An ECM-based culture system for the generation and maintenance of xeno-free human iPS cells

Harnessing the dental cells derived from human induced pluripotent stem cells for hard tissue engineering

INTRODUCTION

Most mineralized tissues in our body are present in bones and teeth. Human induced pluripotent stem cells (hiPSCs) are promising candidates for cell therapy to help regenerate bone defects and teeth loss. The extracellular matrix (ECM) is a non-cellular structure secreted by cells. Studies on the dynamic microenvironment of ECM are necessary for stem cell-based therapies.

OBJECTIVES

We aim to optimize an effective protocol for hiPSC differentiation into dental cells without utilizing animal-derived factors or cell feeders that can be applied to humans and to mineralize differentiated dental cells into hard tissues.

METHODS

For the differentiation of both dental epithelial cells (DECs) and dental mesenchymal cells (DMCs) from hiPSCs, an embryoid body (EB) was formed from hiPSCs. hiPSC were differentiated into neural crest cells with an induction medium utilized in our previous study, and hiPSC-derived DECs were differentiated with a BMP-modulated customized medium. hiPSC-dental cells were then characterized, analyzed, and validated with transcriptomic analysis, western blotting, and RT-qPCR. To form mineralized tissues, hiPSC-derived DECs were recombined with hiPSC-derived DMCs encapsulated in various biomaterials, including gelatin methacryloyl (GelMA), collagen, and agar matrix.

RESULTS

These hiPSC-derived dental cells are highly osteogenic and chondro-osteogenic in photocrosslinkable GelMA hydrogel and collagen type I microenvironments. Furthermore, hiPSC-derived dental cells in agar gel matrix induced the formation of a bioengineered tooth.

CONCLUSION

Our study provides an approach for applying hiPSCs for hard tissue regeneration, including tooth and bone. This study has immense potential to provide a novel technology for bioengineering organs for various regenerative therapies.

Gravity-driven microfluidic device placed on a slow-tilting table enables constant unidirectional perfusion culture of human induced pluripotent stem cells

Gravity-driven microfluidics, which utilizes gravity force to drive liquid flow, offers portability and multi-condition setting flexibility because they do not require pumps or connection tubes to drive the flow. However, because the flow rate decreases with time in gravity-driven microfluidics, it is not suitable for stem cell experiments, which require long-term (at least a day) stability. In this study, gravity-driven microfluidics and a slow-tilting table were developed to culture cells under constant unidirectional perfusion. The microfluidic device was placed on a slow-tilting table, which tilts unidirectionally at a rate of approximately 7° per day to compensate for the reduction in the flow rate. Computational simulations showed that the pulsation of the flow arising from the stepwise movement of the table was less than 0.2%, and the flow was laminar. Hydrophilization of the tanks increased the flow rate, which is consistent with the theoretical values. We showed that vitronectin is better than laminin 511 fragments as a coating material for adhering human induced pluripotent stem cells on a microchamber made of polydimethylsiloxane, and succeeded in culturing the cells for 3 days. It is believed that the system offers easy-to-use cell culture tools, such as conventional multiwell culture vessels, and enables the control of the cell microenvironment.

Hydrogels for Large-Scale Expansion of Stem Cells

Stem cells demonstrate considerable promise for various preclinical and clinical applications, including drug screening, disease treatments, and regenerative medicine. Producing high-quality and large amounts of stem cells is in demand for these applications. Despite challenges, as hydrogel-based cell culture technology has developed, tremendous progress has been made in stem cell expansion and directed differentiation. Hydrogels are soft materials with abundant water. Many hydrogel properties, including biodegradability, mechanical strength, and porosity, have been shown to play essential roles in regulating stem cell proliferation and differentiation. The biochemical and physical properties of hydrogels can be specifically tailored to mimic the native microenvironment that various stem cells reside in vivo. A few hydrogel-based systems have been developed for successful stem cell cultures and expansion in vitro. In this review, we summarize various types of hydrogels that have been designed to effectively enhance the proliferation of hematopoietic stem cells (HSCs), mesenchymal stem/stromal cells (MSCs), and pluripotent stem cells (PSCs), respectively. According to each stem cell type's preference, we also discuss strategies for fabricating hydrogels with biochemical and mechanical cues and other characteristics representing microenvironments of stem cells in vivo. STATEMENT OF SIGNIFICANCE: In this review article we summarize current progress on the construction of hydrogel systems for the culture and expansion of various stem cells, including hematopoietic stem cells (HSCs), mesenchymal stem/stromal cells (MSCs), and pluripotent stem cells (PSCs). The Significance includes: (1) Provide detailed discussion on the stem cell niches that should be considered for stem cell in vitro expansion. (2) Summarize various strategies to construct hydrogels that can largely recapture the microenvironment of native stem cells. (3) Suggest a few future directions that can be implemented to improve current in vitro stem cell expansion systems.

