Heart regeneration

Embryonic stem cell-based cardiopatches improve cardiac function in infarcted rats

Pluripotent stem cell-seeded cardiopatches hold promise for in situ regeneration of infarcted hearts. Here, we describe a novel cardiopatch based on bone morphogenetic protein 2-primed cardiac-committed mouse embryonic stem cells, embedded into biodegradable fibrin matrices and engrafted onto infarcted rat hearts. For in vivo tracking of the engrafted cardiac-committed cells, superparamagnetic iron oxide nanoparticles were magnetofected into the cells, thus enabling detection and functional evaluation by high-resolution magnetic resonance imaging. Six weeks after transplantation into infarcted rat hearts, both local (p < .04) and global (p < .015) heart function, as well as the left ventricular dilation (p < .0011), were significantly improved (p < .001) as compared with hearts receiving cardiopatches loaded with iron nanoparticles alone. Histological analysis revealed that the fibrin scaffolds had degraded over time and clusters of myocyte enhancer factor 2-positive cardiac-committed cells had colonized most of the infarcted myocardium, including the fibrotic area. De novo CD31-positive blood vessels were formed in the vicinity of the transplanted cardiopatch. Altogether, our data provide evidence that stem cell-based cardiopatches represent a promising therapeutic strategy to achieve efficient cell implantation and improved global and regional cardiac function after myocardial infarction.

Forcing stem cells to behave: a biophysical perspective of the cellular microenvironment

Physical factors in the local cellular microenvironment, including cell shape and geometry, matrix mechanics, external mechanical forces, and nanotopographical features of the extracellular matrix, can all have strong influences on regulating stem cell fate. Stem cells sense and respond to these insoluble biophysical signals through integrin-mediated adhesions and the force balance between intracellular cytoskeletal contractility and the resistant forces originated from the extracellular matrix. Importantly, these mechanotransduction processes can couple with many other potent growth-factor-mediated signaling pathways to regulate stem cell fate. Different bioengineering tools and microscale/nanoscale devices have been successfully developed to engineer the physical aspects of the cellular microenvironment for stem cells, and these tools and devices have proven extremely powerful for identifying the extrinsic physical factors and their downstream intracellular signaling pathways that control stem cell functions.

Cardiac telocytes - their junctions and functional implications

Telocytes (TCs) form a cardiac network of interstitial cells. Our previous studies have shown that TCs are involved in heterocellular contacts with cardiomyocytes and cardiac stem/progenitor cells. In addition, TCs frequently establish ‘stromal synapses’ with several types of immunoreactive cells in various organs (www.telocytes.com). Using electron microscopy (EM) and electron microscope tomography (ET), we further investigated the interstitial cell network of TCs and found that TCs form ‘atypical’ junctions with virtually all types of cells in the human heart. EM and ET showed different junction types connecting TCs in a network (puncta adhaerentia minima, processus adhaerentes and manubria adhaerentia). The connections between TCs and cardiomyocytes are ‘dot’ junctions with nanocontacts or asymmetric junctions. Junctions between stem cells and TCs are either ‘stromal synapses’ or adhaerens junctions. An unexpected finding was that TCs have direct cell–cell (nano)contacts with Schwann cells, endothelial cells and pericytes. Therefore, ultrastructural analysis proved that the cardiac TC network could integrate the overall ‘information’ from vascular system (endothelial cells and pericytes), nervous system (Schwann cells), immune system (macrophages, mast cells), interstitium (fibroblasts, extracellular matrix), stem cells/progenitors and working cardiomyocytes. Generally, heterocellular contacts occur by means of minute junctions (point contacts, nanocontacts and planar contacts) and the mean intermembrane distance is within the macromolecular interaction range (10–30 nm). In conclusion, TCs make a network in the myocardial interstitium, which is involved in the long-distance intercellular signaling coordination. This integrated interstitial system appears to be composed of large homotropic zones (TC–TC junctions) and limited (distinct) heterotropic zones (heterocellular junctions of TCs).

