Implication of Potassium Channels in the Pathophysiology of Pulmonary Arterial Hypertension

Genome-wide analysis in over 1 million individuals of European ancestry yields improved polygenic risk scores for blood pressure traits

Hypertension affects more than one billion people worldwide. Here we identify 113 novel loci, reporting a total of 2,103 independent genetic signals (P < 5 × 10-8) from the largest single-stage blood pressure (BP) genome-wide association study to date (n = 1,028,980 European individuals). These associations explain more than 60% of single nucleotide polymorphism-based BP heritability. Comparing top versus bottom deciles of polygenic risk scores (PRSs) reveals clinically meaningful differences in BP (16.9 mmHg systolic BP, 95% CI, 15.5-18.2 mmHg, P = 2.22 × 10-126) and more than a sevenfold higher odds of hypertension risk (odds ratio, 7.33; 95% CI, 5.54-9.70; P = 4.13 × 10-44) in an independent dataset. Adding PRS into hypertension-prediction models increased the area under the receiver operating characteristic curve (AUROC) from 0.791 (95% CI, 0.781-0.801) to 0.826 (95% CI, 0.817-0.836, ∆AUROC, 0.035, P = 1.98 × 10-34). We compare the 2,103 loci results in non-European ancestries and show significant PRS associations in a large African-American sample. Secondary analyses implicate 500 genes previously unreported for BP. Our study highlights the role of increasingly large genomic studies for precision health research.

Endothelial Function in Pulmonary Arterial Hypertension: From Bench to Bedside

Pulmonary arterial hypertension is a complex pathology whose etiology is still not completely well clarified. The pathogenesis of pulmonary arterial hypertension involves different molecular mechanisms, with endothelial dysfunction playing a central role in disease progression. Both individual genetic predispositions and environmental factors seem to contribute to its onset. To further understand the complex relationship between endothelial and pulmonary hypertension and try to contribute to the development of future therapies, we report a comprehensive and updated review on endothelial function in pulmonary arterial hypertension.

A roadmap for therapeutic discovery in pulmonary hypertension associated with left heart failure. A scientific statement of the Heart Failure Association (HFA) of the ESC and the ESC Working Group on Pulmonary Circulation & Right Ventricular Function

Pulmonary hypertension (PH) associated with left heart failure (LHF) (PH-LHF) is one of the most common causes of PH. It directly contributes to symptoms and reduced functional capacity and negatively affects right heart function, ultimately leading to a poor prognosis. There are no specific treatments for PH-LHF, despite the high number of drugs tested so far. This scientific document addresses the main knowledge gaps in PH-LHF with emphasis on pathophysiology and clinical trials. Key identified issues include better understanding of the role of pulmonary venous versus arteriolar remodelling, multidimensional phenotyping to recognize patient subgroups positioned to respond to different therapies, and conduct of rigorous pre-clinical studies combining small and large animal models. Advancements in these areas are expected to better inform the design of clinical trials and extend treatment options beyond those effective in pulmonary arterial hypertension. Enrichment strategies, endpoint assessments, and thorough haemodynamic studies, both at rest and during exercise, are proposed to play primary roles to optimize early-stage development of candidate therapies for PH-LHF.

KCNK3 channel is important for the ventilatory response to hypoxia in rats

To clarify the contribution of KCNK3/TASK-1 channel chemoreflex in response to hypoxia and hypercapnia, we used a unique Kcnk3-deficient rat. We assessed ventilatory variables using plethysmography in Kcnk3-deficient and wild-type rats at rest in response to hypoxia (10% O2) and hypercapnia (4% CO2). Immunostaining for C-Fos, a marker of neuronal activity, was performed to identify the regions of the respiratory neuronal network involved in the observed response.Under basal conditions, we observed increased minute ventilation in Kcnk3-deficient rats, which was associated with increased c-Fos positive cells in the ventrolateral region of the medulla oblongata. Kcnk3-deficient rats show an increase in ventilatory response to hypoxia without changes in response to hypercapnia. In Kcnk3-deficient rats, linked to an increased hypoxia response, we observed a greater increase in c-Fos-positive cells in the first central relay of peripheral chemoreceptors and Raphe Obscurus. This study reports that KCNK3/TASK-1 deficiency in rats induces an inadequate peripheral chemoreflex, alternating respiratory rhythmogenesis, and hypoxic chemoreflex.

