Opioid peptide gene expression primes cardiogenesis in embryonal pluripotent stem cells

Endogenous Opioids and Their Role in Stem Cell Biology and Tissue Rescue

Opioids are considered the oldest drugs known by humans and have been used for sedation and pain relief for several centuries. Nowadays, endogenous opioid peptides are divided into four families: enkephalins, dynorphins, endorphins, and nociceptin/orphanin FQ. They exert their action through the opioid receptors (ORs), transmembrane proteins belonging to the super-family of G-protein-coupled receptors, and are expressed throughout the body; the receptors are the δ opioid receptor (DOR), μ opioid receptor (MOR), κ opioid receptor (KOR), and nociceptin/orphanin FQ receptor (NOP). Endogenous opioids are mainly studied in the central nervous system (CNS), but their role has been investigated in other organs, both in physiological and in pathological conditions. Here, we revise their role in stem cell (SC) biology, since these cells are a subject of great scientific interest due to their peculiar features and their involvement in cell-based therapies in regenerative medicine. In particular, we focus on endogenous opioids' ability to modulate SC proliferation, stress response (to oxidative stress, starvation, or damage following ischemia-reperfusion), and differentiation towards different lineages, such as neurogenesis, vasculogenesis, and cardiogenesis.

Neurons derived from human-induced pluripotent stem cells express mu and kappa opioid receptors

Neuroprotection studies have shown that induced pluripotent stem (iPS) cells have the possibility to transform neuroprotection research. In the present study, iPS cells were generated from human renal epithelial cells and were then differentiated into neurons. Cells in the iPS-cell group were maintained in stem cell medium. In contrast, cells in the iPS-neuron group were first maintained in neural induction medium and expansion medium containing ROCK inhibitors, and then cultivated in neuronal differentiation medium and neuronal maturation medium to induce the neural stem cells to differentiate into neurons. The expression of relevant markers was compared at different stages of differentiation. Immunofluorescence staining revealed that cells in the iPS-neuron group expressed the neural stem cell markers SOX1 and nestin on day 11 of induction, and neuronal markers TUBB3 and NeuN on day 21 of induction. Polymerase chain reaction results demonstrated that, compared with the iPS-cell group, TUBB3 gene expression in the iPS-neuron group was increased 15.6-fold. Further research revealed that, compared with the iPS-cell group, the gene expression and immunoreactivity of mu opioid receptor in the iPS-neuron group were significantly increased (38.3-fold and 5.7-fold, respectively), but those of kappa opioid receptor had only a slight change (1.33-fold and 1.57-fold increases, respectively). Together, these data indicate that human iPS cells can be induced into mu opioid receptor- and kappa opioid receptor-expressing neurons, and that they may be useful to simulate human opioid receptor function in vitro and explore the underlying mechanisms of human conditions.

Intracrine Endorphinergic Systems in Modulation of Myocardial Differentiation

A wide variety of peptides not only interact with the cell surface, but govern complex signaling from inside the cell. This has been referred to as an "intracrine" action, and the orchestrating molecules as "intracrines". Here, we review the intracrine action of dynorphin B, a bioactive end-product of the prodynorphin gene, on nuclear opioid receptors and nuclear protein kinase C signaling to stimulate the transcription of a gene program of cardiogenesis. The ability of intracrine dynorphin B to prime the transcription of its own coding gene in isolated nuclei is discussed as a feed-forward loop of gene expression amplification and synchronization. We describe the role of hyaluronan mixed esters of butyric and retinoic acids as synthetic intracrines, controlling prodynorphin gene expression, cardiogenesis, and cardiac repair. We also discuss the increase in prodynorphin gene transcription and intracellular dynorphin B afforded by electromagnetic fields in stem cells, as a mechanism of cardiogenic signaling and enhancement in the yield of stem cell-derived cardiomyocytes. We underline the possibility of using the diffusive features of physical energies to modulate intracrinergic systems without the needs of viral vector-mediated gene transfer technologies, and prompt the exploration of this hypothesis in the near future.

Physical energies to the rescue of damaged tissues

Rhythmic oscillatory patterns sustain cellular dynamics, driving the concerted action of regulatory molecules, microtubules, and molecular motors. We describe cellular microtubules as oscillators capable of synchronization and swarming, generating mechanical and electric patterns that impact biomolecular recognition. We consider the biological relevance of seeing the inside of cells populated by a network of molecules that behave as bioelectronic circuits and chromophores. We discuss the novel perspectives disclosed by mechanobiology, bioelectromagnetism, and photobiomodulation, both in term of fundamental basic science and in light of the biomedical implication of using physical energies to govern (stem) cell fate. We focus on the feasibility of exploiting atomic force microscopy and hyperspectral imaging to detect signatures of nanomotions and electromagnetic radiation (light), respectively, generated by the stem cells across the specification of their multilineage repertoire. The chance is reported of using these signatures and the diffusive features of physical waves to direct specifically the differentiation program of stem cells in situ, where they already are resident in all the tissues of the human body. We discuss how this strategy may pave the way to a regenerative and precision medicine without the needs for (stem) cell or tissue transplantation. We describe a novel paradigm based upon boosting our inherent ability for self-healing.

Fractionation of embryonic cardiac progenitor cells and evaluation of their differentiation potential

Mid-gestation mouse ventricles (E11.5) contain a larger number of Nkx2.5⁺ cardiac progenitor cells (CPCs). The proliferation rates are consistently higher in CPCs compared to myocyte population of developing ventricles. Recent studies suggested that CPCs are an ideal donor cell type for replacing damaged tissue in diseased hearts. Thus, the ability to isolate and expand CPCs from embryos or stem cell cultures could be useful for cell fate studies and regenerative therapies. Since embryonic CPCs possess fewer mitochondria compared to cardiomyocytes, we reasoned that CPCs can be fractionated using a fluorescent mitochondrial membrane potential dye (TMRM) and these cells may retain cardiomyogenic potential even in the absence of cardiomyocytes (CMs). FACS sorting of TMRM stained embryonic ventricular cells indicated that over 99% of cells in TMRM high fraction stained positive for sarcomeric myosin (MF20) and all of them expressed Nkx2.5. Although majority of cells present in TMRM low fraction expressed Nkx2.5, very few cells (~1%) stained positive for MF20. Further culturing of TMRM low cells over a period of 48 h showed a progressive increase in MF20 positive cells. Additional analyses revealed that MF20 negative cells in TMRM low fraction do not express markers for endothelial cells (vWF, CD31) or smooth muscle cells (SM myosin). Treatment of TMRM low cells with known cardiogenic factors DMSO and dynorphin B significantly increased the percentage of MF20⁺ cells compared to untreated cultures. Collectively, these studies suggest that embryonic CPCs can be separated as a TMRM low fraction and their differentiation potential can be enhanced by exogenous addition of known cardiomyogenic factors.

Mesenchymal Stem Cells in Lipogems, a Reverse Story: from Clinical Practice to Basic Science

The idea that basic science should be the starting point for modern clinical approaches has been consolidated over the years, and emerged as the cornerstone of Molecular Medicine. Nevertheless, there is increasing concern over the low efficiency and inherent costs related to the translation of achievements from the bench to the bedside. These burdens are also perceived with respect to the effectiveness of translating basic discoveries in stem cell biology to the newly developing field of advanced cell therapy or Regenerative Medicine. As an alternative paradigm, past and recent history in Medical Science provides remarkable reverse stories in which clinical observations at the patient's bedside have fed major advances in basic research which, in turn, led to consistent progression in clinical practice. Within this context, we discuss our recently developed method and device, which forms the core of a system (Lipogems) for processing of human adipose tissue solely with the aid of mild mechanical forces to yield a microfractured tissue product.

