Enhanced store-operated Ca²+ entry and TRPC channel expression in pulmonary arteries of monocrotaline-induced pulmonary hypertensive rats

Role of transient receptor potential channels in the regulation of vascular tone

Vascular tone is a major element in the control of hemodynamics. Transient receptor potential (TRP) channels conducting monovalent and/or divalent cations (e.g. Na+ and Ca2+) are expressed in the vasculature. Accumulating evidence suggests that TRP channels participate in regulating vascular tone by regulating intracellular Ca2+ signaling in both vascular smooth muscle cells (VSMCs) and endothelial cells (ECs). Aberrant expression/function of TRP channels in the vasculature is associated with vascular dysfunction in systemic/pulmonary hypertension and metabolic syndromes. This review intends to summarize our current knowledge of TRP-mediated regulation of vascular tone in both physiological and pathophysiological conditions and to discuss potential therapeutic approaches to tackle abnormal vascular tone due to TRP dysfunction.

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.

Stretching Promotes Wound Contraction Through Enhanced Expression of Endothelin Receptor B and TRPC3 in Fibroblasts

One factor that can contribute to the development of hypertrophic scar contracture is mechanical stress. Mechanical cyclic stretch stimuli enhance the secretion of endothelin-1 (ET-1) from keratinocyte. Cyclical stretching of fibroblasts also increases the expression level of the transient receptor potential ion channel (TRPC3), which is known to couple with the endothelin receptor and induce intracellular Ca2+ signaling via the calcineurin/nuclear factor of activated T cells (NFAT) pathway. The aim of this study was to investigate the relationship between keratinocytes and fibroblasts when they are stretched.

Methods

The conditioned medium from stretched keratinocyte was added to the fibroblast populated collagen lattice. Then, we analyzed the levels of endothelin receptor in the human hypertrophic scar tissue and stretched fibroblasts. To address the function of TRPC3, we have used an overexpression system with the collagen lattice. Finally, the TRPC3 overexpressing fibroblasts were transplanted to mouse dorsal skin, and the rate of skin wound contraction was assessed.

Results

Conditioned medium from stretched keratinocytes increased the rate of contraction of fibroblast populated collagen lattice. In human hypertrophic scar and stretched fibroblasts, endothelin receptor type B was increased. Cyclic stretching of TRPC3 overexpressing fibroblasts activated NFATc4, and stretched human fibroblasts showed more activation of NFATc4 in response to ET-1. The wound treated with TRPC3 overexpressing fibroblasts showed more contraction than control wound.

Conclusion

These findings suggest that cyclical stretching of wounds have an effect on both keratinocytes and fibroblasts, where keratinocytes secret more ET-1, and fibroblasts develop more sensitivity to ET-1 by expressing more endothelin receptors and TRPC3.

Deleterious effect in endothelin receptor-mediated coronary artery smooth muscle contractility in high-salt diet rats

BACKGROUND AND AIMS

High-salt diet has been suggested to increase the risk of heart disease. However, the mechanisms underlying coronary artery tension dysfunction caused by high-salt diet are unclear. Previous studies have shown that coronary artery spasm is often induced by endothelin-1 (ET-1) and thromboxane, leading to myocardial ischemia, while the store-operated Ca²⁺ entry (SOCE) function of coronary smooth muscle is very important in this process.

METHODS AND RESULTS

Tension measurements of endothelium-denuded coronary artery ring segments showed that vasocontraction induced by U46619, ET-1, orSTIM1/Orai1-mediated SOCE was significantly lower in 4% high-salt diet rats than in control rats fed a regular diet. The results of western blotting and immunohistochemistry assays showed lower expression levels of endothelial receptors ET_A and ET_B, STIM1 and Orai1 in coronary artery of high-salt intake rats compared with control rats. Fibrosis was observed by using Masson's trichrome staining and picrosirius red staining. The plasma ET-1 concentration in high-salt diet rats was significantly higher than that of controls. The interventricular septum and posterior wall of high-salt diet rats were significantly thickened.

CONCLUSION

Our findings indicated that coronary artery tension was significantly decreased in 4% high-salt diet rats and that this decrease may be due to the change of endothelin receptor and its downstream pathway SOCE related protein expression in coronary artery. Coronary fibrosis was observed in rats fed with high-salt diet. This study provides potential mechanistic insights into high-salt intake-induced heart disease.

Reduced CircSMOC1 Level Promotes Metabolic Reprogramming via PTBP1 (Polypyrimidine Tract-Binding Protein) and miR-329-3p in Pulmonary Arterial Hypertension Rats

BACKGROUND

Pulmonary arterial hypertension maintains rapid cell proliferation and vascular remodeling through metabolic reprogramming. Recent studies suggested that circRNAs play important role in pulmonary vascular remodeling and pulmonary arterial smooth muscle cells proliferation. However, the relationship between circRNA, cell proliferation, and metabolic reprogramming in pulmonary arterial hypertension has not been investigated.

METHODS

RNA-seq and qRT-PCR reveal the differential expression profile of circRNA in pulmonary arteries of pulmonary arterial hypertension rat models. Transfection was used to examine the effects of circSMOC1 on pulmonary artery smooth muscle cells, and the roles of circSMOC1 in vivo were investigated by adenoassociated virus. Mass spectrometry, RNA pull-down, RNA immunoprecipitation, and dual-luciferase reporter assay were performed to investigate the signaling pathway of circSMOC1 regulating the metabolic reprogramming.

RESULTS

CircSMOC1 was significantly downregulated in pulmonary arteries of pulmonary arterial hypertension rats. CircSMOC1 knockdown promoted proliferation and migration and enhanced aerobic glycolysis of pulmonary artery smooth muscle cells. CircSMOC1 overexpression in vivo alleviates pulmonary vascular remodeling, right ventricular pressure, and right heart hypertrophy. In the nucleus, circSMOC1 directly binds to PTBP1 (polypyrimidine tract-binding protein), competitively inhibits the specific splicing of PKM (pyruvate kinase M) premRNA, resulting in the upregulation of PKM2 (pyruvate kinase M2), the key enzyme of aerobic glycolysis, to enhance glycolysis. In the cytoplasm, circSMOC1 acted as a miR-329-3p sponge, and its reduction in pulmonary arterial hypertension suppressed PDHB (pyruvate dehydrogenase E1 subunit beta) expression, leading to the impairment of mitochondrial oxidative phosphorylation.

CONCLUSIONS

circSMOC1 is crucially involved in the metabolic reprogramming of pulmonary artery smooth muscle cells through PTBP1 and miR-329-3p to regulate pulmonary vascular remodeling in pulmonary arterial hypertension.

Potential of the TRPM7 channel as a novel therapeutic target for pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an intractable vascular disease characterized by a progressive increase in pulmonary vascular resistance caused by pulmonary vascular remodeling, which ultimately leads to right-sided heart failure. PAH remains incurable, despite the development of PAH-targeted therapeutics centered on pulmonary artery relaxants. It is necessary to identify the target molecules that contribute to pulmonary artery remodeling. Transient receptor potential (TRP) channels have been suggested to modulate pulmonary artery remodeling. Our study focused on the transient receptor potential ion channel subfamily M, member 7, or the TRPM7 channel, which modulates endothelial-to-mesenchymal transition and smooth muscle proliferation in the pulmonary artery. In this review, we summarize the role and expression profile of TRPM7 channels in PAH progression and discuss TRPM7 channels as possible therapeutic targets. In addition, we discuss the therapeutic effect of a Chinese herbal medicine, Ophiocordyceps sinensis (OCS), on PAH progression, which partly involves TRPM7 inhibition.

Role of store-operated Ca2+ entry in cardiovascular disease

Store-operated channels (SOCs) are highly selective Ca2+ channels that mediate Ca2+ influx in non-excitable and excitable (i.e., skeletal and cardiac muscle) cells. These channels are triggered by Ca2+ depletion of the endoplasmic reticulum and sarcoplasmic reticulum, independently of inositol 1,4,5-trisphosphate (InsP3), which is involved in cell growth, differentiation, and gene transcription. When the Ca2+ store is depleted, stromal interaction molecule1 (STIM1) as Ca2+ sensor redistributes into discrete puncta near the plasma membrane and activates the protein Ca2+ release activated Ca2+ channel protein 1 (Orai1). Accumulating evidence suggests that SOC is associated with several physiological roles in endothelial dysfunction and vascular smooth muscle proliferation that contribute to the progression of cardiovascular disease. This review mainly elaborates on the contribution of SOC in the vasculature (endothelial cells and vascular smooth muscle cells). We will further retrospect the literature implicating a critical role for these proteins in cardiovascular disease.

