Long-term hyperglycemia in diabetic patients leads to human serum albumin (HSA) glycation, which may impair HSA function as a transport protein and affect the therapeutic efficacy of anticoagulants in diabetic patients. In this study, a novel mass spectrometry (MS) approach was developed to reveal the differences in the profiles of HSA glycation sites between diabetic and healthy subjects. K199 was the glycation site most significantly changed in diabetic patients, contributing to different interactions of glycated HSA (gHSA) and normal HSA with two types of anticoagulant drugs, heparin and warfarin. In vitro experiment showed that the binding affinity to warfarin became stronger when HSA was glycated, while HSA binding to heparin was not significantly influenced by glycation. A pharmacokinetic study showed a decreased level of free warfarin in the plasma of diabetic rats. A preliminary retrospective clinical study also revealed that there was a statistically significant difference in the anticoagulant efficacy between diabetic and non-diabetic patients who had been treated with warfarin. Our work suggests that larger studies are needed to provide additional specific guidance for patients with diabetes when administered anticoagulant drugs or drugs for treating other chronic diseases.

Glucagon secretion is regulated by circulating glucose, but it has turned out that amino acids also play an important role, and that hepatic amino acid metabolism and glucagon are linked in a mutual feed-back cycle, the liver-alpha cell axis. On this background, we hypothesized that hepatic steatosis might impair glucagon’s action on hepatic amino acid metabolism and lead to hyperaminoacidemia and hyperglucagonemia. We subjected 15 healthy lean and 15 obese steatotic male participants to a pancreatic clamp with somatostatin and evaluated hepatic glucose and amino acid metabolism during basal and high physiological levels of glucagon. The degree of steatosis was evaluated from liver biopsies. Total RNA sequencing of liver biopsies revealed perturbations in the expression of genes predominantly involved in amino acid metabolism in the obese steatotic individuals. This group was also characterized by fasting hyperglucagonemia, hyperaminoacidemia and an absent lowering of amino acid levels in response to high levels of glucagon. Endogenous glucose production was similar between lean and obese individuals. Our results suggest that hepatic steatosis causes resistance to the effect of glucagon on amino acid metabolism resulting in increased amino acid concentrations as well as increased glucagon secretion providing a likely explanation of fatty liver-associated hyperglucagonemia.

Excessive fructose consumption is closely linked to the pathogenesis of metabolic disease. Carbohydrate response element-binding protein (ChREBP) is a transcription factor essential for fructose tolerance in mice. However, the functional significance of liver ChREBP in fructose metabolism remains unclear. Here, we show that liver ChREBP protects mice against fructose-induced hepatotoxicity by regulating liver glycogen metabolism and ATP homeostasis. Liver-specific ablation of ChREBP did not compromise fructose tolerance, but rather caused severe transaminitis and hepatomegaly with massive glycogen overload in mice fed high-fructose diet, while no obvious inflammation, cell death, or fibrosis was detected in the liver. In addition, liver ATP contents were significantly decreased by ChREBP deficiency in the fed state, and this was rendered more pronounced by fructose feeding. Mechanistically, liver contents of glucose-6-phosphate (G-6-P), an allosteric activator of glycogen synthase, were markedly increased in the absence of liver ChREBP, while fasting-induced glycogen breakdown was not compromised. Furthermore, hepatic overexpression of LPK, a ChREBP target gene in glycolysis, could effectively rescue glycogen overload and ATP reduction, as well as mitigate fructose-induced hepatotoxicity in ChREBP-deficient mice. Taken together, our findings establish a critical role of liver ChREBP in coping with hepatic fructose stress and protecting from hepatotoxicity by regulating LPK.

Progression to diabetes can be viewed as having definable stages characterized by changes in various metabolic parameters and β-cell function. At the very beginning, fasting plasma glucose levels increase from perfectly normal values of ∼4.5 mmol/l (80 mg/dl) to higher values that might be as low as 5.0 mmol/l (89 mg/dl). This change in glycemia would not be recognized as being clinically abnormal because it would fail to reach the official category of impaired fasting glucose (IFG; glucose level ≥5.6 mmol/l or 100 mg/dl) or impaired glucose tolerance (IGT; 2-h postglucose level of ≥7.8 mmol/l or 140 mg/dl) (1). Those destined to develop diabetes then progress to the IFG or IGT range, where they may remain for years before developing frank diabetes. Although this progression is mostly discussed in the context of type 2 diabetes, very similar changes occur as type 1 diabetes unfolds and as pancreas or islet transplants fail.

Glucagon-like peptide 1 (GLP-1) is a potent incretin hormone produced in the L-cells of the distal ileum and colon. In the L-cells, GLP-1 is generated by tissue-specific posttranslational processing of the proglucagon gene (1). Nutrients, including glucose, fatty acids, and dietary fiber, are all known to upregulate the transcription of the gene encoding GLP-1, and they can stimulate the release of this hormone (2). Although the majority of L-cells are located in the distal ileum and colon, the levels of GLP-1 rise rapidly upon food ingestion. It is now well accepted that nutrients, principally sugars and fats, liberate GLP-1 and GLP-1-releasing factors, including glucose-dependent insulinotropic peptide (GIP), gastrin-releasing peptide, and selective neural regulators that also stimulate GLP-1 secretion (rev. in 1–3). Upon its release, GLP-1 affects multiple target tissues throughout the body, actions thought to be mediated by a single G-protein-coupled receptor isoform. GLP-1 receptor transcripts and/or protein have been identified in several tissues, including pancreatic islets, lung, gastrointestinal (GI) tract, and the central nervous system (CNS) (2,3). More questionable is the expression of functional GLP-1 receptors in liver and skeletal muscle tissues, where gene expression has been detected (4). GLP-1’s ability to augment insulin release in a glucose-dependent manner is its most well-characterized physiological effect and one of its most promising characteristics from a clinical perspective.

By Max Bingham, PhD

Fasting hyperinsulinemia precedes the development of type 2 diabetes. However, it is unclear whether fasting insulin hypersecretion is a primary driver of insulin resistance or a consequence of the progressive increase in fasting glycemia induced by insulin resistance in the prediabetic state. Herein, we have discovered a mechanism that specifically regulates non–glucose-stimulated insulin secretion (NGSIS) in pancreatic islets that is activated by nonesterified free fatty acids, the major fuel used by β-cells during fasting. We show that the mitochondrial permeability transition pore regulator cyclophilin D (CypD) promotes NGSIS, but not glucose-stimulated insulin secretion, by increasing mitochondrial proton leak. Islets from prediabetic obese mice show significantly higher CypD-dependent proton leak and NGSIS compared with lean mice. Proton leak–mediated NGSIS is conserved in human islets and is stimulated by exposure to nonesterified free fatty acids at concentrations observed in obese subjects. Mechanistically, proton leak activates islet NGSIS independently of mitochondrial ATP synthesis but ultimately requires closure of the KATP channel. In summary, we have described a novel nonesterified free fatty acid–stimulated pathway that selectively drives pancreatic islet NGSIS, which may be therapeutically exploited as an alternative way to halt fasting hyperinsulinemia and the progression of type 2 diabetes.

Incretin hormone dysregulation contributes to reduced insulin secretion and hyperglycemia in patients with type 2 diabetes mellitus (T2DM). Resistance to glucose-dependent insulinotropic polypeptide (GIP) action may occur through desensitization or downregulation of β-cell GIP receptors (GIP-R). Studies in rodents and cell lines show GIP-R expression can be regulated through peroxisome proliferator–activated receptor γ (PPARγ) response elements (PPREs). Whether this occurs in humans is unknown. To test this, we conducted a randomized, double-blind, placebo-controlled trial of pioglitazone therapy on GIP-mediated insulin secretion and adipocyte GIP-R expression in subjects with well-controlled T2DM. Insulin sensitivity improved, but the insulinotropic effect of infused GIP was unchanged following 12 weeks of pioglitazone treatment. In parallel, we observed increased GIP-R mRNA expression in subcutaneous abdominal adipocytes from subjects treated with pioglitazone. Treatment of cultured human adipocytes with troglitazone increased PPARγ binding to GIP-R PPREs. These results show PPARγ agonists regulate GIP-R expression through PPREs in human adipocytes, but suggest this mechanism is not important for regulation of the insulinotropic effect of GIP in subjects with T2DM. Because GIP has antilipolytic and lipogenic effects in adipocytes, the increased GIP-R expression may mediate accretion of fat in patients with T2DM treated with PPARγ agonists.

