The Role of PRKA-Mediated Stimulation of Fatty Acid Oxidation in the Regulation of Meiotic Maturation in Mouse Oocytes
Date of Award
Doctor of Philosophy (PhD)
Downs, Stephen M.
Meiosis is a defining aspect of sexual reproduction and its outcome often determines reproductive success. In mammalian females, oocytes initiate meiosis in early embryonic stages but arrest in the late prophase of meiosis-I around the time of birth. They remain arrested until hormonal induction during reproductive cycles after puberty, and then resume meiosis until a second arrest at metaphase-II. The process of oocyte meiosis from the release of prophase arrest till the metaphase-II arrest is known as oocyte maturation. Meiotic arrest is a result of maintenance of elevated cAMP levels within the oocyte by its continuous production as well as by the inhibition of its breakdown. A mid-cycle surge of luteinizing hormone culminates in a dramatic increase in cAMP breakdown that eventually results in the activation of MPF (maturation-promoting factor), a cyclin-dependent kinase that orchestrates the downstream events of meiotic resumption. The product of cAMP breakdown is AMP. A high AMP: ATP ratio is known to activate a metabolic switch known as AMP-activated protein kinase (AMPK or PRKA) that turns off energy-consuming pathways while turning on energy-generating pathways. In a series of previous studies, our lab has established that activation of PRKA by pharmaceutical agents induces meiotic resumption, while hormone-induced meiotic resumption requires PRKA activation in mouse oocytes. Since fatty acid oxidation (FAO) is a very important pathway stimulated by PRKA, our lab next investigated its involvement in PRKA-mediated meiotic resumption, and demonstrated that PRKA activator-induced meiotic resumption requires FAO and agents that stimulate FAO induce meiotic resumption in vitro. Therefore, it was hypothesized that PRKA induces meiotic resumption by the stimulation of FAO. In my dissertation research, I demonstrated a requirement of FAO during hormone-induced meiotic resumption. By measuring FAO levels, I showed that hormone-induced meiotic resumption in vitro and in vivo involves a significant increase in FAO. Moreover, I examined the role of PRKA-mediated regulation of FAO by determining the inactivation of acetyl CoA carboxylase (ACC) during meiotic resumption, and showed that ACC inhibitors increase FAO and induce meiotic resumption. These data show that the PRKA-mediated inactivation of ACC and the resulting increase in FAO is required for and stimulatory to meiotic resumption.