Oxytocin induces differentiation of P19 embryonic stem cells to cardiomyocytes

The role of oxytocin in cardiovascular regulation

Studies of body volume expansion have indicated that lesions of the anteroventral third ventricle and median eminence block the release of atrial natriuretic peptide (ANP) into the circulation. Detailed analysis of the lesions showed that activation of oxytocin (OT)-ergic neurons is responsible for ANP release, and it has become clear that activation of neuronal circuitry elicits OT secretion into the circulation, activating atrial OT receptors and ANP release from the heart. Subsequently, we have uncovered the entire functional OT system in the rat and the human heart. An abundance of OT has been observed in the early development of the fetal heart, and the capacity of OT to generate cardiomyocytes (CMs) has been demonstrated in various types of stem cells. OT treatment of mesenchymal stem cells stimulates paracrine factors beneficial for cardioprotection. Cardiovascular actions of OT include: i) lowering blood pressure, ii) negative inotropic and chronotropic effects, iii) parasympathetic neuromodulation, iv) vasodilatation, v) anti-inflammatory activity, vi) antioxidant activity, and vii) metabolic effects. OT actions are mediated by nitric oxide and ANP. The beneficial actions of OT may include the increase in glucose uptake by CMs and stem cells, reduction in CM hypertrophy, oxidative stress, and mitochondrial protection of several cell types. In experimentally induced myocardial infarction in rats, continuous in vivo OT delivery improves cardiac healing and cardiac work, reduces inflammation, and stimulates angiogenesis. Because OT plays anti-inflammatory and cardioprotective roles and improves vascular and metabolic functions, it demonstrates potential for therapeutic use in various pathologic conditions.

Oxytocin-Gly-Lys-Arg stimulates cardiomyogenesis by targeting cardiac side population cells

The functional oxytocin (OT) system is expressed in the human and rodent hearts. OT stimulates differentiation of cardiac stem cells into contracting cardiomyocytes (CM). In this study, we investigated OT receptors (OTR) expressed in the cells of cardiac side population (SP) and the abilities of these cells to differentiate into CM in response to the treatment with OT-Gly-Lys-Arg (OT-GKR), a dominant and biologically active form of OT, in the fetal rodent heart. Immunocytochemistry of whole rat embryo at mid gestation (E11) revealed parallel staining in the heart of OTR and the ATP-binding cassette sub-family G member 2 (brcp1) antigen the marker of the SP phenotype. Using flow cytometry, the SP cells were selected from the newborn CM stained with Höechst 33342: 5.32%±0.06% of SP and 15.2%±1.10 of main population expressed OTR on the cell surface. The OTR was detected in CD29 (6.6%) and then in CD31 (4.7%) but less frequently in CD45 (0.7%) positive SP cell subpopulations. Specifically, the phenotype of SP CD31- cell, but not SP CD31+ cells, proliferates in the presence of OT-GKR and develops large cell aggregates. Then, OT-GKR treatment induced the apparition of beating cell colonies after 11 days (10±2.78%), which increased until day 16 (52±1.21%). The cells in contractile colonies expressed the markers of a CM phenotype, such as troponin, cardiac myosin light chain-2, and actinin. Finally, SP cells stimulated by OT-GKR induced endothelial phenotype. These results suggest that the C-terminally extended OT molecule stimulates cardiac differentiation of SP CD31- cells and is involved in heart growth.

Analysis of the SWI/SNF chromatin-remodeling complex during early heart development and BAF250a repression cardiac gene transcription during P19 cell differentiation

The regulatory networks of differentiation programs and the molecular mechanisms of lineage-specific gene regulation in mammalian embryos remain only partially defined. We document differential expression and temporal switching of BRG1-associated factor (BAF) subunits, core pluripotency factors and cardiac-specific genes during post-implantation development and subsequent early organogenesis. Using affinity purification of BRG1 ATPase coupled to mass spectrometry, we characterized the cardiac-enriched remodeling complexes present in E8.5 mouse embryos. The relative abundance and combinatorial assembly of the BAF subunits provides functional specificity to Switch/Sucrose NonFermentable (SWI/SNF) complexes resulting in a unique gene expression profile in the developing heart. Remarkably, the specific depletion of the BAF250a subunit demonstrated differential effects on cardiac-specific gene expression and resulted in arrhythmic contracting cardiomyocytes in vitro. Indeed, the BAF250a physically interacts and functionally cooperates with Nucleosome Remodeling and Histone Deacetylase (NURD) complex subunits to repressively regulate chromatin structure of the cardiac genes by switching open and poised chromatin marks associated with active and repressed gene expression. Finally, BAF250a expression modulates BRG1 occupancy at the loci of cardiac genes regulatory regions in P19 cell differentiation. These findings reveal specialized and novel cardiac-enriched SWI/SNF chromatin-remodeling complexes, which are required for heart formation and critical for cardiac gene expression regulation at the early stages of heart development.

Cardiomyocyte culture - an update on the in vitro cardiovascular model and future challenges

The success of any work with isolated cardiomyocytes depends on the reproducibility of cell isolation, because the cells do not divide. To date, there is no suitable in vitro model to study human adult cardiac cell biology. Although embryonic stem cells and induced pluripotent stem cells are able to differentiate into cardiomyocytes in vitro, the efficiency of this process is low. Isolation and expansion of human cardiomyocyte progenitor cells from cardiac surgical waste or, alternatively, from fetal heart tissue is another option. However, to overcome various issues related to human tissue usage, especially ethical concerns, researchers use large- and small-animal models to study cardiac pathophysiology. A simple model to study the changes at the cellular level is cultures of cardiomyocytes. Although primary murine cardiomyocyte cultures have their own advantages and drawbacks, alternative strategies have been developed in the last two decades to minimise animal usage and interspecies differences. This review discusses the use of freshly isolated murine cardiomyocytes and cardiomyocyte alternatives for use in cardiac disease models and other related studies.

Identification and characterization of CW108F, a novel β-carboline compound that promotes cardiomyogenesis of stem cells

AIMS

The aim of this study was to identify new compounds that induce cardiomyocyte differentiation of stem cells through cell-based screening and investigate lineage specificity and mechanisms in vitro.

MAIN METHODS

Embryoid bodies (EBs) formed from TC-1/KH2 mouse embryonic stem cells (ESCs) carrying the gene for enhanced green fluorescent protein (EGFP) under the control of the α-myosin heavy chain (MHC) promoter were treated with test compounds. The number of cardiomyocyte-like (EGFP-expressing) cells in EBs was determined by fluorescence-activated cell sorting. Cardiomyocyte differentiation was further confirmed using lineage-specific biochemical assays and by investigating the expression of cardiomyocyte-specific and "stemness"-associated genes. Nuclear factor-kappaB (NF-κB) signaling activity was measured in A549 cells using a reporter-gene assay.

