Khalid Chakir
Johns Hopkins University
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Publication
Featured researches published by Khalid Chakir.
Journal of Clinical Investigation | 2003
Weizhong Zhu; Shi-Qiang Wang; Khalid Chakir; Dongmei Yang; Tong Zhang; Joan Heller Brown; Eric Devic; Brian K. Kobilka; Heping Cheng; Rui-Ping Xiao
beta(1)-adrenergic receptor (beta(1)AR) stimulation activates the classic cAMP/protein kinase A (PKA) pathway to regulate vital cellular processes from the change of gene expression to the control of metabolism, muscle contraction, and cell apoptosis. Here we show that sustained beta(1)AR stimulation promotes cardiac myocyte apoptosis by activation of Ca(2+)/calmodulin kinase II (CaMKII), independently of PKA signaling. beta(1)AR-induced apoptosis is resistant to inhibition of PKA by a specific peptide inhibitor, PKI14-22, or an inactive cAMP analogue, Rp-8-CPT-cAMPS. In contrast, the beta(1)AR proapoptotic effect is associated with non-PKA-dependent increases in intracellular Ca(2+) and CaMKII activity. Blocking the L-type Ca(2+) channel, buffering intracellular Ca(2+), or inhibiting CaMKII activity fully protects cardiac myocytes against beta(1)AR-induced apoptosis, and overexpressing a cardiac CaMKII isoform, CaMKII-deltaC, markedly exaggerates the beta(1)AR apoptotic effect. These findings indicate that CaMKII constitutes a novel PKA-independent linkage of beta(1)AR stimulation to cardiomyocyte apoptosis that has been implicated in the overall process of chronic heart failure.
Circulation | 2008
An L. Moens; Eiki Takimoto; Carlo G. Tocchetti; Khalid Chakir; Djahida Bedja; Gianfranco Cormaci; Elizabeth A. Ketner; Maulik D. Majmudar; Kathleen L. Gabrielson; Marc K. Halushka; James B. Mitchell; Shyam Biswal; Keith M. Channon; Michael S. Wolin; N J Alp; Nazareno Paolocci; Hunter C. Champion; David A. Kass
Background— Sustained pressure overload induces pathological cardiac hypertrophy and dysfunction. Oxidative stress linked to nitric oxide synthase (NOS) uncoupling may play an important role. We tested whether tetrahydrobiopterin (BH4) can recouple NOS and reverse preestablished advanced hypertrophy, fibrosis, and dysfunction. Methods and Results— C57/Bl6 mice underwent transverse aortic constriction for 4 weeks, increasing cardiac mass (190%) and diastolic dimension (144%), lowering ejection fraction (−46%), and triggering NOS uncoupling and oxidative stress. Oral BH4 was then administered for 5 more weeks of pressure overload. Without reducing loading, BH4 reversed hypertrophy and fibrosis, recoupled endothelial NOS, lowered oxidant stress, and improved chamber and myocyte function, whereas untreated hearts worsened. If BH4 was started at the onset of pressure overload, it did not suppress hypertrophy over the first week when NOS activity remained preserved even in untreated transverse aortic constriction hearts. However, BH4 stopped subsequent remodeling when NOS activity was otherwise declining. A broad antioxidant, Tempol, also reduced oxidant stress yet did not recouple NOS or reverse worsened hypertrophy/fibrosis from sustained transverse aortic constriction. Microarray analysis revealed very different gene expression profiles for both treatments. BH4 did not enhance net protein kinase G activity. Finally, transgenic mice with enhanced BH4 synthesis confined to endothelial cells were unprotected against pressure overload, indicating that exogenous BH4 targeted myocytes and fibroblasts. Conclusions— NOS recoupling by exogenous BH4 ameliorates preexisting advanced cardiac hypertrophy/fibrosis and is more effective than a less targeted antioxidant approach (Tempol). These data highlight the importance of myocyte NOS uncoupling in hypertrophic heart disease and support BH4 as a potential new approach to treat this disorder.