High magnesium mitigates the vasoconstriction mediated by different types of calcium influx from monocrotaline-induced pulmonary hypertensive rats

NEW FINDINGS

What is the central question of this study? The aim was to examine and explore the involvement of Mg²⁺ in mitigating the vasoconstriction in PAs and sPAs in the MCT-PAH rat model. What are the main finding and its importance? 1.Both SOCE- and ROCE-mediated vasoconstriction enhanced in the MCT-PAH model. 2.High magnesium inhibited vasoconstriction due to directly antagonizing Ca²⁺ and increasing NO release. 3.The inhibition effect of high magnesium was more notable in sPA.

ABSTRACT

Increased extracellular magnesium concentration ([Mg²⁺ ]_e ) has been evidenced to attenuate the endothelin-1 (ET-1)-induced contractile response via the release of nitric oxide (NO) from the endothelium in proximal pulmonary arteries (PAs) of chronic hypoxic (CH) mice. Here we further examined the involvement of Mg²⁺ in the inhibition of vasoconstriction in PAs and distal smaller pulmonary arteries (sPAs) in a monocrotaline-induced pulmonary arterial hypertension (MCT-PAH) rat model. The data showed that in control rats, vasoconstriction in sPAs is more intense than that in PAs. In MCT-PAH rats, the store-operated Ca²⁺ entry (SOCE)-, and receptor-operated Ca²⁺ entry (ROCE)-mediated contraction was significantly strengthened. However, there was no upregulation of the vasoconstriction mediated by voltage-dependent calcium entry (VDCE). Furthermore, high magnesium greatly inhibited the VDCE-mediated contraction in PAs instead of sPAs, which was opposite to the ROCE-mediated contraction. Moreover, MCT pretreatment partly eliminated the endothelium-dependent vasodilation in PAs, which in sPAs, however, was still promoted by magnesium due to the increased NO release in pulmonary microvascular endothelial cells (PMVECs). In conclusion, the findings suggest that both SOCE- and ROCE-mediated vasoconstriction in the MCT-PAH model are enhanced, especially in sPAs. The inhibition effect of high magnesium on vasoconstriction can be achieved partly by its direct role as a Ca²⁺ antagonist and partly by increasing the NO release in PMVECs. This article is protected by copyright. All rights reserved.

Tanreqing Injection Regulates Cell Function of Hypoxia-Induced Human Pulmonary Artery Smooth Muscle Cells (HPASMCs) through TRPC1/CX3CL1 Signaling Pathway

Hypoxia-induced pulmonary arterial hypertension (HPAH) is due to hypoxia caused by vascular endothelial cell remolding and damage. Previous studies have suggested that CX3CL1 plays an important role in HPAH which is affected by oxidative stress. Ca²⁺ channel activation correlated with increasing NF-κB levels induced by ROS. Tanreqing injection (TRQ) is a traditional Chinese medicine (TCM) for acute upper respiratory tract infection and acute pneumonia. In the present study, we explored the effect of TRQ on human pulmonary artery smooth muscle cells (HPASMCs) undergoing hypoxia and feasible molecular mechanisms involved in. Cell proliferation was assayed using CCK8 kits. Immunofluorescence and western blotting along with ELISA assay were performed to investigate the effect of TRQ on hypoxia-induced ROS, Ca²⁺, hydroxyl free radicals, and the expression of Ca²⁺ channel protein TRPC1, CX3CR1, HIF-1α, NF-κBp65, and p-NF-κBp65 in HPASMCs. Human CX3CL1 and the inhibitor of TRPC1 as SKF96365 were used for further investigation. TRQ inhibited hypoxia-induced increasing cell adhesion, ROS, Ca²⁺, hydroxyl free radicals, CX3CR1, HIF-1α, NF-κBp65 activation, and even on TRPC1 expression in HPASMC which tended to be attenuated even reversed by CX3CL1. Our results suggested that TRQ might help to attenuate remodeling of HPASMC through inhibiting the ROS and TRPC1/CX3CL1 signaling pathway.

Role of Store-Operated Ca2+ Entry in the Pulmonary Vascular Remodeling Occurring in Pulmonary Arterial Hypertension

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

Mechanosensitivity in Pulmonary Circulation: Pathophysiological Relevance of Stretch-Activated Channels in Pulmonary Hypertension

A variety of cell types in pulmonary arteries (endothelial cells, fibroblasts, and smooth muscle cells) are continuously exposed to mechanical stimulations such as shear stress and pulsatile blood pressure, which are altered under conditions of pulmonary hypertension (PH). Most functions of such vascular cells (e.g., contraction, migration, proliferation, production of extracellular matrix proteins, etc.) depend on a key event, i.e., the increase in intracellular calcium concentration ([Ca²⁺]_i) which results from an influx of extracellular Ca²⁺ and/or a release of intracellular stored Ca²⁺. Calcium entry from the extracellular space is a major step in the elevation of [Ca²⁺]_i, involving a variety of plasmalemmal Ca²⁺ channels including the superfamily of stretch-activated channels (SAC). A common characteristic of SAC is that their gating depends on membrane stretch. In general, SAC are non-selective Ca²⁺-permeable cation channels, including proteins of the TRP (Transient Receptor Potential) and Piezo channel superfamily. As membrane mechano-transducers, SAC convert physical forces into biological signals and hence into a cell response. Consequently, SAC play a major role in pulmonary arterial calcium homeostasis and, thus, appear as potential novel drug targets for a better management of PH.

Acid-sensing ion channel 1 contributes to pulmonary arterial smooth muscle cell depolarization following hypoxic pulmonary hypertension

Pulmonary hypertension is characterized by sustained vasoconstriction and remodelling of the small pulmonary arteries, which is associated with persistent depolarization of the resting membrane potential (E_m ) of pulmonary arterial smooth muscle cells (PASMCs). It is well-known that the underlying mechanism of this depolarization includes inhibition of K⁺ channels; however, whether other ion channels contribute to this depolarization is unknown. We previously reported that acid-sensing ion channel 1 (ASIC1), a non-selective cation channel (NSCC) that conducts both Na⁺ and Ca²⁺ , is present in PASMCs and contributes to the development of chronic hypoxia (CH)-induced pulmonary hypertension. Therefore, we tested the hypothesis that ASIC1-mediated Na⁺ influx contributes to PASMC E_m regulation following CH-induced pulmonary hypertension. Using sharp electrode intracellular recordings in isolated, pressurized small pulmonary arteries from rats and mice, we show that exposure to CH leads to PASMC membrane depolarization compared with control animals, and this is independent of intraluminal pressure-induced depolarization. In addition to a decrease in PASMC whole-cell K⁺ currents following CH, we demonstrate that whole-cell NSCC currents are increased and essential to the persistent CH-induced E_m depolarization in PASMCs. Both the specific inhibitor of ASIC1, psalmotoxin 1, and global knockout of ASIC1 (Asic1^-/- ) prevents CH-induced E_m depolarization and largely inhibits whole-cell NSCC currents, without affecting whole-cell K⁺ currents. Our results show a combination of factors, including inhibition of K⁺ efflux and augmented Na⁺ influx, mediate CH-induced PASMC depolarization. Furthermore, this study demonstrates a novel role for ASIC1 in the regulation of E_m in PASMCs during CH-induced pulmonary hypertension. KEY POINTS: In pulmonary hypertensive patients and animal models of pulmonary hypertension, the resting membrane potential (E_m ) of pulmonary arterial smooth muscle cells (PASMCs) is persistently depolarized. In addition to the well-established reduction of K⁺ conductance, we show that non-selective cation channel currents are increased and essential to the persistent E_m depolarization in PASMCs following chronic hypoxia (CH)-induced pulmonary hypertension. The current study provides novel evidence that acid-sensing ion channel 1 (ASIC1)-mediated Na⁺ influx induces membrane depolarization and regulates E_m in PASMCs following CH exposure. Although fairly quiescent under control conditions, our findings demonstrate a pathological function of ASIC1 in the development of chronic hypoxia-induced pulmonary hypertension.

