Dissecting coronary angiogenesis: 3D co-culture of cardiomyocytes with endothelial or mesenchymal cells

Stacking thick perfusable human microvascular grafts enables dense vascularity and rapid integration into infarcted rat hearts

Fabrication of large-scale engineered tissues requires extensive vascularization to support tissue survival and function. Here, we report a modular fabrication approach, by stacking of patterned collagen membranes, to generate thick (2 mm and beyond), large, three-dimensional, perfusable networks of endothelialized vasculature. In vitro, these perfusable vascular networks exhibit remodeling and evenly distributed perfusion among layers, while maintaining their patterned, open-lumen architecture. Compared to non-perfusable, self-assembled vasculature, constructs with perfusable vasculature demonstrated increased gene expression indicative of vascular development and angiogenesis. Upon implantation onto infarcted rat hearts, perfusable vascular networks attain greater host vascular integration than self-assembled controls, indicated by 2.5-fold greater perfused vascular density measured by histological analysis and 5-fold greater perfusion rate measured by optical microangiography. Together, the success of fabricating thick, perfusable tissues with dense vascularity and rapid anastomoses represents an important step forward for vascular bioengineering, and paves the way towards more complex, large scale, highly metabolic engineered tissues.

The interplay of cells, polymers, and vascularization in three-dimensional lung models and their applications in COVID-19 research and therapy

Millions of people have been affected ever since the emergence of the corona virus disease of 2019 (COVID-19) outbreak, leading to an urgent need for antiviral drug and vaccine development. Current experimentation on traditional two-dimensional culture (2D) fails to accurately mimic the in vivo microenvironment for the disease, while in vivo animal model testing does not faithfully replicate human COVID-19 infection. Human-based three-dimensional (3D) cell culture models such as spheroids, organoids, and organ-on-a-chip present a promising solution to these challenges. In this report, we review the recent 3D in vitro lung models used in COVID-19 infection and drug screening studies and highlight the most common types of natural and synthetic polymers used to generate 3D lung models.

Vascularized Tissue Organoids

Tissue organoids hold enormous potential as tools for a variety of applications, including disease modeling and drug screening. To effectively mimic the native tissue environment, it is critical to integrate a microvasculature with the parenchyma and stroma. In addition to providing a means to physiologically perfuse the organoids, the microvasculature also contributes to the cellular dynamics of the tissue model via the cells of the perivascular niche, thereby further modulating tissue function. In this review, we discuss current and developing strategies for vascularizing organoids, consider tissue-specific vascularization approaches, discuss the importance of perfusion, and provide perspectives on the state of the field.

The three-dimensionality of the hiPSC-CM spheroid contributes to the variability of the field potential

Background: Field potential (FP) signals from human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) spheroid which are used for drug safety tests in the preclinical stage are different from action potential (AP) signals and require working knowledge of the multi-electrode array (MEA) system. In this study, we developed in silico three-dimensional (3-D) models of hiPSC-CM spheroids for the simulation of field potential measurement. We compared our model simulation results against in vitro experimental data under the effect of drugs E-4031 and nifedipine. Methods: In silico 3-D models of hiPSC-CM spheroids were constructed in spherical and discoidal shapes. Tetrahedral meshes were generated inside the models, and the propagation of the action potential in the model was obtained by numerically solving the monodomain reaction-diffusion equation. An electrical model of electrode was constructed and FPs were calculated using the extracellular potentials from the AP propagations. The effects of drugs were simulated by matching the simulation results with in vitro experimental data. Results: The simulated FPs from the 3-D models of hiPSC-CM spheroids exhibited highly variable shapes depending on the stimulation and measurement locations. The values of the IC₅₀ of E-4031 and nifedipine calculated by matching the simulated FP durations with in vitro experimental data were in line with the experimentally measured ones reported in the literature. Conclusion: The 3-D in silico models of hiPSC-CM spheroids generated highly variable FPs similar to those observed in in vitro experiments. The in silico model has the potential to complement the interpretation of the FP signals obtained from in vitro experiments.

Fluorescent hiPSC-derived MYH6-mScarlet cardiomyocytes for real-time tracking, imaging, and cardiotoxicity assays

Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) hold great potential in the cardiovascular field for human disease modeling, drug development, and regenerative medicine. However, multiple hurdles still exist for the effective utilization of hiPSC-CMs as a human-based experimental platform that can be an alternative to the current animal models. To further expand their potential as a research tool and bridge the translational gap, we have generated a cardiac-specific hiPSC reporter line that differentiates into fluorescent CMs using CRISPR-Cas9 genome editing technology. The CMs illuminated with the mScarlet fluorescence enable their non-invasive continuous tracking and functional cellular phenotyping, offering a real-time 2D/3D imaging platform. Utilizing the reporter CMs, we developed an imaging-based cardiotoxicity screening system that can monitor distinct drug-induced structural toxicity and CM viability in real time. The reporter fluorescence enabled visualization of sarcomeric disarray and displayed a drug dose–dependent decrease in its fluorescence. The study also has demonstrated the reporter CMs as a biomaterial cytocompatibility analysis tool that can monitor dynamic cell behavior and maturity of hiPSC-CMs cultured in various biomaterial scaffolds. This versatile cardiac imaging tool that enables real time tracking and high-resolution imaging of CMs has significant potential in disease modeling, drug screening, and toxicology testing.

Graphical abstract

A three-dimensional culture system for generating cardiac spheroids composed of cardiomyocytes, endothelial cells, smooth-muscle cells, and cardiac fibroblasts derived from human induced-pluripotent stem cells

Cardiomyocytes (CMs), endothelial cells (ECs), smooth-muscle cells (SMCs), and cardiac fibroblasts (CFs) differentiated from human induced-pluripotent stem cells (hiPSCs) are the fundamental components of cell-based regenerative myocardial therapy and can be used as in-vitro models for mechanistic studies and drug testing. However, newly differentiated hiPSC-CMs tend to more closely resemble fetal CMs than the mature CMs of adult hearts, and current techniques for improving CM maturation can be both complex and labor-intensive. Thus, the production of CMs for commercial and industrial applications will require more elementary methods for promoting CM maturity. CMs tend to develop a more mature phenotype when cultured as spheroids in a three-dimensional (3D) environment, rather than as two-dimensional monolayers, and the activity of ECs, SMCs, and CFs promote both CM maturation and electrical activity. Here, we introduce a simple and reproducible 3D-culture-based process for generating spheroids containing all four cardiac-cell types (i.e., cardiac spheroids) that is compatible with a wide range of applications and research equipment. Subsequent experiments demonstrated that the inclusion of vascular cells and CFs was associated with an increase in spheroid size, a decline in apoptosis, an improvement in sarcomere maturation and a change in CM bioenergetics.

