Iryzyna - nowy mediator homeostazy energetycznej Irisin - a new mediator of energy homeostasis

Summary Skeletal muscles as an active hormonal compartment in the response of physical activity se-crete substances named myokines capable of modulating metabolic processes. Myokines take part in communication between muscles and other tissues. Irisin (Ir) – a newly discovered adipomyokine – is cleaved and secreted to the circulation from a fibronectin type III domain containing protein 5 (FNDC5). The mechanism of Ir action has not been described precisely, and receptors for the molecule are not defined yet, but it has been proposed to promote brow-ning of white adipose tissue into beige fat cells. To date we have distinguished two types of adipose tissue in mammals – white, which not only functions as a store of energy but also can play a pro-inflammatory role (secreting adipokines), and brown adipose tissue. Brown adipose tissue has a high mitochondrial content and can dissipate chemical energy in the form of heat (nonshivering termogenesis). It plays a natural antiobesity role and protects against obesity-re-lated diseases. The development of beige adipose tissue, which in its structure and function is similar to brown adipose tissue, and the possibility to modify its amount through some exter -nal factors, are nowadays among the most important targets of research on fat cell biology.