Recognition of extracellular matrix components by neonatal and adult cardiac myocytes

Primary cardiac fibroblast cell culture: methodological considerations for physiologically relevant conditions

Primary cardiac fibroblast (CF) tissue culture is a necessary tool for interrogating specific signaling mechanisms that dictate the phenotypic heterogeneity observed in vivo in different disease states. Traditional approaches that use tissue culture plastic and nutrient-rich medium have been shown to induce CF activation and, therefore, alter CF subpopulation composition. This shift away from in vivo phenotypes complicate the interpretation of results through the lens of the animal model. As the field works to identify CF diversity, these methodological flaws have begun to be addressed and more studies are focused on the dynamic interaction of CFs with their environment. This review focuses on the aspects of tissue culture that impact CF activation and, therefore, require consideration when designing in vitro experiments. The complexity of CF biology overlaid onto diverse model systems highlight the need for study-specific optimization and validation.

Regulatory Mechanisms That Guide the Fetal to Postnatal Transition of Cardiomyocytes

Heart disease remains a global leading cause of death and disability, necessitating a comprehensive understanding of the heart's development, repair, and dysfunction. This review surveys recent discoveries that explore the developmental transition of proliferative fetal cardiomyocytes into hypertrophic postnatal cardiomyocytes, a process yet to be well-defined. This transition is key to the heart's growth and has promising therapeutic potential, particularly for congenital or acquired heart damage, such as myocardial infarctions. Although significant progress has been made, much work is needed to unravel the complex interplay of signaling pathways that regulate cardiomyocyte proliferation and hypertrophy. This review provides a detailed perspective for future research directions aimed at the potential therapeutic harnessing of the perinatal heart transitions.

Wafer-Scale Patterning of Protein Templates for Hydrogel Fabrication

Human-induced pluripotent stem cell-derived cardiomyocytes are a potentially unlimited cell source and promising patient-specific in vitro model of cardiac diseases. Yet, these cells are limited by immaturity and population heterogeneity. Current in vitro studies aiming at better understanding of the mechanical and chemical cues in the microenvironment that drive cellular maturation involve deformable materials and precise manipulation of the microenvironment with, for example, micropatterns. Such microenvironment manipulation most often involves microfabrication protocols which are time-consuming, require cleanroom facilities and photolithography expertise. Here, we present a method to increase the scale of the fabrication pipeline, thereby enabling large-batch generation of shelf-stable microenvironment protein templates on glass chips. This decreases fabrication time and allows for more flexibility in the subsequent steps, for example, in tuning the material properties and the selection of extracellular matrix or cell proteins. Further, the fabrication of deformable hydrogels has been optimized for compatibility with these templates, in addition to the templates being able to be used to acquire protein patterns directly on the glass chips. With our approach, we have successfully controlled the shapes of cardiomyocytes seeded on Matrigel-patterned hydrogels.

Pharmacological Heart Failure Therapy in Children: Focus on Inotropic Support

Pediatric heart failure is a clinical syndrome, which needs to be distinctly defined and the pathophysiological consequences considered. Pharmacological treatment depends on the disease- and age-specific myocardial characteristics. Acute and chronic low cardiac output is the result of an inadequate heart rate (rhythm), myocardial contractility, preload and afterload, and also ventriculo-ventricular interaction, synchrony, atrio-ventricular and ventricular-arterial coupling. The treatment of choice is curing the cause of heart failure, if possible.Acute HF therapy is still based to the use of catecholamines and inodilators. The cornerstone of chronic HF treatment consists of blocking the endogenous, neuro-humoral axis, in particular the adrenergic and renin-angiotensin-aldosterone system.Before neprilysin inhibitors are used in young children, their potential side-effect for inducing Alzheimer disease needs to be clarified. The focus of the current review is put on the differential use of the inotropic drugs as epinephrine, norepinephrine, dopamine and dobutamine, and also the inodilators milrinone and levosimendan. Considering effects and side-effects of any cardiac stimulating treatment strategy, co-medication with ß-blockers, angiotensin converting inhibitors (ACEIs), angiotensin blockers (ARBs) and mineralocorticoid receptor antagonists (MRAs) is not a contradiction, but a senseful measure, even still during the acute inotropic treatment.Missing sophisticated clinical trials using accurate entry criteria and clinically relevant endpoints, there is especially in cardiovascular diagnosis and treatment of young children a compromise of evidence-based versus pathophysiology-based procedures. But based on the pharmacological and pathophysiological knowledge a hypothesis-driven individualized treatment is already currently possible and therefore indicated.

Micromechanobiology: Focusing on the Cardiac Cell-Substrate Interface

Engineered, in vitro cardiac cell and tissue systems provide test beds for the study of cardiac development, cellular disease processes, and drug responses in a dish. Much effort has focused on improving the structure and function of engineered cardiomyocytes and heart tissues. However, these parameters depend critically on signaling through the cellular microenvironment in terms of ligand composition, matrix stiffness, and substrate mechanical properties-that is, matrix micromechanobiology. To facilitate improvements to in vitro microenvironment design, we review how cardiomyocytes and their microenvironment change during development and disease in terms of integrin expression and extracellular matrix (ECM) composition. We also discuss strategies used to bind proteins to common mechanobiology platforms and describe important differences in binding strength to the substrate. Finally, we review example biomaterial approaches designed to support and probe cell-ECM interactions of cardiomyocytes in vitro, as well as open questions and challenges.

Recombinant spider silk protein eADF4(C16)-RGD coatings are suitable for cardiac tissue engineering

Cardiac tissue engineering is a promising approach to treat cardiovascular diseases, which are a major socio-economic burden worldwide. An optimal material for cardiac tissue engineering, allowing cardiomyocyte attachment and exhibiting proper immunocompatibility, biocompatibility and mechanical characteristics, has not yet emerged. An additional challenge is to develop a fabrication method that enables the generation of proper hierarchical structures and constructs with a high density of cardiomyocytes for optimal contractility. Thus, there is a focus on identifying suitable materials for cardiac tissue engineering. Here, we investigated the interaction of neonatal rat heart cells with engineered spider silk protein (eADF4(C16)) tagged with the tripeptide arginyl-glycyl-aspartic acid cell adhesion motif RGD, which can be used as coating, but can also be 3D printed. Cardiomyocytes, fibroblasts, and endothelial cells attached well to eADF4(C16)-RGD coatings, which did not induce hypertrophy in cardiomyocytes, but allowed response to hypertrophic as well as proliferative stimuli. Furthermore, Kymograph and MUSCLEMOTION analyses showed proper cardiomyocyte beating characteristics on spider silk coatings, and cardiomyocytes formed compact cell aggregates, exhibiting markedly higher speed of contraction than cardiomyocyte mono-layers on fibronectin. The results suggest that eADF4(C16)-RGD is a promising material for cardiac tissue engineering.