KEY FINDINGS

A β-carboline compound, designated CW108F, increased the number of mouse ESCs expressing α-MHC promoter-driven EGFP and the proportion of beating EBs. CW108F also increased expression of MHC in P19 stem cells, but did not induce osteogenesis of MC3T3-E1 cells, suggesting lineage-specific activity toward cardiomyocytes. CW108F upregulated expression of cardiac-specific GATA-4 and atrial natriuretic factor (ANF) genes in TC-1/KH2 cells, but downregulated expression of the stemness genes, Oct-4 and brachyury. CW108F inhibited NF-κB transcriptional activity, an effect that might contribute to its cardiomyogenesis-promoting activity.

SIGNIFICANCE

The results of this study suggest that the novel β-carboline, CW108F, promotes the differentiation of ESCs into cardiomyocytes and may be useful for investigating molecular pathways of cardiomyogenesis and generating cardiomyocytes from ESCs.

Is oxytocin a therapeutic factor for ischemic heart disease?

Ischemic heart disease (IHD) is among the most important and top ranked causes of death in the world, and its preventive and interventional mechanisms are actively being investigated. Preconditioning may still be beneficial in some situations such as IHD. Development of cardioprotective agents to improve myocardial function, to decrease the incidence of arrhythmias, to delay the onset of necrosis, and to limit the total extent of infarction during IHD is of great clinical importance. In order to reduce morbidity, a new treatment modality must be developed, and oxytocin may indeed be one of the candidates. There is increasing experimental evidence indicating that oxytocin may have cardioprotective effects either by decreasing the extent of reperfusion injury or by pharmacologic preconditioning activity. This review shows that in the presence of oxytocin, the cardioprotective effects may be increased to some extent. The presented board of evidence focuses on the valuable effects of oxytocin on myocardial function and candidates it for future clinical studies in the realm of ischemic heart diseases.

Aza-induced cardiomyocyte differentiation of P19 EC-cells by epigenetic co-regulation and ERK signaling

Stem cells in cell based therapy for cardiac injury is being potentially considered. However, genetic regulatory networks involved in cardiac differentiation are not clearly understood. Among stem cell differentiation models, mouse P19 embryonic carcinoma (EC) cells, are employed for studying (epi)genetic regulation of cardiomyocyte differentiation. Here, we comprehensively assessed cardiogenic differentiation potential of 5-azacytidine (Aza) on P19 EC-cells, associated gene expression profiles and the changes in DNA methylation, histone acetylation and activated-ERK signaling status during differentiation. Initial exposure of Aza to cultured EC-cells leads to an efficient (55%) differentiation to cardiomyocyte-rich embryoid bodies with a threefold (16.8%) increase in the cTnI+ cardiomyocytes. Expression levels of cardiac-specific gene markers i.e., Isl-1, BMP-2, GATA-4, and α-MHC were up-regulated following Aza induction, accompanied by differential changes in their methylation status particularly that of BMP-2 and α-MHC. Additionally, increases in the levels of acetylated-H3 and pERK were observed during Aza-induced cardiac differentiation. These studies demonstrate that Aza is a potent cardiac inducer when treated during the initial phase of differentiation of mouse P19 EC-cells and its effect is brought about epigenetically and co-ordinatedly by hypo-methylation and histone acetylation-mediated hyper-expression of cardiogenesis-associated genes and involving activation of ERK signaling.

Cardiogenic and myogenic gene expression in mesenchymal stem cells after 5-azacytidine treatment

Objective: 5-Azacytidine is a hypomethylating agent that is used for the treatment of myelodysplastic syndrome. This histone modifier is widely employed and plays a nonspecific role in influencing the differentiation capability of stem cells. The ability of bone marrow mesenchymal stem cells to differentiate into cardiomyocyte- and myocyte-like cells after exposure to 3 different doses of 5-azacytidine has been evaluated and compared. The aim of the study was to optimize the effective dose of 5-azacytidine for promoting the cardiomyocyte and myocyte differentiation capabilities of human mesenchymal stem cells (MSCs).

Materials and Methods: Human bone marrow aspirations were collected from healthy donors. MSCs were used for the study of mesodermal differentiation. MSCs were cultured to promote osteoblast differentiation and adipocyte differentiation. The evaluation of osteogenic or adipogenic properties was then performed through immunocytochemical staining. BMMSCs were trypsinized into single-cell suspensions and then prepared for flow cytometric analysis. The MSCs were treated with 5, 10, or 15 μM 5-azacytidine for 24 h and then cultured for 3 weeks. Total RNA was extracted from untreated and 5-azacytidine–treated cells. Troponin T and GATA4 antibodies were used as cardiogenic markers, whereas myogenin and MyoD antibodies were used as myocyte markers.

Results: The morphology and growth rate of MSCs that were treated with any of the 3 doses of 5-azacytidine were similar to the morphology and growth rate of control MSCs. An immunofluorescence analysis examining the expression of the cardiac-specific markers GATA4 and troponin T and the skeletal muscle-specific markers MyoD and myogenin revealed that cells treated with 15 μM 5-azacytidine were strongly positive for these markers. Real-time RT-PCR results were examined; these amplifications indicated that there were higher expression levels of cardiac- and skeletal muscle-specific mRNAs in MSCs treated with 15 μm 5-azacytidine than in MSCs that had either been treated with lower doses of 5-azacytidine or left untreated.

Conclusion: MSCs treated with 5-azacytidine demonstrated the capacity to differentiate into both cardiomyocytes and skeletal myocytes, and 15 μM 5-azacytidine could be the optimal dose of this drug. Other promoting factors should be examined to investigate the possibility of promoting the differentiation of MSCs into specific cell types.

Conflict of interest:None declared.

Sympathetic neurons modulate the beat rate of pluripotent cell-derived cardiomyocytes in vitro

Although stem cell-derived cardiomyocytes have great potential for the therapy of heart failure, it is unclear whether their function after grafting can be controlled by the host sympathetic nervous system, a component of the autonomic nervous system (ANS). Here we demonstrate the formation of functional connections between rat sympathetic superior cervical ganglion (SCG) neurons and pluripotent (P19.CL6) cell-derived cardiomyocytes (P19CMs) in compartmentalized co-culture, achieved using photolithographic microfabrication techniques. Formation of synapses between sympathetic neurons and P19CMs was confirmed by immunostaining with antibodies against β-3 tubulin, synapsin I and cardiac troponin-I. Changes in the beat rate of P19CMs were triggered after electrical stimulation of the co-cultured SCG neurons, and were affected by the pulse frequency of the electrical stimulation. Such changes in the beat rate were prevented when propranolol, a β-adrenoreceptor antagonist, was added to the culture medium. These results suggest that the beat rate of differentiated cardiomyocytes can be modulated by electrical stimulation of connected sympathetic neurons.

