Intracoronary adenovirus encoding adenylyl cyclase VI increases left ventricular function in heart failure

Targeted high-efficiency, homogeneous myocardial gene transfer

Myocardial gene therapy continues to show promise as a tool for investigation and treatment of cardiac disease. Progress toward clinical approval has been slowed by limited in vivo delivery methods. We investigated the problem in a porcine model, with an objective of developing a method for high efficiency, homogeneous myocardial gene transfer that could be used in large mammals, and ultimately in humans. Eighty-one piglets underwent coronary catheterization for delivery of viral vectors into the left anterior descending artery and/or the great cardiac vein. The animals were followed for 5 or 28 days, and then transgene efficiency was quantified from histological samples. The baseline protocol included treatment with VEGF, nitroglycerin, and adenosine followed by adenovirus infusion into the LAD. Gene transfer efficiency varied with choice of viral vector, with use of VEGF, adenosine, or nitroglycerin, and with calcium concentration. The best results were obtained by manipulation of physical parameters. Simultaneous infusion of adenovirus through both left anterior descending artery and great cardiac vein resulted in gene transfer to 78+/-6% of myocytes in a larger target area. This method was well tolerated by the animals. We demonstrate targeted, homogeneous, high efficiency gene transfer using a method that should be transferable for eventual human usage.

Adenylylcyclase gene transfer increases function of the failing heart

A persistent question in cardiovascular gene transfer concerns whether an exogenously delivered gene can increase function of the failing heart. Here we test the hypothesis that intracoronary delivery of adenovirus encoding adenylylcyclase type VI (Ad.ACVI) in the setting of active heart failure will increase function of the failing heart. As a model of heart failure, we used transgenic mice with dilated and poorly functioning hearts resulting from cardiac-directed expression of Galphaq.Galphaq mice with equivalent pretreatment impairment in left ventricular (LV) function (echocardiography) received 2.5x1010 viral particles of Ad.ACVI or Ad.EGFP (enhanced green fluorescent protein), or saline, by indirect intracoronary delivery. Serial echocardiograms obtained before and 14 days after gene transfer showed that Ad.ACVI increased LV ejection fraction (p<0.01) and velocity of circumferential fiber shortening (p<0.03). Detailed measurements in isolated hearts showed that ACVI gene transfer increased LV positive dP/dt (p=0.02) and LV negative dP/dt (p=0.01). Gene transfer was confirmed by polymerase chain reaction. These data show that, in an animal model that mimics key aspects of clinical congestive heart failure, cardiac gene transfer of ACVI increases function of the failing heart.

Compartmentation of cyclic nucleotide signaling in the heart: the role of cyclic nucleotide phosphodiesterases

A current challenge in cellular signaling is to decipher the complex intracellular spatiotemporal organization that any given cell type has developed to discriminate among different external stimuli acting via a common signaling pathway. This obviously applies to cAMP and cGMP signaling in the heart, where these cyclic nucleotides determine the regulation of cardiac function by many hormones and neuromediators. Recent studies have identified cyclic nucleotide phosphodiesterases as key actors in limiting the spread of cAMP and cGMP, and in shaping and organizing intracellular signaling microdomains. With this new role, phosphodiesterases have been promoted from the rank of a housekeeping attendant to that of an executive officer.

Adenylyl cyclase 6 overexpression decreases the permeability of endothelial monolayers via preferential enhancement of prostacyclin receptor function

Overexpression of adenylyl cyclase (AC) has been proposed as a potential gene therapy strategy to increase cAMP formation in cardiomyocytes and cardiac function in vivo. The impact of AC overexpression on endothelial cells, which will be traversed by genes delivered in vivo, has not been examined. Hence, the goal of the current study was to determine the consequence of AC overexpression on vascular endothelial cells in terms of G-protein-coupled receptor (GPCR) signaling and endothelial barrier function. We demonstrate that adenoviral-mediated gene transfer of AC6 in human umbilical vein endothelial cells preferentially enhances prostacyclin receptor (versus other GPCR)-stimulated cAMP synthesis and, in parallel, inhibits thrombin-stimulated increases in endothelial cell barrier function. Using multiple strategies, including prostacyclin receptor-targeted small interfering RNA, we identify that the enhancement of endothelial barrier function by AC6 overexpression is dependent on an autocrine/paracrine feedback pathway involving the release of prostacyclin and activation of prostacyclin receptors. AC6 overexpression in endothelial cells may have use as a means to enhance prostacyclin function and reduce endothelial barrier permeability.

