Abstract
Heat stress in dairy cattle is recognized to compromise fertility by altering the functions of ovarian follicle-enclosed cells, e.g., oocyte and granulosa cells (GCs). Catalase is an antioxidant enzyme that plays a significant role in cellular protection against oxidative damage by the degradation of hydrogen peroxide to oxygen and water. In this study, the role and mechanism of CAT on the heat stress (HS)-induced apoptosis and altered proliferation of bovine GCs were studied. The catalase gene was knocked-down successfully in bovine GCs at both the transcriptional and translational levels. After a successful knockdown using siRNA, GCs were divided into HS (40 °C + NC and 40 °C + CAT siRNA) and 38 °C + NC (NC) groups. The GCs were then examined for ROS, viability, mitochondrial membrane potential (MMP), cell cycle, and biosynthesis of progesterone (P4) and estrogen (E2) hormones. The results indicated that CAT silencing promoted ROS production and apoptosis by up-regulating the Bcl-2-associated X protein (BAX) and Caspase-3 genes both at the transcriptional and translational levels. Furthermore, the knockdown of CAT markedly disrupted the MMP, impaired the production of P4 and E2, altered the progression of the G1 phase of the cell cycle, and decreased the number of cells in the S phase. This was further verified by the down-regulation of proliferating cell nuclear antigen (PCNA), CyclinB1, steroidogenic acute regulatory protein (STAR), and cytochrome P450 family 11 subfamily A member 1 (Cyp11A1) genes. Our study presented a novel strategy to characterize how CAT can regulate cell proliferation and apoptosis in GCs under HS. We concluded that CAT is a broad regulatory marker in GCs by regulating apoptosis, cellular progression, and simultaneously by vital fluctuations in hormonal signaling. Our findings infer a crucial evidence of how to boost the fertility of heat-stressed cows.