The Impact of Heterozygous KCNK3 Mutations Associated With Pulmonary Arterial Hypertension on Channel Function and Pharmacological Recovery

Prevalence of apical periodontitis and non-retention of root-filled teeth in hypertensive patients: Systematic review and meta-analysis

BACKGROUND

Several studies have suggested a relationship between AP, as well as the loss of root-filled teeth (RFT), and hypertension (HTN).

OBJECTIVES

The aims of this systematic review and meta-analysis were to investigate the prevalence of AP, and non-retention of RFT, in hypertensive patients.

METHODS

A search was performed in PubMed/MEDLINE, Web of Science, Scopus and EMBASE. The inclusion criteria established were studies published until February 2023, comparing hypertensive subjects with controls, assessing the prevalence of AP and/or providing data on the prevalence of non-retained RFT. Meta-analysis was performed using the RevMan (analyst) tool to determine the pooled prevalence of AP and loss of RFT. Risk of bias was assessed using the Cochrane Risk-of-Bias tool. The quality of evidence was assessed by GRADE.

RESULTS

The search strategy identified 454 articles, and only eight met the inclusion criteria. Six studies had analysed the association between AP and HTN and two studies had analysed the association between non-retention of RFT and HTN. Meta-analysis showed and overall OR = 1.71 (95% CI = 0.92-3.16; p = .09) for the prevalence of AP among patients with HTN. The prevalence of non-retention of RFT among patients with HTN has an overall OR = 1.78 (95% CI = 1.60-1.98; p = .000001). The risk of bias in the individual studies was low or moderate, and the quality of the overall evidence has shown a level of certainty very low.

DISCUSSION

There is no association between the prevalence of AP and HTN. In addition, hypertensive patients have significantly increased odds of losing RFT. Given the high prevalence of hypertension, it is very common to perform root canal treatments on hypertensive patients. It is imperative to communicate this heightened risk to patients and recommend periodic monitoring of oral health and hypertension, paying special attention to this subset of patients.

REGISTRATION

PROSPERO CRD42022302385.

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.

Targets for obstructive sleep apnea pharmacotherapy: principles, approaches, and emerging strategies

INTRODUCTION

Obstructive sleep apnea (OSA) is a common and serious breathing disorder. Several pathophysiological factors predispose individuals to OSA. These factors are quantifiable, and modifiable pharmacologically.

AREAS COVERED

Four key pharmacotherapeutic targets are identified and mapped to the major determinants of OSA pathophysiology. PubMed and Clinicaltrials.gov were searched through April 2023.

EXPERT OPINION

Target #1: Pharyngeal Motor Effectors. Increasing pharyngeal muscle activity and responsivity with noradrenergic-antimuscarinic combination is central to recent breakthrough OSA pharmacotherapy. Assumptions, knowledge gaps, future directions, and other targets are identified. #2: Upper Airway Sensory Afferents. There is translational potential of sensitizing and amplifying reflex pharyngeal dilator muscle responses to negative airway pressure via intranasal delivery of new potassium channel blockers. Rationales, advantages, findings, and potential strategies to enhance effectiveness are identified. #3: Chemosensory Afferents and Ventilatory Control. Strategies to manipulate ventilatory control system sensitivity by carbonic anhydrase inhibitors are supported in theory and initial studies. Intranasal delivery of agents to stimulate central respiratory activity are also introduced. #4: Sleep-Wake Mechanisms. Arousability is the fourth therapeutic target rationalized. Evolving automated tools to measure key pathophysiological factors predisposing to OSA will accelerate pharmacotherapy. Although not currently ready for general clinical settings, the identified targets are of future promise.

