Orai1, 2, 3 and STIM1 promote store-operated calcium entry in pulmonary arterial smooth muscle cells

Sodium Houttuyfonate Alleviates Monocrotaline-induced Pulmonary Hypertension by Regulating Orai1 and Orai2

An increased intracellular Ca2+ concentration ([Ca2+]i) is a key trigger for pulmonary arterial smooth muscle cell (PASMC) proliferation and contributes greatly to pulmonary hypertension (PH). Extracellular Ca2+ influx via a store-operated Ca2+ channel, termed store-operated Ca2+ entry (SOCE), is a crucial mechanism for [Ca2+]i increase in PASMCs. Calcium release-activated calcium modulator (Orai) proteins, consisting of three members (Orai1-3), are the main components of the store-operated Ca2+ channel. Sodium houttuyfonate (SH) is a product of the addition reaction of sodium bisulfite and houttuynin and has antibacterial, antiinflammatory, and other properties. In this study, we assessed the contributions of Orai proteins to monocrotaline (MCT)-enhanced SOCE, [Ca2+]i, and cell proliferation in PASMCs and determined the effect of SH on MCT-PH and the underlying mechanism, focusing on Orai proteins, SOCE, and [Ca2+]i in PASMCs. Our results showed that: 1) Orai1 and Orai2 were selectively upregulated in the distal pulmonary arteries and the PASMCs of MCT-PH rats; 2) knockdown of Orai1 or Orai2 reduced SOCE, [Ca2+]i, and cell proliferation without affecting their expression in PASMCs in MCT-PH rats; 3) SH significantly normalized the characteristic parameters in a dose-dependent manner in the MCT-PH rat model; and 4) SH decreased MCT-enhanced SOCE, [Ca2+]i, and PASMC proliferation via Orai1 or Orai2. These results indicate that SH likely exerts its protective role in MCT-PH by inhibiting the Orai1,2-SOCE-[Ca2+]i signaling pathway.

Identification of Noncoding Functional Regulatory Variants of STIM1 Gene in Idiopathic Pulmonary Arterial Hypertension

BACKGROUND

STIM1 (stromal interaction molecule 1) regulates store-operated calcium entry and is involved in pulmonary artery vasoconstriction and pulmonary artery smooth muscle cell proliferation, leading to pulmonary arterial hypertension (PAH).

METHODS

Bioinformatics analysis and a 2-stage matched case-control study were conducted to screen for noncoding variants that may potentially affect STIM1 transcriptional regulation in 242 patients with idiopathic PAH and 414 healthy controls. Luciferase reporter assay, real-time quantitative polymerase chain reaction, western blot, 5-ethynyl-2'-deoxyuridine (EdU) assay, and intracellular Ca2+ measurement were performed to study the mechanistic roles of those STIM1 noncoding variants in PAH.

RESULTS

Five noncoding variants (rs3794050, rs7934581, rs3750996, rs1561876, and rs3750994) were identified and genotyped using Sanger sequencing. Rs3794050, rs7934581, and rs1561876 were associated with idiopathic PAH (recessive model, all P<0.05). Bioinformatics analysis showed that these 3 noncoding variants possibly affect the enhancer function of STIM1 or the microRNA (miRNA) binding to STIM1. Functional validation performed in HEK293 and pulmonary artery smooth muscle cells demonstrated that the noncoding variant rs1561876-G (STIM1 mutant) had significantly stronger transcriptional activity than the wild-type counterpart, rs1561876-A, by affecting the transcriptional regulatory function of both hsa-miRNA-3140-5p and hsa-miRNA-4766-5p. rs1561876-G enhanced intracellular Ca2+ signaling in human pulmonary artery smooth muscle cells secondary to calcium-sensing receptor activation and promoted proliferation of pulmonary artery smooth muscle cells under both normoxia and hypoxia conditions, suggesting a possible contribution to PAH development.

CONCLUSIONS

The potential clinical implications of the 3 noncoding variants of STIM1, rs3794050, rs7934581, and rs1561876, are 2-fold, as they may help predict the risk and prognosis of idiopathic PAH and guide investigations on novel therapeutic pathway(s).

Orai1/STIMs modulators in pulmonary vascular diseases

Calcium (Ca2+) is a secondary messenger that regulates various cellular processes. However, Ca2+ mishandling could lead to pathological conditions. Orai1 is a Ca2+channel contributing to the store-operated calcium entry (SOCE) and plays a critical role in Ca2+ homeostasis in several cell types. Dysregulation of Orai1 contributed to severe combined immune deficiency syndrome, some cancers, pulmonary arterial hypertension (PAH), and other cardiorespiratory diseases. During its activation process, Orai1 is mainly regulated by stromal interacting molecule (STIM) proteins, especially STIM1; however, many other regulatory partners have also been recently described. Increasing knowledge about these regulatory partners provides a better view of the downstream signalling pathways of SOCE and offers an excellent opportunity to decipher Orai1 dysregulation in these diseases. These proteins participate in other cellular functions, making them attractive therapeutic targets. This review mainly focuses on Orai1 regulatory partners in the physiological and pathological conditions of the pulmonary circulation and inflammation.

Nupr1-mediated vascular smooth muscle cell phenotype transformation involved in methamphetamine induces pulmonary hypertension

AIMS

Nuclear protein 1 (Nupr1) is a multifunctional stress-induced protein involved in the regulation of tumorigenesis, apoptosis, and autophagy. However, its role in pulmonary hypertension (PH) after METH exposure remains unexplored. In this study, we aimed to investigate whether METH can induce PH and describe the role and mechanism of Nupr1 in the development of PH.

