Acellular matrices derived from differentiating embryonic stem cells

Engineering cell-derived extracellular matrix for peripheral nerve regeneration

Extracellular matrices (ECMs) play a key role in nerve repair and are recognized as the natural source of biomaterials. In parallel to extensively studied tissue-derived ECMs (ts-ECMs), cell-derived ECMs (cd-ECMs) also have the capability to partially recapitulate the complicated regenerative microenvironment of native nerve tissues. Notably, cd-ECMs can avoid the shortcomings of ts-ECMs. Cd-ECMs can be prepared by culturing various cells or even autologous cells in vitro under pathogen-free conditions. And mild decellularization can achieve efficient removal of immunogenic components in cd-ECMs. Moreover, cd-ECMs are more readily customizable to achieve the desired functional properties. These advantages have garnered significant attention for the potential of cd-ECMs in neuroregenerative medicine. As promising biomaterials, cd-ECMs bring new hope for the effective treatment of peripheral nerve injuries. Herein, this review comprehensively examines current knowledge about the functional characteristics of cd-ECMs and their mechanisms of interaction with cells in nerve regeneration, with a particular focus on the preparation, engineering optimization, and scalability of cd-ECMs. The applications of cd-ECMs from distinct cell sources reported in peripheral nerve tissue engineering are highlighted and summarized. Furthermore, current limitations that should be addressed and outlooks related to clinical translation are put forward as well.

Cell-Derived Matrix: Production, Decellularization, and Application of Wound Repair

Chronic nonhealing wounds significantly reduce patients' quality of life and are a major burden on healthcare systems. Over the past few decades, tissue engineering materials have emerged as a viable option for wound healing, with cell-derived extracellular matrix (CDM) showing remarkable results. The CDM's compatibility and resemblance to the natural tissue microenvironment confer distinct advantages to tissue-engineered scaffolds in wound repair. This review summarizes the current processes for CDM preparation, various cell decellularization protocols, and common characterization methods. Furthermore, it discusses the applications of CDM in wound healing, including skin defect and wound repair, angiogenesis, and engineered vessels, and offers perspectives on future developments.

Cytosine arabinoside exposure induced cytotoxic effects and neural tube defects in mice and embryo stem cells

Cytosine arabinoside (Ara-C) is one of the most widely used chemotherapeutic agents for hematological malignancies. The residues of Ara-C have been detected in wastewater and river water with increased usage and discharge. As the ability to cross the placenta and the teratogenicity at low ng/L levels, the toxic effects on pregnant women and infants have been concerned. The toxicity of Ara-C exposure on early embryonic neurodevelopment has not been fully elucidated. In this study, pregnant C57BL/6 mice were injected with different doses of Ara-C on Gestation day (GD) 7.5 and assessed on GD11.5 and GD13.5 to explore the neural developmental effects of Ara-C. HE staining, immunofluorescence, western blot, EdU assay, and flow cytometry were utilized to determine the toxic effects of Ara-C in vivo and in vitro. Our results showed that Ara-C (15-22.5 mg/kg body weight) induced the occurrence of neural tube defects (NTDs). The expression of PH3 was markedly reduced in embryos with Ara-C-induced NTDs, compared to the control group (P < 0.05). In contrast, cell apoptosis was markedly increased. Increased expression levels of GFAP and decreased Nestin were observed in the embryonic brain tissues in Ara-C induced NTDs. The level of β-catenin was also decreased on both GD11.5 and GD13.5. These results were confirmed in vitro using mouse Sv129 embryonic stem cells (mESC). Ara-C at a dose comparable to the environment level (0.05 nM) had cytotoxicity. Impaired Wnt/β-catenin signaling pathway is involved in Ara-C exposure induced imbalance between cell proliferation, apoptosis, and differentiation, which might contribute to Ara-C-induced occurrence of NTDs. Our data indicated the environmental concentration of Ara-C had cytotoxicity and that maternal exposure to Ara-C induced NTDs. These results might provide more information to understand the environmental toxic impact of Ara-C on neurodevelopment.

