Barrier and Immune Modulation by Limosilactobacillus reuteri ATCC PTA 6127 in Canine Epithelial and Immune Cells Under Lipopolysaccharide Challenge

Coordinated responses of intestinal epithelial and immune cells are essential for maintaining barrier integrity and immune homeostasis in dogs, yet our mechanistic understanding of probiotic-derived metabolites remains limited due to reliance on non-canine experimental models, highlighting the need for studies in canine-derived systems. Here, we investigated the effects of metabolites derived from Limosilactobacillus reuteri strain ATCC PTA6127 (Lr6127), delivered as a cell-free supernatant (CFS), on canine epithelial MCA-B1 cells and macrophage-like DH82 cells subjected to lipopolysaccharide (LPS)-induced inflammatory stress. Lr6127 CFS significantly reduced epithelial permeability, decreasing FITC–dextran leakage to 94.9 ± 1.9% (normalized relative to LPS-treated control, which was set as 100%) (p < 0.001), despite no detectable transcriptional changes in tight junction, adherens junction, or mucin genes. Barrier effects were instead associated with changes in markers of cellular stress responses, with heme oxygenase expression decreasing from 0.9 ± 0.1 to 0.7 ± 0.1 (p < 0.05). In DH82 immune cells, Lr6127-derived metabolites altered LPS-induced stress- and inflammation-related gene expression patterns; enhanced anti-apoptotic responses, as reflected by the increased BCL2 expression (1.4 ± 0.1 vs. 1.0 ± 0.0; p < 0.01) and elevated BCL2/BAX ratios (p < 0.01); and reduced expression of pro-inflammatory mediators including IL-6 and CCL2 (p < 0.05–0.001). Proteomic analysis corroborated that Lr6127-derived metabolites reduced the abundance of inflammatory and STAT-associated signaling proteins under LPS challenge, while indicating context-dependent changes in immune-related protein profiles under resting condition. Collectively, these results suggest that Lr6127-derived metabolites improved epithelial barrier function, which was accompanied by coordinated changes in cellular stress-related and inflammatory pathways, highlighting their potential to positively influence host responses.