Elsevier

Free Radical Biology and Medicine

Volume 147, 1 February 2020, Pages 242-251
Free Radical Biology and Medicine

Original article
Traffic-related air pollutants (TRAP-PM) promote neuronal amyloidogenesis through oxidative damage to lipid rafts

https://doi.org/10.1016/j.freeradbiomed.2019.12.023Get rights and content

Highlights

  • Exposure to traffic-related air pollutants (TRAP) of nano-particle size (nPM) increases pro-amyloidogenic processing of APP.

  • TRAP increases the oxidative damage to lipid rafts, both in vivo and in vitro, as shown by increased 4-HNE levels.

  • In vitro, antioxidant N-acetyl-cysteine (NAC) attenuated nPM-induced oxidative damage to lipid rafts and APP/Abeta levels.

  • Lipid raft alterations of APP processing represents a novel target of air pollution.

Abstract

Traffic-related air pollution particulate matter (TRAP-PM) is associated with increased risk of Alzheimer Disease (AD). Rodent models respond to nano-sized TRAP-PM (nPM) with increased production of amyloid Aβ peptides, concurrently with oxidative damage. Because pro-Aβ processing of the amyloid precursor protein (APP) occurs on subcellular lipid rafts, we hypothesized that oxidative stress from nPM exposure would alter lipid rafts to favor Aβ production. This hypothesis was tested with J20 mice and N2a cells transgenic for hAPPswe (familial AD). Exposure of J20-APPswe mice to nPM for 150 h caused increased lipid oxidation (4-HNE) and increased the pro-amyloidogenic processing of APP in lipid raft fractions in cerebral cortex; the absence of these changes in cerebellum parallels the AD brain region selectivity for Aβ deposits. In vitro, nPM induced similar oxidative responses in N2a-APPswe cells, with dose-dependent production of NO, oxidative damage (4-HNE, 3NT), and lipid raft alterations of APP with increased Aβ peptides. The antioxidant N-acetyl-cysteine (NAC) attenuated nPM-induced oxidative damage and lipid raft alterations of APP processing. These findings identify neuronal lipid rafts as novel targets of oxidative damage in the pro-amyloidogenic effects of air pollution.

Graphical abstract

Traffic-related air pollutants (TRAP) of nano-particle size (nPM) increase the risk of Alzheimer Disease (AD). We propose a new molecular mechanism in the pro-amyloidogenic effect of TRAP. Exposure of mice or cells to nPM (1) increases the oxidative damage to cell membranes (2). In particular, the oxidation of lipid raft domains (3) alters APP processing (4) to increase production of Aβ fragments (5). Treatment with anti-oxidant N-acetyl-cysteine (NAC) attenuated nPM-induced oxidative damage to lipid rafts and pro-amyloidogenic alterations of APP processing. These findings identify lipid raft alterations of APP processing as a novel target of air pollution relevant to cognitive impairments.

Image 1
  1. Download : Download high-res image (143KB)
  2. Download : Download full-size image

Introduction

Alzheimer disease (AD) and accelerated cognitive aging are associated with traffic-related air pollution particulate matter (TRAP-PM) in several studies [[1], [2], [3], [4], [5]] and other reports critically reviewed in Refs. [6,7]. However, the subcellular mechanisms of TRAP-PM induced neurodegeneration are obscure. We show lipid raft alterations that increase production of the neurotoxic amyloid peptide Aβ as a novel mechanism in air pollution toxicology.

Premature brain deposits of Aβ in children and young adults from a highly polluted Mexican city suggested increased production of brain Aβ as a possible mechanism in TRAP-PM associated AD risk [8]. Correspondingly, young wildtype rodents had increased levels of soluble Aβ peptides from exposure to various TRAP components: diesel exhaust [9], nickel nano-particles [10], and TRAP-PM [11]. While these wildtype rodents do not acquire fibrillar deposits of the endogenous species-specific Aβ, mice carrying the APPswe mutation for familial AD together with human ApoE genes (EFAD genotype) responded to TRAP-nPM with increased Aβ oligomers and fibrillar Aβ plaque load [1]. In vitro, TRAP-nPM also increased Aβ production in neuronal N2a cells transgenic for APPswe [1]. TRAP-nPM is a subfraction of ultrafine PM, <0.2μ in size, collected from a local freeway, which is neurotoxic at low levels in vitro [[12], [13], [14]].

The present study analyzed subcellular mechanisms of nPM-induced Aβ increase with J20 mice and neuronal N2a cells transgenic for APPswe. Processing of the amyloid precursor protein (APP) occurs on lipid rafts, where neuronal APP is sequentially cleaved by the endoproteases α- or β-secretase, and by γ-secretase [15]. The resulting soluble APP fragments (sAPPα and sAPPβ) are then processed to Aβ38-43 peptides [16]. Pro-amyloidogenic processing is also characterized by an increased sAPPβ:sAPPα ratio [16]. Cerebral cortex was compared with the cerebellum, a brain region with minimal amyloid deposits and neurodegeneration in AD [8].

Because TRAP-nPM induces oxidative stress [[12], [13], [14]] and because the lipid oxidation product 4-HNE can increase neuronal Aβ levels [17], we considered oxidative mechanisms in altered APP processing. We also assayed nitric oxide (NO) which is rapidly induced by nPM in vitro together with 4-HNE [13,14]. In vivo and in vitro models tested the hypothesis that nPM exposure would cause lipid raft oxidation and stimulate pro-amyloidogenic APP processing.

