Strain-specific protection of intestinal barrier by heat-treated plant-derived lactic acid bacteria via distinct tight junction modulation.

Intestinal barrier dysfunction is a key pathological factor in various chronic diseases, including inflammatory bowel disease. This study compared the barrier-protective effects and mechanisms of two heat-treated plant-derived lactic acid bacteria (P-LAB) strains, Lactiplantibacillus plantarum LOC1 isolated from tea leaves and Lacticaseibacillus paracasei RO24 isolated from traditional Japanese pickles, using lipopolysaccharide (LPS)-stimulated intestinal epithelial cell models. Barrier integrity was evaluated in Caco-2 and HT29 cells by measuring transepithelial electrical resistance (TEER) and paracellular permeability to Lucifer Yellow, together with analyses of tight junction-related gene expression, inflammatory cytokines, and global proteomic profiling integrated with Ingenuity Pathway Analysis. LPS exposure significantly impaired barrier function in both cell lines. Pretreatment with either strain significantly suppressed LPS-induced increases in paracellular permeability, whereas TEER recovery was strain- and cell-line-dependent. L. plantarum LOC1 effectively restored TEER in Caco-2 cells, while L. paracasei RO24 exerted significant protective effects primarily in HT29 cells. Mechanistic analyses revealed distinct modes of action between the two strains. L. plantarum LOC1 showed broad anti-inflammatory activity and maintained the expression of JAM-A and occludin, representing a comprehensive barrier-protective strategy. In contrast, L. paracasei RO24 selectively preserved Claudin-1, Claudin-3, and Claudin-7, indicating a structural reinforcement strategy. Proteomic and pathway analyses confirmed reactivation of tight junction signaling by both strains. These findings indicate that heat-treated P-LAB strains can exert strain-specific protective effects on intestinal epithelial barrier function under the present experimental conditions.