Developing defined substrates for stem cell culture and differentiation

Human Placenta Decellularized Extracellular Matrix Hydrogel Promotes the Generation of Human Spinal Cord Organoids with Dorsoventral Organization from Human Induced Pluripotent Stem Cells

Spinal cord organoids are of significant value in the research of spinal cord-related diseases by simulating disease states, thereby facilitating the development of novel therapies. However, the complexity of spinal cord structure and physiological functions, along with the lack of human-derived inducing components, presents challenges in the in vitro construction of human spinal cord organoids. Here, we introduce a novel human decellularized placenta-derived extracellular matrix hydrogel (DPECMH) and, combined with a new induction protocol, successfully construct human spinal cord organoids. The human placenta-sourced decellularized extracellular matrix (dECM), verified through hematoxylin and eosin staining, DNA quantification, and immunofluorescence staining, retained essential ECM components such as elastin, fibronectin, type I collagen, laminin, and so forth. The temperature-sensitive hydrogel made from human placenta dECM demonstrated good biocompatibility and promoted the differentiation of human induced pluripotent stem cell (hiPSCs)-derived spinal cord organoids into neurons. It displayed enhanced expression of laminar markers in comparison to Matrigel and showed higher expression of laminar markers compared to Matrigel, accelerating the maturation process of spinal cord organoids and demonstrating its potential as an organoid culture substrate. DPECMH has the potential to replace Matrigel as the standard additive for human spinal cord organoids, thus advancing the development of spinal cord organoid culture protocols and their application in the in vitro modeling of spinal cord-related diseases.

Progress in the generation of spinal cord organoids over the past decade and future perspectives

Spinal cord organoids are three-dimensional tissues derived from stem cells that recapitulate the primary morphological and functional characteristics of the spinal cord in vivo. As emerging bioengineering methods have led to the optimization of cell culture protocols, spinal cord organoids technology has made remarkable advancements in the past decade. Our literature search found that current spinal cord organoids do not only dynamically simulate neural tube formation but also exhibit diverse cytoarchitecture along the dorsal-ventral and rostral-caudal axes. Moreover, fused organoids that integrate motor neurons and other regionally specific organoids exhibit intricate neural circuits that allows for functional assessment. These qualities make spinal cord organoids valuable tools for disease modeling, drug screening, and tissue regeneration. By utilizing this emergent technology, researchers have made significant progress in investigating the pathogenesis and potential therapeutic targets of spinal cord diseases. However, at present, spinal cord organoid technology remains in its infancy and has not been widely applied in translational medicine. Establishment of the next generation of spinal cord organoids will depend on good manufacturing practice standards and needs to focus on diverse cell phenotypes and electrophysiological functionality evaluation.

Cell volume expansion and local contractility drive collective invasion of the basement membrane in breast cancer

Breast cancer becomes invasive when carcinoma cells invade through the basement membrane (BM)-a nanoporous layer of matrix that physically separates the primary tumour from the stroma. Single cells can invade through nanoporous three-dimensional matrices due to protease-mediated degradation or force-mediated widening of pores via invadopodial protrusions. However, how multiple cells collectively invade through the physiological BM, as they do during breast cancer progression, remains unclear. Here we developed a three-dimensional in vitro model of collective invasion of the BM during breast cancer. We show that cells utilize both proteases and forces-but not invadopodia-to breach the BM. Forces are generated from a combination of global cell volume expansion, which stretches the BM, and local contractile forces that act in the plane of the BM to breach it, allowing invasion. These results uncover a mechanism by which cells collectively interact to overcome a critical barrier to metastasis.

Corneal Epithelial Development and the Role of Induced Pluripotent Stem Cells for Regeneration

Severe corneal disorders due to infective aetiologies, trauma, chemical injuries, and chronic cicatricial inflammations, are among vision-threatening pathologies leading to permanent corneal scarring. The whole cornea or lamellar corneal transplantation is often used as a last resort to restore vision. However, limited autologous tissue sources and potential adverse post-allotransplantation sequalae urge the need for more robust and strategic alternatives. Contemporary management using cultivated corneal epithelial transplantation has paved the way for utilizing stem cells as a regenerative potential. Humaninduced pluripotent stem cells (hiPSCs) can generate ectodermal progenitors and potentially be used for ocular surface regeneration. This review summarizes the process of corneal morphogenesis and the signaling pathways underlying the development of corneal epithelium, which is key to translating the maturation and differentiation process of hiPSCs in vitro. The current state of knowledge and methodology for driving efficient corneal epithelial cell differentiation from pluripotent stem cells are highlighted.

Patient-derived organoid culture in epithelial ovarian cancers-Techniques, applications, and future perspectives

Epithelial ovarian cancer (EOC) is a heterogeneous disease composed of different cell types with different molecular aberrations. Traditional cell lines and mice models cannot recapitulate the human tumor biology and tumor microenvironment (TME). Patient-derived organoids (PDOs) are freshly derived from patients' tissues and are then cultured with extracellular matrix and conditioned medium. The high concordance of epigenetic, genomic, and proteomic landscapes between the parental tumors and PDOs suggests that PDOs can provide more reliable results in studying cancer biology, allowing high throughput drug screening, and identifying their associated signaling pathways and resistance mechanisms. However, despite having a heterogeneity of cells in PDOs, some cells in TME will be lost during the culture process. Next-generation organoids have been developed to circumvent some of the limitations. Genetically engineered organoids involving targeted gene editing can facilitate the understanding of tumorigenesis and drug response. Co-culture systems where PDOs are cultured with different cell components like immune cells can allow research using immunotherapy which is otherwise impossible in conventional cell lines. In this review, the limitations of the traditional in vitro and in vivo assays, the use of PDOs, the challenges including some tips and tricks of PDO generation in EOC, and the future perspectives, will be discussed.