Signaling during epicardium and coronary vessel development

The epicardium, the tissue layer covering the cardiac muscle (myocardium), develops from the proepicardium, a mass of coelomic progenitors located at the venous pole of the embryonic heart. Proepicardium cells attach to and spread over the myocardium to form the primitive epicardial epithelium. The epicardium subsequently undergoes an epithelial-to-mesenchymal transition to give rise to a population of epicardium-derived cells, which in turn invade the heart and progressively differentiate into various cell types, including cells of coronary blood vessels and cardiac interstitial cells. Epicardial cells and epicardium-derived cells signal to the adjacent cardiac muscle in a paracrine fashion, promoting its proliferation and expansion. Recently, high expectations have been raised about the epicardium as a candidate source of cells for the repair of the damaged heart. Because of its developmental importance and therapeutic potential, current research on this topic focuses on the complex signals that control epicardial biology. This review describes the signaling pathways involved in the different stages of epicardial development and discusses the potential of epicardial signals as targets for the development of therapies to repair the diseased heart.

Secreted proteins as a fundamental source for biomarker discovery

The proteins secreted by various cells (the secretomes) are a potential rich source of biomarkers as they reflect various states of the cells at real time and at given conditions. To have accessible, sufficient and reliable protein markers is desirable as they mark various stages of disease development and their presence/absence can be used for diagnosis, prognosis, risk stratification and therapeutic monitoring. As direct analysis of blood/plasma, a common and noninvasive patient screening method, can be difficult for candidate protein biomarker identification, the alternative/complementary approaches are required, one of them is the analysis of secretomes in cell conditioned media in vitro. As the proteins secreted by cells as a response to various stimuli are most likely secreted into blood/plasma, the identification and pre-selection of candidate protein biomarkers from cell secretomes with subsequent validation of their presence at higher levels in serum/plasma is a promising approach. In this review, we discuss the proteins secreted by three progenitor cell types (smooth muscle, endothelial and cardiac progenitor cells) and two adult cell types (neonatal rat ventrical myocytes and smooth muscle cells) which can be relevant to cardiovascular research and which have been recently published in the literature. We found, at least for secretome studies included in this review, that secretomes of progenitor and adult cells overlap by 48% but the secretomes are very distinct among progenitor cell themselves as well as between adult cells. In addition, we compared secreted proteins to protein identifications listed in the Human Plasma PeptideAtlas and in two reports with cardiovascular-related proteins and we performed the extensive literature search to find if any of these secreted proteins were identified in a biomarker study. As expected, many proteins have been identified as biomarkers in cancer but 18 proteins (out of 62) have been tested as biomarkers in cardiovascular diseases as well.

Cardiac regeneration

The heart is a pump that is comprised of cardiac myocytes and other cell types and whose proper function is critical to quality of life. The ability to trigger regeneration of heart muscle following injury eludes adult mammals, a deficiency of great clinical impact. Major research efforts are attempting to change this through advances in cell therapy or activating endogenous regenerative mechanisms that exist only early in life. In contrast with mammals, lower vertebrates like zebrafish demonstrate an impressive natural capacity for cardiac regeneration throughout life. This review will cover recent progress in the field of heart regeneration with a focus on endogenous regenerative capacity and its potential manipulation.

Mesenchymal bone marrow cell therapy in a mouse model of chagas disease. Where do the cells go?

BACKGROUND

Chagas disease, resulting from infection with the parasite Trypanosoma cruzi (T. cruzi), is a major cause of cardiomyopathy in Latin America. Drug therapy for acute and chronic disease is limited. Stem cell therapy with bone marrow mesenchymal cells (MSCs) has emerged as a novel therapeutic option for cell death-related heart diseases, but efficacy of MSC has not been tested in Chagas disease.

METHODS AND RESULTS

We now report the use of cell-tracking strategies with nanoparticle labeled MSC to investigate migration of transplanted MSC in a murine model of Chagas disease, and correlate MSC biodistribution with glucose metabolism and morphology of heart in chagasic mice by small animal positron emission tomography (microPET). Mice were infected intraperitoneally with trypomastigotes of the Brazil strain of T. cruzi and treated by tail vein injection with MSC one month after infection. MSCs were labeled with near infrared fluorescent nanoparticles and tracked by an in vivo imaging system (IVIS). Our IVIS results two days after transplant revealed that a small, but significant, number of cells migrated to chagasic hearts when compared with control animals, whereas the vast majority of labeled MSC migrated to liver, lungs and spleen. Additionally, the microPET technique demonstrated that therapy with MSC reduced right ventricular dilation, a phenotype of the chagasic mouse model.