Mesenchymal Stem Cells for Cardiac Regenerative Therapy: Optimization of Cell Differentiation Strategy

With the high mortality rate, coronary heart disease (CHD) has currently become a major life-threatening disease. The main pathological change of myocardial infarction (MI) is the induction of myocardial necrosis in infarction area which finally causes heart failure. Conventional treatments cannot regenerate the functional cell efficiently. Recent researches suggest that mesenchymal stem cells (MSCs) are able to differentiate into multiple lineages, including cardiomyocyte-like cells in vitro and in vivo, and they have been used for the treatment of MI to repair the injured myocardium and improve cardiac function. In this review, we will focus on the recent progress on MSCs derived cardiomyocytes for cardiac regeneration after MI.

Strategies for the chemical and biological functionalization of scaffolds for cardiac tissue engineering: a review

The development of biomaterials for cardiac tissue engineering (CTE) is challenging, primarily owing to the requirement of achieving a surface with favourable characteristics that enhances cell attachment and maturation. The biomaterial surface plays a crucial role as it forms the interface between the scaffold (or cardiac patch) and the cells. In the field of CTE, synthetic polymers (polyglycerol sebacate, polyethylene glycol, polyglycolic acid, poly-l-lactide, polyvinyl alcohol, polycaprolactone, polyurethanes and poly(N-isopropylacrylamide)) have been proven to exhibit suitable biodegradable and mechanical properties. Despite the fact that they show the required biocompatible behaviour, most synthetic polymers exhibit poor cell attachment capability. These synthetic polymers are mostly hydrophobic and lack cell recognition sites, limiting their application. Therefore, biofunctionalization of these biomaterials to enhance cell attachment and cell material interaction is being widely investigated. There are numerous approaches for functionalizing a material, which can be classified as mechanical, physical, chemical and biological. In this review, recent studies reported in the literature to functionalize scaffolds in the context of CTE, are discussed. Surface, morphological, chemical and biological modifications are introduced and the results of novel promising strategies and techniques are discussed.

Cardiac tissue inhibitor of matrix metalloprotease 4 dictates cardiomyocyte contractility and differentiation of embryonic stem cells into cardiomyocytes: Road to therapy

BACKGROUND

TIMP4 (Tissue Inhibitors of Matrix Metalloprotease 4), goes down in failing hearts and mice lacking TIMP4 show poor regeneration capacity after myocardial infarction (MI). This study is based on our previous observation that administration of cardiac inhibitor of metalloproteinase (~TIMP4) attenuates oxidative stress and remodeling in failing hearts. Therefore, we hypothesize that TIMP4 helps in cardiac regeneration by augmenting contractility and inducing the differentiation of cardiac progenitor cells into cardiomyocytes.

METHODS

To validate this hypothesis, we transfected mouse cardiomyocytes with TIMP4 and TIMP4-siRNA and performed contractility studies in the TIMP4 transfected cardiomyocytes as compared to siRNA-TIMP4 transfected cardiomyocytes. We evaluated the calcium channel gene serca2a (sarcoplasmic reticulum calcium ATPase2a) and mir122a which tightly regulates serca2a to explain the changes in contractility. We treated mouse embryonic stem cells with cardiac extract and cardiac extract minus TIMP4 (using TIMP4 monoclonal antibody) to examine the effect of TIMP4 on differentiation of cardiac progenitor cells.

RESULTS

Contractility was augmented in the TIMP4 transfected cardiomyocytes as compared to siRNA-TIMP4 transfected cardiomyocytes. There was elevated expression of serca2a in the TIMP4 transformed myocytes and down regulation of mir122a. The cells treated with cardiac extract containing TIMP4 showed cardiac phenotype in terms of Ckit+, GATA4+ and Nkx2.5 expression.

CONCLUSION

This is a novel report suggesting that TIMP4 augments contractility and induces differentiation of progenitor cells into cardiac phenotype. In view of the failure of MMP9 inhibitors for cardiac therapy, TIMP4 provides an alternative approach, being an indigenous molecule and a natural inhibitor of MMP9.

Amniotic fluid stem cells morph into a cardiovascular lineage: analysis of a chemically induced cardiac and vascular commitment

Mouse embryonic stem cells were previously observed along with mesenchymal stem cells from different sources, after being treated with a mixed ester of hyaluronan with butyric and retinoic acids, to show a significant increase in the yield of cardiogenic and vascular differentiated elements. The aim of the present study was to determine if stem cells derived from primitive fetal cells present in human amniotic fluid (hAFSCs) and cultured in the presence of a mixture of hyaluronic (HA), butyric (BU), and retinoic (RA) acids show a higher yield of differentiation toward the cardiovascular phenotype as compared with untreated cells. During the differentiation process elicited by exposure to HA + BU + RA, genes controlling pluripotency and plasticity of stem cells, such as Sox2, Nanog, and Oct4, were significantly downregulated at the transcriptional level. At this point, a significant increase in expression of genes controlling the appearance of cardiogenic and vascular lineages in HA + BU + RA-treated cells was observed. The protein expression levels typical of cardiac and vascular phenotypes, evaluated by Western blotting, immunofluorescence, and flow cytometry, were higher in hAFSCs cultured in the presence of HA + BU + RA, as compared with untreated control cells. Appearance of the cardiac phenotype was further inferred by ultrastructural analysis using transmission and scanning electron microscopy. These results demonstrate that a mixture of HA + BU + RA significantly increased the yield of elements committed toward cardiac and vascular phenotypes, confirming what we have previously observed in other cellular types.

Radioelectric asymmetric conveyed fields and human adipose-derived stem cells obtained with a nonenzymatic method and device: a novel approach to multipotency

Human adipose-derived stem cells (hASCs) have been recently proposed as a suitable tool for regenerative therapies for their simple isolation procedure and high proliferative capability in culture. Although hASCs can be committed into different lineages in vitro, the differentiation is a low-yield and often incomplete process. We have recently developed a novel nonenzymatic method and device, named Lipogems, to obtain a fat tissue derivative highly enriched in pericytes/mesenchymal stem cells by mild mechanical forces from human lipoaspirates. When compared to enzymatically dissociated cells, Lipogems-derived hASCs exhibited enhanced transcription of vasculogenic genes in response to provasculogenic molecules, suggesting that these cells may be amenable for further optimization of their multipotency. Here we exposed Lipogems-derived hASCs to a radioelectric asymmetric conveyer (REAC), an innovative device asymmetrically conveying radioelectric fields, affording both enhanced differentiating profiles in mouse embryonic stem cells and efficient direct multilineage reprogramming in human skin fibroblasts. We show that specific REAC exposure remarkably enhanced the transcription of prodynorphin, GATA-4, Nkx-2.5, VEGF, HGF, vWF, neurogenin-1, and myoD, indicating the commitment toward cardiac, vascular, neuronal, and skeletal muscle lineages, as inferred by the overexpression of a program of targeted marker proteins. REAC exposure also finely tuned the expression of stemness-related genes, including NANOG, SOX-2, and OCT-4. Noteworthy, the REAC-induced responses were fashioned at a significantly higher extent in Lipogems-derived than in enzymatically dissociated hASCs. Therefore, REAC-mediated interplay between radioelectric asymmetrically conveyed fields and Lipogems-derived hASCs appears to involve the generation of an ideal "milieu" to optimize multipotency expression from human adult stem cells in view of potential improvement of future cell therapy efforts.