Cardiac Organoids: A 3D Technology for Modeling Heart Development and Disease

Cardiac organoids (COs) are miniaturized and simplified organ structures that can be used in heart development biology, drug screening, disease modeling, and regenerative medicine. This cardiac organoid (CO) model is revolutionizing our perspective on answering major cardiac physiology and pathology issues. Recently, many research groups have reported various methods for modeling the heart in vitro. However, there are differences in methodologies and concepts. In this review, we discuss the recent advances in cardiac organoid technologies derived from human embryonic stem cells (hESCs) and human-induced pluripotent stem cells (hiPSCs), with a focus on the summary of methods for organoid generation. In addition, we introduce CO applications in modeling heart development and cardiovascular diseases and discuss the prospects for and common challenges of CO that still need to be addressed. A detailed understanding of the development of CO will help us design better methods, explore and expand its application in the cardiovascular field.

Human Engineered Heart Tissue Models for Disease Modeling and Drug Discovery

The emergence of human induced pluripotent stem cells (hiPSCs) and efficient differentiation of hiPSC-derived cardiomyocytes (hiPSC-CMs) induced from diseased donors have the potential to recapitulate the molecular and functional features of the human heart. Although the immaturity of hiPSC-CMs, including the structure, gene expression, conduct, ion channel density, and Ca²⁺ kinetics, is a major challenge, various attempts to promote maturation have been effective. Three-dimensional cardiac models using hiPSC-CMs have achieved these functional and morphological maturations, and disease models using patient-specific hiPSC-CMs have furthered our understanding of the underlying mechanisms and effective therapies for diseases. Aside from the mechanisms of diseases and drug responses, hiPSC-CMs also have the potential to evaluate the safety and efficacy of drugs in a human context before a candidate drug enters the market and many phases of clinical trials. In fact, novel drug testing paradigms have suggested that these cells can be used to better predict the proarrhythmic risk of candidate drugs. In this review, we overview the current strategies of human engineered heart tissue models with a focus on major cardiac diseases and discuss perspectives and future directions for the real application of hiPSC-CMs and human engineered heart tissue for disease modeling, drug development, clinical trials, and cardiotoxicity tests.

Methods for vascularization and perfusion of tissue organoids

Tissue organoids or "mini organs" can be invaluable tools for understanding health and disease biology, modeling tissue dynamics, or screening potential drug candidates. Effective vascularization of these models is critical for truly representing the in vivo tissue environment. Not only is the formation of a vascular network, and ultimately a microcirculation, essential for proper distribution and exchange of oxygen and nutrients throughout larger organoids, but vascular cells dynamically communicate with other cells to modulate overall tissue behavior. Additionally, interstitial fluid flow, mediated by a perfused microvasculature, can have profound influences on tissue biology. Thus, a truly functionally and biologically relevant organoid requires a vasculature. Here, we review existing strategies for fabricating and incorporating vascular elements and perfusion within tissue organoids.

Early Vascular Cells Improve Microvascularization Within 3D Cardiac Spheroids

Introduction: A key obstacle in the creation of engineered cardiac tissues of clinically relevant sizes is limited diffusion of oxygen and nutrients. Thus, there is a need for organized vascularization within a three-dimensional (3D) tissue environment. Human induced pluripotent stem cell (hiPSC)-derived early vascular cells (EVCs) have shown to improve organization of vascular networks within hydrogels. We hypothesize that introduction of EVCs into 3D microtissue spheroids will lead to increased microvascular formation and improve spheroid formation. Methods: HiPSC-derived cardiomyocytes (CMs) were cocultured with human adult ventricular cardiac fibroblasts (FB) and either human umbilical vein endothelial cells (HUVECs) or hiPSC-derived EVCs for 72 h to form mixed cell spheroids. Three different groups of cell ratios were tested: Group 1 (control) consisted of CM:FB:HUVEC 70:15:15, Group 2 consisted of CM:FB:EVC 70:15:15, and Group 3 consisted of CM:FB:EVC 40:15:45. Vascularization, cell distribution, and cardiac function were investigated. Results: Improved microvasculature was found in EVC spheroids with new morphologies of endothelial organization not found in Group 1 spheroids. CMs were found in a core-shell type distribution in Group 1 spheroids, but more uniformly distributed in EVC spheroids. Contraction rate increased into Group 2 spheroids compared to Group 1 spheroids. Conclusion: The triculture of CM, FB, and EVC within a multicellular cardiac spheroid promotes microvascular formation and cardiac spheroid contraction.

Cardiac Tissue Engineering: Inclusion of Non-cardiomyocytes for Enhanced Features

Engineered cardiac tissues (ECTs) are 3D physiological models of the heart that are created and studied for their potential role in developing therapies of cardiovascular diseases and testing cardio toxicity of drugs. Recreating the microenvironment of the native myocardium in vitro mainly involves the use of cardiomyocytes. However, ECTs with only cardiomyocytes (CM-only) often perform poorly and are less similar to the native myocardium compared to ECTs constructed from co-culture of cardiomyocytes and nonmyocytes. One important goal of co-culture tissues is to mimic the native heart's cellular composition, which can result in better tissue function and maturity. In this review, we investigate the role of nonmyocytes in ECTs and discuss the mechanisms behind the contributions of nonmyocytes in enhancement of ECT features.

Cardiac Tissues From Stem Cells: New Routes to Maturation and Cardiac Regeneration

The ability of human pluripotent stem cells to form all cells of the body has provided many opportunities to study disease and produce cells that can be used for therapy in regenerative medicine. Even though beating cardiomyocytes were among the first cell types to be differentiated from human pluripotent stem cell, cardiac applications have advanced more slowly than those, for example, for the brain, eye, and pancreas. This is, in part, because simple 2-dimensional human pluripotent stem cell cardiomyocyte cultures appear to need crucial functional cues normally present in the 3-dimensional heart structure. Recent tissue engineering approaches combined with new insights into the dialogue between noncardiomyocytes and cardiomyocytes have addressed and provided solutions to issues such as cardiomyocyte immaturity and inability to recapitulate adult heart values for features like contraction force, electrophysiology, or metabolism. Three-dimensional bioengineered heart tissues are thus poised to contribute significantly to disease modeling, drug discovery, and safety pharmacology, as well as provide new modalities for heart repair. Here, we review the current status of 3-dimensional engineered heart tissues.

