What happens in the vagus,...?

Loss of the liver X receptor LXRα/β in peripheral sensory neurons modifies energy expenditure

Peripheral neural sensory mechanisms play a crucial role in metabolic regulation but less is known about the mechanisms underlying vagal sensing itself. Recently, we identified an enrichment of liver X receptor alpha and beta (LXRα/β) in the nodose ganglia of the vagus nerve. In this study, we show mice lacking LXRα/β in peripheral sensory neurons have increased energy expenditure and weight loss when fed a Western diet (WD). Our findings suggest that the ability to metabolize and sense cholesterol and/or fatty acids in peripheral neurons is an important requirement for physiological adaptations to WDs.

DOI:http://dx.doi.org/10.7554/eLife.06667.001

The vagus nerves run from the brainstem to the heart and the digestive system and help to control several processes including digestion and heart rate. Because of their role in regulating food intake, these nerves are attractive targets for scientists hoping to develop treatments for obesity.

There are two types of fat tissue found in mammals: white fat, which is used as an energy store and makes up most of the extra fat seen in obese individuals; and brown fat, which can generate body heat. The vagus nerves monitor fat and cholesterol levels in the body via receptor proteins that respond to messages sent from the fat tissues and the liver. Previous research unexpectedly found that mice genetically engineered to lack these receptor proteins—called LXRα and LXRβ—do not become obese even when fed a high-fat, high-cholesterol diet that would make normal mice gain excessive weight.

Mansuy-Aubert et al. have now investigated in more detail why mice without these receptor proteins are resistant to obesity. When fed a high-fat, high-cholesterol diet, mice that lacked the LXRα and LXRβ receptors in sensory neurons had higher cholesterol levels in their nerve cells than normal mice on the same diet. Mice lacking these receptors also burned more energy and gained less weight than normal mice.

Next, Mansuy-Aubert et al. examined fat tissue from both types of mice. This revealed that the heat-generating brown fat was more active in mice lacking the LXRα and LXRβ receptors. Some of the white fat in these mice had also become more like brown fat, allowing the mice to burn more energy and so gain less weight.

In many Western countries, many people also eat a diet that is high in fat and cholesterol. This raises the possibility that drugs that block the LXRα and LXRβ receptors in sensory neurons in humans could help to treat or prevent obesity, although further work will be needed to investigate this.

DOI:http://dx.doi.org/10.7554/eLife.06667.002