Hongwei Jin

Reversal of Cardiac Dysfunction After Long-Term Expression of SERCA2a by Gene Transfer in a Pre-Clinical Model of Heart Failure

OBJECTIVES The aim of this study was to examine the effects of sarcoplasmic reticulum Ca(2+) ATPase (SERCA2a) gene transfer in a swine heart failure (HF) model. BACKGROUND Reduced expression and activity of SERCA2a have been documented in HF. Prior studies have reported the beneficial effects of short-term SERCA2a overexpression in rodent models. However, the effects of long-term expression of SERCA2a in pre-clinical large animal models are not known. METHODS Yorkshire-Landrace pigs were used (n = 16) to create volume overload by percutaneously severing chordae tendinae of the mitral apparatus with a bioptome to induce mitral regurgitation. At 2 months, pigs underwent intracoronary delivery of either recombinant adeno-associated virus type 1 (rAAV1) carrying SERCA2a under a cytomegalovirus promoter (rAAV1.SERCA2a) (n = 10; group 1) or saline (n = 6; group 2). RESULTS At 2 months, study animals were found to be in a compensated state of volume-overload HF (increased left ventricular internal diastolic and systolic diameters [LVIDd and LVIDs]). At 4 months, gene transfer resulted in: 1) positive left ventricular (LV) inotropic effects (adjusted peak left ventricular pressure rate of rise (dP/dt)max/P, 21.2 +/- 3.2 s(-1) group 1 vs. 15.5 +/- 3.0 s(-1) group 2; p < 0.01); 2) improvement in LV remodeling (% change in LVIDs -3.0 +/- 10% vs. +15 +/- 11%, respectively; p < 0.01). At follow-up, brain natriuretic peptide levels remained stable in group 1 after gene transfer, in contrast to rising levels in group 2. Further, cardiac SERCA2a expression was significantly decreased in group 2 whereas in group 1 it was restored to normal levels. There was no histopathological evidence of acute myocardial inflammation or necrosis. CONCLUSIONS Using a large-animal, volume-overload model of HF, we report that long-term overexpression of SERCA2a by in vivo rAAV1-mediated intracoronary gene transfer preserved systolic function, potentially prevented diastolic dysfunction, and improved ventricular remodeling.

Arrhythmia mechanisms in the failing heart

Background: Heart failure (HF) claims over 200,000 lives annually in the United States alone. Approximately 50% of these deaths are sudden and unexpected, and presumably the consequence of lethal ventricular tachyarrhythmias. Electrical remodeling that occurs at the cellular and tissue network levels predisposes patients with HF to malignant arrhythmias. Our limited understanding of fundamental arrhythmia mechanisms has hampered the development of effective treatment strategies for these patients.

Mechanoelectrical remodeling and arrhythmias during progression of hypertrophy

Despite a clear association between left ventricular (LV) mechanical dysfunction in end‐stage heart failure and the incidence of arrhythmias, the majority of sudden cardiac deaths occur at earlier stages of disease development. The mechanisms by which structural, mechanical, and molecular alterations predispose to arrhythmias at the tissue level before the onset of LV dysfunction remain unclear. In a rat model of pressure overload hypertrophy (PoH) produced by ascending aortic banding, we correlated mechanical and structural changes measured in vivo with key electrophysiological changes measured ex vivo in the same animals. We found that action potential prolongation, a hallmark of electrical remodeling at the tissue level, is highly correlated with changes in LV wall thickness but not mechanical function. In contrast, conduction delays are not predicted by either mechanical or structural changes during disease development. Moreover, disrupted Cx43 phosphorylation at intermediate (increased) and late (decreased) stages of PoH are associated with moderate and severe conduction delays, respectively. Interest‐ingly, the level of interaction between Cx43 and the cytoskeletal protein ZO‐1 is exclusively decreased at the late stage of PoH. Closely coupled action potentials consistent with afterdepolarization‐mediated triggered beats were readily observed in 6 of 15 PoH hearts but never in controls. Similarly, PoH (8/15) but not control hearts exhibited sustained episodes of ventricular tachycardia after rapid stimulation. The initiation and early maintenance of arrhythmias in PoH were formed by rapid and highly uniform activation wavefronts emanating from sites distal to the former site of stimulation. In conclusion, repolarization but not conduction delays are predicted by structural remodeling in PoH. Cx43 phosphorylation is disrupted at intermediate (increased) and late (decreased) stages, which are associated with conduction delays. Dephosphorylation of Cx43 is associated with loss of interaction with ZO‐1 and severe conduction delays. Remodeling at all stages of PoH predisposes to triggers and focal arrhythmias.—Jin, H., Chemaly, E. R., Lee, A., Kho, C., Hadri, L., Hajjar, R. J., Akar, F. G. Mechanoelectrical remodeling and arrhythmias during progression of hypertrophy. FASEBJ. 24, 451–463 (2010). www.fasebj.org

