Background: Refractory ulcerative colitis (rUC) represents a critical therapeutic challenge, with emerging evidence implicating gut vascular barrier (GVB) dysfunction in disease persistence. We investigated whether dysregulation of the endothelial BMP9-ALK1 signaling axis-a pathway not previously studied in UC-is associated with GVB impairment and treatment resistance, and explored its therapeutic potential. Methods: Serum BMP9 and mucosal ALK1 levels were compared across rUC, non-rUC, and healthy cohorts. The therapeutic efficacy of BMP9 was evaluated in DSS-induced murine colitis by examining vascular permeability, histopathology, and inflammatory markers, while mechanistic roles were investigated using human intestinal microvascular endothelial cells. Results: Serum BMP9 levels were significantly reduced in rUC versus non-rUC patients, inversely correlating with post-treatment disease severity (Modified Mayo Score: r = -0.471, 95% CI: -0.618 to -0.293, p p p Conclusions: Dysregulated BMP9-ALK1 signaling may contribute to GVB dysfunction in UC. BMP9 supplementation attenuates vascular leakage and inflammation in experimental colitis, identifying a potential therapeutic target warranting further investigation.
Li et al. (Wed,) studied this question.