Circulation | 2009
Takeshi Aiba; Geoffrey G. Hesketh; Andreas S. Barth; Ting Liu; Samantapudi Daya; Khalid Chakir; Veronica L Dimaano; Theodore P. Abraham; Brian O'Rourke; Fadi G. Akar; David A. Kass; Gordon F. Tomaselli
Background— Cardiac resynchronization therapy (CRT) is widely applied in patients with heart failure and dyssynchronous contraction (DHF), but the electrophysiological consequences of CRT in heart failure remain largely unexplored. Methods and Results— Adult dogs underwent left bundle-branch ablation and either right atrial pacing (190 to 200 bpm) for 6 weeks (DHF) or 3 weeks of right atrial pacing followed by 3 weeks of resynchronization by biventricular pacing at the same pacing rate (CRT). Isolated left ventricular anterior and lateral myocytes from nonfailing (control), DHF, and CRT dogs were studied with the whole-cell patch clamp. Quantitative polymerase chain reaction and Western blots were performed to measure steady state mRNA and protein levels. DHF significantly reduced the inward rectifier K+ current (IK1), delayed rectifier K+ current (IK), and transient outward K+ current (Ito) in both anterior and lateral cells. CRT partially restored the DHF-induced reduction of IK1 and IK but not Ito, consistent with trends in the changes in steady state K+ channel mRNA and protein levels. DHF reduced the peak inward Ca2+ current (ICa) density and slowed ICa decay in lateral compared with anterior cells, whereas CRT restored peak ICa amplitude but did not hasten decay in lateral cells. Calcium transient amplitudes were depressed and the decay was slowed in DHF, especially in lateral myocytes. CRT hastened the decay in both regions and increased the calcium transient amplitude in lateral but not anterior cells. No difference was found in CaV1.2 (α1C) mRNA or protein expression, but reduced CaVβ2 mRNA was found in DHF cells. DHF reduced phospholamban, ryanodine receptor, and sarcoplasmic reticulum Ca2+ ATPase and increased Na+-Ca2+ exchanger mRNA and protein. CRT did not restore the DHF-induced molecular remodeling, except for sarcoplasmic reticulum Ca2+ ATPase. Action potential durations were significantly prolonged in DHF, especially in lateral cells, and CRT abbreviated action potential duration in lateral but not anterior cells. Early afterdepolarizations were more frequent in DHF than in control cells and were reduced with CRT. Conclusions— CRT partially restores DHF-induced ion channel remodeling and abnormal Ca2+ homeostasis and attenuates the regional heterogeneity of action potential duration. The electrophysiological changes induced by CRT may suppress ventricular arrhythmias, contribute to the survival benefit of this therapy, and improve the mechanical performance of the heart.
Circulation | 2008
Khalid Chakir; Samantapudi Daya; Richard S. Tunin; Robert H. Helm; Melissa Byrne; Veronica L Dimaano; Albert C. Lardo; Theodore P. Abraham; Gordon F. Tomaselli; David A. Kass
Background— Cardiac dyssynchrony in the failing heart worsens global function and efficiency and generates regional loading disparities that may exacerbate stress-response molecular signaling and worsen cell survival. We hypothesized that cardiac resynchronization (CRT) from biventricular stimulation reverses such molecular abnormalities at the regional and global levels. Methods and Results— Adult dogs (n=27) underwent left bundle-branch radiofrequency ablation, prolonging the QRS by 100%. Dogs were first subjected to 3 weeks of atrial tachypacing (200 bpm) to induce dyssynchronous heart failure (DHF) and then randomized to either 3 weeks of additional atrial tachypacing (DHF) or biventricular tachypacing (CRT). At 6 weeks, ejection fraction improved in CRT (2.8±1.8%) compared with DHF (−4.4±2.7; P=0.02 versus CRT) dogs, although both groups remained in failure with similarly elevated diastolic pressures and reduced dP/dtmax. In DHF, mitogen-activated kinase p38 and calcium-calmodulin-dependent kinase were disproportionally expressed/activated (50% to 150%), and tumor necrosis factor-&agr; increased in the late-contracting (higher-stress) lateral versus septal wall. These disparities were absent with CRT. Apoptosis assessed by terminal deoxynucleotide transferase-mediated dUTP nick-end labeling staining, caspase-3 activity, and nuclear poly ADP-ribose polymerase cleavage was less in CRT than DHF hearts and was accompanied by increased Akt phosphorylation/activity. Bcl-2 and BAD protein diminished with DHF but were restored by CRT, accompanied by marked BAD phosphorylation, enhanced BAD-14-3-3 interaction, and reduced phosphatase PP1&agr;, consistent with antiapoptotic effects. Other Akt-coupled modulators of apoptosis (FOXO-3&agr; and GSK3&bgr;) were more phosphorylated in DHF than CRT and thus less involved. Conclusions— CRT reverses regional and global molecular remodeling, generating more homogeneous activation of stress kinases and reducing apoptosis. Such changes are important benefits from CRT that likely improve cardiac performance and outcome.
