Potential approaches for myocardial regeneration

Application of tissue-engineered pericardial patch in rat models of myocardial infarction

Myocardial infarction (MI) is a major cause of mortality and morbidity in industrialized societies. Myocardial tissue engineering is an alternative and promising approach for substituting injured myocardium through development and seeding of appropriate scaffolds. In this study, we investigated the efficacy of using an acellular pericardium to deliver autologous mesenchymal stem cells (MSCs) to the infarcted site for regeneration of the myocardium. MI was induced in two groups of rats; G1 or MI group, and G2 or patch-implanted group. In G2 group, rats had undergone transplantation of a pericardial patch which was previously seeded with adipose tissue derived MSCs. To evaluate the efficacy of the pericardial patches, biopsies were taken one month after transplantation. In order to evaluate the extent of regeneration, inflammation and fibrosis, histopathological investigations including hematoxylin and eosin (H&E), Sirius Red and trichrome staining were performed. In addition, immunohistochemical investigations by Desmin as well as CD68, CD45 and CD34 antibodies were performed. Furthermore, Tunnel assay was performed to detect the extent of apoptosis. H&E assessments of biopsies from the patch-implanted group confirmed presence of pre-seeded pericardium containing MSCs along with neo-vessels. Immunohistochemical assessments demonstrated higher number of CD34 positive cells and Desmin-positive cells in the patch implanted group (p < 0.05); these findings are suggestive of cardiomyocyte regeneration in G2 rats. This study demonstrates the advantages of application of natural acellular scaffolds as cell delivery devices and it emphasizes neovascularization following this approach. However, further investigations are required to analyze long-term cardiac function in recipients. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2670-2678, 2018.

Tissue engineering: construction of a multicellular 3D scaffold for the delivery of layered cell sheets

Many tissues, such as the adult human hearts, are unable to adequately regenerate after damage.(2,3) Strategies in tissue engineering propose innovations to assist the body in recovery and repair. For example, TE approaches may be able to attenuate heart remodeling after myocardial infarction (MI) and possibly increase total heart function to a near normal pre-MI level.(4) As with any functional tissue, successful regeneration of cardiac tissue involves the proper delivery of multiple cell types with environmental cues favoring integration and survival of the implanted cell/tissue graft. Engineered tissues should address multiple parameters including: soluble signals, cell-to-cell interactions, and matrix materials evaluated as delivery vehicles, their effects on cell survival, material strength, and facilitation of cell-to-tissue organization. Studies employing the direct injection of graft cells only ignore these essential elements.(2,5,6) A tissue design combining these ingredients has yet to be developed. Here, we present an example of integrated designs using layering of patterned cell sheets with two distinct types of biological-derived materials containing the target organ cell type and endothelial cells for enhancing new vessels formation in the "tissue". Although these studies focus on the generation of heart-like tissue, this tissue design can be applied to many organs other than heart with minimal design and material changes, and is meant to be an off-the-shelf product for regenerative therapies. The protocol contains five detailed steps. A temperature sensitive Poly(N-isopropylacrylamide) (pNIPAAM) is used to coat tissue culture dishes. Then, tissue specific cells are cultured on the surface of the coated plates/micropattern surfaces to form cell sheets with strong lateral adhesions. Thirdly, a base matrix is created for the tissue by combining porous matrix with neovascular permissive hydrogels and endothelial cells. Finally, the cell sheets are lifted from the pNIPAAM coated dishes and transferred to the base element, making the complete construct.

Targeting Wnt signaling to improve wound healing after myocardial infarction

Myocardial infarction is one of the major causes of left ventricular dilatation, frequently leading to heart failure. In the last decade, the wound healing process that takes place in the infarct area after infarction has been recognized as a novel therapeutic target to attenuate left ventricular dilatation and preserve an adequate cardiac function. In this chapter, we discuss the role of Wnt signaling in the wound healing process after infarction, with a specific focus on its modulating effect on myofibroblast characteristics.