Modeling Parkinson's Disease Using Patient-specific Induced Pluripotent Stem Cells

Parkinson’s disease (PD) is the second most common neurodegenerative disorder. It is characterized by the degeneration of nigral dopaminergic (DA) neurons. While over 90% of cases are idiopathic, without a clear etiology, mutations in many genes have been linked to rare, familial forms of PD. It has been quite challenging to develop effective animal models of PD that capture salient features of PD. The discovery of induced pluripotent stem cells (iPSCs) makes it possible to generate patient-specific DA neurons to study PD. Here, we review the methods for the generation of iPSCs and discuss previous studies using iPSC-derived neurons from monogenic forms of PD. These investigations have revealed several converging pathways that intersect with the unique vulnerabilities of human nigral DA neurons. With the rapid development in stem cell biology, it is possible to generate patient-specific neurons that will be increasingly similar to those in the brain of the patient. Combined with the ability to edit the genome to generate isogenic iPSCs, the generation and analysis of patient-specific midbrain DA neurons will transform PD research by providing a valuable tool for mechanistic study and drug discovery.

Leveraging Biomaterial Mechanics to Improve Pluripotent Stem Cell Applications for Tissue Engineering

A primary goal in tissue engineering is to develop functional tissues by recapitulating salient features of complex biological systems that exhibit a diverse range of physical forces. Induced pluripotent stem cells (iPSCs) are promising autologous cell sources to execute these developmental programs and their functions; however, cells require an extracellular environment where they will sense and respond to mechanical forces. Thus, understanding the biophysical relationships between stem cells and their extracellular environments will improve the ability to design complex biological systems through tissue engineering. This article first describes how the mechanical properties of the environment are important determinants of developmental processes, and then further details how biomaterials can be designed to precisely control the mechanics of cell-matrix interactions in order to study and define their reprogramming, self-renewal, differentiation, and morphogenesis. Finally, a perspective is presented on how insights from the mechanics of cell-matrix interactions can be leveraged to control pluripotent stem cells for tissue engineering applications.

Construction of nano-scale cellular environments by coating a multilayer nanofilm on the surface of human induced pluripotent stem cells

Interactions with peripheral environments, such as extracellular matrix (ECM) and other cells, and their balance play a crucial role in the maintenance of pluripotency and self-renewal of human pluripotent stem cells. In this study, we focused on a nano-sized artificial cellular environment that is directly attached to the cytoplasmic membrane as a facile method that can effect intercellular interactions at the single-cell level. We designed multilayered nanofilms that are self-assembled on the surface of human induced pluripotent stem cells (iPSCs), by repetitive adsorption of fibronectin and heparin or chondroitin sulfate. However, the surface modification process could also lead to the loss of cell-cell adhesion, which may result in apoptotic cell death. We investigated the proliferation and pluripotency of the iPSCs coated with the nanofilm in order to establish the suitable nanofilm structure and coating conditions. As a result, the cell viability reduced with the increase in the duration of the coating process, but the undifferentiated state and proliferation of the cells were maintained until 2 bilayers were coated. To suppress the dissociation-induced apoptosis, Y-27632, the Rho-associated kinase inhibitor (ROCKi), was added to the coating solution; this allowed the coating of up to 4 bilayers of the nanofilm onto the iPSCs. These results are expected to accelerate the pace of iPSC studies on 3-dimensional cultures and naïve pluripotency, in which the regulation of cellular interactions plays a critical role.

