The role of k+ channels in determining pulmonary vascular tone, oxygen sensing, cell proliferation, and apoptosis: implications in hypoxic pulmonary vasoconstriction and pulmonary arterial hypertension

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.

ANO1, CaV1.2, and IP3R form a localized unit of EC-coupling in mouse pulmonary arterial smooth muscle

Pulmonary arterial (PA) smooth muscle cells (PASMC) generate vascular tone in response to agonists coupled to Gq-protein receptor signaling. Such agonists stimulate oscillating calcium waves, the frequency of which drives the strength of contraction. These Ca2+ events are modulated by a variety of ion channels including voltage-gated calcium channels (CaV1.2), the Tmem16a or Anoctamin-1 (ANO1)-encoded calcium-activated chloride (CaCC) channel, and Ca2+ release from the sarcoplasmic reticulum through inositol-trisphosphate receptors (IP3R). Although these calcium events have been characterized, it is unclear how these calcium oscillations underly a sustained contraction in these muscle cells. We used smooth muscle-specific ablation of ANO1 and pharmacological tools to establish the role of ANO1, CaV1.2, and IP3R in the contractile and intracellular Ca2+ signaling properties of mouse PA smooth muscle expressing the Ca2+ biosensor GCaMP3 or GCaMP6. Pharmacological block or genetic ablation of ANO1 or inhibition of CaV1.2 or IP3R, or Ca2+ store depletion equally inhibited 5-HT-induced tone and intracellular Ca2+ waves. Coimmunoprecipitation experiments showed that an anti-ANO1 antibody was able to pull down both CaV1.2 and IP3R. Confocal and superresolution nanomicroscopy showed that ANO1 coassembles with both CaV1.2 and IP3R at or near the plasma membrane of PASMC from wild-type mice. We conclude that the stable 5-HT-induced PA contraction results from the integration of stochastic and localized Ca2+ events supported by a microenvironment comprising ANO1, CaV1.2, and IP3R. In this model, ANO1 and CaV1.2 would indirectly support cyclical Ca2+ release events from IP3R and propagation of intracellular Ca2+ waves.

Impact of aging on vascular ion channels: perspectives and knowledge gaps across major organ systems

Individuals aged ≥65 yr will comprise ∼20% of the global population by 2030. Cardiovascular disease remains the leading cause of death in the world with age-related endothelial "dysfunction" as a key risk factor. As an organ in and of itself, vascular endothelium courses throughout the mammalian body to coordinate blood flow to all other organs and tissues (e.g., brain, heart, lung, skeletal muscle, gut, kidney, skin) in accord with metabolic demand. In turn, emerging evidence demonstrates that vascular aging and its comorbidities (e.g., neurodegeneration, diabetes, hypertension, kidney disease, heart failure, and cancer) are "channelopathies" in large part. With an emphasis on distinct functional traits and common arrangements across major organs systems, the present literature review encompasses regulation of vascular ion channels that underlie blood flow control throughout the body. The regulation of myoendothelial coupling and local versus conducted signaling are discussed with new perspectives for aging and the development of chronic diseases. Although equipped with an awareness of knowledge gaps in the vascular aging field, a section has been included to encompass general feasibility, role of biological sex, and additional conceptual and experimental considerations (e.g., cell regression and proliferation, gene profile analyses). The ultimate goal is for the reader to see and understand major points of deterioration in vascular function while gaining the ability to think of potential mechanistic and therapeutic strategies to sustain organ perfusion and whole body health with aging.

Mitochondrial complex I ROS production and redox signaling in hypoxia

Mitochondria are a main source of cellular energy. Oxidative phosphorylation (OXPHOS) is the major process of aerobic respiration. Enzyme complexes of the electron transport chain (ETC) pump protons to generate a protonmotive force (Δp) that drives OXPHOS. Complex I is an electron entry point into the ETC. Complex I oxidizes nicotinamide adenine dinucleotide (NADH) and transfers electrons to ubiquinone in a reaction coupled with proton pumping. Complex I also produces reactive oxygen species (ROS) under various conditions. The enzymatic activities of complex I can be regulated by metabolic conditions and serves as a regulatory node of the ETC. Complex I ROS plays diverse roles in cell metabolism ranging from physiologic to pathologic conditions. Progress in our understanding indicates that ROS release from complex I serves important signaling functions. Increasing evidence suggests that complex I ROS is important in signaling a mismatch in energy production and demand. In this article, we review the role of ROS from complex I in sensing acute hypoxia.

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.

Novel Molecular Mechanisms Involved in the Medical Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a severe condition with a high mortality rate despite advances in diagnostic and therapeutic strategies. In recent years, significant scientific progress has been made in the understanding of the underlying pathobiological mechanisms. Since current available treatments mainly target pulmonary vasodilation, but lack an effect on the pathological changes that develop in the pulmonary vasculature, there is need to develop novel therapeutic compounds aimed at antagonizing the pulmonary vascular remodeling. This review presents the main molecular mechanisms involved in the pathobiology of PAH, discusses the new molecular compounds currently being developed for the medical treatment of PAH and assesses their potential future role in the therapeutic algorithms of PAH.

Mitochondrial dysfunction in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by the increased pulmonary vascular resistance due to pulmonary vasoconstriction and vascular remodeling. PAH has high disability, high mortality and poor prognosis, which is becoming a more common global health issue. There is currently no drug that can permanently cure PAH patients. The pathogenesis of PAH is still not fully elucidated. However, the role of metabolic theory in the pathogenesis of PAH is becoming clearer, especially mitochondrial metabolism. With the deepening of mitochondrial researches in recent years, more and more studies have shown that the occurrence and development of PAH are closely related to mitochondrial dysfunction, including the tricarboxylic acid cycle, redox homeostasis, enhanced glycolysis, and increased reactive oxygen species production, calcium dysregulation, mitophagy, etc. This review will further elucidate the relationship between mitochondrial metabolism and pulmonary vasoconstriction and pulmonary vascular remodeling. It might be possible to explore more comprehensive and specific treatment strategies for PAH by understanding these mitochondrial metabolic mechanisms.

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.

Underlying mechanism of Qiling Jiaogulan Powder in the treatment of broiler ascites syndrome

Broiler ascites syndrome (AS), is a nutritional and metabolic disease that occurs in fast-growing commercial broiler chickens. AS can cause poor growth and a significant increase in the rate of broiler deaths, which has resulted in serious economic losses to the poultry industry. The classic traditional Chinese medicine Qiling Jiaogulan Powder (QLJP) has been demonstrated to have a certain therapeutic effect on broiler AS. However, its pharmacological mechanism remains to be elucidated. This study was performed to investigate the multitarget action mechanism of QLJP in the treatment of broiler AS based on network pharmacology analysis using a broiler AS model. First, all chemical components and targets of QLJP were obtained from the Traditional Chinese Medicine System Pharmacology Analysis Platform (TCMSP). Targets related to broiler AS were further obtained through the GeneCards database and the NCBI Gene sub-database. A protein-protein interaction (PPI) network was constructed. Then, enrichment analyses were performed to predict the potential mechanisms of QLJP in the treatment of broiler AS. Finally, the treatment effect of QLJP on AS was verified in a broiler AS model. Network pharmacology analysis generated 49 active ingredients and 167 core targets of QLJP, and a QLJP-single drug-target-disease network was successfully constructed. Gene enrichment analysis indicated that the core targets have played major roles in the Cell cycle, FOXO signaling pathways, etc. We demonstrated that QLJP improved clinical and organ damage symptoms and significantly reduced the ascites heart index in broilers with AS induced by administration of high-energy, high-protein diets and high-sodium drinking water in a low-temperature environment. QLJP may regulate lung oxidative stress, the cell cycle and apoptosis by activating the FOXO3a signaling pathway to interfere with the occurrence and development of AS in broilers. QLJP administration may be a good clinical strategy for the prevention and treatment of broiler AS.

