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Circulation Research. 2008;103:413-422
Published online before print July 17, 2008, doi: 10.1161/CIRCRESAHA.107.168336
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(Circulation Research. 2008;103:413.)
© 2008 American Heart Association, Inc.


Integrative Physiology

G Protein–Coupled Receptor Kinase 2 Ablation in Cardiac Myocytes Before or After Myocardial Infarction Prevents Heart Failure

Philip W. Raake*, Leif E. Vinge*, Erhe Gao, Matthieu Boucher, Giuseppe Rengo, Xiongwen Chen, Brent R. DeGeorge, Jr, Scot Matkovich, Steven R. Houser, Patrick Most, Andrea D. Eckhart, Gerald W. Dorn, II, Walter J. Koch

From the George Zallie and Family Laboratory for Cardiovascular Gene Therapy (P.W.R., L.E.V., E.G., M.B., G.R., B.R.D., P.M., A.D.E., W.J.K.) and Eugene Feiner Laboratory for Vascular Biology and Thrombosis (A.D.E.), Center for Translational Medicine, Department of Medicine, Thomas Jefferson University, Philadelphia, Pa; Cardiovascular Research Center (X.C., S.R.H.), Department of Physiology, Temple University, Philadelphia, Pa; and Center for Pharmacogenomics (S.M., G.W.D.), Washington University, St Louis, Mo.

Correspondence to Philip W. Raake, MD, Center for Translational Medicine, Department of Medicine, Thomas Jefferson University, 1025 Walnut St, Philadelphia, PA 19107. E-mail Philip.Raake{at}jefferson.edu


*    Abstract
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*Abstract
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down arrowMaterials and Methods
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down arrowDiscussion
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Myocardial G protein–coupled receptor kinase (GRK)2 is a critical regulator of cardiac β-adrenergic receptor (βAR) signaling and cardiac function. Its upregulation in heart failure may further depress cardiac function and contribute to mortality in this syndrome. Preventing GRK2 translocation to activated βAR with a GRK2-derived peptide that binds Gβ{gamma} (βARKct) has benefited some models of heart failure, but the precise mechanism is uncertain, because GRK2 is still present and βARKct has other potential effects. We generated mice in which cardiac myocyte GRK2 expression was normal during embryonic development but was ablated after birth ({alpha}MHC-CrexGRK2 fl/fl) or only after administration of tamoxifen ({alpha}MHC-MerCreMerxGRK2 fl/fl) and examined the consequences of GRK2 ablation before and after surgical coronary artery ligation on cardiac adaptation after myocardial infarction. Absence of GRK2 before coronary artery ligation prevented maladaptive postinfarction remodeling and preserved βAR responsiveness. Strikingly, GRK2 ablation initiated 10 days after infarction increased survival, enhanced cardiac contractile performance, and halted ventricular remodeling. These results demonstrate a specific causal role for GRK2 in postinfarction cardiac remodeling and heart failure and support therapeutic approaches of targeting GRK2 or restoring βAR signaling by other means to improve outcomes in heart failure.


Key Words: heart failure • myocardial infarction • conditional gene targeting • GRK2


*    Introduction
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up arrowAbstract
*Introduction
down arrowMaterials and Methods
down arrowResults
down arrowDiscussion
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The role of myocardial β-adrenergic receptor (βAR) signaling in heart failure (HF) is controversial, with abundant data supporting dominant effects that are either pathological or beneficial. Pathological effects are strongly suggested by the cardiomyopathies that develop under conditions of chronic βAR activation after long-term catecholamine administration1 or as a consequence of high levels of overexpressed cardiac β1- or β2-ARs.2,3 Likewise, enhanced signaling from overexpression of the βAR signal transducer G{alpha}s causes HF.4 Most importantly, however, are the human patient data indicating that βAR signaling is deleterious in HF: genetic polymorphisms that enhance myocardial sympathetic tone are independent risk factors for HF,5 and pharmacological βAR antagonism has been known for more than 2 decades to strikingly prolong life when used as primary therapy in HF.6

Despite the strength of data in experimental systems and the human condition that excessive βAR signaling can contribute to HF, there continue to be those who advocate modulating βARs in HF as a form of therapy.7 This viewpoint is based on observations that 2 transgenic mouse lines overexpressing low levels of β2-AR in the heart, which were developed in 2 independent laboratories, demonstrated enhanced contractile function without myocardial disease,8,9 and β2-ARs can improve function of cardiomyopathy models.10,11 Another group has suggested that transgenic or adenoviral-mediated overexpression of the downstream βAR signaling effector adenylyl cyclase has similar effects.12 Also consistent with this idea are studies pioneered in our laboratory in which prevention of typical HF-associated G protein–coupled receptor kinase (GRK)2-mediated desensitization and downregulation of myocardial βARs has rescued numerous genetic13,14 and physiological15,16 models of HF.

The reasons for the apparently contradictory datasets relating to βAR signaling in failing myocardium are unknown, but understanding them will be essential to fully optimize HF treatment. Regarding GRK2 inhibition, specifically, concerns have been expressed about the specificity and true mechanism of action of the βARKct GRK2 inhibitor used in many of these studies.17 It is also not entirely clear that GRK2 is the best target in HF, because GRK3, GRK5, and GRK6 are also expressed in the heart, and forced expression of GRK5 had similar desensitization effects on myocardial βARs as does forced expression of GRK2.18 Indeed, cardiac-specific ablation of GRK2 in the early embryo actually sensitized adult mice to catecholamine cardiomyopathy, rather than conferring protection, which was interpreted as evidence for pathological effects of βAR signaling.19 These results raise additional questions about whether GRK2 inhibition may have different effects in different experimental HF models or at different time points relative to the induction of HF.

