The Potential Role of Nitric Oxide in Regulation of Meiotic Resumption of Mouse Oocytes

Lisa Wunsch
Carroll College
Mentor: Stephen Downs

The mechanism by which mammalian oocytes resume maturation is not well understood. At birth, mammalian oocytes are arrested in prophase I of meiosis I. Oocyte maturation occurs following a gonadotropin surge and proceeds with breakdown of the germinal vesicle, and progression through metaphase II of meiosis with the formation of the first polar body. Previous studies in the lab have implicated a stress-response kinase, AMP-Activated Protein Kinase (AMPK), in the induction of meiotic resumption of mouse oocytes. AICA riboside (AICAR), an adenosine analog and activator of AMPK, stimulates an increase of AMPK activity and causes mouse oocytes to resume maturation. Follicle-stimulating hormone (FSH) and heat stress have also been shown to activate AMPK and lead to germinal vesicle breakdown.  In addition, Nitric Oxide (NO), a major biological signal, has been shown to influence mouse meiotic maturation and its activity can be modulated by AMPK. Therefore, the present study was carried out to better characterize the role of nitric oxide in oocyte maturation and determine whether NO may be involved in AMPK-mediated maturation. 

Nitric Oxide donors, Sodium Nitroprusside (SNP) and S-nitroso-L-acetyl penicillamine (SNAP), were utilized to determine their effects on meiotic induction, and inhibitors of nitric oxide synthase (NOS), Nw-nitro-L-Argenine methyl ester (L-NAME) and Aminoguanidine (AG),were used to determine whether they could inhibit NO-induced meiotic resumption. In addition, in order to determine if NO had a potential role in AMPK-mediated maturation, NOS inhibitor L-NAME was used to test whether it could  inhibit AICAR, Follicle stimulating hormone, and heat-induced oocyte maturation. NO donor SNP was used in conjunction with Compound C, an established inhibitor of AMPK, in order to see if AMPK is necessary for NO-induced maturation. Nitric oxide donors stimulated oocyte maturation and NO-induced maturation was inhibited by nitiric oxide synthase inhibitors. Inhibition of NO-induced maturation had no effect on AICAR, or FSH-induced maturation, but inhibition of AMPK by Compound C significantly inhibited NO-induced maturation, Therefore, these results suggest that Nitric Oxide is located upstream of AMPK in the meiotic induction pathway and AMPK may be necessary for Nitric-Oxide induced oocyte maturation. However, NO many not be a physiological mediator of meiotic induction. 
 
 
 

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