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

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 5 alpha-dihydrotestosterone (5 alpha-DHT), which is actively involved in sexual differentiation and development, is converted from testosterone (T) by the steroid 5 alpha-reductases type 1, 2, and 3 (Srd5 alpha 1, Srd5 alpha 2, and Srd5 alpha 3). Alternatively, steroid 5 beta-reductase (Srd5 beta) converts T to 5 beta-dihydrotestosterone (5 beta-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, 5 alpha-DHT, and 5 beta-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 srd5 alpha 2, suggesting that this isoform is not regulated by T and 5 alpha-DHT in frogs. However, the DNA methylation of srd5 alpha 2 increased following 5 alpha-DHT treatment suggesting that androgens can modulate epigenetic mechanisms in amphibians. In contrast, the DNA methylation of srd5 alpha 1 and srd5 alpha 3 remained stable after androgen exposure, but the mRNA levels of srd5 alpha 1 and srd5 alpha 3 were modulated by T, 5 alpha-DHT, and 5 beta-DHT in a sex- and tissue-specific manner. While T positively regulates srd5 alpha 1 and srd5 alpha 3 in testes, T negatively regulates srd5 alpha 3 in ovaries. Moreover, exposure to T also increased the mRNA level of srd5 in the male brain suggesting a mechanism to protect the brain from androgen action by elimination of T into 5 beta-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. (C) 2016 Elsevier Inc. All rights reserved.