To address these issues, we created mice in which the GRK2 gene could be selectively ablated in cardiac myocytes in a temporally defined manner and compared the consequences of heart-specific GRK2 ablation before and after induction of HF by myocardial infarction (MI).


*    Materials and Methods
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up arrowAbstract
up arrowIntroduction
*Materials and Methods
down arrowResults
down arrowDiscussion
down arrowReferences
 
An expanded Materials and Methods section is available in the online data supplement at http://circres.ahajournals.org.

Experimental Animals
Conditional mice bearing floxed GRK2 alleles (GRK2 fl/fl) have previously been described.19 Transgenic mice overexpressing Cre-recombinase protein fused to 2 mutant estrogen receptor ligand-binding domains under the control of the {alpha}-myosin heavy chain ({alpha}MHC) promoter ({alpha}MHC-MerCreMer)20 were received from The Jackson Laboratory (JAX Mice and Services, Bar Harbor, Me). Homozygous mice with the floxed GRK2 alleles were crossed with {alpha}MHC-MerCreMer mice, and the resulting {alpha}MHC-MerCreMerxGRK2 fl/fl mice and GRK2 fl/fl, as well as {alpha}MHC-MerCreMer, were studied. To induce Cre recombination and subsequent deletion of GRK2 adult mice were treated with tamoxifen (Tmx) (Sigma-Aldrich, St Louis, Mo).20

In addition, {alpha}MHC-Cre mice21 were bred on to the GRK2 fl/fl background to generate cardiac GRK2-deleted mice, initiated by the activation of the {alpha}MHC-promoter. All animal procedures and experiments were performed in accordance with the guidelines of the Institutional Animal Care and Use Committee of Thomas Jefferson University.

Model of Left Ventricular MI
MI was induced by high ligation of the left anterior descending coronary artery, as described previously.22

Echocardiographic and Hemodynamic Analysis of Cardiac Function
Left ventricular (LV) function was assessed by transthoracic echocardiography. LV hemodynamics were determined in anesthetized mice under baseline conditions and stimulation with the unselective βAR agonist isoproterenol (Sigma-Aldrich)23 and after a single dose of the selective β2-AR agonist fenoterol (Sigma-Aldrich). The peak response, which typically occurred 2 minutes after the injection of fenoterol, was used as readout for the intensity of the β2-AR signal.

Isolation of Cardiac Myocytes
Adult mouse cardiac myocytes were isolated from sham and infarcted GRK2 fl/fl and {alpha}MHC-CrexGRK2 fl/fl mice, as previously described.24

Single Myocyte Contractility Studies
Isolated cardiac myocytes were stimulated in an electric field, and continuously flushed with tyrodes containing 1 mmol/L CaCl2 without (baseline) and with 10–8 mol/L isoproterenol (isoproterenol-stimulation). Single-cell contractions were measured by video edge detection (Fluorescence and Contractility System, IonOptix, Milton, Mass).

RNA Isolation, Reverse Transcription, and Quantitative Real-Time RT-PCR
Isolated LV cardiac myocytes (rescue study) or myocardial tissue from the remote zone (prevention-study) was snap-frozen. Quantitative real-time polymerase chain reaction was performed as described previously.22

Western Blot Analysis
Western blotting was performed as described previously.22 Cardiac protein levels of GRK2 (sc-562, C-15, Santa Cruz Biotechnology, 1:5000), {alpha}-actin (A7811, Sigma-Aldrich, 1:5000), and calsequestrin (CSQ) (208915; Calbiochem; 1:10 000) were assessed in cardiac myocyte cellular preparations.

Statistical Analysis
Data are generally expressed as means±SEM. An unpaired 2-tailed t test, a 1-way ANOVA, and a 2-way repeated measurement ANOVA were performed for between-group comparisons. Survival analysis was performed by the Kaplan–Meier method, and between-group differences in survival were tested by the log-rank test. For all tests, a probability value of <0.05 was considered significant.


*    Results
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up arrowAbstract
up arrowIntroduction
up arrowMaterials and Methods
*Results
down arrowDiscussion
down arrowReferences
 
Defined Loss of GRK2 in Cardiac Myocytes After MI Rescues the HF Phenotype
Survival of HF Is Improved After Loss of GRK2
To gain insight into whether GRK2 ablation could be therapeutic in hearts already in HF, we used Tmx-inducible GRK2 knockout (KO) ({alpha}MHC-MerCreMerxGRK2 fl/fl) mice. These mice along with {alpha}MHC-MerCreMer mice as controls were subjected to coronary artery ligation and loss of GRK2 was induced by 5 consecutive days of Tmx injections (on days 10 to 14 post-MI) (Figure 1A and 1B). We found similar mortality in both mice until {approx}12 to 13 days post-MI (Figure 1C). Interestingly, following the Tmx injections, survival in Tmx-treated {alpha}MHC-MerCreMerxGRK2 fl/fl mice was significantly preserved compared to the continued death seen in Tmx-treated control mice (Figure 1C). Thus, the loss of cardiac GRK2 after MI prevents the significant mortality seen chronically in HF mice with normal levels of GRK2 in their hearts.


Figure 1
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Figure 1. Survival of HF is improved after post-MI–induced loss of GRK2 in cardiac myocytes. A, Experimental protocol showing the study design of the rescue study using Tmx-inducible GRK2 KO mice ({alpha}MHC-MerCreMerx GRK2 fl/fl, GRK2 fl/fl, and {alpha}MHC-MerCreMer mice). B, Time-defined controlled loss of GRK2 in cardiac myocytes from Tmx-inducible {alpha}MHC-MerCreMerxGRK2 fl/fl and {alpha}MHC-MerCreMer mice. Impact of Tmx treatment on cardiac myocyte GRK2 protein levels determined via Western blotting. Representative Western blot of GRK2 and CSQ (as a loading control) and quantification of the results (n=6 animals/group). *P<0.05, {alpha}MHC-MerCreMerxGRK2 fl/fl vs {alpha}MHC-MerCreMer (unpaired 2-tailed t test). C, Survival of Tmx-treated sham and infarcted {alpha}MHC-MerCreMer and {alpha}MHC-MerCreMerxGRK2 fl/fl mice throughout the study period (n=8 to 11 animals/group for sham mice, n=30 to 34 animals/group for infarcted mice). Survival was analyzed by the Kaplan–Meier method, and between-group differences in survival were tested by the log-rank test.