Adipose tissue macrophages (ATMs) are involved in the development of insulin resistance in obesity. We have recently shown that myeloid cell–specific reduction of HMG-CoA reductase ( Hmgcr m−/m− ), which is the rate-limiting enzyme in cholesterol biosynthesis, protects against atherosclerosis by inhibiting macrophage migration in mice. We hypothesized that ATMs are harder to accumulate in Hmgcr m−/m− mice than in control Hmgcr fl/fl mice in the setting of obesity. To test this hypothesis, we fed Hmgcr m−/m− and Hmgcr fl/fl mice a high-fat diet (HFD) for 24 weeks and compared plasma glucose metabolism as well as insulin signaling and histology between the two groups. Myeloid cell–specific reduction of Hmgcr improved glucose tolerance and insulin sensitivity without altering body weight in the HFD-induced obese mice. The improvement was due to a decrease in the number of ATMs. The ATMs were reduced by decreased recruitment of macrophages as a result of their impaired chemotactic activity. These changes were associated with decreased expression of proinflammatory cytokines in adipose tissues. Myeloid cell–specific reduction of Hmgcr also attenuated hepatic steatosis. In conclusion, reducing myeloid HMGCR may be a promising strategy to improve insulin resistance and hepatic steatosis in obesity.

The whitening and loss of brown adipose tissue (BAT) during obesity and aging promote metabolic disorders and related diseases. The imbalance of Ca2+ homeostasis accounts for the dysfunction and clearance of mitochondria during BAT whitening. Capsaicin, a dietary factor activating TRPV1, can inhibit obesity induced by high-fat diet (HFD), but whether capsaicin inhibits BAT loss and the underlying mechanism remain unclear. In this study, we determined that the inhibitory effects of capsaicin on HFD-induced obesity and BAT whitening were dependent on the participation of SIRT3, a critical mitochondrial deacetylase. SIRT3 also mediated all of the beneficial effects of capsaicin on alleviating reactive oxygen species generation, elevating mitochondrial activity, and restricting mitochondrial calcium overload induced by HFD. Mechanistically, SIRT3 inhibits mitochondrial calcium uniporter (MCU)-mediated mitochondrial calcium overload by reducing the H3K27ac level on the MCU promoter in an AMPK-dependent manner. In addition, HFD also inhibits AMPK activity to reduce SIRT3 expression, which could be reversed by capsaicin. Capsaicin intervention also inhibited aging-induced BAT whitening through this mechanism. In conclusion, this study emphasizes a critical role of the AMPK/SIRT3 pathway in the maintenance of BAT morphology and function and suggests that intervention in this pathway may be an effective target for preventing obesity- or age-related metabolic diseases.

The ability to switch fuels for oxidation in response to changes in macronutrient composition of diet (metabolic flexibility) may be informative of individuals’ susceptibility to weight gain. Seventy-nine healthy, weight-stable participants underwent 24-h assessments of energy expenditure and respiratory quotient (RQ) in a whole-room calorimeter during energy balance (EBL) (50% carbohydrate, 30% fat) and then during 24-h fasting and three 200% overfeeding diets in a crossover design. Metabolic flexibility was defined as the change in 24-h RQ from EBL during fasting and standard overfeeding (STOF) (50% carbohydrate, 30% fat), high-fat overfeeding (HFOF) (60% fat, 20% carbohydrate), and high-carbohydrate overfeeding (HCOF) (75% carbohydrate, 5% fat) diets. Free-living weight change was assessed after 6 and 12 months. Compared with EBL, RQ decreased on average by 9% during fasting and by 4% during HFOF but increased by 4% during STOF and by 8% during HCOF. A smaller decrease in RQ, reflecting a smaller increase in lipid oxidation rate, during HFOF but not during the other diets predicted greater weight gain at both 6 and 12 months. An impaired metabolic flexibility to acute HFOF can identify individuals prone to weight gain, indicating that an individual’s capacity to oxidize dietary fat is a metabolic determinant of weight change.

Active maintenance of β-cell identity through fine-tuned regulation of key transcription factors ensures β-cell function. Tacrolimus, a widely used immunosuppressant, accelerates onset of diabetes after organ transplantation, but underlying molecular mechanisms are unclear. Here we show that tacrolimus induces loss of human β-cell maturity and β-cell failure through activation of the BMP/SMAD signaling pathway when administered under mild metabolic stress conditions. Tacrolimus-induced phosphorylated SMAD1/5 acts in synergy with metabolic stress–activated FOXO1 through formation of a complex. This interaction is associated with reduced expression of the key β-cell transcription factor MAFA and abolished insulin secretion, both in vitro in primary human islets and in vivo in human islets transplanted into high-fat diet–fed mice. Pharmacological inhibition of BMP signaling protects human β-cells from tacrolimus-induced β-cell dysfunction in vitro. Furthermore, we confirm that BMP/SMAD signaling is activated in protocol pancreas allograft biopsies from recipients on tacrolimus. To conclude, we propose a novel mechanism underlying the diabetogenicity of tacrolimus in primary human β-cells. This insight could lead to new treatment strategies for new-onset diabetes and may have implications for other forms of diabetes.

A sufficient β-cell mass is crucial for preventing diabetes, and perinatal β-cell proliferation is important in determining the adult β-cell mass. However, it is not yet known how perinatal β-cell proliferation is regulated. Here, we report that serotonin regulates β-cell proliferation through serotonin receptor 2B (HTR2B) in an autocrine/paracrine manner during the perinatal period. In β-cell–specific Tph1 knockout ( Tph1 βKO) mice, perinatal β-cell proliferation was reduced along with the loss of serotonin production in β-cells. Adult Tph1 βKO mice exhibited glucose intolerance with decreased β-cell mass. Disruption of Htr2b in β-cells also resulted in decreased perinatal β-cell proliferation and glucose intolerance in adulthood. Growth hormone (GH) was found to induce serotonin production in β-cells through activation of STAT5 during the perinatal period. Thus, our results indicate that GH-GH receptor-STAT5-serotonin-HTR2B signaling plays a critical role in determining the β-cell mass by regulating perinatal β-cell proliferation, and defects in this pathway affect metabolic phenotypes in adults.

Optimal immune-based therapies for type 1 diabetes (T1D) should restore self-tolerance without inducing chronic immunosuppression. CD4+Foxp3+ regulatory T cells (Tregs) are a key cell population capable of facilitating durable immune tolerance. However, clinical trials with expanded Tregs in T1D and solid-organ transplant recipients are limited by poor Treg engraftment without host manipulation. We showed that Treg engraftment and therapeutic benefit in nonautoimmune models required ablative host conditioning. Here, we evaluated Treg engraftment and therapeutic efficacy in the nonobese diabetic (NOD) mouse model of autoimmune diabetes using nonablative, combinatorial regimens involving the anti-CD3 (αCD3), cyclophosphamide (CyP), and IAC (IL-2/JES6–1) antibody complex. We demonstrate that αCD3 alone induced substantial T-cell depletion, impacting both conventional T cells (Tconv) and Tregs, subsequently followed by more rapid rebound of Tregs. Despite robust depletion of host Tconv and host Tregs, donor Tregs failed to engraft even with interleukin-2 (IL-2) support. A single dose of CyP after αCD3 depleted rebounding host Tregs and resulted in a 43-fold increase in donor Treg engraftment, yet polyclonal donor Tregs failed to reverse diabetes. However, infusion of autoantigen-specific Tregs after αCD3 alone resulted in robust Treg engraftment within the islets and induced remission in all mice. This novel combinatorial therapy promotes engraftment of autoantigen-specific donor Tregs and controls islet autoimmunity without long-term immunosuppression.

