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.