Does iris(in) bring bad news or good news?

Irisin, a novel myokine produced in response to physical activity, promotes white-to-brown fat transdifferentiation. The name irisin referred to the ancient Greek goddess Iris, the messenger who delivered (bad) news from the gods. In mice, it has been demonstrated that irisin plays a key role in metabolic regulation, energy expenditure and glucose homeostasis. New findings from various studies carried out in both animals and humans suggest that irisin might also have other favorable effects, such as increasing bone cortical mass, preventing hepatic lipid accumulation, and improving cognitive functions, thus mediating many exercise-induced health benefits. However, data on the role and function of irisin in humans have prompted controversy, due mostly to the only recent confirmation of the presence of irisin in humans. Another strong limitation to the understanding of irisin mechanisms of action is the lack of knowledge about its receptor, which until now remains unidentified in humans and in animals. This review presents an overall analysis of the history of irisin, its expression, and its involvement in health, especially in humans. Level of Evidence Level V, review.