Harnessing the potential of induced pluripotent stem cells for regenerative medicine

Role of CD133 in human embryonic stem cell proliferation and teratoma formation

Background

Pluripotent stem cells (PSCs), including human embryonic stem cells (hESCs), hold great potential for regenerative medicine and cell therapy. One of the major hurdles hindering the clinical development of PSC-based therapy is the potential risk of tumorigenesis. CD133 (Prominin 1, PROM1) is a transmembrane protein whose mRNA and glycosylated forms are highly expressed in many human cancer cell types. CD133 also serves as a cancer stem cell (CSC) marker associated with cancer progression and patient outcome. Interestingly, CD133 is highly expressed in hESCs as well as in human preimplantation embryos, but its function in hESCs has remained largely unknown.

Methods

CD133 knockout hESC WA26 cell line was generated with CRISPR/Cas9. CD133 knockout and wide type hESC lines were subjected to pluripotency, proliferation, telomere biology, and teratoma tests; the related global changes and underlying mechanisms were further systemically analyzed by RNA-seq.

Results

CD133 deficiency did not affect hESC pluripotency or in vivo differentiation into three germ layers but significantly decreased cell proliferation. RNA-seq revealed that CD133 deficiency dysregulated the p53, PI3K-Akt, AMPK, and Wnt signaling pathways. Alterations in these pathways have been implicated in tumor proliferation and apoptotic escape.

Conclusions

Our data imply that CD133 could be an additional target and used as a selective marker to sort and eliminate undifferentiated cells in reducing potential teratoma formation risk of hESCs in regenerative medicine.

New forms of electrospun nanofiber materials for biomedical applications

Over the past two decades, electrospinning has emerged as an enabling nanotechnology to produce nanofiber materials for various biomedical applications. In particular, therapeutic/cellloaded nanofiber scaffolds have been widely examined in drug delivery, wound healing, and tissue repair and regeneration. However, due to the insufficient porosity, small pore size, noninjectability, and inaccurate spatial control in nanofibers of scaffolds, many efforts have been devoted to exploring new forms of nanofiber materials including expanded nanofiber scaffolds, nanofiber aerogels, short nanofibers, and nanofiber microspheres. This short review discusses the preparation and potential biomedical applications of new forms of nanofiber materials.

The rapidly advancing Class 2 CRISPR-Cas technologies: A customizable toolbox for molecular manipulations

The CRISPR-Cas technologies derived from bacterial and archaeal adaptive immune systems have emerged as a series of groundbreaking nucleic acid-guided gene editing tools, ultimately standing out among several engineered nucleases because of their high efficiency, sequence-specific targeting, ease of programming and versatility. Facilitated by the advancement across multiple disciplines such as bioinformatics, structural biology and high-throughput sequencing, the discoveries and engineering of various innovative CRISPR-Cas systems are rapidly expanding the CRISPR toolbox. This is revolutionizing not only genome editing but also various other types of nucleic acid-guided manipulations such as transcriptional control and genomic imaging. Meanwhile, the adaptation of various CRISPR strategies in multiple settings has realized numerous previously non-existing applications, ranging from the introduction of sophisticated approaches in basic research to impactful agricultural and therapeutic applications. Here, we summarize the recent advances of CRISPR technologies and strategies, as well as their impactful applications.

Histone hyperacetylation may improve the preimplantation development and epigenetic status of cloned embryos

