Human cardiomyocyte progenitor cell-derived cardiomyocytes display a maturated electrical phenotype

HCN4 current during human sinoatrial node-like action potentials

BACKGROUND

Despite the many studies carried out over the past 40 years, the contribution of the HCN4 encoded hyperpolarization-activated 'funny' current (I_f) to pacemaker activity in the mammalian sinoatrial node (SAN), and the human SAN in particular, is still controversial and not fully established.

OBJECTIVE

To study the contribution of I_f to diastolic depolarization of human SAN cells and its dependence on heart rate, cAMP levels, and atrial load.

METHODS

HCN4 channels were expressed in human cardiac myocyte progenitor cells (CMPCs) and HCN4 currents assessed using perforated patch-clamp in traditional voltage clamp mode and during action potential clamp with human SAN-like action potential waveforms with 500-1500 ms cycle length, in absence or presence of forskolin to mimic β-adrenergic stimulation and a -15 mV command potential offset to mimic atrial load.

RESULTS

Forskolin significantly increased the fully-activated HCN4 current density at -140 mV by 14% and shifted the steady-state activation curve by +7.4 mV without affecting its slope. In addition, forskolin significantly accelerated current activation but slowed deactivation. The HCN4 current did not completely deactivate before the subsequent diastolic depolarization during action potential clamp. The amplitude of HCN4 current increased with increasing cycle length, was significantly larger in the presence of forskolin at all cycle lengths, and was significantly increased upon the negative offset to the command potential.

CONCLUSIONS

I_f is active during a human SAN action potential waveform and its amplitude is modulated by heart rate, β-adrenergic stimulation, and diastolic voltage range, such that I_f is under delicate control.

Cardiomyocyte Progenitor Cells as a Functional Gene Delivery Vehicle for Long-Term Biological Pacing

Sustained pacemaker function is a challenge in biological pacemaker engineering. Human cardiomyocyte progenitor cells (CMPCs) have exhibited extended survival in the heart after transplantation. We studied whether lentivirally transduced CMPCs that express the pacemaker current I_f (encoded by HCN4) can be used as functional gene delivery vehicle in biological pacing. Human CMPCs were isolated from fetal hearts using magnetic beads coated with Sca-1 antibody, cultured in nondifferentiating conditions, and transduced with a green fluorescent protein (GFP)- or HCN4-GFP-expressing lentivirus. A patch-clamp analysis showed a large hyperpolarization-activated, time-dependent inward current (−20 pA/pF at −140 mV, n = 14) with properties typical of I_f in HCN4-GFP-expressing CMPCs. Gap-junctional coupling between CMPCs and neonatal rat ventricular myocytes (NRVMs) was demonstrated by efficient dye transfer and changes in spontaneous beating activity. In organ explant cultures, the number of preparations showing spontaneous beating activity increased from 6.3% in CMPC/GFP-injected preparations to 68.2% in CMPC/HCN4-GFP-injected preparations (P < 0.05). Furthermore, in CMPC/HCN4-GFP-injected preparations, isoproterenol induced a significant reduction in cycle lengths from 648 ± 169 to 392 ± 71 ms (P < 0.05). In sum, CMPCs expressing HCN4-GFP functionally couple to NRVMs and induce physiologically controlled pacemaker activity and may therefore provide an attractive delivery platform for sustained pacemaker function.

SCA1+ Cells from the Heart Possess a Molecular Circadian Clock and Display Circadian Oscillations in Cellular Functions

Stem cell antigen 1-positive (SCA1⁺) cells (SPCs) have been investigated in cell-based cardiac repair and pharmacological research, although improved cardiac function after injection has been variable and the mode of action remains unclear. Circadian (24-hr) rhythms are biorhythms regulated by molecular clocks that play an important role in (patho)physiology. Here, we describe (1) the presence of a molecular circadian clock in SPCs and (2) circadian rhythmicity in SPC function. We isolated SPCs from human fetal heart and found that these cells possess a molecular clock based on typical oscillations in core clock components BMAL1 and CRY1. Functional analyses revealed that circadian rhythmicity also governs SPC proliferation, stress tolerance, and growth factor release, with large differences between peaks and troughs. We conclude that SPCs contain a circadian molecular clock that controls crucial cellular functions. Taking circadian rhythms into account may improve reproducibility and outcome of research and therapies using SPCs.

