A previously unknown hormone called irisin was discovered by an international team of scientists from the USA, Denmark and Italy. As the researchers found, it turns out that irisin is released during exercise by skeletal muscles.
The hormone was named after Irida, the goddess of the rainbow, who was the messenger of the Greek gods. According to scientists, this hormone sends important messages to our fat cells. Irisin is made in the muscles and then travels to our fat cells and converts visceral, stored white fat into metabolically active, calorie-burning brown fat. Irisin acts on white adipose tissue cells, where fat is stored in mammals. The effect of the hormone turns them into brown adipose tissue cells, which are responsible for the pr
oduction of heat. When introduced into the blood, irisin increased energy expenditure in mice even without changing their mobility and diet. This caused a decrease in body weight and blood sugar in obese mice. Perhaps irisin will find application as a medicine for people suffering from obesity and diabetes.
Obesity and overweight are one of the major medical problems these days. Obesity is spreading at the rate of an epidemic, and according to some reports, it can really be contagious. It is one of the main risk factors for the development of cardiovascular disease and type 2 diabetes. It has long been known that during exercise, energy expenditure increases disproportionately: more energy is spent than is required for exercise or work. It was also known that during exercise in skeletal muscles, the content of a protein, the transcription factor PGC1-α, increases.
Together with another protein, it was initially found to enhance the production of the thermogenin protein, or UCP 1, in brown adipose tissue (“brown fat”). The brown color is due to a large number of mitochondria. This wonderful fabric does not store energy, but spends it. This happens because during the oxidation of organic matter, the mitochondria of this tissue do not synthesize ATP, but transfer all energy into heat. Thermogenin is responsible for this – it forms pores in the inner membrane of mitochondria that allow protons to pass through, which prevents ATP synthesis.
Brown fat is well developed in newborns: they have a large relative body surface, they are not good at shivering, and brown fat helps them warm themselves. In adults, almost all brown fat is replaced by regular, white fat (only small areas of brown fat remain in the upper chest and neck).
However, subcutaneous white fat can also develop brown fat cells (Fig. 2). In their structure and work, they do not differ from the “real” brown fat cells. In addition, mature white adipose tissue cells (“white” adipocytes) can transform into brown fat cells (“brown” adipocytes).
An international team of scientists from six scientific institutions in the US, Denmark and Italy decided to find out how the increase in the amount of PGC1 in the muscles affects other tissues. As a result, it was possible to discover an important mechanism that can help fight obesity. First, it was found that after 3 weeks of running in a wheel or swimming in the same transgenic mice (with an elevated level of PGC1), the amount of thermogenin in subcutaneous white fat increases sharply (25–65 times), and the number of “brown” adipocytes increases there. To show the direct effect of muscle cells on fat, the scientists treated the culture of “white” adipocytes with a liquid in which they cultivated muscle cells with an increased content of PGC1. As a result, white adipocytes turned brown. At the same time, the medium from under normal muscle cells had no such effect.
Then the scientists proved that irisin is found in the blood plasma of mice and humans. With exercise, after a few weeks, its level rises by 1.5–2 times. The therapeutic effect of irisin https://en.wikipedia.org/wiki/FNDC5 was tested in mice by introducing the FNDC5 gene with an adenoviral vector so that the gene entered the liver cells. As a result, the liver of mice began to produce irisin in large quantities, and its blood level increased by 3-4 times. There were no adverse reactions. After 10 days, the level of thermogenin mRNA in subcutaneous white fat increased 13 times, and typical brown adipocytes appeared there. Then, in the same way, the researchers increased the content of irisin in the blood of mice of a special genetic line, suffering from obesity and type II diabetes (their cells are poorly responsive to insulin ). The level of irisin in their blood increased three times. At the same time, oxygen consumption increased sharply, and after ten days the weight slightly decreased, the concentration of glucose in the blood after meals and the average concentration of insulin dropped noticeably.
The authors note that much remains to be done. For example, you need to establish how a longer intake of irisin will affect body weight and other indicators. It is also necessary to find a receptor through which irisin acts on cells. One way or another, the therapeutic potential of this protein is obvious. But it will not enter clinical practice soon. For now, there is only one way out. No, even two: run or swim!
