An incredible new study led by a team from the Scripps Research Institute has discovered a novel communication pathway between fat cells and the brain. The findings reveal that the brain does not regulate fat burning by just slowly signaling responding to hormonal in the blood, but can directly send messages to fat tissue and influence metabolic processes.
The traditional view on metabolism sees the body use a variety of signaling molecules, such as hormones, to regulate its energy production. Adipose (fat) tissue is like the body’s energy storage system and when we need to tap those supplies for extra fuel in times of high physical activity or stress, certain signals trigger the sympathetic nervous system to start talking to those fat cells.
Up until now it was thought that the nerves extending into fat tissue were mostly linked to this sympathetic nervous system pathway. But understanding exactly what types of neurons are in this kind of tissue had been difficult to study. So to obtain the findings in this study the research team needed to develop entirely new methods of imaging.
Two novel methods were in this research. One is called HYBRiD, and it renders fat tissue transparent, allowing researchers a unique window into the paths of neurons. The other method is called ROOT, and it lets the researchers study exactly how certain neurons localized in fat tissue communicate with other parts of the body.
“This research was really made possible by the way these new methods came together,” explained Yu Wang, first author on the study. “When we first started this project, there weren’t existing tools to answer these questions.”
The big finding from the study was the discovery of sensory neurons that branch out from the spine into fat tissue. These sensory neurons directly communicate with a part of the brain called the dorsal root ganglia.
“The discovery of these neurons suggests for the first time that your brain is actively surveying your fat, rather than just passively receiving messages about it,” said co-senior author Li Ye. “The implications of this finding are profound.”
So what kinds of messages are being sent from these sensory neurons to the brain?
The researchers blocked communication from these sensory neurons and discovered increased metabolic activity in the fat tissue. When sensory neuron communication was silenced, the sympathetic nervous system kicked into gear and began converting the white fat cells into brown fat. This mechanism steps up the body’s fat-burning processes.
The researchers speculate that these two opposing nerve signals may work in tandem to maintain a kind of metabolic equilibrium. The sympathetic nervous system switches fat-burning processes on, while the sensory neuron pathway turns the process off.
“This tells us that there’s not just a one-size-fits-all instruction that brain sends adipose tissue,” explained Li. “It’s more nuanced than that; These two types of neurons are acting like a gas pedal and a brake for burning fat.”
Foundational discoveries often result in a whole host of new questions needing further research, and this study is no exception. All this finding can clearly establish at this stage is that the newly discovered sensory neuron communication pathway is crucial for keeping fat tissue healthy.
But from there the questions quickly start piling up.
For example, how do these sensory neuron signals from fat tissue mechanistically interact with the sympathetic nervous system signaling?
Or perhaps more compelling is exactly what kinds of messages are traveling to and from the brain via these fat tissue sensory neurons? Do different parts of the dorsal root ganglia direct different metabolic functions in fat tissue? And most importantly, can these pathways be therapeutically modulated to treat obesity or metabolic diseases?
The study was published in the journal Nature.
Source: Scripps Research