METHODS AND RESULTS

Mice were made to induce pulmonary hypertension (PH) upon chronic intermittent treatment with METH. Their right ventricular systolic pressure (RVSP) was measured to assess pulmonary artery pressure. Pulmonary artery morphometry was determined by H&E staining and Masson staining. Nupr1 expression and function were detected in human lungs, mice lungs exposed to METH, and cultured pulmonary arterial smooth muscle cells (PASMCs) with METH treatment. Our results showed that chronic intermittent METH treatment successfully induced PH in mice. Nupr1 expression was increased in the cultured PASMCs, pulmonary arterial media from METH-exposed mice, and METH-ingested human specimens compared with control. Elevated Nupr1 expression promoted PASMC phenotype change from contractile to synthetic, which triggered pulmonary artery remodeling and resulted in PH formation. Mechanistically, Nupr1 mediated the opening of store-operated calcium entry (SOCE) by activating the expression of STIM1, thereby promoting Ca2+ influx and inducing phenotypic conversion of PASMCs.

CONCLUSIONS

Nupr1 activation could promote Ca2+ influx through STIM1-mediated SOCE opening, which promoted METH-induced pulmonary artery remodeling and led to PH formation. These results suggested that Nupr1 played an important role in METH-induced PH and might be a potential target for METH-related PH therapy.

Side-by-side comparison of published small molecule inhibitors against thapsigargin-induced store-operated Ca2+ entry in HEK293 cells

Calcium (Ca2+) is a key second messenger in eukaryotes, with store-operated Ca2+ entry (SOCE) being the main source of Ca2+ influx into non-excitable cells. ORAI1 is a highly Ca2+-selective plasma membrane channel that encodes SOCE. It is ubiquitously expressed in mammals and has been implicated in numerous diseases, including cardiovascular disease and cancer. A number of small molecules have been identified as inhibitors of SOCE with a variety of potential therapeutic uses proposed and validated in vitro and in vivo. These encompass both nonselective Ca2+ channel inhibitors and targeted selective inhibitors of SOCE. Inhibition of SOCE can be quantified both directly and indirectly with a variety of assay setups, making an accurate comparison of the activity of different SOCE inhibitors challenging. We have used a fluorescence based Ca2+ addback assay in native HEK293 cells to generate dose-response data for many published SOCE inhibitors. We were able to directly compare potency. Most compounds were validated with only minor and expected variations in potency, but some were not. This could be due to differences in assay setup relating to the mechanism of action of the inhibitors and highlights the value of a singular approach to compare these compounds, as well as the general need for biorthogonal validation of novel bioactive compounds. The compounds observed to be the most potent against SOCE in our study were: 7-azaindole 14d (12), JPIII (17), Synta-66 (6), Pyr 3 (5), GSK5503A (8), CM4620 (14) and RO2959 (7). These represent the most promising candidates for future development of SOCE inhibitors for therapeutic use.

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.

Thrombotic Alterations under Perinatal Hypoxic Conditions: HIF and Other Hypoxic Markers

Hypoxia is considered to be a stressful physiological condition, which may occur during labor and the later stages of pregnancy as a result of, among other reasons, an aged placenta. Therefore, when gestation or labor is prolonged, low oxygen supply to the tissues may last for minutes, and newborns may present breathing problems and may require resuscitation maneuvers. As a result, poor oxygen supply to tissues and to circulating cells may last for longer periods of time, leading to life-threatening conditions. In contrast to the well-known platelet activation that occurs after reperfusion of the tissues due to an ischemia/reperfusion episode, platelet alterations in response to reduced oxygen exposition following labor have been less frequently investigated. Newborns overcome temporal hypoxic conditions by changing their organ functions or by adaptation of the intracellular molecular pathways. In the present review, we aim to analyze the main platelet modifications that appear at the protein level during hypoxia in order to highlight new platelet markers linked to complications arising from temporal hypoxic conditions during labor. Thus, we demonstrate that hypoxia modifies the expression and activity of hypoxic-response proteins (HRPs), including hypoxia-induced factor (HIF-1), endoplasmic reticulum oxidase 1 (Ero1), and carbonic anhydrase (CIX). Finally, we provide updates on research related to the regulation of platelet function due to HRP activation, as well as the role of HRPs in intracellular Ca2+ homeostasis.

SARS-CoV-2 spike protein receptor-binding domain perturbates intracellular calcium homeostasis and impairs pulmonary vascular endothelial cells

Exposure to the spike protein or receptor-binding domain (S-RBD) of SARS-CoV-2 significantly influences endothelial cells and induces pulmonary vascular endotheliopathy. In this study, angiotensin-converting enzyme 2 humanized inbred (hACE2 Tg) mice and cultured pulmonary vascular endothelial cells were used to investigate how spike protein/S-RBD impacts pulmonary vascular endothelium. Results show that S-RBD leads to acute-to-prolonged induction of the intracellular free calcium concentration ([Ca2+]i) via acute activation of TRPV4, and prolonged upregulation of mechanosensitive channel Piezo1 and store-operated calcium channel (SOCC) key component Orai1 in cultured human pulmonary arterial endothelial cells (PAECs). In mechanism, S-RBD interacts with ACE2 to induce formation of clusters involving Orai1, Piezo1 and TRPC1, facilitate the channel activation of Piezo1 and SOCC, and lead to elevated apoptosis. These effects are blocked by Kobophenol A, which inhibits the binding between S-RBD and ACE2, or intracellular calcium chelator, BAPTA-AM. Blockade of Piezo1 and SOCC by GsMTx4 effectively protects the S-RBD-induced pulmonary microvascular endothelial damage in hACE2 Tg mice via normalizing the elevated [Ca2+]i. Comparing to prototypic strain, Omicron variants (BA.5.2 and XBB) of S-RBD induces significantly less severe cell apoptosis. Transcriptomic analysis indicates that prototypic S-RBD confers more severe acute impacts than Delta or Lambda S-RBD. In summary, this study provides compelling evidence that S-RBD could induce persistent pulmonary vascular endothelial damage by binding to ACE2 and triggering [Ca2+]i through upregulation of Piezo1 and Orai1. Targeted inhibition of ACE2-Piezo1/SOCC-[Ca2+]i axis proves a powerful strategy to treat S-RBD-induced pulmonary vascular diseases.