The current study investigated the mechanism of mini pig fetal fibroblasts in improving the epigenetic modification and preimplantation development of cloned embryos. The results showed that the increased AcH3K14 level was dose- and time-dependent. Histone hyperacetylation had no significant effect on cell morphology, cell viability, cell cycle, and relative gene (HDAC1, HAT1, DNMT3A, and BAX) expression. The treated cloned embryos had significantly higher development rates and the total nuclei number than the control (27.62 ± 6.94 % vs. 16.14 ± 10.55 %; 43.90 ± 18.39 vs. 33.06 ± 15.87; P < 0.05). The AcH3K14 level in the treated cloned blastocysts was close to that of IVF blastocysts (5.17 ± 0.93 vs. 5.45 ± 1.91, P > 0.05). The gene transcription (CDX2 and OCT4) of the treated cloned blastocysts was significantly up-regulated than the control (3.32 ± 0.51 vs. 2.05 ± 0.30; 1.21 ± 0.18 vs. 0.81 ± 0.09; P < 0.05). The improvement in the cloned embryo development and the partial correction of abnormal acetylation modification were not necessarily related to the cellular characteristics. This could be caused by histone hyperacetylation of mini pig fetal fibroblasts.

Dynamic proteome profiling of human pluripotent stem cell-derived pancreatic progenitors

A comprehensive characterization of the molecular processes controlling cell fate decisions is essential to derive stable progenitors and terminally differentiated cells that are functional from human pluripotent stem cells (hPSCs). Here, we report the use of quantitative proteomics to describe early proteome adaptations during hPSC differentiation toward pancreatic progenitors. We report that the use of unbiased quantitative proteomics allows the simultaneous profiling of numerous proteins at multiple time points, and is a valuable tool to guide the discovery of signaling events and molecular signatures underlying cellular differentiation. We also monitored the activity level of pathways whose roles are pivotal in the early pancreas differentiation, including the Hippo signaling pathway. The quantitative proteomics data set provides insights into the dynamics of the global proteome during the transition of hPSCs from a pluripotent state toward pancreatic differentiation.

Reprogramming of Primary Human Cells to Induced Pluripotent Stem Cells Using Sendai Virus

Induced pluripotent stem (iPS) cells are important tools for studying differentiation and for use in patient-specific disease modeling. We present a detailed method for the reprogramming of primary human fibroblasts to induced pluripotent stem cells using Sendai virus. These procedures allow for the efficient generation of multiple high-quality feeder-independent iPS cell lines for a given human fibroblast line. The iPS cell lines generated by this protocol can be used in a variety of differentiation and gene expression studies, as well as in genetic manipulations.

Emerging Technologies for Tissue Engineering: From Gene Editing to Personalized Medicine

IMPACT STATEMENT

History has shown us how tissue engineering can be advanced by embracing technological innovation. In this perspective, we highlight some of the most promising emerging technologies and discuss how they can be integrated into existing tissue engineering protocols. The proposed technologies offer the opportunity to reshape how we currently design, engineer, and characterize tissue grafts for improved in vivo regeneration.

Proteomic analysis of decellularized pancreatic matrix identifies collagen V as a critical regulator for islet organogenesis from human pluripotent stem cells

In pancreatic tissue engineering, generating human pancreatic islet organoids from stem cells has been challenging due mainly to a poor understanding of niches required for multicellular tissue self-assembly in vitro. In this study, we aimed to identify bioactive, chemically defined niches from natural, biological materials for islet development in vitro. We investigated the proteomics of decellularized rat pancreatic extracellular matrix (dpECM) hydrogel using advanced bioinformatics analysis, and identified that type V collagen (ColV) is constantly and abundantly present in dpECM hydrogel. Niches provided to human pluripotent stem cells (iPSCs) by presenting ColV in matrix coating substrates permitted stem cells progression into islet-like organoids that consist of all major pancreatic endocrine cell types, i.e. α, β, δ, and pancreatic polypeptide cells. In the presence of ColV niches, gene expressions of all key pancreatic transcription factors and major hormone genes significantly increased in iPSC-derived organoids. Most importantly, ColV-containing microenvironment resulted in enhanced glucose responsive secretions of both insulin and glucagon hormone from organoids. The study demonstrates that ColV is a critical regulator that augments islet self-assembly from iPSCs, and it is feasible to utilize natural biomaterials to build tissue cues essential for multicellular tissue production in vitro.

