Gut microbiota-derived Proline-Leucine dipeptide aggravated sepsis-induced acute lung injury via activating Nod2/NF-κB signaling pathway

Objective: Gut microbiota-derived metabolites can modulate lung tissue damage via the gut-lung axis. This study aimed to delineate the alterations in gut microbiota and metabolites associated with sepsis and elucidate their role in potentiating lung tissue damage. Methods: We employed 16S rDNA sequencing and non-targeted metabolomics to assess the changes in gut microbiota and metabolites, utilizing a rat model of sepsis. Furthermore, we investigated the contributions of the gut microbiota-derived Proline-Leucine (Pro-Leu) dipeptide and lipopolysaccharide (LPS) in driving lung inflammation, utilizing both mouse models and MH-S cells. Results: Our findings indicate that sepsis significantly diminished gut microbiota diversity and markedly increased the relative abundance of Bacteroidetes and Escherichia-Shigella, as well as the metabolite Pro-Leu. Notably, Pro-Leu levels correlated with changes in bacterial communities. Additionally, Pro-Leu effectively exacerbated sepsis-induced lung damage. Both Pro-Leu and LPS notably enhanced pro-inflammatory cytokine production (TNF-alpha, IL-6, and IL-1 beta) by up-regulating C/EBP-beta, p-NF-kappa B, and NOD2 in lung tissues and MH-S cells. Conclusions: Our findings suggest that Pro-Leu and LPS can synergistically intensify lung inflammation by activating the C/EBP-beta/NOD2/NF-kappa B signaling pathways. Importance: Our findings indicate that sepsis can lead to a disruption of the gut microbiota, an increase in pathogenic bacteria such as Escherichia-Shigella and Bacteroides, and that metabolites derived from the gut microbiota can modulate the lung inflammatory response through the gut-lung axis. Notably, Pro-Leu, a metabolite produced by the gut microbiota, was found to aggravate sepsis-induced ALI by activating the C/EBP beta/NOD2/NF-kappa B signaling pathways.