Myokines are one of the key elements of interaction between skeletal muscles and other systems of human body necessary for adaptation to physical loads

Abstract

Muscle tissue makes up a significant percentage of body weight, and its metabolism affects almost all body systems. Despite a sufficiently large number of physiological observations that confirmed the need for regular physical activity to maintain health, the molecular mechanisms of such an effect remained unestablished for a long time. Results of recent research confirmed that skeletal muscles are an endocrine organ that produces a wide range of bioregulators, which synthesis and excretion are stimulated during exercise. At present, many of these factors that mediate metabolic and physiological responses in muscles and other organs have been identified and named myokines. To date the most studied myokines are: interleukins (IL-6, LIF, IL-4, IL-7, IL-8, and IL-15), myostatin, myonectin (CTRP15), irisin, fibroblast growth factor 21 (FGF21), brain-derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), follistatin-like protein-1 (FSTL-1), decorin and SPARC (osteonectin). Most of the myokines exert their effects through paracrine and/or autocrine pathways within muscles, and many of them also act as endocrine agents – via lymph and blood. The biological activity of myokines is realized via modulation of the activity of general global regulatory mechanisms, such as the SMAD signaling cascade, p38/MAPK, Erk1/2 MAPK, PI3K/Akt/GSK-3β, cAMP/Akt, AMPK-dependent regulation, and JNK signaling pathway. At the same time, myokines are involved in the regulation of the activity of the myogenic transcription factors MyoD, myf5, myogenin and a number of proteins involved in the sensing and transport of glucose and fatty acids. Myokines play one of the main roles in the interaction between skeletal muscles, liver, bone and adipose tissues. They increase tissues sensitivity to insulin and are involved in the regulation of important metabolic processes such as carbohydrate, protein and lipid metabolism. Myokines play a significant role in the regulation of myogenesis, osteogenesis, thermogenesis, lipolysis, growth and division of muscle and nerve tissue cells, vascularization, etc. Given the fact that the expression of myokines is induced by muscle contraction, their study allows us to reveal the molecular mechanisms realizing the positive effects of physical exertion. Further studies of myokines and their mechanisms of action are necessary for the development of personalized recommendations for the physical activity of people with metabolic diseases in rehabilitation, physical therapy, medical supervision of physical education and sports.