Calprotectin is released from human skeletal muscle tissue during exercise

Area of Science:

• Exercise Physiology
• Molecular Biology
• Immunology

Background:

• Skeletal muscle functions as a secretory organ, releasing cytokines like IL-6 during exercise.
• IL-6 is implicated in various physiological responses, including inflammatory and metabolic processes.
• The specific downstream effects of IL-6 on skeletal muscle secretory factors require further elucidation.

Purpose of the Study:

• To investigate whether IL-6 infusion induces the production of other secreted factors in skeletal muscle.
• To compare the effects of IL-6 infusion and exercise on S100A8 and S100A9 gene expression and calprotectin release.
• To determine if IL-6 alone is sufficient to cause calprotectin release from skeletal muscle.

Main Methods:

• Healthy young males received IL-6 infusion or performed prolonged cycle ergometer exercise.
• Muscle biopsies were analyzed for gene expression changes using microarray and RT-PCR.
• Plasma calprotectin levels were measured, and arterial-femoral venous differences were assessed during knee extensor exercise.

Main Results:

• IL-6 infusion and exercise significantly upregulated S100A8 and S100A9 mRNA in skeletal muscle.
• Plasma calprotectin increased substantially after exercise but not after IL-6 infusion alone.
• Working skeletal muscle demonstrated a net release of calprotectin, indicating it as a source.

Conclusions:

• Both IL-6 and muscle contractions stimulate S100A8 and S100A9 expression in skeletal muscle.
• While IL-6 contributes to the induction of these genes, it is not the sole factor for calprotectin release.
• Exercise-induced muscle contractions are necessary for the release of calprotectin from skeletal muscle into circulation.