Ion channels and transporters as therapeutic targets in the pulmonary circulation

The TREK-1 potassium channel is a potential pharmacological target for vasorelaxation in pulmonary hypertension

BACKGROUND AND PURPOSE

Pulmonary arterial hypertension (PAH) is a progressive disease in which chronic membrane potential (Em) depolarisation of the pulmonary arterial smooth muscle cells (PASMCs) causes calcium overload, a key pathological alteration. Under resting conditions, the negative Em is mainly set by two pore domain potassium (K2P) channels, of which the TASK-1 has been extensively investigated.

EXPERIMENTAL APPROACH

Ion channel currents and membrane potential of primary cultured human(h) PASMCs were measured using the voltage- and current clamp methods. Intracellular [Ca2+] was monitored using fluorescent microscopy. Pulmonary BP and vascular tone measurements were also performed ex vivo using a rat PAH model.

KEY RESULTS

TREK-1 was the most abundantly expressed K2P in hPASMCs of healthy donors and idiopathic(I) PAH patients. Background K+-current was similar in hPASMCs for both groups and significantly enhanced by the TREK activator ML-335. In donor hPASMCs, siRNA silencing or pharmacological inhibition of TREK-1 caused depolarisation, reminiscent of the electrophysiological phenotype of idiopathic PAH. ML-335 hyperpolarised donor hPASMCs and normalised the Em of IPAH hPASMCs. A close link was found between TREK-1 activity and intracellular Ca2+-signalling using a channel activator, ML-335, and an inhibitor, spadin. In the rat, ML-335 relaxed isolated pre-constricted pulmonary arteries and significantly decreased pulmonary arterial pressure in the isolated perfused lung.

CONCLUSIONS AND IMPLICATIONS

These data suggest that TREK-1is a key factor in Em setting and Ca2+ homeostasis of hPASMC, and therefore, essential for maintenance of a low resting pulmonary vascular tone. Thus TREK-1 may represent a new therapeutic target for PAH.

Up-regulated expression of two-pore domain K+ channels, KCNK1 and KCNK2, is involved in the proliferation and migration of pulmonary arterial smooth muscle cells in pulmonary arterial hypertension

Background

Pulmonary arterial hypertension (PAH) is a severe and rare disease in the cardiopulmonary system. Its pathogenesis involves vascular remodeling of the pulmonary artery, which results in progressive increases in pulmonary arterial pressure. Chronically increased pulmonary arterial pressure causes right ventricular hypertrophy and subsequent right heart failure. Pulmonary vascular remodeling is attributed to the excessive proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs), which are induced by enhanced Ca2+ signaling following the up-/down-regulation of ion channel expression.

Objectives

In the present study, the functional expression of two-pore domain potassium KCNK channels was investigated in PASMCs from idiopathic PAH (IPAH) patients and experimental pulmonary hypertensive (PH) animals.

Results

In IPAH-PASMCs, the expression of KCNK1/TWIK1 and KCNK2/TREK1 channels was up-regulated, whereas that of KCNK3/TASK1 and KCNK6/TWIK2 channels was down-regulated. The similar up-regulated expression of KCNK1 and KCNK2 channels was observed in the pulmonary arterial smooth muscles of monocrotaline-induced PH rats, Sugen 5416/hypoxia-induced PH rats, and hypoxia-induced PH mice. The facilitated proliferation of IPAH-PASMCs was suppressed by the KCNK channel blockers, quinine and tetrapentylammonium. The migration of IPAH-PASMCs was also suppressed by these channel blockers. Furthermore, increases in the proliferation and migration were inhibited by the siRNA knockdown of KCNK1 or KCNK2 channels. The siRNA knockdown also caused membrane depolarization and subsequent decrease in cytosolic [Ca2+]. The phosphorylated level of c-Jun N-terminal kinase (JNK) was elevated in IPAH-PASMCs compared to normal-PASMCs. The increased phosphorylation was significantly reduced by the siRNA knockdown of KCNK1 or KCNK2 channels.

Conclusion

Collectively, these findings indicate that the up-regulated expression of KCNK1 and KCNK2 channels facilitates the proliferation and migration of PASMCs via enhanced Ca2+ signaling and JNK signaling pathway, which is associated with vascular remodeling in PAH.