Role of ryanodine receptor 2 and FK506-binding protein 12.6 dissociation in pulmonary hypertension

Pulmonary hypertension (PH) is a devastating disease characterized by a progressive increase in pulmonary arterial pressure leading to right ventricular failure and death. A major cellular response in this disease is the contraction of smooth muscle cells (SMCs) of the pulmonary vasculature. Cell contraction is determined by the increase in intracellular Ca2+ concentration ([Ca2+]i), which is generated and regulated by various ion channels. Several studies by us and others have shown that ryanodine receptor 2 (RyR2), a Ca2+-releasing channel in the sarcoplasmic reticulum (SR), is an essential ion channel for the control of [Ca2+]i in pulmonary artery SMCs (PASMCs), thereby mediating the sustained vasoconstriction seen in PH. FK506-binding protein 12.6 (FKBP12.6) strongly associates with RyR2 to stabilize its functional activity. FKBP12.6 can be dissociated from RyR2 by a hypoxic stimulus to increase channel function and Ca2+ release, leading to pulmonary vasoconstriction and PH. More specifically, dissociation of the RyR2-FKBP12.6 complex is a consequence of increased mitochondrial ROS generation mediated by the Rieske iron-sulfur protein (RISP) at the mitochondrial complex III after hypoxia. Overall, RyR2/FKBP12.6 dissociation and the corresponding signaling pathway may be an important factor in the development of PH. Novel drugs and biologics targeting RyR2, FKBP12.6, and related molecules may become unique effective therapeutics for PH.

The alkalinizing, lysosomotropic agent ML-9 induces a pH-dependent depletion of ER Ca2+ stores in cellulo

ML-9 elicits a broad spectrum of effects in cells, including inhibition of myosin light chain kinase, inhibition of store-operated Ca²⁺ entry and lysosomotropic actions that result in prostate cancer cell death. Moreover, the compound also affects endoplasmic reticulum (ER) Ca²⁺ homeostasis, although the underlying mechanisms remain unclear. We found that ML-9 provokes a rapid mobilization of Ca²⁺ from ER independently of IP₃Rs or TMBIM6/Bax Inhibitor-1, two ER Ca²⁺-leak channels. Moreover, in unidirectional ⁴⁵Ca²⁺ fluxes in permeabilized cells, ML-9 was able to reduce ER Ca²⁺-store content. Although the ER Ca²⁺ store content was decreased, ML-9 did not directly inhibit SERCA's ATPase activity in vitro using microsomal preparations. Consistent with its chemical properties as a cell-permeable weak alkalinizing agent (calculated pKa of 8.04), ML-9 provoked a rapid increase in cytosolic pH preceding the Ca²⁺ efflux from the ER. Pre-treatment with the weak acid 3NPA blunted the ML-9-evoked increase in intracellular pH and subsequent ML-9-induced Ca²⁺ mobilization from the ER. This experiment underpins a causal link between ML-9's impact on the pH and Ca²⁺ dynamics. Overall, our work indicates that the lysosomotropic drug ML-9 may not only impact lysosomal compartments but also have severe impacts on ER Ca²⁺ handling in cellulo.

Basal Vascular Smooth Muscle Cell Tone in eNOS Knockout Mice Can Be Reversed by Cyclic Stretch and Is Independent of Age

Introduction and Aims: Endothelial nitric oxide synthase (eNOS) knockout mice develop pronounced cardiovascular disease. In the present study, we describe the alterations in aortic physiology and biomechanics of eNOS knockout and C57Bl/6 control mice at 2–12 months of age, including a thorough physiological investigation of age and cyclic stretch-dependent VSMC contractility and aortic stiffness.

Methods and Results: Peripheral blood pressure and aortic pulse wave velocity were measured in vivo, and aortic biomechanical studies and isometric contractions were investigated ex vivo. Age-dependent progression of aortic stiffness, peripheral hypertension, and aortic contractility in eNOS knockout mice was absent, attenuated, or similar to C57Bl/6 control mice. Voltage-gated calcium channel (VGCC)-dependent calcium influx inversely affected isometric contraction and aortic stiffening by α₁-adrenergic stimulation in eNOS knockout mice. Baseline aortic stiffness was selectively reduced in eNOS knockout mice after ex vivo cyclic stretch exposure in an amplitude-dependent manner, which prompted us to investigate cyclic stretch dependent regulation of aortic contractility and stiffness. Aortic stiffness, both in baseline conditions and after activation of vascular smooth muscle cell (VSMC) contraction, was reduced with increasing cyclic stretch amplitude. This cyclic stretch dependency was attenuated with age, although aged eNOS knockout mice displayed better preservation of cyclic stretch-dependency compared to C57Bl/6 control mice. Store operated calcium entry-medicated aortic stiffening as induced by inhibiting sarcoplasmic reticulum calcium ATPase pumps with 10 µM CPA was most pronounced in the aorta of aged mice and at low cyclic stretch amplitude, but independent of eNOS. Basal aortic tonus and VSMC depolarization were highly dependent on eNOS, and were most pronounced at low cyclic stretch, with attenuation at increasing cyclic stretch amplitude.

