This study examined the role of CRH-induced ovarian cell apoptosis in the restraint stress (RS)-induced impairment of oocyte competence. Oocyte percentages of apoptotic cumulus cells (CCs) did not differ between stressed and control mice before in vitro maturation (IVM) but became significantly higher in stressed mice after IVM without serum, growth factor, and hormone. The level of Bcl2 mRNA decreased significantly in mural granulosa cells (MGCs) and ovarian homogenates after RS. Whereas ovarian estradiol, testosterone, and IGF1 decreased, cortisol and progesterone increased significantly following RS. RS increased the level of CRH in serum, ovary, and oocyte while enhancing the expression of CRHR1 in CCs, MGCs, and thecal cells. RS down-regulated ovarian expression of glucocorticoid receptor and brain-derived neurotrophic factor. Furthermore, CRH supplementation to IVM medium impaired oocyte developmental potential while increasing apoptotic CCs, an effect that was completely overcome by addition of the CRHR1 antagonist antalarmin. Results suggest that RS impaired oocyte competence by increasing CRH but not glucocorticoids. Increased CRH initiated a latent apoptotic program in CCs and oocytes during their intraovarian development, which was executed later during IVM to impair oocyte competence. Thus, elevated CRH interacted with increased CRHR1 on thecal cells and MGCs, reducing the production of testosterone, estrogen, and IGF1 while increasing the level of progesterone. The imbalance between estrogen and progesterone and the decreased availability of growth factors triggered apoptosis of MGCs and facilitated CC expression of CRHR1, which interacted with the oocyte-derived CRH later during IVM to induce CC apoptosis and reduce oocyte competence.
Keywords: apoptosis; corticotrophin-releasing hormone (CRH); mouse; oocyte; restraint stress.