Engineering and Assessing Cardiac Tissue Complexity

Cardiac tissue engineering is very much in a current focus of regenerative medicine research as it represents a promising strategy for cardiac disease modelling, cardiotoxicity testing and cardiovascular repair. Advances in this field over the last two decades have enabled the generation of human engineered cardiac tissue constructs with progressively increased functional capabilities. However, reproducing tissue-like properties is still a pending issue, as constructs generated to date remain immature relative to native adult heart. Moreover, there is a high degree of heterogeneity in the methodologies used to assess the functionality and cardiac maturation state of engineered cardiac tissue constructs, which further complicates the comparison of constructs generated in different ways. Here, we present an overview of the general approaches developed to generate functional cardiac tissues, discussing the different cell sources, biomaterials, and types of engineering strategies utilized to date. Moreover, we discuss the main functional assays used to evaluate the cardiac maturation state of the constructs, both at the cellular and the tissue levels. We trust that researchers interested in developing engineered cardiac tissue constructs will find the information reviewed here useful. Furthermore, we believe that providing a unified framework for comparison will further the development of human engineered cardiac tissue constructs displaying the specific properties best suited for each particular application.

Benznidazole modulates release of inflammatory mediators by cardiac spheroids infected with Trypanosoma cruzi

Chagas disease (CD) caused by Trypanosoma cruzi remains a serious public health problem in Latin America. The available treatment is limited to two old drugs, benznidazole (Bz) and nifurtimox, which exhibit limited efficacy and trigger side effects, justifying the search for new therapies. Also, more accurate and sensitive experimental protocols for drug discovery programs are necessary to shrink the translational gaps found among pre-clinical and clinical trials. Presently, cardiac spheroids were used to evaluate host cell cytotoxicity and anti-T.cruzi activity of benznidazole, exploring its effect on the release of inflammatory mediators. Bz presented low toxic profile on 3D matrices (LC₅₀ > 200 μM) and high potency in vitro (EC₅₀ = 0.99 μM) evidenced by qPCR analysis of T.cruzi-infected cardiac spheroids. Flow cytometry appraisal of inflammatory mediators released at the cellular supernatant showed increases in IL - 6 and TNF contents (≈190 and ≈ 25-fold) in parasitized spheroids as compared to uninfected cultures. Bz at 10 μM suppressed parasite load (92%) concomitantly decreasing in IL-6 (36%) and TNF (68%). Our findings corroborate the successful use of 3D cardiac matrices for in vitro identification of novel anti-parasitic agents and potential impact in host cell physiology.

Dioxin Disrupts Dynamic DNA Methylation Patterns in Genes That Govern Cardiomyocyte Maturation

Congenital heart disease (CHD), the leading birth defect worldwide, has a largely unknown etiology, likely to result from complex interactions between genetic and environmental factors during heart development, at a time when the heart adapts to diverse physiological and pathophysiological conditions. Crucial among these is the regulation of cardiomyocyte development and postnatal maturation, governed by dynamic changes in DNA methylation. Previous work from our laboratory has shown that exposure to the environmental toxicant tetrachlorodibenzo-p-dioxin (TCDD) disrupts several molecular networks responsible for heart development and function. To test the hypothesis that the disruption caused by TCDD in the heart results from changes in DNA methylation and gene expression patterns of cardiomyocytes, we established a stable mouse embryonic stem cell line expressing a puromycin resistance selectable marker under control of the cardiomyocyte-specific Nkx2-5 promoter. Differentiation of these cells in the presence of puromycin induces the expression of a large suite of cardiomyocyte-specific markers. To assess the consequences of TCDD treatment on gene expression and DNA methylation in these cardiomyocytes, we subjected them to transcriptome and methylome analyses in the presence of TCDD. Unlike control cardiomyocytes maintained in vehicle, the TCDD-treated cardiomyocytes showed extensive gene expression changes, with a significant correlation between differential RNA expression and DNA methylation in 111 genes, many of which are key elements of pathways that regulate cardiovascular development and function. Our findings provide an important clue toward the elucidation of the complex interactions between genetic and epigenetic mechanisms after developmental TCDD exposure that may contribute to CHD.

Effect of Posaconazole in an in vitro model of cardiac fibrosis induced by Trypanosoma cruzi

Posaconazole (POS) is an inhibitor of ergosterol biosynthesis in clinical use for treating invasive fungal infections. POS has potent and selective anti-Trypanosoma cruzi activity and has been evaluated as a possible treatment for Chagas disease. Microtissues are a 3D culture system that has been shown to reproduce better tissue architecture and functionality than cell cultures in monolayer (2D). It has been used to evaluate chemotropic response as in vitro disease models. We previously developed an in vitro model that reproduces aspects of cardiac fibrosis observed in Chagas cardiomyopathy, using microtissues formed by primary cardiac cells infected by the T. cruzi, here called T. cruzi fibrotic cardiac microtissue (TCFCM). We also showed that the treatment of TCFCM with a TGF-β pathway inhibitor reduces fibrosis. Here, we aimed to evaluate the effect of POS in TCFCM, observing parasite load and molecules involved in fibrosis. To choose the concentration of POS to be used in TCFCM we first performed experiments in a monolayer of primary cardiac cell cultures and, based on the results, TCFCM was treated with 5 nM of POS for 96 h, starting at 144 h post-infection. Our previous studies showed that at this time the TCFCM had established fibrosis, resulting from T. cruzi infection. Treatment with POS of TCFCM reduced 50 % of parasite load as observed by real-time PCR and reduced markedly the fibrosis as observed by western blot and immunofluorescence, associated with a strong reduction in the expression of fibronectin and laminin (45 % and 54 %, respectively). POS treatment also changed the expression of proteins involved in the regulation of extracellular matrix proteins (TGF-β and TIMP-4, increased by 50 % and decreased by 58 %, respectively) in TCFCM. In conclusion, POS presented a potent trypanocidal effect both in 2D and in TCFCM, and the reduction of the parasite load was associated with a reduction of fibrosis in the absence of external immunological effectors.

3D Co-culture of hiPSC-Derived Cardiomyocytes With Cardiac Fibroblasts Improves Tissue-Like Features of Cardiac Spheroids

Purpose: Both cardiomyocytes and cardiac fibroblasts (CF) play essential roles in cardiac development, function, and remodeling. Properties of 3D co-cultures are incompletely understood. Hence, 3D co-culture of cardiomyocytes and CF was characterized, and selected features compared with single-type and 2D culture conditions. Methods: Human cardiomyocytes derived from induced-pluripotent stem cells (hiPSC-CMs) were obtained from Cellular Dynamics or Ncardia, and primary human cardiac fibroblasts from ScienCell. Cardiac spheroids were investigated using cryosections and whole-mount confocal microscopy, video motion analysis, scanning-, and transmission-electron microscopy (SEM, TEM), action potential recording, and quantitative PCR (qPCR). Results: Spheroids formed in hanging drops or in non-adhesive wells showed spontaneous contractions for at least 1 month with frequent media changes. SEM of mechanically opened spheroids revealed a dense inner structure and no signs of blebbing. TEM of co-culture spheroids at 1 month showed myofibrils, intercalated disc-like structures and mitochondria. Ultrastructural features were comparable to fetal human myocardium. We then assessed immunostained 2D cultures, cryosections of spheroids, and whole-mount preparations by confocal microscopy. CF in co-culture spheroids assumed a small size and shape similar to the situation in ventricular tissue. Spheroids made only of CF and cultured for 3 weeks showed no stress fibers and strongly reduced amounts of alpha smooth muscle actin compared to early spheroids and 2D cultures as shown by confocal microscopy, western blotting, and qPCR. The addition of CF to cardiac spheroids did not lead to arrhythmogenic effects as measured by sharp-electrode electrophysiology. Video motion analysis showed a faster spontaneous contraction rate in co-culture spheroids compared to pure hiPSC-CMs, but similar contraction amplitudes and kinetics. Spontaneous contraction rates were not dependent on spheroid size. Applying increasing pacing frequencies resulted in decreasing contraction amplitudes without positive staircase effect. Gene expression analysis of selected cytoskeleton and myofibrillar proteins showed more tissue-like expression patterns in co-culture spheroids than with cardiomyocytes alone or in 2D culture. Conclusion: We demonstrate that the use of 3D co-culture of hiPSC-CMs and CF is superior over 2D culture conditions for co-culture models and more closely mimicking the native state of the myocardium with relevance to drug development as well as for personalized medicine.

