[Show abstract][Hide abstract] ABSTRACT: Human embryonic stem cell-derived endothelial cells (hESC-EC), as well as other stem cell derived endothelial cells, have a range of applications in cardiovascular research and disease treatment. Endothelial cells sense Gram-negative bacteria via the pattern recognition receptors (PRR) Toll-like receptor (TLR)-4 and nucleotide-binding oligomerisation domain-containing protein (NOD)-1. These pathways are important in terms of sensing infection, but TLR4 is also associated with vascular inflammation and atherosclerosis. Here, we have compared TLR4 and NOD1 responses in hESC-EC with those of endothelial cells derived from other stem cells and with human umbilical vein endothelial cells (HUVEC). HUVEC, endothelial cells derived from blood progenitors (blood outgrowth endothelial cells; BOEC), and from induced pluripotent stem cells all displayed both a TLR4 and NOD1 response. However, hESC-EC had no TLR4 function, but did have functional NOD1 receptors. In vivo conditioning in nude rats did not confer TLR4 expression in hESC-EC. Despite having no TLR4 function, hESC-EC sensed Gram-negative bacteria, a response that was found to be mediated by NOD1 and the associated RIP2 signalling pathways. Thus, hESC-EC are TLR4 deficient but respond to bacteria via NOD1. This data suggests that hESC-EC may be protected from unwanted TLR4-mediated vascular inflammation, thus offering a potential therapeutic advantage.
PLoS ONE 01/2014; 9(4):e91119. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to investigate whether caveolin-3 (Cav3) regulates localization of β2-adrenergic receptor (β2AR) and its cAMP signaling in healthy or failing cardiomyocytes. We co-expressed wildtype Cav3 or its dominant-negative mutant (Cav3DN) together with the Förster resonance energy transfer (FRET)-based cAMP sensor Epac2-camps in adult rat ventricular myocytes (ARVMs). FRET and scanning ion conductance microscopy were used to locally stimulate β2AR and to measure cytosolic cAMP. Cav3 overexpression increased the number of caveolae and decreased the magnitude of β2AR-cAMP signal. Conversely, Cav3DN expression resulted in an increased β2AR-cAMP response without altering the whole-cell L-type calcium current. Following local stimulation of Cav3DN-expressing ARVMs, β2AR response could only be generated in T-tubules. However, the normally compartmentalized β2AR-cAMP signal became diffuse, similar to the situation observed in heart failure. Finally, overexpression of Cav3 in failing myocytes led to partial β2AR redistribution back into the T-tubules. In conclusion, Cav3 plays a crucial role for the localization of β2AR and compartmentation of β2AR-cAMP signaling to the T-tubules of healthy ARVMs, and overexpression of Cav3 in failing myocytes can partially restore the disrupted localization of these receptors.
Journal of Molecular and Cellular Cardiology 12/2013; · 5.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cardiac cell replacement therapy by using human embryonic stem cell derivatives remains a potential approach to regenerate myocardium. The major hurdles to clinical application of this technology are immunogenicity and post-transplantation cell death. Here we examined the effects of calcineurin-targeting immunosuppressants cyclosporine A (CsA), and FK506, as well as rapamycin (RAP) and a selective inhibitor of calcineurin-binding downstream NFAT transcription factor VIVIT on the proliferative activity, function and survival of hESC-derived cardiomyocytes (hESC-CM) and endothelial cells (hESC-EC) in culture. As shown by automated microscopy, treatments with CsA, FK506 and RAP all decreased proliferation, reducing the percentage of hESC-CM and hESC-EC cells with the mitotic marker Ki67+ by as much as 60% and 74%, respectively. Administration of the cell permeable analogue 11R-VIVIT protein did not modulate their proliferative activity. All immunosuppressants reversed the pro-apoptotic effect of chelerythrine in hESC-CM demonstrating an inhibitory role of calcineurin/NFAT and mTOR pathways in hESC-CM survival (using apoptotic marker caspase-3) whereas the protection was less obvious in hESC-EC exposed to H2O2. Immunosuppressants did not affect cell viability in hESC-EC. Our results show that immunosuppressants reduce proliferation while offsetting cell loss to a smaller extent by reduction in apoptosis of hESC-CM. Immunosuppressants therapy would be compatible with stem cell transplantation but the resulting reduction in graft expansion capabilities would potentially necessitate implantation of increased cell numbers when immunosuppressants are given. The effects of NFAT-binding immunosuppressant molecules, which do not affect hESC-CM proliferation, may point the way forward for new classes of compounds better suited to cell implantation.
