Abstract
Resistance exercise (RE) activates the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway and increases muscle protein synthesis. Severe fasting induces 5′ adenosine monophosphate‐activated protein kinase (AMPK), which attenuates mTORC1 activation. However, the effect of RE on the response of mTORC1 signaling proteins after a period of severe fasting is unclear. We investigated the effect of RE on rat skeletal muscle protein metabolism after a period of severe fasting. We hypothesized that RE‐induced activation of mTORC1 signaling protein attenuates protein breakdown by autophagy. Male Sprague‐Dawley rats were divided into ordinary‐fed (C) and 72‐h fasting (F) groups. A bout of RE was replicated by percutaneous electrical stimulation in the right gastrocnemius muscle. The tuberous sclerosis complex 2 (TSC2) Ser1387 and autophagy marker of microtubule‐associated protein 1A/1B‐light chain 3‐II (LC3B‐II) expression of the F group increased twice that of the C group in sedentary state (P < 0.05). RE activated the mTORC1 signaling pathway in both groups (P < 0.05); however, in the F group, the magnitude of p70S6K (Thr389) phosphorylation was lower by 40% of that of the C group (P < 0.05). Protein synthesis after RE was increased by 50% from the level at sedentary state in the C group (P < 0.05), but not in the F. In the F group, the expression of LC3B‐II at 3 h after RE was decreased by almost 25% from the level at sedentary state (P < 0.05). Our results suggest that RE suppressed fasting‐induced autophagy but did not increase protein synthesis during severe fasting in rat skeletal muscle.
Highlights
Malnutrition stimulates muscle atrophy, and it is an important problem in certain conditions
Gluconeogenic amino acids did not decrease after 72 h of fasting; plasma glucose a 2019 The Authors
We investigated the effect of a bout of Resistance exercise (RE) on rat skeletal muscle protein metabolism after 72 h fasting
Summary
Malnutrition stimulates muscle atrophy, and it is an important problem in certain conditions. In patients who undergo gastrectomy, postoperative food intake decreases and their skeletal muscle mass is decreased by 6.2% compared with that in the preoperative period (P < 0.001) (Yamaoka et al 2015). Weight-classed athletes lose body mass, which decreases by 13.2% compared with that mass before weight loss by severe food restriction (Kukidome et al 2008). The reduction in skeletal muscle mass leads to reduction in muscle strength, quality of life, postoperative recovery, and competitive performance (Saeki et al 2001; Berkovich et al.2019). Muscle atrophy due to malnutrition is an important problem to understand, but the mechanism that prevents muscle loss during the period of malnutrition remains unclear
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