Probiotic bacteria Bifidobacterium bifidum upregulation of intestinal epithelial tight junction barrier is mediated by TLR-2/TLR-6 receptor complex activation of occludin gene

Defective intestinal epithelial tight junction (TJ) barrier is a key pathogenic factor of inflammatory bowel disease (IBD). Probiotic bacterial upregulation of intestinal TJ barrier has been shown to prevent the development of intestinal inflammation. However, the mechanism of microbe-host interactions responsible for the TJ barrier upregulation remains unclear. This study investigates the molecular mechanisms by which a particular strain of probiotic bacteria, Bifidobacterium bifidum (BB1), upregulates the intestinal epithelial TJ barrier. Using in vitro (filter-grown Caco-2 monolayers) and in vivo (recycling intestinal perfusion in live mice) intestinal epithelial model system, we show that BB1 upregulation of intestinal TJ barrier correlated with an increase in occludin gene activity (occludin promoter activity and occludin mRNA transcription levels) and protein expression, with no changes in other TJ proteins. Occludin knockdown or inhibition of gene transcription prevented the enhancement of the TJ barrier, confirming the essential role of BB1-induced occludin gene activation in TJ barrier enhancement, which was mediated sequentially by BB1 activation of the intestinal epithelial cell TLR-2/TLR-6 complex and IRAK-1 phosphorylation, as well as the apical membrane recruitment of the adapter protein TOLLIP. These findings provide novel mechanistic insight into the microbe-host interactions driving probiotic bacteria upregulation of intestinal TJ barrier.