Background-The mechanism of ECG changes and arrhythmogenesis in Brugada syndrome (BS) patients is unknown. Methods and Results-A BS patient without clinically detected cardiac structural abnormalities underwent cardiac transplantation for intolerable numbers of implantable cardioverter/defibrillator discharges. The patient's explanted heart was studied electrophysiologically and histopathologically. Whole-cell currents were measured in HEK293 cells expressing wild-type or mutated sodium channels from the patient. The right ventricular outflow tract (RVOT) endocardium showed activation slowing and was the origin of ventricular fibrillation without a transmural repolarization gradient. Conduction restitution was abnormal in the RVOT but normal in the left ventricle. Right ventricular hypertrophy and fibrosis with epicardial fatty infiltration were present. HEK293 cells expressing a G1935S mutation in the gene encoding the cardiac sodium channel exhibited enhanced slow inactivation compared with wild-type channels.Computer simulations demonstrated that conduction slowing in the RVOT might have been the cause of the ECG changes. Conclusions-In this patient with BS, conduction slowing based on interstitial fibrosis, but not transmural repolarization differences, caused the ECG signs and was the origin of ventricular fibrillation.
Cardiomyocytes from human pluripotent stem cells (hPSC-CMs) are increasingly used to model cardiac disease, test drug efficacy and for safety pharmacology. Nevertheless, a major hurdle to more extensive use is their immaturity and similarity to fetal rather than adult cardiomyocytes. Here, we provide an overview of the strategies currently being used to increase maturation in culture, which include prolongation of time in culture, exposure to electrical stimulation, application of mechanical strain, growth in three-dimensional tissue configuration, addition of non-cardiomyocytes, use of hormones and small molecules, and alteration of the extracellular environment. By comparing the outcomes of these studies, we identify the approaches most likely to improve functional maturation of hPSC-CMs in terms of their electrophysiology and excitation-contraction coupling.
Background-Pluripotent stem cells (PSCs) offer a new paradigm for modeling genetic cardiac diseases, but it is unclear whether mouse and human PSCs can truly model both gain-and loss-of-function genetic disorders affecting the Na ϩ current (I Na ) because of the immaturity of the PSC-derived cardiomyocytes. To address this issue, we generated multiple PSC lines containing a Na ϩ channel mutation causing a cardiac Na ϩ channel overlap syndrome. Method and Results-Induced PSC (iPSC) lines were generated from mice carrying the Scn5a 1798insD/ϩ (Scn5a-het) mutation. These mouse iPSCs, along with wild-type mouse iPSCs, were compared with the targeted mouse embryonic stem cell line used to generate the mutant mice and with the wild-type mouse embryonic stem cell line. Patch-clamp experiments showed that the Scn5a-het cardiomyocytes had a significant decrease in I Na density and a larger persistent I Na compared with Scn5a-wt cardiomyocytes. Action potential measurements showed a reduced upstroke velocity and longer action potential duration in Scn5a-het myocytes. These characteristics recapitulated findings from primary cardiomyocytes isolated directly from adult Scn5a-het mice. Finally, iPSCs were generated from a patient with the equivalent SCN5A 1795insD/ϩ mutation. Patch-clamp measurements on the derivative cardiomyocytes revealed changes similar to those in the mouse PSC-derived cardiomyocytes. Conclusion-Here, we demonstrate that both embryonic stem cell-and iPSC-derived cardiomyocytes can recapitulate the characteristics of a combined gain-and loss-of-function Na ϩ channel mutation and that the electrophysiological immaturity of PSC-derived cardiomyocytes does not preclude their use as an accurate model for cardiac Na ϩ channel disease. (Circulation. 2012;125:3079-3091.) Key Words: cell differentiation Ⅲ disease models, animal Ⅲ electrophysiology Ⅲ sodium channels Ⅲ pluripotent stem cells M ultiple cardiac arrhythmia syndromes, including long-QT syndrome type 3 (LQT3), Brugada syndrome (BrS), progressive cardiac conduction disease, and sinus node dysfunction, have been linked to mutations in SCN5A, the gene encoding the ␣-subunit of the cardiac sodium (Na ϩ ) channel. 1,2 Most SCN5A mutations associated with LQT3 act by disrupting fast inactivation of the Na ϩ channel, resulting in a persistent inward Na ϩ current (I Na ) during the action potential (AP) plateau phase, subsequently delaying ventricular repolarization and prolonging the QT interval (gain-of-function mutations). 3 In contrast, SCN5A mutations underlying BrS and conduction disease are loss-of-function mutations and are believed to reduce the total amount of available I Na as a result of expression of nonfunctional channels, impaired intracellular trafficking, and decreased membrane surface channel expression or through altered channel gating properties. 1,2 Editorial see p 3055 Clinical Perspective on p 3091Initially, it was believed that these arrhythmia syndromes constituted separate clinical entities, with individual SCN5A Received September 9...