Novel Insights into the Therapeutic Potential of Lung-Targeted Gene Transfer in the Most Common Respiratory Diseases

Over the past decades, a better understanding of the genetic and molecular alterations underlying several respiratory diseases has encouraged the development of new therapeutic strategies. Gene therapy offers new therapeutic alternatives for inherited and acquired diseases by delivering exogenous genetic materials into cells or tissues to restore physiological protein expression and/or activity. In this review, we review (1) different types of viral and non-viral vectors as well as gene-editing techniques; and (2) the application of gene therapy for the treatment of respiratory diseases and disorders, including pulmonary arterial hypertension, idiopathic pulmonary fibrosis, cystic fibrosis, asthma, alpha-1 antitrypsin deficiency, chronic obstructive pulmonary disease, non-small-cell lung cancer, and COVID-19. Further, we also provide specific examples of lung-targeted therapies and discuss the major limitations of gene therapy.

Alzheimer's disease therapy based on acetylcholinesterase inhibitor/blocker effects on voltage-gated potassium channels

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder with progressive loss of memory and other cognitive functions. The pathogenesis of this disease is complex and multifactorial, and remains obscure until now. To enhance the declined level of acetylcholine (ACh) resulting from loss of cholinergic neurons, acetylcholinesterase (AChE) inhibitors are developed and successfully approved for AD treatment in the clinic, with a limited therapeutic effectiveness. At present, it is generally accepted that multi-target strategy is potently useful for designing novel drugs for AD. Accumulated evidence reveals that Kv channels, which are broadly expressed in brain and possess crucial functions in modulating the neuronal activity, are inhibited by several acetylcholinesterase (AChE) inhibitors, such as tacrine, bis(7)-tacrine, donepezil and galantamine. Inhibition of Kv channels by these AChE inhibitors can generate neuroprotective effects by either mitigating Aβ toxicity and neuronal apoptosis, or facilitating cell proliferation. These inhibitory effects provide additional explanations for clinical beneficial effectiveness of AChE inhibitors, meaning that Kv channel is a promising candidate target for novel drugs for AD therapy.

BK channel-forming slo1 proteins mediate the brain artery constriction evoked by the neurosteroid pregnenolone

Pregnenolone is a neurosteroid that modulates glial growth and differentiation, neuronal firing, and several brain functions, these effects being attributed to pregnenolone actions on the neurons and glial cells themselves. Despite the vital role of the cerebral circulation for brain function and the fact that pregnenolone is a vasoactive agent, pregnenolone action on brain arteries remain unknown. Here, we obtained in vivo concentration response curves to pregnenolone on middle cerebral artery (MCA) diameter in anesthetized male and female C57BL/6J mice. In both male and female animals, pregnenolone (1 nM-100 μM) constricted MCA in a concentration-dependent manner, its maximal effect reaching ~22-35% decrease in diameter. Pregnenolone action was replicated in intact and de-endothelialized, in vitro pressurized MCA segments with pregnenolone evoking similar constriction in intact and de-endothelialized MCA. Neurosteroid action was abolished by 1 μM paxilline, a selective blocker of Ca2+ - and voltage-gated K+ channels of large conductance (BK). Cell-attached, patch-clamp recordings on freshly isolated smooth muscle cells from mouse MCAs demonstrated that pregnenolone at concentrations that constricted MCAs in vitro and in vivo (10 μM), reduced BK activity (NPo), with an average decrease in NPo reaching 24.2%. The concentration-dependence of pregnenolone constriction of brain arteries and inhibition of BK activity in intact cells were paralleled by data obtained in cell-free, inside-out patches, with maximal inhibition reached at 10 μM pregnenolone. MCA smooth muscle BKs include channel-forming α (slo1 proteins) and regulatory β1 subunits, encoded by KCNMA1 and KCNMB1, respectively. However, pregnenolone-driven decrease in NPo was still evident in MCA myocytes from KCNMB1-/- mice. Following reconstitution of slo1 channels into artificial, binary phospholipid bilayers, 10 μM pregnenolone evoked slo1 NPo inhibition which was similar to that seen in native membranes. Lastly, pregnenolone failed to constrict MCA from KCNMA1-/- mice. In conclusion, pregnenolone constricts MCA independently of neuronal, glial, endothelial and circulating factors, as well as of cell integrity, organelles, complex membrane cytoarchitecture, and the continuous presence of cytosolic signals. Rather, this action involves direct inhibition of SM BK channels, which does not require β1 subunits but is mediated through direct sensing of the neurosteroid by the channel-forming α subunit.

Chronic Obstructive Pulmonary Disease and the Cardiovascular System: Vascular Repair and Regeneration as a Therapeutic Target

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality worldwide and encompasses chronic bronchitis and emphysema. It has been shown that vascular wall remodeling and pulmonary hypertension (PH) can occur not only in patients with COPD but also in smokers with normal lung function, suggesting a causal role for vascular alterations in the development of emphysema. Mechanistically, abnormalities in the vasculature, such as inflammation, endothelial dysfunction, imbalances in cellular apoptosis/proliferation, and increased oxidative/nitrosative stress promote development of PH, cor pulmonale, and most probably pulmonary emphysema. Hypoxemia in the pulmonary chamber modulates the activation of key transcription factors and signaling cascades, which propagates inflammation and infiltration of neutrophils, resulting in vascular remodeling. Endothelial progenitor cells have angiogenesis capabilities, resulting in transdifferentiation of the smooth muscle cells via aberrant activation of several cytokines, growth factors, and chemokines. The vascular endothelium influences the balance between vaso-constriction and -dilation in the heart. Targeting key players affecting the vasculature might help in the development of new treatment strategies for both PH and COPD. The present review aims to summarize current knowledge about vascular alterations and production of reactive oxygen species in COPD. The present review emphasizes on the importance of the vasculature for the usually parenchyma-focused view of the pathobiology of COPD.

Identifying Potential Mutations Responsible for Cases of Pulmonary Arterial Hypertension

Pulmonary Arterial Hypertension (PAH) is a progressive and devastating disease for which there is an escalating body of genetic and related pathophysiological information on disease pathobiology. Nevertheless, the success to date in identifying susceptibility genes, genetic variants and epigenetic processes has been limited due to PAH clinical multi-faceted variations. A number of germline gene candidates have been proposed but demonstrating consistently the association with PAH has been problematic, at least partly due to the reduced penetrance and variable expressivity. Although the data for bone morphogenetic protein receptor type 2 (BMPR2) and related genes remains undoubtedly the most extensive, recent advanced gene sequencing technologies have facilitated the discovery of further gene candidates with mutations among those with and without familial forms of PAH. An in depth understanding of the multitude of biologic variations associated with PAH may provide novel opportunities for therapeutic intervention in the coming years. This knowledge will irrevocably provide the opportunity for improved patient and family counseling as well as improved PAH diagnosis, risk assessment, and personalized treatment.

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.