Prochondrogenic effect of decellularized extracellular matrix secreted from human induced pluripotent stem cell-derived chondrocytes

Cartilage is mainly composed of chondrocytes and the extracellular matrix (ECM), which exchange important biochemical and biomechanical signals necessary for differentiation and homeostasis. Human articular cartilage has a low ability for regeneration because it lacks blood vessels, nerves, and lymphatic vessels. Currently, cell therapeutics, including stem cells, provide a promising strategy for cartilage regeneration and treatment; however, there are various hurdles to overcome, such as immune rejection and teratoma formation. In this study, we assessed the applicability of the stem cell-derived chondrocyte ECM for cartilage regeneration. Human induced pluripotent stem cell (hiPSC)-derived chondrocytes (iChondrocytes) were differentiated, and decellularized ECM (dECM) was successfully isolated from cultured chondrocytes. Isolated dECM enhanced in vitro chondrogenesis of iPSCs when recellularized. Implanted dECM also restored osteochondral defects in a rat osteoarthritis model. A possible association with the glycogen synthase kinase-3 beta (GSK3β) pathway demonstrated the fate-determining importance of dECM in regulating cell differentiation. Collectively, we suggested the prochondrogenic effect of hiPSC-derived cartilage-like dECM and offered a promising approach as a non-cellular therapeutic for articular cartilage reconstruction without cell transplantation. STATEMENT OF SIGNIFICANCE: Human articular cartilage has low ability for regeneration and cell culture-based therapeutics could aid cartilage regeneration. Yet, the applicability of human induced pluripotent stem cell-derived chondrocyte (iChondrocyte) extracellular matrix (ECM) has not been elucidated. Therefore, we first differentiated iChondrocytes and isolated the secreted ECM by decellularization. Recellularization was performed to confirm the pro-chondrogenic effect of the decellularized ECM (dECM). In addition, we confirmed the possibility of cartilage repair by transplanting the dECM into the cartilage defect in osteochondral defect rat knee joint. We believe that our proof-of-concept study will serve as a basis for investigating the potential of dECM obtained from iPSC-derived differentiated cells as a non-cellular resource for tissue regeneration and other future applications.

Decellularized extracellular matrix mediates tissue construction and regeneration

Contributing to organ formation and tissue regeneration, extracellular matrix (ECM) constituents provide tissue with three-dimensional (3D) structural integrity and cellular-function regulation. Containing the crucial traits of the cellular microenvironment, ECM substitutes mediate cell-matrix interactions to prompt stem-cell proliferation and differentiation for 3D organoid construction in vitro or tissue regeneration in vivo. However, these ECMs are often applied generically and have yet to be extensively developed for specific cell types in 3D cultures. Cultured cells also produce rich ECM, particularly stromal cells. Cellular ECM improves 3D culture development in vitro and tissue remodeling during wound healing after implantation into the host as well. Gaining better insight into ECM derived from either tissue or cells that regulate 3D tissue reconstruction or organ regeneration helps us to select, produce, and implant the most suitable ECM and thus promote 3D organoid culture and tissue remodeling for in vivo regeneration. Overall, the decellularization methodologies and tissue/cell-derived ECM as scaffolds or cellular-growth supplements used in cell propagation and differentiation for 3D tissue culture in vitro are discussed. Moreover, current preclinical applications by which ECM components modulate the wound-healing process are reviewed.

Bioactive Decellularized Extracellular Matrix Derived from 3D Stem Cell Spheroids under Macromolecular Crowding Serves as a Scaffold for Tissue Engineering

Scaffolds for tissue engineering aim to mimic the native extracellular matrix (ECM) that provides physical support and biochemical signals to modulate multiple cell behaviors. However, the majority of currently used biomaterials are oversimplified and therefore fail to provide a niche required for the stimulation of tissue regeneration. In the present study, 3D decellularized ECM (dECM) scaffolds derived from mesenchymal stem cell (MSC) spheroids and with intricate matrix composition are developed. Specifically, application of macromolecular crowding (MMC) to MSC spheroid cultures facilitate ECM assembly in a 3D configuration, resulting in the accumulation of ECM and associated bioactive components. Decellularized 3D dECM constructs produced under MMC are able to adequately preserve the microarchitecture of structural ECM components and are characterized by higher retention of growth factors. This results in a stronger proangiogenic bioactivity as compared to constructs produced under uncrowded conditions. These dECM scaffolds can be homogenously populated by endothelial cells, which direct the macroassembly of the structures into larger cell-carrying constructs. Application of empty scaffolds enhances intrinsic revascularization in vivo, indicating that the 3D dECM scaffolds represent optimal proangiogenic bioactive blocks for the construction of larger engineered tissue constructs.