Animal-derived products in science and current alternatives

More than fifty years after the 3Rs definition and despite the continuous implementation of regulatory measures, animals continue to be widely used in basic research. Their use comprises not only in vivo experiments with animal models, but also the production of a variety of supplements and products of animal origin for cell and tissue culture, cell-based assays, and therapeutics. The animal-derived products most used in basic research are fetal bovine serum (FBS), extracellular matrix proteins such as Matrigel™, and antibodies. However, their production raises several ethical issues regarding animal welfare. Additionally, their biological origin is associated with a high risk of contamination, resulting, frequently, in poor scientific data for clinical translation. These issues support the search for new animal-free products able to replace FBS, Matrigel™, and antibodies in basic research. In addition, in silico methodologies play an important role in the reduction of animal use in research by refining the data previously to in vitro and in vivo experiments. In this review, we depicted the current available animal-free alternatives in in vitro research.

Cell-binding peptides on the material surface guide stem cell fate of adhesion, proliferation and differentiation

Human cells, especially stem cells, need to communicate and interact with extracellular matrix (ECM) proteins, which not only serve as structural components but also guide and support cell fate and properties such as cell adhesion, proliferation, survival and differentiation. The binding of the cells with ECM proteins or ECM-derived peptides via cell adhesion receptors such as integrins activates several signaling pathways that determine the cell fate, morphological change, proliferation and differentiation. The development of synthetic ECM protein-derived peptides that mimic the biological and biochemical functions of natural ECM proteins will benefit academic and clinical application. Peptides derived from or inspired by specific ECM proteins can act as agonists of each ECM protein receptor. Given that most ECM proteins function in cell adhesion via integrin receptors, many peptides have been developed that bind to specific integrin receptors. In this review, we discuss the peptide sequence, immobilization design, reaction method, and functions of several ECM protein-derived peptides. Various peptide sequences derived from mainly ECM proteins, which are used for coating or grafting on dishes, scaffolds, hydrogels, implants or nanofibers, have been developed to improve the adhesion, proliferation or differentiation of stem cells and to culture differentiated cells. This review article will help to inform the optimal choice of ECM protein-derived peptides for the development of scaffolds, implants, hydrogels, nanofibers and 2D cell culture dishes to regulate the proliferation and direct the differentiation of stem cells into specific lineages.

The basement membrane in epidermal polarity, stemness, and regeneration

The epidermis is a specialized epithelium that constitutes the outermost layer of the skin, and it provides a protective barrier against environmental assaults. Primarily consisting of multilayered keratinocytes, the epidermis is continuously renewed by proliferation of stem cells and the differentiation of their progeny, which undergo terminal differentiation as they leave the basal layer and move upward toward the surface, where they die and slough off. Basal keratinocytes rest on a basement membrane at the dermal-epidermal junction that is composed of specific extracellular matrix proteins organized into interactive and mechanically supportive networks. Firm attachment of basal keratinocytes, and their dynamic regulation via focal adhesions and hemidesmosomes, is essential for maintaining major skin processes, such as self-renewal, barrier function, and resistance to physical and chemical stresses. The adhesive integrin receptors expressed by epidermal cells serve structural, signaling, and mechanosensory roles that are critical for epidermal cell anchorage and tissue homeostasis. More specifically, the basement membrane components play key roles in preserving the stem cell pool, and establishing cell polarity cues enabling asymmetric cell divisions, which result in the transition from a proliferative basal cell layer to suprabasal cells committed to terminal differentiation. Finally, through a well-regulated sequence of synthesis and remodeling, the components of the dermal-epidermal junction play an essential role in regeneration of the epidermis during skin healing. Here too, they provide biological and mechanical signals that are essential to the restoration of barrier function.

Long-term in vivo survival of 3D-bioprinted human lipoaspirate-derived adipose tissue: proteomic signature and cellular content

Three-dimensional (3D)-bioprinted lipoaspirate-derived adipose tissue (LAT) is a potential alternative to lipo-injection for correcting soft-tissue defects. This study investigated the long-term in vivo survival of 3D-bioprinted LAT and its proteomic signature and cellular composition. We performed proteomic and multicolour flow cytometric analyses on the lipoaspirate and 3D-bioprinted LAT constructs were transplanted into nude mice, followed by explantation after up to 150 days. LAT contained adipose-tissue-derived stem cells (ASCs), pericytes, endothelial progenitor cells (EPCs) and endothelial cells. Proteomic analysis identified 6,067 proteins, including pericyte markers, adipokines, ASC secretome proteins, proangiogenic proteins and proteins involved in adipocyte differentiation and developmental morphogenic signalling, as well as proteins not previously described in human subcutaneous fat. 3D-bioprinted LAT survived for 150 days in vivo with preservation of the construct shape and size. Furthermore, we identified human blood vessels after 30 and 150 days in vivo, indicating angiogenesis from capillaries. These results showed that LAT has a favourable proteomic signature, contains ASCs, EPCs and blood vessels that survive 3D bioprinting and can potentially facilitate angiogenesis and successful autologous fat grafting in soft-tissue reconstruction.

Neural progenitor cell-derived extracellular matrix as a new platform for neural differentiation of human induced pluripotent stem cells

The culture microenvironment has been demonstrated to regulate stem cell fate and to be a crucial aspect for quality-controlled stem cell maintenance and differentiation to a specific lineage. In this context, extracellular matrix (ECM) proteins are particularly important to mediate the interactions between the cells and the culture substrate. Human induced pluripotent stem cells (hiPSCs) are usually cultured as anchorage-dependent cells and require adhesion to an ECM substrate to support their survival and proliferation in vitro. Matrigel, a common substrate for hiPSC culture is a complex and undefined mixture of ECM proteins which are expensive and not well suited to clinical application. Decellularized cell-derived ECM has been shown to be a promising alternative to the common protein coatings used in stem cell culture. However, very few studies have used this approach as a niche for neural differentiation of hiPSCs. Here, we developed a new stem cell culture system based on decellularized cell-derived ECM from neural progenitor cells (NPCs) for expansion and neural differentiation of hiPSCs, as an alternative to Matrigel and poly-l-ornithine/laminin-coated well plates. Interestingly, hiPSCs were able to grow and maintain their pluripotency when cultured on decellularized ECM from NPCs (NPC ECM). Furthermore, NPC ECM enhanced the neural differentiation of hiPSCs compared to poly-l-ornithine/laminin-coated wells, which are used in most neural differentiation protocols, presenting a statistically significant enhancement of neural gene expression markers, such as βIII-Tubulin and MAP2. Taken together, our results demonstrate that NPC ECM provides a functional microenvironment, mimicking the neural niche, which may have interesting future applications for the development of new strategies in neural stem cell research.