Decellularized Human Dermal Matrix as a Biological Scaffold for Cardiac Repair and Regeneration

The complex and highly organized environment in which cells reside consists primarily of the extracellular matrix (ECM) that delivers biological signals and physical stimuli to resident cells. In the native myocardium, the ECM contributes to both heart compliance and cardiomyocyte maturation and function. Thus, myocardium regeneration cannot be accomplished if cardiac ECM is not restored. We hypothesize that decellularized human skin might make an easily accessible and viable alternate biological scaffold for cardiac tissue engineering (CTE). To test our hypothesis, we decellularized specimens of both human skin and human myocardium and analyzed and compared their composition by histological methods and quantitative assays. Decellularized dermal matrix was then cut into 600-μm-thick sections and either tested by uniaxial tensile stretching to characterize its mechanical behavior or used as three-dimensional scaffold to assess its capability to support regeneration by resident cardiac progenitor cells (hCPCs) in vitro. Histological and quantitative analyses of the dermal matrix provided evidence of both effective decellularization with preserved tissue architecture and retention of ECM proteins and growth factors typical of cardiac matrix. Further, the elastic modulus of the dermal matrix resulted comparable with that reported in literature for the human myocardium and, when tested in vitro, dermal matrix resulted a comfortable and protective substrate promoting and supporting hCPC engraftment, survival and cardiomyogenic potential. Our study provides compelling evidence that dermal matrix holds promise as a fully autologous and cost-effective biological scaffold for CTE.

Extracellular Matrix in Regulation of Contractile System in Cardiomyocytes

The contractile apparatus of cardiomyocytes is considered to be a stable system. However, it undergoes strong rearrangements during heart development as cells progress from their non-muscle precursors. Long-term culturing of mature cardiomyocytes is also accompanied by the reorganization of their contractile apparatus with the conversion of typical myofibrils into structures of non-muscle type. Processes of heart development as well as cell adaptation to culture conditions in cardiomyocytes both involve extracellular matrix changes, which appear to be crucial for the maturation of contractile apparatus. The aim of this review is to analyze the role of extracellular matrix in the regulation of contractile system dynamics in cardiomyocytes. Here, the remodeling of actin contractile structures and the expression of actin isoforms in cardiomyocytes during differentiation and adaptation to the culture system are described along with the extracellular matrix alterations. The data supporting the regulation of actin dynamics by extracellular matrix are highlighted and the possible mechanisms of such regulation are discussed.

Matrix-guided control of mitochondrial function in cardiac myocytes

In ventricular myocardium, extracellular matrix (ECM) remodeling is a hallmark of physiological and pathological growth, coincident with metabolic rewiring of cardiac myocytes. However, the direct impact of the biochemical and mechanical properties of the ECM on the metabolic function of cardiac myocytes is mostly unknown. Furthermore, understanding the impact of distinct biomaterials on cardiac myocyte metabolism is critical for engineering physiologically-relevant models of healthy and diseased myocardium. For these reasons, we systematically measured morphological and metabolic responses of neonatal rat ventricular myocytes cultured on fibronectin- or gelatin-coated polydimethylsiloxane (PDMS) of three elastic moduli and gelatin hydrogels with four elastic moduli. On all substrates, total protein content, cell morphology, and the ratio of mitochondrial DNA to nuclear DNA were preserved. Cytotoxicity was low on all substrates, although slightly higher on PDMS compared to gelatin hydrogels. We also quantified oxygen consumption rates and extracellular acidification rates using a Seahorse extracellular flux analyzer. Our data indicate that several metrics associated with baseline glycolysis and baseline and maximum mitochondrial function are enhanced when cardiac myocytes are cultured on gelatin hydrogels compared to all PDMS substrates, irrespective of substrate rigidity. These results yield new insights into how mechanical and biochemical cues provided by the ECM impact mitochondrial function in cardiac myocytes. STATEMENT OF SIGNIFICANCE: Cardiac development and disease are associated with remodeling of the extracellular matrix coincident with metabolic rewiring of cardiac myocytes. However, little is known about the direct impact of the biochemical and mechanical properties of the extracellular matrix on the metabolic function of cardiac myocytes. In this study, oxygen consumption rates were measured in neonatal rat ventricular myocytes maintained on several commonly-used biomaterial substrates to reveal new relationships between the extracellular matrix and cardiac myocyte metabolism. Several mitochondrial parameters were enhanced on gelatin hydrogels compared to synthetic PDMS substrates. These data are important for comprehensively understanding matrix-regulation of cardiac myocyte physiology. Additionally, these data should be considered when selecting scaffolds for engineering in vitro cardiac tissue models.

Cardiac Extracellular Matrix Modification as a Therapeutic Approach

The cardiac extracellular matrix (cECM) is comprised of proteins and polysaccharides secreted by cardiac cell types, which provide structural and biochemical support to cardiovascular tissue. The roles of cECM proteins and the associated family of cell surface receptor, integrins, have been explored in vivo via the generation of knockout experimental animal models. However, the complexity of tissues makes it difficult to isolate the effects of individual cECM proteins on a particular cell process or disease state. The desire to further dissect the role of cECM has led to the development of a variety of in vitro model systems, which are now being used not only for basic studies but also for testing drug efficacy and toxicity and for generating therapeutic scaffolds. These systems began with 2D coatings of cECM derived from tissue and have developed to include recombinant ECM proteins, ECM fragments, and ECM mimics. Most recently 3D model systems have emerged, made possible by several developing technologies including, and most notably, 3D bioprinting. This chapter will attempt to track the evolution of our understanding of the relationship between cECM and cell behavior from in vivo model to in vitro control systems. We end the chapter with a summary of how basic studies such as these have informed the use of cECM as a direct therapy.

Engineering cardiac microphysiological systems to model pathological extracellular matrix remodeling

Many cardiovascular diseases are associated with pathological remodeling of the extracellular matrix (ECM) in the myocardium. ECM remodeling is a complex, multifactorial process that often contributes to declines in myocardial function and progression toward heart failure. However, the direct effects of the many forms of ECM remodeling on myocardial cell and tissue function remain elusive, in part because conventional model systems used to investigate these relationships lack robust experimental control over the ECM. To address these shortcomings, microphysiological systems are now being developed and implemented to establish direct relationships between distinct features in the ECM and myocardial function with unprecedented control and resolution in vitro. In this review, we will first highlight the most prominent characteristics of ECM remodeling in cardiovascular disease and describe how these features can be mimicked with synthetic and natural biomaterials that offer independent control over multiple ECM-related parameters, such as rigidity and composition. We will then detail innovative microfabrication techniques that enable precise regulation of cellular architecture in two and three dimensions. We will also describe new approaches for quantifying multiple aspects of myocardial function in vitro, such as contractility, action potential propagation, and metabolism. Together, these collective technologies implemented as cardiac microphysiological systems will continue to uncover important relationships between pathological ECM remodeling and myocardial cell and tissue function, leading to new fundamental insights into cardiovascular disease, improved human disease models, and novel therapeutic approaches.

