Heat stress is a major concern in animal reproduction, as testicular temperature must be 3-5 °C below body core temperature for production of motile and fertile sperm in mammals. Although recent studies concluded that increased temperature per se was the underlying pathophysiology of testicular impairment, more studies are required to better understand the mechanisms. Therefore, our objective was to investigate the impacts of mild acute heat stress on sperm and testes, and based on mRNA, elucidate involvement of StAR, Trp53 and Trp53-dependent intrinsic and extrinsic apoptotic pathways in pathophysiology of testicular heat stress. Forty-eight C57 BCL6 elite male mice were equally allocated into six groups, anesthetized and the distal third of their body immersed in a water-bath at 40 or 30 °C (heat treatment and control, respectively) for 20 min. Intervals from heat exposure (Day 0) to euthanasia were: 8 and 24 h and 7, 14 and 21 d (plus a control group at 14 d). The epididymides were excised, minced and placed in Tyrode albumin lactate pyruvate hepes (TALPH) at 37 °C for 15 min to recover sperm. Based on computer assisted sperm analysis (CASA), heat treatment reduced total and progressive motility ∼40% (P < 0.05) on Days 14 and 21. Furthermore, percentage morphologically normal sperm was significantly decreased on Day 7, with greater reductions on Days 14 and 21, mostly due to increased midpiece defects. Acrosome integrity (FITC PSA) was decreased ∼35% at 8 h (P < 0.05) and reached a nadir on Day 14. There were decreases (P < 0.05) in seminiferous tubule diameter and testicular weight (relative to body weight) on Day 14. Testicular RNA was extracted, reverse-transcribed and cDNA used for PCR. Expression of genes Hspa1b (Hsp70) and Gpx1 had 7- and 10-fold increases (P < 0.001 for each) at 8 and 24 h, respectively, with Hspa1b remaining upregulated at 24 h, whereas StAR peaked at Day 14 (15-fold, P < 0.0001) and had returned to baseline on Day 21. Both Trp53 and Casp8 were upregulated (P < 0.05) on Day 14, whereas Bcl-2 was decreased (P < 0.05) on Days 7 and 14. In conclusion, acute mild heat stress severely reduced sperm quality and based on mRNA, there was upregulation of chaperone and antioxidant systems and Trp53-dependent intrinsic and extrinsic apoptotic pathways, with deleterious effects on sperm, spermatocytes and spermatids. These findings provided insights into the pathophysiology of heat stress and should contribute to development of evidence-based approaches to mitigate effects of testicular heating.

中文翻译：

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急性轻度热应激会改变睾丸中的基因表达并降低小鼠的精子质量

热应激是动物繁殖的一个主要问题，因为睾丸温度必须比身体核心温度低 3-5°C，才能在哺乳动物中产生活动和可育精子。尽管最近的研究得出结论，温度升高本身是睾丸损伤的潜在病理生理学，但还需要更多的研究来更好地了解其机制。因此，我们的目标是研究轻度急性热应激对精子和睾丸的影响，并基于 mRNA 阐明 StAR、Trp53 和 Trp53 依赖性内在和外在凋亡途径在睾丸热应激病理生理学中的参与。48 只 C57 BCL6 精英雄性小鼠被均等地分为六组，将其身体的远端三分之一浸入 40 或 30°C 的水浴中（分别为热处理和对照）20 分钟。从热暴露（第 0 天）到安乐死的时间间隔为：8 和 24 小时以及 7、14 和 21 天（加上 14 天的对照组）。将附睾切除、切碎并置于 Tyrode 乳酸丙酮酸白蛋白 (TALPH) 中，在 37°C 下放置 15 分钟以恢复精子。根据计算机辅助精子分析 (CASA)，热处理使第 14 天和第 21 天的总体和进行性运动减少了约 40%（P < 0.05）。此外，形态正常精子的百分比在第 7 天显着减少，第 14 天减少幅度更大和 21，主要是由于中间件缺陷增加。顶体完整性（FITC PSA）在 8 小时时下降了约 35%（P < 0.05），并在第 14 天达到最低点。第 1 天生精小管直径和睾丸重量（相对于体重）下降（P < 0.05） 14.提取睾丸RNA，逆转录和用于 PCR 的 cDNA。基因 Hspa1b (Hsp70) 和 Gpx1 的表达分别在 8 和 24 小时增加了 7 倍和 10 倍（各自 P < 0.001），Hspa1b 在 24 小时保持上调，而 StAR 在第 14 , P < 0.0001) 并在第 21 天恢复到基线。 Trp53 和 Casp8 在第 14 天上调（P < 0.05），而 Bcl-2 在第 7 天和第 14 天下降（P < 0.05）。总之，急性轻度热应激会严重降低精子质量，基于 mRNA，分子伴侣和抗氧化系统以及依赖 Trp53 的内在和外在凋亡途径上调，对精子、精母细胞和精子细胞产生有害影响。