Therapeutic Potential of Human Amniotic Epithelial Cells on Injuries and Disorders in the Central Nervous System

Despite recent advances in neurosurgery and pharmaceuticals, contemporary treatments are ineffective in restoring lost neurological functions in patients with injuries and disorders of the central nervous system (CNS). Therefore, novel and effective therapies are urgently needed. Recent studies have indicated that stem cells, including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and mesenchymal stem cells (MSCs), could repair/replace damaged or degenerative neurons and improve functional recovery in both preclinical and clinical trials. However, there are many unanswered questions and unsolved issues regarding stem cell therapy in terms of potency, stability, oncogenicity, immune response, cell sources, and ethics. Currently, human amniotic epithelial cells (hAECs) derived from the amnion exhibit considerable advantages over other stem cells and have drawn much attention from researchers. hAECs are readily available, pose no ethical concerns, and have little risk of tumorigenicity and immunogenicity. Mounting evidence has shown that hAECs can promote neural cell survival and regeneration, repair affected neurons, and reestablish damaged neural connections. It is suggested that hAECs may be the most promising candidate for cell-based therapy of neurological diseases. In this review, we mainly focus on recent advances and potential applications of hAECs for treating various CNS injuries and neurodegenerative disorders. We also discuss current hurdles and challenges regarding hAEC therapies.

Stem Cells: The Game Changers of Human Cardiac Disease Modelling and Regenerative Medicine

A comprehensive understanding of the molecular basis and mechanisms underlying cardiac diseases is mandatory for the development of new and effective therapeutic strategies. The lack of appropriate in vitro cell models that faithfully mirror the human disease phenotypes has hampered the understanding of molecular insights responsible of heart injury and disease development. Over the past decade, important scientific advances have revolutionized the field of stem cell biology through the remarkable discovery of reprogramming somatic cells into induced pluripotent stem cells (iPSCs). These advances allowed to achieve the long-standing ambition of modelling human disease in a dish and, more interestingly, paved the way for unprecedented opportunities to translate bench discoveries into new therapies and to come closer to a real and effective stem cell-based medicine. The possibility to generate patient-specific iPSCs, together with the new advances in stem cell differentiation procedures and the availability of novel gene editing approaches and tissue engineering, has proven to be a powerful combination for the generation of phenotypically complex, pluripotent stem cell-based cellular disease models with potential use for early diagnosis, drug screening, and personalized therapy. This review will focus on recent progress and future outcome of iPSCs technology toward a customized medicine and new therapeutic options.

Experimental and Computational Approaches to Direct Cell Reprogramming: Recent Advancement and Future Challenges

The process of direct cell reprogramming, also named transdifferentiation, permits for the conversion of one mature cell type directly into another, without returning to a dedifferentiated state. This makes direct reprogramming a promising approach for the development of several cellular and tissue engineering therapies. To achieve the change in the cell identity, direct reprogramming requires an arsenal of tools that combine experimental and computational techniques. In the recent years, several methods of transdifferentiation have been developed. In this review, we will introduce the concept of direct cell reprogramming and its background, and cover the recent developments in the experimental and computational prediction techniques with their applications. We also discuss the challenges of translating this technology to clinical setting, accompanied with potential solutions.

TGFβ signaling hyperactivation-induced tumorigenicity during the derivation of neural progenitors from mouse ESCs