Surface-modified polymers for cardiac tissue engineering

Cardiovascular disease (CVD), leading to myocardial infarction and heart failure, is one of the major causes of death worldwide. The physiological system cannot significantly regenerate the capabilities of a damaged heart. The current treatment involves pharmacological and surgical interventions; however, less invasive and more cost-effective approaches are sought. Such new approaches are developed to induce tissue regeneration following injury. Hence, regenerative medicine plays a key role in treating CVD. Recently, the extrinsic stimulation of cardiac regeneration has involved the use of potential polymers to stimulate stem cells toward the differentiation of cardiomyocytes as a new therapeutic intervention in cardiac tissue engineering (CTE). The therapeutic potentiality of natural or synthetic polymers and cell surface interactive factors/polymer surface modifications for cardiac repair has been demonstrated in vitro and in vivo. This review will discuss the recent advances in CTE using polymers and cell surface interactive factors that interact strongly with stem cells to trigger the molecular aspects of the differentiation or formulation of cardiomyocytes for the functional repair of heart injuries or cardiac defects.

Laminin, laminin-entactin and extracellular matrix are equally appropriate adhesive substrates for isolated adult rat cardiomyocyte culture and experimentation

Although techniques for isolating and culturing adult cardiomyocytes were developed four decades ago, it still remains a challenge to isolate high yields of healthy viable cardiomyocytes, to maintain them in culture, and to use them successfully in experiments. This is due to the difficulty in deciding which adhesive substrate and buffer composition to use. Therefore this study aimed to (1) identify a robust experimental buffer to sustain survival of cultured adult rat cardiomyocytes (ARCMs) during control normoxic conditions, and (2) to identify an adhesive substrate that provides optimal cell adherence, not only during normoxia, but especially during simulated ischemia-reperfusion (SIR) experiments. Adhesion and viability of ARCMs were evaluated on laminin, laminin-entactin (LE), and extracellular matrix (ECM) at concentrations between 25-200 ug/ml, in three different normoxic experimental buffers and under SIR conditions. Differences in normoxic buffer composition had no effect on the adherence of ARCMs, but had a significant effect on mitochondrial function and thus cell viability. HEPES buffered PBS supplemented with 10 mM glucose was not sufficient to sustain cell viability unless 2 mM pyruvate was added, yet a cocktail of PBS and M199 provided an even greater viability. Finally, laminin, LE, and ECM retained similar numbers of ARCMs per concentration, but only provided efficient adhesion at concentrations ≥ 100 ug/ml.

Fibrosis and Fibrotic Gene Expression in Pediatric and Adult Patients With Idiopathic Dilated Cardiomyopathy

BACKGROUND

Although fibrosis seems to be prognostic for adverse outcomes in adults with idiopathic dilated cardiomyopathy (IDC), little is known about the prevalence and development of fibrosis in pediatric IDC hearts. We hypothesized that there is less activation of fibrosis at a molecular level in pediatric IDC hearts than in failing adult hearts.

METHODS AND RESULTS

Pediatric hearts were analyzed histologically to determine the prevalence of fibrosis. Left ventricular tissue from adult and pediatric IDC hearts and adult and pediatric nonfailing (NF) hearts were subjected to quantitative reverse-transcription polymerase chain reaction to study the expression of important mRNAs that affect fibrosis. We found age-specific differences between IDC and NF hearts in the regulation of noncoding galectin-3, Corin, matrix metalloproteinase (MMP) 2, MMP-9, tissue inhibitor of metalloproteinase (TIMP) 2, and TIMP-3. We also found markers that were similarly altered in both adult and pediatric IDC hearts (interleukin-1 receptor-like 1 receptor, TIMP-1, and TIMP-4). Finally, microRNAs 29a-c were significantly decreased in the pediatric IDC patients.

CONCLUSIONS

Pediatric IDC patients demonstrate age-specific differences in the molecular pathways implicated in fibrosis in the adult heart. At the ultrastructural level the unique gene expression pattern appears to limit fibrosis in the failing pediatric heart.

Neonatal Cardiac Scaffolds: Novel Matrices for Regenerative Studies

The only definitive therapy for end stage heart failure is orthotopic heart transplantation. Each year, it is estimated that more than 100,000 donor hearts are needed for cardiac transplantation procedures in the United States^1-2. Due to the limited numbers of donors, only approximately 2,400 transplants are performed each year in the U.S.². Numerous approaches, from cell therapy studies to implantation of mechanical assist devices, have been undertaken, either alone or in combination, in an attempt to coax the heart to repair itself or to rest the failing heart³. In spite of these efforts, ventricular assist devices are still largely used for the purpose of bridging to transplantation and the utility of cell therapies, while they hold some curative promise, is still limited to clinical trials. Additionally, direct xenotransplantation has been attempted but success has been limited due to immune rejection. Clearly, another strategy is required to produce additional organs for transplantation and, ideally, these organs would be autologous so as to avoid the complications associated with rejection and lifetime immunosuppression. Decellularization is a process of removing resident cells from tissues to expose the native extracellular matrix (ECM) or scaffold. Perfusion decellularization offers complete preservation of the three dimensional structure of the tissue, while leaving the bulk of the mechanical properties of the tissue intact⁴. These scaffolds can be utilized for repopulation with healthy cells to generate research models and, possibly, much needed organs for transplantation. We have exposed the scaffolds from neonatal mice (P3), known to retain remarkable cardiac regenerative capabilities,^5-8 to detergent mediated decellularization and we repopulated these scaffolds with murine cardiac cells. These studies support the feasibility of engineering a neonatal heart construct. They further allow for the investigation as to whether the ECM of early postnatal hearts may harbor cues that will result in improved recellularization strategies.

