Irisin: what promise does it hold?

Purpose of reviewThe recently identified myokine, irisin has raised great expectations as a potential target in the conservative treatment of obesity. This review focuses on studies exploring the effects of irisin in humans.Recent findingsPeroxisome proliferator-activated receptor coactivator-1 expression in skeletal muscles is induced by exercise followed by expression of the membrane protein fibronectin type III domain containing 5. After cleavage from fibronectin type III domain containing 5, irisin is secreted into blood increasing thermogenesis by browning of subcutaneous white/beige adipose tissue. Although clear-cut data have been reported in rodents, the thermogenic effect of irisin in humans remains controversial. The initially reported exercise-dependent increase of irisin in humans could not be confirmed in most studies. However, a robust finding in human studies is the association of irisin with BMI.SummaryThe discovery of irisin provides more insight into exercise-induced browning of adipose tissue, and therefore leads to a better understanding of mechanisms underlying body weight regulation and further down the road possibly may lead to treatment strategies of diseases with greatly altered body weight such as obesity or anorexia nervosa.