Suppression of MyD88 disturbs gut microbiota and activates the NLR pathway and hence fails to ameliorate DsS-inducedcolitis

Background:Myeloid differentiation factor 88(MyD88)is the core adaptor for Toll-like receptors defending against microbial invasion and initiating a downstream immune response during microbiota-host interaction.However,the role of MyD88 in the pathogenesis of inflammatory bowel disease is controversial.This study aims to investigate the impact of MyD88 on intestinal inflammation and theunderlyingmechanism.Methods:MyD88 knockout(MyD88^(-/-))mice and the MyD88 inhibitor(TJ-M2010-5)were used to investigate the impact of MyD88 on acute dextran sodium sulfate(Dss)-induced colitis.Disease activity index,colon length,histological score,and inflammatory cytokines were examined to evaluate the severity of colitis.RNA transcriptome analysis and 16S rDNA sequencing were used to detect the potential mechanism.Results:In an acute DSS-colitis model,the severity of colitis was not alleviated in MyD88^(-/-)mice and TJ-M2010-5-treated mice,despite significantly lower levels of NF-kB activation being exhibited compared to control mice.Meanwhile,16S rDNA sequencing and RNA transcriptome analysis revealed a higher abundance of intestinal Proteobacteria and an up-regulation of the nucleotide oligomerization domain-like receptors(NLRs)signaling pathway in colitis mice following MyD88 suppression.Further blockade of the NLRs signaling pathway or elimination of gut microbiota with broad-spectrum antibiotics in DsS-induced colitis mice treated with TJ-M2010-5 ameiorated the disease severity,which was not improved solely by MyD88 inhibition.After treatment with broad-spectrum antibiotics,downregulation of the NLR signaling pathway was observed.Conclusion:Our study suggests that the suppression of MyD88 might be associated with unfavorable changes in the composition of gut microbiota,leading to NLR-mediated immune activation and intestinal inflammation.