Lactobacillus rhamnosus GG Alleviates Colitis by SLC5A12-Mediated Th17/Treg Cell Balance in Mice

Background/Objectives: Lactobacillus rhamnosus GG (LGG) is one of the most widely utilized probiotic strains with a variety of biological functions including prevention and treatment of gastro-intestinal infections and regulation of immune responses. Methods: Here, we explored the role of LGG in regulating the differentiation of naïve CD4⁺ T cells and its effect on alleviating the dextran sulfate sodium (DSS)-induced colitis in mice. Results: In vitro, we showed that LGG-derived metabolites not only promoted the differentiation of naive CD4⁺ T cells into T-helper 17 cells (Th17 cells), but also selectively upregulated the expression of lactate-specific transporter solute carrier family 5 member 12 (SLC5A12). Interestingly, we manipulated a CD4⁺ T cell-monocytes co-culture and found that heated LGG-loaded monocytes modulate naive CD4⁺ T cells to differentiate preferentially into Treg cells rather than Th17 cells. To explain the above-mentioned contradiction, we used an experimental colitis model and found that LGG administration alleviated the DSS-induced colitis in mice, as indicated by decreases in weight loss and disease activity index. Moreover, SLC5A12 blockade (using a specific antibody) further reduced the colonic histological inflammatory score and decreased secretion of proinflammatory cytokines such as IFN-γ, IL-6, IL-17F, and IL-21. Notably, SLC5A12 blockade abolished the LGG-induced differentiation of the IL-17⁺CD4⁺ T (Th17) cells but significantly increased the frequency of Foxp3⁺CD4⁺ T (Treg) cells in the colonic lamina propria. Furthermore, a higher intracellular lactate concentration was observed in the colonic CD4⁺ T cells isolated from the LGG-treated colitic mice compared with other groups. Additionally, we also found elevated levels of oxidative stress indicators such as MDA and H₂O₂, as well as excessive reactive oxygen species (ROS) in colonic tissue of DSS-treated only mice, while LGG can scavenge ROS by inducing nuclear factor-erythroid 2-related factor 2 (Nrf2) expression in enterocytes. Conclusions: Altogether, these results indicate that LGG might alleviate preclinical colitis by modulating the Th17/Treg balance, and SLC5A12 blockade appears to enhance the anti-inflammatory properties of LGG.