CONCLUSIONS

We conclude that the beneficial effects of MSC therapy in chagasic mice arise from an indirect action of the cells in the heart rather than a direct action due to incorporation of large numbers of transplanted MSC into working myocardium.

Emerging roles of the FBW7 tumour suppressor in stem cell differentiation

FBW7 is a ubiquitin E3 ligase substrate adaptor that targets many important oncoproteins-such as Notch, c-Myc, cyclin E and c-Jun-for ubiquitin-dependent proteolysis. By doing so, it plays crucial roles in many cellular processes, including cell cycle progression, cell growth, cellular metabolism, differentiation and apoptosis. Loss of FBW7 has been observed in many types of human cancer, and its role as a tumour suppressor was confirmed by genetic ablation of FBW7 in mice, which leads to the induction of tumorigenesis. How FBW7 exerts its tumour suppression function, and whether loss of FBW7 leads to de-differentiation or acquisition of stemness-a process frequently seen in human carcinomas-remains unclear. Emerging evidence shows that FBW7 controls stem cell self-renewal, differentiation, survival and multipotency in various stem cells, including those of the haematopoietic and nervous systems, liver and intestine. Here, we focus on the function of FBW7 in stem cell differentiation, and its potential relevance to human disease and therapeutics.

Cardiomyocyte death: mechanisms and translational implications

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide. Although treatments have improved, development of novel therapies for patients with CVD remains a major research goal. Apoptosis, necrosis, and autophagy occur in cardiac myocytes, and both gradual and acute cell death are hallmarks of cardiac pathology, including heart failure, myocardial infarction, and ischemia/reperfusion. Pharmacological and genetic inhibition of autophagy, apoptosis, or necrosis diminishes infarct size and improves cardiac function in these disorders. Here, we review recent progress in the fields of autophagy, apoptosis, and necrosis. In addition, we highlight the involvement of these mechanisms in cardiac pathology and discuss potential translational implications.

Concise review: the role of clinical trials in deciphering mechanisms of action of cardiac cell-based therapy

Although the initial promise of cardiac cell-based therapy was based on the concept that stem cells engraft into diseased tissue and differentiate into beating cardiomyocytes, it is now clear that successful cell-based tissue repair involves a more complex orchestration of cellular and molecular events. Many lessons about successful tissue repair can be gleaned from the results of early-stage clinical trials. This body of work shows that cell-based therapy (with various cell sources and delivery methods) effectively prevents and reverses the remodeling process, the sine qua non of the myocardial injury reaction and anatomic substrate for subsequent clinical events. The potentially favorable remodeling responses to cell therapy have prompted a search for mechanisms of action beyond cell repopulation and guided future clinical trial design by providing more clear focus on pathophysiological endpoints signifying favorable responses to cell-based therapy. Perhaps the most important mechanistic insight is that endogenous stem/precursor cells have the potential to participate in tissue healing. With regard to the phenotype of cellular response, it is clear that parameters of remodeling, such as infarct size and ventricular dimensions, should be directly measured, thereby necessitating the use of sophisticated imaging modalities, such as cardiac magnetic resonance imaging or multidetector computed tomography. These new insights offer an optimistic outlook on the state of cell-based therapeutics for cardiac disease and suggest that pivotal clinical trials are warranted. Here, we review lessons learned from clinical trials and evaluate the choice and assessment of endpoints to best predict efficacy of cell therapy.

