Circulating microRNAs and cardiomyocyte proliferation in heart failure patients related to 10 years survival

AIMS

Mechanochemical signalling drives organogenesis and is highly conserved in mammal evolution. Regaining recovery in myocardial jeopardy by inducing principles linking cardiovascular therapy and clinical outcome has been the dream of scientists for decades. Concepts involving embryonic pathways to regenerate adult failing hearts became popular in the early millennium. Since then, abundant data on stem cell research have been published, never reaching widespread application in heart failure therapy. Another conceptual access, using mechanotransduction in cardiac veins to limit myocardial decay, is pressure-controlled intermittent coronary sinus occlusion (PICSO). Recently, we reported acute molecular signs and signals of PICSO activating regulatory miRNA and inducing cell proliferation mimicking cardiac development in adult failing hearts. According to a previously formulated hypothesis, 'embryonic recall', this study aimed to define molecular signals involved in endogenous heart repair during PICSO and study their relation to patient survival.

METHODS AND RESULTS

We previously reported a study on the acute molecular effects of PICSO in an observational non-randomized study. Eight out of the thirty-two patients with advanced heart failure undergoing cardiac resynchronization therapy (CRT) were treated with PICSO. Survival was monitored over 10 years, and coronary sinus blood samples were collected during intervention before and after 20 min and tested for miRNA signalling and proliferation when co-cultured with cardiomyocytes. A numerically lower death rate post-CRT and PICSO as compared with control CRT only, and a non-significant reduction in all-cause mortality risk of 42% was observed (37.5% vs. 54.0%, relative risk = 0.58, 95% confidence interval: 0.17-2.05; P = 0.402). Four miRNAs involved in cell cycle, proliferation, morphogenesis, embryonic development, and apoptosis significantly increased concomitantly in survivors and PICSO compared with a decrease in non-survivors (hsa-miR Let7b, P < 0.01; hsa-miR- 421, P < 0.006; hsa-miR 363-3p, P < 0.03 and hsa-miR 19b-3p P < 0.01). In contrast, three miRNAs involved in proliferation and survival, determining cell fate, and recycling endosomes decreased in survivors and PICSO (hsa miR 101-3p, P < 0.03; hsa-miR 25-3p, P < 002; hsa-miR 30d-5p P < 0.04). In vitro cellular proliferation increased in survivors and lowered in non-survivors showing a pattern distinction, discriminating longevity according to up to 10-year survival in heart failure patients.

CONCLUSIONS

This study proposes that generating regenerative signals observed during PICSO intervention relate to patient outcomes. Morphogenetic pathways induced by periods of flow reversal in cardiac veins in a domino-like pattern transform embryonic into regenerative signals. Studies supporting the conversion of mechanochemical signals into regenerative molecules during PICSO are warranted to substantiate predictive power on patient longevity, opening new therapeutic avenues in otherwise untreatable heart failure.

Angiotensin II type 1 receptor localizes at the blood-bile barrier in humans and pigs

Animal models and clinical studies suggest an influence of angiotensin II (AngII) on the pathogenesis of liver diseases via the renin–angiotensin system. AngII application increases portal blood pressure, reduces bile flow, and increases permeability of liver tight junctions. Establishing the subcellular localization of angiotensin II receptor type 1 (AT1R), the main AngII receptor, helps to understand the effects of AngII on the liver. We localized AT1R in situ in human and porcine liver and porcine gallbladder by immunohistochemistry. In order to do so, we characterized commercial anti-AT1R antibodies regarding their capability to recognize heterologous human AT1R in immunocytochemistry and on western blots, and to detect AT1R using overlap studies and AT1R-specific blocking peptides. In hepatocytes and canals of Hering, AT1R displayed a tram-track-like distribution, while in cholangiocytes AT1R appeared in a honeycomb-like pattern; i.e., in liver epithelia, AT1R showed an equivalent distribution to that in the apical junctional network, which seals bile canaliculi and bile ducts along the blood–bile barrier. In intrahepatic blood vessels, AT1R was most prominent in the tunica media. We confirmed AT1R localization in situ to the plasma membrane domain, particularly between tight and adherens junctions in both human and porcine hepatocytes, cholangiocytes, and gallbladder epithelial cells using different anti-AT1R antibodies. Localization of AT1R at the junctional complex could explain previously reported AngII effects and predestines AT1R as a transmitter of tight junction permeability.

Cav2.3 R-type calcium channels: from its discovery to pathogenic de novo CACNA1E variants: a historical perspective

So-called pharmacoresistant (R-type) voltage-gated Ca²⁺ channels are structurally only partially characterized. Most of them are encoded by the CACNA1E gene and are expressed as different Ca_v2.3 splice variants (variant Ca_v2.3a to Ca_v2.3e or f) as the ion conducting subunit. So far, no inherited disease is known for the CACNA1E gene but recently spontaneous mutations leading to early death were identified, which will be brought into focus. In addition, a short historical overview may highlight the development to understand that upregulation during aging, easier activation by spontaneous mutations or lack of bioavailable inorganic cations (Zn²⁺ and Cu²⁺) may lead to similar pathologies caused by cellular overexcitation.

In vitro and in vivo phosphorylation of the Cav2.3 voltage-gated R-type calcium channel

During the recording of whole cell currents from stably transfected HEK-293 cells, the decline of currents carried by the recombinant human Cav2.3+β3 channel subunits is related to adenosine triphosphate (ATP) depletion after rupture of the cells. It reduces the number of functional channels and leads to a progressive shift of voltage-dependent gating to more negative potentials (Neumaier F., et al., 2018). Both effects can be counteracted by hydrolysable ATP, whose protective action is almost completely prevented by inhibition of serine/threonine but not tyrosine or lipid kinases. These findings indicate that ATP promotes phosphorylation of either the channel or an associated protein, whereas dephosphorylation during cell dialysis results in run-down. Protein phosphorylation is required for Ca_v2.3 channel function and could directly influence the normal features of current carried by these channels. Therefore, results from in vitro and in vivo phosphorylation of Ca_v2.3 are summarized to come closer to a functional analysis of structural variations in Ca_v2.3 splice variants.