Clinical therapies of pluripotent stem cells (PSCs)-based transplantation have been hindered by frequent development of teratomas or tumors in animal models and clinical patients. Therefore, clarifying the mechanism of carcinogenesis in stem cell therapy is of great importance for reducing the risk of tumorigenicity. Here we differentiate Oct4-GFP mouse embryonic stem cells (mESCs) into neural progenitor cells (NPCs) and find that a minority of Oct4+ cells are continuously sustained at Oct4+ state. These cells can be enriched and proliferated in a standard ESC medium. Interestingly, the differentiation potential of these enriched cells is tightly restricted with much higher tumorigenic activity, which are thus defined as differentiation-resistant ESCs (DR-ESCs). Transcriptomic and epigenomic analyses show that DR-ESCs are characterized by primordial germ cell-like gene signatures (Dazl, Rec8, Stra8, Blimp1, etc.) and specific epigenetic patterns distinct from mESCs. Moreover, the DR-ESCs possess germ cell potential to generate Sycp3+ haploid cells and are able to reside in sperm-free spermaduct induced by busulfan. Finally, we find that TGFβ signaling is overactivated in DR-ESCs, and inhibition of TGFβ signaling eliminates the tumorigenicity of mESC-derived NPCs by inducing the full differentiation of DR-ESCs. These data demonstrate that these TGFβ-hyperactivated germ cell-like DR-ESCs are the main contributor for the tumorigenicity of ESCs-derived target cell therapy and that inhibition of TGFβ signaling in ESC-derived NPC transplantation could drastically reduce the risk of tumor development.

Chromatin Accessibility Dynamics during Chemical Induction of Pluripotency

Despite its exciting potential, chemical induction of pluripotency (CIP) efficiency remains low and the mechanisms are poorly understood. We report the development of an efficient two-step serum- and replating-free CIP protocol and the associated chromatin accessibility dynamics (CAD) by assay for transposase-accessible chromatin (ATAC)-seq. CIP reorganizes the somatic genome to an intermediate state that is resolved under 2iL condition by re-closing previously opened loci prior to pluripotency acquisition with gradual opening of loci enriched with motifs for the OCT/SOX/KLF families. Bromodeoxyuridine, a critical ingredient of CIP, is responsible for both closing and opening critical loci, at least in part by preventing the opening of loci enriched with motifs for the AP1 family and facilitating the opening of loci enriched with SOX/KLF/GATA motifs. These changes differ markedly from CAD observed during Yamanaka-factor-driven reprogramming. Our study provides insights into small-molecule-based reprogramming mechanisms and reorganization of nuclear architecture associated with cell-fate decisions.

Comprehensive Cell Surface Antigen Analysis Identifies Transferrin Receptor Protein-1 (CD71) as a Negative Selection Marker for Human Neuronal Cells

Cell state‐, developmental stage‐, and lineage‐specific combinatorial expression of cluster of differentiation (CD) molecules enables the identification of cellular subsets via multicolor flow cytometry. We describe an exhaustive characterization of neural cell types by surface antigens, exploiting human pluripotent stem cell‐derived neural cell systems. Using multiwell screening approaches followed by detailed validation of expression patterns and dynamics, we exemplify a strategy for resolving cellular heterogeneity in stem cell paradigms. In addition to providing a catalog of surface antigens expressed in the neural lineage, we identified the transferrin receptor‐1 (CD71) to be differentially expressed in neural stem cells and differentiated neurons. In this context, we describe a role for N‐Myc proto‐oncogene (MYCN) in maintaining CD71 expression in proliferating neural cells. We report that in vitro human stem cell‐derived neurons lack CD71 surface expression and that the observed differential expression can be used to identify and enrich CD71⁻ neuronal derivatives from heterogeneous cultures. stem cells2019;37:1293–1306

Recent advances in the applications of iPSC technology

Pluripotent stems cells (PSCs) can be expanded indefinitely and differentiated into almost any organ-specific cell type. This has enabled the generation of disease relevant tissues from patients in scalable quantities. iPSC-derived organs and organoids are currently being evaluated both in regenerative therapy which are proceeding towards clinical trials, and for disease modeling, which are facilitating drug screening efforts for discovery of novel therapeutics. Here we will review the current efforts and advances in iPSC technology and its subsequent applications and provide a brief commentary on future outlook of this promising technology.

