Increase of Reactive Oxygen Species Associates with the Achievement of Meiotic Competency in Rat Oocytes Cultured In Vitro

Abstract

Reactive oxygen species (ROS) play an important role during meiotic maturation and ovulation. The downstream impact of ROS during the achievement of meiotic competency remains ill understood. The present study was aimed to find out the impact of ROS on the level of cyclic nucleotides and maturation promoting factor (MPF) during the achievement of meiotic competency. For this purpose, cumulus oocyte complexes (COCs) were collected from the ovary of experimental rats injected with 20 IU pregnant mare’s serum gonadotropin (PMSG) for 48 h, and PMSG was followed by 20 IU human chorionic gonadotropin (hCG) for 14 h. The morphological changes, meiotic status of oocyte, brilliant cresyl blue (BCB) staining for meiotic competency, total ROS, hydrogen peroxide (H 2 O 2 ), adenosine 3′,5′-cyclic monophosphate (cAMP), guanosine 3′,5′-cyclic monophosphate (cGMP), cell division cycle 25B (Cdc25B), Wee1, specific phosphorylation status of cyclin-dependent kinase 1 (Cdk1), and cyclin B1 expression levels were analyzed. Data suggest that the culture of diplotene-arrested COCs in vitroresulted in spontaneous as well as hCG-induced meiotic exit from diplotene arrest (EDA) in a time-dependent manner, but the first polar body (PB-I) was not extruded. However, 20 IU hCG surge induced extrusion of PB-I in majority of ovulated oocytes. A moderate increase of total ROS as well as H 2 O 2 levels associate with EDA. The cAMP, cGMP, Cdc25B, Thr161 phosphorylated Cdk1 as well as cyclin B1 levels were decreased, while Wee1 and Thr14/Tyr15 phosphorylated Cdk1 levels were significantly increased leading to MPF destabilization. The destabilized MPF resulted in spontaneous EDA in rat COCs cultured in vitro. Taken together, these data suggest that a moderate increase of ROS decreases the cyclic nucleotides level that destabilizes MPF. The destabilized MPF results in EDA in rat COCs cultured in vitro.