Skeletal Muscle, Myokines and Health

Accumulating epidemiological data suggest that a physically active life plays an independent role in the protection against metabolic syndrome, type 2 diabetes, cardiovascular diseases, cancer and dementia. For most of the last century, researchers sought a link between muscle contraction and humoral changes in the form of an 'exercise factor', which could be released from skeletal muscle during contraction and regulate some of the exercise-induced metabolic changes in other organs such as the liver, the adipose tissue and other tissues. Researchers have indicate that cytokines or other peptides that are produced, expressed and released by muscle fibers exert autocrine, paracrine or endocrine effects should be classified as 'myokines'. Given that skeletal muscle is the largest organ in the human body, researchers’ discovery that contracting skeletal muscle secretes proteins sets a novel paradigm: skeletal muscle is an endocrine organ producing and releasing myokines, which work in a hormonelike model, exerting specific endocrine effects on other organs. Other myokines work via paracrine mechanisms, exerting local effects on signaling pathways involved in muscle metabolism. It has been shown that skeletal muscle has the capacity to express several myokines including tumor necrosis factor--α (TNF-α), brain-derived neurotrophic factor (BDNF), interleukin-6 (IL-6), IL-8, IL-15 and IL-17. Moreover, myokines contribute to exercise-induced protection against several chronic diseases. Myokines such as IL-6 is likely to show the anti-inflammatory effects of exercise and inhibit low-level TNF-α production. By this ways, TNF-α-induced insulin resistance reveals an important role in mediating the beneficial health effects of exercise.