Calcium efflux activity of plasma membrane Ca2+ ATPase-4 (PMCA4) mediates cell cycle progression in vascular smooth muscle cells

Potential Roles of Metals in the Pathogenesis of Pulmonary and Systemic Hypertension

Pulmonary and systemic hypertension (PH, SH) are characterized by vasoconstriction and vascular remodeling resulting in increased vascular resistance and pulmonary/aortic artery pressures. The chronic stress leads to inflammation, oxidative stress, and infiltration by immune cells. Roles of metals in these diseases, particularly PH are largely unknown. This review first discusses the pathophysiology of PH including vascular oxidative stress, inflammation, and remodeling in PH; mitochondrial dysfunction and metabolic changes in PH; ion channel and its alterations in the pathogenesis of PH as well as PH-associated right ventricular (RV) remodeling and dysfunctions. This review then summarizes metal general features and essentiality for the cardiovascular system and effects of metals on systemic blood pressure. Lastly, this review explores non-essential and essential metals and potential roles of their dyshomeostasis in PH and RV dysfunction. Although it remains early to conclude the role of metals in the pathogenesis of PH, emerging direct and indirect evidence implicates the possible contributions of metal-mediated toxicities in the development of PH. Future research should focus on comprehensive clinical metallomics study in PH patients; mechanistic evaluations to elucidate roles of various metals in PH animal models; and novel therapy clinical trials targeting metals. These important discoveries will significantly advance our understandings of this rare yet fatal disease, PH.

Combined Treatment with KV Channel Inhibitor 4-Aminopyridine and either γ-Cystathionine Lyase Inhibitor β-Cyanoalanine or Epinephrine Restores Blood Pressure, and Improves Survival in the Wistar Rat Model of Anaphylactic Shock

Simple Summary

Allergic diseases are presenting a constant increase all over the world and caused by such different substances as food, drugs, and pollens. Anaphylactic shock is the more severe complication of allergy which can induce death if the treatment is not administered immediately. Some patients do not respond to the recommended treatment, intra venous or intramuscular epinephrine. The pathophysiology of anaphylactic shock is still under investigation. The mediators released after the activation of mast cells and basophiles act on endothelial cells and smooth muscle cells, inducing the vasodilation responsible for hypotension and shock. Nitric oxide and hydrogen sulphide are both intracellular mediators that induce vasodilation. The role of potassium voltage dependent channels is suspected. We aimed to demonstrate the ability of a blocker of potassium voltage dependent channels, 4-aminopyridine, alone or in combination with inhibitors of cystathionine γ-lyase to restore blood pressure and improve survival in an ovalbumin rat anaphylactic shock model. The blockade of potassium voltage dependent channels alone or combined with inhibitors of cystathionine γ-lyase, dl-propargylglycine, or β-cyanoalanine restored blood pressure and improved survival. These findings suggest possible investigative treatment pathways for research concerning epinephrine-refractory anaphylactic shock in patients.

Abstract

The mechanism of anaphylactic shock (AS) remains incompletely understood. The potassium channel blocker 4-aminopyridine (4-AP), the inhibitors of cystathionine γ-lyase (ICSE), dl-propargylglycine (DPG) or β-cyanoalanine (BCA), and the nitric oxide (NO) synthase produce vasoconstriction and could be an alternative for the treatment of AS. The aim of this study was to demonstrate the ability of L-NAME, ICSE alone or in combination with 4-AP to restore blood pressure (BP) and improve survival in ovalbumin (OVA) rats AS. Experimental groups included non-sensitized Wistar rats (n = 6); AS (n = 6); AS (n = 10 per group) treated i.v. with 4-AP (AS+4-AP), epinephrine (AS+EPI), AS+DPG, AS+BCA, or with L-NAME (AS+L-NAME); or AS treated with drug combinations 4-AP+DPG, 4-AP+BCA, 4-AP+L-NAME, or 4-AP+EPI. AS was induced by i.v. OVA (1 mg). Treatments were administered i.v. one minute after AS induction. Mean arterial BP (MAP), heart rate (HR), and survival were monitored for 60 min. Plasma levels of histamine, prostaglandin E2 (PGE2) and F2 (PGF2α), leukotriene B4 and C4, angiotensin II, vasopressin, oxidative stress markers, pH, HCO3, PaO2, PaCO2, and K+ were measured. OVA induced severe hypotension and all AS rats died. Moreover, 4-AP, 4-AP+EPI, or 4-AP+BCA normalized both MAP and HR and increased survival. All sensitized rats treated with 4-AP alone or with 4-AP+BCA survived. The time-integrated MAP “area under the curve” was significantly higher after combined 4-AP treatment with ICSE. Metabolic acidosis was not rescued and NO, ICSE, and Kv inhibitors differentially alter oxidative stress and plasma levels of anaphylactic mediators. The AS-induced reduction of serum angiotensin II levels was prevented by 4-AP treatment alone or in combination with other drugs. Further, 4-AP treatment combined with EPI or with BCA also increased serum PGF2α, whereas only the 4-AP+EPI combination increased serum LTB4. Serum vasopressin and angiotensin II levels were increased by 4-AP treatment alone or in combination with other drugs. Moreover, 4-AP alone and in combination with inhibition of cystathionine γ-lyase or EPI normalizes BP, increases serum vasoconstrictor levels, and improves survival in the Wistar rat model of AS. These findings suggest possible investigative treatment pathways for research into epinephrine-refractory anaphylactic shock in patients.

