Utilizing Human-Induced Pluripotent Stem Cells to Study Cardiac Electroporation Pulsed-Field Ablation

BACKGROUND

Electroporation is a promising nonthermal ablation method for cardiac arrhythmia treatment. Although initial clinical studies found electroporation pulsed-field ablation (PFA) both safe and efficacious, there are significant knowledge gaps concerning the mechanistic nature and electrophysiological consequences of cardiomyocyte electroporation, contributed by the paucity of suitable human in vitro models. Here, we aimed to establish and characterize a functional in vitro model based on human-induced pluripotent stem cells (hiPSCs)-derived cardiac tissue, and to study the fundamentals of cardiac PFA.

METHODS

hiPSC-derived cardiomyocytes were seeded as circular cell sheets and subjected to different PFA protocols. Detailed optical mapping, cellular, and molecular characterizations were performed to study PFA mechanisms and electrophysiological outcomes.

RESULTS

PFA generated electrically silenced lesions within the hiPSC-derived cardiac circular cell sheets, resulting in areas of conduction block. Both reversible and irreversible electroporation components were identified. Significant electroporation reversibility was documented within 5 to 15-minutes post-PFA. Irreversibly electroporated regions persisted at 24-hours post-PFA. Per single pulse, high-frequency PFA was less efficacious than standard (monophasic) PFA, whereas increasing pulse-number augmented lesion size and diminished reversible electroporation. PFA augmentation could also be achieved by increasing extracellular Ca2+ levels. Flow-cytometry experiments revealed that regulated cell death played an important role following PFA. Assessing for PFA antiarrhythmic properties, sustainable lines of conduction block could be generated using PFA, which could either terminate or isolate arrhythmic activity in the hiPSC-derived cardiac circular cell sheets.

CONCLUSIONS

Cardiac electroporation may be studied using hiPSC-derived cardiac tissue, providing novel insights into PFA temporal and electrophysiological characteristics, facilitating electroporation protocol optimization, screening for potential PFA-sensitizers, and investigating the mechanistic nature of PFA antiarrhythmic properties.

Utilizing human induced pluripotent stem cells to study atrial arrhythmias in the short QT syndrome

BACKGROUND

Among the monogenic inherited causes of atrial fibrillation is the short QT syndrome (SQTS), a rare channelopathy causing atrial and ventricular arrhythmias. One of the limitations in studying the mechanisms and optimizing treatment of SQTS-related atrial arrhythmias has been the lack of relevant human atrial tissues models.

OBJECTIVE

To generate a unique model to study SQTS-related atrial arrhythmias by combining the use of patient-specific human induced pluripotent stem cells (hiPSCs), atrial-specific differentiation schemes, two-dimensional tissue modeling, optical mapping, and drug testing.

METHODS AND RESULTS

SQTS (N588K KCNH2 mutation), isogenic-control, and healthy-control hiPSCs were coaxed to differentiate into atrial cardiomyocytes using a retinoic-acid based differentiation protocol. The atrial identity of the cells was confirmed by a distinctive pattern of MLC2v downregulation, connexin 40 upregulation, shorter and triangular-shaped action potentials (APs), and expression of the atrial-specific acetylcholine-sensitive potassium current. In comparison to the healthy- and isogenic control cells, the SQTS-hiPSC atrial cardiomyocytes displayed abbreviated APs and refractory periods along with an augmented rapidly activating delayed-rectifier potassium current (IKr). Optical mapping of a hiPSC-based atrial tissue model of the SQTS displayed shortened APD and altered biophysical properties of spiral waves induced in this model, manifested by accelerated spiral-wave frequency and increased rotor curvature. Both AP shortening and arrhythmia irregularities were reversed by quinidine and vernakalant treatment, but not by sotalol.

CONCLUSIONS

Patient-specific hiPSC-based atrial cellular and tissue models of the SQTS were established, which provide examples on how this type of modeling can shed light on the pathogenesis and pharmacological treatment of inherited atrial arrhythmias.

shRNAs Targeting a Common KCNQ1 Variant Could Alleviate Long-QT1 Disease Severity by Inhibiting a Mutant Allele

Long-QT syndrome type 1 (LQT1) is caused by mutations in KCNQ1. Patients heterozygous for such a mutation co-assemble both mutant and wild-type KCNQ1-encoded subunits into tetrameric Kv7.1 potassium channels. Here, we investigated whether allele-specific inhibition of mutant KCNQ1 by targeting a common variant can shift the balance towards increased incorporation of the wild-type allele to alleviate the disease in human-induced pluripotent stem-cell-derived cardiomyocytes (hiPSC-CMs). We identified the single nucleotide polymorphisms (SNP) rs1057128 (G/A) in KCNQ1, with a heterozygosity of 27% in the European population. Next, we determined allele-specificity of short-hairpin RNAs (shRNAs) targeting either allele of this SNP in hiPSC-CMs that carry an LQT1 mutation. Our shRNAs downregulated 60% of the A allele and 40% of the G allele without affecting the non-targeted allele. Suppression of the mutant KCNQ1 allele by 60% decreased the occurrence of arrhythmic events in hiPSC-CMs measured by a voltage-sensitive reporter, while suppression of the wild-type allele increased the occurrence of arrhythmic events. Furthermore, computer simulations based on another LQT1 mutation revealed that 60% suppression of the mutant KCNQ1 allele shortens the prolonged action potential in an adult cardiomyocyte model. We conclude that allele-specific inhibition of a mutant KCNQ1 allele by targeting a common variant may alleviate the disease. This novel approach avoids the need to design shRNAs to target every single mutation and opens up the exciting possibility of treating multiple LQT1-causing mutations with only two shRNAs.

