Integrative genomic analyses in adipocytes implicate DNA methylation in human obesity and diabetes

DNA methylation variations are prevalent in human obesity, but evidence of a causative role in disease pathogenesis is limited. In this study, we combine epigenome-wide association and integrative genomics to investigate the impact of subcutaneous and visceral adipocyte DNA methylation variations in extreme human obesity. We identify extensive DNA methylation changes that are robustly associated with extreme obesity in combined discovery and replication analyses (N=190 samples, 691 loci in subcutaneous and 173 loci in visceral adipocytes, P<1x10-7). Using functional interaction maps and methylation-expression association testing in human adipocytes, we connect extreme obesity-associated methylation variations to transcriptomic changes at >500 target genes. We find that disease-associated methylation variations localise to active genomic regions and transcription factor binding sites, at which DNA methylation influences transcription factor-target gene co-expression relationships. In Mendelian Randomisation analyses, we infer causal effects of DNA methylation on human obesity and obesity-induced metabolic disturbances, under genetic control, at 28 independent loci. Silencing of two target genes of causal DNA methylation variations, the PRRC2A and LIMD2 genes, further reveals novel metabolic effects in adipocytes. Our results indicate DNA methylation is an important determinant of human obesity and its metabolic complications, and reveal genomic and molecular mechanisms through which altered DNA methylation may impact adipocyte cellular functions.