Sleep-disordered breathing (SDB) has been associated with various benign cardiac arrhythmias occurring during sleep.
The purpose of this study was to demonstrate that SDB contributes to the ...development of life-threatening ventricular arrhythmias in patients with an established arrhythmic substrate.
We prospectively studied the association between SDB and timing of life-threatening ventricular arrhythmic events in 45 patients with an implantable cardioverter-defibrillator (ICD). SDB was defined as an apnea-hypopnea index (AHI) >10 events/hour based on an overnight sleep study. The primary outcome measure was appropriate ICD therapy, defined as antitachycardia pacing or shock for ventricular tachycardia or ventricular fibrillation during 1-year follow-up.
SDB was present in 26 (57.8%) patients. Appropriate ICD therapies were higher among patients with SDB (73% vs 47%, P = .02). Logistic regression identified SDB as a predictor of any appropriate ICD therapy (odds ratio 4.4, 95% confidence interval 1.4-15.3, P = .01). The risk for ventricular arrhythmias was higher in patients with SDB solely due to an increase in events occurring between midnight and 6 AM (odds ratio 5.6, 95% confidence interval 2.0-15.6, P = .001) with no discernible effect on appropriate ICD therapy during nonsleeping hours (odds ratio 0.7, 95% confidence interval 0.2-2.3, P = .61).
Patients with an ICD and SDB have a striking increase in the onset of life-threatening ventricular arrhythmic events during sleeping hours. These findings provide a rationale for SDB screening in patients with appropriate ICD therapy if device interrogation reveals a predominance of nocturnal onset of arrhythmias.
In this issue of Cell Stem Cell, Mills et al. (2019) use multidimensional functional screening to identify pro-proliferative compounds in cell-cycle-arrested human cardiac organoids. Using this ...model, the authors identify two hit compounds that restart cardiomyocyte proliferation by synergistically activating the mevalonate pathway and cell-cycle-related pathways.
In this issue of Cell Stem Cell, Mills et al. (2019) use multidimensional functional screening to identify pro-proliferative compounds in cell-cycle-arrested human cardiac organoids. Using this model, the authors identify two hit compounds that restart cardiomyocyte proliferation by synergistically activating the mevalonate pathway and cell-cycle-related pathways.
Interferon Regulatory Factor-8 (IRF-8) serves as a key factor in the hierarchical differentiation towards monocyte/dendritic cell lineages. While much insight has been accumulated into the mechanisms ...essential for its hematopoietic specific expression, the mode of restricting IRF-8 expression in non-hematopoietic cells is still unknown. Here we show that the repression of IRF-8 expression in restrictive cells is mediated by its 3rd intron. Removal of this intron alleviates the repression of Bacterial Artificial Chromosome (BAC) IRF-8 reporter gene in these cells. Fine deletion analysis points to conserved regions within this intron mediating its restricted expression. Further, the intron alone selectively initiates gene silencing only in expression-restrictive cells. Characterization of this intron's properties points to its role as an initiator of sustainable gene silencing inducing chromatin condensation with suppressive histone modifications. This intronic element cannot silence episomal transgene expression underlining a strict chromatin-dependent silencing mechanism. We validated this chromatin-state specificity of IRF-8 intron upon in-vitro differentiation of induced pluripotent stem cells (iPSCs) into cardiomyocytes. Taken together, the IRF-8 3rd intron is sufficient and necessary to initiate gene silencing in non-hematopoietic cells, highlighting its role as a nucleation core for repressed chromatin during differentiation.
CTG repeat expansion in DMPK, the cause of myotonic dystrophy type 1 (DM1), frequently results in hypermethylation and reduced SIX5 expression. The contribution of hypermethylation to disease ...pathogenesis and the precise mechanism by which SIX5 expression is reduced are unknown. Using 14 different DM1-affected human embryonic stem cell (hESC) lines, we characterized a differentially methylated region (DMR) near the CTGs. This DMR undergoes hypermethylation as a function of expansion size in a way that is specific to undifferentiated cells and is associated with reduced SIX5 expression. Using functional assays, we provide evidence for regulatory activity of the DMR, which is lost by hypermethylation and may contribute to DM1 pathogenesis by causing SIX5 haplo-insufficiency. This study highlights the power of hESCs in disease modeling and describes a DMR that functions both as an exon coding sequence and as a regulatory element whose activity is epigenetically hampered by a heritable mutation.