Radio electric conveyed fields directly reprogram human dermal skin fibroblasts toward cardiac, neuronal, and skeletal muscle-like lineages

Somatic cells can be directly reprogrammed to alternative differentiated fates without first becoming stem/progenitor cells. Nevertheless, the initial need for viral-mediated gene delivery renders this strategy unsafe in humans. Here, we provide evidence that exposure of human skin fibroblasts to a Radio Electric Asymmetric Conveyer (REAC), an innovative device delivering radio electric conveyed fields at a radiofrequency of 2.4 GHz, afforded remarkable commitment toward cardiac, neuronal, and skeletal muscle lineages. REAC induced the transcription of tissue-restricted genes, including Mef2c, Tbx5, GATA4, Nkx2.5, and prodynorphin for cardiac reprogramming, as well as myoD, and neurogenin 1 for skeletal myogenesis and neurogenesis, respectively. Conversely, REAC treatment elicited a biphasic effect on a number of stemness-related genes, leading to early transcriptional increase of Oct4, Sox2, cMyc, Nanog, and Klf4 within 6-20 h, followed by a downregulation at later times. The REAC action bypassed a persistent reprogramming toward an induced pluripotent stem cell-like state and involved the transcriptional induction of the NADPH oxidase subunit Nox4. Our results show for the first time the feasibility of using a physical stimulus to afford the expression of pluripotentiality in human adult somatic cells up to the attainment of three major target lineages for regenerative medicine.

Ascorbic acid rescues cardiomyocyte development in Fgfr1(-/-) murine embryonic stem cells

Fibroblast growth factor receptor 1 (Fgfr1) gene knockout impairs cardiomyocyte differentiation in murine embryonic stem cells (mESC). Here, various chemical compounds able to enhance cardiomyocyte differentiation in mESC [including dimethylsulfoxide, ascorbic acid (vitC), free radicals and reactive oxygen species] were tested for their ability to rescue the cardiomyogenic potential of Fgfr1(-/-) mESC. Among them, only the reduced form of vitC, l-ascorbic acid, was able to recover beating cell differentiation in Fgfr1(-/-) mESC. The appearance of contracting cells was paralleled by the expression of early and late cardiac gene markers, thus suggesting their identity as cardiomyocytes. In the attempt to elucidate the mechanism of action of vitC on Fgfr1(-/-) mESC, we analyzed several parameters related to the intracellular redox state, such as reactive oxygen species content, Nox4 expression, and superoxide dismutase activity. The results did not show any relationship between the antioxidant capacity of vitC and cardiomyocyte differentiation in Fgfr1(-/-) mESC. No correlation was found also for the ability of vitC to modulate the expression of pluripotency genes. Then, we tested the hypothesis that vitC was acting as a prolyl hydroxylase cofactor by maintaining iron in a reduced state. We first analyze hypoxia inducible factor (HIF)-1α mRNA and protein levels that were found to be slightly upregulated in Fgfr1(-/-) cells. We treated mESC with Fe(2+) or the HIF inhibitor CAY10585 during the first phases of the differentiation process and, similar to vitC, the two compounds were able to rescue cardiomyocyte formation in Fgfr1(-/-) mESC, thus implicating HIF-1α modulation in Fgfr1-dependent cardiomyogenesis.

The voyage of stem cell toward terminal differentiation: a brief overview

Presently, worldwide attempts are being made to apply stem cells and stem cell-derived products to a wide range of clinical applications and for the development of cell-based therapies. In order to harness stem cells and manipulate them for therapeutic application, it is very important to understand the basic biology of stem cells and identify the factors that govern the dynamics of these cells in the body. Several signaling pathways have emerged as key regulators of stem cells. Some of these signaling pathways regulate the stem cell's proliferative capacity and therefore act as direct regulators of the stem cell, whereas others are involved in shaping and maintaining the stem cell niche and therefore act as indirect regulators of the stem cell. It is difficult to identify which signaling pathways critically affect the stem cell's behavior and which are important for maintaining the quiescent population. A stem cell receives different extrinsic signals compared with the bulk population and responds to them differently. In order to manipulate these adult cells for therapeutic approaches it is crucial to identify how signaling pathways regulate stem cells either directly by regulating proliferative status or indirectly by influencing the niche. The main challenge is to identify whether different factors provide diverse extrinsic signals to the stem cell and its daughter cell population, or whether there are intrinsic differences in stem cell and daughter cell populations that is reflected in their behavior. In this study, we will focus on the various aspects of stem cell biology and differentiation, as well as exploring the potential strategies to intervene the differentiation process in order to obtain the desired yield of cells applicable in regenerative medicine.

G protein-coupled receptor signalling in the cardiac nuclear membrane: evidence and possible roles in physiological and pathophysiological function

G protein-coupled receptors (GPCRs) play key physiological roles in numerous tissues, including the heart, and their dysfunction influences a wide range of cardiovascular diseases. Recently, the notion of nuclear localization and action of GPCRs has become more widely accepted. Nuclear-localized receptors may regulate distinct signalling pathways, suggesting that the biological responses mediated by GPCRs are not solely initiated at the cell surface but may result from the integration of extracellular and intracellular signalling pathways. Many of the observed nuclear effects are not prevented by classical inhibitors that exclusively target cell surface receptors, presumably because of their structures, lipophilic properties, or affinity for nuclear receptors. In this topical review, we discuss specifically how angiotensin-II, endothelin, β-adrenergic and opioid receptors located on the nuclear envelope activate signalling pathways, which convert intracrine stimuli into acute responses such as generation of second messengers and direct genomic effects, and thereby participate in the development of cardiovascular disorders.

Impact of stirred suspension bioreactor culture on the differentiation of murine embryonic stem cells into cardiomyocytes

Background

Embryonic stem cells (ESCs) can proliferate endlessly and are able to differentiate into all cell lineages that make up the adult organism. Under particular in vitro culture conditions, ESCs can be expanded and induced to differentiate into cardiomyocytes in stirred suspension bioreactors (SSBs). However, in using these systems we must be cognizant of the mechanical forces acting upon the cells. The effect of mechanical forces and shear stress on ESC pluripotency and differentiation has yet to be clarified. The purpose of this study was to investigate the impact of the suspension culture environment on ESC pluripotency during cardiomyocyte differentiation.

Results

Murine D3-MHC-neo^r ESCs formed embyroid bodies (EBs) and differentiated into cardiomyocytes over 25 days in static culture and suspension bioreactors. G418 (Geneticin) was used in both systems from day 10 to enrich for cardiomyocytes by eliminating non-resistant, undifferentiated cells. Treatment of EBs with 1 mM ascorbic acid and 0.5% dimethyl sulfoxide from day 3 markedly increased the number of beating EBs, which displayed spontaneous and cadenced contractile beating on day 11 in the bioreactor. Our results showed that the bioreactor differentiated cells displayed the characteristics of fully functional cardiomyocytes. Remarkably, however, our results demonstrated that the bioreactor differentiated ESCs retained their ability to express pluripotency markers, to form ESC-like colonies, and to generate teratomas upon transplantation, whereas the cells differentiated in adherent culture lost these characteristics.

Conclusions

This study demonstrates that although cardiomyocyte differentiation can be achieved in stirred suspension bioreactors, the addition of medium enhancers is not adequate to force complete differentiation as fluid shear forces appear to maintain a subpopulation of cells in a transient pluripotent state. The development of successful ESC differentiation protocols within suspension bioreactors demands a more complete understanding of the impacts of shear forces on the regulation of pluripotency and differentiation in pluripotent stem cells.

