Comparison of antioxidant capacity and apoptosis-related molecular changes in testicular tissue of Tibetan sheep at different altitudes.

The high-altitude hypoxic environment threatens the reproductive function of male animals. Although Tibetan sheep are well-adapted to the plateau, the molecular mechanisms underlying testicular functional maintenance remain unclear. Using testicular tissues from Tibetan sheep at three altitudes (2300, 3300, and 4000 m), this study systematically compared histomorphology, antioxidant status, apoptosis-related molecular changes, and related gene expression through histological, biochemical, molecular, and cellular assays. The aim was to multi-dimensionally analyze altitudinal differences in testicular antioxidant stress and apoptosis regulation, thereby exploring their association with high-altitude hypoxia adaptation. The results demonstrated that high-altitude Tibetan sheep exhibited significant reductions (P < 0.05) in seminiferous tubule diameter, seminiferous epithelium thickness, diameters of primary spermatocytes and spermatids, and Sertoli cell number. With increasing altitude, the total antioxidant capacity (T-AOC) and activities of key antioxidant enzymes (T-SOD, CAT, GSH-Px) were significantly lowered (P < 0.05), whereas malondialdehyde (MDA) content increased significantly (P < 0.05). At the molecular level, the relative expression of the anti-apoptotic protein Bcl-2 and Caspase 3 rose significantly with altitude (P < 0.05), while that of the pro-apoptotic protein Bax declined (P < 0.01), leading to a decreased Bax/Bcl-2 ratio (P < 0.01). Consistently, gene expression analysis showed significant elevations in Bcl-2, Caspase 3, SOD1, and Nrf2 (P < 0.05), but decreases in Bax, GPX3, and HO-1 (P < 0.05). In conclusion, the high-altitude hypoxic environment induces structural remodeling of spermatogenic function and exacerbates testicular oxidative stress in Tibetan sheep. In response, the testes deploy a coordinated adaptive mechanism, which involves regulating apoptosis-related molecular networks, altering antioxidant gene transcription, and initiating structural adjustments within the seminiferous epithelium to mitigate the challenges posed by hypoxia.