Effect of Estrogen on Mitochondrial ATP Synthase in Fetal Skeletal Muscle
 
Soon Ok Kim¹, Eugene D. Albrecht² and Gerald J. Pepe¹
Department of Physiological Sciences¹, Eastern Virginia Medical School, Norfolk, VA, USA;
Department of Obstetrics/Gynecology/Reproductive Sciences and Physiology², University of Maryland School of Medicine, Baltimore, MD, USA
 
We previously showed that offspring delivered to baboons in which levels of estradiol (E₂) were suppressed during the second half of gestation exhibited insulin resistance which typically precedes onset of type 2 diabetes. Mitochondria are essential for energy production and cellular homeostasis. Moreover, skeletal muscle of type 2 diabetics exhibited downregulation of key genes involved in mitochondrial function including oxidative phosphorylation which is controlled in part by the ATP synthase enzyme complex. However, whether alterations in mitochondria are the cause or the result of insulin resistance and are developmentally regulated remains to be determined. Therefore, using a multiplexing microplate kit, the current study determined whether mitochondrial ATP synthase expression and activity were altered in fetal vastus lateralis skeletal muscle obtained at day 165-175 of gestation from baboons untreated (n = 6) or treated daily with the aromatase inhibitor letrozole (n = 6; E₂ suppressed > 95%) on days 100-164/174 (term = day 184). The activity and content of ATP synthase were lower (P <0.05) in enriched fractions of mitochondria from skeletal muscle of E₂-suppressed fetuses (9.8 ± 1.8 and 268 ± 49 arbitrary units/min/mg protein, respectively) compared to levels in untreated animals (17.1 ± 1.7 and 455 ± 65 arbitrary units/min/mg protein, respectively). The decrease in ATP synthase activity in estrogen-suppressed fetuses appears to reflect a decrease in the amount of enzyme. Thus, the ratio of enzyme activity: content (x 100) was similar in fetal skeletal muscle mitochondria of untreated (4.0 ± 0.5) and letrozole-treated (4.3 ± 0.8) animals. In contrast, fetal skeletal muscle mitochondrial citrate synthase activity was not altered by estrogen. These results indicate that mitochondrial ATP synthase expression and activity is decreased in fetal skeletal muscle of estrogen-suppressed animals and support our hypothesis that estrogen in utero plays a critical role in programming factors in skeletal muscle important for insulin sensitivity and glucose homeostasis in offspring.