Characterization of the mechanism by which a nonsense variant in RYR2 leads to disordered calcium handling

Heterozygous missense variants of the cardiac ryanodine receptor gene (RYR2) cause catecholaminergic polymorphic ventricular tachycardia (CPVT). These missense variants of RYR2 result in a gain of function of the ryanodine receptors, characterized by increased sensitivity to activation by calcium that results in an increased propensity to develop calcium waves and delayed afterdepolarizations. We have recently detected a nonsense variant in RYR2 in a young patient who suffered an unexplained cardiac arrest. To understand the mechanism by which this variant in RYR2, p.(Arg4790Ter), leads to ventricular arrhythmias, human induced pluripotent stem cells (hiPSCs) harboring the novel nonsense variant in RYR2 were generated and differentiated into cardiomyocytes (RYR2-hiPSC-CMs) and molecular and calcium handling properties were studied. RYR2-hiPSC-CMs displayed significant calcium handling abnormalities at baseline and following treatment with isoproterenol. Treatment with carvedilol and nebivolol resulted in a significant reduction in calcium handling abnormalities in the RYR2-hiPSC-CMs. Expression of the mutant RYR2 allele was confirmed at the mRNA level and partial silencing of the mutant allele resulted in a reduction in calcium handling abnormalities at baseline. The nonsense variant behaves similarly to other gain of function variants in RYR2. Carvedilol and nebivolol may be suitable treatments for patients with gain of function RYR2 variants.

Optogenetic Control of Human Induced Pluripotent Stem Cell-Derived Cardiac Tissue Models

Background

Optogenetics, using light‐sensitive proteins, emerged as a unique experimental paradigm to modulate cardiac excitability. We aimed to develop high‐resolution optogenetic approaches to modulate electrical activity in 2‐ and 3‐dimensional cardiac tissue models derived from human induced pluripotent stem cell (hiPSC)‐derived cardiomyocytes.

Methods and Results

To establish light‐controllable cardiac tissue models, opsin‐carrying HEK293 cells, expressing the light‐sensitive cationic‐channel CoChR, were mixed with hiPSC‐cardiomyocytes to generate 2‐dimensional hiPSC‐derived cardiac cell‐sheets or 3‐dimensional engineered heart tissues. Complex illumination patterns were designed with a high‐resolution digital micro‐mirror device. Optical mapping and force measurements were used to evaluate the tissues' electromechanical properties. The ability to optogenetically pace and shape the tissue's conduction properties was demonstrated by using single or multiple illumination stimulation sites, complex illumination patterns, or diffuse illumination. This allowed to establish in vitro models for optogenetic‐based cardiac resynchronization therapy, where the electrical activation could be synchronized (hiPSC‐derived cardiac cell‐sheets and engineered heart tissue models) and contractile properties improved (engineered heart tissues). Next, reentrant activity (rotors) was induced in the hiPSC‐derived cardiac cell‐sheets and engineered heart tissue models through optogenetics programmed‐ or cross‐field stimulations. Diffuse illumination protocols were then used to terminate arrhythmias, demonstrating the potential to study optogenetics cardioversion mechanisms and to identify optimal illumination parameters for arrhythmia termination.

Conclusions

By combining optogenetics and hiPSC technologies, light‐controllable human cardiac tissue models could be established, in which tissue excitability can be modulated in a functional, reversible, and localized manner. This approach may bring a unique value for physiological/pathophysiological studies, for disease modeling, and for developing optogenetic‐based cardiac pacing, resynchronization, and defibrillation approaches.

Study and modulation of cardiac electroporation with a novel model utilizing human induced pluripotent stem cells

Background

Cardiac electroporation is a promising novel non-thermal ablation method, gaining significant interest with recent first-in-man data suggesting effective cardiac lesion generation with no collateral damage. Nevertheless, significant knowledge gaps exist regarding its electrophysiological consequences in cardiomyocytes, including; cell specificity, protocol optimization, irreversibility threshold, recovery time-constants, and the mechanistic nature of its cytolytic and anti-arrhythmic properties.

Purpose

Establishing an innovative in-vitro model for the study of cardiac electroporation-ablation, utilizing human induced pluripotent stem cells (hiPSCs).

Methods and results

Healthy-control hiPSC-derived cardiomyocytes were enzymatically dissociated and seeded as circular cell sheets (hiPSC-CCSs). Electroporation-ablation experiments were performed using a custom designed high-frequency electroporation (HF-EP) generator. Two needle-shaped electrodes were used for HF-EP delivery (Figure 1). Subsequently, detailed voltage- and Ca2+-mapping studies of the hiPSC-CCSs were conducted (Figure 2). HF-EP application resulted in the generation of electrically isolated lesions within the hiPSC-CCSs (Figure 3). Further characterization of the temporal changes and electrophysiological properties following electroporation revealed that; (1) lesions persisted over prolonged periods of time (days), indicating irreversible electroporation, (2) a temporal decrease in lesion dimensions was noted, consistent with a significant reversible electroporation component (Figures 3–5), (3) most tissue recovery had occurred within the first 15 minutes following electroporation, with little recovery beyond that time-frame, (4) increasing pulse-number augmented lesion area as well as the proportion of irreversible damage, and (5) electroporation sensitization was achieved by increasing extracellular Ca2+, indicating its crucial role in electroporation cytolysis, potentially via direct cellular toxicity and apoptosis facilitation (Figures 5–6). Finally, evaluating for HF-EP anti-arrhythmic properties, we targeted multiple rotors or focal triggered-activity generated in the hiPSC-CCSs. HF-EP application generated sustained line-blocks, isolating arrhythmogenic substrates within the hiPSC-CCSs while blocking the propagation of arrhythmic wavefronts (Figure 7).

Conclusion

Our results demonstrate the ability to study cardiac electroporation utilizing hiPSC-derived cardiomyocytes, provide novel insights into its temporal and electrophysiological characteristics, facilitate electroporation protocol optimization, screen for potential electroporation sensitizers, and to study its mechanistic nature and anti-arrhythmic properties.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): Division of Cardiology, and Tamman Cardiovascular Research Institute, Leviev Heart Center, Sheba Medical Center - Tel Hashomer, Ramat-Gan, Israel Figures 1–4Figures 5–7

Light-controllable recellularized ventricular and atrial tissues

Introduction

Construction of three-dimensional ventricular and atrial patches using decellularized extracellular matrix could allow the creation of “organ-like” structures for disease modeling, drug testing and regenerative medicine applications. To engineer functional artificial anatomical hearts several obstacles need to be overcome including generation of chamber-specific cells, prevention of immune reaction and donor/host tissue electrical coupling.

