Cell wall fraction of Enterococcus hirae ameliorates TNF-α-induced barrier impairment in the human epithelial tight junction

Aims: The evaluation of the effects of Enterococcus hirae, an intestinal bacterium in the adjacent mucosa (mucosal bacterium), on tumour necrosis factor-alpha (TNF-α)-induced barrier impairment in human epithelial Caco-2 cells. Methods and Results: The filter-grown Caco-2 monolayers were used as an intestinal epithelial model system. In Caco-2 cells, heat-killed E. hirae ATCC 9790^T suppressed the TNF-α-induced barrier impairment and increase in interleukin-8 (IL-8) secretion, but lipase- and mutanolysin-treated E. hirae ATCC 9790^T did not have these effects. It was demonstrated that lipoteichoic acid (LTA) from E. hirae ATCC 9790^T is responsible for Caco-2 cells' recovery from TNF-α-induced impairments. In addition, Caco-2 cells had the same response to Toll-like receptor 2 (TLR2) ligand, Pam₃Cys-Ser-(Lys)₄ as they did to LTA. Increased expression of zonula occludens-1 was observed by the addition of E. hirae ATCC 9790^T to TNF-α-treated Caco-2 cells, and decreased expression of myosin light chain kinase was observed by the addition of LTA and Pam ₃Cys-Ser-(Lys)₄; this, in turn, led to barrier enforcement. Conclusions: Enterococcus hirae ATCC 9790^T cell wall fractions, such as LTA, protect against intestinal impairment by regulation of epithelial tight junction via TLR2 signalling. Significance and Impact of the Study: Enterococcus hirae could be useful in the treatment of inflammatory bowel disease, as well as other intestinal disorders.