Muscles are able to take care of the nutrition of the body

Denis Strigun, Naked Science

The main regulator of energy homeostasis in mammals are muscles, especially cardiac and skeletal. When glucose is deficient, for example during periods of hunger or physical exertion, they use lipids for nutrition. The accumulation of the latter in peripheral tissues mediates the joint work of the liver and adipocytes and is vital for the normal functioning of the body. At the same time, the muscles themselves as an endocrine organ can affect metabolism in other parts of the body, including the liver. However, the details of this mechanism and its relationship to the muscle needs for additional energy are unclear. It is known that switching from glucose to lipids is caused by Foxo proteins.

According to past studies, Foxo muscles in Drosophila (Drosophila melanogaster) regulates the production of a ligand that activates the JAK/STAT signaling pathway (plays an important role in ontogenesis) and is similar to mammalian leptin. To find out how the interaction between adipose tissue and muscles occurs, specialists from the Texas A&M Health Research Center conducted a series of experiments on D.melanogaster. The choice of a model organism was due to the similarity of the agents involved in the metabolism of these insects and vertebrates, as well as the comparative availability for genetic engineering. At the first stage, scientists knocked out the gene encoding Foxo.

Subsequent analysis showed that the disruption of the transcription factor led to an almost twofold reduction in the volume of reserves in the adipose body – a special tissue between organs that provides insect metabolism. In addition, the amount of lipids circulating in the hemolymph also decreased. In addition to the transport of oxygen, inorganic salts and other organic compounds, this liquid serves as a storage of fatty acids that muscles can quickly extract. The researchers then tested how crucial the localization of Foxo in the muscles is to mediate the effect. Curiously, the shutdown of protein in the fat body did not affect the volume of reserves.

A model of fat storage in D. melanogaster
©Xiao Zhao et al., Current Biology, 2017

Finally, the authors studied the mechanism by which the transcription factor regulates fat metabolism. It turned out that blocking Foxo through an increase in ligand expression causes the growth of adipokinin (AKH), an analog of glucagon, a pancreatic hormone. The latter, in turn, accelerates the decomposition of nutrients in cells. Thus, fruit flies with a mutant protein consumed reserves faster than control ones, which led to a reduction in lipids needed for muscles. The cascade at the same time depended on circadian rhythms, being activated in the daytime. According to scientists, the work confirms that muscles are involved in the systemic formation of energy reserves.

The article was published in the journal Current Biology.

Portal "Eternal youth" http://vechnayamolodost.ru  10.07.2017