Germ cell apoptosis regulation is pivotal in order to maintain proper daily sperm production. Several reports have shown that endocrine disruptors such as Bisphenol-A (BPA) and Nonylphenol (NP) induce germ cell apoptosis along with a decrease in sperm production. Given their ubiquitous distribution in plastic products used by humans it is important to clarify their mechanism of action. TACE/ADAM17 is a widely distributed extracellular metalloprotease and participates in the physiological apoptosis of germ cells during spermatogenesis. The aims of this work were: 1) to determine whether BPA and NP induce ADAM17 activation; and 2) to study whether ADAM17 and/or ADAM10 are involved in germ cell apoptosis induced by BPA and NP in the pubertal rat testis. A single dose of BPA or NP (50 mg/kg) induces germ cell apoptosis in 21-day-old male rats, which was prevented by a pharmacological inhibitor of ADAM17, but not by an inhibitor of ADAM10. In vitro, we showed that BPA and NP, at similar concentrations to those found in human samples, induce the shedding of exogenous and endogenous (TNF-α) ADAM17 substrates in primary rat Sertoli cell cultures and TM4 cell line. In addition, pharmacological inhibitors of metalloproteases and genetic silencing of ADAM17 prevent the shedding induced in vitro by BPA and NP. Finally, we showed that in vivo BPA and NP induced early activation (phosphorylation) of p38 MAPK and translocation of ADAM17 to the cell surface. Interestingly, the inhibition of p38 MAPK prevents germ cell apoptosis and translocation of ADAM17 to the cell surface. These results show for the first time that xenoestrogens can induce activation of ADAM17 at concentrations similar to those found in human samples, suggesting a mechanism by which they could imbalance para/juxtacrine cell-to-cell-communication and induce germ cell apoptosis.

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Constitutive germ cell apoptosis during mammalian spermatogenesis is a key process for controlling sperm output and to eliminate damaged or unwanted cells. An increase or decrease in the apoptosis rate has deleterious consequences and leads to low sperm production. Apoptosis in spermatogenesis has been widely studied, but the mechanism by which it is induced under physiological or pathological conditions has not been clarified. We have recently identified the metalloprotease ADAM17 (TACE) as a putative physiological inducer of germ cell apoptosis. The mechanisms involved in regulating the shedding of the ADAM17 extracellular domain are still far from being understood, although they are important in order to understand cell-cell communications. Here, we review the available data regarding apoptosis during mammalian spermatogenesis and the localization of ADAM proteins in the male reproductive tract. We propose an integrative working model where ADAM17, p38 MAPK, protein kinase C (PKC) and the tyrosine kinase c-Abl participate in the physiological signalling cascade inducing apoptosis in germ cells. In our model, we also propose a role for the Sertoli cell in regulating the Fas/FasL system in order to induce the extrinsic pathway of apoptosis in germ cells. This working model could be applied to further understand constitutive apoptosis in spermatogenesis and in pathological conditions (e.g., varicocele) or following environmental toxicants exposure (e.g., genotoxicity or xenoestrogens).

The xenoestrogens bisphenol-A (BPA) and nonylphenol (NP) are endocrine disruptors used in the plastic polymer industry to manufacture different products for human use. Previous studies have suggested a role of these compounds in the shedding of signaling molecules, such as tumor necrosis factor α (TNF-α). The aim of this work was to evaluate the effect of BPA and NP on the sheddase ADAM17 and its newly discovered regulators iRhom1 and iRhom2 in the release of EGFR-ligands. We report that BPA and NP can stimulate the release of the ADAM17-substrates HB-EGF and TGF-α. In cells lacking ADAM17 (Adam17 mEFs) BPA-stimulated release of HB-EGF, but not TGF-α, was strongly reduced, whereas NP-stimulated shedding of HB-EGF and TGF-α was completely abolished. Inactivation of both ADAM17 and the related ADAM10 (Adam10/17 mEFs) completely prevented the release of these substrates. In the absence of iRhom1, BPA- or NP-stimulated release of HB-EGF or TGF-α was comparable to wild-type control mEFs, conversely the BPA-induced release of HB-EGF was abolished in iRhom2 mEFs. The defect in shedding of HB-EGF in iRhom2 mEF cells could be rescued by overexpressing iRhom2. Interestingly, the NP-stimulated release of HB-EGF was not affected by the absence of iRhom2, suggesting that NP could potentially activate both ADAM10 and ADAM17. We tested this hypothesis using betacellulin (BTC), an EGFR-ligand that is a substrate for ADAM10. We found that NP, but not BPA stimulated the release of BTC in Adam17 , iRhom2 , or iRhom1/2 , but not in Adam10/17 cells. Taken together, our results suggest that BPA and NP stimulate the release of EGFR-ligands by differentially activating ADAM17 or ADAM10. The identification of specific effects of these endocrine disruptors on ADAM10 and ADAM17 will help to provide a better understanding of their roles in cell signaling and proinflammatory processes, and provide new potential targets for treatment of reproductive or inflammatory diseases such as asthma or breast cancer that are promoted by xenoestrogens.