Genetic Delivery and Gene Therapy in Pulmonary Hypertension

Pulmonary hypertension (PH) is a progressive complex fatal disease of multiple etiologies. Hyperproliferation and resistance to apoptosis of vascular cells of intimal, medial, and adventitial layers of pulmonary vessels trigger excessive pulmonary vascular remodeling and vasoconstriction in the course of pulmonary arterial hypertension (PAH), a subgroup of PH. Multiple gene mutation/s or dysregulated gene expression contribute to the pathogenesis of PAH by endorsing the proliferation and promoting the resistance to apoptosis of pulmonary vascular cells. Given the vital role of these cells in PAH progression, the development of safe and efficient-gene therapeutic approaches that lead to restoration or down-regulation of gene expression, generally involved in the etiology of the disease is the need of the hour. Currently, none of the FDA-approved drugs provides a cure against PH, hence innovative tools may offer a novel treatment paradigm for this progressive and lethal disorder by silencing pathological genes, expressing therapeutic proteins, or through gene-editing applications. Here, we review the effectiveness and limitations of the presently available gene therapy approaches for PH. We provide a brief survey of commonly existing and currently applicable gene transfer methods for pulmonary vascular cells in vitro and describe some more recent developments for gene delivery existing in the field of PH in vivo.

On a Magical Mystery Tour with 8-Bromo-Cyclic ADP-Ribose: From All-or-None Block to Nanojunctions and the Cell-Wide Web

A plethora of cellular functions are controlled by calcium signals, that are greatly coordinated by calcium release from intracellular stores, the principal component of which is the sarco/endooplasmic reticulum (S/ER). In 1997 it was generally accepted that activation of various G protein-coupled receptors facilitated inositol-1,4,5-trisphosphate (IP3) production, activation of IP3 receptors and thus calcium release from S/ER. Adding to this, it was evident that S/ER resident ryanodine receptors (RyRs) could support two opposing cellular functions by delivering either highly localised calcium signals, such as calcium sparks, or by carrying propagating, global calcium waves. Coincidentally, it was reported that RyRs in mammalian cardiac myocytes might be regulated by a novel calcium mobilising messenger, cyclic adenosine diphosphate-ribose (cADPR), that had recently been discovered by HC Lee in sea urchin eggs. A reputedly selective and competitive cADPR antagonist, 8-bromo-cADPR, had been developed and was made available to us. We used 8-bromo-cADPR to further explore our observation that S/ER calcium release via RyRs could mediate two opposing functions, namely pulmonary artery dilation and constriction, in a manner seemingly independent of IP3Rs or calcium influx pathways. Importantly, the work of others had shown that, unlike skeletal and cardiac muscles, smooth muscles might express all three RyR subtypes. If this were the case in our experimental system and cADPR played a role, then 8-bromo-cADPR would surely block one of the opposing RyR-dependent functions identified, or the other, but certainly not both. The latter seemingly implausible scenario was confirmed. How could this be, do cells hold multiple, segregated SR stores that incorporate different RyR subtypes in receipt of spatially segregated signals carried by cADPR? The pharmacological profile of 8-bromo-cADPR action supported not only this, but also indicated that intracellular calcium signals were delivered across intracellular junctions formed by the S/ER. Not just one, at least two. This article retraces the steps along this journey, from the curious pharmacological profile of 8-bromo-cADPR to the discovery of the cell-wide web, a diverse network of cytoplasmic nanocourses demarcated by S/ER nanojunctions, which direct site-specific calcium flux and may thus coordinate the full panoply of cellular processes.

NFATc3 regulation of collagen V expression contributes to cellular immunity to collagen type V and hypoxic pulmonary hypertension

Chronic hypoxia (CH)-induced pulmonary hypertension (PH) results, in part, from T helper-17 (T_H17) cell-mediated perivascular inflammation. However, the antigen(s) involved is unknown. Cellular immunity to collagen type V (col V) develops after ischemia-reperfusion injury during lung transplant and is mediated by naturally occurring (n)T_H17 cells. Col5a1 gene codifies for the α1-helix of col V, which is normally hidden from the immune system within type I collagen in the extracellular matrix. COL5A1 promoter analysis revealed nuclear factor of activated T cells, cytoplasmic 3 (NFATc3) binding sites. Therefore, we hypothesized that smooth muscle NFATc3 upregulates col V expression, leading to nT_H17 cell-mediated autoimmunity to col V in response to CH, representing an upstream mechanism in PH development. To test our hypothesis, we measured indexes of PH in inducible smooth muscle cell (SMC)-specific NFATc3 knockout (KO) mice exposed to either CH (380 mmHg) or normoxia and compared them with wild-type (WT) mice. KO mice did not develop PH. In addition, COL5A1 was one of the 1,792 genes differentially affected by both CH and SMC NFATc3 in isolated intrapulmonary arteries, which was confirmed by RT-PCR and immunostaining. Cellular immunity to col V was determined using a trans vivo delayed-type hypersensitivity assay (Tv-DTH). Tv-DTH response was evident only when splenocytes were used from control mice exposed to CH but not from KO mice, and mediated by nT_H17 cells. Our results suggest that SMC NFATc3 is important for CH-induced PH in adult mice, in part, by regulating the expression of the lung self-antigen COL5A1 protein contributing to col V-reactive nT_H17-mediated inflammation and hypertension.

hsa_circNFXL1_009 modulates apoptosis, proliferation, migration, and potassium channel activation in pulmonary hypertension

In this study, we explored the circular RNA (circRNA) profile in pulmonary arterial hypertension (PAH) patients caused by chronic obstructive pulmonary disease (COPD) and the effects of hsa_circNFXL1_009 on abnormal proliferation, apoptosis, and migration of human pulmonary arterial smooth muscle cells (hPASMCs) driven by hypoxia. Using microarrays, we screened the circRNA profile in whole-blood samples from three pairs of subjects and found 158 dysregulated circRNAs in patients with PAH-COPD. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis further validated that hsa_circNFXL1_009 was dramatically downregulated with the highest area under a receiver operating characteristic curve (ROC) in 21 pairs of subjects. Consistently, exposure to hypoxia markedly reduced the hsa_circNFXL1_009 level in cultured hPASMCs. Delivery of exogenous hsa_circNFXL1_009 attenuated hypoxia-induced proliferation, apoptotic resistance, and migration of hPASMCs, as evidenced by immunocytochemistry, 5-ethynyl-2′-deoxyuridine incorporation, wound healing, and a TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling) assay. A luciferase assay showed that hsa_circNFXL1_009 directly sponged hsa-miR-29b-2-5p (miR-29b) and positively regulated the expression of voltage-gated potassium (K⁺) channel subfamily B member 1 (KCNB1) at the mRNA level. Using patch-clamp electrophysiology, we proved that overexpression of hsa_circNFXL1_009 promoted a whole-cell K⁺ current in hPASMCs. Taken together, these studies identify hsa_circNFXL1_009 as a key regulator of PAH, and it may be used as a potential therapeutic target for the treatment of PAH.

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.