Loss of genomic integrity induced by lysosphingolipid imbalance drives ageing in the heart

Cardiac dysfunctions dramatically increase with age. Revealing a currently unknown contributor to cardiac ageing, we report the age-dependent, cardiac-specific accumulation of the lysosphingolipid sphinganine (dihydrosphingosine, DHS) as an evolutionarily conserved hallmark of the aged vertebrate heart. Mechanistically, the DHS-derivative sphinganine-1-phosphate (DHS1P) directly inhibits HDAC1, causing an aberrant elevation in histone acetylation and transcription levels, leading to DNA damage. Accordingly, the pharmacological interventions, preventing (i) the accumulation of DHS1P using SPHK2 inhibitors, (ii) the aberrant increase in histone acetylation using histone acetyltransferase (HAT) inhibitors, (iii) the DHS1P-dependent increase in transcription using an RNA polymerase II inhibitor, block DHS-induced DNA damage in human cardiomyocytes. Importantly, an increase in DHS levels in the hearts of healthy young adult mice leads to an impairment in cardiac functionality indicated by a significant reduction in left ventricular fractional shortening and ejection fraction, mimicking the functional deterioration of aged hearts. These molecular and functional defects can be partially prevented in vivo using HAT inhibitors. Together, we report an evolutionarily conserved mechanism by which increased DHS levels drive the decline in cardiac health.

yylncT Defines a Class of Divergently Transcribed lncRNAs and Safeguards the T-mediated Mesodermal Commitment of Human PSCs

Human protein-coding genes are often accompanied by divergently transcribed non-coding RNAs whose functions, especially in cell fate decisions, are poorly understood. Using an hESC-based cardiac differentiation model, we define a class of divergent lncRNAs, termed yin yang lncRNAs (yylncRNAs), that mirror the cell-type-specific expression pattern of their protein-coding counterparts. yylncRNAs are preferentially encoded from the genomic loci of key developmental cell fate regulators. Most yylncRNAs are spliced polyadenylated transcripts showing comparable expression patterns in vivo in mouse and in human embryos. Signifying their developmental function, the key mesoderm specifier BRACHYURY (T) is accompanied by yylncT, which localizes to the active T locus during mesoderm commitment. yylncT binds the de novo DNA methyltransferase DNMT3B, and its transcript is required for activation of the T locus, with yylncT depletion specifically abolishing mesodermal commitment. Collectively, we report a lncRNA-mediated regulatory layer safeguarding embryonic cell fate transitions.

Acute molecular effects of pressure-controlled intermittent coronary sinus occlusion in patients with advanced heart failure

Aims

Cardiac repair has steered clinical attention and remains an unmet need, because available regenerative therapies lack robust mechanistic evidence. Pressure‐controlled intermittent coronary sinus occlusion (PICSO), known to induce angiogenetic and vasoactive molecules as well as to reduce regional ischemia, may activate endogenous regenerative processes in failing myocardium. We aimed to investigate the effects of PICSO in patients with advanced heart failure undergoing cardiac resynchronization therapy.

Methods and results

Eight out of 32 patients were treated with PICSO, and the remainder served as controls. After electrode testing including left ventricular leads, PICSO was performed for 20 min. To test immediate molecular responses, in both patient groups, coronary venous blood samples were taken at baseline and after 20 min, the time required for the intervention. Sera were tested for microRNAs and growth factors. To test the ability of up‐regulated soluble factors on cell proliferation and expression of transcription factors [e.g. Krüppel‐like factor 4 (KLF‐4)], sera were co‐cultured with human cardiomyocytes and fibroblasts. As compared with controls, significant differential expression (differences between pre‐values and post‐values in relation to both patient cohorts) of microRNA patterns associated with cardiac development was observed with PICSO. Importantly, miR‐143 (P < 0.048) and miR‐145 (P < 0,047) increased, both targeting a network of transcription factors (including KLF‐4) that promote differentiation and repress proliferation of vascular smooth muscle cells. Additionally, an increase of miR‐19b (P < 0.019) known to alleviate endothelial cell apoptosis was found, whereas disadvantageous miR‐320b (P < 0.023) suspect to impair expression of c‐myc, normally provoking cell cycle re‐entry in post‐mitotic myocytes and miR‐25 (P < 0.023), decreased, a target of anti‐miR application to improve contractility in the failing heart. Co‐cultured post‐PICSO sera significantly increased cellular proliferation both in fibroblasts (P < 0.001) and adult cardiomycytes (P < 0.004) sampled from a transplant recipient as compared with controls. Adult cardiomyocytes showed a seven‐fold increase of the transcription factor KLF‐4 protein when co‐cultured with treated sera as compared with controls.

Conclusions

Here, we show for the first time that PICSO, a trans‐coronary sinus catheter intervention, is associated with an increase in morphogens secreted into cardiac veins, normally present during cardiac development, and a significant induction of cell proliferation. Present findings support the notion that epigenetic modifications, that is, haemodynamic stimuli on venous vascular cells, may reverse myocardial deterioration. Further investigations are needed to decipher the maze of complex interacting molecular pathways in failing myocardium and the potential role of PICSO to reinitiate developmental processes to prevent further myocardial decay eventually reaching clinical significance.

