Oxidative and endoplasmic reticulum stress defense mechanisms of bovine granulosa cells exposed to heat stress.

In most mammalian species including cattle, heat stress has detrimental effects on ovarian function through disturbing estradiol production and viability of granulosa cells. However, effect of heat stress and underlying cellular defense mechanisms of bovine granulosa cells is not fully understood. Here, we aimed to investigate the effect of heat stress on granulosa cells function and the associated defense mechanism. For this an in vitro granulosa cell model was used to investigate the role of elevated temperature (41 °C) on granulosa cell functions at 24 h and 48 h exposure compared to the control cultured at 37 °C. The results showed that reactive oxygen species level was higher in cells under 41 °C at 24 h compared to control. In response to increased reactive oxygen species level, the expression of NRF2 and its antioxidant genes, CAT and PRDX1 were higher in bovine granulosa cells exposed to heat stress. Interestingly, heat stress markedly increased expression of endoplasmic reticulum stress marker genes; GRP78 and GRP94, in cultured bovine granulosa cells at 24 h, and higher protein accumulation of GRP78 accompanied by increased expression of apoptotic genes, BAX and CASPASE-3. Moreover, heat stress significantly decreased the bovine granulosa cells proliferation, which was supported by decreased in the expression of proliferation marker gene PCNA. All in all heat stress induce reactive oxygen species accumulation, apoptosis and reduced proliferation, which trigger the NRF2 mediated oxidative stress and endoplasmic reticulum stress response by bovine granulosa cells.