Myofibroblasts in the infarct area: concepts and challenges

Myofibroblasts are differentiated fibroblasts that hold a key role in wound healing and remodeling following myocardial infarction (MI). A large repertoire of stimuli, such as mechanical stretch, growth factors, cytokines, and vasoactive peptides, induces myofibroblast differentiation. Myofibroblasts are responsible for the production and deposition of collagen, leading to the establishment of a dense extracellular matrix that strengthens the infarcted tissue and minimizes dilatation of the infarct area. In addition, cells contributing to fibrosis act on sites distal from the infarct area and promote collagen deposition in noninfarcted tissue, thus contributing to adverse remodeling and consequently to the development of congestive heart failure (CHF). Current drugs that are used to treat post-MI CHF do influence fibroblasts and myofibroblasts; however, their therapeutic efficacy is far from being regarded as ideal. Novel therapeutic agents targeting (myo)fibroblasts are being developed to successfully prevent the cardiac remodeling of sites remote from the infarct area and therefore hinder the establishment of CHF. The purpose of this review article is to discuss the basic concepts of the myofibroblasts' actions in cardiac wound healing processes, factors that influence them, currently available pharmacological agents, and future challenges in this area.

Cell-based therapy in Chagas disease

Chagas disease was first described one century ago, yet the mechanisms underlying chagasic cardiomyopathy remain elusive. Disease progression often leads to heart failure and patients with this infectious cardiomyopathy have a poor prognosis. Treatment options for heart failure due to Chagas disease are not different from standard therapy. Over the past decade, cell-based therapies have emerged as a new alternative in the treatment of this disease, not only because of the possibility of replacing lost vessels and cardiomyocytes but also because these cells could potentially influence the microenvironmental changes that perpetuate the disease. In this chapter, we will review current knowledge on cell-based therapies for the treatment of Chagas disease.

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Chagas disease which is caused by the parasite Trypanosoma cruzi is an important cause of cardiomyopathy in Latin America. In later stages chagasic cardiomyopathy is associated with congestive heart failure which is often refractory to medical therapy. In these individuals heart transplantation has been attempted. However, this procedure is fraught with many problems attributable to the surgery and the postsurgical administration of immunosuppressive drugs. Studies in mice suggest that the transplantation of bone-marrow-derived cells ameliorates the inflammation and fibrosis in the heart associated with this infection. Cardiac magnetic resonance imaging reveals that bone marrow transplantation ameliorates the infection induced right ventricular enlargement. On the basis of these animal studies the safety of autologous bone marrow transplantation has been assessed in patients with chagasic end-stage heart disease. The initial results are encouraging and more studies need to be performed.

Concise review: stem cells, myocardial regeneration, and methodological artifacts

This review discusses the current controversy about the role that endogenous and exogenous progenitor cells have in cardiac homeostasis and myocardial regeneration following injury. Although great enthusiasm was created by the possibility of reconstituting the damaged heart, the opponents of this new concept of cardiac biology have interpreted most of the findings supporting this possibility as the product of technical artifacts. This article challenges this established, static view of cardiac growth and favors the notion that the mammalian heart has the inherent ability to replace its cardiomyocytes through the activation of a pool of resident primitive cells or the administration of hematopoietic stem cells.

Embryonic Myocardium Shows Increased Longevity as a Functional Tissue When Cultured in the Presence of a Noncardiac Tissue Layer

A major aim of regenerative medicine is the construction of bioengineered organs and tissue for transplantation into human patients; yet living tissue is dynamic, and thus arranging cellular and extracellular constituents into an architecture resembling normal adult organs may not be sufficient to maintain tissue stability. In this study, we used cultures of embryonic chick heart tissue as a model to explore how newly formed cardiac tissue constructs can sustain their morphological structure and functional capabilities over extended periods. During the initial days of incubation, embryonic cardiac explants will thrive as beating three-dimensional tissue aggregates. However, within the first week of culture, cardiac aggregates lose their contractile function and flatten. After 2 weeks of incubation, the cardiac cells will have spread out into a homogeneous monolayer and dedifferentiated to a noncardiac phenotype. In contrast, when the embryonic heart tissue was co-cultured with a noncardiac cell layer obtained from adult bone marrow, the cardiac aggregates maintained their contractile function, three-dimensional tissue morphology, and myocyte phenotype for a full month of incubation. The capacity of this noncardiac cell layer to sustain the phenotype and morphology of the cardiac explants was partially replicated by treatment of the heart tissue with conditioned media from bone marrow cells. These findings are discussed in regard to the importance of adjacent cell layers for facilitating organogenesis in the developing embryo and having potential utility in producing stable bioengineered tissue constructs.