Stem cells and development 11/2013; · 4.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Therapeutic options which directly enhance cardiomyocyte contractility in chronic heart failure (HF) therapy are currently limited and do not improve prognosis. In fact, most positive inotropic agents, such as β-adrenoreceptor agonists and phosphodiesterase inhibitors, which have been assessed in HF patients cause increased mortality as a result of arrhythmia and sudden cardiac death. Cardiac sarcoplasmic reticulum Ca(2+) ATPase2a (SERCA2a) is a key protein involved in sequestration of Ca(2+) into the sarcoplasmic reticulum (SR) during diastole. There is a reduction of SERCA2a protein level and function in HF, which has been successfully targeted via viral transfection of the SERCA2a gene into cardiac tissue in-vivo. This has enhanced cardiac contractility and reduced mortality in several preclinical models of HF. Theoretical concerns have been raised regarding the possibility of arrhythmogenic adverse effects of SERCA2a gene therapy due to enhanced SR Ca(2+) load and induction of SR Ca(2+) leak as a result. Contrary to these concerns SERCA2a gene therapy in a wide variety of pre-clinical models, including acute ischaemia/reperfusion, chronic pressure overload, and chronic myocardial infarction, has resulted in a reduction in ventricular arrhythmias. The potential mechanisms for this unexpected beneficial effect, as well as mechanisms of enhancement of cardiac contractile function, are reviewed in this article.
British Journal of Pharmacology 10/2013; · 5.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Professor Sian Harding talks to Caroline Telfer, Assistant Commissioning Editor. Professor Sian Harding obtained her PhD in Pharmacology from King's College, London (UK) in 1981. She became Professor of Cardiac Pharmacology at the National Heart and Lung Institute, a division of the Imperial College Faculty of Medicine, in 2002. Her work has been funded by the British Heart Foundation, the Wellcome Trust, the Medical Research Council, the Biochemical and Biophysical Research Council, the The National Centre for the Replacement, Refinement and Reduction of Animals in Research, Pfizer, GlaxoSmithKline and SmithKline Beecham. Harding is former president of the European Section of the International Society for Heart Research and has organized international cardiovascular science meetings for this society, as well as for the European Society of Cardiology. She is the principal investigator for the first UK gene therapy trial aimed at improving cardiac contractility, organized jointly at Harefield and Papworth Hospitals. Harding is a member of the Nuffield Council on Bioethics and the Medical Research Coucil Regenerative Medicine Research Committee, and Director of a recently awarded British Heart Foundation Cardiovascular Regenerative Medicine Centre. She has been elected Fellow of the American Heart Association, European Society of Cardiology, International Society for Heart Research, Society of Biology and British Society of Pharmacology.
