Lactobacillus plantarum surface layer adhesive protein protects intestinal epithelial cells against tight junction injury induced by enteropathogenic Escherichia coli.

Lactobacillus plantarum (LP) has previously been used for the treatment and prevention of intestinal disorders and disease. However, the role of the LP surface layer adhesive protein (SLAP) in inhibition of epithelial cell disruption is not fully understood. The aim of the present study was to investigate the protective effects of purified SLAP on Caco-2 cells infected with enteropathogenic Escherichia coli (EPEC). The role of ERK in LP-mediated inhibition of tight junction (TJ) injury was also evaluated in order to determine the molecular mechanisms underlying the protective effects of LP in epithelial cells. SLAP was extracted and purified from LP cells using a porcine stomach mucin-Sepharose 4B column. SLAP-mediated inhibition of bacterial adhesion was measured using a competition-based adhesion assay. Expression of TJ-associated proteins, maintenance of TJ structure, and levels of extracellular signal regulated kinase (ERK) and ERK phosphorylation were assessed in SLAP-treated cells by a combination of real-time PCR, western blotting, and immunofluorescence microscopy. Cell permeability was analyzed by measurement of trans-epithelial electrical resistance (TER) and dextran permeability. The effect of SLAP on levels of apoptosis in epithelial cells was assessed by flow cytometry. Results from these experiments revealed that treatment with SLAP decreased the level of adhesion of EPEC to Caco-2 cells. SLAP treatment also enhanced expression of TJ proteins at both the mRNA and protein levels and affected F-actin distribution. Although ERK levels remained unchanged, ERK phosphorylation was increased by SLAP treatment. Caco-2 cells treated with SLAP exhibited increased TER and decreased macromolecular permeability, which was accompanied by a decrease in the level of apoptosis. Together, these results suggest that LP-produced SLAP protects intestinal epithelial cells from EPEC-induced injury, likely through a mechanism involving ERK activation.