Differential effects of retinoids and inhibitors of ERK and p38 signaling on adipogenic and myogenic differentiation of P19 stem cells

All-trans-retinoic acid (atRA) is an essential signaling molecule in embryonic development. It regulates cell differentiation by activating nuclear retinoic acid receptors (RAR) and retinoid-X receptors (RXR), which both control gene expression. In addition, atRA could act in the cytoplasm by modulating the activity of mitogen-activated protein kinases (MAPK) ERK and p38, which also have a role in cell differentiation. AtRA can induce the differentiation of P19 embryonic carcinoma stem cells into adipocytes, cardiomyocytes, and skeletal muscle cells, concurrently, in the same culture. We postulated that combinations of atRA, atRA analogs exhibiting selectivity for RAR or RXR, and inhibitors of ERK and p38 signaling (ERKi and p38i) could be used to favor one mesodermal fate over the others in the P19 model. In a first series of experiments, we replaced atRA by an agonist of RXR (LG100268) or RAR (TTNPB) to preferentially stimulate one group of receptors over the other. LG100268 was as adipogenic and myogenic as atRA, whereas TTNPB strongly induced adipogenesis, but not myogenesis. ERKi enhanced the myogenic action of atRA, and p38i increased both adipogenesis and myogenesis. In a second series of experiments, we combined atRA with an RAR or RXR antagonist (RARatg or RXRatg) to preferentially deactivate each receptor group in turn. The combinations atRA+RXRatg and atRA+RARatg, including or not ERKi, had similar mesodermal actions as atRA. In contrast, there was no myogenesis with atRA+RXRatg+p38i treatment, and there were no myogenesis and no adipogenesis with the atRA+RARatg+p38i combination. Overall, the results indicate that p38 has a role in mesodermal differentiation that depends on the retinoid context. Indeed, p38 in conjunction with RXR is important in myogenesis, and p38 and RAR in adipogenesis. Under the conditions tested, it was possible to stimulate adipogenesis with a block on myogenesis, whereas increased myogenesis was accompanied by adipogenesis.

Human embryonic stem cell-derived cardiomyocytes: drug discovery and safety pharmacology

Human embryonic stem cells (hESCs) can provide potentially unlimited quantities of a wide range of human cell types that can be used in drug discovery and development, basic research and regenerative medicine. In this review, the authors describe the differentiation of hESCs into cardiomyocytes and outline the properties of hESC-derived cardiomyocytes (hESC-CMs), including their cardiac-type action potentials and contractile characteristics. In vitro cellular assays using hESC-CMs, which can be genetically engineered to create target-specific reporters as well as human disease models, will have applications at multiple stages of the drug discovery process. Furthermore, cardiac safety pharmacology assays evaluating the risk of proarrhythmic side effects associated with QT prolongation may be enhanced in their predictive value with the use of hESC-CMs.

Preconditioning of stem cells by oxytocin to improve their therapeutic potential

Principal limitation of cell therapy is cell loss after transplantation because of the interplay between ischemia, inflammation, and apoptosis. We investigated the mechanism of preconditioning of mesenchymal stem cells (MSCs) with oxytocin (OT), which has been proposed as a novel strategy for enhancing therapeutic potential of these cells in ischemic heart. In this study, we demonstrate that rat MSCs express binding sites for OT receptor and OT receptor transcript and protein as detected by RT-PCR and immunofluorescence, respectively. In response to OT (10(-10) to 10(-6) M) treatment, MSCs respond with rapid calcium mobilization and up-regulation of the protective protein kinase B (PKB or Akt) and phospho-ERK1/2 proteins. In OT-stimulated cells, phospho-Akt accumulates intracellularly close to the mitochondrial marker cytochrome c oxidase subunit 4. Functional analyses reveal the involvement of Akt/ERK1/2 pathways in cell proliferation, migration, and protection against the cytotoxic and apoptotic effects of hypoxia and serum deprivation. In addition, OT preconditioning increases MSC glucose uptake. Genes with angiogenic, antiapoptotic, and cardiac antiremodeling properties, such as heat shock proteins (hsps) HSP27, HSP32, HSP70, vascular endothelial growth factor, thrombospondin, tissue inhibitor of metalloproteinase (TIMP)-1, TIMP-2, TIMP-3, and matrix metalloproteinase-2, were also up-regulated upon OT exposure. Moreover, coculture with OT-preconditioned MSC reduces apoptosis, as measured using terminal transferase dUTP nick end labeling assay in newborn rat cardiomyocytes exposed to hypoxia and reoxygenation. In conclusion, these results indicate that OT treatment evokes MSC protection through both intrinsic pathways and secretion of cytoprotective factors. Ex vivo cellular treatment with OT represents an attractive strategy aimed to maximize the biological and functional properties of effector cells.

The heart's content-renewable resources

Heart regeneration is a huge, complex area involving numerous lines of research ranging from the stem cell therapy to xenografts and bioengineering. This review will focus on two avenues of regenerative research, cardiac progenitor cells and adult cardiomyocyte proliferation, both of which offer great promise for the field of heart regeneration. However, the principles behind how this could be achieved by either technique are very different. Cardiac progenitor cells represent a population of somatic stem cells which reside within the adult heart. These cells appear to have the capacity to proliferate and differentiate into the different cell types found within the adult heart and thus have the potential, if the correct stimuli can be found, to effectively regenerate a heart damaged by ischemia/infarction. Inducing adult cardiomyocytes to proliferate offers a different approach to achieving the same goal. In this case, the cardiomyocytes that remain after the damage has occurred would need to be stimulated into effecting a regenerative response. In this review, we will discuss the current understanding of how heart regeneration could be achieved by either of these very different approaches.

Comparative analysis of cardiomyocyte differentiation from human embryonic stem cells under 3-D and 2-D culture conditions

Post-myocardial infarction cardiomyocytes are the most important target cell types for cardiac repair. Many of the applications envisaged for human embryonic stem cells (hESC)-derived cardiomyocytes demand that the differentiation procedure be robust, cost effective and high yielding. Various lines of evidence including our earlier study suggest that hESCs have distinct preferences to become heart cells. However, a direct comparison between different protocols has not yet been reported to date. Here, we performed a logical and systematic comparison of cardiomyocytes obtained from hESCs via embryoid bodies (EBs) in suspension versus adherent static cultures of feeder-free hES colonies representing three-dimensional (3-D) and two-dimensional (2-D) culture systems, respectively. An in-depth characterization of the beating cells revealed appropriate cardiac marker expression both at gene and protein levels. Despite using similar media, 3-D and 2-D cultures showed significant variation in growth and ability to form beating areas. While the expression of pre-cardiac mesoderm markers like GATA-4, HAND1, Myf5, Msx1, and BMP-IIR remained unaltered; levels of functional heart-specific markers such as MLC-2A/2V, cTnT, ANP, Phospholamban, α-MHC and KV4.3 were substantially up-regulated in 3-D compared to 2-D cultures. Concurrently we observed a sharp decline in the expression of ESC, ectoderm and endoderm markers including Oct-4, Sox-2, NFH, Sox-1, Sox-17 and AFP. Further immunocytochemistry and flow cytometry demonstrated a higher percentage of cells positive for Brachyury, desmin and cardiac troponin in 3-D cultures. Our results underscore the higher efficiency of cardiomyocytes derived via 3-D cultures. This finding enriches our basic understanding of the differentiation pattern in hESC-derived cardiomyocytes.