Loss of Cardiac GRK2 in Already Established HF Rescues Cardiac Function
Importantly, all groups of mice 10 days post-MI had similar levels of chamber dilatation and cardiac dysfunction compared to pre-MI measurements, as assessed by echocardiography (Figure 2A and 2B). The 3 sham groups showed no alterations in cardiac function or dimensions at any time point. Following loss of GRK2 in {alpha}MHC-MerCreMerxGRK2 fl/fl mice, echocardiography at 42 and 120 days post-MI showed stabilization of LV remodeling (Figure 2A). Furthermore, significant enhancement of cardiac function (as measured by fractional shortening percentage [FS]) was observed after the loss of cardiac GRK2 compared to both groups of Tmx-treated control mice ({alpha}MHC-MerCreMer and GRK2 fl/fl) (Figure 2B).


Figure 2
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Figure 2. Induced loss of GRK2 rescues adverse LV remodeling and cardiac function post-MI. A, Echocardiographic assessment of end-diastolic dimension (EDD) pre-MI, 10 days post-MI (before Tmx treatment), 42 days post-MI (28 days post-Tmx treatment), and 120 days post-MI. B, Echocardiographic assessment of FS pre-MI, 10 days post-MI (before Tmx treatment), 42 days post-MI (28 days post-Tmx treatment), and 120 days post-MI (n=6 to 8 animals/group for sham-operated mice, n=12 to 16 animals/group for MI mice). *P<0.05 vs MI {alpha}MHC-MerCreMer and MI GRK2 fl/fl. Hemodynamic measurements of LV contractility (as measured by LV dP/dtmax) (C) and relaxation (as measured by LV dP/dtmin) (D) and LVEDP (E) 120 days post-MI (106 days post-Tmx) (n=5 animals/group for sham-operated mice, n=9 to 11 animals/group for MI mice). §P<0.05, MI {alpha}MHC-MerCreMerxGRK2 fl/fl vs MI {alpha}MHC-MerCreMer under respective condition; #P<0.05, MI {alpha}MHC-MerCreMer vs sham groups under respective condition; {ddagger}P<0.05, MI {alpha}MHC-MerCreMer vs MI {alpha}MHC-MerCreMerxGRK2 fl/fl and sham groups (2-way ANOVA for A through D; 1-way ANOVA for E).

Measurements of LV hemodynamics 120 days post-MI showed preserved responsiveness to βAR stimulation in infarcted Tmx-treated {alpha}MHC-MerCreMerxGRK2 fl/fl mice, whereas infarcted Tmx-treated {alpha}MHC-MerCreMer mice revealed an impaired βAR reserve compared to sham mice (Figure 2C and 2D). LV end-diastolic pressure (LVEDP) was significantly lower in infarcted {alpha}MHC-MerCreMerxGRK2 fl/fl mice as compared to infarcted {alpha}MHC-MerCreMer mice (Figure 2E).

Loss of GRK2 in Post-MI Failing Cardiac Myocytes Reduces Activation of the Fetal Gene Program
RT-PCR analysis was performed 5 weeks post-MI (3 weeks after the last dose of Tmx) on cardiac myocytes isolated from the LV. Interestingly, less induction of selected fetal genes (atrial natriuretic peptide [ANP], brain natriuretic peptide [BNP], and βMHC) was found in infarcted Tmx-treated {alpha}MHC-MerCreMerxGRK2 fl/fl mice as compared to post-MI Tmx-treated {alpha}MHC-MerCreMer cardiac myocytes (Figure 3).


Figure 3
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Figure 3. GRK2 abolishment in the post-MI failing heart alters gene expression. Quantitative RT-PCR analysis on cardiac myocytes isolated from the LV 5 weeks post-MI (3 weeks after the last dose of Tmx). A, ANP. B, BNP. C, βMHC. D, GRK2. All values were normalized to 18S levels (n=5 to 6 animals/group for sham mice, n=7 to 11 animals/group for MI mice). *P<0.05, MI {alpha}MHC-MerCreMer vs MI {alpha}MHC-MerCreMerxGRK2 fl/fl and sham groups; #P<0.05, MI {alpha}MHC-MerCreMer vs sham groups (1-way ANOVA).

We also examined expression of GRK mRNA post-MI in cardiac myocytes isolated from the LV. As expected in control Tmx-treated {alpha}MHC-MerCreMer mice, MI produced a significant increase in GRK2 expression over sham levels, whereas infarcted Tmx-treated {alpha}MHC-MerCreMerxGRK2 fl/fl mice showed significantly lower GRK2 levels (Figure 3D). Interestingly, GRK5 mRNA was selectively upregulated in infarcted Tmx-treated {alpha}MHC-MerCreMer mice (Figure V in the online data supplement).

