The ability to generate patient-specific human induced pluripotent stem cells (iPSCs) offers a new paradigm for modelling human disease and for individualizing drug testing. Congenital long QT syndrome (LQTS) is a familial arrhythmogenic syndrome characterized by abnormal ion channel function and sudden cardiac death. Here we report the development of a patient/disease-specific human iPSC line from a patient with type-2 LQTS (which is due to the A614V missense mutation in the KCNH2 gene). The generated iPSCs were coaxed to differentiate into the cardiac lineage. Detailed whole-cell patch-clamp and extracellular multielectrode recordings revealed significant prolongation of the action-potential duration in LQTS human iPSC-derived cardiomyocytes (the characteristic LQTS phenotype) when compared to healthy control cells. Voltage-clamp studies confirmed that this action-potential-duration prolongation stems from a significant reduction of the cardiac potassium current I(Kr). Importantly, LQTS-derived cells also showed marked arrhythmogenicity, characterized by early-after depolarizations and triggered arrhythmias. We then used the LQTS human iPSC-derived cardiac-tissue model to evaluate the potency of existing and novel pharmacological agents that may either aggravate (potassium-channel blockers) or ameliorate (calcium-channel blockers, K(ATP)-channel openers and late sodium-channel blockers) the disease phenotype. Our study illustrates the ability of human iPSC technology to model the abnormal functional phenotype of an inherited cardiac disorder and to identify potential new therapeutic agents. As such, it represents a promising paradigm to study disease mechanisms, optimize patient care (personalized medicine), and aid in the development of new therapies.

Cell therapy is emerging as a promising strategy for myocardial repair. This approach is hampered, however, by the lack of sources for human cardiac tissue and by the absence of direct evidence for functional integration of donor cells into host tissues. Here we investigate whether cells derived from human embryonic stem (hES) cells can restore myocardial electromechanical properties. Cardiomyocyte cell grafts were generated from hES cells in vitro using the embryoid body differentiating system. This tissue formed structural and electromechanical connections with cultured rat cardiomyocytes. In vivo integration was shown in a large-animal model of slow heart rate. The transplanted hES cell-derived cardiomyocytes paced the hearts of swine with complete atrioventricular block, as assessed by detailed three-dimensional electrophysiological mapping and histopathological examination. These results demonstrate the potential of hES-cell cardiomyocytes to act as a rate-responsive biological pacemaker and for future myocardial regeneration strategies.

Transplantation of hESC-CMs after extensive myocardial infarction in rats results in the formation of stable cardiomyocyte grafts, attenuation of the remodeling process, and functional benefit. These findings highlight the potential of hESCs for myocardial cell therapy strategies.

Hydrolysis of guanosine triphosphate (GTP) by the small guanosine triphosphatase (GTPase) adenosine diphosphate ribosylation factor-1 (ARF1) depends on a GTPase-activating protein (GAP). A complementary DNA encoding the ARF1 GAP was cloned from rat liver and predicts a protein with a zinc finger motif near the amino terminus. The GAP function required an intact zinc finger and additional amino-terminal residues. The ARF1 GAP was localized to the Golgi complex and was redistributed into a cytosolic pattern when cells were treated with brefeldin A, a drug that prevents ARF1-dependent association of coat proteins with the Golgi. Thus, the GAP is likely to be recruited to the Golgi by an ARF1-dependent mechanism.

Background-The ability to derive human induced pluripotent stem (hiPS) cell lines by reprogramming of adult fibroblasts with a set of transcription factors offers unique opportunities for basic and translational cardiovascular research. In the present study, we aimed to characterize the cardiomyocyte differentiation potential of hiPS cells and to study the molecular, structural, and functional properties of the generated hiPS-derived cardiomyocytes. Methods and Results-Cardiomyocyte differentiation of the hiPS cells was induced with the embryoid body differentiation system. Gene expression studies demonstrated that the cardiomyocyte differentiation process of the hiPS cells was characterized by an initial increase in mesoderm and cardiomesoderm markers, followed by expression of cardiacspecific transcription factors and finally by cardiac-specific structural genes. Cells in the contracting embryoid bodies were stained positively for cardiac troponin-I, sarcomeric ␣-actinin, and connexin-43. Reverse-transcription polymerase chain reaction studies demonstrated the expression of cardiac-specific sarcomeric proteins and ion channels. Multielectrode array recordings established the development of a functional syncytium with stable pacemaker activity and action potential propagation. Positive and negative chronotropic responses were induced by application of isoproterenol and carbamylcholine, respectively. Administration of quinidine, E4031 (I Kr blocker), and chromanol 293B (I Ks blocker) significantly affected repolarization, as manifested by prolongation of the local field potential duration. Conclusions-hiPS cells can differentiate into myocytes with cardiac-specific molecular, structural, and functional properties. These results, coupled with the potential of this technology to generate patient-specific hiPS lines, hold great promise for the development of in vitro models of cardiac genetic disorders, for drug discovery and testing, and for the emerging field of cardiovascular regenerative medicine.