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.

Generation, characterization, and potential therapeutic applications of cardiomyocytes from various stem cells

Heart failure is one of the leading causes of death worldwide. Myocardial cell transplantation emerges as a novel therapeutic strategy for heart failure, but this approach has been hampered by severe shortage of human cardiomyocytes. We have recently induced mouse embryonic stem cells to differentiate into embryoid bodies and eventually, cardiomyocytes. Here, we address recent advancements in cardiomyocyte differentiation from cardiac stem cells and pluripotent stem cells. We highlight the methodologies, using growth factors, endoderm-like cell cocultures, small molecules, and biomaterials, in directing the differentiation of pluripotent stem cells into cardiomyocytes. The characterization and identification of pluripotent stem cell-derived cardiomyocytes by morphological, phenotypic, and functional features are also discussed. Notably, increasing evidence demonstrates that cardiomyocytes may be generated from the stem cells of several tissues outside the cardiovascular system, including skeletal muscles, bone marrow, testes, placenta, amniotic fluid, and adipose tissues. We further address the potential applications of cardiomyocytes derived from various kinds of stem cells. The differentiation of stem cells into functional cardiomyocytes, especially from an extra-cardiac stem cell source, would circumvent the scarcity of heart donors and human cardiomyocytes, and, most importantly, it would offer an ideal and promising cardiomyocyte source for cell therapy and tissue engineering in treating heart failure.

Oxytocin revisited: its role in cardiovascular regulation

Traditionally associated with female reproduction, oxytocin (OT) was revisited recently and was revealed to have several new roles in the cardiovascular system. Functional OT receptors have been discovered in the rat and human heart, as well as in vascular beds. The cardiovascular activities of OT include: (i) lowering blood pressure; (ii) negative cardiac inotropy and chronotropy; (iii) parasympathetic neuromodulation; (iv) vasodilatation; (v) anti-inflammatory; (vi) antioxidative; and (vii) metabolic effects. These outcomes are mediated, at least in part, by stimulating cardioprotective mediators, such as nitric oxide and atrial natriuretic peptide. OT and its extended form OT-Gly-Lys-Arg have been shown to be abundant in the foetal mouse heart. OT has the capacity to generate cardiomyocytes from various types of stem cells, including the cardiac side population. Mesenchymal cells transfected with OT-Gly-Lys-Arg, or preconditioned with OT, are resistant to apoptosis and express endothelial cell markers. OT increases glucose uptake in cultured cardiomyocytes from newborn and adult rats, in normal, hypoxic and even insulin resistance conditions. In rats with experimentally-induced myocardial infarction, continuous in vivo OT delivery improves the cardiac healing process, as well as cardiac work, reduces inflammation and stimulates angiogenesis. Therefore, in pathological conditions, OT exerts anti-inflammatory and cardioprotective properties, and improves vascular and metabolic functions. Thus, OT has potential for therapeutic use.

Bone marrow-derived human mesenchymal stem cells express cardiomyogenic proteins but do not exhibit functional cardiomyogenic differentiation potential

Despite their paracrine activites, cardiomyogenic differentiation of bone marrow (BM)-derived mesenchymal stem cells (MSCs) is thought to contribute to cardiac regeneration. To systematically evaluate the role of differentiation in MSC-mediated cardiac regeneration, the cardiomyogenic differentiation potential of human MSCs (hMSCs) and murine MSCs (mMSCs) was investigated in vitro and in vivo by inducing cardiomyogenic and noncardiomyogenic differentiation. Untreated hMSCs showed upregulation of cardiac tropopin I, cardiac actin, and myosin light chain mRNA and protein, and treatment of hMSCs with various cardiomyogenic differentiation media led to an enhanced expression of cardiomyogenic genes and proteins; however, no functional cardiomyogenic differentiation of hMSCs was observed. Moreover, co-culturing of hMSCs with cardiomyocytes derived from murine pluripotent cells (mcP19) or with murine fetal cardiomyocytes (mfCMCs) did not result in functional cardiomyogenic differentiation of hMSCs. Despite direct contact to beating mfCMCs, hMSCs could be effectively differentiated into cells of only the adipogenic and osteogenic lineage. After intramyocardial transplantation into a mouse model of myocardial infarction, Sca-1(+) mMSCs migrated to the infarcted area and survived at least 14 days but showed inconsistent evidence of functional cardiomyogenic differentiation. Neither in vitro treatment nor intramyocardial transplantation of MSCs reliably generated MSC-derived cardiomyocytes, indicating that functional cardiomyogenic differentiation of BM-derived MSCs is a rare event and, therefore, may not be the main contributor to cardiac regeneration.

Ischemic cardiac tissue conditioned media induced differentiation of human mesenchymal stem cells into early stage cardiomyocytes

Mesenchymal stem cells (MSCs) are multipotent, can be easily expanded in culture and hence are an attractive therapeutic tool for cardiac repair. MSCs have tremendous potential to transdifferentiate to cardiac lineage both in vitro and in vivo. The present study examined the differentiation capacity of conditioned media derived from ischemic cardiac tissue on human MSCs. Human Bone marrow-derived MSCs after due characterization by immunocytochemistry and flow cytometry for MSC specific markers were induced by culture media derived from ischemic (n = 13) and non-ischemic (n = 18) human cardiac tissue. Parallel cultures were treated with 5-azacytidine (5-azaC), a potent cardiomyogen. MSCs induced with ischemic conditioned media formed myotube like structures, expressed sarcomeric Troponin I, alpha myosin heavy chain proteins and were positive for cardiac specific markers (Nkx2.5, human atrial natriuretic peptide, myosin light chain-2a, GATA-4) as was observed in 5-azaC treated cells. However, uninduced MSCs as well as those induced with non-ischemic cardiac conditioned media still maintained the fibroblast morphology even after 3 weeks post-induction. Transmission electron microscopic studies of cardiomyocyte-like cells derived from MSCs revealed presence of sarcomeric bands but failed to show gap junctions and intercalated discs as of adult cardiomyocytes. These findings demonstrate that ischemic cardiac conditioned media induces morphological and molecular changes in MSCs with cardiac features, but at a primitive stage. Proteomics analysis of the ischemic conditioned media revealed differential expression of three relevant proteins (C-type lectin superfamily member 13, Testis-specific chromodomain protein Y2 and ADP/ATP translocase 1), whose exact role in cardiac regeneration needs further analysis.