Isolation, Characterization, and Agent-Based Modeling of Mesenchymal Stem Cells in a Bio-construct for Myocardial Regeneration Scaffold Design

Regenerative medicine involves methods to control and modify normal tissue repair processes. Polymer and cell constructs are under research to create tissue that replaces the affected area in cardiac tissue after myocardial infarction (MI). The aim of the present study is to evaluate the behavior of differentiated and undifferentiated mesenchymal stem cells (MSCs) in vitro and in silico and to compare the results that both offer when it comes to the design process of biodevices for the treatment of infarcted myocardium in biomodels. To assess in vitro behavior, MSCs are isolated from rat bone marrow and seeded undifferentiated and differentiated in multiple scaffolds of a gelled biomaterial. Subsequently, cell behavior is evaluated by trypan blue and fluorescence microscopy, which showed that the cells presented high viability and low cell migration in the biomaterial. An agent-based model intended to reproduce as closely as possible the behavior of individual MSCs by simulating cellular-level processes was developed, where the in vitro results are used to identify parameters in the agent-based model that is developed, and which simulates cellular-level processes: Apoptosis, differentiation, proliferation, and migration. Thanks to the results obtained, suggestions for good results in the design and fabrication of the proposed scaffolds and how an agent-based model can be helpful for testing hypothesis are presented in the discussion. It is concluded that assessment of cell behavior through the observation of viability, proliferation, migration, inflammation reduction, and spatial composition in vitro and in silico, represents an appropriate strategy for scaffold engineering.

Bioprinting of Vascularized Tissue Scaffolds: Influence of Biopolymer, Cells, Growth Factors, and Gene Delivery

Over the past decades, tissue regeneration with scaffolds has achieved significant progress that would eventually be able to solve the worldwide crisis of tissue and organ regeneration. While the recent advancement in additive manufacturing technique has facilitated the biofabrication of scaffolds mimicking the host tissue, thick tissue regeneration remains challenging to date due to the growing complexity of interconnected, stable, and functional vascular network within the scaffold. Since the biological performance of scaffolds affects the blood vessel regeneration process, perfect selection and manipulation of biological factors (i.e., biopolymers, cells, growth factors, and gene delivery) are required to grow capillary and macro blood vessels. Therefore, in this study, a brief review has been presented regarding the recent progress in vasculature formation using single, dual, or multiple biological factors. Besides, a number of ways have been presented to incorporate these factors into scaffolds. The merits and shortcomings associated with the application of each factor have been highlighted, and future research direction has been suggested.

Engineering human ventricular heart tissue based on macroporous iron oxide scaffolds

Myocardial infarction (MI) is a primary cardiovascular disease threatening human health and quality of life worldwide. The development of engineered heart tissues (EHTs) as a transplantable artificial myocardium provides a promising therapy for MI. Since most MIs occur at the ventricle, engineering ventricular-specific myocardium is therefore more desirable for future applications. Here, by combining a new macroporous 3D iron oxide scaffold (IOS) with a fixed ratio of human pluripotent stem cell (hPSC)-derived ventricular-specific cardiomyocytes and human umbilical cord-derived mesenchymal stem cells, we constructed a new type of engineered human ventricular-specific heart tissue (EhVHT). The EhVHT promoted expression of cardiac-specific genes, ion exchange, and exhibited a better Ca²⁺ handling behaviors and normal electrophysiological activity in vitro. Furthermore, when patched on the infarcted area, the EhVHT effectively promoted repair of heart tissues in vivo and facilitated the restoration of damaged heart function of rats with acute MI. Our results show that it is feasible to generate functional human ventricular heart tissue based on hPSC-derived ventricular myocytes for the treatment of ventricular-specific myocardium damage. STATEMENT OF SIGNIFICANCE: We successfully generated highly purified homogenous human ventricular myocytes and developed a method to generate human ventricular-specific heart tissue (EhVHT) based on three-dimensional iron oxide scaffolds. The EhVHT promoted expression of cardiac-specific genes, ion exchange, and exhibited a better Ca²⁺ handling behaviors and normal electrophysiological activity in vitro. Patching the EhVHT on the infarct area significantly improved cardiac function in rat acute MI models. This EhVHT has a great potential to meet the specific requirements for ventricular damages in most MI cases and for screening drugs specifically targeting ventricular myocardium.

Unveiling the molecular crosstalk in a human induced pluripotent stem cell-derived cardiac model

In vitro cell-based models that better mimic the human heart tissue are of utmost importance for drug development and cardiotoxicity testing but also as tools to understand mechanisms related with heart disease at cellular and molecular level. Besides, the implementation of analytical tools that allow the depiction and comprehensive understanding of the molecular mechanisms of the crosstalk between the different cell types is also relevant. In this work, we implemented a human cardiac tissue-like in vitro model, derived from human-induced pluripotent stem cell (hiPSC), and evaluated the relevance of the cell-cell communication between the two of the most representative cell populations of the human heart: cardiomyocytes (hiPSC-CM) and endothelial cells (hiPSC-EC). We observed that heterotypic cell communication promotes: (a) structural maturation of hiPSC-CM and (b) deposition of several extracellular matrix components (such as collagens and fibronectin). Overall, the toolbox of analytical techniques used in our study not only enabled us to validate previous reports from the literature on the importance of the presence of hiPSC-EC on hiPSC-CM maturation, but also bring new insights on the molecular mechanisms involved in the communication between these two cell types when cocultured in vitro.