Purpose

In order to tackle these challenges we aimed to combine human induced pluripotent stem cell (hiPSC) technology, developmental biology inspired differentiation system to generate chamber-specific cardiomyocytes, decellularization/recellularization processes, and optogenetics utilizing light-sensitive ion channels to generate light-controllable atrial/ventricular tissue engineered patches.

Material and method

Atrial and ventricular patches of adult rats were decellularized using 1% SDS, 3% triton-X. The decellularized scaffolds were then recellularized with hiPSC- derived cardiomyocytes (2x107 atrial or ventricular cells). Adenoviral transduction was used to express the light-sensitive cationic channel ChR2 in the tissue engineered constructs.

Results and discussion

Eight days after cell seeding, we observed the development of spontaneous contraction of the atrial/ventricular tissues. Immunostaining for atrial (Cx40) or ventricular (MLC-2V) markers, gene expression, action-potential morphology, and the response to chamber-specific pharmacology confirmed the atrial/ventricular specific identity of the patches. Histological examination confirmed the preservation of the macro/micro- atrial/ventricular anatomical features in the generated chamber-specific recellularized patches. Optical mapping, using an EM-CCD camera, was used to characterize the conduction and repolarization properties of the generated tissues. The engineered patches could be paced and their electrical activity controlled by either electrical or optogenetic stimulation. Finally, arrhythmogenic reentrant arrhythmias could be induced in the tissue models and terminated by using optogenetic stimulation (“optogenetic-defibrillation”).

Conclusions

Three-dimensional light-sensitive chamber-specific engineered heart patches could be generated that could be controlled and manipulated through electrical and light pacing. These tissue could be used for several pathophysiological, drug testing, disease modeling and regenerative medicine applications.

Funding Acknowledgement

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): H2020-ERC-COG

Optogenetic modulation of cardiac action potential properties may prevent arrhythmogenesis in short and long QT syndromes

Abnormal action potential (AP) properties, as occurs in long or short QT syndromes (LQTS and SQTS, respectively), can cause life-threatening arrhythmias. Optogenetics strategies, utilizing light-sensitive proteins, have emerged as experimental platforms for cardiac pacing, resynchronization, and defibrillation. We tested the hypothesis that similar optogenetic tools can modulate the cardiomyocyte's AP properties, as a potentially novel antiarrhythmic strategy. Healthy control and LQTS/SQTS patient-specific human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were transduced to express the light-sensitive cationic channel channelrhodopsin-2 (ChR2) or the anionic-selective opsin, ACR2. Detailed patch-clamp, confocal-microscopy, and optical mapping studies evaluated the ability of spatiotemporally defined optogenetic protocols to modulate AP properties and prevent arrhythmogenesis in the hiPSC-CMs cell/tissue models. Depending on illumination timing, light-induced ChR2 activation induced robust prolongation or mild shortening of AP duration (APD), while ACR2 activation allowed effective APD shortening. Fine-tuning these approaches allowed for the normalization of pathological AP properties and suppression of arrhythmogenicity in the LQTS/SQTS hiPSC-CM cellular models. We next established a SQTS-hiPSC-CMs-based tissue model of reentrant-arrhythmias using optogenetic cross-field stimulation. An APD-modulating optogenetic protocol was then designed to dynamically prolong APD of the propagating wavefront, completely preventing arrhythmogenesis in this model. This work highlights the potential of optogenetics in studying repolarization abnormalities and in developing novel antiarrhythmic therapies.

Using Decellularization/Recellularization Processes to Prepare Liver and Cardiac Engineered Tissues

Tissue engineering provides unique opportunities for disease modeling, drug testing, and regenerative medicine applications. The use of cell-seeded scaffolds to promote tissue development is the hallmark of the tissue engineering. Among the different types of scaffolds (derived from either natural or synthetic polymers) used in the field, the use of decellularized tissues/organs is specifically attractive. The decellularization process involves the removal of native cells from the original tissue, allowing for the preservation of the three-dimensional (3D) macroscopic and microscopic structures of the tissue and extracellular matrix (ECM) composition. Following recellularization, the resulting scaffold provides the seeded cells with the appropriate biological signals and mechanical properties of the original tissue. Here, we describe different methods to create viable scaffolds from decellularized heart and liver as useful tools to study and exploit ECM biological key factors for the generation of engineered tissues with enhanced regenerative properties.

Development, behaviour and sensory processing in Marshall-Smith syndrome and Malan syndrome: phenotype comparison in two related syndromes

BACKGROUND

Ultrarare Marshall-Smith and Malan syndromes, caused by changes of the gene nuclear factor I X (NFIX), are characterised by intellectual disability (ID) and behavioural problems, although questions remain. Here, development and behaviour are studied and compared in a cross-sectional study, and results are presented with genetic findings.

METHODS

Behavioural phenotypes are compared of eight individuals with Marshall-Smith syndrome (three male individuals) and seven with Malan syndrome (four male individuals). Long-term follow-up assessment of cognition and adaptive behaviour was possible in three individuals with Marshall-Smith syndrome.

RESULTS

Marshall-Smith syndrome individuals have more severe ID, less adaptive behaviour, more impaired speech and less reciprocal interaction compared with individuals with Malan syndrome. Sensory processing difficulties occur in both syndromes. Follow-up measurement of cognition and adaptive behaviour in Marshall-Smith syndrome shows different individual learning curves over time.

CONCLUSIONS

Results show significant between and within syndrome variability. Different NFIX variants underlie distinct clinical phenotypes leading to separate entities. Cognitive, adaptive and sensory impairments are common in both syndromes and increase the risk of challenging behaviour. This study highlights the value of considering behaviour within developmental and environmental context. To improve quality of life, adaptations to environment and treatment are suggested to create a better person-environment fit.

Engineered heart tissue models from hiPSC-derived cardiomyocytes and cardiac ECM for disease modeling and drug testing applications

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. STATEMENT OF SIGNIFICANCE: 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).