Celastrol Dilates and Counteracts Ethanol-Induced Constriction of Cerebral Arteries

The increasing recognition of the role played by cerebral artery dysfunction in brain disorders has fueled the search for new cerebrovascular dilators. Celastrol, a natural triterpene undergoing clinical trials for treating obesity, exerts neuroprotection, which was linked to its antioxidant/anti-inflammatory activities. We previously showed that celastrol fit pharmacophore criteria for activating calcium- and voltage-gated potassium channels of large conductance (BK channels) made of subunits cloned from cerebrovascular smooth muscle (SM). These recombinant BK channels expressed in a heterologous system were activated by celastrol. Activation of native SM BK channels is well known to evoke cerebral artery dilation. Current data demonstrate that celastrol (1-100 µM) dilates de-endothelialized, ex vivo pressurized middle cerebral arteries (MCAs) from rats, with EC₅₀ = 45 µM and maximal effective concentration (E_max)= 100 µM and with MCA diameter reaching a 10% increase over vehicle-containing, time-matched values (P < 0.05). A similar vasodilatory efficacy is achieved when celastrol is probed on MCA segments with intact endothelium. Selective BK blocking with 1 μM paxilline blunts celastrol vasodilation. Similar blunting is achieved with 0.8 mM 4-aminopirydine, which blocks voltage-gated K⁺ channels other than BK. Using an in vivo rat cranial window, we further demonstrate that intracarotid injections of 45 μM celastrol into pial arteries branching from MCA mimics celastrol ex vivo action. MCA constriction by ethanol concentrations reached in blood during moderate-heavy alcohol drinking (50 mM), which involves SM BK inhibition, is both prevented and reverted by celastrol. We conclude that celastrol could be an effective cerebrovascular dilator and antagonist of alcohol-induced cerebrovascular constriction, with its efficacy being uncompromised by conditions that disrupt endothelial and/or BK function. SIGNIFICANCE STATEMENT: Our study demonstrates for the first time that celastrol significantly dilates rat cerebral arteries both ex vivo and in vivo and both prevents and reverses ethanol-induced cerebral artery constriction. Celastrol actions are endothelium-independent but mediated through voltage-gated (K_V) and calcium- and voltage-gated potassium channel of large conductance (BK) K⁺ channels. This makes celastrol an appealing new agent to evoke cerebrovascular dilation under conditions in which endothelial and/or BK channel function are impaired.

Kv7 Channels in Lung Diseases

Lung diseases constitute a global health concern causing disability. According to WHO in 2016, respiratory diseases accounted for 24% of world population mortality, the second cause of death after cardiovascular diseases. The Kv7 channels family is a group of voltage-dependent K⁺ channels (Kv) encoded by KCNQ genes that are involved in various physiological functions in numerous cell types, especially, cardiac myocytes, smooth muscle cells, neurons, and epithelial cells. Kv7 channel α-subunits are regulated by KCNE1–5 ancillary β-subunits, which modulate several characteristics of Kv7 channels such as biophysical properties, cell-location, channel trafficking, and pharmacological sensitivity. Kv7 channels are mainly expressed in two large groups of lung tissues: pulmonary arteries (PAs) and bronchial tubes. In PA, Kv7 channels are expressed in pulmonary artery smooth muscle cells (PASMCs); while in the airway (trachea, bronchus, and bronchioles), Kv7 channels are expressed in airway smooth muscle cells (ASMCs), airway epithelial cells (AEPs), and vagal airway C-fibers (VACFs). The functional role of Kv7 channels may vary depending on the cell type. Several studies have demonstrated that the impairment of Kv7 channel has a strong impact on pulmonary physiology contributing to the pathophysiology of different respiratory diseases such as cystic fibrosis, asthma, chronic obstructive pulmonary disease, chronic coughing, lung cancer, and pulmonary hypertension. Kv7 channels are now recognized as playing relevant physiological roles in many tissues, which have encouraged the search for Kv7 channel modulators with potential therapeutic use in many diseases including those affecting the lung. Modulation of Kv7 channels has been proposed to provide beneficial effects in a number of lung conditions. Therefore, Kv7 channel openers/enhancers or drugs acting partly through these channels have been proposed as bronchodilators, expectorants, antitussives, chemotherapeutics and pulmonary vasodilators.

miR-125a-5p inhibits glycolysis by targeting hexokinase-II to improve pulmonary arterial hypertension

Purpose: The aim of this study was to investigate the effect of microRNAs on the proliferation of pulmonary arterial smooth muscle cells (PASMCs) as a result of targeting hexokinase-II (HK-II) and its mechanism of action.

Results: Differences in metabolic patterns were found between the normal group and monocrotaline-induced pulmonary arterial hypertension (MCT-PH) group. miR-125a-5p decreased glycolysis levels of monocrotaline (MCT)-induced PASMCs by targeting HK-II and inhibiting its proliferation. In vivo experiments found that miR-125a-5p agomir upregulated HK-II expression in the MCT-PH. Right ventricular hypertrophy was reversed and cardiac function improved as a result of decreased mean pulmonary artery pressure (mPAP).

Conclusion: In vitro and in vivo experiments both confirmed that miR-125a-5p could inhibit cell glycolysis and PASMC proliferation to improve PAH by targeting HK-II.

Methods: HK-II overexpression was constructed, and differentially expressed microRNAs were screened for using microarrays. Serum metabolites were detected using Nuclear Magnetic Resonance (NMR). Through screening for characteristic metabolites in rat body fluids and by analyzing biological functions, disordered metabolic pathways were identified. Activity of the miR-125a-5p target HK-II was measured using a luciferase reporter assay. Expression of downstream molecules was measured by RT–qPCR and/or western blot. Glucose consumption and lactic acid production were analyzed and used as a reflection of glycolysis.

Notch enhances Ca2+ entry by activating calcium-sensing receptors and inhibiting voltage-gated K+ channels

The increase in cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) and upregulation of calcium-sensing receptor (CaSR) and stromal interaction molecule 2 (STIM2) along with inhibition of voltage-gated K⁺ (K_V) channels in pulmonary arterial smooth muscle cells (PASMC) have been implicated in the development of pulmonary arterial hypertension; however, the precise upstream mechanisms remain elusive. Activation of CaSR, a G protein-coupled receptor (GPCR), results in Ca²⁺ release from the endoplasmic/sarcoplasmic reticulum (ER/SR) and Ca²⁺ influx through receptor-operated and store-operated Ca²⁺ channels (SOC). Upon Ca²⁺ depletion from the SR, STIM forms clusters to mediate store-operated Ca²⁺ entry. Activity of K_V channels, like KCNA5/K_V1.5 and KCNA2/K_V1.2, contributes to regulating membrane potential, and inhibition of K_V channels results in membrane depolarization that increases [Ca²⁺]_cyt by opening voltage-dependent Ca²⁺ channels. In this study, we show that activation of Notch by its ligand Jag-1 promotes the clustering of STIM2, and clustered STIM2 subsequently enhances the CaSR-induced Ca²⁺ influx through SOC channels. Extracellular Ca²⁺-mediated activation of CaSR increases [Ca²⁺]_cyt in CASR-transfected HEK293 cells. Treatment of CASR-transfected cells with Jag-1 further enhances CaSR-mediated increase in [Ca²⁺]_cyt. Moreover, CaSR-mediated increase in [Ca²⁺]_cyt was significantly augmented in cells co-transfected with CASR and STIM2. CaSR activation results in STIM2 clustering in CASR/STIM2-cotransfected cells. Notch activation also induces significant clustering of STIM2. Furthermore, activation of Notch attenuates whole cell K⁺ currents in KCNA5- and KCNA2-transfected cells. Together, these results suggest that Notch activation enhances CaSR-mediated increases in [Ca²⁺]_cyt by enhancing store-operated Ca²⁺ entry and inhibits KCNA5/K_V1.5 and KCNA2/K_V1.2, ultimately leading to voltage-activated Ca²⁺ entry.