Electron microscopic study of mouse embryonic stem cell-derived cardiomyocytes

Differentiation of embryonic stem cell (ESC)-derived embryoid bodies (EBs) is a heterogeneous process. ESCs can differentiate in vitro into different cell types including beating cardiomyocytes. The main aim of the present study was to develop an improved preparation method for scanning electron microscopic study of ESC-derived cardiac bundles and to investigate the fine structural characteristics of mouse ESCs-derived cardiomyocytes using electron microscopy. The mouse ESCs differentiation was induced by EBs' development through hanging drop, suspension and plating stages. Cardiomyocytes appeared in the EBs' outgrowth as beating clusters that grew in size and formed thick branching bundles gradually. Cardiac bundles showed cross striation even when they were observed under an inverted microscope. They showed a positive immunostaining for cardiac troponin I and α-actinin. Transmission and scanning electron microscopy (TEM & SEM) were used to study the structural characteristics of ESC-derived cardiomyocytes. Three weeks after plating, differentiated EBs showed a superficial layer of compact fibrous ECM that made detailed observation of cardiac bundles impossible. We tried several preparation methods to remove unwanted cells and fibers, and finally we revealed the branching bundles of cardiomyocytes. In TEM study, most cardiomyocytes showed parallel arrays of myofibrils with a mature sarcomeric organization marked by H-bands, M-lines and numerous T-tubules. Cardiomyocytes were connected to each other by intercalated discs composed of numerous gap junctions and fascia adherences.

Radiofrequency energy loop primes cardiac, neuronal, and skeletal muscle differentiation in mouse embryonic stem cells: a new tool for improving tissue regeneration

Radiofrequency (RF) waves from Wi-Fi (wireless fidelity) technologies have become ubiquitous, with Internet access spreading into homes, and public areas. The human body harbors multipotent stem cells with various grading of potentiality. Whether stem cells may be affected by Wi-Fi RF energy remains unknown. We exposed mouse embryonic stem (ES) cells to a Radio Electric Asymmetric Conveyer (REAC), an innovative device delivering Wi-Fi RF of 2.4 GHz with its conveyer electrodes immersed into the culture medium. Cell responses were investigated by real-time PCR, Western blot, and confocal microscopy. Single RF burst duration, radiated power, electric and magnetic fields, specific absorption rate, and current density in culture medium were monitored. REAC stimulation primed transcription of genes involved in cardiac (GATA4, Nkx-2.5, and prodynorphin), skeletal muscle (myoD) and neuronal (neurogenin1) commitment, while downregulating the self renewal/pluripotency-associated genes Sox2, Oct4, and Nanog. REAC exposure enhanced the expression of cardiac, skeletal, and neuronal lineage-restricted marker proteins. The number of spontaneously beating ES-derived myocardial cells was also increased. In conclusion, REAC stimulation provided a "physical milieu" optimizing stem cell expression of pluripotentiality and the attainment of three major target lineages for regenerative medicine, without using chemical agonists or vector-mediated gene delivery.

Genetic architecture of susceptibility to PCB126-induced developmental cardiotoxicity in zebrafish

Variability in risk of developmental defects caused by dioxin-like compounds (DLCs) has been demonstrated within and among several vertebrate species. Beyond our knowledge of the aryl hydrocarbon receptor (AHR) and its role in mediating toxicity for this class of compounds, little else is known concerning precise downstream targets influencing this vulnerability. In the present study, zebrafish with divergent genetic backgrounds were screened for susceptibility to developmental cardiotoxicity caused by the prototypical DLC, 3,3',4,4',5-pentachlorobiphenyl (PCB126); a range up to ∼40-fold differences was observed. Differentially sensitive zebrafish were chosen for a genetic cross, and the recombinant generation was used for genome-wide quantitative trait loci (QTL) mapping. Multiple QTLs were identified--several acting alone, one additively, and two others via epistatic interaction. Together, these QTLs account for 24% of the phenotypic variance observed in cardioteratogenicity resulting from PCB126 exposure (logarithm of the odds = 13.55, p = 1.89 × 10⁻¹⁰). Candidate genes in these QTL regions include the following: ahr2, bcor, and capn1 (Chr 22); e2f1 and pdyn (Chr 23); ctnnt2, plcg1, eno3, tgm1, and tgm2 (interacting on Chr 23); and vezf1 (Chr 15). These data demonstrate that DLC-induced cardiac teratogenicity is a multifactorial complex trait influenced by gene × gene and gene × environment interactions. The identified QTLs harbor many DLC-responsive genes critical to cardiovascular development and provide insight into the genetic basis of susceptibility to AHR-mediated developmental toxicity.

Mitogen-activated protein kinase in endothelin-1-induced cardiac differentiation of mouse embryonic stem cells

Endothelin-1(ET-1) is a potent vasoconstrictor involved in the development of cardiovascular diseases and is an important regulator of heart development. However, the role of ET-1 in cardiac differentiation of mouse embryonic stem cells (mESCs) and the underlying molecular mechanisms remain poorly understood. In the present study, we showed that ET-1 significantly up-regulated gene expression of the cardiac specific transcriptional factors Nkx2.5, GATA4, and conduction system specific marker CX40, with no affect on the gene expression of α-MHC and β-MHC in cardiac differentiation of mESCs. The percentage of beating embryoid bodies (EB) and the Troponin T (TnT) positive area in total EBs was unchanged following ET-1 treatment, while the percentage of spindle cells that stained positively with TnT was increased in the presence of ET-1. Further investigation indicated that the percentage of beating EBs and the TnT positive area were decreased by the extracellular signal-related kinases (ERK)-1/2 inhibitor U0126 and the p38 inhibitor SB203580, but not by the Jun amino-terminal kinases (JNK) inhibitor SP600125. Inhibition of ERK1/2, p38, and JNK pathways also blocked the up-regulation of Nkx2.5 and GATA4 by ET-1, however only inhibition of the ERK1/2 pathway had negatively effects on the increase in CX40 expression in response to ET-1. ET-1 induced an increase in the percentage of spindle cells was also inhibited by U0126. Our results suggest that ET-1 plays a significant role in the cardiac differentiation of mESCs, especially in those cells committed to the conduction system, with the ERK1/2 pathway playing a critical role in this process.

Hyaluronan esters drive Smad gene expression and signaling enhancing cardiogenesis in mouse embryonic and human mesenchymal stem cells

Background

Development of molecules chemically modifying the expression of crucial orchestrator(s) of stem cell commitment may have significant biomedical impact. We have recently developed hyaluronan mixed esters of butyric and retinoic acids (HBR), turning cardiovascular stem cell fate into a high-yield process. The HBR mechanism(s) remain still largely undefined.

Methodology/Principal Findings

We show that in both mouse embryonic stem (ES) cells and human mesenchymal stem cells from fetal membranes of term placenta (FMhMSCs), HBR differentially affected the patterning of Smad proteins, one of the major conductors of stem cell cardiogenesis. Real-time RT-PCR and Western blot analyses revealed that in both cell types HBR enhanced gene and protein expression of Smad1,3, and 4, while down-regulating Smad7. HBR acted at the transcriptional level, as shown by nuclear run-off experiments in isolated nuclei. Immunofluorescence analysis indicated that HBR increased the fluorescent staining for Smad1,3, and 4, confirming that the transcriptional action of HBR encompassed the upregulation of the encoded Smad proteins. Chromatin immune precipitation and transcriptional analyses showed that HBR increased the transcription of the cardiogenic gene Nkx-2.5 through Smad4 binding to its own consensus Smad site. Treatment of mouse ES cells and FMhMSCs with HBR led to the concomitant overexpression of both Smad4 and α-sarcomeric actinin. Smad4 silencing by the aid of lentiviral-mediated Smad4 shRNA confirmed a dominant role of Smad4 in HBR-induced cardiogenesis.