Bearing My Heart: The Role of Extracellular Matrix on Cardiac Development, Homeostasis, and Injury Response

The extracellular matrix (ECM) is an essential component of the heart that imparts fundamental cellular processes during organ development and homeostasis. Most cardiovascular diseases involve severe remodeling of the ECM, culminating in the formation of fibrotic tissue that is deleterious to organ function. Treatment schemes effective at managing fibrosis and promoting physiological ECM repair are not yet in reach. Of note, the composition of the cardiac ECM changes significantly in a short period after birth, concurrent with the loss of the regenerative capacity of the heart. This highlights the importance of understanding ECM composition and function headed for the development of more efficient therapies. In this review, we explore the impact of ECM alterations, throughout heart ontogeny and disease, on cardiac cells and debate available approaches to deeper insights on cell–ECM interactions, toward the design of new regenerative therapies.

Secretome Analysis Performed During in vitro Cardiac Differentiation: Discovering the Cardiac Microenvironment

Human pluripotent stem cells are an important tool for the study of developmental processes, such as cardiomyogenic differentiation. Despite the advances made in this field, the molecular and cellular signals involved in the commitment of embryonic stem cells to the cardiac phenotype are still under investigation. Therefore, this study focuses on identifying the extracellular signals involved in in vitro cardiac differentiation of human embryonic stem cells. Using a three-dimensional cardiomyogenic differentiation protocol, the conditioned medium and the extracellular matrix (ECM) of embryoid body cultures were collected and characterized at four specific time points. Mass spectrometry (MS) and antibody array analysis of the secretome identified a number of secreted proteins related to signaling pathways, such as Wnt and TGFβ, as well as many ECM proteins. When comparing the proteins identified at selected time points, our data pointed out protein interactions and biological process related to cardiac differentiation. Interestingly, the great changes in secretome profile occurred during the cardiac progenitor specification. The secretome results were also compared with our previous RNAseq data, indicating that the secreted proteins undergo some level of gene regulation. During cardiac commitment it was observed an increase in complexity of the ECM, and some proteins as IGFBP7, FN1, HSPG2, as well as other members of the basal lamina could be highlighted. Thus, these findings contribute valuable information about essential microenvironmental signals working on cardiomyogenic differentiation that may be used in future strategies for cardiac differentiation, cardiomyocyte maturation, and in advances for future acellular therapies.

In Vitro Biocompatibility of Decellularized Cultured Plant Cell-Derived Matrices

There has been a recent increase in exploring the use of decellularized plant tissue as a novel "green" material for biomedical applications. As part of this effort, we have developed a technique to decellularize cultured plant cells (tobacco BY-2 cells and rice cells) and tissue (tobacco hairy roots) that uses deoxyribonuclease I (DNase I)). As a proof of concept, all cultured plant cells and tissue were transformed to express recombinant enhanced green fluorescent protein (EGFP) to show that the proteins of interest could be retained within the matrices. Decellularization of lyophilized tobacco BY-2 cells with DNase for 30 min depleted the DNA content from 1503 ± 459 to 31 ± 5 ng/sample. The decellularization procedure resulted in approximately 36% total protein retention (154 ± 60 vs 424 ± 70 μg/sample) and 33% EGFP retention. Similar results for DNA removal and protein retention were observed with the rice cells and tobacco hairy root matrices. When exposed to decellularized BY-2 cell-derived matrices, monolayer cultures of human foreskin fibroblasts (hFFs) maintained or increased metabolic activity, which is an indicator of cell viability. Furthermore, hFFs were able to attach, spread, and proliferate when cultured with the decellularized BY-2 cell-derived matrices in an aggregate model. Overall, these studies demonstrate that cultured plant cells and tissue can be effectively decellularized with DNase I with substantial protein retention. The resulting material has a positive impact on hFF metabolic activity and could be employed to create a three-dimensional environment for cell growth. These results thus show the promise of using naturally derived cellulose matrices from cultured plant cells and tissues for biomedical applications.