Insulin-induced hypoglycemia leads to far-ranging negative consequences in patients with diabetes. Components of the counterregulatory response (CRR) system that help minimize and reverse hypoglycemia and coordination between those components are well studied but not yet fully characterized. Here, we tested the hypothesis that acyl-ghrelin, a hormone that defends against hypoglycemia in a preclinical starvation model, is permissive for the normal CRR to insulin-induced hypoglycemia. Ghrelin knockout (KO) mice and wild-type (WT) littermates underwent an insulin bolus-induced hypoglycemia test and a low-dose hyperinsulinemic-hypoglycemic clamp procedure. Clamps also were performed in ghrelin-KO mice and C57BL/6N mice administered the growth hormone secretagogue receptor agonist HM01 or vehicle. Results show that hypoglycemia, as induced by an insulin bolus, was more pronounced and prolonged in ghrelin-KO mice, supporting previous studies suggesting increased insulin sensitivity upon ghrelin deletion. Furthermore, during hyperinsulinemic-hypoglycemic clamps, ghrelin-KO mice required a 10-fold higher glucose infusion rate (GIR) and exhibited less robust corticosterone and growth hormone responses. Conversely, HM01 administration, which reduced the GIR required by ghrelin-KO mice during the clamps, increased plasma corticosterone and growth hormone. Thus, our data suggest that endogenously produced acyl-ghrelin not only influences insulin sensitivity but also is permissive for the normal CRR to insulin-induced hypoglycemia.

This study aims to model genetic, immunologic, metabolomics, and proteomic biomarkers for development of islet autoimmunity (IA) and progression to type 1 diabetes in a prospective high-risk cohort. We studied 67 children: 42 who developed IA (20 of 42 progressed to diabetes) and 25 control subjects matched for sex and age. Biomarkers were assessed at four time points: earliest available sample, just prior to IA, just after IA, and just prior to diabetes onset. Predictors of IA and progression to diabetes were identified across disparate sources using an integrative machine learning algorithm and optimization-based feature selection. Our integrative approach was predictive of IA (area under the receiver operating characteristic curve [AUC] 0.91) and progression to diabetes (AUC 0.92) based on standard cross-validation (CV). Among the strongest predictors of IA were change in serum ascorbate, 3-methyl-oxobutyrate, and the PTPN22 (rs2476601) polymorphism. Serum glucose, ADP fibrinogen, and mannose were among the strongest predictors of progression to diabetes. This proof-of-principle analysis is the first study to integrate large, diverse biomarker data sets into a limited number of features, highlighting differences in pathways leading to IA from those predicting progression to diabetes. Integrated models, if validated in independent populations, could provide novel clues concerning the pathways leading to IA and type 1 diabetes.

Lipodystrophies are a group of disorders characterized by absence or loss of adipose tissue and abnormal fat distribution, commonly accompanied by metabolic dysregulation. Although considered rare disorders, their prevalence in the general population is not well understood. We aimed to evaluate the clinical and genetic prevalence of lipodystrophy disorders in a large clinical care cohort. We interrogated the electronic health record (EHR) information of >1.3 million adults from the Geisinger Health System for lipodystrophy diagnostic codes. We estimate a clinical prevalence of disease of 1 in 20,000 individuals. We performed genetic analyses in individuals with available genomic data to identify variants associated with inherited lipodystrophies and examined their EHR for comorbidities associated with lipodystrophy. We identified 16 individuals carrying the p.R482Q pathogenic variant in LMNA associated with Dunnigan familial partial lipodystrophy. Four had a clinical diagnosis of lipodystrophy, whereas the remaining had no documented clinical diagnosis despite having accompanying metabolic abnormalities. We observed a lipodystrophy-associated variant carrier frequency of 1 in 3,082 individuals in our cohort with substantial burden of metabolic dysregulation. We estimate a genetic prevalence of disease of ∼1 in 7,000 in the general population. Partial lipodystrophy is an underdiagnosed condition. and its prevalence, as defined molecularly, is higher than previously reported. Genetically guided stratification of patients with common metabolic disorders, like diabetes and dyslipidemia, is an important step toward precision medicine.

Night shift work, behavioral rhythms, and the common MTNR1B risk single nucleotide polymorphism (SNP), rs10830963, associate with type 2 diabetes; however, whether they exert joint effects to exacerbate type 2 diabetes risk is unknown. Among employed participants of European ancestry in the UK Biobank ( N = 189,488), we aimed to test the cross-sectional independent associations and joint interaction effects of these risk factors on odds of type 2 diabetes ( n = 5,042 cases) and HbA1c levels ( n = 175,156). Current shift work, definite morning or evening preference, and MTNR1B rs10830963 risk allele associated with type 2 diabetes and HbA1c levels. The effect of rs10830963 was not modified by shift work schedules. While marginal evidence of interaction between self-reported morningness-eveningness preference and rs10830963 on risk of type 2 diabetes was seen, this interaction did not persist when analysis was expanded to include all participants regardless of employment status and when accelerometer-derived sleep midpoint was used as an objective measure of morningness-eveningness preference. Our findings suggest that MTNR1B risk allele carriers who carry out shift work or have more extreme morningness-eveningness preference may not have enhanced risk of type 2 diabetes.

In the article cited above, affiliation 1 was mistakenly included for authors Yi Tan and Lu Cai. The author byline should have read Yi Tan2,5,9 and Lu Cai2,5,9 rather than Yi Tan1,2,5,9 and Lu Cai1,2,5,9. The authors apologize for the errors.

In the article cited above, funding was mistakenly omitted for author Xiaoyan Bai. The following statement has been added to correct this: “X.B. was supported by National Key R&D Program of China (2018YFC1314000), National Natural Science Foundation of China (grant 81873616), and ‘Group-type’ Special Support Project for Education Talents in Universities (G619080438, 4SG19002G, 4SG19044G).” The authors apologize for the omission.

In the article cited above, nPOD funding information was mistakenly omitted. The following statement has been added to the Funding section to correct this: “This research was performed with the support of the Network for Pancreatic Organ donors with Diabetes (nPOD; RRID:SCR_014641), a collaborative type 1 diabetes research project sponsored by JDRF (nPOD: 5-SRA-2018-557-Q-R) and The Leona M. & Harry B. Helmsley Charitable Trust (grant no. 2018PG-T1D053). The content and views expressed are the responsibility of the authors and do not necessarily reflect the official view of nPOD. Organ Procurement Organizations (OPO) partnering with nPOD to provide research resources are listed at https://www.jdrfnpod.org/for-partners/npod-partners/ .” The authors apologize for the omission.

The 67th annual American Diabetes Association Advanced Postgraduate Course will be held in San Francisco, CA, from 31 January to 2 February 2020. Join your colleagues and diabetes experts for presentations and discussions on cutting-edge clinical research in diabetes. The course will cover the latest clinical research translated into evidence-based treatment strategies to improve outcomes in your patients with diabetes. Discuss clinical cases with world-renowned faculty and take home practical patient management tools that you can use immediately in your practice. For more information, …

F-box only protein 2 (FBXO2, or FBX2) is an E3 ubiquitin protein ligase highly expressed in the brain and cochlea but not the liver (1,2). It was reported by Liu et al. (3) that hepatic FBXO2 elevation causes hyperglycemia in obese mice. Here, we share some comments on their article.

We appreciate Wong et al. (1) for their interest in our article (2). The specificity of an antibody could be affected by many factors including the detergents, blocking reagent, and incubating time and temperature as well as the quantity of secondary antibody. Wong et al. claimed that F-box only protein 2 (FBXO2) might not mediate glucose homeostasis in mice. Although the reason for this inconsistency is unclear, the animal models and feeding conditions were different in the two studies. In our study, to specifically explore the metabolic role of FBXO2 in the liver, adenovirus-mediated hepatic overexpression or knockdown was used. In contrast, Wong et al. used FBXO2 global knockout mice. As FBXO2 is widely expressed, the whole-body deletion of FBXO2 might differ from the liver-specific suppression of FBXO2. This phenomenon has been reported in many other studies. For example, severe insulin resistance was only observed in liver-specific insulin receptor (IR) knockout mice and not in skeletal muscle– or fat-specific IR knockout mice (3–5). In addition, TRB3 was shown to inhibit insulin signaling and promote insulin resistance in the liver (6–8). However, serum glucose or insulin levels, insulin sensitivity or glucose tolerance, and energy metabolism were not altered in genetic TRB3 deficient mice (9). Therefore, global TRB3 knockout mice displayed normal hepatic insulin signaling and glucose homeostasis (9). Thus, further studies are still needed to extensively investigate the metabolic role of FBXO2 in the liver under different physiological or pathophysiological conditions.

