Increased level of reactive oxygen species persuades postovulatory aging-mediated spontaneous egg activation in rat eggs cultured in vitro

Abstract

The present study was aimed to find out whether increased level of reactive oxygen species (ROS) particularity hydrogen peroxide (H2O2) could persuade postovulatory aging-mediated abortive spontaneous egg activation (SEA) in rat eggs cultured in vitro. For this purpose, ROS and H2O2 levels, mitochondria distribution and its membrane potential, p286-CaMK-II, Emi2, Thr-161 phophorylated cyclin-dependent protein kinase1 (Cdk1) as well as cyclin B1 levels, in vitro effects of 3-tert-butyl-4 hydroxy anisole (BHA), pentoxifylline and dibutyryl-adenosine 3',5'-cyclic monophosphate (db-cAMP) were analyzed during postovulatory aging-induced abortive SEA in vitro. Data of the present study suggest that postovulatory aging increased H2O2 levels, disturbed mitochondrial distribution pattern and mitochondrial membrane potential (MMP) in eggs. There was an significant increase of p286-CaMK-II level, while Emi2 level reduced significantly during egg aging in vitro. The reduced Emi2 level was associated with decreased Thr-161 phosphorylated cyclin-dependent kinase-1 (Cdk1) as well as cyclin B1 level in aged eggs that underwent abortive SEA. Further, supplementation of pentoxifylline, db-cAMP, and BHA protected postovulatory aging-mediated abortive SEA in concentration-dependent manner. These data suggest that postovulatory aging increased H2O2 levels, reduced MMP, and increased p286-CaMK-II. The increased p286-CaMK-II was associated with reduced Emi2 level and maturation-promoting factor levels during postovulatory aging-mediated abortive SEA. Drugs that elevate cAMP directly or indirectly and BHA protected postovulatory aging-mediated abortive SEA possibly by reducing ROS level in rat eggs cultured in vitro.

Calcium Signaling During Meiotic Cell Cycle Regulation and Apoptosis in Mammalian Oocytes

“…These oocytes remain arrested at M‐II stage even after ovulation until fertilization (Tripathi et al, ; Prasad et al, ,; Tiwari et al, ). However, in some mammalian species, if fertilization does not occur, postovulatory oocyte aging mediates spontaneous exit from M‐II arrest by inducing the initiation of extrusion of second polar body (PB‐II) (Premkumar and Chaube, , ). The PB‐II does not get completely extruded and ovulated oocytes are further arrested at metaphase‐III (M‐III) like stage without forming pronuclei (Chebotareva et al, ; Premkumar and Chaube, , ; Prasad et al, ,, ,).…”

“…The active Wee 1 destabilizes MPF by inducing Thr14/Tyr15 phosphorylation of Cdk1 and degradation of cyclin B1 (Kubiak et al, ; Oh, ). The destabilized MPF finally results in spontaneous exit from M‐II arrest (Madgwick and Jones, ; Premkumar and Chaube, ). The increased ROS level associates with the decreased level of cAMP (Cheon et al, ; Nunes et al, ; Prasad et al, ; Premkumar and Chaube, ).…”

“…The destabilized MPF finally results in spontaneous exit from M‐II arrest (Madgwick and Jones, ; Premkumar and Chaube, ). The increased ROS level associates with the decreased level of cAMP (Cheon et al, ; Nunes et al, ; Prasad et al, ; Premkumar and Chaube, ). The increased ROS level and decreased cAMP level trigger specific phosphorylation status of Cdk1 and cyclin B1 degradation that results in MPF destabilization (Markoulaki et al, ; Prasad et al, ; Premkumar and Chaube, ) (Fig.…”

“…). The destabilized MPF triggers meiotic exit from M‐II arrest in mice (Nixon et al, ; Kubiak et al, ; Oh, ) and rat oocytes (Ito et al, ; Yoo and Smith, ; Premkumar and Chaube, , , ; Prasad et al, ,, ,). Thus, similar to meiotic resumption from diplotene arrest, a moderate increase of Ca ++ as well as ROS levels under physiological range and transient decrease of cAMP level are important to destabilize MPF and/or Cdk1 activity.…”

“…The increase of [Ca þþ ]i level triggers activation of CaMKII (Ito et al, 2006;Yoo and Smith, 2007;Nader et al, 2013) as well as generation of ROS (Takahashi et al, 2009;Premkumar and Chaube, 2016). The CaMKII activates Wee 1, a tyrosine kinase (Oh, 2011).…”