Screening of pure synthetic coating substrates for induced pluripotent stem cells and iPSC-derived neuroepithelial progenitors with short peptide based integrin array

Simple and pure synthetic coating substrates are needed to overcome the disadvantages of traditional coating products like animal derived Matrigel in stem cell research. Since integrins are of great importance in cell adhesion and cell-ECM communication, in this study, a commercially available integrin array established by synthetic integrin binding peptides is used to screen coating substrates for iPSCs and NEPs. The results showed that binding peptides of integrin α₅β₁, α_Vβ₁, α_Mβ₂ and α_IIbβ₃ supported cell adhesion of iPSCs, while α₅β₁, α_Vβ₁ and α_IIbβ₃ binding peptides supported NEPs adhesion. Additionally, integrin α5β1 binding peptide was revealed to support rapid expansion of iPSCs and iPSC-derived NEPs, as well as the process of NEPs generation, with equal efficiency as Matrigel. In this work, we demonstrated that by supporting stem cell growth in an integrin dependent manner, the integrin array and coating system has the potential to develop more precise and efficient systems in neurological disease modeling.

Insoluble Microenvironment Facilitating the Generation and Maintenance of Pluripotency

Induced pluripotent stem cells (iPSCs) hold enormous potential as a tool to generate cells for tissue engineering and regenerative medicine. Since the initial report of iPSCs in 2006, many different methods have been developed to enhance the safety and efficiency of this technology. Recent studies indicate that the extracellular signals can promote the production of iPSCs, and even replace the Yamanaka factors. Noticeably, abundant evidences suggest that the insoluble microenvironment, including the culture substrate and neighboring cells, directly regulates the expression of core pluripotency genes and the epigenetic modification of the chromatins, hence, impacts the reprogramming dynamics. These studies provide new strategies for developing safer and more efficient method for iPSC generation. In this review, we examine the publications addressing the insoluble extracellular microenvironment that boosts iPSC generation and self-renewal. We also discuss cell adhesion-mediated molecular mechanisms, through which the insoluble extracellular cues interplay with reprogramming.

Development of demineralized bone matrix-based implantable and biomimetic microcarrier for stem cell expansion and single-step tissue-engineered bone graft construction

Tissue engineered bone grafts (TEBG) using mesenchymal stem cells (MSCs) demonstrate great potential for bone defect treatment.

Fibroblast-like cells as an effective feeder for the cultivation and derivation of new lines of human induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) can be a highly informative model of hereditary and sporadic human diseases. In the future, such cells can be used in substitution and regenerative therapy of a wide range of diseases and for the treatment of injuries and burns. The ability of iPSCs derived from patients with Parkinson's disease to differentiate into fibroblast-like cells (derivatives) was studied. It was found that these cells can serve as an effective feeder layer not only to maintain the pluripotency of allogenic and autologous iPSCs but also to derive new iPSC lines.

Biomaterials for pluripotent stem cell engineering: From fate determination to vascularization

Recent advancements in material science and engineering may hold the key to overcoming reproducibility and scalability limitations currently hindering the clinical translation of stem cell therapies. Biomaterial assisted differentiation commitment of stem cells and modulation of their in vivo function could have significant impact in stem cell-centred regenerative medicine approaches and next gen technological platforms. Synthetic biomaterials are of particular interest as they provide a consistent, chemically defined, and tunable way of mimicking the physical and chemical properties of the natural tissue or cell environment. Combining emerging biomaterial and biofabrication advancements may finally give researchers the tools to modulate spatiotemporal complexity and engineer more hierarchically complex, physiologically relevant tissue mimics. In this review we highlight recent research advancements in biomaterial assisted pluripotent stem cell (PSC) expansion and three dimensional (3D) tissue formation strategies. Furthermore, since vascularization is a major challenge affecting the in vivo function of engineered tissues, we discuss recent developments in vascularization strategies and assess their ability to produce perfusable and functional vasculature that can be integrated with the host tissue.