Materials for Neural Differentiation, Trans-Differentiation, and Modeling of Neurological Disease

Neuron regeneration from pluripotent stem cells (PSCs) differentiation or somatic cells trans-differentiation is a promising approach for cell replacement in neurodegenerative diseases and provides a powerful tool for investigating neural development, modeling neurological diseases, and uncovering the mechanisms that underlie diseases. Advancing the materials that are applied in neural differentiation and trans-differentiation promotes the safety, efficiency, and efficacy of neuron regeneration. In the neural differentiation process, matrix materials, either natural or synthetic, not only provide a structural and biochemical support for the monolayer or three-dimensional (3D) cultured cells but also assist in cell adhesion and cell-to-cell communication. They play important roles in directing the differentiation of PSCs into neural cells and modeling neurological diseases. For the trans-differentiation of neural cells, several materials have been used to make the conversion feasible for future therapy. Here, the most current applications of materials for neural differentiation for PSCs, neuronal trans-differentiation, and neurological disease modeling is summarized and discussed.

Crosslinking of extracellular matrix scaffolds derived from pluripotent stem cell aggregates modulates neural differentiation

At various developmental stages, pluripotent stem cells (PSCs) and their progeny secrete a large amount of extracellular matrices (ECMs) which could interact with regulatory growth factors to modulate stem cell lineage commitment. ECMs derived from PSC can be used as unique scaffolds that provide broad signaling capacities to mediate cellular differentiation. However, the rapid degradation of ECMs can impact their applications as the scaffolds for in vitro cell expansion and in vivo transplantation. To address this issue, this study investigated the effects of crosslinking on the ECMs derived from embryonic stem cells (ESCs) and the regulatory capacity of the crosslinked ECMs on the proliferation and differentiation of reseeded ESC-derived neural progenitor cells (NPCs). To create different biological cues, undifferentiated aggregates, spontaneous embryoid bodies, and ESC-derived NPC aggregates were decellularized. The derived ECMs were crosslinked using genipin or glutaraldehyde to enhance the scaffold stability. ESC-derived NPC aggregates were reseeded on different ECM scaffolds and differential cellular compositions of neural progenitors, neurons, and glial cells were observed. The results indicate that ESC-derived ECM scaffolds affect neural differentiation through intrinsic biological cues and biophysical properties. These scaffolds have potential for in vitro cell culture and in vivo tissue regeneration study.

STATEMENT OF SIGNIFICANCE

Dynamic interactions of acellular extracellular matrices and stem cells are critical for lineage-specific commitment and tissue regeneration. Understanding the synergistic effects of biochemical, biological, and biophysical properties of acellular matrices would facilitate scaffold design and the functional regulation of stem cells. The present study assessed the influence of crosslinked embryonic stem cell-derived extracellular matrix on neural differentiation and revealed the synergistic interactions of various matrix properties. While embryonic stem cell-derived matrices have been assessed as tissue engineering scaffolds, the impact of crosslinking on the embryonic stem cell-derived matrices to modulate neural differentiation has not been studied. The results from this study provide novel knowledge on the interface of embryonic stem cell-derived extracellular matrix and neural aggregates. The findings reported in this manuscript are significant for stem cell differentiation toward the applications in stem cell-based drug screening, disease modeling, and cell therapies.

Decellularized Extracellular Matrix as an In Vitro Model to Study the Comprehensive Roles of the ECM in Stem Cell Differentiation

Stem cells are a promising cell source for regenerative medicine. Stem cell differentiation must be regulated for applications in regenerative medicine. Stem cells are surrounded by extracellular matrix (ECM) in vivo. The ECM is composed of many types of proteins and glycosaminoglycans that assemble into a complex structure. The assembly of ECM molecules influences stem cell differentiation through orchestrated intracellular signaling activated by many ECM molecules. Therefore, it is important to understand the comprehensive role of the ECM in stem cell differentiation as well as the functions of the individual ECM molecules. Decellularized ECM is a useful in vitro model for studying the comprehensive roles of ECM because it retains a native-like structure and composition. Decellularized ECM can be obtained from in vivo tissue ECM or ECM fabricated by cells cultured in vitro. It is important to select the correct decellularized ECM because each type has different properties. In this review, tissue-derived and cell-derived decellularized ECMs are compared as in vitro ECM models to examine the comprehensive roles of the ECM in stem cell differentiation. We also summarize recent studies using decellularized ECM to determine the comprehensive roles of the ECM in stem cell differentiation.