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SCA1⁺ cells are a cell source used in pharmacology studies and cardiac repair

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SCA1⁺ cells possess a molecular circadian (24-hr) clock

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Proliferation, stress tolerance, and paracrine secretion follow a circadian pattern

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Taking rhythmicity into account may improve studies using SCA1⁺ cells

mAb C19 targets a novel surface marker for the isolation of human cardiac progenitor cells from human heart tissue and differentiated hESCs

AIMS

Cardiac progenitor cells (CPCs) have been isolated from adult and developing hearts using an anti-mouse Sca-1 antibody. However, the absence of a human Sca-1 homologue has hampered the clinical application of the CPCs. Therefore, we generated novel monoclonal antibodies (mAbs) specifically raised against surface markers expressed by resident human CPCs. Here, we explored the suitability of one of these mAbs, mAb C19, for the identification, isolation and characterization of CPCs from fetal heart tissue and differentiating cultures of human embryonic stem cells (hESCs).

METHODS & RESULTS

Using whole-cell immunization, mAbs were raised against Sca-1+ CPCs and screened for reactivity to various CPC lines by flow cytometry. mAb C19 was found to be specific for Sca-1+ CPCs, with high cell surface binding capabilities. mAb C19 stained small stem-like cells in cardiac tissue sections. Moreover, during differentiation of hESCs towards cardiomyocytes, a transient population of cells with mAb C19 reactivity was identified and isolated using magnetic-activated cell sorting. Their cell fate was tracked and found to improve cardiomyocyte purity from hESC-derived cultures. mAb C19+ CPCs, from both hESC differentiation and fetal heart tissues, were maintained and expanded in culture, while retaining their CPC-like characteristics and their ability to further differentiate into cardiomyocytes by stimulation with TGFβ1. Finally, gene expression profiling of these mAb C19+ CPCs suggested a highly angiogenic nature, which was further validated by cell-based angiogenesis assays.

CONCLUSION

mAb C19 is a new surface marker for the isolation of multipotent CPCs from both human heart tissues and differentiating hESCs.

Generating an in vitro 3D cell culture model from zebrafish larvae for heart research

We describe here a novel, fast and inexpensive method for producing a 3D 'heart' structure that forms spontaneously, in vitro, from larval zebrafish (ZF). We have named these 3D 'heart' structures 'zebrafish heart aggregate(s)' (ZFHAs) and have characterised their basic morphology and structural composition using histology, immunohistochemistry, electron microscopy and mass spectrometry. After 2 days in culture, the ZFHA spontaneously form and become a stable contractile syncytium consisting of cardiac tissue derived by in vitro maturation, which beats rhythmically and consistently for more than 8 days. We propose this model as a platform technology, which can be developed further to study in vitro cardiac maturation, regeneration, tissue engineering and safety pharmacological/toxicology testing.

Prion protein- and cardiac troponin T-marked interstitial cells from the adult myocardium spontaneously develop into beating cardiomyocytes

Atypically-shaped cardiomyocytes (ACMs) constitute a novel subpopulation of beating heart cells found in the cultures of cardiac myocyte-removed crude fraction cells obtained from adult mouse cardiac ventricles. Although ~500 beating ACMs are observed under microscope in the cell cultures obtained from the hearts of either male or female mice, the origin of these cells in cardiac tissue has yet to be elucidated due to the lack of exclusive markers. In the present study, we demonstrate the efficacy of cellular prion protein (PrP) as a surface marker of ACMs. Cells expressing PrP at the plasma membrane in the culture of the crude fraction cells were found to develop into beating ACMs by themselves or fuse with each other to become larger multinuclear beating ACMs. Combining PrP with a cardiac-specific contractile protein cardiac troponin T (cTnT) allowed us to identify native ACMs in the mouse cardiac ventricles as either clustered or solitary cells. PrP- and cTnT-marked cells were also found in the adult, even aged, human cardiac ventricles. These findings suggest that interstitial cells marked by PrP and cTnT, native ACMs, exhibit life-long survival in the cardiac ventricles of both mice and humans.

