Faculty Bibliography

In the heart, voltage-gated sodium (Nav) channel (Nav1.5) is defined by its pore-forming alpha-subunit and its auxiliary beta-subunits, both of which are important for its critical contribution to the initiation and maintenance of the cardiac action potential (AP) that underlie normal heart rhythm. The physiological relevance of Nav1.5 is further marked by the fact that inherited or congenital mutations in Nav1.5 channel gene SCN5A lead to altered functional expression (including expression, trafficking, and current density), and are generally manifested in the form of distinct cardiac arrhythmic events, epilepsy, neuropathic pain, migraine, and neuromuscular disorders. However, despite significant advances in defining the pathophysiology of Nav1.5, the molecular mechanisms that underlie its regulation and contribution to cardiac disorders are poorly understood. It is rapidly becoming evident that the functional expression (localization, trafficking and gating) of Nav1.5 may be under modulation by post-translational modifications that are associated with phosphorylation. We review here the molecular basis of cardiac Na channel regulation by kinases (PKA and PKC) and the resulting functional consequences. Specifically, we discuss: (1) recent literature on the structural, molecular, and functional properties of cardiac Nav1.5 channels; (2) how these properties may be altered by phosphorylation in disease states underlain by congenital mutations in Nav1.5 channel and/or subunits such as long QT and Brugada syndromes. Our expectation is that understanding the roles of these distinct and complex phosphorylation processes on the functional expression of Nav1.5 is likely to provide crucial mechanistic insights into Na channel associated arrhythmogenic events and will facilitate the development of novel therapeutic strategies.

Sudden cardiac death (SCD) accounts for approximately 360,000 deaths annually in the United States. Ischemic heart disease is the major cause of death in the general adult population. SCD can be due to arrhythmic or nonarrhythmic cardiac causes. Arrhythmic SCD may be caused by ventricular tachyarrhythmia or pulseless electrical activity/asystole. This article reviews the most recent pathophysiology and risk stratification strategies for SCD, emphasizing electrophysiologic surrogates of conduction disorder, dispersion of repolarization, and autonomic imbalance. Factors that modify arrhythmic death are addressed.

OBJECTIVE: Increasing evidence indicates systemic inflammation as a new potential cause of acquired long QT syndrome (LQTS), via cytokine-mediated changes in cardiomyocyte ion channels. Torsade de pointes (TdP) is a life-threatening polymorphic ventricular tachycardia occurring in patients with LQTS, usually when multiple QT-prolonging factors are simultaneously present. Since classical risk factors cannot fully explain TdP events in a number of patients, we hypothesised that systemic inflammation may represent a currently overlooked risk factor contributing to TdP development in the general population. METHODS: Forty consecutive patients who experienced TdP (TdP cohort) were consecutively enrolled and circulating levels of C-reactive protein (CRP) and proinflammatory cytokines (interleukin-6 (IL-6),tumour necrosis factor alpha (TNFalpha), interleukin-1 (IL-1)) were compared with patients with active rheumatoid arthritis (RA), comorbidity or healthy controls. An additional 46 patients with different inflammatory conditions (acute infections, n=31; immune-mediated diseases, n=12; others, n=3) and elevated CRP (inflammatory cohort) were prospectively enrolled, and corrected QT (QTc) and cytokine levels were measured during active disease and after a CRP decrease of >75% subsequent to therapy. RESULTS: In the TdP cohort, 80% of patients showed elevated CRP levels (median: ~3 mg/dL), with a definite inflammatory disease identifiable in 18/40 cases (acute infections, n=12; immune-mediated diseases, n=5; others, n=1). In these subjects, IL-6, but not TNFalpha and IL-1, was ~15-20 times higher than in controls, and comparable to RA patients. In the inflammatory cohort, where QTc prolongation was common (mean values: 456.6+/-30.9 ms), CRP reduction was associated with IL-6 level decrease and significant QTc shortening (-22.3 ms). CONCLUSION: The data are first to show that systemic inflammation via elevated IL-6 levels may represent a novel QT-prolonging risk factor contributing to TdP occurrence in the presence of other classical risk factors. If confirmed, this could open new avenues in antiarrhythmic therapy.

