Chronic hypoxia facilitates Alzheimer's disease through demethylation of γ-secretase by downregulating DNA methyltransferase 3b

Introduction: Environmental factors and epigenetic mechanisms are believed to contribute to Alzheimer's disease (AD). We previously documented that prenatal hypoxia aggravated the cognitive impairment and neuropathology in offspring mice. Here, we investigate the chronic hypoxiainduced epigenetic modifications in AD. Methods: The 3-month-old APP(swe)/PS1(dE9) mice were exposed to hypoxic environment 6 hour/day for 30 days, followed by learning and memory tests and biochemical and neuropathology measurement at the age of 4, 6, and 9 months. Results: We found hypoxia exaggerated the neuropathology and cognitive impairment in AD mice. Chronic hypoxia induced demethylation on genomic DNA and decreased the expression of DNA methyltransferase 3b (DNMT3b) in vivo. We further found that DNMTs inhibition elevated the protein levels of amyloid precursor protein, beta- and gamma-secretases, whereas overexpression of DNMT3b suppressed the levels of them in vitro. Discussion: Our study suggests chronic hypoxia can aggravate AD progression through demethylation of genes encoding gamma-secretase components by downregulation of DNMT3b. (C) 2016 The Alzheimer's Association. Published by Elsevier Inc. All rights reserved.