Increased cardiac adenylyl cyclase expression is associated with increased survival after myocardial infarction

BACKGROUND

Cardiac-directed expression of adenylyl cyclase type VI (AC(VI)) in mice results in structurally normal hearts with normal basal heart rate and function but increased responses to catecholamine stimulation. We tested the hypothesis that increased left ventricular (LV) AC(VI) content would increase mortality after acute myocardial infarction (MI).

METHODS AND RESULTS

Transgenic mice with cardiac-directed AC(VI) expression and their transgene-negative littermates (control) underwent coronary ligation, and survival, infarct size, and LV size and function were assessed 1 to 7 days after MI. Mice with increased AC(VI) expression had increased survival (control 41%, AC(VI) 74%; P = 0.004). Infarct size and myocardial apoptotic rates were similar in AC(VI) and control mice; however, AC(VI) mice had less LV dilation (P < 0.001) and increased ejection fractions (P < 0.03). Three days after MI, studies in isolated perfused hearts showed that basal LV +dP/dt was similar, but graded dobutamine infusion was associated with a more robust LV contractile response in AC(VI) mice (P < 0.05). Increased LV function was associated with increases in cAMP generation (P = 0.0002), phospholamban phosphorylation (P < 0.04), sarcoplasmic reticulum Ca2+-ATPase (SERCA2a) affinity for calcium (P < 0.015), and reduced AV block (P = 0.04).

CONCLUSIONS

In acute MI, increased cardiac AC(VI) content attenuates adverse LV remodeling, preserves LV contractile function, and reduces mortality.

Cardiac-directed expression of adenylyl cyclase VI facilitates atrioventricular nodal conduction

OBJECTIVES

The purpose of this study was to test the hypothesis that cardiac-directed expression of adenylyl cyclase VI (AC(VI)) facilitates atrioventricular (AV) nodal conduction.

BACKGROUND

Cardiac-directed expression of AC(VI), unlike other strategies to increase cyclic adenosine monophosphate generation, reduces mortality in murine cardiomyopathy. Recent reports suggest that AC(VI) expression may also protect against lethal bradycardia.

METHODS

We performed immunofluorescence staining for AC(VI) in the AV node of transgenic mice. We then performed electrophysiologic studies (EPSs) using a 1.7-F octapolar catheter at the AV junction in 11 transgenic AC(VI) mice and 14 control mice.

RESULTS

Immunofluorescence staining revealed increased AC(VI) expression in the AV node of transgenic mice versus controls. During EPS, AV intervals approximated PR intervals (R2 = 0.99) and related linearly to atrial-to-His intervals (R2 = 0.98; both p < 0.0001). Thus, we studied AV intervals to avoid electrocardiogram pacing artifacts and inconsistent inscription of His bundle electrograms. At baseline, AC(VI) mice had shorter AV intervals (47 +/- 9 ms) than controls (57 +/- 11 ms; p = 0.02), despite similar sinus rates. In pacing, AV intervals were shorter in AC(VI) mice than controls for a wide cycle-length range (p < 0.01). The AC(VI) mice also had shorter AV Wenckebach cycle lengths (AC(VI): 114 +/- 12 ms; control: 131 +/- 28 ms; p = 0.05) and ventriculo-atrial effective refractory periods (AC(VI): 97 +/- 21 ms; control: 127 +/- 15 ms; p = 0.05). We observed no differences between groups in sinus node function, and ventricular arrhythmias were not inducible.

CONCLUSIONS

Cardiac-directed expression of AC(VI) facilitates AV nodal conduction without altering sinus node function. These results suggest the need to define a role for AC(VI) gene transfer in treating diseases of AV conduction.

Molecular aspects of ischemic heart disease: ischemia/reperfusion-induced genetic changes and potential applications of gene and RNA interference therapy

Molecular biologic techniques have a variety of applications in the study of ischemic heart disease, including roles in elucidating cardiac genetic changes resulting from ischemia as well as in developing therapeutic interventions to treat ischemic heart disease. This review describes recent studies documenting genetic changes associated with myocardial ischemia and infarction as well as those investigating the safety and effectiveness of gene therapy for stimulating angiogenesis, protecting the heart against reperfusion injury, and treating heart failure. Also discussed are future research directions, including the potential use of RNA interference and combined stem cell therapy and gene therapy for the treatment of cardiovascular disease.