Measurement of Contractility and Calcium Release in Cardiac Spheroids

There is a need for organotypic in vitro models that resemble the native tissue in functionality and tissue architecture for disease models and drug development. To this end, many 3D culture formats have been developed over time. Among the most often used type is the scaffold-free multicellular aggregate, also called spheroid, that forms by self-assembly. However, working with 3D cultures can be challenging because single cells are not as accessible as in 2D cultures and standard lab procedures must be adapted or replaced altogether. This chapter describes methods to create cardiac spheroids consisting of human iPSC-derived cardiomyocytes and cardiac fibroblasts and how to measure contractility or calcium signals using quantitative video analysis and confocal microscopy. Emphasis is on the particular challenges that 3D cultures pose and on affordable methods that do not require specialized equipment.

Inhibition of TGF-β pathway reverts extracellular matrix remodeling in T. cruzi-infected cardiac spheroids

Chagasic cardiomyopathy (CC) is the main manifestation of Chagas Disease (CD). CC is a progressive dysfunctional illness, in which transforming growth factor beta (TGF-β) plays a central role in fibrogenesis and hypertrophy. In the present study, we tested in a three-dimensional (3D) model of cardiac cells culture (named cardiac spheroids), capable of mimicking the aspects of fibrosis and hypertrophy observed in CC, the role of TGF-β pathway inhibition in restoring extracellular matrix (ECM) balance disrupted by T. cruzi infection. Treatment of T. cruzi-infected cardiac spheroids with SB 431542, a selective inhibitor of TGF-β type I receptor, resulted in a reduction in the size of spheroids, which was accompanied by a decrease in parasite load and in fibronectin expression. The inhibition of TGF-β pathway also promoted an increase in the activity of matrix metalloproteinase (MMP)-2 and a decrease in tissue inhibitor of matrix metalloproteinase (TIMP)-1 expression, which may be one of the mechanisms regulating extracellular matrix remodeling. Therefore, our study provides new insights into the molecular mechanisms by which inhibition of TGF-β signaling reverts fibrosis and hypertrophy generated by T. cruzi during CC and also highlights the use of cardiac spheroids as a valuable tool for the study of fibrogenesis and anti-fibrotic compounds.

Cardiac spheroids as promising in vitro models to study the human heart microenvironment

Three-dimensional in vitro cell systems are a promising alternative to animals to study cardiac biology and disease. We have generated three-dimensional in vitro models of the human heart ("cardiac spheroids", CSs) by co-culturing human primary or iPSC-derived cardiomyocytes, endothelial cells and fibroblasts at ratios approximating those present in vivo. The cellular organisation, extracellular matrix and microvascular network mimic human heart tissue. These spheroids have been employed to investigate the dose-limiting cardiotoxicity of the common anti-cancer drug doxorubicin. Viability/cytotoxicity assays indicate dose-dependent cytotoxic effects, which are inhibited by the nitric oxide synthase (NOS) inhibitor L-NIO, and genetic inhibition of endothelial NOS, implicating peroxynitrous acid as a key damaging agent. These data indicate that CSs mimic important features of human heart morphology, biochemistry and pharmacology in vitro, offering a promising alternative to animals and standard cell cultures with regard to mechanistic insights and prediction of toxic effects in human heart tissue.

Inspiration from heart development: Biomimetic development of functional human cardiac organoids

Recent progress in human organoids has provided 3D tissue systems to model human development, diseases, as well as develop cell delivery systems for regenerative therapies. While direct differentiation of human embryoid bodies holds great promise for cardiac organoid production, intramyocardial cell organization during heart development provides biological foundation to fabricate human cardiac organoids with defined cell types. Inspired by the intramyocardial organization events in coronary vasculogenesis, where a diverse, yet defined, mixture of cardiac cell types self-organizes into functional myocardium in the absence of blood flow, we have developed a defined method to produce scaffold-free human cardiac organoids that structurally and functionally resembled the lumenized vascular network in the developing myocardium, supported hiPSC-CM development and possessed fundamental cardiac tissue-level functions. In particular, this development-driven strategy offers a robust, tunable system to examine the contributions of individual cell types, matrix materials and additional factors for developmental insight, biomimetic matrix composition to advance biomaterial design, tissue/organ-level drug screening, and cell therapy for heart repair.

Naturally Engineered Maturation of Cardiomyocytes

Ischemic heart disease remains one of the most prominent causes of mortalities worldwide with heart transplantation being the gold-standard treatment option. However, due to the major limitations associated with heart transplants, such as an inadequate supply and heart rejection, there remains a significant clinical need for a viable cardiac regenerative therapy to restore native myocardial function. Over the course of the previous several decades, researchers have made prominent advances in the field of cardiac regeneration with the creation of in vitro human pluripotent stem cell-derived cardiomyocyte tissue engineered constructs. However, these engineered constructs exhibit a functionally immature, disorganized, fetal-like phenotype that is not equivalent physiologically to native adult cardiac tissue. Due to this major limitation, many recent studies have investigated approaches to improve pluripotent stem cell-derived cardiomyocyte maturation to close this large functionality gap between engineered and native cardiac tissue. This review integrates the natural developmental mechanisms of cardiomyocyte structural and functional maturation. The variety of ways researchers have attempted to improve cardiomyocyte maturation in vitro by mimicking natural development, known as natural engineering, is readily discussed. The main focus of this review involves the synergistic role of electrical and mechanical stimulation, extracellular matrix interactions, and non-cardiomyocyte interactions in facilitating cardiomyocyte maturation. Overall, even with these current natural engineering approaches, pluripotent stem cell-derived cardiomyocytes within three-dimensional engineered heart tissue still remain mostly within the early to late fetal stages of cardiomyocyte maturity. Therefore, although the end goal is to achieve adult phenotypic maturity, more emphasis must be placed on elucidating how the in vivo fetal microenvironment drives cardiomyocyte maturation. This information can then be utilized to develop natural engineering approaches that can emulate this fetal microenvironment and thus make prominent progress in pluripotent stem cell-derived maturity toward a more clinically relevant model for cardiac regeneration.

Maturation of human pluripotent stem cell derived cardiomyocytes is improved in cardiovascular construct

In order to translate preclinical data into the clinical studies, relevant in vitro models with structure and key functional properties similar to native human tissue should be used. In vitro cardiac models with vascular structures mimic the highly vascularized myocardium and provide interactions between endothelial cells, stromal cells and cardiomyocytes. Currently, human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have been shown to present immature morphology and fetal-like electrophysiological properties that may limit their use as physiological test platform. The aim of this study was to develop multicellular in vitro cardiovascular construct modeling human heart tissue. In the cardiovascular construct, hPSC-CMs were cultured with a vascular-like network formed by human foreskin fibroblasts and human umbilical vein endothelial cells that served as a platform in the construct. Cardiomyocyte orientation, maturation, electrophysiological properties and drug responses of the cardiovascular construct were characterized and compared to CM monoculture. hPSC-CMs in cardiovascular construct showed elongated morphology and aligned with the vascular-like network. Electrophysiological properties and calcium metabolism of hPSC-CMs as well as response to E-4031 and adrenaline demonstrated normal physiological behavior. Increased expression of cardiac structural proteins and ion channels in cardiovascular construct compared to CM monoculture were detected. In conclusion, vascular-like network supports the structural and functional maturation of hPSC-CMs. Our results suggest that cardiovascular construct presents more mature in vitro cardiac model compared to CM monoculture and could therefore serve as an advanced test system for cardiac safety and efficacy assessment as well as a model system for biomedical research.