LncPTSR Triggers Vascular Remodeling in Pulmonary Hypertension by Regulating [Ca2+]i in Pulmonary Arterial Smooth Muscle Cells

Pulmonary hypertension (PH) is characterized by vascular remodeling and sustained increase in right ventricular systolic pressure (RVSP). The molecular mechanisms behind PH development remain unclear. Here, a long non-coding RNA (lncRNA) attenuated by platelet-derived growth factor BB (PDGF-BB) was identified and its functional roles were investigated in vitro and in vivo. Using RNA-seq data and rapid amplification of cDNA ends, a lncRNA neighboring the locus of plasma membrane calcium transporting ATPase 4 (PMCA4) was identified and named lncPTSR. It is a highly-conserved nuclear lncRNA, and was downregulated in pulmonary arterial smooth muscle cells (PASMCs) with PDGF-BB stimulation or hypoxia induction. Gene interruption/overexpression assays revealed that lncPTSR negatively regulates rat PASMCs proliferation, apoptosis, and migration. LncPTSR interruption in Sprague Dawley (SD) rats using adenovirus associated virus type 9 (AAV9)-mediated short-hairpin RNA (shRNA) resulted in a significant increase in RVSP and vascular remodeling in normoxic condition. LncPTSR knockdown also suppressed PMCA4 expression and attenuated the intracellular Ca2+ efflux of PASMCs in vitro and in vivo. Further studies suggest a complex cross-talk between lncPTSR and mitogen-activated protein kinase (MAPK) pathway: inhibition of mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated kinase (ERK) abolishes the PDGF-BB-mediated lncPTSR downregulation, and lncPTSR plays a feedback regulation for MAPK signaling molecules. The present study suggests that lncPTSR participates in pulmonary artery (PA) remodeling via modulating the expression of PMCA4 and intracellular Ca2+ homeostasis downstream of PDGF-BB driven MEK/ERK signaling. These results suggest lncPTSR may be a promising therapeutic target in PH treatment.

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

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

Plasma Membrane Ca2+ ATPase Isoform 4 (PMCA4) Has an Important Role in Numerous Hallmarks of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is largely resistant to standard treatments leading to poor patient survival. The expression of plasma membrane calcium ATPase-4 (PMCA4) is reported to modulate key cancer hallmarks including cell migration, growth, and apoptotic resistance. Data-mining revealed that PMCA4 was over-expressed in pancreatic ductal adenocarcinoma (PDAC) tumors which correlated with poor patient survival. Western blot and RT-qPCR revealed that MIA PaCa-2 cells almost exclusively express PMCA4 making these a suitable cellular model of PDAC with poor patient survival. Knockdown of PMCA4 in MIA PaCa-2 cells (using siRNA) reduced cytosolic Ca²⁺ ([Ca²⁺]_i) clearance, cell migration, and sensitized cells to apoptosis, without affecting cell growth. Knocking down PMCA4 had minimal effects on numerous metabolic parameters (as assessed using the Seahorse XF analyzer). In summary, this study provides the first evidence that PMCA4 is over-expressed in PDAC and plays a role in cell migration and apoptotic resistance in MIA PaCa-2 cells. This suggests that PMCA4 may offer an attractive novel therapeutic target in PDAC.

