myokiner

Myokines are cytokines and other small proteins released by skeletal muscle tissue in response to contraction. They act as signaling molecules that can have autocrine effects on muscle itself, paracrine effects on neighboring cells, or endocrine effects on distant organs through the bloodstream. This signaling network positions skeletal muscle as an endocrine organ that communicates with liver, adipose tissue, brain, bone and other tissues to regulate metabolism, energy balance and immune responses.

The term myokine was popularized in the early 2000s to describe muscle-derived factors that mediate exercise-related benefits beyond the muscle. Muscle contraction triggers the release of these factors via cellular pathways linked to calcium signaling and metabolic stress, allowing rapid communication with other tissues. Among the best-studied myokines is interleukin-6 (IL-6), which has both pro- and anti-inflammatory roles depending on context. Other proposed myokines include irisin, myostatin, IL-15, BAIBA, FGF21 and brain-derived neurotrophic factor (BDNF). Some of these signals have contested roles or may function differently in humans compared with animal models.

Physiologically, myokines contribute to the metabolic adaptations seen with exercise, such as improved insulin sensitivity, enhanced lipid oxidation and anti-inflammatory effects. They are also explored for potential therapeutic applications in obesity, type 2 diabetes, sarcopenia and other metabolic or neurodegenerative conditions. However, many myokines remain incompletely defined, and their effects can be context-dependent, with ongoing debates about measurement, relevance, and inter-species differences.