Patient-specific induced pluripotent stem cells (iPSCs) will assist research on genetic cardiac maladies if the disease phenotype is recapitulated in vitro. However, genetic background variations may confound disease traits, especially for disorders with incomplete penetrance, such as long-QT syndromes (LQTS). To study the LQT2-associated c.A2987T (N996I) KCNH2 mutation under genetically defined conditions, we derived iPSCs from a patient carrying this mutation and corrected it. Furthermore, we introduced the same point mutation in human embryonic stem cells (hESCs), generating two genetically distinct isogenic pairs of LQTS and control lines. Correction of the mutation normalized the current (IKr) conducted by the HERG channel and the action potential (AP) duration in iPSC-derived cardiomyocytes (CMs). Introduction of the same mutation reduced IKr and prolonged the AP duration in hESC-derived CMs. Further characterization of N996I-HERG pathogenesis revealed a trafficking defect. Our results demonstrated that the c.A2987T KCNH2 mutation is the primary cause of the LQTS phenotype. Precise genetic modification of pluripotent stem cells provided a physiologically and functionally relevant human cellular context to reveal the pathogenic mechanism underlying this specific disease phenotype.
A fish oil diet increases omega3-PUFA content in the ventricular sarcolemma, decreases I(Ca,L) and I(NCX), and increases I(K1) and I(Ks), resulting in AP shortening. Incorporation of omega3-PUFAs in the sarcolemma may have consequences for arrhythmias independent of circulating omega3-PUFAs.
Congenital heart defects can be caused by mutations in genes that guide cardiac lineage formation. Here, we show deletion of NKX2-5, a critical component of the cardiac gene regulatory network, in human embryonic stem cells (hESCs), results in impaired cardiomyogenesis, failure to activate VCAM1 and to downregulate the progenitor marker PDGFRα. Furthermore, NKX2-5 null cardiomyocytes have abnormal physiology, with asynchronous contractions and altered action potentials. Molecular profiling and genetic rescue experiments demonstrate that the bHLH protein HEY2 is a key mediator of NKX2-5 function during human cardiomyogenesis. These findings identify HEY2 as a novel component of the NKX2-5 cardiac transcriptional network, providing tangible evidence that hESC models can decipher the complex pathways that regulate early stage human heart development. These data provide a human context for the evaluation of pathogenic mutations in congenital heart disease.
SummaryDiminished mitochondrial function is causally related to some heart diseases. Here, we developed a human disease model based on cardiomyocytes from human embryonic stem cells (hESCs), in which an important pathway of mitochondrial gene expression was inactivated. Repression of PGC-1α, which is normally induced during development of cardiomyocytes, decreased mitochondrial content and activity and decreased the capacity for coping with energetic stress. Yet, concurrently, reactive oxygen species (ROS) levels were lowered, and the amplitude of the action potential and the maximum amplitude of the calcium transient were in fact increased. Importantly, in control cardiomyocytes, lowering ROS levels emulated this beneficial effect of PGC-1α knockdown and similarly increased the calcium transient amplitude. Our results suggest that controlling ROS levels may be of key physiological importance for recapitulating mature cardiomyocyte phenotypes, and the combination of bioassays used in this study may have broad application in the analysis of cardiac physiology pertaining to disease.
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