Expression of interleukin-15 in human skeletal muscle – effect of exercise and muscle fibre type composition

• Published in: The Journal of physiology Vol. 584; no. 1; pp. 305 - 312
• Main Authors: Nielsen, Anders Rinnov, Mounier, Remi, Plomgaard, Peter, Mortensen, Ole Hartvig, Penkowa, Milena, Speerschneider, Tobias, Pilegaard, Henriette, Pedersen, Bente Klarlund
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 01.10.2007; Blackwell Publishing Ltd
• Subjects: Adult; Exercise - physiology; Gene Expression; Humans; Immunohistochemistry; Interleukin-15 - blood; Interleukin-15 - metabolism; Male; Muscle Fibers, Fast-Twitch - metabolism; Muscle, Skeletal - metabolism; Quadriceps Muscle - metabolism; RNA, Messenger - metabolism; Skeletal Muscle And Exercise
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2007.139618

The cytokine interleukin-15 (IL-15) has been demonstrated to have anabolic effects in cell culture systems. We tested the hypothesis that IL-15 is predominantly expressed by type 2 skeletal muscle fibres, and that resistance exercise regulates IL-15 expression in muscle. Triceps brachii, vastus lateralis quadriceps and soleus muscle biopsies were obtained from normally physically active, healthy, young male volunteers ( n = 14), because these muscles are characterized by having different fibre-type compositions. In addition, healthy, normally physically active male subjects ( n = 8) not involved in any kind of resistance exercise underwent a heavy resistance exercise protocol that stimulated the vastus lateralis muscle and biopsies were obtained from this muscle pre-exercise as well as 6, 24 and 48 h post-exercise. IL-15 mRNA levels were twofold higher in the triceps (type 2 fibre dominance) compared with the soleus muscle (type 1 fibre dominance), but Western blotting and immunohistochemistry revealed that muscle IL-15 protein content did not differ between triceps brachii, quadriceps and soleus muscles. Following resistance exercise, IL-15 mRNA levels were up-regulated twofold at 24 h of recovery without any changes in muscle IL-15 protein content or plasma IL-15 at any of the investigated time points. In conclusion, IL-15 mRNA level is enhanced in skeletal muscles dominated by type 2 fibres and resistance exercise induces increased muscular IL-15 mRNA levels. IL-15 mRNA levels in skeletal muscle were not paralleled by similar changes in muscular IL-15 protein expression suggesting that muscle IL-15 may exist in a translationally inactive pool.