Type 2 diabetes accounts for 90% of diabetic population, and these patients are generally obese and hyperlipidemic. In addition to hyperglycemia, hyperlipidemia is also closely related with diabetic retinopathy. Aim was to investigate retinopathy in a model closely mimicking the normal progression and metabolic features of type 2 diabetic population, and elucidate the molecular mechanism. Retinopathy was evaluated in rats fed 45% kcal as fat diet for eight weeks before administering streptozotocin, 30mg/kg BW (T2D), and was compared with age- and duration-matched type 1 diabetic rats (T1D, 60mg/kg streptozotocin). The role of epigenetic modifications in mitochondrial damage was evaluated in retinal microvasculature. T2D rats were obese and severely hyperlipidemic, with impaired glucose and insulin tolerance compared to age-matched T1D rats. While at four months of diabetes, T1D rats had no detectable retinopathy, T2D rats had significant retinopathy, their mitochondrial copy numbers were lower, and mtDNA and Rac1 promoter DNA methylation were exacerbated. At six months, retinopathy was comparable in T2D and T1D rats, suggesting that obesity exaggerates hyperglycemia-induced epigenetic modifications, accelerating mitochondrial damage and diabetic retinopathy. Thus, maintenance of good life style and body mass index could be beneficial in regulating epigenetic modifications and preventing/retarding retinopathy in diabetic patients.

Schwann cell-derived exosomes communicate with dorsal root ganglia (DRG) neurons. The present study investigated the therapeutic effect of exosomes derived from healthy Schwann cells (SC-Exos) on diabetic peripheral neuropathy (DPN). We found that intravenous administration of SC-Exos to type II diabetic db/db mice with peripheral neuropathy remarkably ameliorated DPN by improving sciatic nerve conduction velocity and increasing thermal and mechanical sensitivity. These functional improvements were associated with the augmentation of epidermal nerve fibers, and remyelination of sciatic nerves. Quantitative RT-PCR and Western blot analysis of sciatic nerve tissues showed that the SC-Exo treatment reversed diabetes-reduced microRNA (miR)-21, -27a and -146a and diabetes-increased Semaphorin 6A (SEMA6A), Ras homolog gene family, member A (RhoA), phosphatase and tensin homolog (PTEN), and nuclear factor-κB (NF-κB). In vitro data showed that SC-Exos promoted neurite outgrowth of diabetic DRG neurons and migration of Schwann cells challenged by high glucose. Collectively, these novel data provide evidence that SC-Exos have a therapeutic effect on DPN in mice and suggest that SC-Exos modulation of miRs contribute to this therapy.

SGLT2 inhibitors lower plasma glucose but stimulate endogenous glucose production. The aim of the present study was to examine the effect of dapagliflozin on EGP while clamping plasma glucose, insulin and glucagon concentrations at their fasting level. 38 T2DM patients received an 8-hour measurement of EGP (3H-glucose) on 3 occasions. After a 3-hour tracer equilibration, subjects received: (i) dapagliflozin 10 mg (n=26) or placebo (n=12); (ii) repeat EGP measurement with plasma glucose concentration clamped at the fasting level; (iii) repeat EGP measurement with inhibition of insulin and glucagon secretion with somatostatin infusion and replacement of basal plasma insulin and glucagon concentrations. In Study 1, the change in EGP (baseline to last hour of EGP measurement) in subjects receiving dapagliflozin was 22% greater (+0.66 ±0.11 mg/kg.min, p<0.05 ) than in subjects receiving placebo, and it was associated with a significant increase in plasma glucagon and decrease in plasma insulin concentration compared to placebo. Under glucose clamp conditions (Study 2), the change in plasma insulin and glucagon concentrations was comparable in subjects receiving dapagliflozin and placebo, yet the difference in EGP between dapagliflozin and placebo persisted (+0.71 ±0.13 mg/kg.min, p<0.01). Under pancreatic clamp conditions (Study 3), dapagliflozin produced an initial large decrease in EGP (8% below placebo) followed by progressive increase in EGP that was 10.6% greater than placebo during the last hour. Collectively, these results indicate that: (1) the changes in plasma insulin and glucagon concentration following SGLT2i administration are secondary to the decrease in plasma glucose concentration, and (2) the dapagliflozin-induced increase in EGP cannot be explained by the increase in plasma glucagon or decrease in plasma insulin or glucose concentrations.

Reduced storage of dietary fatty acids (DFA) in abdominal adipose tissues with their enhanced cardiac partitioning has been shown in subjects with type 2 diabetes (T2D) and pre-diabetes. We measured DFA metabolism and organ partitioning using positron-emission-tomography with oral and i.v.long-chain fatty acid and glucose tracers during a standard liquid meal in 12 obese subjects with T2D prior to and 8 to 12 days after bariatric surgery (sleeve gastrectomy and biliopancreatic diversion). Bariatric surgery reduced cardiac DFA uptake (from 1.75 \[1.39-2.57\] (median [interquartile range]) before to 1.09 [1.04-1.53] standard uptake value (SUV) after surgery, P < 0.01) and systemic DFA spillover (from 56.7 before to 24.7mmol over 6h after meal intake after surgery; P =0.01) with significant increase in intra-abdominal adipose tissue DFA uptake (from 0.15 [0.04-0.31] before to 0.49 [0.20-0.59] SUV after surgery, P =0.008). Hepatic insulin resistance was significantly reduced in close association with increased DFA storage in intra-abdominal adipose tissues (r = -0.79, P = 0.05) and reduced DFA spillover (r = 0.76, P = 0.01).We conclude that bariatric surgery in T2D subjects rapidly reduces cardiac DFA partitioning and hepatic insulin resistance at least in part through increased intra-abdominal DFA storage and reduced spillover.

Diabetic retinopathy is the most common microvascular complication of diabetes, characterized by the formation of fibrovascular membranes that consist of a variety of cells including vascular endothelial cells (ECs). New therapeutic approaches for this diabetic complication are urgently needed. Here, we report that in cultured human retinal microvascular (HRECs) high glucose induced expression of p110δ, which was also expressed in ECs of fibrovascular membranes from diabetic patients. This catalytic subunit of a receptor regulated PI3K isoform δ is known to be highly-enriched in leukocytes. Using genetic and pharmacological approaches, we show that p110δ activity in cultured ECs controls Akt activation, cell proliferation, migration, and tube formation induced by vascular endothelial growth factor, basic fibroblast growth factor, and epidermal growth factor. Using a mouse model of oxygen-induced retinopathy, p110δ inactivation was found to attenuate pathological retinal angiogenesis. p110δ inhibitors have been approved for use in human B-cell malignancies. Our data suggest that antagonizing p110δ constitutes a previously-unappreciated therapeutic opportunity for diabetic retinopathy.

Subjects with low serum HDL-cholesterol levels are reported to be susceptible to diabetes mellitus, with insulin resistance believed to be the underlying pathological mechanism. Apolipoprotein M (ApoM) is a carrier of sphingosine 1-phosphate (S1P), a multifunctional lipid mediator, on HDL, and the pleiotropic effects of HDL are believed to be mediated by S1P. In the present study, we attempted to investigate the potential association between apoM/S1P and insulin resistance. We observed that the serum levels of apoM were lower in patients with type 2 diabetes mellitus and that they were negatively correlated with the BMI and the insulin resistance index. While deletion of apoM in mice was associated with worsening of insulin resistance, overexpression of apoM was associated with improvement of insulin resistance. Presumably, apoM/S1P exerts its protective effect against insulin resistance by activating insulin signaling pathways, such as the AKT and AMPK pathways, and also improving the mitochondrial functions through upregulating the SIRT1 protein levels. These actions of apoM/S1P appear to be mediated via activation of S1P1 and/or S1P3. These results suggest that ApoM/S1P exerts protective roles against the development of insulin resistance.