Osteogenic embryoid body-derived material induces bone formation in vivo

The progressive loss of endogenous regenerative capacity that accompanies mammalian aging has been attributed at least in part to alterations in the extracellular matrix (ECM) composition of adult tissues. Thus, creation of a more regenerative microenvironment, analogous to embryonic morphogenesis, may be achieved via pluripotent embryonic stem cell (ESC) differentiation and derivation of devitalized materials as an alternative to decellularized adult tissues, such as demineralized bone matrix (DBM). Transplantation of devitalized ESC materials represents a novel approach to promote functional tissue regeneration and reduce the inherent batch-to-batch variability of allograft-derived materials. In this study, the osteoinductivity of embryoid body-derived material (EBM) was compared to DBM in a standard in vivo ectopic osteoinduction assay in nude mice. EBM derived from EBs differentiated for 10 days with osteogenic media (+β-glycerophosphate) exhibited similar osteoinductivity to active DBM (osteoinduction score = 2.50 ± 0.27 vs. 2.75 ± 0.16) based on histological scoring, and exceeded inactive DBM (1.13 ± 0.13, p < 0.005). Moreover, EBM stimulated formation of new bone, ossicles, and marrow spaces, similar to active DBM. The potent osteoinductivity of EBM demonstrates that morphogenic factors expressed by ESCs undergoing osteogenic differentiation yield a novel devitalized material capable of stimulating de novo bone formation in vivo.

Decellularization technology in CNS tissue repair

Decellularization methodologies have been successfully used in a variety of tissue engineering and regenerative technologies and methods of decellularization have been developed for target tissues and organs of interest. The technology to promote regeneration and functional recovery in the CNS, including brain and spinal cord, has, however, made slow progress mainly because the intrinsic regenerative potential of the CNS is regarded as low. To date, currently available therapies have been unable to provide significant functional recovery and successful therapies, which could provide functional restoration to the injured brain and spinal cord are controversial. In this review, the authors provide a critical analysis, comparing the advantages and limitations of the major decellularization methods and considering the effects of these methods upon the biologic scaffold material. The authors also review studies that supplement decellularized grafts with exogenous factors, such as stem cells and growth factors, to both promote and enhance regeneration through decellularized allografts.

Cell-derived matrices for tissue engineering and regenerative medicine applications

The development and application of decellularized extracellular matrices (ECM) has grown rapidly in the fields of cell biology, tissue engineering and regenerative medicine in recent years. Similar to decellularized tissues and whole organs, cell-derived matrices (CDMs) represent bioactive, biocompatible materials consisting of a complex assembly of fibrillar proteins, matrix macromolecules and associated growth factors that often recapitulate, at least to some extent, the composition and organization of native ECM microenvironments. The unique ability to engineer CDMs de novo based on cell source and culture methods makes them an attractive alternative to conventional allogeneic and xenogeneic tissue-derived matrices that are currently harvested from cadaveric sources, suffer from inherent heterogeneity, and have limited ability for customization. Although CDMs have been investigated for a number of biomedical applications, including adhesive cell culture substrates, synthetic scaffold coatings, and tissue engineered products, such as heart valves and vascular grafts, the state of the field is still at a relatively nascent stage of development. In this review, we provide an overview of the various applications of CDM and discuss successes to date, current limitations and future directions.

Tissue engineering and regenerative repair in wound healing

Wound healing is a highly evolved defense mechanism against infection and further injury. It is a complex process involving multiple cell types and biological pathways. Mammalian adult cutaneous wound healing is mediated by a fibroproliferative response leading to scar formation. In contrast, early to mid-gestational fetal cutaneous wound healing is more akin to regeneration and occurs without scar formation. This early observation has led to extensive research seeking to unlock the mechanism underlying fetal scarless regenerative repair. Building upon recent advances in biomaterials and stem cell applications, tissue engineering approaches are working towards a recapitulation of this phenomenon. In this review, we describe the elements that distinguish fetal scarless and adult scarring wound healing, and discuss current trends in tissue engineering aimed at achieving scarless tissue regeneration.

Engineering three-dimensional stem cell morphogenesis for the development of tissue models and scalable regenerative therapeutics

The physiochemical stem cell microenvironment regulates the delicate balance between self-renewal and differentiation. The three-dimensional assembly of stem cells facilitates cellular interactions that promote morphogenesis, analogous to the multicellular, heterotypic tissue organization that accompanies embryogenesis. Therefore, expansion and differentiation of stem cells as multicellular aggregates provides a controlled platform for studying the biological and engineering principles underlying spatiotemporal morphogenesis and tissue patterning. Moreover, three-dimensional stem cell cultures are amenable to translational screening applications and therapies, which underscores the broad utility of scalable suspension cultures across laboratory and clinical scales. In this review, we discuss stem cell morphogenesis in the context of fundamental biophysical principles, including the three-dimensional modulation of adhesions, mechanics, and molecular transport and highlight the opportunities to employ stem cell spheroids for tissue modeling, bioprocessing, and regenerative therapies.