Circulation | 2003
Rui-Ping Xiao; Sheng Jun Zhang; Khalid Chakir; Pavel Avdonin; Weizhong Zhu; Richard A. Bond; C. William Balke; Edward G. Lakatta; Heping Cheng
Background—Myocardial contractile response to &bgr;1- and &bgr;2-adrenergic receptor (AR) stimulation is severely impaired in chronic heart failure, in which Gi signaling and the ratio of &bgr;2/&bgr;1 are often increased. Because &bgr;2-AR but not &bgr;1-AR couples to Gs and Gi with the Gi coupling negating the Gs-mediated contractile response, we determined whether the heart failure–associated augmentation of Gi signaling contributes differentially to the defects of these &bgr;-AR subtypes and, if so, whether inhibition of Gi or selective activation of &bgr;2-AR/Gs by ligands restores &bgr;2-AR contractile response in the failing heart. Methods and Results—Cardiomyocytes were isolated from 18- to 24-month-old failing spontaneously hypertensive (SHR) or age-matched Wistar-Kyoto (WKY) rat hearts. In SHR cardiomyocytes, either &bgr;-AR subtype–mediated inotropic effect was markedly diminished, whereas Gi proteins and the &bgr;2/&bgr;1 ratio were increased. Disruption of Gi signaling by pertussis toxin (PTX) enabled &bgr;2- but not &bgr;1-AR to induce a full positive inotropic response in SHR myocytes. Furthermore, screening of a panel of &bgr;2-AR ligands revealed that the contractile response mediated by most &bgr;2-AR agonists, including zinterol, salbutamol, and procaterol, was potentiated by PTX, indicating concurrent Gs and Gi activation. In contrast, fenoterol, another &bgr;2-AR agonist, induced a full positive inotropic effect in SHR myocytes even in the absence of PTX. Conclusions—We conclude that enhanced Gi signaling is selectively involved in the dysfunction of &bgr;2- but not &bgr;1-AR in failing SHR hearts and that disruption of Gi signaling by PTX or selective activation of &bgr;2-AR/Gs signaling by fenoterol restores the blunted &bgr;2-AR contractile response in the failing heart.
Circulation | 2009
Khalid Chakir; Samantapudi Daya; Takeshi Aiba; Richard S. Tunin; Veronica L Dimaano; Theodore P. Abraham; Kathryn Jacques; Edwin W. Lai; Karel Pacak; Wei Zhong Zhu; Rui-Ping Xiao; Gordon F. Tomaselli; David A. Kass
Background— Cardiac resynchronization therapy (CRT) is the first clinical heart failure treatment that improves chamber systolic function in both the short-term and long-term yet also reduces mortality. The mechanical impact of CRT is immediate and well documented, yet its long-term influences on myocyte function and adrenergic modulation that may contribute to its sustained benefits are largely unknown. Methods and Results— We used a canine model of dyssynchronous heart failure (DHF; left bundle ablation, atrial tachypacing for 6 weeks) and CRT (DHF for 3 weeks, biventricular tachypacing for subsequent 3 weeks), contrasting both to nonfailing controls. CRT restored contractile synchrony and improved systolic function compared with DHF. Myocyte sarcomere shortening and calcium transients were markedly depressed at rest and after isoproterenol stimulation in DHF (both anterior and lateral walls), and CRT substantially improved both. In addition, &bgr;1 and &bgr;2 stimulation was enhanced, coupled to increased &bgr;1 receptor abundance but no change in binding affinity. CRT also augmented adenylate cyclase activity over DHF. Inhibitory G-protein (G&agr;i) suppression of &bgr;-adrenergic stimulation was greater in DHF and reversed by CRT. G&agr;i expression itself was unaltered; however, expression of negative regulators of G&agr;i signaling (particularly RGS3) rose uniquely with CRT over DHF and controls. CRT blunted elevated myocardial catecholamines in DHF, restoring levels toward control. Conclusions— CRT improves rest and &bgr;-adrenergic-stimulated myocyte function and calcium handling, upregulating &bgr;1 receptors and adenylate cyclase activity and suppressing Gi-coupled signaling associated with novel RGS upregulation. The result is greater rest and sympathetic reserve despite reduced myocardial neurostimulation as components underlying its net benefit.
