Abstract 15625: Targeting Mitochondrial Hsp90: A New Promising Avenue for Reversing Pulmonary Arterial Hypertension
Introduction: Pulmonary arterial hypertension (PAH) is a vascular remodeling disease with a poor prognosis and no therapeutic option. Although the causal pathomechanisms contributing to remodeling of the pulmonary vascular bed in PAH are still unclear, several features including hyperproliferation and resistance to apoptosis of pulmonary smooth muscle cells (PASMCs) sustained by oncogenic pathways activation and metabolic alterations, have led to the emergence of the cancer-like concept. The molecular chaperone heat shock protein 90 (Hsp90), by interacting with its client proteins, is directly associated with malignant growth. In addition to be highly expressed in the cytosol, Hsp90 exists in a subcellular pool compartimentalized in the mitochondria (mtHsp90) of tumor cells where it promotes cell survival.
Hypothesis: Hsp90 up-regulation in PAH triggers PASMC proliferation and resistance to apoptosis.
Methods and Results: Using Western blot (WB), we showed that Hsp90 is up-regulated in lungs and isolated PASMCs of PAH patients compared to control donors (n=3-7, p<0.05). Using pharmacological inhibitors (17-AAG and AT13387), we demonstrated that cytosolic Hsp90 stabilizes the expression of numerous clients proteins overexpressed in PAH that promote cell growth and survival. More importantly, using WB on mitochondrial fraction and co-labeling experiments, we demonstrated that Hsp90 is specifically expressed in PAH-PASMCs mitochondria, and not in healthy cells (n=3), maintaining energy production (Seahorse assay, n=3, p<0.05). Whereas cytosolic Hsp90 inhibition displays a lack of absolute specificity for PAH-PASMCs, selective inhibition of mtHsp90 with Gamitrinib decreased PAH-PASMC proliferation and resistance to apoptosis without affecting control cells (Ki67, MTT, AnnexinV, n=3, p<0.05). In the monocrotaline and fawn-hooded rat models, Gamitrinib improves established PAH (mean PA pressure, cardiac output, total pulmonary resistance) and provided beneficial effects on vascular remodeling (H&E) (n=5-9 per group, p<0.05).
Conclusion: We demonstrated for the first time that accumulation of mtHsp90 is a cardinal feature of PAH-PASMCs exerting cytoprotective functions. Its selective inhibition is able to reverse PAH.
Author Disclosures: O. Boucherat: None. S. Breuils-Bonnet: None. J. Meloche: None. S. Chabot: None. C. Lambert: None. E. Tremblay: None. G. Sutendra: None. E. Michelakis: None. Y. Chae: None. D. Altieri: None. R. Paulin: None. S. Provencher: None. S. Bonnet: None.
- © 2016 by American Heart Association, Inc.