From state-of-the-art cell therapy to endogenous cardiac repair

Clinical heart failure prevention and contemporary therapy often involve breaking the vicious cycle of global haemodynamic consequences of myocardial decay. The lack of effective regenerative therapies results in a primary focus on preventing further deterioration of cardiac performance. The cellular transplantation hypothesis has been evaluated in many different preclinical models and a handful of important clinical trials. The primary expectation that cellular transplants will be embedded into failing myocardium and fuse with existing functioning cells appears unlikely. A multitude of cellular formulas, access routes and clinical surrogate endpoints for evaluation add to the complexity of cellular therapies. Several recent large clinical trials have provided insights into both the regenerative potential and clinical improvement from non-regenerative mechanisms. Initiating endogenous repair seems to be another meaningful alternative to recover structural integrity in myocardial injury. This option may be achieved using a transcoronary sinus catheter intervention, implying the understanding of basic principles in biology. With intermittent reduction of outflow in cardiac veins (PICSO), vascular cells appear to be activated and restart a programme similar to pathways in the developing heart. Structural regeneration may be possible without requiring exogenous agents, or a combination of both approaches may become clinical reality in the next decade.

A practical guide to the preparation and use of metal ion-buffered systems for physiological research

Recent recognition that mobile pools of Zn²⁺ and Cu²⁺ are involved in the regulation of neuronal, endocrine and other cells has stimulated the development of tools to visualize and quantify the level of free trace metal ions. Most of the methods used to measure or control loosely bound metals require reference media that contain exactly defined free concentrations of the target ions. Despite the central importance of proper metal ion buffering, there is still a lack of international standards and beginners in the field may have difficulties finding a coherent description of how to prepare trace metal ion buffers, especially when experiments are to be performed in multimetal systems. To close this gap, we provide a guide for the design, preparation and use of metal ion-buffered systems that facilitate immediate application under physiologically relevant ionic conditions. Thermodynamic and kinetic concepts of chemical speciation as well as general protocols and specific examples are outlined for the accurate preparation of single- and dual-metal ion buffers. In addition, experiments have been performed with FluoZin-3 to illustrate that metal ion-buffered systems are required for reliable preparation of nanomolar Zn²⁺ solutions and that dual-metal ion buffers can be used to calibrate suitable fluorescent Zn²⁺ sensors in the presence of millimolar Ca²⁺ concentrations. Together, the information provided should sensitize readers to the many potential pitfalls and uncertainties that exist when working with physiologically relevant concentrations of trace metal ions and enable them to formulate their own metal ion buffers for most in vitro applications.

Murine Short Axis Ventricular Heart Slices for Electrophysiological Studies

Murine cardiomyocytes have been extensively used for in vitro studies of cardiac physiology and new therapeutic strategies. However, multicellular preparations of dissociated cardiomyocytes are not representative of the complex in vivo structure of cardiomyocytes, non-myocytes and extracellular matrix, which influences both mechanical and electrophysiological properties of the heart. Here we describe a technique to prepare viable ventricular slices of adult mouse hearts with a preserved in vivo like tissue structure, and demonstrate their suitability for electrophysiological recordings. After excision of the heart, ventricles are separated from the atria, perfused with Ca²⁺-free solution containing 2,3-butanedione monoxime and embedded in a 4% low-melt agarose block. The block is placed on a microtome with a vibrating blade, and tissue slices with a thickness of 150-400 µm are prepared keeping the vibration frequency of the blade at 60-70 Hz and moving the blade forward as slowly as possible. Thickness of the slices depends on the further application. Slices are stored in ice cold Tyrode's solution with 0.9 mM Ca²⁺ and 2,3-butanedione monoxime (BDM) for 30 min. Afterwards, slices are transferred to 37 °C DMEM for 30 min to wash out the BDM. Slices can be used for electrophysiological studies with sharp electrodes or micro electrode arrays, for force measurements to analyze contractile function or to investigate the interaction of transplanted stem cell-derived cardiomyocytes and host tissue. For sharp electrode recordings, a slice is placed into a 3 cm cell culture dish on the heating plate of an inverted microscope. The slice is stimulated with a unipolar electrode, and intracellular action potentials of cardiomyocytes within the slice are recorded with a sharp glass electrode.

Medium-chain fatty acids modulate myocardial function via a cardiac odorant receptor

Several studies have demonstrated the expression of odorant receptors (OR) in various human tissues and their involvement in different physiological and pathophysiological processes. However, the functional role of ORs in the human heart is still unclear. Here, we firstly report the functional characterization of an OR in the human heart. Initial next-generation sequencing analysis revealed the OR expression pattern in the adult and fetal human heart and identified the fatty acid-sensing OR51E1 as the most highly expressed OR in both cardiac development stages. An extensive characterization of the OR51E1 ligand profile by luciferase reporter gene activation assay identified 2-ethylhexanoic acid as a receptor antagonist and various structurally related fatty acids as novel OR51E1 ligands, some of which were detected at receptor-activating concentrations in plasma and epicardial adipose tissue. Functional investigation of the endogenous receptor was carried out by Ca²⁺ imaging of human stem cell-derived cardiomyocytes. Application of OR51E1 ligands induced negative chronotropic effects that depended on activation of the OR. OR51E1 activation also provoked a negative inotropic action in cardiac trabeculae and slice preparations of human explanted ventricles. These findings indicate that OR51E1 may play a role as metabolic regulator of cardiac function.

A lncRNA Perspective into (Re)Building the Heart

Our conception of the human genome, long focused on the 2% that codes for proteins, has profoundly changed since its first draft assembly in 2001. Since then, an unanticipatedly expansive functionality and convolution has been attributed to the majority of the genome that is transcribed in a cell-type/context-specific manner into transcripts with no apparent protein coding ability. While the majority of these transcripts, currently annotated as long non-coding RNAs (lncRNAs), are functionally uncharacterized, their prominent role in embryonic development and tissue homeostasis, especially in the context of the heart, is emerging. In this review, we summarize and discuss the latest advances in understanding the relevance of lncRNAs in (re)building the heart.

