Desmin modifications associate with amyloid-like oligomers deposition in heart failure.

AIMS: The ultimate cause of heart failure (HF) is not known to date. The cytoskeletal protein desmin is differentially modified and forms amyloid-like oligomers in HF. We postulated that desmin post-translational modifications (PTMs) could drive aberrant desmin aggregation in HF. Therefore, we identified these PTMs and investigated their impact on desmin amyloidogenicity in human and experimental HF. METHODS AND RESULTS: We detected increased levels of selectively phosphorylated and cleaved desmin in a canine pacing model of dyssynchronous HF (DHF) compared with either controls or animals treated with cardiac resynchronization therapy (CRT). This unique animal model combines clinically relevant features with the possibility of a partly rescued phenotype. We confirmed analogous changes in desmin modifications in human HF and identified two phosphorylation sites within a glycogen synthase kinase 3 (GSK3) consensus sequence. Desmin-positive oligomers were also increased in DHF hearts compared with controls. Their amyloid properties were decreased by treatment with CRT or an anti-amyloid small molecule. Finally, we confirmed GSK3's involvement with desmin phosphorylation using an in vitro model. CONCLUSIONS: Based on these findings, we postulate a new mechanism of cardiac toxicity based on the PTM-driven accumulation of desmin amyloid-like oligomers. Phosphorylation and cleavage as well as oligomers formation are reduced by treatment (CRT) indicating a relationship between the three. Finally, the decrease of desmin amyloid-like oligomers with CRT or small molecules points both to a general mechanism of HF based on desmin toxicity that is independent of protein mutations and to novel potential therapies.

Ultrastructure and regulation of lateralized connexin43 in the failing heart.

RATIONALE: Gap junctions mediate cell-to-cell electric coupling of cardiomyocytes. The primary gap junction protein in the working myocardium, connexin43 (Cx43), exhibits increased localization at the lateral membranes of cardiomyocytes in a variety of heart diseases, although the precise location and function of this population is unknown. OBJECTIVE: To define the subcellular location of lateralized gap junctions at the light and electron microscopic level, and further characterize the biochemical regulation of gap junction turnover. METHODS AND RESULTS: By electron microscopy, we characterized gap junctions formed between cardiomyocyte lateral membranes in failing canine ventricular myocardium. These gap junctions were varied in structure and appeared to be extensively internalizing. Internalized gap junctions were incorporated into multilamellar membrane structures, with features characteristic of autophagosomes. Intracellular Cx43 extensively colocalized with the autophagosome marker GFP-LC3 when both proteins were exogenously expressed in HeLa cells, and endogenous Cx43 colocalized with GFP-LC3 in neonatal rat ventricular myocytes. Furthermore, a distinct phosphorylated form of Cx43, as well as the autophagosome-targeted form of LC3 (microtubule-associated protein light chain 3) targeted to lipid rafts in cardiac tissue, and both were increased in heart failure. CONCLUSIONS: Our data demonstrate a previously unrecognized pathway of gap junction internalization and degradation in the heart and identify a cellular pathway with potential therapeutic implications.

Cardiac resynchronization therapy corrects dyssynchrony-induced regional gene expression changes on a genomic level.

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.

Calcium-mediated dual-mode regulation of cardiac sodium channel gating.

Intracellular Ca(2+) ([Ca(2+)](i)) can trigger dual-mode regulation of the voltage gated cardiac sodium channel (Na(V)1.5). The channel components of the Ca(2+) regulatory system are the calmodulin (CaM)-binding IQ motif and the Ca(2+) sensing EF hand-like (EFL) motif in the carboxyl terminus of the channel. Mutations in either motif have been associated with arrhythmogenic changes in expressed Na(V)1.5 currents. Increases in [Ca(2+)](i) shift the steady-state inactivation of Na(V)1.5 in the depolarizing direction and slow entry into inactivated states. Mutation of the EFL (Na(V)1.5(4X)) shifts inactivation in the hyperpolarizing direction compared with the wild-type channel and eliminates the Ca(2+) sensitivity of inactivation gating. Modulation of the steady-state availability of Na(V)1.5 by [Ca(2+)](i) is more pronounced after the truncation of the carboxyl terminus proximal to the IQ motif (Na(V)1.5(Delta1885)), which retains the EFL. Mutating the EFL (Na(V)1.5(4X)) unmasks CaM-mediated regulation of the kinetics and voltage dependence of inactivation. This latent CaM modulation of inactivation is eliminated by mutation of the IQ motif (Na(V)1.5(4X-IQ/AA)). The LQT3 EFL mutant channel Na(V)1.5(D1790G) exhibits Ca(2+) insensitivity and unmasking of CaM regulation of inactivation gating. The enhanced effect of CaM on Na(V)1.5(4X) gating is associated with significantly greater fluorescence resonance energy transfer between enhanced cyan fluorescent protein-CaM and Na(V)1.5(4X) channels than is observed with wild-type Na(V)1.5. Unlike other isoforms of the Na channel, the IQ-CaM interaction in the carboxyl terminus of Na(V)1.5 is latent under physiological conditions but may become manifest in the presence of disease causing mutations in the CT of Na(V)1.5 (particularly in the EFL), contributing to the production of potentially lethal ventricular arrhythmias.