Pulmonary hypertension associated with diazoxide: the SUR1 paradox

The ATP-sensitive potassium channels and their regulatory subunits, sulfonylurea receptor 1 (SUR1/Kir6.2) and SUR2/Kir6.1, contribute to the pathophysiology of pulmonary hypertension (PH). Loss-of-function pathogenic variants in the ABCC8 gene, which encodes for SUR1, have been associated with heritable pulmonary arterial hypertension. Conversely, activation of SUR1 and SUR2 leads to the relaxation of pulmonary arteries and reduces cell proliferation and migration. Diazoxide, a SUR1 activator, has been shown to alleviate experimental PH, suggesting its potential as a therapeutic option. However, there are paradoxical reports of diazoxide-induced PH in infants. This review explores the role of SUR1/2 in the pathophysiology of PH and the contradictory effects of diazoxide on the pulmonary vascular bed. Additionally, we conducted a comprehensive literature review of cases of diazoxide-associated PH and analysed data from the World Health Organization pharmacovigilance database (VigiBase). Significant disproportionality signals link diazoxide to PH, while no other SUR activators have been connected with pulmonary vascular disease. Diazoxide-associated PH seems to be dose-dependent and potentially related to acute effects on the pulmonary vascular bed. Further research is required to decipher the differing pulmonary vascular consequences of diazoxide in different age populations and experimental models.

Defining the clinical validity of genes reported to cause pulmonary arterial hypertension

PURPOSE

Pulmonary arterial hypertension (PAH) is a rare, progressive vasculopathy with significant cardiopulmonary morbidity and mortality. Genetic testing is currently recommended for adults diagnosed with heritable, idiopathic, anorexigen-, hereditary hemorrhagic telangiectasia-, and congenital heart disease-associated PAH, PAH with overt features of venous/capillary involvement, and all children diagnosed with PAH. Variants in at least 27 genes have putative evidence for PAH causality. Rigorous assessment of the evidence is needed to inform genetic testing.

METHODS

An international panel of experts in PAH applied a semi-quantitative scoring system developed by the NIH Clinical Genome Resource to classify the relative strength of evidence supporting PAH gene-disease relationships based on genetic and experimental evidence.

RESULTS

Twelve genes (BMPR2, ACVRL1, ATP13A3, CAV1, EIF2AK4, ENG, GDF2, KCNK3, KDR, SMAD9, SOX17, and TBX4) were classified as having definitive evidence and 3 genes (ABCC8, GGCX, and TET2) with moderate evidence. Six genes (AQP1, BMP10, FBLN2, KLF2, KLK1, and PDGFD) were classified as having limited evidence for causal effects of variants. TOPBP1 was classified as having no known PAH relationship. Five genes (BMPR1A, BMPR1B, NOTCH3, SMAD1, and SMAD4) were disputed because of a paucity of genetic evidence over time.

CONCLUSION

We recommend that genetic testing includes all genes with definitive evidence and that caution be taken in the interpretation of variants identified in genes with moderate or limited evidence. Genes with no known evidence for PAH or disputed genes should not be included in genetic testing.

Physiological and pathophysiological roles of the KCNK3 potassium channel in the pulmonary circulation and the heart

Potassium channel subfamily K member 3 (KCNK3), encoded by the KCNK3 gene, is part of the two-pore domain potassium channel family, constitutively active at resting membrane potentials in excitable cells, including smooth muscle and cardiac cells. Several physiological and pharmacological mediators, such as intracellular signalling pathways, extracellular pH, hypoxia and anaesthetics, regulate KCNK3 channel function. Recent studies show that modulation of KCNK3 channel expression and function strongly influences pulmonary vascular cell and cardiomyocyte function. The altered activity of KCNK3 in pathological situations such as atrial fibrillation, pulmonary arterial hypertension and right ventricular dysfunction demonstrates the crucial role of KCNK3 in cardiovascular homeostasis. Furthermore, loss of function variants of KCNK3 have been identified in patients suffering from pulmonary arterial hypertension and atrial fibrillation. This review focuses on current knowledge of the role of the KCNK3 channel in pulmonary circulation and the heart, in healthy and pathological conditions.