R-Type Voltage-Gated Ca²⁺ Channels in Cardiac and Neuronal Rhythmogenesis

During the past decades, an increasing number of ion channel and transporter types have been identified acting together to produce cardiac and neuronal pacemaker action potentials. The basis of pacemaker activity was understood in more detail by using single-microelectrode recordings on cells isolated from pacemaker regions. Meanwhile, this powerful technique was complemented by computer modeling and recombinant technologies, including gene inactivation of ion channels and transporters, which may be involved in the generation of the electrical activity of pacemaker cells. Several genes of the voltage-gated Ca(2+) channel (VGCC) family have been ablated, and their role in cardiac and neuronal pacemaking is compared in the present summary, focusing on the role of murine R-type voltage-gated Ca(2+) channels encoded by cacna1e and expressing the ion conducting subunit Cav2.3.

Neuronal developmental gene and miRNA signatures induced by histone deacetylase inhibitors in human embryonic stem cells

Human embryonic stem cells (hESCs) may be applied to develop human-relevant sensitive in vitro test systems for monitoring developmental toxicants. The aim of this study was to identify potential developmental toxicity mechanisms of the histone deacetylase inhibitors (HDAC) valproic acid (VPA), suberoylanilide hydroxamic acid (SAHA) and trichostatin A (TSA) relevant to the in vivo condition using a hESC model in combination with specific differentiation protocols and genome-wide gene expression and microRNA profiling. Analysis of the gene expression data showed that VPA repressed neural tube and dorsal forebrain (OTX2, ISL1, EMX2 and SOX10)-related transcripts. In addition, VPA upregulates axonogenesis and ventral forebrain-associated genes, such as SLIT1, SEMA3A, DLX2/4 and GAD2. HDACi-induced expression of miR-378 and knockdown of miR-378 increases the expression of OTX2 and EMX2, which supports our hypothesis that HDACi targets forebrain markers through miR-378. In conclusion, multilineage differentiation in vitro test system is very sensitive for monitoring molecular activities relevant to in vivo neuronal developmental toxicity. Moreover, miR-378 seems to repress the expression of the OTX2 and EMX2 and therefore could be a regulator of the development of neural tube and dorsal forebrain neurons.

Neuregulin-1β induces mature ventricular cardiac differentiation from induced pluripotent stem cells contributing to cardiac tissue repair

Stem cell-derived cardiomyocytes (CMs) are often electrophysiologically immature and heterogeneous, which represents a major barrier to their in vitro and in vivo application. Therefore, the purpose of this study was to examine whether Neuregulin-1β (NRG-1β) treatment could enhance in vitro generation of mature "working-type" CMs from induced pluripotent stem (iPS) cells and assess the regenerative effects of these CMs on cardiac tissue after acute myocardial infarction (AMI). With that purpose, adult mouse fibroblast-derived iPS from α-MHC-GFP mice were derived and differentiated into CMs through NRG-1β and/or dimethyl sulfoxide (DMSO) treatment. Cardiac specification and maturation of the iPS was analyzed by gene expression array, quantitative real-time polymerase chain reaction, immunofluorescence, electron microscopy, and patch-clamp techniques. In vivo, the iPS-derived CMs or culture medium control were injected into the peri-infarct region of hearts after coronary artery ligation, and functional and histology changes were assessed from 1 to 8 weeks post-transplantation. On differentiation, the iPS displayed early and robust in vitro cardiogenesis, expressing cardiac-specific genes and proteins. More importantly, electrophysiological studies demonstrated that a more mature ventricular-like cardiac phenotype was achieved when cells were treated with NRG-1β and DMSO compared with DMSO alone. Furthermore, in vivo studies demonstrated that iPS-derived CMs were able to engraft and electromechanically couple to heart tissue, ultimately preserving cardiac function and inducing adequate heart tissue remodeling. In conclusion, we have demonstrated that combined treatment with NRG-1β and DMSO leads to efficient differentiation of iPS into ventricular-like cardiac cells with a higher degree of maturation, which are capable of preserving cardiac function and tissue viability when transplanted into a mouse model of AMI.

Mesenchymal stem cells and their conditioned medium improve integration of purified induced pluripotent stem cell-derived cardiomyocyte clusters into myocardial tissue

Induced pluripotent stem cell-derived cardiomyocytes (iPS-CMs) might become therapeutically relevant to regenerate myocardial damage. Purified iPS-CMs exhibit poor functional integration into myocardial tissue. The aim of this study was to investigate whether murine mesenchymal stem cells (MSCs) or their conditioned medium (MScond) improves the integration of murine iPS-CMs into myocardial tissue. Vital or nonvital embryonic murine ventricular tissue slices were cocultured with purified clusters of iPS-CMs in combination with murine embryonic fibroblasts (MEFs), MSCs, or MScond. Morphological integration was assessed by visual scoring and functional integration by isometric force and field potential measurements. We observed a moderate morphological integration of iPS-CM clusters into vital, but a poor integration into nonvital, slices. MEFs and MSCs but not MScond improved morphological integration of CMs into nonvital slices and enabled purified iPS-CMs to confer force. Coculture of vital slices with iPS-CMs and MEFs or MSCs resulted in an improved electrical integration. A comparable improvement of electrical coupling was achieved with the cell-free MScond, indicating that soluble factors secreted by MSCs were involved in electrical coupling. We conclude that cells such as MSCs support the engraftment and adhesion of CMs, and confer force to noncontractile tissue. Furthermore, soluble factors secreted by MSCs mediate electrical coupling of purified iPS-CM clusters to myocardial tissue. These data suggest that MSCs may increase the functional engraftment and therapeutic efficacy of transplanted iPS-CMs into infarcted myocardium.

