Reproductive physiological impacts of high ambient temperature on animals: the impaired testicular function and compromised sperm quality in C57BL/6 mice

Global warming poses one of the most formidable challenges confronting the contemporary world, exerting extensive and profound impacts on both natural ecosystems and human society. Nevertheless, the detrimental effects of elevated temperatures on reproductive system in animals and humans remains elusive. In this study, C57BL/6 mice were exposed to high ambient temperatures (HAT). Subsequently, the testes and sperm parameters of the mice were evaluated following the exposure. The HAT mice had significantly lower weight, food and water intake than those in the control group. The weight of testis and epididymis was significantly lower in the HAT group. The HAT group showed significant reductions in seminiferous tubule area, spermatogenic epithelium area, and seminiferous epithelium thickness. The HAT group exhibited significantly reduced sperm density, viability, and plasma membrane integrity rate. The HAT group exhibited a significantly elevated rate of sperm malformation. Moreover, the expression levels of Dnah8 and Dnah17, two genes associated with Multiple Morphological Abnormalities of the Flagella (MMAF), were markedly reduced in the HAT group. The proportion of TUNEL-positive cells significantly increased in the HAT group. Furthermore, there was a significant upregulation in mRNA expression levels of apoptotic genes Caspase-3 and Bax in the HAT group. Conversely, there was a notable decrease in mRNA expression level of anti-apoptotic gene Bcl-2. The concentration of MDA in the HAT group was significantly higher, while SOD activity and T-AOC were significantly lower. Therefore, it can be inferred that elevated air temperature leads to multi-layered damage to animal reproduction. This suggests that extreme high temperatures resulting from climate warming will have a detrimental impact on animal reproduction. This study provides support for elucidating the mechanism underlying the reproductive effects of high temperature.