Impact of Induced Pluripotent Stem Cells in Bone Repair and Regeneration

PURPOSE OF REVIEW

The main objective of this article is to investigate the current trends in the use of induced pluripotent stem cells (iPSCs) for bone tissue repair and regeneration.

RECENT FINDINGS

Pluripotent stem cell-based tissue engineering has extended innovative therapeutic approaches for regenerative medicine. iPSCs have shown osteogenic differentiation capabilities and would be an innovative resource of stem cells for bone tissue regenerative applications. This review recapitulates the current knowledge and recent progress regarding utilization of iPSCs for bone therapy. A review of current findings suggests that a combination of a three-dimensional scaffolding system with iPSC technology to mimic the physiological complexity of the native stem cell niche is highly favorable for bone tissue repair and regeneration.

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.

Reprogramming the Epigenome With Vitamin C

The erasure of epigenetic modifications across the genome of somatic cells is an essential requirement during their reprogramming into induced pluripotent stem cells (iPSCs). Vitamin C plays a pivotal role in remodeling the epigenome by enhancing the activity of Jumonji-C domain-containing histone demethylases (JHDMs) and the ten-eleven translocation (TET) proteins. By maintaining differentiation plasticity in culture, vitamin C also improves the quality of tissue specific stem cells derived from iPSCs that are highly sought after for use in regenerative medicine. The ability of vitamin C to potentiate the activity of histone and DNA demethylating enzymes also has clinical application in the treatment of cancer. Vitamin C deficiency has been widely reported in cancer patients and has recently been shown to accelerate cancer progression in disease models. Therapies involving high-dose vitamin C administration are currently gaining traction in the treatment of epigenetic dysregulation, by targeting aberrant histone and DNA methylation patterns associated with cancer progression.

Enhancement of human induced pluripotent stem cells adhesion through multilayer laminin coating

Bioengineered cell substrates are a highly promising tool to govern the differentiation of stem cells in vitro and to modulate the cellular behavior in vivo. While this technology works fine for adult stem cells, the cultivation of human induced pluripotent stem cells (hiPSCs) is challenging as these cells typically show poor attachment on the bioengineered substrates, which among other effects causes substantial cell death. Thus, very limited types of surfaces have been demonstrated suitable for hiPSC cultures. The multilayer coating approach that renders the surface with diverse chemical compositions, architectures, and functions can be used to improve the adhesion of hiPSCs on the bioengineered substrates. We hypothesized that a multilayer formation based on the attraction of molecules with opposite charges could functionalize the polystyrene (PS) substrates to improve the adhesion of hiPSCs. Polymeric substrates were stepwise coated, first with dopamine to form a polydopamine (PDA) layer, second with polylysine and last with Laminin-521. The multilayer formation resulted in the variation of hydrophilicity and chemical functionality of the surfaces. Hydrophilicity was detected using captive bubble method and the amount of primary and secondary amines on the surface was quantified by fluorescent staining. The PDA layer effectively immobilized the upper layers and thereby improved the attachment of hiPSCs. Cell adhesion was enhanced on the surfaces coated with multilayers, as compared to those without PDA and/or polylysine. Moreover, hiPSCs spread well over this multilayer laminin substrate. These cells maintained their proliferation capacity and differentiation potential. The multilayer coating strategy is a promising attempt for engineering polymer-based substrates for the cultivation of hiPSCs and of interest for expanding the application scope of hiPSCs.