Ca2+ signaling in human induced pluripotent stem cell-derived cardiomyocytes (iPS-CM) from normal and catecholaminergic polymorphic ventricular tachycardia (CPVT)-afflicted subjects

Derivation of cardiomyocytes from induced pluripotent stem cells (iPS-CMs) allowed us to probe the Ca(2+)-signaling parameters of human iPS-CMs from healthy- and catecholaminergic polymorphic ventricular tachycardia (CPVT1)-afflicted individuals carrying a novel point mutation p.F2483I in ryanodine receptors (RyR2). iPS-CMs were dissociated on day 30-40 of differentiation and patch-clamped within 3-6 days. Calcium currents (ICa) averaged ∼8pA/pF in control and mutant iPS-CMs. ICa-induced Ca(2+)-transients in control and mutant cells had bell-shaped voltage-dependence similar to that of ICa, consistent with Ca(2+)-induced Ca(2+)-release (CICR) mechanism. The ratio of ICa-activated to caffeine-triggered Ca(2+)-transients was ∼0.3 in both cell types. Caffeine-induced Ca(2+)-transients generated significantly smaller Na(+)-Ca(2+) exchanger current (INCX) in mutant cells, reflecting their smaller Ca(2+)-stores. The gain of CICR was voltage-dependent as in adult cardiomyocytes. Adrenergic agonists enhanced ICa, but differentially altered the CICR gain, diastolic Ca(2+), and Ca(2+)-sparks in mutant cells. The mutant cells, when Ca(2+)-overloaded, showed longer and wandering Ca(2+)-sparks that activated adjoining release sites, had larger CICR gain at -30mV yet smaller Ca(2+)-stores. We conclude that control and mutant iPS-CMs express the adult cardiomyocyte Ca(2+)-signaling phenotype. RyR2 F2483I mutant myocytes have aberrant unitary Ca(2+)-signaling, smaller Ca(2+)-stores, higher CICR gains, and sensitized adrenergic regulation, consistent with functionally altered Ca(2+)-release profile of CPVT syndrome.

Embryonic stem cells facilitate the isolation of persistent clonal cardiovascular progenitor cell lines and leukemia inhibitor factor maintains their self-renewal and myocardial differentiation potential in vitro

Compelling evidence for the existence of somatic stem cells in the heart of different mammalian species has been provided by numerous groups; however, so far it has not been possible to maintain these cells as self-renewing and phenotypically stable clonal cell lines in vitro. Thus, we sought to identify a surrogate stem cell niche for the isolation and persistent maintenance of stable clonal cardiovascular progenitor cell lines, enabling us to study the mechanism of self-renewal and differentiation in these cells. Using postnatal murine hearts with a selectable marker as the stem cell source and embryonic stem cells and leukemia inhibitory factor (LIF)-secreting fibroblasts as a surrogate niche, we succeeded in the isolation of stable clonal cardiovascular progenitor cell lines. These cell lines self-renew in an LIF-dependent manner. They express both stemness transcription factors Oct4, Sox2, and Nanog and early myocardial transcription factors Nkx2.5, GATA4, and Isl-1 at the same time. Upon LIF deprivation, they exclusively differentiate to functional cardiomyocytes and endothelial and smooth muscle cells, suggesting that these cells are mesodermal intermediates already committed to the cardiogenic lineage. Cardiovascular progenitor cell lines can be maintained for at least 149 passages over 7 years without phenotypic changes, in the presence of LIF-secreting fibroblasts. Isolation of wild-type cardiovascular progenitor cell lines from adolescent and old mice has finally demonstrated the general feasibility of this strategy for the isolation of phenotypically stable somatic stem cell lines.

Effects of spermine NONOate and ATP on protein aggregation: light scattering evidences

BACKGROUND AND OBJECTIVE

Regulating protein function in the cell by small molecules, provide a rapid, reversible and tunable tool of metabolic control. However, due to its complexity the issue is poorly studied so far. The effects of small solutes on protein behavior can be studied by examining changes of protein secondary structure, in its hydrodynamic radius as well as its thermal aggregation. The study aim was to investigate effects of adenosine-5'-triphosphate (ATP), spermine NONOate (NO donor) as well as sodium/potassium ions on thermal aggregation of albumin and hemoglobin. To follow aggregation of the proteins, their diffusion coefficients were measured by quasi-elastic light scattering (QELS) at constant pH (7.4) in the presence of solutes over a temperature range from 25°C to 80°C.

RESULTS AND DISCUSSION

1) Spermine NONOate persistently decreased the hemoglobin aggregation temperature Tairrespectively of the Na+/K+ environment, 2) ATP alone had no effect on the protein's thermal stability but it facilitated protein's destabilization in the presence of spermine NONOate and 3) mutual effects of ATP and NO were strongly influenced by particular buffer ionic compositions.

CONCLUSION

The ATP effect on protein aggregation was ambiguous: ATP alone had no effect on the protein's thermal stability but it facilitated protein's destabilization in the presence of nitric oxide. The magnitude and direction of the observed effects strongly depended on concentrations of K+ and Na+ in the solution.

Current status of human pluripotent stem cell based in vitro toxicity tests

The present review assesses the current status of in vitro tests based on human pluripotent stem cell-derived toxicologically relevant target cells. The majority of the evaluated test systems are in the phase of test development. In particular the success rates of differentiation protocols and their reproducibility are varying depending on different culture conditions but also on the assessed marker panel and the functional evaluation of the cells. However, the amount of differentiated cells decreases in relation to their maturation status. No harmonization has been achieved yet about the required maturation status of the cellular models to be used for toxicological applications. Even with an established cellular model, the selection of appropriate readouts is challenging. Some areas of toxicity, such as developmental toxicity, suffer from insufficient knowledge on predictive biomarkers which leads to difficulties in the selection of the most appropriate endpoints. In this heterogeneous context the rapidly increasing knowledge about 'omics' technologies, might lead to an improvement of the current situation and allow the establishment of more predictive human in vitro toxicity tests.

