Controlled and cardiac-restricted overexpression of the arginine vasopressin V1A receptor causes reversible left ventricular dysfunction through Gαq-mediated cell signaling

BACKGROUND

[Arg8]-vasopressin (AVP) activates 3 G-protein-coupled receptors: V1A, V2, and V1B. The AVP-V1A receptor is the primary AVP receptor in the heart; however, its role in cardiac homeostasis is controversial. To better understand AVP-mediated signaling in the heart, we created a transgenic mouse with controlled overexpression of the V1A receptor.

METHODS AND RESULTS

The V1A receptor transgene was placed under the control of the tetracycline-regulated, cardiac-specific α-myosin heavy chain promoter (V1A-TG). V1A-TG mice had a normal cardiac function phenotype at 10 weeks of age; however, by 24 weeks of age, tetracycline-transactivating factor/V1A-TG mouse hearts had reduced cardiac function, cardiac hypertrophy, and dilatation of the ventricular cavity. Contractile dysfunction was also observed in isolated adult cardiac myocytes. When V1A receptor transgene was induced to be expressed in adult mice (V1A-TG(Ind)), left ventricular dysfunction and dilatation were also seen, albeit at a later time point. Because the V1A receptor mediates cell signaling through Gα(q) protein, we blocked Gα(q) signaling by crossing tetracycline-transactivating factor/V1A mice with transgenic mice that expressed a small inhibitory peptide against Gα(q). Gα(q) blockade abrogated the development of the heart failure phenotype in tetracycline-transactivating factor/V1A-TG mice. The heart failure phenotype could be reversed by administration of doxycycline.

CONCLUSIONS

Our results demonstrate a role for V1A-mediated signaling in the development of heart failure and support a role for V1A blockade in the treatment of patients with elevated levels of vasopressin.

Carvedilol and its new analogs suppress arrhythmogenic store overload-induced Ca2+ release

Carvedilol is one of the most effective beta blockers for preventing ventricular tachyarrhythmias in heart failure, but the mechanisms underlying its favorable antiarrhythmic benefits remain unclear. Spontaneous Ca(2+) waves, also called store overload-induced Ca(2+) release (SOICR), evoke ventricular tachyarrhythmias in individuals with heart failure. Here we show that carvedilol is the only beta blocker tested that effectively suppresses SOICR by directly reducing the open duration of the cardiac ryanodine receptor (RyR2). This unique anti-SOICR activity of carvedilol, combined with its beta-blocking activity, probably contributes to its favorable antiarrhythmic effect. To enable optimal titration of carvedilol's actions as a beta blocker and as a suppressor of SOICR separately, we developed a new SOICR-inhibiting, minimally beta-blocking carvedilol analog, VK-II-86. VK-II-86 prevented stress-induced ventricular tachyarrhythmias in RyR2-mutant mice and did so more effectively when combined with either of the selective beta blockers metoprolol or bisoprolol. Combining SOICR inhibition with optimal beta blockade has the potential to provide antiarrhythmic therapy that can be tailored to individual patients.

Rationale and design of the treatment of hyponatremia based on lixivaptan in NYHA class III/IV cardiac patient evaluation (THE BALANCE) study

Hyponatremia is a common electrolyte disorder in patients with heart failure (HF) associated with cognitive dysfunction and increased mortality and rehospitalization rates. Loop diuretics worsen renal function, produce neurohormonal activation, and induce electrolyte imbalances. Lixivaptan is a selective, oral vasopressin V(2) -receptor antagonist that improves hyponatremia by promoting electrolyte-free aquaresis without significant side effects. The Treatment of Hyponatremia Based on Lixivaptan in NYHA Class III/IV Cardiac Patient Evaluation (BALANCE) study is a randomized, double-blind, placebo-controlled, phase 3 trial designed to evaluate the effects of lixivaptan on serum sodium in patients hospitalized with worsening heart failure (target N= 650), signs of congestion and serum sodium concentrations <135 mEq/L. Other endpoints include assessment of dyspnea, body weight, cognitive function, and days of hospital-free survival. Patients are randomized 1:1 to lixivaptan or matching placebo for 60 days, with a 30-day safety follow-up. Doses of lixivaptan or placebo are adjusted based on serum sodium and volume status. Lixivaptan was shown to increase serum sodium and reduce body weight, without renal dysfunction or hypokalemia. BALANCE seeks to address unmet questions regarding the use of vasopressin antagonists including their effects on cognitive function and clinical outcomes in patients with hyponatremia and worsening heart failure.