[Show abstract][Hide abstract] ABSTRACT: The potential of stem cell-based disease modelling is enhanced by the realisation that cardiomyocytes from human embryonic stem cells (hESC-CM) and induced pluripotent stem cells (hiPSC-CM) can be obtained with disease-specificity. Hypertrophy is a high priority target because of its central role in the transition to heart failure. Strikingly, here we found that hiPSC-CM are relatively unresponsive to major hypertrophic signals compared to hESC-CM. We show that the normal alpha-adrenergic receptor 1A subtype (ADRA1A) is not expressed robustly in either cell type. ADRA1A is reversibly silenced during differentiation, accompanied by up-regulation of ADRA1B, resulting in a distinct gene profile from that in adult human cardiomyocytes. Loss of ADRA1A is more pronounced in hiPSC-CM, due to greater epigenetic silencing and more marked up-regulation of HIF-1α, but ultimately both cell types differ from adult in their reliance on active ADRA1B rather than ADRA1A. ADRA1B up-regulation is sufficient in hESC-CM for hypertrophic changes such as cell size, cell volume and ANF. However, in hiPSC-CM, additional decreased G-protein signalling and tonically inhibitory pathway networks suppress the effect of alpha-adrenoceptor stimulation on growth. Superficial similarities between hESC-CM, hiPSC-CM and adult cardiomyocytes may mask complex differences in signalling. These data raise serious questions regarding the hiPSC-CM as a valid model system for certain aspects of cardiac disease.
Human Gene Therapy 05/2013; 24(5):A9. · 4.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The beta1-adrenoceptors (β(1)AR) and beta-2 (β(2)AR) adrenoceptors represent the predominant pathway for sympathetic control of myocardial function. Diverse mechanisms have evolved to translate signalling via these two molecules into differential effects on physiology. In this review we discuss how the functions of the βAR are o rganized from the level of secondary messengers to the whole heart to achieve this. Using novel microscopy and bio-imaging methods researchers have uncovered subtle organization of the control of cAMP, the predominant positively inotropic pathway for the βAR. The β(2)AR in particular is demonstrated to give rise to highly compartmentalized, spatially confined cAMP signals. Organization of β(2)AR within the t-tubule and caveolae of cardiomyocytes concentrates this receptor with molecules which buffer and shape its cAMP signal to give fine control. This situation is undermined in various forms of heart failure. Human and animal models of heart failure demonstrate disruption of cellular micro-architecture which contributes to the change in response to cardiac βARs. Loss of cellular structure has proven key to the observed loss of confined β(2)AR signaling. Some pharmacological and genetic treatments have been successful in returning failing cells to a more structured phenotype. Within these cells it has been possible to observe the partial restoration of normal β(2)AR signalling. At the level of the organ, expression of the two βAR sub-types varies between regions with the β(2)AR forming a greater proportion of the βAR population at the apex. This distribution may contribute to regional wall motion abnormalities in Takotsubo cardiomyopathy, a syndrome of high sympathetic activity, where the phosphorylated β(2)AR can signal via G(i) protein to produce negatively inotropic effects.
Cardiovascular research 01/2013; · 5.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: AIM: Ca(2+) waves are thought to be important in the aetiology of ventricular tachyarrhythmias. There have been conflicting results regarding whether flecainide reduces Ca(2+) waves in isolated cardiomyocytes. We sought to confirm whether flecainide inhibits waves in the intact cardiomyocyte and to elucidate the mechanism.Methods and ResultsWe imaged spontaneous sarcoplasmic reticulum (SR) Ca(2+) release events in healthy adult rat cardiomyocytes. Variation in stimulation frequency was used to produce Ca(2+) sparks or waves. Spark frequency, wave frequency and wave velocity were reduced by flecainide in the absence of a reduction of SR Ca(2+) content. Inhibition of I(Na) via alternative pharmacological agents (tetrodotoxin, propafenone or lidocaine) produced similar changes. To assess the contribution of I(Na) to spark and wave production voltage clamping was used to activate contraction from holding potentials of -80 mV or -40 mV. This confirmed that reducing Na(+) influx during myocyte stimulation is sufficient to reduce waves and that flecainide only causes Ca(2+) wave reduction when I(Na) is active. It was found that Na(+)/Ca(2+)-exchanger (NCX)-mediated Ca(2+) efflux was significantly enhanced by flecainide and that the effects of flecainide on wave frequency could be reversed by reducing [Na(+)](o), suggesting an important downstream role for NCX function. CONCLUSIONS: Flecainide reduces spark and wave frequency in the intact rat cardiomyocyte at therapeutically relevant concentrations but the mechanism involves I(Na) reduction rather than direct ryanodine receptor (RyR2) inhibition. Reduced I(Na) results in increased Ca(2+) efflux via NCX across the sarcolemma, reducing Ca(2+) concentration in the vicinity of the RyR2.