Human Induced Pluripotent Stem Cell-Derived Cardiac Cell Sheets Expressing Genetically Encoded Voltage Indicator for Pharmacological and Arrhythmia Studies

Fulfilling the potential of human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes for studying conduction and arrhythmogenesis requires development of multicellular models and methods for long-term repeated tissue phenotyping. We generated confluent hiPSC-derived cardiac cell sheets (hiPSC-CCSs), expressing the genetically encoded voltage indicator ArcLight. ArcLight-based optical mapping allowed generation of activation and action-potential duration (APD) maps, which were validated by mapping the same hiPSC-CCSs with the voltage-sensitive dye, Di-4-ANBDQBS. ArcLight mapping allowed long-term assessment of electrical remodeling in the hiPSC-CCSs and evaluation of drug-induced conduction slowing (carbenoxolone, lidocaine, and quinidine) and APD prolongation (quinidine and dofetilide). The latter studies also enabled step-by-step depiction of drug-induced arrhythmogenesis ("torsades de pointes in the culture dish") and its prevention by MgSO₄ and rapid pacing. Phase-mapping analysis allowed biophysical characterization of spiral waves induced in the hiPSC-CCSs and their termination by electrical cardioversion and overdrive pacing. In conclusion, ArcLight mapping of hiPSC-CCSs provides a powerful tool for drug testing and arrhythmia investigation.

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Optical mapping of hiPSC-derived cardiac cell sheets expressing ArcLight

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Evaluating effects of drugs and time (weeks) on conduction and APD

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Mapping drug-induced TdP and electrically induced spiral waves (rotors)

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Evaluating interventions aiming to prevent or terminate arrhythmias in the model

Patient-Specific Drug Screening Using a Human Induced Pluripotent Stem Cell Model of Catecholaminergic Polymorphic Ventricular Tachycardia Type 2

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia type 2 (CPVT2) results from autosomal recessive CASQ2 mutations, causing abnormal Ca²⁺-handling and malignant ventricular arrhythmias. We aimed to establish a patient-specific human induced pluripotent stem cell (hiPSC) model of CPVT2 and to use the generated hiPSC-derived cardiomyocytes to gain insights into patient-specific disease mechanism and pharmacotherapy.

METHODS AND RESULTS

hiPSC cardiomyocytes were derived from a CPVT2 patient (D307H-CASQ2 mutation) and from healthy controls. Laser-confocal Ca²⁺ and voltage imaging showed significant Ca²⁺-transient irregularities, marked arrhythmogenicity manifested by early afterdepolarizations and triggered arrhythmias, and reduced threshold for store overload-induced Ca²⁺-release events in the CPVT2-hiPSC cardiomyocytes when compared with healthy control cells. Pharmacological studies revealed the prevention of adrenergic-induced arrhythmias by β-blockers (propranolol and carvedilol), flecainide, and the neuronal sodium-channel blocker riluzole; a direct antiarrhythmic action of carvedilol (independent of its α/β-adrenergic blocking activity), flecainide, and riluzole; and suppression of abnormal Ca²⁺ cycling by the ryanodine stabilizer JTV-519 and carvedilol. Mechanistic insights were gained on the different antiarrhythmic actions of the aforementioned drugs, with carvedilol and JTV-519 (but not flecainide or riluzole) acting primarily through sarcoplasmic reticulum stabilization. Finally, comparable outcomes were found between flecainide and labetalol antiarrhythmic effects in vitro and the clinical results in the same patient.

CONCLUSIONS

These results demonstrate the ability of hiPSCs cardiomyocytes to recapitulate CPVT2 disease phenotype and drug response in the culture dish, to provide novel insights into disease and drug therapy mechanisms, and potentially to tailor patient-specific drug therapy.

Monitoring Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes with Genetically Encoded Calcium and Voltage Fluorescent Reporters

The advent of the human-induced pluripotent stem cell (hiPSC) technology has transformed biomedical research, providing new tools for human disease modeling, drug development, and regenerative medicine. To fulfill its unique potential in the cardiovascular field, efficient methods should be developed for high-resolution, large-scale, long-term, and serial functional cellular phenotyping of hiPSC-derived cardiomyocytes (hiPSC-CMs). To achieve this goal, we combined the hiPSC technology with genetically encoded voltage (ArcLight) and calcium (GCaMP5G) fluorescent indicators. Expression of ArcLight and GCaMP5G in hiPSC-CMs permitted to reliably follow changes in transmembrane potential and intracellular calcium levels, respectively. This allowed monitoring short- and long-term changes in action-potential and calcium-handling properties and the development of arrhythmias in response to several pharmaceutical agents and in hiPSC-CMs derived from patients with different inherited arrhythmogenic syndromes. Combining genetically encoded fluorescent reporters with hiPSC-CMs may bring a unique value to the study of inherited disorders, developmental biology, and drug development and testing.

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Expression of genetically encoded voltage and calcium reporters in hiPSC-CMs

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Analysis of the electrophysiological and calcium-handling properties of hiPSC-CMs

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Drug screening using the optically derived action potentials and calcium transients

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Modeling of inherited disorders with hiPSC-CMs expressing fluorescent reporters

Corynebacterium species nasal carriage in pigs and their farmers in Bavaria, Germany: implications for public health

Reports on cases of human diphtheria caused by toxigenic Corynebacterium ulcerans that were linked to occupational swine contact as well as isolation of C ulcerans from wild boars have suggested that pigs might serve as reservoir for human infections. Therefore, a prevalence study on Corynebacterium species nasal carriage in pigs and their farmers was performed between August 1 and December 31, 2009, in 41 swine farms from Bavaria, Germany. All 411 asymptomatic pigs and 29 of 30 healthy farmers were colonised with Corynebacterium strains of up to 11 different species. No potentially toxigenic Corynebacterium strain was isolated either from the pigs or from their farmers, respectively. The patterns of the species composition in the pigs and the farmers were very similar, suggesting a potential transmission of strains between animals and humans.

Seltene Lokalisation eines adenoidzystischen Karzinoms im Nasenrachenraum

We report the case of a 63-year-old patient suffering from a nasopharyngeal adenoid cystic carcinoma. She presented with increased oral secretion and pharyngeal irritation, Horner's syndrome, and trigeminal neuralgia. Magnetic resonance imaging scans revealed a tumor of the nasopharyngeal space invading the right cranial base. Lymph node metastases were clinically excluded. The histological sample confirmed an adenoid cystic carcinoma, which was therapeutically treated with adequate radiotherapy. Based on the presented case report and a review of the literature, we discuss the diagnosis and treatment of adenoid cystic carcinomas of the nasopharynx.

