title: Redox proteins are constitutively secreted by skeletal muscle.
abstract: Myokines are skeletal muscle-derived hormones. In this study, using a C2C12 myotube contraction system, we sought to determine whether the skeletal muscle secreted thioredoxin (TRX) and related redox proteins. Redox proteins such as TRXs, peroxiredoxins, and glutaredoxins were detected in the C2C12 myotube culture medium in the absence of any stimulation. The amounts of TRXs, peroxiredoxins, and glutaredoxins secreted by the C2C12 myotubes were not affected by the contraction, unless the myotubes were injured. Because TRX-1 was known to be a secreted protein that lacks a signal peptide, we examined whether this protein was secreted via exosome vesicles. The results indicated that TRX-1 was not secreted via exosome vesicles. We concluded that TRX-1 and related redox proteins are myokines that are constitutively secreted by the skeletal muscle cells. Although the mechanism of TRX-1 secretion remains unclear, our findings suggest that the skeletal muscle is an endocrine organ and the redox proteins that are constitutively secreted from the skeletal muscle may exert antioxidant and systemic health-promoting effects.
authors.affiliation: Department of Health Promotion Sciences, Graduate School of Human Health Sciences, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, 192-0397, Japan.
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Manabe
authors.forename: Mayumi
authors.initials: M
authors.lastname: Takagi
authors.forename: Mio
authors.initials: M
authors.lastname: Nakamura-Yamada
authors.forename: Naoko
authors.initials: N
authors.lastname: Goto-Inoue
authors.forename: Masato
authors.initials: M
authors.lastname: Taoka
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Isobe
authors.forename: Nobuharu L
authors.initials: NL
authors.lastname: Fujii
mesh_terms: D000818:Animals; D002460:Cell Line; D055354:Exosomes / Q000378:metabolism; D054477:Glutaredoxins / Q000378:metabolism; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010084:Oxidation-Reduction; D054464:Peroxiredoxins / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism; D013879:Thioredoxins / Q000378:metabolism*
chemical_list: D054477:Glutaredoxins; D013879:Thioredoxins; D054464:Peroxiredoxins