Conclusion: eNOS knockout mice display attenuated progression of arterial disease as compared to C57Bl/6 control mice. Basal VSMC tone in eNOS knockout mice could be reduced by ex vivo exposure to cyclic stretch through stretch-dependent regulation of cytosolic calcium. Both baseline and active aortic stiffness were highly dependent on cyclic stretch regulation, which was more pronounced in young versus aged mice. Other mediators of VSMC contraction and calcium handling were dependent on cyclic stretch mechanotransduction, but independent of eNOS.

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.

Crucial Role of Stromal Interaction Molecule-Activated TRPC-ORAI Channels in Vascular Remodeling and Pulmonary Hypertension Induced by Intermittent Hypoxia

Obstructive sleep apnea (OSA), a sleep breathing disorder featured by chronic intermittent hypoxia (CIH), is associate with pulmonary hypertension. Rats exposed to CIH develop lung vascular remodeling and pulmonary hypertension, which paralleled the upregulation of stromal interaction molecule (STIM)-activated TRPC-ORAI Ca2+ channels (STOC) in the lung, suggesting that STOC participate in the pulmonary vascular alterations. Accordingly, to evaluate the role played by STOC in pulmonary hypertension we studied whether the STOC blocker 2-aminoethoxydiphenyl borate (2-APB) may prevent the vascular remodeling and the pulmonary hypertension induced by CIH in a rat model of OSA. We assessed the effects of 2-APB on right ventricular systolic pressure (RVSP), pulmonary vascular remodeling, α-actin and proliferation marker Ki-67 levels in pulmonary arterial smooth muscle cells (PASMC), mRNA levels of STOC subunits, and systemic and pulmonary oxidative stress (TBARS) in male Sprague-Dawley (200 g) rats exposed to CIH (5% O2, 12 times/h for 8h) for 28 days. At 14 days of CIH, osmotic pumps containing 2-APB (10 mg/kg/day) or its vehicle were implanted and rats were kept for 2 more weeks in CIH. Exposure to CIH for 28 days raised RVSP &gt; 35 mm Hg, increased the medial layer thickness and the levels of α-actin and Ki-67 in PASMC, and increased the gene expression of TRPC1, TRPC4, TRPC6 and ORAI1 subunits. Treatment with 2-APB prevented the raise in RVSP and the increment of the medial layer thickness, as well as the increased levels of α-actin and Ki-67 in PASMC, and the increased gene expression of STOC subunits. In addition, 2-APB did not reduced the lung and systemic oxidative stress, suggesting that the effects of 2-APB on vascular remodeling and pulmonary hypertension are independent on the reduction of the oxidative stress. Thus, our results supported that STIM-activated TRPC-ORAI Ca2+ channels contributes to the lung vascular remodeling and pulmonary hypertension induced by CIH.

Gut Microbial Metabolite Trimethylamine N-Oxide Aggravates Pulmonary Hypertension

Trimethylamine N-oxide (TMAO), a metabolite derived from intestine microbial flora, enhances vascular inflammation in a variety of cardiovascular disease, and the bacterial communities associated with trimethylamine N-oxide (TMAO) metabolism is higher in pulmonary hypertension (PH) patients. The effects of TMAO on PH, however, has not been elucidated. In the present study, we found that circulating TMAO was elevated in intermediate to high-risk PH patients when compared to healthy control or low-risk PH patients. In monocrotaline-induced rat PH models, circulating TMAO was elevated; and reduction of TMAO using 3,3-dimethyl-1-butanol (DMB) significantly decreased right ventricle systolic pressure, pulmonary vascular muscularization in both monocrotaline-induced rat PH and hypoxia induced mice PH models. RNA sequencing of rat lungs revealed that DMB treatment significant suppressed the pathways involved in cytokine-cytokine receptor interaction, and cytokine and chemokine signaling. Protein-protein interaction analysis of the differentially expressed transcripts regulated by DMB showed 5 hub genes with a strong connectivity of proinflammatory cytokines and chemokines including Kng1, Cxcl1, Cxcl2, CxcL6 and Il6. In vitro, TMAO significantly increased the expression of Kng1, Cxcl1, Cxcl2, CxcL6 and Il6 in bone marrow derived macrophage. And TMAO-treated conditioned medium from macrophage increased the proliferation and migration of pulmonary artery smooth muscle cells; but TMAO treatment did not change the proliferation or migration of pulmonary artery smooth muscle cells. In conclusion, our study demonstrates that TMAO is increased in severe PH, and the reduction of TMAO decreases pulmonary vascular muscularization and alleviates PH via suppressing the macrophage production of chemokines and cytokines.

The Action of 2-Aminoethyldiphenyl Borinate on the Pulmonary Arterial Hypertension and Remodeling of High-Altitude Hypoxemic Lambs

