Myokine

A myokine is one of several hundred cytokines or other small proteins (~5–20 kDa) and proteoglycan peptides that are produced and released by muscle cells (myocytes) in response to muscular contractions. They have , paracrine and/or endocrine effects; their systemic effects occur at picomolar concentrations.

Receptors for myokines are found on muscle, fat, liver, pancreas, bone, heart, immune, and brain cells. The location of these receptors explain the fact that myokines have multiple functions. Foremost, they are involved in exercise-associated metabolic changes, as well as in the metabolic changes following training adaptation. They also participate in tissue regeneration and repair, maintenance of healthy bodily functioning, immunomodulation; and cell signaling, expression and differentiation.

The present definition of the term myokine is attributed to Dr. Bente Klarlund Pedersen et al., who suggested its use in 2003. In 2008, the first myokine, myostatin, was identified. The gp130 receptor cytokine IL-6 (Interleukin 6) was the first myokine found to be secreted into the blood stream in response to muscle contractions.

There is an emerging understanding of skeletal muscle as a secretory organ, and of myokines as mediators of physical fitness through the practice of regular physical exercise (aerobic exercise and strength training), as well as new awareness of the anti-inflammatory and thus disease prevention aspects of exercise. Different muscle fiber types -slow twitch muscle fibers, oxidative muscle fibers, intermediate twitch muscle fibers, and fast twitch muscle fibers - release different clusters of myokines during contraction. This implies that variation of exercise types, particularly aerobic training/endurance training and muscle contraction against resistance (strength training) may offer differing myokine-induced benefits. This topic has been discussed by fitness training specialists.

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