Fatty Acid Oxidation and Hormone-Induced Meiotic Resumption in Mouse Oocytes.

Abstract

Previous results from our lab showed that fatty acid oxidation (FAO) is required for the pharmacological induction of meiotic maturation in mouse oocytes in vitro. The results indicated that treatment of meiotically arrested oocytes with AICAR, an activator of AMP-activated protein kinase (AMPK), led to germinal vesicle breakdown (GVB) by stimulating FAO. Since AMPK mediates the meiosis-inducing action of hormones, the present study was carried out to examine the role of FAO in hormonal induction of meiotic resumption. For all experiments, 3-week-old C57BL/6J X SJL/J F1 mice were primed with 5 IU PMSG and for most experiments cumulus-cell-enclosed oocytes (CEO) were harvested two days later for experimentation. The culture medium used for all experiments was MEM supplemented with BSA and pyruvate. CEO kept in meiotic arrest with dibutyryl cyclic AMP (dbcAMP) were stimulated to mature in vitro by FSH or Amphiregulin and exposed to increasing concentrations of Etomoxir, Mercaptoacetate or Malonyl CoA, all inhibitors of FAO. Whereas Etomoxir and Mercaptoacetate are pharmacological inhibitors, Malonyl CoA is a physiological inhibitor produced from acetyl CoA by the enzyme acetyl CoA carboxylase. In all cases, these inhibitors significantly blocked the stimulatory effect of FSH and Amphiregulin on meiotic resumption, in many cases, to control levels. FAO inhibitors also blocked GVB in cultured follicles stimulated with hCG. On the other hand, addition of the fatty acid palmitate increased the percentage of maturation in FSH-treated CEO. To further examine this relationship, we have developed a hanging drop assay for FAO that measures the production of 14CO2 from 14C-palmitate during 4.5 h culture. Initial results show activity in spontaneously maturing CEO that is significantly augmented by hormonal stimulation. Taken together, our data indicate that fatty acid oxidation is a vital component of meiotic maturation induced by physiological signals.