Reciprocality Between Estrogen Biology and Calcium Signaling in the Cardiovascular System

17β-Estradiol (E₂) is the main estrogenic hormone in the body and exerts many cardiovascular protective effects. Via three receptors known to date, including estrogen receptors α (ERα) and β (ERβ) and the G protein-coupled estrogen receptor 1 (GPER, aka GPR30), E₂ regulates numerous calcium-dependent activities in cardiovascular tissues. Nevertheless, effects of E₂ and its receptors on components of the calcium signaling machinery (CSM), the underlying mechanisms, and the linked functional impact are only beginning to be elucidated. A picture is emerging of the reciprocality between estrogen biology and Ca²⁺ signaling. Therein, E₂ and GPER, via both E₂-dependent and E₂-independent actions, moderate Ca²⁺-dependent activities; in turn, ERα and GPER are regulated by Ca²⁺ at the receptor level and downstream signaling via a feedforward loop. This article reviews current understanding of the effects of E₂ and its receptors on the cardiovascular CSM and vice versa with a focus on mechanisms and combined functional impact. An overview of the main CSM components in cardiovascular tissues will be first provided, followed by a brief review of estrogen receptors and their Ca²⁺-dependent regulation. The effects of estrogenic agonists to stimulate acute Ca²⁺ signals will then be reviewed. Subsequently, E₂-dependent and E₂-independent effects of GPER on components of the Ca²⁺ signals triggered by other stimuli will be discussed. Finally, a case study will illustrate how the many mechanisms are coordinated to moderate Ca²⁺-dependent activities in the cardiovascular system.

Down-regulation of Suv39h1 attenuates neointima formation after carotid artery injury in diabetic rats

Patients with diabetes have an increased risk of vascular complications. Suv39h1, a histone methyltransferase, plays a protective role against myocardial injury in diabetes. Herein, we intend to explore whether Suv39h1 could affect neointimal formation after vascular injury in diabetic rats and reveal the underlying mechanism. In this study, we generated adenovirus expressing Suv39h1 as well as lentivirus expressing Suv39h1‐targeting shRNA and evaluated the significance of Suv39h1 in vascular smooth muscle cells (VSMCs) under diabetic conditions. In vitro, we examined proliferative and migratory behaviours as well as the underlying signalling mechanisms in VSMCs in response to high glucose treatment. In vivo, we induced diabetes in SD rats with streptozocin and established the common carotid artery balloon injury model. Suv39h1 was found to be both necessary and sufficient to promote VSMC proliferation and migration under high glucose conditions. We observed corresponding changes in intracellular signalling molecules including complement C3 and phosphor‐ERK1/2. However, either up‐regulating or down‐regulating Suv39h1, phosphor‐p38 level was not significantly affected. Consistently, Suv39h1 overexpression led to accelerated neointima formation, while knocking down Suv39h1 reduced it following carotid artery injury in diabetic rats. Using microarray analyses, we showed that altering the Suv39h1 level in vivo dramatically altered the expression of myriad genes mediating different biological processes and molecular function. This study reveals the novel role of Suv39h1 in VSMCs of diabetes and suggests its potential role as a therapeutic target in diabetic vascular injury.

In vitro evaluation of MgSr and MgCaSr alloys via direct culture with bone marrow derived mesenchymal stem cells

Magnesium (Mg) and its alloys have been widely investigated as the most promising biodegradable metals to replace conventional non-degradable metals for temporary medical implant applications. New Mg alloys have been developed for medical applications in recent years; and the concept of alloying Mg with less-toxic elements have aroused tremendous interests due to the promise to address the problems associated with rapid degradation of Mg without compromising its cytocompatibility and biocompatibility. Of particular interests for orthopedic/spinal implant applications are the additions of calcium (Ca) and strontium (Sr) into Mg matrix because of their beneficial properties for bone regeneration. In this study, degradation and cytocompatibility of four binary MgSr alloys (Mg-xSr, x = 0.2, 0.5, 1 and 2 wt%) and four ternary MgCaSr alloys (Mg-1Ca-xSr, x = 0.2, 0.5, 1 and 2 wt%) were investigated and compared via direct culture with bone marrow-derived mesenchymal stem cells (BMSCs). The influence of the alloy composition on the degradation rates were studied and compared. Moreover, the cellular responses to the binary MgSr alloys and the ternary MgCaSr alloys were comparatively evaluated; and the critical factors influencing BMSC behaviors were discussed. This study screened the degradability and in vitro cytocompatibility of the binary MgSr alloys and the ternary MgCaSr alloys. Mg-1Sr, Mg-1Ca-0.5Sr and Mg-1Ca-1Sr alloys are recommended for further in vivo studies toward clinical translation due to their best overall performances in terms of degradation and cytocompatibility among all the alloys studied in the present work.

