Role of Ca2+-independent phospholipase A2 and store-operated pathway in urocortin-induced vasodilatation of rat coronary artery

Alterations of the Ca2+ clearing mechanisms by type 2 diabetes in aortic smooth muscle cells of Zucker diabetic fatty rat

Type 2 Diabetes Mellitus (T2DM) is a rapidly rising disease with cardiovascular complications constituting the most common cause of death among diabetic patients. Chronic hyperglycemia can induce vascular dysfunction through damage of the components of the vascular wall, such as vascular smooth muscle cells (VSMCs), which regulate vascular tone and contribute to vascular repair and remodeling. These functions are dependent on intracellular Ca²⁺ changes. The mechanisms by which T2DM affects Ca²⁺ handling in VSMCs still remain poorly understood. Therefore, the objective of this study was to determine whether and how T2DM affects Ca²⁺ homeostasis in VSMCs. We evaluated intracellular Ca²⁺ signaling in VSMCs from Zucker Diabetic Fatty rats using Ca²⁺ imaging with Fura-2/AM. Our results indicate that T2DM decreases Ca²⁺ release from the sarcoplasmic reticulum (SR) and increases the activity of store-operated channels (SOCs). Moreover, we were able to identify an enhancement of the activity of the main Ca²⁺ extrusion mechanisms (SERCA, PMCA and NCX) during the early stage of the decay of the ATP-induced Ca²⁺ transient. In addition, we found an increase in Ca²⁺ entry through the reverse mode of NCX and a decrease in SERCA and PMCA activity during the late stage of the signal decay. These effects were appreciated as a shortening of ATP-induced Ca²⁺ transient during the early stage of the decay, as well as an increase in the amplitude of the following plateau. Enhanced cytosolic Ca²⁺ activity in VSMCs could contribute to vascular dysfunction associated with T2DM.

Tissue engineered in-vitro vascular patch fabrication using hybrid 3D printing and electrospinning

Three-dimensional (3D) engineered cardiovascular tissues have shown great promise to replace damaged structures. Specifically, tissue engineering vascular grafts (TEVG) have the potential to replace biological and synthetic grafts. We aimed to design an in-vitro patient-specific patch based on a hybrid 3D print combined with vascular smooth muscle cells (VSMC) differentiation. Based on the medical images of a 2 months-old girl with aortic arch hypoplasia and using computational modelling, we evaluated the most hemodynamically efficient aortic patch surgical repair. Using the designed 3D patch geometry, the scaffold was printed using a hybrid fused deposition modelling (FDM) and electrospinning techniques. The scaffold was seeded with multipotent mesenchymal stem cells (MSC) for later maturation to derived VSMC (dVSMC). The graft showed adequate resistance to physiological aortic pressure (burst pressure 101 ​± ​15 ​mmHg) and a porosity gradient ranging from 80 to 10 ​μm allowing cells to infiltrate through the entire thickness of the patch. The bio-scaffolds showed good cell viability at days 4 and 12 and adequate functional vasoactive response to endothelin-1. In summary, we have shown that our method of generating patient-specific patch shows adequate hemodynamic profile, mechanical properties, dVSMC infiltration, viability and functionality. This innovative 3D biotechnology has the potential for broad application in regenerative medicine and potentially in heart disease prevention.

Cardioprotective and Vasoprotective Effects of Corticotropin-Releasing Hormone and Urocortins: Receptors and Signaling

Despite the recent progress in research and therapy, cardiovascular diseases are still the most common cause of death worldwide, thus new approaches are still needed. The aim of this review is to highlight the cardioprotective potential of urocortins and corticotropin-releasing hormone (CRH) and their signaling. It has been documented that urocortins and CRH reduce ischemic and reperfusion (I/R) injury, prevent reperfusion ventricular tachycardia and fibrillation, and improve cardiac contractility during reperfusion. Urocortin-induced increase in cardiac tolerance to I/R depends mainly on the activation of corticotropin-releasing hormone receptor-2 (CRHR2) and its downstream pathways including tyrosine kinase Src, protein kinase A and C (PKA, PKCε) and extracellular signal-regulated kinase (ERK1/2). It was discussed the possibility of the involvement of interleukin-6, Janus kinase-2 and signal transducer and activator of transcription 3 (STAT3) and microRNAs in the cardioprotective effect of urocortins. Additionally, phospholipase-A2 inhibition, mitochondrial permeability transition pore (MPT-pore) blockade and suppression of apoptosis are involved in urocortin-elicited cardioprotection. Chronic administration of urocortin-2 prevents the development of postinfarction cardiac remodeling. Urocortin possesses vasoprotective and vasodilator effect; the former is mediated by PKC activation and prevents an impairment of endothelium-dependent coronary vasodilation after I/R in the isolated heart, while the latter includes both cAMP and cGMP signaling and its downstream targets. As CRHR2 is expressed by both cardiomyocytes and vascular endothelial cells. Urocortins mediate both endothelium-dependent and -independent relaxation of coronary arteries.

Metabolic syndrome inhibits store-operated Ca2+ entry and calcium-induced calcium-release mechanism in coronary artery smooth muscle

BACKGROUND AND PURPOSE

Metabolic syndrome causes adverse effects on the coronary circulation including altered vascular responsiveness and the progression of coronary artery disease (CAD). However the underlying mechanisms linking obesity with CAD are intricated. Augmented vasoconstriction, mainly due to impaired Ca²⁺ homeostasis in coronary vascular smooth muscle (VSM), is a critical factor for CAD. Increased calcium-induced calcium release (CICR) mechanism has been associated to pathophysiological conditions presenting persistent vasoconstriction while increased store operated calcium (SOC) entry appears to activate proliferation and migration in coronary vascular smooth muscle (VSM). We analyze here whether metabolic syndrome might alter SOC entry as well as CICR mechanism in coronary arteries, contributing thus to a defective Ca²⁺ handling and therefore accelerating the progression of CAD.

EXPERIMENTAL APPROACH

Measurements of intracellular Ca²⁺ ([Ca²⁺]_i) and tension and of Ca²⁺ channels protein expression were performed in coronary arteries (CA) from lean Zucker rats (LZR) and obese Zucker rats (OZR).

KEY RESULTS

SOC entry stimulated by emptying sarcoplasmic reticulum (SR) Ca²⁺ store with cyclopiazonic acid (CPA) was decreased and associated to decreased STIM-1 and Orai1 protein expression in OZR CA. Further, CICR mechanism was blunted in these arteries but Ca²⁺ entry through voltage-dependent L-type channels was preserved contributing to maintain depolarization-induced increases in [Ca²⁺]_i and vasoconstriction in OZR CA. These results were associated to increased expression of voltage-operated L-type Ca²⁺ channel alpha 1C subunit (Ca_V1.2) but unaltered ryanodine receptor (RyR) and sarcoendoplasmic reticulum Ca²⁺-ATPase (SERCA) pump protein content in OZR CA.

CONCLUSION AND IMPLICATIONS

The present manuscript provides evidence of impaired Ca²⁺ handling mechanisms in coronary arteries in metabolic syndrome where a decrease in both SOC entry and CICR mechanism but preserved vasoconstriction are reported in coronary arteries from obese Zucker rats. Remarkably, OZR CA VSM at this state of metabolic syndrome seemed to have developed a compensation mechanism for impaired CICR by overexpressing Ca_V1.2 channels.

Ion channels as effectors of cyclic nucleotide pathways: Functional relevance for arterial tone regulation

Numerous mediators and drugs regulate blood flow or arterial pressure by acting on vascular tone, involving cyclic nucleotide intracellular pathways. These signals lead to regulation of several cellular effectors, including ion channels that tune cell membrane potential, Ca²⁺ influx and vascular tone. The characterization of these vasocontrictive or vasodilating mechanisms has grown in complexity due to i) the variety of ion channels that are expressed in both vascular endothelial and smooth muscle cells, ii) the heterogeneity of responses among the various vascular beds, and iii) the number of molecular mechanisms involved in cyclic nucleotide signalling in health and disease. This review synthesizes key data from literature that highlight ion channels as physiologically relevant effectors of cyclic nucleotide pathways in the vasculature, including the characterization of the molecular mechanisms involved. In smooth muscle cells, cation influx or chloride efflux through ion channels are associated with vasoconstriction, whereas K⁺ efflux repolarizes the cell membrane potential and mediates vasodilatation. Both categories of ion currents are under the influence of cAMP and cGMP pathways. Evidence that some ion channels are influenced by CN signalling in endothelial cells will also be presented. Emphasis will also be put on recent data touching a variety of determinants such as phosphodiesterases, EPAC and kinase anchoring, that complicate or even challenge former paradigms.