Involvement of SUR2/Kir6.1 channel in the physiopathology of pulmonary arterial hypertension

Aims

We 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 results

Using 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.

Conclusion

We 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.

Quinazoline-based human phosphodiesterase 5 inhibitors exhibited a selective vasorelaxant effect on rat isolated pulmonary arteries involving NO-sGC-cGMP pathway and calcium inhibitory effects

Phosphodiesterase 5 (PDE5) inhibitors are an attractive option among the currently available therapies in the management of pulmonary arterial hypertension (PAH). Good selectivity for PDE5 is associated with reduced side effects and greater vasorelaxant effect on pulmonary arteries (PA). This study investigated the vasorelaxant effects of a series of quinazoline-based PDE5 inhibitors and their precise mechanisms action using rat isolated PA and aorta, as compared to sildenafil. Their effects on rat hepatocytes (viability and CYP activities) were also evaluated. Compounds 5 and 11 displayed lower human PDE5 IC₅₀ of the analogs studied here and induced a greater relaxant effect on PA (EC₅₀ 0.94 ± 0.30 and 1.03 ± 0.23 μM, respectively). As compared to sildenafil (EC₅₀ = 0.05 ± 0.02 μM on PA), the relaxant effect of 5 and 11 on PA was lower but their selectivity for PA compared to aorta was higher. The effects of 5 and 11 were reduced by N^G-nitro-L-arginine methyl ester, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one, but not by indomethacin or potassium channels blockers. They also enhanced the relaxant effect of sodium nitroprusside, and inhibited extracellular Ca²⁺ influx and intracellular Ca²⁺release. Compounds 5 and 11 did not reduce hepatocyte viability except at concentration > 10 μM, inhibited CYP3A at 10 μM, like sildenafil, but did not induce CYP1A. In conclusion, this study identified 2 quinazoline analogues with good PDE5 inhibitory activity and good selectivity for the pulmonary vasculature. Their relaxant effect involves both the potentiation of nitric oxide-sGC-cGMP pathway and calcium inhibition. These compounds are potential leads for developing new drugs for PAH.

Advances in the Understanding of Two-Pore Domain TASK Potassium Channels and Their Potential as Therapeutic Targets

TWIK-related acid-sensitive K⁺ (TASK) channels, including TASK-1, TASK-3, and TASK-5, are important members of the two-pore domain potassium (K_2P) channel family. TASK-5 is not functionally expressed in the recombinant system. TASK channels are very sensitive to changes in extracellular pH and are active during all membrane potential periods. They are similar to other K_2P channels in that they can create and use background-leaked potassium currents to stabilize resting membrane conductance and repolarize the action potential of excitable cells. TASK channels are expressed in both the nervous system and peripheral tissues, including excitable and non-excitable cells, and are widely engaged in pathophysiological phenomena, such as respiratory stimulation, pulmonary hypertension, arrhythmia, aldosterone secretion, cancers, anesthesia, neurological disorders, glucose homeostasis, and visual sensitivity. Therefore, they are important targets for innovative drug development. In this review, we emphasized the recent advances in our understanding of the biophysical properties, gating profiles, and biological roles of TASK channels. Given the different localization ranges and biologically relevant functions of TASK-1 and TASK-3 channels, the development of compounds that selectively target TASK-1 and TASK-3 channels is also summarized based on data reported in the literature.

