Gut Microbiota-Derived Trimethylamine-N-Oxide Protects Pulmonary Vascular Barrier Integrity via VAV3-Mediated Cytoskeletal Remodeling in Acute Lung Injury

Acute respiratory distress syndrome (ARDS) and acute lung injury (ALI) are characterized by increased pulmonary capillary permeability, but lack effective pharmacotherapies. Emerging evidence implicates gut-lung axis dysregulation contributes to ARDS pathogenesis through microbiome-host interactions, but the effects of the microbiota-derived metabolite, trimethylamine-N-oxide (TMAO) remains unclear. Here, we demonstrate that plasma TMAO levels are significantly elevated in ARDS patients compared to healthy controls, correlating positively with hypersensitive C-reactive protein (hs-CRP). In a murine lipopolysaccharide (LPS)-induced ALI model, TMAO administration reduced lung vascular leakage and neutrophil infiltration, whereas inhibition of gut-microbiome-derived TMAO synthesis worsened injury. Mechanistically, TMAO enhances endothelial barrier integrity by upregulating VAV3, which drives Rac1-dependent cortical actin reorganization. Knockdown of VAV3 abolished TMAO-mediated endothelial barrier protection, confirming its necessity. Our study identifies TMAO as an adaptive mediator involved in gut-lung axis, that mitigates pulmonary vascular hyperpermeability via VAV3-Rac1-cytoskeletal signaling, highlighting its therapeutic potential for ALI/ARDS.