Extracellular Vesicles Shed from Senescent Neonatal Pulmonary Microvascular Endothelial Cells Contribute to Pulmonary Vascular Remodeling.

Extracellular vesicles (EVs) are critical mediators of intercellular communication but their role in bronchopulmonary dysplasia (BPD) complicated by pulmonary hypertension (BPD-PH) is unclear. Here we test the hypothesis that hyperoxia induces neonatal pulmonary microvascular endothelial cell (PMEC) senescence and that EVs shed from these cells potentiate pulmonary vascular remodeling. Newborn PMECs exposed to 75% O2 had increased expression of senescence markers and young adult rats exposed to neonatal hyperoxia showed increased p16, p21 and p53 expression in pulmonary endothelial cells. In vivo, EVs isolated from the supernatant of senescent PMECs (senescent EVs) induced pulmonary vascular remodelling and PH in newborn rats. miRNA (miR) sequencing revealed 31 differentially expressed miRs in senescent EVs as compared to control EVs. Top upregulated miRs included miR-421, miR-4508, and miR-3960. Senescent EVs differentially regulated 271 genes in the lungs of newborn rats. The most downregulated gene was myocyte enhancer binding factor-2 (MEF2C), a known miR-421 target, involved in smooth cell plasticity. To further interrogate the mechanisms by which senescent EVs induce vascular remodelling, pulmonary artery smooth muscle cells (PASMs) were incubated with control and senescent EVs, and smooth muscle cell phenotype was assessed. Senescent EVs down-regulated MEF2C and induced a synthetic PASM phenotype. EV uptake inhibition and miR-421 antagomir partially restored MEF2C expression and attenuated these changes. Together, these findings demonstrate that hyperoxia induces PMEC senescence and EVs shed from these senescent cells deliver a miR-421-MEF2C signal that potentiates pulmonary vascular remodelling. Strategies targeting this axis may have important implications for the treatment of BPD-PH.