Metabolic Regulation by Stress Mediators in Fetal Ovine Skeletal Muscle and Adult Bovine Myoblasts

Our objective was to determine the effect of stress mediators such as inflammatory cytokines and β adrenergic agonists on developing skeletal muscle. Fetal sheep exposed to chronic maternal inflammation had decreased skeletal muscle glucose oxidation rates when stimulated with insulin or TNFα. In addition, activation of Akt by insulin was decreased after maternal inflammation when compared to controls and there were not differences in skeletal muscle fiber type ratios between the two treatment groups. This indicates that maternal inflammation does not affect overall oxidative capacity in the developing fetus, but rather insulin signaling pathways are disrupted. We sought to determine whether the metabolic response to β adrenergic and insulin stimulation previously shown in mature skeletal muscle is a phenotypic trait passed to the mature muscle from developing muscle stem cells. Bovine myoblasts were differentiated in media containing either β1 adrenergic agonist +/- insulin or β2 adrenergic agonist +/- insulin. Glucose oxidation was increased in the myoblasts simulated by β2 adrenergic agonist compared to myoblasts stimulated by β1 adrenergic agonists suggesting that the β2 adrenergic agonist is more effective at enhancing glucose metabolic efficiency than the β1 adrenergic agonist. Furthermore, we determined that when stimulated by β2 adrenergic agonist and insulin, myoblasts had decreased glucose oxidation rates compared to insulin alone. This is opposite of the effects seen in a similar study conducted utilizing mature skeletal muscle, indicating that this response is not necessarily derived from the muscle stem cell. In a final study, we evaluated mitochondrial respiration rate in bovine myoblasts from cows that had been classified as having either High or Low concentrations of androstenedione (A4) in their follicular fluid. Calves born to cows classified as High A4 had increased weaning weights compared to calves born to cows classified as Low A4. By performing a mitochondrial stress test using an XF-96 Seahorse Bioanalyzer, we were able to measure cellular respiration. We hypothesized that myoblasts from the High A4 cows would have enhanced metabolic efficiency compared to the Low A4 cows. However, we found no differences in mitochondrial oxidation rates among treatments but did find a tendency (P = 0.1) for muscle stem cells from High A4 cows in the absence of insulin and from Low A4 cows when insulin was present to have increased rates of glycolysis. This indicates that the enhanced growth efficiency of the calves born to the High A4 cows is likely due to a different biological mechanism. Advisor: Dustin T. Yate