Smoking-associated AHRR hypomethylation enables monocyte-specific enhancer activation, and upregulation of noncoding and coding RNA

While tobacco smoke exposure strongly influences DNA methylation and is causative in numerous human diseases, the underlying mechanistic links are obscure. Here we investigated genome-wide smoking-associated differentially methylated regions (SM-DMRs) using CD14 monocytes of smokers (n=47) and nonsmokers (n=46) from two independently recruited populations, the Multi-Ethnic Study of Atherosclerosis (MESA) and Clinical Research Unit (CRU) at NIEHS. We found that SM-DMRs preferentially occur at genomic regions with the characteristics of putative enhancer, open chromatin, and the enrichment of TF binding indicated by ENCODE/Roadmap Epigenome/BLUEPRINT datasets. Most of our selected candidate SM-DMRs identified in the two populations were also observed in other hematopoietic cell types (CD15 granulocytes, CD19 B cells, CD4 T cells, CD8 T cells, CD56 NK cells) and were successfully validated using a second method in an independently recruited group of subjects. Aryl-Hydrocarbon Receptor Repressor (AHRR) SM-DMR, located at an intragenic enhancer, was the most significantly affected DMR and we have previously reported that a methylation level of a CpG in this gene was associated with subclinical atherosclerosis. The AHRR DMR was also detected in saliva DNA and these results were highly correlated with effects in monocytes (r2 = 0.90), suggesting that saliva may provide a potential alternative, noninvasive source for biomarkers that use DNA. Mechanistically, our results suggested that AHRR SM-DMR upregulated AHRR mRNA through activating AHRR enhancer in monocytes of smokers but not in granulocytes, indicated by increased noncoding RNA. Taken together, our study suggests that cell type-specific activation of enhancers at SM-DMRs may represent a mechanism driving smoking-related disease. RRBS using DNA samples of circulating CD14+ monocytes from MESA and CRU populations. ***This study complies with the NIH Genomic Data Sharing (GDS) Policy. DNA samples were collected under NIH approved IRB protocols from volunteers who provided informed consent for analysis. We provide here the DNA methylation values at individual nonpolymorphic CpGs for individual subjects (equivalent to 450K datasets) but not sequence read data which could be used to identify individuals.***