In Vitro expression of natriuretic peptides in cardiomyocytes differentiated from monkey embryonic stem cells

Functional characterization of ES cell-derived cardiomyocytes is important for differentiation control and application to the cell therapy. One of the crucial functions of cardiomyocytes is a production of atrial and brain natriuretic peptides (ANP and BNP, respectively), which have important endocrine, autocrine, and paracrine functions. In this study, we focused on the functional aspect of the cardiomyocytes differentiated from monkey ES cells in vitro and investigated the expression of ANP and BNP. Spontaneously contracting cells showed nodal-like action potentials, and expression of ANP and BNP by RT-PCR and immunocytochemistry. Interestingly, ANP and BNP expressions were detected as immunoreactive granules in the perinuclear area and these signals appeared to co-localize with trans-Golgi network. These findings suggest that monkey ES cells were able to differentiate into cardiomyocytes with functional characteristics in vitro and therefore can be used as a useful model to study mechanisms and functions in early cardiogenesis.

Globotriaosylceramide accumulation in the Fabry kidney is cleared from multiple cell types after enzyme replacement therapy

BACKGROUND

Fabry disease, a lysosomal storage disease caused by deficient lysosomal alpha-galactosidase A activity, is characterized by globotriaosylceramide (GL-3) accumulation in multiple cell types, particularly the vasculature, leading to end organ failure. Accumulation in the kidney is responsible for progressive decline in renal function in male patients with the classical phenotype, resulting in renal failure in their third to fifth decades of life. With the advent of recombinant protein synthesis technology, enzyme replacement therapy has become a viable alternative to dialysis or renal transplantation, previously the only available treatment options for end-stage renal disease.

METHODS

The pre- and post-treatment renal biopsies were analyzed from fifty-eight Fabry patients enrolled in a Phase 3 double-blind, randomized, placebo-controlled trial followed by a six-month open label extension study of the recombinant human enzyme, alpha-galactosidase A (r-halphaGalA), administered IV at 1 mg/kg biweekly. The purpose of this investigation was to detail the pathologic changes in glycosphingolipid distribution and the pattern of post-treatment clearance in the kidney.

RESULTS

Baseline evaluations revealed GL-3 accumulations in nearly all renal cell types including vascular endothelial cells, vascular smooth muscle cells, mesangial cells and interstitial cells, with particularly dense accumulations in podocytes and distal tubular epithelial cells. After 11 months of r-halphaGalA treatment there was complete clearance of glycolipid from the endothelium of all vasculature as well as from the mesangial cells of the glomerulus and interstitial cells of the cortex. Moderate clearance was noted from the smooth muscle cells of arterioles and small arteries. Podocytes and distal tubular epithelium also demonstrated evidence for decreased GL-3, although this clearance was more limited than that observed in other cell types. No evidence of immune complex disease was found by immunofluorescence despite circulating anti-r-halphaGalA IgG antibodies.

CONCLUSIONS

These findings indicate a striking reversal of renal glycosphingolipid accumulation in the vasculature and in other renal cell types, and suggest that long-term treatment with r-halphaGalA may halt the progression of pathology and prevent renal failure in patients with Fabry disease.

