SAA1 Drives Microglial Inflammation via TLR4/NF-κB-Dependent NLRP3 Activation in Sepsis-Associated Encephalopathy

Sepsis-associated encephalopathy (SAE) is a sepsis-induced neurological disorder characterized by neuroinflammatory responses and cognitive impairment; however, the molecular mechanisms underlying microglial inflammatory activation in SAE remain incompletely understood. A caecal ligation and puncture (CLP)-induced sepsis model and lipopolysaccharide (LPS)-exposed primary microglia were used to evaluate the contribution of serum amyloid A1 (SAA1) to SAE. Multiomics profiling combined with functional manipulation, coimmunoprecipitation, glutathione S-transferase (GST) pull-down assays, and in silico virtual screening were applied to investigate the mechanistic basis of SAA1-mediated responses and evaluate the effects of Forsythoside I (FI). CLP induced significant cognitive impairment, hippocampal injury, neuroinflammation, and microglial pyroptosis. Multiomics analyses identified SAA1 as a markedly upregulated inflammatory mediator that is predominantly localized in microglia. SAA1 knockdown alleviated cognitive deficits, reduced neuroinflammation, and suppressed NLRP3 inflammasome activation and pyroptosis. Mechanistically, SAA1 physically interacted with TLR4 and promoted downstream NF-κB activation, leading to increased NLRP3 inflammasome activation and pyroptosis. Rescue experiments further demonstrated that the proinflammatory effects of SAA1 were dependent on TLR4 signalling. In addition, computational analyses predicted a potential interaction between FI and SAA1, while FI treatment attenuated SAE-associated neuroinflammatory injury and was accompanied by reduced SAA1 expression and suppression of downstream TLR4/NF-κB signalling and NLRP3 inflammasome activation. These results indicate that SAA1 contributes to microglial inflammatory activation and pyroptosis in SAE through TLR4/NF-κB-dependent NLRP3 inflammasome signalling. FI exerts neuroprotective and anti-inflammatory effects accompanied by modulation of SAA1-associated inflammatory signalling; however, whether SAA1 represents a direct molecular target of FI remains to be established. Collectively, pharmacological modulation of SAA1-associated inflammatory signalling may represent a potential therapeutic strategy for SAE.