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Weigong Liao, Mingchun Cai, Jian Chen, Jian Huang, Fuyu Liu, Chunhua Jiang and Yuqi Gao

The study was conducted to explore the effects of hypobaric hypoxia on spermatogenesis in rats. Adult male Wistar rats were randomly divided into four groups: three hypoxia-exposed groups and one normoxic control group. Rats in the normoxic control group were raised at an altitude of 300 m, while rats in the 5-, 15-, and 30-day hypoxic groups were raised in a hypobaric chamber simulating a high altitude of 5000 m for 5, 15, and 30 days respectively. Flow cytometry was used to detect the DNA content of testicular spermatogenic cells in rats. The apoptosis of germ cells in testis was analyzed by using TUNEL assay. Spermatogenesis was also evaluated by morphology. Flow cytometry analysis revealed that 5–30 days of hypobaric hypoxia exposure significantly reduced the percentage of tetraploid cell population in rat testis. After rats were exposed to hypobaric hypoxia for 30 days, the ratio of haploid and diploid cell populations in testis reduced significantly. Seminiferous tubules with apoptotic germ cell increased after exposure to hypoxia. Most apoptotic germ cells were spermatogonia and spermatocytes. Hypoxia also caused decrease of cellularity of seminiferous epithelium, degeneration and sloughing of seminiferous epithelial cells occasionally. The data suggest that hypobaric hypoxia inhibits the spermatogenesis in rats. Decrease of tetraploid spermatogenic cells (primary spermatocytes) induced by hypoxia is an important approach to suppress spermatogenesis. The apoptosis of primary spermatocytes and spermatogonia may contribute to the loss of tetraploid cell populations.

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