The influence of dexamethasone administration on the protection against doxorubicin-induced cardiotoxicity in purified embryonic stem cell-derived cardiomyocytes

Embryonic stem cells (ESCs) have various uses in drug toxicity, as they can be easily differentiated in vitro. However, one of the major obstacles in the assessment of these differentiated cells is the presence of a heterogeneous cell population. To circumvent this problem, purified ESC-derived desired cells by means of the tissue-specific GFP and/or antibiotic resistance gene expression has been proposed. Therefore, this study aimed to assess the role of doxorubicin (DOX) in cardiotoxicity by using genetically engineered purified ESC-derived cardiomyocytes under the control alpha-myosin heavy chain promoter. The results revealed that ESCs are suitable for evaluation of DOX cardiotoxicity. This study showed that DOX cardiotoxicity was reduced as detected by beating cardiomyocytes and caspase activity only by pretreatment with dexamethasone (DEX), not during or post-DOX treatment. DEX influence appears to be mediated via glucocorticoid receptor and enhances cardiomyocyte-specific gene expression. Therefore, for the general assessment of cytotoxicity, non-genetically engineered ESC-derived cardiomyocytes are sufficient but for the molecular assessment of DOX-induced toxicity, genetically engineered purified ESC-derived cardiomyocytes are necessary.

In vitro cellular models for cardiac development and pharmacotoxicology

Permanent cultures of cardiac cells described so far have limited value for studying cell biology and pharmacology of the developing heart because of the loss of proliferative capacity and cardiac-specific properties of cardiomyocytes during long-term cultivation. Pluripotent embryonic carcinoma (EC) and embryonic stem (ES) cells cultivated as permanent lines offer a new approach for studying cardiogenic differentiation in vitro. We describe cardiogenesis in vitro by differentiating EC and ES cells by way of embryo-like aggregates (embryoid bodies) into spontaneously beating cardiomyocytes. During cardiomyocyte differentiation three distinct developmental stages were defined by expression of specific action potentials and ionic currents measured by the whole-cell patch-clamp technique. Whereas early differentiated cardiomyocytes are characterized by action potentials and ionic currents typical for early pacemaker cells, terminally differentiated cardiomyocytes show action potentials and ionic currents inherent to ventricular-, atrial- or sinus nodal-like cells. These functional characteristics are in accordance with the expression of alpha- and beta-cardiac myosin heavy chain at early differentiation stages and the additional expression of ventricular-specific MLC-2V and atrial-specific ANF genes at terminal stages demonstrated by reverse transcription polymerase chain reaction (RT-PCR) analysis. Pharmacological studies performed by measuring chronotropic responses and by analysing the Ca(2+) channel activity correspond to data obtained with cardiac cells from living organisms. For testing the influence of exogenous compounds on cardiac differentiation the teratogenic compound retinoic acid (RA) was applied during distinct stages of embryoid body development. A temporally controlled influence of RA on cardiac differentiation and expression of cardiac-specific genes was found. We conclude that ES cell-derived cardiomyocytes provide an excellent cellular model to study early cardiac development and to perform pharmacological and embryotoxicological investigations.

Effects of spermine NONOate and ATP on the thermal stability of hemoglobin

Background

Minor changes in protein structure induced by small organic and inorganic molecules can result in significant metabolic effects. The effects can be even more profound if the molecular players are chemically active and present in the cell in considerable amounts. The aim of our study was to investigate effects of a nitric oxide donor (spermine NONOate), ATP and sodium/potassium environment on the dynamics of thermal unfolding of human hemoglobin (Hb). The effect of these molecules was examined by means of circular dichroism spectrometry (CD) in the temperature range between 25°C and 70°C. The alpha-helical content of buffered hemoglobin samples (0.1 mg/ml) was estimated via ellipticity change measurements at a heating rate of 1°C/min.

Results

Major results were: 1) spermine NONOate persistently decreased the hemoglobin unfolding temperature _Tuirrespectively of the ^{Na +} /^{K +} environment, 2) ATP instead increased the unfolding temperature by 3°C in both sodium-based and potassium-based buffers and 3) mutual effects of ATP and NO were strongly influenced by particular buffer ionic compositions. Moreover, the presence of potassium facilitated a partial unfolding of alpha-helical structures even at room temperature.

Conclusion

The obtained data might shed more light on molecular mechanisms and biophysics involved in the regulation of protein activity by small solutes in the cell.

Time-course of the electrophysiological maturation and integration of transplanted cardiomyocytes

Electrophysiological maturation and integration of transplanted cardiomyocytes are essential to enhance safety and efficiency of cell replacement therapy. Yet, little is known about these important processes. The aim of our study was to perform a detailed analysis of electrophysiological maturation and integration of transplanted cardiomyocytes. Fetal cardiomyocytes expressing enhanced green fluorescent protein were transplanted into cryoinjured mouse hearts. At 6, 9 and 12 days after transplantation, viable slices of recipient hearts were prepared and action potentials of transplanted and host cardiomyocytes within the slices were recorded by microelectrodes. In transplanted cells embedded in healthy host myocardium, action potential duration at 50% repolarization (APD50) decreased from 32.2 ± 3.3 ms at day 6 to 27.9 ± 2.6 ms at day 9 and 19.6 ± 1.6 ms at day 12. The latter value matched the APD50 of host cells (20.5 ± 3.2 ms, P=0.78). Integration improved in the course of time: 26% of cells at day 6 and 53% at day 12 revealed no conduction blocks up to a stimulation frequency of 10 Hz. APD50 was inversely correlated to the quality of electrical integration. In transplanted cells embedded into the cryoinjury, which showed no electrical integration, APD50 was 49.2 ± 4.3 ms at day 12. Fetal cardiomyocytes transplanted into healthy myocardium integrate electrically and mature after transplantation, their action potential properties after 12 days are comparable to those of host cardiomyocytes. Quality of electrical integration improves over time, but conduction blocks still occur at day 12 after transplantation. The pace of maturation correlates with the quality of electrical integration. Transplanted cells embedded in cryoinjured tissue still possess immature electrophysiological properties after 12 days.