Conclusions/Significance

The use of HBR may pave the way to novel combinatorial strategies of molecular and stem cell therapy based on fine tuning of targeted Smad transciption and signaling leading to a high-throughput of cardiogenesis without the needs of gene transfer technologies.

Strategies for ensuring that regenerative cardiomyocytes function properly and in cooperation with the host myocardium

In developed countries, in which people have nutrient-rich diets, convenient environments, and access to numerous medications, the disease paradigm has changed. Nowadays, heart failure is one of the major causes of death. In spite of this, the therapeutic efficacies of medications are generally unsatisfactory. Although whole heart transplantation is ideal for younger patients with heart failure, many patients are deemed to be unsuitable for this type of surgery due to complications and/or age. The need for therapeutic alternatives to heart transplantation is great. Regenerative therapy is a strong option. For this purpose, several cell sources have been investigated, including intrinsic adult stem or progenitor cells and extrinsic pluripotent stem cells. Most intrinsic stem cells seem to contribute to a regenerative environment via paracrine factors and/or angiogenesis, whereas extrinsic pluripotent stem cells are unlimited sources of cardiomyocytes. In this review, we summarize the various strategies for using regenerative cardiomyocytes including our recent progressions: non-genetic approaches for the purification of cardiomyocytes and efficient transplantation. We expect that use of intrinsic and extrinsic stem cells in combination will enhance therapeutic effectiveness.

Skeletal and cardiac myogenesis accompany adipogenesis in P19 embryonal stem cells

P19 embryonic carcinoma cells resemble normal embryonic stem (ES) cells. They generate cardiac and skeletal myocytes in response to retinoic acid (RA) or oxytocin (OT). RA treatment followed by exposure to triiodothyronine (T3) and insulin induces ES cells differentiation into adipocytes and skeletomyocytes. On the other hand, OT (10(-7) M) was reported to inhibit 3T3 preadipocyte maturation. The present work was undertaken to determine whether P19 cells have an adipogenic potential that could be affected by OT. Cells were treated with RA (10(-6) M)/T3+insulin (adipogenic protocol) or 10(-7) M OT (cardiomyogenic protocol), and analyzed by polymerase chain reaction, immunotechniques, and cytochemistry. Oil-Red-O staining and expression of peroxisome proliferator-activated receptor-gamma (PPARgamma) and aP2 indicated the generation of adipocytes in cultures submitted to the adipogenic protocol. Contracting cells were also generated. Cells positive for sarcomeric actinin and negative for cardiac troponin inhibitor (cTpnI) indicated generation of skeletomyocytes, and cTpnI positive cells revealed generation of cardiomyocytes. Levels of cTpnI and of the skeletal marker MyoD were almost similar in both protocols, whereas no Oil-Red-O staining was associated with the cardiomyogenic protocol. Addition of 10(-7) M OT to the adipogenic protocol did not affect Oil-Red-O staining and PPARgamma expression. Interestingly, Oct3/4 pluripotency marker disappeared in the adipogenic protocol but remained expressed in the cardiomyogenic one. P19 cells thus have an adipogenic potential non affected by 10(-7) M OT. RA/T3+insulin combination generates a larger spectrum of mesodermal cell derivatives and is a more potent morphogenic treatment than OT. P19 cells could help investigating mechanisms of cell fate decision during development.

Engineering microenvironments for embryonic stem cell differentiation to cardiomyocytes

Embryonic stem cells and induced pluripotent stem cells have the potential to be a renewable source of cardiomyocytes for use in myocardial cell replacement strategies. Although progress has been made towards differentiating stem cells to specific cell lineages, the efficiency is often poor and the number of cells generated is not suitable for therapeutic usage. Recent studies demonstrated that controlling the stem cell microenvironment can influence differentiation. Components of the extracellular matrix are important physiological regulators and can provide mechanical cues, direct differentiation and improve cell engraftment into damaged tissue. Bioreactors are used to control the microenvironment and produce large numbers of desired cells. This article describes recent methods to achieve cardiomyocyte differentiation by engineering the stem cell microenvironment. Successful translation of stem cell research to therapeutic applications will need to address large-scale cardiomyocyte differentiation and purification, assessment of cardiac function and synchronization, and safety concerns.

Association of matrix metalloproteinase-3 with cardiogenic activity during Noggin-induced differentiation of mouse embryonic stem cells

BACKGROUND

Despite the pluripotency of embryonic stem (ES) cells, their clinical applications have been hindered due to the lack of reliable differentiation methods. Recently, it was shown that Noggin could effectively induce cardiomyocyte differentiation by transient treatment of ES cells.

METHODS

To determine how Noggin may induce cardiac differentiation, we compared differentially expressed genes during Noggin-induced differentiation of ES cells using microarray analysis. We found Matrix metalloproteinase-3 (Mmp-3) expression was highly up-regulated by Noggin treatment. To understand the role of Mmp-3 in the cardiac differentiation of ES cells, we inhibited Mmp-3 activity by treating with a specific Mmp-3 inhibitor during Noggin-induced cardiac differentiation of ES cells. We also analyzed the expression levels of cardiac markers and the ratio of spontaneously beating embryoid bodies (EBs) in the presence of the Mmp-3 inhibitor.

RESULTS

We analyzed EB samples from zero, two, and four days with or without Noggin treatment, and found that the expression levels of 2 (0 day), 56 (2 days), and 805 (4 days) genes were altered with Noggin treatment. Up-regulation of Mmp-3 was closely associated with relative increases of cardiogenic, vasculogenic, and hematopoietic genes in EB treated with Noggin. By inhibiting Mmp-3 activity, we verified that Mmp-3 activation is partly responsible for both the expression of cardiac markers and the elevated ratio of spontaneously beating to non-beating EBs.

CONCLUSIONS

The concurrent expression of Mmp-3 with many cardiogenic genes and the specific inhibition of Mmp-3 revealed a critical role for Mmp-3 in Noggin-induced cardiac differentiation of ES cells.

TGF-beta1 enhances cardiomyogenic differentiation of skeletal muscle-derived adult primitive cells

The optimal medium for cardiac differentiation of adult primitive cells remains to be established. We quantitatively compared the efficacy of IGF-1, dynorphin B, insulin, oxytocin, bFGF, and TGF-beta1 in inducing cardiomyogenic differentiation. Adult mouse skeletal muscle-derived Sca1+/CD45-/c-kit-/Thy-1+ (SM+) and Sca1-/CD45-/c-kit-/Thy-1+ (SM-) cells were cultured in basic medium (BM; DMEM, FBS, IGF-1, dynorphin B) alone and BM supplemented with insulin, oxytocin, bFGF, or TGF-beta1. Cardiac differentiation was evaluated by the expression of cardiac-specific markers at the mRNA (qRT-PCR) and protein (immunocytochemistry) levels. BM+TGF-beta1 upregulated mRNA expression of Nkx2.5 and GATA-4 after 4 days and Myl2 after 9 days. After 30 days, BM+TGF-beta1 induced the greatest extent of cardiac differentiation (by morphology and expression of cardiac markers) in SM- cells. We conclude that TGF-beta1 enhances cardiomyogenic differentiation in skeletal muscle-derived adult primitive cells. This strategy may be utilized to induce cardiac differentiation as well as to examine the cardiomyogenic potential of adult tissue-derived stem/progenitor cells.

