Diet-induced- and genetic-obesity differentially alters male germline histones

Obesity, an established risk factor for male subfertility or infertility, is primarily due to genetic and environmental causes. Our earlier studies have shown differential effects of high-fat diet-induced- (DIO) and genetically inherited- (GIO) obesity on DNA methylation in male germline and its subsequent effect on fertility. Here, we hypothesized that the effects of DIO and GIO on histone modifications in male germline could also contribute to fertility defects. We observed that DIO affected both active (H3K4me3, H3ac, and H4ac) and repressive (H3K9me3 and H3K27me3) histone marks in testis and their cell types, whereas GIO solely altered acetylated histones. This correlated with the deregulation of histone-modifying enzymes in the testis of both obese groups. Further, we also observed a decrease in chromatin remodelers in the testis of the DIO group, which were increased in the GIO group. Besides, there was an increase in core histones and a decrease in histone marks along with protamine deficiency in spermatozoa of the DIO group, whereas only H3K4me3 levels were increased in spermatozoa of the GIO group. Moreover, we observed alterations in the expression and enrichment patterns of a few developmental genes harbored by the active histone mark in resorbed embryos and spermatozoa of DIO rats. Together these epigenetic defects in the male germline could alter sperm quality and cause fertility defects in these obese groups. Differential changes in two obese groups could also be attributed to differences in their pathophysiological variations. Our study highlights epigenetic differences between DIO and GIO in the male germline and their subsequent impact on male fertility.