Extracellular matrices decellularized from embryonic stem cells maintained their structure and signaling specificity

Embryonic stem cells (ESCs) emerge as a promising tool for tissue engineering and regenerative medicines due to their extensive self-renewal ability and the capacity to give rise to cells from all three-germ layers. ESCs also secrete a large amount of endogenous extracellular matrices (ECMs), which play an important role in regulating ESC self-renewal, lineage commitment, and tissue morphogenesis. ECMs derived from ESCs have a broader signaling capacity compared to somatic ECMs and are predicted to have a lower risk of tumor formation associated with ESCs. In this study, ECMs from undifferentiated ESC monolayers, undifferentiated aggregates, or differentiated embryoid bodies at different developmental stages and lineage specifications were decellularized and their capacities to direct ESC proliferation and differentiation were characterized. The results demonstrate that the ESC-derived ECMs were able to influence ESC proliferation and differentiation by direct interactions with the cells and by influencing the signaling functions of the regulatory macromolecules such as retinoic acid. Such matrices have the potential to present regulatory signals to direct lineage- and development-specific cellular responses for in vitro applications or cell delivery.

Extracellular matrix aggregates from differentiating embryoid bodies as a scaffold to support ESC proliferation and differentiation

Embryonic stem cells (ESCs) have emerged as potential cell sources for tissue engineering and regeneration owing to its virtually unlimited replicative capacity and the potential to differentiate into a variety of cell types. Current differentiation strategies primarily involve various growth factor/inducer/repressor concoctions with less emphasis on the substrate. Developing biomaterials to promote stem cell proliferation and differentiation could aid in the realization of this goal. Extracellular matrix (ECM) components are important physiological regulators, and can provide cues to direct ESC expansion and differentiation. ECM undergoes constant remodeling with surrounding cells to accommodate specific developmental event. In this study, using ESC derived aggregates called embryoid bodies (EB) as a model, we characterized the biological nature of ECM in EB after exposure to different treatments: spontaneously differentiated and retinoic acid treated (denoted as SPT and RA, respectively). Next, we extracted this treatment-specific ECM by detergent decellularization methods (Triton X-100, DOC and SDS are compared). The resulting EB ECM scaffolds were seeded with undifferentiated ESCs using a novel cell seeding strategy, and the behavior of ESCs was studied. Our results showed that the optimized protocol efficiently removes cells while retaining crucial ECM and biochemical components. Decellularized ECM from SPT EB gave rise to a more favorable microenvironment for promoting ESC attachment, proliferation, and early differentiation, compared to native EB and decellularized ECM from RA EB. These findings suggest that various treatment conditions allow the formulation of unique ESC-ECM derived scaffolds to enhance ESC bioactivities, including proliferation and differentiation for tissue regeneration applications.

Emerging strategies for spatiotemporal control of stem cell fate and morphogenesis

Stem cell differentiation is regulated by the complex interplay of multiple parameters, including adhesive intercellular interactions, cytoskeletal and extracellular matrix remodeling, and gradients of agonists and antagonists that individually and collectively vary as a function of spatial locale and temporal stages of development. Current approaches to direct stem cell differentiation focus on systematically understanding the relative influences of microenvironmental perturbations and simultaneously engineering platforms aimed at recapitulating physicochemical aspects of tissue morphogenesis. This review focuses on novel approaches to control the spatiotemporal dynamics of stem cell signaling and morphogenic remodeling to direct the differentiation of stem cells and develop functional tissues for in vitro screening and regenerative medicine technologies.

Gene expression signatures of extracellular matrix and growth factors during embryonic stem cell differentiation