Tacrine modulates Kv2.1 channel gene expression and cell proliferation

Purpose/Aim: Besides as a cholinesterase (ChE) inhibitor, tacrine is able to act on multiple targets such as nicotinic receptors (nAChRs) and voltage-gated K⁺ (Kv) channels. Kv2.1, a Kv channel subunit underlying delayed rectifier currents with slow kinetics of inactivation, is highly expressed in the mammalian brain, especially in the hippocampus. Nevertheless, limited data are available concerning the relationship between tacrine and Kv2.1 channels. In the present study, we explore the possible effects of tacrine on Kv2.1 channels in heterologous expression systems and N2A cells.Materials and methods: The change of expression and currents of Kv2.1 after treatment with tacrine was detected by PCR and whole-cell recordings, respectively. WST-8 experiments were performed to reveal the effects of tacrine on cell proliferation.Results: Incubation with tacrine induced a significant reduction of the mRNA level of Kv2.1 channels in HEK293 cells. The decline of corresponding currents carried by Kv2.1 was also observed. Moreover, the proliferation rates of HEK293 cells with Kv2.1 channel were substantially enhanced after treatment with this chemical for 24 h. Similar results were also detected after exposure to tacrine in N2A cells with native expression of Kv2.1 channels.Conclusion: These lines of evidence indicate that application of tacrine downregulates the expression of Kv2.1 channels and increase cell proliferation. The effect of tacrine on Kv2.1 channels may provide an alternative explanation for its neuroprotective action.

MicroRNA-mediated downregulation of K+ channels in pulmonary arterial hypertension

Downregulated expression of K+ channels and decreased K+ currents in pulmonary artery smooth muscle cells (PASMC) have been implicated in the development of sustained pulmonary vasoconstriction and vascular remodeling in patients with idiopathic pulmonary arterial hypertension (IPAH). However, it is unclear exactly how K+ channels are downregulated in IPAH-PASMC. MicroRNAs (miRNAs) are small non-coding RNAs that are capable of posttranscriptionally regulating gene expression by binding to the 3'-untranslated regions of their targeted mRNAs. Here, we report that specific miRNAs are responsible for the decreased K+ channel expression and function in IPAH-PASMC. We identified 3 miRNAs (miR-29b, miR-138, and miR-222) that were highly expressed in IPAH-PASMC in comparison to normal PASMC (>2.5-fold difference). Selectively upregulated miRNAs are correlated with the decreased expression and attenuated activity of K+ channels. Overexpression of miR-29b, miR-138, or miR-222 in normal PASMC significantly decreased whole cell K+ currents and downregulated voltage-gated K+ channel 1.5 (KV1.5/KCNA5) in normal PASMC. Inhibition of miR-29b in IPAH-PASMC completely recovered K+ channel function and KV1.5 expression, while miR-138 and miR-222 had a partial or no effect. Luciferase assays further revealed that KV1.5 is a direct target of miR-29b. Additionally, overexpression of miR-29b in normal PASMC decreased large-conductance Ca2+-activated K+ (BKCa) channel currents and downregulated BKCa channel β1 subunit (BKCaβ1 or KCNMB1) expression, while inhibition of miR-29b in IPAH-PASMC increased BKCa channel activity and BKCaβ1 levels. These data indicate upregulated miR-29b contributes at least partially to the attenuated function and expression of KV and BKCa channels in PASMC from patients with IPAH.

Beraprost Upregulates KV Channel Expression and Function via EP4 Receptor in Pulmonary Artery Smooth Muscle Cells Obtained from Rats with Hypoxia-Induced Pulmonary Hypertension

The reduced expression and function of voltage-dependent potassium (KV) channels have been involved in the pathogenesis of hypoxia-induced pulmonary hypertension (HPH), leading to pulmonary vasoconstriction and vascular remodeling, while the upregulation of KV channels is of therapeutic significance for pulmonary hypertension. Beraprost sodium (BPS) has been shown to be effective in patients with pulmonary hypertension. However, the effect of BPS on O2-sensitive KV channels in pulmonary artery smooth muscle cells (PASMCs) remains unclear. In the present study, the effect of BPS on rats with HPH was observed, and the influence of BPS on the expression and function of O2-sensitive KV channels in PASMCs was investigated. The results revealed that BPS reduced mean pulmonary artery pressure, suppressed right ventricular hypertrophy, and attenuated the remodeling of pulmonary arteries in rats exposed to discontinuous hypoxia for 4 weeks (8 h/day). This was accompanied with the significantly upregulated expression of KV channel α-subunits (KV1.2, KV1.5 and KV2.1) and O2-sensitive voltage-gated K+ (KV) channel current (IK(V)) in small pulmonary arteries in HPH model rats, as well as in hypoxia-induced PASMCs. Furthermore, in vitrostudies have revealed that the upregulation of BPS on O2-sensitive KV channels was significantly inhibited after treatment with prostaglandin E2 receptor subtype EP4 antagonist GW627368X. Taken together, these results suggest that BPS attenuates the development of HPH through the upregulation of O2-sensitive KV channels, which was probably via the EP4 receptor-related pathway.

Identification of Novel Therapeutic Targets for Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) are fatal diseases; however, their pathogenesis still remains to be elucidated. We have recently screened novel pathogenic molecules and have performed drug discovery targeting those molecules. Pulmonary artery smooth muscle cells (PASMCs) in patients with PAH (PAH-PASMCs) have high proliferative properties like cancer cells, which leads to thickening and narrowing of distal pulmonary arteries. Thus, we conducted a comprehensive analysis of PAH-PASMCs and lung tissues to search for novel pathogenic proteins. We validated the pathogenic role of the selected proteins by using tissue-specific knockout mice. To confirm its clinical significance, we used patient-derived blood samples to evaluate the potential as a biomarker for diagnosis and prognosis. Finally, we conducted a high throughput screening and found inhibitors for the pathogenic proteins.

Kv channels and vascular smooth muscle cell proliferation

Kv channels are present in virtually all VSMCs and strongly influence contractile responses. However, they are also instrumental in the proliferative, migratory, and secretory functions of synthetic, dedifferentiated VSMCs upon PM. In fact, Kv channels not only contribute to all these processes but also are active players in the phenotypic switch itself. This review is focused on the role(s) of Kv channels in VSMC proliferation, which is one of the best characterized functions of dedifferentiated VSMCs. VSMC proliferation is a complex process requiring specific Kv channels at specific time and locations. Their identification is further complicated by their large diversity and the differences in expression across vascular beds. Of interest, both conserved changes in some Kv channels and vascular bed-specific regulation of others seem to coexist and participate in VSMC proliferation through complementary mechanisms. Such a system will add flexibility to the process while providing the required robustness to preserve this fundamental cellular response.

Regulation of voltage-gated potassium channels in vascular smooth muscle during hypertension and metabolic disorders

Voltage-gated potassium (KV ) channels are key regulators of vascular smooth muscle contractility and vascular tone, and thus have major influence on the microcirculation. KV channels are important determinants of vascular smooth muscle membrane potential (Em ). A number of KV subunits are expressed in the plasma membrane of smooth muscle cells. Each subunit confers distinct kinetics and regulatory properties that allow for fine control of Em to orchestrate vascular tone. Modifications in KV subunit expression and/or channel activity can contribute to changes in vascular smooth muscle contractility in response to different stimuli and in diverse pathological conditions. Consistent with this, a number of studies suggest alterations in KV subunit expression and/or function as underlying contributing mechanisms for small resistance artery dysfunction in pathologies such as hypertension and metabolic disorders, including diabetes. Here, we review our current knowledge on the effects of these pathologies on KV channel expression and function in vascular smooth muscle cells, and the repercussions on (micro)vascular function.

