Biologists have identified a brain hormone that appears to trigger fat burning in the gut. Their findings in animal models could have implications for future pharmaceutical development.
Previous studies had shown that the neurotransmitter serotonin can drive fat loss. Yet no one was sure exactly how. Srinivasan, Assistant Professor at The Scripps Research Institute in the US and her colleagues, experimented with roundworms called C elegans, which are often used as model organisms in biology.
While their metabolic pathways are fairly primitive, their neural networks are such that the hormones and neurotransmitters in them resemble those of human beings.
Scientists eliminated certain genes in these worms to see if the pathways between serotonin and fat-burning could be disrupted.
By testing gene after gene, the researchers hoped to find a gene, the elimination of which would stop fat-burning in its tracks. This led them to find a neuropeptide named FLP-7.
"That was a big moment for us," said Srinivasan. And understandably so, as this is the first time that researchers discovered a brain hormone that selectively and particularly spurs the fat-burning process without affecting food intake.
Altogether, the newly discovered fat-burning pathway works like this: a neural circuit in the brain produces serotonin in response to sensory cues, such as food availability. This signals another set of neurons to begin producing FLP-7. FLP-7 then activates a receptor in intestinal cells, and the intestines begin turning fat into energy.
Next, the researchers investigated the consequences of manipulating FLP-7 levels. While increasing serotonin itself can have a broad impact on an animal's food intake, movement and reproductive behavior, the researchers found that increasing FLP-7 levels farther downstream didn't come with any obvious side effects. The worms continued to function normally while simply burning more fat.
It was the moment of truth for science. Serotonin is secreted in the brain due to food intake. In the worms, the fat-burning process continued unabated while the worms behaved in a natural manner. It seemed that this manipulation of serotonin levels was a sort of balancing act.