Genes in pediatric pulmonary arterial hypertension and the most promising BMPR2 gene therapy

Pulmonary arterial hypertension (PAH) is a rare but progressive and lethal vascular disease of diverse etiologies, mainly caused by proliferation of endothelial cells, smooth muscle cells in the pulmonary artery, and fibroblasts, which ultimately leads to right-heart hypertrophy and cardiac failure. Recent genetic studies of childhood-onset PAH report that there is a greater genetic burden in children than in adults. Since the first-identified pathogenic gene of PAH, BMPR2, which encodes bone morphogenetic protein receptor 2, a receptor in the transforming growth factor-β superfamily, was discovered, novel causal genes have been identified and substantially sharpened our insights into the molecular genetics of childhood-onset PAH. Currently, some newly identified deleterious genetic variants in additional genes implicated in childhood-onset PAH, such as potassium channels (KCNK3) and transcription factors (TBX4 and SOX17), have been reported and have greatly updated our understanding of the disease mechanism. In this review, we summarized and discussed the advances of genetic variants underlying childhood-onset PAH susceptibility and potential mechanism, and the most promising BMPR2 gene therapy and gene delivery approaches to treat childhood-onset PAH in the future.

Potassium Channels as Therapeutic Targets in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease with high morbidity and mortality. Deleterious remodeling in the pulmonary arterial system leads to irreversible arterial constriction and elevated pulmonary arterial pressures, right heart failure, and eventually death. The difficulty in treating PAH stems in part from the complex nature of disease pathogenesis, with several signaling compounds known to be involved (e.g., endothelin-1, prostacyclins) which are indeed targets of PAH therapy. Over the last decade, potassium channelopathies were established as novel causes of PAH. More specifically, loss-of-function mutations in the KCNK3 gene that encodes the two-pore-domain potassium channel KCNK3 (or TASK-1) and loss-of-function mutations in the ABCC8 gene that encodes a key subunit, SUR1, of the ATP-sensitive potassium channel (KATP) were established as the first two potassium channelopathies in human cohorts with pulmonary arterial hypertension. Moreover, voltage-gated potassium channels (Kv) represent a third family of potassium channels with genetic changes observed in association with PAH. While other ion channel genes have since been reported in association with PAH, this review focuses on KCNK3, KATP, and Kv potassium channels as promising therapeutic targets in PAH, with recent experimental pharmacologic discoveries significantly advancing the field.

Molecular genetics of pulmonary hypertension in children

Until recently, the molecular aetiology of paediatric pulmonary hypertension (PH) was relatively poorly understood. While the TGF-β/BMP pathway was recognised as central to disease progression, genetic analyses in children were largely confined to targeted screening of risk genes in small cohorts, with clinical management extrapolated from adult data. In recent years, next-generation sequencing has highlighted notable differences in the genetic architecture underlying childhood-onset cases, with a higher genetic burden in children partly explained by comorbidities such as congenital heart disease. Here, we review recent genetic advances in paediatric PH and highlight important risk factors such as dysregulation of the transcription factors SOX17 and TBX4. Given the poorer prognosis in paediatric cases, molecular diagnosis offers a vital tool to enhance clinical care of children with PH.

Pulmonary Vasculature Responsiveness to Phosphodiesterase-5A Inhibition in Heart Failure With Reduced Ejection Fraction: Possible Role of Plasma Potassium

Introduction

Phosphodiesterase-5a inhibition (PDE5i) leads to favorable changes in pulmonary hemodynamic and cardiac output (CO) in patients with advanced heart failure (HF) and reduced ejection fraction (HFrEF). The hemodynamic response to PDE5i could be heterogeneous and the clinical variables associated with these changes are scarcely investigated.

Materials and Methods

Of 260 patients with advanced HFrEF referred for advanced therapies [cardiac transplant/left ventricular assist device (LVAD)], 55 had pulmonary hypertension (PH) and fulfilled the criteria for the PDE5i vasoreactivity test. Right heart catheterization (RHC) was performed as a part of clinical evaluation before and after 20-mg intravenous sildenafil. Absolute and relative changes in pulmonary vascular resistance (PVR) were evaluated to assess hemodynamic response to PDE5i. Clinical, biochemical, and hemodynamic factors associated with PVR changes were identified.

