Potential Role of Fatty Acid Oxidation Pathways in 
Regulation of Meiotic Resumption in Mouse Oocytes

Jessica L. Odette
Alma College, Alma, MI
Mentor:  Dr. Stephen Downs

The mechanism of mammalian oocyte maturation is not well understood.  Oocyte maturation is initiated by chromosome condensation and breakdown of the nuclear membrane, or germinal vesical, and is completed with progression to metaphase II and extrusion of the first polar body.  Within cells, AMP-activated protein kinase (AMPK) acts as a fuel guage so that at time of energy stress it regulates metabolic pathways to conserve ATP.  Activation of AMPK in mouse oocytes stimulates meiotic resumption.  One of the substrates of AMPK is acetyl CoA carboxylase (ACC), an important enzyme in fatty acid metabolism.  Phosphorylation of ACC by AMPK inactivates ACC, resulting in the suppression of fatty acid synthesis (conserving ATP) and stimulation of fatty acid oxidation (producing ATP).  This study was carried out to investigate the effects of stimulators and inhibitors of specific areas along the fatty acid oxidative pathway on meiotic resumption.

Immature F1 mice, 19-23 days old, were primed with 5IU equine chorionic gonadotropin and sacrificed 48 hours later.  Ovaries are removed and placed in MEM/BSA culture medium supplemented with 300µM dbcAMP or 4mM hypoxanthine.  Cumulus cell-enclosed oocytes (CEOs) are obtained by puncturing follicles with sterile needles.  Denuded oocytes (DOs) are then prepared by repeat pipetting of CEOs with a Pasteur pipet.  CEOs or DOs were cultured with varying doses of fatty acid oxidation stimulators or inhibitors overnight (17-18 hours) or for 4 hours.

C75, a potent stimulator of carnatine palmitoyl transferase 1 (CPT 1), and thus, of fatty acid oxidation, was stimulatory to meiotic resumption in CEOs and DOs arrested with dbcAMP, as well as in CEOs arrested with hypoxanthine.  Conversely, etomoxir, an inhibitor of fatty acid oxidation suppressed meiotic induction in AICAR-stimulated DOs and FSH-stimulated CEOs.  TOFA, an inhibitor of acetyl CoA carboxylase (ACC) that stimulates fatty acid oxidation, stimulated maturation in dbcAMP-arrested CEOs, but not DOs.  Malonyl CoA, a natural inhibitor of CPT1 that inhibits fatty acid oxidation, prevents meiotic induction in both AICAR stimulated DOs and FSH-stimulated CEOs.  Citrate, a stimulator of ACC and thus an inhibitor of fatty acid oxidation, was inhibitory to FSH-stimulated CEOs.  Acetyl CoA was also inhibitory to FSH-stimulated CEOs.  Together, these results support the idea that fatty acid oxidation is required for meiotic resumption in mouse oocytes.
 
 

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