Halofuginone, a promising drug for treatment of pulmonary hypertension

BACKGROUND AND PURPOSE

Halofuginone is a febrifugine derivative originally isolated from Chinese traditional herb Chang Shan that exhibits anti-hypertrophic, anti-fibrotic and anti-proliferative effects. We sought to investigate whether halofuginone induced pulmonary vasodilation and attenuates chronic hypoxia-induced pulmonary hypertension (HPH).

EXPERIMENTAL APPROACH

Patch-clamp experiments were conducted to examine the activity of voltage-dependent Ca²⁺ channels (VDCCs) in pulmonary artery smooth muscle cells (PASMCs). Digital fluorescence microscopy was used to measure intracellular Ca²⁺ concentration in PASMCs. Isolated perfused and ventilated mouse lungs were used to measure pulmonary artery pressure (PAP). Mice exposed to hypoxia (10% O₂ ) for 4 weeks were used as model of HPH for in vivo experiments.

KEY RESULTS

Halofuginone increased voltage-gated K⁺ (K_v ) currents in PASMCs and K⁺ currents through KCNA5 channels in HEK cells transfected with KCNA5 gene. HF (0.03-1 μM) inhibited receptor-operated Ca²⁺ entry in HEK cells transfected with calcium-sensing receptor gene and attenuated store-operated Ca²⁺ entry in PASMCs. Acute (3-5 min) intrapulmonary application of halofuginone significantly and reversibly inhibited alveolar hypoxia-induced pulmonary vasoconstriction dose-dependently (0.1-10 μM). Intraperitoneal administration of halofuginone (0.3 mg·kg^-1 , for 2 weeks) partly reversed established PH in mice.

CONCLUSION AND IMPLICATIONS

Halofuginone is a potent pulmonary vasodilator by activating K_v channels and blocking VDCC and receptor-operated and store-operated Ca²⁺ channels in PASMCs. The therapeutic effect of halofuginone on experimental PH is probably due to combination of its vasodilator effects, via inhibition of excitation-contraction coupling and anti-proliferative effects, via inhibition of the PI3K/Akt/mTOR signalling pathway.

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

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

Catechin-Rich Green Tea Extract and the Loss-of-TLR4 Signaling Differentially Alter the Hepatic Metabolome in Mice with Nonalcoholic Steatohepatitis

SCOPE

Catechin-rich green tea extract (GTE) limits inflammation in nonalcoholic steatohepatitis (NASH) consistent with a Toll-like receptor 4 (TLR4)-dependent mechanism. It is hypothesized that GTE supplementation during NASH will shift the hepatic metabolome similar to that attributed to the loss-of-TLR4 signaling.

METHODS AND RESULTS

Wild-type (WT) and loss-of-function TLR4-mutant (TLR4mut ) mice are fed a high-fat diet containing 0% or 2% GTE for 8 weeks prior to performing untargeted mass spectrometry-based metabolomics on liver tissue. The loss-of-TLR4 signaling and GTE shift the hepatic metabolome away from that of WT mice. However, relatively few metabolites are altered by GTE in WT mice to the same extent as the loss-of-TLR4 signaling in TLR4mut mice. GTE increases acetyl-coenzyme A precursors and spermidine to a greater extent than the loss-of-TLR4 signaling. Select metabolites associated with thiol metabolism are similarly affected by GTE and the loss-of-TLR4 signaling. Glycerophospholipid catabolites are decreased by GTE, but are unaffected in TLR4mut mice. Conversely, the loss-of-TLR4 signaling but not GTE increases several bile acid metabolites.

CONCLUSION

GTE limitedly alters the hepatic metabolome consistent with a TLR4-dependent mechanism. This suggests that the anti-inflammatory activities of GTE and loss-of-TLR4 signaling that regulate hepatic metabolism to abrogate NASH are likely due to distinct mechanisms.

Preventive treatment with ginsenoside Rb1 ameliorates monocrotaline-induced pulmonary arterial hypertension in rats and involves store-operated calcium entry inhibition

CONTEXT

Ginsenoside Rb1, the main active ingredient of ginseng, exhibits ex vivo depression of store-operated calcium entry (SOCE) and related vasoconstriction in pulmonary arteries derived from pulmonary hypertension (PH) rats. However, the in vivo effects of ginsenoside Rb1 on PH remain unclear.

OBJECTIVE

This study explored the possibility of using ginsenoside Rb1 as an in vivo preventive medication for type I PH, i.e., pulmonary arterial hypertension (PAH), and potential mechanisms involving SOCE.

MATERIALS AND METHODS

Male Sprague-Dawley rats (170-180 g) were randomly divided into Control, MCT, and MCT + Rb1 groups (n = 20). Control rats received only saline injection. Rats in the MCT + Rb1 and MCT groups were intraperitoneally administered single doses of 50 mg/kg monocrotaline (MCT) combined with 30 mg/kg/day ginsenoside Rb1 or equivalent volumes of saline for 21 consecutive days. Subsequently, comprehensive parameters related to SOCE, vascular tone, histological changes and hemodynamics were measured.

RESULTS

Ginsenoside Rb1 reduced MCT-induced STIM1, TRPC1, and TRPC4 expression by 35.00, 31.96, and 32.24%, respectively, at the protein level. SOCE-related calcium entry and pulmonary artery contraction decreased by 162.6 nM and 71.72%. The mean pulmonary artery pressure, right ventricle systolic pressure, and right ventricular mass index decreased by 19.5 mmHg, 21.6 mmHg, and 39.50%. The wall thickness/radius ratios decreased by 14.67 and 17.65%, and the lumen area/total area ratios increased by 18.55 and 15.60% in intrapulmonary vessels with 51-100 and 101-150 μm o.d.

CONCLUSION

Ginsenoside Rb1, a promising candidate for PH prevention, inhibited SOCE and related pulmonary vasoconstriction, and relieved MCT-induced PAH in rats.

The Role and Regulation of Pulmonary Artery Smooth Muscle Cells in Pulmonary Hypertension

Pulmonary hypertension (PH) is one of the most devastating cardiovascular diseases worldwide and it draws much attention from numerous scientists. As an indispensable part of pulmonary artery, smooth muscle cells are worthy of being carefully investigated. To elucidate the pathogenesis of PH, several theories focusing on pulmonary artery smooth muscle cells (PASMC), such as hyperproliferation, resistance to apoptosis, and cancer theory, have been proposed and widely studied. Here, we tried to summarize the studies, concentrating on the role of PASMC in the development of PH, feasible molecular basis to intervene, and potential treatment to PH.

[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.

Redox Regulation of Ion Channels and Receptors in Pulmonary Hypertension

Significance: Pulmonary hypertension (PH) is characterized by elevated vascular resistance due to vasoconstriction and remodeling of the normally low-pressure pulmonary vasculature. Redox stress contributes to the pathophysiology of this disease by altering the regulation and activity of membrane receptors, K+ channels, and intracellular Ca2+ homeostasis. Recent Advances: Antioxidant therapies have had limited success in treating PH, leading to a growing appreciation that reductive stress, in addition to oxidative stress, plays a role in metabolic and cell signaling dysfunction in pulmonary vascular cells. Reactive oxygen species generation from mitochondria and NADPH oxidases has substantial effects on K+ conductance and membrane potential, and both receptor-operated and store-operated Ca2+ entry. Critical Issues: Some specific redox changes resulting from oxidation, S-nitrosylation, and S-glutathionylation are known to modulate membrane receptor and ion channel activity in PH. However, many sites of regulation that have been elucidated in nonpulmonary cell types have not been tested in the pulmonary vasculature, and context-specific molecular mechanisms are lacking. Future Directions: Here, we review what is known about redox regulation of membrane receptors and ion channels in PH. Further investigation of the mechanisms involved is needed to better understand the etiology of PH and develop better targeted treatment strategies.