GPR146 regulates pulmonary vascular remodeling by promoting pulmonary artery smooth muscle cell proliferation through 5-lipoxygenase

The pathological feature of hypoxic pulmonary hypertension (PH) is pulmonary vascular remodeling (PVR), primarily attributed to the hyperproliferation and apoptosis resistance of pulmonary artery smooth muscle cells (PASMCs). Existing PH-targeted drugs have difficulties in reversing PVR. Therefore, it is vital to discover a new regulatory mechanism for PVR and develop new targeted drugs. G protein-coupled receptor 146 (GPR146) is believed to participate in this process. This study aimed to investigate the role of GPR146 in PASMCs during PH. We investigated the role of GPR146 in PVR and its underlying mechanism using hypoxic PASMCs and mouse model (Sugen 5416 (20 mg/kg)/hypoxia). In our recent study, we have observed a significant increase in the expression of GPR146 protein in animal models of PH as well as in patients diagnosed with pulmonary arterial hypertension (PAH). Through immunohistochemistry, we found that GPR146 was mainly localized in the smooth muscle and endothelial layers of the pulmonary vasculature. GPR146 deficiency induction exhibited protective effects against hypoxia-induced elevation of right ventricular systolic blood pressure (RVSP), right ventricular hypertrophy, and pulmonary vascular remodeling in mice. In particular, the deletion of GPR146 attenuated the hypoxia-triggered proliferation of PASMCs. Furthermore, 5-lipoxygenase (5-LO) was related to PH development. Hypoxia and overexpression of GPR146 increased 5-LO expression, which was reversed through GPR146 knockdown or siRNA intervention. Our study discovered that GPR146 exhibited high expression in the pulmonary vessels of pulmonary hypertension. Subsequent research revealed that GPR146 played a crucial role in the development of hypoxic PH by promoting lipid peroxidation and 5-LO expression. In conclusion, GPR146 may regulate pulmonary vascular remodeling by promoting PASMCs proliferation through 5-LO, which presents a feasible target for PH prevention and treatment.

Pimaric acid reduces vasoconstriction via BKCa channel activation and VDCC inhibition in rat pulmonary arterial smooth muscles

Pulmonary vessels play a pivotal role in oxygen circulation. We previously demonstrated that pimaric acid (PiMA) activated large-conductance Ca2+-activated K+ (BKCa) channels and inhibited voltage-dependent Ca2+ channels (VDCCs). In the present study, PiMA attenuated vasoconstriction induced by high K+ or endothelin-1 in rat pulmonary arterial smooth muscles (PASMs). PiMA also reduced high K+-induced cytosolic [Ca2+] increase in PASM cells. PiMA increased BKCa currents and decreased VDCC currents. BKCa channels and VDCCs were formed by the α/β1 and α1C/α1D/β2/β3 subunits, respectively. These results indicate that PiMA induces vasorelaxation through the dual effects of BKCa channel activation and VDCC inhibition in PASMs.

Corosolic acid ameliorates vascular remodeling in pulmonary arterial hypertension via the downregulation of STAT3 signaling

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease that is characterized by vascular remodeling of the pulmonary artery. PAH remodeling is primarily caused by the excessive proliferation of pulmonary arterial smooth muscle cells (PASMCs). Therefore, an inhibitory mechanism is expected as a target for the treatment of PAH. Corosolic acid (CRA) is a pentacyclic triterpenoid extracted from the leaves of Banaba (Lagerstroemia speciosa) that exerts anti-diabetic, anti-inflammatory, and anti-tumor effects. In the present study, the effects of CRA on PAH remodeling were examined using PASMCs from idiopathic pulmonary arterial hypertension (IPAH) patients and monocrotaline (MCT)-induced pulmonary hypertensive (PH) rats. CRA inhibited the excessive proliferation of IPAH-PASMCs in a concentration-dependent manner (IC₅₀ = 14.1 μM). It also reduced the migration of IPAH-PASMCs. The CRA treatment downregulated the expression of signal transducer and activator of transcription 3 (STAT3) in IPAH-PASMCs. In MCT-PH rats, the administration of CRA (1 mg/kg/day) attenuated increases in right ventricular systolic pressure, pulmonary vascular remodeling, and right ventricular hypertrophy. CRA also decreased the expression of STAT3 in pulmonary arterial smooth muscles from MCT-PH rats. In conclusion, the anti-proliferative and anti-migratory effects of CRA in PASMCs ameliorated PAH remodeling by downregulating STAT3 signaling pathways.