The endothelium in hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) in combination with hypercapnic pulmonary vasoconstriction redistributes pulmonary blood flow from poorly aerated to better ventilated lung regions by an active process of local vasoconstriction. Impairment of HPV results in ventilation-perfusion mismatch and is commonly associated with various lung diseases including pneumonia, sepsis, or cystic fibrosis. Although several regulatory pathways have been identified, considerable knowledge gaps persist, and a unifying concept of the signaling pathways that underlie HPV and their impairment in lung diseases has not yet emerged. In the past, conceptual models of HPV have focused on pulmonary arterial smooth muscle cells (PASMC) acting as sensor and effector of hypoxia in the pulmonary vasculature. In contrast, the endothelium was considered a modulating bystander in this scenario. For an ideal design, however, the oxygen sensor in HPV should be located in the region of gas exchange, i.e., in the alveolar capillary network. This concept requires the retrograde propagation of the hypoxic signal along the endothelial layer of the vascular wall and subsequent contraction of PASMC in upstream arterioles that is elicited via temporospatially tightly controlled endothelial-smooth muscle cell crosstalk. The present review summarizes recent work that provides proof-of-principle for the existence and functional relevance of such signaling pathway in HPV that involves important roles for connexin 40, epoxyeicosatrienoic acids, sphingolipids, and cystic fibrosis transmembrane conductance regulator. Of translational relevance, implication of these molecules provides for novel mechanistic explanations for impaired ventilation/perfusion matching in patients with pneumonia, sepsis, cystic fibrosis, and presumably various other lung diseases.

Ion channels of the lung and their role in disease pathogenesis

Maintenance of normal epithelial ion and water transport in the lungs includes providing a thin layer of surface liquid that coats the conducting airways. This airway surface liquid is critical for normal lung function in a number of ways but, perhaps most importantly, is required for normal mucociliary clearance and bacterial removal. Preservation of the appropriate level of hydration, pH, and viscosity for the airway surface liquid requires the proper regulation and function of a battery of different types of ion channels and transporters. Here we discuss how alterations in ion channel/transporter function often lead to lung pathologies.

Hemodynamic and Pathologic Characterization of the TASK-1-/- Mouse Does Not Demonstrate Pulmonary Hypertension

Introduction

Pulmonary hypertension (PH) carries significant associated morbidity and mortality and the underlying molecular mechanisms of PH are not well understood. Loss-of-function mutations in TASK-1 potassium channels are associated with PH in humans. Although TASK-1 has been considered in the development of PH for over a decade, characterization of TASK-1 knockout mice has been limited to in vitro studies or in vivo studies in room air at isolated time points. The purpose of this study was twofold. First, we sought to determine if TASK^-/- male and female mice developed PH over the span of one year. Second, we sought to determine the effect of chronic hypoxia, a stimulus for PH, and its recovery on PH in TASK-1^-/- mice.

Methods

We measured right ventricular systolic pressure (RVSP) and vascular remodeling in male and female C57BL/6 WT and TASK-1^-/- mice at separate time points: 20-24 weeks and 1 year of age. Additionally, we measured RVSP and vascular remodeling in TASK-1^-/- and wild-type mice between 13 and 16 weeks of age exposed to 10% hypoxia for 3 weeks followed by recovery to room air conditions for an additional 6 weeks.

Results

RVSP was similar between WT and TASK^-/- mice. Male and female WT and TASK-1^-/- mice all demonstrated age-related increases in RVSP, which correlated to age-related vascular remodeling in male mice but not in female mice. Male TASK-1^-/- and WT mice exposed to chronic hypoxia demonstrated increased RVSP, which decreased following room air recovery. WT and TASK-1^-/- male mice demonstrated vascular remodeling upon exposure to hypoxia that persisted in room air recovery.

Conclusion

Female and male TASK-1^-/- mice do not develop hemodynamic or vascular evidence for PH, but RVSP rises in an age-dependent manner independent of genotype. TASK-1^-/- and WT male mice develop hypoxia-induced elevations in RVSP that decrease to baseline after recovery in room air. TASK-1^-/- and WT male mice demonstrate vascular remodeling after exposure to hypoxia that persists despite recovery to room air conditions and does not correlate with RVSP normalization.

Unique aspects of the developing lung circulation: structural development and regulation of vasomotor tone

This review summarizes our current knowledge on lung vasculogenesis and angiogenesis during normal lung development and the regulation of fetal and postnatal pulmonary vascular tone. In comparison to that of the adult, the pulmonary circulation of the fetus and newborn displays many unique characteristics. Moreover, altered development of pulmonary vasculature plays a more prominent role in compromised pulmonary vasoreactivity than in the adult. Clinically, a better understanding of the developmental changes in pulmonary vasculature and vasomotor tone and the mechanisms that are disrupted in disease states can lead to the development of new therapies for lung diseases characterized by impaired alveolar structure and pulmonary hypertension.

The role of nuclear factor of activated T cells in pulmonary arterial hypertension

Nuclear factor of activated T cells (NFAT) was first identified as a transcription factor about 3 decades ago and was not well studied until the development of immunosuppressant. Numerous studies confirm that calcineurin/NFAT signaling is very important in the development of vasculature and cardiovascular system during embryogenesis and is involved in the development of vascular diseases such as hypertension, atherosclerosis and restenosis. Recent studies demonstrated that NFAT proteins also regulate immune response and vascular cells in the pulmonary microenvironment. In this review, we will discuss how different NFAT isoforms contribute to pulmonary vascular remodeling and potential new therapeutic targets for treating pulmonary arterial hypertension.

The role of genetics in pulmonary arterial hypertension

Group 1 pulmonary hypertension or pulmonary arterial hypertension (PAH) is a rare disease characterized by proliferation and occlusion of small pulmonary arterioles, leading to progressive elevation of pulmonary artery pressure and pulmonary vascular resistance, and right ventricular failure. Historically, it has been associated with a high mortality rate, although, over the last decade, treatment has improved survival. PAH includes idiopathic PAH (IPAH), heritable PAH (HPAH), and PAH associated with certain medical conditions. The aetiology of PAH is heterogeneous, and genetics play an important role in some cases. Mutations in BMPR2, encoding bone morphogenetic protein receptor 2, a member of the transforming growth factor-β superfamily of receptors, have been identified in 70% of cases of HPAH, and in 10-40% of cases of IPAH. Other genetic causes of PAH include mutations in the genes encoding activin receptor-like type 1, endoglin, SMAD9, caveolin 1, and potassium two-pore-domain channel subfamily K member 3. Mutations in the gene encoding T-box 4 have been identified in 10-30% of paediatric PAH patients, but rarely in adults with PAH. PAH in children is much more heterogeneous than in adults, and can be associated with several genetic syndromes, congenital heart disease, pulmonary disease, and vascular disease. In addition to rare mutations as a monogenic cause of HPAH, common variants in the gene encoding cerebellin 2 increase the risk of PAH by approximately two-fold. A PAH panel of genes is available for clinical testing, and should be considered for use in clinical management, especially for patients with a family history of PAH. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The emerging role of AMPK in the regulation of breathing and oxygen supply

