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 (H2O2), 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 vitro resulted in spontaneous as well as hCGinduced 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 H2O2 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.

Inability to Maintain Metaphase-II Arrest due to Increase of Reactive Oxygen Species in Rat Eggs

“…The CTCF analysis of fluorescence intensity of the respective egg further confirms above finding (Figure 1F3; p < 0.001). These results suggest that increased level of ROS could modulate membrane potential of internal stores resulting in the increase of cytosolic free Ca 2+ in rat eggs in vitro [2,3,5,25,26] and EM-II in rat eggs in vitro [27].…”

“…However, under experimental conditions, collection of cumulus oocyte complexes (COCs), removal of cumulus cells (shear force), and other physical factors may accelerate meiotic resumption from M-II arrest and thereby SEA [22][23][24]. Although a moderate increase of ROS does not cause oxidative stress, it is good enough to modulate meiosis in rat eggs cultured in vitro [2,3,25,26]. ROS induce release of Ca 2+ from the endoplasmic reticulum [27,28].…”

Maturation rate of sheep oocytes cultured in suboptimal environment using CO2 exhaled by human and glutathione addition

“…High ROS in the oocytes would decrease the maturation promoting factor (MPF), which ultimately leads to a decrease of oocyte competence to resume its meiotic process. As is generally known, the MPF functions to control mitosis and meiotic processes, and it also serves to induce the metaphase process in the oocyte (Tiwari and Chaube, 2017). As such, the presence of GSH during maturation acts as a gamete defense mechanism against ROS.…”

Cysteamine in Maturation Medium Enhances Nuclear Maturation and Fertilization Rate of Sheep Oocytes In Vitro

“…It is well known that the culture systems increase ROS production since animal death started to culture process. The research by Tiwari and Chaube (2017) reported that in vitro culture systems could increase ROS levels in oocyte. A multitude of key factors regulate the generation of ROS in the media and include various cellular metabolic reactions, oxygen concentration, light, oocyte handling, and general physicochemical parameters that may have a negative impact on oocyte physiology by inducing apoptosis (Khazaei and Aghaz 2017).…”