Extracellular matrix downregulation in the Drosophila heart preserves contractile function and improves lifespan

Aging is associated with extensive remodeling of the heart, including basement membrane (BM) components that surround cardiomyocytes. Remodeling is thought to impair cardiac mechanotransduction, but the contribution of specific BM components to age-related lateral communication between cardiomyocytes is unclear. Using a genetically tractable, rapidly aging model with sufficient cardiac genetic homology and morphology, e.g. Drosophila melanogaster, we observed differential regulation of BM collagens between laboratory strains, correlating with changes in muscle physiology leading to cardiac dysfunction. Therefore, we sought to understand the extent to which BM proteins modulate contractile function during aging. Cardiac-restricted knockdown of ECM genes Pericardin, Laminin A, and Viking in Drosophila prevented age-associated heart tube restriction and increased contractility, even under viscous load. Most notably, reduction of Laminin A expression correlated with an overall preservation of contractile velocity with age and extension of organismal lifespan. Global heterozygous knockdown confirmed these data, which provides new evidence of a direct link between BM homeostasis, contractility, and maintenance of lifespan.

Cardiomyocytes from human pluripotent stem cells: From laboratory curiosity to industrial biomedical platform

Cardiomyocytes from human pluripotent stem cells (hPSCs-CMs) could revolutionise biomedicine. Global burden of heart failure will soon reach USD $90bn, while unexpected cardiotoxicity underlies 28% of drug withdrawals. Advances in hPSC isolation, Cas9/CRISPR genome engineering and hPSC-CM differentiation have improved patient care, progressed drugs to clinic and opened a new era in safety pharmacology. Nevertheless, predictive cardiotoxicity using hPSC-CMs contrasts from failure to almost total success. Since this likely relates to cell immaturity, efforts are underway to use biochemical and biophysical cues to improve many of the ~30 structural and functional properties of hPSC-CMs towards those seen in adult CMs. Other developments needed for widespread hPSC-CM utility include subtype specification, cost reduction of large scale differentiation and elimination of the phenotyping bottleneck. This review will consider these factors in the evolution of hPSC-CM technologies, as well as their integration into high content industrial platforms that assess structure, mitochondrial function, electrophysiology, calcium transients and contractility. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

Partially Digested Adult Cardiac Extracellular Matrix Promotes Cardiomyocyte Proliferation In Vitro

Stimulating or maintaining the proliferative capacity of postnatal mammalian cardiomyocytes is a major challenge to cardiac regeneration. Previously, it is found that fetal cardiac extracellular matrix (ECM) can promote neonatal rat cardiomyocyte proliferation in vitro better than neonatal or adult ECM. It is hypothesized that partial digestion of adult ECM (PD-ECM) would liberate less crosslinked components that promote cardiomyocyte proliferation, similar to fetal ECM. Neonatal rat cardiac cells are seeded onto substrates coated with adult rat cardiac ECM that has been solubilized in pepsin-HCl for 1, 3, 6, 12, 24, or 48 h. Cardiomyocyte proliferation and fold-change in numbers from 1 to 5 d are highest on 1 and 3 h PD-ECM compared to other conditions. Sarcomeres tend to mature on 24 and 48 h PD-ECM where low proliferation is observed. 3 h PD-ECM is primarily composed of Fibrillin-1, Fibrinogen, and Laminins while 48 h PD-ECM is dominated by Collagen I. Our results suggest that adult ECM retains regenerative cues that may be masked by more abundant, mature ECM components. PD-ECM provides a simple yet powerful approach to promoting cardiomyocyte proliferation.

Expression of metalloproteases by cardiac myocytes and fibroblasts in vitro

Regulation of the turnover of extracellular matrix (ECM) components has been attributed in part to matrix metalloproteases (MMP). Isolated cardiac myocytes and fibroblasts from different developmental stages express different patterns of MMPs in vitro. Zymography of media and cell extracts of fibroblasts and myocytes indicated several apparent molecular weights (Mr) with gelatinolytic activity with prominent bands at 92 and 72 kDa. No caseinolytic activity was detected. These MMPs were characteristic of known MMP-2 and MMP-9. Fibroblasts predominantly expressed the latent 72-kDa MMP, whereas myocytes expressed a latent 92-kDa MMP. Expression of these MMPs was not affected by density of culture or the type of ECM substrate on which the cells were grown. Sodium dodecyl sulfate (SDS)-activated MMP-2 showed specific cleavage patterns on collagen types I and III but not on fibronectin, collagen type IV, or laminin. The reaction of SDS-activated MMP-2 produced a 140-kDa fragment from collagen types I and III. No specific substrate patterns were observed with activated MMP-9. MMP-2 from fibroblasts could also be activated by mechanical tension developed by fibroblasts within collagen gels or by cyclically stretching Silastic membranes on which the fibroblasts were grown. When mechanical tension was inhibited in collagen gels by antibodies against the β1 integrin, the 72-kDa MMP, or cytochalasin D, the activated band at 62 kDa was not detected. Immunocytochemical localization with antibodies against MMP-2 showed a weak reaction on cardiac myocytes, but intense staining around the focal adhesions of migrating fibroblasts. In collagen gels, staining was localized to the leading pseudopodia of the fibroblasts. Together, these data indicate that the rat MMP-2 is a collagenase primarily associated with cardiac fibroblasts, activated by mechanical tension, and may be important in cellular ECM interactions.

Cardiac fibroblasts form and function

The formation and structure of the extracellular matrix (ECM) that makes up the cardiac interstitum is well known yet the underlying mechanisms that regulate the interstitum are poorly known. This review focuses on the role of the cardiac fibroblast in the formation and regulation of the ECM components during cardiac development and in response to physiological and pathological stimulation. The role of ECM receptors (integrins), cellular phenotype, and chemical and mechanical signaling by cardiac fibroblasts are discussed.

Measuring the contractile forces of human induced pluripotent stem cell-derived cardiomyocytes with arrays of microposts

Human stem cell-derived cardiomyocytes hold promise for heart repair, disease modeling, drug screening, and for studies of developmental biology. All of these applications can be improved by assessing the contractility of cardiomyocytes at the single cell level. We have developed an in vitro platform for assessing the contractile performance of stem cell-derived cardiomyocytes that is compatible with other common endpoints such as microscopy and molecular biology. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were seeded onto elastomeric micropost arrays in order to characterize the contractile force, velocity, and power produced by these cells. We assessed contractile function by tracking the deflection of microposts beneath an individual hiPSC-CM with optical microscopy. Immunofluorescent staining of these cells was employed to assess their spread area, nucleation, and sarcomeric structure on the microposts. Following seeding of hiPSC-CMs onto microposts coated with fibronectin, laminin, and collagen IV, we found that hiPSC-CMs on laminin coatings demonstrated higher attachment, spread area, and contractile velocity than those seeded on fibronectin or collagen IV coatings. Under optimized conditions, hiPSC-CMs spread to an area of approximately 420 μm2, generated systolic forces of approximately 15 nN/cell, showed contraction and relaxation rates of 1.74 μm/s and 1.46 μm/s, respectively, and had a peak contraction power of 29 fW. Thus, elastomeric micropost arrays can be used to study the contractile strength and kinetics of hiPSC-CMs. This system should facilitate studies of hiPSC-CM maturation, disease modeling, and drug screens as well as fundamental studies of human cardiac contraction.