Mesenchymal stem cells from umbilical cord tissue as potential therapeutics for cardiomyodegenerative diseases - a review

Heart failure is one of the leading causes of death worldwide. End stage disease often requires heart transplantation, which is hampered by donor organ shortage. Tissue engineering represents a promising alternative approach for cardiac repair. For the generation of artificial heart muscle tissue several cell types, scaffold materials and bioreactor designs are under investigation. In this review, the use of mesenchymal stem cells derived from human umbilical cord tissue (UCMSC) for cardiac tissue engineering will be discussed.

The hypothalamic neuropeptide oxytocin is required for formation of the neurovascular interface of the pituitary

The hypothalamo-neurohypophyseal system (HNS) is the neurovascular structure through which the hypothalamic neuropeptides oxytocin and arginine-vasopressin exit the brain into the bloodstream, where they go on to affect peripheral physiology. Here, we investigate the molecular cues that regulate the neurovascular contact between hypothalamic axons and neurohypophyseal capillaries of the zebrafish. We developed a transgenic system in which both hypothalamic axons and neurohypophyseal vasculature can be analyzed in vivo. We identified the cellular organization of the zebrafish HNS as well as the dynamic processes that contribute to formation of the HNS neurovascular interface. We show that formation of this interface is regulated during development by local release of oxytocin, which affects endothelial morphogenesis. This cell communication process is essential for the establishment of a tight axovasal interface between the neurons and blood vessels of the HNS. We present a unique example of axons affecting endothelial morphogenesis through secretion of a neuropeptide.

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.

Chemical compound 31002 stimulates cardiomyogenic differentiation of embryonic stem cells

Embryonic stem cells (ESCs) are an emerging source for cell-based therapies aimed at repairing damaged organ tissues; however, the efficiency of directed differentiation is low and refinement of differentiation protocols is hampered by incomplete understanding of the mechanisms involved in this process. To find new compounds which can improve the efficiency of directed differentiation of ESCs to cardiomyocytes, we screened several thousand chemical compounds and identified a promising group. All of the compounds found have a common structure of 1H-pyrrole,2,2'-(phenylmethylene)bis. Here we report the potential mechanism of action for 31002 which showed the strongest activity among the compounds selected. In the presence of 31002, 15 times more cardiomyocytes differentiated from ESCs, i.e., 3.5% to 52% of total differentiated cells. Moreover, the cardiomyocytes showed functional characteristics including rhythmic beating and marker gene expression. 31002 inhibited the down-regulation of genes related to the three germ layers in the late stage of ESCs differentiation, implying that 31002 supports a continuous fate commitment of undifferentiated ESCs to the cardiac lineage by prolonging the three germ layer stages. Therefore, compounds in this group, including 31002, might be useful as directed cardiomyogenic differentiation-inducers to produce cells for use in cell therapy aimed at restoring damaged heart tissue.

TGFβ1 contributes to cardiomyogenic-like differentiation of human bone marrow mesenchymal stem cells

BACKGROUND

The majority of the protocols for cardiomyocyte differentiation of MSC use 5-azacytidine as an inducer. As transforming growth factor β1 and 5-azacytidine share similar target signaling pathways, we examined whether transforming growth factor β1 can play a role in cardiac differentiation process in human mesenchymal stem cell of bone marrow origin.

METHODS

The differentiation protocol involving transforming growth factor β1 was compared with that of 5-azacytidine in these cells. The two differentiation regimes were compared using reverse transcriptase PCR, flow cytometry, and quantitative PCR.

RESULTS

We observed that in both cases, acquired morphological features were similar. Protein and gene expression assays also indicated similar cardiac marker expression profile in both the differentiation conditions. Furthermore, transforming growth factor β1 and 5-azacytidine allowed the acquisition of comparable levels of cardiac cell like molecular characteristic as attested by evaluation of myosin light chain-2v expression.

CONCLUSION

In conclusion, we demonstrate that transforming growth factor β1 can play a similar role in cardiac differentiation process of human bone marrow mesenchymal stem cells.

Priming of mesenchymal stem cells with oxytocin enhances the cardiac repair in ischemia/reperfusion injury

Oxytocin stimulates the cardiomyogenesis of embryonic stem cells and adult cardiac stem cells. We previously reported that oxytocin has a promigratory effect on umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs). In this study, UCB-MSCs were cultured with oxytocin and examined for their therapeutic effect in an infarcted heart. UCB-MSCs were pretreated with 100 nM oxytocin and cardiac markers were assessed by immunofluorescence staining. Next, oxytocin-supplemented USC-MSCs (OT-USCs) were cocultured with hypoxia/reoxygenated neonatal rat cardiomyocytes and cardiac markers and dye transfer were then examined. For the in vivo study, ischemia/reperfusion was induced in rats, and phosphate-buffered saline (group 1), 1-day OT-USCs (group 2), or 7-day OT-USCs (group 3) were injected into the infarcted myocardium. Two weeks after injection, histological changes and cardiac function were examined. UCB-MSCs expressed connexin 43 (Cnx43), cardiac troponin I (cTnI), and α-sarcomeric actin (α-SA) after oxytocin supplementation and coculture with cardiomyocytes. Functional gap junction formation was greater in group 3 than in groups 1 and 2. Cardiac fibrosis and macrophage infiltration were lower in group 3 than in group 2. Restoration of Cnx43 expression was greater in group 3 than in group 2. Cnx43- and cTnI-positive OT-USCs in the peri-infarct zone were observed in group 2 and more frequently in group 3. The ejection fraction (EF) was increased in groups 2 and 3 in 2 weeks. The improved EF was sustained for 4 weeks only in group 3. Our findings suggest that the supplementation of UCB-MSCs with oxytocin can contribute to the cardiogenic potential for cardiac repair.