Calcium signaling is key for the contraction, differentiation, and proliferation of pulmonary arterial smooth muscle cells. Furthermore, calcium influx through store-operated channels (SOCs) is particularly important in the vasoconstrictor response to hypoxia. Previously, we found a decrease in pulmonary hypertension and remodeling in normoxic newborn lambs partially gestated under chronic hypoxia, when treated with 2-aminoethyldiphenyl borinate (2-APB), a non-specific SOC blocker. However, the effects of 2-APB are unknown in neonates completely gestated, born, and raised under environmental hypoxia. Accordingly, we studied the effects of 2-APB-treatment on the cardiopulmonary variables in lambs under chronic hypobaric hypoxia. Experiments were done in nine newborn lambs gestated, born, and raised in high altitude (3,600 m): five animals were treated with 2-APB [intravenous (i.v.) 10 mg kg^–1] for 10 days, while other four animals received vehicle. During the treatment, cardiopulmonary variables were measured daily, and these were also evaluated during an acute episode of superimposed hypoxia, 1 day after the end of the treatment. Furthermore, pulmonary vascular remodeling was assessed by histological analysis 2 days after the end of the treatment. Basal cardiac output and mean systemic arterial pressure (SAP) and resistance from 2-APB- and vehicle-treated lambs did not differ along with the treatment. Mean pulmonary arterial pressure (mPAP) decreased after the first day of 2-APB treatment and remained lower than the vehicle-treated group until the third day, and during the fifth, sixth, and ninth day of treatment. The net mPAP increase in response to acute hypoxia did not change, but the pressure area under the curve (AUC) during hypoxia was slightly lower in 2-APB-treated lambs than in vehicle-treated lambs. Moreover, the 2-APB treatment decreased the pulmonary arterial wall thickness and the α-actin immunoreactivity and increased the luminal area with no changes in the vascular density. Our findings show that 2-APB treatment partially reduced the contractile hypoxic response and reverted the pulmonary vascular remodeling, but this is not enough to normalize the pulmonary hemodynamics in chronically hypoxic newborn lambs.

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.

ORAI3 contributes to hypoxia-inducible factor 1/2α-sensitive colon cell migration

BACKGROUND

Hypoxia is a pivotal initiator of tumor angiogenesis and growth through the stabilization of hypoxia-inducible factors (HIFs). This study set out to examine the involvement of HIF-1α and HIF-2α in colon cancer and ascertained whether ORAI3 was involved in the pathway.

MATERIALS AND METHODS

Patients and murine models as well as human colorectal adenocarcinoma tumor (CW2) cells were included to examine the levels of ORAI1/3 and HIF-1/2α levels. Calcium imaging was utilized to ascertain the activity of calcium channel. Scratch assay was used to assess the migration capacity of the cells.

RESULTS

Tumors from murine colon cancer xenograft models and patients with colon cancer displayed high ORAI1/3 and HIF-1/2α levels. Hypoxia treatment, mimicking the tumor microenvironment in vitro, increased ORAI1/3 and HIF-1/2α expression as well as store-operated Ca2+ entry (SOCE). Of note is that HIF-1/2α silencing decreased SOCE, and HIF-1/2α overexpression facilitated SOCE. Furthermore, ORAI3 rather than ORAI1 expression was inhibited by HIF-1/2α silencing while increased by ML228. Luciferase assay also confirmed that ORAI3 was elevated in the presence of ML228, indicating the linkage between HIF-1/2α and ORAI3. Additionally, colony-forming potential and cell migration capacity were decreased in siHIF-1α and siHIF-2α as well as siORAI3 cells, and the facilitating effect of ML228 on cell migration and colony-forming potential was also decreased in siORAI3 CW-2 cells, which points out the importance of ORAI3 in HIF1/2α pathway.

CONCLUSION

Our findings allow to conclude that both HIF-1α and HIF-2α facilitate ORAI3 expression, hence enhancing colon cancer progression.

Upregulation of Piezo1 (Piezo Type Mechanosensitive Ion Channel Component 1) Enhances the Intracellular Free Calcium in Pulmonary Arterial Smooth Muscle Cells From Idiopathic Pulmonary Arterial Hypertension Patients

[Figure: see text].

Proteins Interacting with STIM1 and Store-Operated Ca2+ Entry

The endoplasmic reticulum (ER) Ca²⁺ sensor stromal interaction molecule 1 (STIM1) interacts with ORAI Ca²⁺ channels at the plasma membrane to regulate immune and muscle cell function. The conformational changes underlying STIM1 activation, translocation, and ORAI1 trapping and gating, are stringently regulated by post-translational modifications and accessory proteins. Here, we review the recent progress in the identification and characterization of ER and cytosolic proteins interacting with STIM1 to control its activation and deactivation during store-operated Ca²⁺ entry (SOCE).

Calcium Channels in Adult Brain Neural Stem Cells and in Glioblastoma Stem Cells

The brain of adult mammals, including humans, contains neural stem cells (NSCs) located within specific niches of which the ventricular-subventricular zone (V-SVZ) is the largest one. Under physiological conditions, NSCs proliferate, self-renew and produce new neurons and glial cells. Several recent studies established that oncogenic mutations in adult NSCs of the V-SVZ are responsible for the emergence of malignant primary brain tumors called glioblastoma. These aggressive tumors contain a small subpopulation of cells, the glioblastoma stem cells (GSCs), that are endowed with proliferative and self-renewal abilities like NSCs from which they may arise. GSCs are thus considered as the cells that initiate and sustain tumor growth and, because of their resistance to current treatments, provoke tumor relapse. A growing body of studies supports that Ca²⁺ signaling controls a variety of processes in NSCs and GSCs. Ca²⁺ is a ubiquitous second messenger whose fluctuations of its intracellular concentrations are handled by channels, pumps, exchangers, and Ca²⁺ binding proteins. The concerted action of the Ca²⁺ toolkit components encodes specific Ca²⁺ signals with defined spatio-temporal characteristics that determine the cellular responses. In this review, after a general overview of the adult brain NSCs and GSCs, we focus on the multiple roles of the Ca²⁺ toolkit in NSCs and discuss how GSCs hijack these mechanisms to promote tumor growth. Extensive knowledge of the role of the Ca²⁺ toolkit in the management of essential functions in healthy and pathological stem cells of the adult brain should help to identify promising targets for clinical applications.

