title: Restoration of myocardial beta-adrenergic receptor signaling after left ventricular assist device support.
abstract: OBJECTIVE
  Left ventricular assist device support for patients with chronic heart failure can significantly improve beta-adrenergic receptor signaling, which is likely critical to myocardial recovery. The mechanism underlying the restoration of beta-adrenergic receptor signaling is unclear. This study investigates our hypothesis that restoration of cardiac beta-adrenergic receptor signaling by left ventricular assist devices results from inhibition of the G protein-coupled receptor kinase-2, a G protein-coupled receptor kinase that specifically phosphorylates and desensitizes agonist-occupied beta-adrenergic receptors.
  
  
  METHODS
  Left ventricular beta-adrenergic receptor signaling was assessed in biopsy specimens taken from patients with chronic heart failure (n = 12) at the time of left ventricular assist device implantation (heart failure group) and again at the time of heart transplantation (left ventricular assist device group). Signaling was also studied in left ventricular biopsy specimens from nonfailing control (n = 8) hearts (nonfailing control group). Signaling was assessed by measuring sarcolemmal membrane beta-adrenergic receptor density, adenylyl cyclase activity, G protein expression, and G protein-coupled receptor kinase-2 expression and activity.
  
  
  RESULTS
  Left ventricular beta-adrenergic receptor signaling was severely decreased in the heart failure group versus that seen in the nonfailing control group, as demonstrated by adenylyl cyclase activity. G protein-coupled receptor kinase-2 expression and activity was increased 3-fold in the heart failure group versus that seen in the nonfailing control group. After left ventricular assist device support, beta-adrenergic receptor signaling was restored to levels similar to those seen in the nonfailing control group. G protein-coupled receptor kinase-2 expression and activity were markedly diminished after left ventricular assist device support compared with that seen in the heart failure group and were not different from that seen in the nonfailing control group.
  
  
  CONCLUSIONS
  In chronic heart failure left ventricular assist device support leads to restoration of cardiac beta-adrenergic receptor signaling. The primary mechanism appears to be diminished myocardial G protein-coupled receptor kinase-2 activity. This demonstrates the potentially beneficial effects of G protein-coupled receptor kinase-2 inhibition on beta-adrenergic receptor signaling in heart failure and might represent a novel therapeutic strategy for this disease process.
authors: Department of Surgery, Section of Cardiothoracic Surgery, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0558, USA.
authors: Prakash K
authors: PK
authors: Pandalai
authors: Christian F
authors: CF
authors: Bulcao
authors: Walter H
authors: WH
authors: Merrill
authors: Shahab A
authors: SA
authors: Akhter