Circulation Research | 2005
Wei Zhong Zhu; Khalid Chakir; Shengjun Zhang; Dongmei Yang; Catherine Lavoie; Michel Bouvier; Terence E. Hébert; Edward G. Lakatta; Heping Cheng; Rui-Ping Xiao
Intermolecular interactions between members of both similar and divergent G protein-coupled receptor subfamilies have been shown in various experimental systems. Here, we demonstrate heterodimerization of predominant β-adrenergic receptor (βAR) subtypes expressed in the heart, β1AR, and β2AR, and its physiological relevance. In intact adult-mouse cardiac myocytes lacking native β1AR and β2AR, coexpression of both βAR subtypes led to receptor heterodimerization, as evidenced by their coimmunoprecipitation, colocalization at optical resolution, and markedly increased binding affinity for subtype-selective ligands. As a result, the dose-response curve of myocyte contraction to βAR agonist stimulation with isoproterenol (ISO) was shifted leftward by ≈1.5 orders of magnitude, and the response of cellular cAMP formation to ISO was enhanced concomitantly, indicating that intermolecular interactions of βAR subtypes resulted in sensitization of these receptors in response to agonist stimulation. In contrast, the presence of β1AR greatly suppressed ligand-independent spontaneous activity of coexisting β2ARs. Thus, heterodimerization of β1AR and β2AR in intact cardiac myocytes creates a novel population of βARs with distinct functional and pharmacological properties, resulting in enhanced signaling efficiency in response to agonist stimulation while silencing ligand-independent receptor activation, thereby optimizing β-adrenergic modulation of cardiac contractility.
Circulation-cardiovascular Genetics | 2010
Giulio Agnetti; Nina Kaludercic; Lesley A. Kane; Steven T. Elliott; Yurong Guo; Khalid Chakir; Daya Samantapudi; Nazareno Paolocci; Gordon F. Tomaselli; David A. Kass; Jennifer E. Van Eyk
Background—Cardiac resynchronization therapy (CRT) improves chamber mechanoenergetics and morbidity and mortality of patients manifesting heart failure with ventricular dyssynchrony; however, little is known about the molecular changes underlying CRT benefits. We hypothesized that mitochondria may play an important role because of their involvement in energy production. Methods and Results—Mitochondria isolated from the left ventricle in a canine model of dyssynchronous or resynchronized (CRT) heart failure were analyzed by a classical, gel-based, proteomic approach. Two-dimensional gel electrophoresis revealed that 31 mitochondrial proteins where changed when controlling the false discovery rate at 30%. Key enzymes in anaplerotic pathways, such as pyruvate carboxylation and branched-chain amino acid oxidation, were increased. These concerted changes, along with others, suggested that CRT may increase the pool of Krebs cycle intermediates and fuel oxidative phosphorylation. Nearly 50% of observed changes pertained to subunits of the respiratory chain. ATP synthase-&bgr; subunit of complex V was less degraded, and its phosphorylation modulated by CRT was associated with increased formation (2-fold, P=0.004) and specific activity (+20%, P=0.05) of the mature complex. The importance of these modifications was supported by coordinated changes in mitochondrial chaperones and proteases. CRT increased the mitochondrial respiratory control index with tightened coupling when isolated mitochondria were reexposed to substrates for both complex I (glutamate and malate) and complex II (succinate), an effect likely related to ATP synthase subunit modifications and complex quantity and activity. Conclusions—CRT potently affects both the mitochondrial proteome and the performance associated with improved cardiac function.