Cellular cardiomyoplasty--a novel approach to treat heart disease

Cell transplantation is a novel experimental strategy to treat heart disease, such as myocardial infarction and heart failure. Its beneficial effects may include active contribution of transplanted cells to contractile function, passive improvement of the mechanics of the heart, induction of neoangiogenesis or other indirect influences on the biology of the heart. Several cell types have been used for cardiac cell transplantation including cardiac cells from fetal or newborn animals and cardiac muscle cell lines, skeletal myoblasts and skeletal muscle cell lines, smooth muscle cells, and a variety of stem cells, either adult or embryonic. With many of these cells, encouraging results in experimental ischemic and nonischemic heart disease have been obtained including successful cell survival after transplantation, integration into the host myocardium, and improvement of the function of diseased hearts. Most of these studies found cardiac contractility improved and some found enhanced angiogenesis. However, the mechanisms of these effects remain obscure, and the impact of dosage (cell number) on functional response is completely unclear. In addition, not enough comparative studies were performed to allow preference of one cell type over the other. The current data suggest that whatever cell species is used, the best survival and integration may be accomplished if immature and undifferentiated cells are used. Any kind of stem cell has obvious advantages in terms of endless reproducibility and plasticity, but the complete differentiation and maturation into cardiac myocytes still needs to be proven. At present several clinical studies are exploring the therapeutic benefits of cellular cardiomyoplasty in patients with ischemic heart disease, but it has to be noted that there are many issues that need to be addressed before this strategy will add to the therapeutic options for patients with heart disease.

Efficiency of embryoid body formation and hematopoietic development from embryonic stem cells in different culture systems

Embryonic stem (ES) cells have tremendous potential as a cell source for cell-based therapies. Realization of that potential will depend on our ability to understand and manipulate the factors that influence cell fate decisions and to develop scalable methods of cell production. We compared four standard ES cell differentiation culture systems by measuring aspects of embryoid body (EB) formation efficiency and cell proliferation, and by tracking development of a specific differentiated tissue type-blood-using functional (colony-forming cell) and phenotypic (Flk-1 and CD34 expression) assays. We report that individual murine ES cells form EBs with an efficiency of 42 +/- 9%, but this value is rarely obtained because of EB aggregation-a process whereby two or more individual ES cells or EBs fuse to form a single, larger cell aggregate. Regardless of whether EBs were generated from a single ES cell in methylcellulose or liquid suspension culture, or aggregates of ES cells in hanging drop culture, they grew to a similar maximum cell number of 28,000 +/- 9,000 cells per EB. Among the three methods for EB generation in suspension culture there were no differences in the kinetics or frequency of hematopoietic development. Thus, initiating EBs with a single ES cell and preventing EB aggregation should allow for maximum yield of differentiated cells in the EB system. EB differentiation cultures were also compared to attached differentiation culture using the same outputs. Attached colonies were not similarly limited in cell number; however, hematopoietic development in attached culture was impaired. The percentage of early Flk-1 and CD34 expressing cells was dramatically lower than in EBs cultured in suspension, whereas hematopoietic colony formation was almost completely inhibited. These results provide a foundation for development of efficient, scalable bioprocesses for ES cell differentiation, and inform novel methods for the production of hematopoietic tissues.

Perfusion improves tissue architecture of engineered cardiac muscle

Cardiac muscle with a certain threshold thickness, uniformity of tissue architecture, and functionality would expand the therapeutic options currently available to patients with congenital or acquired cardiac defects. Cardiac constructs cultured in well-mixed medium had an approximately 100-microm-thick peripheral tissue-like region around a relatively cell-free interior, a structure consistent with the presence of concentration gradients within the tissue. We hypothesized that direct perfusion of cultured constructs can reduce diffusional distances for mass transport, improve control of oxygen, pH, nutrients and metabolites in the cell microenvironment, and thereby increase the thickness and spatial uniformity of engineered cardiac muscle. To test this hypothesis, constructs (9.5-mm-diameter, 2-mm-thick discs) based on neonatal rat cardiac myocytes and fibrous polyglycolic acid scaffolds were cultured either directly perfused with medium or in control spinner flasks. Perfusion improved the spatial uniformity of cell distribution and enhanced the expression of cardiac-specific markers, presumably due to the improved control of local microenvironmental conditions within the forming tissue. Medium perfusion could thus be utilized to better mimic the transport conditions within native cardiac muscle and enable in vitro engineering of cardiac constructs with clinically useful thicknesses.

