Systemic LPS-Induced RACK1 Downregulation Contributes to Neuronal Necroptosis in the Limbic System in Mice: A Mechanism of Sepsis-Associated Encephalopathy and a Potential Target of Tanshinone IIA

Abstract

Background: Sepsis-associated encephalopathy (SAE) is a frequent severe complication of surviving sepsis patients, associated with persistent cognitive impairments. Even though neuronal activity strongly impacts the functionality of the limbic system, the specific prevention and therapy for SAE remain limited since its underlying network mechanisms are still poorly understood.

Methods: Receptor for activated protein kinase C 1 (RACK1) siRNA was transfected in SH-SY5Y and systemic LPS injection-induced depressive and anxiety-like behaviors mice model to evaluate the potential contribution of endogenous RACK1 in response to systemic LPS-induced neuronal necroptosis. Molecular docking and co-immunoprecipitation were employed to explore the relationship between RACK1 and RIPK1. The neuroprotective effect and molecular mechanism of Tanshinone IIA (Tan IIA) on neuronal necroptosis was explored through behavioral tests, histopathological analysis, and western blotting.

Findings: Hippocampal RACK1 protein expression was downregulated and associated with systemic LPS injection-induced depressive and anxiety-like behaviors in mice. The knockdown of RACK1 promotes systemic LPS-induced depressive and anxiety-like behaviors and neuronal necroptosis in mice and contributes to potentiating the LPS-associated activation of MLKL. LPS induced the RACK1/RIPK1 complex formation in neurons. Tan IIA significantly improved systemic LPS-induced cognitive impairments in mice through the upregulation of RACK1, suppressing neuronal necroptosis. Mechanically, Tan IIA promoted the formation of the RACK1/RIPK1 complex in neurons, thus inhibiting TNFR-triggered necroptosis.

Interpretation: Endogenous RACK1 is the critical protective factor in the limbic system against neuronal necroptosis and improves long-term cognitive dysfunction in SAE. Additionally, Tan IIA protects the septic-associated neurocognitive function by inhibiting neuronal necroptosis via upregulating RACK1 in the limbic system.

Funding: This work was supported by the Fundamental Research Funds for the Central Universities (No. SCU2023D022), Joint Funds of the National Natural Science Foundation of China (No. U21A20333), and the Key Project of the Science and Technology Department in Sichuan Province (No. 2023YFS0223).

Declaration of Interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Ethical Approval: Animal ethics and experimental procedures were approved by the West China School of Basic Medical Sciences and Forensic Medicine of Sichuan University by the Committee on the Ethics of Animal Experiments of Sichuan University (No. K2022005).

Keywords: RACK1, neuronal necroptosis, limbic system, sepsis-associated encephalopathy, Tanshinone IIA