Abstractβ-adrenergic receptor (βAR) blockade is standard therapy for cardiac failure and ischemia. G-protein coupled receptor kinases (GRKs) desensitize βAR, 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 (AA), substituting leucine (L) for glutamine (Q) at position 41. GRK5-L41 more effectively uncoupled isoproterenol-stimulated responses than GRK5-Q41 in transfected cells and transgenic mice, and like pharmacological βAR blockade, GRK5-L41 protected against experimental catecholamine-induced cardiomyopathy. Human association studies showed a pharmacogenomic interaction between GRK5-L41 and β-blocker treatment on mortality outcome in independent cohorts of AA cardiac failure (P=0.036) and ischemia (P=0.023). In 375 prospectively followed AA heart failure subjects, GRK5-L41 was protective against death/cardiac transplant (single allele: RR=0.28, 95% CI=0.12-0.66; two alleles: RR=0.08, 95% CI=0.04-0.19; P=0.004). The gain-of-function GRK5-L41 polymorphism facilitates βAR desensitization during catecholamine excess, imparting "genetic β-blockade" and improving survival in heart failure.

Following myocardial infarction, nonischemic myocyte death results in infarct expansion, myocardial loss, and ventricular dysfunction. Here, we demonstrate that a specific proapoptotic gene, Bnip3, minimizes ventricular remodeling in the mouse, despite having no effect on early or late infarct size. We evaluated the effects of ablating Bnip3 on cardiomyocyte death, infarct size, and ventricular remodeling after surgical ischemia/reperfusion (IR) injury in mice. Immediately following IR, no significant differences were observed between Bnip3(-/-) and WT mice. However, at 2 days after IR, apoptosis was diminished in Bnip3(-/-) periinfarct and remote myocardium, and at 3 weeks after IR, Bnip3(-/-) mice exhibited preserved LV systolic performance, diminished LV dilation, and decreased ventricular sphericalization. These results suggest myocardial salvage by inhibition of apoptosis. Forced cardiac expression of Bnip3 increased cardiomyocyte apoptosis in unstressed mice, causing progressive LV dilation and diminished systolic function. Conditional Bnip3 overexpression prior to coronary ligation increased apoptosis and infarct size. These studies identify postischemic apoptosis by myocardial Bnip3 as a major determinant of ventricular remodeling in the infarcted heart, suggesting that Bnip3 may be an attractive therapeutic target.

Abstract-Abnormal calcium cycling, characteristic of experimental and human heart failure, is associated with impaired sarcoplasmic reticulum calcium uptake activity. This reflects decreases in the cAMP-pathway signaling and increases in type 1 phosphatase activity. The increased protein phosphatase 1 activity is partially due to dephosphorylation and inactivation of its inhibitor-1, promoting dephosphorylation of phospholamban and inhibition of the sarcoplasmic reticulum calcium-pump. Indeed, cardiac-specific expression of a constitutively active inhibitor-1 results in selective enhancement of phospholamban phosphorylation and augmented cardiac contractility at the cellular and intact animal levels. Furthermore, the ␤-adrenergic response is enhanced in the transgenic hearts compared with wild types. On aortic constriction, the hypercontractile cardiac function is maintained, hypertrophy is attenuated and there is no decompensation in the transgenics compared with wild-type controls. Notably, acute adenoviral gene delivery of the active inhibitor-1, completely restores function and partially reverses remodeling, including normalization of the hyperactivated p38, in the setting of pre-existing heart failure. Thus, the inhibitor 1 of the type 1 phosphatase may represent an attractive new therapeutic target. Key Words: protein phosphatase 1 Ⅲ protein phosphatase 1 inhibitor 1 Ⅲ heart failure Ⅲ hypertrophy Ⅲ phospholamban Ⅲ gene therapy R eversible protein phosphorylation represents the cellular basis for integration of key signaling pathways, mediating a fine crosstalk between external effector molecules and intracellular events. In the heart, Ca 2ϩ cycling and contractility are controlled by a fine balance of protein kinase and phosphatase activities in response to various second messenger signals. Demands on the heart's pumping action, during fight-or-flight situations, can increase human cardiac output by nearly 5-fold. This is linked to ␤-adrenergic activation of the cAMP dependent protein kinase (PKA). PKA then phosphorylates a set of key regulatory Ca 2ϩ handling proteins that control excitation-contraction coupling cycle, such as phospholamban, the ryanodine receptor, the L-type Ca 2ϩ channel, and troponin I. 1 The protein kinases and their phosphoprotein substrates underlying augmentation of the heart's pumping action have been well characterized. However, similar studies on the protein phosphatases, reversing the increased cardiac contractility, are less well developed. The major Ser/Thr phosphatases [type 1, type 2A, and type 2B (calcineurin)] stem from a common gene family and are highly homologous proteins (40% to 50%) that play critical roles in the control of cardiac contractility and hypertrophy.Overexpression of the catalytic subunit of the protein phosphatase 1 at similar levels observed in human heart failure was associated with dephosphorylation of phospholamban, depressed cardiac function, dilated cardiomyopathy, and premature mortality. 2 Furthermore, PP2A and PP2B (calcineurin) overexpressio...

Background-Pathological cardiac hypertrophy inevitably remodels, leading to functional decompensation. Although modulation of apoptosis-regulating genes occurs in cardiac hypertrophy, a causal role for programmed cardiomyocyte death in left ventricular (LV) remodeling has not been established. Methods and Results-We targeted the gene for proapoptotic Nix, which is transcriptionally upregulated in pressure overload and Gq-dependent hypertrophies, in the mouse germ line or specifically in cardiomyocytes (knockout [KO]) and conditionally overexpressed it in the heart (transgenic [TG]