Dynamics of cardiac wound healing following myocardial infarction: observations in genetically altered mice

Recent improvements in the clinical management of acute myocardial infarction (MI) have resulted in a dramatic decrease in mortality because of this condition. This implies that more patients enter the process of infarct healing. This is a highly complex cascade of events which, although studied for decades, is still not completely understood. An increasing number of genetically altered mice can now be studied in a mouse model of MI, to investigate the contribution of the product of the targeted gene to the infarct healing process. In this review, we will discuss the defects in infarct healing that have been observed in null mutants for plasminogen, urokinase-type plasminogen activator (u-PA), matrix metalloproteinases (MMPS), thrombospondin-2 and dishevelled-1. These studies provide new insights in the infarct healing process itself, but may also help to define new diagnostic and therapeutic targets in humans suffering from MI.

Heart regeneration in adult MRL mice

The reaction of cardiac tissue to acute injury involves interacting cascades of cellular and molecular responses that encompass inflammation, hormonal signaling, extracellular matrix remodeling, and compensatory adaptation of myocytes. Myocardial regeneration is observed in amphibians, whereas scar formation characterizes cardiac ventricular wound healing in a variety of mammalian injury models. We have previously shown that the MRL mouse strain has an extraordinary capacity to heal surgical wounds, a complex trait that maps to at least seven genetic loci. Here, we extend these studies to cardiac wounds and demonstrate that a severe transmural, cryogenically induced infarction of the right ventricle heals extensively within 60 days, with the restoration of normal myocardium and function. Scarring is markedly reduced in MRL mice compared with C57BL/6 mice, consistent with both the reduced hydroxyproline levels seen after injury and an elevated cardiomyocyte mitotic index of 10-20% for the MRL compared with 1-3% for the C57BL/6. The myocardial response to injury observed in these mice resembles the regenerative process seen in amphibians.

Life and death of a cardiac myocyte: principles of cellular biology

If the future of extracorporeal circulation is to include approaches to enhance localized or widespread distribution of cells, and/or gene transfer for augmentation of cardiac function, it is imperative that we gain an increased understanding of the mechanisms that define the cardiac myocyte phenotype. The purpose of this paper is to review the natural history of the cardiac myocyte. A variety of signals determine the cellular processes that characterize birth, growth, differentiation and death of cardiomyocytes. Examined here are primary aspects of the molecular genetics of growth and development, including signal transduction, protein phosphorylation, the cell division cycle, and transcriptional activation. This review is intended to be an update on insights into molecular aspects of the cell, with emphasis on gene expression during cardiac myogenesis and a discussion of its relevance to the field of extracorporeal circulation. In addition, the current status of research in myogenesis is presented.

Tissue engineering of functional cardiac muscle: molecular, structural, and electrophysiological studies

The primary aim of this study was to relate molecular and structural properties of in vitro reconstructed cardiac muscle with its electrophysiological function using an in vitro model system based on neonatal rat cardiac myocytes, three-dimensional polymeric scaffolds, and bioreactors. After 1 wk of cultivation, we found that engineered cardiac muscle contained a 120- to 160-microm-thick peripheral region with cardiac myocytes that were electrically connected through gap junctions and sustained macroscopically continuous impulse propagation over a distance of 5 mm. Molecular, structural, and electrophysiological properties were found to be interrelated and depended on specific model system parameters such as the tissue culture substrate, bioreactor, and culture medium. Native tissue and the best experimental group (engineered cardiac muscle cultivated using laminin-coated scaffolds, rotating bioreactors, and low-serum medium) were comparable with respect to the conduction velocity of propagated electrical impulses and spatial distribution of connexin43. Furthermore, the structural and electrophysiological properties of the engineered cardiac muscle, such as cellularity, conduction velocity, maximum signal amplitude, capture rate, and excitation threshold, were significantly improved compared with our previous studies.

