Valerie Myers

Temple University, Philadelphia, Pennsylvania, United States

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Publications (10)77.86 Total impact

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    ABSTRACT: -Enhanced arginine vasopressin (AVP) levels are associated with increased mortality during end-stage human heart failure (HF), and cardiac AVP type 1A receptor (V1AR) expression becomes increased. Additionally, mice with cardiac-restricted V1AR overexpression develop cardiomyopathy and decreased β-adrenergic receptor (βAR) responsiveness. This led us to hypothesize that V1AR signaling regulated βAR responsiveness and in doing so contributes to HF development.
    Circulation 09/2014; · 15.20 Impact Factor
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    ABSTRACT: The most common cause of dilated cardiomyopathy and heart failure (HF) is ischemic heart disease; however, in a third of all patients the cause remains undefined and patients are diagnosed as having idiopathic dilated cardiomyopathy (IDC). Recent studies suggest that many patients with IDC have a family history of HF and rare genetic variants in over 35 genes have been shown to be causative of disease. We employed whole-exome sequencing to identify the causative variant in a large family with autosomal dominant transmission of dilated cardiomyopathy. Sequencing and subsequent informatics revealed a novel 10-nucleotide deletion in the BCL2-associated athanogene 3 (BAG3) gene ((Ch10:del 121436332_12143641: del. 1266_1275 [NM 004281]) that segregated with all affected individuals. The deletion predicted a shift in the reading frame with the resultant deletion of 135 amino acids from the C-terminal end of the protein. Consistent with genetic variants in genes encoding other sarcomeric proteins there was a considerable amount of genetic heterogeneity in the affected family members. Interestingly, we also found that the levels of BAG3 protein were significantly reduced in the hearts from unrelated patients with end-stage HF undergoing cardiac transplantation when compared with non-failing controls. Diminished levels of BAG3 protein may be associated with both familial and non-familial forms of dilated cardiomyopathy. J. Cell. Physiol. © 2014 Wiley Periodicals, Inc.
    Journal of Cellular Physiology 03/2014; · 4.22 Impact Factor
  • Journal of the American College of Cardiology 10/2013; · 14.09 Impact Factor
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    ABSTRACT: Circulating levels of arginine vasopressin (AVP) are elevated during hypovolemia and during cardiac stress. AVP activates V1A-Gαq coupled receptors in the heart and vasculature and V2-Gαs coupled receptors in the kidney. However, little is known regarding the signaling pathways that influence the effects of V1A receptor (V1AR) activation during cellular injury. Using hypoxia-reoxygenation (H/R) as a cell injury model, we evaluated cell survival and caspase 3/7 activity in H9c2 myoblasts after treatment with AVP. Pretreatment of H9c2 cells with AVP significantly reduced H/R-induced cell death and caspase 3/7 activity, effects that were blocked via both selective V1AR inhibition and MEK1/2 inhibition. AVP increased ERK1/2 phosphorylation in a concentration-dependent manner that was sensitive to MEK1/2 inhibition and V1AR inhibition, but not V1BR or V2R inhibition. Discrete elements of the V1A-Gαq-protein kinase C (PKC) and V1A-G protein-coupled receptor kinase (GRK)-β-arrestin signaling cascades were inhibited in order to dissect the pathways responsible for the protective effects of V1AR signaling: Gαq (over-expression of GqI), PKC (administration of Ro 31-82425), GRK2 (βARKct overexpression and siRNA knockdown), GRK5 (siRNA knockdown) and β-arrestin1 (siRNA knockdown). These studies demonstrated that both Gαq/PKC- and GRK2/β-arrestin1-dependent V1AR signaling were capable of inducing ERK1/2 phosphorylation in response to AVP stimulation. However, AVP-mediated protection against H/R was elicited only via GRK2- and β-arrestin1-dependent signaling. These results suggest that activation of the V1AR in H9c2 cells mediates protective signaling via a GRK2-β-arrestin1-ERK1/2-dependent mechanism that leads to decreased caspase 3/7 activity and enhanced survival under conditions of ischemic stress.
    Molecular pharmacology 05/2013; · 4.53 Impact Factor
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    ABSTRACT: Adenosine binds to three G protein-coupled receptors (R) located on the cardiomyocyte (A(1)-R, A(2A)-R and A(3)-R) and provides cardiac protection during both ischemic and load-induced stress. While the role of adenosine receptor-subtypes has been well defined in the setting of ischemia-reperfusion, far less is known regarding their roles in protecting the heart during other forms of cardiac stress. Because of its ability to increase cardiac contractility and heart rate, we hypothesized that enhanced signaling through A(2A)-R would protect the heart during the stress of transverse aortic constriction (TAC). Using a cardiac-specific and inducible promoter, we selectively over-expressed A(2A)-R in FVB mice. Echocardiograms were obtained