Pathophysiology and pathogenic mechanisms of pulmonary hypertension: role of membrane receptors, ion channels, and Ca2+ signaling

The pulmonary circulation is a low-resistance, low-pressure, and high-compliance system that allows the lungs to receive the entire cardiac output. Pulmonary arterial pressure is a function of cardiac output and pulmonary vascular resistance, and pulmonary vascular resistance is inversely proportional to the fourth power of the intraluminal radius of the pulmonary artery. Therefore, a very small decrease of the pulmonary vascular lumen diameter results in a significant increase in pulmonary vascular resistance and pulmonary arterial pressure. Pulmonary arterial hypertension is a fatal and progressive disease with poor prognosis. Regardless of the initial pathogenic triggers, sustained pulmonary vasoconstriction, concentric vascular remodeling, occlusive intimal lesions, in situ thrombosis, and vascular wall stiffening are the major and direct causes for elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension and other forms of precapillary pulmonary hypertension. In this review, we aim to discuss the basic principles and physiological mechanisms involved in the regulation of lung vascular hemodynamics and pulmonary vascular function, the changes in the pulmonary vasculature that contribute to the increased vascular resistance and arterial pressure, and the pathogenic mechanisms involved in the development and progression of pulmonary hypertension. We focus on reviewing the pathogenic roles of membrane receptors, ion channels, and intracellular Ca2+ signaling in pulmonary vascular smooth muscle cells in the development and progression of pulmonary hypertension.

Gene-based association study reveals a distinct female genetic signal in primary hypertension

Hypertension is a polygenic disease that affects over 1.2 billion adults aged 30-79 worldwide. It is a major risk factor for renal, cerebrovascular, and cardiovascular diseases. The heritability of hypertension is estimated to be high; nevertheless, our understanding of its underlying mechanisms remains scarce and incomplete. This study covered the entries from European ancestry from the UK-Biobank (UKB), with 74,090 cases diagnosed with essential (primary) hypertension and 200,734 controls. We compared the findings from large-scale genome-wide association studies (GWAS) to the gene-based method of proteome-wide association studies (PWAS). We focused on 70 statistically significant associated genes, most of which failed to reach significance in variant-based GWAS. A total of 30% of the PWAS-associated genes were validated against independent cohorts, including the Finnish Biobank. Furthermore, gene-based analyses that were performed on both sexes revealed sex-dependent genetics with a stronger genetic component associated with females. Analysis of systolic and diastolic blood pressure measurements confirms a strong genetic effect associated with females. We demonstrated that gene-based approaches provide insight into the underlying biology of hypertension. Specifically, the expression profiles of the identified genes exposed the enrichment of endothelial cells from multiple organs. Furthermore, females' top-ranked significant genes are involved in cellular immunity. We conclude that studying hypertension and blood pressure via gene-based association methods improves interpretability and exposes sex-dependent genetic effects, which enhances clinical utility.

Long non-coding RNAs: The growth controller of vascular smooth muscle cells in cardiovascular diseases

The active proliferation and migration of vascular smooth muscle cells supports the healing of vessel damage while their abnormal aggression or destitution contribute to the aberrant intima-medial structure and function in various cardiovascular diseases, so the understanding of the proliferation disorders of vascular smooth muscle cell and the related mechanism is the basis of effective intervention and control for cardiovascular diseases. Recently, long non-coding RNAs have stood out as upstream switchers for multiple proliferative signaling pathways and molecules, and many of them have been shown to conduce to the dysregulated proliferation and apoptosis of vascular smooth muscle cells under various pathogenic stimuli. This article discusses the long non-coding RNAs disclosed and linked to atherosclerosis, pulmonary hypertension, and aneurysms, and focuses upon their modulation of vascular smooth muscle cell population affecting three deadly cardiovascular diseases.

Gain-of-function mutations in KCNK3 cause a developmental disorder with sleep apnea

Sleep apnea is a common disorder that represents a global public health burden. KCNK3 encodes TASK-1, a K+ channel implicated in the control of breathing, but its link with sleep apnea remains poorly understood. Here we describe a new developmental disorder with associated sleep apnea (developmental delay with sleep apnea, or DDSA) caused by rare de novo gain-of-function mutations in KCNK3. The mutations cluster around the 'X-gate', a gating motif that controls channel opening, and produce overactive channels that no longer respond to inhibition by G-protein-coupled receptor pathways. However, despite their defective X-gating, these mutant channels can still be inhibited by a range of known TASK channel inhibitors. These results not only highlight an important new role for TASK-1 K+ channels and their link with sleep apnea but also identify possible therapeutic strategies.

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.

