Title

Effects of endurance exercise on skeletal muscle protein turnover and intracellular signaling in female runners

Date of Completion

January 2005

Keywords

Biology, Molecular|Health Sciences, Nutrition|Health Sciences, Recreation

Degree

Ph.D.

Abstract

The role of exercise in influencing skeletal muscle protein turnover (SMPTO) has been studied for several years yet there are still several unanswered questions regarding the metabolic events leading to muscle growth. While the basis for skeletal muscle hypertrophy involves the relationship between rates of synthesis and rates of breakdown, exactly how exercise, particularly endurance exercise, influences these processes has not been fully characterized. Additionally, despite known differences in the metabolic response to exercise, whether gender differences exist regarding SMPTO is unclear. Recently, the relationship between signaling pathways and SMPTO has moved to the forefront of exercise physiology. Regarding endurance exercise, investigations of these pathways, particularly the PI3K-mTOR pathway, are in their infancy. ^ The purpose of Study I was to evaluate the SMPTO response to a 75 minute run at 70%VO2peak in trained female runners. Mixed muscle fractional synthetic rates (FSR) decreased 51% from rest. There was a trend for increased fractional breakdown rates (FBR) and a more negative net muscle protein balance (NET) post-exercise. These data suggest that with regards to SMPTO, endurance exercise leads to a more catabolic state than that noted at rest. ^ The purpose of Study II was to determine whether gender differences exist in SMPTO following a 75 minute run at 70%VO2peak performed by endurance trained males and females. We found FSR was similar between genders. However, females had increased FBR and a more negative NET post-exercise. These data identify gender differences in SMPTO response to endurance exercise, with a more catabolic state observed in women. ^ The purpose of Study III was to determine the response of signaling proteins of the PI3K-mTOR pathway (involved in translation) following endurance exercise, and to examine the relationship between these proteins and SMPTO. There was an increase of total AKT expression and phosphorylation of Ser473 post-exercise. Total S6K1 expression and phosphorylation was not affected immediately post-exercise, but total expression and phosphorylation of Thr389 and Thr421/Ser424 were decreased at 3-hours post-exercise. We interpret this data to suggest that endurance exercise influences proteins of this pathway and decreased expression and activation of S6K1 is associated with decreased FSR. ^