Voltage Gated Calcium Channel Dysregulation May Contribute to Neurological Symptoms in Calmodulinopathies.

Calmodulinopathies are caused by mutations in calmodulin (CaM), and result in debilitating cardiac arrythmias such as long-QT syndrome (LQTS) and catecholaminergic polymorphic ventricular tachycardia (CPVT). In addition, many patients exhibit neurological comorbidities, including developmental delay and autism spectrum disorder. Until now, most work into these mutations has focused on cardiac effects, identifying impairment of Ca /CaM-dependent inactivation (CDI) of Ca 1.

Impaired Ca1.2 inactivation reduces the efficacy of calcium channel blockers in the treatment of LQT8.

Mutations in the Ca1.2 L-type calcium channel can cause a profound form of long-QT syndrome known as long-QT type 8 (LQT8), which results in cardiac arrhythmias that are often fatal in early childhood. A growing number of such pathogenic mutations in Ca1.

Fibroblast growth factor homologous factors serve as a molecular rheostat in tuning arrhythmogenic cardiac late sodium current.

Voltage-gated sodium (Nav1.5) channels support the genesis and brisk spatial propagation of action potentials in the heart. Disruption of Na1.

Altered Electrical, Biomolecular, and Immunologic Phenotypes in a Novel Patient-Derived Stem Cell Model of Desmoglein-2 Mutant ARVC.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a progressive heart condition which causes fibro-fatty myocardial scarring, ventricular arrhythmias, and sudden cardiac death. Most cases of ARVC can be linked to pathogenic mutations in the cardiac desmosome, but the pathophysiology is not well understood, particularly in early phases when arrhythmias can develop prior to structural changes. Here, we created a novel human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) model of ARVC from a patient with a c.

Infanticide vs. inherited cardiac arrhythmias.

Aims: In 2003, an Australian woman was convicted by a jury of smothering and killing her four children over a 10-year period. Each child died suddenly and unexpectedly during a sleep period, at ages ranging from 19 days to 18 months. In 2019 we were asked to investigate if a genetic cause could explain the children's deaths as part of an inquiry into the mother's convictions.

Enhancement of human iPSC-derived cardiomyocyte maturation by chemical conditioning in a 3D environment.

Recent advances in the understanding and use of pluripotent stem cells have produced major changes in approaches to the diagnosis and treatment of human disease. An obstacle to the use of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for regenerative medicine, disease modeling and drug discovery is their immature state relative to adult myocardium. We show the effects of a combination of biochemical factors, thyroid hormone, dexamethasone, and insulin-like growth factor-1 (TDI) on the maturation of hiPSC-CMs in 3D cardiac microtissues (CMTs) that recapitulate aspects of the native myocardium.

A Net Mold-Based Method of Biomaterial-Free Three-Dimensional Cardiac Tissue Creation.

Ischemic cardiomyopathy poses a significant public health burden due to the irreversible loss of functional cardiac tissue. Alternative treatment strategies include creation of three-dimensional (3D) cardiac tissues to both replace and augment injured native tissue. In this study, we utilize a net mold-based method to create a biomaterial-free 3D cardiac tissue and compare it to current methods using biomaterials.

Creation of Cardiac Tissue Exhibiting Mechanical Integration of Spheroids Using 3D Bioprinting.

This protocol describes 3D bioprinting of cardiac tissue without the use of biomaterials, using only cells. Cardiomyocytes, endothelial cells and fibroblasts are first isolated, counted and mixed at desired cell ratios. They are co-cultured in individual wells in ultra-low attachment 96-well plates.

Biomaterial-Free Three-Dimensional Bioprinting of Cardiac Tissue using Human Induced Pluripotent Stem Cell Derived Cardiomyocytes.

We have developed a novel method to deliver stem cells using 3D bioprinted cardiac patches, free of biomaterials. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), fibroblasts (FB) and endothelial cells (EC) were aggregated to create mixed cell spheroids. Cardiac patches were created from spheroids (CM:FB:EC = 70:15:15, 70:0:30, 45:40:15) using a 3D bioprinter.

A Precision Medicine Approach to the Rescue of Function on Malignant Calmodulinopathic Long-QT Syndrome.

Rationale: Calmodulinopathies comprise a new category of potentially life-threatening genetic arrhythmia syndromes capable of producing severe long-QT syndrome (LQTS) with mutations involving CALM1, CALM2, or CALM3. The underlying basis of this form of LQTS is a disruption of Ca/calmodulin (CaM)-dependent inactivation of L-type Ca channels.

