Controlled and Cardiac-Restricted Overexpression of the Arginine Vasopressin V1A Receptor Causes Reversible Left Ventricular Dysfunction Through G q-Mediated Cell Signaling

Center For Translational Medicine, Department of Medicine, Jefferson Medical College, Philadelphia, PA 19107, USA.
Circulation (Impact Factor: 14.43). 08/2011; 124(5):572-81. DOI: 10.1161/CIRCULATIONAHA.111.021352
Source: PubMed


[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.

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    • "Since V 1A R/Ga q protein coupling induces the activation of PKC, regulating the hypertrophic gene program (Li et al., 2011), we tested whether Ga q protein/PKC–mediated signaling is involved in AVP-induced P-ERK1/2 and cell survival responses. Overexpression of the peptide inhibitor of Ga q (GqI) inhibited the acute P-ERK1/2 response to AVP (2 and 5 minutes, by 90% 6 3% and 52% 6 6%, respectively, versus GFP control), but had no effect on the AVP-induced prolonged responses at 30 and 60 minutes (Fig. 3, A and C). "
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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.
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    • "IP3 generation can be measured by the stable accumulation of IP1 in cells in the presence of LiCl following agonist binding to Gq-coupled receptors [32]. IP1 measurements were performed by ELISA (Cisbio), according to the manufacturer’s protocol, and optical density at 450 nm was read using a Victor plate reader. "
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