Mechanisms of pulmonary vascular dysfunction in pulmonary hypertension and implications for novel therapies

Pulmonary hypertension (PH) is a serious disease characterized by various degrees of pulmonary vasoconstriction and progressive fibroproliferative remodeling and inflammation of the pulmonary arterioles that lead to increased pulmonary vascular resistance, right ventricular hypertrophy, and failure. Pulmonary vascular tone is regulated by a balance between vasoconstrictor and vasodilator mediators, and a shift in this balance to vasoconstriction is an important component of PH pathology, Therefore, the mainstay of current pharmacological therapies centers on pulmonary vasodilation methodologies that either enhance vasodilator mechanisms such as the NO-cGMP and prostacyclin-cAMP pathways and/or inhibit vasoconstrictor mechanisms such as the endothelin-1, cytosolic Ca2+, and Rho-kinase pathways. However, in addition to the increased vascular tone, many patients have a "fixed" component in their disease that involves altered biology of various cells in the pulmonary vascular wall, excessive pulmonary artery remodeling, and perivascular fibrosis and inflammation. Pulmonary arterial smooth muscle cell (PASMC) phenotypic switch from a contractile to a synthetic and proliferative phenotype is an important factor in pulmonary artery remodeling. Although current vasodilator therapies also have some antiproliferative effects on PASMCs, they are not universally successful in halting PH progression and increasing survival. Mild acidification and other novel approaches that aim to reverse the resident pulmonary vascular pathology and structural remodeling and restore a contractile PASMC phenotype could ameliorate vascular remodeling and enhance the responsiveness of PH to vasodilator therapies.

Extracellular matrix degradation pathways and fatty acid metabolism regulate distinct pulmonary vascular cell types in pulmonary arterial hypertension

Pulmonary arterial hypertension describes a group of diseases characterised by raised pulmonary vascular resistance, resulting from vascular remodelling in the pre-capillary resistance arterioles. Left untreated, patients die from right heart failure. Pulmonary vascular remodelling involves all cell types but to date the precise roles of the different cells is unknown. This study investigated differences in basal gene expression between pulmonary arterial hypertension and controls using both human pulmonary microvascular endothelial cells and human pulmonary artery smooth muscle cells. Human pulmonary microvascular endothelial cells and human pulmonary artery smooth muscle cells from pulmonary arterial hypertension patients and controls were cultured to confluence, harvested and RNA extracted. Whole genome sequencing was performed and after transcript quantification and normalisation, we examined differentially expressed genes and applied gene set enrichment analysis to the differentially expressed genes to identify putative activated pathways. Human pulmonary microvascular endothelial cells displayed 1008 significant (p ≤ 0.0001) differentially expressed genes in pulmonary arterial hypertension samples compared to controls. In human pulmonary artery smooth muscle cells, there were 229 significant (p ≤ 0.0001) differentially expressed genes between pulmonary arterial hypertension and controls. Pathway analysis revealed distinctive differences: human pulmonary microvascular endothelial cells display down-regulation of extracellular matrix organisation, collagen formation and biosynthesis, focal- and cell-adhesion molecules suggesting severe endothelial barrier dysfunction and vascular permeability in pulmonary arterial hypertension pathogenesis. In contrast, pathways in human pulmonary artery smooth muscle cells were mainly up-regulated, including those for fatty acid metabolism, biosynthesis of unsaturated fatty acids, cell–cell and adherens junction interactions suggesting a more energy-driven proliferative phenotype. This suggests that the two cell types play different mechanistic roles in pulmonary arterial hypertension pathogenesis and further studies are required to fully elucidate the role each plays and the interactions between these cell types in vascular remodelling in disease progression.

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.