Monophasic and biphasic electrical stimulation induces a precardiac differentiation in progenitor cells isolated from human heart

Electrical stimulation (ES) of cells has been shown to induce a variety of responses, such as cytoskeleton rearrangements, migration, proliferation, and differentiation. In this study, we have investigated whether monophasic and biphasic pulsed ES could exert any effect on the proliferation and differentiation of human cardiac progenitor cells (hCPCs) isolated from human heart fragments. Cells were cultured under continuous exposure to monophasic or biphasic ES with fixed cycles for 1 or 3 days. Results indicate that neither stimulation protocol affected cell viability, while the cell shape became more elongated and reoriented more perpendicular to the electric field direction. Moreover, the biphasic ES clearly induced the upregulation of early cardiac transcription factors, MEF2D, GATA-4, and Nkx2.5, as well as the de novo expression of the late cardiac sarcomeric proteins, troponin T, cardiac alpha actinin, and SERCA 2a. Both treatments increased the expression of connexin 43 and its relocation to the cell membrane, but biphasic ES was faster and more effective. Finally, when hCPCs were exposed to both monophasic and biphasic ES, they expressed de novo the mRNA of the voltage-dependent calcium channel Cav 3.1(α1G) subunit, which is peculiar of the developing heart. Taken together, these results show that ES alone is able to set the conditions for early differentiation of adult hCPCs toward a cardiac phenotype.

Comparison of cardiac stem cells and mesenchymal stem cells transplantation on the cardiac electrophysiology in rats with myocardial infarction

INTRODUCTION

Whether transplanted cardiac stem cells (CSCs) and mesenchymal stem cells (MSCs) improved ventricular fibrillation threshold (VFT) similarly is still unclear. We sought to compare the effects of the CSC and MSC transplantation on the electrophysiological characteristics and VFT in rats with myocardial infarction (MI).

METHODS

MI was induced in 30 male Sprague-Dawley rats. Two weeks later, animals were randomized to receive 5 × 10(6) CSCs labeled with PKH26 in PBS or 5 × 10(6) MSCs labeled with PKH26 in phosphate buffer solution(PBS) or PBS alone injection into the infarcted anterior ventricular free wall. Six weeks after the injection, electrophysiological characteristics and VFT were measured. Labeled CSCs and MSCs were observed in 5 μm cryostat sections from each heart.

RESULTS

Malignant ventricular arrhythmias were significantly (P = 0.0055) less inducible in the CSC group than the MSC group. The VFTs were improved in the CSC group compared with the MSC group. Labeled CSCs and MSCs were identified in the infarct zone and infarct marginal zone. Labeled CSCs expressed Connexin-43, von Willebrand factor, α-smooth muscle actin and α-sarcomeric actin,while the Labeled MSCs expressed von Willebrand factor, α-smooth muscle actin and α-sarcomeric actin in vivo.

CONCLUSIONS

After 6 weeks of cell transplantation, CSCs are superior to MSCs in modulating the electrophysiological abnormality and improving the VFT in rats with MI. CSCs and MSCs express markers that suggest muscle, endothelium and vascular smooth muscle phenotypes in vivo, but MSCs rarely express Connexin-43.

Cardiac stem cells and their roles in myocardial infarction

Myocardial infarction leads to loss of cardiomyocytes, scar formation, ventricular remodeling and eventually deterioration of heart function. Over the past decade, stem cell therapy has emerged as a novel strategy for patients with ischemic heart disease and its beneficial effects have been demonstrated by substantial preclinical and clinical studies. Efficacy of several types of stem cells in the therapy of cardiovascular diseases has already been evaluated. However, repair of injured myocardium through stem cell transplantation is restricted by critical safety issues and ethic concerns. Recently, the discovery of cardiac stem cells (CSCs) that reside in the heart itself brings new prospects for myocardial regeneration and reconstitution of cardiac tissues. CSCs are positive for various stem cell markers and have the potential of self-renewal and multilineage differentiation. They play a pivotal role in the maintenance of heart homeostasis and cardiac repair. Elucidation of their biological characteristics and functions they exert in myocardial infarction are very crucial to further investigations on them. This review will focus on the field of cardiac stem cells and discuss technical and practical issues that may involve in their clinical applications in myocardial infarction.

