Metabolic stress drives sympathetic neuropathy within the liver

The nervous system instructs the body's metabolism, including that in the liver. However, the neural anatomy of the liver under either normal or metabolically stressed conditions remains to be unequivocally assessed. Here, we examined neural distributions in the mouse, nonhuman primate, and human livers with advanced 3D imaging. We observed that neural innervations within the liver are predominantly sympathetic, but not para-sympathetic, inputs. Moreover, we discovered the profound and reversible loss of such sympathetic innervations during metabolic challenges. This hepatic sympathetic neuropathy was caused by TNF alpha derived from CD11b(+) F4/80(+) immune cells under high-fat-diet (HFD) condition. We further demonstrated that the Sarm1 deletion mitigated the hepatic sympathetic neuropathy and improved metabolic parameters in HFD-challenged mice. Mechanistically, the sympathetic neurotransmitter norepinephrine attenuated the immune-cell inflammation that would otherwise trigger the insulin insensitivity of hepatocytes. These results together reveal the previously unrecognized neuropathic event in the liver with metabolic relevance.

Automated summary

This study revealed that the liver is predominantly innervated by sympathetic nerves, and the loss of sympathetic innervations during metabolic challenges was found to be caused by TNFα derived from immune cells. Deletion of Sarm1 alleviated hepatic sympathetic neuropathy and improved metabolic parameters in mice challenged with a high-fat diet. Mechanistically, the sympathetic neurotransmitter norepinephrine attenuated immune cell inflammation, preventing insulin insensitivity in hepatocytes.