Upregulated ClC3 channels/transporters elicit swelling-activated Cl- currents and induce excessive cell proliferation in idiopathic pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by vascular remodeling of the pulmonary artery, which is mainly attributed to the excessive proliferation of pulmonary arterial smooth muscle cells (PASMCs) comprising the medial layer of pulmonary arteries. The activity of ion channels associated with cytosolic Ca²⁺ signaling regulates the pathogenesis of PAH. Limited information is currently available on the role of Cl^- channels in PASMCs. Therefore, the functional expression of ClC3 channels/transporters was herein investigated in the PASMCs of normal subjects and patients with idiopathic pulmonary arterial hypertension (IPAH). Expression analyses revealed the upregulated expression of ClC3 channels/transporters at the mRNA and protein levels in IPAH-PASMCs. Hypoosmotic perfusion (230 mOsm) evoked swelling-activated Cl^- currents (I_Cl-swell) in normal-PASMCs, whereas 100 μM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) exerted the opposite effects. The siRNA knockdown of ClC3 did not affect I_Cl-swell. On the other hand, I_Cl-swell was larger in IPAH-PASMCs and inhibited by DIDS and the siRNA knockdown of ClC3. IPAH-PASMCs grew more than normal-PASMCs. The growth of IPAH-PASMCs was suppressed by niflumic acid and DIDS, but not by 9-anthracenecarboxylic acid or T16A_inh-A01. The siRNA knockdown of ClC3 also inhibited the proliferation of IPAH-PASMCs. Collectively, the present results indicate that upregulated ClC3 channels/transporters are involved in I_Cl-swell and the excessive proliferation of IPAH-PASMCs, thereby contributing to the pathogenesis of PAH. Therefore, ClC3 channels/transporters have potential as a target of therapeutic drugs for the treatment of PAH.

Potassium Channels in the Transition from Fetal to the Neonatal Pulmonary Circulation

The transition from the fetal to the neonatal circulation includes dilatation of the pulmonary arteries (PA) and closure of the Ductus Arteriosus Botalli (DAB). The resting membrane potential and various potassium channel activities in smooth muscle cells (SMC) from fetal and neonatal PA and DAB obtained from the same species has not been systematically analyzed. The key issue addressed in this paper is how the resting membrane potential and the whole-cell potassium current (IK) change when PASMC or DABSMC are transitioned from hypoxia, reflecting the fetal state, to normoxia, reflecting the post-partal state. Patch-clamp measurements were employed to characterize whole-cell K⁺ channel activity in fetal and post-partal (newborn) PASMC and DABSMC. The main finding of this paper is that the SMC from both tissues use a similar set of K⁺ channels (voltage-dependent (Kv), calcium-sensitive (KCa), TASK-1 and probably also TASK-2 channels); however, their activity level depends on the cell type and the oxygen level. Furthermore, we provide the first evidence for pH-sensitive non-inactivating K⁺ current in newborn DABSMC and PASMC, suggesting physiologically relevant TASK-1 and TASK-2 channel activity, the latter particularly in the Ductus Arteriosus Botalli.

SKF96365 activates calcium-sensing receptors in pulmonary arterial smooth muscle cells

In pulmonary arterial smooth muscle cells (PASMCs), an increase in the cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) is involved in many physiological processes such as cell contraction and proliferation. However, chronic [Ca²⁺]_cyt increases cause pulmonary vasoconstriction and vascular remodeling, resulting in pulmonary arterial hypertension (PAH). Therefore, [Ca²⁺]_cyt signaling plays a substantial role in the regulation of physiological and pathological functions in PASMCs. In the present study, the effects of SKF96365 on [Ca²⁺]_cyt were examined in PASMCs from normal subjects and idiopathic pulmonary arterial hypertension (IPAH) patients. SKF96365 is widely used as a blocker of non-selective cation channels. SKF96365 did not affect the resting [Ca²⁺]_cyt in normal-PASMCs. However, SKF96365 increased [Ca²⁺]_cyt in IPAH-PASMCs in a concentration-dependent manner (EC₅₀ = 18 μM). The expression of Ca²⁺-sensing receptors (CaSRs) was higher in IPAH-PASMCs than in normal-PASMCs. The SKF96365-induced [Ca²⁺]_cyt increase was inhibited by CaSR antagonists, NPS2143 and Calhex 231. The CaSR-mediated [Ca²⁺]_cyt increase was facilitated by SKF96365 and the activation was blocked by NPS2143 or Calhex 231. In addition, the SKF96365-induced [Ca²⁺]_cyt increase was reduced by siRNA knockdown of CaSRs. Taken together, SKF96365 activates CaSRs in IPAH-PASMCs and promotes [Ca²⁺]_cyt signaling.