Isogenic human pluripotent stem cell pairs reveal the role of a KCNH2 mutation in long-QT syndrome

Patient-specific induced pluripotent stem cells (iPSCs) will assist research on genetic cardiac maladies if the disease phenotype is recapitulated in vitro. However, genetic background variations may confound disease traits, especially for disorders with incomplete penetrance, such as long-QT syndromes (LQTS). To study the LQT2-associated c.A2987T (N996I) KCNH2 mutation under genetically defined conditions, we derived iPSCs from a patient carrying this mutation and corrected it. Furthermore, we introduced the same point mutation in human embryonic stem cells (hESCs), generating two genetically distinct isogenic pairs of LQTS and control lines. Correction of the mutation normalized the current (I_Kr) conducted by the HERG channel and the action potential (AP) duration in iPSC-derived cardiomyocytes (CMs). Introduction of the same mutation reduced I_Kr and prolonged the AP duration in hESC-derived CMs. Further characterization of N996I-HERG pathogenesis revealed a trafficking defect. Our results demonstrated that the c.A2987T KCNH2 mutation is the primary cause of the LQTS phenotype. Precise genetic modification of pluripotent stem cells provided a physiologically and functionally relevant human cellular context to reveal the pathogenic mechanism underlying this specific disease phenotype.

Isogenic pairs of patient-derived iPS- and ES-cell lines reveal the molecular problems contributing to cardiac arrest in long-QT syndrome.

Laser patterning for the study of MSC cardiogenic differentiation at the single-cell level

Mesenchymal stem cells (MSCs) have been cited as contributors to heart repair through cardiogenic differentiation and multiple cellular interactions, including the paracrine effect, cell fusion, and mechanical and electrical couplings. Due to heart-muscle complexity, progress in the development of knowledge concerning the role of MSCs in cardiac repair is heavily based on MSC-cardiomyocyte coculture. In conventional coculture systems, however, the in vivo cardiac muscle structure, in which rod-shaped cells are connected end-to-end, is not sustained; instead, irregularly shaped cells spread randomly, resulting in randomly distributed cell junctions. Consequently, contact-mediated cell-cell interactions (e.g., the electrical triggering signal and the mechanical contraction wave that propagate through MSC-cardiomyocyte junctions) occur randomly. Thus, the data generated on the beneficial effects of MSCs may be irrelevant to in vivo biological processes. In this study, we explored whether cardiomyocyte alignment, the most important phenotype, is relevant to stem cell cardiogenic differentiation. Here, we report (i) the construction of a laser-patterned, biochip-based, stem cell-cardiomyocyte coculture model with controlled cell alignment; and (ii) single-cell-level data on stem cell cardiogenic differentiation under in vivo-like cardiomyocyte alignment conditions.

Human cardiomyocyte progenitor cells: a short history of nearly everything

The high occurrence of cardiac disease in the Western world has driven clinicians and cardiovascular biologists to look for alternative strategies to treat patients. A challenging approach is the use of stem cells to repair the heart, in itself an inspiring thought. In the past 10 years, stem cells from different sources have been under intense investigation and, as a result, a multitude of studies have been published on the identification, isolation, and characterization, of cardiovascular progenitor cells and repair in different animal models. However, relatively few cardiovascular progenitor populations have been identified in human hearts, including, but not limited to, cardiosphere-derived cells, cKit+ human cardiac stem cells , Isl1+ cardiovascular progenitors, and, in our lab, cardiomyocyte progenitor cells (CMPCs). Here, we aim to provide a comprehensive summary of the past findings and present challenges for future therapeutic potential of CMPCs.