Cardiovascular research 01/2013; · 5.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) have been widely proposed as in vitro models of myocardial physiology and disease. A significant obstacle, however, is their immature phenotype. We hypothesised that Ca(2+) cycling of iPSC-CM is influenced by culture conditions and can be manipulated to obtain a more mature cellular behaviour. To test this hypothesis we seeded iPSC-CM onto fibronectin coated microgrooved polydimethylsiloxane (PDMS) scaffolds fabricated using photolithography, or onto unstructured PDMS membrane. After two weeks in culture, the structure and function of iPSC-CM were studied. PDMS microgrooved culture substrates brought about cellular alignment (p < 0.0001) and more organised sarcomere. The Ca(2+) cycling properties of iPSC-CM cultured on these substrates were significantly altered with a shorter time to peak amplitude (p = 0.0002 at 1 Hz), and more organised sarcoplasmic reticulum (SR) Ca(2+) release in response to caffeine (p < 0.0001), suggesting improved SR Ca(2+) cycling. These changes were not associated with modifications in gene expression. Whilst structured tissue culture may make iPSC-CM more representative of adult myocardium, further construct development and characterisation is required to optimise iPSC-CM as a model of adult myocardium.
[Show abstract][Hide abstract] ABSTRACT: Imperial College London (UK) was the showcase for the second in the 'Frontiers in Cardiovascular Biology' series, a biennial meeting of the European Society of Cardiology Council on basic cardiovascular sciences, held from 30 March to 1 April 2012. The aim of this series is to bring researchers together to learn the very latest findings in cardiac and vascular sciences, and to see state-of-the-art and developing technologies that could impact cardiovascular research. Five keynote lectures, 25 scientific symposia and two translational lunchtime symposia were grouped around the central themes of bioimaging, degeneration and regeneration, and inflammation.
[Show abstract][Hide abstract] ABSTRACT: Human pluripotent stem cell-derived cardiomyocytes (hPSC-CM) are being investigated as a new source of cardiac cells for drug safety assessment. We developed a novel scalable high content microscopy-based method for the detection of cell death in hPSC-CM that can serve for future predictive in vitro cardio-toxicological screens. Using rat neonatal ventricular cardiomyocytes (RVNC) or hPSC-CM, assays for nuclear remodelling, mitochondrial status, apoptosis and necrosis were designed using a combination of fluorescent dyes and antibodies on an automated microscopy platform. This allowed the observation of a chelerythrine-induced concentration-dependent apoptosis to necrosis switch and time-dependent progression of early apoptotic cells towards a necrotic-like phenotype. Susceptibility of hPSC-CM to chelerythrine-stimulated apoptosis varied with time after differentiation, but at most time points, hPSC-CM were more resistant than RVNC. This simple and scalable humanized high-content assay generates accurate cardiotoxicity profiles that can serve as a base for further assessment of cardioprotective strategies and drug safety.
Journal of Cardiovascular Translational Research 08/2012; 5(5):593-604. · 3.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Takotsubo cardiomyopathy is an acute heart failure syndrome characterized by myocardial hypocontractility from the mid left ventricle to the apex. It is precipitated by extreme stress and can be triggered by intravenous catecholamine administration, particularly epinephrine. Despite its grave presentation, Takotsubo cardiomyopathy is rapidly reversible, with generally good prognosis. We hypothesized that this represents switching of epinephrine signaling through the pleiotropic β(2)-adrenergic receptor (β(2)AR) from canonical stimulatory G-protein-activated cardiostimulant to inhibitory G-protein-activated cardiodepressant pathways.
