Perivascular stromal cells derived from CD34+CD45+ cells promote pulmonary vascular barrier repair in a rat model of phosgene-induced acute lung injury via the VEGF-PI3K/AKT/eNOS signaling pathway.

Phosgene inhalation causes acute lung injury (ALI) with high mortality and no effective antidote, and stem cell therapy is limited by poor cell survival and low engraftment efficiency. Here, we identified a rare endogenous CD34+CD45+ cell fraction that reside in bone marrow, peripheral blood, and bronchoalveolar lavage fluid (∼1% baseline), exhibits a "decrease-then-recovery" dynamic after phosgene injury, and displays MSC-like properties with trilineage (osteogenic, adipogenic, and chondrogenic) potential in vitro. Intravenous administration of expanded CD34+CD45+-derived stromal cells (CD34/CD45-DSCs) significantly alleviated pulmonary vascular leakage and inflammatory in a rat model of phosgene-induced ALI (P-ALI). In vivo bioluminescence imaging further revealed that CD34/CD45-DSCs exhibited prolonged pulmonary retention compared with BMSCs (11.3 days vs. 48 h), proliferated, engrafted around the pulmonary vasculature, and acquired a perivascular stromal cell (PVSC)-like phenotype expressing late-stage mesenchymal progenitor, pericyte, and fibroblast markers. In a bleomycin-induced pulmonary fibrosis model, CD34/CD45-DSCs did not exacerbate fibrotic changes at day 28. Mechanistically, VEGF knockdown or neutralization abolished the barrier-protective effect, which was rescued by an AKT agonist and blocked by an inhibitor. Moreover, CD34/CD45-DSCs upregulated tight junction proteins ZO-1 and Occludin in injured endothelial cells via VEGF-PI3K/AKT/eNOS signaling. Collectively, our study defines the origin, spatiotemporal dynamics, perivasucular engraftment, PVSC-like fate acquisition, and VEGF-PI3K/AKT/eNOS-dependent mechanism of CD34/CD45-DSCs, supporting their potential as a relatively safe, long-engrafting, and mechanistically transparent cell-based strategy for ALI.