Myocardial fibroblast-matrix interactions and potential therapeutic targets

The cardiac extracellular matrix (ECM) is a dynamic structure, adapting to physiological and pathological stresses placed on the myocardium. Deposition and organization of the matrix fall under the purview of cardiac fibroblasts. While often overlooked compared to myocytes, fibroblasts play a critical role in maintaining ECM homeostasis under normal conditions and in response to pathological stimuli assume an activated, myofibroblast phenotype associated with excessive collagen accumulation contributing to impaired cardiac function. Complete appreciation of fibroblast function is hampered by the lack of fibroblast-specific reagents and the heterogeneity of fibroblast precursors. This is further complicated by our ability to dissect the role of myofibroblasts versus fibroblasts in myocardial in remodeling. This review highlights critical points in the regulation of collagen deposition by fibroblasts, the current panel of molecular tools used to identify fibroblasts and the role of fibroblast-matrix interactions in fibroblast function and differentiation into the myofibroblast phenotype. The clinical potential of exploiting differences between fibroblasts and myofibroblasts and using them to target specific fibroblast populations is also discussed. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium."

Adsorption of cellular proteins to polyelectrolyte-functionalized gold nanorods: a mechanism for nanoparticle regulation of cell phenotype?

Cell behavior in the presence of nanomaterials is typically explored through simple viability assays, but there is mounting evidence that nanomaterials can have more subtle effects on a variety of cellular functions. Previously our lab demonstrated that gold nanorods functionalized with polyelectrolyte multi-layers inhibited rat cardiac fibroblast-mediated remodeling of type I collagen scaffolds by altering fibroblast phenotype and the mechanical properties of the collagen network. In this work, we examine a possible mechanism for these effects: adsorption of cellular proteins by the nanorods. Mass spectrometric and gel electrophoresis of media collected from cultured cells suggests that a number of proteins, some of which mediate cell-cell and cell-matrix interactions, adsorb onto the surface of these nanoparticles in vitro. Polyethylene glycol coating of the nanorods largely mitigates protein adsorption and fibroblast-mediated collagen remodeling. These results suggest that adsorption of proteins by nanorods could have a significant effect on cell functions, including fibroblast-mediated matrix remodeling.

Origin, development, and differentiation of cardiac fibroblasts

Cardiac fibroblasts are the most abundant cell in the mammalian heart. While they have been historically underappreciated in terms of their functional contributions to cardiac development and physiology, they and their activated form, myofibroblasts, are now known to play key roles in both development and disease through structural, paracrine, and electrical interactions with cardiomyocytes. The lack of specific markers for fibroblasts currently convolutes the study of this dynamic cell lineage, but advances in marker analysis and lineage mapping technologies are continuously being made. Understanding how to best utilize these tools, both individually and in combination, will help to elucidate the functional significance of fibroblast-cardiomyocyte interactions in vivo. Here we review what is currently known about the diverse roles played by cardiac fibroblasts and myofibroblasts throughout development and periods of injury with the intent of emphasizing the duality of their nature. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium ".

Temporal changes in integrin-mediated cardiomyocyte adhesion secondary to chronic cardiac volume overload in rats

Previous studies have established integrins as cell surface receptors that mediate cardiomyocyte-extracellular matrix (ECM) attachments. This study sought to determine the contributions of the myocardial β1- and β3-integrin subunits to ventricular dilatation and coronary flow regulation using a blood-perfused isolated heart preparation. Furthermore, cardiomyocyte adhesion to collagen types I and IV, fibronectin, and laminin with and without a β1-integrin subunit neutralizing antibody was assessed during the course of remodeling secondary to a sustained cardiac volume overload, including the onset of heart failure. Isolated cardiomyocytes were obtained during the initial, compensated, and decompensated phases of remodeling resulting from an aortocaval fistula created in 8-wk-old male Sprague-Dawley rats. Blocking the β1-integrin subunit in isolated normal hearts produced ventricular dilatation, whereas this was not the case when the β3-subunit was blocked. Substantial reductions in cardiomyocyte adhesion coincided with the previously documented development of ventricular dilatation and decreased contractility postfistula, with the β1-integrin contribution to adhesion ranging from 28% to 73% over the course of remodeling being essentially substrate independent. In contrast, both integrin subunits were found to be involved in regulating coronary vascular resistance. It is concluded that marked reductions in integrin-mediated cardiomyocyte adhesion to the ECM play a significant role in the progression of adverse myocardial remodeling that leads to heart failure. Furthermore, although both the β1- and β3-integrin subunits were involved in regulating coronary vascular resistance, only inhibition of β1-integrin-mediated adhesion resulted in ventricular dilatation of the normal heart.

Confocal microscopy of cardiac myocytes

Detailed methods are provided for the preparation and confocal imaging of cardiac myocyte development and differentiation. Examples include protocols for the analysis of cultured myocytes as well as vibratome sections of hearts from embryonic and adult tissue. Techniques include routine labeling of F-actin with phalloidin as well as multiple labeling protocols for colocalization studies and cell volume analysis.

Lack of specificity of fibroblast-specific protein 1 in cardiac remodeling and fibrosis

Understanding the role of fibroblasts in pathologic conditions is hampered by the absence of specific markers. Fibroblast-specific protein (FSP)1 has been suggested as a fibroblast-specific marker in normal and fibrotic tissues; FSP1 reporter mice and FSP1-Cre-driven gene deletion are considered reliable strategies to investigate fibroblast biology. Because fibroblasts are abundant in normal and injured mammalian hearts, we studied the identity of FSP1(+) cells in the infarcted and remodeling myocardium using mice with green fluorescent protein (GFP) expression driven by the FSP1 promoter. Neonatal and adult mouse hearts had low numbers of FSP1(+) cells. Myocardial infarction induced marked infiltration with FSP1-expressing cells that peaked after 72 h of reperfusion. Using flow cytometry, we identified 50% of FSP1(+) cells as hematopoietic cells; many endothelial cells were also FSP1(+). Increased infiltration with FSP1(+) cells was also noted in the pressure-overloaded myocardium. Although some FSP1(+) cells had fibroblast morphology, >30% were identified as hematopoietic cells, endothelial cells, or vascular smooth muscle cells. In contrast, periostin did not stain leukocytes or vascular cells but labeled spindle-shaped interstitial cells and, as a typical matricellular protein, was deposited in the matrix. CD11b(+) myeloid cells sorted from the infarcted heart had higher FSP1 expression than corresponding CD11b-negative cells, highlighting the predominant expression by hematopoietic cells. FSP1 is not a specific marker for fibroblasts in cardiac remodeling and fibrosis.