We describe an in vivo rat model in which a high intravenous epinephrine, but not norepinephrine, bolus produces the characteristic reversible apical depression of myocardial contraction coupled with basal hypercontractility. The effect is prevented via G(i) inactivation by pertussis toxin pretreatment. β(2)AR number and functional responses were greater in isolated apical cardiomyocytes than in basal cardiomyocytes, which confirmed the higher apical sensitivity and response to circulating epinephrine. In vitro studies demonstrated high-dose epinephrine can induce direct cardiomyocyte cardiodepression and cardioprotection in a β(2)AR-Gi-dependent manner. Preventing epinephrine-G(i) effects increased mortality in the Takotsubo model, whereas β-blockers that activate β(2)AR-G(i) exacerbated the epinephrine-dependent negative inotropic effects without further deaths. In contrast, levosimendan rescued the acute cardiac dysfunction without increased mortality.
We suggest that biased agonism of epinephrine for β(2)AR-G(s) at low concentrations and for G(i) at high concentrations underpins the acute apical cardiodepression observed in Takotsubo cardiomyopathy, with an apical-basal gradient in β(2)ARs explaining the differential regional responses. We suggest this epinephrine-specific β(2)AR-G(i) signaling may have evolved as a cardioprotective strategy to limit catecholamine-induced myocardial toxicity during acute stress.
[Show abstract][Hide abstract] ABSTRACT: Cardiomyocyte surface morphology and T-tubular structure are significantly disrupted in chronic heart failure, with important functional sequelae, including redistribution of sarcolemmal β(2)-adrenergic receptors (β(2)AR) and localized secondary messenger signaling. Plasticity of these changes in the reverse remodeled failing ventricle is unknown. We used AAV9.SERCA2a gene therapy to rescue failing rat hearts and measured z-groove index, T-tubule density, and compartmentalized β(2)AR-mediated cAMP signals, using a combined nanoscale scanning ion conductance microscopy-Förster resonance energy transfer technique.
Cardiomyocyte surface morphology, quantified by z-groove index and T-tubule density, was normalized in reverse-remodeled hearts after SERCA2a gene therapy. Recovery of sarcolemmal microstructure correlated with functional β(2)AR redistribution back into the z-groove and T-tubular network, whereas minimal cAMP responses were initiated after local β(2)AR stimulation of crest membrane, as observed in failing cardiomyocytes. Improvement of β(2)AR localization was associated with recovery of βAR-stimulated contractile responses in rescued cardiomyocytes. Retubulation was associated with reduced spatial heterogeneity of electrically stimulated calcium transients and recovery of myocardial BIN-1 and TCAP protein expression but not junctophilin-2.
In summary, abnormalities of sarcolemmal structure in heart failure show plasticity with reappearance of z-grooves and T-tubules in reverse-remodeled hearts. Recovery of surface topology is necessary for normalization of β(2)AR location and signaling responses.
[Show abstract][Hide abstract] ABSTRACT: Phosphodiesterases (PDEs) are key enzymes controlling cAMP and cGMP levels and spatial distribution within cardiomyocytes. Despite the clinical importance of several classes of PDE inhibitor there has not been a complete characterization of the PDE profile within the human cardiomyocyte, and no attempt to assess which species might best be used to model this for drug evaluation in heart disease.
Ventricular cardiomyocytes were isolated from failing human hearts of patients with various etiologies of disease, and from rat and guinea pig hearts. Expression of PDE isoforms was determined using RT-PCR. cAMP- and cGMP-PDE hydrolytic activity was determined by scintillation proximity assay, before and after treatment with PDE inhibitors for PDEs 1, 2, 3, 4, 5 and 7. Functional effects of cAMP PDEi were determined on the contraction of single human, rat and guinea pig cardiomyocytes.
The presence and activity of PDE5 were confirmed in ventricular cardiomyocytes from failing and hypertrophied human heart, as well as PDE3, with ventricle-specific results for PDE4 and a surprisingly large contribution from PDE1 for hydrolysis of both cAMP and cGMP. The total PDE activity of human cardiomyocytes, and the profile of inhibition by PDE1, 3, 4, and 5 inhibitors, was modelled well in guinea pig but not rat cardiomyocytes.