KCNK3 Mutation Causes Altered Immune Function in Pulmonary Arterial Hypertension Patients and Mouse Models

Loss of function KCNK3 mutation is one of the gene variants driving hereditary pulmonary arterial hypertension (PAH). KCNK3 is expressed in several cell and tissue types on both membrane and endoplasmic reticulum and potentially plays a role in multiple pathological process associated with PAH. However, the role of various stressors driving the susceptibility of KCNK3 mutation to PAH is unknown. Hence, we exposed kcnk3^fl/fl animals to hypoxia, metabolic diet and low dose lipopolysaccharide (LPS) and performed molecular characterization of their tissue. We also used tissue samples from KCNK3 patients (skin fibroblast derived inducible pluripotent stem cells, blood, lungs, peripheral blood mononuclear cells) and performed microarray, immunohistochemistry (IHC) and mass cytometry time of flight (CyTOF) experiments. Although a hypoxic insult did not alter vascular tone in kcnk3^fl/fl mice, RNASeq study of these lungs implied that inflammatory and metabolic factors were altered, and the follow-up diet study demonstrated a dysregulation of bone marrow cells in kcnk3^fl/fl mice. Finally, a low dose LPS study clearly showed that inflammation could be a possible second hit driving PAH in kcnk3^fl/fl mice. Multiplex, IHC and CyTOF immunophenotyping studies on human samples confirmed the mouse data and strongly indicated that cell mediated, and innate immune responses may drive PAH susceptibility in these patients. In conclusion, loss of function KCNK3 mutation alters various physiological processes from vascular tone to metabolic diet through inflammation. Our data suggests that altered circulating immune cells may drive PAH susceptibility in patients with KCNK3 mutation.

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.

'There and Back Again'-Forward Genetics and Reverse Phenotyping in Pulmonary Arterial Hypertension

Although the invention of right heart catheterisation in the 1950s enabled accurate clinical diagnosis of pulmonary arterial hypertension (PAH), it was not until 2000 when the landmark discovery of the causative role of bone morphogenetic protein receptor type II (BMPR2) mutations shed new light on the pathogenesis of PAH. Since then several genes have been discovered, which now account for around 25% of cases with the clinical diagnosis of idiopathic PAH. Despite the ongoing efforts, in the majority of patients the cause of the disease remains elusive, a phenomenon often referred to as "missing heritability". In this review, we discuss research approaches to uncover the genetic architecture of PAH starting with forward phenotyping, which in a research setting should focus on stable intermediate phenotypes, forward and reverse genetics, and finally reverse phenotyping. We then discuss potential sources of "missing heritability" and how functional genomics and multi-omics methods are employed to tackle this problem.

Implication of Potassium Channels in the Pathophysiology of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a rare and severe cardiopulmonary disease without curative treatments. PAH is a multifactorial disease that involves genetic predisposition, epigenetic factors, and environmental factors (drugs, toxins, viruses, hypoxia, and inflammation), which contribute to the initiation or development of irreversible remodeling of the pulmonary vessels. The recent identification of loss-of-function mutations in KCNK3 (KCNK3 or TASK-1) and ABCC8 (SUR1), or gain-of-function mutations in ABCC9 (SUR2), as well as polymorphisms in KCNA5 (Kv1.5), which encode two potassium (K⁺) channels and two K⁺ channel regulatory subunits, has revived the interest of ion channels in PAH. This review focuses on KCNK3, SUR1, SUR2, and Kv1.5 channels in pulmonary vasculature and discusses their pathophysiological contribution to and therapeutic potential in PAH.

Inhibition of RELM-β prevents hypoxia-induced overproliferation of human pulmonary artery smooth muscle cells by reversing PLC-mediated KCNK3 decline

AIMS

Although resistin-like molecule β (RELM-β) is involved in the pathological processes of various lung diseases, such as pulmonary inflammation, asthma and fibrosis, its potential roles in hypoxic pulmonary arterial hypertension (PAH) remain largely unknown. The study aims to investigate whether RELM-β contributes to hypoxia-induced excessive proliferation of human pulmonary artery smooth muscle cells (PASMCs) and to explore the potential mechanisms of this process.

MAIN METHODS

Human PASMCs were exposed to normoxia or hypoxia (1% O₂) for 24 h. siRNA targeting RELM-β was transfected into cells. Protein levels of KCNK3, RELM-β, pSTAT3 and STAT3 were determined by immunoblotting. The translocation of NFATc2 and expression of KCNK3 were visualized by immunofluorescence. 5-ethynyl-2'-deoxyuridine assays and cell counting kit-8 assays were performed to assess the proliferation of PASMCs.

