Skeletal muscle as a gene regulatory endocrine organ

Skeletal muscle is gaining increased attention as an endocrine organ. Recently, novel myokines and new effects of already established myokines have been identified. The objective of this review is to give an update on the recent advances in the field.

Several hundred putative myokines have been described, some of which are induced by contraction and differentially regulated between healthy and metabolically diseased individuals. Interleukin-6 (IL-6) is the prototype myokine, which was identified as a muscle-derived cytokine 15 years ago. Recently, IL-6 has been linked to β-cell survival and inhibition of cancer-cell growth. Moreover, trans-signaling appears to determine whether IL-6 acts as a proinflammatory or an anti-inflammatory cytokine. Irisin has been shown to be a secreted myokine, which contribute to circulating concentrations dependent on training status. IL-15 has been established as a cytokine mediating cross-talk between skeletal muscle and skin tissue, and decorin has been characterized as a contraction-induced myokine which apparently is differentially regulated between healthy and dysglycemic individuals.

Skeletal muscle is an endocrine organ which, by the release of myokines, may influence metabolism in virtually all organs in the body. This knowledge may potentially open up for the possibility of designing new drugs that mimic the effects of myokine signaling.