequential advection of frozen fronts from the center of the droplet to its boundaries. This phenomenon is examined by combining elements of classical nucleation theory to the large-scale hydrodynamics on the droplet scale, bringing together two subfields which traditionally have been quite separated. Furthermore, we report a self-peeling phenomenon of a frozen splat that is driven by the existence of a transient crystalline state during solidification.

    更新日期:2020-01-26
  • Selective reduction of CO to acetaldehyde with CuAg electrocatalysts [Engineering]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Lei Wang, Drew C. Higgins, Yongfei Ji, Carlos G. Morales-Guio, Karen Chan, Christopher Hahn, Thomas F. Jaramillo

    Electrochemical CO reduction can serve as a sequential step in the transformation of CO2 into multicarbon fuels and chemicals. In this study, we provide insights on how to steer selectivity for CO reduction almost exclusively toward a single multicarbon oxygenate by carefully controlling the catalyst composition and its surrounding reaction conditions. Under alkaline reaction conditions, we demonstrate that planar CuAg electrodes can reduce CO to acetaldehyde with over 50% Faradaic efficiency and over 90% selectivity on a carbon basis at a modest electrode potential of −0.536 V vs. the reversible hydrogen electrode. The Faradaic efficiency to acetaldehyde was further enhanced to 70% by increasing the roughness factor of the CuAg electrode. Density functional theory calculations indicate that Ag ad-atoms on Cu weaken the binding energy of the reduced acetaldehyde intermediate and inhibit its further reduction to ethanol, demonstrating that the improved selectivity to acetaldehyde is due to the electronic effect from Ag incorporation. These findings will aid in the design of catalysts that are able to guide complex reaction networks and achieve high selectivity for the desired product.

    更新日期:2020-01-26
  • Reciprocity and behavioral heterogeneity govern the stability of social networks [Psychological and Cognitive Sciences]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Roslyn Dakin, T. Brandt Ryder

    The dynamics of social networks can determine the transmission of information, the spread of diseases, and the evolution of behavior. Despite this broad importance, a general framework for predicting social network stability has not been proposed. Here we present longitudinal data on the social dynamics of a cooperative bird species, the wire-tailed manakin, to evaluate the potential causes of temporal network stability. We find that when partners interact less frequently and when social connectedness increases, the network is subsequently less stable. Social connectivity was also negatively associated with the temporal persistence of coalition partnerships on an annual timescale. This negative association between connectivity and stability was surprising, especially given that individual manakins who were more connected also had more stable partnerships. This apparent paradox arises from a within-individual behavioral trade-off between partnership quantity and quality. Crucially, this trade-off is easily masked by behavioral variation among individuals. Using a simulation, we show that these results are explained by a simple model that combines among-individual behavioral heterogeneity and reciprocity within the network. As social networks become more connected, individuals face a trade-off between partnership quantity and maintenance. This model also demonstrates how among-individual behavioral heterogeneity, a ubiquitous feature of natural societies, can improve social stability. Together, these findings provide unifying principles that are expected to govern diverse social systems.

    更新日期:2020-01-26
  • FOXO1 and FOXO3 transcription factors have unique functions in meniscus development and homeostasis during aging and osteoarthritis [Medical Sciences]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Kwang Il Lee, Sungwook Choi, Tokio Matsuzaki, Oscar Alvarez-Garcia, Merissa Olmer, Shawn P. Grogan, Darryl D. D’Lima, Martin K. Lotz

    The objective of this study was to examine FoxO expression and FoxO function in meniscus. In menisci from human knee joints with osteoarthritis (OA), FoxO1 and 3 expression were significantly reduced compared with normal menisci from young and old normal donors. The expression of FoxO1 and 3 was also significantly reduced in mouse menisci during aging and OA induced by surgical meniscus destabilization or mechanical overuse. Deletion of FoxO1 and combined FoxO1, 3, and 4 deletions induced abnormal postnatal meniscus development in mice and these mutant mice spontaneously displayed meniscus pathology at 6 mo. Mice with Col2Cre-mediated deletion of FoxO3 or FoxO4 had normal meniscus development but had more severe aging-related damage. In mature AcanCreERT2 mice, the deletion of FoxO1, 3, and 4 aggravated meniscus lesions in all experimental OA models. FoxO deletion suppressed autophagy and antioxidant defense genes and altered several meniscus-specific genes. Expression of these genes was modulated by adenoviral FoxO1 in cultured human meniscus cells. These results suggest that FoxO1 plays a key role in meniscus development and maturation, and both FoxO1 and 3 support homeostasis and protect against meniscus damage in response to mechanical overuse and during aging and OA.

    更新日期:2020-01-26
  • IL-4 controls activated neutrophil Fc{gamma}R2b expression and migration into inflamed ȷoints [Immunology and Inflammation]
    PNAS (IF 9.580) Pub Date : 2020-01-24
    Sudeepta Kumar Panda, Gustaf Wigerblad, Long Jiang, Yanek Jiménez-Andrade, Vaishnavi Srinivasan Iyer, Yunbing Shen, Sanjaykumar V. Boddul, André Ortlieb Guerreiro-Cacais, Bruno Raposo, Zsolt Kasza, Fredrik Wermeling

    Neutrophils are the most abundant immune cells found in actively inflamed joints of patients with rheumatoid arthritis (RA), and most animal models for RA depend on neutrophils for the induction of joint inflammation. Exogenous IL-4 and IL-13 protect mice from antibody-mediated joint inflammation, although the mechanism is not understood. Neutrophils display a very strong basal expression of STAT6, which is responsible for signaling following exposure to IL-4 and IL-13. Still, the role of IL-4 and IL-13 in neutrophil biology has not been well studied. This can be explained by the low neutrophil surface expression of the IL-4 receptor α-chain (IL-4Rα), essential for IL-4– and IL-13–induced STAT6 signaling. Here we identify that colony stimulating factor 3 (CSF3), released during acute inflammation, mediates potent STAT3-dependent neutrophil IL-4Rα up-regulation during sterile inflammatory conditions. We further demonstrate that IL-4 limits neutrophil migration to inflamed joints, and that CSF3 combined with IL-4 or IL-13 results in a prominent neutrophil up-regulation of the inhibitory Fcγ receptor (FcγR2b). Taking these data together, we demonstrate that the IL-4 and CSF3 pathways are linked and play important roles in regulating proinflammatory neutrophil behavior.

    更新日期:2020-01-26
  • Polymeric sheet actuators with programmable bioinstructivity [Biophysics and Computational Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Zijun Deng, Weiwei Wang, Xun Xu, Oliver E. C. Gould, Karl Kratz, Nan Ma, Andreas Lendlein

    Stem cells are capable of sensing and processing environmental inputs, converting this information to output a specific cell lineage through signaling cascades. Despite the combinatorial nature of mechanical, thermal, and biochemical signals, these stimuli have typically been decoupled and applied independently, requiring continuous regulation by controlling units. We employ a programmable polymer actuator sheet to autonomously synchronize thermal and mechanical signals applied to mesenchymal stem cells (MSCs). Using a grid on its underside, the shape change of polymer sheet, as well as cell morphology, calcium (Ca2+) influx, and focal adhesion assembly, could be visualized and quantified. This paper gives compelling evidence that the temperature sensing and mechanosensing of MSCs are interconnected via intracellular Ca2+. Up-regulated Ca2+ levels lead to a remarkable alteration of histone H3K9 acetylation and activation of osteogenic related genes. The interplay of physical, thermal, and biochemical signaling was utilized to accelerate the cell differentiation toward osteogenic lineage. The approach of programmable bioinstructivity provides a fundamental principle for functional biomaterials exhibiting multifaceted stimuli on differentiation programs. Technological impact is expected in the tissue engineering of periosteum for treating bone defects.