Cardiac Regenerative Medicine: The Potential of a New Generation of Stem Cells

Cardiac stem cell therapy holds great potential to prompt myocardial regeneration in patients with ischemic heart disease. The selection of the most suitable cell type is pivotal for its successful application. Various cell types, including crude bone marrow mononuclear cells, skeletal myoblast, and hematopoietic and endothelial progenitors, have already advanced into the clinical arena based on promising results from different experimental and preclinical studies. However, most of these so-called first-generation cell types have failed to fully emulate the promising preclinical data in clinical trials, resulting in heterogeneous outcomes and a critical lack of translation. Therefore, different next-generation cell types are currently under investigation for the treatment of the diseased myocardium. This review article provides an overview of current stem cell therapy concepts, including the application of cardiac stem (CSCs) and progenitor cells (CPCs) and lineage commitment via guided cardiopoiesis from multipotent cells such as mesenchymal stem cells (MSCs) or pluripotent cells such as embryonic and induced pluripotent stem cells. Furthermore, it introduces new strategies combining complementary cell types, such as MSCs and CSCs/CPCs, which can yield synergistic effects to boost cardiac regeneration.

Rebuilding the Damaged Heart: Mesenchymal Stem Cells, Cell-Based Therapy, and Engineered Heart Tissue

Mesenchymal stem cells (MSCs) are broadly distributed cells that retain postnatal capacity for self-renewal and multilineage differentiation. MSCs evade immune detection, secrete an array of anti-inflammatory and anti-fibrotic mediators, and very importantly activate resident precursors. These properties form the basis for the strategy of clinical application of cell-based therapeutics for inflammatory and fibrotic conditions. In cardiovascular medicine, administration of autologous or allogeneic MSCs in patients with ischemic and nonischemic cardiomyopathy holds significant promise. Numerous preclinical studies of ischemic and nonischemic cardiomyopathy employing MSC-based therapy have demonstrated that the properties of reducing fibrosis, stimulating angiogenesis, and cardiomyogenesis have led to improvements in the structure and function of remodeled ventricles. Further attempts have been made to augment MSCs' effects through genetic modification and cell preconditioning. Progression of MSC therapy to early clinical trials has supported their role in improving cardiac structure and function, functional capacity, and patient quality of life. Emerging data have supported larger clinical trials that have been either completed or are currently underway. Mechanistically, MSC therapy is thought to benefit the heart by stimulating innate anti-fibrotic and regenerative responses. The mechanisms of action involve paracrine signaling, cell-cell interactions, and fusion with resident cells. Trans-differentiation of MSCs to bona fide cardiomyocytes and coronary vessels is also thought to occur, although at a nonphysiological level. Recently, MSC-based tissue engineering for cardiovascular disease has been examined with quite encouraging results. This review discusses MSCs from their basic biological characteristics to their role as a promising therapeutic strategy for clinical cardiovascular disease.

Microtissues in Cardiovascular Medicine: Regenerative Potential Based on a 3D Microenvironment

More people die annually from cardiovascular diseases than from any other cause. In particular, patients who suffer from myocardial infarction may be affected by ongoing adverse remodeling processes of the heart that may ultimately lead to heart failure. The introduction of stem and progenitor cell-based applications has raised substantial hope for reversing these processes and inducing cardiac regeneration. However, current stem cell therapies using single-cell suspensions have failed to demonstrate long-lasting efficacy due to the overall low retention rate after cell delivery to the myocardium. To overcome this obstacle, the concept of 3D cell culture techniques has been proposed to enhance therapeutic efficacy and cell engraftment based on the simulation of an in vivo-like microenvironment. Of great interest is the use of so-called microtissues or spheroids, which have evolved from their traditional role as in vitro models to their novel role as therapeutic agents. This review will provide an overview of the therapeutic potential of microtissues by addressing primarily cardiovascular regeneration. It will accentuate their advantages compared to other regenerative approaches and summarize the methods for generating clinically applicable microtissues. In addition, this review will illustrate the unique properties of the microenvironment within microtissues that makes them a promising next-generation therapeutic approach.

Stem cell death and survival in heart regeneration and repair

Cardiovascular diseases are major causes of mortality and morbidity. Cardiomyocyte apoptosis disrupts cardiac function and leads to cardiac decompensation and terminal heart failure. Delineating the regulatory signaling pathways that orchestrate cell survival in the heart has significant therapeutic implications. Cardiac tissue has limited capacity to regenerate and repair. Stem cell therapy is a successful approach for repairing and regenerating ischemic cardiac tissue; however, transplanted cells display very high death percentage, a problem that affects success of tissue regeneration. Stem cells display multipotency or pluripotency and undergo self-renewal, however these events are negatively influenced by upregulation of cell death machinery that induces the significant decrease in survival and differentiation signals upon cardiovascular injury. While efforts to identify cell types and molecular pathways that promote cardiac tissue regeneration have been productive, studies that focus on blocking the extensive cell death after transplantation are limited. The control of cell death includes multiple networks rather than one crucial pathway, which underlies the challenge of identifying the interaction between various cellular and biochemical components. This review is aimed at exploiting the molecular mechanisms by which stem cells resist death signals to develop into mature and healthy cardiac cells. Specifically, we focus on a number of factors that control death and survival of stem cells upon transplantation and ultimately affect cardiac regeneration. We also discuss potential survival enhancing strategies and how they could be meaningful in the design of targeted therapies that improve cardiac function.

Development of a three-dimensional pre-vascularized scaffold-free contractile cardiac patch for treating heart disease

BACKGROUND

The aim of our study was to develop a completely scaffold-free, viable, contractile cardiac tissue capable of being grafted into the damaged native heart.

METHODS

Our technology is based on the fundamental characteristics of the self-assembling nature of cells. We created contractile cardiac spheroids by plating a mixture of rat neonatal ventricular cardiomyocytes, human dermal fibroblasts, and human coronary microartery endothelial cells in ultralow attachment plates. First, the optimal cell ratios for the 3 cell sources were determined. Next, approximately 1 × 10(4) optimal spheroids were fused into a patch-like construct, and the morphologic characteristics and mechanical functions of these patches were evaluated. Finally, the cardiac patches were grafted into the hearts of F344 nude rats, and histologic studies were performed after transplantation.