Myocardial viability and survival in ischemic left ventricular dysfunction

BACKGROUND

The assessment of myocardial viability has been used to identify patients with coronary artery disease and left ventricular dysfunction in whom coronary-artery bypass grafting (CABG) will provide a survival benefit. However, the efficacy of this approach is uncertain.

METHODS

In a substudy of patients with coronary artery disease and left ventricular dysfunction who were enrolled in a randomized trial of medical therapy with or without CABG, we used single-photon-emission computed tomography (SPECT), dobutamine echocardiography, or both to assess myocardial viability on the basis of prespecified thresholds.

RESULTS

Among the 1212 patients enrolled in the randomized trial, 601 underwent assessment of myocardial viability. Of these patients, we randomly assigned 298 to receive medical therapy plus CABG and 303 to receive medical therapy alone. A total of 178 of 487 patients with viable myocardium (37%) and 58 of 114 patients without viable myocardium (51%) died (hazard ratio for death among patients with viable myocardium, 0.64; 95% confidence interval [CI], 0.48 to 0.86; P=0.003). However, after adjustment for other baseline variables, this association with mortality was not significant (P=0.21). There was no significant interaction between viability status and treatment assignment with respect to mortality (P=0.53).

CONCLUSIONS

The presence of viable myocardium was associated with a greater likelihood of survival in patients with coronary artery disease and left ventricular dysfunction, but this relationship was not significant after adjustment for other baseline variables. The assessment of myocardial viability did not identify patients with a differential survival benefit from CABG, as compared with medical therapy alone. (Funded by the National Heart, Lung, and Blood Institute; STICH ClinicalTrials.gov number, NCT00023595.).

Cost of medical services in older patients with heart failure: those receiving enhanced monitoring using a computer-based telephonic monitoring system compared with those in usual care: the Heart Failure Home Care trial

BACKGROUND

Prior studies suggest that disease management programs may be effective in improving clinical and economic outcomes in patients with heart failure. Whether these types of programs can lower health care cost and be adapted to the primary care setting is unknown. This study was designed to assess the impact of a home-based disease management program, the Alere DayLink HF Monitoring System (HFMS), on the clinical and economic outcomes of Medicare beneficiaries recently hospitalized for heart failure who received the care from a community-based primary care practitioner.

METHODS AND RESULTS

The Heart Failure Home Care trial was a multicenter, randomized, controlled trial of sophisticated, monitoring of heart failure patients with an interactive program versus standard heart failure care with enhanced patient education and follow-up (SC) in Medicare-eligible patients. The study endpoints included cardiovascular death or rehospitalization for heart failure, length of hospital stay, total patient cost, and cost to Medicare at 6 months of enrollment. A total of 315 patients age ≥ 65 years old were randomized: 160 to the HFMS and 155 to SC. There were no significant statistical differences between the groups in regards to 6-month cardiac mortality, rehospitalizations for heart failure, or length of hospital stay. Of those, 304 patients had their Medicare data available. The information from the Medicare claims data was used to determine the cost. Information from the trial was used to determine costs of out-patient drugs and the interventions. The 6-month mean Medicare costs were estimated to be $17,837 and $13,886 for the HFMS and the SC groups, respectively. We found that overall medical costs of medicare patients were significantly higher for patients who were randomized to the HFMS arm than they were for the patients randomized to the SC arm.

CONCLUSIONS

Our study results suggest that enhanced patient education and follow-up is as successful as a sophisticated home monitoring device with an interactive program and less costly in patients who are elderly and receive the care from a community-based primary care practitioner.

Adenosine receptor subtypes and the heart failure phenotype: translating lessons from mice to man

Adenosine plays an important role in the pathophysiology of heart failure and in myocardial protection during ischemia and reperfusion. The action of adenosine in the heart is mediated by four G-protein-coupled receptors: A(1)-AR and A(3)-AR, which act via Gα(1), and A(2A)-AR and A(2B)-AR, which act via Gα(s). Understanding of cellular signaling pathways triggered by adenosine has been complicated by the availability of only partially specific adenosine agonists/antagonists. Adenosine signaling appears to be at times redundant in receptor function, and cellular signaling pathways for adenosine are multiple, parallel, and interrelated. Data obtained about the specific role of individual adenosine receptors, through the genetic modulation of receptors in murine hearts have provided important information about the role of adenosine receptors in the heart. Here we review existing data and present new results that clarify the function of individual adenosine receptors in the heart and their role in the development of left ventricular dysfunction, and about the downstream signaling systems that are modified by adenosine receptor activation.