    更新日期:2020-01-24
  • SYNPLA, a method to identify synapses displaying plasticity after learning [Neuroscience]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Kim Dore, Yvonne Pao, Jose Soria Lopez, Sage Aronson, Huiqing Zhan, Sanchari Ghosh, Sabina Merrill, Anthony M. Zador, Roberto Malinow, Justus M. Kebschull

    Which neural circuits undergo synaptic changes when an animal learns? Although it is widely accepted that changes in synaptic strength underlie many forms of learning and memory, it remains challenging to connect changes in synaptic strength at specific neural pathways to specific behaviors and memories. Here we introduce SYNPLA (synaptic proximity ligation assay), a synapse-specific, high-throughput, and potentially brain-wide method capable of detecting circuit-specific learning-induced synaptic plasticity.

    更新日期:2020-01-24
  • Molecular adaptations of the blood-brain barrier promote stress resilience vs. depression [Systems Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Katarzyna A. Dudek, Laurence Dion-Albert, Manon Lebel, Katherine LeClair, Simon Labrecque, Ellen Tuck, Carmen Ferrer Perez, Sam A. Golden, Carol Tamminga, Gustavo Turecki, Naguib Mechawar, Scott J. Russo, Caroline Menard

    Preclinical and clinical studies suggest that inflammation and vascular dysfunction contribute to the pathogenesis of major depressive disorder (MDD). Chronic social stress alters blood–brain barrier (BBB) integrity through loss of tight junction protein claudin-5 (cldn5) in male mice, promoting passage of circulating proinflammatory cytokines and depression-like behaviors. This effect is prominent within the nucleus accumbens, a brain region associated with mood regulation; however, the mechanisms involved are unclear. Moreover, compensatory responses leading to proper behavioral strategies and active resilience are unknown. Here we identify active molecular changes within the BBB associated with stress resilience that might serve a protective role for the neurovasculature. We also confirm the relevance of such changes to human depression and antidepressant treatment. We show that permissive epigenetic regulation of cldn5 expression and low endothelium expression of repressive cldn5-related transcription factor foxo1 are associated with stress resilience. Region- and endothelial cell-specific whole transcriptomic analyses revealed molecular signatures associated with stress vulnerability vs. resilience. We identified proinflammatory TNFα/NFκB signaling and hdac1 as mediators of stress susceptibility. Pharmacological inhibition of stress-induced increase in hdac1 activity rescued cldn5 expression in the NAc and promoted resilience. Importantly, we confirmed changes in HDAC1 expression in the NAc of depressed patients without antidepressant treatment in line with CLDN5 loss. Conversely, many of these deleterious CLDN5-related molecular changes were reduced in postmortem NAc from antidepressant-treated subjects. These findings reinforce the importance of considering stress-induced neurovascular pathology in depression and provide therapeutic targets to treat this mood disorder and promote resilience.

    更新日期:2020-01-24
  • Structural analysis of the intrinsically disordered splicing factor Spp2 and its binding to the DEAH-box ATPase Prp2 [Biophysics and Computational Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Florian Hamann, Andreas Schmitt, Filippo Favretto, Romina Hofele, Piotr Neumann, ShengQi Xiang, Henning Urlaub, Markus Zweckstetter, Ralf Ficner

    The spliceosome consists of five small RNAs and more than 100 proteins. Almost 50% of the human spliceosomal proteins were predicted to be intrinsically disordered or to contain disordered regions, among them the G-patch protein Spp2. The G-patch region of Spp2 binds to the DEAH-box ATPase Prp2, and both proteins together are essential for promoting the transition from the Bact to the catalytically active B* spliceosome. Here we show by circular dichroism and nuclear magnetic resonance (NMR) spectroscopy that Spp2 is intrinsically disordered in solution. Crystal structures of a complex consisting of Prp2-ADP and the G-patch domain of Spp2 demonstrate that the G-patch gains a defined fold when bound to Prp2. While the N-terminal region of the G-patch always folds into an α-helix in five different crystal structures, the C-terminal part is able to adopt two alternative conformations. NMR studies further revealed that the N-terminal part of the Spp2 G-patch, which is the most conserved region in different G-patch proteins, transiently samples helical conformations, possibly facilitating a conformational selection binding mechanism. The structural analysis unveils the role of conserved residues of the G-patch in the dynamic interaction mode of Spp2 with Prp2, which is vital to maintain the binding during the Prp2 domain movements needed for RNA translocation.

    更新日期:2020-01-24
  • Genome-scale transcriptional dynamics and environmental biosensing [Systems Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Garrett Graham, Nicholas Csicsery, Elizabeth Stasiowski, Gregoire Thouvenin, William H. Mather, Michael Ferry, Scott Cookson, Jeff Hasty

    Genome-scale technologies have enabled mapping of the complex molecular networks that govern cellular behavior. An emerging theme in the analyses of these networks is that cells use many layers of regulatory feedback to constantly assess and precisely react to their environment. The importance of complex feedback in controlling the real-time response to external stimuli has led to a need for the next generation of cell-based technologies that enable both the collection and analysis of high-throughput temporal data. Toward this end, we have developed a microfluidic platform capable of monitoring temporal gene expression from over 2,000 promoters. By coupling the “Dynomics” platform with deep neural network (DNN) and associated explainable artificial intelligence (XAI) algorithms, we show how machine learning can be harnessed to assess patterns in transcriptional data on a genome scale and identify which genes contribute to these patterns. Furthermore, we demonstrate the utility of the Dynomics platform as a field-deployable real-time biosensor through prediction of the presence of heavy metals in urban water and mine spill samples, based on the the dynamic transcription profiles of 1,807 unique Escherichia coli promoters.

    更新日期:2020-01-24
  • ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE 1 (ADPG1) releases latent defense signals in stems with reduced lignin content [Plant Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Lina Gallego-Giraldo, Chang Liu, Sara Pose-Albacete, Sivakumar Pattathil, Angelo Gabriel Peralta, Jenna Young, Jan Westpheling, Michael G. Hahn, Xiaolan Rao, J. Paul Knox, Barbara De Meester, Wout Boerjan, Richard A. Dixon

    There is considerable interest in engineering plant cell wall components, particularly lignin, to improve forage quality and biomass properties for processing to fuels and bioproducts. However, modifying lignin content and/or composition in transgenic plants through down-regulation of lignin biosynthetic enzymes can induce expression of defense response genes in the absence of biotic or abiotic stress. Arabidopsis thaliana lines with altered lignin through down-regulation of hydroxycinnamoyl CoA:shikimate/quinate hydroxycinnamoyl transferase (HCT) or loss of function of cinnamoyl CoA reductase 1 (CCR1) express a suite of pathogenesis-related (PR) protein genes. The plants also exhibit extensive cell wall remodeling associated with induction of multiple cell wall-degrading enzymes, a process which renders the corresponding biomass a substrate for growth of the cellulolytic thermophile Caldicellulosiruptor bescii lacking a functional pectinase gene cluster. The cell wall remodeling also results in the release of size- and charge-heterogeneous pectic oligosaccharide elicitors of PR gene expression. Genetic analysis shows that both in planta PR gene expression and release of elicitors are the result of ectopic expression in xylem of the gene ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE 1 (ADPG1), which is normally expressed during anther and silique dehiscence. These data highlight the importance of pectin in cell wall integrity and the value of lignin modification as a tool to interrogate the informational content of plant cell walls.

