Irisin is a novel muscle factor which was discovered in 2012 and is a hydrolyzed product of FNDC5. The result of the mass spectrometry analysis reveals that Irisin is a soluble N-glycosylated protein hormone with a molecular weight of approximately 12 kDa consisting of 112 amino acids. Irisin is highly conserved in evolution and the mouse and human irisin share 100% identity in the sequences. Irisin is synthesized and secreted by skeletal muscle, white adipose tissue, etc. And the skeletal muscle is the main source.

    Irisin was identified at the beginning of discovery as having the biological effects of promoting browning of white adipose tissue, accelerating body energy expenditure, regulating energy metabolism, and improving insulin resistance. Subsequent investigations show that irisin also plays an important role in neurological diseases, cardiovascular diseases, non-alcoholic fatty liver, and tumors.

    Irisin can promote the expression of UCP1 which can promote browning of white adipose tissue, accelerate body energy expenditure, regulate energy metabolism and can reduce insulin resistance by promoting beta-trophin and β-cell regeneration; irisin can reduce atherosclerotic plaque, lipid deposition, and macrophage accumulation by up-regulating the expression of ERK-dependent microRNA126-5p; irisin can activate AMPK-Akt-eNOS pathway which promotes the release of nitric oxide from endothelial cells thus lowers blood pressure; irisin also improves the skill of learning and memory by regulating the expression of BDNF which promotes dopamine release and increases neuronal survival. The molecular mechanism has yet to be further studied.