Extracellular Matrix-Dependent Generation of Integration- and Xeno-Free iPS Cells Using a Modified mRNA Transfection Method

Human induced pluripotent stem cells (iPS cells) hold great promise in the field of regenerative medicine, especially immune-compatible cell therapy. The most important safety-related issues that must be resolved before the clinical use of iPS cells include the generation of “footprint-free” and “xeno-free” iPS cells. In this study, we sought to examine whether an extracellular matrix- (ECM-) based xeno-free culture system that we recently established could be used together with a microRNA-enhanced mRNA reprogramming method for the generation of clinically safe iPS cells. The notable features of this method are the use of a xeno-free/feeder-free culture system for the generation and expansion of iPS cells rather than the conventional labor-intensive culture systems using human feeder cells or human feeder-conditioned medium and the enhancement of mRNA-mediated reprogramming via the delivery of microRNAs. Strikingly, we observed the early appearance of iPS cell colonies (~11 days), substantial reprogramming efficiency (~0.2–0.3%), and a high percentage of ESC-like colonies among the total colonies (~87.5%), indicating enhanced kinetics and reprogramming efficiency. Therefore, the combined method established in this study provides a valuable platform for the generation and expansion of clinically safe (i.e., integration- and xeno-free) iPS cells, facilitating immune-matched cell therapy in the near future.

Modeling Viral Infectious Diseases and Development of Antiviral Therapies Using Human Induced Pluripotent Stem Cell-Derived Systems

The recent biotechnology breakthrough of cell reprogramming and generation of induced pluripotent stem cells (iPSCs), which has revolutionized the approaches to study the mechanisms of human diseases and to test new drugs, can be exploited to generate patient-specific models for the investigation of host–pathogen interactions and to develop new antimicrobial and antiviral therapies. Applications of iPSC technology to the study of viral infections in humans have included in vitro modeling of viral infections of neural, liver, and cardiac cells; modeling of human genetic susceptibility to severe viral infectious diseases, such as encephalitis and severe influenza; genetic engineering and genome editing of patient-specific iPSC-derived cells to confer antiviral resistance.

Human-induced pluripotent stem cells generated from intervertebral disc cells improve neurologic functions in spinal cord injury

Introduction

Induced pluripotent stem cells (iPSCs) have emerged as a promising cell source for immune-compatible cell therapy. Although a variety of somatic cells have been tried for iPSC generation, it is still of great interest to test new cell types, especially those which are hardly obtainable in a normal situation.

Methods

In this study, we generated iPSCs by using the cells originated from intervertebral disc which were removed during a spinal operation after spinal cord injury. We investigated the pluripotency of disc cell-derived iPSCs (diPSCs) and neural differentiation capability as well as therapeutic effect in spinal cord injury.

Results

The diPSCs displayed similar characteristics to human embryonic stem cells and were efficiently differentiated into neural precursor cells (NPCs) with the capability of differentiation into mature neurons in vitro.

When the diPSC-derived NPCs were transplanted into mice 9 days after spinal cord injury, we detected a significant amelioration of hindlimb dysfunction during follow-up recovery periods. Histological analysis at 5 weeks after transplantation identified undifferentiated human NPCs (Nestin⁺) as well as early (Tuj1⁺) and mature (MAP2⁺) neurons derived from the transplanted NPCs. Furthermore, NPC transplantation demonstrated a preventive effect on spinal cord degeneration resulting from the secondary injury.

Conclusion

This study revealed that intervertebral discs removed during surgery for spinal stabilization after spinal cord injury, previously considered a “waste” tissue, may provide a unique opportunity to study iPSCs derived from difficult-to-access somatic cells and a useful therapeutic resource for autologous cell replacement therapy in spinal cord injury.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0118-x) contains supplementary material, which is available to authorized users.

