The Regulatory Role And Molecular Mechanism Of Gut Microbiota In Sepsis-associated Encephalopathy

BackgroundSepsis-associated encephalopathy(SAE)is a diffuse brain dysfunction in patients with sepsis without evidence of direct central nervous system infection or structural abnormalities,and is a common symptom in critically ill patients.SAE patients have a high mortality rate,and survivors often suffer from long-term mental damage,and there is still a lack of effective clinical treatments.The gut microbiota is closely related to sepsis and brain function,respectively.However,the role of gut microbiota in sepsis-associated encephalopathy has not been fully elucidated.Based on the "microbe-gut-brain axis" theory,this study explored the regulatory role and molecular mechanism of gut microbiota in the pathogenesis of sepsis-related encephalopathy.ObjectiveTo explore the role of intestinal microbiota in the susceptibility of septic mice to SAE;to identify metabolites of intestinal microbiota that protect septic mice against SAE;to elucidate the specific mechanisms by which the metabolites regulate SAE susceptibility.Contents and methods1.To explore the relationship between intestinal microbiota and SAE susceptibility(1)The sepsis mouse model was constructed by cecal ligation and puncture(CLP)method,and SAE-susceptible(SES)and SAE-resistant(SER)mice were screened using neurologic scoring.(2)16 s rRNA sequencing was used to analyze the differences in the intestinal microbiota of SES and SER mice before and after modeling.2.Screening and validation of key gut microbiota metabolite that protect septic mice against SAE(1)Validate the role of gut microbiota in neuroinflammation in mice with sepsis using fecal transplantation experiments.(2)Using metabolomic methods to screen out the microbiota metabolites associated with SAE resistance in mice.(3)To explore the relationship between intestinal microbiota and serum levels of this metabolite.(4)To verify the protective effect of this metabolite in SAE.3.To explore the specific mechanism of the key metabolite in alleviating SAE(1)The NLRP3 inflammasome-related protein was detected in the cerebral cortex of septic mice,and it was speculated that this metabolite may inhibit neuroinflammation.(2)Primary microglia were cultured,and in vitro experiments further verified that this metabolite can inhibit the activation of NLRP3 inflammasome in microglia stimulated by lipopolysaccharide(LPS).(3)Exploring the target receptor for the metabolite to exert its effect.Results(1)Mice with a neurological score≤6 at 36 hours after CLP were defined as SES,while those with a score>6 were defined as SER.Compared with SER mice,SES mice had decreased gut microbiota diversity and enriched Enterobacteriaceae.(2)The levels of IL-1β and TNF-α were higher in the cortex of the mice treated with SES compared with those treated with SER.SER mice were enriched in indole-3-Propionic acid(IPA)in feces.IPA can improve anxiety behavior and memory impairment in sepsis mice.(3)IPA-dependent aryl hydrocarbon receptors in microglia inhibit the activation of NLRP3 inflammasome and reduce neuroinflammation in septic mice.ConclusionsSepsis-induced disruption of gut microbiota composition and reduced metabolite IPA predisposes septic mice to SAE.IPA inhibits LPS-stimulated NLPR3 inflammasome activation and L-1β secretion in microglia via AhR.Our study sheds light on the underlying mechanism by which the gut microbiota mediates SAE susceptibility and enriches our understanding of the "microbe-gut-brain" axis in the course of sepsis.