Results

Sildenafil administration reduced PVR (− 45.3%) and transpulmonary gradient (TPG; − 34.8%) and increased CO (+ 13.6%). Relative change analysis showed a negative moderate association between baseline plasma potassium and changes in PVR (r = − 0.48; p = 0.001) and TPG (r = − 0.43; p = 0.005) after PDE5i. Aldosterone concentration shows a direct moderate association with PVR changes after PDE5i. A significant moderate association was also demonstrated between CO improvement and the severity of mitral (r = 0.42; p = 0.002) and tricuspid (r = 0.39; p = 0.004) regurgitation.

Conclusion

We identified plasma potassium, plasma aldosterone level, and atrioventricular valve regurgitations as potential cofounders of hemodynamic response to acute administration of PDE5i. Whether modulation of potassium levels could enhance pulmonary vasoreactivity in advanced HFrEF deserves further research.

TWIK-Related Acid-Sensitive Potassium Channels (TASK-1) Emerge as Contributors to Tone Regulation in Renal Arteries at Alkaline pH

Aim: TASK-1 channels are established regulators of pulmonary artery tone but their contribution to the regulation of vascular tone in systemic arteries is poorly understood. We tested the hypothesis that TASK-1 channel functional impact differs among systemic vascular beds, that this is associated with differences in their expression and may increase with alkalization of the extracellular environment. Therefore, we evaluated the expression level of TASK-1 channels and their vasomotor role in mesenteric and renal arteries.

Methods: Pulmonary, mesenteric and renal arteries from male Wistar rats were used for TASK-1 channel mRNA (qPCR) and protein content (Western blotting) measurements. The functional role of TASK-1 channels was studied by wire myography using the TASK-1 channel blocker AVE1231. In some experiments, the endothelium was removed with a rat whisker.

Results: Expression levels of both mRNA and protein of the TASK-1 channel pore-forming subunit were highest in pulmonary arteries, lowest in mesenteric arteries and had an intermediate value in renal arteries. Blockade of TASK-1 channels by 1 µM AVE1231 increased U46619-induced contractile responses of pulmonary arteries but did not affect basal tone and contractile responses to methoxamine of mesenteric and renal arteries at physiological extracellular pH (pHo = 7.41). At alkaline extracellular pH = 7.75 (increase of NaHCO3 to 52 mM) AVE1231 evoked the development of basal tone and increased contractile responses to low concentrations of methoxamine in renal but not mesenteric arteries. This effect was independent of the endothelium.

Conclusion: In the rat systemic circulation, TASK-1 channels are abundant in renal arteries and have an anticontractile function under conditions of extracellular alkalosis.

New Mutations and Pathogenesis of Pulmonary Hypertension: Progress and Puzzles in Disease Pathogenesis

Pulmonary arterial hypertension (PAH) is a complex multifactorial disease with poor prognosis characterized by functional and structural alterations of the pulmonary circulation causing marked increase in pulmonary vascular resistance, ultimately leading to right heart failure and death. Mutations in the gene encoding BMPRII-a receptor for the TGF-β (transforming growth factor-beta) superfamily-account for over 70% of families with PAH and ≈20% of sporadic cases. In recent years, however, less common or rare mutations in other genes have been identified. This review will consider how these newly discovered PAH genes could help to provide a better understanding of the molecular and cellular bases of the maintenance of the pulmonary vascular integrity, as well as their role in the PAH pathogenesis underlying occlusion of arterioles in the lung. We will also discuss how insights into the genetic contributions of these new PAH-related genes may open up new therapeutic targets for this, currently incurable, cardiopulmonary disorder.

Role of Ion Channel Remodeling in Endothelial Dysfunction Induced by Pulmonary Arterial Hypertension

Endothelial dysfunction is a key player in advancing vascular pathology in pulmonary arterial hypertension (PAH), a disease essentially characterized by intense remodeling of the pulmonary vasculature, vasoconstriction, endothelial dysfunction, inflammation, oxidative stress, and thrombosis in situ. These vascular features culminate in an increase in pulmonary vascular resistance, subsequent right heart failure, and premature death. Over the past years, there has been a great development in our understanding of pulmonary endothelial biology related to the genetic and molecular mechanisms that modulate the endothelial response to direct or indirect injury and how their dysregulation can promote PAH pathogenesis. Ion channels are key regulators of vasoconstriction and proliferative/apoptotic phenotypes; however, they are poorly studied at the endothelial level. The current review will describe and categorize different expression, functions, regulation, and remodeling of endothelial ion channels (K+, Ca2+, Na+, and Cl− channels) in PAH. We will focus on the potential pathogenic role of ion channel deregulation in the onset and progression of endothelial dysfunction during the development of PAH and its potential therapeutic role.

