Altered Regulation of Contraction-Induced Akt/mTOR/p70S6k Pathway Signaling in Skeletal Muscle of the Obese Zucker Rat

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.

Akt/protein kinase B in skeletal muscle physiology and pathology

“…1). For example, Katta et al (2009a,b) showed that Akt serine and threonine phosphorylation is increased in lean but not insulin resistant obese Zucker rats following a bout of eccentric exercise. This defect of Akt activation in the obese Zucker is associated with diminished activation of the Akt downstream mTOR and p70S6k (Katta et al, 2009a,b), a signaling cascade critical for protein synthesis and exercise‐induced muscle hypertrophy.…”

Type 2 diabetes causes skeletal muscle atrophy but does not impair resistance training‐mediated myonuclear accretion and muscle mass gain in rats

“…Additionally, although activity of mTORC1‐targeting substrates is reduced in T2DM under insulin exposure, the response of muscle hypertrophy to RT did not differ between T2DM and healthy rats. Previously, it was observed that although fed‐state mTORC1 activity is reduced due to T2DM, the response of mTORC1 activation by high‐force muscle contraction does not necessarily diminish (Katta et al., , ). Furthermore, a previous study showed that streptozotocin‐induced pharmacological lack of insulin secretion caused muscle atrophy, but did not impair muscle hypertrophy to overload in murine skeletal muscle (Fortes et al., ).…”

“…These adaptations were related to both the muscle protein synthesis response via the activation of mTORC1 (Ogasawara et al., ; West et al., ) and myonuclear accretion via the satellite cells (Egner, Bruusgaard, & Gundersen, ; Fry et al., ; McCarthy et al., ; Snijders et al., ). Interestingly, previous rodent and human experiments showed that, unlike a nutritional stimulus, mTORC1 activation and the MPS response to acute resistance exercise or high‐force muscle contraction were not impaired in T2DM (Hulston et al., ; Katta et al., ). Furthermore, a previous animal study observed that satellite cell activation to muscle contraction is not impaired in the T2DM model rat (Peterson et al., ).…”

Mtorc1 Signaling-Activated Increases in Muscle Protein Synthesis Induced by Leucine and Phosphatidic Acid: A Brief Review

“…This multi-protein eIF4F complex functions to assist in the binding of mRNA towards the 40S ribosomal subunit [8,9] , and subsequently initiation protein translation and MPS [11][12][13][14] . The mTOR pathway also activates p70S6K, which then phosphorylates its effector ribosomal protein S6 (rpS6) that can assist in the enhancement of protein translation from template mRNA [5,8,10,15] . The activation of p70S6K, and the subsequent phosphorylation of rpS6, can induce enhanced translation of mR-NAs containing the 5' terminal oligopyrimidine tract (5'-TOP) (encoding elongation factors as well as ribosomal proteins.…”