Abstract 9512: Involvement of Orai1 Ca 2+ Channel in the Pathogenesis of Pulmonary Arterial Hypertension. Orai1 as a New Potential Therapeutic Target?

Introduction: Pulmonary arterial hypertension (PAH) is a devastating disease, characterized by a progressive obstruction of distal pulmonary artery (PA) leading to right ventricular hypertrophy and failure. Exacerbated intracellular Ca 2+ signalling contributes to functional abnormalities in pulmonary arterial smooth muscle cells (PASMCs), including aberrant proliferation, apoptosis resistance, exacerbated migration and pulmonary artery contractility. The role of archetypal Store-Operated Ca 2+ entry (SOCE) Orai1 Ca 2+ channel in PAH pathogenesis is unclear. Methods: Using a combination of Ca 2+ imaging, molecular biology, in vitro , ex vivo and in vivo approaches, we decipher the role of Orai1 Ca 2+ channel in pulmonary artery remodelling in PAH. We also analyzed the consequence of in vivo pharmacological inhibition of Orai1 in experimental models of PH. Results: We demonstrated that SOCE is increased in human PASMCs (hPASMCs) from patients with idiopathic PAH (iPAH) associated with an increased expression of Orai1 at mRNA and protein levels. Moreover, in vitro in iPAH-hPASMCs the pharmacological inhibition of Orai1 (by two different inhibitors) or the knockdown of Orai1 by siRNA reduced the SOCE as well as aberrant proliferation, apoptosis resistance phenotype and exacerbated cell migration. In addition, Orai1 knockdown reduced the exacerbated calcineurin activity in iPAH-hPASMCs. Using myograph experiments on isolated human and rat PAs we showed that pharmacological inhibition of Orai1 channels reduced the capacity of PAs to constrict. In rat experimental PH induced by Monocrotaline (MCT)-exposure or by Chronic-Hypoxia (CH) we found an overexpression of Orai1. Finally, in vivo pharmacological inhibition of Orai1 by three different blockers (BTP2, JPIII and 5J4) reduced experimental-PH in these experimental PH-models. Conclusion: In human PAH and experimental PH, the expression of Orai1 is increased compared to controls. In vitro and in vivo inhibition of Orai1 normalize the PAH phenotype of cultured iPAH-hPASMCs and reduce experimental-PH (MCT and CH). These results provide proof of concept that Orai1 contributes to PAH pathogenesis and that pharmacological inhibition of Orai1 should be considered as a new therapeutic target in PAH.