STATEMENT OF SIGNIFICANCE

Traditional Mg alloys with slower degradation often contain aluminum or rare earth elements as alloying components, which raised safety and regulatory concerns. To circumvent unsafe elements, nutrient elements such as calcium (Ca) and strontium (Sr) were selected to create Mg-Sr binary alloys and Mg-Ca-Sr ternary alloys to improve the safety and biocompatibility of bioresorbable Mg alloys for medical implant applications. In this study, in vitro degradation and cellular responses to four binary Mg-xSr alloys and four ternary Mg-1Ca-xSr alloys with increasing Sr content (up to 2 wt%) were evaluated in direct culture with bone marrow derived mesenchymal stem cells (BMSCs). The roles of Sr and Ca in tuning the alloy microstructure, degradation behaviors, and BMSC responses were collectively compared in the BMSC direct culture system for the first time. The most promising alloys were identified and recommended for further in vivo studies toward clinical translation.

Acute inhibition of PMCA4, but not global ablation, reduces blood pressure and arterial contractility via a nNOS-dependent mechanism

Cardiovascular disease is the world's leading cause of morbidity and mortality, with high blood pressure (BP) contributing to increased severity and number of adverse outcomes. Plasma membrane calcium ATPase 4 (PMCA4) has been previously shown to modulate systemic BP. However, published data are conflicting, with both overexpression and inhibition of PMCA4 in vivo shown to increase arterial contractility. Hence, our objective was to determine the role of PMCA4 in the regulation of BP and to further understand how PMCA4 functionally regulates BP using a novel specific inhibitor to PMCA4, aurintricarboxylic acid (ATA). Our approach assessed conscious BP and contractility of resistance arteries from PMCA4 global knockout (PMCA4KO) mice compared to wild‐type animals. Global ablation of PMCA4 had no significant effect on BP, arterial structure or isolated arterial contractility. ATA treatment significantly reduced BP and arterial contractility in wild‐type mice but had no significant effect in PMCA4KO mice. The effect of ATAin vivo and ex vivo was abolished by the neuronal nitric oxide synthase (nNOS) inhibitor Vinyl‐l‐NIO. Thus, this highlights differences in the effects of PMCA4 ablation and acute inhibition on the vasculature. Importantly, for doses here used, we show the vascular effects of ATA to be specific for PMCA4 and that ATA may be a further experimental tool for elucidating the role of PMCA4.

The Plasma Membrane Calcium ATPases and Their Role as Major New Players in Human Disease

The Ca²⁺ extrusion function of the four mammalian isoforms of the plasma membrane calcium ATPases (PMCAs) is well established. There is also ever-increasing detail known of their roles in global and local Ca²⁺ homeostasis and intracellular Ca²⁺ signaling in a wide variety of cell types and tissues. It is becoming clear that the spatiotemporal patterns of expression of the PMCAs and the fact that their abundances and relative expression levels vary from cell type to cell type both reflect and impact on their specific functions in these cells. Over recent years it has become increasingly apparent that these genes have potentially significant roles in human health and disease, with PMCAs1-4 being associated with cardiovascular diseases, deafness, autism, ataxia, adenoma, and malarial resistance. This review will bring together evidence of the variety of tissue-specific functions of PMCAs and will highlight the roles these genes play in regulating normal physiological functions and the considerable impact the genes have on human disease.