Urinary albumin-creatinine ratio is a marker of diabetic nephropathy and microvascular damage. Metabolic-related traits are observationally associated with ACR but their causal role is uncertain. Here, we confirmed ACR as a marker of microvascular damage and tested whether metabolic-related traits have causal relationships with ACR. The association between ACR and microvascular function (responses to acetylcholine and sodium nitroprusside) were tested in the SUMMIT study. Two sample Mendelian randomization (MR) was used to infer the causal effects of eleven metabolic risk factors, including glycemic, lipid and adiposity traits on ACR. MR was performed in up to 440,000 UK Biobank and 54,451 CKDGen participants. ACR was robustly associated with microvascular function measures in SUMMIT. Using MR we inferred that higher triglyceride and LDL-cholesterol levels caused elevated ACR. A one standard deviation (SD) higher triglyceride and LDL-C level caused a 0.062 [95%CI: 0.040, 0.083] and a 0.026 [95%CI: 0.008, 0.044] SD higher ACR respectively. There was evidence that higher body fat and visceral body fat distribution caused elevated ACR, whilst a metabolically “favourable adiposity” phenotype lowered ACR. ACR is a valid marker for microvascular function. MR suggested that 7 traits have causal effects on ACR, highlighting the role of adiposity related traits in causing lower microvascular function.

Autoimmunity against pancreatic β-cell autoantigens is a characteristic of childhood type 1 diabetes. Autoimmunity usually appears in genetically susceptible children with the development of autoantibodies against (pro)insulin in early childhood. The offspring of mothers with type 1 diabetes are protected from this process. The aim of this study was to determine whether the protection conferred by maternal type 1 diabetes is associated with improved neonatal tolerance against (pro)insulin. Consistent with improved neonatal tolerance, the offspring of mothers with type 1 diabetes had reduced cord blood CD4+ T cell responses to proinsulin and insulin, a reduction in the inflammatory profile of their proinsulin-responsive CD4+ T cells, and improved regulation of CD4+ T cell responses to proinsulin at 9 months of age, as compared with offspring with a father or sibling with type 1 diabetes. Maternal type 1 diabetes was also associated with a modest reduction in CpG methylation of the INS gene in cord blood mononuclear cells from offspring with a susceptible INS genotype. Our findings support the concept that a maternal type 1 diabetes environment improves neonatal immune tolerance against the autoantigen (pro)insulin.

Studies implicating sodium-glucose-cotransporter-2 (SGLT2) inhibitors in glucagon secretion by pancreatic alpha cells reported controversial results. We hypothesized that inter-individual heterogeneity in SGLT2 expression and regulation may impact on glucagon secretion by human alpha cells in response to SGLT2 inhibitors. An unbiased RNA-seq analysis of 207 donors revealed an unprecedented level of heterogeneity of SLC5A2 expression. To determine heterogeneity of SGLT2 expression at the protein level, the anti-SGLT2 antibody was first rigorously evaluated for specificity, followed by Western blot and immunofluorescence analysis on islets from 10-12 donors. The results revealed a high inter-donor variability of SGLT2 protein expression. Quantitative analysis of 665 human islets reaffirmed SGLT2 protein co-localization with glucagon-positive cells, but not with insulin or somatostatin. Moreover, glucagon secretion by islets from 31 donors at low-glucose (1 mM) was also heterogeneous, and correlated with dapagliflozin-induced glucagon secretion at 6 mM glucose. Intriguingly, islets from 3 donors did not secrete glucagon in response to either 1 mM glucose or dapagliflozin, indicating a functional impairment of the islets of these donors to glucose-sensing and SGLT2 inhibition. Collectively, these data indicate that heterogeneous expression of SGLT2 protein and corresponding variability in glucagon secretory responses contribute to inter-individual differences in response to SGLT2 inhibitors.

The signal peptide of preproinsulin is a major source for HLA class I autoantigen epitopes implicated in CTL-mediated beta-cell destruction in Type 1 Diabetes (T1D). Among them, the 10-mer epitope located at the C-terminal end of the signal peptide was found to be the most prevalent in recent onset T1D patients. While the combined action of signal peptide peptidase and endoplasmic reticulum aminopeptidase 1 (ERAP1) is required for processing of the signal peptide, the mechanisms controlling signal peptide trimming and the contribution of the T1D inflammatory milieu on these mechanisms are unknown. Here, we show in human beta cells that ER stress regulates ERAP1 gene expression at post-transcriptional level via the IRE1α/miR-17-5p axis and demonstrate that inhibition of the IRE1α activity impairs processing of preproinsulin signal peptide antigen and its recognition by specific autoreactive CTLs during inflammation. These results underscore the impact of ER stress in the increased visibility of beta cells to the immune system and position the IRE1α/miR-17 pathway as a central component in beta cell destruction processes and as potential target for the treatment of autoimmune T1D.

Secretion of glucagon from the pancreatic alpha cells is conventionally seen as the first and most important defense against hypoglycemia. Recent findings, however, show that alpha cell signals stimulate insulin secretion from the neighboring beta cell. This perspective focuses on these seemingly counterintuitive local actions of alpha cells and describes how they impact islet biology and glucose metabolism. It is mostly based on studies published in the last decade on the physiology of alpha cells in human islets and incorporates results from rodents where appropriate. As this and the accompanying perspective articles show, the emerging picture of alpha cell function is one of increased complexity that needs to be considered when developing new therapies aimed at promoting islet function in the context of diabetes.

Diabetes triggers peripheral nerve alterations at a structural and functional level, collectively referred to as Diabetic Peripheral Neuropathy (DPN). This work highlights the role of the oxysterol/LXR signaling pathway and the crosstalk with the reactive oxygen species (ROS) producing enzyme, NADPH oxidase-4 (Nox4) in the pathogenesis of DPN. Herein, we assess behavioral, molecular and physio-pathological changes in cultured Schwann cells as well as in the sciatic nerve of a type 1 diabetic (T1DM) murine model, and skin biopsies from type 2 diabetic (T2DM) patients. T1DM animals exhibit neurophysiological defects and sensorimotor abnormalities paralleled by a defective peripheral myelin genes expression in MPZ and PMP22. These alterations were concomitant with a significant reduction in LXR expression and increase in Nox4 expression and activity in SCs and peripheral nerves, which were further verified in T2DM patients. Moreover, targeted activation of LXR or specific inhibition of Nox4 in vivo and in vitro was shown to attenuate diabetes-induced ROS production, SC and peripheral nerve dysfunction and preserve the homeostatic profiles of MPZ and PMP22. Taken together, our findings are the first to identify novel, key mediators in the pathogenesis of DPN and suggest the targeting of the LXR/Nox4 axis as a promising therapeutic approach.

The BMP2/4 antagonist and novel adipokine, Gremlin 1, is highly expressed in human adipose cells and increased in hypertrophic obesity. As a secreted antagonist it inhibits the effect of BMP2/4 on adipose precursor cell commitment/differentiation. We examined mRNA levels of Gremlin in key target tissues for insulin and also measured tissue and serum levels in several carefully phenotyped human cohorts. Gremlin 1 expression was high in adipose tissue, higher in visceral than in subcutaneous tissue, increased in obesity and further increased in Type 2 diabetes (T2D). A similar high expression was seen in liver biopsies but expression was considerably lower in skeletal muscles. Serum levels were increased in obesity but most prominently in T2D. Transcriptional activation in both adipose tissue and liver as well as serum levels were strongly associated with markers of insulin resistance in vivo (euglycemic clamps and HOMA-IR), and the presence of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). We also found Gremlin 1 to antagonize insulin signaling and action in human primary adipocytes, skeletal muscle and liver cells. Thus, Gremlin 1 is a novel secreted insulin antagonist and biomarker as well as potential therapeutic target in obesity and its complications T2D and NAFLD/NASH.

Permanent neonatal diabetes is caused by reduced β-cell number or impaired β-cell function. Understanding the genetic basis of this disorder highlights fundamental β-cell mechanisms. We performed trio genome sequencing for 44 permanent neonatal diabetes patients and their unaffected parents to identify causative de novo variants. Replication studies were performed in 188 patients diagnosed with diabetes before 2 years of age without a genetic diagnosis. EIF2B1 (encoding the eIF2B complex α subunit) was the only gene with novel de novo variants (all missense) in at least three patients. Replication studies identified 2 further patients with de novo EIF2B1 variants. In addition to diabetes, 4/5 patients had hepatitis-like episodes in childhood. The EIF2B1 de novo mutations were found to map to the same protein surface. We propose that these variants render the eIF2B complex insensitive to eIF2 phosphorylation which occurs under stress conditions and triggers expression of stress-response genes. Failure of eIF2B to sense eIF2 phosphorylation likely leads to unregulated unfolded protein response and cell death. Our results establish de novo EIF2B1 mutations as a novel cause of permanent diabetes and liver dysfunction. These findings confirm the importance of cell stress regulation for β-cells and highlight EIF2B1’s fundamental role within this pathway.

