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Jun Yin, Bing Ni, Yi-dong Yang, Zhong-wei Tang, Zhi-qi Gao, Lan Feng, Wei-gong Liao and Yu-qi Gao

Autophagy and apoptosis are interlocked in an extensive crosstalk. Our previous study demonstrated that hypotonic hypoxia-induced marked apoptosis of a spermatocyte-derived cell line (GC-2). However, whether hypoxia-induced apoptosis is mediated by inhibition of autophagy under hypoxic conditions remains unclear. In this study, GC-2 cells were cultured in 1% O2 and harvested at different time points. Autophagy was determined by acridine orange staining, cyto-ID staining, mCherry-GFP-LC3B adenovirus transfection and Western blotting for various autophagy markers. Apoptosis was detected by TUNEL staining, flow cytometry, JC-1 staining and Western blotting of apoptosis-related proteins. We found that hypoxia-induced apoptosis of GC-2 cells through mitochondrial and death receptor pathways and inhibited autophagic flux in GC-2 cells in a time-dependent manner. However, while marked autolysosome formation was observed in GC-2 cells before 24-h culture in hypoxic conditions, apparent apoptosis was observed only after 24-h culture in hypoxic conditions. Caspase-8 siRNA treatment induced cell survival, accompanied by induction of the mature autophagosome, acidic vesicular organelle formation and autophagic flux. Furthermore, Beclin-1 overexpression markedly attenuated the impairment of spermatogenesis in mice by inhibiting apoptosis of spermatocytes. The results of this study demonstrate that hypoxia inhibits autophagy, which further enhances hypoxia-induced apoptosis of mouse spermatocytes by promoting caspase-8 activation in a time-dependent manner, suggesting that combined application of apoptosis inhibition and autophagy activation might be a therapeutic strategy for treating hypoxia-induced male infertility.