    更新日期:2020-01-24
  • Release of a disordered domain enhances HspB1 chaperone activity toward tau [Biochemistry]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Hannah E. R. Baughman, Thanh-Hau T. Pham, Chloe S. Adams, Abhinav Nath, Rachel E. Klevit

    Small heat shock proteins (sHSPs) are a class of ATP-independent molecular chaperones that play vital roles in maintaining protein solubility and preventing aberrant protein aggregation. They form highly dynamic, polydisperse oligomeric ensembles and contain long intrinsically disordered regions. Experimental challenges posed by these properties have greatly impeded our understanding of sHSP structure and mechanism of action. Here we characterize interactions between the human sHSP HspB1 (Hsp27) and microtubule-associated protein tau, which is implicated in multiple dementias, including Alzheimer’s disease. We show that tau binds both to a well-known binding groove within the structured alpha-crystallin domain (ACD) and to sites within the enigmatic, disordered N-terminal region (NTR) of HspB1. However, only interactions involving the NTR lead to productive chaperone activity, whereas ACD binding is uncorrelated with chaperone function. The tau-binding groove in the ACD also binds short hydrophobic regions within HspB1 itself, and HspB1 mutations that disrupt these intrinsic ACD–NTR interactions greatly enhance chaperone activity toward tau. This leads to a mechanism in which the release of the disordered NTR from a binding groove on the ACD enhances chaperone activity toward tau. The study advances understanding of the mechanisms by which sHSPs achieve their chaperone activity against amyloid-forming clients and how cells defend against pathological tau aggregation. Furthermore, the resulting mechanistic model points to ways in which sHSP chaperone activity may be increased, either by native factors within the cell or by therapeutic intervention.

    更新日期:2020-01-24
  • Skin permeability barrier formation by the ichthyosis-causative gene FATP4 through formation of the barrier lipid {omega}-O-acylceramide [Biochemistry]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Haruka Yamamoto, Miku Hattori, Walee Chamulitrat, Yusuke Ohno, Akio Kihara

    The epidermis-specific lipid acylceramide plays a pivotal role in the formation of the permeability barrier in the skin; abrogation of its synthesis causes the skin disorder ichthyosis. However, the acylceramide synthetic pathway has not yet been fully elucidated: Namely, the acyl-CoA synthetase (ACS) involved in this pathway remains to be identified. Here, we hypothesized it to be encoded by FATP4/ACSVL4, the causative gene of ichthyosis prematurity syndrome (IPS). In vitro experiments revealed that FATP4 exhibits ACS activity toward an ω-hydroxy fatty acid (FA), an intermediate of the acylceramide synthetic pathway. Fatp4 knockout (KO) mice exhibited severe skin barrier dysfunction and morphological abnormalities in the epidermis. The total amount of acylceramide in Fatp4 KO mice was reduced to ∼10% of wild-type mice. Decreased levels and shortening of chain lengths were observed in the saturated, nonacylated ceramides. FA levels were not decreased in the epidermis of Fatp4 KO mice. The expression levels of the FA elongase Elovl1 were reduced in Fatp4 KO epidermis, partly accounting for the reduction and shortening of saturated, nonacylated ceramides. A decrease in acylceramide levels was also observed in human keratinocytes with FATP4 knockdown. From these results, we conclude that skin barrier dysfunction observed in IPS patients and Fatp4 KO mice is caused mainly by reduced acylceramide production. Our findings further elucidate the molecular mechanism governing acylceramide synthesis and IPS pathology.

    更新日期:2020-01-24
  • Structural instability and divergence from conserved residues underlie intracellular retention of mammalian odorant receptors [Cell Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Kentaro Ikegami, Claire A. de March, Maira H. Nagai, Soumadwip Ghosh, Matthew Do, Ruchira Sharma, Elise S. Bruguera, Yueyang Eric Lu, Yosuke Fukutani, Nagarajan Vaidehi, Masafumi Yohda, Hiroaki Matsunami

    Mammalian odorant receptors are a diverse and rapidly evolving set of G protein-coupled receptors expressed in olfactory cilia membranes. Most odorant receptors show little to no cell surface expression in nonolfactory cells due to endoplasmic reticulum retention, which has slowed down biochemical studies. Here we provide evidence that structural instability and divergence from conserved residues of individual odorant receptors underlie intracellular retention using a combination of large-scale screening of odorant receptors cell surface expression in heterologous cells, point mutations, structural modeling, and machine learning techniques. We demonstrate the importance of conserved residues by synthesizing consensus odorant receptors that show high levels of cell surface expression similar to conventional G protein-coupled receptors. Furthermore, we associate in silico structural instability with poor cell surface expression using molecular dynamics simulations. We propose an enhanced evolutionary capacitance of olfactory sensory neurons that enable the functional expression of odorant receptors with cryptic mutations.

    更新日期:2020-01-24
  • Wireless, battery-free subdermally implantable photometry systems for chronic recording of neural dynamics [Neuroscience]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Alex Burton, Sofian N. Obaid, Abraham Vázquez-Guardado, Matthew B. Schmit, Tucker Stuart, Le Cai, Zhiyuan Chen, Irawati Kandela, Chad R. Haney, Emily A. Waters, Haijiang Cai, John A. Rogers, Luyao Lu, Philipp Gutruf

    Recording cell-specific neuronal activity while monitoring behaviors of freely moving subjects can provide some of the most significant insights into brain function. Current means for monitoring calcium dynamics in genetically targeted populations of neurons rely on delivery of light and recording of fluorescent signals through optical fibers that can reduce subject mobility, induce motion artifacts, and limit experimental paradigms to isolated subjects in open, two-dimensional (2D) spaces. Wireless alternatives eliminate constraints associated with optical fibers, but their use of head stages with batteries adds bulk and weight that can affect behaviors, with limited operational lifetimes. The systems introduced here avoid drawbacks of both types of technologies, by combining highly miniaturized electronics and energy harvesters with injectable photometric modules in a class of fully wireless, battery-free photometer that is fully implantable subdermally to allow for the interrogation of neural dynamics in freely behaving subjects, without limitations set by fiber optic tethers or operational lifetimes constrained by traditional power supplies. The unique capabilities of these systems, their compatibility with magnetic resonant imaging and computed tomography and the ability to manufacture them with techniques in widespread use for consumer electronics, suggest a potential for broad adoption in neuroscience research.