Differentiation of Cardiomyocytes from Human Pluripotent Stem Cells Using Monolayer Culture

Human pluripotent stem cells (PSCs) are a promising cell source for cardiac tissue engineering and cell-based therapies for heart repair because they can be expanded in vitro and differentiated into most cardiovascular cell types, including cardiomyocytes. During embryonic heart development, this differentiation occurs under the influence of internal and external stimuli that guide cells to go down the cardiac lineage. In order to differentiate PSCs in vitro, these or similar stimuli need to be provided in a controlled manner. However, because it is not possible to completely recapitulate the embryonic environment, the factors essential for cardiac differentiation of PSCs in vitro need to be experimentally determined and validated. Since PSCs were first developed, significant progress has been made in optimizing techniques for their differentiation toward cardiomyocytes. In this review, we will summarize recent advances in these techniques, with particular focus on monolayer-based methods that have improved the efficiency and scalability of cardiomyocyte differentiation.

Induction of pluripotency in human umbilical cord mesenchymal stem cells in feeder layer-free condition

Induced Pluripotent Stem Cells (iPSCs) has been produced by the reprogramming of several types of somatic cells through the expression of different sets of transcription factors. This study consists of a technique to obtain iPSCs from human umbilical cord mesenchymal stem cells (UC-MSCs) in a feeder layer-free process using a mini-circle vector containing defined reprogramming genes, Lin28, Nanog, Oct4 and Sox2. The human MSCs transfected with the minicircle vector were cultured in iPSCs medium. Human embryonic stem cell (ESC)-like colonies with tightly packed domelike structures appeared 7-10 days after the second transfection. In the earliest stages, the colonies were green fluorescence protein (GFP)-positive, while upon continuous culture and passage, genuine hiPSC clones expressing GFP were observed. The induced cells, based on the ectopic expression of the pluripotent markers, exhibited characteristics similar to the embryonic stem cells. These iPSCs demonstrated in vitro capabilities for differentiation into the three main embryonic germ layers by embryoid bodies formation. There was no evidence of transgenes integration into the genome of the iPSCs in this study. In conclusion, this method offers a means of producing iPSCs without viral delivery that could possibly overcome ethical concerns and immune rejection in the use of stem cells in medical applications.

Application of biomaterials to advance induced pluripotent stem cell research and therapy

Derived from any somatic cell type and possessing unlimited self-renewal and differentiation potential, induced pluripotent stem cells (iPSCs) are poised to revolutionize stem cell biology and regenerative medicine research, bringing unprecedented opportunities for treating debilitating human diseases. To overcome the limitations associated with safety, efficiency, and scalability of traditional iPSC derivation, expansion, and differentiation protocols, biomaterials have recently been considered. Beyond addressing these limitations, the integration of biomaterials with existing iPSC culture platforms could offer additional opportunities to better probe the biology and control the behavior of iPSCs or their progeny in vitro and in vivo. Herein, we discuss the impact of biomaterials on the iPSC field, from derivation to tissue regeneration and modeling. Although still exploratory, we envision the emerging combination of biomaterials and iPSCs will be critical in the successful application of iPSCs and their progeny for research and clinical translation.

Footprint- and xeno-free human iPSCs derived from urine cells using extracellular matrix-based culture conditions

The efficient generation of integration- and xeno-free iPSCs is a prerequisite for their use in clinical applications. Furthermore, non-invasiveness of somatic cell acquisition for iPSC generation is another factor to consider. In this study, we established a practical, simple, and convenient method to generate integration- and xeno-free iPSCs from urine cells which can be obtained in a non-invasive manner. Our method was based on extracellular matrix-based xeno-free iPSC culture condition and episomal transfection, and worked efficiently with both urine cells and adipose-derived stromal cells (ADSCs). To obtain strictly xeno-free iPSCs, we also formulated a new xeno-free culture medium for primary urine cells. Intriguingly, urine cells displayed slower growth, and more dramatic increase in apoptosis at high passage numbers than ADSCs. However, urine cells at low passage (<P3) displayed modest apoptosis (~7-8%) and relatively high (~0.29%) efficiency of iPSC generation. This study reports the generation of integration- and xeno-free iPSCs from non-invasively obtained urine cells.