Role of Orai1 and L-type CaV1.2 channels in Endothelin-1 mediated coronary contraction under ischemia and reperfusion

Ischemia and Reperfusion (I/R) injuries are associated with coronary artery hypercontracture. They are mainly originated by an exacerbated response to agonists released by endothelium such as Endothelin (ET-1), involving the alteration in intracellular calcium handling. Recent evidences have highlighted the implication of Store-Operated Calcium Channels (SOCC) in intracellular calcium homeostasis in coronary artery. However, little is known about the role of SOCC in the regulation of coronary vascular tone under I/R. The aim of this study was to evaluate the role of SOCC and l-type Ca²⁺ channels (LTCC) in coronary artery vasoconstriction originated by ET-1 in I/R. We used Left Anterior Descendent coronary artery (LAD) rings, isolated from Wistar rats, to study the contractility and intracellular Ca²⁺ concentration ([Ca²⁺]_i) under a simulated I/R protocol. We observed that responses to high-KCL induced depolarization and caffeine-induced Ca²⁺ release are attenuated in coronary artery under I/R. Furthermore, ET-1 addition in ischemia promotes transient and small rise of [Ca²⁺]_i and coronary vascular tone. Meanwhile, these effects are significantly potentiated during reperfusion. The resulting ET-1-induced vasoconstrictions and [Ca²⁺]_i increase were abolished by; GSK-7975A and gadolinium, inhibitors of SOCC; and nifedipine a widely used inhibitor of LTCC. Interestingly, using in situ Proximity Ligation Assay (PLA) in isolated coronary smooth muscle cells we found significant colocalization of LTCC Ca_V1.2 isoform with Orai1, the pore forming subunit of SOCC, and TRPC1 under I/R. Our data suggest that hypercontraction of coronary artery induced by ET-1 after I/R involves the co-activation of LTCC and SOCC, which colocalize significantly in the sarcolemma of coronary smooth muscle cells.

GPR55-mediated effects on brain microvascular endothelial cells and the blood-brain barrier

GPR55, an atypical cannabinoid receptor activated by lysophosphatidylinositol (LPI) has been involved in various physiological and pathological processes. We examined the effect of GPR55 activation on rat brain microvascular endothelial cells (RBMVEC), an essential component of the blood-brain barrier (BBB). GPR55 was detected in RBMVEC by western blot and immunocytochemistry. Treatment of RBMVEC with LPI increased cytosolic Ca²⁺ concentration, [Ca²⁺]_i, in a concentration-dependent manner; the effect was abolished by the GPR55 antagonist, ML-193. Repetitive application of LPI induced tachyphylaxis. LPI-induced increase in [Ca²⁺]_i was not sensitive to U-73122, a phospholipase C inhibitor, but was abolished by the blockade of voltage-gated Ca²⁺ channels or in Ca²⁺-free saline, indicating that Ca²⁺ influx was involved in this response. LPI induced a biphasic change in RBMVEC membrane potential: a fast depolarization followed by a long-lasting hyperpolarization. The hyperpolarization phase was prevented by apamin and charibdotoxin, inhibitors of small- and intermediate-conductance Ca²⁺-activated K⁺ channels (K_Ca). Immunofluorescence studies indicate that LPI produced transient changes in tight and adherens junctions proteins and F-actin stress fibers. LPI decreased the electrical resistance of RBMVEC monolayer assessed with Electric Cell-Substrate Impedance Sensing (ECIS) in a dose-dependent manner. In vivo studies indicate that systemic administration of LPI increased the permeability of the BBB, assessed with Evans Blue method. Taken together, our results indicate that GPR55 activation modulates the function of endothelial cells of brain microvessels, produces a transient reduction in endothelial barrier function and increases BBB permeability.

Terminal Deoxynucleotidyl Transferase-Catalyzed Preparation of pH-Responsive DNA Nanocarriers for Tumor-Targeted Drug Delivery and Therapy

Developing a highly efficient carrier for tumor-targeted delivery and site-specific release of anticancer drugs is a good way to overcome the side effects of traditional cancer chemotherapy. Benefiting from the nontoxic and biocompatible characteristics, DNA-based drug carriers have attracted increasing attention. Herein, we reported a novel and readily manipulated strategy to construct spherical DNA nanocarriers. In this strategy, terminal deoxynucleotidyl transferase (TdT)-catalyzed DNA extension reaction is used to prepare a thick DNA layer on a gold nanoparticle (AuNP) surface by extending long poly(C) sequences from DNA primers immobilized on AuNPs. The poly(C) extension products can then hybridize with G-rich oligonucleotides to give CG-rich DNA duplexes (for loading anticancer drug doxorubicin, Dox) and multiple AS1411 aptamers. Via synergic recognition of multiple aptamer units to nucleolin proteins, biomarker of malignant tumors, Dox-loaded DNA carrier can be efficiently internalized in cancer cells and achieve burst release of drugs in acidic organelles because of i-motif formation-induced DNA duplex destruction. An as-prepared pH-responsive drug carrier was demonstrated to be promising for highly efficient delivery of Dox and selective killing of cancer cells in both in vitro and in vivo experiments, thus showing a huge potential in anticancer therapy.

Natural and synthetic peptides in the cardiovascular diseases: An update on diagnostic and therapeutic potentials

Several peptides play an important role in physiological and pathological conditions into the cardiovascular system. In addition to well-known vasoactive agents such as angiotensin II, endothelin, serotonin or natriuretic peptides, the vasoconstrictor Urotensin-II (Uro-II) and the vasodilators Urocortins (UCNs) and Adrenomedullin (AM) have been implicated in the control of vascular tone and blood pressure as well as in cardiovascular disease states including congestive heart failure, atherosclerosis, coronary artery disease, and pulmonary and systemic hypertension. Therefore these peptides, together with their receptors, become important therapeutic targets in cardiovascular diseases (CVDs). Circulating levels of these agents in the blood are markedly modified in patients with specific CVDs compared with those in healthy patients, becoming also potential biomarkers for these pathologies. This review will provide an overview of current knowledge about the physiological roles of Uro-II, UCN and AM in the cardiovascular system and their implications in cardiovascular diseases. It will further focus on the structural modifications carried out on original peptide sequences in the search of analogues with improved physiochemical properties as well as in the delivery methods. Finally, we have overviewed the possible application of these peptides and/or their precursors as biomarkers of CVDs.

Urocortin-2 Prevents Dysregulation of Ca2+ Homeostasis and Improves Early Cardiac Remodeling After Ischemia and Reperfusion

Aims: Urocortin-2 (Ucn-2) is a potent cardioprotector against Ischemia and Reperfusion (I/R) injuries. However, little is known about its role in the regulation of intracellular Ca²⁺ concentration ([Ca²⁺]_i) under I/R. Here, we examined whether the addition of Ucn-2 in reperfusion promotes cardioprotection focusing on ([Ca²⁺]_i handling.

Methods and Results: Cardiac Wistar rat model of I/R was induced by transient ligation of the left coronary artery and experiments were conducted 1 week after surgery in tissue and adult cardiomyocytes isolated from risk and remote zones. We observed that I/R promoted significant alteration in cardiac contractility as well as an increase in hypertrophy and fibrosis in both zones. The study of confocal [Ca²⁺]_i imaging in adult cardiomyocytes revealed that I/R decreased the amplitude of [Ca²⁺]_i transient and cardiomyocytes contraction in risk and remote zones. Interestingly, intravenous infusion of Ucn-2 before heart’s reperfusion recovered significantly cardiac contractility and prevented fibrosis, but it didn’t affect cardiac hypertrophy. Moreover, Ucn-2 recovered the amplitude of [Ca²⁺]_i transient and modulated the expression of several proteins related to [Ca²⁺]_i homeostasis, such as TRPC5 and Orai1 channels. Using Neonatal Rat Ventricular Myocytes (NRVM) we demonstrated that Ucn-2 blunted I/R-induced Store Operated Ca²⁺ Entry (SOCE), decreased the expression of TRPC5 and Orai1 as well as their interaction in reperfusion.