Revisiting the Large-Conductance Calcium-Activated Potassium (BKCa) Channels in the Pulmonary Circulation

Potassium ion concentrations, controlled by ion pumps and potassium channels, predominantly govern a cell's membrane potential and the tone in the vessels. Calcium-activated potassium channels respond to two different stimuli-changes in voltage and/or changes in intracellular free calcium. Large conductance calcium-activated potassium (BKCa) channels assemble from pore forming and various modulatory and auxiliary subunits. They are of vital significance due to their very high unitary conductance and hence their ability to rapidly cause extreme changes in the membrane potential. The pathophysiology of lung diseases in general and pulmonary hypertension, in particular, show the implication of either decreased expression and partial inactivation of BKCa channel and its subunits or mutations in the genes encoding different subunits of the channel. Signaling molecules, circulating humoral molecules, vasorelaxant agents, etc., have an influence on the open probability of the channel in pulmonary arterial vascular cells. BKCa channel is a possible therapeutic target, aimed to cause vasodilation in constricted or chronically stiffened vessels, as shown in various animal models. This review is a comprehensive collation of studies on BKCa channels in the pulmonary circulation under hypoxia (hypoxic pulmonary vasoconstriction; HPV), lung pathology, and fetal to neonatal transition, emphasising pharmacological interventions as viable therapeutic options.

3'-Oxo-tabernaelegantine A (OTNA) selectively relaxes pulmonary arteries by inhibiting AhR

BACKGROUND

Pulmonary arterial hypertension (PAH), characterized by pulmonary artery constriction and vascular remodeling, has a high mortality rate. New drugs for the treatment of PAH urgently need to be developed.

PURPOSE

This study was designed to investigate the vasorelaxant activity of OTNA in isolated pulmonary arteries, and explore its molecular mechanism.

METHODS

Pulmonary arteries and thoracic aortas were isolated from mice, and vascular tone was tested with a Wire Myograph System. Nitric oxide levels were determined with DAF-FM DA and DAX-J2™ Red. Cellular thermal shift assays, microscale thermophoresis, and molecular docking were used to identify the interaction between OTNA and aryl hydrocarbon receptor (AhR). The levels of PI3K, p-PI3K, Akt, p-Akt, eNOS, p-eNOS, and AhR were analyzed by Western blotting.

RESULTS

OTNA selectively relaxed the isolated pulmonary artery rings in an endothelium-dependent manner. Mechanistic study showed that OTNA induced NO production through activation of the PI3K/Akt/eNOS pathway in endothelial cells. Furthermore, we also found that OTNA directly bound to AhR and activated the PI3K/Akt/eNOS pathway to dilate pulmonary arteries by inhibiting AhR.

CONCLUSIONS

OTNA relaxes pulmonary arteries by antagonizing AhR. This study provides a new natural antagonist of AhR as a promising lead compound for PAH treatment.

PDGF/MEK/ERK axis represses Ca2+ clearance via decreasing the abundance of plasma membrane Ca2+ pump PMCA4 in pulmonary arterial smooth muscle cells

Pulmonary arterial hypertension (PAH) is a rare and lethal disease characterized by vascular remodeling and vasoconstriction, which is associated with increased intracellular calcium ion concentration ([Ca2+]i). Platelet-derived growth factor-BB (PDGF-BB) is the most potent mitogen for pulmonary arterial smooth muscle cells (PASMCs) and is involved in vascular remodeling during PAH development. PDGF signaling has been proved to participate in maintaining Ca2+ homeostasis of PASMCs; however, the mechanism needs to be further elucidated. Here, we illuminate that the expression of plasma membrane calcium-transporting ATPase 4 (PMCA4) was downregulated in PASMCs after PDGF-BB stimulation, which could be abolished by restraining the mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK/ERK). Functionally, suppression of PMCA4 attenuated the [Ca2+]i clearance in PASMCs after Ca2+ entry, promoting cell proliferation and elevating cell locomotion through mediating formation of focal adhesion. Additionally, the expression of PMCA4 was decreased in the pulmonary artery of monocrotaline (MCT)- or hypoxia-induced PAH rats. Moreover, knockdown of PMCA4 could increase the right ventricular systolic pressure (RVSP) and wall thickness (WT) of pulmonary artery in rats raised under normal conditions. Taken together, our findings demonstrate the importance of the PDGF/MEK/ERK/PMCA4 axis in intracellular Ca2+ homeostasis in PASMCs, indicating a functional role of PMCA4 in pulmonary arterial remodeling and PAH development.