Our results provide the first full characterisation of human cardiomyocyte PDE isoforms, and suggest that guinea pig myocytes provide a better model than rat for PDE levels and activity.
Life sciences 02/2012; 90(9-10):328-36. · 2.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Impaired myocardial sarcoplasmic reticulum calcium ATPase 2a (SERCA2a) activity is a hallmark of failing hearts, and SERCA2a gene therapy improves cardiac function in animals and patients with heart failure (HF). Deregulation of microRNAs has been demonstrated in HF pathophysiology. We studied the effects of therapeutic AAV9.SERCA2a gene therapy on cardiac miRNome expression and focused on regulation, expression, and function of miR-1 in reverse remodelled failing hearts.
We studied a chronic post-myocardial infarction HF model treated with AAV9.SERCA2a gene therapy. Heart failure resulted in a strong deregulation of the cardiac miRNome. miR-1 expression was decreased in failing hearts, but normalized in reverse remodelled hearts after AAV9.SERCA2a gene delivery. Increased Akt activation in cultured cardiomyocytes led to phosphorylation of FoxO3A and subsequent exclusion from the nucleus, resulting in miR-1 gene silencing. In vitro SERCA2a expression also rescued miR-1 in failing cardiomyocytes, whereas SERCA2a inhibition reduced miR-1 levels. In vivo, Akt and FoxO3A were highly phosphorylated in failing hearts, but reversed to normal by AAV9.SERCA2a, leading to cardiac miR-1 restoration. Likewise, enhanced sodium-calcium exchanger 1 (NCX1) expression during HF was normalized by SERCA2a gene therapy. Validation experiments identified NCX1 as a novel functional miR-1 target.
SERCA2a gene therapy of failing hearts restores miR-1 expression by an Akt/FoxO3A-dependent pathway, which is associated with normalized NCX1 expression and improved cardiac function.
European Heart Journal 02/2012; 33(9):1067-75. · 14.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cardiomyocytes derived from human pluripotent stem cells have advantages for modeling in terms of phenotype, longevity in culture, ease of transfection, and high-throughput capability.
Annals of the New York Academy of Sciences 12/2011; 1245:48-9. · 4.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Human embryonic stem cell-derived endothelial cells (hESC-EC) are being investigated as research tools and cell therapy for vascular inflammation. We have shown that hESC-EC do not respond to certain bacteria pathogen associated molecular patterns (PAMP). Endothelial cells also respond to viral PAMPs via toll-like receptor-3 (TLR3) which couples with IRF transcription factors. IRF can also be activated by interferons (IFN) which are also released during immune reactions. We have compared PolyIC (10 μg/ml; TLR3 agonist), and IFN (30 ng/ml) responses in hESC-EC and human umbilical vein endothelial cells (HUVEC). CXCL8 and IP10 were measured by ELISA as biomarkers for NF-κB and IRF pathways respectively. All data are % control (100) ± SEM n=5-6. Both hESC-EC (IFNα; 289.8±71.6, IFNβ; 656.8±182.3, IFNγ; 878.6±275.9, IFNλ 55.1±18.7) and HUVEC (IFNα; 1419.3±445.8, IFNβ; 3144.8±946.6, IFNγ; 2982.7±583.9, IFNλ; 132.8±30.1) released IP10 in response to each IFN (p<0.05; one-sample t test) except IFNλ (p>0.05; one-sample t test). HUVEC (3593.4±1269.4) but not hESC-EC (73.3±12.0) also responded to PolyIC with release of IP10. CXCL8 was not elevated by any treatment in either cell type. hESC-EC and HUVEC have a functional IRF transcription factor pathway that is activated in response IFNα, β and γ but not IFNλ. hESC-EC do not have a detectable TLR3 function. These findings may have implications for the use of hESC-EC in research and therapy and a more thorough investigation of these pathways is needed.