Abstract P097: Soluble TNF Receptor II Levels are Associated With Leukocyte DNA Methylation in the Major Histocompatibility Complex Region in the Framingham Heart Study

Background: Transmembrane TNF receptors are involved in signal transduction for inflammatory, apoptotic, and proliferative processes, and can be shed into the bloodstream in response to various stimuli. Soluble TNF receptor II (sTNFR2) levels are predictive of incident cardiovascular disease events. We speculate that sTNFR2 is associated with ‘epigenetic priming’ of leukocytes in community dwelling adults, which may relate to the pathophysiology underlying atherogenic risk. Methods: We conducted a methylome-wide association study of sTNFR2 levels among participants in the Framingham Offspring cohort (examination 8; 2005-2008). Methylation of whole-blood derived DNA was assayed by microarray (Infinium HumanMethylation450 BeadChip, Illumina). sTNFR2 was quantitated by an enzyme-linked immunosorbent assay (Quantikine, R&D Systems). We excluded individuals with known autoimmune diseases or on medications that affect inflammatory response. We conducted linear mixed effects models adjusting for age, sex, body mass index, smoking, imputed cell count, and technical covariates. A Bonferroni-adjusted p-value for 485k tests (p<1x10 -7 ) was considered significant. sTNFR2-related CpGs were tested for enrichment in DNAse I Hypersensitivity (DHS) hotspots and overlapping chromatin marks across various cell and tissues lines from ENCODE, Epigenomics Roadmap and Blueprint data. Genes annotated to sTNFR2-related CpGs were tested for overrepresentation for protein class and biological process gene ontologies. Results: Our study included 2472 participants (mean±SD: age 66±9 years, 54% female, sTNFRII 2658±1093 pg/ml). In the multivariable-adjusted model, methylation at 168 CpGs was associated with sTNFR2 levels (p<10 -7 , λ GC =1.4). Identified CpGs were enriched in active regulatory regions (DHS hotspots) across most blood cell lines (especially inflammatory macrophages, p<10 -15 ), but also vascular and cardiac tissues (p<10 -4 ). sTNFR2-related CpGs were enriched in loci that overlapped histone modifications indicative of enhancers (H3K4me1), and to a lesser extent, promoters (H3K4me3) and actively transcribed gene bodies (H3K36me3). A substantial proportion of the identified CpGs (27 CpGs; 16%) were located in the major histocompatibility complex (MHC) region. Overall, there was enrichment in the protein class ‘MHC antigen’ (p=3x10 -5 ) and the biological process ‘antigen processing and presentation’ (p=2x10 -4 ). Other top loci were in gene regions involved in NF-κB/cytokine pathways, such as NLRC5 , SOCS3 , BCL3, and SBNO2 . Conclusions: We identify numerous loci in the MHC region and near specific NF-κB pathway genes that are differentially methylated in blood in relation to sTNFR2 levels. We present a foundation of candidate loci for future studies to determine relevance for targeting to prevent, treat, or improve risk prediction for cardiovascular disease.