<i>Limosilactobacillus reuteri</i> modulates porcine intestinal Occludin and Claudin-1 proteins through MAPK signalling pathway

The present study aimed to evaluate the effects of Limosilactobacillus reuteri (L. reuteri) on porcine intestinal tight junction (TJ) proteins and explore the underlying molecular mechanisms. For in vitro experiments, the cell viability and transepithelial electrical resistance of IPEC-J2 cells with different concentrations of L. reuteri I5007 were tested to choose the suitable condition. Then, IPEC-J2 cells were pre-treated with inhibitors of mitogen-Activated Protein Kinase (MAPK) and L. reuteri I5007 for 6h. The results showed that L. reuteri treatment significantly increased the expression of TJ proteins, but pre-treatment with the p38 MAPK inhibitor SB203580 or p-c-Jun N-terminal Kinase (JNK) inhibitor SP600125 decreased the expression level of TJs. In vivo, twenty weaned piglets (ten piglets/group) were fed a basal diet or a basal diet contained 109 CFU/kg of L. reuteri I5007 for a 14–d period, respectively. Then the piglets were sacrificed and the 5–7 cm middle jejunal and ileal samples were collected. L. reuteri I5007 significantly up-regulated the mRNA expression of occludin, claudin-1, and claudin-2 in both intestinal tissues, as well as the mRNA levels of ileal zo-1 and claudin-3; additionally, the protein levels of intestinal Occludin, ZO-1, Claudin-1, and jejunal Claudin-2 and ileal Claudin-3 were also increased. L. reuteri I5007 significantly reduced the phosphorylation level of jejunal p-p38 MAPK and JNK and ileal p-p38 MAPK. In conclusion, L. reuteri I5007 promotes the expression of TJ proteins in intestinal epithelial cells through the MAPK pathway, thereby reducing stress damage to the intestinal TJ barrier of weaned piglets.