Peptide/Receptor Co-evolution Explains the Lipolytic Function of the Neuropeptide TLQP-21

Structural and functional diversity of peptides and GPCR result from long evolutionary processes. Even small changes in sequence can alter receptor activation, affecting therapeutic efficacy. We conducted a structure-function relationship study on the neuropeptide TLQP-21, a promising target for obesity, and its complement 3a receptor (C3aR1). After having characterized the TLQP-21/C3aR1 lipolytic mechanism, a homology modeling and molecular dynamics simulation identified the TLQP-21 binding motif and C3aR1 binding site for the human (h) and mouse (m) molecules. mTLQP-21 showed enhanced binding affinity and potency for hC3aR1 compared with hTLQP-21. Consistently, mTLQP-21, but not hTLQP-21, potentiates lipolysis in human adipocytes. These findings led us to uncover five mutations in the C3aR1 binding pocket of the rodent Murinae subfamily that are causal for enhanced calculated affinity and measured potency of TLQP-21. Identifying functionally relevant peptide/receptor co-evolution mechanisms can facilitate the development of innovative pharmacotherapies for obesity and other diseases implicating GPCRs.

Increased caveolin-1 expression enhances the receptor-operated Ca2+ entry in the aorta of two-kidney, one-clip hypertensive rats

NEW FINDINGS

What is the central question of this study? The aim was to examine and compare the contributions of caveolin-1 to the contractile responses mediated by L-type voltage-dependent calcium channels, store-operated Ca²⁺ channels and receptor-operated Ca²⁺ channels in two different types of arteries from two-kidney, one-clip hypertensive rats. What is the main finding and its importance? We demonstrated that the density of caveolae and caveolin-1 expression were significantly upregulated in the aorta of two-kidney, one-clip hypertensive rats, but not in the third-order branches of mesenteric arteries. We highlight that caveolin-1 plays an important role in aortic constriction by enhancing receptor-operated Ca²⁺ entry in the hypertensive rat model.

ABSTRACT

Calcium and its multiple regulatory mechanisms are crucial for the development of hypertension. Among these regulatory mechanisms, store-operated Ca²⁺ entry (SOCE) and receptor-operated Ca²⁺ entry (ROCE) mediate agonist-induced calcium influx, contributing to vascular contraction. The SOCE and ROCE are regulated by a variety of mechanisms involving caveolin-1 (Cav1), which has been found to be strongly associated with hypertension in gene polymorphism. In the present study, we investigated the role of Cav1 during the enhanced activity of calcium channels in hypertensive arteries. We demonstrated that the expression level of Cav1 was significantly increased in the aorta of two-kidney, one-clip (2K1C) hypertensive rats. The disruption of caveolae by methyl-β-cyclodextrin did not cause a marked difference in agonist-induced vasoconstriction in the third-order branches of the mesenteric arteries but strongly suppressed the aortic contractile response to endothelin-1 in the 2K1C group, which was not found in the control group. The increase in Cav1 by introduction of Cav1 scaffolding domain enhancing peptide promoted the 1-oleoyl-2-acetyl-glycerol-induced ROCE in hypertensive aortic smooth muscle cells but did not enhance the cyclopiazonic acid-induced SOCE. In the resistance arteries, similar changes were not observed, and no statistical changes of Cav1 expression were evident in the third-order branches of the mesenteric arteries. Our results indicate that increased Cav1 expression might promote the altered [Ca²⁺ ]_i -induced aortic vasoreactivity by enhancing ROCE and be involved in the pathogenesis of hypertension.

Regulation of the TRPC1 channel by endothelin-1 in human atrial myocytes

BACKGROUND

Our recent study demonstrated that the nonselective cation current mediated by the transient receptor potential canonical 1 (TRPC1) channel is activated by endothelin-1 (ET-1) in human atrial myocytes; however, the related signal molecules involved are unknown.

OBJECTIVE

The purpose of this study was to investigate how the TRPC1 channel is regulated by ET-1 and whether it is upregulated in human atria from patients with atrial fibrillation (AF).

METHODS

Whole-cell patch technique and molecular biology techniques were used in the study.

RESULTS

The ET-1-evoked TRPC1 current was inhibited by the ET-1 type A (ET_A) receptor antagonist BQ123 and the ET-1 type B (ET_B) receptor antagonist BQ788 as well as the protein kinase C inhibitor chelerythrine. ET_A receptor-mediated TRPC1 channel activity was selectively inhibited by the phosphoinositide-3-kinase inhibitor wortmannin, while ET_B receptor-mediated TRPC1 activity was inhibited by the phospholipase C inhibitor U73122. The messenger RNAs and proteins of the TRPC1 channel and ET_A receptor, but not the ET_B receptor, were significantly upregulated in atria from patients with AF. The basal TRPC1 current increased in AF myocytes, and the response to ET-1 was greater in AF myocytes than in sinus rhythm myocytes. ET-1 induced a delayed repolarization in 20% of AF myocytes.

CONCLUSION

These results demonstrate for the first time that TRPC1 activation by ET-1 is mediated by protein kinase C through the distinct phospholipids pathways phosphoinositide-3-kinase and phospholipase C and that the TRPC1 channel and ET_A receptor are upregulated in AF atria, which are likely involved in atrial electrical remodeling in patients with AF.

HMGB1 is mechanistically essential in the development of experimental pulmonary hypertension

Pulmonary hypertension (PH) is a mortal disease featuring pulmonary vascular constriction and remodeling, right heart failure, and eventual death. Several reports showed that high-mobility group box 1 (HMGB1) appears to be critical for the development of PH; the underlying mechanism, however, has not been revealed. Experiments in the present study demonstrated that HMGB1 levels were elevated in the lung tissue and blood plasma of rats after chronic hypoxia exposure and monocrotaline treatment. HMGB1 was originally located within the nucleus and translocated to the cytoplasm of pulmonary artery smooth muscle cells (PASMCs) upon hypoxia exposure, a process that appeared to be mediated by endogenous H₂O₂. Exposure to HMGB1 mobilized calcium signaling in PASMCs, a response that was attenuated by extracellular Ca²⁺ removal, Toll-like receptor 4 (TLR4) inhibition by TAK-242, or transient receptor potential channel (TRPC) suppression with 2-aminoethoxydiphenyl borate (2-APB) and SKF-96365. The sustained phosphorylation of the Akt pathway modulated HMGB1-induced migration of PASMCs. The blockage of HMGB1 with glycyrrhizin or anti-HMGB1 neutralizing antibody attenuated lung inflammation and PH establishment in rats after hypoxia exposure and monocrotaline treatment. The above findings reveal the mechanistic importance of HMGB1 in PH through TLR4- and TRPC-associated Ca²⁺ influx and Akt phosphorylation-driven PASMC migration.

A novel S-nitrosocaptopril monohydrate for pulmonary arterial hypertension: H2O and -SNO intermolecular stabilization chemistry

S-nitrosocaptopril (CapNO) possesses dual capacities of both Captopril and an NO donor with enhanced efficacy and reduced side effects. CapNO crystals are difficult to make due to its unstable S-NO bond. Here, we report a novel stable S-nitrosocaptopril monohydrate (CapNO·H₂O) that is stabilized by intermolecular five-membered structure, where one H of H₂O forms a hydrogen bond with O^- of the stable resonance zwitterion Cap-S⁺=N-O^-, and the O in H₂O forms the dipole-dipole interaction with S⁺ through two unpaired electrons. With the chelation and common ion effect, we synthesized and characterized CapNO·H₂O that is stable at 4 °C for 180 days and thereafter without significant degradation. Compared to Captopril, CapNO showed direct vasorelaxation and beneficial effect on PAH rats, and could be self-assembled in rat stomach when Captopril and NaNO₂ were given separately. This novel CapNO·H₂O with low entropy paves an avenue for its clinical trials and commercialization.

Topotecan prevents hypoxia-induced pulmonary arterial hypertension and inhibits hypoxia-inducible factor-1α and TRPC channels

BACKGROUND

This study aimed to investigate the effects of topotecan (TPT) on the hypoxia-induced pulmonary arterial hypertension (PAH) in a rat model, and to explore the underlying mechanism.

METHODS

The experiments were carried out in vitro using rat PASMCs and in vivo using a rat model of hypoxia-induced PAH.