Embryonic and foetal Islet-1 positive cells in human hearts are also positive to c-Kit

During embryogenesis, the mammalian heart develops from a primitive heart tube originating from two bilateral primary heart fields located in the lateral plate mesoderm. Cells belongings to the pre-cardiac mesoderm will differentiate into early cardiac progenitors, which express early transcription factors which are also common to the Isl-1 positive cardiac progenitor cells isolated from the developing pharyngeal mesoderm and the foetal and post-natal mice hearts. A second population of cardiac progenitor cells positive to c-Kit has been abundantly isolated from adult hearts. Until now, these two populations have been considered two different sets of progenitor cells present in the heart in different stages of an individual life. In the present study we collected embryonic, foetal and infant hearts, and we tested the hypotheses that c-Kit positive cells, usually isolated from the adult heart, are also present in the intra-uterine life and persist in the adult heart after birth, and that foetal Isl-1 positive cells are also positive to c-Kit. Using immunohistochemistry we studied the temporal distribution of Isl-1 positive and c-Kit/CD105 double positive cells, and by immunofluorescence and confocal analysis we studied the co-localization of c-Kit and Isl-1 positive cells. The results indicated that cardiomyocytes and interstitial cells were positive for c-Kit from the 9th to the 19th gestational week, that cells positive for both c-Kit and CD105 appeared in the interstitium at the 17th gestational week and persisted in the postnatal age, and that the Isl-1 positive cells were a subset of the c-Kit positive population.

Stem cell senescence and regenerative paradigms

The term "cellular senescence" denotes a cellular response to several stressors that results in irreversible growth arrest, alterations of the gene expression profile, epigenetic modifications, and an altered secretome, all of which eventually impair the reparative properties of primitive cells, adding a layer of complexity to the field of regenerative medicine. The purpose of this review is to illustrate how cellular senescence could affect tissue repair and to propose interventions that aim at interfering with it.

Nuclear cardiac troponin and tropomyosin are expressed early in cardiac differentiation of rat mesenchymal stem cells

Nuclear actin - which is immunologically distinct from cytoplasmic actin - has been documented in a number of differentiated cell types, and cardiac isoforms of troponin I (cTnI) and troponin T (cTnT) have been detected in association with nuclei of adult human cardiac myocytes. It is not known whether these and related proteins are present in undifferentiated stem cells, or when they appear in cardiomyogenic cells following differentiation. We first tested the hypothesis that nuclear actin and cardiac isoforms of troponin C (cTnC) and tropomyosin (cTm) are present along with cTnI and cTnT in nuclei of isolated, neonatal rat cardiomyocytes in culture. We also tested the hypothesis that of these five proteins, only actin is present in nuclei of multipotent, bone marrow-derived mesenchymal stem cells (BM-MSCs) from adult rats in culture, but that cTnC, cTnI, cTnT and cTm appear early and uniquely following cardiomyogenic differentiation. Here we show that nuclear actin is present within nuclei of both ventricular cardiomyocytes and undifferentiated, multipotent BM-MSCs. We furthermore show that cTnC, cTnI, cTnT and cTm are not only present in myofilaments of ventricular cardiomyocytes in culture but are also within their nuclei; significantly, these four proteins appear between days 3 and 5 in both myofilaments and nuclei of BM-MSCs treated to differentiate into cardiomyogenic cells. These observations indicate that cardiac troponin and tropomyosin could have important cellular function(s) beyond Ca(2+)-regulation of contraction. While the roles of nuclear-associated actin, troponin subunits and tropomyosin in cardiomyocytes are not known, we anticipate that the BM-MSC culture system described here will be useful for elucidating their function(s), which likely involve cardiac-specific, Ca(2+)-dependent signaling in the nucleus.

Synthetic matrices to serve as niches for muscle cell transplantation

Poor cell retention and limited cell survival after grafting are major limitations of cell therapy. Recent studies showed that the use of matrices as vehicles at the time of cell injection can significantly improve cell engraftment by providing an appropriate structure and physical support for the injected cells. Properly designed matrices can also promote the organization of the cells into a functioning cardiac-like tissue and enhance integration between the host and the engrafted tissue. Furthermore, the use of an injectable biomaterial provides an opportunity to release in situ bioactive molecules that can further enhance the beneficial effects of cell transplantation. In this article we review a large variety of biologically derived synthetic and hybrid materials that have been tested as matrices for cardiac repair. We summarize the optimal parameters required for an ideal matrix including biocompatibility, injectability, degradation rate, and mechanical properties. Using an in vivo subcutaneous grafting model, we also provide novel data involving a side-by-side comparison of six synthetic matrices derived from maltodextrin. By systematically varying polymer molecular weight, cross-link density, and availability of cell adhesion motifs, a synthetic matrix was identified that supported skeletal myotube formation similar to Matrigel™. Our results emphasize not only the need to have a range of tunable matrices for cardiac cell therapy but also the importance of further characterizing the physical properties required for an ideal injectable matrix.