Conclusion: Our study provides the first evidences demonstrating that Ucn-2 addition at the onset of reperfusion attenuates I/R-induced adverse cardiac remodeling, involving the [Ca²⁺]_i handling and inhibiting the expression and interaction between TRPC5 and Orai1.

Modulation of Iris Sphincter and Ciliary Muscles by Urocortin 2

Urocortin 2 (UCN2) is a peptide related to corticotropin-releasing factor, capable of activating CRF-R2. Among its multisystemic effects, it has actions in all 3 muscle subtypes. This study’s aim was to determine its potential role in two of the intrinsic eye muscle kinetics. Strips of iris sphincter (rabbit) and ciliary (bovine) muscles were dissected and mounted in isometric force-transducer systems filled with aerated-solutions. Contraction was elicited using carbachol (10-6 M for iris sphincter, 10-5 M for ciliary muscle), prior adding to all testing substances. UCN2 induced relaxation in iris sphincter muscle, being the effect maximal at 10-7 M concentrations (-12.2 % variation vs. control). This effect was abolished with incubation of indomethacin, antisauvagine-30, chelerytrine and SQ22536, but preserved with L-nitro-L-arginine. In carbachol pre-stimulated ciliary muscle, UCN2 (10-5 M) enhanced contraction (maximal effect of 18.2 % increase vs. control). UCN2 is a new modulator of iris sphincter relaxation, dependent of CRF-R2 activation, synthesis of prostaglandins (COX pathway) and both adenylate cyclase and PKC signaling pathways, but independent of nitric oxide production. Regarding ciliary muscle, UCN2 enhances carbachol-induced contraction, in higher doses.

Chondroprotection by urocortin involves blockade of the mechanosensitive ion channel Piezo1

Osteoarthritis (OA) is characterised by progressive destruction of articular cartilage and chondrocyte cell death. Here, we show the expression of the endogenous peptide urocortin1 (Ucn1) and two receptor subtypes, CRF-R1 and CRF-R2, in primary human articular chondrocytes (AC) and demonstrate its role as an autocrine/paracrine pro-survival factor. This effect could only be removed using the CRF-R1 selective antagonist CP-154526, suggesting Ucn1 acts through CRF-R1 when promoting chondrocyte survival. This cell death was characterised by an increase in p53 expression, and cleavage of caspase 9 and 3. Antagonism of CRF-R1 with CP-154526 caused an accumulation of intracellular calcium (Ca2+) over time and cell death. These effects could be prevented with the non-selective cation channel blocker Gadolinium (Gd3+). Therefore, opening of a non-selective cation channel causes cell death and Ucn1 maintains this channel in a closed conformation. This channel was identified to be the mechanosensitive channel Piezo1. We go on to determine that this channel inhibition by Ucn1 is mediated initially by an increase in cyclic adenosine monophosphate (cAMP) and a subsequent inactivation of phospholipase A2 (PLA2), whose metabolites are known to modulate ion channels. Knowledge of these novel pathways may present opportunities for interventions that could abrogate the progression of OA.

Orai1 and TRPC1 Proteins Co-localize with CaV1.2 Channels to Form a Signal Complex in Vascular Smooth Muscle Cells

Voltage-dependent Ca_V1.2 L-type Ca²⁺ channels (LTCC) are the main route for calcium entry in vascular smooth muscle cells (VSMC). Several studies have also determined the relevant role of store-operated Ca²⁺ channels (SOCC) in vascular tone regulation. Nevertheless, the role of Orai1- and TRPC1-dependent SOCC in vascular tone regulation and their possible interaction with Ca_V1.2 are still unknown. The current study sought to characterize the co-activation of SOCC and LTCC upon stimulation by agonists, and to determine the possible crosstalk between Orai1, TRPC1, and Ca_V1.2. Aorta rings and isolated VSMC obtained from wild type or smooth muscle-selective conditional Ca_V1.2 knock-out (Ca_V1.2^KO) mice were used to study vascular contractility, intracellular Ca²⁺ mobilization, and distribution of ion channels. We found that serotonin (5-HT) or store depletion with thapsigargin (TG) enhanced intracellular free Ca²⁺ concentration ([Ca²⁺]_i) and stimulated aorta contraction. These responses were sensitive to LTCC and SOCC inhibitors. Also, 5-HT- and TG-induced responses were significantly attenuated in Ca_V1.2^KO mice. Furthermore, hyperpolarization induced with cromakalim or valinomycin significantly reduced both 5-HT and TG responses, whereas these responses were enhanced with LTCC agonist Bay-K-8644. Interestingly, in situ proximity ligation assay revealed that Ca_V1.2 interacts with Orai1 and TRPC1 in untreated VSMC. These interactions enhanced significantly after stimulation of cells with 5-HT and TG. Therefore, these data indicate for the first time a functional interaction between Orai1, TRPC1, and Ca_V1.2 channels in VSMC, confirming that upon agonist stimulation, vessel contraction involves Ca²⁺ entry due to co-activation of Orai1- and TRPC1-dependent SOCC and LTCC.

Phospholipase A2 as a Molecular Determinant of Store-Operated Calcium Entry

Activation of phospholipases A2 (PLA2) leads to the generation of biologically active lipid products that can affect numerous cellular events. Ca(2+)-independent PLA2 (iPLA2), also called group VI phospholipase A2, is one of the main types forming the superfamily of PLA2. Beside of its role in phospholipid remodeling, iPLA2 has been involved in intracellular Ca(2+) homeostasis regulation. Several studies proposed iPLA2 as an essential molecular player of store operated Ca(2+) entry (SOCE) in a large number of excitable and non-excitable cells. iPLA2 activation releases lysophosphatidyl products, which were suggested as agonists of store operated calcium channels (SOCC) and other TRP channels. Herein, we will review the important role of iPLA2 on the intracellular Ca(2+) handling focusing on its role in SOCE regulation and its implication in physiological and/or pathological processes.

Orai1 forms a signal complex with SK3 channel in gallbladder smooth muscle

Orai1 is one of the key components of store-operated Ca(2+) entry (SOCE) involved in diverse physiological functions. Orai1 may associate with other proteins to form a signaling complex. In the present study, we investigated the interaction between Orai1 and small conductance Ca(2+)-activated potassium channel 3 (SK3). With the use of RNA interference technique, we found that the SOCE and its associated membrane hyperpolarization were reduced while Orai1 was knocked down by a specific Orai1 siRNA in guinea pig gallbladder smooth muscle. However, with the use of isometric tension measurements, our results revealed that agonist-induced muscle contractility was significantly enhanced after Orai1 protein was knocked down or the tissue was treated by SK3 inhibitor apamin, but not affected by larger conductance Ca(2+)-activated potassium channel inhibitor iberiotoxin or intermediate conductance Ca(2+)-activated potassium channel inhibitor TRAM-34. In addition, in the presence of apamin, Orai1 siRNA had no additional effect on agonist-induced contraction. In coimmunoprecipitation experiment, SK3 and Orai1 pulled down each other. These data suggest that, Orai1 physically associated with SK3 to form a signaling complex in gallbladder smooth muscle. Ca(2+) entry via Orai1 activates SK3, resulting in membrane hyperpolarization in gallbladder smooth muscle. This hyperpolarizing effect of Orai1-SK3 coupling could serve to prevent excessive contraction of gallbladder smooth muscle in response to contractile agonists.

Leptin suppresses non-apoptotic cell death in ischemic rat cardiomyocytes by reduction of iPLA(2) activity

Caspase-independent, non-apoptotic cell death is an important therapeutic target in myocardial ischemia. Leptin, an adipose-derived hormone, is known to exhibit cytoprotective effects on the ischemic heart, but the mechanisms are poorly understood. In this research, we found that pretreatment of leptin strongly suppressed ischemic-augmented nuclear shrinkage and non-apoptotic cell death on cardiomyocytes. Leptin was also shown to significantly inhibit the activity of iPLA2, which is considered to play crucial roles in non-apoptotic cell death, resulting in effective prevention of ischemia-induced myocyte death. These findings provide the first evidence of a protective mechanism of leptin against ischemia-induced non-apoptotic cardiomyocyte death.