Loss of GRK2 Before MI Prevents the Development of HF
Loss of Cardiac Myocyte GRK2 Before MI Reduces Infarct-Related Mortality
To study the consequence of GRK2 loss on the development of HF, adult (8-week-old) {alpha}MHC-CrexGRK2 fl/fl mice and their corresponding littermate controls (GRK2 fl/fl) were subjected to coronary artery ligation and subsequent MI (Figure 4A). {alpha}MHC-CrexGRK2 fl/fl mice have an {approx}80% loss of cardiac myocyte GRK2 (Figure 4B). Of note, infarct size was not different 24 hours or 28 days after MI between mice with normal levels of GRK2 and the GRK2 KO mice (supplemental Figure II). Interestingly, survival was significantly improved in male {alpha}MHC-CrexGRK2 fl/fl mice subjected to MI compared to control GRK2 fl/fl mice (see Figure 4C). There was a trend toward improved survival in infarcted {alpha}MHC-CrexGRK2 fl/fl mice of both sexes (P=0.06) (supplemental Figure III). The differences in survival were present, despite only the {alpha}MHC-CrexGRK2 fl/fl mice and not the control mice in this study (GRK2 fl/fl) possessed Cre recombinase, which has been proven previously to contribute to cardiac pathology.25


Figure 4
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Figure 4. Infarct-related mortality is reduced with loss of GRK2 in cardiac myocytes before MI. A, Experimental protocol showing the study design of the prevention-study using conditional GRK2 KO mice ({alpha}MHC-CrexGRK2 fl/fl and GRK2 fl/fl mice). B, Conventional conditional loss of GRK2 in cardiac myocytes in {alpha}MHC-CrexGRK2 fl/fl and GRK2 fl/fl mice. Western blot analysis for GRK2 protein and actin (as a loading control) in isolated cardiac myocytes. C, Survival of male GRK2 fl/fl and {alpha}MHC-MHCxGRK2 fl/fl mice throughout the study period (n=8 animals/group for sham mice, n=49 to 58 animals/group for infarcted mice). Survival was analyzed by the Kaplan–Meier method, and between-group differences in survival were tested by the log-rank test.

Loss of GRK2 in Cardiac Myocytes Before MI Reduces the Extent and Progression of Cardiac Dysfunction
In vivo cardiac function was assessed by echocardiography before and 28 days after MI (or sham). Twenty-eight days after MI, control GRK2 fl/fl mice displayed significantly depressed systolic function and enlarged cardiac chambers as compared to pre-MI values (Figure 5A and 5B). In striking contrast, {alpha}MHC-CrexGRK2 fl/fl mice subjected to MI did not display the same degree of cardiac deterioration (Figure 5A and B).


Figure 5
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Figure 5. Constitutive loss of GRK2 in cardiac myocytes before MI reduces the extent of cardiac dysfunction. Echocardiographic assessment 28 days post-MI of end-diastolic dimension (EDD) (A) and FS (B) (n=8 to 10 animals/group for sham mice, n=21 to 30 animals/group for MI mice). *P<0.01 MI vs sham for respective group; #P<0.05, MI {alpha}MHC-CrexGRK2 fl/fl vs MI GRK2 fl/fl (2-way ANOVA). Hemodynamic measurements of LV contractility (as measured by LV dP/dtmax) (C and E) and relaxation (as measured by LV dP/dtmin) (D and F) at baseline and in response to increasing intraperitoneal injected doses of isoproterenol (C and D) or a single intraperitoneal dose of fenoterol (E and F). G, LVEDP (n=5 animals/group for sham-operated mice, n=9 to 13 animals/group for MI mice). {dagger}P<0.05, isoproterenol 0.5 µg vs basal for each group; *P<0.05, MI GRK2 fl/fl vs sham GRK2 fl/fl for each condition; #P<0.05, MI {alpha}MHC-CrexGRK2 fl/fl vs MI GRK2 fl/fl for each condition (2-way ANOVA for C through F; 1-way ANOVA for G). H, Heart-to-body weight ratio at day 28 post-MI. *P<0.01, MI vs sham; #P<0.05, MI {alpha}MHC-CrexGRK2 fl/fl vs MI GRK2 fl/fl (1-way ANOVA).

Loss of Myocyte GRK2 Before MI Improves LV Hemodynamics and Preserves βAR Responsiveness
LV contractility (as measured by dP/dtmax) and LV relaxation (as measured by LV dP/dtmin) after isoproterenol were significantly impaired in control GRK2 fl/fl mice compared to sham control mice, demonstrating a loss of inotropic reserve consistent with HF (Figure 5C and 5D). Similarly, hemodynamic studies on {alpha}MHC-CrexGRK2 fl/fl mice revealed signs of cardiac dysfunction at baseline; however, responses to isoproterenol were significantly improved compared to post-MI control mice showing improved contractile reserve and preserved βAR signaling in hearts without GRK2 (Figure 5C and 5D). Interestingly, the response to fenoterol was significantly enhanced in {alpha}MHC-CrexGRK2 fl/fl mice post-MI compared to GRK2 fl/fl mice, arguing in favor of facilitated β2-AR signaling with GRK2 silencing (Figure 5E and 5F). Finally, elevated LVEDP in control post-MI GRK2 fl/fl mice was significantly lowered in mice with GRK2 expression lost (Figure 5G).

Loss of GRK2 Is Associated With a Lower Extent of Cardiac Hypertrophy and Normalized Gene Expression After MI
Heart-to-body weight (HW/BW) ratio was significantly increased 28 days post-MI in control GRK2 fl/fl mice compared to corresponding sham-operated animals (Figure 5H). Although {alpha}MHC-CrexGRK2 fl/fl mice subjected to MI displayed LV hypertrophy compared to sham-operated controls, the extent of hypertrophy was significantly less than that observed in GRK2 fl/fl mice subjected to MI (Figure 5H).

Consistent with decreased hypertrophy in GRK2 KO mice, RT-PCR analysis of the remote (nonischemic) portion of the LV 28 days post-MI showed significantly less induction of selected fetal genes (ANP, BNP, and βMHC) as seen in post-MI control hearts, which showed significant upregulation of these genes compared to sham-controls (Figure 6A through 6C). Upregulation of the mRNAs encoding matrix metalloproteinase-9 and collagen-1 (Coll-1) in the nonischemic LV zone were also seen in post-MI GRK2 fl/fl mice, indicating adverse remodeling; however, in GRK2 KO mice, these changes in matrix metalloproteinase-9 and collagen-1 were not seen (Figure 6D and 6E). These observations in combination with the attenuation of LV chamber dilation (see above) argue in favor of significant repression of adverse LV remodeling by the loss of GRK2 in myocytes.


