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Background: Pulmonary arterial hypertension (PAH) is characterized by progressive distal pulmonary artery (PA) obstruction, leading to right ventricular hypertrophy and failure. Exacerbated intracellular calcium (Ca 2+ ) signaling contributes to abnormalities in PA smooth muscle cells (PASMCs), including aberrant proliferation, apoptosis resistance, exacerbated migration, and arterial contractility. Store-operated Ca 2+ entry is involved in Ca 2+ homeostasis in PASMCs, but its properties in PAH are unclear. Methods: Using a combination of Ca 2+ imaging, molecular biology, in vitro, ex vivo, and in vivo approaches, we investigated the roles of the Orai1 SOC channel in PA remodeling in PAH and determined the consequences of pharmacological Orai1 inhibition in vivo using experimental models of pulmonary hypertension (PH). Results: Store-operated Ca 2+ entry and Orai1 mRNA and protein were increased in human PASMCs (hPASMCs) from patients with PAH (PAH-hPASMCs). We found that MEK1/2, NFAT (nuclear factor of activated T cells), and NFκB (nuclear factor-kappa B) contribute to the upregulation of Orai1 expression in PAH-hPASMCs. Using siRNA and Orai1 inhibitors, we found that Orai1 inhibition reduced store-operated Ca 2+ entry, mitochondrial Ca 2+ uptake, aberrant proliferation, apoptosis resistance, migration, and excessive calcineurin activity in PAH-hPASMCs. Orai1 inhibitors reduced agonist-evoked constriction in human PAs. In experimental rat models of PH evoked by chronic hypoxia, monocrotaline, or Sugen/hypoxia, administration of Orai1 inhibitors (BTP2, JPIII, or 5J4) protected against PH. Conclusions: In human PAH and experimental PH, Orai1 expression and activity are increased. Orai1 inhibition normalizes the PAH-hPASMCs phenotype and attenuates PH in rat models. These results suggest that Orai1 should be considered as a relevant therapeutic target for PAH.

Pulmonary arterial hypertension (PAH) is a severe and multifactorial disease. PAH pathogenesis mostly involves pulmonary arterial endothelial and pulmonary arterial smooth muscle cell (PASMC) dysfunction, leading to alterations in pulmonary arterial tone and distal pulmonary vessel obstruction and remodeling. Unfortunately, current PAH therapies are not curative, and therapeutic approaches mostly target endothelial dysfunction, while PASMC dysfunction is under investigation. In PAH, modifications in intracellular Ca2+ homoeostasis could partly explain PASMC dysfunction. One of the most crucial actors regulating Ca2+ homeostasis is store-operated Ca2+ channels, which mediate store-operated Ca2+ entry (SOCE). This review focuses on the main actors of SOCE in human and experimental PASMC, their contribution to PAH pathogenesis, and their therapeutic potential in PAH.

Introduction: Over time and despite optimal medical management of patients with pulmonary hypertension (PH), the right ventricle (RV) function deteriorates from an adaptive to maladaptive phenotype, leading to RV failure (RVF). Although RV function is well recognized as a prognostic factor of PH, no predictive factor of RVF episodes has been elucidated so far. We hypothesized that determining RV metabolic alterations could help to understand the mechanism link to the deterioration of RV function as well as help to identify new biomarkers of RV failure. Methods: In the current study, we aimed to characterize the metabolic reprogramming associated with the RV remodeling phenotype during experimental PH induced by chronic-hypoxia-(CH) exposure or monocrotaline-(MCT) exposure in rats. Three weeks after PH initiation, we hemodynamically characterized PH (echocardiography and RV catheterization), and then we used an untargeted metabolomics approach based on liquid chromatography coupled to high-resolution mass spectrometry to analyze RV and LV tissues in addition to plasma samples from MCT-PH and CH-PH rat models. Results: CH exposure induced adaptive RV phenotype as opposed to MCT exposure which induced maladaptive RV phenotype. We found that predominant alterations of arginine, pyrimidine, purine, and tryptophan metabolic pathways were detected on the heart (LV+RV) and plasma samples regardless of the PH model. Acetylspermidine, putrescine, guanidinoacetate RV biopsy levels, and cytosine, deoxycytidine, deoxyuridine, and plasmatic thymidine levels were correlated to RV function in the CH-PH model. It was less likely correlated in the MCT model. These pathways are well described to regulate cell proliferation, cell hypertrophy, and cardioprotection. These findings open novel research perspectives to find biomarkers for early detection of RV failure in PH.

AimsWe hypothesized that the ATP-sensitive K+ channels (KATP) regulatory subunit (ABCC9) contributes to PAH pathogenesis. ABCC9 gene encodes for two regulatory subunits of KATP channels: the SUR2A and SUR2B proteins. In the KATP channel, the SUR2 subunits are associated with the K+ channel Kir6.1. We investigated how the SUR2/Kir6.1 channel contributes to PAH pathogenesis and its potential as a therapeutic target in PAH.Methods and resultsUsing in vitro, ex vivo, and in vivo approaches, we analyzed the localization and expression of SUR2A, SUR2B, and Kir6.1 in the pulmonary vasculature of controls and patients with PAH as in experimental pulmonary hypertension (PH) rat models and its contribution to PAH physiopathology. Finally, we deciphered the consequences of in vivo activation of SUR2/Kir6.1 in the monocrotaline (MCT)-induced PH model. We found that SUR2A, SUR2B, and Kir6.1 were expressed in the lungs of controls and patients with PAH and MCT-induced PH rat models. Organ bath studies showed that SUR2 activation by pinacidil induced relaxation of pulmonary arterial in rats and humans. In vitro experiments on human pulmonary arterial smooth muscle cells and endothelial cells (hPASMCs and hPAECs) in controls and PAH patients showed decreased cell proliferation and migration after SUR2 activation. We demonstrated that SUR2 activation in rat right ventricular (RV) cardiomyocytes reduced RV action potential duration by patch-clamp. Chronic pinacidil administration in control rats increased heart rate without changes in hemodynamic parameters. Finally, in vivo pharmacological activation of SUR2 on MCT and Chronic-hypoxia (CH)-induced-PH rats showed improved PH.ConclusionWe showed that SUR2A, SUR2B, and Kir6.1 are presented in hPASMCs and hPAECs of controls and PAH patients. In vivo SUR2 activation reduced the MCT-induced and CH-induced PH phenotype, suggesting that SUR2 activation should be considered for treating PAH.

Right ventricular failure (RVF) is the most important prognostic factor for morbidity and mortality in pulmonary arterial hypertension (PAH) or pulmonary hypertension (PH) caused by left heart diseases. However, right ventricle (RV) remodeling is understudied and not targeted by specific therapies. This can be partly explained by the lack of basic knowledge of RV remodeling. Since the physiology and hemodynamic function of the RV differ from those of the left ventricle (LV), the mechanisms of LV dysfunction cannot be generalized to that of the RV, albeit a knowledge of these being helpful to understanding RV remodeling and dysfunction. Store-operated Ca2+ entry (SOCE) has recently emerged to participate in the LV cardiomyocyte Ca2+ homeostasis and as a critical player in Ca2+ mishandling in a pathological context. In this paper, we highlight the current knowledge on the SOCE contribution to the LV and RV dysfunctions, as SOCE molecules are present in both compartments. he relative lack of studies on RV dysfunction indicates the necessity of further investigations, a significant challenge over the coming years.

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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.