Novel DNA Methylation Sites Influence GPR15 Expression in Relation to Smoking

Abstract

Smoking is a major risk factor for cardiovascular diseases and has been implicated in the regulation of the G protein-coupled receptor 15 (GPR15) by affecting CpG methylation. The G protein-coupled receptor 15 is involved in angiogenesis and inflammation. An effect on <i>GPR15</i> gene regulation has been shown for the CpG site CpG3.98251294. We aimed to analyze the effect of smoking on <i>GPR15</i> expression and methylation sites spanning the <i>GPR15</i> locus. DNA methylation of nine <i>GPR15</i> CpG sites was measured in leukocytes from 1291 population-based individuals using the EpiTYPER. Monocytic <i>GPR15</i> expression was measured by qPCR at baseline and five-years follow up. <i>GPR15</i> gene expression was upregulated in smokers (beta (ß) = -2.699, <i>p</i>-value (<i>p</i>) = 1.02 × 10^-77) and strongly correlated with smoking exposure (ß = -0.063, <i>p</i> = 2.95 × 10^-34). Smoking cessation within five years reduced <i>GPR15</i> expression about 19% (<i>p</i> = 9.65 × 10^-5) with decreasing <i>GPR15</i> expression over time (ß = 0.031, <i>p</i> = 3.81 × 10^-6). Additionally, three novel CpG sites within <i>GPR15</i> affected by smoking were identified. For CpG3.98251047, DNA methylation increased steadily after smoking cessation (ß = 0.123, <i>p</i> = 1.67 × 10^-3) and strongly correlated with changes in <i>GPR15</i> expression (ß = 0.036, <i>p</i> = 4.86 × 10^-5). Three novel <i>GPR15</i> CpG sites were identified in relation to smoking and <i>GPR15</i> expression. Our results provide novel insights in the regulation of GPR15, which possibly linked smoking to inflammation and disease progression.