Mdm2 regulates cardiac contractility by inhibiting GRK2-mediated desensitization of β-adrenergic receptor signaling.
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2017-09
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Abstract
The oncoprotein Mdm2 is a RING domain-containing E3 ubiquitin ligase that ubiquitinates G protein-coupled receptor kinase 2 (GRK2) and β-arrestin2, thereby regulating β-adrenergic receptor (βAR) signaling and endocytosis. Previous studies showed that cardiac Mdm2 expression is critical for controlling p53-dependent apoptosis during early embryonic development, but the role of Mdm2 in the developed adult heart is unknown. We aimed to identify if Mdm2 affects βAR signaling and cardiac function in adult mice. Using Mdm2/p53-KO mice, which survive for 9-12 months, we identified a critical and potentially novel role for Mdm2 in the adult mouse heart through its regulation of cardiac β1AR signaling. While baseline cardiac function was mostly similar in both Mdm2/p53-KO and wild-type (WT) mice, isoproterenol-induced cardiac contractility in Mdm2/p53-KO was significantly blunted compared with WT mice. Isoproterenol increased cAMP in left ventricles of WT but not of Mdm2/p53-KO mice. Additionally, while basal and forskolin-induced calcium handling in isolated Mdm2/p53-KO and WT cardiomyocytes were equivalent, isoproterenol-induced calcium handling in Mdm2/p53-KO was impaired. Mdm2/p53-KO hearts expressed 2-fold more GRK2 than WT. GRK2 polyubiquitination via lysine-48 linkages was significantly reduced in Mdm2/p53-KO hearts. Tamoxifen-inducible cardiomyocyte-specific deletion of Mdm2 in adult mice also led to a significant increase in GRK2, and resulted in severely impaired cardiac function, high mortality, and no detectable βAR responsiveness. Gene delivery of either Mdm2 or GRK2-CT in vivo using adeno-associated virus 9 (AAV9) effectively rescued β1AR-induced cardiac contractility in Mdm2/p53-KO. These findings reveal a critical p53-independent physiological role of Mdm2 in adult hearts, namely, regulation of GRK2-mediated desensitization of βAR signaling.
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Jean-Charles, Pierre-Yves, Samuel Mon-Wei Yu, Dennis Abraham, Reddy Peera Kommaddi, Lan Mao, Ryan T Strachan, Zhu-Shan Zhang, Dawn E Bowles, et al. (2017). Mdm2 regulates cardiac contractility by inhibiting GRK2-mediated desensitization of β-adrenergic receptor signaling. JCI insight, 2(17). p. 95998. 10.1172/jci.insight.95998 Retrieved from https://hdl.handle.net/10161/31640.
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Scholars@Duke
Dennis M Abraham
Lan Mao
I. Research:
As the director of mouse physiology laboratory, in charge for the all events related with Dr. Howard Rockman's molecular biology laboratory studies needs.
Participate in research in rodents model:
Perform surgery and serve as co-investigator in studies on transgenic mice with heart failure. Develop models of hypertrophy in small animal using micro-surgical techniques (aortic constriction, left ventricular infarction and abdominal aortocaval fistula) and perform a variety physiological studies, obtain and analysis data on hemodynamic study and prepare tissue specimens for father molecular biological study.
Develop and apply surgical techniques for in vivo myocardial function study on small animal, such as, using new developed devices study in vivo mice cardiac function (pressure-volume lop), instrumented mice for conscious blood pressure measure or administration of medicine---carotid artery or gull duck catheterization, and conscious mice echocardiography.
Develop techniques for micro-injection of proteins and vectors in to mouse left ventricle, coronary artery and portal vein.
II. Teaching
10% of time allocated/spent---
Train postdoctoral fellows, visiting scientists and students from all over the world in laboratory procedure involving, including endotracheal intubations, cardiac catheterization, coronary occlusion and intrathoracic/intra-abdominal surgical procedures.
Teach methods of data recording and analysis using laboratory equipment and computer programs, echocardiography apply and measurement.
III. Consultant
Consult and teach microsurgical techniques related on small animals such as, rabbits, rat, hamsters and mice, like mice heart-lung transplantation, portal vein injection and mini-pump implant.
Co-laboratory with large range of Universities and Research Institutes from United States an other countries.
Dawn Elizabeth Bowles
Jonathan Andrew Stiber
Walter J. Koch
My research interests are centered on the molecular mechanisms involved in the regulation of signaling through cardiovascular adrenergic receptors (ARs) including the specific in vivo interactions between ARs and myocardial G protein-coupled receptor kinases (GRKs). This includes the role of ARs and GRKs in cardiovascular disease. The β-adrenergic receptor kinase (betaARK1) is a prototypic member of the GRK family that targets and phosphorylates agonist-occupied G protein-coupled receptors which causes functional uncoupling and a dampening of signaling, a process termed desensitization. There is a growing body of evidence demonstrating that the actions of GRKs in the heart are extremely important in modulating myocardial adrenergic signaling and hence cardiac function. Of particular interest to my laboratory, are the biochemical and physiological consequences of altering myocardial AR and GRK signaling. To address this, we are utilizing several in vitro and in vivo model systems. Of special interest, are the endogenous alterations that occur in myocardial GRKs and ARs during cardiovascular diseases such as heart failure (HF). We are also interested in the role of adrenergic signaling in the transplanted heart.