Obesity-associated type 2 diabetes mellitus (T2DM) entails insulin resistance and loss of β-cell mass. Adipose tissue mitochondrial dysfunction is emerging as a key component in the etiology of T2DM. Identifying approaches to preserve mitochondrial function, adipose tissue integrity and β-cell mass during obesity is a major challenge. Mitochondrial ferritin (FtMT) is a mitochondrial matrix protein that chelates iron. We sought to determine whether perturbation of adipocyte mitochondria influences energy metabolism during obesity. We utilized an adipocyte-specific doxycycline-inducible mouse model of FtMT overexpression (FtMT-Adip mice). During dietary challenge, FtMT-Adip mice are leaner, however exhibit glucose intolerance, low adiponectin levels, increased ROS damage, elevated GDF15 and FGF21 levels; indicating metabolically dysfunctional fat. Paradoxically, despite harboring highly dysfunctional fat, transgenic mice display massive β-cell hyperplasia; reflecting a beneficial mitochondria-induced fat-to-pancreas inter-organ signaling axis. This identifies the unique and critical impact that adipocyte mitochondrial dysfunction has on increasing β-cell mass during obesity-related insulin resistance.

The molecular mechanisms of β-cell compensation to metabolic stress are poorly understood. We previously observed that nutrient-induced β-cell proliferation in rats is dependent on Epidermal Growth Factor Receptor (EGFR) signaling. The aim of this study was to determine the role of the EGFR ligand Heparin-Binding EGF-like Growth Factor (HB-EGF) in the β-cell proliferative response to glucose, a β-cell mitogen and key regulator of β-cell mass in response to increased insulin demand. We show that exposure of isolated rat and human islets to HB-EGF stimulates β-cell proliferation. In rat islets, inhibition of EGFR or HB-EGF blocks the proliferative response not only to HB-EGF but also to glucose. Furthermore, knockdown of HB-EGF in rat islets blocks β-cell proliferation in response to glucose ex vivo and in vivo in transplanted glucose-infused rats. Mechanistically, we demonstrate that HB-EGF mRNA levels are increased in β cells in response to glucose in a Carbohydrate Response Element Binding Protein (ChREBP)-dependent manner. In addition, chromatin-immunoprecipitation studies identified ChREBP binding sites in proximity to the HB-EGF gene. Finally, inhibition of Src family kinases, known to be involved in HB-EGF processing, abrogated glucose-induced β-cell proliferation. Our findings identify a novel glucose/HB-EGF/EGFR axis implicated in β-cell compensation to increased metabolic demand.

The placenta participates in maternal insulin sensitivity changes during pregnancy, however mechanisms remain unclear. We investigated associations between maternal insulin sensitivity and placental DNA methylation markers across the genome. We analyzed data from 430 mother-offspring dyads in the Gen3G cohort. All women underwent 75g oral glucose tolerance tests at ∼26 weeks of gestation; we used glucose and insulin measures to estimate insulin sensitivity (Matsuda index). At delivery, we collected samples from placenta (fetal side) and measured DNA methylation using IlluminaEPIC arrays. Using linear regression models to quantify associations at 720,077 CpGs, adjusted for maternal age, gravidity, smoking, body mass index, child sex and gestational age at delivery, we identified 188 CpG sites where placental DNA methylation was associated with Matsuda index ( P <6.94x10-8). Among genes annotated to these 188 CpGs, we found enrichment in targets for microRNAs, histone modifications, and in parent-of-origin DNA methylation including H19/MIR675 locus (paternally imprinted). We identified 12 known placenta imprinted genes, including KCNQ1 . Mendelian Randomization analyses revealed 5 loci where placenta DNA methylation may causally influence maternal insulin sensitivity, including the maternally imprinted gene DLGAP2. Our results suggest that placental DNA methylation is fundamentally linked to the regulation of maternal insulin sensitivity in pregnancy.

By Max Bingham, PhD

Diabetes is associated with a loss of somatosensory and motor function, leading to impairments in gait, balance, and manual dexterity. Data-driven neuroimaging studies frequently report a negative impact of diabetes on sensorimotor regions in the brain; however, relationships with sensorimotor behavior are rarely considered. The goal of this review is to consider existing diabetes neuroimaging evidence through the lens of sensorimotor neuroscience. We review evidence for diabetes-related disruptions to three critical circuits for movement control: the cerebral cortex, the cerebellum, and the basal ganglia. In addition, we discuss how central nervous system (CNS) degeneration might interact with the loss of sensory feedback from the limbs due to peripheral neuropathy to result in motor impairments in individuals with diabetes. We argue that our understanding of movement impairments in individuals with diabetes is incomplete without the consideration of disease complications in both the central and peripheral nervous systems. Neuroimaging evidence for disrupted central sensorimotor circuitry suggests that there may be unrecognized behavioral impairments in individuals with diabetes. Applying knowledge from the existing literature on CNS contributions to motor control and motor learning in healthy individuals provides a framework for hypothesis generation for future research on this topic.

A declining first-phase insulin response (FPIR) is associated with positivity for multiple islet autoantibodies, irrespective of class II HLA DR-DQ genotype. We examined the associations of FPIR with genetic variants outside the HLA DR-DQ region in the Finnish Type 1 Diabetes Prediction and Prevention (DIPP) study in children with and without multiple autoantibodies. Association between FPIR and class I alleles A*24 and B*39 and eight single nucleotide polymorphisms outside the HLA region were analyzed in 438 children who had one or more FPIR results available after seroconversion. Hierarchical linear mixed models were used to analyze repeated measurements of FPIR. In children with multiple autoantibodies, the change in FPIR over time was significantly different between those with various PTPN2 (rs45450798), FUT2 (rs601338), CTSH (rs3825932), and IKZF4 (rs1701704) genotypes in at least one of the models. In general, children carrying susceptibility alleles for type 1 diabetes experienced a more rapid decline in insulin secretion compared with children without susceptibility alleles. The presence of the class I HLA A*24 allele was also associated with a steeper decline of FPIR over time in children with multiple autoantibodies. Certain genetic variants outside the class II HLA region may have a significant impact on the longitudinal pattern of FPIR.

Adipose tissue is the key organ coordinating whole-body energy homeostasis. Although it has been reported that ring finger protein 20 (RNF20) regulates lipid metabolism in the liver and kidney, the roles of RNF20 in adipose tissue have not been explored. Here, we demonstrate that RNF20 promotes adipogenesis by potentiating the transcriptional activity of peroxisome proliferator–activated receptor-γ (PPARγ). Under normal chow diet feeding, Rnf20 defective ( Rnf20 +/− ) mice exhibited reduced fat mass with smaller adipocytes compared with wild-type littermates. In addition, high-fat diet–fed Rnf20 +/− mice alleviated systemic insulin resistance accompanied by a reduced expansion of fat tissue. Quantitative proteomic analyses revealed significantly decreased levels of PPARγ target proteins in adipose tissue of Rnf20 +/− mice. Mechanistically, RNF20 promoted proteasomal degradation of nuclear corepressor 1 (NCoR1), which led to stimulation of the transcriptional activity of PPARγ. Collectively, these data suggest that RNF20-NCoR1 is a novel axis in adipocyte biology through fine-tuning the transcriptional activity of PPARγ.

Abnormalities of methyl-CpG binding protein 2 (Mecp2) cause neurological disorders with metabolic dysfunction; however, its role in adipose tissues remains unclear. Here, we report upregulated Mecp2 in white adipose tissues (WAT) of obese humans, as well as in obese mice and during in vitro adipogenesis. Normal chow–fed adipocyte-specific Mecp2 knockout mice ( Mecp2 Adi KO mice) showed a lean phenotype, with downregulated lipogenic genes and upregulated thermogenic genes that were identified using RNA sequencing. Consistently, the deficiency of Mecp2 in adipocytes protected mice from high-fat diet (HFD)–induced obesity and inhibited in vitro adipogenesis. Furthermore, Mecp2 Adi KO mice showed increased browning under different stimuli, including cold treatment. Mechanistically, Mecp2 bound to the promoter of secretory leukocyte protease inhibitor ( Slpi ) and negatively regulated its expression. Knockdown of Slpi in inguinal WAT of Mecp2 Adi KO mice prevented cold-induced browning. Moreover, recombinant SLPI treatment reduced the HFD-induced obesity via enhancing browning. Together, our results suggest a novel non–central nervous system function of Mecp2 in obesity by suppressing browning, at least partially, through regulating adipokine Slpi.