Extrinsic regulation of cardiomyocyte differentiation of embryonic stem cells

Cardiovascular disease is one of leading causes of death throughout the U.S. and the world. The damage of cardiomyocytes resulting from ischemic injury is irreversible and leads to the development of progressive heart failure, which is characterized by the loss of functional cardiomyocytes. Because cardiomyocytes are unable to regenerate in the adult heart, cell-based therapy of transplantation provides a potential alternative approach to replace damaged myocardial tissue and restore cardiac function. A major roadblock toward this goal is the lack of donor cells; therefore, it is urgent to identify the cardiovascular cells that are necessary for achieving cardiac muscle regeneration. Pluripotent embryonic stem (ES) cells have enormous potential as a source of therapeutic tissues, including cardiovascular cells; however, the regulatory elements mediating ES cell differentiation to cardiomyocytes are largely unknown. In this review, we will focus on extrinsic factors that play a role in regulating different stages of cardiomyocyte differentiation of ES cells.

The physiological basis of intracrine stem cell regulation

Intracrine peptides and proteins participate in the regulation of adult and pleuripotential embryonic-like stem cells. Included among these factors are VEGF, dynorphin, the readthrough form of acetylcholinesterase, Oct3/4, Pdx-1, Pax-6, and high-mobility group protein B1, among others. In some cases, the establishment of intracrine feedback loops can be shown to be relevant to this regulation, consistent with previously proposed principles of intracrine action. Here the role of intracrines in stem cell regulation is reviewed, with particular attention to the intracrine regulation of cardiac stem cells. The reprogramming of cells to restore the pleuripotent phenotype and the possible role of stem/progenitor cells in neoplasia are also discussed.

Endogenous morphine/nitric oxide-coupled regulation of cellular physiology and gene expression: implications for cancer biology

Cancer is a simplistic, yet complicated, process that promotes uncontrolled growth. In this regard, this unconstrained proliferation may represent primitive phenomena whereby cellular regulation is suspended or compromised. Given the new empirical evidence for a morphinergic presence and its profound modulatory actions on several cellular processes it is not an overstatement to hypothesize that morphine may represent a key chemical messenger in the process of modulating proliferation of diverse cells. This has been recently demonstrated by the finding of a novel opiate-alkaloid selective receptor subtype in human multilineage progenitor cells (MLPC). Adding to the significance of morphinergic signaling are the findings of its presence in plant, invertebrate and vertebrate cells, which also have been shown to synthesize this messenger as well. Interestingly, we and others have shown that some cancerous tissues contain morphine. Furthermore, in medullary histolytic reticulosis, which is exemplified by cells having hyperactivity, the mu3 (mu3) opiate select receptor was not present. Thus, it would appear that morphinergic signaling has inserted itself in many processes taking a long time to evolve, including those regulating the proliferation of cells across diverse phyla.

Creating prodynorphin-expressing stem cells alerted for a high-throughput of cardiogenic commitment

BACKGROUND

The development of cell therapy for the rescue of damaged heart muscle is a major area of inquiry. Within this context, the establishment of a cardiogenic cell line may remarkably facilitate the molecular dissection of cardiac fate specification, a low-efficiency and still poorly understood process, paving the way for novel approaches in the use of stem cells for cardiac repair.

METHODS & RESULTS

We used GTR1 cells, a derivative of mouse R1 embryonic stem cells bearing the puromycin-resistance gene driven by the cardiomyocyte-specific alpha-myosin heavy chain promoter, affording a gene trapping selection of a virtually pure population of embryonic stem cell-derived cardiomyocytes. Third-generation lentiviral vectors were used to overexpress the prodynorphin gene, previously shown to orchestrate a dynorphinergic system acting as a major conductor of embryonic stem cell cardiogenesis. Lentiviral prodynorphin transduction remarkably enhanced the transcription of GATA-4 and Nkx-2.5, two cardiac lineage-promoting genes, resulting in a dramatic increase in the number of spontaneously beating cardiomyocytes. Transduced cells also exhibited a subcellular redistribution patterning of protein kinase C-beta, -delta and -epsilon, a major requirement in cardiac lineage commitment. This activation resulted from a sustained increase in the transcription of targeted protein kinase C genes. Prodynorphin transduction was selective in nature and failed to activate genes responsible for skeletal myogenesis or neuronal specification.

CONCLUSIONS

The cell line developed in this study provides a powerful in vitro model of cardiomyogenesis that may help clarify the cascade of transcriptional activation and signaling networks that push multipotent cells to take on the identity of a cardiac myocyte.

Human embryonic stem cell-derived cardiomyocytes: inducing strategies

Cell-based therapy is emerging as an innovative approach for the treatment of degenerative diseases, and stem cells appear to be an ideal source of cells for this. In cardiology, in particular, human embryonic stem cell (hESC)-derived cardiomyocytes theoretically fulfill most, if not all, of the properties of an ideal donor cell, but several critical obstacles need to be overcome. Many research projects are focusing on set-up strategies for directing hESC differentiation toward the cardiac lineage. It is one of the main difficulties in the search to provide a valuable source of cells to effect regeneration of myocardial tissue in patients with severe heart failure. To date, there are no easy and efficient protocols for the induction of hESC differentiation toward the cardiac lineage. Discovering new molecules or tools capable of doing this is imperative.

Effect of bone morphogenetic protein-4 (BMP-4) on cardiomyocyte differentiation from mouse embryonic stem cell

The present study was designed to evaluate the effect of BMP-4 on mouse embryonic stem cells (ESCs)-derived cardiomyocyte. Cardiac differentiation of the mouse ESCs was initiated by embryoid bodies (EBs) formation in hanging drops, transfer of EBs to the suspension culture and then plating onto gelatin-coated tissue culture plates. BMP-4 was added to culture medium throughout the suspension period. Cultures were observed daily with an inverted microscope for the appearance of contracting clusters. At the early, intermediate and terminal stages of differentiation, the choronotropic responses of cardiomyocytes to cardioactive drugs were assessed, and the cardiomyocytes immunostained for cardiac troponin I, desmin, alpha-actinin and nebulin. The contracting clusters were isolated for ultrastructural evaluation, at day 14 after plating. Moreover, total RNA extracted from contracting EBs of early and terminal stages of differentiation were examined for oct-4, alpha- and beta-myosin heavy chain, myosin light chain-2V and atrial natriuretic factor expression. The BMP-4 treatment resulted in a decrease in the percent of beating EBs and the percent of developing cardiomyocytes per EBs. As a whole, the chronotropic responses of beating cardiac clusters to cardioactive drugs in control group were better than BMP-4 treated group. The cardiomyocytes of both groups were positive immunostained for applied antibodies except for nebulin. Moreover, in the BMP-4 treated group, the ultrastructural characteristics and cardiac-specific genes expression were all retarded in the terminal stage of cardiomyocytes development. In conclusion, BMP-4 had an inhibitory effect on cardiomyocyte differentiation from the mouse ESCs in terms of ultrastructural characteristics, genes expression and functional properties.