Gene therapy for heart failure

Congestive heart failure (CHF) remains a leading cause of morbidity and mortality in the United States and in many other countries. Current heart failure therapies, including multidrug treatment regimens, biventricular pacing, and mechanical support such as left ventricular assist devices, are often hindered by limited benefits or significant associated procedural complications or side effects. Therefore, new forms of treatment, which could ideally target the underlying biological processes affecting the ailing cardiomyocyte, would be of significant potential benefit to the population of individuals with CHF. Gene transfer strategies, including modification of cellular contractile signaling and regulatory pathways, represent a promising new form of such biologic therapy for heart disease.

Regulatory properties of adenylate cyclases type 5 and 6: A progress report

Adenylate cyclases (AC) type 5 and 6 comprise the calcium-inhibited family of adenylate cyclase isoforms. Here we review recent discoveries in the regulation of AC5 and AC6 with a focus on posttranslational modifications including glycosylation, nitrosylation, and phosphorylation by the cyclic AMP-dependent protein kinase (PKA), protein kinase C (PKC), and Raf1. We also describe novel signaling interactions such as Galpha(q)-mediated potentiation of AC6 activation. Novel regulators of AC5 and AC6, including small molecules and proteins that physically interact with AC5 and AC6 such as snapin, regulator of G protein signaling 2 (RGS2), protein associated with myc (PAM), and caveolin peptides are discussed. We also describe several recent studies that demonstrate the usefulness of transgenic or adenoviral overexpression of AC5 and AC6 in models for disease states such as cardiovascular hypertrophy. The discovery of novel regulatory mechanisms for AC5 and AC6 and their potential role in crucial physiological processes provide new avenues for research into therapeutic interventions targeting the cyclic AMP pathway.

Myocardial gene transfer and long-term expression following intracoronary delivery of adeno-associated virus

Adeno-associated viral vectors (AAV) can direct long-term gene expression in post-mitotic cells. Previous studies have established that long-term cardiac gene transfer results from intramuscular injection into the heart. Cardiac gene transfer after direct intracoronary delivery of AAV in vivo, however, has been minimal in degree, and indirect intracoronary delivery, an approach used in an increasing number of studies, appears to be receiving more attention. To determine the utility of indirect intracoronary gene transfer of AAV, we used aortic and pulmonary artery cross clamping followed by proximal aortic injection of AAV encoding enhanced green fluorescent protein (AAV.EGFP) at 10(11) DNase resistant particles (drp; high-performance liquid chromatography (HPLC)-purified) per rat. Gene expression was quantified by fluorescent microscopy at four time points up to 1 year after vector delivery, revealing 20-32% transmural gene expression in the left ventricle at each time point. Histological analysis revealed little or no inflammatory response and levels of transgene expression were low in liver and undetectable in lung. In subsequent studies in pigs, direct intracoronary delivery into the left circumflex coronary artery of AAV.EGFP (2.64-5.28 x 10(13) drp; HPLC-purified) resulted in gene expression in 3 of 4 pigs 8 weeks following injection with no inflammatory response in the heart. PCR analysis confirmed AAV vector presence in the left circumflex perfusion bed. These data indicate that intracoronary delivery of AAV vector is associated with transgene expression in the heart, providing a means to obtain long-term expression of therapeutic genes.

Adenylyl cyclase type V deletion increases basal left ventricular function and reduces left ventricular contractile responsiveness to beta-adrenergic stimulation

