Maternal diabetes adversely affects AMP-activated protein kinase activity and cellular metabolism in murine oocytes

Abstract

Maternal diabetes is associated with an increased risk of miscarriages and congenital anomalies. Preovulatory oocytes in murine models also experience maturational delay and greater granulosa cell apoptosis. The objective of this study was to examine whether maternal diabetes influences preovulatory oocyte metabolism and impacts meiotic maturation. Streptozotocin-induced diabetic B6SJLF1 mice were superovulated, and oocytes were collected at 0, 2, and 6 h after human chorionic gonadotropin (hCG) injection. Individual oocyte concentrations of ATP, 5'-AMP, glycogen, and fructose-1,6-phosphate (FBP) and enzyme activities of glucose-6-phosphate dehydrogenase (G6PDH), adenylate kinase, hydroxyacyl-CoA dehydrogenase (Hadh2), and glutamic pyruvate transaminase (Gpt2) were measured. Protein levels of phosphorylated AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) were also measured. ATP levels were significantly lower in oocytes from diabetic mice, and the percent change in the AMP-to-ATP ratio was significantly higher in these oocytes. In contrast, activities of Hadh2 and Gpt2, two enzymes activated by AMPK, were significantly less in these oocytes. Additionally, glycogen and FBP levels, both endogenous inhibitors of AMPK, were elevated. Phosphorylated ACC, a downstream target of AMPK, and phosphorylated AMPK were both decreased in diabetic oocytes, thus confirming decreased AMPK activity. Finally, addition of the activator AICAR to the in vitro maturation assay restored AMPK activity and corrected the maturation defect experienced by the oocytes from diabetic mice. In conclusion, maternal diabetes adversely alters cellular metabolism leading to abnormal AMPK activity in murine oocytes. Increasing AMPK activity in these oocytes during the preovulatory phase reverses the metabolic changes and corrects delays in meiotic maturation.