The Impact of Graphene Oxide on Polycaprolactone PCL Surfaces: Antimicrobial Activity and Osteogenic Differentiation of Mesenchymal Stem Cell

In dentistry, bone regeneration requires osteoinductive biomaterial with antibacterial properties. Polycaprolactone (PCL) may be combined with different nanofillers including reduced graphene oxide (rGO). Here, the amount of rGO filler was defined to obtain a biocompatible and antibacterial PCL-based surface supporting the adhesion and differentiation of human mesenchymal stem cells (MSCs). Compounds carrying three different percentages of rGO were tested. Among all, the 5% rGO-PCL compound is the most bacteriostatic against Gram-positive bacteria. All scaffolds are biocompatible. MSCs adhere and proliferate on all scaffolds; however, 5% rGO-PCL surface supports the growth of cells and implements the expression of extracellular matrix components necessary to anchor the cells to the surface itself. Moreover, the 5% rGO-PCL surface has superior osteoinductive properties confirmed by the improved alkaline phosphatase activity, mineral matrix deposition, and osteogenic markers expression. These results suggest that 5% rGO-PCL has useful properties for bone tissue engineering purposes.

Everything You Always Wanted to Know About Organoid-Based Models (and Never Dared to Ask)

Homeostatic functions of a living tissue, such as the gastrointestinal tract, rely on highly sophisticated and finely tuned cell-to-cell interactions. These crosstalks evolve and continuously are refined as the tissue develops and give rise to specialized cells performing general and tissue-specific functions. To study these systems, stem cell-based in vitro models, often called organoids, and non-stem cell-based primary cell aggregates (called spheroids) appeared just over a decade ago. These models still are evolving and gaining complexity, making them the state-of-the-art models for studying cellular crosstalk in the gastrointestinal tract, and to investigate digestive pathologies, such as inflammatory bowel disease, colorectal cancer, and liver diseases. However, the use of organoid- or spheroid-based models to recapitulate in vitro the highly complex structure of in vivo tissue remains challenging, and mainly restricted to expert developmental cell biologists. Here, we condense the founding knowledge and key literature information that scientists adopting the organoid technology for the first time need to consider when using these models for novel biological questions. We also include information that current organoid/spheroid users could use to add to increase the complexity to their existing models. We highlight the current and prospective evolution of these models through bridging stem cell biology with biomaterial and scaffold engineering research areas. Linking these complementary fields will increase the in vitro mimicry of in vivo tissue, and potentially lead to more successful translational biomedical applications. Deepening our understanding of the nature and dynamic fine-tuning of intercellular crosstalks will enable identifying novel signaling targets for new or repurposed therapeutics used in many multifactorial diseases.

Effect of niche components on masseter satellite cell differentiation on fibrin coatings

In skeletal muscles, niche factors stimulate satellite cells to activate and induce muscle regeneration after injury. In vitro, matrigel is widely used for myoblast differentiation, however, is unsuitable for clinical applications. Therefore, this study aimed to analyze attachment and differentiation of satellite cells into myotubes on fibrin coatings with selected niche components. The attachment of satellite cells to fibrin alone and fibrin with niche components (laminin, collagen‐IV, laminin‐entactin complex [LEC]) were compared to matrigel. Only on matrigel and fibrin with LEC, Pax7‐positive cells attached well. Then, LEC was selected to analyze proliferation, differentiation, and fusion indices. The proliferation index at day 1 on fibrin‐LEC (22.5%, SD 9.1%) was similar to that on matrigel (30.8% [SD 11.1%]). The differentiation index on fibrin‐LEC (28.7% [SD 6.1%] at day 5 and 32.8% [SD 6.7%] at day 7) was similar to that on matrigel (40.1% [5.1%] at day 5 and 27.1% [SD 4.3%] at day 7). On fibrin‐LEC, the fusion index at day 9 (26.9% [SD 11.5%]) was similar to that on matrigel (25.5% [SD 4.7%]). Our results showed that the addition of LEC enhances the formation of myotubes on fibrin. Fibrin with LEC might be suitable to enhance muscle regeneration after surgery such as cleft palate repair and other muscle defects.

Hydrogels derived from decellularized liver tissue support the growth and differentiation of cholangiocyte organoids

Human cholangiocyte organoids are promising for regenerative medicine applications, such as repair of damaged bile ducts. However, organoids are typically cultured in mouse tumor-derived basement membrane extracts (BME), which is poorly defined, highly variable and limits the direct clinical applications of organoids in patients. Extracellular matrix (ECM)-derived hydrogels prepared from decellularized human or porcine livers are attractive alternative culture substrates. Here, the culture and expansion of human cholangiocyte organoids in liver ECM(LECM)-derived hydrogels is described. These hydrogels support proliferation of cholangiocyte organoids and maintain the cholangiocyte-like phenotype. The use of LECM hydrogels does not significantly alter the expression of selected genes or proteins, such as the cholangiocyte marker cytokeratin-7, and no species-specific effect is found between human or porcine LECM hydrogels. Proliferation rates of organoids cultured in LECM hydrogels are lower, but the differentiation capacity of the cholangiocyte organoids towards hepatocyte-like cells is not altered by the presence of tissue-specific ECM components. Moreover, human LECM extracts support the expansion of ICO in a dynamic culture set up without the need for laborious static culture of organoids in hydrogel domes. Liver ECM hydrogels can successfully replace tumor-derived BME and can potentially unlock the full clinical potential of human cholangiocyte organoids.

