Dissecting the Epigenomic Differences between Smoking and Nicotine Dependence in a Veteran Cohort

BackgroundSmoking is a serious public health issue linked to more than 8 million deaths per year worldwide. It also may lead to nicotine dependence (ND). Smoking can induce long-lasting epigenetic changes. Although epigenetic alterations related to tobacco smoke have been largely studied, few works have investigated ND and its interaction with smoking status (SS). ObjectiveWe investigated the peripheral epigenomic profile of SS and ND in a U.S. male veteran cohort. MethodsDNA from saliva was collected from 1,135 European American (EA) male U.S. military veterans. DNAm was assessed using the Illumina Infinium Human MethylationEPIC BeadChip array. SS was evaluated as: current smokers (n=137; 12.1%) and non-current smokers (never and former smokers; n=998; 87.9%). ND was assessed using the Fagerstrom Test for Nicotine Dependence (FTND). EWAS and co-methylation analyses were conducted for SS and ND. ResultsA total of 450 and 22 genome-wide significant differentially methylated sites (DMS) were associated with SS and ND, respectively (fifteen overlapped sites). We identified 97 DMS (43 genes) in SS-EWAS previously reported in the literature, including AHRR, and F2RL3 genes (p-value range: 1.95x10-83 to 4.5x10-33). ND novel DMS mapped to NEUROG1, ANPEP, and SLC29A1. Co-methylation analysis identified 386 modules (11 SS-related and 19 ND-related). SS-related modules showed enrichment for alcoholism, chemokine signaling pathway, and neurogenesis; while ND-related modules were enriched for cellular adhesion, and nicotine addiction. ConclusionsThis study confirms previous findings and identifies novel and -potentially specific - epigenetic signatures for SS and ND in a sample of EA male veterans.