Researchers have identified a previously unknown communication pathway allowing fat to communicate directly with the brain, at least in mice. By eliminating this connection, the rodents burned more fat. More work is needed, but disrupting this communication network may one day help treat obesity in humans.
We’ve known for a long time that the brain uses neurons in the sympathetic nervous system to tell the body to burn more fat. Until now, however, scientists believed that the reverse communication (from fat to brain) was less direct, with fat sending messages to the brain by releasing hormones into the bloodstream.
A new study published in the journal Nature shows that fat also sends messages directly to the brain via sensory nerve cells called dorsal root ganglia.
Beige fat to fight obesity
Located near the spinal cord, the dorsal root ganglia (DRGs) extend long threads to peripheral organs. The collected sensory information is then sent to the brain through the spinal cord. Researchers have long known that DRGs carry information from the skin and muscles to the brain. Until now, however, it has always been difficult to determine what information neurons transmit from fatty tissue to the brain via DRGs because of the difficulty of visualizing these neurons in action.
Eventually, researchers found a way to do it. As part of this work, neuroscientist Li Ye and his team at the Scripps Research Institute in La Jolla, Calif., fluorescently labeled extended DRG neurons in the fat tissue of several mice. Using a previously developed system to see through animal tissue, the researchers were able to observe the action of DRGs from their origins near the spinal cord to the fat pads.
As a reminder, fat comes in many colors depending on how the body uses it. The brunette burns for example for generate heat. The white is mostly stored (it’s what you want to see disappear). Finally, the beige is placed between the two. When the body needs to burn more fat, these fatty tissues can turn into brown fat in an effort to generate heat. When the body does not need to burn it, beige fat turns white and is therefore stored.
These fatty tissues are therefore more “dynamic” than the others. For this reason, researchers believe they may play an important role in obesity issues. For this study, the team therefore focused on it.
Cut “car brakes”
During their experiments, the researchers suppressed the DRG neurons that connected to this beige fat by means of a virus. As a result, genes related to fat production and heat generation intensified. In other words, mice burned more fat. Their beige fat also turned browner, a sign that the rodents’ temperature had risen.
One way to better appreciate the process is to imagine the following analogy. If the body is a car and fat is fuel, then the sympathetic nervous system acts like the accelerator pedal telling the body to burn more fuel (thus more fat). Conversely, the newly discovered fat-brain communication system appears to work like a brake pedal, acting in opposition to the accelerator pedal of the sympathetic nervous system. Here, the researchers have cut the brakes, which promoted fat burning.
The researchers hypothesize that this “braking system” tells the brain how much fat is being burned, ensuring that the body isn’t burning too much. This is only preliminary work, but it would be interesting to see if such a process could be at work in humans, and if so, if this process could be manipulated in hopes of eventually helping obese people to lose weight.