Regulation of breathing is critical to our capacity to accommodate deficits in oxygen availability and demand during, for example, sleep and ascent to altitude. It is generally accepted that a fall in arterial oxygen increases afferent discharge from the carotid bodies to the brainstem and thus delivers increased ventilatory drive, which restores oxygen supply and protects against hypoventilation and apnoea. However, the precise molecular mechanisms involved remain unclear. We recently identified as critical to this process the AMP-activated protein kinase (AMPK), which is key to the cell-autonomous regulation of metabolic homoeostasis. This observation is significant for many reasons, not least because recent studies suggest that the gene for the AMPK-α1 catalytic subunit has been subjected to natural selection in high-altitude populations. It would appear, therefore, that evolutionary pressures have led to AMPK being utilized to regulate oxygen delivery and thus energy supply to the body in the short, medium and longer term. Contrary to current consensus, however, our findings suggest that AMPK regulates ventilation at the level of the caudal brainstem, even when afferent input responses from the carotid body are normal. We therefore hypothesize that AMPK integrates local hypoxic stress at defined loci within the brainstem respiratory network with an index of peripheral hypoxic status, namely afferent chemosensory inputs. Allied to this, AMPK is critical to the control of hypoxic pulmonary vasoconstriction and thus ventilation-perfusion matching at the lungs and may also determine oxygen supply to the foetus by, for example, modulating utero-placental blood flow.

AMP-activated protein kinase inhibits Kv 1.5 channel currents of pulmonary arterial myocytes in response to hypoxia and inhibition of mitochondrial oxidative phosphorylation

KEY POINTS

Progression of hypoxic pulmonary hypertension is thought to be due, in part, to suppression of voltage-gated potassium channels (Kv ) in pulmonary arterial smooth muscle by hypoxia, although the precise molecular mechanisms have been unclear. AMP-activated protein kinase (AMPK) has been proposed to couple inhibition of mitochondrial metabolism by hypoxia to acute hypoxic pulmonary vasoconstriction and progression of pulmonary hypertension. Inhibition of complex I of the mitochondrial electron transport chain activated AMPK and inhibited Kv 1.5 channels in pulmonary arterial myocytes. AMPK activation by 5-aminoimidazole-4-carboxamide riboside, A769662 or C13 attenuated Kv 1.5 currents in pulmonary arterial myocytes, and this effect was non-additive with respect to Kv 1.5 inhibition by hypoxia and mitochondrial poisons. Recombinant AMPK phosphorylated recombinant human Kv 1.5 channels in cell-free assays, and inhibited K(+) currents when introduced into HEK 293 cells stably expressing Kv 1.5. These results suggest that AMPK is the primary mediator of reductions in Kv 1.5 channels following inhibition of mitochondrial oxidative phosphorylation during hypoxia and by mitochondrial poisons.

ABSTRACT

Progression of hypoxic pulmonary hypertension is thought to be due, in part, to suppression of voltage-gated potassium channels (Kv ) in pulmonary arterial smooth muscle cells that is mediated by the inhibition of mitochondrial oxidative phosphorylation. We sought to determine the role in this process of the AMP-activated protein kinase (AMPK), which is intimately coupled to mitochondrial function due to its activation by LKB1-dependent phosphorylation in response to increases in the cellular AMP:ATP and/or ADP:ATP ratios. Inhibition of complex I of the mitochondrial electron transport chain using phenformin activated AMPK and inhibited Kv currents in pulmonary arterial myocytes, consistent with previously reported effects of mitochondrial inhibitors. Myocyte Kv currents were also markedly inhibited upon AMPK activation by A769662, 5-aminoimidazole-4-carboxamide riboside and C13 and by intracellular dialysis from a patch-pipette of activated (thiophosphorylated) recombinant AMPK heterotrimers (α2β2γ1 or α1β1γ1). Hypoxia and inhibitors of mitochondrial oxidative phosphorylation reduced AMPK-sensitive K(+) currents, which were also blocked by the selective Kv 1.5 channel inhibitor diphenyl phosphine oxide-1 but unaffected by the presence of the BKCa channel blocker paxilline. Moreover, recombinant human Kv 1.5 channels were phosphorylated by AMPK in cell-free assays, and K(+) currents carried by Kv 1.5 stably expressed in HEK 293 cells were inhibited by intracellular dialysis of AMPK heterotrimers and by A769662, the effects of which were blocked by compound C. We conclude that AMPK mediates Kv channel inhibition by hypoxia in pulmonary arterial myocytes, at least in part, through phosphorylation of Kv 1.5 and/or an associated protein.

Iptakalim influences the proliferation and apoptosis of human pulmonary artery smooth muscle cells

The aim of the present study was to determine the effect of an ATP-sensitive K+ (KATP) channel opener iptakalim (IPT) on the proliferation and apoptosis of human pulmonary artery smooth muscle cells (HPASMCs), and examine the potential value of IPT to hypoxic pulmonary hyper-tension (HPH) at a cellular level. HPASMCs were divided into the control, ET-1, ET-1+IPT and ET-1+IPT+glibenclamide (GLI) groups. GLI was administered 30 min prior to ET-1 and IPT. The 4 groups were incubated with corresponding reagents for 24 h. Cell viability was evaluated using a CCK-8 assay, cell proliferation by 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay, and cell apoptosis via the expression of apoptosis-related proteins, i.e., Bcl-2-associated X protein (Bax) and B-cell lymphoma 2 (Bcl-2) using western blotting. We incubated HPASMCs with varying concentrations of ET-1 for 24, 48 and 72 h, and found that cell survival rate was increased in a dose-dependent manner (P<0.05) rather than in a time-dependent manner (P>0.05). After co-incubation of HPASMCs with varying concentrations of IPT and ET-1 for 24 h, the cell survival rate was decreased in a dose-dependent manner. The cell survival rate in the IPT+ET-1 group was significantly lower than that in the ET-1 group (P<0.05). The cell viability (P<0.05) and proliferation (P<0.05) in the ET-1 group were higher than those in the control group, and the expression of Bax/Bcl-2 was lower than the control group (P<0.05). The cell viability (P<0.05) and proliferation (P<0.05) in the ET-1+IPT group were lower than those in the ET-1 group, and the expression of Bax/Bcl-2 was higher than that in the ET-1 group (P<0.05). The cell viability (P<0.05) and proliferation (P<0.05) in the ET-1+IPT+GLI group were higher than those in the ET-1+IPT group, and the expression of Bax/Bcl-2 was lower than that in the ET-1+IPT group (P<0.05). In conclusion, IPT inhibited ET-1‑induced HPASMC proliferation and promoted cell apoptosis. Thus, it may play an important role in the treatment of HPH.

