Enhanced histone H3K9 tri-methylation suppresses steroidogenesis in rat testis chronically exposed to arsenic

Arsenic poses a profound health risk including male reproductive dysfunction upon prolonged exposure. Histone methylation is an important epigenetic driver; however, its role in arsenic- induced steroidogenic pathogenesis remains obscure. In current study, we investigated the effect of histone H3K9 tri-methylation (H3K9me3) on expression pattern of steroidogenic genes in rat testis after long-term arsenic exposure. Our results revealed that arsenic exposure down-regulated the mRNA expressions of all studied steroidogenic genes (Lhr, Star, P450scc, Hsd3b, Cyp17a1, Hsd17b and Arom). Moreover, arsenic significantly increased the H3K9me3 level in rat testis. The plausible explanation of increased H3K9me3 was attributable to the up-regulation of histone H3K9me3 methyltransferase, Suv39h1 and down-regulation of demethylase, Jmjd2a. Since H3K9me3 activation leads to gene repression, we further investigated whether the down-regulation of steroidogenic genes was ascribed to the increased H3K9me3 level. To elucidate this, we determined the H3K9me3 levels in steroidogenic gene promoters, which also showed significant increase of H3K9me3 in the investigated regions after arsenic exposure. In conclusion, arsenic exposure suppressed the steroidogenic gene expression by activating H3K9me3 status, which contributed to steroidogenic inhibition in rat testis.