irisin, Preptin and adropin are three co-workers in the regulation of energy homeostasis.
Irisin is one of the most recently discovered and isolated hormones, derived from mouse skeletal muscle in 2012. Irisin is secreted from muscles in response to exercise and may mediate some beneficial effects of exercise in humans, such as weight loss and thermoregulation.
Since irisin works on muscles and fat, it is a myokine and an adipokine. Myokines are a type of cytokines that have autocrine, paracrine and endocrine effects, mostly secreted by skeletal muscle. Irisin is generated by exercise and acts as an insulin-sensitizing hormone. Irisin is so powerful that even moderately increased levels of circulating irisin potently increases energy.
There are two types of adipose tissue: white or brown. In humans, fat consists mainly of white adipose tissue (WAT), which is highly involved in homeostasis and capable of establishing auto, para-, and endocrine ways of communicating with other tissues and organs. Fat also contains endothelial cells, multipotential mesenchymal cells, nerve cells, and immune cells participating in inflammatory and metabolic/hormonal responses. It secretes cytokines called adipokines (adipocytokines) which impact inflammation, angiogenesis, and metabolic processes. Some of these adipokines are primarily secreted by the adipocyte (e.g., leptin, adiponectin, resistin, chemerin, and visfatin) but many are secreted by other cell types as well . As these molecules can generate signals at local and peripheral level, it is believed that they influence many metabolic pathways as well as the differentiation of adipocytes. They also serve as mediators linking inflammation and immunity with obesity and its comorbidities/complications. WAT may in fact be the largest endocrine organ, generating an abundance of hormones, growth and complement factors, and other molecules including receptors for many of these biological agents.
Irisin improves weight loss by inducing PGC1α.
PGC1α is induced in muscle by exercise and stimulates many of the best known beneficial effects of exercise in muscle: mitochondrial biogenesis, angiogenesis and fiber-type switching.
PGC1α induces FNDC5. FNDC5 is the precursor of irisin. FNDC5 promotes the conversion of white fat to brown fat (thermogenesis via PPARα).FNDC5 influneces UCP1, which also contributes to the browning of white fat. Brown fat has more mitochondria than white fat, so it is able to burn faster and give you more energy. Irisin can also decrease food intake.When rats were injected with irisin into the hypotalamus, they ate less.
In mice, irisin released from skeletal muscle during exercise acts directly on bone by increasing cortical bone mineral density, bone perimeter and polar moment of inertia.
It may promote bone formation so that bones can better adapt to the increased load during persistent exercise. It can do it without browning response of adipose tissue when given at a lower dose. It may help with osteoperosis. It also provides resistance to muscular dystrophy and denervation-linked muscular atrophy. Irisin has also been shown to be positively correlated with bone mineral density in adolescent women.
this hormone is pretty much new and has not been studied enough yet so do not think you might not hear any contradictory research on this subject in the future.
Sources:
sciencedirect.com,frontiersin.org, mybiohack.com, healthline.com