KEY FINDINGS

(1) Chronic hypoxia significantly decreased KCNK3 protein levels while upregulating RELM-β protein levels in human PASMCs, which was accompanied by excessive proliferation of cells. (2) RELM-β could promote human PASMCs proliferation and activate the STAT3/NFAT axis by downregulating KCNK3 protein under normoxia. (3) Inhibition of RELM-β expression effectively prevented KCNK3-mediated cell proliferation under hypoxia. (4) Phospholipase C (PLC) inhibitor U-73122 could not only prevent the hypoxia/RELM-β-induced decrease in KCNK3 protein, but also inhibit the enhanced cell viability caused by hypoxia/RELM-β. (5) Both hypoxia and RELM-β could downregulate membrane KCNK3 protein levels by enhancing endocytosis.

SIGNIFICANCE

RELM-β activation is responsible for hypoxia-induced excessive proliferation of human PASMCs. Interfering with RELM-β may alleviate the progression of hypoxic PAH by upregulating PLC-dependent KCNK3 expression.

Molecular genetic framework underlying pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare, progressive disorder typified by occlusion of the pulmonary arterioles owing to endothelial dysfunction and uncontrolled proliferation of pulmonary artery smooth muscle cells and fibroblasts. Vascular occlusion can lead to increased pressure in the pulmonary arteries, often resulting in right ventricular failure with shortness of breath and syncope. Since the identification of BMPR2, which encodes a receptor in the transforming growth factor-β superfamily, the development of high-throughput sequencing approaches to identify novel causal genes has substantially advanced our understanding of the molecular genetics of PAH. In the past 6 years, additional pathways involved in PAH susceptibility have been described through the identification of deleterious genetic variants in potassium channels (KCNK3 and ABCC8) and transcription factors (TBX4 and SOX17), among others. Although familial PAH most often has an autosomal-dominant pattern of inheritance, cases of incomplete penetrance and evidence of genetic heterogeneity support a model of PAH as a Mendelian disorder with complex disease features. In this Review, we outline the latest advances in the detection of rare and common genetic variants underlying PAH susceptibility and disease progression. These findings have clinical implications for lung vascular function and can help to identify mechanistic pathways amenable to pharmacological intervention.

TASK Channels Pharmacology: New Challenges in Drug Design

Rational drug design targeting ion channels is an exciting and always evolving research field. New medicinal chemistry strategies are being implemented to explore the wild chemical space and unravel the molecular basis of the ion channels modulators binding mechanisms. TASK channels belong to the two-pore domain potassium channel family and are modulated by extracellular acidosis. They are extensively distributed along the cardiovascular and central nervous systems, and their expression is up- and downregulated in different cancer types, which makes them an attractive therapeutic target. However, TASK channels remain unexplored, and drugs designed to target these channels are poorly selective. Here, we review TASK channels properties and their known blockers and activators, considering the new challenges in ion channels drug design and focusing on the implementation of computational methodologies in the drug discovery process.

Potassium channels in vascular smooth muscle: a pathophysiological and pharmacological perspective

Potassium (K⁺ ) ion channel activity is an important determinant of vascular tone by regulating cell membrane potential (MP). Activation of K⁺ channels leads to membrane hyperpolarization and subsequently vasodilatation, while inhibition of the channels causes membrane depolarization and then vasoconstriction. So far five distinct types of K⁺ channels have been identified in vascular smooth muscle cells (VSMCs): Ca⁺² -activated K⁺ channels (BK_{C a} ), voltage-dependent K⁺ channels (K_V ), ATP-sensitive K⁺ channels (K_ATP ), inward rectifier K⁺ channels (K_ir ), and tandem two-pore K⁺ channels (K₂ P). The activity and expression of vascular K⁺ channels are changed during major vascular diseases such as hypertension, pulmonary hypertension, hypercholesterolemia, atherosclerosis, and diabetes mellitus. The defective function of K⁺ channels is commonly associated with impaired vascular responses and is likely to become as a result of changes in K⁺ channels during vascular diseases. Increased K⁺ channel function and expression may also help to compensate for increased abnormal vascular tone. There are many pharmacological and genotypic studies which were carried out on the subtypes of K⁺ channels expressed in variable amounts in different vascular beds. Modulation of K⁺ channel activity by molecular approaches and selective drug development may be a novel treatment modality for vascular dysfunction in the future. This review presents the basic properties, physiological functions, pathophysiological, and pharmacological roles of the five major classes of K⁺ channels that have been determined in VSMCs.

