The specific functions of ERs and AR underline
The specific functions of ERs and AR underline their crucial roles during different phases of spermatogenesis. Their deregulation could affect numerous downstream targets, thereby, disrupting spermatogenesis and male fertility. Various studies have shown that estrogen-like chemicals in the environment can cause changes in ERα, ERβ, and AR gene expression in the testis, thus affecting spermatogenesis. Dietary exposure of diethylstilbestrol (DES), a synthetic estrogen, caused a 50% reduction in testicular AR expression in rats . On the other hand, estradiol administered to neonatal rats increased AR and ERβ mRNA levels in testis . Neonatal exposure of bisphenol A (BPA), a selective Benzethonium Chloride receptor receptor modulator (SERM), in male mice disrupted spermatogenesis and increased the levels of ERα and ERβ in developing testis . Also, administration of Aroclor 1254 (a polychlorinated bisphenol) to male mice led to disrupted spermatogenesis and increase in ERα and β expression . Most of these studies are done in neonates and there is a dearth of studies in adults, where spermatogenesis is already ongoing. A study done by Kaushik et al. showed that adult male rats exposed to supraphysiological dose of estradiol, had increased ERα and AR transcript levels in the testis .
In vivo models of endocrine disruption, which involve administration of estradiol or SERMs like BPA, alter physiological levels of estradiol and androgens, and result in a combination of effects. Therefore, in these models it is not possible to identify whether the changes in ERs and AR levels are due to estradiol or androgen. Thus, there is no consensus on the regulation of expression of these steroid receptors by steroid hormones during spermatogenesis and a lack of clear understanding of the mechanism of regulation. In the present study, we evaluated the receptor expressions in a well-established exogenous E2 administration model , followed by investigation of the mechanism by which the individual receptors regulate expression by binding to EREs and AREs upstream of the ER and AR genes. We also delineate ER and AR expression in a receptor subtype-specific manner using in vitro and in vivo models.
Materials and Methods
Results and Discussion In the present study, we report the regulation of estrogen and androgen receptor expression by estrogen and androgen through their cognate receptors and the mechanism involved. We began this study using a well-established model in our lab in which exogenous E2 exposure to adult male rats disrupted spermatogenesis by causing spermiation failure and germ cell apoptosis [17,27]. Since the E2 treatment in this model causes an increase in intra-testicular E2 and decrease in intra-testicular T, we have further used in vitro and in vivo models of ER and AR stimulation and antagonism to delineate the regulation by the two steroids [10,18,26]. Finally, we also demonstrate presence of functional EREs and AREs upstream of ER and AR genes that control ER and AR expression.
Conclusion Our results delineate for the first time the direct regulation of ERs and AR expression by the sex steroid hormones in the testis. By further employing in vitro and in vivo models of ERs and AR stimulation, we demonstrate the intricate auto-regulatory and inhibitory loops of regulations. ERα stimulates the expression of both the ERs; whereas, ERβ and AR seem to play a similar inhibitory role in the expression of both ERβ and AR by direct binding to upstream regulatory regions. We can now appreciate the individual contribution of the ERs and AR in the regulation of the sex steroid receptors during spermatogenesis.
Acknowledgements The study (RA/506/07-2017) was supported by National Institute for Research in Reproductive Health (NIRRH) budget to N.H. Balasinor and the fellowships of Anita Kumar (3/1/2/4/16-RBMH) and Kushaan Dumasia (RBMH/FW/2015-25340/3) were provided by Indian Council of Medical Research. The authors acknowledge technical assistance provided by Mr. Suryakant Mandavkar for animal handling, injections and dissection as well as Mr. D. Shelar for other technical help. Assistance from Ms. Surbhi Mistry in optimization of Sertoli cell culture is also acknowledged.