The effect of repeated bouts of electrical stimulation‐induced muscle contractions on proteolytic signaling in rat skeletal muscle

• Published in: Physiological reports 2021-05, Vol.9 (9), p.e14842-n/a
• Main Authors: Kotani, Takaya, Takegaki, Junya, Tamura, Yuki, Kouzaki, Karina, Nakazato, Koichi, Ishii, Naokata
• Format: Article
• Language: English
• Subjects: Animals; Autophagosomes - metabolism; Autophagy; Calpain; Calpain - metabolism; Committees; Electric Stimulation; Electrical stimuli; Experiments; Gene expression; Isoenzymes - metabolism; Kinases; LC3; Male; Mechanistic Target of Rapamycin Complex 1 - metabolism; Microtubule-Associated Proteins - metabolism; mTORC1; Muscle Contraction; muscle protein breakdown; Muscle Proteins - metabolism; Muscle, Skeletal - metabolism; Muscle, Skeletal - physiology; Musculoskeletal system; Original; Phagocytosis; Phosphorylation; Physical Conditioning, Animal - methods; Proteasomes; Protein biosynthesis; Protein synthesis; Proteins; Proteolysis; Rapamycin; Rats; Rats, Sprague-Dawley; resistance exercise; Ribosomal Protein S6 - metabolism; Ribosomal Protein S6 Kinases, 70-kDa - metabolism; Signal Transduction; Skeletal muscle; TOR protein; Ubiquitin; ubiquitinated protein; Ubiquitination
• ISSN: 2051-817X
• DOI: 10.14814/phy2.14842

Mechanistic target of rapamycin complex 1 (mTORC1) plays a central role in muscle protein synthesis and repeated bouts of resistance exercise (RE) blunt mTORC1 activation. However, the changes in the proteolytic signaling when recurrent RE bouts attenuate mTORC1 activation are unclear. Using a RE model of electrically stimulated rat skeletal muscle, this study aimed to clarify the effect of repeated RE bouts on acute proteolytic signaling, particularly the calpain, autophagy‐lysosome, and ubiquitin‐proteasome pathway. p70S6K and rpS6 phosphorylation, indicators of mTORC1 activity, were attenuated by repeated RE bouts. Calpain 3 protein was decreased at 6 h post‐RE in all exercised groups regardless of the bout number. Microtubule‐associated protein 1 light chain 3 beta‐II, an indicator of autophagosome formation, was increased at 3 h and repeated RE bouts increased at 6 h, post‐RE. Ubiquitinated proteins were increased following RE, but these increases were independent of the number of RE bouts. These results suggest that the magnitude of autophagosome formation was increased following RE when mTORC1 activity was attenuated with repeated bouts of RE. Repeated bouts of resistance exercise (RE) attenuate the degree of exercise‐induced mechanistic target of rapamycin complex 1 (mTORC1) activation in skeletal muscle. The present study suggests that repeated bouts of RE increased light chain 3 beta (LC3)‐II protein (an indicator of autophagosome formation) following RE when mTORC1 activation was attenuated with repeated bouts of RE in rat skeletal muscle.