G protein-coupled estrogen receptor 1 mediates relaxation of coronary arteries via cAMP/PKA-dependent activation of MLCP

Activation of GPER exerts a protective effect in hypertension and ischemia-reperfusion models and relaxes arteries in vitro. However, our understanding of the mechanisms of GPER-mediated vascular regulation is far from complete. In the current study, we tested the hypothesis that GPER-induced relaxation of porcine coronary arteries is mediated via cAMP/PKA signaling. Our findings revealed that vascular relaxation to the selective GPER agonist G-1 (0.3-3 μM) was associated with increased cAMP production in a concentration-dependent manner. Furthermore, inhibition of adenylyl cyclase (AC) with SQ-22536 (100 μM) or of PKA activity with either Rp-8-CPT-cAMPS (5 μM) or PKI (5 μM) attenuated G-1-induced relaxation of coronary arteries preconstricted with PGF2α (1 μM). G-1 also increased PKA activity in cultured coronary artery smooth muscle cells (SMCs). To determine downstream signals of the cAMP/PKA cascade, we measured RhoA activity in cultured human and porcine coronary SMCs and myosin-light chain phosphatase (MLCP) activity in these artery rings by immunoblot analysis of phosphorylation of myosin-targeting subunit protein-1 (p-MYPT-1; the MLCP regulatory subunit). G-1 decreased PGF2α-induced p-MYPT-1, whereas Rp-8-CPT-cAMPS prevented this inhibitory effect of G-1. Similarly, G-1 inhibited PGF2α-induced phosphorylation of MLC in coronary SMCs, and this inhibitory effect was also reversed by Rp-8-CPT-cAMPS. RhoA activity was downregulated by G-1, whereas G36 (GPER antagonist) restored RhoA activity. Finally, FMP-API-1 (100 μM), an inhibitor of the interaction between PKA and A-kinase anchoring proteins (AKAPs), attenuated the effect of G-1 on coronary artery relaxation and p-MYPT-1. These findings demonstrate that localized cAMP/PKA signaling is involved in GPER-mediated coronary vasodilation by activating MLCP via inhibition of RhoA pathway.

Urocortin increased endothelial ICAM1 by cPLA2-dependent NF-κB and PKA pathways in HUVECs

Urocortin (Ucn1), a member of the corticotrophin-releasing hormone (CRH) family, has been reported to participate in inflammation. The increased expression of intercellular adhesion molecule 1 (ICAM1) plays important roles in inflammation and immune responses. Our previous results demonstrated that Ucn1 significantly enhanced the expression of ICAM1. However, the underlying mechanisms are still unknown. The purpose of this study is to investigate the detailed mechanisms of Ucn1-induced upregulation of ICAM1. Here, we characterized the mechanisms of Ucn1 usage to regulate ICAM1 expression in human umbilical vein endothelial cells (HUVECs). Our data revealed that Ucn1 increased ICAM1 and cyclooxygenase 2 (COX2) expressions in a time-dependent manner via CRH receptor 2 (CRHR2). In addition, COX2 was involved in ICAM1 upregulation. Furthermore, Ucn1 could increase the expression and phosphorylation of cytosolic phospholipases A2 (cPLA2) in a time-dependent manner via CRHR2 and CRHR1. Moreover, ablation of cPLA2 by the inhibitor pyrrophenone or siRNA attenuated the ICAM1 increase induced by Ucn1. In addition, nuclear factor κB (NF-κB) was activated, indicated by the increase in nuclear p65NF-κB expression and phosphorylation of p65NF-κB, depending on cPLA2 and CRHR2 activation. Pyrrolidinedithiocarbamic acid, an inhibitor of NF-κB, abolished the elevation of ICAM1 but not COX2. Also, Ucn1 increased the production of prostaglandin E2 (PGE2) which further activated protein kinase A (PKA)-CREB pathways dependent of cPLA2 via CRHR2. Moreover, the increase in NF-κB phosphorylation was not affected by the selective COX2 inhibitor NS-398 or the PKA inhibitor H89. In conclusion, these data indicate that Ucn1 increase the ICAM1 expression via cPLA2-NF-κB and cPLA2-COX2-PGE2-PKA-CREB pathways by means of CRHR2.

Urotensin-II promotes vascular smooth muscle cell proliferation through store-operated calcium entry and EGFR transactivation

AIMS

Urotensin-II (UII) is a vasoactive peptide that promotes vascular smooth muscle cells (VSMCs) proliferation and is involved in the pathogenesis of atherosclerosis, restenosis, and vascular remodelling. This study aimed to determine the role of calcium (Ca(2+))-dependent signalling and alternative signalling pathways in UII-evoked VSMCs proliferation focusing on store-operated Ca(2+) entry (SOCE) and epithelium growth factor receptor (EGFR) transactivation.

METHODS AND RESULTS

We used primary cultures of VSMCs isolated from Wistar rat aorta to investigate the effects of UII on intracellular Ca(2+) mobilization, and proliferation determined by the 5-bromo-2-deoxyuridine (BrdU) assay. We found that UII enhanced intracellular Ca(2+) concentration ([Ca(2+)]i) which was significantly reduced by classical SOCE inhibitors and by knockdown of essential components of the SOCE such as stromal interaction molecule 1 (STIM1), Orai1, or TRPC1. Moreover, UII activated a Gd(3+)-sensitive current with similar features of the Ca(2+) release-activated Ca(2+) current (ICRAC). Additionally, UII stimulated VSMCs proliferation and Ca(2+)/cAMP response element-binding protein (CREB) activation through the SOCE pathway that involved STIM1, Orai1, and TRPC1. Co-immunoprecipitation experiments showed that UII promoted the association between Orai1 and STIM1, and between Orai1 and TRPC1. Moreover, we determined that EGFR transactivation, extracellular signal-regulated kinase (ERK) and Ca(2+)/calmodulin-dependent kinase (CaMK) signalling pathways were involved in both UII-mediated Ca(2+) influx, CREB activation and VSMCs proliferation.

CONCLUSION

Our data show for the first time that UII-induced VSMCs proliferation and CREB activation requires a complex signalling pathway that involves on the one hand SOCE mediated by STIM1, Orai1, and TRPC1, and on the other hand EGFR, ERK, and CaMK activation.

Functional vascular smooth muscle-like cells derived from adult mouse uterine mesothelial cells

In mammalian visceral organs, vascular smooth muscle cells (VSMCs) originate from an epithelial-to-mesenchymal transition (EMT) of embryonic mesothelial cells (MCs). The ability of adult MCs to recapitulate EMT and to acquire smooth muscle (SM) markers upon provasculogenic culture suggested they might retain embryonic vasculogenic differentiation potential. However, it remains unknown whether adult MCs-derived SM-like cells may acquire specific vascular SM lineage markers and the functionality of differentiated contractile VSMCs. Here, we describe how a gentle trypsinization of adult mouse uterine cords could selectively detach their outermost uterine mesothelial layer cells. As other MCs; uterine MCs (UtMCs) uniformly expressed the epithelial markers β-catenin, ZO-1, E-cadherin, CD54, CD29, and CK18. When cultured in a modified SM differentiation media (SMDM) UtMCs initiated a loss of epithelial characteristics and gained markers expression of EMT (Twist, Snail, and Slug), stem and progenitor (Nanog, Sox2, C-kit, Gata-4, Isl-1, and nestin), SM (α-SMA, calponin, caldesmon, SM22α, desmin, SM-MHC, and smoothelin-B) and cardiac (BMP2, BMP4, ACTC1, sACTN, cTnI, cTnT, ANF, Cx43, and MLC2a). UtMCs repeatedly subcultured in SMDM acquired differentiated VSM-like characteristics and expressed smoothelin-B in the typical stress-fiber pattern expression of contractile VSMCs. Relevantly, UtMCs-derived VSM-like cells could generate "mechanical force" to compact collagen lattices and displayed in diverse degree voltage (K(+)) and receptor (endothelin-1, oxytocin, norepinephrine, carbachol and vasopressin)-induced [Ca(2+)](i) rises and contraction. Thus, we show for the first time that UtMCs could recapitulate in vitro differentiative events of early cardiovascular differentiation and transdifferentiate in cells exhibiting molecular and functional characteristics of VSMCs.

