Effects of paternal exposure to cigarette smoke on sperm DNA methylation and long-term metabolic syndrome in offspring.

BACKGROUND: Although paternal exposure to cigarette smoke may contribute to obesity and metabolic syndrome in offspring, the underlying mechanisms remain uncertain. METHODS: In the present study, we analyzed the sperm DNA-methylation profiles in tobacco-smoking normozoospermic (SN) men, non-tobacco-smoking normozoospermic (N) men, and non-smoking oligoasthenozoospermic (OA) men. Using a mouse model, we also analyzed global methylation and differentially methylated regions (DMRs) of the DLK1 gene in paternal spermatozoa and the livers of progeny. In addition, we quantified DLK1 expression, executed an intra-peritoneal glucose tolerance test (IPGTT), measured serum metabolites, and analyzed liver lipid accumulation in the F1 offspring. RESULTS: Global sperm DNA-methylation levels were significantly elevated (p < 0.05) in the SN group, and the methylation patterns were different among N, SN, and OA groups. Importantly, the methylation level of the DLK1 locus (cg11193865) was significantly elevated in the SN group compared to both N and OA groups (p < 0.001). In the mouse model, the group exposed to cigarette smoke extract (CSE) exhibited a significantly higher global methylation DNA level in spermatozoa (p < 0.001) and on the DMR sites of Dlk1 in 10-week-old male offspring (p < 0.05), with a significant increase in Dlk1 expression in their livers (p < 0.001). In addition, IPGTT and LDL levels were significantly altered (p < 0.001), with elevated liver fat accumulation (p < 0.05) in F1 offspring. CONCLUSION: Paternal exposure to cigarette smoke led to increased global methylation of sperm DNA and alterations to the DMR of the DLK1 gene in the F1 generation, which may be inherited parentally and may perturb long-term metabolic function.