The molecular basis for an allosteric inhibition of K+-flux gating in K2P channels

Two-pore-domain potassium (K_2P) channels are key regulators of many physiological and pathophysiological processes and thus emerged as promising drug targets. As for other potassium channels, there is a lack of selective blockers, since drugs preferentially bind to a conserved binding site located in the central cavity. Thus, there is a high medical need to identify novel drug-binding sites outside the conserved lipophilic central cavity and to identify new allosteric mechanisms of channel inhibition. Here, we identified a novel binding site and allosteric inhibition mechanism, disrupting the recently proposed K⁺-flux gating mechanism of K_2P channels, which results in an unusual voltage-dependent block of leak channels belonging to the TASK subfamily. The new binding site and allosteric mechanism of inhibition provide structural and mechanistic insights into the gating of TASK channels and the basis for the drug design of a new class of potent blockers targeting specific types of K_2P channels.

Twik-2-/- mouse demonstrates pulmonary vascular heterogeneity in intracellular pathways for vasocontractility

We have previously shown Twik-2-/- mice develop pulmonary hypertension and vascular remodeling. We hypothesized that distal pulmonary arteries (D-PAs) of the Twik-2-/- mice are hypercontractile under physiological venous conditions due to altered electrophysiologic properties between the conduit and resistance vessels in the pulmonary vascular bed. We measured resting membrane potential and intracellular calcium through Fura-2 in freshly digested pulmonary artery smooth muscles (PASMCs) from both the right main (RM-PA) and D-PA (distal) regions of pulmonary artery from WT and Twik-2-/- mice. Whole segments of RM-PAs and D-PAs from 20 to 24-week-old wildtype (WT) and Twik-2-/- mice were also pressurized between two glass micropipettes and bathed in buffer with either arterial or venous conditions. Abluminally-applied phenylephrine (PE) and U46619 were added to the buffer at log increments and vessel diameter was measured. All values were expressed as averages with ±SEM. Vasoconstrictor responses did not differ between WT and Twik-2-/- RM-PAs under arterial conditions. Under venous conditions, Twik-2-/- RM-PAs showed an increased sensitivity to PE with a lower EC50 (P = 0.02). Under venous conditions, Twik-2-/- D-PAs showed an increase maximal vasoconstrictor response to both phenylephrine and U46619 compared to the WT mice (P < 0.05). Isolated PASMCs from Twik-2 -/- D-PA were depolarized and had higher intracellular calcium levels compared to PASMCs from RM-PA of both WT and Twik-2-/- mice. These studies suggest that hypercontractile responses and electrophysiologic properties unique to the anatomic location of the D-PAs may contribute to pulmonary hypertensive vasculopathy.

Characterization and regulation of wild-type and mutant TASK-1 two pore domain potassium channels indicated in pulmonary arterial hypertension

Key points

The TASK‐1 channel gene (KCNK3) has been identified as a possible disease‐causing gene in heritable pulmonary arterial hypertension (PAH).

In the present study, we show that novel mutated TASK‐1 channels, seen in PAH patients, have a substantially reduced current compared to wild‐type TASK‐1 channels.

These mutated TASK‐1 channels are located at the plasma membrane to the same degree as wild‐type TASK‐1 channels.

ONO‐RS‐082 and alkaline pH 8.4 both activate TASK‐1 channels but do not recover current through mutant TASK‐1 channels.

We show that the guanylate cyclase activator, riociguat, a novel treatment for PAH, enhances current through TASK‐1 channels but does not recover current through mutant TASK‐1 channels.