Channelopathy Genes in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a rare, progressive vasculopathy with significant cardiopulmonary morbidity and mortality. The underlying pathogenetic mechanisms are heterogeneous and current therapies aim to decrease pulmonary vascular resistance but no curative treatments are available. Causal genetic variants can be identified in ~13% of adults and 43% of children with PAH. Knowledge of genetic diagnoses can inform clinical management of PAH, including multimodal medical treatment, surgical intervention and transplantation decisions, and screening for associated conditions, as well as risk stratification for family members. Roles for rare variants in three channelopathy genes—ABCC8, ATP13A3, and KCNK3—have been validated in multiple PAH cohorts, and in aggregate explain ~2.7% of PAH cases. Complete or partial loss of function has been demonstrated for PAH-associated variants in ABCC8 and KCNK3. Channels can be excellent targets for drugs, and knowledge of mechanisms for channel mutations may provide an opportunity for the development of PAH biomarkers and novel therapeutics for patients with hereditary PAH but also potentially more broadly for all patients with PAH.

Smouldering fire or conflagration? An illustrated update on the concept of inflammation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare condition that is characterised by a progressive increase of pulmonary vascular resistances that leads to right ventricular failure and death, if untreated. The underlying narrowing of the pulmonary vasculature relies on several independent and interdependent biological pathways, such as genetic predisposition and epigenetic changes, imbalance of vasodilating and vasoconstrictive mediators, as well as dysimmunity and inflammation that will trigger endothelial dysfunction, smooth muscle cell proliferation, fibroblast activation and collagen deposition. Progressive constriction of the pulmonary vasculature, in turn, initiates and sustains hypertrophic and maladaptive myocardial remodelling of the right ventricle. In this review, we focus on the role of inflammation and dysimmunity in PAH which is generally accepted today, although existing PAH-specific medical therapies still lack targeted immune-modulating approaches.

Ion channels as convergence points in the pathology of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a fatal disease of the cardiopulmonary system that lacks curative treatments. The main pathological event in PAH is elevated vascular resistance in the pulmonary circulation, caused by abnormal vasoconstriction and vascular remodelling. Ion channels are key determinants of vascular smooth muscle tone and homeostasis, and four PAH channelopathies (KCNK3, ABCC8, KCNA5, TRPC6) have been identified so far. However, the contribution of ion channels in other forms of PAH, which account for the majority of PAH patients, has been less well characterised. Here we reason that a variety of triggers of PAH (e.g. BMPR2 mutations, hypoxia, anorectic drugs) that impact channel function may contribute to the onset of the disease. We review the molecular mechanisms by which these ‘extrinsic’ factors converge on ion channels and provoke their dysregulation to promote the development of PAH. Ion channels of the pulmonary vasculature are therefore promising therapeutic targets because of the modulation they provide to both vasomotor tone and proliferation of arterial smooth muscle cells.

Novel Genetic and Molecular Pathways in Pulmonary Arterial Hypertension Associated with Connective Tissue Disease

Pulmonary Arterial Hypertension (PAH) is a severe complication of Connective Tissue Disease (CTD), with remarkable morbidity and mortality. However, the molecular and genetic basis of CTD-PAH remains incompletely understood. This study aimed to screen for genetic defects in a cohort of patients with CTD-PAH, using a PAH-specific panel of 35 genes. During recruitment, 79 patients were studied, including 59 Systemic Sclerosis patients (SSc) and 69 females. Disease-associated variants were observed in nine patients: 4 pathogenic/likely pathogenic variants in 4 different genes (TBX4, ABCC8, KCNA5 and GDF2/BMP9) and 5 Variants of Unknown Significance (VUS) in 4 genes (ABCC8, NOTCH3, TOPBP1 and CTCFL). One patient with mixed CTD had a frameshift pathogenic variant in TBX4. Two patients with SSc-PAH carried variants in ABCC8. A patient diagnosed with Systemic Lupus Erythematous (SLE) presented a pathogenic nonsense variant in GDF2/BMP9. Another patient with SSc-PAH presented a pathogenic variant in KCNA5. Four patients with SSc-PAH carried a VUS in NOTCH1, CTCFL, CTCFL and TOPBP1, respectively. These findings suggest that genetic factors may contribute to Pulmonary Vascular Disease (PVD) in CTD patients.