Objective: To gain insight into the mechanistic underpinnings of calmodulinopathies and devise new therapeutic strategies for the treatment of this form of LQTS.

Mechanisms of a human skeletal myotonia produced by mutation in the C-terminus of NaV1.4: is Ca2+ regulation defective?

Mutations in the cytoplasmic tail (CT) of voltage gated sodium channels cause a spectrum of inherited diseases of cellular excitability, yet to date only one mutation in the CT of the human skeletal muscle voltage gated sodium channel (hNaV1.4F1705I) has been linked to cold aggravated myotonia. The functional effects of altered regulation of hNaV1.

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).

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.

Key pathways associated with heart failure development revealed by gene networks correlated with cardiac remodeling.

Heart failure (HF) is the leading cause of morbidity and mortality in the industrialized world. While the transcriptomic changes in end-stage failing myocardium have received much attention, no information is available on the gene expression patterns associated with the development of HF in large mammals. Therefore, we used a well-controlled canine model of tachycardia-induced HF to examine global gene expression in left ventricular myocardium with Affymetrix canine oligonucleotide arrays at various stages after initiation of rapid ventricular pacing (days 3, 7, 14, and 21).

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.

Dynamic changes in conduction velocity and gap junction properties during development of pacing-induced heart failure.

End-stage heart failure (HF) is characterized by changes in conduction velocity (CV) that predispose to arrhythmias. Here, we investigate the time course of conduction changes with respect to alterations in connexin 43 (Cx43) properties and mechanical function during the development of HF. We perform high-resolution optical mapping in arterially perfused myocardial preparations from dogs subjected to 0, 3, 7, 14, and 21 days of rapid pacing to produce variable degrees of remodeling.

A conserved ring of charge in mammalian Na+ channels: a molecular regulator of the outer pore conformation during slow inactivation.

The molecular mechanisms underlying slow inactivation in sodium channels are elusive. Our results suggest that EEDD, a highly conserved ring of charge in the external vestibule of mammalian voltage-gated sodium channels, undermines slow inactivation. By employing site-directed mutagenesis, we found that charge alterations in this asymmetric yet strong local electrostatic field of the EEDD ring significantly altered the kinetics of slow inactivation gating.

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.

Transmural heterogeneity of Na+-Ca2+ exchange: evidence for differential expression in normal and failing hearts.

Spatial electrical heterogeneity has a profound effect on normal cardiac electrophysiology and genesis of cardiac arrhythmias in diseased hearts. The Na+-Ca2+ exchanger (NCX) is a key linker, through Ca2+ signaling, between contractility and arrhythmias. Here we characterize the differential transmural expression of NCX in normal and rapid pacing-induced failing canine hearts.

Molecular mechanisms underlying K+ current downregulation in canine tachycardia-induced heart failure.

Heart failure (HF) is characterized by marked prolongation of action potential duration and reduction in cellular repolarization reserve. These changes are caused in large part by HF-induced K(+) current downregulation. Molecular mechanisms underlying these changes remain unclear.

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.

Regional alterations in protein expression in the dyssynchronous failing heart.

Background: Left ventricular (LV) mechanical dyssynchrony induces regional heterogeneity of mechanical load and is an independent predictor of mortality and sudden death in heart failure (HF) patients. We tested whether dyssynchrony also induces localized disparities in the expression of proteins involved with mechanical stress, function, and arrhythmia susceptibility.

Methods And Results: Eleven dogs underwent tachycardia-induced HF pacing, either from the right atrium or high right ventricular free wall.

Regulation of Kv4.3 current by KChIP2 splice variants: a component of native cardiac I(to)?

Background: The transient outward potassium current (I(to)) encoded by the Kv4 family of potassium channels is important in the repolarization of cardiac myocytes. KChIPs are a recently identified group of Ca2+-binding accessory subunits that modulate Kv4-encoded currents. KChIP2 is the only family member expressed in the heart.

Isoform-specific modulation of voltage-gated Na(+) channels by calmodulin.

Calmodulin (CaM) is a calcium-sensing protein that binds to Na(+) channels, with unknown functional consequences. Wild-type CaM produced a hyperpolarizing shift in the steady-state availability of expressed skeletal muscle (micro1) but not cardiac (hH1) Na(+) channels. Mutant CaM(1234) did not alter the voltage dependence or the kinetics of gating of either micro1 or hH1.