A GRK5 polymorphism that inhibits beta-adrenergic receptor signaling is protective in heart failure

Abstract

Beta-adrenergic receptor (betaAR) blockade is a standard therapy for cardiac failure and ischemia. G protein-coupled receptor kinases (GRKs) desensitize betaARs, suggesting that genetic GRK variants might modify outcomes in these syndromes. Re-sequencing of GRK2 and GRK5 revealed a nonsynonymous polymorphism of GRK5, common in African Americans, in which leucine is substituted for glutamine at position 41. GRK5-Leu41 uncoupled isoproterenol-stimulated responses more effectively than did GRK5-Gln41 in transfected cells and transgenic mice, and, like pharmacological betaAR blockade, GRK5-Leu41 protected against experimental catecholamine-induced cardiomyopathy. Human association studies showed a pharmacogenomic interaction between GRK5-Leu41 and beta-blocker treatment, in which the presence of the GRK5-Leu41 polymorphism was associated with decreased mortality in African Americans with heart failure or cardiac ischemia. In 375 prospectively followed African-American subjects with heart failure, GRK5-Leu41 protected against death or cardiac transplantation. Enhanced betaAR desensitization of excessive catecholamine signaling by GRK5-Leu41 provides a 'genetic beta-blockade' that improves survival in African Americans with heart failure, suggesting a reason for conflicting results of beta-blocker clinical trials in this population.

Figure 1. Characteristics of mouse hearts expressing GRK5-Q41 and GRK5-L41

a. Time dependent accumulation of cAMP in GRK5-transfected cells stimulated with isoproterenol, 10 μM. b. (top) Immunoblot analysis of cardiac GRK5 from multiple lines of GRK5-Q41 and GRK5-L41 transgenic mice. (bottom) Comparative subcellular localization of GRK5-Q41 and –L41. c. Rhodopsin phosphorylation (bottom panel) by buffer (b) and cardiac membranes from nontransgenic (ntg), Q41, and L41 hearts. Top panel shows immunoreactive GRK5 from same fractions. d. Comparative immunoblot analysis of GRK5 and GRK2 in mouse hearts. e. Representative M-mode echocardiograms. ef In vivo contractile dose-response (+dP/dt) to isoproterenol in GRK5-Q41 (black squares) and L41 (black triangles) mice. Nontransgenic (NTG, open circles) are shown for comparison. *P<0.05 vs ntg for Q41 and L41; #P<0.05 for L41. g. Mean data for time-dependent desensitization of dP/dt response to infused isoproterenol in closed chest in vivo catheterization studies. n=12/group. *P<0.05 vs ntg and Q41; # P=0.081 vs ntg and Q41.

Figure 2. Cardiac expression of GRK5-L41, but not -Q41, confers resistance to catecholamine-induced cardiomyopathy

a–c. Time course for development of catecholamine cardiomyopathy in normal mice (closed triangles) and effect of β-blockade with propanolol (open triangles). LVEDD, left ventricular end diastolic dimension; cVcf, velocity of circumferential shortening corrected for heart rate. (n=6/group, *P<0.05 vs no propanolol). d–g. % change in cardiac parameters before and after 8 days of chronic isoproterenol treatment in vehicle (black, n=12/group) and propanolol (grey, n=6/group) treated mice.. P values compare GRK5-Q41 and –L41 responses. *P<0.05 for propanolol vs vehicle at day eight. ntg is shown for comparison.

Figure 3. Prospective analysis of GRK5 polymorphism interaction with β-blockade as a determinant of heart failure outcome in African Americans

Kaplan-Meier curves for time from diagnosis of heart failure to death or cardiac transplantation (a–d) or death alone (e,f). a. GRK5-Q41 by β-blocker usage. b. GRK5-L41 by β-blocker usage. c. GRK5-Q41 no β-blocker use vs. GRK5-L41 no β-blocker use. d. GRK5-Q41 β-blocker users vs. GRK5-L41 β-blocker users. e. GRK5-Q41 by β-blocker usage. f. GRK5-L41 by β-blocker usage.