Figure 6
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Figure 6. Loss of GRK2 in cardiac myocytes alters gene expression in the failing heart. Quantitative RT-PCR analysis 28 days post-MI in the remote noninfarcted region of the LV. A, ANP. B, BNP. C, βMHC. D, Collagen-1 (Coll-1). E, Matrix metalloproteinase 9 (MMP-9). F, GRK2. G, GRK5. All values were normalized to 28S levels (n=6 to 8 animals/group). *P<0.05, MI GRK2 fl/fl vs MI {alpha}MHC-CrexGRK2 fl/fl and sham GRK2 fl/fl and sham {alpha}MHC-CrexGRK2 fl/fl; #P<0.05, MI GRK2 fl/fl vs sham GRK2 fl/fl (1-way ANOVA).

Furthermore, MI in control mice led to a significant increase in GRK2 mRNA expression over sham levels, which was absent in GRK2 KO mice (Figure 6F). Interestingly, GRK5, another major GRK found in the heart,26 which was upregulated in post-MI control (GRK2 fl/fl) hearts, was not significantly changed in the hearts of post-MI {alpha}MHC-CrexGRK2 fl/fl mice compared to sham (Figure 6G). The fact that the GRK2 KO mice had no increase in GRK5 argues for a lack of compensation by this GRK. Of note, GRK3 a close homologue of GRK2 was not altered in any of our groups post-MI (data not shown).

Loss of GRK2 Normalizes βAR Responsiveness of Single Cardiac Myocytes Post-MI
Figure 7A shows representative steady-state twitches from cardiac myocytes (from sham and infarcted GRK2 fl/fl and {alpha}MHC-CrexGRK2 fl/fl mice) under baseline conditions (left) and following isoproterenol stimulation (10–8 mol/L) (right). Isolated cardiac myocytes from post-MI {alpha}MHC-CrexGRK2 fl/fl mice demonstrated significantly enhanced FS, improved rate of cell shortening (+dL/dt) and improved rate of relengthening (–dL/dt) under isoproterenol stimulation compared to control, post-MI GRK2(fl/fl) myocytes (Figure 7B and 7C). These results indicate that βAR responsiveness post-MI is preserved by the loss of GRK2.


Figure 7
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Figure 7. Loss of GRK2 improves post-MI βAR responsiveness of single cardiac myocytes. A, Representative tracings of single myocyte contractility under baseline conditions and stimulation with isoproterenol. B, Quantitative data of FS. C, Maximum rate of cardiac myocyte contractility and relengthening. Cardiac myocytes were measured at baseline conditions and after stimulation with isoproterenol (n=3 animals/group for sham mice, n=6 animals/group for MI mice). *P<0.05, MI {alpha}MHC-Cre/GRK2(fl/fl) vs MI GRK2(fl/fl) for respective condition (2-way ANOVA).


*    Discussion
up arrowTop
up arrowAbstract
up arrowIntroduction
up arrowMaterials and Methods
up arrowResults
*Discussion
down arrowReferences
 
The incidence of HF is increasing, and its long-term prognosis has remained at 50% survival after 5 years despite the broad application of life-saving antineurohormonal pharmacological therapies with angiotensin-converting enzyme inhibition and β-blockade more than 2 decades ago.6 Thus, more efficient HF therapeutics are needed, which may be achieved by identifying nontraditional molecular targets downstream of the neurohormonal ligand-receptor interaction. For a number of years, we have proposed that GRK2, a kinase that regulates the signaling activity and number of βAR in the heart and that, itself, is regulated in HF, might represent such a nontraditional target.27 Indeed, transgenic and adenoviral expression of a peptide inhibitor of GRK2 translocation, βARKct, has benefited a number of experimental HF models.13,14 Mechanistically, however, questions have arisen about the specific effects of βARKct and about the specific pathophysiological role of GRK2 in heart disease. In the present studies, we attempted to unambiguously define the role of GRK2 in postischemic HF and to assess the efficacy of its genetic ablation in a highly relevant model of HF, MI, and at clinically relevant times in the course of the disease, ie, both before and after the inciting ischemic event. In short, our data contains definitive evidence that GRK2 contributes to ischemic HF, and demonstrate a critical role for this kinase in the disease. Moreover our data show the striking efficacy of restoring cardiac βAR signaling homeostasis by GRK2 ablation either before or after MI.

GRK2 Is the Critical GRK in the Failing Heart
Using constitutive (starting postnatally) {alpha}MHC-Cre or inducible {alpha}MHC-MerCreMer mice, we were able to test the role of GRK2 expression in adult cardiac myocytes in both the development of and rescue of ischemic cardiomyopathy. The use of these mice is necessary because global GRK2 KO mice die in utero.19 Interestingly, mortality post-MI was similar between groups until the Tmx treatment when the induced loss of GRK2 prevented further death up to 120 days post-MI. Thus, the loss of GRK2 expression in myocytes after MI, when HF was already established, clearly led to significantly improved survival chronically after MI. Furthermore, loss of GRK2 before MI significantly reduced mortality in male GRK2 KO mice. In addition, GRK2 abolishment prevented LV dilatation and deterioration of cardiac function that is seen in control mice post-MI. This is the first study showing that controlled loss of GRK2 in failing cardiac myocytes rescues a model of established HF and directly demonstrates that minimizing GRK2 activity in the failing heart is beneficial. Although the loss of GRK2 was not complete, this loss of HF-associated upregulation of cardiac myocyte GRK2 essentially restored in vivo cardiac systolic and diastolic function. Our data strongly suggest GRK2 as the primary GRK critically involved in the functional regulation of the failing heart.

