High fat diet-induced- and genetically inherited- obesity differential alters DNA demethylation pathways in the germline of adult male rats

Abstract

Obesity is a multifactorial condition with predominantly genetic and environmental causes and is an emerging risk factor for male infertility/subfertility. Epigenetic mechanisms are vulnerable to genetic and environmental changes. Our earlier studies have shown differential effects of genetically inherited (GIO) - and diet-induced- obesity (DIO) on DNA methylation in male germline. Contrary to DNA methylation is DNA demethylation, which also regulates the gene expression by activating transcription. The present study aimed to delineate the effects of obesity on the DNA demethylation pathway using two rat models: GIO (WNIN/Ob) and DIO (high-fat diet). We observed differential alterations in enzymes involved in DNA demethylation by oxidation (Tet1-3) pathway in testis in both groups. An increase in Tets in DIO group and a decrease in GIO group were noted. Analysis of oxidation pathway intermediates (5-hmC, 5-fC, and 5-caC) did not show any effect on testis in DIO group but an increase in 5-hmC and decrease in 5-caC levels in GIO group was observed. Analysis of transcript levels of enzymes related to deamination pathway in testis showed an increase (Gadd45a, Aicda, and Tdg) in DIO group and a decrease (Gadd45a, Aicda, and Tdg) in GIO group. Also, 5-hmC levels were differentially altered in the spermatozoa of both groups without any changes in Tet enzyme levels. These findings highlight differences in effects of GIO and DIO on DNA demethylation mechanisms in male germline, which could be due to differences in endocrine and metabolic profile as well as white fat distribution observed earlier in two groups.