Modeling of arrhythmogenic right ventricular cardiomyopathy with human induced pluripotent stem cells

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a primary heart muscle disorder resulting from desmosomal protein mutations. ARVC is characterized pathologically by fibrofatty infiltration and clinically by arrhythmias and sudden cardiac death. We aimed to establish a patient-/disease-specific human induced pluripotent stem cell (hiPSC) model of ARVC.

METHODS AND RESULTS

Dermal fibroblasts were obtained from 2 patients with ARVC with plakophilin-2 (PKP2) mutations, reprogrammed to generate hiPSCs, coaxed to differentiate into cardiomyocytes (CMs), and then compared with healthy control hiPSC-derived CMs (hiPSC-CMs). Real-time polymerase chain reaction showed a significant decrease in the expression of PKP2 in the ARVC-hiPSC-CMs. Immunostainings revealed reduced densities of PKP2, the associated desmosomal protein plakoglobin, and the gap-junction protein connexin-43. Electrophysiological assessment demonstrated prolonged field potential rise time in the ARVC-hiPSC-CMs. Transmission electron microscopy identified widened and distorted desmosomes in the ARVC-hiPSC-CMs. Clusters of lipid droplets were identified in the ARVC-CMs that displayed the more severe desmosomal pathology. This finding was associated with upregulation of the proadipogenic transcription factor peroxisome proliferator-activated receptor-γ. Exposure of the cells to apidogenic stimuli augmented desmosomal distortion and lipid accumulation. The latter phenomenon was prevented by application of a specific inhibitor of glycogen synthase kinase 3β (6-bromoindirubin-3'-oxime).

CONCLUSIONS

This study highlights the unique potential of the hiPSC technology for modeling inherited cardiac disorders in general and ARVC specifically. The hiPSC-CMs were demonstrated to recapitulate the ARVC phenotype in the dish, provide mechanistic insights into early disease pathogenesis, and provide a unique platform for drug discovery and testing in this disorder.

Modeling of catecholaminergic polymorphic ventricular tachycardia with patient-specific human-induced pluripotent stem cells

OBJECTIVES

The goal of this study was to establish a patient-specific human-induced pluripotent stem cells (hiPSCs) model of catecholaminergic polymorphic ventricular tachycardia (CPVT).

BACKGROUND

CPVT is a familial arrhythmogenic syndrome characterized by abnormal calcium (Ca(2+)) handling, ventricular arrhythmias, and sudden cardiac death.

METHODS

Dermal fibroblasts were obtained from a CPVT patient due to the M4109R heterozygous point RYR2 mutation and reprogrammed to generate the CPVT-hiPSCs. The patient-specific hiPSCs were coaxed to differentiate into the cardiac lineage and compared with healthy control hiPSCs-derived cardiomyocytes (hiPSCs-CMs).

RESULTS

Intracellular electrophysiological recordings demonstrated the development of delayed afterdepolarizations in 69% of the CPVT-hiPSCs-CMs compared with 11% in healthy control cardiomyocytes. Adrenergic stimulation by isoproterenol (1 μM) or forskolin (5 μM) increased the frequency and magnitude of afterdepolarizations and also led to development of triggered activity in the CPVT-hiPSCs-CMs. In contrast, flecainide (10 μM) and thapsigargin (10 μM) eliminated all afterdepolarizations in these cells. The latter finding suggests an important role for internal Ca(2+) stores in the pathogenesis of delayed afterdepolarizations. Laser-confocal Ca(2+) imaging revealed significant whole-cell [Ca(2+)] transient irregularities (frequent local and large-storage Ca(2+)-release events, broad and double-humped transients, and triggered activity) in the CPVT cardiomyocytes that worsened with adrenergic stimulation and Ca(2+) overload and improved with beta-blockers. Store-overload-induced Ca(2+) release was also identified in the hiPSCs-CMs and the threshold for such events was significantly reduced in the CPVT cells.

CONCLUSIONS

This study highlights the potential of hiPSCs for studying inherited arrhythmogenic syndromes, in general, and CPVT specifically. As such, it represents a promising paradigm to study disease mechanisms, optimize patient care, and aid in the development of new therapies.

Derivation and cardiomyocyte differentiation of induced pluripotent stem cells from heart failure patients

AIMS

Myocardial cell replacement therapies are hampered by a paucity of sources for human cardiomyocytes and by the expected immune rejection of allogeneic cell grafts. The ability to derive patient-specific human-induced pluripotent stem cells (hiPSCs) may provide a solution to these challenges. We aimed to derive hiPSCs from heart failure (HF) patients, to induce their cardiomyocyte differentiation, to characterize the generated hiPSC-derived cardiomyocytes (hiPSC-CMs), and to evaluate their ability to integrate with pre-existing cardiac tissue.

METHODS AND RESULTS

Dermal fibroblasts from two HF patients were reprogrammed by retroviral delivery of Oct4, Sox2, and Klf4 or by using an excisable polycistronic lentiviral vector. The resulting HF-hiPSCs displayed adequate reprogramming properties and could be induced to differentiate into cardiomyocytes with the same efficiency as control hiPSCs (derived from human foreskin fibroblasts). Gene expression and immunostaining studies confirmed the cardiomyocyte phenotype of the differentiating HF-hiPSC-CMs. Multi-electrode array recordings revealed the development of a functional cardiac syncytium and adequate chronotropic responses to adrenergic and cholinergic stimulation. Next, functional integration and synchronized electrical activities were demonstrated between hiPSC-CMs and neonatal rat cardiomyocytes in co-culture studies. Finally, in vivo transplantation studies in the rat heart revealed the ability of the HF-hiPSC-CMs to engraft, survive, and structurally integrate with host cardiomyocytes.