Human embryonic stem cell-derived cardiomyocytes (hES-CMs) are thought to recapitulate the embryonic development of heart cells. Given the exciting potential of hES-CMs as replacement tissue in diseased hearts, we investigated the pharmacological sensitivity and ionic current of mid-stage hES-CMs (20-35 days post plating). A high-resolution microelectrode array was used to assess conduction in multicellular preparations of hES-CMs in spontaneously contracting embryoid bodies (EBs). TTX (10 µM) dramatically slowed conduction velocity from 5.1 to 3.2 cm s −1 while 100 µM TTX caused complete cessation of spontaneous electrical activity in all EBs studied. In contrast, the Ca 2+ channel blockers nifedipine or diltiazem (1 µM) had a negligible effect on conduction. These results suggested a prominent Na + channel current, and therefore we patch-clamped isolated cells to record Na + current and action potentials (APs). We found for isolated hES-CMs a prominent Na + current (244 ± 42 pA pF −1 at 0 mV; n = 19), and a hyperpolarization-activated current (HCN), but no inward rectifier K + current. In cell clusters, 3 µM TTX induced longer AP interpulse intervals and 10 µM TTX caused cessation of spontaneous APs. In contrast nifedipine (Ca 2+ channel block) and 2 mM Cs + (HCN complete block) induced shorter AP interpulse intervals. In single cells, APs stimulated by current pulses had a maximum upstroke velocity (dV /dt max ) of 118 ± 14 V s −1 in control conditions; in contrast, partial block of Na + current significantly reduced stimulated dV /dt max (38 ± 15 V s −1 ). RT-PCR revealed Na V 1.5, Ca V 1.2, and HCN-2 expression but we could not detect Kir2.1. We conclude that hES-CMs at mid-range development express prominent Na + current. The absence of background K + current creates conditions for spontaneous activity that is sensitive to TTX in the same range of partial block of Na V 1.5; thus, the Na V 1.5 Na + channel is important for initiating spontaneous excitability in hES-derived heart cells.

BackgroundThe ability to establish human induced pluripotent stem cells (hiPSCs) by reprogramming of adult fibroblasts and to coax their differentiation into cardiomyocytes opens unique opportunities for cardiovascular regenerative and personalized medicine. In the current study, we investigated the Ca2+-handling properties of hiPSCs derived-cardiomyocytes (hiPSC-CMs).Methodology/Principal FindingsRT-PCR and immunocytochemistry experiments identified the expression of key Ca2+-handling proteins. Detailed laser confocal Ca2+ imaging demonstrated spontaneous whole-cell [Ca2+]i transients. These transients required Ca2+ influx via L-type Ca2+ channels, as demonstrated by their elimination in the absence of extracellular Ca2+ or by administration of the L-type Ca2+ channel blocker nifedipine. The presence of a functional ryanodine receptor (RyR)-mediated sarcoplasmic reticulum (SR) Ca2+ store, contributing to [Ca2+]i transients, was established by application of caffeine (triggering a rapid increase in cytosolic Ca2+) and ryanodine (decreasing [Ca2+]i). Similarly, the importance of Ca2+ reuptake into the SR via the SR Ca2+ ATPase (SERCA) pump was demonstrated by the inhibiting effect of its blocker (thapsigargin), which led to [Ca2+]i transients elimination. Finally, the presence of an IP3-releasable Ca2+ pool in hiPSC-CMs and its contribution to whole-cell [Ca2+]i transients was demonstrated by the inhibitory effects induced by the IP3-receptor blocker 2-Aminoethoxydiphenyl borate (2-APB) and the phosopholipase C inhibitor U73122.Conclusions/SignificanceOur study establishes the presence of a functional, SERCA-sequestering, RyR-mediated SR Ca2+ store in hiPSC-CMs. Furthermore, it demonstrates the dependency of whole-cell [Ca2+]i transients in hiPSC-CMs on both sarcolemmal Ca2+ entry via L-type Ca2+ channels and intracellular store Ca2+ release.

Human embryonic stem cells (hESC) are pluripotent lines that can differentiate in vitro into cell derivatives of all three germ layers, including cardiomyocytes. Successful application of these unique cells in the areas of cardiovascular research and regenerative medicine has been hampered by difficulties in identifying and selecting specific cardiac progenitor cells from the mixed population of differentiating cells. We report the generation of stable transgenic hESC lines, using lentiviral vectors, and single-cell clones that express a reporter gene (eGFP) under the transcriptional control of a cardiac-specific promoter (the human myosin light chain-2V promoter). Our results demonstrate the appearance of eGFP-expressing cells during the differentiation of the hESC as embryoid bodies (EBs) that can be identified and sorted using FACS (purity>95%, viability>85%). The eGFP-expressing cells were stained positively for cardiac-specific proteins (>93%), expressed cardiac-specific genes, displayed cardiac-specific action-potentials, and could form stable myocardial cell grafts following in vivo cell transplantation. The generation of these transgenic hESC lines may be used to identify and study early cardiac precursors for developmental studies, to robustly quantify the extent of cardiomyocyte differentiation, to label the cells for in vivo grafting, and to allow derivation of purified cell populations of cardiomyocytes for future myocardial cell therapy strategies.