STING Mediates Necroptosis in Hippocampal Neurons of Mice With Sepsis-Associated Encephalopathy

Sepsis-associated encephalopathy (SAE) is a common and severe neurological syndrome induced by sepsis and characterized by brain dysfunction. The incidence of SAE is as high as 76%. After onset, the mortality rate is as high as 60%. Even if patients survive, about 20% have long-term cognitive impairment. At present, the exact pathogenesis of SAE remains unknown. Our results showed that necroptotic protein was obviously elevated in the hippocampus of SAE mice, but the internal mechanism was still unclear. The stimulator of interferon gene (STING) protein has been reported to be a key molecule in the regulation of programmed cell death. However, the critical role of STING in the progression of SAE remains elusive. We explored the mechanism by which STING regulates hippocampal neuronal necroptosis in SAE.

A cannula was embedded into the lateral ventricle of mice, and mixed lineage kinase domain-like protein (MLKL) inhibitor necrosulfonamide (NSA) and STING inhibitor C-178 were injected. The motor ability and memory function of mice after cecal ligation and puncture (CLP) were assessed by the open field test (OFT) and barnes maze test (BMT), respectively. The expression and distribution of ^S345p-MLKL and ^S366p-STING proteins in the hippocampal region of SAE mice were analyzed, and the expression levels of ^S366p-STING/STING, ^S232p-receptor-interacting protein kinase 3 (RIPK3)/RIPK3, ^S345p-MLKL/MLKL, and ^S166p-RIPK1/RIPK1 proteins in the hippocampal tissue of SAE mice were examined. Co-immunoprecipitation (CO-IP) was used to detect the relationship between STING and RIPK3 protein.

The surviving mice after CLP had cognitive dysfunction. The hippocampal tissues of SAE mice showed upregulated expression of ^S232p-RIPK3/RIPK3, ^S345p-MLKL/MLKL, and ^S166p-RIPK1/RIPK1 proteins. Mice in the CLP+NSA group showed better cognitive performance than the mice in the CLP+dimethyl sulfoxide (DMSO) group. The results showed that the expression of ^S366p-STING protein was elevated in neurons of the hippocampal cornu ammonis 1 (CA1) region in SAE mice, and there was an interaction between STING and RIPK3 proteins. STING inhibitor C-178 inhibited the protein expression level of ^S232p-RIPK3/RIPK3 and ^S345p-MLKL/MLKL and alleviated SAE mice with cognitive dysfunction.

STING is implicated in the development of cognitive dysfunction in SAE by regulating necroptosis in hippocampal neurons. Inhibition of the STING pathway reduced necroptosis-related protein expression and partially improved BMT performance. This result provides a new potential therapeutic target for the prevention and treatment of SAE.