RESULTS

Synchronous beating of the cardiac patch was confirmed electrophysiologically and mechanically. A micronetwork of endothelial cells was also demonstrated in the construct, and the histologic study performed 5 days after transplantation showed the grafts to be viable, with functioning microvascular structures inside the graft tissue.

CONCLUSIONS

We consider the application of our scaffold-free 3-dimensional tissue engineering technology to cardiac regeneration therapy is feasible and expect that this technology will become a promising tool for the treatment of end-stage heart failure.

Cell therapy, 3D culture systems and tissue engineering for cardiac regeneration

Ischemic Heart Disease (IHD) still represents the "Number One Killer" worldwide accounting for the death of numerous patients. However the capacity for self-regeneration of the adult heart is very limited and the loss of cardiomyocytes in the infarcted heart leads to continuous adverse cardiac-remodeling which often leads to heart-failure (HF). The concept of regenerative medicine comprising cell-based therapies, bio-engineering technologies and hybrid solutions has been proposed as a promising next-generation approach to address IHD and HF. Numerous strategies are under investigation evaluating the potential of regenerative medicine on the failing myocardium including classical cell-therapy concepts, three-dimensional culture techniques and tissue-engineering approaches. While most of these regenerative strategies have shown great potential in experimental studies, the translation into a clinical setting has either been limited or too rapid leaving many key questions unanswered. This review summarizes the current state-of-the-art, important challenges and future research directions as to regenerative approaches addressing IHD and resulting HF.

3D in vitro tissue models and their potential for drug screening

INTRODUCTION

The development of one standard, simplified in vitro three-dimensional tissue model suitable to biological and pathological investigation and drug-discovery may not yet be feasible, but standardized models for individual tissues or organs are a possibility. Tissue bioengineering, while concerned with finding methods of restoring functionality in disease, is developing technology that can be miniaturized for high throughput screening (HTS) of putative drugs. Through collaboration between biologists, physicists and engineers, cell-based assays are expanding into the realm of tissue analysis. Accordingly, three-dimensional (3D) micro-organoid systems will play an increasing role in drug testing and therapeutics over the next decade. Nevertheless, important hurdles remain before these models are fully developed for HTS.

AREAS COVERED

We highlight advances in the field of tissue bioengineering aimed at enhancing the success of drug candidates through pre-clinical optimization. We discuss models that are most amenable to high throughput screening with emphasis on detection platforms and data modeling.

EXPERT OPINION

Modeling 3D tissues to mimic in-vivo architecture remains a major challenge. As technology advances to provide novel methods of HTS analysis, so do potential pitfalls associated with such models and methods. We remain hopeful that integration of biofabrication with HTS will significantly reduce attrition rates in drug development.

Formation of Cell Aggregates Using Microfabricated Hydrogel Chambers for Assembly into Larger Tissues

This paper presents a fabrication process for cell aggregates with controlled shapes that can be used as building units for constructing relatively large tissue models. Microfabricated hydrogel-based chambers with non-adhesive surface characteristics were prepared via a micromolding process. Alginate was used as the hydrogel matrix, which facilitated the efficient formation of aggregates from cells retained inside the microchamber. We employed several types of toroidal and lattice-shaped hydrogel microchambers with different geometries. We examined the effect of cell type on the aggregate formation process using NIH-3T3, C2C12, and HepG2 cells and clearly observed that aggregation behavior is highly dependent on cell type. In addition, we tried to construct 2-layered capillarylike tissues by stacking heterotypic toroidal cell aggregates, which mimic blood vessels. The presented cell aggregate-based tissue fabrication process could become a versatile approach for preparing complex and scaffold-free 3D tissue models.

Transcatheter based electromechanical mapping guided intramyocardial transplantation and in vivo tracking of human stem cell based three dimensional microtissues in the porcine heart

Stem cells have been repeatedly suggested for cardiac regeneration after myocardial infarction (MI). However, the low retention rate of single cell suspensions limits the efficacy of current therapy concepts so far. Taking advantage of three dimensional (3D) cellular self-assembly prior to transplantation may be beneficial to overcome these limitations. In this pilot study we investigate the principal feasibility of intramyocardial delivery of in-vitro generated stem cell-based 3D microtissues (3D-MTs) in a porcine model. 3D-MTs were generated from iron-oxide (MPIO) labeled human adipose-tissue derived mesenchymal stem cells (ATMSCs) using a modified hanging-drop method. Nine pigs (33 ± 2 kg) comprising seven healthy ones and two with chronic MI in the left ventricle (LV) anterior wall were included. The pigs underwent intramyocardial transplantation of 16 × 10(3) 3D-MTs (1250 cells/MT; accounting for 2 × 10(7) single ATMSCs) into the anterior wall of the healthy pigs (n = 7)/the MI border zone of the infarcted (n = 2) of the LV using a 3D NOGA electromechanical mapping guided, transcatheter based approach. Clinical follow-up (FU) was performed for up to five weeks and in-vivo cell-tracking was performed using serial magnet resonance imaging (MRI). Thereafter, the hearts were harvested and assessed by PCR and immunohistochemistry. Intramyocardial transplantation of human ATMSC based 3D-MTs was successful in eight animals (88.8%) while one pig (without MI) died during the electromechanical mapping due to sudden cardiac-arrest. During FU, no arrhythmogenic, embolic or neurological events occurred in the treated pigs. Serial MRI confirmed the intramyocardial presence of the 3D-MTs by detection of the intracellular iron-oxide MPIOs during FU. Intramyocardial retention of 3D-MTs was confirmed by PCR analysis and was further verified on histology and immunohistochemical analysis. The 3D-MTs appeared to be viable, integrated and showed an intact micro architecture. We demonstrate the principal feasibility and safety of intramyocardial transplantation of in-vitro generated stem cell-based 3D-MTs. Multimodal cell-tracking strategies comprising advanced imaging and in-vitro tools allow for in-vivo monitoring and post-mortem analysis of transplanted 3D-MTs. The concept of 3D cellular self-assembly represents a promising application format as a next generation technology for cell-based myocardial regeneration.

Mesenchymal stem cells for cardiovascular regeneration

Despite recent studies suggesting that the heart has instrinsic mechanisms of self-regeneration following myocardial infarction, it cannot regenerate itself to an optimal level. Mesenchymal stem cells (MSCs) are currently being investigated for regeneration of mesenchyme-derived tissues, such as bone, cartilage and tendon. In vitro evidence suggests that MSCs can also differentiate into cardiomyogenic and vasculogenic lineages, offering another cell source for cardiovascular regeneration. In vivo, MSCs may contribute to the re-growth and protection of vasculature and cardiomyocytes, mediated by paracrine actions, and/or persist within the myocardium in a differentiated state; although proof of cardiomyocytic phenotype and functional integration remains elusive. Herein, we review the evidence of MSCs as a cell source for cardiovascular regeneration, as well as their limitations that may prevent them from being effectively used in the clinic.