Transmembrane protein 16A/anoctamin 1 inhibitor T16A inh ‐A01 reversed monocrotaline‐induced rat pulmonary arterial hypertension

Transmembrane protein 16A was involved in the development of the monocrotaline-induced pulmonary arterial hypertension model through ERK1/2 activation, and it was considered as potential target for pulmonary arterial hypertension treatment. A pulmonary arterial hypertension rat model was established by intraperitoneal administration of monocrotaline. Noninvasive pulsed-wave Doppler and histological analysis was performed, and it revealed proliferation and remodeling of pulmonary arterioles and right ventricle hypertrophy. In addition, transmembrane protein 16A, proliferating cell nuclear antigen—a proliferate marker, P-ERK1/2 increased following monocrotaline treatment. Expression of transmembrane protein 16A in the pulmonary arteries was co-localized with a specific marker of vascular smooth muscle α-actin. Then, a specific inhibitor of transmembrane protein 16A-T16A_inh-A01 was administered to pulmonary arterial hypertension rats. It was found to alleviate the remodeling of pulmonary arterioles and right ventricle hypertrophy significantly, and decrease the upregulation of proliferating cell nuclear antigen in monocrotaline-induced pulmonary arteries. In addition, T16A_inh-A01 could inhibit the activation of ERK1/2 in pulmonary arterial hypertension model. Transmembrane protein 16A mediated the proliferation and remodeling of pulmonary arterioles in the monocrotaline-induced pulmonary arterial hypertension model. ERK1/2 pathway is one of downstream factors. Long-term use of T16A_inh-A01 in vivo could alleviate remodeling and pressure in pulmonary arterial hypertension.

[Pathophysiological roles of TRPC6 channels in pulmonary arterial hypertension]

Pulmonary arterial hypertension (PAH) is a progressive and lethal disease of the pulmonary artery. The pathogenesis of PAH is mainly sustained vasoconstriction and vascular remodeling of the pulmonary artery. These pathogeneses cause progressive elevations in pulmonary vascular resistance and pulmonary arterial pressure in PAH patients. Elevated pulmonary arterial pressure leads to right heart failure and finally death. The vascular remodeling is caused by the enhanced proliferation and reduced apoptosis of pulmonary arterial smooth muscle cells (PASMCs). Excitable abnormality in the pulmonary artery of PAH patients is mostly mediated by an elevated cytosolic Ca²⁺ concentration. PASMCs express several Ca²⁺-permeable channels including voltage-dependent Ca²⁺ channels, store-operated Ca²⁺ (SOC) channels, and receptor-operated Ca²⁺ (ROC) channels. The activation and upregulation of these Ca²⁺ channels have been reported in PASMCs from PAH patients. Here, we analyzed pathophysiological functions of enhanced Ca²⁺ signaling mediated by SOC and ROC channels using PASMCs from idiopathic PAH patients and animal PAH models. Notch signal enhanced transient receptor potential canonical 6 (TRPC6) "SOC" channels via direct (non-genomic and stimulatory) and indirect (genomic and upregulating) effects in PAH. On the other hand, the activation of Ca²⁺-sensing receptors evoked Ca²⁺ influx through TRPC6 "ROC" channels in PAH. In addition, TRPC6 channel blocker and TRPC6 gene deletion inhibited the development of PAH. Specifically, TRPC6 channels potentially form both ROC and SOC channels in PASMCs, which are involved in the pathophysiological events in PAH. Therefore, targeting TRPC6 channels in PASMCs may help develop novel therapeutic approach for PAH.

Determinants of Ion-Transporter Cancer Cell Death

Recently, we showed that synthetic anion transporters DSC4P-1 and SA-3 had activity related to cancer cell death. They were found to increase intracellular chloride and sodium ion concentrations. They were also found to induce apoptosis (DSC4P-1) and both induce apoptosis and inhibit autophagy (SA-3). However, determinants underlying these phenomenological findings were not elucidated. The absence of mechanistic understanding has limited the development of yet-improved systems. Here, we show that three synthetic anion transporters, DSC4P-1, SA-3, and 8FC4P, induce osmotic stress in cells by increasing intracellular ion concentrations. This triggers the generation of reactive oxygen species via a sequential process and promotes caspase-dependent apoptosis. In addition, two of the transporters, SA-3 and 8FC4P, induce autophagy by increasing the cytosolic calcium ion concentration promoted by osmotic stress. However, they eventually inhibit the autophagy process as a result of their ability to disrupt lysosome function through a transporter-mediated decrease in a lysosomal chloride ion concentration and an increase in the lysosomal pH.