We tested the hypothesis that deletion of adenylyl cyclase type V (AC(V)) would be associated with decreased left ventricular (LV) contractile function and responsiveness to beta-adrenergic receptor (betaAR) stimulation. Absence of cardiac AC(V) expression was confirmed by RT-PCR and immunoblotting in AC(V)-deleted mice (AC(V) (-/-)). Compared to sibling mice with normal amounts of AC(V) (CON), basal and water-soluble forskolin derivative NKH477-stimulated cAMP production was reduced in both LV homogenates and in isolated cardiac myocytes. Basal LV +dP/dt (isolated perfused hearts) was increased (CON: 3,649 +/- 247 mmHg/s; AC(V) (-/-): 4,625 +/- 350 mmHg/s; p = 0.035, n = 10), but the potency of dobutamine on LV +dP/dt was decreased by AC(V) deletion (log EC(50): CON: -6.83 +/- 0.14 M; AC(V) (-/-): -5.99 +/- 0.15 M; p = 0.0007, n = 10). The initial rates of ATP-dependent sarcoplasmic reticulum calcium uptake, assessed in LV homogenates, showed that AC(V) deletion increased SERCA2a affinity for Ca(2+) (log EC(50): CON: -5.94 +/- 0.03 M; AC(V) (-/-): -6.09 +/- 0.02 M; p = 0.001, n = 8). AC(V) deletion is also associated with increased phospholamban phosphorylation, decreased type 1 protein phosphatase catalytic subunit content and activity, and reduced cardiac Galphas protein content. In conclusion, AC(V) deletion has a favorable effect on basal LV function despite reduced cAMP levels. Increased SERCA2a affinity for Ca(2+) and increased phospholamban phosphorylation are contributing factors. However, AC(V) deletion is associated with reduced LV contractile responsiveness to betaAR stimulation, an effect that is associated with reduced Galphas protein content and reduced cAMP generating capacity in cardiac myocytes.

Genetic therapies for cardiovascular diseases

Recent advances in understanding the molecular and cellular basis of cardiovascular diseases, together with the availability of tools for genetic manipulation of the cardiovascular system, offer possibilities for new treatments. Gene therapies have demonstrated potential usefulness for treating complex cardiovascular diseases, such as hypertension, atherosclerosis and myocardial ischemia, in various animal models. Some of these experimental therapies are now undergoing clinical evaluation in patients with cardiovascular disease. However, the successful transition of these therapies into mainstream clinical practice awaits further improvements to vector platforms and delivery tools and the documentation of clinical feasibility, safety and efficacy through multi-center randomized trials.

Gene therapy targeted at calcium handling as an approach to the treatment of heart failure

Chronic congestive heart failure primarily of ischemic origin remains a leading cause of morbidity and mortality in the United States and other leading countries. The current main stream of therapy is, however, palliative and uses a complex regimen of drugs, the actions of which are not understood completely. On the other hand, unfavorable remodeling after cardiac injuries of multiple causes has been thought to lead to cardiac contractile dysfunction in heart failure, and a body of scientific evidence points to a central role of intrinsic defects in intracellular calcium handling in cardiomyocytes that arise from the distorted functions of several key regulatory molecules on plasma membrane or sarcoplasmic reticulum (SR), a muscle-specific intracellular membrane complex that stores calcium at high concentration. Accordingly, the initial appetite to use gene transfer strategies to modulate calcium regulatory proteins was to validate molecular targets for the development of new pharmaceuticals; however, remarkable therapeutic efficacies found in an initial series of studies using various heart failure animal models immediately promoted us to seek ways to directly apply gene transfer to cure clinical heart failure. The first part of this article reviews our up-to-date knowledge of various functional components to regulate calcium handling in cardiomyocytes, including beta-adrenergic receptor, L-type calcium channel, ryanodine receptor (RyR) and its associated proteins, sarco-endoplasmic reticulum calcium ATPase (SERCA), and phospholamban (PLN), and their abnormalities in failing hearts. A series of new somatic gene transfer attempts targeting calcium handling in cardiomyocytes are discussed thereafter.

Adenylyl cyclase type VI corrects cardiac sarcoplasmic reticulum calcium uptake defects in cardiomyopathy

Calcium malfunction plays a central role in heart failure. Here, we provide evidence that adenylyl cyclase type VI restores sarco(endo)plasmic reticulum 2a (SERCA2a) affinity for calcium and maximum velocity of cardiac calcium uptake by sarcoplasmic reticulum in murine dilated cardiomyopathy. Restoration of normal SERCA2a affinity for calcium is associated not only with decreased phospholamban protein expression but also with increased phospholamban phosphorylation by PKA activation. The ratio of phosphorylated ryanodine receptor 2 (RyR2) to RyR2 protein was increased, but the amount of phosphorylated RyR2 was unaffected. These data provide a possible mechanism by which adenylyl cyclase type VI (in contrast to other signaling elements associated with increased cAMP generation) has a salutary effect in the failing heart.