Gene transfer and models of gene therapy for the myocardium

1. Gene transfer into the myocardium can be achieved through direct injection of plasmid DNA or through the delivery of viral vectors, either directly or through the coronary vasculature. Direct DNA injection has proven extremely valuable in studies aimed at characterizing the activities of promoter elements in cardiac tissue and for examining the influence of the pathophysiological state of the myocardium on expression of transferred foreign genes. 2. Viral vectors, in particular adenoviruses and adeno-associated virus, are capable of transfecting genetic material with high transduction efficiencies and have been applied to a range of model systems for in vivo gene transfer. Efficient gene transfer has been achieved into the coronary vessels and surrounding myocardium by intracoronary infusion of adenovirus. 3. Because the immunogenicity of viral vectors can limit transgene expression, much attention has been paid to strategies for circumventing this, including the development of new modified adenovirus and adeno-associated virus vectors that do not elicit significant inflammatory responses. While cellular transplantation may prove valuable for the repair of myocardial tissue, confirmation of its value awaits establishment of a functional improvement in the myocardium following cell grafting. 4. Because gene transfer into the myocardium can now be achieved with high efficiency in the absence of significant inflammatory responses, the ability to regulate foreign gene expression in response to an endogenous disease phenotype will enable the development of new effective viral vectors with direct clinical applicability for specified therapeutic targets.

Cardiac muscle tissue engineering: toward an in vitro model for electrophysiological studies

The objective of this study was to establish a three-dimensional (3-D) in vitro model system of cardiac muscle for electrophysiological studies. Primary neonatal rat ventricular cells containing lower or higher fractions of cardiac myocytes were cultured on polymeric scaffolds in bioreactors to form regular or enriched cardiac muscle constructs, respectively. After 1 wk, all constructs contained a peripheral tissue-like region (50-70 micrometer thick) in which differentiated cardiac myocytes were organized in multiple layers in a 3-D configuration. Indexes of cell size (protein/DNA) and metabolic activity (tetrazolium conversion/DNA) were similar for constructs and neonatal rat ventricles. Electrophysiological studies conducted using a linear array of extracellular electrodes showed that the peripheral region of constructs exhibited relatively homogeneous electrical properties and sustained macroscopically continuous impulse propagation on a centimeter-size scale. Electrophysiological properties of enriched constructs were superior to those of regular constructs but inferior to those of native ventricles. These results demonstrate that 3-D cardiac muscle constructs can be engineered with cardiac-specific structural and electrophysiological properties and used for in vitro impulse propagation studies.

Myoblast cell grafting into heart muscle: cellular biology and potential applications

This review surveys a wide range of cellular and molecular approaches to strengthening the injured or weakened heart, focusing on strategies to replace dysfunctional, necrotic, or apoptotic cardiomyocytes with new cells of mesodermal origin. A variety of cell types, including myogenic cell lines, adult skeletal myoblasts, immoratalized atrial cells, embryonic and adult cardiomyocytes, embryonic stem cells, tetratoma cells, genetically altered fibroblasts, smooth muscle cells, and bone marrow-derived cells have all been proposed as useful cells in cardiac repair and may have the capacity to perform cardiac work. We focus on the implantation of mesodermally derived cells, the best developed of the options. We review the developmental and cell biology that have stimulated these studies, examine the limitations of current knowledge, and identify challenges for the future, which we believe are considerable.

Regeneration of skeletal and cardiac muscle in mammals: do nonprimate models resemble human pathology?

Most of the available information regarding the regenerative potential and compensatory remodeling of mammalian tissues has been obtained from nonprimate animals, mainly rodent experimental models. The increasing use of transgenic mice for studies of the mechanisms controlling organogenesis and regeneration also requires a clear understanding of their applicability as experimental models for studies of similar processes in humans and other mammals. Application of modern cell biology methods to studies of regenerative processes has provided new insights into similarity and differences in cellular responses to injury in the tissues of different mammalian species. During more than 200-million years of progressive divergent evolution of mammals, cellular mechanisms of tissue regeneration and compensatory remodeling evolved together with increasingly adaptive functional specialization and structural complexity of mammalian tissues and organs. Rodents represent a phylogenetically ancient order of mammals that has conservatively retained a number of morphofunctional characteristics of early representatives of this class, which include enhanced regenerative capacity of tissues. A comparative analysis of regenerative processes in skeletal and cardiac muscle, as well as in several other mammalian tissues, shows that time courses and intensities of regeneration in response to the same type of injury vary even within taxonomically related species (e.g., rat, mouse, and hamster). The warm bloodedness of mammals facilitated the development of more complex mechanisms of metabolic, immune, and neurohumoral regulation, which resulted in a stronger dependence of regenerative processes on vascularization and innervation. For this reason, interspecies modifications of regenerative responses are limited by the capacity of the animal to resorb rapidly the foci of necrosis and to revascularize and reinnervate the volume of the regenerating tissue. These differences, among other factors, result in significantly lower rates of reparative regeneration in mammals possessing larger body sizes than rodents. A review of these data strongly indicates that the phylogenetic age and biological differences between different species should be taken into account before extrapolation of regenerative properties of nonprimate tissues on the regenerative responses in the primates.