Platelet-derived growth factor up-regulates Ca2+-sensing receptors in idiopathic pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease associated with remodeling of the pulmonary artery. We previously reported that the Ca²⁺-sensing receptor (CaSR) is up-regulated in pulmonary arterial smooth muscle cells (PASMCs) from patients with idiopathic PAH (IPAH) and contributes to enhanced Ca²⁺ responses and excessive cell proliferation. However, the mechanisms underlying the up-regulation of CaSR have not yet been elucidated. We herein examined involvement of platelet-derived growth factor (PDGF) on CaSR expression, Ca²⁺ responses, and proliferation in PASMCs. The expression of PDGF receptors was higher in PASMCs from patients with IPAH than in PASMCs from normal subjects. In addition, PDGF-induced activation of PDGF receptors and their downstream molecules [ERK1/2, p38, protein kinase B, and signal transducer and activator of transcription (STAT) 1/3] were sustained longer in PASMCs from patients with IPAH. The PDGF-induced CaSR up-regulation was attenuated by small interfering RNA knockdown of PDGF receptors and STAT1/3, and by the treatment with imatinib. In monocrotaline-induced pulmonary hypertensive rats, the up-regulation of CaSR was reduced by imatinib. The combination of NPS2143 and imatinib additively inhibited the development of pulmonary hypertension. These results suggest that enhanced PDGF signaling is involved in CaSR up-regulation, leading to excessive PASMC proliferation and vascular remodeling in patients with IPAH. The linkage between CaSR and PDGF signals is a novel pathophysiological mechanism contributing to the development of PAH.-Yamamura, A., Nayeem, M. J., Al Mamun, A., Takahashi, R., Hayashi, H., Sato, M. Platelet-derived growth factor up-regulates Ca²⁺-sensing receptors in idiopathic pulmonary arterial hypertension.

Pathobiology, pathology and genetics of pulmonary hypertension: Update from the Cologne Consensus Conference 2018

The European guidelines, which focus on clinical aspects of pulmonary hypertension (PH), provide only minimal information about the pathophysiological concepts of PH. Here, we review this topic in greater detail, focusing on specific aspects in the pathobiology, pathology and genetics, which include mechanisms of vascular inflammation, the role of transcription factors, ion channels/ion channel diseases, hypoxic pulmonary vasoconstriction, genetics/epigenetics, metabolic dysfunction, and the potential future role of histopathology of PH in the modern era of PH therapy. In addition to new insights in the pathobiology of this disease, this working group of the Cologne Consensus Conference also highlights novel concepts and potential new therapeutic targets to further improve the treatment options in PAH.

Rare variants in SOX17 are associated with pulmonary arterial hypertension with congenital heart disease

BACKGROUND

Pulmonary arterial hypertension (PAH) is a rare disease characterized by distinctive changes in pulmonary arterioles that lead to progressive pulmonary arterial pressures, right-sided heart failure, and a high mortality rate. Up to 30% of adult and 75% of pediatric PAH cases are associated with congenital heart disease (PAH-CHD), and the underlying etiology is largely unknown. There are no known major risk genes for PAH-CHD.

METHODS

To identify novel genetic causes of PAH-CHD, we performed whole exome sequencing in 256 PAH-CHD patients. We performed a case-control gene-based association test of rare deleterious variants using 7509 gnomAD whole genome sequencing population controls. We then screened a separate cohort of 413 idiopathic and familial PAH patients without CHD for rare deleterious variants in the top association gene.

RESULTS

We identified SOX17 as a novel candidate risk gene (p = 5.5e-7). SOX17 is highly constrained and encodes a transcription factor involved in Wnt/β-catenin and Notch signaling during development. We estimate that rare deleterious variants contribute to approximately 3.2% of PAH-CHD cases. The coding variants identified include likely gene-disrupting (LGD) and deleterious missense, with most of the missense variants occurring in a highly conserved HMG-box protein domain. We further observed an enrichment of rare deleterious variants in putative targets of SOX17, many of which are highly expressed in developing heart and pulmonary vasculature. In the cohort of PAH without CHD, rare deleterious variants of SOX17 were observed in 0.7% of cases.

CONCLUSIONS

These data strongly implicate SOX17 as a new risk gene contributing to PAH-CHD as well as idiopathic/familial PAH. Replication in other PAH cohorts and further characterization of the clinical phenotype will be important to confirm the precise role of SOX17 and better estimate the contribution of genes regulated by SOX17.