Design by Nature: Emerging Applications of Native Liver Extracellular Matrix for Cholangiocyte Organoid-Based Regenerative Medicine

Organoid technology holds great promise for regenerative medicine. Recent studies show feasibility for bile duct tissue repair in humans by successfully transplanting cholangiocyte organoids in liver grafts during perfusion. Large-scale expansion of cholangiocytes is essential for extending these regenerative medicine applications. Human cholangiocyte organoids have a high and stable proliferation capacity, making them an attractive source of cholangiocytes. Commercially available basement membrane extract (BME) is used to expand the organoids. BME allows the cells to self-organize into 3D structures and stimulates cell proliferation. However, the use of BME is limiting the clinical applications of the organoids. There is a need for alternative tissue-specific and clinically relevant culture substrates capable of supporting organoid proliferation. Hydrogels prepared from decellularized and solubilized native livers are an attractive alternative for BME. These hydrogels can be used for the culture and expansion of cholangiocyte organoids in a clinically relevant manner. Moreover, the liver-derived hydrogels retain tissue-specific aspects of the extracellular microenvironment. They are composed of a complex mixture of bioactive and biodegradable extracellular matrix (ECM) components and can support the growth of various hepatobiliary cells. In this review, we provide an overview of the clinical potential of native liver ECM-based hydrogels for applications with human cholangiocyte organoids. We discuss the current limitations of BME for the clinical applications of organoids and how native ECM hydrogels can potentially overcome these problems in an effort to unlock the full regenerative clinical potential of the organoids.

Towards organoid culture without Matrigel

Organoids-cellular aggregates derived from stem or progenitor cells that recapitulate organ function in miniature-are of growing interest in developmental biology and medicine. Organoids have been developed for organs and tissues such as the liver, gut, brain, and pancreas; they are used as organ surrogates to study a wide range of questions in basic and developmental biology, genetic disorders, and therapies. However, many organoids reported to date have been cultured in Matrigel, which is prepared from the secretion of Engelbreth-Holm-Swarm mouse sarcoma cells; Matrigel is complex and poorly defined. This complexity makes it difficult to elucidate Matrigel-specific factors governing organoid development. In this review, we discuss promising Matrigel-free methods for the generation and maintenance of organoids that use decellularized extracellular matrix (ECM), synthetic hydrogels, or gel-forming recombinant proteins.

A Substrate-Mimicking Basement Membrane Drives the Organization of Human Mesenchymal Stromal Cells and Endothelial Cells Into Perivascular Niche-Like Structures

Extracellular matrix-derived products (e.g. Matrigel) are widely used for in vitro cell cultures both as two-dimensional (2D) substrates and as three-dimensional (3D) encapsulation gels because of their ability to control cell phenotypes through biospecific cues. However, batch-to-batch variations, poor stability, cumbersome handling, and the relatively high costs strictly limit their use. Recently, a new substrate known as PhenoDrive-Y has been used as 2D coating of tissue culture plastic showing to direct the bone marrow mesenchymal stromal cells (MSCs) toward the formation of 3D spheroids. When organized into 3D spheroids, the MSCs expressed levels of pluripotency markers and of paracrine angiogenic activity higher than those of the MSCs adhering as fibroblast-like colonies on tissue culture plastic. The formation of the spheroids was attributed to the properties of this biomaterial that resemble the main features of the basement membrane by mimicking the mesh structure of collagen IV and by presenting the cells with orderly spaced laminin bioligands. In this study, PhenoDrive-Y was compared to Matrigel for its ability to drive the formation of perivascular stem cell niche-like structures in 2D co-culture conditions of human endothelial cells and adult bone marrow MSCs. Morphological analyses demonstrated that, when compared to Matrigel, PhenoDrive-Y led endothelial cells to sprout into a more consolidated tubular network and that the MSCs nestled as compact spheroids above the anastomotic areas of this network resemble more closely the histological features of the perivascular stem cell niche. A study of the expressions of relevant markers led to the identification of the pathways linking the PhenoDrive-Y biomimicking properties to the acquired histological features, demonstrating the enhanced levels of stemness, renewal potential, predisposition to migration, and paracrine activities of the MSCs.

Poly(vinyl alcohol-co-itaconic acid) hydrogels grafted with several designed peptides for human pluripotent stem cell culture and differentiation into cardiomyocytes

We developed poly(vinyl alcohol-co-itaconic acid) (PV) hydrogels grafted with laminin-derived peptides that had different joint segments and several specific designs, including dual chain motifs. PV hydrogels grafted with a peptide derived from laminin-β4 (PMQKMRGDVFSP) containing a joint segment, dual chain motif and cationic amino acid insertion could attach human pluripotent stem (hPS) cells and promoted high expansion folds in long-term culture (over 10 passages) with low differentiation rates, whereas hPS cells attached poorly on PV hydrogels grafted with laminin-α5 peptides that had joint segments with and without a cationic amino acid or on PV hydrogels grafted with laminin-β4 peptides containing the joint segment only. The inclusion of a cationic amino acid in the laminin-β4 peptide was critical for hPS cell attachment on PV hydrogels, which contributed to the zeta potential shifting to higher values (3-4 mV enhancement). The novel peptide segment-grafted PV hydrogels developed in this study supported hPS cell proliferation, which induced better hPS cell expansion than recombinant vitronectin-coated dishes (gold standard of hPS cell culture dishes) in xeno-free culture conditions. After long-term culture on peptide-grafted hydrogels, hPS cells could be induced to differentiate into specific lineages of cells, such as cardiomyocytes, with high efficiency.

