Skeletal muscle releases to circulation several hormones denomined myokines acting as endocrine organ. Thus during exercise PGC1α is activated inducing FNDC5 release which is cleaved to irisin. Irisin can act on different tissues, thereby brown adipose tissue activates UCP1 in mitochondria triggering transport protons chain in the mitochondrial membrane, resulting ATP increased and dissipating energy in form of heat. This process increases energy expenditure, reduces body weight, and improves metabolic parameters such as insulin sensitivity. Irisin on white adipose tissue stimulates BAT-like phenotypes changes, increasing PGC1α expression and thereby UCP1 and oxygen consumption while decreases WAT genes, process in which WAT stops behaving as energy reservoir for to use fat as energy source as in BAT, process named browning. For all of this, irisin has been proposed as a possible novel treatment in diabetes and obesity. Other target of irisin is nervous system where preliminary studies suggest that it could act on adipocyte metabolism through a novel neural pathway and on the other hand irisin induces neural proliferation and adequate neural differentiation, so it could also be a therapeutic target for neurodegenerative diseases such as Alzheimer or Parkinson.
