Mitomycin C induces pulmonary vascular endothelial‐to‐mesenchymal transition and pulmonary veno‐occlusive disease via Smad3‐dependent pathway in rats

Background and Purpose: Pulmonary veno-occlusive disease (PVOD) is a rare dis- ease characterized by the obstruction of small pulmonary veins leading to pulmonary hypertension. However, the mechanisms underlying pulmonary vessel occlusion remain largely unclear. Experimental Approach: A mitomycin C (MMC)-induced PVOD rat model was used as in vivo animal model, and primarily cultured rat pulmonary microvascular endothe- lial cells (PMVECs) were used as in vitro cell model. Key Results: Our 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 endo- thelial marker von Willebrand factor (vWF) and mesenchymal marker α-smooth mus- cle 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, dra- matically abolished the MMC-induced EndoMT. Notably, treatment with SIS3 remarkably prevented the pathogenesis of MMC-induced PVOD in rats. Conclusions and Implications: Our data indicated that targeted inhibition of Smad3 leads to a potential, novel strategy for PVOD therapy, likely by inhibiting the EndoMT in pulmonary microvasculature.