Section snippets

nPM collection and extraction

Nano-sized particulate matter (nPM, <0.2 μm in diameter) was collected on Teflon filters by a High-Volume Ultrafine Particle (HVUP) Sampler [18] at 400 L/min flow, 150 m downwind of the I-110 Freeway in central Los Angeles. These TRAP-PM0.2 particles are a mix of fresh ambient PM from vehicular traffic and industrial sources [19,20]. Filter-trapped nPM were eluted by sonication into deionized water and stored at −20 °C. Their chemical composition matched prior studies, with enrichment of ions

Results

Chronic nPM exposure of J20-hAPPswe mice increased Aβ, APP, oxidation in lipid rafts.

Cerebral cortex of male mice exposed to nPM for 150 total hours over 10 weeks had increased soluble Aβ and plaque Aβ load: total SDS-soluble Aβ40, +5-fold, p < 0.05; Aβ42, +10-fold, p < 0.05 (Fig. 1a); plaque Aβ, + 45%, p < 0.05 (Fig. 1b). Lipid raft enriched subcellular fractions had increased APP (65%, p < 0.05) (Fig. 1c and d). In contrast, no changes were detected in the endoproteases responsible for the

Discussion

This is the first evidence that air pollutants alter lipid rafts in neuronal cells in vivo and in vitro, and the first evidence associating lipid raft oxidation from air pollutants with pro-amyloidogenic processes relevant to AD. The relation of pro-amyloidogenic processes to membrane oxidation to lipid rafts was shown in vivo and in vitro with J20 mice and N2a cells carrying the familial AD gene, APPswe, that increases Aβ42 production. The mouse and cell findings are summarized in Table 1.

Funding

This study was supported by Cure Alzheimer's Fund and National Institute on Aging R21AG050201 and R01AG051521 and P50AG05142-31 to CEF, and National Institute of Environmental Health Sciences (NIEHS) ES023864 to HJF.

Acknowledgments

We thank Prof. Myron Goodman (USC) for use of the ultracentrifuge. This study was supported by Cure Alzheimer's Fund and National Institute on Aging R21AG050201 and R01AG051521and P50AG05142-31 to CEF, and National Institute of Environmental Health Sciences (NIEHS) ES023864 to HJF.

References (50)

  • G. Premasekharan

    Iron-mediated lipid peroxidation and lipid raft disruption in low-dose silica-induced macrophage cytokine production

    Free Radic. Biol. Med.

    (2011)
  • J.L. Macdonald et al.

    A simplified method for the preparation of detergent-free lipid rafts

    J. Lipid Res.

    (2005)
  • H. Laudon et al.

    The Alzheimer's disease-associated gamma-secretase complex: functional domains in the presenilin 1 protein

    Physiol. Behav.

    (2007)
  • K.L. Youmans

    APOE4-specific changes in Abeta accumulation in a new transgenic mouse model of Alzheimer disease

    J. Biol. Chem.

    (2012)
  • P. Picon-Pages et al.

    Functions and dysfunctions of nitric oxide in brain

    Biochim. Biophys. Acta (BBA) - Mol. Basis Dis.

    (2019)
  • X. Yang

    Uptake of silica nanoparticles: neurotoxicity and Alzheimer-like pathology in human SK-N-SH and mouse neuro2a neuroblastoma cells

    Toxicol. Lett.

    (2014)
  • H.J. Forman et al.

    A critical review of assays for hazardous components of air pollution

    Free Radic. Biol. Med.

    (2018)
  • M. Cacciottolo

    Particulate air pollutants, APOE alleles and their contributions to cognitive impairment in older women and to amyloidogenesis in experimental models

    Transl. Psychiatry

    (2017)
  • X. Zhang et al.

    The impact of exposure to air pollution on cognitive performance

    Proc. Natl. Acad. Sci. U. S. A.

    (2018)
  • L. Calderon-Garciduenas et al.

    Combustion and friction-derived nanoparticles and industrial-sourced nanoparticles: the culprit of Alzheimer and Parkinson's diseases

    Environ. Res.

    (2019)
  • K.C. Paul

    Ambient air pollution, noise, and late-life cognitive decline and dementia risk

    Annu. Rev. Public Health

    (2019)
  • R. Peters

    Air pollution and dementia: a systematic review

    J. Alzheimer's Dis.

    (2019)
  • L. Calderon-Garciduenas

    Long-term air pollution exposure is associated with neuroinflammation, an altered innate immune response, disruption of the blood-brain barrier, ultrafine particulate deposition, and accumulation of amyloid beta-42 and alpha-synuclein in children and young adults

    Toxicol. Pathol.

    (2008)
  • S. Levesque

    Air pollution & the brain: subchronic diesel exhaust exposure causes neuroinflammation and elevates early markers of neurodegenerative disease

    J. Neuroinflammation

    (2011)
  • D.P. Bhatt

    A pilot study to assess effects of long-term inhalation of airborne particulate matter on early Alzheimer-like changes in the mouse brain

    PLoS One

    (2015)
  • Cited by (0)

    View full text