Mu- and kappa-opioids induce the differentiation of embryonic stem cells to neural progenitors

Growth factors, hormones, and neurotransmitters have been implicated in the regulation of stem cell fate. Since various neural precursors express functional neurotransmitter receptors, which include G protein-coupled receptors, it is anticipated that they are involved in cell fate decisions. We detected mu-opioid receptor (MOR-1) and kappa-opioid receptor (KOR-1) expression and immunoreactivity in embryonic stem (ES) cells and in retinoic acid-induced ES cell-derived, nestin-positive, neural progenitors. Moreover, these G protein-coupled receptors are functional, since [D-Ala(2),MePhe(4),Gly-ol(5)]enkephalin, a MOR-selective agonist, and U69,593, a KOR-selective agonist, induce a sustained activation of extracellular signal-regulated kinase (ERK) signaling throughout a 24-h treatment period in undifferentiated, self-renewing ES cells. Both opioids promote limited proliferation of undifferentiated ES cells via the ERK/MAP kinase signaling pathway. Importantly, biochemical and immunofluorescence data suggest that [D-Ala(2),MePhe(4),Gly-ol(5)]enkephalin and U69,593 divert ES cells from self-renewal and coax the cells to differentiate. In retinoic acid-differentiated ES cells, opioid-induced signaling features a biphasic ERK activation profile and an opioid-induced, ERK-independent inhibition of proliferation in these neural progenitors. Collectively, the data suggest that opioids may have opposite effects on ES cell self-renewal and ES cell differentiation and that ERK activation is only required by the latter. Finally, opioid modulation of ERK activity may play an important role in ES cell fate decisions by directing the cells to specific lineages.

p204 Is Required for the Differentiation of P19 Murine Embryonal Carcinoma Cells to Beating Cardiac Myocytes

Among 10 adult mouse tissues tested, the p204 protein levels were highest in heart and skeletal muscle. We described previously that the MyoD-inducible p204 protein is required for the differentiation of cultured murine C2C12 skeletal muscle myoblasts to myotubes. Here we report that p204 was also required for the differentiation of cultured P19 murine embryonal carcinoma stem cells to beating cardiac myocytes. As shown by others, this process can be triggered by dimethyl sulfoxide (DMSO). We established that DMSO induced the formation of 204RNA and p204. Ectopic p204 could partially substitute for DMSO in inducing differentiation, whereas ectopic 204 antisense RNA inhibited the differentiation. Experiments with reporter constructs, including regulatory regions from the Ifi204 gene (encoding p204) in P19 cells and in cultured newborn rat cardiac myocytes, as well as chromatin coimmunoprecipitations with transcription factors, revealed that p204 expression was synergistically transactivated by the cardiac Gata4, Nkx2.5, and Tbx5 transcription factors. Furthermore, ectopic p204 triggered the expression of Gata4 and Nkx2.5 in P19 cells. p204 contains a nuclear export signal and was partially translocated to the cytoplasm during the differentiation. p204 from which the nuclear export signal was deleted was not translocated, and it did not induce differentiation. The various mechanisms by which p204 promoted the differentiation are reported in the accompanying article (Ding, B., Liu, C., Huang, Y., Yu, J., Kong, W., and Lengyel, P. (2006) J. Biol. Chem. 281, 14893-14906).

Differentiation Pathways in Human Embryonic Stem Cell-Derived Cardiomyocytes

Human embryonic stem (hES) cells are pluripotent cell lines derived from the inner cell mass of the blastocyst-stage embryo. These unique cell lines can be propagated in the undifferentiated state in culture, while retaining the capacity to differentiate into derivatives of all three germ layers, including cardiomyocytes. The derivation of the hES cell lines presents a powerful tool to explore the early events of cardiac progenitor cell specification and differentiation, and it also provides a novel cell source for the emerging field of cardiovascular regenerative medicine. A spontaneous differentiation system of these stem cells to cardiomyocytes was established and the generated myocytes displayed molecular, structural, and functional properties of early-stage heart cells. In order to follow the in vitro differentiation process, the temporal expression of signaling molecules and transcription factors governing early cardiac differentiation was examined throughout the process. A characteristic pattern was noted recapitulating the normal in vivo cardiac differentiation scheme observed in other model systems. This review discusses the known pathways involved in cardiac specification and the possible factors that may be used to enhance cardiac differentiation of hES cells, as well as the steps required to fully harness the enormous potential of these unique cells.

Embryonic and adult stem cell-derived cardiomyocytes: lessons from in vitro models

For years, research has focused on how to treat heart failure by sustaining the overloaded remaining cardiomyocytes. Recently, the concept of cell replacement therapy as a treatment of heart diseases has opened a new area of investigation. In vitro-generated cardiomyocytes could be injected into the heart to rescue the function of a damaged myocardium. Embryonic and/or adult stem cells could provide cardiac cells for this purpose. Knowledge of fundamental cardiac differentiation mechanisms unraveled by studies on animal models has been improved using in vitro models of cardiogenesis such as mouse embryonal carcinoma cells, mouse embryonic stem cells and, recently, human embryonic stem cells. On the other hand, studies suggesting the existence of cardiac stem cells and the potential of adult stem cells from bone marrow or skeletal muscle to differentiate toward unexpected phenotypes raise hope and questions about their potential use for cardiac cell therapy. In this review, we compare the specificities of embryonic vs adult stem cell populations regarding their cardiac differentiation potential, and we give an overview of what in vitro models have taught us about cardiogenesis.

Cardiomyocytes

Derivation of cardiomyocytes from embryonic stem cells would be a boon for treatment of the many millions of people worldwide who suffer significant cardiac tissue damage in a myocardial infarction. Such cells could be used for transplantation, either as loose cells, as organized pieces of cardiac tissue, or even as pieces of organs. Eventual derivation of human embryonic stem cells via somatic cell nuclear cloning would provide cells that not only may replace damaged cardiac tissue, but also would replace tissue without fear that the patient's immune system will reject the implant. Embryonic stem cells can differentiate spontaneously into cardiomyocytes. In vitro differentiation of embryonic stem cells normally requires an initial aggregation step to form structures called embryoid bodies that differentiate into a wide variety of specialized cell types, including cardiomyocytes. This chapter discusses methods of encouraging embryoid body formation, causing pluripotent stem cells to develop into cardiomyocytes, and expanding the numbers of cardiomyocytes so that the cells may achieve functionality in transplantation, all in the mouse model system. Such methods may be adaptable and/or modifiable to produce cardiomyocytes from human embryonic stem cells.

κ-opioids induce a reversible inhibition of CFU-GM from CD133+ cord blood cells

BACKGROUND

Opioid agonists have been shown to exert an inhibitory action on a number of malignant and non-malignant cell types. However, there are no reports dealing with their effect on hemopoietic progenitors. Based upon our previous experience of opioid agonists we examined whether opioids could interfere with the growth of CFU-GM from CD133(+) cord blood cells.

METHODS

Cord blood samples were subjected to CD133(+) column selection, with subsequent exposure to opioid agonists and antagonists or both, in semi-solid cultures for CFU-GM growth. Colonies of day 7 of culture were replated in fresh medium in the absence of opioids. The colonies were evaluated at 7 and 14 days of culture. RT-PCR was performed for the detection of opioid and somatostatin receptors. Apoptosis tests and immunophenotypic evaluations were employed in liquid cultures in conditions identical to those of the semi-solid ones.

RESULTS AND DISCUSSION

Our results suggest that opioids can induce a significant inhibition of CFU-GM growth, which is reversible and not mediated through opioid or somatostatin receptors, while apoptosis is not implicated. Whether this finding could be used for clinical intervention remains to be examined.