Characterization of the Skeletal Muscle Secretome Reveals a Role for Extracellular Vesicles and IL1α/IL1β in Restricting Fibro/Adipogenic Progenitor Adipogenesis

Repeated mechanical stress causes injuries in the adult skeletal muscle that need to be repaired. Although muscle regeneration is a highly efficient process, it fails in some pathological conditions, compromising tissue functionality. This may be caused by aberrant cell-cell communication, resulting in the deposition of fibrotic and adipose infiltrates. Here, we investigate in vivo changes in the profile of skeletal muscle secretome during the regeneration process to suggest new targetable regulatory circuits whose failure may lead to tissue degeneration in pathological conditions. We describe the kinetic variation of expression levels of 76 secreted proteins during the regeneration process. In addition, we profile the gene expression of immune cells, endothelial cells, satellite cells, and fibro-adipogenic progenitors. This analysis allowed us to annotate each cell-type with the cytokines and receptors they have the potential to synthetize, thus making it possible to draw a cell-cell interaction map. We next selected 12 cytokines whose receptors are expressed in FAPs and tested their ability to modulate FAP adipogenesis and proliferation. We observed that IL1α and IL1β potently inhibit FAP adipogenesis, while EGF and BTC notably promote FAP proliferation. In addition, we characterized the cross-talk mediated by extracellular vesicles (EVs). We first monitored the modulation of muscle EV cargo during tissue regeneration. Using a single-vesicle flow cytometry approach, we observed that EVs differentially affect the uptake of RNA and proteins into their lumen. We also investigated the EV capability to interact with SCs and FAPs and to modulate their proliferation and differentiation. We conclude that both cytokines and EVs secreted during muscle regeneration have the potential to modulate adipogenic differentiation of FAPs. The results of our approach provide a system-wide picture of mechanisms that control cell fate during the regeneration process in the muscle niche.

Effect of Ascorbic Acid on Differentiation, Secretome and Stemness of Stem Cells from Human Exfoliated Deciduous Tooth (SHEDs)

Stem cells from human exfoliated deciduous teeth (SHEDs) are considered a type of mesenchymal stem cells (MSCs) because of their unique origin from the neural crest. SHEDs can self-renewal and multi-lineage differentiation with the ability to differentiate into odontoblasts, osteoblast, chondrocytes, neuronal cells, hepatocytes, adipocytes, etc. They are emerging as an ideal source of MSCs because of their easy availability and extraordinary cell number. Ascorbic acid, or vitamin C, has many cell-based applications, such as bone regeneration, osteoblastic differentiation, or extracellular matrix production. It also impacts stem cell plasticity and the ability to sustain pluripotent activity. In this study, we evaluate the effects of ascorbic acid on stemness, paracrine secretion, and differentiation into osteoblast, chondrocytes, and adipocytes. SHEDs displayed enhanced multifaceted activity, which may have applications in regenerative therapy.

3D biomaterial models of human brain disease

Inherent limitations of the traditional approaches to study brain function and disease, such as rodent models and 2D cell culture platforms, have led to the development of 3D in vitro cell culture systems. These systems, products of multidisciplinary efforts encompassing stem cell biology, materials engineering, and biofabrication, have quickly shown great potential to mimic biochemical composition, structural properties, and cellular morphology and diversity found in the native brain tissue. Crucial to these developments have been the advancements in stem cell technology and cell reprogramming protocols that allow reproducible generation of human subtype-specific neurons and glia in laboratory conditions. At the same time, biomaterials have been designed to provide cells in 3D with a microenvironment that mimics functional and structural aspects of the native extracellular matrix with increasing fidelity. In this article, we review the use of biomaterials in 3D in vitro models of neurological disorders with focus on hydrogel technology and with biochemical composition and physical properties of the in vivo environment as reference.

Discovery of a Novel Polymer for Xeno-Free, Long-Term Culture of Human Pluripotent Stem Cell Expansion

Human pluripotent stem cells (hPSCs) can be expanded and differentiated in vitro into almost any adult tissue cell type, and thus have great potential as a source for cell therapies with biomedical application. In this study, a fully-defined polymer synthetic substrate is identified for hPSC culture in completely defined, xenogenic (xeno)-free conditions. This system can overcome the cost, scalability, and reproducibility limitations of current hPSC culture strategies, and facilitate large-scale production. A high-throughput, multi-generational polymer microarray platform approach is used to test over 600 unique polymers and rapidly assess hPSC-polymer interactions in combination with the fully defined xeno-free medium, Essential 8 (E8). This study identifies a novel nanoscale phase separated blend of poly(tricyclodecane-dimethanol diacrylate) and poly(butyl acrylate) (2:1 v/v), which supports long-term expansion of hPSCs and can be readily coated onto standard cultureware. Analysis of cell-polymer interface interactions through mass spectrometry and integrin blocking studies provides novel mechanistic insight into the role of the E8 proteins in promoting integrin-mediated hPSC attachment and maintaining hPSC signaling, including ability to undergo multi-lineage differentiation. This study therefore identifies a novel substrate for long-term serial passaging of hPSCs in serum-free, commercial chemically-defined E8, which provides a promising and economic hPSC expansion platform for clinical-scale application.

Differentiation of induced pluripotent stem cells into definitive endoderm on Activin A-functionalized gradient surfaces

Activin A plays a central role in the differentiation of stem cells into definitive endoderm, the first step in embryonic development and function development in many organ systems. The aims of this study were to induce controlled and fine-tuned cell differentiation using a gradient nanotechnology and compare this with a classic protocol and to investigate how induced pluripotent stem cells differentiated depending on the gradual increase of Activin A. The density difference was tested by attaching Activin A to a gold nanoparticle gradient for high-precision density continuity. Cells expressed the definitive endoderm markers SRY-box transcription factor 17 and transcription factor GATA-4 to different extents along the gradient, indicating a density-dependent cell response to Activin A. In both the gradient and the classic differentiation setups, the protein expression increased from days 1 to 5, but a significant increase already on day 3 was found only in the gradient-based setup. By utilizing the gradient technology to present the right amount of active biomolecules to cells in vitro, we were able to find an optimal setting for differentiation into definitive endoderm. The use of gradient surfaces for differentiation allows for improvements, such as efficiency and faster differentiation, compared with a classic protocol.