Emerging roles for native Orai Ca2+ channels in cardiovascular disease

Orai proteins form highly calcium (Ca(2+))-selective channels located in the plasma membrane of both nonexcitable and excitable cells, where they make important contributions to many cellular processes. The well-characterized Ca(2+) release-activated Ca(2+) current is mediated by Orai1 multimers and is activated, upon depletion of inositol 1,4,5-trisphosphate-sensitive stores, by direct interaction of Orai1 with the endoplasmic reticulum Ca(2+) sensor, stromal interaction molecule 1 (STIM1). This pathway is known as capacitative Ca(2+) entry or store-operated Ca(2+) entry. While most investigations have focused on STIM1 and Orai1 in their store-dependent mode, emerging evidence suggests that Orai1 and Orai3 heteromultimeric channels can form store-independent Ca(2+)-selective channels. The role of store-dependent and store-independent channels in excitation-transcription coupling and the pathological remodeling of the cardiovascular system are beginning to come forth. Recent evidence suggests that STIM/Orai-generated Ca(2+) signaling couples to gene transcription and subsequent phenotypic changes associated with the processes of cardiac and vascular remodeling. This short review will explore the contributions of native Orai channels to heart and vessel physiology and their role in cardiovascular diseases.

Platelet-activating factor receptor initiates contact of Acinetobacter baumannii expressing phosphorylcholine with host cells

Adhesion is an initial and important step in Acinetobacter baumannii causing infections. However, the exact molecular mechanism of such a step between A. baumannii and the host cells remains unclear. Here, we demonstrated that the phosphorylcholine (ChoP)-containing outer membrane protein of A. baumannii binds to A549 cells through platelet-activating factor receptor (PAFR), resulting in activation of G protein and intracellular calcium. Upon A. baumannii expressing ChoP binding to PAFR, clathrin and β-arrestins, proteins involved in the direction of the vacuolar movement, are activated during invasion of A. baumannii. PAFR antagonism restricts the dissemination of A. baumannii in the pneumonia model. These results define a role for PAFR in A. baumannii interaction with host cells and suggest a mechanism for the entry of A. baumannii into the cytoplasm of host cells.

Urocortin is a novel regulator of osteoclast differentiation and function through inhibition of a canonical transient receptor potential 1-like cation channel

This study investigated the role of urocortin (UCN), a member of the corticotrophin-releasing factor (CRF) family of peptides, in osteoclast maturation and function. We found that 10(-7) M UCN significantly (P<0.05) suppressed osteoclast differentiation from bone marrow precursor cells in culture and reduced the expression of several osteoclastic markers. Furthermore, UCN potently suppressed osteoclast bone resorption, by significantly inhibiting both the plan area of bone resorbed by osteoclasts and actin ring formation within osteoclasts at 10(-9) M (P<0.05), with complete inhibition at 10(-7) M (P<0.001). UCN also inhibited osteoclast motility (10(-7) M) but had no effect on osteoclast survival. Osteoclasts expressed mRNA encoding both UCN and the CRF receptor 2β subtype. Pre-osteoclasts however, expressed CRF receptor 2β alone. Unstimulated osteoclasts contained constitutively active cation channel currents with a unitary conductance of 3-4 pS, which were inhibited by over 70% with UCN (10(-7) M). Compounds that regulate calcium signalling and energy status of the cell, both crucial for osteoclast activity were investigated. The non-selective cation channel blockers, lanthanum (La(3)(+)) and gadolinium (Gd(3)(+)), inhibited actin ring formation in osteoclasts, whereas modulators of voltage-dependent Ca(2)(+) channels and K(ATP) channels had no effect. These findings show for the first time that UCN is a novel anti-resorptive molecule that acts through a direct effect on osteoclasts and their precursor cells.

Urotensin-II signaling mechanism in rat coronary artery: role of STIM1 and Orai1-dependent store operated calcium influx in vasoconstriction

OBJECTIVE

Human urotensin-II (UII) is considered the most potentendogenous vasoconstrictor discovered to date, although the precise mechanism activated downstream of its receptor UTS2R in blood vessels remains elusive. The aim of this study was to determine the role of the store operated Ca(2+) entry (SOCE) signaling pathway in UII-induced coronary artery vasoconstriction.

METHODS AND RESULTS

We used a combination of isometric tension measurement, Ca(2+) imaging, pharmacology, and molecular approaches to study UII-mediated rat coronary artery vasoconstriction and intracellular Ca(2+) mobilization in coronary smooth muscle cells. We found that UII promoted dose-dependent vasoconstriction and elicited Ca(2+) and Mn(2+) influx, which were sensitive to classical SOCE inhibitors. In addition, knockdown of either STIM1 or Orai1 essentially inhibited UII-mediated SOCE and prevented UII but not high-KCL evoked contraction in transfected coronary artery. Moreover, we found that Ca(2+)-independent phospholipase A(2)β was involved in UII effects and that is colocalized with STIM1 in different submembrane compartments. Importantly, STIM1 but not Orai1 downregulation inhibits significantly independent phospholipase A(2) activation. Furthermore, lysophosphatidylcholine, an independent phospholipase A(2) product, activated Orai1 but not STIM1-dependent contraction and SOCE.

CONCLUSIONS

Here, we demonstrated that different critical players of SOCE signaling pathway are required for UII-induced vasoconstriction of rat coronary artery.

Urocortins improve dystrophic skeletal muscle structure and function through both PKA- and Epac-dependent pathways

In Duchenne muscular dystrophy, the absence of dystrophin causes progressive muscle wasting and premature death. Excessive calcium influx is thought to initiate the pathogenic cascade, resulting in muscle cell death. Urocortins (Ucns) have protected muscle in several experimental paradigms. Herein, we demonstrate that daily s.c. injections of either Ucn 1 or Ucn 2 to 3-week-old dystrophic mdx(5Cv) mice for 2 weeks increased skeletal muscle mass and normalized plasma creatine kinase activity. Histological examination showed that Ucns remarkably reduced necrosis in the diaphragm and slow- and fast-twitch muscles. Ucns improved muscle resistance to mechanical stress provoked by repetitive tetanizations. Ucn 2 treatment resulted in faster kinetics of contraction and relaxation and a rightward shift of the force-frequency curve, suggesting improved calcium homeostasis. Ucn 2 decreased calcium influx into freshly isolated dystrophic muscles. Pharmacological manipulation demonstrated that the mechanism involved the corticotropin-releasing factor type 2 receptor, cAMP elevation, and activation of both protein kinase A and the cAMP-binding protein Epac. Moreover, both STIM1, the calcium sensor that initiates the assembly of store-operated channels, and the calcium-independent phospholipase A(2) that activates these channels were reduced in dystrophic muscle by Ucn 2. Altogether, our results demonstrate the high potency of Ucns for improving dystrophic muscle structure and function, suggesting that these peptides may be considered for treatment of Duchenne muscular dystrophy.

Orai1 and Ca2+-independent phospholipase A2 are required for store-operated Icat-SOC current, Ca2+ entry, and proliferation of primary vascular smooth muscle cells

Store-operated Ca(2+) entry (SOCE) is important for multiple functions of vascular smooth muscle cells (SMC), which, depending of their phenotype, can resemble excitable and nonexcitable cells. Similar to nonexcitable cells, Orai1 was found to mediate Ca(2+)-selective (CRAC-like) current and SOCE in dedifferentiated cultured SMC and smooth muscle-derived cell lines. However, the role of Orai1 in cation-selective store-operated channels (cat-SOC), which are responsible for SOCE in primary SMC, remains unclear. Here we focus on primary SMC, and assess the role of Orai1 and Ca(2+)-independent phospholipase A(2) (iPLA(2)β, or PLA2G6) in activation of cat-SOC current (I(cat-SOC)), SOCE, and SMC proliferation. Using molecular, electrophysiological, imaging, and functional approaches, we demonstrate that molecular knockdown of either Orai1 or iPLA(2)β leads to similar inhibition of the whole cell cat-SOC current and SOCE in primary aortic SMC and results in significant reduction in DNA synthesis and impairment of SMC proliferation. This is the first demonstration that Orai1 and iPLA(2)β are equally important for cat-SOC, SOCE, and proliferation of primary aortic SMC.