The dynamic role of cardiac fibroblasts in development and disease

Cardiac fibroblasts are the most abundant cell in the mammalian heart. While they have been historically overlooked in terms of functional contributions to development and physiology, cardiac fibroblasts are now front and center. They are currently recognized as key protagonists during both normal development and cardiomyopathy disease, and work together with cardiomyocytes through paracrine, structural, and potentially electrical interactions. However, the lack of specific biomarkers and fibroblast heterogeneous nature currently convolutes the study of this dynamic cell lineage; though, efforts to advance marker analysis and lineage mapping technologies are ongoing. These tools will help elucidate the functional significance of fibroblast-cardiomyocyte interactions in vivo and delineate the dynamic nature of normal and pathological cardiac fibroblasts. Since therapeutic promise lies in understanding the interface between developmental biology and the postnatal injury response, future studies to understand the divergent roles played by cardiac fibroblasts both in utero and following cardiac insult are essential.

Matricellular proteins in cardiac adaptation and disease

The term matricellular proteins describes a family of structurally unrelated extracellular macromolecules that, unlike structural matrix proteins, do not play a primary role in tissue architecture, but are induced following injury and modulate cell-cell and cell-matrix interactions. When released to the matrix, matricellular proteins associate with growth factors, cytokines, and other bioactive effectors and bind to cell surface receptors transducing signaling cascades. Matricellular proteins are upregulated in the injured and remodeling heart and play an important role in regulation of inflammatory, reparative, fibrotic and angiogenic pathways. Thrombospondin (TSP)-1, -2, and -4 as well as tenascin-C and -X secreted protein acidic and rich in cysteine (SPARC), osteopontin, periostin, and members of the CCN family (including CCN1 and CCN2/connective tissue growth factor) are involved in a variety of cardiac pathophysiological conditions, including myocardial infarction, cardiac hypertrophy and fibrosis, aging-associated myocardial remodeling, myocarditis, diabetic cardiomyopathy, and valvular disease. This review discusses the properties and characteristics of the matricellular proteins and presents our current knowledge on their role in cardiac adaptation and disease. Understanding the role of matricellular proteins in myocardial pathophysiology and identification of the functional domains responsible for their actions may lead to design of peptides with therapeutic potential for patients with heart disease.

Sphingosine-1-phosphate as a mediator involved in development of fibrotic diseases

Fibrosis is a pathological process characterized by massive deposition of extracellular matrix (ECM) such as type I/III collagens and fibronectin that are secreted by an expanded pool of myofibroblasts, which are phenotypically altered fibroblasts with more contractile, proliferative, migratory and secretory activities. Fibrosis occurs in various organs including the lung, heart, liver and kidney, resulting in loss of normal tissue architecture and functions. Myofibroblasts could originate from multiple sources including tissue-resident fibroblasts, epithelial and endothelial cells through mechanisms of epithelial/endothelial-mesenchymal transition (EMT/EndMT), and bone marrow-derived circulating progenitors called fibrocytes. Emerging evidence in recent years shows that sphingosine-1-phosphate (S1P) acts on several types of target cells and is engaged in pro-fibrotic inflammatory process and fibrogenic process through multiple mechanisms, which include vascular permeability change, leukocyte infiltration, and migration, proliferation and myofibroblast differentiation of fibroblasts. Many of these S1P actions are receptor subtype-specific. In these actions, S1P has multiple cross-talks with other cytokines, particularly transforming growth factor-β (TGFβ), which plays a major role in fibrosis. The cross-talks include the regulation of S1P production through altered expression and activity of sphingosine kinases in fibrotic lesions, altered expression of S1P receptors, and S1P receptor-mediated transactivation of TGFβ signaling pathway. These cross-talks may give rise to a feed-forward, amplifying loop between S1P and TGFβ, and possibly with other cytokines in stimulating fibrogenesis. Another lysophospholipid mediator lysophosphatidic acid has also been recently implicated in fibrosis. The lysophospholipid signaling pathways represent novel, promising therapeutic targets for treating refractory fibrotic diseases. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Mechanotransduction: the role of mechanical stress, myocyte shape, and cytoskeletal architecture on cardiac function

Mechanotransduction refers to the conversion of mechanical forces into biochemical or electrical signals that initiate structural and functional remodeling in cells and tissues. The heart is a kinetic organ whose form changes considerably during development and disease, requiring cardiac myocytes to be mechanically durable and capable of fusing a variety of environmental signals on different time scales. During physiological growth, myocytes adaptively remodel to mechanical loads. Pathological stimuli can induce maladaptive remodeling. In both of these conditions, the cytoskeleton plays a pivotal role in both sensing mechanical stress and mediating structural remodeling and functional responses within the myocyte.

Collagen Matrix Alignment Using Inkjet Printer Technology

Collagen fiber orientation plays an important role in many cell properties and actions in vivo. Collagen and other matrix proteins are aligned in many tissues during normal functioning. For example, cardiomyocytes align in the heart to produce a synchronously beating tissue. The extra-cellular matrix environment, including collagen, is aligned along the cells. This matrix helps with cell adhesion and the alignment of the fibers also contributes to the anisotropic mechanical property of the tissue. While it is easy to replicate randomly oriented collagen in vitro, it is much more difficult to create aligned collagen matrices for cell culture. In this work, a novel inkjet printer-based collagen alignment technique was established. A 1 mg/ml rat tail collagen type I solution was printed, using a modified HP DeskJet 500 printer, onto plasma cleaned and UV sterilized glass slides. The collagen was printed in an eight line pattern, designed in Microsoft Word with 87.5 μm by 23.1 mm lines. The pattern was printed three successive times on each slide to complete the alignment. Immunofluorescence imaging of primary antibodies specific to collagen type I indicated that the heat involved in the printing process was not great enough to denature the collagen. The extent of collagen alignment was quantified using atomic force microscopy and compared to random collagen films and collagen films aligned using a mechanical scraping method. Additionally, neonatal rat cardiomyocytes were cultured on the aligned matrices. These cells require extracellular matrix alignment to maintain their in vivo-like phenotype during in vitro culture. The cells grew along the lines of collagen and coordinated beating, indicating the success of the aligned matrix. This collagen alignment technique is cheap, fast, precise, and easy to use in comparison to other current techniques. It can be used to align collagen on any type of substrate, such as a gel, which makes it a useful tool in many applications. This technique may also be used to align other extra-cellular matrix proteins and could even be used to create a three dimensional construct with varying fiber orientations.