Bioprinting Neural Systems to Model Central Nervous System Diseases

To date, pharmaceutical progresses in central nervous system (CNS) diseases are clearly hampered by the lack of suitable disease models. Indeed, animal models do not faithfully represent human neurodegenerative processes and human in vitro 2D cell culture systems cannot recapitulate the in vivo complexity of neural systems. The search for valuable models of neurodegenerative diseases has recently been revived by the addition of 3D culture that allows to re-create the in vivo microenvironment including the interactions among different neural cell types and the surrounding extracellular matrix (ECM) components. In this review, the new challenges in the field of CNS diseases in vitro 3D modeling are discussed, focusing on the implementation of bioprinting approaches enabling positional control on the generation of the 3D microenvironments. The focus is specifically on the choice of the optimal materials to simulate the ECM brain compartment and the biofabrication technologies needed to shape the cellular components within a microenvironment that significantly represents brain biochemical and biophysical parameters.

Mesenchymal Stromal Cell-Produced Components of Extracellular Matrix Potentiate Multipotent Stem Cell Response to Differentiation Stimuli

Extracellular matrix (ECM) provides both structural support and dynamic microenvironment for cells regulating their behavior and fate. As a critical component of stem cell niche ECM maintains stem cells and activates their proliferation and differentiation under specific stimuli. Mesenchymal stem/stromal cells (MSCs) regulate tissue-specific stem cell functions locating in their immediate microenvironment and producing various bioactive factors, including ECM components. We evaluated the ability of MSC-produced ECM to restore stem and progenitor cell microenvironment in vitro and analyzed the possible mechanisms of its effects. Human MSC cell sheets were decellularized by different agents (detergents, enzymes, and apoptosis inductors) to select the optimized combination (CHAPS and DNAse I) based on the conservation of decellularized ECM (dECM) structure and effectiveness of DNA removal. Prepared dECM was non-immunogenic, supported MSC proliferation and formation of larger colonies in colony-forming unit-assay. Decellularized ECM effectively promoted MSC trilineage differentiation (adipogenic, osteogenic, and chondrogenic) compared to plastic or plastic covered by selected ECM components (collagen, fibronectin, laminin). Interestingly, dECM produced by human fibroblasts could not enhance MSC differentiation like MSC-produced dECM, indicating cell-specific functionality of dECM. We demonstrated the significant integrin contribution in dECM-cell interaction by blocking the stimulatory effects of dECM with RGD peptide and suggested the involvement of key intracellular signaling pathways activation (pERK/ERK and pFAK/FAK axes, pYAP/YAP and beta-catenin) in the observed processes based on the results of inhibitory analysis. Taken together, we suppose that MSC-produced dECM may mimic stem cell niche components in vitro and maintain multipotent progenitor cells to insure their effective response to external differentiating stimuli upon activation. The obtained data provide more insights into the possible role of MSC-produced ECM in stem and progenitor cell regulation within their niches. Our results are also useful for the developing of dECM-based cell-free products for regenerative medicine.

Chemically defined human vascular laminins for biologically relevant culture of hiPSC-derived brain microvascular endothelial cells

BACKGROUND

In recent years, differentiation of human induced pluripotent stem cells (hiPSCs) into brain-specific microvascular endothelial cells (iBMECs) has frequently been used to model the blood-brain barrier (BBB). However, there are limitations in the use of iBMECs for in vitro studies, such as transendothelial electrical resistance (TEER) instability, weak junctional expression of VE-cadherin, and lack of proper fluid shear stress response. In vivo, the basement membrane (BM) composition of the BBB evolves throughout development, and laminins become the dominant component of the mature vascular BM. However, laminin isoforms of the endothelial BM have not been used for culture of differentiated iBMECs. The main goal of this study is to investigate the effect of different laminin isoforms of the endothelial BM on iBMEC functionality and to determine whether better recapitulation of the physiological BM in vitro can address the aforementioned limitations of iBMECs.

METHODS

Using a previously reported method, hiPSCs were differentiated into iBMECs. The influence of main laminins of the endothelial BM, LN 411 and LN 511, on iBMEC functionality was studied and compared to a collagen IV and fibronectin mixture (CN IV-FN). Quantitative RT-PCR, immunocytochemistry, and TEER measurement were utilized to assess gene and protein expression and barrier properties of iBMECs on different extracellular matrices. Single-channel microfluidic devices were used to study the effect of shear stress on iBMECs.

RESULTS

LN 511, but not LN 411, improved iBMEC barrier properties and resulted in more sustained TEER stability. Immunocytochemistry showed improved junctional protein expression compared to iBMECs cultured on CN IV-FN. iBMECs cultured on LN 511 showed a reduction of stress fibers, indicating resting endothelial phenotype, whereas gene expression analysis revealed upregulation of multiple genes involved in endothelial activation in iBMECs on CN IV-FN. Finally, culturing iBMECs on LN 511 enhanced physiological responses to shear stress, including morphological changes and enhanced junctional protein association.

CONCLUSION

LN 511 improves the functionality and long-term barrier stability of iBMECs. Our findings suggest that incorporation of physiologically relevant LN 511 in iBMEC culture would be beneficial for disease modeling applications and BBB-on-a-chip platforms that accommodate fluid flow.

