Abstract 578: β-arrestin-Biased β2-Adrenergic Receptor Signaling Enhances Cardiomyocyte Contractility via ROCK-Dependent Signaling
Okyere, AD; de Lucia, C; Song, J; Carter, RL; Benovic, JL; Koch, WJ; Cheung, JY; Tilley, DG
Published in: Circulation Research
During heart failure, chronically decreased cardiac output can be treated with positive inotropes, but classic inotropes such as β-adrenergic receptor (βAR) agonists that increase cAMP-dependent Ca
mobilization and contractility ultimately enhance patient mortality. Thus, an alternate approach would be to enhance cardiomyocyte contractility without alterations in cAMP and Ca
levels, such as regulation of sarcomeric proteins. Recently, we demonstrated that a small lipidated pepducin designed from the 1
intracellular loop of β2AR (ICL1-9) enhanced cardiomyocyte contractility in a Ca
-independent, β-arrestin-dependent manner. We also showed that β2AR stimulation in hearts in vivo or neonatal rat ventricular myocytes (NRVM) in vitro activates RhoA in a βarr-dependent manner, therefore we sought to determine whether ICL1-9-dependent cardiomyocyte contractility is mediated downstream of RhoA. Using adult murine cardiomyocytes isolated from wild-type C57Bl/6J mice, we measured basal, ICL1-9- and isoproterenol (ISO, as a positive control)-promoted contractility either alone or in the presence of inhibitors of myosin light chain kinase (ML7), ROCK1 (Y-27632) and MEK (PD181452). Consistent with RhoA activation by ICL1-9, ROCK1 inhibition was able to attenuate ICL1-9-mediated contractility, as was inhibition of MLCK, though inhibition of MEK/ERK signaling had no effect. Through the use of GPCR kinase 5 knockout (GRK5KO) cardiomyocytes, we observed that ICL1-9 was unable to enhance contractility in the absence of GRK5 expression. Further, treatment of isolated cardiomyocytes with ICL1-9 increased phoshphorylation of the myosin light chain regulatory subunit (RLC). Therefore, ICL1-9 acts proximally via β2AR/GRK5/βarr-dependent engagement of RhoA/ROCK1 signaling to distally increase RLC phosphorylation, representing a new signaling paradigm for the enhancement of cardiomyocyte contractility.