Scaffold-free culture of mesenchymal stem cell spheroids in suspension preserves multilineage potential

While traditional cell culture methods have relied on growing cells as monolayers, three-dimensional (3D) culture systems can provide a convenient in vitro model for the study of complex cell-cell and cell-matrix interactions in the absence of exogenous substrates and may benefit the development of regenerative medicine strategies. In this study, mesenchymal stem cell (MSC) spheroids, or "mesenspheres", of different sizes, were formed using a forced aggregation technique and maintained in suspension culture for extended periods of time thereafter. Cell proliferation and differentiation potential within mesenspheres and dissociated cells retrieved from spheroids were compared to conventional adherent monolayer cultures. Mesenspheres maintained in growth medium exhibited no evidence of cell necrosis or differentiation, while mesenspheres in differentiation media exhibited differentiation similar to conventional 2D culture methods based on histological markers of osteogenic and adipogenic commitment. Furthermore, when plated onto tissue culture plates, cells that had been cultured within mesenspheres in growth medium recovered morphology typical of cells cultured continuously in adherent monolayers and retained their capacity for multi-lineage differentiation potential. In fact, more robust matrix mineralization and lipid vacuole content were evident in recovered MSCs when compared to monolayers, suggesting enhanced differentiation by cells cultured as 3D spheroids. Thus, this study demonstrates the development of a 3D culture system for mesenchymal stem cells that may circumvent limitations associated with conventional monolayer cultures and enhance the differentiation potential of multipotent cells.

Mesenchymal stem cells for cardiac cell therapy

Despite refinements of medical and surgical therapies, heart failure remains a fatal disease. Myocardial infarction is the most common cause of heart failure, and only palliative measures are available to relieve symptoms and prolong the patient's life span. Because mammalian cardiomyocytes irreversibly exit the cell cycle at about the time of birth, the heart has traditionally been considered to lack any regenerative capacity. This paradigm, however, is currently shifting, and the cellular composition of the myocardium is being targeted by various regeneration strategies. Adult progenitor and stem cell treatment of diseased human myocardium has been carried out for more than 10 years (Menasche et al., 2001; Stamm et al., 2003), and it has become clear that, in humans, the regenerative capacity of hematopoietic stem cells and endothelial progenitor cells, despite potent proangiogenic effects, is limited (Stamm et al., 2009). More recently, mesenchymal stem cells (MSCs) and related cell types are being evaluated in preclinical models of heart disease as well as in clinical trials (see Published Clinical Trials, below). MSCs have the capacity to self-renew and to differentiate into lineages that normally originate from the embryonic mesenchyme (connective tissues, blood vessels, blood-related organs) (Caplan, 1991; Prockop, 1997; Pittenger et al., 1999). The current definition of MSCs includes plastic adherence in cell culture, specific surface antigen expression (CD105(+)/CD90(+)/CD73(+), CD34(-)/CD45(-)/CD11b(-) or CD14(-)/CD19(-) or CD79α(-)/HLA-DR1(-)), and multilineage in vitro differentiation potential (osteogenic, chondrogenic, and adipogenic) (Dominici et al., 2006 ). If those criteria are not met completely, the term "mesenchymal stromal cells" should be used for marrow-derived adherent cells, or other terms for MSC-like cells of different origin. For the purpose of this review, MSCs and related cells are discussed in general, and cell type-specific properties are indicated when appropriate. We first summarize the preclinical data on MSCs in models of heart disease, and then appraise the clinical experience with MSCs for cardiac cell therapy.

Interplay of cysteinyl leukotrienes and TGF-β in the activation of hepatic stellate cells from Schistosoma mansoni granulomas

Hepatic stellate cells (HSCs) have a critical role in liver physiology, and in the pathogenesis of liver inflammation and fibrosis. Here, we investigated the interplay between leukotrienes (LT) and TGF-β in the activation mechanisms of HSCs from schistosomal granulomas (GR-HSCs). First, we demonstrated that GR-HSCs express 5-lipoxygenase (5-LO), as detected by immunolocalization in whole cells and confirmed in cell lysates through western blotting and by mRNA expression through RT-PCR. Moreover, mRNA expression of 5-LO activating protein (FLAP) and LTC(4)-synthase was also documented, indicating that GR-HSCs have the molecular machinery required for LT synthesis. Morphological analysis of osmium and Oil-Red O-stained HSC revealed large numbers of small lipid droplets (also known as lipid bodies). We observed co-localization of lipid droplet protein marker (ADRP) and 5-LO by immunofluorescence microscopy. We demonstrated that GR-HSCs were able to spontaneously release cysteinyl-LTs (CysLTs), but not LTB(4,) into culture supernatants. CysLT production was highly enhanced after TGF-β-stimulation. Moreover, the 5-LO inhibitor zileuton and 5-LO gene deletion were able to inhibit the TGF-β-stimulated proliferation of GR-HSCs, suggesting a role for LTs in HSC activation. Here, we extend the immunoregulatory function of HSC by demonstrating that HSC from liver granulomas of schistosome-infected mouse are able to release Cys-LTs in a TGF-β-regulated manner, potentially impacting pathogenesis and liver fibrosis in schistosomiasis.

Osteoblasts and bone marrow mesenchymal stromal cells control hematopoietic stem cell migration and proliferation in 3D in vitro model

Background

Migration, proliferation, and differentiation of hematopoietic stem cells (HSCs) are dependent upon a complex three-dimensional (3D) bone marrow microenvironment. Although osteoblasts control the HSC pool, the subendosteal niche is complex and its cellular composition and the role of each cell population in HSC fate have not been established. In vivo models are complex and involve subtle species-specific differences, while bidimensional cultures do not reflect the 3D tissue organization. The aim of this study was to investigate in vitro the role of human bone marrow–derived mesenchymal stromal cells (BMSC) and active osteoblasts in control of migration, lodgment, and proliferation of HSCs.

Methodology/Principal Findings

A complex mixed multicellular spheroid in vitro model was developed with human BMSC, undifferentiated or induced for one week into osteoblasts. A clear limit between the two stromal cells was established, and deposition of extracellular matrix proteins fibronectin, collagens I and IV, laminin, and osteopontin was similar to the observed in vivo. Noninduced BMSC cultured as spheroid expressed higher levels of mRNA for the chemokine CXCL12, and the growth factors Wnt5a and Kit ligand. Cord blood and bone marrow CD34⁺ cells moved in and out the spheroids, and some lodged at the interface of the two stromal cells. Myeloid colony-forming cells were maintained after seven days of coculture with mixed spheroids, and the frequency of cycling CD34⁺ cells was decreased.

Conclusions/Significance

Undifferentiated and one-week osteo-induced BMSC self-assembled in a 3D spheroid and formed a microenvironment that is informative for hematopoietic progenitor cells, allowing their lodgment and controlling their proliferation.