title: Interleukin-6 receptor expression in contracting human skeletal muscle: regulating role of IL-6.
abstract: Contracting muscle fibers produce and release IL-6, and plasma levels of this cytokine are markedly elevated in response to physical exercise. We recently showed autocrine regulation of IL-6 in human skeletal muscle in vivo and hypothesized that this may involve up-regulation of the IL-6 receptor. Therefore, we investigated IL-6 receptor regulation in response to exercise and IL-6 infusion in humans. Furthermore, using IL-6-deficient mice, we investigated the role of IL-6 in the IL-6 receptor response to exercise. Human skeletal muscle biopsies were obtained in relation to: 3 h of bicycle exercise and rest (n=6+5), or recombinant human IL-6 infusion (rhIL-6) or saline infusion (n=6+6). We further obtained skeletal muscle samples from IL-6 knockout (KO) mice and wild-type C57/BL-6 mice in response to a 1-h bout of exercise. In exercising human skeletal muscle, IL-6 receptor mRNA increased sixfold with a peak at 6 h postexercise. Detection of the IL-6 receptor protein by immunohistochemistry revealed a pronounced staining following exercise that was primarily located at the cell membrane of the muscle fibers, whereas muscle gp130 expression and plasma levels of soluble IL-6 receptor were unaffected. Infusion of rhIL-6 to humans had no effect on the mRNA level of the IL-6 receptor, whereas there was an increase at the protein level. IL-6 receptor mRNA increased similarly in muscle of both IL-6 KO mice and wild-type mice in response to exercise. In conclusion, exercise increases IL-6 receptor production in human skeletal muscle. This effect is most prominent 6 h after the end of the exercise bout, suggesting a postexercise-sensitizing mechanism to IL-6 when plasma IL-6 is concomitantly low. Exercise-induced increases in IL-6 receptor mRNA most likely occurs via an IL-6 independent mechanism as shown in IL-6 KO mice and the human rhIL-6 infusion study, whereas IL-6 receptor protein levels are responsive to elevated plasma IL-6 levels.
authors.affiliation: Centre of Inflammation and Metabolism, Department of Infectious Diseases, University Hospital of Copenhagen, Copenhagen, Denmark. pernillekeller@yahoo.com
authors.forename: Pernille
authors.initials: P
authors.lastname: Keller
authors.forename: Milena
authors.initials: M
authors.lastname: Penkowa
authors.forename: Charlotte
authors.initials: C
authors.lastname: Keller
authors.forename: Adam
authors.initials: A
authors.lastname: Steensberg
authors.forename: Christian P
authors.initials: CP
authors.lastname: Fischer
authors.forename: Mercedes
authors.initials: M
authors.lastname: Giralt
authors.forename: Juan
authors.initials: J
authors.lastname: Hidalgo
authors.forename: Bente Klarlund
authors.initials: BK
authors.lastname: Pedersen
mesh_terms: D000328:Adult; D000818:Animals; D050822:Cytokine Receptor gp130 / Q000502:physiology; D015444:Exercise; D005260:Female; D006801:Humans; D015850:Interleukin-6 / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D019947:Receptors, Interleukin-6 / Q000235:genetics*
chemical_list: D015850:Interleukin-6; D012333:RNA, Messenger; D019947:Receptors, Interleukin-6; D050822:Cytokine Receptor gp130