Urocortin-2 induces vasorelaxation of coronary arteries isolated from patients with heart failure

1. Urocortin-2 (Ucn2) is a vasoactive peptide belonging to the corticotrophin-releasing factor (CRF) family that has potent cardiovascular actions. It has been suggested that Ucn2 participates in the pathophysiology of heart failure. However, little is known about the mechanisms underlying the action of Ucn2 in human coronary arteries. The aim of the present study was to assess the effects of Ucn2 on the vascular tone of human coronary arteries dissected from heart failure patients. 2. Human coronary arteries were dissected from the hearts of patients subjected to orthotopic heart transplantation. Coronary arteries were obtained from 17 patients with heart failure due to dilated cardiomyopathy of ischaemic origin in Stage III-IV of the New York Heart Association classification. Changes in tone were measured in arterial rings using force transducers. 3. Application of increasing concentrations of Ucn2 (5-20 nmol/L) to arterial rings precontracted with agonists induced dose-dependent relaxation of the coronary artery, which was independent of endothelial cell activation. Furthermore, the inhibition of the adenylyl cyclase by MDL-12 (100 nmol/L) and protein kinase A (PKA) by H89 (1 μmol/L) prevented Ucn2-mediated relaxation of coronary artery rings. 4. The results of the present study suggest that, in heart failure patients, Ucn2 could be useful in modulating coronary artery circulation independent of endothelial integrity through mechanisms that involve adenylyl cyclase activation and PKA stimulation. The findings warrant further investigation of the role of Ucn2 in circulatory regulation and its potential therapeutic application in heart disease.

Acinetobacter baumannii-induced lung cell death: role of inflammation, oxidative stress and cytosolic calcium

A growing body of evidence supports the notion that susceptible Acinetobacter baumannii strain ATCC 19606 induces human epithelial cells death. However, most of the cellular and molecular mechanisms associated with this cell death remain unknown, and also the degree of the cytotoxic effects of a clinical panresistant strain compared with a susceptible strain has never been studied. Due to the role of proinflammatory cytokine release, oxidative stress and cytosolic calcium increase in the cell death-induced by other Gram-negative bacteria, we investigated whether these intracellular targets were involved in the cell death induced by clinical panresistant 113-16 and susceptible ATCC 19606 strains. Data presented here show that 113-16 and ATCC 19606 induce time-dependent cell death of lung epithelial cells involving a perturbation of cytosolic calcium homeostasis with subsequent calpain and caspase-3 activation. Prevention of this cell death by TNF-α and interleukin-6 blockers and antioxidant highlights the involvement of proinflammatory cytokines and oxidative stress in this phenomenon. These results demonstrate the involvement of calpain calcium-dependent in cell death induced by A. baumannii and the impact of proinflammatory cytokines and oxidative stress in this cell death; it is noteworthy to stress that some mechanisms are less induced by the panresistant strain.

Protein kinases modulate store-operated channels in pulmonary artery smooth muscle cells

Background

This study investigates whether protein kinase G (PKG), protein kinase A (PKA) and protein kinase C (PKC) are involved in the regulatory mechanisms of store-operated channel (SOC) in pulmonary arteries.

Methods

Pulmonary artery smooth muscle cells (PASMCs) were enzymatically dissociated from rat intralobar pulmonary arteries. Whole cell, cell-attached and inside-out patch-clamp electrophysiology were used to monitor SOCs in isolated PASMCs.

Results

Initially the Ca²⁺-ATPase inhibitor cyclopiazonic acid (CPA, 10 μM) initiated a whole cell current that was reduced by the SOC blocker SKF-96365 (10 μM). Subsequent work using both cell-attached and whole cell configurations revealed that the PKG and PKA inhibitors, KT5823 (3 μM) and H-89 (10 μM), also stimulated SOC activity; this augmentation was attenuated by the SOC blockers SKF-96365 (10 μM) and Ni²⁺ (0.1 mM). Finally using the inside-out configuration, the PKC activator phorbol 12-myristate 13-acetate (PMA, 10 μM) was confirmed to modestly stimulate SOC activity although this augmentation appeared to be more substantial following the application of 10 μM inositol 1,4,5-triphosphate (Ins(1,4,5)P₃).

Conclusions

SOC activity in PASMCs was stimulated by the inhibition of PKG and PKA and the activation of PKC. Our findings suggest that the SOC could be a substrate of these protein kinases, which therefore would regulate the intracellular concentration of calcium and pulmonary arteriopathy via SOC.

Store-operated Ca(2+) entry is not essential for PDGF-BB induced phenotype modulation in rat aortic smooth muscle

Suppression of smooth muscle cell (SMC) differentiation marker genes is central to SMC phenotype modulation during vasculo-proliferative diseases such as atherosclerosis and restenosis. Upregulation of the intermediate-conductance Ca(2+)-activated K(+) channel (K(Ca)3.1) is integral for mitogen-induced suppression of SMC marker genes and post-angioplasty restenosis. Modulation of SMC marker gene expression has been observed following Ca(2+) influx from multiple sources, however, it is unknown whether upregulation of K(Ca)3.1 and/or suppression of SMC differentiation genes is dependent on a Ca(2+) mediated mechanism. The purpose of this study was to determine the dependence of mitogen-induced SMC phenotype modulation on store-operated Ca(2+) entry (SOCE). In growth-arrested, differentiated rat aortic SMCs, platelet-derived growth factor-BB (PDGF-BB) augmented SOCE. However, PDGF-BB induced upregulation of K(Ca)3.1 and downregulation of the SMC marker gene smooth muscle myosin heavy chain (SMMHC) and myocardin was not dependent on SOCE. Co-treatment with the iPLA2 inhibitor bromoenol lactone (BEL) inhibited the effects of PDGF-BB on SMC phenotype modulation and SOCE. Our results indicate SOCE is not required for PDGF-BB induced phenotype modulation in rat aortic SMCs. Rather, we implicate a novel BEL-sensitive mechanism which regulates both SOCE and phenotype modulation, independently.

Biphasic effects of nitric oxide on calcium influx in human platelets

In this study the effects of nitric oxide (NO) donors on intracellular free calcium ([Ca(2+)](i)) in human platelets was examined. Inhibition of guanylyl cyclase (GC) with either methylene blue or ODQ slightly inhibited the ability of submaximal concentrations of thrombin to increase [Ca(2+)](i) which suggests that a small portion of the thrombin mediated increase in [Ca(2+)](i) was due to an increase in NO and subsequent increase in cGMP and activation of cGMP dependent protein kinase (cGPK). Thrombin predominantly increases [Ca(2+)](i) by stimulating store-operated Ca(2+) entry (SOCE). The NO donor GEA3162 was previously shown to stimulate SOCE in some cells. In platelets GEA3162 had no effect to increase [Ca(2+)](i) however it inhibited the ability of thrombin to increase [Ca(2+)](i) and this effect was reversed by ODQ. The addition of low concentrations (2.0 - 20 nM) of the NO donor sodium nitroprusside (SNP) slightly potentiated the ability of thrombin to increase [Ca(2+)](i) whereas higher concentrations (>200 nM) of SNP inhibited thrombin induced increases in [Ca(2+)](i). Both of these effects of SNP were reversed by ODQ which implies that they were both mediated by cGPK. Ba(2+) influx was stimulated by low concentrations (2.0 nM) of SNP and inhibited by high concentrations (>200 nM) of SNP and both effects were inhibited by ODQ. Previous studies showed that Ba(2+) influx was blocked by the SOCE inhibitors 2-aminoethoxydipheny borate and diethylstilbestrol. It was concluded that low levels of SNP can stimulate SOCE in platelets and this effect may account for the increased aggregation and secretion previously observed with low concentrations of NO donors. Of the proteins known to be involved in SOCE (e.g. stromal interaction molecule 1 (Stim1), Stim2 and Orai1) only Stim2 has cGPK phosphorylation sites. The possibility that Stim2 phosphorylation regulates SOCE in platelets is discussed.

