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Summary: Several studies have reported an association between the farnesoid X receptor alpha (FXRα) and estrogenic signaling pathways. Fxrα could thus be involved in the reprotoxic effects of endocrine disruptors such as bisphenol-A (BPA). To test this hypothesis, mice were exposed to BPA and/or stigmasterol (S), an FXRα antagonist. Following the exposure to both molecules, wild-type animals showed impaired fertility and lower sperm cell production associated with the alteration of the establishment and maintenance of the undifferentiated germ cell pool. The crosstalk between BPA and FXRα is further supported by the lower impact of BPA in mice genetically ablated for Fxrα and the fact that BPA counteracted the effects of FXRα agonists. These effects might result from the downregulation of Fxrα expression following BPA exposure. BPA and S act additively in human testis. Our data demonstrate that FXRα activity modulates the impact of BPA on male gonads and on undifferentiated germ cell population. : In this article, Dr Volle and colleagues show that Fxrα participate in the reprotoxic effects of endocrine disruptors such as bisphenol-A (BPA). The present study shows that modulation of FXRa signaling pathway by the FXRα antagonist, namely stigmasterol, acts additively with BPA, leading to impaired fertility and lower sperm cell production associated with the alteration of the establishment and maintenance of the undifferentiated germ cell pool. In addition these additive effects were also observed in human testis. Keywords: testis, germ cell, FXRα, bisphenol-A, fertility

Spermatogenesis is the process by which spermatozoa are generated from spermatogonia. This cell population is heterogeneous, with self-renewing spermatogonial stem cells (SSCs) and progenitor spermatogonia that will continue on a path of differentiation. Only SSCs have the ability to regenerate and sustain spermatogenesis. This makes the testis a good model to investigate stem cell biology. The Farnesoid X Receptor alpha (FXRα) was recently shown to be expressed in the testis. However, its global impact on germ cell homeostasis has not yet been studied. Here, using a phenotyping approach in Fxrα−/− mice, we describe unexpected roles of FXRα on germ cell physiology independent of its effects on somatic cells. FXRα helps establish and maintain an undifferentiated germ cell pool and in turn influences male fertility. FXRα regulates the expression of several pluripotency factors. Among these, in vitro approaches show that FXRα controls the expression of the pluripotency marker Lin28 in the germ cells.