CONCLUSIONS

Human-induced pluripotent stem cells can be established from patients with advanced heart failure and coaxed to differentiate into cardiomyocytes, which can integrate with host cardiac tissue. This novel source for patient-specific heart cells may bring a unique value to the emerging field of cardiac regenerative medicine.

In vivo assessment of the electrophysiological integration and arrhythmogenic risk of myocardial cell transplantation strategies

Cell replacement strategies are promising interventions aiming to improve myocardial performance. Yet, the electrophysiological impact of these approaches has not been elucidated. We assessed the electrophysiological consequences of grafting of two candidate cell types, that is, skeletal myoblasts and human embryonic stem cell-derived cardiomyocytes (hESC-CMs). The fluorescently labeled (DiO) candidate cells were grafted into the rat's left ventricular myocardium. Two weeks later, optical mapping was performed using the Langendorff-perfused rat heart preparation. Images were obtained with appropriate filters to delineate the heart's anatomy, to identify the DiO-labeled cells, and to associate this information with the voltage-mapping data (using the voltage-sensitive dye PGH-I). Histological examination revealed the lack of gap junctions between grafted skeletal myotubes and host cardiomyocytes. In contrast, positive Cx43 immunostaining was observed between donor and host cardiomyocytes in the hESC-CMs-transplanted hearts. Optical mapping demonstrated either normal conduction (four of six) or minimal conduction slowing (two of six) at the hESC-CMs engraftment sites. In contrast, marked slowing of conduction or conduction block was seen (seven of eight) at the myoblast transplantation sites. Ventricular arrhythmias could not be induced in the hESC-CM hearts following programmed electrical stimulation but were inducible in 50% of the myoblast-engrafted hearts. In summary, a unique method for assessment of the electrophysiological impact of myocardial cell therapy is presented. Our results demonstrate the ability of hESC-CMs to functionally integrate with host tissue. In contrast, transplantation of cells that do not form gap junctions (skeletal myoblats) led to localized conduction disturbances and to the generation of a proarrhythmogenic substrate.

Calcium handling in human induced pluripotent stem cell derived cardiomyocytes

BACKGROUND

The 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 Ca(2+)-handling properties of hiPSCs derived-cardiomyocytes (hiPSC-CMs).

METHODOLOGY/PRINCIPAL FINDINGS

RT-PCR and immunocytochemistry experiments identified the expression of key Ca(2+)-handling proteins. Detailed laser confocal Ca(2+) imaging demonstrated spontaneous whole-cell [Ca(2+)](i) transients. These transients required Ca(2+) influx via L-type Ca(2+) channels, as demonstrated by their elimination in the absence of extracellular Ca(2+) or by administration of the L-type Ca(2+) channel blocker nifedipine. The presence of a functional ryanodine receptor (RyR)-mediated sarcoplasmic reticulum (SR) Ca(2+) store, contributing to [Ca(2+)](i) transients, was established by application of caffeine (triggering a rapid increase in cytosolic Ca(2+)) and ryanodine (decreasing [Ca(2+)](i)). Similarly, the importance of Ca(2+) reuptake into the SR via the SR Ca(2+) ATPase (SERCA) pump was demonstrated by the inhibiting effect of its blocker (thapsigargin), which led to [Ca(2+)](i) transients elimination. Finally, the presence of an IP3-releasable Ca(2+) pool in hiPSC-CMs and its contribution to whole-cell [Ca(2+)](i) transients was demonstrated by the inhibitory effects induced by the IP3-receptor blocker 2-Aminoethoxydiphenyl borate (2-APB) and the phospholipase C inhibitor U73122.

CONCLUSIONS/SIGNIFICANCE

Our study establishes the presence of a functional, SERCA-sequestering, RyR-mediated SR Ca(2+) store in hiPSC-CMs. Furthermore, it demonstrates the dependency of whole-cell [Ca(2+)](i) transients in hiPSC-CMs on both sarcolemmal Ca(2+) entry via L-type Ca(2+) channels and intracellular store Ca(2+) release.

A multiplex one-step real-time RT-PCR assay for influenza surveillance

For surveillance purposes real-time PCR assays for influenza viruses had to be adapted to the pandemic influenza A(H1N1)2009 strain. We combined published primers and probes for influenza A, influenza B and an internal amplification control with a detection system for influenza A(H1N1)2009 to set up a rapid, reliable, simple and cost-effective high-throughput multiplex one-step real-time RT-PCR. The workflow also includes automated sample preparation for high-throughput screening. The lower limit of detection of the multiplex assay was 3.5x102 RNA copies per PCR reaction. The diagnostic sensitivity of the multiplex assay was 87.7%, but increased to 99.4% for influenza-positive samples yielding Ct values of less than 34 cycles in the respective diagnostic assay. High specificity was confirmed by sequencing and correct detection of 15 reference samples from two quality assurance studies. The multiplex PCR was introduced for surveillance of samples from a network of general practitioners and paediatricians in Bavaria, Germany during the influenza pandemic of 2009. Comparison with surveillance data from reported cases proved the reliability of the multiplex assay for influenza surveillance programmes.

A multiplex one-step real-time RT-PCR assay for influenza surveillance

For surveillance purposes real-time PCR assays for influenza viruses had to be adapted to the pandemic influenza A(H1N1)2009 strain. We combined published primers and probes for influenza A, influenza B and an internal amplification control with a detection system for influenza A(H1N1)2009 to set up a rapid, reliable, simple and cost-effective high-throughput multiplex one-step real-time RT-PCR. The workflow also includes automated sample preparation for high-throughput screening. The lower limit of detection of the multiplex assay was 3.5x10(2) RNA copies per PCR reaction. The diagnostic sensitivity of the multiplex assay was 87.7%, but increased to 99.4% for influenza-positive samples yielding C(t) values of less than 34 cycles in the respective diagnostic assay. High specificity was confirmed by sequencing and correct detection of 15 reference samples from two quality assurance studies. The multiplex PCR was introduced for surveillance of samples from a network of general practitioners and paediatricians in Bavaria, Germany during the influenza pandemic of 2009. Comparison with surveillance data from reported cases proved the reliability of the multiplex assay for influenza surveillance programmes.