Rho-Kinase Inhibition Ameliorates Dasatinib-Induced Endothelial Dysfunction and Pulmonary Hypertension

The multi-kinase inhibitor dasatinib is used for treatment of imatinib-resistant chronic myeloid leukemia, but is prone to induce microvascular dysfunction. In lung this can manifest as capillary leakage with pleural effusion, pulmonary edema or even pulmonary arterial hypertension. To understand how dasatinib causes endothelial dysfunction we examined the effects of clinically relevant concentrations of dasatinib on both human pulmonary arterial macro- and microvascular endothelial cells (ECs). The effects of dasatinib was compared to imatinib and nilotinib, two other clinically used BCR/Abl kinase inhibitors that do not inhibit Src. Real three-dimensional morphology and high resolution stiffness mapping revealed softening of both macro- and microvascular ECs upon dasatinib treatment, which was not observed in response to imatinib. In a dose-dependent manner, dasatinib decreased transendothelial electrical resistance/impedance and caused a permeability increase as well as disruption of tight adherens junctions in both cell types. In isolated perfused and ventilated rat lungs, dasatinib increased mean pulmonary arterial pressure, which was accompanied by a gain in lung weight. The Rho-kinase inhibitor Y27632 partly reversed the dasatinib-induced changes in vitro and ex vivo, presumably by acting downstream of Src. Co-administration of the Rho-kinase inhibitor Y27632 completely blunted the increased pulmonary pressure in response to dasatinib. In conclusion, a dasatinib-induced permeability increase in human pulmonary arterial macro- and microvascular ECs might explain many of the adverse effects of dasatinib in patients. Rho-kinase inhibition might be suitable to ameliorate these effects.

Important role of endothelium-dependent hyperpolarization in the pulmonary microcirculation in male mice: implications for hypoxia-induced pulmonary hypertension

Endothelium-dependent hyperpolarization (EDH) plays important roles in the systemic circulation, whereas its role in the pulmonary circulation remains largely unknown. Furthermore, the underlying mechanisms of pulmonary hypertension (PH) also remain to be elucidated. We thus aimed to elucidate the role of EDH in pulmonary circulation in general and in PH in particular. In isolated perfused lung and using male wild-type mice, endothelium-dependent relaxation to bradykinin (BK) was significantly reduced in the presence of Nω-nitro-l-arginine by ~50% compared with those in the presence of indomethacin, and the combination of apamin plus charybdotoxin abolished the residual relaxation, showing the comparable contributions of nitric oxide (NO) and EDH in the pulmonary microcirculation under physiological conditions. Catalase markedly inhibited EDH-mediated relaxation, indicating the predominant contribution of endothelium-derived H2O2. BK-mediated relaxation was significantly reduced at day 1 of hypoxia, whereas it thereafter remained unchanged until day 28. EDH-mediated relaxation was diminished at day 2 of hypoxia, indicating a transition from EDH to NO in BK-mediated relaxation before the development of hypoxia-induced PH. Mechanistically, chronic hypoxia enhanced endothelial NO synthase expression and activity associated with downregulation of caveolin-1. Nitrotyrosine levels were significantly higher in vascular smooth muscle of pulmonary microvessels under chronic hypoxia than under normoxia. A similar transition of the mediators in BK-mediated relaxation was also noted in the Sugen hypoxia mouse model. These results indicate that EDH plays important roles in the pulmonary microcirculation in addition to NO under normoxic conditions and that impaired EDH-mediated relaxation and subsequent nitrosative stress may be potential triggers of the onset of PH.

NEW & NOTEWORTHY This study provides novel evidence that both endothelium-dependent hyperpolarization and nitric oxide play important roles in endothelium-dependent relaxation in the pulmonary microcirculation under physiological conditions in mice and that hypoxia first impairs endothelium-dependent hyperpolarization-mediated relaxation, with compensatory upregulation of nitric oxide, before the development of hypoxia-induced pulmonary hypertension.

TASK-1 (KCNK3) channels in the lung: from cell biology to clinical implications

TWIK-related acid-sensitive potassium channel 1 (TASK-1 encoded by KCNK3) belongs to the family of two-pore domain potassium channels. This gene subfamily is constitutively active at physiological resting membrane potentials in excitable cells, including smooth muscle cells, and has been particularly linked to the human pulmonary circulation. TASK-1 channels are sensitive to a wide array of physiological and pharmacological mediators that affect their activity such as unsaturated fatty acids, extracellular pH, hypoxia, anaesthetics and intracellular signalling pathways. Recent studies show that modulation of TASK-1 channels, either directly or indirectly by targeting their regulatory mechanisms, has the potential to control pulmonary arterial tone in humans. Furthermore, mutations in KCNK3 have been identified as a rare cause of both familial and idiopathic pulmonary arterial hypertension. This review summarises our current state of knowledge of the functional role of TASK-1 channels in the pulmonary circulation in health and disease, with special emphasis on current advancements in the field.

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.