Derivation Of ES Cells From Early Stage Preimplantation Embryos And Characterisation Of Their Cardiac Differentiation Potential In Mice

Most murine embryonic stem cell lines have been derived from the inner cell mass of blastocysts and extensively studied in different aspects including generation of organ specific cells. However, no detailed studies have been made on cardiac specific gene expression, immunocytochemical and electrophysiological characterisation of cardiomyocytes generated from early stage (preimplantation) embryo derived embryonic stem cells in mice. In the present study, new embryonic stem cell lines were derived from early stage preimplanatation embryos in mice. In vitro differentiation of such cell lines readily generated cardiomyocytes, which expressed different cardiac specific genes in a temporally regulated manner as well as cardiac cells specific proteins. This is probably the first report, which showed the temporal pattern of cardiac specific genes as well as protein expression in cardiac cells generated from in vitro differentiation of preimplantation embryo derived ES cells.

Contractile properties of early human embryonic stem cell-derived cardiomyocytes: beta-adrenergic stimulation induces positive chronotropy and lusitropy but not inotropy

Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) provide the unique opportunity to study the very early development of the human heart. The aim of this study was to investigate the effect of calcium and beta-adrenergic stimulation on the contractile properties of early hESC-CMs. Beating clusters containing hESC-CMs were co-cultured in vitro with noncontractile slices of neonatal murine ventricles. After 5-7 days, when beating clusters had integrated morphologically into the damaged tissue, isometric force measurements were performed during spontaneous beating as well as during electrical field stimulation. Spontaneous beating stopped when extracellular calcium ([Ca²⁺](ec)) was removed or after administration of the Ca²⁺ channel blocker nifedipine. During field stimulation at a constant rate, the developed force increased with incremental concentrations of [Ca²⁺](ec). During spontaneous beating, rising [Ca²⁺](ec) increased beating rate and developed force up to a [Ca²⁺](ec) of 2.5 mM. When [Ca²⁺](ec) was increased further, spontaneous beating rate decreased, whereas the developed force continued to increase. The beta-adrenergic agonist isoproterenol induced a dose-dependent increase of the frequency of spontaneous beating; however, it did not significantly change the developed force during spontaneous contractions or during electrical stimulation at a constant rate. Force developed by early hESC-CMs depends on [Ca²⁺](ec) and on the L-type Ca²⁺ channel. The lack of an inotropic reaction despite a pronounced chronotropic response after beta-adrenergic stimulation most likely indicates immaturity of the sarcoplasmic reticulum. For cell-replacement strategies, further maturation of cardiac cells has to be achieved either in vitro before or in vivo after transplantation.

Characterisation of a neural teratogenicity assay based on human ESCs differentiation following exposure to valproic acid

The development of in vitro testing strategies for chemical and drug screening is a priority need in order to protect human health, to increase safety, to reduce the number of animals required for conventional testing methods and finally to meet the deadlines of current legislations. The aim of this work was to design an alternative testing method based on human embryonic stem cells for the detection of prenatal neural toxicity. For this purpose we have created a model based on the generation of neural rosettes, reproducing in vitro the gastrulation events recapitulating the formation of the neural tube in vivo. To validate the model we have exposed this complex cell system to increasing concentrations of valproic acid, a known teratogenic agent, to analyse the morphological and molecular changes induced by the toxicant. Specific assays were applied to discriminate between cytotoxicity and specific neural toxicity. Transcriptomic analysis was performed with a microarray Affimetrix platform and validated by quantitative real time RT-PCR for the expression of genes involved in early neural development, neural tube formation and neural cells migration, key biological processes in which the effect of valproic acid is most relevant. The results demonstrated that neural rosette cells respond to valproic acid exposure with molecular and morphological changes similar to those observed in vivo, indicating that this method represents a promising alternative test for the detection of human prenatal neural toxicity.

Effect of chemopreventive agents on differentiation of mouse embryonic stem cells

Chemopreventive agents are derived from edible plants and from ancient time is a part of daily intake for many humans and animals. There are several lines of compelling evidence from epidemiological, clinical and laboratory studies that these dietary constituents are associated in reducing cancer risks. However, developmental toxicity of these natural compounds cannot be excluded. In the present study, we examined the effect of chemopreventive agents on the differentiation of mouse embryonic stem cells (ESCs) as an in vitro embryotoxicity model. We assumed that inhibition of developmentally regulated genes in vitro might predict developmental toxicity also under in vivo conditions. We found that epigallocatechin gallate (EGCG) (20 microM) induced the expression of mesodermal and cardiomyocyte genes and a significant increase in the number and the percentage of cardiomyocytes. The increase of the subpopulation correlated with higher numbers of beating foci and beating frequencies. Curcumin on the other hand at 0.4 mM was seen to enhance expression of ectodermal transcripts. Quercetin (2.5 microM) was found to inhibit several developmentally regulated genes.

A tanscriptomics study to elucidate the toxicological mechanism of methylmercury chloride in a human stem cell based in vitro test

Traditional approaches in evaluating the hazard of drug candidates on the developing offspring are often time-consuming and cost-intensive. Moreover, variations in the toxicological response of different animal species to the tested substance cause severe problems when extrapolating safety dosages for humans. Therefore, more predictive and relevant toxicological systems based on human cell models are required. In the presented study the environmental toxicant methylmercury chloride (MeHgCl), known to cause structural developmental abnormalities in the brain, was used as reference compound to develop a concept contributing to a mechanistic understanding of the toxicity of an investigated substance. Despite the fact, that there are significant data available from animal studies and from poisonings in Japan and Iraq, uncertainties on the mechanism of MeHgCl during human development are still remaining and qualify the substance for further analysis. Transcriptomics analysis in combination with a human cell based in vitro model has been used in order to elucidate the toxicity of MeHgCl at molecular level. Differentiating neural precursor cells that have been exposed continuously to non- and low-cytotoxic concentrations of MeHgCl were investigated. Quantitative change in the mRNA expression profiles of selected genes demonstrated the sensitivity of the cell model and its qualification for a transcriptomics study screening changes in the expression profile of the complete human genome of MeHgCl-treated human neural cells. Potential biomarkers were identified and these candidate marker genes as well as their involvement in a possible toxic mechanism of MeHgCl during the human neurulation process are hereby introduced. The study confirmed the hypothesis that a cellular model based on a human stem cell line can be applied for elucidating unknown mode of actions of developmental toxicants.