Akt and Src mediate the photocrosslinked fibroin-induced neural differentiation

Neural transplantation is a promising modality for treatment of neurodegenerative diseases, traumatic brain injury and stroke. Biocompatible scaffolds with optimized properties improve the survival of transplanted neural cells and differentiation of progenitor cells into the desired types of neurons. Silk fibroin is a biocompatible material for tissue engineering. Here, we describe thin-film scaffolds based on photocrosslinked methacrylated silk fibroin (FBMA). These scaffolds exhibit an increased mechanical stiffness and improved water stability. Photocrosslinking of fibroin increased its rigidity from 25 to 480 kPa and the contact angle from 59.7 to 70.8, the properties important for differentiation of neural cells. Differentiation of SH-SY5Y neuroblastoma cells on FBMA increased the length of neurites as well as the levels of neural differentiation markers MAP2 and βIII-tubulin. Growth of SH-SY5Y cells on the unmodified fibroin and FBMA substrates led to a spontaneous phosphorylation of Src and Akt protein kinases critical for neuronal differentiation; this effect was paralleled by neural cell adhesion molecule elevation. Thus, FBMA is an easily manufactured, cytocompatible material with improved and sustainable properties applicable for neural tissue engineering.

Growth and Spatial Control of Murine Neural Stem Cells on Reflectin Films

Stem cells have attracted significant attention due to their regenerative capabilities and their potential for the treatment of disease. Consequently, significant research effort has focused on the development of protein- and polypeptide-based materials as stem cell substrates and scaffolds. Here, we explore the ability of reflectin, a cephalopod structural protein, to support the growth of murine neural stem/progenitor cells (mNSPCs). We observe that the binding, growth, and differentiation of mNSPCs on reflectin films is comparable to that on more established protein-based materials. Moreover, we find that heparin selectively inhibits the adhesion of mNSPCs on reflectin, affording spatial control of cell growth and leading to a >30-fold change in cell density on patterned substrates. The described findings highlight the potential utility of reflectin as a stem cell culture material.

Peptide gels of fully-defined composition and mechanics for probing cell-cell and cell-matrix interactions in vitro

Current materials used for in vitro 3D cell culture are often limited by their poor similarity to human tissue, batch-to-batch variability and complexity of composition and manufacture. Here, we present a "blank slate" culture environment based on a self-assembling peptide gel free from matrix motifs. The gel can be customised by incorporating matrix components selected to match the target tissue, with independent control of mechanical properties. Therefore the matrix components are restricted to those specifically added, or those synthesised by encapsulated cells. The flexible 3D culture platform provides full control over biochemical and physical properties, allowing the impact of biochemical composition and tissue mechanics to be separately evaluated in vitro. Here, we demonstrate that the peptide gels support the growth of a range of cells including human induced pluripotent stem cells and human cancer cell lines. Furthermore, we present proof-of-concept that the peptide gels can be used to build disease-relevant models. Controlling the peptide gelator concentration allows peptide gel stiffness to be matched to normal breast (<1 kPa) or breast tumour tissue (>1 kPa), with higher stiffness favouring the viability of breast cancer cells over normal breast cells. In parallel, the peptide gels may be modified with matrix components relevant to human breast, such as collagen I and hyaluronan. The choice and concentration of these additions affect the size, shape and organisation of breast epithelial cell structures formed in co-culture with fibroblasts. This system therefore provides a means of unravelling the individual influences of matrix, mechanical properties and cell-cell interactions in cancer and other diseases.

A nanopillar array on black titanium prepared by reactive ion etching augments cardiomyogenic commitment of stem cells

A major impediment in the clinical translation of stem cell therapy has been the inability to efficiently and reproducibly direct differentiation of a large population of stem cells. Thus, we aimed to engineer a substrate for culturing stem cells to efficiently induce cardiomyogenic lineage commitment. In this work, we present a nanopillar array on the surface of titanium that was prepared by mask-less reactive ion etching. Scanning electron and atomic force microscopy revealed that the surface was covered by vertically aligned nanopillars each of ≈1 μm with a diameter of ≈80 nm. The nanopillars supported the attachment and proliferation of human mesenchymal stem cells (hMSCs). Cardiomyogenic lineage commitment of the stem cells was more enhanced on the nanopillars than on the smooth surface. When co-cultured with neonatal rat cardiomyocytes, the cyclic pattern of calcium transport observed distinctly in cells differentiated on the arrays compared to the cells cultured on the smooth surface was the functional validation of differentiation. The use of small molecule inhibitors revealed that integrins namely, α₂β₁ and α_vβ₃, are essential for cardiomyogenesis on the nanostructured surface, which is further mediated by FAK, Erk and Akt cell signaling pathways. This study demonstrates that the nanopillar array efficiently promotes the cardiomyogenic lineage commitment of stem cells via integrin-mediated signaling and can potentially serve as a platform for the ex vivo differentiation of stem cells toward cell therapy in cardiac tissue repair and regeneration.

Customizable Implant-specific and Tissue-Specific Extracellular Matrix Protein Coatings Fabricated Using Atmospheric Plasma

Progression in implant science has benefited from ample amount of technological contributions from various disciplines, including surface biotechnology. In this work, we successfully used atmospheric plasma to enhance the biological functions of surgical implants by coating them with extracellular matrix proteins. The developed collagen and laminin coatings demonstrate advantageous material properties. Chemical analysis by XPS and morphological investigation by SEM both suggested a robust coating. Contact angle goniometry and dissolution study in simulated body fluid (SBF) elicited increased hydrophilicity and physiological durability. Furthermore, these coatings exhibited improved biological interactions with human mesenchymal and neural stem cells (NSCs). Cell adhesion, proliferation, and differentiation proved markedly refined as shown by enzymatic detachment, flow cytometry, and ELISA data, respectively. Most importantly, using the pathway-specific PCR array, our study discovered dozens of deregulated genes during osteogenesis and neurogenesis on our newly fabricated ECM coatings. The coating-induced change in molecular profile serves as a promising clue for designing future implant-based therapy. Collectively, we present atmospheric plasma as a versatile tool for enhancing surgical implants, through customizable implant-specific and tissue-specific coatings.