ILK induces cardiomyogenesis in the human heart

Background

Integrin-linked kinase (ILK) is a widely conserved serine/threonine kinase that regulates diverse signal transduction pathways implicated in cardiac hypertrophy and contractility. In this study we explored whether experimental overexpression of ILK would up-regulate morphogenesis in the human fetal heart.

Methodology/Principal Findings

Primary cultures of human fetal myocardial cells (19–22 weeks gestation) yielded scattered aggregates of cardioblasts positive for the early cardiac lineage marker nk×2.5 and containing nascent sarcomeres. Cardiac cells in colonies uniformly expressed the gap junction protein connexin 43 (C×43) and displayed a spectrum of differentiation with only a subset of cells exhibiting the late cardiomyogenic marker troponin T (cTnT) and evidence of electrical excitability. Adenovirus-mediated overexpression of ILK potently increased the number of new aggregates of primitive cardioblasts (p<0.001). The number of cardioblast colonies was significantly decreased (p<0.05) when ILK expression was knocked down with ILK targeted siRNA. Interestingly, overexpression of the activation resistant ILK mutant (ILK^R211A) resulted in much greater increase in the number of new cell aggregates as compared to overexpression of wild-type ILK (ILK^WT). The cardiomyogenic effects of ILK^R211A and ILK^WT were accompanied by concurrent activation of β-catenin (p<0.001) and increase expression of progenitor cell marker islet-1, which was also observed in lysates of transgenic mice with cardiac-specific over-expression of ILK^R211A and ILK^WT. Finally, endogenous ILK expression was shown to increase in concert with those of cardiomyogenic markers during directed cardiomyogenic differentiation in human embryonic stem cells (hESCs).

Conclusions/Significance

In the human fetal heart ILK activation is instructive to the specification of mesodermal precursor cells towards a cardiomyogenic lineage. Induction of cardiomyogenesis by ILK overexpression bypasses the requirement of proximal PI3K activation for transduction of growth factor- and β1-integrin-mediated differentiation signals. Altogether, our data indicate that ILK represents a novel regulatory checkpoint during human cardiomyogenesis.

Isolation of cardiovascular precursor cells from the human fetal heart

Weakening of cardiac function in patients with heart failure results from a loss of cardiomyocytes in the damaged heart. Cell replacement therapies as a way to induce myocardial regeneration in humans could represent attractive alternatives to classical drug-based approaches. However, a suitable source of precursor cells, which could produce a functional myocardium after transplantation, remains to be identified. In the present study, we isolated cardiovascular precursor cells from ventricles of human fetal hearts at 12 weeks of gestation. These cells expressed Nkx2.5 but not late cardiac markers such as α-actinin and troponin I. In addition, proliferating cells expressed the mesenchymal stem cell markers CD73, CD90, and CD105. Evidence for functional cardiogenic differentiation in vitro was demonstrated by the upregulation of cardiac gene expression as well as the appearance of cells with organized sarcomeric structures. Importantly, differentiated cells presented spontaneous and triggered calcium signals. Differentiation into smooth muscle cells was also detected. In contrast, precursor cells did not produce endothelial cells. The engraftment and differentiation capacity of green fluorescent protein (GFP)-labeled cardiac precursor cells were then tested in vivo after transfer into the heart of immunodeficient severe combined immunodeficient mice. Engrafted human cells were readily detected in the mouse myocardium. These cells retained their cardiac commitment and differentiated into α-actinin-positive cardiomyocytes. Expression of connexin-43 at the interface between GFP-labeled and endogenous cardiomyocytes indicated that precursor-derived cells connected to the mouse myocardium. Together, these results suggest that human ventricular nonmyocyte cells isolated from fetal hearts represent a suitable source of precursors for cell replacement therapies.

Improvements of cardiac electrophysiologic stability and ventricular fibrillation threshold in rats with myocardial infarction treated with cardiac stem cells

OBJECTIVES

Arrhythmia is of concern after cardiac stem cell transplantation in repairing infarcted myocardium. However, whether transplantation improved the ventricular fibrillation threshold and whether severe malignant ventricular arrhythmia is induced in the myocardial infarction model are still unclear. We sought to investigate the electrophysiologic characteristics and ventricular fibrillation threshold in rats with myocardial infarction by treatment with allogeneic cardiac stem cells.