Ischemic preconditioning increases the bioavailability of cardiac enkephalins

Growing evidence suggests that cardiac enkephalins and their receptors are involved in ischemic preconditioning (IPC). Because there is no evidence for vesicular storage of small bioactive enkephalins in the heart, studies were designed to test the hypothesis that ischemia depletes cardiac enkephalins and that IPC preserves the same enkephalins by accelerating their processing from the larger proenkephalin precursor (PEP) pool. The precursors and two bioactive representatives, Met-enkephalin (ME) and Met-enkephalin-Arg-Phe (MEAP), were separated by size-exclusion chromatography and quantified by radioimmunoassay. Isolated perfused rat hearts were prepared and exposed to global ischemia. After 30 min of global ischemia and 40 min of reflow, the PEP pool was reduced (from 17.99 ± 1.52 to 14.20 ± 2.38 pmol/g wet wt), MEAP increased by 53%, and ME declined by 68%. The sum of the two smaller peptides was unchanged (9.78 ± 0.83 vs. 9.33 ± 2.81). Thus the total enkephalin peptide content was not altered (27.77 ± 1.69 vs. 24.10 ± 4.75). Peptide distribution after ischemia and reflow was also unaltered by pretreatment with peptidase inhibitors. However, when the hearts were preconditioned, the PEP pool remained significantly lower and both of the bioactive peptides, MEAP and ME, were elevated (+49% and +86%, respectively). The decline in the PEP pool was prevented by peptidase inhibition and the rise in MEAP was exaggerated. In separate protocols, synthetic enkephalins (ME, MEAP, and Leu-enkephalin) were added to the coronary inflow before 30 min of global ischemia and throughout the subsequent reflow. The added enkephalins (10−8M) had no inotropic effect on baseline function but completely prevented the mechanical dysfunction observed in untreated controls during reflow. Thus IPC appears to increase available bioactive enkephalins (MEAP + ME) within the heart by enhancing synthesis of precursors and their subsequent processing from the PEP pool.

Focal adhesion kinase signaling regulates cardiogenesis of embryonic stem cells

The signaling steps that induce cardiac differentiation in embryonic stem (ES) cells are incompletely understood. We examined the effect of adhesion signaling including Src and focal adhesion kinase (FAK) on cardiogenesis in mouse ES cells using alpha-myosin heavy chain promoter-driven enhanced green fluorescent protein or luciferase as reporters. Cardiac transcription factors including Nkx2.5 and Tbx5 mRNA were first expressed at day 4 in hanging drop embryoid bodies, and adhesion of embryoid bodies to surfaces at or before that day strongly inhibited differentiation of ES cells to cardiomyocytes. Since adhesion signaling could suppress cardiogenesis through Src kinases, embryoid bodies were exposed to the small molecule PP2, known as a Src family kinase inhibitor. PP2 during embryoid body adhesion dramatically increased cardiomyocyte differentiation and decreased mRNA expression of neuronal cellular adhesion molecule and alpha-fetoprotein, neuroectodermal, and endodermal markers, respectively. Surprisingly, although there was an interaction between Src and FAK in cardiogenesis, the procardiogenic effect of PP2 appeared incompletely explained by Src kinase inhibition, since another Src family kinase inhibitor, SU6656, failed to induce cardiogenesis. Instead, PP2 specifically inhibited adhesion-induced FAK phosphorylation. In ES cells stably expressing FAK-related nonkinase, which functions as a dominant negative FAK, cell migration from embryoid bodies was inhibited, whereas alpha-myosin heavy chain expression and myosin-stained cardiomyocytes were increased, suggesting that reducing cell motility may contribute to cardiogenesis. These data indicate that FAK is a key regulator of cardiogenesis in mouse ES cells and that FAK signaling within embryoid bodies can direct stem cell lineage commitment.

CAM and cell fate targeting: molecular and energetic insights into cell growth and differentiation

Evidence-based medicine is switching from the analysis of single diseases at a time toward an integrated assessment of a diseased person. Complementary and alternative medicine (CAM) offers multiple holistic approaches, including osteopathy, homeopathy, chiropractic, acupuncture, herbal and energy medicine and meditation, all potentially impacting on major human diseases. It is now becoming evident that acupuncture can modify the expression of different endorphin genes and the expression of genes encoding for crucial transcription factors in cellular homeostasis. Extremely low frequency magnetic fields have been found to prime the commitment to a myocardial lineage in mouse embryonic stem cells, suggesting that magnetic energy may direct stem cell differentiation into specific cellular phenotypes without the aid of gene transfer technologies. This finding may pave the way to novel approaches in tissue engineering and regeneration. Different ginseng extracts have been shown to modulate growth and differentiation in pluripotent cells and to exert wound-healing and antitumor effects through opposing activities on the vascular system, prompting the hypothesis that ancient compounds may be the target for new logics in cell therapy. These observations and the subtle entanglement among different CAM systems suggest that CAM modalities may deeply affect both the signaling and transcriptional level of cellular homeostasis. Such a perception holds promises for a new era in CAM, prompting reproducible documentation of biological responses to CAM-related strategies and compounds. To this end, functional genomics and proteomics and the comprehension of the cell signaling networks may substantially contribute to the development of a molecular evidence-based CAM.

Whether modern cell technologies can break down biological limitations of tissue-specific regeneration of the myocardium

The paper reviews modern concepts of physiological and reparative regeneration of the myocardium as a highly specific and highly differentiated tissue system. Special attention was given to evaluation of the proliferative potential of cardiomyocytes, in particular, to the existence of a population of resident cardiac stem cells in the myocardium. Modern approaches to replenishment of massive cardiomyocyte loss via transplantation and transdifferentiation of adult and embryonic stem cells are discussed and the possibilities of using cell technologies for induction of tissue-specific regeneration of the myocardium are analyzed.

Embryonic stem cells for basic research and potential clinical applications in cardiology

Embryonic stem (ES) cells are pluripotent, possessing the unique property to differentiate into any somatic cell type while retaining the ability to proliferate indefinitely. Due to their ability to recapitulate embryonic differentiation, ES cells are an ideal tool to study the process of early embryogenesis in vitro. Signalling cascades and genes involved in differentiation can be easily studied, and functional genomics approaches aim to identify the regulatory networks underlying lineage commitment. Their unique ability to differentiate into any cell type make ES cells a prime candidate for cell replacement therapy (CRT) of various degenerative disorders. Results from various disease models are promising and have demonstrated their principal suitability as a therapeutic agent in diseases such as myocardial infarctions, diabetes mellitus and Parkinson's disease. Prior to clinical trials in humans, two issues remain to be solved: due to their high proliferative potential, ES cells can form teratocarcinomas in the recipient, and depending on the source of the cells, ES cell grafts may be rejected by the host organism. This review discusses the current state of basic ES cell research with a focus on cardiac differentiation and gives an overview of their use in CRT approaches.

Turning on stem cell cardiogenesis with extremely low frequency magnetic fields

Modulation of stem cell differentiation is an important assignment for cellular engineering. Embryonic stem (ES) cells can differentiate into cardiomyocytes, but the efficiency is typically low. Here, we show that exposure of mouse ES cells to extremely low frequency magnetic fields triggered the expression of GATA-4 and Nkx-2.5, acting as cardiac lineage-promoting genes in different animal species, including humans. Magnetic fields also enhanced prodynorphin gene expression, and the synthesis and secretion of dynorphin B, an endorphin playing a major role in cardiogenesis. These effects occurred at the transcriptional level and ultimately ensued into a remarkable increase in the yield of ES-derived cardiomyocytes. These results demonstrate the potential use of magnetic fields for modifying the gene program of cardiac differentiation in ES cells without the aid of gene transfer technologies and may pave the way for novel approaches in tissue engineering and cell therapy.