    更新日期:2020-01-24
  • A molecular basis for the T cell response in HLA-DQ2.2 mediated celiac disease [Immunology and Inflammation]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Yi Tian Ting, Shiva Dahal-Koirala, Hui Shi Keshia Kim, Shuo-Wang Qiao, Ralf S. Neumann, Knut E. A. Lundin, Jan Petersen, Hugh H. Reid, Ludvig M. Sollid, Jamie Rossjohn

    The highly homologous human leukocyte antigen (HLA)-DQ2 molecules, HLA-DQ2.5 and HLA-DQ2.2, are implicated in the pathogenesis of celiac disease (CeD) by presenting gluten peptides to CD4+ T cells. However, while HLA-DQ2.5 is strongly associated with disease, HLA-DQ2.2 is not, and the molecular basis underpinning this differential disease association is unresolved. We here provide structural evidence for how the single polymorphic residue (HLA-DQ2.5-Tyr22α and HLA-DQ2.2-Phe22α) accounts for HLA-DQ2.2 additionally requiring gluten epitopes possessing a serine at the P3 position of the peptide. In marked contrast to the biased T cell receptor (TCR) usage associated with HLA-DQ2.5–mediated CeD, we demonstrate with extensive single-cell sequencing that a diverse TCR repertoire enables recognition of the immunodominant HLA-DQ2.2-glut-L1 epitope. The crystal structure of two CeD patient-derived TCR in complex with HLA-DQ2.2 and DQ2.2-glut-L1 (PFSEQEQPV) revealed a docking strategy, and associated interatomic contacts, which was notably distinct from the structures of the TCR:HLA-DQ2.5:gliadin epitope complexes. Accordingly, while the molecular surfaces of the antigen-binding clefts of HLA-DQ2.5 and HLA-DQ2.2 are very similar, differences in the nature of the peptides presented translates to differences in responding T cell repertoires and the nature of engagement of the respective antigen-presenting molecules, which ultimately is associated with differing disease penetrance.

    更新日期:2020-01-24
  • GABA-mediated tonic inhibition differentially modulates gain in functional subtypes of cortical interneurons [Neuroscience]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Alexander Bryson, Robert John Hatch, Bas-Jan Zandt, Christian Rossert, Samuel F. Berkovic, Christopher A. Reid, David B. Grayden, Sean L. Hill, Steven Petrou

    The binding of GABA (γ-aminobutyric acid) to extrasynaptic GABAA receptors generates tonic inhibition that acts as a powerful modulator of cortical network activity. Despite GABA being present throughout the extracellular space of the brain, previous work has shown that GABA may differentially modulate the excitability of neuron subtypes according to variation in chloride gradient. Here, using biophysically detailed neuron models, we predict that tonic inhibition can differentially modulate the excitability of neuron subtypes according to variation in electrophysiological properties. Surprisingly, tonic inhibition increased the responsiveness (or gain) in models with features typical for somatostatin interneurons but decreased gain in models with features typical for parvalbumin interneurons. Patch-clamp recordings from cortical interneurons supported these predictions, and further in silico analysis was then performed to seek a putative mechanism underlying gain modulation. We found that gain modulation in models was dependent upon the magnitude of tonic current generated at depolarized membrane potential—a property associated with outward rectifying GABAA receptors. Furthermore, tonic inhibition produced two biophysical changes in models of relevance to neuronal excitability: 1) enhanced action potential repolarization via increased current flow into the dendritic compartment, and 2) reduced activation of voltage-dependent potassium channels. Finally, we show theoretically that reduced potassium channel activation selectively increases gain in models possessing action potential dynamics typical for somatostatin interneurons. Potassium channels in parvalbumin-type models deactivate rapidly and are unavailable for further modulation. These findings show that GABA can differentially modulate interneuron excitability and suggest a mechanism through which this occurs in silico via differences of intrinsic electrophysiological properties.

    更新日期:2020-01-24
  • Designing effective control of dengue with combined interventions [Systems Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-23
    Thomas J. Hladish, Carl A. B. Pearson, Kok Ben Toh, Diana Patricia Rojas, Pablo Manrique-Saide, Gonzalo M. Vazquez-Prokopec, M. Elizabeth Halloran, Ira M. Longini

    Viruses transmitted by Aedes mosquitoes, such as dengue, Zika, and chikungunya, have expanding ranges and seem unabated by current vector control programs. Effective control of these pathogens likely requires integrated approaches. We evaluated dengue management options in an endemic setting that combine novel vector control and vaccination using an agent-based model for Yucatán, Mexico, fit to 37 y of data. Our intervention models are informed by targeted indoor residual spraying (TIRS) experiments; trial outcomes and World Health Organization (WHO) testing guidance for the only licensed dengue vaccine, CYD-TDV; and preliminary results for in-development vaccines. We evaluated several implementation options, including varying coverage levels; staggered introductions; and a one-time, large-scale vaccination campaign. We found that CYD-TDV and TIRS interfere: while the combination outperforms either alone, performance is lower than estimated from their separate benefits. The conventional model hypothesized for in-development vaccines, however, performs synergistically with TIRS, amplifying effectiveness well beyond their independent impacts. If the preliminary performance by either of the in-development vaccines is upheld, a one-time, large-scale campaign followed by routine vaccination alongside aggressive new vector control could enable short-term elimination, with nearly all cases avoided for a decade despite continuous dengue reintroductions. If elimination is impracticable due to resource limitations, less ambitious implementations of this combination still produce amplified, longer-lasting effectiveness over single-approach interventions.

    更新日期:2020-01-24
  • Island of hope for the threatened Nassau grouper [Commentaries]
    PNAS (IF 9.580) Pub Date : 2020-01-22
    Yvonne Sadovy de Mitcheson

    In January 1971, a young biologist braved strong currents to dive on a massive spawning aggregation (gathering of reproductive adults) of Nassau grouper (family Epinephelidae) at Cat Cay in The Bahamas. The paper he published was the first-ever eye-witness account in the scientific literature describing a spectacular gathering of 30,000 to 100,000 large adult Nassau grouper (Epinephelus striatus) preparing to spawn (1). Historically, this grouper was among the most important fishery species in the tropical western Atlantic, with earlier accounts also documenting abundance during its reproductive season (2⇓⇓⇓–6). In 2003, barely 30 y after Lavett-Smith’s (1) account, the species was listed as threatened on the International Union for Conservation of Nature (IUCN) Red List. By 2016 it was included on the United States Endangered Species List and in 2017 was added to Annex III of the Specially Protected Areas and Wildlife (SPAW) protocol. All listings were unusual for a commercial reef fish and highlighted the growing crisis for this iconic species brought about by uncontrolled fishing on its spawning aggregations and a many-hundredfold decline in production from historic levels.

    更新日期:2020-01-23
  • Requirement for epithelial p38{alpha} in KRAS-driven lung tumor progression [Medical Sciences]
    PNAS (IF 9.580) Pub Date : 2020-01-22
    Jessica Vitos-Faleato, Sebastián M. Real, Nuria Gutierrez-Prat, Alberto Villanueva, Elisabet Llonch, Matthias Drosten, Mariano Barbacid, Angel R. Nebreda

    Malignant transformation entails important changes in the control of cell proliferation through the rewiring of selected signaling pathways. Cancer cells then become very dependent on the proper function of those pathways, and their inhibition offers therapeutic opportunities. Here we identify the stress kinase p38α as a nononcogenic signaling molecule that enables the progression of KrasG12V-driven lung cancer. We demonstrate in vivo that, despite acting as a tumor suppressor in healthy alveolar progenitor cells, p38α contributes to the proliferation and malignization of lung cancer epithelial cells. We show that high expression levels of p38α correlate with poor survival in lung adenocarcinoma patients, and that genetic or chemical inhibition of p38α halts tumor growth in lung cancer mouse models. Moreover, we reveal a lung cancer epithelial cell-autonomous function for p38α promoting the expression of TIMP-1, which in turn stimulates cell proliferation in an autocrine manner. Altogether, our results suggest that epithelial p38α promotes KrasG12V-driven lung cancer progression via maintenance of cellular self-growth stimulatory signals.