DESIGN

Prospective, randomized, controlled study.

SETTING

University-affiliated hospital.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Myocardial infarction was induced in 20 male Sprague-Dawley rats. Two weeks later, animals were randomized to receive 5 × 10(6) cardiac stem cells labeled with PKH26 in phosphate buffer solution or a phosphate buffer solution-alone injection into the infarcted anterior ventricular-free wall.

MEASUREMENTS AND MAIN RESULTS

Six weeks after the cardiac stem cell or phosphate buffer solution injection, electrophysiologic characteristics and ventricular fibrillation threshold were measured at the infarct area, infarct marginal zone, and noninfarct zone. Labeled cardiac stem cells were observed in 5-μm cryostat sections from each harvested heart. The unipolar electrogram activation recovery time dispersions were shorter in the cardiac stem cell group compared with those at the phosphate buffer solution group (15.5 ± 4.4 vs. 38.6 ± 14.9 msecs, p = .000177). Malignant ventricular arrhythmias were significantly (p = .00108) less inducible in the cardiac stem cell group (one of ten) than the phosphate buffer solution group (nine of ten). The ventricular fibrillation thresholds were greatly improved in the cardiac stem cell group compared with the phosphate buffer solution group. Labeled cardiac stem cells were identified in the infarct zone and infarct marginal zone and expressed Connexin-43, von Willebrand factor, α-smooth muscle actin, and α-sarcomeric actin.

CONCLUSIONS

Cardiac stem cells may modulate the electrophysiologic abnormality and improve the ventricular fibrillation threshold in rats with myocardial infarction treated with allogeneic cardiac stem cells and cardiac stem cell express markers that suggest muscle, endothelium, and vascular smooth muscle phenotypes in vivo.

Laser-guidance-based cell deposition microscope for heterotypic single-cell micropatterning

Cell patterning methods enable researchers to control specific homotypic and heterotypic contact-mediated cell-cell and cell-ECM interactions and to impose defined cell and tissue geometries. To micropattern individual cells to specific points on a substrate with high spatial resolution, we have developed a cell deposition microscope based on the laser-guidance technique. We discuss the theory of optical forces for generating laser guidance and the optimization of the optical configuration (NA ≈ 0.1) to manipulate cells with high speed in three dimensions. Our cell deposition microscope is capable of patterning different cell types onto and within standard cell research devices and providing on-stage incubation for long-term cell culturing. Using this cell deposition microscope, rat mesenchymal stem cells from bone marrow were micropatterned with cardiomyocytes into a substrate microfabricated with polydimethylsiloxane on a 22 mm × 22 mm coverglass to form a single-cell coculturing microenvironment, and their electrophysiological property changes were investigated during the coculturing days.

Foetal and adult cardiomyocyte progenitor cells have different developmental potential

In the past years, cardiovascular progenitor cells have been isolated from the human heart and characterized. Up to date, no studies have been reported in which the developmental potential of foetal and adult cardiovascular progenitors was tested simultaneously. However, intrinsic differences will likely affect interpretations regarding progenitor cell potential and application for regenerative medicine. Here we report a direct comparison between human foetal and adult heart-derived cardiomyocyte progenitor cells (CMPCs). We show that foetal and adult CMPCs have distinct preferences to differentiate into mesodermal lineages. Under pro-angiogenic conditions, foetal CMPCs form more endothelial but less smooth muscle cells than adult CMPCs. Foetal CMPCs can also develop towards adipocytes, whereas neither foetal nor adult CMPCs show significant osteogenic differentiation. Interestingly, although both cell types differentiate into heart muscle cells, adult CMPCs give rise to electrophysiologically more mature cardiomyocytes than foetal CMPCs. Taken together, foetal CMPCs are suitable for molecular cell biology and developmental studies. The potential of adult CMPCs to form mature cardiomyocytes and smooth muscle cells may be essential for cardiac repair after transplantation into the injured heart.