Gut commensal metabolite rhamnose promotes macrophages phagocytosis by activating SLC12A4 and protects against sepsis in mice

Sepsis progression is significantly associated with the disruption of gut eubiosis. However, the modulatory mechanisms of gut microbiota operating during sepsis are still unclear. Herein, we investigated how gut commensals impact sepsis development in a pre-clinical model. Cecal ligation and puncture (CLP) surgery was used to establish polymicrobial sepsis in mice. Mice depleted of gut microbiota by an antibiotic cocktail (ABX) exhibited a significantly higher level of mortality than controls. As determined by metabolomics analysis, ABX treatment has depleted many metabolites, and subsequent supplementation with L-rhamnose (rhamnose, Rha), a bacterial carbohydrate metabolite, exerted profound immunomodulatory properties with a significant enhancement in macrophage phagocytosis, which in turn improved organ damage and mortality. Mechanistically, rhamnose binds directly to and activates the solute carrier family 12 (potassium-chloride symporter), member 4 (SLC12A4) in macrophages and promotes phagocytosis by activating the small G-proteins, Ras-related C3 botulinum toxin substrate1 (Rac1) and cell division control protein 42 homolog (Cdc42). Interestingly, rhamnose has enhanced the phagocytosis capacity of macrophages from sepsis patients. In conclusion, by identifying SLC12A4 as the host interacting protein, we disclosed that the gut commensal metabolite rhamnose is a functional molecular that could promote the phagocytosis capacity of macrophages and protect the host against sepsis.