Increased proinflammatory interleukin-6 (IL-6) levels are associated with acquired long QT-syndrome (LQTS) in patients with systemic inflammation, leading to higher risks for life-threatening ...polymorphic ventricular tachycardia such as Torsades de Pointes. However, the functional and molecular mechanisms of this association are not known. In most cases of acquired LQTS, the target ion channel is the human ether-á-go-go-related gene (hERG) encoding the rapid component of the delayed rectifier K current, IKr, which plays a critical role in cardiac repolarization. Here, we tested the hypothesis that IL-6 may cause QT prolongation by suppressing IKr. Electrophysiological and biochemical assays were used to assess the impact of IL-6 on the functional expression of IKr in HEK293 cells and adult guinea-pig ventricular myocytes (AGPVM). In HEK293 cells, IL-6 alone or in combination with the soluble IL-6 receptor (IL-6R), produced a significant depression of IKr peak and tail current densities. Block of IL-6R or Janus kinase (JAK) reversed the inhibitory effects of IL-6 on IKr. In AGPVM, IL-6 prolonged action potential duration (APD) which was further prolonged in the presence of IL-6R. Similar to heterologous cells, IL-6 reduced endogenous guinea pig ERG channel mRNA and protein expression. The data are first to demonstrate that IL-6 inhibition of IKr and the resulting prolongation of APD is mediated via IL-6R and JAK pathway activation and forms the basis for the observed clinical QT interval prolongation. These novel findings may guide the development of targeted anti-arrhythmic therapeutic interventions in patients with LQTS and inflammatory disorders.
Potassium channels belong to the super family of ion channels and play a fundamental role in cell excitability. Kir channels are potassium channels with an inwardly rectifying property. They play a ...role in setting the resting membrane potential of many excitable cells including neurons. Although putative Kir channel family genes can be found in the Apis mellifera genome, their functional expression, biophysical properties, and sensitivity to small molecules with insecticidal activity remain to be investigated. We cloned six Kir channel isoforms from Apis mellifera that derive from two Kir genes, AmKir1 and AmKir2, which are present in the Apis mellifera genome. We studied the tissue distribution, the electrophysiological and pharmacological characteristics of three isoforms that expressed functional currents (AmKir1.1, AmKir2.2, and AmKir2.3). AmKir1.1, AmKir2.2, and AmKir2.3 isoforms exhibited distinct characteristics when expressed in Xenopus oocytes. AmKir1.1 exhibited the largest potassium currents and was impermeable to cesium whereas AmKir2.2 and AmKir2.3 exhibited smaller currents but allowed cesium to permeate. AmKir1 exhibited faster opening kinetics than AmKir2. Pharmacological experiments revealed that both AmKir1.1 and AmKir2.2 are blocked by the divalent ion barium, with IC
values of 10
and 10
M, respectively. The concentrations of VU041, a small molecule with insecticidal properties required to achieve a 50% current blockade for all three channels were higher than those needed to block Kir channels in other arthropods, such as the aphid Aphis gossypii and the mosquito Aedes aegypti. From this, we conclude that Apis mellifera AmKir channels exhibit lower sensitivity to VU041.
Myotonic dystrophy type 1 (DM1) is the most prevalent adult-onset muscular dystrophy affecting 1 in 8,000 individuals. It is characterized by multisystemic symptoms, primarily myopathy. The root ...cause of DM1 is a heterozygous CTG triplet expansion beyond the normal size threshold in the non-coding region of the DM1 protein kinase gene (DMPK). In our study, we generated and characterized three distinct DM1 induced pluripotent stem cell (iPSC) lines with CTG repeat expansions ranging from 900 to 2000 in the DMPK gene. These iPSC lines maintained normal karyotypes, exhibited distinctive colony morphology, robustly expressed pluripotency markers, differentiated into the three primary germ layers, and lacked residual viral vectors.