Since heart disease accounts for nearly 40% of all deaths annually in this country, it is of importance to learn more of the molecular pathology present in diseased myocardium. For example, in human HF regardless of the cause, a specific constellation of biochemical defects in cardiac tissue has been noted including loss of specific betaAR density and uncoupling of remaining receptors. Moreover, it has been shown that the levels of betaARK1 rise 3-5 fold in human HF, probably contributing to the dysfunction. Interestingly, it has recently been demonstrated that cardiovascular GRK levels (i.e. betaARK1) and activity were also increased in other disorders including myocardial hypertrophy and hypertension. Thus, a primary objective of my laboratory is to investigate the molecular mechanisms involved in myocardial GRK alterations and how these changes relate to adrenergic signaling. This research includes studying and exploring novel protein binding partners of GRKs in the myocardium using a variety of molecular biochemical assays including GRK-affinity columns.
Over the last several years, my laboratory has been investigating the consequences of altering myocardial ARs and GRKs in several in vivo model systems. Original studies were done in transgenic mice where AR and GRK-based transgenes were targeted specifically to the heart. These studies have been done in close collaboration with Dr. Robert Lefkowitz and Dr. Howard Rockman here at Duke University. We have found that altering AR signaling in the hearts of transgenic mice has profound effects on cardiovascular physiology including the findings that overexpression of beta2ARs or a peptide inhibitor of betaARK1 known as the betaARKct, significantly enhances in vivo cardiac contractility. We now have transgenic animals with myocardial-targeted overexpression of several ARs (alpha and beta) or GRKs and are studying the specific in vivo interactions of these molecules in the heart. Moreover, in collaboration with Drs. Lefkowitz and Rockman, we are generating a host of tissue and temporal specific conditional-knockout mice targeting the myocardial betaAR and GRK systems. Another area of transgenic animals being studied exclusively in my laboratory is altered betaAR and GRK activity specifically targeted to arterial smooth muscle in order to determine the role of AR signaling and desensitization in hypertension and other vascular diseases. These mice have recently been generated in our laboratory and are the target of current investigations.
Over the last year, we have been able to specifically study the role of betaAR desensitization and the role of betaARK1 in HF using genetically engineered mouse models of cardiomyopathy and HF. These studies have lead to the findings that inhibition of betaARK1 through myocardial-targeted betaARKct expression has rescued three separate genetic mouse models of cardiomyopathy, preventing the development of HF. The molecular study of these genetic models through DNA array technology is a logical step in the evolution of these studies and this is a new area of focus in the laboratory. Thus, we are analyzing the hearts of mice with altered betaAR and/or betaARK1 signaling by gene (DNA) chips to determine other genes that have been induced or silenced by our transgenes or gene knockouts. We are excited about using this technology in the laboratory taking advantage of our novel mouse models. Specifically, comparing differential gene expression in a failing mouse heart and comparing the genetic pattern in a heart that has been "rescued" by the betaARKct could lead to the elucidation of specific genes involved in the pathogenesis of HF. Importantly, this may also lead to novel therapeutic approaches to treating this disease as well as other cardiovascular disorders.
Our findings in mice that show that we can genetically enhance the functional contractility of the heart form the basis of another major focus of my research program which is the investigation of enhancing the in vivo function of the compromised heart via acute genetic manipulation using gene therapy. My laboratory heads the Cardiovascular Gene Therapy Program at Duke University Medical Center. The ability to manipulate betaAR density or receptor desensitization in the diseased heart is of great interest since it may provide unique inotropic support and improve existing therapeutic strategies. Gene transfer to the heart in vivo is a powerful approach to study the specific role of GRKs and adrenergic desensitization in both normal and diseased myocardium. Currently, we are employing various in vivo gene delivery techniques using adenoviruses, in order to effectively express specific betaAR and GRK-based transgenes which may produce alterations in myocardial signaling and global cardiac function. We also have established several surgical models of compromised heart function to use in these gene transfer studies including experimental HF in rabbits and pigs, and cardiac transplantation models in rats and rabbits. In addition to studying the feasibility of gene therapy approaches to HF, the Cardiovascular Gene Therapy Program here at Duke has developed a molecular gene therapy strategy to prevention of pathological vascular smooth muscle intimal hyperplasia such as coronary artery restenosis after angioplasty. Our first clinical trial employing adenoviral-mediated gene therapy for restenosis is tentatively planned for the end of 2002.
Howard Allan Rockman
Rockman Lab: Molecular Mechanisms of Hypertrophy and Heart Failure
Overall Research Direction: The major focus of this laboratory is to understand the molecular mechanisms of hypertrophy and heart failure. My laboratory uses a strategy that combines state of the art molecular techniques to generate transgenic and gene targeted mouse models, combined with sophisticated physiologic measures of in vivo cardiac function. In this manner, candidate molecules are either selectively overexpressed in the mouse heart or genes ablated followed by an in-depth analysis of the physiological phenotype. To model human cardiac disease, we have created several models of cardiac overload in the mouse using both microsurgical techniques and genetic models of cardiac dysfunction.
Areas of Research
1) Signaling: G protein-coupled receptor signaling in hypertrophy and heart failure focusing on the concept of biased signaling of 7 transmembrane receptors.
2) Molecular physiology: In depth physiological analysis of cardiac function in genetically altered mice to understand the role of G protein-coupled receptor signaling pathways on the development of heart failure in vivo.
Sudha Kaup Shenoy
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