The use of stem cells for the repair of cardiac tissue in ischemic heart disease

Ischemic heart diseases are the leading cause of death in the Western world. With increasing numbers of patients surviving their acute myocardial infarction owing to effective heart catheter techniques and intensive care treatment, congestive heart failure has become an increasing health concern. With therapeutic options for the prevention and treatment of ischemic heart disease being limited at present, huge efforts have been made in the field of stem cell research to try to establish new approaches for myocardial tissue regeneration. Owing to their pronounced differentiation potential, pluripotent stem cells seem to represent the most promising cell source for future engineering of myocardial replacement tissue. However, several crucial hurdles regarding cell yield and purity of the cultured cardiovascular progenitor cells have still not been overcome to facilitate a clinical application today. By contrast, plenty of adult stem and progenitor cells have already been well characterized and investigated in human disease. However, all of these heterogeneous cell lines primarily seem to work in a paracrine manner on ischemic myocardial tissue, rather than transdifferentiating into contractile cardiomyocytes. This article will focus on the production, application and present limitations of stem cells potentially applicable for myocardial repair.

Differentiation of embryonic stem cells into cardiomyocytes in a compliant microfluidic system

The differentiation process of murine embryonic stem cells into cardiomyocytes was investigated with a compliant microfluidic platform which allows for versatile cell seeding arrangements, optical observation access, long-term cell viability, and programmable uniaxial cyclic stretch. Specifically, two environmental cues were examined with this platform--culture dimensions and uniaxial cyclic stretch. First, the cardiomyogenic differentiation process, assessed by a GFP reporter driven by the α-MHC promoter, was enhanced in microfluidic devices (µFDs) compared with conventional well-plates. The addition of BMP-2 neutralizing antibody reduced the enhancement observed in the µFDs and the addition of exogenous BMP-2 augmented the cardiomyogenic differentiation in well plates. Second, 24 h of uniaxial cyclic stretch at 1 Hz and 10% strain on day 9 of differentiation was found to have a negative impact on cardiomyogenic differentiation. This microfluidic platform builds upon an existing design and extends its capability to test cellular responses to mechanical strain. It provides capabilities not found in other systems for studying differentiation, such as seeding embryoid bodies in 2D or 3D in combination with cyclic strain. This study demonstrates that the microfluidic system contributes to enhanced cardiomyogenic differentiation and may be a superior platform compared with conventional well plates. In addition to studying the effect of cyclic stretch on cardiomyogenic differentiation, this compliant platform can also be applied to investigate other biological mechanisms.

Isotocin controls ion regulation through regulating ionocyte progenitor differentiation and proliferation

The present study using zebrafish as a model explores the role of isotocin, a homolog of oxytocin, in controlling ion regulatory mechanisms. Double-deionized water treatment for 24 h significantly stimulated isotocin mRNA expression in zebrafish embryos. Whole-body Cl(-), Ca(2+), and Na(+) contents, mRNA expressions of ion transporters and ionocyte-differentiation related transcription factors, and the number of skin ionocytes decreased in isotocin morphants. In contrast, overexpression of isotocin caused an increase in ionocyte numbers. Isotocin morpholino caused significant suppression of foxi3a mRNA expression, while isotocin cRNA stimulated foxi3a mRNA expressions at the tail-bud stage of zebrafish embryos. The density of P63 (an epidermal stem cell marker)-positive cells was downregulated by isotocin morpholinos and was upregulated by isotocin cRNA. Taken together, isotocin stimulates the proliferation of epidermal stem cells and differentiation of ionocyte progenitors by regulating the P63 and Foxi3a transcription factors, consequently enhancing the functional activities of ionocytes.

Oxytocin-Gly-Lys-Arg: a novel cardiomyogenic peptide

Background

Oxytocin (OT), synthesized in the heart, has the ability to heal injured hearts and to promote cardiomyogenesis from stem cells. Recently, we reported that the OT-GKR molecule, a processing intermediate of OT, potently increased the spontaneous formation of cardiomyocytes (CM) in embryonic stem D3 cells and augmented glucose uptake in newborn rat CM above the level stimulated by OT. In the present experiments, we investigated whether OT-GKR exists in fetal and newborn rodent hearts, interacts with the OT receptors (OTR) and primes the generation of contracting cells expressing CM markers in P19 cells, a model for the study of early heart differentiation.

Methodology/Principal Findings

High performance liquid chromatography of newborn rat heart extracts indicated that OT-GKR was a dominant form of OT. Immunocytochemistry of mouse embryos (embryonic day 15) showed cardiac OT-GKR accumulation and OTR expression. Computerized molecular modeling revealed OT-GKR docking to active OTR sites and to V1a receptor of vasopressin. In embryonic P19 cells, OT-GKR induced contracting cell colonies and ventricular CM markers more potently than OT, an effect being suppressed by OT antagonists and OTR-specific small interfering (si) RNA. The V1a receptor antagonist and specific si-RNA also significantly reduced OT-GKR-stimulated P19 contracting cells. In comparison to OT, OT-GKR induced in P19 cells less α-actinin, myogenin and MyoD mRNA, skeletal muscle markers.

Conclusions/Significance

These results raise the possibility that C-terminally extended OT molecules stimulate CM differentiation and contribute to heart growth during fetal life.

Involvement of the nitric oxide-soluble guanylyl cyclase pathway in the oxytocin-mediated differentiation of porcine bone marrow stem cells into cardiomyocytes

Bone marrow stem cells (BMSCs) express cardiac markers in vitro and in vivo upon induction. Cardiomyogenic differentiation of embryonic stem cells induced by oxytocin (OT) involves the nitric oxide (NO)-soluble guanylyl cyclase (sGC) pathway. Also, OT improved cardiomyogenic differentiation of porcine BMSCs (pBMSCs). Here, we document the role of NO pathway in OT-mediated cardiomyogenic differentiation of pBMSCs obtained from bone marrow aspirates of juvenile pigs. Cells were exposed (OT cells) or not (control cells) to OT, in presence or absence of a NO synthase inhibitor (L-NAME) and a sGC inhibitor (ODQ). Gene (RT-PCR) and protein expression (immunocytochemistry) of NOS was up-regulated after OT induction. Exposure of OT cells to L-NAME, ODQ, or both, leaded to a significant reduction in cardiac troponin I transcripts, and protein (Western Blot) expression. For the latter, ODQ looked more performing in inhibition than L-NAME. Expression of cardiac troponin T and myosin heavy chain (immunocytochemistry) was less abundant in OT cells exposed to inhibitors without apparent synergic effect between L-NAME and ODQ. In control cells, protein expression remained low. Moreover, OT-induced cell proliferation, and this effect was counteracted by NOS/sGC inhibitors. Inhibiting NO production and NO effector, sGC, affected the OT-mediated differentiation of pBMSCs, because abundance of cardiac proteins was reduced to levels similar to those observed in control cells. We propose that following treatment with OT, activation of NO pathway directs pBMSCs to a preferential cardiomyogenic phenotype and stimulates cell proliferation.

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.