Myotonic dystrophy Type 1 (DM1) is a severe inherited neuromuscular disease and is the most prevalent form of muscular dystrophy in adults. DM1 involves not only the striated muscles including ...skeletal, and cardiac but also other organs such as the eye, brain and gonads. We have generated and characterized 4 adult heterozygous DM1 iPSC lines carrying between 1300 and 1600 CTG repeat expansion in the DM1 protein kinase gene, and a control from an apparently healthy individual. They all show strong pluripotency markers, differentiation capacity, the absence of residual viral vectors as well as normal karyotypes and colony morphologies.
Abstract
Cardiomyocytes derived from patient-specific induced pluripotent stem cells (iPSC-CMs) successfully reproduce the mechanisms of several channelopathies. However, this approach involve cell ...reprogramming from somatic tissue biopsies or genomic editing in healthy iPSCs for every mutation found and to be investigated. We aim to knockout (KO) Na
V
1.5, the cardiac sodium channel, in a healthy human iPSC line, characterize the model and then, use it to express variants of Na
V
1.5. We develop a homozygous Na
V
1.5 KO iPSC line able to differentiate into cardiomyocytes with CRISPR/Cas9 tool. The Na
V
1.5 KO iPSC-CMs exhibited an organized contractile apparatus, spontaneous contractile activity, and electrophysiological recordings confirmed the major reduction in total Na
+
currents. The action potentials (APs) exhibited a reduction in their amplitude and in their maximal rate of rise. Voltage optical mapping recordings revealed that the conduction velocity Ca
2+
transient waves propagation velocities were slow. A wild-type (WT) Na
V
1.5 channel expressed by transient transfection in the KO iPSC-CMs restored Na
+
channel expression and AP properties. The expression of Na
V
1.5/delQKP, a long QT type 3 (LQT3) variant, in the Na
V
1.5 KO iPSC-CMs showed that dysfunctional Na
+
channels exhibited a persistent Na
+
current and caused prolonged AP duration that led to arrhythmic events, characteristics of LQT3.
Myotonic dystrophy type 1 (DM1) is a multisystemic and heterogeneous disorder caused by the expansion of CTG repeats in the 3’ UTR of the myotonic dystrophy protein kinase (DMPK) gene. There is a ...congenital form (CDM1) of the disease characterized by severe hypotonia, respiratory insufficiency as well as developmental delays and intellectual disabilities. CDM1 infants manifest important brain structure abnormalities present from birth while, in contrast, older patients with adult-onset DM1 often present neurodegenerative features and milder progressive cognitive deficits. Promising therapies targeting central molecular mechanisms contributing to the symptoms of adult-onset DM1 are currently in development, but their relevance for treating cognitive impairment in CDM1, which seems to be a partially distinct neurodevelopmental disorder, remain to be elucidated. Here, we provide an update on the clinical presentation of CDM1 and review recent in vitro and in vivo models that have provided meaningful insights on its consequences in development, with a particular focus on the brain. We discuss how enhanced toxic gain-of-function of the mutated DMPK transcripts with larger CUG repeats and the resulting dysregulation of RNA-binding proteins may affect the developing cortex in utero. Because the methylation of CpG islets flanking the trinucleotide repeats has emerged as a strong biomarker of CDM1, we highlight the need to investigate the tissue-specific impacts of these chromatin modifications in the brain. Finally, we outline promising potential therapeutic treatments for CDM1 and propose future in vitro and in vivo models with great potential to shed light on this disease.
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•CDM1 is a neurodevelopmental disorder while adult-onset DM1 is neurodegenerative.•Dysregulation of MBNL and CELF alter neurogenesis and synaptic activity.•DMPK hypermethylation may be implicated in brain development.•GSK3β inhibitor and antisense oligonucleotides are promising therapies for CDM1.
Myotonic dystrophy type 1 (DM1) is a genetic neuromuscular disorder that affects many organs, including the heart. DM1 is caused by a heterozygous CTG triplet expansion exceeding the normal size ...threshold in the non-coding region of the DM1 protein kinase gene (DMPK). We generated and characterized a DM1 iPSC line carrying a 700 CTG repeat expansion as well as a control iPSC line from a healthy individual. The two iPSC lines expressed several pluripotency markers, had the capacity to differentiate into the three primary germ layers, had no residual viral vectors, had normal karyotypes, and had a typical colony morphology.
