Pre-treatment with TLR2 ligand induces protection in swine intestinal epithelial cells damaged by deoxynivalenol

Abstract

Intestinal epithelial cells play a major role in innate immune responses and protect host from external hazards including pathogenic microorganisms and toxins. Intestinal epithelium is the first line of defense against food and feed contaminants. Deoxynivalneol is a secondary toxic metabolite from fusarium mycotoxin that is harmful to humans and animals, and pigs being the most sensitive. Deoxynivalenol is known to disrupt intestinal structure and interrupt with the intestinal barrier function. Toll-like receptor (TLR) 2 in intestinal epithelial cells are selectively expressed on the basolateral membrane fraction in response to its ligands and plays an important role in protection by inducing inflammatory activity at the local area. TLR2 signaling pathway enhancing epithelial membrane integrity has not been fully elucidated, however certain synthetic TLR2 ligands induced the increase of epithelial membrane resistance in human and mouse in vitro. In addition, colitis-induced mice administered with TLR2 ligand, Pam3CysK4 showed remarkable decrease on apoptosis and inflammatory response of intestinal epithelial cells by enhancing the tight junction barrier formation and membrane integrity. Although, it has been shown that TLR2 ligands affect the expression of tight junction proteins in mice and humans, their effect on swine intestinal epithelial cells is yet to be fully elucidated. In the present study, I investigated the effect of TLR2 ligands on the expression of tight junction proteins, induction of barrier integrity and anti-apoptotic effect in IPEC-J2, swine intestinal epithelial cells treated with deoxynivalenol. Interestingly, pre-treatment with TLR2 ligands significantly suppressed the level of deoxynivalenol-mediated apoptosis in IPEC-J2 cells when compared to the cells without pre-treatment. IPEC-J2 cells treated with TLR2 ligands, contrary to the cells without treatment, showed the increased expression of tight junction proteins, claudin-3, zonula occluden-1 (ZO-1), and occludin and their integrity. The results using confluent IPEC-J2 cells have shown resistant effect of PCSK and LTA on the reduction of TEER induced by deoxynivalenol suggesting that TLR2 ligands induced increase of tight junction proteins in intestinal epithelial cells, which enhanced the paracellular resistance. It was noting that the blockade of TLR2 signaling leads to failure of PCSK- and LTA-mediated barrier protection against the damage induced by deoxynivalenol. In human and mice intestinal epithelium, TLR2 stimulation via phosphatidylinositil-3-kinase/Akt (PI3K-Akt) pathway preserved integrity against stress-induced damage. Therefore, I examined the importance of PI3K-Akt signaling in IPEC-J2 cells treated with TLR2 ligand. The results indicated that PSCK and LTA induced the expression of tight junction proteins in IPEC-J2 cells, which was dependent on the activation of PI3K-Akt signaling pathway. This was further validated that IPEC-J2 cells pre-treated with PCSK or LTA induced barrier protection was significantly suppressed by PI3K inhibitor. In conclusion, the present study showed that pre-treatment of TLR2 ligands to swine intestinal epithelial barrier could have protective role against the damage induced by deoxynivalenol through PI3K-Akt pathway.