Cardiac regeneration therapy: connections to cardiac physiology

Without heart transplantation, a large number of patients with failing hearts worldwide face poor outcomes. By means of cardiomyocyte regeneration, cardiac regeneration therapy is emerging with great promise as a means for restoring loss of cardiac function. However, the limited success of clinical trials using bone marrow-derived cells and myoblasts with heterogeneous constituents, transplanted at a wide range of cell doses, has led to disagreement on the efficacy of cell therapy. It is therefore essential to reevaluate the evidence for the efficacy of cell-based cardiac regeneration therapy, focusing on targets, materials, and methodologies. Meanwhile, the revolutionary innovation of cardiac regeneration therapy is sorely needed to help the millions of people who suffer heart failure from acquired loss of cardiomyocytes. Cardiac regeneration has been used only in limited species or as a developing process in the rodent heart; now, the possibility of cardiomyocyte turnover in the human heart is being revisited. In the pursuit of this concept, the use of cardiac stem/progenitor stem cells in the cardiac niche must be focused to usher in a second era of cardiac regeneration therapy for the severely injured heart. In addition, tissue engineering and cellular reprogramming will advance the next era of treatment that will enable current cell-based therapy to progress to "real" cardiac regeneration therapy. Although many barriers remain, the prevention of refractory heart failure through cardiac regeneration is now becoming a realistic possibility.

Regeneration of the heart

The death of cardiac myocytes diminishes the heart's pump function and is a major cause of heart failure, one of the dominant causes of death worldwide. Other than transplantation, there are no therapies that directly address the loss of cardiac myocytes, which explains the current excitement in cardiac regeneration. The field is evolving in two important directions. First, although endogenous mammalian cardiac regeneration clearly seems to decline rapidly after birth, it may still persist in adulthood. The careful elucidation of the cellular and molecular mechanisms of endogenous heart regeneration may therefore provide an opportunity for developing therapeutic interventions that amplify this process. Second, recent breakthroughs have enabled reprogramming of cells that were apparently terminally differentiated, either by dedifferentiation into pluripotent stem cells or by transdifferentiation into cardiac myocytes. These achievements challenge our conceptions of what is possible in terms of heart regeneration. In this review, we discuss the current status of research on cardiac regeneration, with a focus on the challenges that hold back therapeutic development.

When is Having a Big Heart a Problem?

Cardiac enlargement is a common and important post-mortem finding. The presence of a big heart may provide a basis for determination of the mechanisms of death in an otherwise negative autopsy. In this article we will 1) define terms used to describe the morphology of the heart; 2) describe the ways the heart can enlarge; 3) review the reasons the heart may enlarge and 4) discuss the consequences of that enlargement. In so doing, we hope to assist the pathologist in evaluating cardiomegaly at autopsy and recognizing the significance of the cardiac enlargement.

MicroRNAs regulating cell pluripotency and vascular differentiation

Human embryonic stem cells (hESC) offer broad potential for regenerative medicine owing to their capacity for self renewal, exponential scale up and differentiation into any cell type in the adult body. hESC have been proposed as a potentially unlimited source for the generation of transplantable, healthy, functional vascular cells for repair of ischemic tissues. To optimally harness this potential necessitates precise control over biological processes that govern maintenance, pluripotency and cell differentiation including signalling cascades, gene expression profiles and epigenetic modification. Such control may be elicited by microRNAs, which are powerful negative regulators of gene expression. Here, we review the role for miRNAs in both the maintenance of pluripotency and differentiation of cells to a cardiovascular lineage including endothelial cells, vascular smooth muscle cells and cardiomyocytes and put this into context for regenerative medicine in the cardiovascular system.