RESULTS

TPT significantly suppressed the hypoxia-induced upregulation of HIF-1α and TRPC1/4/6 expression both in pulmonary arterial smooth muscle cells (PASMCs) from normal rats and in pulmonary arteries from PAH model rats. Furthermore, TPT effectively inhibited intracellular Ca²⁺ concentration ([Ca²⁺]i) change (Ca²⁺ influx) in PASMCs from both normal rats and PAH model rats. Importantly, TPT treatment significantly inhibited the hypoxia-induced proliferation, migration and a contractile-to-synthetic phenotypic switching of normal rat PASMCs in vitro, where the effect was abrogated by overexpression of TRPC1/4/6. Furthermore, TPT administration potently attenuated the hypoxia-induced PAH-associated pulmonary arteriolar remodeling in PAH model rats, as evidenced by amelioration of elevated hemodynamic parameters, and enhanced right ventricle hypertrophy and wall thickening.

CONCLUSION

TPT ameliorates the hypoxia-induced pulmonary vascular remodeling in PAH, and the mechanism is associated with TPT-mediated inhibition of hypoxia-induced upregulation of HIF-1α and TRPC1/4/6 expression, Ca²⁺ influx, and PASMCs proliferation.

Bone Marrow-Derived Endothelial Progenitor Cells Contribute to Monocrotaline-Induced Pulmonary Arterial Hypertension in Rats via Inhibition of Store-Operated Ca2+ Channels

Purpose

This study aimed to explore whether bone marrow- (BM-) derived endothelial progenitor cells (EPCs) contributing to monocrotaline- (MCT-) induced pulmonary arterial hypertension (PAH) in rats via modulating store-operated Ca²⁺ channels (SOC).

Methods

Sprague Dawley (SD) rats were assigned into MCT group (n = 30) and control group (n = 20). Rats in MCT group were subcutaneously administered with 60 mg/kg MCT solution, and rats in control group were injected with equal amount of vehicle. After 3 weeks of treatment, right ventricular systolic pressure (RVSP) and right ventricular hypertrophy index (RVHI) of two groups were measured, and BM-derived EPCs were isolated. Immunochemistry identification and vasculogenesis detection of EPCs were then performed. [Ca²⁺]_cyt measurement was performed to detect store-operated calcium entry (SOCE) in two groups, followed by determination of Orai and canonical transient receptor potential (TRPC) channels expression.

Results

After 3 weeks of treatment, there were significant increases in RVSP and RVHI in MCT group compared with control group, indicating that MCT successfully induced PAH in rats. Moreover, the SOCE ([Ca²⁺]_cyt rise) in BM-derived EPCs of MCT group was lower than that of control group. Furthermore, the expression levels of Orai3, TRPC1, TRPC3, and TRPC6 in BM-derived EPCs were decreased in MCT group in comparison with control group.

Conclusions

The SOC activities were inhibited in BM-derived EPCs of MCT-treated rats. These results may be associated with the depressed expression of Orai3, TRPC1, TRPC3, and TRPC6, which are major mediators of SOC.

Transient Receptor Potential Melastatin-8 Activation Induces Relaxation of Pulmonary Artery by Inhibition of Store-Operated Calcium Entry in Normoxic and Chronic Hypoxic Pulmonary Hypertensive Rats

Pulmonary hypertension (PH) is characterized by enhanced vasoconstriction and vascular remodeling, which are attributable to the alteration of Ca²⁺ homeostasis in pulmonary arterial smooth muscle cells (PASMCs). It is well established that store-operated Ca²⁺ entry (SOCE) is augmented in PASMCs during PH and that it plays a crucial role in PH development. Our previous studies showed that the melastatin-related transient receptor potential 8 (TRPM8) is down-regulated in PASMCs of PH animal models, and activation of TRPM8 causes relaxation of pulmonary arteries (PAs). However, the mechanism of TRPM8-induced PA relaxation is unclear. Here we examined the interaction of TRPM8 and SOCE in PAs and PASMCs of normoxic and chronic hypoxic pulmonary hypertensive (CHPH) rats, a model of human group 3 PH. We found that TRPM8 was down-regulated and TRPM8-mediated cation entry was reduced in CHPH-PASMCs. Activation of TRPM8 with icilin caused concentration-dependent relaxation of cyclopiazonic acid (CPA) and endothelin-1 contracted endothelium-denuded PAs, and the effect was abolished by the SOCE antagonist Gd³⁺ Application of icilin to PASMCs suppressed CPA-induced Mn²⁺ quenching and Ca²⁺ entry, which was reversed by the TRPM8 antagonist N-(3-aminopropyl)-2-([(3-methylphenyl)methyl])-oxy-N-(2-thienylmethyl)benzamide hydrochloride salt (AMTB). Moreover, the inhibitory effects of icilin on SOCE in PA and PASMCs of CHPH rats were significantly augmented due to enhanced SOCE activity in PH. Our results, therefore, demonstrated a novel mechanism of TRPM8-mediated inhibition of SOCE in pulmonary vasculature. Because SOCE is important for vascular remodeling and enhanced vasoconstriction, down-regulation of TRPM8 in PASMCs of CHPH rats may minimize its inhibitory influence to allow unimpeded SOCE activity for PH development.

The effects of transient receptor potential channel (TRPC) on airway smooth muscle cell isolated from asthma model mice

This study aimed to validate whether transient receptor potential channel1 (TRPC1) and TRPC3 participate in the regulation the proliferation of airway smooth muscle cells (ASMCs) through modulating calcium ion (Ca²⁺ ) influx in vitro. Chronic model of murine asthma was induced and ASMCs isolated from asthmatic mice were used in this whole study. TRPC1 and TRPC3 were upregulated in asthmatic mouse ASMCs and selected for further investigation. Ca²⁺ concentration and the cell viability of asthmatic mouse ASMCs were significantly higher than that from non- asthma mice, however, TRPC channels blocker SKF96365 alleviated these effects. Furthermore, TRPC1 or TRPC3 overexpression markedly increased Ca²⁺ concentration and significantly induced the viability of ASMCs; whereas TRPC1 or TRPC3 knockdown exerted the completely conversed effects. Moreover, knockdown of TRPC1 and TRPC3 also exerted different effects on the protein expression of growth-related proteins p-p38, p-JNK, cleaved caspase-3 and Bcl-2, as well as on cell cycle. Finally, we found Ca²⁺ chelator EGTA or BAPTA-AM significantly diminished the effects of si-TRPC1 and si-TRPC3 on the cell viability, cell cycle, and the protein expression of p-p38, p-JNK, cleaved caspase-3, and Bcl-2 in asthmatic mouse ASMCs. Our findings demonstrated that the effects of TRPC1 and TRPC3 on the cell viability and cell cycle of ASMCs were, at least partially, through regulating Ca²⁺ influx.

Magnesium attenuates endothelin-1-induced vasoreactivity and enhances vasodilatation in mouse pulmonary arteries: Modulation by chronic hypoxic pulmonary hypertension

NEW FINDINGS

What is the central question of this study? The central goal of this study was to elucidate the role of magnesium in the regulation of pulmonary vascular reactivity in relationship to hypoxic pulmonary hypertension. What is the main finding and its importance? We found that magnesium is essential for normal vasoreactivity of the pulmonary artery. Increasing the magnesium concentration attenuates vasoconstriction and improves vasodilatation via release of nitric oxide. Pulmonary hypertension is associated with endothelial dysfunction resulting in the suppression of magnesium modulation of vasodilatation. These results provide evidence that magnesium is important for the modulation of pulmonary vascular function.