    更新日期:2020-01-23
  • Plasmodium falciparum evades immunity of anopheline mosquitoes by interacting with a Pfs47 midgut receptor [Microbiology]
    PNAS (IF 9.580) Pub Date : 2020-01-22
    Alvaro Molina-Cruz, Gaspar E. Canepa, Thiago Luiz Alves e Silva, Adeline E. Williams, Simardeep Nagyal, Lampouguin Yenkoidiok-Douti, Bianca M. Nagata, Eric Calvo, John Andersen, Martin J. Boulanger, Carolina Barillas-Mury

    The surface protein Pfs47 allows Plasmodium falciparum parasites to survive and be transmitted by making them “undetectable” to the mosquito immune system. P. falciparum parasites express Pfs47 haplotypes compatible with their sympatric vectors, while those with incompatible haplotypes are eliminated by the mosquito. We proposed that Pfs47 serves as a “key” that mediates immune evasion by interacting with a mosquito receptor “the lock,” which differs in evolutionarily divergent anopheline mosquitoes. Recombinant Pfs47 (rPfs47) was used to identify the mosquito Pfs47 receptor protein (P47Rec) using far-Western analysis. rPfs47 bound to a single 31-kDa band and the identity of this protein was determined by mass spectrometry. The mosquito P47Rec has two natterin-like domains and binds to Pfs47 with high affinity (17 to 32 nM). P47Rec is a highly conserved protein with submicrovillar localization in midgut cells. It has structural homology to a cytoskeleton-interacting protein and accumulates at the site of ookinete invasion. Silencing P47Rec expression reduced P. falciparum infection, indicating that the interaction of Pfs47 with the receptor is critical for parasite survival. The binding specificity of P47Rec from distant anophelines (Anopheles gambiae, Anopheles dirus, and Anopheles albimanus) with Pfs47-Africa (GB4) and Pfs47-South America (7G8) haplotypes was evaluated, and it is in agreement with the previously documented compatibility between P. falciparum parasites expressing different Pfs47 haplotypes and these three anopheline species. Our findings give further support to the role of Pfs47 in the adaptation of P. falciparum to different vectors.

    更新日期:2020-01-23
  • Arrhythmogenic late Ca2+ sparks in failing heart cells and their control by action potential configuration [Physiology]
    PNAS (IF 9.580) Pub Date : 2020-01-22
    Ewan D. Fowler, Nan Wang, Melanie Hezzell, Guillaume Chanoit, Jules C. Hancox, Mark B. Cannell

    Sudden death in heart failure patients is a major clinical problem worldwide, but it is unclear how arrhythmogenic early afterdepolarizations (EADs) are triggered in failing heart cells. To examine EAD initiation, high-sensitivity intracellular Ca2+ measurements were combined with action potential voltage clamp techniques in a physiologically relevant heart failure model. In failing cells, the loss of Ca2+ release synchrony at the start of the action potential leads to an increase in number of microscopic intracellular Ca2+ release events (“late” Ca2+ sparks) during phase 2–3 of the action potential. These late Ca2+ sparks prolong the Ca2+ transient that activates contraction and can trigger propagating microscopic Ca2+ ripples, larger macroscopic Ca2+ waves, and EADs. Modification of the action potential to include steps to different potentials revealed the amount of current generated by these late Ca2+ sparks and their (subsequent) spatiotemporal summation into Ca2+ ripples/waves. Comparison of this current to the net current that causes action potential repolarization shows that late Ca2+ sparks provide a mechanism for EAD initiation. Computer simulations confirmed that this forms the basis of a strong oscillatory positive feedback system that can act in parallel with other purely voltage-dependent ionic mechanisms for EAD initiation. In failing heart cells, restoration of the action potential to a nonfailing phase 1 configuration improved the synchrony of excitation–contraction coupling, increased Ca2+ transient amplitude, and suppressed late Ca2+ sparks. Therapeutic control of late Ca2+ spark activity may provide an additional approach for treating heart failure and reduce the risk for sudden cardiac death.

    更新日期:2020-01-23
  • Guided transition waves in multistable mechanical metamaterials [Engineering]
    PNAS (IF 9.580) Pub Date : 2020-01-22
    Lishuai Jin, Romik Khajehtourian, Jochen Mueller, Ahmad Rafsanjani, Vincent Tournat, Katia Bertoldi, Dennis M. Kochmann

    Transition fronts, moving through solids and fluids in the form of propagating domain or phase boundaries, have recently been mimicked at the structural level in bistable architectures. What has been limited to simple one-dimensional (1D) examples is here cast into a blueprint for higher dimensions, demonstrated through 2D experiments and described by a continuum mechanical model that draws inspiration from phase transition theory in crystalline solids. Unlike materials, the presented structural analogs admit precise control of the transition wave’s direction, shape, and velocity through spatially tailoring the underlying periodic network architecture (locally varying the shape or stiffness of the fundamental building blocks, and exploiting interactions of transition fronts with lattice defects such as point defects and free surfaces). The outcome is a predictable and programmable strongly nonlinear metamaterial motion with potential for, for example, propulsion in soft robotics, morphing surfaces, reconfigurable devices, mechanical logic, and controlled energy absorption.

    更新日期:2020-01-23
  • Dynamical control by water at a molecular level in protein dimer association and dissociation [Chemistry]
    PNAS (IF 9.580) Pub Date : 2020-01-22
    Puja Banerjee, Biman Bagchi

    Water, often termed as the “lubricant of life,” is expected to play an active role in navigating protein dissociation–association reactions. In order to unearth the molecular details, we first compute the free-energy surface (FES) of insulin dimer dissociation employing metadynamics simulation, and then carry out analyses of insulin dimerization and dissociation using atomistic molecular-dynamics simulation in explicit water. We select two sets of initial configurations from 1) the dissociated state and 2) the transition state, and follow time evolution using several long trajectories (∼1–2 μs). During the process we not only monitor configuration of protein monomers, but also the properties of water. Although the equilibrium structural properties of water between the two monomers approach bulklike characteristics at a separation distance of ∼5 nm, the dynamics differ considerably. The complex association process is observed to be accompanied by several structural and dynamical changes of the system, such as large-scale correlated water density fluctuations, coupled conformational fluctuation of protein monomers, a dewettinglike transition with the change of intermonomeric distance RMM from ∼4 to ∼2 nm, orientation of monomers and hydrophobic hydration in the monomers. A quasistable, solvent-shared, protein monomer pair (SSPMP) forms at around 2 nm during association process which is a local free-energy minimum having ∼50–60% of native contacts. Simulations starting with arrangements sampled from the transition state (TS) of the dimer dissociation reveal that the final outcome depends on relative orientation of the backbone in the “hotspot” region.

