Contraction and AICAR Stimulate IL-6 Vesicle Depletion From Skeletal Muscle Fibers In Vivo
- Hans P.M.M. Lauritzen1,
- Josef Brandauer2,
- Peter Schjerling3,
- Ho-Jin Koh1,
- Jonas T. Treebak4,
- Michael F. Hirshman1,
- Henrik Galbo5 and
- Laurie J. Goodyear1⇑
- 1Research Division, Joslin Diabetes Center and Harvard Medical School, Boston, Massachusetts
- 2Department of Health Sciences, Gettysburg College, Gettysburg, Pennsylvania
- 3Department of Orthopedic Surgery M, Institute of Sports Medicine, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
- 4The Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
- 5Department of Rheumatology and Institute of Inflammation Research, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
- Corresponding author: Laurie J. Goodyear, .
H.P.M.M.L. and J.B. contributed equally to the study.
Recent studies suggest that interleukin 6 (IL-6) is released from contracting skeletal muscles; however, the cellular origin, secretion kinetics, and signaling mechanisms regulating IL-6 secretion are unknown. To address these questions, we developed imaging methodology to study IL-6 in fixed mouse muscle fibers and in live animals in vivo. Using confocal imaging to visualize endogenous IL-6 protein in fixed muscle fibers, we found IL-6 in small vesicle structures distributed throughout the fibers under basal (resting) conditions. To determine the kinetics of IL-6 secretion, intact quadriceps muscles were transfected with enhanced green fluorescent protein (EGFP)-tagged IL-6 (IL-6-EGFP), and 5 days later anesthetized mice were imaged before and after muscle contractions in situ. Contractions decreased IL-6-EGFP–containing vesicles and protein by 62% (P < 0.05), occurring rapidly and progressively over 25 min of contraction. However, contraction-mediated IL-6-EGFP reduction was normal in muscle-specific AMP-activated protein kinase (AMPK) α2-inactive transgenic mice. In contrast, the AMPK activator AICAR decreased IL-6-EGFP vesicles, an effect that was inhibited in the transgenic mice. In conclusion, resting skeletal muscles contain IL-6–positive vesicles that are expressed throughout myofibers. Contractions stimulate the rapid reduction of IL-6 in myofibers, occurring through an AMPKα2-independent mechanism. This novel imaging methodology clearly establishes IL-6 as a contraction-stimulated myokine and can be used to characterize the secretion kinetics of other putative myokines.
- Received September 12, 2012.
- Accepted June 8, 2013.
- © 2013 by the American Diabetes Association.
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