Cardiovascular disease (CVD) continues to be the most common cause of death worldwide, and cardiac arrhythmias account for approximately one half of these deaths. The morbidity and mortality from CVD ...have been reduced significantly over the past few decades; however, disparities in racial or ethnic populations still exist. This review is based on available literature to date and focuses on known cardiac channelopathies and other inherited disorders associated with sudden cardiac death in African American/Black subjects and the role of epigenetics in phenotypic manifestations of CVD, and illustrates existing disparities in treatment and outcomes. The review also highlights the knowledge gaps that limit understanding of the manifestation of phenotypic abnormalities across racial or ethnic groups and discusses disparities associated with device underuse in the management of patients at risk for sudden cardiac death. We discuss factors related to reports in the United States, that the overall mortality attributed to CVD and the number of out-of-hospital cardiac arrests are higher among African American/Black subjects when compared with other racial or ethnic groups. African American/Black subjects are disproportionally affected by CVD, including cardiac arrhythmias and sudden cardiac death, thus highlighting a major concern in this population that remains underrepresented in clinical trials with limited genetic testing and device underuse. The proposed solutions include (1) early identification of genetic variants, which is crucial in tailoring a preventive management strategy; (2) inclusion of diverse racial or ethnic groups in clinical trials; (3) compliance with guideline-directed medical treatment and referral to cardiovascular subspecialists; and (4) training and mentoring of underrepresented junior faculty in cardiovascular health disparities research.
Myotonic dystrophy type 1 (DM1) is a dominant genetic disease in which the expansion of long CTG trinucleotides in the 3′ UTR of the myotonic dystrophy protein kinase (DMPK) gene results in toxic RNA ...gain-of-function and gene mis-splicing affecting mainly the muscles, the heart, and the brain. The CUG-expanded transcripts are a suitable target for the development of antisense oligonucleotide (ASO) therapies. Various chemical modifications of the sugar-phosphate backbone have been reported to significantly enhance the affinity of ASOs for RNA and their resistance to nucleases, making it possible to reverse DM1-like symptoms following systemic administration in different transgenic mouse models. However, specific tissue delivery remains to be improved to achieve significant clinical outcomes in humans. Several strategies, including ASO conjugation to cell-penetrating peptides, fatty acids, or monoclonal antibodies, have recently been shown to improve potency in muscle and cardiac tissues in mice. Moreover, intrathecal administration of ASOs may be an advantageous complementary administration route to bypass the blood-brain barrier and correct defects of the central nervous system in DM1. This review describes the evolution of the chemical design of antisense oligonucleotides targeting CUG-expanded mRNAs and how recent advances in the field may be game-changing by forwarding laboratory findings into clinical research and treatments for DM1 and other microsatellite diseases.
Ca
2+
plays a crucial role in excitation-contraction coupling in cardiac myocytes. Dysfunctional Ca
2+
regulation alters the force of contraction and causes cardiac arrhythmias. Ca
2+
entry into ...cardiomyocytes is mediated mainly through L-type Ca
2+
channels, leading to the subsequent Ca
2+
release from the sarcoplasmic reticulum. L-type Ca
2+
channels are composed of the conventional Ca
v
1.2, ubiquitously expressed in all heart chambers, and the developmentally regulated Ca
v
1.3, exclusively expressed in the atria, sinoatrial node, and atrioventricular node in the adult heart. As such, Ca
v
1.3 is implicated in the pathogenesis of sinoatrial and atrioventricular node dysfunction as well as atrial fibrillation. More recently, Ca
v
1.3
de novo
expression was suggested in heart failure. Here, we review the functional role, expression levels, and regulation of Ca
v
1.3 in the heart, including in the context of cardiac diseases. We believe that the elucidation of the functional and molecular pathways regulating Ca
v
1.3 in the heart will assist in developing novel targeted therapeutic interventions for the aforementioned arrhythmias.
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