    更新日期:2020-01-23
  • Identifying determinants of bacterial fitness in a model of human gut microbial succession [Microbiology]
    PNAS (IF 9.580) Pub Date : 2020-01-22
    Lihui Feng, Arjun S. Raman, Matthew C. Hibberd, Jiye Cheng, Nicholas W. Griffin, Yangqing Peng, Semen A. Leyn, Dmitry A. Rodionov, Andrei L. Osterman, Jeffrey I. Gordon

    Human gut microbiota development has been associated with healthy growth but understanding the determinants of community assembly and composition is a formidable challenge. We cultured bacteria from serially collected fecal samples from a healthy infant; 34 sequenced strains containing 103,102 genes were divided into two consortia representing earlier and later stages in community assembly during the first six postnatal months. The two consortia were introduced alone (singly), or sequentially in different order, or simultaneously into young germ-free mice fed human infant formula. The pattern of fitness of bacterial strains observed across the different colonization conditions indicated that later-phase strains substantially outcompete earlier-phase strains, although four early-phase members persist. Persistence was not determined by order of introduction, suggesting that priority effects are not prominent in this model. To characterize succession in the context of the metabolic potential of consortium members, we performed in silico reconstructions of metabolic pathways involved in carbohydrate utilization and amino acid and B-vitamin biosynthesis, then quantified the fitness (abundance) of strains in serially collected fecal samples and their transcriptional responses to different histories of colonization. Applying feature-reduction methods disclosed a set of metabolic pathways whose presence and/or expression correlates with strain fitness and that enable early-stage colonizers to survive during introduction of later colonizers. The approach described can be used to test the magnitude of the contribution of identified metabolic pathways to fitness in different community contexts, study various ecological processes thought to govern community assembly, and facilitate development of microbiota-directed therapeutics.

    更新日期:2020-01-23
  • Tool-using puffins prickle the puzzle of cognitive evolution [Commentaries]
    PNAS (IF 9.580) Pub Date : 2020-01-22
    Auguste M. P. von Bayern, Ivo Jacobs, Mathias Osvath

    In PNAS, Fayet et al. (1) report on two cases of tool use in a seabird. In two distant populations they recorded Arctic puffins (Fratercula arctica) using sticks to scratch themselves (Fig. 1). The documentation of tool use in this species expands the ever-growing list of tool-using birds through rare observations under natural conditions. Although it is neither the first observation of tool use in wild seabirds, nor the first of stick-tool use outside of a foraging context in wild birds, these findings contribute to the debate on the evolutionary and cognitive origins of tool use.

    更新日期:2020-01-23
  • Correction for Hu et al., Structural bases for F plasmid conjugation and F pilus biogenesis in Escherichia coli [Correction]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    National Academy of Sciences

    MICROBIOLOGY Correction for “Structural bases for F plasmid conjugation and F pilus biogenesis in Escherichia coli,” …

    更新日期:2020-01-22
  • Correction for Porter et al., Epithelial to mesenchymal plasticity and differential response to therapies in pancreatic ductal adenocarcinoma [Corrections]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    National Academy of Sciences

    MEDICAL SCIENCES Correction for “Epithelial to mesenchymal plasticity and differential response to therapies in pancreatic ductal adenocarcinoma,” by Rebecca L. Porter, Neelima K. C. Magnus, Vishal Thapar, Robert Morris, Annamaria Szabolcs, Azfar Neyaz, Anupriya S. Kulkarni, Eric Tai, Abhijit Chougule, Alessandra Hillis, Gabriel Golczer, …

    更新日期:2020-01-22
  • Correction for Mann, Core Concept: To improve weather and climate models, researchers are chasing atmospheric gravity waves [Corrections]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    National Academy of Sciences

    CORE CONCEPTS Correction for “Core Concept: To improve weather and climate models, researchers are chasing atmospheric gravity waves,” by Adam Mann, …

    更新日期:2020-01-22
  • Correction for Perkins, Core Concept: Albedo is a simple concept that plays complicated roles in climate and astronomy [Corrections]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    National Academy of Sciences

    CORE CONCEPTS Correction for “Core Concept: Albedo is a simple concept that plays complicated roles in climate and …

    更新日期:2020-01-22
  • A randomized trial of a lab-embedded discourse intervention to improve research ethics
    PNAS (IF 9.580) Pub Date : 2020-01-21
    Dena K. Plemmons, Erica N. Baranski, Kyle Harp, David D. Lo, Courtney K. Soderberg, Timothy M. Errington, Brian A. Nosek, Kevin M. Esterling

    We report a randomized trial of a research ethics training intervention designed to enhance ethics communication in university science and engineering laboratories, focusing specifically on authorship and data management. The intervention is a project-based research ethics curriculum that was designed to enhance the ability of science and engineering research laboratory members to engage in reason giving and interpersonal communication necessary for ethical practice. The randomized trial was fielded in active faculty-led laboratories at two US research-intensive institutions. Here, we show that laboratory members perceived improvements in the quality of discourse on research ethics within their laboratories and enhanced awareness of the relevance and reasons for that discourse for their work as measured by a survey administered over 4 mo after the intervention. This training represents a paradigm shift compared with more typical module-based or classroom ethics instruction that is divorced from the everyday workflow and practices within laboratories and is designed to cultivate a campus culture of ethical science and engineering research in the very work settings where laboratory members interact.

    更新日期:2020-01-22
  • Scientists’ incentives and attitudes toward public communication
    PNAS (IF 9.580) Pub Date : 2020-01-21
    Kathleen M. Rose, Ezra M. Markowitz, Dominique Brossard

    In an era of large-scale science-related challenges and rapid advancements in groundbreaking science with major societal implications, communicating about science is critical. The profile of science communication has increased over the last few decades, with multiple sectors calling for such activities. As scientists respond to calls for public-facing communication, we need to evaluate where the scientific community stands. We conducted a unique census of science faculty at land-grant universities across the United States intended to spur the next generation of science communicators and research. Despite scientists’ strong approval of science communication efforts, potential areas of tension, attributable to lack of institutional support and confidence in communication skills, constrain these efforts.

    更新日期:2020-01-22
  • The rhizobial autotransporter determines the symbiotic nitrogen fixation activity of Lotus japonicus in a host-specific manner [Plant Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    Yoshikazu Shimoda, Yuki Nishigaya, Hiroko Yamaya-Ito, Noritoshi Inagaki, Yosuke Umehara, Hideki Hirakawa, Shusei Sato, Toshimasa Yamazaki, Makoto Hayashi

    Leguminous plants establish endosymbiotic associations with rhizobia and form root nodules in which the rhizobia fix atmospheric nitrogen. The host plant and intracellular rhizobia strictly control this symbiotic nitrogen fixation. We recently reported a Lotus japonicus Fix− mutant, apn1 (aspartic peptidase nodule-induced 1), that impairs symbiotic nitrogen fixation. APN1 encodes a nodule-specific aspartic peptidase involved in the Fix− phenotype in a rhizobial strain-specific manner. This host-strain specificity implies that some molecular interactions between host plant APN1 and rhizobial factors are required, although the biological function of APN1 in nodules and the mechanisms governing the interactions are unknown. To clarify how rhizobial factors are involved in strain-specific nitrogen fixation, we explored transposon mutants of Mesorhizobium loti strain TONO, which normally form Fix− nodules on apn1 roots, and identified TONO mutants that formed Fix+ nodules on apn1. The identified causal gene encodes an autotransporter, part of a protein secretion system of Gram-negative bacteria. Expression of the autotransporter gene in M. loti strain MAFF3030399, which normally forms Fix+ nodules on apn1 roots, resulted in Fix− nodules. The autotransporter of TONO functions to secrete a part of its own protein (a passenger domain) into extracellular spaces, and the recombinant APN1 protein cleaved the passenger protein in vitro. The M. loti autotransporter showed the activity to induce the genes involved in nodule senescence in a dose-dependent manner. Therefore, we conclude that the nodule-specific aspartic peptidase, APN1, suppresses negative effects of the rhizobial autotransporter in order to maintain effective symbiotic nitrogen fixation in root nodules.