Docosahexaenoic acid causes rapid pulmonary arterial relaxation via KCa channel-mediated hyperpolarisation in pulmonary hypertension

Cardioprotective benefits of ω-3 fatty acids such as docosahexaenoic acid (DHA) are well established, but the regulatory effect of DHA on vascular tone and pressure in pulmonary hypertension is largely unknown.As DHA is a potent regulator of K⁺ channels, we hypothesised that DHA modulates the membrane potential of pulmonary artery smooth muscle cells (PASMCs) through K⁺ channels and thus exerts its effects on pulmonary vascular tone and pressure.We show that DHA caused dose-dependent activation of the calcium-activated K⁺ (KCa) current in primary human PASMCs and endothelium-dependent relaxation of pulmonary arteries. This vasodilation was significantly diminished in KCa^-/- (Kcnma1^-/-) mice. In vivo, acute DHA returned the right ventricular systolic pressure in the chronic hypoxia-induced pulmonary hypertension animal model to the level of normoxic animals. Interestingly, in idiopathic pulmonary arterial hypertension the KCa channels and their subunits were upregulated. DHA activated KCa channels in these human PASMCs and hyperpolarised the membrane potential of the idiopathic pulmonary arterial hypertension PASMCs to that of the PASMCs from healthy donors.Our findings indicate that DHA activates PASMC KCa channels leading to vasorelaxation in pulmonary hypertension. This effect might provide a molecular explanation for the previously undescribed role of DHA as an acute vasodilator in pulmonary hypertension.

The mechanistic basis of prostacyclin and its stable analogues in pulmonary arterial hypertension: Role of membrane versus nuclear receptors

Pulmonary arterial hypertension (PAH) is a progressive disease of distal pulmonary arteries in which patients suffer from elevated pulmonary arterial pressure, extensive vascular remodelling and right ventricular failure. To date prostacyclin (PGI2) therapy remains the most efficacious treatment for PAH and is the only approved monotherapy to have a positive impact on long-term survival. A key thing to note is that improvement exceeds that predicted from vasodilator testing strongly suggesting that additional mechanisms contribute to the therapeutic benefit of prostacyclins in PAH. Given these agents have potent antiproliferative, anti-inflammatory and endothelial regenerating properties suggests therapeutic benefit might result from a slowing, stabilization or even some reversal of vascular remodelling in vivo. This review discusses evidence that the pharmacology of each prostacyclin (IP) receptor agonist so far developed is distinct, with non-IP receptor targets clearly contributing to the therapeutic and side effect profile of PGI2 (EP3), iloprost (EP1), treprostinil (EP2, DP1) along with a family of nuclear receptors known as peroxisome proliferator-activated receptors (PPARs), to which PGI2 and some analogues directly bind. These targets are functionally expressed to varying degrees in arteries, veins, platelets, fibroblasts and inflammatory cells and are likely to be involved in the biological actions of prostacylins. Recently, a highly selective IP agonist, selexipag has been developed for PAH. This agent should prove useful in distinguishing IP from other prostanoid receptors or PPAR binding effects in human tissue. It remains to be determined whether selectivity for the IP receptor gives rise to a superior or inferior clinical benefit in PAH.

The role of inflammation in hypoxic pulmonary hypertension: from cellular mechanisms to clinical phenotypes

Hypoxic pulmonary hypertension (PH) comprises a heterogeneous group of diseases sharing the common feature of chronic hypoxia-induced pulmonary vascular remodeling. The disease is usually characterized by mild to moderate pulmonary vascular remodeling that is largely thought to be reversible compared with the progressive irreversible disease seen in World Health Organization (WHO) group I disease. However, in these patients, the presence of PH significantly worsens morbidity and mortality. In addition, a small subset of patients with hypoxic PH develop "out-of-proportion" severe pulmonary hypertension characterized by pulmonary vascular remodeling that is irreversible and similar to that in WHO group I disease. In all cases of hypoxia-related vascular remodeling and PH, inflammation, particularly persistent inflammation, is thought to play a role. This review focuses on the effects of hypoxia on pulmonary vascular cells and the signaling pathways involved in the initiation and perpetuation of vascular inflammation, especially as they relate to vascular remodeling and transition to chronic irreversible PH. We hypothesize that the combination of hypoxia and local tissue factors/cytokines ("second hit") antagonizes tissue homeostatic cellular interactions between mesenchymal cells (fibroblasts and/or smooth muscle cells) and macrophages and arrests these cells in an epigenetically locked and permanently activated proremodeling and proinflammatory phenotype. This aberrant cellular cross-talk between mesenchymal cells and macrophages promotes transition to chronic nonresolving inflammation and vascular remodeling, perpetuating PH. A better understanding of these signaling pathways may lead to the development of specific therapeutic targets, as none are currently available for WHO group III disease.