Pluripotent stem cells are uniquely capable of differentiating into somatic cell derivatives of all three germ lineages, therefore holding tremendous promise for developmental biology studies and regenerative medicine therapies. Although temporal patterns of phenotypic gene expression have been relatively well characterized during the course of differentiation, coincident patterns of endogenous extracellular matrix (ECM) and growth factor expression that accompany pluripotent stem cell differentiation remain much less well-defined. Thus, the objective of this study was to examine the global dynamic profiles of ECM and growth factor genes associated with early stages of pluripotent mouse embryonic stem cell (ESC) differentiation. Gene expression analysis of ECM and growth factors by ESCs differentiating as embryoid bodies for up to 14 days was assessed using PCR arrays (172 unique genes total), and the results were examined using a variety of data mining methods. As expected, decreases in the expression of genes regulating pluripotent stem cell fate preceded subsequent increases in morphogen expression associated with differentiation. Pathway analysis generated solely from ECM and growth factor gene expression highlighted morphogenic cell processes within the embryoid bodies, such as cell growth, migration, and intercellular signaling, that are required for primitive tissue and organ developmental events. In addition, systems analysis of ECM and growth factor gene expression alone identified intracellular molecules and signaling pathways involved in the progression of pluripotent stem cell differentiation that were not contained within the array data set. Overall, these studies represent a novel framework to dissect the complex, dynamic nature of the extracellular biochemical milieu of stem cell microenvironments that regulate pluripotent cell fate decisions and morphogenesis.

Stem cell paracrine actions and tissue regeneration

Stem cells have emerged as a key element of regenerative medicine therapies due to their inherent ability to differentiate into a variety of cell phenotypes, thereby providing numerous potential cell therapies to treat an array of degenerative diseases and traumatic injuries. A recent paradigm shift has emerged suggesting that the beneficial effects of stem cells may not be restricted to cell restoration alone, but also due to their transient paracrine actions. Stem cells can secrete potent combinations of trophic factors that modulate the molecular composition of the environment to evoke responses from resident cells. Based on this new insight, current research directions include efforts to elucidate, augment and harness stem cell paracrine mechanisms for tissue regeneration. This article discusses the existing studies on stem/progenitor cell trophic factor production, implications for tissue regeneration and cancer therapies, and development of novel strategies to use stem cell paracrine delivery for regenerative medicine.

Controlling stem cell fate with material design

Advances in our understanding of stem cell interactions with their environment are leading to the development of new materials-based approaches to control stem cell behavior toward cellular culture and tissue regeneration applications. Materials can provide cues based on chemistry, mechanics, structure, and molecule delivery that control stem cell fate decisions and matrix formation. These approaches are helping to advance clinical translation of a range of stem cell types through better expansion techniques and scaffolding for use in tissue engineering approaches for the regeneration of many tissues. With this in mind, this progress report covers basic concepts and recent advances in the use of materials for manipulating stem cells.

Engineering microenvironments for embryonic stem cell differentiation to cardiomyocytes

Embryonic stem cells and induced pluripotent stem cells have the potential to be a renewable source of cardiomyocytes for use in myocardial cell replacement strategies. Although progress has been made towards differentiating stem cells to specific cell lineages, the efficiency is often poor and the number of cells generated is not suitable for therapeutic usage. Recent studies demonstrated that controlling the stem cell microenvironment can influence differentiation. Components of the extracellular matrix are important physiological regulators and can provide mechanical cues, direct differentiation and improve cell engraftment into damaged tissue. Bioreactors are used to control the microenvironment and produce large numbers of desired cells. This article describes recent methods to achieve cardiomyocyte differentiation by engineering the stem cell microenvironment. Successful translation of stem cell research to therapeutic applications will need to address large-scale cardiomyocyte differentiation and purification, assessment of cardiac function and synchronization, and safety concerns.

Acellularization of embryoid bodies via physical disruption methods

Embryonic stem cells (ESCs) are capable of differentiating into all somatic cell types and have therefore attracted significant interest for use in tissue repair and regeneration therapies. Transplanted ESCs can not only integrate into compromised tissues, but can also stimulate endogenous regeneration via secreted factors. In this study, several acellularization protocols were applied to spheroids of differentiating ESCs, termed embryoid bodies (EBs), to develop a potential route to deliver ESC-derived molecules, independent of cells, to damaged tissues. The objective of this study was to physically disrupt EBs via lyophilization or freeze-thaw cycling, and in combination with DNase treatment, determine the efficacy of acellularization based upon cell viability, DNA removal, and protein retention. Mechanical disruption and DNase treatment of EBs efficiently inhibited viability and removed DNA while retaining protein content to produce an acellular EB matrix. The EB-derived acellular matrices permitted attachment and repopulation of the constructs by 3T3 fibroblasts in vitro. Overall, these studies demonstrate that effective mechanical means to acellularize EBs may be used in order to further elucidate the composition and function of embryonic extracellular matrices and serve as novel naturally-derived scaffolds for tissue repair and regeneration.