Cardiomyoblast-like cells differentiated from human adipose tissue-derived mesenchymal stem cells improve left ventricular dysfunction and survival in a rat myocardial infarction model

Adipose tissue-derived mesenchymal stem cells (ADMSCs) are multipotent cells. Here we examined whether human ADMSCs (hADMSCs) could differentiate into cardiomyoblast-like cells (CLCs) by induction with dimethylsulfoxide and whether the cells would be utilized to treat cardiac dysfunction. Dimethylsulfoxide induced the expression of various cardiac markers in hADMSCs, such as alpha-cardiac actin, cardiac myosin light chain, and myosin heavy chain; none of which were detected in noncommitted hADMSCs. The induced cells were thus designated as hADMSC-derived CLCs (hCLCs). To confirm their beneficial effect on cardiac function, hCLC patches were transplanted onto the Nude rat myocardial infarction model, and compared with noncommitted hADMSC patch transplants and sham operations. Echocardiography demonstrated significant short-term improvement of cardiac function in both the patch-transplanted groups. However, long-term follow-up showed rescue and maintenance of cardiac function in the hCLC patch-transplanted group only, but not in the noncommitted hADMSC patch-transplanted animals. The hCLCs, but not the hADMSCs, engrafted into the scarred myocardium and differentiated into human cardiac troponin I-positive cells, and thus regarded as cardiomyocytes. Transplantation of the hCLC patches also resulted in recovery of cardiac function and improvement of long-term survival rate. Thus, transplantation of hCLC patches is a potentially effective therapeutic strategy for future cardiac tissue regeneration.

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.

Cardiac oxytocin receptor blockade stimulates adverse cardiac remodeling in ovariectomized spontaneously hypertensive rats

An increasing amount of evidence demonstrates the beneficial role of oxytocin (OT) in the cardiovascular system. Similar actions are attributed to genistein, an isoflavonic phytoestrogen. The treatment with genistein activates the OT system in the aorta of ovariectomized (OVX) Sprague-Dawley (SD) rats. The objective of this study was to determine the effects of low doses of genistein on the OT-induced effects in rat hypertension. The hypothesis tested was that treatment of OVX spontaneously hypertensive rats (SHRs) with genistein improves heart structure and heart work through a mechanism involving the specific OT receptor (OTR). OVX SHRs or SD rats were treated with genistein (in microg/g body wt sc, 10 days) in the presence or absence of an OT antagonist (OTA) [d(CH(2))(5), Tyr(Me)(2), Orn(8)]-vasotocin or a nonspecific estrogen receptor antagonist (ICI-182780). Vehicle-treated OVX rats served as controls. RT-PCR and Western blot analysis demonstrated that left ventricular (LV) OTR, downregulated by ovariectomy, increased in response to genistein. In SHRs or SD rats, this effect was blocked by OTA or ICI-182780 administration. The OTR was mainly localized in microvessels expressing the CD31 marker and colocalized with endothelial nitric oxide synthase. In SHRs, the genistein-stimulated OTR increases were associated with improved fractional shortening, decreased blood pressure (12 mmHg), decreased heart weight-to-body weight ratio, decreased fibrosis, and lowered brain natriuretic peptide in the LV. The prominent finding of the study is the detrimental effect of OTA treatment on the LV of SHRs. OTA treatment of OVX SHRs resulted in a dramatic worsening of ejection fractions and an augmented fibrosis. In conclusion, these results demonstrate that cardiac OTRs are involved in the regulation of cardiac function of OVX SHRs. The decreases of OTRs may contribute to cardiac pathology following menopause.

Oxytocin signaling in mouse taste buds

BACKGROUND

The neuropeptide, oxytocin (OXT), acts on brain circuits to inhibit food intake. Mutant mice lacking OXT (OXT knockout) overconsume salty and sweet (i.e. sucrose, saccharin) solutions. We asked if OXT might also act on taste buds via its receptor, OXTR.

METHODOLOGY/PRINCIPAL FINDINGS

Using RT-PCR, we detected the expression of OXTR in taste buds throughout the oral cavity, but not in adjacent non-taste lingual epithelium. By immunostaining tissues from OXTR-YFP knock-in mice, we found that OXTR is expressed in a subset of Glial-like (Type I) taste cells, and also in cells on the periphery of taste buds. Single-cell RT-PCR confirmed this cell-type assignment. Using Ca2+ imaging, we observed that physiologically appropriate concentrations of OXT evoked [Ca2+]i mobilization in a subset of taste cells (EC50 approximately 33 nM). OXT-evoked responses were significantly inhibited by the OXTR antagonist, L-371,257. Isolated OXT-responsive taste cells were neither Receptor (Type II) nor Presynaptic (Type III) cells, consistent with our immunofluorescence observations. We also investigated the source of OXT peptide that may act on taste cells. Both RT-PCR and immunostaining suggest that the OXT peptide is not produced in taste buds or in their associated nerves. Finally, we also examined the morphology of taste buds from mice that lack OXTR. Taste buds and their constituent cell types appeared very similar in mice with two, one or no copies of the OXTR gene.

CONCLUSIONS/SIGNIFICANCE

We conclude that OXT elicits Ca2+ signals via OXTR in murine taste buds. OXT-responsive cells are most likely a subset of Glial-like (Type I) taste cells. OXT itself is not produced locally in taste tissue and is likely delivered through the circulation. Loss of OXTR does not grossly alter the morphology of any of the cell types contained in taste buds. Instead, we speculate that OXT-responsive Glial-like (Type I) taste bud cells modulate taste signaling and afferent sensory output. Such modulation would complement central pathways of appetite regulation that employ circulating homeostatic and satiety signals.

Neuroendocrine and cardiovascular parameters during simulation of stress-induced rise in circulating oxytocin in the rat

Physiological functions of oxytocin released during stress are not well understood. We have (1) investigated the release of oxytocin during chronic stress using two long-term stress models and (2) simulated stress-induced oxytocin secretion by chronic treatment with oxytocin via osmotic minipumps. Plasma oxytocin levels were significantly elevated in rats subjected to acute immobilization stress for 120 min, to repeated immobilization for 7 days and to combined chronic cold stress exposure for 28 days with 7 days immobilization. To simulate elevation of oxytocin during chronic stress, rats were implanted with osmotic minipumps subcutaneously and treated with oxytocin (3.6 microg/100 g body weight/day) or vehicle for 2 weeks. Chronic subcutaneous oxytocin infusion led to an increase in plasma oxytocin, adrenocorticotropic hormone, corticosterone, adrenal weights and heart/body weight ratio. Oxytocin treatment had no effect on the incorporation of 5-bromo-2-deoxyuridine into DNA in the heart ventricle. Mean arterial pressure response to intravenous phenylephrine was reduced in oxytocin-treated animals. Decrease in adrenal tyrosin hydroxylase mRNA following oxytocin treatment was not statistically significant. Oxytocin treatment failed to modify food intake and slightly increased water consumption. These data provide evidence on increased concentrations of oxytocin during chronic stress. It is possible that the role of oxytocin released during stress is in modulating hypothalamic-pituitary-adrenocortical axis and selected sympathetic functions.