at baseline, 2, 4, 8, 12, 14 weeks and hearts were harvested at 14 weeks, when WT mice developed a significant decrease in cardiac function, an increase in end systolic and diastolic dimensions, a higher heart weight to body weight ratio (HW/BW), and marked fibrosis when compared with sham-operated WT. More importantly, these changes were significantly attenuated by over expression of the A(2A)-R. Furthermore, WT mice also demonstrated marked increases in the hypertrophic genes β-myosin heavy chain (β-MHC), and atrial natriuretic factor (ANF)--changes that are mediated by activation of the transcription factor GATA-4. Levels of the mRNAs encoding β-MHC, ANP, and GATA-4 were significantly lower in myocardium from A(2A)-R TG mice after TAC when compared with WT and sham-operated controls. In addition, three inflammatory factors genes encoding cysteine dioxygenase, complement component 3, and serine peptidase inhibitor, member 3N, were enhanced in WT TAC mice, but their expression was suppressed in A(2A)-R TG mice. A(2A)-R over-expression is protective against pressure-induced heart failure secondary to TAC. These cardioprotective effects are associated with attenuation of GATA-4 expression and inflammatory factors. The A(2A)-R may provide a novel new target for pharmacologic therapy in patients with cardiovascular disease.
    PLoS ONE 01/2012; 7(7):e39919. · 3.53 Impact Factor
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    ABSTRACT: Phosphorylation of a threonine residue (T308 in Akt1) in the activation loop of Akt kinases is a prerequisite for deregulated Akt activity frequently observed in neoplasia. Akt phosphorylation in vivo is balanced by the opposite activities of kinases and phosphatases. Here we describe that targeting Akt kinase to the cell membrane markedly reduced sensitivity of phosphorylated Akt to dephosphorylation by protein phosphatase 2A. This effect was amplified by occupancy of the ATP binding pocket by either ATP or ATP-competitive inhibitors. Mutational analysis revealed that R273 in Akt1 and the corresponding R274 in Akt2 are essential for shielding T308 in the activation loop against dephosphorylation. Thus, occupancy of the nucleotide binding pocket of Akt kinases enables intramolecular interactions that restrict phosphatase access and sustain Akt phosphorylation. This mechanism provides an explanation for the "paradoxical" Akt hyperphosphorylation induced by ATP-competitive inhibitor, A-443654. The lack of phosphatase resistance further contributes insight into the mechanism by which the human Akt2 R274H missense mutation may cause autosomal-dominant diabetes mellitus.
    Proceedings of the National Academy of Sciences 11/2011; 108(46):E1120-7. · 9.81 Impact Factor
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    ABSTRACT: Akt2 protein kinase has been shown to promote cell migration and actin polymerization in several cell types, including macrophages. Because migrating macrophages constitute an important inflammatory response after myocardial ischemia, we determined cardiac macrophage expression after ischemia-reperfusion (I/R) injury and cryo-injury in mice lacking Akt2 (Akt2-KO). At 7 days post-I/R, Akt2-KO cardiac tissues showed an increase in immunohistochemical staining for macrophage markers (Galectin 3 and F4/80) compared with wild-type (WT) mice, indicating macrophage density was increased in the injured Akt2-KO myocardium. This change was time dependent because macrophage density was similar between WT and Akt2-KO myocardium at 3 days post-I/R, but by 7 and 14 days post-I/R, macrophage density was significantly increased in Akt2-KO myocardium. Concomitantly, infarct size was larger and cardiac function was reduced in Akt2-KO mice subjected to I/R. However, when cryo-infarction produced similar infarct sizes in the anterior wall in both WT and Akt2-KO mice, macrophage density remained higher in Akt2-KO mouse myocardium, suggesting Akt2 regulates myocardial macrophage density independent of infarct size. Consistently, bone marrow from Akt2-KO mice enhanced myocardial macrophage density in both C57/B6 WT and Akt2-KO recipient mice. Finally, reciprocal ex-vivo coculturing of macrophages and cardiac myocytes showed that activated Akt2-KO peritoneal macrophages had reduced mobility and adhesion when compared with WT littermate controls. Thus, although Akt-2 KO mice did not affect the initial inflammation response after injury and Akt2 deficiency has been shown to impair cell migration or motility in macrophages, our data suggested a novel mechanism in which increasing retention of Akt2-KO macrophages resulted in increasing cardiac Akt2-KO macrophage density in the myocardial space.
    AJP Heart and Circulatory Physiology 09/2011; 301(5):H1932-40. · 4.01 Impact Factor