ABSTRACT

Pulmonary hypertension (PH) is characterized by enhanced vasoreactivity and sustained pulmonary vasoconstriction, arising from aberrant Ca²⁺ homeostasis in pulmonary arterial (PA) smooth muscle cells. In addition to Ca²⁺ , magnesium, the most abundant intracellular divalent cation, also plays crucial roles in many cellular processes that regulate cardiovascular function. Recent findings suggest that magnesium regulates vascular functions by altering the vascular responses to vasodilator and vasoactive agonists and affects endothelial function by modulating endothelium-dependent vasodilatation in hypertension. Administration of magnesium also decreased pulmonary arterial pressure and improved cardiac output in animal models of PH. However, the role of magnesium in the regulation of pulmonary vascular function related to PH has not been studied. In this study, we examined the effects of magnesium on endothelin-1 (ET-1)-induced vasoconstriction, ACh-induced vasodilatation and the generation of NO in PAs of normoxic mice and chronic hypoxia (CH)-treated mice. Our data showed that removal of extracellular magnesium suppressed vasoreactivity of PAs to both ET-1 and ACh. A high concentration of magnesium (4.8 mm) inhibited ET-1-induced vasoconstriction in endothelium-intact or endothelium-disrupted PAs of normoxic and CH-treated mice, and enhanced the ACh-induced production of NO in PAs of normoxic mice. Moreover, magnesium enhanced ACh-induced vasodilatation in PAs of normoxic mice, and the enhancement was completely abolished after exposure to CH. Hence, in this study we demonstrated that increasing the magnesium concentration can attenuate the ET-1-induced contractile response and improve vasodilatation via release of NO from the endothelium. We also demonstrated that chronic exposure to hypoxia can cause endothelial dysfunction resulting in suppression of the magnesium-dependent modulation of vasodilatation.

Molecular pathogenesis and current pathology of pulmonary hypertension

Following its initial description over a century ago, pulmonary arterial hypertension (PAH) continues to challenge researchers committed to understanding its pathobiology and finding a cure. The last two decades have seen major developments in our understanding of the genetics and molecular basis of PAH that drive cells within the pulmonary vascular wall to produce obstructive vascular lesions; presently, the field of PAH research has taken numerous approaches to dissect the complex amalgam of genetic, molecular and inflammatory pathways that interact to initiate and drive disease progression. In this review, we discuss the current understanding of PAH pathology and the role that genetic factors and environmental influences share in the development of vascular lesions and abnormal cell function. We also discuss how animal models can assist in elucidating gene function and the study of novel therapeutics, while at the same time addressing the limitations of the most commonly used rodent models. Novel experimental approaches based on application of next generation sequencing, bioinformatics and epigenetics research are also discussed as these are now being actively used to facilitate the discovery of novel gene mutations and mechanisms that regulate gene expression in PAH. Finally, we touch on recent discoveries concerning the role of inflammation and immunity in PAH pathobiology and how they are being targeted with immunomodulatory agents. We conclude that the field of PAH research is actively expanding and the major challenge in the coming years is to develop a unified theory that incorporates genetic and mechanistic data to address viable areas for disease modifying drugs that can target key processes that regulate the evolution of vascular pathology of PAH.

Canonical Transient Receptor Potential Channels and Their Link with Cardio/Cerebro-Vascular Diseases

The canonical transient receptor potential channels (TRPCs) constitute a series of nonselective cation channels with variable degrees of Ca²⁺ selectivity. TRPCs consist of seven mammalian members, TRPC1, TRPC2, TRPC3, TRPC4, TRPC5, TRPC6, and TRPC7, which are further divided into four subtypes, TRPC1, TRPC2, TRPC4/5, and TRPC3/6/7. These channels take charge of various essential cell functions such as contraction, relaxation, proliferation, and dysfunction. This review, organized into seven main sections, will provide an overview of current knowledge about the underlying pathogenesis of TRPCs in cardio/cerebrovascular diseases, including hypertension, pulmonary arterial hypertension, cardiac hypertrophy, atherosclerosis, arrhythmia, and cerebrovascular ischemia reperfusion injury. Collectively, TRPCs could become a group of drug targets with important physiological functions for the therapy of human cardio/cerebro-vascular diseases.

VEGF-induced intracellular Ca2+ oscillations are down-regulated and do not stimulate angiogenesis in breast cancer-derived endothelial colony forming cells

Endothelial colony forming cells (ECFCs) represent a population of truly endothelial precursors that promote the angiogenic switch in solid tumors, such as breast cancer (BC). The intracellular Ca²⁺ toolkit, which drives the pro-angiogenic response to VEGF, is remodelled in tumor-associated ECFCs such that they are seemingly insensitive to this growth factor. This feature could underlie the relative failure of anti-VEGF therapies in cancer patients. Herein, we investigated whether and how VEGF uses Ca²⁺ signalling to control angiogenesis in BC-derived ECFCs (BC-ECFCs). Although VEGFR-2 was normally expressed, VEGF failed to induce proliferation and in vitro tubulogenesis in BC-ECFCs. Likewise, VEGF did not trigger robust Ca²⁺ oscillations in these cells. Similar to normal cells, VEGF-induced intracellular Ca²⁺ oscillations were triggered by inositol-1,4,5-trisphosphate-dependent Ca²⁺ release from the endoplasmic reticulum (ER) and maintained by store-operated Ca²⁺ entry (SOCE). However, InsP₃-dependent Ca²⁺ release was significantly lower in BC-ECFCs due to the down-regulation of ER Ca²⁺ levels, while there was no remarkable difference in the amplitude, pharmacological profile and molecular composition of SOCE. Thus, the attenuation of the pro-angiogenic Ca²⁺ response to VEGF was seemingly due to the reduction in ER Ca²⁺ concentration, which prevents VEGF from triggering robust intracellular Ca²⁺ oscillations. However, the pharmacological inhibition of SOCE prevented BC-ECFC proliferation and in vitro tubulogenesis. These findings demonstrate for the first time that BC-ECFCs are insensitive to VEGF, which might explain at cellular and molecular levels the failure of anti-VEGF therapies in BC patients, and hint at SOCE as a novel molecular target for this disease.

The Role of Transient Receptor Potential Channel 6 Channels in the Pulmonary Vasculature

Canonical or classical transient receptor potential channel 6 (TRPC6) is a Ca²⁺-permeable non-selective cation channel that is widely expressed in the heart, lung, and vascular tissues. The use of TRPC6-deficient (“knockout”) mice has provided important insights into the role of TRPC6 in normal physiology and disease states of the pulmonary vasculature. Evidence indicates that TRPC6 is a key regulator of acute hypoxic pulmonary vasoconstriction. Moreover, several studies implicated TRPC6 in the pathogenesis of pulmonary hypertension. Furthermore, a unique genetic variation in the TRPC6 gene promoter has been identified, which might link the inflammatory response to the upregulation of TRPC6 expression and ultimate development of pulmonary vascular abnormalities in idiopathic pulmonary arterial hypertension. Additionally, TRPC6 is critically involved in the regulation of pulmonary vascular permeability and lung edema formation during endotoxin or ischemia/reperfusion-induced acute lung injury. In this review, we will summarize latest findings on the role of TRPC6 in the pulmonary vasculature.

Nanojunctions of the Sarcoplasmic Reticulum Deliver Site- and Function-Specific Calcium Signaling in Vascular Smooth Muscles

Vasoactive agents may induce myocyte contraction, dilation, and the switch from a contractile to a migratory-proliferative phenotype(s), which requires changes in gene expression. These processes are directed, in part, by Ca²⁺ signals, but how different Ca²⁺ signals are generated to select each function is enigmatic. We have previously proposed that the strategic positioning of Ca²⁺ pumps and release channels at membrane-membrane junctions of the sarcoplasmic reticulum (SR) demarcates cytoplasmic nanodomains, within which site- and function-specific Ca²⁺ signals arise. This chapter will describe how nanojunctions of the SR may: (1) define cytoplasmic nanospaces about the plasma membrane, mitochondria, contractile myofilaments, lysosomes, and the nucleus; (2) provide for functional segregation by restricting passive diffusion and by coordinating active ion transfer within a given nanospace via resident Ca²⁺ pumps and release channels; (3) select for contraction, relaxation, and/or changes in gene expression; and (4) facilitate the switch in myocyte phenotype through junctional reorganization. This should serve to highlight the need for further exploration of cellular nanojunctions and the mechanisms by which they operate, that will undoubtedly open up new therapeutic horizons.

Upregulation of Transient Receptor Potential Canonical Channels Contributes to Endotoxin-Induced Pulmonary Arterial Stenosis

Background

Septic shock is a pathologic condition caused by endotoxin-producing bacteria, and often associated with severe pulmonary hypertension. Inflammation is a major systemic response to endotoxin; however, it is unknown whether endotoxin has a direct impact on pulmonary arteries that contributes to pathogenesis of pulmonary hypertension.