The plasma membrane calcium ATPase 4 signalling in cardiac fibroblasts mediates cardiomyocyte hypertrophy

The heart responds to pathological overload through myocyte hypertrophy. Here we show that this response is regulated by cardiac fibroblasts via a paracrine mechanism involving plasma membrane calcium ATPase 4 (PMCA4). Pmca4 deletion in mice, both systemically and specifically in fibroblasts, reduces the hypertrophic response to pressure overload; however, knocking out Pmca4 specifically in cardiomyocytes does not produce this effect. Mechanistically, cardiac fibroblasts lacking PMCA4 produce higher levels of secreted frizzled related protein 2 (sFRP2), which inhibits the hypertrophic response in neighbouring cardiomyocytes. Furthermore, we show that treatment with the PMCA4 inhibitor aurintricarboxylic acid (ATA) inhibits and reverses cardiac hypertrophy induced by pressure overload in mice. Our results reveal that PMCA4 regulates the development of cardiac hypertrophy and provide proof of principle for a therapeutic approach to treat this condition.

Plasma membrane calcium ATPases (PMCAs) as potential targets for the treatment of essential hypertension

The incidence of hypertension, the major modifiable risk factor for cardiovascular disease, is increasing. Thus, there is a pressing need for the development of new and more effective strategies to prevent and treat hypertension. Development of these relies on a continued evolution of our understanding of the mechanisms which control blood pressure (BP). Resistance arteries are important in the regulation of total peripheral resistance and BP; changes in their structure and function are strongly associated with hypertension. Anti-hypertensives which both reduce BP and reverse changes in resistance arterial structure reduce cardiovascular risk more than therapies which reduce BP alone. Hence, identification of novel potential vascular targets which modify BP is important. Hypertension is a multifactorial disorder which may include a genetic component. Genome wide association studies have identified ATP2B1, encoding the calcium pump plasma membrane calcium ATPase 1 (PMCA1), as having a strong association with BP and hypertension. Knockdown or reduced PMCA1 expression in mice has confirmed a physiological role for PMCA1 in BP and resistance arterial regulation. Altered expression or inhibition of PMCA4 has also been shown to modulate these parameters. The mechanisms whereby PMCA1 and 4 can modulate vascular function remain to be fully elucidated but may involve regulation of intracellular calcium homeostasis and/or comprise a structural role. However, clear physiological links between PMCA and BP, coupled with experimental studies directly linking PMCA1 and 4 to changes in BP and arterial function, suggest that they may be important targets for the development of new pharmacological modulators of BP.

Multifaceted plasma membrane Ca(2+) pumps: From structure to intracellular Ca(2+) handling and cancer

Plasma membrane Ca(2+) ATPases (PMCAs) are intimately involved in the control of intracellular Ca(2+) concentration. They reduce Ca(2+) in the cytosol not only by direct ejection, but also by controlling the formation of inositol-1,4,5-trisphosphate and decreasing Ca(2+) release from the endoplasmic reticulum Ca(2+) pool. In mammals four genes (PMCA1-4) are expressed, and alternative RNA splicing generates more than twenty variants. The variants differ in their regulatory characteristics. They localize into highly specialized membrane compartments and respond to the incoming Ca(2+) with distinct temporal resolution. The expression pattern of variants depends on cell type; a change in this pattern can result in perturbed Ca(2+) homeostasis and thus altered cell function. Indeed, PMCAs undergo remarkable changes in their expression pattern during tumorigenesis that might significantly contribute to the unbalanced Ca(2+) homeostasis of cancer cells. This article is part of a Special Issue entitled: Calcium and Cell Fate. Guest Editors: Jacques Haiech, Claus Heizmann, Joachim Krebs, Thierry Capiod and Olivier Mignen.

Plasma membrane calcium ATPases: From generic Ca(2+) sump pumps to versatile systems for fine-tuning cellular Ca(2.)