Since its initial description by Jervell and Lange-Nielsen in 1957, the congenital long QT syndrome (LQTS) has been the most investigated cardiac ion channelopathy. A prolonged QT interval in the surface electrocardiogram is the sine qua non of the LQTS and is a surrogate measure of the ventricular action potential duration (APD). Congenital as well as acquired alterations in certain cardiac ion channels can affect their currents in such a way as to increase the APD and hence the QT interval. The inhomogeneous lengthening of the APD across the ventricular wall results in dispersion of APD. This together with the tendency of prolonged APD to be associated with oscillations at the plateau level, termed early afterdepolarizations (EADs), provides the substrate of ventricular tachyarrhythmia associated with LQTS, usually referred to as torsade de pointes (TdP) VT. This review will discuss the genetic, molecular, and phenotype characteristics of congenital LQTS as well as current management strategies and future directions in the field.

Chronic diseases are the primary cause of mortality worldwide, accounting for 67% of deaths. One of the major challenges in developing new treatments is the lack of understanding of the exact underlying biological and molecular mechanisms. Chronic cardiovascular diseases are the single most common cause of death worldwide, and sudden deaths due to cardiac arrhythmias account for approximately 50% of all such cases. Traditional genetic screening for genes involved in cardiac disorders is labourious and frequently fails to detect the mutation that explains or causes the disorder. However, when mutations are identified, human induced pluripotent stem cells (hiPSCs) derived from affected patients make it possible to address fundamental research questions directly relevant to human health. As such, hiPSC technology has recently been used to model human diseases and patient-specific hiPSC-derived cardiomyocytes (hiPSC-CMs) thus offer a unique opportunity to investigate potential disease-causing genetic variants in their natural environment. The purpose of this review is to present the current state of knowledge regarding hiPSC-CMs, including their potential, limitations, and challenges and to discuss future prospects.

Cardiac arrhythmias confer a considerable burden of morbidity and mortality in industrialized countries. Although coronary artery disease and heart failure are the prevalent causes of cardiac arrest, in 5-15% of patients, structural abnormalities at autopsy are absent. In a proportion of these patients, mutations in genes encoding cardiac ion channels are documented (inherited channelopathies), but, to date, the molecular autopsy is negative in nearly 70% of patients. Emerging evidence indicates that autoimmunity is involved in the pathogenesis of cardiac arrhythmias. In particular, several arrhythmogenic autoantibodies targeting specific calcium, potassium, or sodium channels in the heart have been identified. Experimental and clinical studies demonstrate that these autoantibodies can promote conduction disturbances and life-threatening tachyarrhythmias by inducing substantial electrophysiological changes. In this Review, we propose the term 'autoimmune cardiac channelopathies' to define this novel pathogenic mechanism of cardiac arrhythmias, which could be more frequent and clinically relevant than previously appreciated. Indeed, pathogenic autoantibodies against ion channels are detectable not only in patients with manifest autoimmune disease, but also in apparently healthy individuals, which suggests a causal role in some cases of unexplained arrhythmias and cardiac arrest. Considering this possibility and performing specific testing in patients with 'idiopathic' rhythm disturbances could create novel treatment opportunities.

BACKGROUND:The ability to differentiate patient-specific human induced pluripotent stem cells in cardiac myocytes (hiPSC-CM) offers novel perspectives for cardiovascular research. A number of studies, that reported mainly on current-voltage curves used hiPSC-CM to model voltage-gated Na+ channel (Nav) dysfunction. However, the expression patterns and precise biophysical and pharmacological properties of Nav channels from hiPSC-CM remain unknown. Our objective was to study the characteristics of Nav channels from hiPSC-CM and assess the appropriateness of this novel cell model. METHODS:We generated hiPSC-CM using the recently described monolayer-based differentiation protocol. RESULTS:hiPSC-CM expressed cardiac-specific markers, exhibited spontaneous electrical and contractile activities, and expressed distinct Nav channels subtypes. Electrophysiological, pharmacological, and molecular characterizations revealed that, in addition to the main Nav1.5 channel, the neuronal tetrodotoxin (TTX)-sensitive Nav1.7 channel was also significantly expressed in hiPSC-CM. Most of the Na+ currents were resistant to TTX block. Therapeutic concentrations of lidocaine, a class I antiarrhythmic drug, also inhibited Na+ currents in a use-dependent manner. Nav1.5 and Nav1.7 expression and maturation patterns of hiPSC-CM and native human cardiac tissues appeared to be similar. The 4 Navβ regulatory subunits were expressed in hiPSC-CM, with β3 being the preponderant subtype. CONCLUSIONS:The findings indicated that hiPSC-CM robustly express Nav1.5 channels, which exhibited molecular and pharmacological properties similar to those in native cardiac tissues. Interestingly, neuronal Nav1.7 channels were also expressed in hiPSC-CM and are likely to be responsible for the TTX-sensitive Nav current.