The interplay between NF-kappaB and E2F1 coordinately regulates inflammation and metabolism in human cardiac cells

Pyruvate dehydrogenase kinase 4 (PDK4) inhibition by nuclear factor-κB (NF-κB) is related to a shift towards increased glycolysis during cardiac pathological processes such as cardiac hypertrophy and heart failure. The transcription factors estrogen-related receptor-α (ERRα) and peroxisome proliferator-activated receptor (PPAR) regulate PDK4 expression through the potent transcriptional coactivator PPARγ coactivator-1α (PGC-1α). NF-κB activation in AC16 cardiac cells inhibit ERRα and PPARβ/δ transcriptional activity, resulting in reduced PGC-1α and PDK4 expression, and an enhanced glucose oxidation rate. However, addition of the NF-κB inhibitor parthenolide to these cells prevents the downregulation of PDK4 expression but not ERRα and PPARβ/δ DNA binding activity, thus suggesting that additional transcription factors are regulating PDK4. Interestingly, a recent study has demonstrated that the transcription factor E2F1, which is crucial for cell cycle control, may regulate PDK4 expression. Given that NF-κB may antagonize the transcriptional activity of E2F1 in cardiac myocytes, we sought to study whether inflammatory processes driven by NF-κB can downregulate PDK4 expression in human cardiac AC16 cells through E2F1 inhibition. Protein coimmunoprecipitation indicated that PDK4 downregulation entailed enhanced physical interaction between the p65 subunit of NF-κB and E2F1. Chromatin immunoprecipitation analyses demonstrated that p65 translocation into the nucleus prevented the recruitment of E2F1 to the PDK4 promoter and its subsequent E2F1-dependent gene transcription. Interestingly, the NF-κB inhibitor parthenolide prevented the inhibition of E2F1, while E2F1 overexpression reduced interleukin expression in stimulated cardiac cells. Based on these findings, we propose that NF-κB acts as a molecular switch that regulates E2F1-dependent PDK4 gene transcription.

Regulation of in vivo cardiac contractility by phospholemman: role of Na+/Ca2+ exchange

Phospholemman (PLM), when phosphorylated at serine 68, relieves its inhibition on Na(+)-K(+)-ATPase but inhibits Na(+)/Ca(2+) exchanger 1 (NCX1) in cardiac myocytes. Under stress when catecholamine levels are high, enhanced Na(+)-K(+)-ATPase activity by phosphorylated PLM attenuates intracellular Na(+) concentration ([Na(+)](i)) overload. To evaluate the effects of PLM on NCX1 on in vivo cardiac contractility, we injected recombinant adeno-associated virus (serotype 9) expressing either the phosphomimetic PLM S68E mutant or green fluorescent protein (GFP) directly into left ventricles (LVs) of PLM-knockout (KO) mice. Five weeks after virus injection, ∼40% of isolated LV myocytes exhibited GFP fluorescence. Expression of S68E mutant was confirmed with PLM antibody. There were no differences in protein levels of α(1)- and α(2)-subunits of Na(+)-K(+)-ATPase, NCX1, and sarco(endo)plasmic reticulum Ca(2+)-ATPase between KO-GFP and KO-S68E LV homogenates. Compared with KO-GFP myocytes, Na(+)/Ca(2+) exchange current was suppressed, but resting [Na(+)](i), Na(+)-K(+)-ATPase current, and action potential amplitudes were similar in KO-S68E myocytes. Resting membrane potential was slightly lower and action potential duration at 90% repolarization (APD(90)) was shortened in KO-S68E myocytes. Isoproterenol (Iso; 1 μM) increased APD(90) in both groups of myocytes. After Iso, [Na(+)](i) increased monotonically in paced (2 Hz) KO-GFP but reached a plateau in KO-S68E myocytes. Both systolic and diastolic [Ca(2+)](i) were higher in Iso-stimulated KO-S68E myocytes paced at 2 Hz. Echocardiography demonstrated similar resting heart rate, ejection fraction, and LV mass between KO-GFP and KO-S68E mice. In vivo closed-chest catheterization demonstrated enhanced contractility in KO-S68E compared with KO-GFP hearts stimulated with Iso. We conclude that under catecholamine stress when [Na(+)](i) is high, PLM minimizes [Na(+)](i) overload by relieving its inhibition of Na(+)-K(+)-ATPase and preserves inotropy by simultaneously inhibiting Na(+)/Ca(2+) exchanger.

Left ventricular dysfunction in murine models of heart failure and in failing human heart is associated with a selective decrease in the expression of caveolin-3

BACKGROUND

Caveolins are scaffolding proteins that are integral components of caveolae, flask-shaped invaginations in the membranes of all mammalian cells. Caveolin-1 and -2 are expressed ubiquitously, whereas caveolin-3 is found only in muscle. The role of caveolin-3 in heart muscle disease is controversial.