Stim-activated TRPC-ORAI channels in pulmonary hypertension induced by chronic intermittent hypoxia

Obstructive sleep apnea (OSA), a breathing disorder featured by chronic intermittent hypoxia (CIH) is associated with pulmonary hypertension (PH). Rodents exposed to CIH develop pulmonary vascular remodeling and PH, but the pathogenic mechanisms are not well known. Overexpression of Stim-activated Transient Receptor Potential Channels (TRPC) and Calcium Release-Activated Calcium Channel Protein (ORAI) TRPC-ORAI Ca²⁺ channels (STOC) has been involved in pulmonary vascular remodeling and PH in sustained hypoxia. However, it is not known if CIH may change STOC levels. Accordingly, we studied the effects of CIH on the expression of STOC subunits in the lung and if these changes paralleled the progression of the vascular pulmonary remodeling and PH in a preclinical model of OSA. Male Sprague-Dawley rats (∼200 g) were exposed to CIH (5%O₂, 12 times/h for 8 h) for 14, 21, and 28 days. We measured right ventricular systolic pressure (RVSP), cardiac morphometry with MRI, pulmonary vascular remodeling, and wire-myographic arterial responses to KCl and endothelin-1 (ET-1). Pulmonary RNA and protein STOC levels of TRPC1, TRPC4, TRPC6, ORAI 1, ORAI 2, and STIM1 subunits were measured by qPCR and western blot, and results were compared with age-matched controls. CIH elicited a progressive increase of RVSP and vascular contractile responses to KCl and ET-1, leading to vascular remodeling and augmented right ventricular ejection fraction, which was significant at 28 days of CIH. The levels of TRPC1, TRPC4, TRPC 6, ORAI 1, and STIM 1 channels increased following CIH, and some of them paralleled morphologic and functional changes. Our findings show that CIH increased pulmonary STOC expression, paralleling vascular remodeling and PH.

Vasoconstrictor Mechanisms in Chronic Hypoxia-Induced Pulmonary Hypertension: Role of Oxidant Signaling

Elevated resistance of pulmonary circulation after chronic hypoxia exposure leads to pulmonary hypertension. Contributing to this pathological process is enhanced pulmonary vasoconstriction through both calcium-dependent and calcium sensitization mechanisms. Reactive oxygen species (ROS), as a result of increased enzymatic production and/or decreased scavenging, participate in augmentation of pulmonary arterial constriction by potentiating calcium influx as well as activation of myofilament sensitization, therefore mediating the development of pulmonary hypertension. Here, we review the effects of chronic hypoxia on sources of ROS within the pulmonary vasculature including NADPH oxidases, mitochondria, uncoupled endothelial nitric oxide synthase, xanthine oxidase, monoamine oxidases and dysfunctional superoxide dismutases. We also summarize the ROS-induced functional alterations of various Ca2+ and K+ channels involved in regulating Ca2+ influx, and of Rho kinase that is responsible for myofilament Ca2+ sensitivity. A variety of antioxidants have been shown to have beneficial therapeutic effects in animal models of pulmonary hypertension, supporting the role of ROS in the development of pulmonary hypertension. A better understanding of the mechanisms by which ROS enhance vasoconstriction will be useful in evaluating the efficacy of antioxidants for the treatment of pulmonary hypertension.

Long-term chronic intermittent hypoxia: a particular form of chronic high-altitude pulmonary hypertension

In some subjects, high-altitude hypobaric hypoxia leads to high-altitude pulmonary hypertension. The threshold for the diagnosis of high-altitude pulmonary hypertension is a mean pulmonary artery pressure of 30 mmHg, even though for general pulmonary hypertension is ≥25 mmHg. High-altitude pulmonary hypertension has been associated with high hematocrit findings (chronic mountain sickness), and although these are two separate entities, they have a synergistic effect that should be considered. In recent years, a new condition associated with high altitude was described in South America named long-term chronic intermittent hypoxia and has appeared in individuals who commute to work at high altitude but live and rest at sea level. In this review, we discuss the initial epidemiological pattern from the early studies done in Chile, the clinical presentation and possible molecular mechanism and a discussion of the potential management of this condition.

TRPC Channels in the SOCE Scenario

Transient receptor potential (TRP) proteins form non-selective Ca²⁺ permeable channels that contribute to the modulation of a number of physiological functions in a variety of cell types. Since the identification of TRP proteins in Drosophila, it is well known that these channels are activated by stimuli that induce PIP₂ hydrolysis. The canonical TRP (TRPC) channels have long been suggested to be constituents of the store-operated Ca²⁺ (SOC) channels; however, none of the TRPC channels generate Ca²⁺ currents that resemble I_CRAC. STIM1 and Orai1 have been identified as the components of the Ca²⁺ release-activated Ca²⁺ (CRAC) channels and there is a body of evidence supporting that STIM1 is able to gate Orai1 and TRPC1 in order to mediate non-selective cation currents named I_SOC. STIM1 has been found to interact to and activate Orai1 and TRPC1 by different mechanisms and the involvement of TRPC1 in store-operated Ca²⁺ entry requires both STIM1 and Orai1. In addition to the participation of TRPC1 in the I_SOC currents, TRPC1 and other TRPC proteins might play a relevant role modulating Orai1 channel function. This review summarizes the functional role of TRPC channels in the STIM1–Orai1 scenario.

Pathophysiological Significance of Store-Operated Calcium Entry in Cardiovascular and Skeletal Muscle Disorders and Angiogenesis

Store-Operated Ca²⁺ Entry (SOCE) is an important Ca²⁺ influx pathway expressed by several excitable and non-excitable cell types. SOCE is recognized as relevant signaling pathway not only for physiological process, but also for its involvement in different pathologies. In fact, independent studies demonstrated the implication of essential protein regulating SOCE, such as STIM, Orai and TRPCs, in different pathogenesis and cell disorders, including cardiovascular disease, muscular dystrophies and angiogenesis. Compelling evidence showed that dysregulation in the function and/or expression of isoforms of STIM, Orai or TRPC play pivotal roles in cardiac hypertrophy and heart failure, vascular remodeling and hypertension, skeletal myopathies, and angiogenesis. In this chapter, we summarized the current knowledge concerning the mechanisms underlying abnormal SOCE and its involvement in some diseases, as well as, we discussed the significance of STIM, Orai and TRPC isoforms as possible therapeutic targets for the treatment of angiogenesis, cardiovascular and skeletal muscle diseases.

