Pulmonary arterial hypertension (PAH) is a vascular remodeling disease of complex etiology. Despite environmental stressful conditions, pulmonary artery (PA) smooth muscle cells (PASMCs) and endothelial cells (PAECs) exhibit a pro-proliferative and anti-apoptotic phenotype. HDAC6 is a cytoplasmic histone deacetylase overexpressed in response to stress and implicated in the regulation of multiple pro-survival mechanisms in cancer cells. Therefore, we hypothesized that HDAC6 expression is increased in PAH-PASMCs and PAH-PAECs allowing them to survive and proliferate, thus contributing to vascular remodeling in PAH.
Using a multidisciplinary and translational approach we aimed to demonstrate that HDAC6 inhibition is a promising strategy to improve PAH.
Methods and results
HDAC6 is significantly up-regulated (immunoblot) in lungs, distal PAs, and isolated PASMCs and PAECs from 10 PAH patients and 15 experimental PAH animal (5 Sugen/hypoxia rats; 5 monocrotaline rats and 5 chronic hypoxic mice) compared to controls. Molecular (siRNA) and pharmacological inhibition (Tubastatin and ACY-775) of HDAC6 reduces dose-dependently PAH-PASMC/PAEC proliferation (Ki67 assay) and resistance to apoptosis (Annexin V assay) in vitro sparing control cells. Mechanistically, we demonstrated that HDAC6 deacetylates Ku70, blocking the translocation of Bax to mitochondria and preventing apoptosis.In vivo inhibition of HDAC6 (Tubastatin A 25mg/kg/day for 2 weeks) significantly improved (n=5 to 10 p<0.05) established PAH by decreasing mean PA pressure, total pulmonary resistance and increasing cardiac output in two experimental models (Sugen/hypoxia and monocrotaline). In addition, we showed that HDAC6 inhibitor can be safely given in combination with currently approved PAH therapies (macitentan and tadalafil). Finally, Hdac6 K.O mice have significantly lower right ventricle systolic pressure in response to 3 weeks of chronic-hypoxia compared to wild-type mice.
We showed for the first time that HDAC6 is implicated in PAH development and represents a new promising therapeutic target to improve PAH.