Alteration of Transforming Growth Factor-β Signaling System Expression in Adult Rat Germ Cells with a Chronic Apoptotic Cell Death Process after Fetal Androgen Disruption

Abstract

In utero exposure to chemicals with antiandrogen activity induces undescended testis, hypospadias, and sub- or infertility. The hypospermatogenesis observed in the adult rat testis exposed in utero to the antiandrogen flutamide has been reported to be a result of a long-term apoptotic cell death process in mature germ cells. However, little if anything is known about the upstream signaling mechanisms controlling this apoptosis. In the present study, we have investigated the possibility that the TGF-beta signaling pathway may be at play in this control of the apoptotic germ cell death process. By using a model of adult rat exposed in utero to 0, 0.4, 2, or 10 mg/kg.d flutamide, we observed that pro-TGF-beta signaling members, such as the three isoforms of TGF-beta ligands (TGF-beta1-3), the two TGF-beta receptors (TGF-betaRI and -RII) and the R-Smads Smad 1, Smad 2, Smad 3, and Smad 5 were inhibited at the mRNA and protein levels, whereas the anti-TGF-beta signaling member Smad 7 was overexpressed. Furthermore, we report that the overexpression of Smad 7 mRNA could induce an activation of c-Jun N-terminal kinase, because of the observed c-Jun overexpression, activation, and nuclear translocation leading to an increase in the transcription of the proapoptotic factor Fas-L. Together, the alterations of TGF-beta signaling may represent upstream mechanisms underlying the adult germ cell apoptotic process evidenced in adult rat testis exposed in utero to antiandrogenic compounds such as flutamide.