Material/Methods

Rat pulmonary arteries and primary pulmonary arterial smooth muscle cells (PASMCs) were cultured in vitro and treated with lipopolysaccharide (LPS) and blockers of transient receptor potential canonical (TRPC) channels. Neointimal growth and arterial stenosis were observed on cryosections of cultured pulmonary arteries. Proliferation of PASMCs was examined by a WST-1 (water-soluble tetrazolium salt) assay. Expression of TRPC genes in pulmonary arteries and PASMCs were detected and quantified by real-time polymerase chain reaction and Western blotting.

Results

LPS significantly induced neointimal growth and stenosis of pulmonary arteries and promoted proliferation of PASMCs. TRPC channel blockers 2-aminoethoxydiphenyl borate and SKF-96365 inhibited LPS-induced remodeling of pulmonary arteries and PASMC proliferation. Expression of TRPC1/3/4/6 was detected in pulmonary arteries and PASMCs. LPS treatment dramatically increased the expression of TRPC3 and TRPC4 at both messenger RNA and protein levels.

Conclusions

LPS stimulates stenosis of pulmonary arteries through enhancement of TRPC-mediated Ca²⁺ entry into PASMCs, which is caused by upregulation of TRPC3 and TRPC4 channels.

From contraction to gene expression: nanojunctions of the sarco/endoplasmic reticulum deliver site- and function-specific calcium signals

Calcium signals determine, for example, smooth muscle contraction and changes in gene expression. How calcium signals select for these processes is enigmatic. We build on the "panjunctional sarcoplasmic reticulum" hypothesis, describing our view that different calcium pumps and release channels, with different kinetics and affinities for calcium, are strategically positioned within nanojunctions of the SR and help demarcate their respective cytoplasmic nanodomains. SERCA2b and RyR1 are preferentially targeted to the sarcoplasmic reticulum (SR) proximal to the plasma membrane (PM), i.e., to the superficial buffer barrier formed by PM-SR nanojunctions, and support vasodilation. In marked contrast, SERCA2a may be entirely restricted to the deep, perinuclear SR and may supply calcium to this sub-compartment in support of vasoconstriction. RyR3 is also preferentially targeted to the perinuclear SR, where its clusters associate with lysosome-SR nanojunctions. The distribution of RyR2 is more widespread and extends from this region to the wider cell. Therefore, perinuclear RyR3s most likely support the initiation of global calcium waves at L-SR junctions, which subsequently propagate by calcium-induced calcium release via RyR2 in order to elicit contraction. Data also suggest that unique SERCA and RyR are preferentially targeted to invaginations of the nuclear membrane. Site- and function-specific calcium signals may thus arise to modulate stimulus-response coupling and transcriptional cascades.

Enhanced expression of transient receptor potential channel 3 in uterine smooth muscle tissues of lipopolysaccharide-induced preterm delivery mice

OBJECTIVES

We aimed to investigate the influence of transient receptor potential channel 3 (TRPC3) on lipopolysaccharide-induced (LPS) preterm delivery mice.

MATERIALS AND METHODS

Mice were randomly assigned to the four groups: an unpregnant group, a mid-pregnancy group (E15), a term delivery group, and an LPS-induced preterm delivery group (intraperitoneal injection LPS at 15 days). Uterine smooth muscles were obtained through caesarean section; TRPC3 expression was measured by real-time PCR, western blotting, and immunohistochemistry. A specific inhibitor of TRPC3 (SKF96365) was injected into the LPS-induced preterm delivery group to determine whether the delivery interval was prolonged.

RESULTS

TRPC3 was primarily expressed in the uterine smooth muscle layer. In addition, the LPS-induced preterm delivery group had an obviously higher expression level of TRPC3 mRNA and protein compared with the unpregnant and E15 groups, which were close to term delivery. More importantly, SKF96365 prolongs the delivery interval of LPS-induced preterm delivery mice.

CONCLUSION

Enhanced expression of TRPC3 may be associated with LPS-induced preterm delivery in mice. The specific inhibitor of TRPC3 (SKF96365) may be helpful for clinical treatment of preterm delivery.

Lung Circulation

The circulation of the lung is unique both in volume and function. For example, it is the only organ with two circulations: the pulmonary circulation, the main function of which is gas exchange, and the bronchial circulation, a systemic vascular supply that provides oxygenated blood to the walls of the conducting airways, pulmonary arteries and veins. The pulmonary circulation accommodates the entire cardiac output, maintaining high blood flow at low intravascular arterial pressure. As compared with the systemic circulation, pulmonary arteries have thinner walls with much less vascular smooth muscle and a relative lack of basal tone. Factors controlling pulmonary blood flow include vascular structure, gravity, mechanical effects of breathing, and the influence of neural and humoral factors. Pulmonary vascular tone is also altered by hypoxia, which causes pulmonary vasoconstriction. If the hypoxic stimulus persists for a prolonged period, contraction is accompanied by remodeling of the vasculature, resulting in pulmonary hypertension. In addition, genetic and environmental factors can also confer susceptibility to development of pulmonary hypertension. Under normal conditions, the endothelium forms a tight barrier, actively regulating interstitial fluid homeostasis. Infection and inflammation compromise normal barrier homeostasis, resulting in increased permeability and edema formation. This article focuses on reviewing the basics of the lung circulation (pulmonary and bronchial), normal development and transition at birth and vasoregulation. Mechanisms contributing to pathological conditions in the pulmonary circulation, in particular when barrier function is disrupted and during development of pulmonary hypertension, will also be discussed.

Regulation of Intestinal Glucose Absorption by Ion Channels and Transporters

The absorption of glucose is electrogenic in the small intestinal epithelium. The major route for the transport of dietary glucose from intestinal lumen into enterocytes is the Na⁺/glucose cotransporter (SGLT1), although glucose transporter type 2 (GLUT2) may also play a role. The membrane potential of small intestinal epithelial cells (IEC) is important to regulate the activity of SGLT1. The maintenance of membrane potential mainly depends on the activities of cation channels and transporters. While the importance of SGLT1 in glucose absorption has been systemically studied in detail, little is currently known about the regulation of SGLT1 activity by cation channels and transporters. A growing line of evidence suggests that cytosolic calcium ([Ca²⁺]_cyt) can regulate the absorption of glucose by adjusting GLUT2 and SGLT1. Moreover, the absorption of glucose and homeostasis of Ca²⁺ in IEC are regulated by cation channels and transporters, such as Ca²⁺ channels, K⁺ channels, Na⁺/Ca²⁺ exchangers, and Na⁺/H⁺ exchangers. In this review, we consider the involvement of these cation channels and transporters in the regulation of glucose uptake in the small intestine. Modulation of them may be a potential strategy for the management of obesity and diabetes.

Molecular and functional significance of Ca(2+)-activated Cl(-) channels in pulmonary arterial smooth muscle

Increased peripheral resistance of small distal pulmonary arteries is a hallmark signature of pulmonary hypertension (PH) and is believed to be the consequence of enhanced vasoconstriction to agonists, thickening of the arterial wall due to remodeling, and increased thrombosis. The elevation in arterial tone in PH is attributable, at least in part, to smooth muscle cells of PH patients being more depolarized and displaying higher intracellular Ca(2+) levels than cells from normal subjects. It is now clear that downregulation of voltage-dependent K(+) channels (e.g., Kv1.5) and increased expression and activity of voltage-dependent (Cav1.2) and voltage-independent (e.g., canonical and vanilloid transient receptor potential [TRPC and TRPV]) Ca(2+) channels play an important role in the functional remodeling of pulmonary arteries in PH. This review focuses on an anion-permeable channel that is now considered a novel excitatory mechanism in the systemic and pulmonary circulations. It is permeable to Cl(-) and is activated by a rise in intracellular Ca(2+) concentration (Ca(2+)-activated Cl(-) channel, or CaCC). The first section outlines the biophysical and pharmacological properties of the channel and ends with a description of the molecular candidate genes postulated to encode for CaCCs, with particular emphasis on the bestrophin and the newly discovered TMEM16 and anoctamin families of genes. The second section provides a review of the various sources of Ca(2+) activating CaCCs, which include stimulation by mobilization from intracellular Ca(2+) stores and Ca(2+) entry through voltage-dependent and voltage-independent Ca(2+) channels. The third and final section summarizes recent findings that suggest a potentially important role for CaCCs and the gene TMEM16A in PH.