Conversion of Stem Cells to Cancer Stem Cells: Undercurrent of Cancer Initiation

Cancer stem cells (CSCs) also known as cancer-initiating cells (CIC), are responsible for the sustained and uncontrolled growth of malignant tumors and are proposed to play significant roles in metastasis and recurrence. Several hypotheses have proposed that the events in either stem and/or differentiated cells, such as genomic instability, inflammatory microenvironment, cell fusion, and lateral gene transfer, should be considered as the possible origin of CSCs. However, until now, the exact origin of CSC has been obscure. The development of induced pluripotent stem cells (iPSCs) in 2007, by Yamanaka's group, has been met with much fervency and hailed as a breakthrough discovery by the scientific and research communities, especially in regeneration therapy. The studies on the development of CSC from iPSCs should also open a new page of cancer research, which will help in designing new therapies applicable to CSCs. Currently most reviews have focused on CSCs and CSC niches. However, the insight into the niche before the CSC niche should also be of keen interest. This review introduces the novel concept of cancer initiation introducing the conversion of iPSCs to CSCs and proposes a relationship between the inflammatory microenvironment and cancer initiation as the key concept of the cancer-inducing niche responsible for the development of CSC.

3D bioprinting for high-throughput screening: Drug screening, disease modeling, and precision medicine applications

High-throughput technologies have become essential in many fields of pharmaceutical and biological development and production. Such technologies were initially developed with compatibility with liquid handling-based cell culture techniques to produce large-scale 2D cell culture experiments for the compound analysis of candidate drug compounds. Over the past two decades, tools for creating 3D cell cultures, organoids, and other 3D in vitro models, such as cell supportive biomaterials and 3D bioprinting, have rapidly advanced. Concurrently, a significant body of evidence has accumulated which speaks to the many benefits that 3D model systems have over traditional 2D cell cultures. Specifically, 3D cellular models better mimic aspects such as diffusion kinetics, cell-cell interactions, cell-matrix interactions, inclusion of stroma, and other features native to in vivo tissue and as such have become an integral part of academic research. However, most high throughput assays were not developed to specifically support 3D systems. Here, we describe the need for improved compatibility and relevant advances toward deployment and adoption of high throughput 3D models to improve disease modeling, drug efficacy testing, and precision medicine applications.

Endothelial Differentiation G Protein-Coupled Receptor 5 Plays an Important Role in Induction and Maintenance of Pluripotency

Direct reprogramming of human somatic cells toward induced pluripotent stem cells holds great promise for regenerative medicine and basic biology. We used a high-throughput small interfering RNA screening assay in the initiation phase of reprogramming for 784 genes belonging to kinase and phosphatase families and identified 68 repressors and 22 effectors. Six new candidates belonging to the family of the G protein-coupled receptors (GPCRs) were identified, suggesting an important role for this key signaling pathway during somatic cell-induced reprogramming. Downregulation of one of the key GPCR effectors, endothelial differentiation GPCR5 (EDG5), impacted the maintenance of pluripotency, actin cytoskeleton organization, colony integrity, and focal adhesions in human embryonic stem cells, which were associated with the alteration in the RhoA-ROCK-Cofilin-PAXILLIN-actin signaling pathway. Similarly, downregulation of EDG5 during the initiation stage of somatic cell-induced reprogramming resulted in alteration of cytoskeleton, loss of human-induced pluripotent stem cell colony integrity, and a significant reduction in partially and fully reprogrammed cells as well as the number of alkaline phosphatase positive colonies at the end of the reprogramming process. Together, these data point to an important role of EDG5 in the maintenance and acquisition of pluripotency. Stem Cells 2019;37:318-331.

Bioengineering human vascular networks: trends and directions in endothelial and perivascular cell sources

