Effects of heat stress on gene expression associated with antioxidant capacity of bovine early antral follicles

Heat exposure at the physiological level of oocyte-cumulus-granulosa cell complexes (OCGCs) during in vitro growth (IVG) culture decreases the reduced glutathione (GSH) level of oocytes, an antioxidant, but its mechanism has been unclear. We subjected OCGCs to IVG for 4, 8, or 12 days and investigated the effects of heat exposure on the gene expression of cumulus-granulosa cells associated with antioxidant capacity. Heat exposure did not alter the expression of genes related to GSH synthesis or reuse. Conversely, heat exposure increased mRNA expression of superoxide dismutase 2 and decreased that of glutathione peroxidase 1, which are antioxidant enzymes. Ultimately, heat exposure alters the gene expression of antioxidant enzymes in growing follicles, which may indirectly decrease the GSH level of oocytes.