Estrogen promotes fetal skeletal muscle mitochondrial distribution and ATP synthase activity important for insulin sensitivity in offspring.

Purpose: We previously showed that offspring delivered to baboons in which levels of estradiol (E₂) were suppressed during the second half of gestation exhibit insulin resistance. Mitochondria are essential for the production of ATP as the main source of energy for intracellular metabolic pathways, and skeletal muscle of type 2 diabetics exhibit mitochondrial abnormalities. Mitochondria express estrogen receptor β and E₂ enhances mitochondrial function in adults. Therefore, the current study ascertained whether exposure of the fetus to E₂ is essential for mitochondrial development.

Methods: Levels of ATP synthase and citrate synthase and the morphology of mitochondria were determined in fetal skeletal muscle obtained near term from baboons untreated or treated daily with the aromatase inhibitor letrozole or letrozole plus E₂.

Results: Specific activity and amount of ATP synthase were 2-fold lower (P < 0.05) in mitochondria from skeletal muscle of E₂ suppressed letrozole-treated fetuses and restored to normal by treatment with letrozole plus E₂. Immunocytochemistry showed that in contrast to the punctate formation of mitochondria in myocytes of untreated and letrozole plus E₂ treated animals, mitochondria appeared to be diffuse in myocytes of estrogen-suppressed fetuses. However, citrate synthase activity and levels of proteins that control mitochondrial fission/fusion were similar in estrogen replete and suppressed animals.

Conclusion: We suggest that estrogen is essential for fetal skeletal muscle mitochondrial development and thus glucose homeostasis in adulthood.