Fibroblasts facilitate the engraftment of embryonic stem cell-derived cardiomyocytes on three-dimensional collagen matrices and aggregation in hanging drops

There is growing interest in the use of cardiomyocytes purified from embryonic stem (ES) cells for tissue engineering and cardiomyoplasty. However, most transplanted cells are lost shortly after transplantation due to the lack of integration into the host tissue and subsequent apoptosis. Here we examine whether murine embryonic fibroblasts (MEFs) can support the integration of purified murine ES cell-derived cardiomyocytes in a 3-dimensional tissue culture model based on a freezed-dryed collagen matrix with tubular structure. Collagen matrix was seeded either with cardiomyocytes alone or in combination with MEFs. The collagen sponges that were transplanted with cardiomyocytes alone showed neither morphological nor functional integration of viable cells. Cardiomyocytes also did not appear to be capable of attaching quantitatively to any of 16 different 2-dimensional biomaterials. However, cardiomyocytes co-cultured with MEFs formed fiber-like structures of rod-shaped cells with organized sarcomeric structure that contracted spontaneously. Electrical coupling between cardiomyocytes was suggested by strong expression of connexin 43. In addition, MEFs as well as cardiac fibroblasts supported re-aggregation of dissociated cardiomyocytes in hanging drops in the absence of collagen matrix. We conclude that fibroblasts promote cardiomyocyte engraftment and formation of functional 3-dimensional tissue in vitro. Elucidation of the mechanism of this phenomenon may help improve the integration of cardiomyocytes in vivo.

The dynamics of fibroblast-myocyte-capillary interactions in the heart

In the heart, electrical, mechanical, and chemical signals create an environment essential for normal cellular responses to developmental and pathologic cues. Communication between fibroblasts, myocytes, and endothelial cells, as well as the extracellular matrix, are critical to fluctuations in heart composition and function during normal development and pathology. Recent evidence suggests that cytokines play a role in cell-cell signaling in the heart. Indeed, we find that interactions between myocytes and cardiac fibroblasts results in increased interleukin-6 and tumor necrosis factor-alpha secretion. We also used confocal and transmission electron microscopy to observe close relationships and possible direct communication between these cells in vivo. Our results highlight the importance of direct cell-cell communication in the heart, and indicate that interactions between fibroblasts, myocytes, and capillary endothelium results in differential cytokine expression. Studying these cell-cell interactions has many implications for the process of cardiac remodeling and overall heart function during development and cardiopathology.

The many facets of the matricelluar protein periostin during cardiac development, remodeling, and pathophysiology

Periostin is a member of a growing family of matricellular proteins, defined by their ability to interact with components of the extracellular milieu, and with receptors at the cell surface. Through these interactions, periostin has been shown to play a crucial role as a profibrogenic molecule during tissue morphogenesis. Tissues destined to become fibrous structures are dependent on cooperative interactions between periostin and its binding partners, whereas in its absence, these structures either totally or partially fail to become mature fibrous entities. Within the heart, fibrogenic differentiation is required for normal tissue maturation, remodeling and function, as well as in response to a pathological myocardial insult. In this review, aspects related to the function of periostin during cardiac morphogenesis, remodeling and pathology are summarized.

Polyelectrolyte-coated gold nanorods and their interactions with type I collagen

Gold nanorods (AuNRs) have unique optical properties for numerous biomedical applications, but the interactions between AuNRs and proteins, particularly those of the extracellular matrix (ECM), are poorly understood. Here the effects of AuNRs on the self-assembly, mechanics, and remodeling of type I collagen gels were examined in vitro. AuNRs were modified with polyelectrolyte multilayers (PEMs) to minimize cytotoxicity, and AuNRs with different terminal polymer chemistries were examined for their interactions with collagen by turbidity assays, rheological tests, and microscopy. Gel contraction assays were used to examine the effects of the PEM-coated AuNRs on cell-mediated collagen remodeling. Polyanion-terminated AuNRs significantly reduced the lag (nucleation) phase of collagen self-assembly and significantly increased the dynamic shear modulus of the polymerized gels, whereas polycation-terminated AuNRs had no effect on the mechanical properties of the collagen. Both polyanion- and polycation-terminated AuNRs significantly inhibited collagen gel contraction by cardiac fibroblasts, and the nanoparticles were localized in intra-, peri-, and extracellular compartments, suggesting that PEM-coated AuNRs influence cell behavior via multiple mechanisms. These results demonstrate the significance of nanoparticle-ECM interactions in determining the bioactivity of nanoparticles.

Cardiac fibroblasts: at the heart of myocardial remodeling

Cardiac fibroblasts are the most prevalent cell type in the heart and play a key role in regulating normal myocardial function and in the adverse myocardial remodeling that occurs with hypertension, myocardial infarction and heart failure. Many of the functional effects of cardiac fibroblasts are mediated through differentiation to a myofibroblast phenotype that expresses contractile proteins and exhibits increased migratory, proliferative and secretory properties. Cardiac myofibroblasts respond to proinflammatory cytokines (e.g. TNFalpha, IL-1, IL-6, TGF-beta), vasoactive peptides (e.g. angiotensin II, endothelin-1, natriuretic peptides) and hormones (e.g. noradrenaline), the levels of which are increased in the remodeling heart. Their function is also modulated by mechanical stretch and changes in oxygen availability (e.g. ischaemia-reperfusion). Myofibroblast responses to such stimuli include changes in cell proliferation, cell migration, extracellular matrix metabolism and secretion of various bioactive molecules including cytokines, vasoactive peptides and growth factors. Several classes of commonly prescribed therapeutic agents for cardiovascular disease also exert pleiotropic effects on cardiac fibroblasts that may explain some of their beneficial outcomes on the remodeling heart. These include drugs for reducing hypertension (ACE inhibitors, angiotensin receptor blockers, beta-blockers), cholesterol levels (statins, fibrates) and insulin resistance (thiazolidinediones). In this review, we provide insight into the properties of cardiac fibroblasts that underscores their importance in the remodeling heart, including their origin, electrophysiological properties, role in matrix metabolism, functional responses to environmental stimuli and ability to secrete bioactive molecules. We also review the evidence suggesting that certain cardiovascular drugs can reduce myocardial remodeling specifically via modulatory effects on cardiac fibroblasts.