Circulation-cardiovascular Genetics | 2009
Andreas S. Barth; Takeshi Aiba; Victoria L. Halperin; Deborah DiSilvestre; Khalid Chakir; Carlo Colantuoni; Richard S. Tunin; Victoria Lea Dimaano; Wayne Yu; Theodore P. Abraham; David A. Kass; Gordon F. Tomaselli
Background—Cardiac electromechanical dyssynchrony causes regional disparities in workload, oxygen consumption, and myocardial perfusion within the left ventricle. We hypothesized that such dyssynchrony also induces region-specific alterations in the myocardial transcriptome that are corrected by cardiac resynchronization therapy (CRT). Methods and Results—Adult dogs underwent left bundle branch ablation and right atrial pacing at 200 bpm for either 6 weeks (dyssynchronous heart failure, n=12) or 3 weeks, followed by 3 weeks of resynchronization by biventricular pacing at the same pacing rate (CRT, n=10). Control animals without left bundle branch block were not paced (n=13). At 6 weeks, RNA was isolated from the anterior and lateral left ventricular (LV) walls and hybridized onto canine-specific 44K microarrays. Echocardiographically, CRT led to a significant decrease in the dyssynchrony index, while dyssynchronous heart failure and CRT animals had a comparable degree of LV dysfunction. In dyssynchronous heart failure, changes in gene expression were primarily observed in the anterior LV, resulting in increased regional heterogeneity of gene expression within the LV. Dyssynchrony-induced expression changes in 1050 transcripts were reversed by CRT to levels of nonpaced hearts (false discovery rate <5%). CRT remodeled transcripts with metabolic and cell signaling function and greatly reduced regional heterogeneity of gene expression as compared with dyssynchronous heart failure. Conclusions—Our results demonstrate a profound effect of electromechanical dyssynchrony on the regional cardiac transcriptome, causing gene expression changes primarily in the anterior LV wall. CRT corrected the alterations in gene expression in the anterior wall, supporting a global effect of biventricular pacing on the ventricular transcriptome that extends beyond the pacing site in the lateral wall.
Circulation Research | 2004
Veronique Leblais; Su Hyun Jo; Khalid Chakir; Victor A. Maltsev; Ming Zheng; Michael T. Crow; Wang Wang; Edward G. Lakatta; Rui-Ping Xiao
Phosphoinositide 3-kinase (PI3K) has been implicated in &bgr;2-adrenergic receptor (&bgr;2-AR)/Gi-mediated compartmentation of the concurrent Gs-cAMP signaling, negating &bgr;2-AR–induced phospholamban phosphorylation and the positive inotropic and lusitropic responses in cardiomyocytes. However, it is unclear whether PI3K crosstalks with the &bgr;1-AR signal transduction, and even more generally, with the cAMP/PKA pathway. In this study, we show that selective &bgr;1-AR stimulation markedly increases PI3K activity in adult rat cardiomyocytes. Inhibition of PI3K by LY294002 significantly enhances &bgr;1-AR–induced increases in L-type Ca2+ currents, intracellular Ca2+ transients, and myocyte contractility, without altering the receptor-mediated phosphorylation of phospholamban. The LY294002 potentiating effects are completely prevented by &bgr;ARK-ct, a peptide inhibitor of &bgr;-adrenergic receptor kinase-1 (&bgr;ARK1) as well as G&bgr;&ggr; signaling, but not by disrupting Gi function with pertussis toxin. Moreover, forskolin, an adenylyl cyclase activator, also elevates PI3K activity and inhibition of PI3K enhances forskolin-induced contractile response in a &bgr;ARK-ct sensitive manner. In contrast, PI3K inhibition affects neither the basal contractility nor high extracellular Ca2+-induced increase in myocyte contraction. These results suggest that &bgr;1-AR stimulation activates PI3K via a PKA-dependent mechanism, and that G&bgr;&ggr; and the subsequent activation of &bgr;ARK1 are critically involved in the PKA-induced PI3K signaling which, in turn, negates cAMP-induced positive inotropic effect via inhibiting sarcolemmal Ca2+ influx and the subsequent increase in intracellular Ca2+ transients, without altering the receptor-mediated phospholamban phosphorylation, in intact cardiomyocytes.