A Moderate Increase of Hydrogen Peroxide Level Is Beneficial for Spontaneous Resumption of Meiosis from Diplotene Arrest in Rat Oocytes Cultured In Vitro

Hydrogen peroxide (H(2)O(2)) acts as a signaling molecule and modulates various aspects of cell functions in a wide variety of cells including mammalian germ cells. We examined whether a decreased level of intra-oocyte cyclic 3′,5′-adenosine monophosphate (cAMP) leads to accumulation of H(2)O(2), and if so, whether a moderate increase of H(2)O(2) inactivates maturation promoting factor (MPF) during spontaneous resumption of meiosis in rat oocytes cultured in vitro. Removal of cumulus cells and culture of denuded oocytes in vitro significantly decreased oocyte cAMP level and led to spontaneous meiotic resumption from diplotene arrest. The reduced oocyte cAMP level was associated with an increased oocyte H(2)O(2) level and reduced catalase activity. Exogenous supplementation of H(2)O(2) induced meiotic resumption from diplotene arrest in a concentration- and time-dependent manner in oocytes treated with 0.1 mM of 3-isobutyl-1-methylxanthine, while dibutyryl-cAMP and 3-t-butyl-4-hydroxyanisole inhibited the stimulatory effect of exogenous H(2)O(2). The increased intra-oocyte H(2)O(2) level induced Thr-14/Tyr-15 phosphorylation of CDK1, while Thr-161 phosphorylated CDK1 and cyclin B1 levels were reduced significantly. These results suggest that a decreased level of intra-oocyte cAMP is associated with an increased level of H(2)O(2). The increased level of H(2)O(2) was associated with high phosphorylation of Thr-14/Tyr-15 and dephosphorylation of the Thr-161 residue of CDK1 and reduced the cyclin B1 level, which eventually inactivated MPF. The MPF inactivation triggered spontaneous resumption of meiosis from diplotene arrest in rat oocytes cultured in vitro.