KChIP2 attenuates cardiac hypertrophy through regulation of Ito and intracellular calcium signaling

Recent evidence shows that the auxiliary subunit KChIP2, which assembles with pore-forming Kv4-subunits, represents a new potential regulator of the cardiac calcium-independent transient outward potassium current (I(to)) density. In hypertrophy and heart failure, KChIP2 expression has been found to be significantly decreased. Our aim was to examine the role of KChIP2 in cardiac hypertrophy and the effect of restoring its expression on electrical remodeling and cardiac mechanical function using a combination of molecular, biochemical and gene targeting approaches. KChIP2 overexpression through gene transfer of Ad.KChIP2 in neonatal cardiomyocytes resulted in a significant increase in I(to)-channel forming Kv4.2 and Kv4.3 protein levels. In vivo gene transfer of KChIP2 in aortic banded adult rats showed that, compared to sham-operated or Ad.beta-gal-transduced hearts, KChIP2 significantly attenuated the developed left ventricular hypertrophy, robustly increased I(to) densities, shortened action potential duration, and significantly altered myocyte mechanics by shortening contraction amplitudes and maximal rates of contraction and relaxation velocities and decreasing Ca(2+) transients. Interestingly, blocking I(to) with 4-aminopyridine in KChIP2-overexpressing adult cardiomyocytes significantly increased the Ca(2+) transients to control levels. One-day-old rat pups intracardially transduced with KChIP2 for two months then subjected to aortic banding for 6-8 weeks (to induce hypertrophy) showed similar echocardiographic, electrical and mechanical remodeling parameters. In addition, in cultured adult cardiomyocytes, KChIP2 overexpression increased the expression of Ca(2+)-ATPase (SERCA2a) and sodium calcium exchanger but had no effect on ryanodine receptor 2 or phospholamban expression. In neonatal myocytes, KChIP2 notably reversed Ang II-induced hypertrophic changes in protein synthesis and MAP-kinase activation. It also significantly decreased calcineurin expression, NFATc1 expression and nuclear translocation and its downstream target, MCiP1.4. Altogether, these data show that KChIP2 can attenuate cardiac hypertrophy possibly through modulation of intracellular calcium concentration and calcineurin/NFAT pathway.

Altered Spatiotemporal Dynamics of the Mitochondrial Membrane Potential in the Hypertrophied Heart

Chronically elevated levels of oxidative stress resulting from increased production and/or impaired scavenging of reactive oxygen species are a hallmark of mitochondrial dysfunction in left ventricular hypertrophy. Recently, oscillations of the mitochondrial membrane potential (DeltaPsi(m)) were mechanistically linked to changes in cellular excitability under conditions of acute oxidative stress produced by laser-induced photooxidation of cardiac myocytes in vitro. Here, we investigate the spatiotemporal dynamics of DeltaPsi(m) within the intact heart during ischemia-reperfusion injury. We hypothesize that altered metabolic properties in left ventricular hypertrophy modulate DeltaPsi(m) spatiotemporal properties and arrhythmia propensity.

Mechanical work and energetic analysis of eccentric cardiac remodeling in a volume overload heart failure in rats

Eccentric cardiac remodeling seen in dilated cardiomyopathy or regurgitant valvular disease is a well-known process of heart failure progression, but its mechanoenergetic profile has not been yet established. We made a volume overload (VO) heart failure model in rats and for the first time investigated left ventricular (LV) mechanical work and energetics in cross-circulated whole heart preparations. Laparotomy was performed in 14 Wistar male rats, and abdominal aortic-inferior vena caval shunt was created in seven rats (VO group). Another seven rats underwent a sham operation without functional shunt (Sham group). LV dimensions changes were followed with weekly transthoracic echocardiography. Three months after surgery, we measured LV pressure and volume and myocardial O(2) consumption in isolated heart cross circulation. LV internal dimensions in both systolic and diastolic phases were significantly increased in the VO group versus the Sham group (P < 0.05). LV pressure was markedly decreased in the VO group versus in the Sham group (P < 0.05). LV end-systolic pressure-volume relation shifted downward, and myocardial O(2) consumption related to Ca(2+) handling significantly decreased. The contractile response to Ca(2+) infusion was attenuated. Nevertheless, the increase in Ca(2+) handling-related O(2) consumption per unit change in LV contractility in the VO group was significantly higher than that in the Sham group (P < 0.05). The levels of sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a protein were reduced in the VO group (P < 0.01). In conclusion, VO failing rat hearts had a character of marked contractile dysfunction accompanied with less efficient energy utilization in the Ca(2+) handling processes. These results suggest that restoring Ca(2+) handling in excitation-contraction coupling would improve the contractility of the myocardium after eccentric cardiac remodeling.