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J Physiol Volume 584, Number 1, 305-312, October 1, 2007 DOI: 10.1113/jphysiol.2007.139618
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SKELETAL MUSCLE AND EXERCISE

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

 Anders Rinnov Nielsen1,2, Remi Mounier1,2, Peter Plomgaard1,2, Ole Hartvig Mortensen1,2, Milena Penkowa3, Tobias Speerschneider4, Henriette Pilegaard4 and Bente Klarlund Pedersen1,2

1 The Centre of Inflammation and Metabolism at the Department of Infectious Diseases Rigshospitalet
2 The Copenhagen Muscle Research Centre, Rigshospitalet
3 The Centre of Inflammation and Metabolism, Section of Neuroprotection, the Panum Institute
4 The Centre of Inflammation and Metabolism, Department of Molecular Biology, the August Krogh Building, University of Copenhagen, Denmark

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.

(Received 26 June 2007; accepted after revision 6 August 2007; first published online 9 August 2007)
Corresponding author B. K. Pedersen: CIM, Rigshospitale – section 7641, Blegdamsvej 9, DK-2100, Copenhagen, Denmark. Email: bkp{at}rh.dk






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