Reprogramming of telomeric regions during the generation of human induced pluripotent stem cells and subsequent differentiation into fibroblast-like derivatives

Human induced pluripotent stem (hiPS) cells provide therapeutic promises, as well as a potent in vitro model for studying biological processes which take place during human embryonic development and subsequent differentiation in normal and disease states. The epigenetic characteristics of iPS cells are reprogrammed to the embryonic state at which they acquire pluripotency. In addition, telomeres in hiPS cell must elongate sufficiently to provide the necessary replicative potential. Recent studies have demonstrated that the epigenetic characteristics of telomeric and subtelomeric regions are pivotal in regulating telomere length. Here we study telomere length, subtelomeric DNA methylation and telomeric-repeat-containing RNA (TERRA) expression in several hiPS cell clones derived from normal neonatal foreskin fibroblasts. We find that telomeres lengthen significantly in hiPS cells in comparison to the parental fibroblast source, and progressively shorten after differentiation back into fibroblast-like cells, concomitantly with telomerase activation and down-regulation, respectively. Subtelomeres in hiPS cells were found to be generally hypermethylated in comparison to the parental source. However bisulfite analysis revealed that at several subtelomeres examined, methylation levels differed between hiPS clones and that both de novo methylation and demethylation processes occurred during telomere reprogramming. Notably, although subtelomeres were in general very highly methylated, TERRA levels were elevated in hiPS cells, albeit to different degrees in the various clones. TERRA elevation may reflect enhanced stability or impaired degradation in hiPS cells, and/or alternatively, increased transcription from the hypomethylated subtelomeres. We suggest that TERRA may play a role in regulation of appropriate telomere function and length in hiPS cells.

Matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometry as a tool for rapid diagnosis of potentially toxigenic Corynebacterium species in the laboratory management of diphtheria-associated bacteria

The rapid identification of the potentially toxigenic Corynebacterium species, C. diphtheriae, C. ulcerans and C. pseudotuberculosis is essential for diagnosis and treatment of diphtheria and diphtheria-like diseases. We used matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDIT-OF MS) in comparison with classical microbiological and molecular methods on 116 Corynebacterium strains. All 90 potentially toxigenic Corynebacterium strains collected by the German National Consiliary Laboratory on Diphtheria in a period of more than ten years were correctly identified by MALDI-TOF MS. We propose an algorithm for fast and reliable diagnosis of diphtheria incorporating MALDI-TOF MS, real-time tox PCR and Elek testing.

Rapid detection and differentiation of Campylobacter jejuni, Campylobacter coli, and Campylobacter lari in food, using multiplex real-time PCR

A multiplex real-time PCR assay based on four differently labeled TaqMan probes for detection and differentiation of the thermophilic Campylobacter species C. jejuni, C. coli, and C. lari was established and validated in food products. This assay combines two previously published PCR assays for C. jejuni and C. coli with a newly developed detection assay for C. lari and an internal amplification control system. The selectivity of the method was determined by analyzing 70 Campylobacter strains and 43 strains of other bacteria. The sensitivity was 50 fg of C. jejuni and C. lari DNA and 500 fg of C. coli DNA per PCR. It was possible to detect 1 to 10 CFU/25 g of food before preenrichment of all three species. More than 400 samples of various foods (poultry, seafood, and meat) were analyzed after 48 h of preenrichment parallel to the conventional diagnostic method of culture and biochemical identification. Using the established real-time PCR assay, 55.4% of the samples were recognized as positive for thermophilic Campylobacter species, whereas with the conventional method only 40.3% of the samples were positive. The real-time PCR assay also detected contaminations with two different Campylobacter species in 32.6% of the analyzed poultry samples, a finding of epidemiological interest. Compared with the original PCR method, which was established for the differentiation of bacterial isolates of C. jejuni and C. coli, this new method also detects and distinguishes C. lari, was validated as an analytical tool for food analysis, and provides reliable and extensive results within 2 days.

Methods for human embryonic stem cells derived cardiomyocytes cultivation, genetic manipulation, and transplantation

A decade has passed since the initial derivation of human embryonic stem cells (hESC). The ensuing years have witnessed a significant progress in the development of methodologies allowing cell cultivation, differentiation, genetic manipulation, and in vivo transplantation. Specifically, the potential to derive human cardiomyocytes from the hESC lines, which can be used for several basic and applied cardiovascular research areas including in the emerging field of cardiac regenerative medicine, attracted significant attention from the scientific community. This resulted in the development of protocols for the cultivation of hESC and their successful differentiation toward the cardiomyocyte lineage fate. In this chapter, we will describe in detail methods related to the cultivation, genetic manipulation, selection, and in vivo transplantation of hESC-derived cardiomyocytes.

Cardiomyocyte differentiation of human induced pluripotent stem cells

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 cardiac-specific transcription factors and finally by cardiac-specific structural genes. Cells in the contracting embryoid bodies were stained positively for cardiac troponin-I, sarcomeric alpha-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.

Cell therapy for modification of the myocardial electrophysiological substrate

BACKGROUND

Traditional antiarrhythmic pharmacological therapies are limited by their global cardiac action, low efficacy, and significant proarrhythmic effects. We present a novel approach for the modification of the myocardial electrophysiological substrate using cell grafts genetically engineered to express specific ionic channels.

METHODS AND RESULTS

To test the aforementioned concept, we performed ex vivo, in vivo, and computer simulation studies to determine the ability of fibroblasts transfected to express the voltage-sensitive potassium channel Kv1.3 to modify the local myocardial excitable properties. Coculturing of the transfected fibroblasts with neonatal rat ventricular myocyte cultures resulted in a significant reduction (68%) in the spontaneous beating frequency of the cultures compared with baseline values and cocultures seeded with naive fibroblasts. In vivo grafting of the transfected fibroblasts in the rat ventricular myocardium significantly prolonged the local effective refractory period from an initial value of 84+/-8 ms (cycle length, 200 ms) to 154+/-13 ms (P<0.01). Margatoxin partially reversed this effect (effective refractory period, 117+/-8 ms; P<0.01). In contrast, effective refractory period did not change in nontransplanted sites (86+/-7 ms) and was only mildly increased in the animals injected with wild-type fibroblasts (73+/-5 to 88+/-4 ms; P<0.05). Similar effective refractory period prolongation also was found during slower pacing drives (cycle length, 350 to 500 ms) after transplantation of the potassium channels expressing fibroblasts (Kv1.3 and Kir2.1) in pigs. Computer modeling studies confirmed the in vivo results.