Postinfarct treatment with oxytocin improves cardiac function and remodeling via activating cell-survival signals and angiogenesis

BACKGROUND

We investigated whether postinfarct treatment with oxytocin (OT) improves left ventricular (LV) function and remodeling via cardiac repair of myocardial ischemia-reperfusion injury.

METHODS AND RESULTS

Experiments were performed with 30 minutes of coronary occlusion and 2 or 14 days of reperfusion rabbit model of myocardial infarction. LV function and remodeling were significantly improved in the OT group. The infarct size was significantly reduced in the OT group. The number of CD31-positive microvessels was increased significantly in the OT group. There were no Ki67-positive myocytes in either group. The expression of the OT receptor, phosphorylated (p)-Akt protein kinase, p-extracellular signal-regulated protein kinase, p-enodthelial NO synthase, p-signal transducer and activator of transcription 3, vascular endothelial growth factor, B-cell lymphoma 2, and matrix metalloproteinase-1 (MMP-1) were markedly increased in the OT group days 2 and 14 post myocardial infarction.

CONCLUSIONS

Postinfarct treatment with OT reduces myocardial infarct size and improves LV function and remodeling by activating OT receptors and prosurvival signals and by exerting antifibrotic and angiogenic effects through activation of MMP-1, endothelial NO synthase, and vascular endothelial growth factor. These findings provide new insight into therapeutic strategies for ischemic heart disease.

Effective and steady differentiation of a clonal derivative of P19CL6 embryonal carcinoma cell line into beating cardiomyocytes

The P19CL6 cell line is a useful model to study cardiac differentiation in vitro. However, large variations were noticed in the differentiation rates among previous reports as well as our individual experiments. To overcome the unstable differentiation, we established P19CL6-A1, a new clonal derivative of P19CL6 that could differentiate into cardiomyocytes more efficiently and stably than the parent using the double stimulation with 5-Aza and DMSO based on the previous report. We also introduced a new software, Visorhythm, that can analyze the temporal variations in the beating rhythms and can chart correlograms displaying the oscillated rhythms. Using P19CL6-A1-derived cardiomyocytes and the software, we demonstrated that the correlograms could clearly display the enhancement of beating rates by cardiotonic reagents. These indicate that a combination of P19CL6-A1 and Visorhythm is a useful tool that can provide invaluable assistance in inotropic drug discovery, drug screening, and toxicity testing.

Chemical induction of cardiac differentiation in p19 embryonal carcinoma stem cells

P19 cells, a pluripotent cell line derived from a teratocarcinoma induced in C3H/HeHa mice, have been widely used as a model system to study cardiac differentiation. We have used these cells to evaluate the extent to which exposure to DMSO and/or cardiogenol C for 4 days in suspension culture enhanced their differentiation into cardiomyocytes. Cardiac differentiation was assessed by observing beating clusters and further confirmed using immunocytochemical, biochemical, and pharmacological approaches. The presence of functional gap junctions in differentiated P19 cells was identified through calcium wave analyses. Proliferation rate and cell death were analyzed by BrdU incorporation and activated caspase-3 immunodetection, respectively. Beating clusters of differentiated P19 cells were only found in cultures treated with DMSO. In addition, groups treated with DMSO up-regulated cardiac troponin-T expression. However, when DMSO was used together with cardiogenol C the up-regulation was less than that with DMSO alone, approximately 1.5 times. Moreover, P19 cells cultured in DMSO or DMSO plus 0.25 microM cardiogenol C had lower proliferation rates and higher numbers of activated caspase-3-positive cells. In summary, using several methodological approaches we have demonstrated that DMSO can induce cardiac differentiation of P19 cells but that cardiogenol C does not.

Oxytocin increases glucose uptake in neonatal rat cardiomyocytes

We have recently shown that an entire oxytocin (OT) system, a peptide and its cognate receptors, is synthesized in the heart. In fetal and newborn hearts, OT exists in its extended three-amino acid form, OT-Gly-Lys-Arg (OT-GKR). OT translocates glucose transporter type 4 to the plasma membrane in human endothelial cells. Therefore, we hypothesized that the cardiac OT/OT-GKR system may be involved in the regulation of myocardial glucose uptake in physiological conditions and during metabolic stress such as hypoxia. Primary cultures of neonatal rat cardiomyocytes (CM) and cardiac progenitor cells expressing ATP-binding cassette efflux transporter G2 transporter (stem cell marker) were studied. OT (10 nm) increased basal glucose uptake in CM to 4.0 +/- 0.2 fmol/mg protein, with OT-GKR (10 nm) elevating it to 5.3 +/- 0.4 fmol/mg protein (P < 0.001) in comparison with 2.2 fmol/mg in control cells. OT had a moderate synergistic effect with 0.1 mm 2,4-dinitrophenol, augmenting basal glucose uptake to 5.5 +/- 0.5 fmol/mg. OT-GKR (10 nm) was even more potent in combination with 2,4-dinitrophenol, increasing glucose uptake to 9.0 +/- 1.0 fmol/mg. Wortmannin (0.1 microm), an inhibitor of phosphatidylinositol-3-kinase, significantly suppressed the effect of OT and insulin (10 nm) (P < 0.001), indicating common pathways. Our data suggest that OT and OT-GKR influence glucose uptake in neonatal rat CM and may thus play a role in the maintenance of cardiac function and cell survival during metabolic stress.

Nitric oxide repression of Nanog promotes mouse embryonic stem cell differentiation

Exposure of mouse embryonic stem (mES) cells to high concentrations of chemical nitric oxide (NO) donors promotes differentiation, but the mechanisms involved in this process at the gene expression level are poorly defined. In this study we report that culture of mES cells in the presence of 0.25-1.0 mM diethylenetriamine nitric oxide adduct (DETA-NO) leads to downregulation of Nanog and Oct4, the two master genes involved in the control of the pluripotent state. This action of NO was also apparent in the human ES cell line, HS 181. The suppressive action of NO on Nanog gene depends on the activation of p53 repressor protein by covalent modifications, such as pSer15, pSer315, pSer392 and acetyl Lys 379. NO-induced repression of Nanog is also associated with binding of trimethylated histone H3 and pSer315 p53 to its promoter region. In addition, exposure to 0.5 mM DETA-NO induces early differentiation events of cells with acquisition of epithelial morphology and expression of markers of definitive endoderm, such as FoxA2, Gata4, Hfn1-beta and Sox 17. This phenotype was increased when cells were treated with valproic acid (VPA) for 10 days.