Effect of mechanical loading on three-dimensional cultures of embryonic stem cell-derived cardiomyocytes

Cardiomyocytes selected from murine embryonic stem cells (ESCs) using the cardiac-specific promoter alpha-myosin heavy chain were embedded into collagen and fibronectin scaffolds. A custom-built device was used to expose these constructs to mechanical loading (10% stretch at 1, 2, or 3 Hz) or no loading. Constructs were evaluated using reverse transcriptase polymerase chain reaction, histology, and immunohistochemistry. Mechanical loading significantly affected gene expression, and these changes were dependent on the frequency of stretch. A 1 Hz cyclical stretch resulted in significantly lower gene expression, whereas a 3 Hz cyclical stretch resulted in significantly greater gene expression than in unstretched controls. These constructs also developed cardiac-specific cell structures similar to those found in vivo. This study describes a 3-dimensional model to examine the direct effect of mechanical loading on the differentiation of ESC-derived cardiomyocytes embedded in a defined extracellular matrix scaffold. A technique was also developed to isolate the areas within the constructs undergoing the most homogeneous strain so that the effect of mechanical loading on gene expression could be directly evaluated. These experiments emphasize that ESC-derived cardiomyocytes are actively responding to cues from their environment and that those cues can drive phenotypic control and cardiomyocyte differentiation.

Effect of mechanical loading on three-dimensional cultures of embryonic stem cell-derived cardiomyocytes

Cardiomyocytes selected from murine embryonic stem cells (ESCs) using the cardiac-specific promoter alpha-myosin heavy chain were embedded into collagen and fibronectin scaffolds. A custom-built device was used to expose these constructs to mechanical loading (10% stretch at 1, 2, or 3 Hz) or no loading. Constructs were evaluated using reverse transcriptase polymerase chain reaction, histology, and immunohistochemistry. Mechanical loading significantly affected gene expression, and these changes were dependent on the frequency of stretch. A 1 Hz cyclical stretch resulted in significantly lower gene expression, whereas a 3 Hz cyclical stretch resulted in significantly greater gene expression than in unstretched controls. These constructs also developed cardiac-specific cell structures similar to those found in vivo. This study describes a 3-dimensional model to examine the direct effect of mechanical loading on the differentiation of ESC-derived cardiomyocytes embedded in a defined extracellular matrix scaffold. A technique was also developed to isolate the areas within the constructs undergoing the most homogeneous strain so that the effect of mechanical loading on gene expression could be directly evaluated. These experiments emphasize that ESC-derived cardiomyocytes are actively responding to cues from their environment and that those cues can drive phenotypic control and cardiomyocyte differentiation.

Adaptive changes in cardiac fibroblast morphology and collagen organization as a result of mechanical environment

There is a growing body of work in the literature that demonstrates the significant differences between 2D versus 3D environments in cell morphologies, spatial organization, cell-ECM interactions, and cell signaling. The 3D environments are generally considered more realistic tissue models both because they offer cells a surrounding environment rather than just a planar surface with which to interact, and because they provide the potential for more diverse mechanical environments. Many studies have examined cellular-mediated contraction of 3D matrices; however, because the 3D environment is much more complex and the scale more difficult to study, little is known regarding how mechanical environment, cell and collagen architecture, and collagen remodeling are linked. In the current work, we examine the spatial arrangement of neonatal cardiac fibroblasts and the associated collagen organization in constrained and unconstrained collagen gels over a 24 h period. Collagen gels that are constrained by their physical attachment to a mold and similar gels, which have been detached (unconstrained) from the mold and subsequently contract, offer two simple mechanical models by which the mechanisms of tissue homeostasis and wound repair might be examined. Our observations suggest the presence of two mechanical regimes in the unconstrained gels: an outer ring where cells orient circumferentially and local collagen aligns with the elongated cells; and a central region where unaligned stellate/bipolar cells are radially surrounded by collagen, similar to that seen throughout constrained gels. The evolving organization of cell alignment and surrounding collagen organization suggests that cellular response may be due to the cellular perception of the apparent stiffness of local physical environment.

Periostin is required for maturation and extracellular matrix stabilization of noncardiomyocyte lineages of the heart

The secreted periostin protein, which marks mesenchymal cells in endocardial cushions following epithelial-mesenchymal transformation and in mature valves following remodeling, is a putative valvulogenesis target molecule. Indeed, periostin is expressed throughout cardiovascular morphogenesis and in all 4 adult mice valves (annulus and leaflets). Additionally, periostin is expressed throughout the fibrous cardiac skeleton and endocardial cushions in the developing heart but is absent from both normal and/or pathological mouse cardiomyocytes. Periostin (peri(lacZ)) knockout mice exhibit viable valve disease, with neonatal lethality in a minority and latent disease with leaflet abnormalities in the viable majority. Surviving peri(lacZ)-null leaflets are truncated, contain ectopic cardiomyocytes and smooth muscle, misexpress the cartilage proteoglycan aggrecan, demonstrate disorganized matrix stratification, and exhibit reduced transforming growth factor-beta signaling. Neonatal peri(lacZ) nulls that die (14%) display additional defects, including leaflet discontinuities, delamination defects, and deposition of acellular extracellular matrix. Assessment of collagen production, 3D lattice formation ability, and transforming growth factor-beta responsiveness indicate periostin-deficient fibroblasts are unable to support normal valvular remodeling and establishment of a mature cardiac skeleton. Furthermore, pediatric stenotic bicuspid aortic valves that have lost normal extracellular matrix trilaminar stratification have greatly reduced periostin. This suggests that loss of periostin results in inappropriate differentiation of mesenchymal cushion cells and valvular abnormalities via a transforming growth factor-beta-dependent pathway during establishment of the mature heart. Thus, peri(lacZ) knockouts provide a new model of viable latent valve disease.

Effects of elevated glucose levels on interactions of cardiac fibroblasts with the extracellular matrix

Exposure of fibroblasts to high glucose levels promotes a fibrotic response characterized by increased expression of extracellular matrix components including interstitial collagens. Little is known about the effects of glucose levels on other aspects of fibroblast function. Fibroblasts in the myocardium are surrounded by an extensive extracellular matrix composed predominantly of type I collagen. Interactions between fibroblasts and the myocardial extracellular matrix are thought to affect heart function by altering ventricular diastolic properties. The purpose of the present study was to determine the effects of elevated glucose levels on the interactions between heart fibroblasts and the collagenous extracellular matrix. Studies were performed to determine the effects of relative glucose levels on the ability of fibroblasts to migrate on and contract a three-dimensional collagenous substratum. These experiments illustrated that exposure of cardiac fibroblasts to high glucose levels (25 mM) resulted in decreased migratory activity of fibroblasts on a collagen matrix and decreased fibroblast proliferation. In addition, high glucose stimulated collagen and collagen-binding integrin expression and contraction of three-dimensional collagen gels by cardiac fibroblasts. These studies illustrate that altered glucose levels induce important changes in the interactions of cardiac fibroblasts with the collagenous extracellular matrix.