Identification of phosphodiesterase 9A as a cyclic guanosine monophosphate-specific phosphodiesterase in germinal vesicle oocytes: A proposed role in the resumption of meiosis

Objective: To identify a cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase (PDE) in nonhuman primate germinal vesicle (GV) oocytes and establish a proposed effect on oocyte maturation through preliminary experiments in mouse GV oocytes. Design: Controlled nonhuman primate and rodent experiments. Setting: Academic research institution. Animal(s): Rhesus macaques and B6/129F1 mice. Intervention(s): Stimulation of Rhesus macaques with follicle-stimulating hormone (FSH) to collect GV oocytes and cumulus for gene expression analysis, and stimulation of female mice with pregnant mare serum gonadotropin to collect GV oocytes. Main Outcome Measure(s): Expression of PDE transcript in primate GV oocytes and cumulus cells, measurement of fluorescence polarization of phosphodiesterase 3A (PDE3A) activity, and analysis of spontaneous resumption of meiosis in mouse GV oocytes. Result(s): Of five PDE transcripts detected in Rhesus GV oocytes, only PDE9A was cGMP-specific. The fluorescence polarization assays indicated cGMP has an inhibitory effect on PDE3A while the phosphodiesterase 9A (PDE9) inhibitor, BAY73-6691, does not. Similarly, BAY73-6691 had little effect on preventing spontaneous maturation in oocytes, but did augment the inhibitory effects of cGMP. Inclusion of 0 μM (control), 10 μM, 100 μM, and 1 mM BAY73-6691 statistically significantly increased the proportion of mouse oocytes maintaining GV arrest in the presence of the cGMP analog 8-Br-cGMP at 100 μM (8.8%, 11.4%, 18.8%, and 28%), 500 μM (21.1%, 38.1%, 74.5%, and 66.5%), and 1 mM (57.8%, 74.5%, 93.9%, and 94.0%), respectively. Conclusion(s): Phosphodiesterase 9A (PDE9A) is a cGMP-specific hydrolyzing enzyme present in primate oocytes, and PDE9 antagonists augment the inhibitory effect of cGMP during spontaneous in vitro maturation of GV mouse oocytes.