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 disease 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 endothelial cells (PMVECs) were used as in vitro cell model. 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 compare to the control vessels, vessels from both PVOD patients and PVOD rats represented 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. Then, in both the lung tissues of MMC-induced PVOD rats and MMC-treated rat PMVECs, decreased levels of endothelial markers (e.g. VE-cadherin, CD31) and increased mesenchymal markers (e.g. Vimentin, Fibronectin, α-SMA) were detected, also indicating EndoMT. Moreover, MMC induced activation of the TGFβ/Smad3/Snail axis, while blockage of this pathway with either specific Smad3 inhibitor (SIS3) or small interfering RNA (siRNA) against Smad3, both dramatically abolished the MMC-induced EndoMT. Notably, treatment with SIS3 remarkably prevented the pathogenesis of MMC-induced PVOD in rats. CONCLUSIONS 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.