Statins are cholesterol-lowering agents that increase the incidence of diabetes and impair glucose tolerance via their detrimental effects on nonhepatic tissues, such as pancreatic islets, but the underlying mechanism has not been determined. In atorvastatin (ator)-treated high-fat diet–fed mice, we found reduced pancreatic β-cell size and β-cell mass, fewer mature insulin granules, and reduced insulin secretion and glucose tolerance. Transcriptome profiling of primary pancreatic islets showed that ator inhibited the expression of pancreatic transcription factor, mechanistic target of rapamycin (mTOR) signaling, and small G protein (sGP) genes. Supplementation of the mevalonate pathway intermediate geranylgeranyl pyrophosphate (GGPP), which is produced by 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, significantly restored the attenuated mTOR activity, v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MafA) expression, and β-cell function after ator, lovastatin, rosuvastatin, and fluvastatin treatment; this effect was potentially mediated by sGP prenylation. Rab5a, the sGP in pancreatic islets most affected by ator treatment, was found to positively regulate mTOR signaling and β-cell function. Rab5a knockdown mimicked the effect of ator treatment on β-cells. Thus, ator impairs β-cell function by regulating sGPs, for example, Rab5a, which subsequently attenuates islet mTOR signaling and reduces functional β-cell mass. GGPP supplementation could constitute a new approach for preventing statin-induced hyperglycemia.

Within the human pancreas, exocrine and endocrine cells control secretion of digestive enzymes and production of hormones to maintain metabolic homeostasis, respectively. While the vast majority of type 1 diabetes research efforts have focused on endocrine function and autoimmunity, recent studies identified a series of unique features (e.g., reduced weight and volume, increased density of leukocytes) within the exocrine pancreas in this disease, but the mechanisms underlying these aberrancies are unknown. Therefore, we histologically assessed amylase, insulin, glucagon, lipase, and/or trypsinogen in 78 organ donor pancreata from birth through adulthood in control subjects and those at various stages of type 1 diabetes. While amylase-positive (AMY+) acinar cells were detectable in pancreata from all study groups, tissues from individuals >2 years of age contained clusters of acinar cells devoid of amylase (AMY−). A majority of these AMY− cell clusters localized proximal to islets (i.e., peri-islet). Additionally, most AMY− clusters were positive for the exocrine enzymes lipase and trypsinogen. Interestingly, type 1 diabetes pancreata displayed significant reductions in the frequency of these AMY− cell clusters. These results support a contribution of the islet-acinar axis in pancreatic development and underscore a potential role for the exocrine pancreas in the pathogenesis of type 1 diabetes.

Insulin secretion is tightly regulated by membrane trafficking. RILP (Rab7 interacting lysosomal protein) regulates the endocytic trafficking, but its role in insulin secretion has not been investigated. In this study, we found that overexpression of RILP inhibited insulin secretion in both the β-cell lines and freshly isolated islets. Consequently, the expression of RILP in islets suppressed the ability to recover the glucose homeostasis in type 1 diabetes mice upon transplantation. Of physiological relevance is that RILP expression was upregulated in the diabetic mouse islets. Mechanistically, overexpression of RILP induced insulin granule clustering, decreased the number of proinsulin-containing granules in β-cells, and significantly promoted proinsulin degradation. Conversely, RILP depletion sustained proinsulin and increased insulin secretion. The proinsulin degradation induced by RILP expression was inhibited by lysosomal inhibitors and was Rab7-dependent. Finally, we showed that RILP interacts with insulin granule–associated Rab26 to restrict insulin secretion. This study presents a new pathway regulating insulin secretion and mechanically demonstrates a novel function of RILP in modulating insulin secretion through mediating the lysosomal degradation of proinsulin.

The sequelae of diabetes include microvascular complications such as diabetic kidney disease (DKD), which involves glucose-mediated renal injury associated with a disruption in mitochondrial metabolic agility, inflammation, and fibrosis. We explored the role of the innate immune complement component C5a, a potent mediator of inflammation, in the pathogenesis of DKD in clinical and experimental diabetes. Marked systemic elevation in C5a activity was demonstrated in patients with diabetes; conventional renoprotective agents did not therapeutically target this elevation. C5a and its receptor (C5aR1) were upregulated early in the disease process and prior to manifest kidney injury in several diverse rodent models of diabetes. Genetic deletion of C5aR1 in mice conferred protection against diabetes-induced renal injury. Transcriptomic profiling of kidney revealed diabetes-induced downregulation of pathways involved in mitochondrial fatty acid metabolism. Interrogation of the lipidomics signature revealed abnormal cardiolipin remodeling in diabetic kidneys, a cardinal sign of disrupted mitochondrial architecture and bioenergetics. In vivo delivery of an orally active inhibitor of C5aR1 (PMX53) reversed the phenotypic changes and normalized the renal mitochondrial fatty acid profile, cardiolipin remodeling, and citric acid cycle intermediates. In vitro exposure of human renal proximal tubular epithelial cells to C5a led to altered mitochondrial respiratory function and reactive oxygen species generation. These experiments provide evidence for a pivotal role of the C5a/C5aR1 axis in propagating renal injury in the development of DKD by disrupting mitochondrial agility, thereby establishing a new immunometabolic signaling pathway in DKD.

Endothelial dysfunction plays a crucial role in the progress of diabetic vasculopathy. C1q/tumor necrosis factor–related protein 13 (CTRP13) is a secreted adipokine that can ameliorate atherosclerosis and vascular calcification. However, the role of CTRP13 in regulating endothelial function in diabetes has yet to be explored. In this study, CTRP13 treatment improved endothelium-dependent relaxation in the aortae and mesenteric arteries of both db/db mice and streptozotocin-injected mice. CTRP13 supplement also rescued the impaired endothelium-dependent relaxation ex vivo in the db/db mouse aortae and in high glucose (HG)–treated mouse aortae. Additionally, CTRP13 treatment reduced reactive oxygen species overproduction and improved nitric oxide (NO) production and endothelial NO synthase (eNOS) coupling in the aortae of diabetic mice and in HG-treated human umbilical vein endothelial cells. Mechanistically, CTRP13 could increase GTP cyclohydrolase 1 (GCH1) expression and tetrahydrobiopterin (BH4) levels to ameliorate eNOS coupling. More importantly, CTRP13 rescued HG-induced inhibition of protein kinase A (PKA) activity. Increased PKA activity enhanced phosphorylation of the peroxisome proliferator–activated receptor α and its recruitment to the GCH1 promoter, thus activating GCH1 transcription and, ultimately, endothelial relaxation. Together, these results suggest that CTRP13 preserves endothelial function in diabetic mice by regulating GCH1/BH4 axis-dependent eNOS coupling, suggesting the therapeutic potential of CTRP13 against diabetic vasculopathy.

Coronary artery disease (CAD) is more frequent among individuals with dysglycemia. Preventive interventions for diabetes can improve cardiometabolic risk factors (CRFs), but it is unclear whether the benefits on CRFs are similar for individuals at different genetic risk for CAD. We built a 201-variant polygenic risk score (PRS) for CAD and tested for interaction with diabetes prevention strategies on 1-year changes in CRFs in 2,658 Diabetes Prevention Program (DPP) participants. We also examined whether separate lifestyle behaviors interact with PRS and affect changes in CRFs in each intervention group. Participants in both the lifestyle and metformin interventions had greater improvement in the majority of recognized CRFs compared with placebo ( P < 0.001) irrespective of CAD genetic risk ( P interaction > 0.05). We detected nominal significant interactions between PRS and dietary quality and physical activity on 1-year change in BMI, fasting glucose, triglycerides, and HDL cholesterol in individuals randomized to metformin or placebo, but none of them achieved the multiple-testing correction for significance. This study confirms that diabetes preventive interventions improve CRFs regardless of CAD genetic risk and delivers hypothesis-generating data on the varying benefit of increasing physical activity and improving diet on intermediate cardiovascular risk factors depending on individual CAD genetic risk profile.

