Androgens modulate gene expression and specific DNA methylation pattern of steroid 5α-reductases in the frog Silurana tropicalis

Abstract

In vertebrates, androgens are essential in many biological functions, including reproduction, immune system, metabolism, cardiovascular function, and the central nervous system. The most potent androgen 5α-dihydrotestosterone (5α-DHT), which is actively involved in sexual differentiation and development, is converted from testosterone (T) by the steroid 5α-reductases type 1, 2, and 3 (Srd5α1, Srd5α2, and Srd5α3). Alternatively, steroid 5β-reductase (Srd5β) converts T to 5β-dihydrotestosterone (5β-DHT), a metabolite believed to be involved in steroid clearance. Recent studies suggested that Srd5 isoforms are targets for endocrine disruption. Thus, understanding the regulation of Srd5 is important to expand our knowledge on how exogenous compounds can interfere with these enzymes. In this study, we exposed frog brain, liver, and gonads ex vivo to T, 5α-DHT, and 5β-DHT in order to investigate the regulation of srd5 in response to androgens as a simulation of endocrine disrupting chemicals with androgenic properties. Androgens did not modulate srd5α2, suggesting that this isoform is not regulated by T and 5α-DHT in frogs. However, the DNA methylation of srd5α2 increased following 5α-DHT treatment suggesting that androgens can modulate epigenetic mechanisms in amphibians. In contrast, the DNA methylation of srd5α1 and srd5α3 remained stable after androgen exposure, but the mRNA levels of srd5α1 and srd5α3 were modulated by T, 5α-DHT, and 5β-DHT in a sex- and tissue-specific manner. While T positively regulates srd5α1 and srd5α3 in testes, T negatively regulates srd5α3 in ovaries. Moreover, exposure to T also increased the mRNA level of srd5β in the male brain suggesting a mechanism to protect the brain from androgen action by elimination of T into 5β-DHT. Thus, exogenous compounds with androgenic properties potentially interact with srd5 transcription and DNA methylation pattern, which could adversely affect biological functions of vertebrates during development and reproduction.