CONCLUSIONS

Genetically engineered cell grafts, transfected to express potassium channels, can couple with host cardiomyocytes and alter the local myocardial electrophysiological properties by reducing cardiac automaticity and prolonging refractoriness.

Identification and selection of cardiomyocytes during human embryonic stem cell differentiation

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.

Electromechanical integration of cardiomyocytes derived from human embryonic stem cells

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.

Mechanism of spontaneous excitability in human embryonic stem cell derived cardiomyocytes

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 microm) dramatically slowed conduction velocity from 5.1 to 3.2 cm s(-1) while 100 microm TTX caused complete cessation of spontaneous electrical activity in all EBs studied. In contrast, the Ca2+channel blockers nifedipine or diltiazem (1 microm) 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 microm TTX induced longer AP interpulse intervals and 10 microm TTX caused cessation of spontaneous APs. In contrast nifedipine (Ca2+ 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/dtmax) of 118 +/- 14 V s(-1) in control conditions; in contrast, partial block of Na+ current significantly reduced stimulated dV/dtmax (38 +/- 15 V s(-1)). RT-PCR revealed NaV1.5, CaV1.2, 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 NaV1.5; thus, the NaV1.5 Na+ channel is important for initiating spontaneous excitability in hES-derived heart cells.

Cytogenetic mapping and orientation of the rhesus macaque MHC

Applying fluorescence in situ hybridisation (FISH), six cosmid clones of rhesus macaque origin containing the genes SACM2L, RING1, BAT1 and MIC2, MIC3, MICD, and MOG of the major histocompatibility complex (MHC) were localised to the long arm of the rhesus macaque chromosome 6 in 6q24, the orthologous region to human 6p21.3. Furthermore, centromere to telomere orientation of the rhesus macaque MHC as well as the internal order of the MHC genes tested are the same as in human. Fiber-FISH allows a rough estimate of distances between these MHC genes in the rhesus macaque, and, as in the human, the rhesus macaque MHC comprises about 3 to 4 Mb.

Phylogenetic analysis and in situ identification of the intestinal microbial community of rainbow trout (Oncorhynchus mykiss, Walbaum)

AIMS

To identify the dominant culturable and nonculturable microbiota of rainbow trout intestine.

METHODS AND RESULTS

Microbial density of rainbow trout intestine was estimated by direct microscopic counts (4',6-diamidino-2-phenylindole, DAPI) and by culturing on tryptone soya agar (TSA). Differential gradient gel electrophoresis analysis of bacterial DNA from intestinal samples, re-amplification of bands and sequence analysis was used to identify the bacteria that dominated samples where aerobic counts were < or =2% of the DAPI counts. 16S rDNA gene sequences of 146 bacterial isolates and three sequences of uncultured bacteria were identified. A set of oligonucleotide probes was constructed and used to detect and enumerate the bacterial community structure of the gastrointestinal tract of rainbow trout by fluorescence in situ hybridization (FISH). Members of the gamma subclass of Proteobacteria (mainly Aeromonas and Enterobacteriaceae) dominated the bacterial population structure. Acinetobacter, Pseudomonas, Shewanella, Plesiomonas and Proteus were also identified together with isolates belonging to the beta subclass of Proteobacteria and Gram-positive bacteria with high and low DNA G + C content. In most samples, the aerobic count (on TSA) was 50-90% of the direct (DAPI) count. A bacterium representing a previously unknown phylogenetic lineage with only 89% 16S rRNA gene sequence similarity to Anaerofilum pentosovorans was detected in intestinal samples where aerobic counts were < or =2% of direct (DAPI) counts. Ten to 75% of the microbial population in samples with low aerobic counts hybridized (FISH) with a probe constructed against this not-yet cultured bacterium.

CONCLUSIONS

Proteobacteria belonging to the gamma subclass dominated the intestinal microbiota of rainbow trout. However, in some samples the microflora was dominated by uncultivated, presumed anaerobic, micro-organisms. The bacterial population structure of rainbow trout intestine, as well as total bacterial counts, varied from fish to fish.

SIGNIFICANCE AND IMPACT OF THE STUDY

Good correlation was seen between cultivation results and in situ analysis, however, a molecular approach was crucial for the identification of organisms uncultivated on TSA.

Neurological phenotype and synaptic function in mice lacking the CaV1.3 alpha subunit of neuronal L-type voltage-dependent Ca2+ channels

Neuronal L-type calcium channels have been implicated in pain perception and neuronal synaptic plasticity. To investigate this we have examined the effect of disrupting the gene encoding the CaV1.3 (alpha 1D) alpha subunit of L-type Ca2+ channels on neurological function, acute nociceptive behavior, and hippocampal synaptic function in mice. CaV1.3 alpha 1 subunit knockout (CaV1.3 alpha 1(-/-)) mice had relatively normal neurological function with the exception of reduced auditory evoked behavioral responses and lower body weight. Baseline thermal and mechanical thresholds were unaltered in these animals. CaV1.3 alpha 1(-/-) mice were also examined for differences in N-methyl-D-aspartate (NMDA) receptor-dependent (100 Hz tetanization for 1 s) and NMDA receptor-independent (200 Hz in 100 microM DL-2-amino-5-phosphopentanoic acid) long-term potentiation within the CA1 region of the hippocampus. Both NMDA receptor-dependent and NMDA receptor-independent forms of long-term potentiation were expressed normally. Radioligand binding studies revealed that the density of (+)[3H]isradipine binding sites in brain homogenates was reduced by 20-25% in CaV1.3 alpha 1(-/-) mice, without any detectable change in CaV1.2 (alpha 1C) protein levels as detected using Western blot analysis. Taken together these data indicate that following loss of CaV1.3 alpha 1 subunit expression there is sufficient residual activity of other Ca2+ channel subtypes to support NMDA receptor-independent long-term potentiation and some forms of sensory behavior/function.