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•We identify a disease-associated, differentially methylated region in DM1 hESCs•CTG expansion size correlates with the degree of methylation specifically in DM1 hESCs•DMPK hypermethylation hampers the activity of a regulatory element for SIX5•DM1 hESCs provide an opportunity to study diseased cardiomyocytes in vitro
Eiges and colleagues used a large cohort of myotonic dystrophy type 1-affected hESCs to characterize a disease-associated, differentially methylated region that hypermethylates as a function of expansion size and, when unmethylated, promotes the expression of a neighboring gene, SIX5, in undifferentiated cells and in in vitro-differentiated cardiomyocytes.
: Human embryonic stem (hES) cells are pluripotent cell lines derived from the inner cell mass of the blastocyst‐stage embryo. These unique cell lines can be propagated in the undifferentiated state ...in culture, while retaining the capacity to differentiate into derivatives of all three germ layers, including cardiomyocytes. The derivation of the hES cell lines presents a powerful tool to explore the early events of cardiac progenitor cell specification and differentiation, and it also provides a novel cell source for the emerging field of cardiovascular regenerative medicine. A spontaneous differentiation system of these stem cells to cardiomyocytes was established and the generated myocytes displayed molecular, structural, and functional properties of early‐stage heart cells. In order to follow the in vitro differentiation process, the temporal expression of signaling molecules and transcription factors governing early cardiac differentiation was examined throughout the process. A characteristic pattern was noted recapitulating the normal in vivo cardiac differentiation scheme observed in other model systems. This review discusses the known pathways involved in cardiac specification and the possible factors that may be used to enhance cardiac differentiation of hES cells, as well as the steps required to fully harness the enormous potential of these unique cells.
The D1790G mutation was found in all 24 patients of an extended long QT family but not in 200 chromosomes carried by healthy individuals. We describe a 37-year-old man presenting with a typical ...spontaneous type 1 Brugada pattern who in electrophysiological testing had easily inducible ventricular fibrillation. At the age of 47 years he had an atrial ventricular type 2 block documented by an exercise test and a Holter monitor. Genetic analysis revealed a known D1790G mutation in the gene encoding of the sodium channel (SCN5A) that until now has been associated only with the long QT phenotype. Although this mutation has not been associated with a reduction of sodium channel expression, we hypothesize that sodium currents are further diminished due to the 20-mV shift of the steady-state inactivation curve, and this could contribute to the Brugada phenotype. This case is important as it allows a better understanding of the underlying molecular mechanisms of Brugada syndrome. Moreover, this observation raises concern about the safety of class IC drug therapy in long QT type 3 patients and quinidine therapy in Brugada patients, and emphasizes the importance of a thorough clinical and genetic evaluation.
Optogenetics approaches, utilizing light-sensitive proteins, have emerged as unique experimental paradigms to modulate neuronal excitability. We aimed to evaluate whether a similar strategy could be ...used to control cardiac-tissue excitability.
A combined cell and gene therapy strategy was developed in which fibroblasts were transfected to express the light-activated depolarizing channel Channelrhodopsin-2 (ChR2). Patch-clamp studies confirmed the development of a robust inward current in the engineered fibroblasts following monochromatic blue-light exposure. The engineered cells were co-cultured with neonatal rat cardiomyocytes (or human embryonic stem cell-derived cardiomyocytes) and studied using a multielectrode array mapping technique. These studies revealed the ability of the ChR2-fibroblasts to electrically couple and pace the cardiomyocyte cultures at varying frequencies in response to blue-light flashes. Activation mapping pinpointed the source of this electrical activity to the engineered cells. Similarly, diffuse seeding of the ChR2-fibroblasts allowed multisite optogenetics pacing of the co-cultures, significantly shortening their electrical activation time and synchronizing contraction. Next, optogenetics pacing in an in vitro model of conduction block allowed the resynchronization of the tissue's electrical activity. Finally, the ChR2-fibroblasts were transfected to also express the light-sensitive hyperpolarizing proton pump Archaerhodopsin-T (Arch-T). Seeding of the ChR2/ArchT-fibroblasts allowed to either optogentically pace the cultures (in response to blue-light flashes) or completely suppress the cultures' electrical activity (following continuous illumination with 624 nm monochromatic light, activating ArchT).