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.

Glucose-mediated inhibition of calcium-activated potassium channels limits α-cell calcium influx and glucagon secretion

Pancreatic α-cells exhibit oscillations in cytosolic Ca²⁺ (Ca²⁺_c), which control pulsatile glucagon (GCG) secretion. However, the mechanisms that modulate α-cell Ca²⁺_c oscillations have not been elucidated. As β-cell Ca²⁺_c oscillations are regulated in part by Ca²⁺-activated K⁺ (K_slow) currents, this work investigated the role of K_slow in α-cell Ca²⁺ handling and GCG secretion. α-Cells displayed K_slow currents that were dependent on Ca²⁺ influx through L- and P/Q-type voltage-dependent Ca²⁺ channels (VDCCs) as well as Ca²⁺ released from endoplasmic reticulum stores. α-Cell K_slow was decreased by small-conductance Ca²⁺-activated K⁺ (SK) channel inhibitors apamin and UCL 1684, large-conductance Ca²⁺-activated K⁺ (BK) channel inhibitor iberiotoxin (IbTx), and intermediate-conductance Ca²⁺-activated K⁺ (IK) channel inhibitor TRAM 34. Moreover, partial inhibition of α-cell K_slow with apamin depolarized membrane potential ( V_m) (3.8 ± 0.7 mV) and reduced action potential (AP) amplitude (10.4 ± 1.9 mV). Although apamin transiently increased Ca²⁺ influx into α-cells at low glucose (42.9 ± 10.6%), sustained SK (38.5 ± 10.4%) or BK channel inhibition (31.0 ± 11.7%) decreased α-cell Ca²⁺ influx. Total α-cell Ca²⁺_c was similarly reduced (28.3 ± 11.1%) following prolonged treatment with high glucose, but it was not decreased further by SK or BK channel inhibition. Consistent with reduced α-cell Ca²⁺_c following prolonged K_slow inhibition, apamin decreased GCG secretion from mouse (20.4 ± 4.2%) and human (27.7 ± 13.1%) islets at low glucose. These data demonstrate that K_slow activation provides a hyperpolarizing influence on α-cell V_m that sustains Ca²⁺ entry during hypoglycemic conditions, presumably by preventing voltage-dependent inactivation of P/Q-type VDCCs. Thus, when α-cell Ca²⁺_c is elevated during secretagogue stimulation, K_slow activation helps to preserve GCG secretion.

Role of HIF1α Regulatory Factors in Stem Cells

Hypoxia-inducible factor 1 (HIF1) is a master transcription factor that induces the transcription of genes involved in the metabolism and behavior of stem cells. HIF1-mediated adaptation to hypoxia is required to maintain the pluripotency and survival of stem cells under hypoxic conditions. HIF1 activity is well known to be tightly controlled by the alpha subunit of HIF1 (HIF1α). Understanding the regulatory mechanisms that control HIF1 activity in stem cells will provide novel insights into stem cell biology under hypoxia. Recent research has unraveled the mechanistic details of HIF1α regulating processes, suggesting new strategies for regulating stem cells. This review summarizes recent experimental studies on the role of several regulatory factors (including calcium, 2-oxoglutarate-dependent dioxygenase, microtubule network, importin, and coactivators) in regulating HIF1α activity in stem cells.

ORAI channels in cellular remodeling of cardiorespiratory disease

Cardiorespiratory disease, which includes systemic arterial hypertension, restenosis, atherosclerosis, pulmonary arterial hypertension, asthma, and chronic obstructive pulmonary disease (COPD) are highly prevalent and devastating diseases with limited therapeutic modalities. A common pathophysiological theme to these diseases is cellular remodeling, which is contributed by changes in expression and activation of ion channels critical for either excitability or growth. Calcium (Ca²⁺) signaling and specifically ORAI Ca²⁺ channels have emerged as significant regulators of smooth muscle, endothelial, epithelial, platelet, and immune cell remodeling. This review details the dysregulation of ORAI in cardiorespiratory diseases, and how this dysregulation of ORAI contributes to cellular remodeling.

ORAI Channels as Potential Therapeutic Targets in Pulmonary Hypertension

Pulmonary hypertension is a complex and fatal disease that lacks treatments. Its pathophysiology involves pulmonary artery hyperreactivity, endothelial dysfunction, wall remodelling, inflammation, and thrombosis, which could all depend on ORAI Ca²⁺ channels. We review the knowledge about ORAI channels in pulmonary artery and discuss the interest to target them in the treatment of pulmonary hypertension.

Protease-activated receptor 2 activates CRAC-mediated Ca2+ influx to cause prostate smooth muscle contraction

Protease activated receptor 2 (PAR2) is a G-protein coupled receptor that contributes to prostate fibrosis and lower urinary tract symptoms (LUTS). In addition to fibrosis, aberrant smooth muscle tone in the prostate has been hypothesized to play a role. We therefore examined PAR2 expression in primary human prostate smooth muscle cells (PSMC) and studied the downstream signaling effects of PAR2 activation. Signaling pathways involved in the process were assessed using the PAR2 activating peptide SLIGKV-NH2. We show that PAR2 is expressed in PSMC and that PAR2 activation mediates a biphasic elevation in intracellular Ca²⁺ and phosphorylation of myosin light chain 20 (MLC20), causing cellular contraction as assessed in a gel contraction assay. Intracellular Ca²⁺ flux was inhibited by a phosphoinositide hydrolysis inhibitor, U73122, showing a requirement for phospholipase C β (PLCβ) activation. PSMC expressed mRNA for L-type voltage dependent Ca²⁺ channels (VDCC) as well as Ca²⁺ release activated channels (CRAC), a hitherto unreported finding. Secondary intracellular Ca²⁺ oscillations were abrogated only by BTP2, the CRAC channel inhibitor, but not by nifedipine, an inhibitor of VDCC. These data suggest that, PAR2 activation and subsequent Ca²⁺ entry through CRAC channels are important mechanisms in prostate smooth muscle contraction.

