Vitamin D-VDR Signaling Modulates Epithelial-Driven Intra-Alveolar Coagulation via NF-κB in Sepsis-Associated ARDS

Sepsis-associated acute respiratory distress syndrome (ARDS) is characterized by excessive inflammation and dysregulated intra-alveolar coagulation, leading to fibrin deposition and impaired alveolar function. The regulatory role of vitamin D-vitamin D receptor (VDR) signaling in epithelial coagulation responses remains incompletely defined. We investigated the role of vitamin D-VDR signaling in regulating epithelial-driven intra-alveolar coagulation in sepsis-associated lung injury using vitamin D-deficient mice, LPS-induced acute lung injury models, RLE-6TN alveolar epithelial cells, and clinical samples from patients with ARDS. Expression of VDR, NF-κB p65, tissue factor (TF), and plasminogen activator inhibitor-1 (PAI-1) was assessed using qRT-PCR, Western blotting, ELISA, and immunohistochemistry. Functional experiments included 1,25(OH)₂D₃ supplementation, VDR silencing, and NF-κB p65 gain- and loss-of-function approaches. Vitamin D deficiency significantly exacerbated LPS-induced lung injury, pulmonary edema, and intra-alveolar hypercoagulation, as reflected by increased TF and PAI-1 expression in lung tissue and bronchoalveolar lavage fluid. LPS challenge suppressed VDR expression and concurrently activated NF-κB signaling In Vivo and in alveolar epithelial cells. Supplementation with 1,25(OH)₂D₃ restored VDR expression and attenuated TF and PAI-1 induction. Conversely, VDR silencing enhanced NF-κB p65 activation and amplified epithelial procoagulant responses. Mechanistically, NF-κB p65 was required for TF and PAI-1 upregulation, and its overexpression abolished the inhibitory effects of vitamin D-VDR signaling. Clinically, patients with ARDS exhibited reduced circulating 25(OH)D levels and decreased VDR expression compared with healthy controls. Vitamin D-VDR signaling acts as an endogenous protective axis that restrains NF-κB-driven epithelial procoagulant activation in sepsis-associated ARDS. Disruption of this pathway promotes TF- and PAI-1-mediated intra-alveolar coagulation, suggesting that restoration of vitamin D-VDR signaling may represent a potential adjunctive therapeutic strategy for ARDS.