The results of this proof-of-concept study highlight the unique potential of optogenetics for future biological pacemaking and resynchronization therapy applications and for the development of novel anti-arrhythmic strategies.
Myocardial stem cell therapies are emerging as exciting new experimental strategies for treatment of a variety of cardiovascular disorders. This review describes the electrophysiologic implications ...associated with these emerging strategies. The electrophysiologic considerations associated with cell therapy for myocardial infarct repair are described from the mechanistic point of view (assessing electromechanical coupling between donor and host cells) and from the therapeutic (possibly preventing malignant ventricular arrhythmias) and potential adverse effects (increasing arrhythmogenesis) points of view. The potential of different stem cell therapy approaches for the treatment of bradyarrhythmias, are discussed. Such therapy includes efforts to generate biologic pacemakers either by genetically modifying mesenchymal stem cells to overexpress the pacemaker current I(f) or by inducing differentiation of human embryonic stem cells into cardiomyocytes having pacemaking properties. The ability of cell therapy using genetically modified cells to modulate the electrophysiologic substrate in an attempt to treat different tachyarrhythmias is described. The potential advantages and shortcomings of each strategy are discussed, as are the obstacles that must be overcome before these exciting strategies can become a clinical reality.
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Cardiac tissue engineering provides unique opportunities for cardiovascular disease modeling, drug testing, and regenerative medicine applications. To recapitulate human heart tissue, ...we combined human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) with a chitosan-enhanced extracellular-matrix (ECM) hydrogel, derived from decellularized pig hearts. Ultrastructural characterization of the ECM-derived engineered heart tissues (ECM-EHTs) revealed an anisotropic muscle structure, with embedded cardiomyocytes showing more mature properties than 2D-cultured hiPSC-CMs. Force measurements confirmed typical force-length relationships, sensitivity to extracellular calcium, and adequate ionotropic responses to contractility modulators. By combining genetically-encoded calcium and voltage indicators with laser-confocal microscopy and optical mapping, the electrophysiological and calcium-handling properties of the ECM-EHTs could be studied at the cellular and tissue resolutions. This allowed to detect drug-induced changes in contraction rate (isoproterenol, carbamylcholine), optical signal morphology (E-4031, ATX2, isoproterenol, ouabin and quinidine), cellular arrhythmogenicity (E-4031 and ouabin) and alterations in tissue conduction properties (lidocaine, carbenoxolone and quinidine). Similar assays in ECM-EHTs derived from patient-specific hiPSC-CMs recapitulated the abnormal phenotype of the long QT syndrome and catecholaminergic polymorphic ventricular tachycardia. Finally, programmed electrical stimulation and drug-induced pro-arrhythmia led to the development of reentrant arrhythmias in the ECM-EHTs.
In conclusion, a novel ECM-EHT model was established, which can be subjected to high-resolution long-term serial functional phenotyping, with important implications for cardiac disease modeling, drug testing and precision medicine.
One of the main objectives of cardiac tissue engineering is to create an in-vitro muscle tissue surrogate of human heart tissue. To this end, we combined a chitosan-enforced cardiac-specific ECM hydrogel derived from decellularized pig hearts with human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from healthy-controls and patients with inherited cardiac disorders. We then utilized genetically-encoded calcium and voltage fluorescent indicators coupled with unique optical imaging techniques and force-measurements to study the functional properties of the generated engineered heart tissues (EHTs). These studies demonstrate the unique potential of the new model for physiological and pathophysiological studies (assessing contractility, conduction and reentrant arrhythmias), novel disease modeling strategies (“disease-in-a-dish” approach) for studying inherited arrhythmogenic disorders, and for drug testing applications (safety pharmacology).
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