Cell cycle control in the terminally differentiated myocyte. A platform for myocardial repair?

Currently available pharmaceuticals exert beneficial effects on morbidity and mortality in heart failure. Only cardiac transplantation, however, provides a definitive solution to the irreversible loss of cardiomyocytes in the failing heart. The limited availability of donor hearts leaves the vast majority of afflicted patients in need. The need for innovative approaches to improve care for these patients is apparent.

Culture of organized cell communities

Cells cultured in vitro will tend to retain their differentiated phenotype under conditions that resemble their natural in vivo environment, for example, when cultured on polymer scaffolds in tissue culture bioreactors. In this chapter, we define organized cell communities as three-dimensional in vitro grown cell-polymer constructs that display important structural and functional features of the natural tissue. We review representative studies in which the research goal was to culture organized cell communities resembling cartilage, bone, skeletal muscle or cardiac-like tissue. These constructs can potentially serve as tissue equivalents for in vivo transplantation or as a model system for the in vitro testing of cell and tissue-level responses to molecular, mechanical or genetic manipulations.

Development of a model of complete heart block in rats

Atrioventricular (AV) block is a useful substrate for the study of cardiac physiology. The objective of this investigation was to develop a straightforward and reproducible model of permanent AV block in rats. Working through a sternotomy, we used an epicardial fat pad between the aortic root and the right atrial wall of the rat as a landmark for the site for injection of 70% ethanol (5-10 microl) into the myocardium 3 mm below the epicardial surface. Stable, complete heart block was produced in 23 of 28 rats (82%) with a success rate of 100% in the last 16 rats of the series. Saline injection produced no heart block in 15 rats. A separate group of 14 animals was allowed to recover. Chronic heart block was achieved in all ethanol-injected animals for up to 7 days before death. The survival rate in the recovered rats was 90% in the ethanol-injected group and 100% in the saline-injected control group. Acute hemodynamic changes following the production of heart block consisted of an increase in central venous pressure, a decrease in systolic blood pressure, a decrease in left ventricular pressure, and a decrease in change in pressure over time. Chronic hemodynamic changes demonstrated a return to baseline of the central venous pressure, a persistent decrease in systolic blood pressure, and a decrease in left ventricular pressure. After the rats were killed and the hearts were dissected, discrete areas of myocardial damage were identified histologically in the atrial septum near the AV conduction axis tissue in the ethanol-injected hearts. Complete heart block was associated only with lesions extending into the specialized muscle of the AV node or His bundle. Focal mild hemorrhage, inflammation, and damaged myocardial fibers were observed in the acute stage, whereas healing lesions were characterized by granulation tissue and fibrosis replacing conduction tissue. The simple technique described provides a reproducible model for permanent, complete heart block and the study of cardiac function.

Molecular and cellular prospects for repair, augmentation, and replacement of the failing heart

Molecular and cellular biology offer the promise of new approaches to the treatment of heart failure. This article discusses the basic science background, the current state of investigation, and the potential for therapeutic application of these new sciences. It also emphasizes the limitations and unknowns in this frontier. Three approaches are presented: First, increasing the number of myocytes in the heart, previously held to be untenable because postnatal cardiomyocytes do not divide, may be possible by regulating the cell cycle to reinduce cardiac growth. Also, nonmyocytes extant in the heart may be coaxed into differentiating into cardiomyocytes, or exogenous muscle cells may be grafted into the myocardium. Second, cardiac function may be augmented by molecular therapies that increase contractile protein function or regulate beta-adrenergic receptors or Ca++ channels. Third, improved prospects for transplantation of the failed heart may occur by genetic modification of a xenograft donor heart that reduces the chance of immune rejection by the human recipient. The formulation for the successful application of any of these therapies depends on not only the creativity of scientists but also the wisdom of physicians.