EFFECTS OF AGE AND EXERCISE TRAINING ON INSULIN SIGNALING PROTEIN LEVELS IN SKELETAL MUSCLE

Abstract

Both age and exercise training can alter abundance of some insulin signaling proteins in skeletal muscle of rats, but previous studies have not evaluated training effects in old age. Therefore, the purpose of this study was to measure the abundance of key insulin signaling proteins in trained (T) or untrained (UT) young (Y; 3 mo at beginning of training) and old (O; 23 mo at beginning of training) rats. Male Fisher 344 rats were randomly assigned to either UT or T (treadmill running, 5d/wk, 45 min/d, for 10-wk) groups. After the 10-wk period, animals were sacrificed and plantaris muscles were removed. Muscles were processed and subjected to SDS-PAGE followed by immunoblotting. Immunoblots were then subjected to enhanced chemiluminescence and respective protein bands quantitated by densitometry. Results revealed a significant (p ≤ 0.05) main effect of age on insulin receptor (O>Y), insulin receptor substrate-1 (IRS-1; Y>O), and p85 subunit of phosphatidylinositol-3-kinase (PI3K; O>Y). There was a significant (p ≤ 0.05) main effect of training, on insulin receptor (T>UT) and IRS-1 (T>UT), and a similar trend (p = 0.07) for PI3K (T>UT). Post-hoc analysis indicated that training induced significantly (p ≤ 0.05) greater insulin receptor abundance in muscle from young (YT>YUT), but not old rats. In contrast, training elicited significantly (p ≤ 0.05) greater IRS-1 abundance in muscle from old (OT>OUT), but not young rats. We conclude that exercise training may have differential effects on key insulin signaling proteins in muscle from young adult compared to old rats. Supported by NIH AG10026 (GDC) and AFAR (LEG).