Restoration of βAR Signaling in the Failing Heart by GRK2 Ablation Similar to Effects of the GRK2 Inhibitor Peptide βARKct
Both early and late following the acute inciting event, our present data provide further support for the benefits of restoration or normalization of βAR signaling in HF. The increased LV hemodynamic response and the improved contractility of isolated single LV cardiac myocytes to βAR stimulation in mice lacking cardiac myocyte GRK2 show that signaling through this inotropic system is preserved despite the presence of a large MI. Moreover, these data are consistent with previous rescue studies using the βARKct and demonstrate and support the primary mechanism of action of this Gβ{gamma}-sequestering peptide in HF therapeutics to be GRK2 inhibition. In addition, previous studies with βARKct and our present study with conditional GRK2 ablation provide strong evidence that GRK2 is the critical GRK regulating inotropic responsiveness and adverse βAR desensitization after MI. Interestingly, we found novel and significant evidence that β2-AR signaling is enhanced in GRK2 KO mice post-MI. Because β2-AR mediates protective effects likely through Gi and downstream activation of phosphatidylinositol 3-kinase and Akt,28,29 the enhanced β2-signal might, at least in part, contribute to the benefits seen with GRK2 silencing.

An Apparent Narrow Therapeutic Window for Altering βAR signaling in HF
GRK2 is a major regulator of myocardial βAR signaling, and dysfunctional βAR signaling is a consequence of HF and might, at least in part, contribute to the progression of cardiac dysfunction because failing human myocardium is characterized by diminished βAR responsiveness, loss of overall cardiac and single myocyte contractility, and disruption of intracellular Ca2+-cycling.27,30 Importantly, βAR derangements include the upregulation of GRK2.31,32 βAR stimulation in myocardium modulates intracellular Ca2+ fluxes and Ca2+ responsiveness of the sarcomere, thereby linking βAR signaling to cardiac myocyte contractility. Of note, chronic upstream activation of the βAR-signaling cascade by cardiac overexpression of the β1-AR2 or the adenylyl cyclase–stimulating G protein {alpha}-subunit (G{alpha}s)4 led to the development of dilated cardiomyopathy in mice. Moreover, overexpression of protein kinase A, a downstream effector of βAR-Gs signaling also resulted in fatal dilated cardiomyopathy.33 Despite the evidence showing detrimental effects of chronic βAR and downstream activation in the heart, other studies manipulating βAR signaling have led to positive outcomes. This includes studies by us showing the prevention and rescue of HF using the βARKct,13,14 as well as overexpression of adenylyl cyclase VI, that has been shown to increase contractile function in the heart, as well as inhibiting the development of HF post-MI.34,35 Recently, β1-AR transactivation of the epidermal growth factor receptor mediated by β-arrestin was shown to confer cardioprotection in stressed hearts.36 Taken together, these genetic manipulations at different levels of βAR signaling demonstrate that the point of intervention is important to the function of the heart and suggest that it is more desirable to circumvent βAR desensitization than to simply facilitate βAR activation. Overall, the data discussed and our data suggest a narrow therapeutic window for βAR signaling in HF and indicate that normalization of βAR signaling, which can be best achieved by preventing their uncoupling and downregulation through GRK2 inhibition/ablation, might be the optimal approach, rather than forced overexpression of receptors or their downstream signaling effectors.

Conclusions
Protein kinases are rapidly emerging as a new pharmacological approach that may complement the existing drug classes targeting G protein–coupled receptors. Taken together, our present results show that targeted deletion and lowering of cardiac myocyte GRK2 activity leads to a novel protective and inotropic phenotype, which prevents postischemic HF and rescues a phenotype of established HF. Our results herein, combined with our previous βARKct data, add to the significance of the βAR system in the failing heart because it is clear that resensitization can positively affect cardiac function. We have not ruled out that other G protein–coupled receptors signals, no doubt altered by the loss of GRK2, are also contributing to the above phenotypes; however, the above-described changes in βAR inotropic reserve are significant. Overall, our data demonstrate that GRK2 activity is pathogenic in HF and targeted inhibition or lowering its expression led to beneficial effects for contractile function of the heart and this lone molecular change in the postischemic heart can prevent and rescue structural HF and offer novel benefits over existing HF therapies.


*    Acknowledgments
 
Sources of Funding

This work was supported, in part, by Deutsche Forschungsgemeinschaft grant Ra 1668/1-1 (to P.W.R.) and NIH grants R01 HL61690, R01 HL56205, and P01 HL075443 (Project 2) (to W.J.K.). W.J.K. is the W.W. Smith Professor of Medicine. The research performed by G.W.D. for this study was supported by NIH R01 HL87871.

Disclosures

None.


*    Footnotes
 
*Both authors contributed equally to this work. Back

Original received November 20, 2007; revision received June 30, 2008; accepted July 3, 2008.