METHODS AND RESULTS

The present study was undertaken to assess the effects of left ventricular dysfunction on the expression of caveolin proteins using 2 well characterized models of murine heart failure and failing human heart. Transgenic mice with constitutive overexpression of A(1)-adenosine receptor (A(1)-TG) demonstrated cardiac dilatation and decreased left ventricular function at 10 weeks of age. This was accompanied by a marked decrease in caveolin-3 mRNA and protein levels compared with non-TG control mice. The change in caveolin-3 expression was selective, because levels of caveolin-1 and -2 did not change. Confocal imaging of myocytes isolated from A(1)-TG mice demonstrated a loss of the plate-like appearance of T tubules. Caveolin-3 levels were also reduced in hearts from mice overexpressing tumor necrosis factor α. There was a direct relationship between caveolin-3 expression and fractional shortening in all mice that were studied (r = 0.65; P < .001). Although we could not demonstrate a significant decrease in caveolin-3 levels in failing human heart, we did find a direct correlation (r = 0.7; P < .05) between levels of caveolin-3 protein and Ca(2+)-adenosine triphosphatase, a marker of the heart failure phenotype.

CONCLUSIONS

These results suggest a relationship between left ventricular dysfunction and caveolin-3 levels and suggest that caveolin-3 may provide a novel target for heart failure therapy.

Advancing the research mission in an academic department: the creation of a center for translational medicine

Multidisciplinary research centers have multiplied in academic medical centers over the past decade and several recent reports have described their structure, strengths and limitations, and the difficulties that they may face. However, little attention has been paid to the role of a multidisciplinary center in the context of a single academic department. In 2003, the Department of Medicine at Jefferson Medical College launched the Center for Translational Medicine in order to facilitate multidisciplinary research, optimally utilize space and resources, enhance the educational experience for trainees, link basic investigation with clinical research programs, and develop a program of research excellence. Herein, we describe the structure of the Center and provide evidence of its success. The development of the Center has resulted in increased total funding, an increased number of students and residents pursuing translational research, a more effective utilization of space, the development of multidisciplinary research projects, and a significant increase in the number of individual and programmatic federally funded grants. Though the creation of the Center was not without challenges, the overall benefits for the department and the university have been substantial. The concept of a translational medicine center may be useful for many departments of academic medical centers.

Myocardial Fas and cytokine expression in end-stage heart failure: impact of LVAD support

Left ventricular assist device (LVAD) support may facilitate myocardial recovery. We evaluated the impact of LVAD support on Fas expression in a cohort with end-stage heart failure. Myocardial gene expression was assessed pre- and post-LVAD by RNase protection assay and compared to control donor hearts. The expression of Fas is markedly elevated at the time of LVAD support and is tightly correlated with TNF expression. While interleukin (IL)-6 was significantly reduced by LVAD support, the impact of support on Fas was highly variable and tightly linked to tumor necrosis factor (TNF). The role of Fas in predicting recovery after LVAD support requires further investigation.

Cardiac-restricted overexpression of the A(2A)-adenosine receptor in FVB mice transiently increases contractile performance and rescues the heart failure phenotype in mice overexpressing the A(1)-adenosine receptor

In the heart, adenosine binds to pharmacologically distinct G-protein-coupled receptors (A(1)-R, A(2A)-R, and A(3)-R). While the role of A(1)- and A(3)-Rs in the heart has been clarified, the effect of genetically manipulating the A(2A)-R has not been defined. Thus, we created mice overexpressing a cardiac-restricted A(2A)-R transgene. Mice with both low (Lo) and high (Hi) levels of A(2A)-R overexpression demonstrated an increase in cardiac contractility at 12 weeks. These changes were associated with a significantly higher systolic but not diastolic [Ca(2+)]i, higher maximal contraction amplitudes, and a significantly enhanced sarcoplasmic reticulum Ca(2+) uptake activity. At 20 weeks, the effects of A(2A)-R overexpression on cardiac contractility diminished. The positive effects elicited by A(2A)-R overexpression differ from the heart failure phenotype we observed with A(1)-R overexpression. Interestingly, coexpression of A(2A)-R TG(Hi), but not A(2A)-R TGLo, enhanced survival, prevented the development of left ventricular dysfunction and heart failure, and improved Ca(2+) handling in mice overexpressing the A(1)-R. These results suggest that adenosine-mediated signaling in the heart requires a balance between A(1)- and A(2A)-Rs--a finding that may have important implications for the ongoing clinical evaluation of adenosine receptor subtype-specific agonists and antagonists for the treatment of cardiovascular diseases.