It is estimated that ∼1% of European ancestry patients clinically diagnosed with type 1 diabetes (T1D) actually have monogenic forms of the disease. Because of the much lower incidence of true T1D in East Asians, we hypothesized that the percentage would be much higher. To test this, we sequenced the exome of 82 Chinese Han patients clinically diagnosed with T1D but negative for three autoantibodies. Analysis focused on established or proposed monogenic diabetes genes. We found credible mutations in 18 of the 82 autoantibody-negative patients (22%). All mutations had consensus pathogenicity support by five algorithms. As in Europeans, the most common gene was HNF1A (MODY3), in 6 of 18 cases. Surprisingly, almost as frequent were diallelic mutations in WFS1 , known to cause Wolfram syndrome but also described in nonsyndromic cases. Fasting C-peptide varied widely and was not predictive. Given the 27.4% autoantibody negativity in Chinese and 22% mutation rate, we estimate that ∼6% of Chinese with a clinical T1D diagnosis have monogenic diabetes. Our findings support universal sequencing of autoantibody-negative cases as standard of care in East Asian patients with a clinical T1D diagnosis. Nonsyndromic diabetes with WSF1 mutations is not rare in Chinese. Its response to alternative treatments should be investigated.

The American Diabetes Association’s Scientific Sessions Planning Committee is soliciting noteworthy abstract submissions for the 80th Scientific Sessions, which will take place 12–16 June 2020 at the McCormick Place Convention Center in Chicago, IL. The committee encourages submissions that are innovative, challenge current treatment paradigms, and represent the latest advances in basic, clinical, and translational science. The submission deadline is 12 January 2020. Please visit professional.diabetes.org/scientific-sessions for further information. Webcasts from the 79th annual American Diabetes Association Scientific Sessions are available. Held in June 2019, …

Loss of functional β cell mass is an essential feature of type 2 diabetes, and maintaining mature β cell identity is important for preserving a functional β cell mass. However, it is unclear how β cells achieve and maintain their mature identity. Here, we demonstrate a novel function of PRMT1 in maintaining mature β cell identity. Prmt1 knockout in fetal and adult β cells induced diabetes, which was aggravated by high fat diet-induced metabolic stress. Deletion of Prmt1 in adult β cells resulted in the immediate loss of histone H4 arginine 3 asymmetric di-methylation (H4R3me2a) and the subsequent loss of β cell identity. The expression levels of genes involved in mature β cell function and identity were robustly downregulated as soon as Prmt1 deletion was induced in adult β cells. ChIP-seq and ATAC-seq analyses revealed that PRMT1-dependent H4R3me2a increases chromatin accessibility at the binding sites for CTCF and β cell transcription factors. In addition, PRMT1-dependent open chromatin regions may show an association with the risk of diabetes in humans. Together, our results indicate that PRMT1 plays an essential role in maintaining β cell identity by regulating chromatin accessibility.

M2 macrophages play an important role in tissue repair and regeneration. They have also been found to modulate beta cell replication in mouse models of pancreatic injury and disease. We have previously reported that beta cell replication is strongly increased in a subgroup of human organ donors characterized by prolonged duration of stay in an intensive care unit (ICU) and increased number of leucocytes in the pancreatic tissue. In the present study we investigated the relationship between duration of stay in ICU, M2 macrophages, vascularization and pancreatic cell replication. Pancreatic organs from 50 non-diabetic donors with different duration of stay in ICU were analyzed by immunostaining and digital image analysis. The number of CD68+CD206+ M2 macrophages increased 3- to 6-fold from ≥6 days duration of stay in ICU onwards. This was accompanied by a 3-fold increased vascular density and a 4- to 9-fold increase in pancreatic cells positive for the replication marker Ki67. A strong correlation was observed between the number of M2 macrophages and beta cell replication. These results show that prolonged duration of stay in ICU is associated with an increased M2 macrophage number, increased vascular density and an overall increase in replication of all pancreatic cell types. Our data show evidence of marked levels of tissue repair in the human donor pancreas.

Type 1 Diabetes (T1D) is an autoimmune mediated disease that culminates in the targeted destruction of insulin producing β cells. CD4 responses in non-obese diabetic mice are dominated by InsB9-23 specificity, and mutation of the key TCR contact residue within the epitope prevents diabetes development. However, it is not clear how insulin self-antigen controls the selection of autoimmune and T regulatory cells. Here we demonstrate that mutation of insulin epitope results in escape of highly pathogenic T cells. We observe an increase in antigen reactivity, clonality and pathogenicity of insulin specific T cells that develop in the absence of cognate antigen. Using single TCR system, we demonstrate that Treg development is greatly diminished in mice with Y16A mutant epitope. Collectively, these results suggest that the tyrosine residue at position 16 is necessary to constrain TCR reactivity for InsB9-23 by both limiting the development of pathogenic T cells and supporting the selection of regulatory T cells.

Human but not mouse islets transplanted into immunodeficient NSG mice effectively accumulate lipid droplets (LDs). Because chronic lipid exposure is associated with islet β cell dysfunction, we investigated LD accumulation in the intact human and mouse pancreas over a range of ages and states of diabetes. Very few LDs were found in normal human juvenile pancreatic acinar and islet cells, with numbers subsequently increasing throughout adulthood. While accumulation appeared evenly distributed in post-juvenile acinar and islet cells in non-diabetic donors, LDs were enriched in islet α and β cells from type 2 diabetes mellitus (T2D). LDs were also found in the islet β-like cells produced from human embryonic cell derived β cell clusters (i.e. termed eBCs). In contrast, LD accumulation was nearly undetectable in the adult rodent pancreas, even in hyperglycemic and hyperlipidemic models or 1.5 year-old mice. Taken together, there appears to be significant differences in pancreas islet cell lipid handling between species, and the human juvenile and adult cell populations. Moreover, our results suggest that LD enrichment could be impactful to T2D islet cell function.

Insulin-like growth factors (IGFs), specifically IGF1 and IGF2, promote glucose metabolism with their availability regulated by IGF binding proteins (IGFBPs). We hypothesized that IGF1 and IGF2 levels, or their bioavailability, are reduced during type 1 diabetes development. Total serum IGF1, IGF2, and IGFBP1–7 levels were measured in an age-matched, cross-sectional cohort at varying stages of progression to type 1 diabetes. IGF1 and IGF2 levels were significantly lower in autoantibody (AAb)+ compared to AAb- relatives of type 1 diabetes subjects. Most high-affinity IGFBPs were unchanged in individuals with pre-type 1 diabetes, suggesting that total IGF levels may reflect bioactivity. We also measured serum IGFs from a cohort of fasted type 1 diabetes subjects. IGF1 levels significantly decreased with disease duration, in parallel with declining β-cell function. Additionally, plasma IGF levels were assessed in an AAb+ cohort drawn monthly for a year. IGF1 and IGF2 showed longitudinal stability in single AAb+ subjects, but IGF1 levels decreased over time in subjects with multiple AAb and those who progressed to type 1 diabetes, particularly post-diagnosis. In sum, IGFs are dysregulated both before and after the clinical diagnosis of type 1 diabetes and may serve as novel biomarkers to improve disease prediction.

Studies on magnetic resonance neurography (MRN) in diabetic polyneuropathy (DPN) have found proximal sciatic nerve lesions. The aim of this study was to evaluate the functional relevance of sciatic nerve lesions in DPN, expecting correlations with the impairment of large fiber function. 61 patients with diabetes mellitus type 2 (48 with, 13 without DPN) and 12 controls were enrolled, undergoing MRN, quantitative sensory testing, and electrophysiological examinations. There were differences in mechanical detection (Aβ fibers) and mechanical pain (Aδ fibers), but not in thermal pain and thermal detection clusters (C fibers) between the groups. Lesion load correlated with lower Aα, Aβ, and Aδ fiber, but not C fiber function in all participants. Patients with lower function showed a higher load of nerve lesions than patients with elevated function or no measurable deficit despite apparent DPN. Longer diabetes duration was associated with higher lesion load in patients with DPN, suggesting that nerve lesions in DPN may accumulate over time and become clinically relevant once a critical amount of nerve fascicles is affected. Moreover, MRN is an objective method for determining lower function mainly in medium and large fibers in DPN.