|Weber, Gregory - Greg|
Submitted to: American Journal of Physiology - Regulatory Integrative & Comparative Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2002
Publication Date: 12/19/2002
Citation: RODGERS, B.D., WEBER, G.M., KELLY, K.M., LEVINE, M.A. Prolonged Fasting and Cortisol Reduce Myostatin mRNA Levels in Tilapia Larvae, Short-term Fasting Elevates. AMER J OF PHYSIOLOGY REGULATORY INTEGRATIVE & COMPARATIVE PHYSIOLOGY. Volume 284, pp. 1277-1286. 2003. Interpretive Summary: Nutritional status has profound effects on the growth and development of somatic tissues, particularly skeletal muscle. We know little about how nutritional status affects the regulatory mechanisms controlling these processes in fish. We therefore sought to determine whether levels of mRNA for the muscle regulator myostatin were altered in fasting fish, using tilapia as a model. Our results indicate that prolonged fasting simultaneously reduces growth and myostatin mRNA levels in larvae, albeit after an initial rise in myostatin mRNA. The exogenous administration of cortisol, a stress hormone whose blood concentrations are known to rise in many different fasting vertebrates, including the fasted larvae of these studies, also reduced whole larval myostatin mRNA. Our data suggest myostatin is affected by nutritional status, and a rise in cortisol could contribute to the effects of a prolonged fast on myostatin mRNA levels.
Technical Abstract: Myostatin negatively regulates muscle growth and development and has recently been characterized in several fishes. We measured fasting myostatin mRNA levels in adult tilapia skeletal muscle and in whole larvae. Although fasting reduced some growth indices in adults, skeletal muscle myostatin mRNA levels were unaffected. By contrast, larval myostatin mRNA levels were elevated after a short-term fast and reduced with prolonged fasting. These effects were specific for myostatin as mRNA levels of glyceraldehyde-3-phosphate dehydrogenase and glucose 6-phosphatase were unchanged. Cortisol levels were elevated in fasted larvae with reduced myostatin mRNA while in addition, immersion of larvae in 1 ppm (2.8 mM) cortisol reduced myostatin mRNA in a time-dependent fashion. These results suggest that larval myostatin mRNA levels initially rise, but ultimately fall during a prolonged fast. The reduction is likely mediated by fasting-induced hypercortisolemia, indicating divergent evolutionary mechanisms of glucocorticoid regulation of myostatin mRNA since these steroids upregulate myostatin gene expression in mammals.