Targeted inhibition of survivin with YM155 promotes apoptosis of hypoxic human pulmonary arterial smooth muscle cells via the upregulation of voltage-dependent K⁺ channels

Hypoxic pulmonary hypertension (PH) is a common disease characterized by a disturbance to the balance of apoptosis and cell proliferation in pulmonary artery smooth muscle cells (PASMCs). The anti-apoptotic protein, survivin, has been observed to be upregulated in pulmonary arteries (PAs) of chronic hypoxia-induced PH rats. The present study aimed to investigate the therapeutic potential of sepantronium bromide (YM155), a selective survivin inhibitor, on hypoxic human PASMCs and examine the potential underlying mechanisms. Cultured human PASMCs (HPASMCs) were randomly divided into the following groups: i) Normoxia (N); ii) normoxia + 100 nmol/l YM155 (NY100); iii) hypoxia (H); iv) hypoxia + 1 nmol/l YM155 (HY1); v) hypoxia + 10 nmol/l YM155 (HY10); and hypoxia + 100 nmol/l YM155 (HY100) groups. The cells were exposed to the different conditions for 24 h, according to the group. Cell viability was then determined using a Cell Counting Kit-8 assay, and apoptosis was detected using a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling assay. The expression levels of survivin were determined using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), immunocytochemistry and Western blot analyses. The expression levels of the voltage-dependent K⁺ (K_v) channels, K_v1.5 and K_v2.1, were measured using RT-qPCR and Western blotting. Cell proliferation in the hypoxic PASMCs was significantly increased by hypoxia, however, apoptosis of the HPASMCs was suppressed, the expression of survivin were upregulated and the expression levels of K_v1.5 and K_v2.1 were downregulated. YM155 treatment ameliorated the hypoxia-induced increase in cell proliferation and expression of survivin in a concentration-dependent manner, increased apoptosis, and increased the expression levels of K_v1.5 and K_v2.1 (P<0.05). By contrast, YM155 treatment in normoxic HPASMCs had no significant effects on proliferation, apop-tosis, or the expression levels of survivin and K_v channels in the PASMCs. The present study is the first, to the best of our knowledge, to demonstrate that YM155, a selective survivin inhibitor, has a beneficial therapeutic effect on hypoxic HPASMCs, and that YM155 induces a pro-apoptotic effect by downregulating the apoptosis inhibitor, survivin, possibly through a K_v channel-mediated mechanism.

Recent advances in therapeutic strategies that focus on the regulation of ion channel expression

A number of different ion channel types are involved in cell signaling networks, and homeostatic regulatory mechanisms contribute to the control of ion channel expression. Profiling of global gene expression using microarray technology has recently provided novel insights into the molecular mechanisms underlying the homeostatic and pathological control of ion channel expression. It has demonstrated that the dysregulation of ion channel expression is associated with the pathogenesis of neural, cardiovascular, and immune diseases as well as cancers. In addition to the transcriptional, translational, and post-translational regulation of ion channels, potentially important evidence on the mechanisms controlling ion channel expression has recently been accumulated. The regulation of alternative pre-mRNA splicing is therefore a novel therapeutic strategy for the treatment of dominant-negative splicing disorders. Epigenetic modification plays a key role in various pathological conditions through the regulation of pluripotency genes. Inhibitors of pre-mRNA splicing and histone deacetyalase/methyltransferase have potential as potent therapeutic drugs for cancers and autoimmune and inflammatory diseases. Moreover, membrane-anchoring proteins, lysosomal and proteasomal degradation-related molecules, auxiliary subunits, and pharmacological agents alter the protein folding, membrane trafficking, and post-translational modifications of ion channels, and are linked to expression-defect channelopathies. In this review, we focused on recent insights into the transcriptional, spliceosomal, epigenetic, and proteasomal regulation of ion channel expression: Ca(2+) channels (TRPC/TRPV/TRPM/TRPA/Orai), K(+) channels (voltage-gated, KV/Ca(2+)-activated, KCa/two-pore domain, K2P/inward-rectifier, Kir), and Ca(2+)-activated Cl(-) channels (TMEM16A/TMEM16B). Furthermore, this review highlights expression of these ion channels in expression-defect channelopathies.

O2 sensing, mitochondria and ROS signaling: The fog is lifting

Mitochondria are responsible for the majority of oxygen consumption in cells, and thus represent a conceptually appealing site for cellular oxygen sensing. Over the past 40 years, a number of mechanisms to explain how mitochondria participate in oxygen sensing have been proposed. However, no consensus has been reached regarding how mitochondria could regulate transcriptional and post-translational responses to hypoxia. Nevertheless, a growing body of data continues to implicate a role for increased reactive oxygen species (ROS) signals from the electron transport chain (ETC) in triggering responses to hypoxia in diverse cell types. The present article reviews our progress in understanding this field and considers recent advances that provide new insight, helping to lift the fog from this complex topic.

Vascular Dysfunction in Pneumocystis-Associated Pulmonary Hypertension Is Related to Endothelin Response and Adrenomedullin Concentration

Pulmonary hypertension subsequent to an infectious disease can be due to vascular structural remodeling or to functional alterations within various vascular cell types. In our previous mouse model of Pneumocystis-associated pulmonary hypertension, we found that vascular remodeling was not responsible for observed increases in right ventricular pressures. Here, we report that the vascular dysfunction we observed could be explained by an enhanced response to endothelin-1 (20% greater reduction in lumen diameter, P ≤ 0.05), corresponding to an up-regulation of similar magnitude (P ≤ 0.05) of the endothelin A receptor in the lung tissue. This effect was potentially augmented by a decrease in production of the pulmonary vasodilator adrenomedullin of almost 70% (P ≤ 0.05). These changes did not occur in interferon-γ knockout mice similarly treated, which do not develop pulmonary hypertension under these circumstances. Surprisingly, we did not observe any relevant changes in the vascular endothelial nitric oxide synthase vasodilatory response, which is a common potential site of inflammatory alterations to pulmonary vascular function. Our results indicate the diverse mechanisms by which inflammatory responses to prior infections can cause functionally relevant changes in vascular responses in the lung, promoting the development of pulmonary hypertension.

A mitochondrial redox oxygen sensor in the pulmonary vasculature and ductus arteriosus

The mammalian homeostatic oxygen sensing system (HOSS) initiates changes in vascular tone, respiration, and neurosecretion that optimize oxygen uptake and tissue oxygen delivery within seconds of detecting altered environmental or arterial PO2. The HOSS includes carotid body type 1 cells, adrenomedullary cells, neuroepithelial bodies, and smooth muscle cells (SMCs) in pulmonary arteries (PAs), ductus arteriosus (DA), and fetoplacental arteries. Hypoxic pulmonary vasoconstriction (HPV) optimizes ventilation-perfusion matching. In utero, HPV diverts placentally oxygenated blood from the non-ventilated lung through the DA. At birth, increased alveolar and arterial oxygen tension dilates the pulmonary vasculature and constricts the DA, respectively, thereby transitioning the newborn to an air-breathing organism. Though modulated by endothelial-derived relaxing and constricting factors, O2 sensing is intrinsic to PASMCs and DASMCs. Within the SMC's dynamic mitochondrial network, changes in PO2 alter the reduction-oxidation state of redox couples (NAD(+)/NADH, NADP(+)/NADPH) and the production of reactive oxygen species, ROS (e.g., H2O2), by complexes I and III of the electron transport chain (ETC). ROS and redox couples regulate ion channels, transporters, and enzymes, changing intracellular calcium [Ca(2+)]i and calcium sensitivity and eliciting homeostatic responses to hypoxia. In PASMCs, hypoxia inhibits ROS production and reduces redox couples, thereby inhibiting O2-sensitive voltage-gated potassium (Kv) channels, depolarizing the plasma membrane, activating voltage-gated calcium channels (CaL), increasing [Ca(2+)]i, and causing vasoconstriction. In DASMCs, elevated PO2 causes mitochondrial fission, increasing ETC complex I activity and ROS production. The DASMC's downstream response to elevated PO2 (Kv channel inhibition, CaL activation, increased [Ca(2+)]i, and rho kinase activation) is similar to the PASMC's hypoxic response. Impaired O2 sensing contributes to human diseases, including pulmonary arterial hypertension and patent DA.