Abstract Tu0060: VEGF-D, unlike VEGF-A, improves vascular integrity in the lung and exerts a protective effect during acute lung injury

Introduction: Disorders in pulmonary vascular integrity are a prominent feature in many lung diseases. Paracrine signals are enriched throughout the lung tissue and are critical in maintaining functional microvascular homeostasis. However, the specific local cell-cell crosstalk signals that maintain pulmonary microvascular stability in adult animals and humans remain largely unexplored. Hypothesis: Local factors expressed under physiological conditions within the lung microvascular niche facilitate barrier protection and exhibit anti-inflammatory properties and serve as potential therapeutic targets to enhance vascular integrity during acute lung injury (ALI). Methods: We employed scRNAseq-based computational pipelines to systematically profile ligand-receptor (L/R) interactions within the lung microvascular niche. The impact of identified ligands on vascular barrier function and anti-inflammatory response was further assessed in vitro cell culture assays and lipopolysaccharide (LPS)-induced ALI models. Results: Our scRNAseq data revealed that soluble L/R interactions between mesenchymal cells and capillary endothelial cells are predominantly associated with pathways involved in maintaining vascular integrity. Upon treatment with top ligands, we observed that VEGF-D, unlike VEGF-A and VEGF-C, significantly enhanced endothelial barrier function and conferred protection against inflammatory challenges induced by TNF-α, IL-1β, and thrombin. This barrier-protective and anti-inflammatory effect of VEGF-D was significantly attenuated by inhibition of VEGFR2. Intravenous administration of recombinant VEGF-D in LPS-induced ALI models significantly reduced vascular permeability (7339 ± 2510 (LPS) v.s. 5350 ± 1821 (LPS + VEGF-D), p < 0.05) and immune cell infiltration (0.791 ± 0.199 x 10 6 WBC/mL (LPS) v.s. 0.540 ± 0.190 x 10 6 WBC/mL (LPS + VEGF-D), p < 0.01) into the lung tissue. Levels of pro-inflammatory markers, including TNF-α and IL-6, in bronchoalveolar lavage fluid were also significantly decreased. Importantly, in VEGFR2 iECKO mice, the impact of VEGF-D on immune cell infiltration and lung injury index was abolished, confirming that VEGF-D mediates its effects via VEGFR2-dependent signaling. Conclusions: This study demonstrates an unexpected protective role for VEGF-D in promoting lung endothelial barrier integrity, distinguishing it from VEGF-A, and suggests that paracrine signaling from the mesenchymal niche contributes critically to lung capillary homeostasis.