Augmentation of cardiac contractility mediated by the human beta(3)-adrenergic receptor overexpressed in the hearts of transgenic mice.

Abstract

BACKGROUND: Stimulation of beta(1)- and beta(2)-adrenergic receptors (ARs) in the heart results in positive inotropy. In contrast, it has been reported that the beta(3)AR is also expressed in the human heart and that its stimulation leads to negative inotropic effects. METHODS AND RESULTS: To better understand the role of beta(3)ARs in cardiac function, we generated transgenic mice with cardiac-specific overexpression of 330 fmol/mg protein of the human beta(3)AR (TGbeta(3) mice). Hemodynamic characterization was performed by cardiac catheterization in closed-chest anesthetized mice, by pressure-volume-loop analysis, and by echocardiography in conscious mice. After propranolol blockade of endogenous beta(1)- and beta(2)ARs, isoproterenol resulted in an increase in contractility in the TGbeta(3) mice (30%), with no effect in wild-type mice. Similarly, stimulation with the selective human beta(3)AR agonist L-755,507 significantly increased contractility in the TGbeta(3) mice (160%), with no effect in wild-type mice, as determined by hemodynamic measurements and by end-systolic pressure-volume relations. The underlying mechanism of the positive inotropy incurred with L-755,507 in the TGbeta(3) mice was investigated in terms of beta(3)AR-G-protein coupling and adenylyl cyclase activation. Stimulation of cardiac membranes from TGbeta(3) mice with L-755,507 resulted in a pertussis toxin-insensitive 1.33-fold increase in [(35)S]GTPgammaS loading and a 1.6-fold increase in adenylyl cyclase activity. CONCLUSIONS: Cardiac overexpression of human beta(3)ARs results in positive inotropy only on stimulation with a beta(3)AR agonist. Overexpressed beta(3)ARs couple to G(s) and activate adenylyl cyclase on agonist stimulation.

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Scholars@Duke

Lan Mao

Assistant Professor Emeritus in Medicine

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.

Rockman

Howard Allan Rockman

Edward S. Orgain Distinguished Professor of Cardiology, in the School of Medicine

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.


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