*    References
up arrowTop
up arrowAbstract
up arrowIntroduction
up arrowMaterials and Methods
up arrowResults
up arrowDiscussion
*References
 
1. Kudej RK, Iwase M, Uechi M, Vatner DE, Oka N, Ishikawa Y, Shannon RP, Bishop SP, Vatner SF. Effects of chronic beta-adrenergic receptor stimulation in mice. J Mol Cell Cardiol. 1997; 29: 2735–2746.[CrossRef][Medline] [Order article via Infotrieve]

2. Engelhardt S, Hein L, Wiesmann F, Lohse MJ. Progressive hypertrophy and heart failure in beta1-adrenergic receptor transgenic mice. Proc Natl Acad Sci U S A. 1999; 96: 7059–7064.[Abstract/Free Full Text]

3. Liggett SB, Tepe NM, Lorenz JN, Canning AM, Jantz TD, Mitarai S, Yatani A, Dorn GW II. Early and delayed consequences of beta(2)-adrenergic receptor overexpression in mouse hearts: critical role for expression level. Circulation. 2000; 101: 1707–1714.[Abstract/Free Full Text]

4. Iwase M, Bishop SP, Uechi M, Vatner DE, Shannon RP, Kudej RK, Wight DC, Wagner TE, Ishikawa Y, Homcy CJ, Vatner SF. Adverse effects of chronic endogenous sympathetic drive induced by cardiac GS alpha overexpression. Circ Res. 1996; 78: 517–524.[Abstract/Free Full Text]

5. Mialet Perez J, Rathz DA, Petrashevskaya NN, Hahn HS, Wagoner LE, Schwartz A, Dorn GW, Liggett SB. Beta 1-adrenergic receptor polymorphisms confer differential function and predisposition to heart failure. Nat Med. 2003; 9: 1300–1305.[CrossRef][Medline] [Order article via Infotrieve]

6. Goldstein S. Benefits of beta-blocker therapy for heart failure: weighing the evidence. Arch Intern Med. 2002; 162: 641–648.[Abstract/Free Full Text]

7. Birks EJ, Tansley PD, Hardy J, George RS, Bowles CT, Burke M, Banner NR, Khaghani A, Yacoub MH. Left ventricular assist device and drug therapy for the reversal of heart failure. N Engl J Med. 2006; 355: 1873–1884.[Abstract/Free Full Text]

8. Cross HR, Steenbergen C, Lefkowitz RJ, Koch WJ, Murphy E. Overexpression of the cardiac beta(2)-adrenergic receptor and expression of a beta-adrenergic receptor kinase-1 (betaARK1) inhibitor both increase myocardial contractility but have differential effects on susceptibility to ischemic injury. Circ Res. 1999; 85: 1077–1084.[Abstract/Free Full Text]

9. Milano CA, Allen LF, Rockman HA, Dolber PC, McMinn TR, Chien KR, Johnson TD, Bond RA, Lefkowitz RJ. Enhanced myocardial function in transgenic mice overexpressing the beta 2-adrenergic receptor. Science. 1994; 264: 582–586.[Abstract/Free Full Text]

10. Dorn GW II, Tepe NM, Lorenz JN, Koch WJ, Liggett SB. Low- and high-level transgenic expression of beta2-adrenergic receptors differentially affect cardiac hypertrophy and function in Galphaq-overexpressing mice. Proc Natl Acad Sci U S A. 1999; 96: 6400–6405.[Abstract/Free Full Text]

11. Shah AS, Lilly RE, Kypson AP, Tai O, Hata JA, Pippen A, Silvestry SC, Lefkowitz RJ, Glower DD, Koch WJ. Intracoronary adenovirus-mediated delivery and overexpression of the beta(2)-adrenergic receptor in the heart: prospects for molecular ventricular assistance. Circulation. 2000; 101: 408–414.[Abstract/Free Full Text]

12. Lai NC, Roth DM, Gao MH, Tang T, Dalton N, Lai YY, Spellman M, Clopton P, Hammond HK. Intracoronary adenovirus encoding adenylyl cyclase VI increases left ventricular function in heart failure. Circulation. 2004; 110: 330–336.[Abstract/Free Full Text]

13. Harding VB, Jones LR, Lefkowitz RJ, Koch WJ, Rockman HA. Cardiac beta ARK1 inhibition prolongs survival and augments beta blocker therapy in a mouse model of severe heart failure. Proc Natl Acad Sci U S A. 2001; 98: 5809–5814.[Abstract/Free Full Text]

14. Rockman HA, Chien KR, Choi DJ, Iaccarino G, Hunter JJ, Ross J Jr, Lefkowitz RJ, Koch WJ. Expression of a beta-adrenergic receptor kinase 1 inhibitor prevents the development of myocardial failure in gene-targeted mice. Proc Natl Acad Sci U S A. 1998; 95: 7000–7005.[Abstract/Free Full Text]

15. Tachibana H, Naga Prasad SV, Lefkowitz RJ, Koch WJ, Rockman HA. Level of beta-adrenergic receptor kinase 1 inhibition determines degree of cardiac dysfunction after chronic pressure overload-induced heart failure. Circulation. 2005; 111: 591–597.[Abstract/Free Full Text]

16. Shah AS, White DC, Emani S, Kypson AP, Lilly RE, Wilson K, Glower DD, Lefkowitz RJ, Koch WJ. In vivo ventricular gene delivery of a beta-adrenergic receptor kinase inhibitor to the failing heart reverses cardiac dysfunction. Circulation. 2001; 103: 1311–1316.[Abstract/Free Full Text]

17. Li Z, Laugwitz KL, Pinkernell K, Pragst I, Baumgartner C, Hoffmann E, Rosport K, Munch G, Moretti A, Humrich J, Lohse MJ, Ungerer M. Effects of two Gbetagamma-binding proteins–N-terminally truncated phosducin and beta-adrenergic receptor kinase C terminus (betaARKct)–in heart failure. Gene Ther. 2003; 10: 1354–1361.[CrossRef][Medline] [Order article via Infotrieve]

18. Chen EP, Bittner HB, Akhter SA, Koch WJ, Davis RD. Myocardial function in hearts with transgenic overexpression of the G protein-coupled receptor kinase 5. Ann Thorac Surg. 2001; 71: 1320–1324.[Abstract/Free Full Text]

19. Matkovich SJ, Diwan A, Klanke JL, Hammer DJ, Marreez Y, Odley AM, Brunskill EW, Koch WJ, Schwartz RJ, Dorn GW II. Cardiac-specific ablation of G-protein receptor kinase 2 redefines its roles in heart development and beta-adrenergic signaling. Circ Res. 2006; 99: 996–1003.[Abstract/Free Full Text]

