Researchers have been analysing the intricacies of the alimentary canal and nervous system for decades now, but the mechanism behind the signalling pathway of the action of leptin monitoring the breakdown of fats has remained elusive. Findings of a new study, published in Cell, seem to have shed light on the subject: scientists have witnessed for the first time how nerve cells excited via leptin wrap around fat cells to deplete them.
Groups of nerve cells (red) wrapping around fat cells (green). Photo credits: Ana Domingos, Instituto Gulbenkian De Ciência.
The human body is perfectly made for its needs and responses to be regulated such that it is able to function accordingly. One of its amazing features is how it deals with the intake of food, including fats, with relation to the body’s demands for energy: a hormone known as leptin is secreted to inform the brain that fats have to be broken down to provide energy. The study has provided invaluable insight into leptin’s action, specially that obese people grow resistant to the hormone, and thus experience great difficulty in losing weight. The findings are, therefore, deemed to be helpful to assist researchers treat such patients.
Leptin, produced by fat cells known as adipocytes, helps to keep body fat within a certain range. It is secreted in concentrations proportional to the body fat mass of the person. It travels to the brain in the blood to signal satiety, to reduce hunger, and to boost metabolism causing adipocytes to burn fatty molecules to release energy. Therefore, if leptin is not produced in the adequate amounts, hunger is not appeased increasing appetite, and mebolism is disrupted. The new study shows how leptin brings about these processes.
With the means of highly sensitive microscopy, the researchers analysed fat tissues in rodents. They discovered that some nerve cells – previously unidentified – were surrounding individual adipocytes, thereby creating a link between the nervous system and fats. Using specific markers, the researchers found that the nerves belonged to the sympathetic nervous system whose function is to transmit data to and from the brain and spinal cord with the aim of making the necessary adjustments to keep the body’s internal environment constant.
After their observation, the researchers selectively activated this type of nerves in live mice. They were thus enabled to reproduce the events that occur in the aftermath of leptin signalling when fatty molecules broke down accounting for a decrease in fat mass. This increase in metabolism was stimulated by chemical norepinephrine from the neurons.
Furthermore, mice genetically engineered to lack these neurones would not respond to leptin signals, leading to no breakdown of fat.
These findings might prove to be helpful to obesity treatment, but more research has to be done.