Involvement of CFTR in the pathogenesis of pulmonary arterial hypertension

INTRODUCTION

A reduction in pulmonary artery (PA) relaxation is a key event in pulmonary arterial hypertension (PAH) pathogenesis. CFTR dysfunction in airway epithelial cells plays a central role in cystic fibrosis (CF); CFTR is also expressed in PAs and has been shown to control endothelium-independent relaxation.

AIM AND OBJECTIVES

We aimed to delineate the role of CFTR in PAH pathogenesis through observational and interventional experiments in human tissues and animal models.

METHODS AND RESULTS

RT-Q-PCR, confocal imaging and electron microscopy showed that CFTR expression was reduced in PAs from patients with idiopathic PAH (iPAH) and in rats with monocrotaline-induced pulmonary hypertension (PH). Moreover, using myograph on human, pig and rat PAs, we demonstrated that CFTR activation induces PAs relaxation. CFTR-mediated PA relaxation was reduced in PAs from iPAH patients and rats with monocrotaline- or chronic hypoxia-induced PH. Long-term in vivo CFTR inhibition in rats significantly increased right ventricular systolic pressure, which was related to exaggerated pulmonary vascular cell proliferation in situ and vessel neomuscularization. Pathologic assessment of lungs from patients with severe CF (F508del-CFTR) revealed severe PA remodeling with intimal fibrosis and medial hypertrophy. Lungs from homozygous F508delCftr rats exhibited pulmonary vessel neomuscularization. The elevations in right ventricular systolic pressure and end diastolic pressure in monocrotaline-exposed rats with chronic CFTR inhibition were more prominent than those in vehicle-exposed rats.

CONCLUSIONS

CFTR expression is strongly decreased in PA smooth muscle and endothelial cells in human and animal models of PH. CFTR inhibition increases vascular cell proliferation and strongly reduces PA relaxation.

Potassium (K+) channels in the pulmonary vasculature: Implications in pulmonary hypertension Physiological, pathophysiological and pharmacological regulation

The large K⁺ channel functional diversity in the pulmonary vasculature results from the multitude of genes expressed encoding K⁺ channels, alternative RNA splicing, the post-transcriptional modifications, the presence of homomeric or heteromeric assemblies of the pore-forming α-subunits and the existence of accessory β-subunits modulating the functional properties of the channel. K⁺ channels can also be regulated at multiple levels by different factors controlling channel activity, trafficking, recycling and degradation. The activity of these channels is the primary determinant of membrane potential (Em) in pulmonary artery smooth muscle cells (PASMC), providing an essential regulatory mechanism to dilate or contract pulmonary arteries (PA). K⁺ channels are also expressed in pulmonary artery endothelial cells (PAEC) where they control resting Em, Ca²⁺ entry and the production of different vasoactive factors. The activity of K⁺ channels is also important in regulating the population and phenotype of PASMC in the pulmonary vasculature, since they are involved in cell apoptosis, survival and proliferation. Notably, K⁺ channels play a major role in the development of pulmonary hypertension (PH). Impaired K⁺ channel activity in PH results from: 1) loss of function mutations, 2) downregulation of its expression, which involves transcription factors and microRNAs, or 3) decreased channel current as a result of increased vasoactive factors (e.g., hypoxia, 5-HT, endothelin-1 or thromboxane), exposure to drugs with channel-blocking properties, or by a reduction in factors that positively regulate K⁺ channel activity (e.g., NO and prostacyclin). Restoring K⁺ channel expression, its intracellular trafficking and the channel activity is an attractive therapeutic strategy in PH.