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.

Stim and Orai mediate constitutive Ca2+ entry and control endoplasmic reticulum Ca2+ refilling in primary cultures of colorectal carcinoma cells

Store-operated Ca²⁺ entry (SOCE) provides a major Ca²⁺ entry route in cancer cells. SOCE is mediated by the assembly of Stim and Orai proteins at endoplasmic reticulum (ER)-plasma membrane junctions upon depletion of the ER Ca²⁺ store. Additionally, Stim and Orai proteins underpin constitutive Ca²⁺ entry in a growing number of cancer cell types due to the partial depletion of their ER Ca²⁺ reservoir. Herein, we investigated for the first time the structure and function of SOCE in primary cultures of colorectal carcinoma (CRC) established from primary tumor (pCRC) and metastatic lesions (mCRC) of human subjects. Stim1-2 and Orai1-3 transcripts were equally expressed in pCRC and mCRC cells, although Stim1 and Orai3 proteins were up-regulated in mCRC cells. The Mn²⁺-quenching technique revealed that constitutive Ca2⁺ entry was significantly enhanced in pCRC cells and was inhibited by the pharmacological and genetic blockade of Stim1, Stim2, Orai1 and Orai3. The larger resting Ca²⁺ influx in pCRC was associated to their lower ER Ca²⁺ content as compared to mCRC cells. Pharmacological and genetic blockade of Stim1, Stim2, Orai1 and Orai3 prevented ER-dependent Ca²⁺ release, thereby suggesting that constitutive SOCE maintains ER Ca²⁺ levels. Nevertheless, pharmacological and genetic blockade of Stim1, Stim2, Orai1 and Orai3 did not affect CRC cell proliferation and migration. These data provide the first evidence that Stim and Orai proteins mediate constitutive Ca²⁺ entry and replenish ER with Ca²⁺ in primary cultures of CRC cells. However, SOCE is not a promising target to design alternative therapies for CRC.

Revisiting the Role of TRP, Orai, and ASIC Channels in the Pulmonary Arterial Response to Hypoxia

The pulmonary arteries are exquisitely responsive to oxygen changes. They rapidly and proportionally contract as arterial PO₂ decrease, and they relax as arterial PO₂ is re-established. The hypoxic pulmonary vasoconstriction (HPV) is intrinsic since it does not require neural or endocrine factors, as evidenced in isolated vessels. On the other hand, pulmonary arteries also respond to sustained hypoxia with structural and functional remodeling, involving growth of smooth muscle medial layer and later recruitment of adventitial fibroblasts, secreted mitogens from endothelium and changes in the response to vasoconstrictor and vasodilator stimuli. Hypoxic pulmonary arterial vasoconstriction and remodeling are relevant biological responses both under physiological and pathological conditions, to explain matching between ventilation and perfusion, fetal to neonatal transition of pulmonary circulation and pulmonary artery over-constriction and thickening in pulmonary hypertension. Store operated channels (SOC) and receptor operated channels (ROC) are plasma membrane cationic channels that mediate calcium influx in response to depletion of internal calcium stores or receptor activation, respectively. They are involved in both HPV and pathological remodeling since their pharmacological blockade or genetic suppression of several of the Stim, Orai, TRP, or ASIC proteins in SOC or ROC complexes attenuate the calcium increase, the tension development, the pulmonary artery smooth muscle proliferation, and pulmonary arterial hypertension. In this Mini Review, we discussed the evidence obtained in in vivo animal models, at the level of isolated organ or cells of pulmonary arteries, and we identified and discussed the questions for future research needed to validate these signaling complexes as targets against pulmonary hypertension.

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 Complex Role of Store Operated Calcium Entry Pathways and Related Proteins in the Function of Cardiac, Skeletal and Vascular Smooth Muscle Cells

Cardiac, skeletal, and smooth muscle cells shared the common feature of contraction in response to different stimuli. Agonist-induced muscle's contraction is triggered by a cytosolic free Ca²⁺ concentration increase due to a rapid Ca²⁺ release from intracellular stores and a transmembrane Ca²⁺ influx, mainly through L-type Ca²⁺ channels. Compelling evidences have demonstrated that Ca²⁺ might also enter through other cationic channels such as Store-Operated Ca²⁺ Channels (SOCCs), involved in several physiological functions and pathological conditions. The opening of SOCCs is regulated by the filling state of the intracellular Ca²⁺ store, the sarcoplasmic reticulum, which communicates to the plasma membrane channels through the Stromal Interaction Molecule 1/2 (STIM1/2) protein. In muscle cells, SOCCs can be mainly non-selective cation channels formed by Orai1 and other members of the Transient Receptor Potential-Canonical (TRPC) channels family, as well as highly selective Ca²⁺ Release-Activated Ca²⁺ (CRAC) channels, formed exclusively by subunits of Orai proteins likely organized in macromolecular complexes. This review summarizes the current knowledge of the complex role of Store Operated Calcium Entry (SOCE) pathways and related proteins in the function of cardiac, skeletal, and vascular smooth muscle cells.