Induced pluripotent stem cells as custom therapeutics for retinal repair: progress and rationale

Human pluripotent stem cells have made a remarkable impact on science, technology and medicine by providing a potentially unlimited source of human cells for basic research and clinical applications. In recent years, knowledge gained from the study of human embryonic stem cells and mammalian somatic cell reprogramming has led to the routine production of human induced pluripotent stem cells (hiPSCs) in laboratories worldwide. hiPSCs show promise for use in transplantation, high throughput drug screening, "disease-in-a-dish" modeling, disease gene discovery, and gene therapy testing. This review will focus on the first application, beginning with a discussion of methods for producing retinal lineage cells that are lost in inherited and acquired forms of retinal degenerative disease. The selection of appropriate hiPSC-derived donor cell type(s) for transplantation will be discussed, as will the caveats and prerequisite steps to formulating a clinical Good Manufacturing Practice (cGMP) product for clinical trials.

Derivation of transgene-free human induced pluripotent stem cells from human peripheral T cells in defined culture conditions

Recently, induced pluripotent stem cells (iPSCs) were established as promising cell sources for revolutionary regenerative therapies. The initial culture system used for iPSC generation needed fetal calf serum in the culture medium and mouse embryonic fibroblast as a feeder layer, both of which could possibly transfer unknown exogenous antigens and pathogens into the iPSC population. Therefore, the development of culture systems designed to minimize such potential risks has become increasingly vital for future applications of iPSCs for clinical use. On another front, although donor cell types for generating iPSCs are wide-ranging, T cells have attracted attention as unique cell sources for iPSCs generation because T cell-derived iPSCs (TiPSCs) have a unique monoclonal T cell receptor genomic rearrangement that enables their differentiation into antigen-specific T cells, which can be applied to novel immunotherapies. In the present study, we generated transgene-free human TiPSCs using a combination of activated human T cells and Sendai virus under defined culture conditions. These TiPSCs expressed pluripotent markers by quantitative PCR and immunostaining, had a normal karyotype, and were capable of differentiating into cells from all three germ layers. This method of TiPSCs generation is more suitable for the therapeutic application of iPSC technology because it lowers the risks associated with the presence of undefined, animal-derived feeder cells and serum. Therefore this work will lead to establishment of safer iPSCs and extended clinical application.

Biomaterial strategies for stem cell maintenance during in vitro expansion

Stem cells, having the potential for self-renewal and multilineage differentiation, are the building blocks for tissue/organ regeneration. Stem cells can be isolated from various sources but are, in general, available in too small numbers to be used directly for clinical purpose without intermediate expansion procedures in vitro. Although this in vitro expansion of undifferentiated stem cells is necessary, stem cells typically diminish their ability to self-renew and proliferate during passaging. Consequently, maintaining the stemness of stem cells has been recognized as a major challenge in stem cell-based research. This review focuses on the latest developments in maintaining the self-renewal ability of stem cells during in vitro expansion by biomaterial strategies. Further, this review highlights what should be the focus for future studies using stem cells for regenerative applications.

Defining synthetic surfaces for human pluripotent stem cell culture

Human pluripotent stem cells (hPSCs) are able to self-renew indefinitely and to differentiate into all adult cell types. hPSCs therefore show potential for application to drug screening, disease modelling and cellular therapies. In order to meet this potential, culture conditions must be developed that are consistent, defined, scalable, free of animal products and that facilitate stable self-renewal of hPSCs. Several culture surfaces have recently been reported to meet many of these criteria although none of them have been widely implemented by the stem cell community due to issues with validation, reliability and expense. Most hPSC culture surfaces have been derived from extracellular matrix proteins (ECMPs) and their cell adhesion molecule (CAM) binding motifs. Elucidating the CAM-mediated cell-surface interactions that are essential for the in vitro maintenance of pluripotency will facilitate the optimisation of hPSC culture surfaces. Reports indicate that hPSC cultures can be supported by cell-surface interactions through certain CAM subtypes but not by others. This review summarises the recent reports of defined surfaces for hPSC culture and focuses on the CAMs and ECMPs involved.