Urocortin 2 lowers blood pressure and reduces plasma catecholamine levels in mice with hyperadrenergic activity

Exaggerated adrenergic activity is associated with human hypertension. The peptide urocortin 2 (Ucn 2) inhibits catecholamine synthesis and secretion from adrenal chromaffin cells in vitro and administration to mammals lowers blood pressure (BP). The chromogranin A-null mouse (Chga-/-) manifests systemic hypertension because of excessive catecholamine secretion from the adrenal and decreased catecholamine storage. In the present study, we investigated whether systemic administration of Ucn 2 could reduce BP and adrenal and plasma levels of catecholamines in vivo. Ucn 2 peptide was administered to freely moving, conscious Chga-/- and wild-type control mice. Telemetry and HPLC measured changes in BP and catecholamine levels, respectively. In both groups of mice, Ucn 2 dose-dependently decreased BP, and this effect was mediated by corticotropin factor-receptor type 2. However, in Chga-/- mice, the maximal percentage decrease of systolic BP from basal systolic BP was 37% compared with only a 23% reduction in wild-type mice (P=0.04). In Chga-/- mice only, Ucn 2 decreased adrenal and plasma levels of catecholamines as well as adrenal levels of tyrosine hydroxylase protein and phosphorylation. In vitro mechanistic studies demonstrated that Ucn 2 reduces both catecholamine secretion and tyrosine hydroxylase promoter activity, suggesting that the exaggerated action of Ucn 2 to reduce BP in the Chga-/- mouse is mediated through inhibition of both catecholamine synthesis and secretion. The data suggest that Ucn 2 may be therapeutically useful in regulating the exaggerated sympathoadrenal function of hyperadrenergic hypertension.

Diethylstilbestrol and other nonsteroidal estrogens: novel class of store-operated calcium channel modulators

BACKGROUND

Compounds with the stilbene pharmacophore and other nonsteroidal estrogens have previously been shown to inhibit thrombin-induced elevation of intracellular free calcium ([Ca]i) in human platelets. Thrombin elevates [Ca]i in platelets predominantly by activating a store-operated Ca entry (SOCE) mechanism, probably involving STIM1 and Orai1 although other components may be involved.

METHODS

Human platelets were loaded with the Ca sensitive indicator fura-2, various concentrations of stilbene compounds and other nonsteroidal estrogens were added to the platelets, and thrombin was added to elevate [Ca]i. The degree of inhibition by each compound was determined at the peak increase in [Ca]i induced by thrombin.

RESULTS

The additional compounds that were examined in the present study were analogs of diethylstilbestrol (DES), namely trans-resveratrol, hexestrol, tetrahydrochrysene (THC), indenestrol, isoflavones, flavones, and flavanones. DES, indenestrols, and substituted THC diols had the highest inhibitory activity. Dietary polyphenols were less active, and isoflavones were more active than flavones. Glycosides of flavones, flavanones, and isoflavones were inactive. Equol (a product of isoflavone metabolism) had low activity. Among the compounds with a stilbene moiety the presence of unsubstituted phenyl hydroxyls in the para- position were required for activity. Esterification of hydroxyls and bulky substituents at a hydroxyl group diminished or abolished activity. Presence of the ethyl side chains enhanced activity, and shortening or removal of these side chains was detrimental to activity. Presence of the conjugated double bound was necessary for activity. Reduction of the double bond (in fused rings such as equol, dihydrogenistein, indanestrol, or in open chain stilbene derivatives) or repositioning of this double bond outside the stilbene moiety was detrimental to activity, because phenyl rings are not co-planar and have to be at a certain angle to each other.

CONCLUSION

DES likely represents the pharmacophore of this group of nonsteroidal estrogens as an inhibitor of SOCE in platelets.

Role of store-operated calcium entry in imperatorin-induced vasodilatation of rat small mesenteric artery

Store-operated Ca(2+) entry (SOCE) has recently been proposed to contribute to Ca(2+) influx in vascular smooth muscle cells (VSMCs). Imperatorin is known for its potent vasodilatory effects as a dietary furanocoumarin. The study was designed to examine the hypothesis that SOCE have a functional role in imperatorin-induced vasodilation. Small mesenteric resistance arteries and mesenteric VSMCs were obtained from rats. Isometric tensions of isolated artery rings were measured by a sensitive myograph system. Laser scanning confocal microscopy was used to determine the intracellular Ca(2+) concentration of fluo-3-loaded VSMCs. Imperatorin (1-100 μM) relaxed artery rings precontracted by phenylephrine in a concentration-dependent manner. In cultured mesenteric VSMCs, passive store depletion by thapsigargin and active store depletion by phenylephrine both induced Ca(2+) influx due to SOCE. Imperatorin didn't inhibit SOCE-mediated increases in cytosolic Ca(2+) levels evoked by the emptying of the stores. In isolated artery rings, imperatorin didn't inhibit SOCE-induced contractions due to store depletion. Our results exclude SOCE mechanism of vasodilatation by imperatorin. But imperatorin is partly similar with nifedipine in vasorelaxation effect.

GPR55-dependent and -independent ion signalling in response to lysophosphatidylinositol in endothelial cells

BACKGROUND AND PURPOSE

The glycerol-based lysophospholipid lysophosphatidylinositol (LPI) is an endogenous agonist of the G-protein-coupled receptor 55 (GPR55) exhibiting cannabinoid receptor-like properties in endothelial cells. To estimate the contribution of GPR55 to the physiological effects of LPI, the GPR55-dependent and -independent electrical responses in this cell type were investigated.

EXPERIMENTAL APPROACH

Applying small interference RNA-mediated knock-down and transient overexpression, GPR55-dependent and -independent effects of LPI on cytosolic free Ca(2+) concentration, membrane potential and transmembrane ion currents were studied in EA.hy296 cells.

KEY RESULTS

In a GPR55-dependent, GDPbetaS and U73122-sensitive manner, LPI induced rapid and transient intracellular Ca(2+) release that was associated with activation of charybdotoxin-sensitive, large conductance, Ca(2+)-activated, K(+) channels (BK(Ca)) and temporary membrane hyperpolarization. Following these initial electrical reactions, LPI elicited GPR55-independent long-lasting Na(+) loading and a non-selective inward current causing sustained membrane depolarization that depended on extracellular Ca(2+) and Na(+) and was partially inhibited by Ni(2+) and La(3+). This inward current was due to the activation of a voltage-independent non-selective cation current. The Ni(2+) and La(3+)-insensitive depolarization with LPI was prevented by inhibition of the Na/K-ATPase by ouabain.

CONCLUSIONS AND IMPLICATIONS

LPI elicited a biphasic response in endothelial cells of which the immediate Ca(2+) signalling depends on GPR55 while the subsequent depolarization is due to Na(+) loading via non-selective cation channels and an inhibition of the Na/K-ATPase. Thus, LPI is a potent signalling molecule that affects endothelial functions by modulating several cellular electrical responses that are only partially linked to GPR55.

Effects of endoplasmic reticulum stress on group VIA phospholipase A2 in beta cells include tyrosine phosphorylation and increased association with calnexin

The Group VIA phospholipase A(2) (iPLA(2)β) hydrolyzes glycerophospholipids at the sn-2-position to yield a free fatty acid and a 2-lysophospholipid, and iPLA(2)β has been reported to participate in apoptosis, phospholipid remodeling, insulin secretion, transcriptional regulation, and other processes. Induction of endoplasmic reticulum (ER) stress in β-cells and vascular myocytes with SERCA inhibitors activates iPLA(2)β, resulting in hydrolysis of arachidonic acid from membrane phospholipids, by a mechanism that is not well understood. Regulatory proteins interact with iPLA(2)β, including the Ca(2+)/calmodulin-dependent protein kinase IIβ, and we have characterized the iPLA(2)β interactome further using affinity capture and LC/electrospray ionization/MS/MS. An iPLA(2)β-FLAG fusion protein was expressed in an INS-1 insulinoma cell line and then adsorbed to an anti-FLAG matrix after cell lysis. iPLA(2)β and any associated proteins were then displaced with FLAG peptide and analyzed by SDS-PAGE. Gel sections were digested with trypsin, and the resultant peptide mixtures were analyzed by LC/MS/MS with database searching. This identified 37 proteins that associate with iPLA(2)β, and nearly half of them reside in ER or mitochondria. They include the ER chaperone calnexin, whose association with iPLA(2)β increases upon induction of ER stress. Phosphorylation of iPLA(2)β at Tyr(616) also occurs upon induction of ER stress, and the phosphoprotein associates with calnexin. The activity of iPLA(2)β in vitro increases upon co-incubation with calnexin, and overexpression of calnexin in INS-1 cells results in augmentation of ER stress-induced, iPLA(2)β-catalyzed hydrolysis of arachidonic acid from membrane phospholipids, reflecting the functional significance of the interaction. Similar results were obtained with mouse pancreatic islets.

