What is Irisin?

1st February , 2012

Irisin and fat

A previously unknown hormone, irisin, released from muscle in resonce to exercise was describe in the most recent edition of Nature (http://www.ncbi.nlm.nih.gov/pubmed/22237023). Before I completely loose your attention you should also know it has potential therapeutic uses in the treatment of obesity and type 2 diabetes and you will hear a lot more about it in the future. This study while done in mice also identified the human equivalent which is 100% identical which is a remarkable similarity when compared to other factors. This suggest the mechanisms may be well conserved between mammals.

“Irisin is induced with exercise in mice and humans, and mildly increased irisin levels in the blood causes an increase in energy expenditure in mice with no changes in movement or food intake. This results in improvements in obesity and glucose homeostasis. “

It does this by converting fat storing “white fat” cells which make up the vast majority of the fat in the body to “brown fat” cells which have very different properties.

Brown fat or brown adipose tissue (BAT) expresses a special protein (UCP1) that allows it to burn fat and release the energy as heat rather than the bodies chemical energy ATP. Cells exposed to irisin increased their levels of UCP1 50 times or more.

This fat burning BAT is activated by cold expose to generate heat but it is also known to be activated by exercise. It si also known that exercise results in burning more energy than that actually required to perform the physical work but it is not know exactly why.

“it is likely that irisin is responsible for at least some of the beneficial effects of exercise on the browning of adipose tissues and increases in
energy expenditure”

This raises the question why exercise (a condition where you would think you need to conserve energy) should activate a mechanism which burns energy fustily.

“One explanation for increased irisin expression with exercise in mouse and man may be that it evolved as a consequence of muscle contraction during shivering. Muscle secretion of a hormone that activates adipose thermogenesis during this process might provide a broader, more robust defence against hypothermia”

You may also be asking will this help me exercise or not? Unfortunately apart from helping you keep weight off irisin will probably not help your muscle utilise fat for energy but there has been no research done on this to date.

The fact that is helps combat diet induced obesity and diabetes (even if just in rats at this stage) means irisin and irisin mimetics will be be hotly pursued as theraputics over the next few years.