OC 19.2 - HDAC6 regulates endothelial dysfunction in thromboembolic venous disease

Background: Venous thromboembolism (VTE), which encompasses pulmonary embolism and deep vein thrombosis, is a frequent disease associated with vein wall remodeling. Hence, fibrosis might result from endothelial-to-mesenchymal transition (EndMT), characterized by the loss of endothelial markers and the acquisition of mesenchymal markers. In chronic thromboembolic pulmonary hypertension, transforming growth factor (TGFβ), the most potent inducer of EndMT, impairs thrombus resolution. However, the molecular mechanisms implicated in TGFβ signaling in the context of VTE are unknown. We hypothesized that epigenetic processes regulate the TGFβ signaling pathway in endothelial cells promoting EndMT and recurrent venous thromboembolism.

Aims: To determine if histone deacetylases (HDACs) regulate the TGFβ signaling pathway in endothelial cells promoting EndMT and VTE recurrence.

Methods: To study the role of HDAC6 in EndMT, endothelial cells were transfected with a siRNA against HDAC6 or treated with a pharmacological inhibitor (TSC20b) and incubated with TGFβ and thrombin during 3 to 5 days. Real time PCR were performed to analyze endothelial and mesenchymal marker expression. An experimental model of VTE was used to study the role of HDAC6 on thrombus size overtime. Animals were treated or not with a specific HDAC6 inhibitor (tubastatin A) for 7 to 21 days. Thrombus resolution was measured by ultrasound-doppler. Within group and treatment differences were analyzed using two-way ANOVA and Tukey’s multiple comparisons.

Results: Expression of the mesenchymal markers, calponin and α-smooth muscle actin (SMA), was increased by TGFβ and thrombin. Interestingly these changes were inhibited in presence of HDAC6 siRNA or TSC20b. Importantly, 7 and 17 days after surgery, thrombus size was smaller in the tubastatin A treated group compared to control.

Conclusion(s): We found that HDAC6 contributes to EndMT in venous thrombosis and impairs thrombus resolution. Thus, HDAC6 might represent an attractive therapeutic target for patients with a high risk of recurrent VTE.