Tissue engineering holds great promise in regenerative medicine. However, the field of tissue engineering faces a myriad of difficulties. A major challenge is the necessity to integrate vascular networks into bioengineered constructs to enable physiological functions including adequate oxygenation, nutrient delivery, and removal of waste products. The last two decades have seen remarkable progress in our collective effort to bioengineer human-specific vascular networks. Studies have included both in vitro and in vivo investigations, and multiple methodologies have found varying degrees of success. What most approaches to bioengineer human vascular networks have in common, however, is the synergistic use of both (1) endothelial cells (ECs)-the cells used to line the lumen of the vascular structures and (2) perivascular cells-usually used to support EC function and provide perivascular stability to the networks. Here, we have highlighted trends in the use of various cellular sources over the last two decades of vascular network bioengineering research. To this end, we comprehensively reviewed all life science and biomedical publications available at the MEDLINE database up to 2018. Emphasis was put on selective studies that definitively used human ECs and were specifically related to bioengineering vascular networks. To facilitate this analysis, all papers were stratified by publication year and then analyzed according to their use of EC and perivascular cell types. This study provides an illustrating discussion on how each alternative source of cells has come to be used in the field. Our intention was to reveal trends and to provide new insights into the trajectory of vascular network bioengineering with regard to cellular sources.

Sirt6 regulates efficiency of mouse somatic reprogramming and maintenance of pluripotency

BACKGROUND

Mouse somatic cells can be reprogrammed into induced pluripotent stem cells (iPSCs) by defined factors known to regulate pluripotency, including Oct4, Sox2, Klf4, and c-Myc. It has been reported that Sirtuin 6 (Sirt6), a member of the sirtuin family of NAD+-dependent protein deacetylases, is involved in embryonic stem cell differentiation. However, whether and how Sirt6 influences epigenetic reprogramming remains unknown.

METHODS

Mouse embryonic fibroblasts isolated from transgenic Oct4-GFP reporter mice with or without Sirt6 were used for reprogramming by Yamanaka factors. Alkaline phosphatase-positive and OCT4-GFP-positive colony were counted to calculate reprogramming efficiency. OP9 feeder cell co-culture system was used to measure the hematopoietic differentiation from mouse ES and iPS cells. RNA sequencing was measured to identify the differential expressed genes due to loss of Sirt6 in somatic and pluripotent cells.

RESULTS

In this study, we provide evidence that Sirt6 is involved in mouse somatic reprogramming. We found that loss of function of Sirt6 could significantly decrease reprogramming efficiency. Furthermore, we showed that Sirt6-null iPS-like cell line has intrinsically a differentiation defect even though the establishment of normal self-renewal. Particularly, by performing transcriptome analysis, we observed that several pluripotent transcriptional factors increase in knockout cell line, which explains the underlying loss of pluripotency in Sirt6-null iPS-like cell line.

CONCLUSIONS

Taken together, we have identified a new regulatory role of Sirt6 in reprogramming and maintenance of pluripotency.

Aberrant hiPSCs-Derived from Human Keratinocytes Differentiates into 3D Retinal Organoids that Acquire Mature Photoreceptors

Human induced pluripotent stem cell (hiPSC)-derived three-dimensional retinal organoids are a new platform for studying the organoidogenesis. However, recurrent genomic aberration, acquired during generation of hiPSCs, limit its biomedical application and/or aberrant hiPSCs has not been evaluated for generation of differentiated derivatives, such as organoids and retinal pigment epithelium (RPE). In this study, we efficiently differentiated mosaic hiPSCs into retinal organoids containing mature photoreceptors. The feeder-free hiPSCs were generated from the human epidermal keratinocytes that were rapid in process with improved efficiency over several passages and maintained pluripotency. But, hiPSCs were cytogenetically mosaic with normal and abnormal karyotypes, while copy number variation analysis revealed the loss of chromosome 8q. Despite this abnormality, the stepwise differentiation of hiPSCs to form retinal organoids was autonomous and led to neuronal lamination. Furthermore, the use of a Notch inhibitor, DAPT, at an early timepoint from days 29⁻42 of culture improved the specification of the retinal neuron and the use of retinoic acid at days 70⁻120 led to the maturation of photoreceptors. hiPSC-derived retinal organoids acquired all subtypes of photoreceptors, such as RHODOPSIN, B-OPSIN and R/G-OPSIN. Additionally, the advanced maturation of photoreceptors was observed, revealing the development of specific sensory cilia and the formation of the outer-segment disc. This report is the first to show that hiPSCs with abnormal chromosomal content are permissive to the generation of three-dimensional retinal organoids.