The plasma membrane calcium ATPases (PMCAs) are ATP-driven primary ion pumps found in all eukaryotic cells. They are the major high-affinity calcium extrusion system for expulsion of Ca(2+) ions from the cytosol and help restore the low resting levels of intracellular [Ca(2+)] following the temporary elevation of Ca(2+) generated during Ca(2+) signaling. Due to their essential role in the maintenance of cellular Ca(2+) homeostasis they were initially thought to be "sump pumps" for Ca(2+) removal needed by all cells to avoid eventual calcium overload. The discovery of multiple PMCA isoforms and alternatively spliced variants cast doubt on this simplistic assumption, and revealed instead that PMCAs are integral components of highly regulated multi-protein complexes fulfilling specific roles in calcium-dependent signaling originating at the plasma membrane. Biochemical, genetic, and physiological studies in gene-manipulated and mutant animals demonstrate the important role played by specific PMCAs in distinct diseases including those affecting the peripheral and central nervous system, cardiovascular disease, and osteoporosis. Human PMCA gene mutations and allelic variants associated with specific disorders continue to be discovered and underline the crucial role of different PMCAs in particular cells, tissues and organs.

IQGAP1 modulates the proliferation and migration of vascular smooth muscle cells in response to estrogen

Vascular smooth muscle cell (VSMC) proliferation and migration has been proven to be a critical event in the development of varicosity. Variations in estrogen levels, a pathological event related to age and pregnancy, play a role in the pathogenesis of varicosity. Previous studies have reported a different response of VSMCs following estrogen stimulation. However, the exact mechanisms involved have not yet been elucidated. In the present study, we examined the responses of lesion and normal VSMCs treated with 10(-8) M 17β-estradiol (E2) for 24 h. A differential effect of exposure to E2 was observed in these cells. IQ-domain GTPase-activating protein 1 (IQGAP1), a scaffold protein, was overexpressed in the lesion VSMCs and was shown to modulate VSMC proliferation and migration in response to E2. Furthermore, the increased expression of IQGAP1 was found to be intimately associated with a high activity of estrogen receptor α (ERα), which has been implicated in the regulation of VSMC physiological function. Additionally, we found that two critical kinases, Akt and extracellular signal-regulated kinase (ERK), mediated the activation of ERα and VSMC proliferation. According to our results, we thus concluded that high levels of IQGAP1 in VSMCs regulate the physiological reaction of the cells in response to estrogen exposure, and that kinases are involved in the process by mediating ERα activation. In view of the essential role of IQGAP1 in the physiological function of VSMCs, targeting this molecule may prove to be a promising strategy for the treatment of varicosity.

Regulators of G-protein-signaling proteins: negative modulators of G-protein-coupled receptor signaling

Regulators of G-protein-signaling (RGS) proteins are a category of intracellular proteins that have an inhibitory effect on the intracellular signaling produced by G-protein-coupled receptors (GPCRs). RGS along with RGS-like proteins switch on through direct contact G-alpha subunits providing a variety of intracellular functions through intracellular signaling. RGS proteins have a common RGS domain that binds to G alpha. RGS proteins accelerate GTPase and thus enhance guanosine triphosphate hydrolysis through the alpha subunit of heterotrimeric G proteins. As a result, they inactivate the G protein and quickly turn off GPCR signaling thus terminating the resulting downstream signals. Activity and subcellular localization of RGS proteins can be changed through covalent molecular changes to the enzyme, differential gene splicing, and processing of the protein. Other roles of RGS proteins have shown them to not be solely committed to being inhibitors but behave more as modulators and integrators of signaling. RGS proteins modulate the duration and kinetics of slow calcium oscillations and rapid phototransduction and ion signaling events. In other cases, RGS proteins integrate G proteins with signaling pathways linked to such diverse cellular responses as cell growth and differentiation, cell motility, and intracellular trafficking. Human and animal studies have revealed that RGS proteins play a vital role in physiology and can be ideal targets for diseases such as those related to addiction where receptor signaling seems continuously switched on.

Collagen and related extracellular matrix proteins in atherosclerotic plaque development

PURPOSE OF REVIEW

The structure, composition and turnover of the extracellular matrix (ECM) as well as cell-matrix interactions are crucial in the developing atherosclerotic plaque. There is a need for further insight into specific proteins in the ECM and their functions in the developing plaque, and during the last few years a number of publications have highlighted this very important field of research. These novel findings will be addressed in the present review.

RECENT FINDINGS

This review covers literature focused on collagen and ECM proteins interacting with collagen, and what their roles may be in plaque development.

SUMMARY

Acute myocardial infarction and stroke are common diseases that cause disability and mortality, and the underlying mechanism is often the rupture of a vulnerable atherosclerotic plaque. The vascular ECM and the tissue repair in the atherosclerotic lesion are important players in plaque progression. Understanding how specific proteins in the ECM interact with cells in the plaque and affect the fate of the plaque can lead to new treatments for cardiovascular disease.

