Global Chromatin Remodeling and Widespread Differential Methylation Changes Underlie Brown Adipose Dysfunction and Dysregulated Metabolism in Response to Chronic Air Pollution Exposure: A Key Role for Reciprocal Regulation by HDAC9 and KDN2b
The Global Burden of Disease implicates air pollution in mediating as much as 20% of Type 2 Diabetes mellitus globally. This profound impact of air pollution is supported by experimental studies suggesting effects on whole body metabolism and insulin resistance. We explored the effect of chronic inhalational air pollution exposure for 12 weeks, using a whole body inhalation device in mice that allows for daily exposure to concentrated ambient particulate matter <2.5 microns (6 hours/day, 5 days a week) on whole body metabolism and brown adipose tissue (BAT) function, with detailed investigation of differentially methylated regions (DMRs), chromatin accessibility (differential accessible regions or DARs), and differential gene expression (DEGs) levels using a combination of whole genome bisulfite sequencing, ATAC-sequencing, and RNA-sequencing respectively. A significant impact of chronic PM2.5 exposure on BAT function and whole-body metabolism through alterations in key BAT transcriptional programs resulting in increased redox stress, lipid deposition, fibrosis and reduced thermogenic function of BAT was observed. Significant differential methylation with evidence for both hypomethylation and hypermethylation involving target regions corresponding to both circadian and Nrf2 target genes including sites enriched for transcription factor binding sites implicated in redox stress, insulin resistance and BAT function in response to PM2.5. ATAC sequencing revealed widespread chromatin remodeling involving intronic regions and enhancer elements and loss of DARs in Ucp1 and Gclc major regulatory genes associated with thermogenesis and glutathione synthesis. DARs-DEGs interaction analysis pointed to functional pathways linked to diabetes development, fatty acid biosynthesis activation and activation of JAK-STAT, and MAPK in PM-exposed mice. Integrated analysis of DARs, DEGs and DMRs uncovered the Histone de-acetylase Hdac9 and Kdm2b, a Histone demethylase that demethylates 'Lys-4' and 'Lys-36' of histone H3. ChiP studies demonstrated that Hdac9 physically interacts with the BAT transcription factor Prdm16 and rora in BAT decreasing their expression and providing at least one direct mechanism for our observations. Collectively our results results link DNA methylation with control of chromatin accessibility and gene expression changes involved in the alteration of brown fat metabolism linking chronic air pollution exposure with alterations in BAT and whole-body metabolism Overall design: WGBS and ATAC-seq were performed to compare the epigenome of air pollution exposed mice and control mice