Venous thromboembolism (VTE), which encompasses pulmonary embolism and deep vein thrombosis, is a frequent disease that is associated with vein wall fibrosis. Endothelial cells undergo phenotypical changes named endothelial-to-mesenchymal transition (EndMT), characterized by the loss of endothelial markers and the acquisition of mesenchymal markers leading to fibrosis. Transforming growth factor (TGFβ) is the most potent inducer of EndMT. A recent study showed that in chronic thromboembolic pulmonary hypertension, TGFβ induces EndMT and impaired thrombus resolution. However, the molecular mechanisms implicated in TGFβ signaling in the context of venous thromboembolism and recurrent events are unknown. In addition, epigenetic mechanisms regulate EndMT. We hypothesized that epigenetic processes regulate the TGFβ signalling pathway in endothelial cells promoting EndMT and recurrent thrombosis. The aim of this study was to test if EndMT is regulated by epigenetic mechanisms in recurrent thrombosis.

Endothelial cells were treated with TGFβ, thrombin or both during 5 days. To study the role of histone deacetylase (HDAC) in EndMT, endothelial cells were also incubated in presence of vorinostat, an HDAC inhibitor or TCS HDAC6 20b, a specific HDAC6 inhibitor. Real time PCR were performed to analyze endothelial and mesenchymal marker expression.

Expression of the mesenchymal markers, calponin (CNN1) and α-smooth muscle actin (SM22), is increased by TGFβ and thrombin. CD146 expression, an endothelial marker, appears to be reduced by these treatments. Interestingly these changes appear to be inhibited in presence of vorinostat or TCS HDAC6 20b. Our results suggest that TGFβ and thrombin induce EndMT and that HDAC6 contribute to this mechanism.

We found that treatment of endothelial cells with TGFβ and thrombin is associated with EndMT. Our preliminary data suggest that HDAC6 contribute to EndMT. Deciphering the mechanisms by which epigenetic is regulating EndMT might lead to the discovery of biomarkers or new therapeutic targets would be instrumental in guiding decisions of treatment for patients with a high risk of recurrent VTE.