Hypoxia-induced apoptosis of mouse spermatocytes is mediated by HIF-1 through a death receptor pathway and a mitochondrial pathway

Hypoxia in vivo induces oligozoospermia, azoospermia, and degeneration of the germinal epithelium, but the underlying molecular mechanism of this induction is not fully clarified. The aim of this study was to investigate the role of the death receptor pathway and the mitochondrial pathway in hypoxia-induced apoptosis of mouse GC-2spd (GC-2) cells and the relationship between HIF-1 and apoptosis of GC-2 cells induced by hypoxia. GC-2 cells were subjected to 1% oxygen for 48hr. Apoptosis was detected by flow cytometry, TUNEL staining, LDH, caspase-3/8/9 in the absence and presence of HIF-1 siRNA. The protein levels of apoptosis-related markers were determined by Western blot in the presence and absence of HIF-1 siRNA. Mitochondrial transmembrane potential change was observed by in situ JC-1 staining. Cell viability was assessed upon treatment of caspase-8 and 9 inhibitors. The results indicated that hypoxia at 1% oxygen for 48hr induced apoptosis of GC-2 cells. A prolonged exposure of GC-2 cells to hypoxic conditions caused downregulation of c-FLIP, DcR2 and Bcl-2 and upregulation of DR5, TRAIL, Fas, p53, and Bax, with an overproduction of caspase-3/8/9. Moreover, hypoxia at this level had an effect on mitochondrial depolarization. In addition, specific inhibitors of caspase-8/9 partially suppressed hypoxia-induced GC-2 cell apoptosis, and the anti-apoptotic effects of the caspase inhibitors were additive. Of note, HIF-1 knockdown attenuated hypoxia and induced apoptosis of GC-2 cells. In conclusion, our data suggest that the death receptor pathway and mitochondrial pathway, which are likely mediated by HIF-1, contribute to hypoxia-induced GC-2 cell apoptosis.