RSPO3 is a novel contraction-inducible factor identified in an “in vitro exercise model” using primary human myotubes

• Published in: Scientific reports Vol. 12; no. 1; p. 14291
• Main Authors: Takahashi, Tadahisa, Li, Yuqing, Chen, Weijian, Nyasha, Mazvita R, Ogawa, Kazumi, Suzuki, Kazuaki, Koide, Masashi, Hagiwara, Yoshihiro, Itoi, Eiji, Aizawa, Toshimi, Tsuchiya, Masahiro, Suzuki, Naoki, Aoki, Masashi, Kanzaki, Makoto
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 22.08.2022; Nature Publishing Group UK; Nature Portfolio
• Subjects: Biopsy; Cell culture; Cell density; Cytokines; Experiments; Fibroblasts; Interleukin 8; Metformin; mRNA; Muscle contraction; Muscles; Myoblasts; Myogenesis; Myotubes; Orthopedics; Paracrine signalling; Physical training; Polyethylene terephthalate; Satellite cells; Sciatic nerve; Skeletal muscle
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-022-18190-z

Abstract The physiological significance of skeletal muscle as a secretory organ is now well known but we can only speculate as to the existence of as-yet-unidentified myokines, especially those upregulated in response to muscle contractile activity. We first attempted to establish an “insert-chamber based in vitro exercise model” allowing the miniature but high cell-density culture state enabling highly developed contractile human myotubes to be readily obtained by applying electric pulse stimulation (EPS). By employing this in vitro exercise model, we identified R-spondin 3 (RSPO3) as a novel contraction-inducible myokine produced by cultured human myotubes. Contraction-dependent muscular RSPO3 mRNA upregulation was confirmed in skeletal muscles of mice subjected to sciatic nerve mediated in situ contraction as well as those of mice after 2 h of running. Pharmacological in vitro experiments demonstrated a relatively high concentration of metformin (millimolar range) to suppress the contraction-inducible mRNA upregulation of human myokines including RSPO3, interleukin (IL)-6, IL-8 and CXCL1. Our data also suggest human RSPO3 to be a paracrine factor that may positively participate in the myogenesis processes of myoblasts and satellite cells. Thus, the “insert chamber-based in vitro exercise model” is a potentially valuable research tool for investigating contraction-inducible biological responses of human myotubes usually exhibiting poorer contractility development even in the setting of EPS treatment.