• Olivier Boucherat, Thibaut Peterlini, Alice Bourgeois, Valérie Nadeau, Sandra Breuils-Bonnet, Stéphanie Boilet-Molez, François Potus, Jolyane Meloche, Sophie Chabot, Caroline Lambert, Eve Tremblay, Young Chan Chae, Dario C Altieri, Gopinath Sutendra, Evangelos D Michelakis, Roxane Paulin, Steeve Provencher, and Sébastien Bonnet.
• 1 Pulmonary Hypertension Research Group, Centre de Recherche de l'Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec City, Québec, Canada.
• Am. J. Respir. Crit. Care Med. 2018 Jul 1; 198 (1): 90-103.

RationalePulmonary arterial hypertension (PAH) is a vascular remodeling disease with a poor prognosis and limited therapeutic options. Although the mechanisms contributing to vascular remodeling in PAH are still unclear, several features, including hyperproliferation and resistance to apoptosis of pulmonary artery smooth muscle cells (PASMCs), have led to the emergence of the cancer-like concept. The molecular chaperone HSP90 (heat shock protein 90) is directly associated with malignant growth and proliferation under stress conditions. In addition to being highly expressed in the cytosol, HSP90 exists in a subcellular pool compartmentalized in the mitochondria (mtHSP90) of tumor cells, but not in normal cells, where it promotes cell survival.ObjectivesWe hypothesized that mtHSP90 in PAH-PASMCs represents a protective mechanism against stress, promoting their proliferation and resistance to apoptosis.MethodsExpression and localization of HSP90 were analyzed by Western blot, immunofluorescence, and immunogold electron microscopy. In vitro, effects of mtHSP90 inhibition on mitochondrial DNA integrity, bioenergetics, cell proliferation and resistance to apoptosis were assessed. In vivo, the therapeutic potential of Gamitrinib, a mitochondria-targeted HSP90 inhibitor, was tested in fawn-hooded and monocrotaline rats.Measurements And Main ResultsWe demonstrated that, in response to stress, HSP90 preferentially accumulates in PAH-PASMC mitochondria (dual immunostaining, immunoblot, and immunogold electron microscopy) to ensure cell survival by preserving mitochondrial DNA integrity and bioenergetic functions. Whereas cytosolic HSP90 inhibition displays a lack of absolute specificity for PAH-PASMCs, Gamitrinib decreased mitochondrial DNA content and repair capacity and bioenergetic functions, thus repressing PAH-PASMC proliferation (Ki67 labeling) and resistance to apoptosis (Annexin V assay) without affecting control cells. In vivo, Gamitrinib improves PAH in two experimental rat models (monocrotaline and fawn-hooded rat).ConclusionsOur data show for the first time that accumulation of mtHSP90 is a feature of PAH-PASMCs and a key regulator of mitochondrial homeostasis contributing to vascular remodeling in PAH.

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