Abstract
Increased muscle loading results in the phosphorylation of the 70 kDa ribosomal S6 kinase (p70S6k), and this event is strongly correlated with the degree of muscle adaptation following resistance exercise. Whether insulin resistance or the comorbidities associated with this disorder may affect the ability of skeletal muscle to activate p70S6k signaling following an exercise stimulus remains unclear. Here, we compare the contraction-induced activation of p70S6k signaling in the plantaris muscles of lean and insulin resistant obese Zucker rats following a single bout of increased contractile loading. Compared to lean animals, the basal phosphorylation of p70S6k (Thr389; 37.2% and Thr421/Ser424; 101.4%), Akt (Thr308; 25.1%), and mTOR (Ser2448; 63.0%) was higher in obese animals. Contraction increased the phosphorylation of p70S6k (Thr389), Akt (Ser473), and mTOR (Ser2448) in both models however the magnitude and kinetics of activation differed between models. These results suggest that contraction-induced activation of p70S6k signaling is altered in the muscle of the insulin resistant obese Zucker rat.
Highlights
Insulin resistance is an important health concern that is rapidly increasing worldwide
How mammalian target of rapamycin (mTOR) activity is modulated is not entirely clear; previous studies have reported that resistance exercise increases mTOR activity via an upstream pathway involving phosphoinositide 3-kinase (PI3K) and protein kinase B (PKB)/Akt [15, 18, 19]
Other work has suggested that the activity of PI3K/Akt signaling pathway can be negatively regulated by the phosphatase and Experimental Diabetes Research tensin homologue deleted on chromosome 10 (PTEN) [20]
Summary
Insulin resistance is an important health concern that is rapidly increasing worldwide. Recent in vitro and in vivo studies have suggested that increased muscle loading correlates with increases in the rates of accumulation and synthesis of muscle protein [11,12,13,14]. This increase in protein synthesis, at least in part, is thought to be regulated by the phosphorylation of the p70 ribosomal protein S6 kinase (p70S6k) [11, 15, 16] and the mammalian target of rapamycin (mTOR) which functions as a growth factor and nutrient-sensing signaling molecule in mammalian cells [17]. How the activity of these pathways are regulated following increased muscle contraction and if insulin resistance affects these processes are not well understood
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