Role of store-operated Ca(2+) entry in adenosine-induced vasodilatation of rat small mesenteric artery

Store-operated Ca(2+) entry (SOCE) has recently been proposed to contribute to Ca(2+) influx in vascular smooth muscle cells (VSMCs). Adenosine is known for its protective role against hypoxia and ischemia by increasing nutrient and oxygen supply through vasodilation. This study was designed to examine the hypothesis that SOCE have a functional role in adenosine-induced vasodilation. Small mesenteric resistance arteries and mesenteric VSMCs were obtained from rats. Isometric tensions of isolated artery rings were measured by a sensitive myograph system. Laser-scanning confocal microscopy was used to determine the intracellular Ca(2+) concentration of fluo 3-loaded VSMCs. Adenosine (0.1-100 microM) relaxed artery rings that were precontracted by phenylephrine in a concentration-dependent manner. In cultured mesenteric VSMCs, passive store depletion by thapsigargin and active store depletion by phenylephrine both induced Ca(2+) influx due to SOCE. Adenosine inhibited SOCE-mediated increases in cytosolic Ca(2+) levels evoked by the emptying of the stores. In isolated artery rings, adenosine inhibited SOCE-induced contractions due to store depletion. A(2A) receptor antagonism with SCH-58261 and adenylate cyclase inhibition with SQ-22536 largely attenuated adenosine responses. The cAMP analog 8-bromo-cAMP mimicked the effects of adenosine on SOCE. Our results indicate a novel mechanism of vasodilatation by adenosine that involves regulation of SOCE through the cAMP signaling pathway due to activation of adenosine A(2A) receptors.

Urocortin 2 protects against retinal degeneration following bilateral common carotid artery occlusion in the rat

Urocortin 2 (Ucn 2) is corticotropin-releasing factor (CRF) paralog that preferentially activates CRF(2) receptors. Ucns exert CRF(2)-mediated cytoprotective effects against ischemia-reperfusion injury in cardiomyocytes. However, little is known regarding potential retinoprotective effects of Ucns despite the known presence of CRF family peptides and their receptors (predominantly CRF(2 alpha)) in retina. Therefore, the present study investigated the effects of post-ischemic intravitreal Ucn 2 (2 nmol) administration on ischemia-induced retinal degeneration. Two-month-old rats were subjected to permanent bilateral common carotid artery occlusion, and their retinas were processed histologically after two weeks survival to determine the density of viable cells in the ganglion cell layer and the thickness of all retinal layers. In vehicle-treated subjects, carotid occlusion reduced retina thickness by approximately 60% as compared to sham-operated animals. In contrast, intraocular Ucn 2 treatment led to a marked amelioration of the retinal layers, and the thickness of all layers was significantly increased by 40% compared to ischemic vehicle-treated subjects. Ucn 2 treatment also increased the number of cells by 55% in the ganglion cell layer as compared to those from carotid-occluded retinas of vehicle-treated subjects. These findings suggest that intraocular Ucn 2 treatment may protect against ischemia-induced retinal degeneration, results with potential therapeutic implications for ophthalmic diseases.

Caffeine inhibits InsP3 responses and capacitative calcium entry in canine pulmonary arterial smooth muscle cells

Caffeine is a well described and characterized ryanodine receptor (RyR) activator. Previous evidence from independent research studies also indicate caffeine inhibits InsP3 receptor functionality, which is important to activation of capacitative Ca2+ entry (CCE) in some cell types. In addition, RyR activation elicits excitatory-coupled Ca2+ entry (ECCE) in skeletal muscle myotubes. Recent studies by our group show that canine pulmonary arterial smooth muscle cells (PASMCs) have functional InsP3 receptors as well as RyRs, and that CCE is dependent on InsP3 receptor activity. The potential for caffeine to activate ECCE as well as inhibit InsP3 receptor function and CCE was examined using fura-2 fluorescent imaging in canine PASMCs. The data show caffeine causes transient as well as sustained cytosolic Ca2+ increases, though this is not due to CCE or ECCE activity as evidenced by a lack of an increase in Mn2+ quench of fura-2. The experiments also show caffeine reversibly inhibits 5-HT elicited-InsP3 mediated Ca2+ responses with an IC50 of 6.87x10(-4) M and 10 mM caffeine fully inhibits CCE. These studies provide the first evidence that caffeine is an inhibitor of InsP3 generated Ca2+ signals and CCE in PASMCs.

Complex regulation of store-operated Ca2+entry pathway by PKC-ε in vascular SMCs

The role of PKC in the regulation of store-operated Ca2+entry (SOCE) is rather controversial. Here, we used Ca2+-imaging, biochemical, pharmacological, and molecular techniques to test if Ca2+-independent PLA2β (iPLA2β), one of the transducers of the signal from depleted stores to plasma membrane channels, may be a target for the complex regulation of SOCE by PKC and diacylglycerol (DAG) in rabbit aortic smooth muscle cells (SMCs). We found that the inhibition of PKC with chelerythrine resulted in significant inhibition of thapsigargin (TG)-induced SOCE in proliferating SMCs. Activation of PKC by the diacylglycerol analog 1-oleoyl-2-acetyl- sn-glycerol (OAG) caused a significant depletion of intracellular Ca2+stores and triggered Ca2+influx that was similar to TG-induced SOCE. OAG and TG both produced a PKC-dependent activation of iPLA2β and Ca2+entry that were absent in SMCs in which iPLA2β was inhibited by a specific chiral enantiomer of bromoenol lactone ( S-BEL). Moreover, we found that PKC regulates TG- and OAG-induced Ca2+entry only in proliferating SMCs, which correlates with the expression of the specific PKC-ε isoform. Molecular downregulation of PKC-ε impaired TG- and OAG-induced Ca2+influx in proliferating SMCs but had no effect in confluent SMCs. Our results demonstrate that DAG (or OAG) can affect SOCE via multiple mechanisms, which may involve the depletion of Ca2+stores as well as direct PKC-ε-dependent activation of iPLA2β, resulting in a complex regulation of SOCE in proliferating and confluent SMCs.

Diverse properties of store-operated TRPC channels activated by protein kinase C in vascular myocytes

In vascular smooth muscle, store-operated channels (SOCs) contribute to many physiological functions including vasoconstriction and cell growth and proliferation. In the present work we compared the properties of SOCs in freshly dispersed myocytes from rabbit coronary and mesenteric arteries and portal vein. Cyclopiazonic acid (CPA)-induced whole-cell SOC currents were sixfold greater at negative membrane potentials and displayed markedly different rectification properties and reversal potentials in coronary compared to mesenteric artery myocytes. Single channel studies showed that endothelin-1, CPA and the cell-permeant Ca(2+) chelator BAPTA-AM activated the same 2.6 pS SOC in coronary artery. In 1.5 mM [Ca(2+)](o) the unitary conductance of SOCs was significantly greater in coronary than in mesenteric artery. Moreover in 0 mM [Ca(2+)](o) the conductance of SOCs in coronary artery was unaltered whereas the conductance of SOCs in mesenteric artery was increased fourfold. In coronary artery SOCs were inhibited by the protein kinase C (PKC) inhibitor chelerythrine and activated by the phorbol ester phorbol 12,13-dibutyrate (PDBu), the diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG) and a catalytic subunit of PKC. These data infer an important role for PKC in activation of SOCs in coronary artery similar to mesenteric artery and portal vein. Anti-TRPC1 and -TRPC5 antibodies inhibited SOCs in coronary and mesenteric arteries and portal vein but anti-TRPC6 blocked SOCs only in coronary artery and anti-TRPC7 blocked SOCs only in portal vein. Immunoprecipitation showed associations between TRPC1 and TRPC5 in all preparations but between TRPC5 and TRPC6 only in coronary artery and between TRPC5 and TRPC7 only in portal vein. Finally, flufenamic acid increased SOC activity in coronary artery but inhibited SOCs in mesenteric artery and portal vein myocytes. These data provide strong evidence that vascular myocytes express diverse SOC isoforms, which are likely to be composed of different TRPC proteins and have different physiological functions.