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    ABSTRACT: [Arg8]-vasopressin (AVP) activates 3 G-protein-coupled receptors: V1A, V2, and V1B. The AVP-V1A receptor is the primary AVP receptor in the heart; however, its role in cardiac homeostasis is controversial. To better understand AVP-mediated signaling in the heart, we created a transgenic mouse with controlled overexpression of the V1A receptor. The V1A receptor transgene was placed under the control of the tetracycline-regulated, cardiac-specific α-myosin heavy chain promoter (V1A-TG). V1A-TG mice had a normal cardiac function phenotype at 10 weeks of age; however, by 24 weeks of age, tetracycline-transactivating factor/V1A-TG mouse hearts had reduced cardiac function, cardiac hypertrophy, and dilatation of the ventricular cavity. Contractile dysfunction was also observed in isolated adult cardiac myocytes. When V1A receptor transgene was induced to be expressed in adult mice (V1A-TG(Ind)), left ventricular dysfunction and dilatation were also seen, albeit at a later time point. Because the V1A receptor mediates cell signaling through Gα(q) protein, we blocked Gα(q) signaling by crossing tetracycline-transactivating factor/V1A mice with transgenic mice that expressed a small inhibitory peptide against Gα(q). Gα(q) blockade abrogated the development of the heart failure phenotype in tetracycline-transactivating factor/V1A-TG mice. The heart failure phenotype could be reversed by administration of doxycycline. Our results demonstrate a role for V1A-mediated signaling in the development of heart failure and support a role for V1A blockade in the treatment of patients with elevated levels of vasopressin.
    Circulation 08/2011; 124(5):572-81. · 15.20 Impact Factor
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    ABSTRACT: Caveolins are scaffolding proteins that are integral components of caveolae, flask-shaped invaginations in the membranes of all mammalian cells. Caveolin-1 and -2 are expressed ubiquitously, whereas caveolin-3 is found only in muscle. The role of caveolin-3 in heart muscle disease is controversial. The present study was undertaken to assess the effects of left ventricular dysfunction on the expression of caveolin proteins using 2 well characterized models of murine heart failure and failing human heart. Transgenic mice with constitutive overexpression of A(1)-adenosine receptor (A(1)-TG) demonstrated cardiac dilatation and decreased left ventricular function at 10 weeks of age. This was accompanied by a marked decrease in caveolin-3 mRNA and protein levels compared with non-TG control mice. The change in caveolin-3 expression was selective, because levels of caveolin-1 and -2 did not change. Confocal imaging of myocytes isolated from A(1)-TG mice demonstrated a loss of the plate-like appearance of T tubules. Caveolin-3 levels were also reduced in hearts from mice overexpressing tumor necrosis factor α. There was a direct relationship between caveolin-3 expression and fractional shortening in all mice that were studied (r = 0.65; P < .001). Although we could not demonstrate a significant decrease in caveolin-3 levels in failing human heart, we did find a direct correlation (r = 0.7; P < .05) between levels of caveolin-3 protein and Ca(2+)-adenosine triphosphatase, a marker of the heart failure phenotype. These results suggest a relationship between left ventricular dysfunction and caveolin-3 levels and suggest that caveolin-3 may provide a novel target for heart failure therapy.
    Journal of cardiac failure 03/2011; 17(3):253-63. · 3.25 Impact Factor
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    ABSTRACT: Activation of the A(2A) adenosine receptor (A(2A)R) has been shown to be cardioprotective. We hypothesized that A(2A)R overexpression could protect the heart from adriamycin-induced cardiomyopathy. Transgenic (TG) mice overexpressing the A(2A)R and wild-type mice (WT) were injected with adriamycin (5 mg.kg(-1).wk(-1) ip, 4 wk). All WT mice survived adriamycin treatment while A(2A)R TG mice suffered 100% mortality at 4 wk. Telemetry showed progressive prolongation of the QT interval, bradyarrhythmias, heart block, and sudden death in adriamycin-treated A(2A)R TG but not WT mice. Both WT and A(2A)R TG demonstrated similar decreases in heart function at 3 wk after treatment. Adriamycin significantly increased end-diastolic intracellular Ca(2+) concentration in A(2A)R TG but not in WT myocytes (P < 0.05). Compared with WT myocytes, action potential duration increased dramatically in A(2A)R TG myocytes (P < 0.05) after adriamycin treatment. Expression of connexin 43 was decreased in adriamycin treated A(2A)R TG but not WT mice. In sharp contrast, A(2A)R overexpression induced after the completion of adriamycin treatment resulted in no deaths and enhanced cardiac performance compared with WT adriamycin-treated mice. Our results indicate that the timing of A(2A)R activation is critical in terms of exacerbating or protecting adriamycin-induced cardiotoxicity. Our data have direct relevance on the clinical use of adenosine agonists or antagonists in the treatment of patients undergoing adriamycin therapy.
    AJP Heart and Circulatory Physiology 04/2010; 298(6):H1738-47. · 4.01 Impact Factor

Publication Stats

44 Citations
77.86 Total Impact Points

Institutions

  • 2012–2014
    • Temple University
      • Department of Physiology
      Philadelphia, Pennsylvania, United States
  • 2011
    • Thomas Jefferson University
      • Division of Hospital Medicine
      Philadelphia, PA, United States