Calmodulin regulation of Nav1.4 current: role of binding to the carboxyl terminus.

Calmodulin (CaM) regulates steady-state inactivation of sodium currents (Na(V)1.4) in skeletal muscle. Defects in Na current inactivation are associated with pathological muscle conditions such as myotonia and paralysis. The mechanisms of CaM modulation of expression and function of the Na channel are incompletely understood. A physical association between CaM and the intact C terminus of Na(V)1.4 has not previously been demonstrated. FRET reveals channel conformation-independent association of CaM with the C terminus of Na(V)1.4 (CT-Na(V)1.4) in mammalian cells. Mutation of the Na(V)1.4 CaM-binding IQ motif (Na(V)1.4(IQ/AA)) reduces cell surface expression of Na(V)1.4 channels and eliminates CaM modulation of gating. Truncations of the CT that include the IQ region abolish Na current. Na(V)1.4 channels with one CaM fused to the CT by variable length glycine linkers exhibit CaM modulation of gating only with linker lengths that allowed CaM to reach IQ region. Thus one CaM is sufficient to modulate Na current, and CaM acts as an ancillary subunit of Na(V)1.4 channels that binds to the CT in a conformation-independent fashion, modulating the voltage dependence of inactivation and facilitating trafficking to the surface membrane.

Transcriptomic profiling of the canine tachycardia-induced heart failure model: global comparison to human and murine heart failure.

Alterations of cardiac gene expression are central to ventricular dysfunction in human heart failure (HF). The canine tachycardia pacing-induced HF model is known to reproduce the main hemodynamic, echocardiographic and electrophysiological changes observed in human HF. In this study, we use this HF model to compare gene expression profiles in the left and right ventricles (LV, RV) of normal and end-stage failing canine hearts and compare the transcription profiles to those in human and murine models of HF. In end-stage HF, the LV exhibits down regulation of genes involved in energy production, cardiac contraction, and modulation of excitation-contraction coupling as compared with normal LV. The majority of transcriptomic changes between normal and end-stage canine HF were shared by the RV and LV. Genes down regulated only in the LV included those involved in aerobic energy production pathways, regulation of actin filament length, and enzyme-linked receptor protein signaling pathways. In normal canine hearts, genes encoding specific components of the contractile apparatus exhibit LV-RV asymmetric expression patterns; in failing hearts, cardiac fetal transcription factors MEF2 and MITF and the stress-responsive transcription factor ATF4 showed interventricular differences in expression. The comparison among the canine tachypacing, mouse transgenic, and human HF reveals that human disease involves down regulation of genes in a broad range of biological processes while experimentally induced HF is associated with down regulation of energy pathways, and that human ischemic HF and canine HF share a similar over representation of transcriptional pathways in the up regulated genes. This study provides insights into the molecular pathways leading to end-stage tachycardia-induced HF, and into global transcriptomic differences between the animal HF models and human HF.

Molecular correlates of altered expression of potassium currents in failing rabbit myocardium.

Action potential (AP) prolongation is a hallmark of failing myocardium. Functional downregulation of K currents is a prominent feature of cells isolated from failing ventricles. The detailed changes in K current expression differ depending on the species, the region of the heart, and the mechanism of induction of heart failure. We used complementary approaches to study K current downregulation in pacing tachycardia-induced heart failure in the rabbit. The AP duration (APD) at 90% repolarization was significantly longer in cells isolated from failing hearts compared with controls (539 +/- 162 failing vs. 394 +/- 114 control, P < 0.05). The major K currents in the rabbit heart, inward rectifier potassium current (I(K1)), transient outward (I(to)), and delayed rectifier current (I(K)) were functionally downregulated in cells isolated from failing ventricles. The mRNA levels of Kv4.2, Kv1.4, KChIP2, and Kir2.1 were significantly downregulated, whereas the Kv4.3, Erg, KvLQT1, and minK were unaltered in the failing ventricles compared with the control left ventricles. Significant downregulation in the long splice variant of Kv4.3, but not in the total Kv4.3, Kv4.2, and KChIP2 immunoreactive protein, was observed in cells isolated from the failing ventricle with no change in Kv1.4, KvLQT1, and in Kir2.1 immunoreactive protein levels. Multiple cellular and molecular mechanisms underlie the downregulation of K currents in the failing rabbit ventricle.

Gene expression profiles in end-stage human idiopathic dilated cardiomyopathy: altered expression of apoptotic and cytoskeletal genes.

Dilated cardiomyopathy is now the leading cause of cardiovascular morbidity and mortality. While the molecular basis of this disease remains uncertain, evidence is emerging that gene expression profiles of left ventricular myocardium isolated from failing versus nonfailing patients differ dramatically. In this study, we use high-density oligonucleotide microarrays with approximately 22000 probes to characterize differences in the expression profiles further. To facilitate interpretation of experimental data, we evaluate algorithms for normalization of hybridization data and for computation of gene expression indices using a control spike-in data set. We then use these methods to identify statistically significant changes in the expression levels of genes not previously implicated in the molecular phenotype of heart failure. These regulated genes take part in diverse cellular processes, including transcription, apoptosis, sarcomeric and cytoskeletal function, remodeling of the extracellular matrix, membrane transport, and metabolism.