20. Sohal DS, Nghiem M, Crackower MA, Witt SA, Kimball TR, Tymitz KM, Penninger JM, Molkentin JD. Temporally regulated and tissue-specific gene manipulations in the adult and embryonic heart using a tamoxifen-inducible Cre protein. Circ Res. 2001; 89: 20–25.[Abstract/Free Full Text]

21. Agah R, Frenkel PA, French BA, Michael LH, Overbeek PA, Schneider MD. Gene recombination in postmitotic cells. Targeted expression of Cre recombinase provokes cardiac-restricted, site-specific rearrangement in adult ventricular muscle in vivo. J Clin Invest. 1997; 100: 169–179.[Medline] [Order article via Infotrieve]

22. Most P, Seifert H, Gao E, Funakoshi H, Volkers M, Heierhorst J, Remppis A, Pleger ST, DeGeorge BR Jr, Eckhart AD, Feldman AM, Koch WJ. Cardiac S100A1 protein levels determine contractile performance and propensity toward heart failure after myocardial infarction. Circulation. 2006; 114: 1258–1268.[Abstract/Free Full Text]

23. Funakoshi H, Kubota T, Kawamura N, Machida Y, Feldman AM, Tsutsui H, Shimokawa H, Takeshita A. Disruption of inducible nitric oxide synthase improves beta-adrenergic inotropic responsiveness but not the survival of mice with cytokine-induced cardiomyopathy. Circ Res. 2002; 90: 959–965.[Abstract/Free Full Text]

24. Zhou YY, Wang SQ, Zhu WZ, Chruscinski A, Kobilka BK, Ziman B, Wang S, Lakatta EG, Cheng H, Xiao RP. Culture and adenoviral infection of adult mouse cardiac myocytes: methods for cellular genetic physiology. Am J Physiol Heart Circ Physiol. 2000; 279: H429–H436.[Abstract/Free Full Text]

25. Buerger A, Rozhitskaya O, Sherwood MC, Dorfman AL, Bisping E, Abel ED, Pu WT, Izumo S, Jay PY. Dilated cardiomyopathy resulting from high-level myocardial expression of Cre-recombinase. J Card Fail. 2006; 12: 392–398.[CrossRef][Medline] [Order article via Infotrieve]

26. Vinge LE, Oie E, Andersson Y, Grogaard HK, Andersen G, Attramadal H. Myocardial distribution and regulation of GRK and beta-arrestin isoforms in congestive heart failure in rats. Am J Physiol Heart Circ Physiol. 2001; 281: H2490–H2499.[Abstract/Free Full Text]

27. Rockman HA, Koch WJ, Lefkowitz RJ. Seven-transmembrane-spanning receptors and heart function. Nature. 2002; 415: 206–212.[CrossRef][Medline] [Order article via Infotrieve]

28. Zhu WZ, Zheng M, Koch WJ, Lefkowitz RJ, Kobilka BK, Xiao RP. Dual modulation of cell survival and cell death by beta(2)-adrenergic signaling in adult mouse cardiac myocytes. Proc Natl Acad Sci U S A. 2001; 98: 1607–1612.[Abstract/Free Full Text]

29. Lefkowitz RJ, Rajagopal K, Whalen EJ. New roles for beta-arrestins in cell signaling: not just for seven-transmembrane receptors. Mol Cell. 2006; 24: 643–652.[CrossRef][Medline] [Order article via Infotrieve]

30. Piacentino V III, Weber CR, Chen X, Weisser-Thomas J, Margulies KB, Bers DM, Houser SR. Cellular basis of abnormal calcium transients of failing human ventricular myocytes. Circ Res. 2003; 92: 651–658.[Abstract/Free Full Text]

31. Ungerer M, Bohm M, Elce JS, Erdmann E, Lohse MJ. Altered expression of beta-adrenergic receptor kinase and beta 1-adrenergic receptors in the failing human heart. Circulation. 1993; 87: 454–463.[Abstract/Free Full Text]

32. Iaccarino G, Barbato E, Cipolletta E, De Amicis V, Margulies KB, Leosco D, Trimarco B, Koch WJ. Elevated myocardial and lymphocyte GRK2 expression and activity in human heart failure. Eur Heart J. 2005; 26: 1752–1758.[Abstract/Free Full Text]

33. Antos CL, Frey N, Marx SO, Reiken S, Gaburjakova M, Richardson JA, Marks AR, Olson EN. Dilated cardiomyopathy and sudden death resulting from constitutive activation of protein kinase a. Circ Res. 2001; 89: 997–1004.[Abstract/Free Full Text]

34. Gao MH, Lai NC, Roth DM, Zhou J, Zhu J, Anzai T, Dalton N, Hammond HK. Adenylylcyclase increases responsiveness to catecholamine stimulation in transgenic mice. Circulation. 1999; 99: 1618–1622.[Abstract/Free Full Text]

35. Takahashi T, Tang T, Lai NC, Roth DM, Rebolledo B, Saito M, Lew WY, Clopton P, Hammond HK. Increased cardiac adenylyl cyclase expression is associated with increased survival after myocardial infarction. Circulation. 2006; 114: 388–396.[Abstract/Free Full Text]

36. Noma T, Lemaire A, Naga Prasad SV, Barki-Harrington L, Tilley DG, Chen J, Le Corvoisier P, Violin JD, Wei H, Lefkowitz RJ, Rockman HA. Beta-arrestin-mediated beta1-adrenergic receptor transactivation of the EGFR confers cardioprotection. J Clin Invest. 2007; 117: 2445–2458.[CrossRef][Medline] [Order article via Infotrieve]




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