Mitomycin C Induces Pulmonary Vessel Endothelial-To-Mesenchymal Transition and Pulmonary Veno-Occlusive Disease Via Smad3-Dependent Pathway in Rats

Background and PurposePulmonary veno‐occlusive disease (PVOD) is a rare disease characterized by the obstruction of small pulmonary veins leading to pulmonary hypertension. However, the mechanisms underlying pulmonary vessel occlusion remain largely unclear.Experimental ApproachA mitomycin C (MMC)‐induced PVOD rat model was used as in vivo animal model, and primarily cultured rat pulmonary microvascular endothelial cells (PMVECs) were used as in vitro cell model.Key ResultsOur data suggested an endothelial‐to‐mesenchymal transition (EndoMT) may be present in the pulmonary microvessels isolated from either PVOD patients or MMC‐induced PVOD rats. In comparison to the control vessels, vessels from both PVOD patients and PVOD rats had co‐localized staining of specific endothelial marker von Willebrand factor (vWF) and mesenchymal marker α‐smooth muscle actin (α‐SMA), suggesting the presence of cells that co‐express endothelial and mesenchymal markers. In both the lung tissues of MMC‐induced PVOD rats and MMC‐treated rat PMVECs there were decreased levels of endothelial markers (e.g. VE‐cadherin and CD31) and increased mesenchymal markers (e.g. vimentin, fibronectin and α‐SMA) were detected indicating EndoMT. Moreover, MMC‐induced activation of the TGFβ/Smad3/Snail axis, while blocking this pathway with either selective Smad3 inhibitor (SIS3) or small interfering RNA (siRNA) against Smad3, dramatically abolished the MMC‐induced EndoMT. Notably, treatment with SIS3 remarkably prevented the pathogenesis of MMC‐induced PVOD in rats.Conclusions and ImplicationsOur data indicated that targeted inhibition of Smad3 leads to a potential, novel strategy for PVOD therapy, likely by inhibiting the EndoMT in pulmonary microvasculature.