Clostridium butyricum improves cognitive dysfunction in ICV-STZ-induced Alzheimer’s disease mice via suppressing TLR4 signaling pathway through the gut-brain axis

In recent years, the relationship between gut-brain axis and Alzheimer’s disease (AD) attracted increasing attention. The aim of this study is to investigate the therapeutic effect of Clostridium butyricum (CB) on intraventricular injection of streptozotocin (ICV-STZ)-induced mice and the potential mechanisms. ICV-STZ mice were treated with CB by gavage for 21 consecutive days. The pharmacological effect of CB was assessed by behavior test, brain tissue H&E staining and tau protein phosphorylation levels of hippocampus tissues. The expression levels of TLR4, MYD88, NF-κB p65, TNF-α, iNOS, Occludin and ZO-1 in hippocampal and colonic tissues were detected by Western-blot method. 16S rRNA gene sequencing analysis was used to analyze the intestinal microbiota of mice. The results showed that CB improved the cognitive dysfunction of ICV-STZ mice, restored the structure and cell number of hippocampal and cortical neurons, decreased the protein levels of p(Ser404)-tau protein in hippocampal tissues and TLR4, MYD88, NF-κB p65 and iNOS in hippocampal and colonic tissues, and increased the protein levels of Occludin and ZO-1 in colonic tissues. Meanwhile, CB reversed the changes of intestinal microbiota in AD mice. Therefore, the mechanisms of cognitive function and brain pathological changes in AD mice improved by CB may be related to the regulation of TLR4 signaling pathway and intestinal microbiota. This study supports the potential anti-AD effect of CB and initially revealed its pharmacological mechanism of CB, providing a theoretical basis for further clinical application of CB.