In vitro modeling of ryanodine receptor 2 dysfunction using human induced pluripotent stem cells

BACKGROUND/AIMS

Induced pluripotent stem (iPS) cells generated from accessible adult cells of patients with genetic diseases open unprecedented opportunities for exploring the pathophysiology of human diseases in vitro. Catecholaminergic polymorphic ventricular tachycardia type 1 (CPVT1) is an inherited cardiac disorder that is caused by mutations in the cardiac ryanodine receptor type 2 gene (RYR2) and is characterized by stress-induced ventricular arrhythmia that can lead to sudden cardiac death in young individuals. The aim of this study was to generate iPS cells from a patient with CPVT1 and determine whether iPS cell-derived cardiomyocytes carrying patient specific RYR2 mutation recapitulate the disease phenotype in vitro.

METHODS

iPS cells were derived from dermal fibroblasts of healthy donors and a patient with CPVT1 carrying the novel heterozygous autosomal dominant mutation p.F2483I in the RYR2. Functional properties of iPS cell derived-cardiomyocytes were analyzed by using whole-cell current and voltage clamp and calcium imaging techniques.

RESULTS

Patch-clamp recordings revealed arrhythmias and delayed afterdepolarizations (DADs) after catecholaminergic stimulation of CPVT1-iPS cell-derived cardiomyocytes. Calcium imaging studies showed that, compared to healthy cardiomyocytes, CPVT1-cardiomyocytes exhibit higher amplitudes and longer durations of spontaneous Ca(2+) release events at basal state. In addition, in CPVT1-cardiomyocytes the Ca(2+)-induced Ca(2+)-release events continued after repolarization and were abolished by increasing the cytosolic cAMP levels with forskolin.

CONCLUSION

This study demonstrates the suitability of iPS cells in modeling RYR2-related cardiac disorders in vitro and opens new opportunities for investigating the disease mechanism in vitro, developing new drugs, predicting their toxicity, and optimizing current treatment strategies.

Effective surface-based cryopreservation of human embryonic stem cells by vitrification

Human embryonic stem cells (hESCs) are candidates for many applications in the areas of regenerative medicine, tissue engineering, basic scientific research as well as pharmacology and toxicology. However, use of hESCs is limited by their sensitivity to freezing and thawing procedures. Hence, this emerging science needs new, reliable preservation methods for the long-term storage of large quantities of functional hESCs remaining pluripotent after post-thawing and culturing. Here, we present a highly efficient, surface based vitrification method for the cryopreservation of large numbers of adherent hESC colonies, using modified cell culture substrates. This technique results in much better post-thaw survival rate compared to cryopreservation in suspension and allows a quick and precise handling and storage of the cells, indicating low differentiation rates.

Cytosine arabinoside induces ectoderm and inhibits mesoderm expression in human embryonic stem cells during multilineage differentiation

BACKGROUND AND PURPOSE

Teratogenic substances induce adverse effects during the development of the embryo. Multilineage differentiation of human embryonic stem cells (hESCs) mimics the development of the embryo in vitro. Here, we propose a transcriptomic approach in hESCs for monitoring specific toxic effects of compounds as an alternative to traditional time-consuming and cost-intensive in vivo tests requiring large numbers of animals. This study was undertaken to explore the adverse effects of cytosine arabinoside (Ara-C) on randomly differentiated hESCs.

EXPERIMENTAL APPROACH

Human embryonic stem cells were used to investigate the effects of a developmental toxicant Ara-C. Sublethal concentrations of Ara-C were given for two time points, day 7 and day 14 during the differentiation. Gene expression was assessed with microarrays to determine the dysregulated transcripts in presence of Ara-C.

KEY RESULTS

Randomly differentiated hESCs were able to generate the multilineage markers. The low concentration of Ara-C (1 nM) induced the ectoderm and inhibited the mesoderm at day 14. The induction of ectodermal markers such as MAP2, TUBB III, PAX6, TH and NESTIN was observed with an inhibition of mesodermal markers such as HAND2, PITX2, GATA5, MYL4, TNNT2, COL1A1 and COL1A2. In addition, no induction of apoptosis was observed. Gene ontology revealed unique dysregulated biological process related to neuronal differentiation and mesoderm development. Pathway analysis showed the axon guidance pathway to be dysregulated.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that hESCs in combination with toxicogenomics offer a sensitive in vitro developmental toxicity model as an alternative to traditional animal experiments.

Fibroblasts support functional integration of purified embryonic stem cell-derived cardiomyocytes into avital myocardial tissue

Transplantation of purified pluripotent stem cell-derived cardiomyocytes into damaged myocardium might become a therapy to improve contractile function after myocardial infarction. However, engraftment remains problematic. Aim of this study was to investigate whether murine embryonic fibroblasts (MEFs) support the functional integration of purified embryonic stem cell-derived cardiomyocytes (ES-CMs). Neonatal murine ventricular tissue slices were subjected to oxygen and glucose deprivation to simulate irreversible ischemia. Vital tissue slices served as control. Vital and avital tissue slices were cultured with or without MEFs before coculturing with clusters of puromycin-selected ES-CMs. Integration of ES-CM clusters was assessed morphologically, motility by long-term microscopy, and functional integration by isometric force measurements. We observed a good morphological integration into vital but a poor integration into avital slices. Adding MEFs improved morphological integration into irreversibly damaged slices and enabled purified ES-CMs to migrate and to confer force. We conclude that noncardiomyocytes like MEFs support morphological integration and force transmission of purified ES-CMs by enabling adhesion and migration.