Ca entry through atrial L-type Calcium channels (alpha1C and alpha1D) play an important role in muscular contraction, regulation of gene expression, and release of hormones including atrial natriuretic peptide (ANP), and brain natriuretic peptide (BNP). alpha1D Ca channel is exclusively expressed in atria, and has been shown to play a key role in the pathogenesis of atrial fibrillation. Recent data have shown that the small conductance calcium-activated potassium channel, SK4 is also atrial specific and also contributes prominently to the secretion of ANP and BNP. However, its functional role in the heart is still poorly understood. Here we used alpha1D gene heterozygous (alpha1D+/-) mice and HL-1 cells to determine the functional contribution of SK4 channels to alpha1D-dependent regulation of ANP and BNP secretion in response to endothelin (ET), and/or mechanical stretch. Immunoprecipitation with alpha1D specific antibody and western blotting with SK4 specific antibody on the immuno-precipitated protein complex showed a band at 50 KDa confirming the presence of SK4 in the complex and provided evidence of interaction between SK4 and alpha1D channels. Using RT-PCR, we observed a 2.9 fold decrease in expression of Cacna1d (gene encoding alpha1D) mRNA in atria from alpha1D+/-mice. The decrease in alpha1D mRNA corresponded with a 4.2 fold decrease in Kcnn4 (gene encoding SK4) mRNA from alpha1D+/- mice. These changes were paralleled with a 77% decrease in BNP serum levels from alpha1D+/- mice. When alpha1D was knocked down in HL-1cardiomyocytes using CRISPR/Cas9 technology, a 97% decrease in secreted BNP was observed even in cells subjected to stretch and endothelin. In conclusion, our data are first to show that alpha1D Ca and SK4 channels are coupled in the atria, and that deletion of alpha1D leads to decreased SK4 mRNA and BNP secretion providing evidence for a novel role of alpha1D in atrial endocrine function. Elucidating the regulatory factors that underlie the secretory function of atria will identify novel therapeutic targets for treatment and prevention of cardiac arrhythmias such as atrial fibrillation.

OBJECTIVES: To reduce respondent burden for future evaluations of the National Heart, Lung, and Blood Institute-supported Programs to Increase Diversity Among Individuals Engaged in Health-Related Research (PRIDE), a mentored-research education program, we sought to shorten the 33-item Ragins and McFarlin Mentor Role Instrument (RMMRI), measuring mentor-role appraisals, and the 69-item Clinical Research Appraisal Inventory (CRAI), measuring research self-efficacy. METHODS: Three nationally recruited, junior-faculty cohorts attended two, annual 2-3 week Summer Institutes (SI-1/SI-2: 2011/2012, 2012/2013, 2013/2014) at one of six PRIDE sites. Mentees completed the RMMRI two months after mentor assignment and the CRAI at baseline (pre-SI-1) and 6-month (mid-year) and 12-month (post-SI-2) follow-up. Publications data obtained from Scopus in October 2015 were verified with mentees' curriculum vitae. The RMMRI and CRAI were shortened using an iterative process of principal-components analysis. The shortened measures were examined in association with each other (multiple linear regression) and with increase in publications (repeated-measures analysis of covariance). RESULTS: PRIDE enrolled 152 mentees (70% women; 60% Black, 35% Hispanic/Latino). Cronbach's alphas for the new 9-item RMMRI, 19-item CRAI, and four CRAI-19 subscales were excellent. Controlling for baseline self-efficacy and cohort, RMMRI-9 scores were independently, positively associated with post-SI-2 scores on the CRAI-19 and three subscales (writing, study design/data analysis, and collaboration/grant preparation). Controlling for cohort, higher RMMRI-9 and post-SI-2 CRAI-19 scores were each associated with greater increase in publications. CONCLUSIONS: The RMMRI-9 and CRAI-19 retained the excellent psychometric properties of the longer measures. Findings support use of the shortened measures in future evaluations of PRIDE.