Plasma membrane Ca2+-ATPase regulates Ca2+ signaling and the proliferation of airway smooth muscle cells

Plasma membrane Ca2+-ATPase (PMCA) plays an important role in regulating intracellular Ca2+ homeostasis by extruding excessive Ca2+ to extracellular spaces. PMCA has four isoforms and is widely expressed in different tissues and cells including airway smooth muscle cells (ASMCs). In the present study, we investigated the role of PMCA in the maintenance of Ca2+ homeostasis and regulation of ASMCs proliferation. By using Ca2+ fluorescence, we found that inhibition of PMCA with LaCl3 or carboxyeosin (CE) decreased the decay rate of Ca2+ transient induced by bradykinin (BK). No obvious decay was observed when SERCA was inhibited by thapsigargin (TpG). LaCl3 and CE also induced a spontaneous [Ca2+]i increase in the presence of TpG even in Ca2+-free bath solution. Both LaCl3 and CE inhibited UTP-induced Ca2+ oscillations in ASMCs. PCR assay found that PMCA1 and PMCA4 mRNA were expressed in rat ASMCs. The expression of PMCA4 was downregulated in proliferating ASMCs when compared to resting cells. Both the isoform-nonselective PMCA inhibitor caloxin 2a1 and PMCA4-selective inhibitor caloxin 1b1 decreased the decay rate of Ca2+ transient induced by TpG or BK. PMCA inhibitors except caloxin 2a1 promoted ASMCs proliferation. Annexin-V apoptosis assay detected that caloxin 2a1 increased ASMCs apoptosis, suggesting that inhibition of PMCA with different blockers results in different [Ca2+]i and thus different cellular response. Our results provide evidences to support the hypothesis that PMCA is involved in the regulation of Ca2+ homeostasis and ASMCs proliferation. These data suggest that PMCA may be a new target in the treatment of chronic asthma.

Enhanced proliferation and altered calcium handling in RGS2-deficient vascular smooth muscle cells

CONTEXT

Regulator of G-protein signaling-2 (RGS2) inhibits Gq-mediated regulation of Ca(2+) signalling in vascular smooth muscle cells (VSMC).

OBJECTIVE

RGS2 knockout (RGS2KO) mice are hypertensive and show arteriolar remodeling. VSMC proliferation modulates intracellular Ca(2+) concentration [Ca(2+)]i. RGS2 involvement in VSMC proliferation had not been examined.

METHODS

Thymidine incorporation and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) conversion assays measured cell proliferation. Fura-2 ratiometric imaging quantified [Ca(2+)]i before and after UTP and thapsigargin. [(3)H]-labeled inositol was used for phosphoinositide hydrolysis. Quantitative RT-PCR and confocal immunofluorescence of select Ca(2+) transporters was performed in primary aortic VSMC.

RESULTS AND DISCUSSION

Platelet-derived growth factor (PDGF) increased S-phase entry and proliferation in VSMC from RGS2KO mice to a greater extent than in VSMC from wild-type (WT) controls. Consistent with differential PDGF-induced changes in Ca(2+) homeostasis, RGS2KO VSMC showed lower resting [Ca(2+)]i but higher thapsigargin-induced [Ca(2+)]i as compared with WT. RGS2KO VSMC expressed lower mRNA levels of plasma membrane Ca(2+) ATPase-4 (PMCA4) and Na(+) Ca(2+) Exchanger (NCX), but higher levels of sarco-endoplasmic reticulum Ca(2+) ATPase-2 (SERCA2). Western blot and immunofluorescence revealed similar differences in PMCA4 and SERCA2 protein, while levels of NCX protein were not reduced in RGS2KO VSMC. Consistent with decreased Ca(2+) efflux activity, (45)Ca-extrusion rates were lower in RGS2KO VSMC. These differences were reversed by the PMCA inhibitor La(3+), but not by replacing extracellular Na(+) with choline, implicating differences in the activity of PMCA and not NCX.

CONCLUSION

RGS2-deficient VSMC exhibit higher rates of proliferation and coordinate plasticity of Ca(2+)-handling mechanisms in response to PDGF stimulation.