    更新日期:2020-01-22
  • The maize heterotrimeric G protein {beta} subunit controls shoot meristem development and immune responses [Plant Biology]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    Qingyu Wu, Fang Xu, Lei Liu, Si Nian Char, Yezhang Ding, Byoung Il Je, Eric Schmelz, Bing Yang, David Jackson

    Heterotrimeric G proteins are important transducers of receptor signaling, functioning in plants with CLAVATA receptors in controlling shoot meristem size and with pathogen-associated molecular pattern receptors in basal immunity. However, whether specific members of the heterotrimeric complex potentiate cross-talk between development and defense, and the extent to which these functions are conserved across species, have not yet been addressed. Here we used CRISPR/Cas9 to knock out the maize G protein β subunit gene (Gβ) and found that the mutants are lethal, differing from those in Arabidopsis, in which homologous mutants have normal growth and fertility. We show that lethality is caused not by a specific developmental arrest, but by autoimmunity. We used a genetic diversity screen to suppress the lethal Gβ phenotype and also identified a maize Gβ allele with weak autoimmune responses but strong development phenotypes. Using these tools, we show that Gβ controls meristem size in maize, acting epistatically with G protein α subunit gene (Gα), suggesting that Gβ and Gα function in a common signaling complex. Furthermore, we used an association study to show that natural variation in Gβ influences maize kernel row number, an important agronomic trait. Our results demonstrate the dual role of Gβ in immunity and development in a cereal crop and suggest that it functions in cross-talk between these competing signaling networks. Therefore, modification of Gβ has the potential to optimize the trade-off between growth and defense signaling to improve agronomic production.

    更新日期:2020-01-22
  • Specialized stellate cells offer a privileged route for rapid water flux in Drosophila renal tubule [Physiology]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    Pablo Cabrero, Selim Terhzaz, Anthony J. Dornan, Saurav Ghimire, Heather L. Holmes, Daniel R. Turin, Michael F. Romero, Shireen A. Davies, Julian A. T. Dow

    Insects are highly successful, in part through an excellent ability to osmoregulate. The renal (Malpighian) tubules can secrete fluid faster on a per-cell basis than any other epithelium, but the route for these remarkable water fluxes has not been established. In Drosophila melanogaster, we show that 4 genes of the major intrinsic protein family are expressed at a very high level in the fly renal tissue: the aquaporins (AQPs) Drip and Prip and the aquaglyceroporins Eglp2 and Eglp4. As predicted from their structure, and by their transport function by expressing these proteins in Xenopus oocytes, Drip, Prip, and Eglp2 show significant and specific water permeability, whereas Eglp2 and Eglp4 show very high permeability to glycerol and urea. Knockdowns of any of these genes result in impaired hormone-induced fluid secretion. The Drosophila tubule has 2 main secretory cell types: active cation-transporting principal cells, wherein the aquaglyceroporins localize to opposite plasma membranes, and small stellate cells, the site of the chloride shunt conductance, with these AQPs localizing to opposite plasma membranes. This suggests a model in which osmotically obliged water flows through the stellate cells. Consistent with this model, fluorescently labeled dextran, an in vivo marker of membrane water permeability, is trapped in the basal infoldings of the stellate cells after kinin diuretic peptide stimulation, confirming that these cells provide the major route for transepithelial water flux. The spatial segregation of these components of epithelial water transport may help to explain the unique success of the higher insects in regulating their internal environments.

    更新日期:2020-01-22
  • Internal fluid pressure influences muscle contractile force [Physiology]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    David A. Sleboda, Thomas J. Roberts

    Fluid fills intracellular, extracellular, and capillary spaces within muscle. During normal physiological activity, intramuscular fluid pressures develop as muscle exerts a portion of its developed force internally. These pressures, typically ranging between 10 and 250 mmHg, are rarely considered in mechanical models of muscle but have the potential to affect performance by influencing force and work produced during contraction. Here, we test a model of muscle structure in which intramuscular pressure directly influences contractile force. Using a pneumatic cuff, we pressurize muscle midcontraction at 260 mmHg and report the effect on isometric force. Pressurization reduced isometric force at short muscle lengths (e.g., −11.87% of P0 at 0.9 L0), increased force at long lengths (e.g., +3.08% of P0 at 1.25 L0), but had no effect at intermediate muscle lengths ∼1.1–1.15 L0. This variable response to pressurization was qualitatively mimicked by simple physical models of muscle morphology that displayed negative, positive, or neutral responses to pressurization depending on the orientation of reinforcing fibers representing extracellular matrix collagen. These findings show that pressurization can have immediate, significant effects on muscle contractile force and suggest that forces transmitted to the extracellular matrix via pressurized fluid may be important, but largely unacknowledged, determinants of muscle performance in vivo.

    更新日期:2020-01-22
  • Optimizing Brownian escape rates by potential shaping [Physics]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    Marie Chupeau, Jannes Gladrow, Alexei Chepelianskii, Ulrich F. Keyser, Emmanuel Trizac

    Brownian escape is key to a wealth of physico-chemical processes, including polymer folding and information storage. The frequency of thermally activated energy barrier crossings is assumed to generally decrease exponentially with increasing barrier height. Here, we show experimentally that higher, fine-tuned barrier profiles result in significantly enhanced escape rates, in breach of the intuition relying on the above scaling law, and address in theory the corresponding conditions for maximum speed-up. Importantly, our barriers end on the same energy on which they start. For overdamped dynamics, the achievable boost of escape rates is, in principle, unbounded so that the barrier optimization has to be regularized. We derive optimal profiles under 2 different regularizations and uncover the efficiency of N-shaped barriers. We then demonstrate the viability of such a potential in automated microfluidic Brownian dynamics experiments using holographic optical tweezers and achieve a doubling of escape rates compared to unhindered Brownian motion. Finally, we show that this escape rate boost extends into the low-friction inertial regime.

