A study published in Science Advances describes, for the first time, a neuromuscular circuit that links muscle fat burning to protein action in the brain. The findings, obtained by researchers from the University of Campinas (Unicamp) and the University of São Paulo (USP), help to understand how physical exercise helps with weight loss and reinforces the habit’s importance for health.

The work aims to study the action of a protein called interleukin-6 . [IL-6], which has an inflammatory property, but in some cases, such as physical exercise, performs different functions. In this case, the fat burns in the muscle,” explains Eduardo Rubel, a professor at Unicamp College of Applied Sciences (FCA), in Limeira, who coordinated the study with support from FAPESP.

The group led by the researcher had already noticed that the mice injected with the protein directly into the brain immediately began the process of oxidizing fat in the foot muscle. This part of the study was conducted during a master’s degree from Thayana Micheletti, FAPESP Fellow. Micheletti performed part of the analysis during an internship at the University of Santiago de Compostela in Spain.

With the findings, the researchers sought to understand whether there was a circuit linking IL-6 production in the hypothalamus, the part of the brain that controls various functions, with the lipolysis observed in skeletal muscle tissue. This phase of the research was conducted in collaboration with Carlos Katashima, who is currently conducting postdoctoral training in the Laboratory of Exercise Molecular Biology (LaBMEx) at FCA-Unicamp, coordinated by Ropelle.

Previous studies indicated that a specific part of the hypothalamus, the middle ventral part, can alter muscle metabolism when stimulated. Upon discovering the presence of an IL-6 receptor in that part of the brain, Brazilian researchers hypothesized that the action of the protein produced there could trigger a neuromuscular circuit, favoring fat burning in skeletal muscle tissue.

To prove the existence of the circuit, several experiments were performed. In one, Katashima and colleagues cut the sciatic nerve, which connects the spine to the thigh muscle, in one of the mice’s paws.

When IL-6 was injected into the brain, fat burning occurred as expected in the intact paw, but not in the nerve-severed paw. “Experience has shown, therefore, that muscle fat burning occurs only thanks to the neural connection between the hypothalamus and the muscle,” says Katashima. (With information from Viver Bem)