Aim： To investigate the activation of the nuclear factor of activated T cells （NFAT） and its function in the corticosterone （CORT）-induced apoptosis of rat Leydig cells. Methods： NFAT in rat Leydig cells was detected by Western blotting and immunohistochemical staining. Cyclosporin A （CsA） was used to evaluate potential involvement of NFAT in the CORT-induced apoptosis of Leydig cells. Intracellular Ca^2＋ was monitored in CORT-treated Leydig cells using Fluo-3/AM. After the Leydig cells were incubated with either CORT or CORT plus CsA for 12 h, the levels of NFAT2 in the nuclei and in the cytoplasm were measured by semi-quantitative Western blotting. The role of NFAT2 in CORT- induced Leydig cell apoptosis was further evaluated by observing the effects of NFAT2 overexpression and the inhibition of NFAT2 activation by CsA on FasL expression and apoptosis. Results： We found that NFAT2 was the predominant isoform in Leydig cells. CsA blocked the CORT-induced apoptosis of the Leydig cells. The intracellular Ca^2＋ level in the Leydig cells was significantly increased after the CORT treatment. The CORT increased the level of NFAT2 in the nuclei and decreased its level in the cytoplasm. CsA blocked the CORT-induced nuclear translocation of NFAT2 in the Leydig cells. Both CORT-induced apoptosis and FasL expression in the rat Leydig cells were enhanced by the overexpression of NFAT2 and antagonized by CsA. Conclusion： NFAT2 was activated in CORT-induced Leydig cell apoptosis. The effects of NFAT2 overexpression and the inhibition of NFAT2 activation suggest that NFAT2 may potentially play a pro-apoptotic role in CORT-induced Leydig cell apoptosis through the up-regulation of FasL.