Quantified forces between HepG2 hepatocarcinoma and WA07 pluripotent stem cells with natural biomaterials correlate with in vitro cell behavior

In vitro cell culture or tissue models that mimic in vivo cellular response have potential in tissue engineering and regenerative medicine, and are a more economical and accurate option for drug toxicity tests than animal experimentation. The design of in vivo-like cell culture models should take into account how the cells interact with the surrounding materials and how these interactions affect the cell behavior. Cell-material interactions are furthermore important in cancer metastasis and tumor progression, so deeper understanding of them can support the development of new cancer treatments. Herein, the colloidal probe microscopy technique was used to quantify the interactions of two cell lines (human pluripotent stem cell line WA07 and human hepatocellular carcinoma cell line HepG2) with natural, xeno-free biomaterials of different chemistry, morphology, and origin. Key components of extracellular matrices -human collagens I and IV, and human recombinant laminin-521-, as well as wood-derived, cellulose nanofibrils -with evidenced potential for 3D cell culture and tissue engineering- were analysed. Both strength of adhesion and force curve profiles depended on biomaterial nature and cell characteristics. The successful growth of the cells on a particular biomaterial required cell-biomaterial adhesion energies above 0.23 nJ/m. The information obtained in this work supports the development of new materials or hybrid scaffolds with tuned cell adhesion properties for tissue engineering, and provides a better understanding of the interactions of normal and cancerous cells with biomaterials in the human body.

Designer human tissue: coming to a lab near you

Human pluripotent stem cells (PSCs) offer a scalable alternative to primary and transformed human tissue. PSCs include human embryonic stem cells, derived from the inner cell mass of blastocysts unsuitable for human implantation; and induced PSCs, generated by the reprogramming of somatic cells. Both cell types display the ability to self-renew and retain pluripotency, promising an unlimited supply of human somatic cells for biomedical application. A distinct advantage of using PSCs is the ability to select for genetic background, promising personalized modelling of human biology ‘in a dish’ or immune-matched cell-based therapies for the clinic. This special issue will guide the reader through stem cell self-renewal, pluripotency and differentiation. The first articles focus on improving cell fidelity, understanding the innate immune system and the importance of materials chemistry, biofabrication and bioengineering. These are followed by articles that focus on industrial application, commercialization and label-free assessment of tissue formation. The special issue concludes with an article discussing human liver cell-based therapies past, present and future.

This article is part of the theme issue ‘Designer human tissue: coming to a lab near you’.

Maintenance of an undifferentiated state of human-induced pluripotent stem cells through botulinum hemagglutinin-mediated regulation of cell behavior

Applications of human induced pluripotent stem cell (hiPSC) culture are impaired by problems with long term maintenance of pluripotency. In this study, we report that exposure to botulinum hemagglutinin (HA), an E-cadherin function-blocking agent, suppressed deviation from an undifferentiated state in hiPSC colonies. Time-lapse imaging of live cells revealed that cells in central regions of colonies moved slowly and underwent a morphological change to a cobblestone-like shape via interaction between contacting cells, forming dense, multiple layers. Staining and migration analysis showed that actin stress fibers and paxillin spots were diminished in colony central regions, and this was associated with alteration of cellular morphology and migratory behavior. However, in culture with HA exposure, cells in the central and peripheral regions of hiPSC colonies were migratory and arranged in loose monolayers, resulting in relatively uniform dispersion of cells in colonies. We also found that a well-organized network of actin stress fibers was of significance in the central and peripheral regions of a colony, resulting in activation of paxillin and E-cadherin expression in hiPSCs. After routine application of HA for serial passages, hiPSCs remained pluripotent and capable of differentiating into all three germ layers. These observations indicate that relaxation of cell-cell junctions by HA induced rearrangements of the cytoskeleton and cell adhesion in hiPSC colonies by promoting migratory behaviors. These results suggest that this simple and readily reproducible culture strategy is a potentially useful tool for improving the robust and scalable maintenance of undifferentiated hiPSC cultures.

The inevitability of change

Change is an absolute so long as time does not stand still. We should expect it, embrace it, and try to predict its direction. Dermatology, as a specialty practice, has been changing rapidly over the past 30 years concurrent with the changes in medicine. What are these changes, how did they come about, and what may be the consequences? The goal of this review is to follow the march of time, as we move from one era to the other in step with what is happening in the world as a whole and the United States in particular. The growth of our specialty, Dermatology, is divided into 3 eras which are quite different in generational cultures. The first era spanning the 1980s and 1990s is dubbed as "old school." The second era begins with the new century, 2000 until today. This era will forever be remembered as the business era, the rise of elite cultures, and the losses and threats to academia. The third era begins now; it is that of technology which is fast progressing into the future. One can theoretically project what may occur during this technologic revolution and the directions in medicine as a whole. Dermatology can be at the forefront of this era or it could be lost as a whole if we do nothing to keep up. These eras are based on my personal experience as a dermatologist in a large academic institution in the United States and may not apply to other communities or societies elsewhere. The United States serves as a good example of a western technologically oriented society that is often emulated by others.

The Vasoreparative Potential of Endothelial Colony Forming Cells: A Journey Through Pre-clinical Studies

For over a decade various cell populations have been investigated for their vasoreparative potential. Cells with the capacity to promote blood vessel regeneration are commonly known as endothelial progenitor cells (EPCs); although such a definition is currently considered too simple for the complexity of cell populations involved in the reparative angiogenic process. A subset of EPCs called endothelial colony forming cells (ECFCs) have emerged as a suitable candidate for cytotherapy, primarily due to their clonogenic progenitor characteristics, unequivocal endothelial phenotype, and inherent ability to promote vasculogenesis. ECFCs can be readily isolated from human peripheral and cord blood, expanded ex vivo and used to revascularize ischemic tissues. These cells have demonstrated efficacy in several in vivo preclinical models such as the ischemic heart, retina, brain, limb, lung and kidney. This review will summarize the current pre-clinical evidence for ECFC cytotherapy and discuss their potential for clinical application.