    更新日期:2020-01-22
  • Microglial IRF5-IRF4 regulatory axis regulates neuroinflammation after cerebral ischemia and impacts stroke outcomes [Neuroscience]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    Abdullah Al Mamun, Anjali Chauhan, Shaohua Qi, Conelius Ngwa, Yan Xu, Romana Sharmeen, Amy L. Hazen, Jun Li, Jaroslaw A. Aronowski, Louise D. McCullough, Fudong Liu

    Microglial activation plays a central role in poststroke inflammation and causes secondary neuronal damage; however, it also contributes in debris clearance and chronic recovery. Microglial pro- and antiinflammatory responses (or so-called M1-M2 phenotypes) coexist and antagonize each other throughout the disease progress. As a result of this balance, poststroke immune responses alter stroke outcomes. Our previous study found microglial expression of interferon regulatory factor 5 (IRF5) and IRF4 was related to pro- and antiinflammatory responses, respectively. In the present study, we genetically modified the IRF5 and IRF4 signaling to explore their roles in stroke. Both in vitro and in vivo assays were utilized; IRF5 or IRF4 small interfering RNA (siRNA), lentivirus, and conditional knockout (CKO) techniques were employed to modulate IRF5 or IRF4 expression in microglia. We used a transient middle cerebral artery occlusion model to induce stroke and examined both acute and chronic stroke outcomes. Poststroke inflammation was evaluated with flow cytometry, RT-PCR, MultiPlex, and immunofluorescence staining. An oscillating pattern of the IRF5-IRF4 regulatory axis function was revealed. Down-regulation of IRF5 signaling by siRNA or CKO resulted in increased IRF4 expression, enhanced M2 activation, quenched proinflammatory responses, and improved stroke outcomes, whereas down-regulation of IRF4 led to increased IRF5 expression, enhanced M1 activation, exacerbated proinflammatory responses, and worse functional recovery. Up-regulation of IRF4 or IRF5 by lentivirus induced similar results. We conclude that the IRF5-IRF4 regulatory axis is a key determinant in microglial activation. The IRF5-IRF4 regulatory axis is a potential therapeutic target for neuroinflammation and ischemic stroke.

    更新日期:2020-01-22
  • Robust hepatitis E virus infection and transcriptional response in human hepatocytes [Microbiology]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    Daniel Todt, Martina Friesland, Nora Moeller, Dimas Praditya, Volker Kinast, Yannick Brüggemann, Leonard Knegendorf, Thomas Burkard, Joerg Steinmann, Rani Burm, Lieven Verhoye, Avista Wahid, Toni Luise Meister, Michael Engelmann, Vanessa M. Pfankuche, Christina Puff, Florian W. R. Vondran, Wolfgang Baumgärtner, Philip Meuleman, Patrick Behrendt, Eike Steinmann

    Hepatitis E virus (HEV) is the causative agent of hepatitis E in humans and the leading cause for acute viral hepatitis worldwide. The virus is classified as a member of the genus Orthohepevirus A within the Hepeviridae family. Due to the absence of a robust cell culture model for HEV infection, the analysis of the viral life cycle, the development of effective antivirals and a vaccine is severely limited. In this study, we established a protocol based on the HEV genotype 3 p6 (Kernow C-1) and the human hepatoma cell lines HepG2 and HepG2/C3A with different media conditions to produce intracellular HEV cell culture-derived particles (HEVcc) with viral titers between 105 and 106 FFU/mL. Viral titers could be further enhanced by an HEV variant harboring a mutation in the RNA-dependent RNA polymerase. These HEVcc particles were characterized in density gradients and allowed the trans-complementation of subgenomic reporter HEV replicons. In addition, in vitro produced intracellular-derived particles were infectious in liver-humanized mice with high RNA copy numbers detectable in serum and feces. Efficient infection of primary human and swine hepatocytes using the developed protocol could be observed and was inhibited by ribavirin. Finally, RNA sequencing studies of HEV-infected primary human hepatocytes demonstrated a temporally structured transcriptional defense response. In conclusion, this robust cell culture model of HEV infection provides a powerful tool for studying viral–host interactions that should facilitate the discovery of antiviral drugs for this important zoonotic pathogen.

    更新日期:2020-01-22
  • A promiscuous inflammasome sparks replication of a common tumor virus [Microbiology]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    Eric M. Burton, Raphaela Goldbach-Mansky, Sumita Bhaduri-McIntosh

    Viruses activate inflammasomes but then subvert resulting inflammatory responses to avoid elimination. We asked whether viruses could instead use such activated or primed inflammasomes to directly aid their propagation and spread. Since herpesviruses are experts at coopting cellular functions, we investigated whether Epstein−Barr virus (EBV), an oncoherpesvirus, exploits inflammasomes to activate its replicative or lytic phase. Indeed, our experiments reveal that EBV exploits several inflammasome sensors to actually activate its replicative phase from quiescence/latency. In particular, TXNIP, a key inflammasome intermediary, causes assembly of the NLRP3 inflammasome, resulting in caspase-1−mediated depletion of the heterochromatin-inducing epigenetic repressor KAP1/TRIM28 in a subpopulation of cells. As a result, only TXNIPhiKAP1lo cells, that is, in a primed/prolytic state, turn expression of the replication/lytic/reactivation switch protein on to enter the replicative phase. Our findings 1) demonstrate that EBV dovetails its escape strategy to a key cellular danger-sensing mechanism, 2) indicate that transcription may be regulated by KAP1 abundance aside from canonical regulation through its posttranslational modification, 3) mechanistically link diabetes, which frequently activates the NLRP3 inflammasome, to deregulation of a tumor virus, and 4) demonstrate that B lymphocytes from NOMID (neonatal onset multisystem inflammatory disease) patients who have NLRP3 mutations and suffer from hyperactive innate responses are defective in controlling a herpesvirus.

    更新日期:2020-01-22
  • Mitochondrial dysfunctions trigger the calcium signaling-dependent fungal multidrug resistance [Microbiology]
    PNAS (IF 9.580) Pub Date : 2020-01-21
    Yeqi Li, Yuanwei Zhang, Chi Zhang, Hongchen Wang, Xiaolei Wei, Peiying Chen, Ling Lu

    Drug resistance in fungal pathogens has risen steadily over the past decades due to long-term azole therapy or triazole usage in agriculture. Modification of the drug target protein to prevent drug binding is a major recognized route to induce drug resistance. However, mechanisms for nondrug target-induced resistance remain only loosely defined. Here, we explore the molecular mechanisms of multidrug resistance resulted from an efficient adaptation strategy for survival in drug environments in the human pathogen Aspergillus fumigatus. We show that mutants conferring multidrug resistance are linked with mitochondrial dysfunction induced by defects in heme A biosynthesis. Comparison of the gene expression profiles between the drug-resistant mutants and the parental wild-type strain shows that multidrug-resistant transporters, chitin synthases, and calcium-signaling-related genes are significantly up-regulated, while scavenging mitochondrial reactive oxygen species (ROS)-related genes are significantly down-regulated. The up-regulated-expression genes share consensus calcium-dependent serine threonine phosphatase-dependent response elements (the binding sites of calcium-signaling transcription factor CrzA). Accordingly, drug-resistant mutants show enhanced cytosolic Ca2+ transients and persistent nuclear localization of CrzA. In comparison, calcium chelators significantly restore drug susceptibility and increase azole efficacy either in laboratory-derived or in clinic-isolated A. fumigatus strains. Thus, the mitochondrial dysfunction as a fitness cost can trigger calcium signaling and, therefore, globally up-regulate a series of embedding calcineurin-dependent–response-element genes, leading to antifungal resistance. These findings illuminate how fitness cost affects drug resistance and suggest that disruption of calcium signaling might be a promising therapeutic strategy to fight against nondrug target-induced drug resistance.

    更新日期:2020-01-22
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