Transient receptor potential channels in the vasculature

The mammalian genome encodes 28 distinct members of the transient receptor potential (TRP) superfamily of cation channels, which exhibit varying degrees of selectivity for different ionic species. Multiple TRP channels are present in all cells and are involved in diverse aspects of cellular function, including sensory perception and signal transduction. Notably, TRP channels are involved in regulating vascular function and pathophysiology, the focus of this review. TRP channels in vascular smooth muscle cells participate in regulating contractility and proliferation, whereas endothelial TRP channel activity is an important contributor to endothelium-dependent vasodilation, vascular wall permeability, and angiogenesis. TRP channels are also present in perivascular sensory neurons and astrocytic endfeet proximal to cerebral arterioles, where they participate in the regulation of vascular tone. Almost all of these functions are mediated by changes in global intracellular Ca(2+) levels or subcellular Ca(2+) signaling events. In addition to directly mediating Ca(2+) entry, TRP channels influence intracellular Ca(2+) dynamics through membrane depolarization associated with the influx of cations or through receptor- or store-operated mechanisms. Dysregulation of TRP channels is associated with vascular-related pathologies, including hypertension, neointimal injury, ischemia-reperfusion injury, pulmonary edema, and neurogenic inflammation. In this review, we briefly consider general aspects of TRP channel biology and provide an in-depth discussion of the functions of TRP channels in vascular smooth muscle cells, endothelial cells, and perivascular cells under normal and pathophysiological conditions.

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.

Ion channels and transporters as therapeutic targets in the pulmonary circulation

Pulmonary circulation is a low pressure, low resistance, high flow system. The low resting vascular tone is maintained by the concerted action of ion channels, exchangers and pumps. Under physiological as well as pathophysiological conditions, they are targets of locally secreted or circulating vasodilators and/or vasoconstrictors, leading to changes in expression or to posttranslational modifications. Both structural changes in the pulmonary arteries and a sustained increase in pulmonary vascular tone result in pulmonary vascular remodeling contributing to morbidity and mortality in pediatric and adult patients. There is increasing evidence demonstrating the pivotal role of ion channels such as K(+) and Cl(-) or transient receptor potential channels in different cell types which are thought to play a key role in vasoconstrictive remodeling. This review focuses on ion channels, exchangers and pumps in the pulmonary circulation and summarizes their putative pathophysiological as well as therapeutic role in pulmonary vascular remodeling. A better understanding of the mechanisms of their actions may allow for the development of new options for attenuating acute and chronic pulmonary vasoconstriction and remodeling treating the devastating disease pulmonary hypertension.

Remodeling of rat pulmonary artery induced by chronic smoking exposure

OBJECTIVE

To evaluate the dominant role in rat pulmonary artery (PA) remodeling induced by chronic smoking exposure (CSE).

METHODS

Thirty-five male Sprague-Dawley (SD) rats were exposed to 36 cigarettes per day, 6 days per week, for 1, 3, or 5 months. Another 35 SD rats were sham-exposed during the same period. Hemodynamic measurement, evaluation of the right ventricular hypertrophy index (RVHI) plus right ventricle-to-weight ratio, and hematoxylin eosin staining was performed. Wall thickness, artery radius, luminal area, and total area were measured morphometrically. Western blotting assessed expression of PPAR-γ BMP4, BMPR2, and TRPC1/4/6 in the artery and lung. Store-operated calcium entry (SOCE) and [Ca(2+)]i were measured using Fura-2 as dye.

RESULTS

Mean right ventricular pressure increased after 3 months of smoking exposure and continued to increase through 5 months. Right ventricular systolic pressure (RVSP) increased after 3 months of exposure and then stabilized. RVHI increased after 5 months; right ventricle-to-weight ratio was elevated after 3 months and further increased after 5 months. Wall thickness-to-radius ratio does-dependently increased after 3 months through 5 months, in parallel with the decreased luminal area/total area ratio after 5 months. Other changes included the development of inflammatory responses, enlargement of the alveolar spaces, and reductions in the endothelial lining of PAs, proliferative smooth muscle cells, fibroblasts, and adventitia. Moreover, BMP4 and TRPC1/4/6 expression increased to varying degrees in the arteries and lungs of smoking-exposed animals, whereas BMPR expression and SOCE increased only in the arteries, and PPAR-γ was downregulated in both the arteries and lungs.

CONCLUSIONS

In SD rats, smoking exposure induces pulmonary vascular remodeling. The consequences of increased SOCE include increase in TRPC1/4/6, probably via augmented BMP4 expression, which also contribute to inflammatory responses in the lung. Moreover, interactions between BMP4 and PPAR-γ may play a role in preventing inflammation under normal physiological conditions.

Role of ASIC1 in the development of chronic hypoxia-induced pulmonary hypertension

Chronic hypoxia (CH) associated with respiratory disease results in elevated pulmonary vascular intracellular Ca(2+) concentration, which elicits enhanced vasoconstriction and promotes vascular arterial remodeling and thus has important implications in the development of pulmonary hypertension (PH). Store-operated Ca(2+) entry (SOCE) contributes to this elevated intracellular Ca(2+) concentration and has also been linked to acute hypoxic pulmonary vasoconstriction (HPV). Since our laboratory has recently demonstrated an important role for acid-sensing ion channel 1 (ASIC1) in mediating SOCE, we hypothesized that ASIC1 contributes to both HPV and the development of CH-induced PH. To test this hypothesis, we examined responses to acute hypoxia in isolated lungs and assessed the effects of CH on indexes of PH, arterial remodeling, and vasoconstrictor reactivity in wild-type (ASIC1(+/+)) and ASIC1 knockout (ASIC1(-/-)) mice. Restoration of ASIC1 expression in pulmonary arterial smooth muscle cells from ASIC1(-/-) mice rescued SOCE, confirming the requirement for ASIC1 in this response. HPV responses were blunted in lungs from ASIC1(-/-) mice. Both SOCE and receptor-mediated Ca(2+) entry, along with agonist-dependent vasoconstrictor responses, were diminished in small pulmonary arteries from control ASIC(-/-) mice compared with ASIC(+/+) mice. The effects of CH to augment receptor-mediated vasoconstrictor and SOCE responses in vessels from ASIC1(+/+) mice were not observed after CH in ASIC1(-/-) mice. In addition, ASIC1(-/-) mice exhibited diminished right ventricular systolic pressure, right ventricular hypertrophy, and arterial remodeling in response to CH compared with ASIC1(+/+) mice. Taken together, these data demonstrate an important role for ASIC1 in both HPV and the development of CH-induced PH.

Effects of chronic exposure to cigarette smoke on canonical transient receptor potential expression in rat pulmonary arterial smooth muscle

To clarify the possible mechanism of cigarette smoke (CS)-induced pulmonary hypertension and furthermore provide effective targets for prevention and treatment, the effects of chronic CS on rat pulmonary arterial smooth muscle in vivo and nicotine treatment on rat pulmonary arterial smooth muscle cells (PASMCs) in vitro were investigated. In this study, we demonstrated that chronic CS exposure led to rat weight loss, right ventricular hypertrophy, and pulmonary arterial remodeling. A fluorescence microscope was used to measure intracellular calcium concentration ([Ca(2+)]i) in rat distal PASMCs. Results showed that basal [Ca(2+)]i and store-operated calcium entry (SOCE) levels in PASMCs from 3- and 6-mo CS-exposed rats were markedly higher than those in cells from the unexposed control animals (the increases in 6-mo CS group were more significant than that in 3-mo group), accompanied with increased canonical transient receptor potential 1 (TRPC1) and TRPC6 expression at both mRNA and protein levels in isolated distal PA. Simultaneously, in vitro study showed that nicotine treatment (10 nM) significantly increased basal [Ca(2+)]i and SOCE and upregulated TRPC1 and TRPC6 expression in cultured rat distal PASMCs. TRPC siRNA knockdown strategies revealed that the elevations of basal [Ca(2+)]i and SOCE induced by nicotine in PASMCs were TRPC1 and TRPC6 dependent. These results suggested that chronic CS-induced changes in vascular tone and structure in PA and the development of pulmonary hypertension might be largely due to upregulation of TRPC1 and TRPC6 expression in PASMCs, in which nicotine played an important role.