MYOKINE IRISIN – A MOLECULAR SIGNAL MEDIATING THE BENEFICIAL EFFECT OF PHYSICAL ACTIVITY ON BRAIN FUNCTION AND THE CIRCADIAN SYSTEM (A REVIEW)

Abstract

Aim. This paper provides a review of the current understanding of the central activity of myokine irisin. Materials and methods. A theoretical analysis of scientific publications from 2010 to 2023 was conducted to examine the physiological role of irisin in mediating the beneficial effects of physical acti­vity on brain function and the circadian system. Results. Myokine irisin, discovered in 2012, is a cleavage product of the fibronectin type III domain-containing protein (FNDC5). Produced in skeletal muscle during contraction, it is released into the systemic circulation. Irisin has numerous peripheral effects, including stimulating the conversion of white to brown adipocytes. Moreover, irisin can penetrate the blood-brain barrier and exert central effects, acting as a chemical mediator of the beneficial effects of physical activity on brain function. As a signalling molecule within the muscle-brain axis, irisin mediates various positive central effects in health and disease, such as improving cognitive function, mental state, synaptic plasticity, and memory, slowing neurodegenerative disease progression, and providing neuroprotective effects. In the circadian system, irisin contributes to the synchronization of the suprachiasmatic nucleus with physical acti­vity levels. While αVβ5 integrin has been identified as the irisin receptor in adipose and bone tissue, irisin receptors in the CNS remain unidentified, complicating the elucidation of its central activity mechanisms. The central activity of irisin may be associated with its ability to stimulate brain-derived neurotrophic factor (BDNF) expression. Research has shown that BDNF plays a crucial role in the photic entrainment of the circadian clock, mediating circadian rhythm phase shifts.