Abstract

Pulmonary arterial hypertension (PAH) affects ∼15–50 people per million. KCNK3, the gene that encodes the two pore domain potassium channel TASK‐1 (K2P3.1), has been identified as a possible disease‐causing gene in heritable PAH. Recently, two new mutations have been identified in KCNK3 in PAH patients: G106R and L214R. The present study aimed to characterize the functional properties and regulation of wild‐type (WT) and mutated TASK‐1 channels and determine how these might contribute to PAH and its treatment. Currents through WT and mutated human TASK‐1 channels transiently expressed in tsA201 cells were measured using whole‐cell patch clamp electrophysiology. Localization of fluorescence‐tagged channels was visualized using confocal microscopy and quantified with in‐cell and on‐cell westerns. G106R or L214R mutated channels were located at the plasma membrane to the same degree as WT channels; however, their current was markedly reduced compared to WT TASK‐1 channels. Functional current through these mutated channels could not be restored using activators of WT TASK‐1 channels (pH 8.4, ONO‐RS‐082). The guanylate cyclase activator, riociguat, enhanced current through WT TASK‐1 channels; however, similar to the other activators investigated, riociguat did not have any effect on current through mutated TASK‐1 channels. Thus, novel mutations in TASK‐1 seen in PAH substantially alter the functional properties of these channels. Current through these channels could not be restored by activators of TASK‐1 channels. Riociguat enhancement of current through TASK‐1 channels could contribute to its therapeutic benefit in the treatment of PAH.

The TASK‐1 channel gene (KCNK3) has been identified as a possible disease‐causing gene in heritable pulmonary arterial hypertension (PAH).

In the present study, we show that novel mutated TASK‐1 channels, seen in PAH patients, have a substantially reduced current compared to wild‐type TASK‐1 channels.

These mutated TASK‐1 channels are located at the plasma membrane to the same degree as wild‐type TASK‐1 channels.

ONO‐RS‐082 and alkaline pH 8.4 both activate TASK‐1 channels but do not recover current through mutant TASK‐1 channels.

We show that the guanylate cyclase activator, riociguat, a novel treatment for PAH, enhances current through TASK‐1 channels but does not recover current through mutant TASK‐1 channels.

Ion Channels in Pulmonary Hypertension: A Therapeutic Interest?

Pulmonary arterial hypertension (PAH) is a multifactorial and severe disease without curative therapies. PAH pathobiology involves altered pulmonary arterial tone, endothelial dysfunction, distal pulmonary vessel remodeling, and inflammation, which could all depend on ion channel activities (K⁺, Ca²⁺, Na⁺ and Cl^-). This review focuses on ion channels in the pulmonary vasculature and discusses their pathophysiological contribution to PAH as well as their therapeutic potential in PAH.

Loss-of-Function ABCC8 Mutations in Pulmonary Arterial Hypertension

BACKGROUND

In pulmonary arterial hypertension (PAH), pathological changes in pulmonary arterioles progressively raise pulmonary artery pressure and increase pulmonary vascular resistance, leading to right heart failure and high mortality rates. Recently, the first potassium channelopathy in PAH, because of mutations in KCNK3, was identified as a genetic cause and pharmacological target.

METHODS

Exome sequencing was performed to identify novel genes in a cohort of 99 pediatric and 134 adult-onset group I PAH patients. Novel rare variants in the gene identified were independently identified in a cohort of 680 adult-onset patients. Variants were expressed in COS cells and function assessed by patch-clamp and rubidium flux analysis.

RESULTS

We identified a de novo novel heterozygous predicted deleterious missense variant c.G2873A (p.R958H) in ABCC8 in a child with idiopathic PAH. We then evaluated all individuals in the original and a second cohort for rare or novel variants in ABCC8 and identified 11 additional heterozygous predicted damaging ABCC8 variants. ABCC8 encodes SUR1 (sulfonylurea receptor 1)-a regulatory subunit of the ATP-sensitive potassium channel. We observed loss of ATP-sensitive potassium channel function for all ABCC8 variants evaluated and pharmacological rescue of all channel currents in vitro by the SUR1 activator, diazoxide.

CONCLUSIONS

Novel and rare missense variants in ABCC8 are associated with PAH. Identified ABCC8 mutations decreased ATP-sensitive potassium channel function, which was pharmacologically recovered.