Tissue Engineering for the Temporomandibular Joint

Tissue engineering potentially offers new treatments for disorders of the temporomandibular joint which frequently afflict patients. Damage or disease in this area adversely affects masticatory function and speaking, reducing patients' quality of life. Effective treatment options for patients suffering from severe temporomandibular joint disorders are in high demand because surgical options are restricted to removal of damaged tissue or complete replacement of the joint with prosthetics. Tissue engineering approaches for the temporomandibular joint are a promising alternative to the limited clinical treatment options. However, tissue engineering is still a developing field and only in its formative years for the temporomandibular joint. This review outlines the anatomical and physiological characteristics of the temporomandibular joint, clinical management of temporomandibular joint disorder, and current perspectives in the tissue engineering approach for the temporomandibular joint disorder. The tissue engineering perspectives have been categorized according to the primary structures of the temporomandibular joint: the disc, the mandibular condyle, and the glenoid fossa. In each section, contemporary approaches in cellularization, growth factor selection, and scaffold fabrication strategies are reviewed in detail along with their achievements and challenges.

Establishment and Identification of a CiPSC Lineage Reprogrammed from FSP-tdTomato Mouse Embryonic Fibroblasts (MEFs)

Safety issues associated with transcription factors or viruses may be avoided with the use of chemically induced pluripotent stem cells (CiPSCs), thus promoting their clinical application. Previously, we had successfully developed and standardized an induction method using small-molecule compound, with simple operation, uniform induction conditions, and clear constituents. In order to verify that the CiPSCs were indeed reprogrammed from mouse embryonic fibroblasts (MEFs), and further explore the underlying mechanisms, FSP-tdTomato mice were used to construct a fluorescent protein-tracking system of MEFs, for revealing the process of CiPSC reprogramming. CiPSCs were identified by morphological analysis, mRNA, and protein expression of pluripotency genes, as well as teratoma formation experiments. Results showed that after 40-day treatment of tdTomato-MEFs with small-molecule compounds, the cells were presented with prominent nucleoli, high core-to-cytoplasmic ratio, round shape, group and mass arrangement, and high expression of pluripotency gene. These cells could differentiate into three germ layer tissues in vivo. As indicated by the above results, tdTomato-MEFs could be reprogrammed into CiPSCs, a lineage that possesses pluripotency similar to mouse embryonic stem cells (mESCs), with the use of small-molecule compounds. The establishment of CiPSC lineage, tracked by fluorescent protein, would benefit further studies exploring its underlying mechanisms. With continuous expression of fluorescent proteins during cellular differentiation, this cell lineage could be used for tracking CiPSC transplantation and differentiation into functional cells.

Effect of migratory behaviors on human induced pluripotent stem cell colony formation on different extracellular matrix proteins

Introduction

Understanding how extracellular matrix (ECM) protein composition regulates the process of human induced pluripotent stem cell (hiPSC) colony formation may facilitate the design of optimal cell culture environments. In this study, we investigated the effect of migratory behaviors on hiPSC colony formation on various ECM-coated surfaces.

Methods

To quantify how different ECM proteins affect migratory behavior during the colony formation process, single cells were seeded onto surfaces coated with varying concentrations of different ECM proteins. Cell behavior was monitored by time-lapse observation, and quantitative analysis of migration rates in relation to colony formation patterns was performed. Actin cytoskeleton, focal adhesions, and cell–cell interactions were detected by fluorescence microscopy.

Results

Time-lapse observations revealed that different mechanisms of colony formation were dependent upon the migratory behavior of cells on different ECM surfaces. HiPSCs formed tight colonies on concentrated ECM substrates, while coating with dilute concentrations of ECM yielded more motile cells and colonies capable of splitting into single cells or small clusters. Enhanced migration caused a reduction of cell–cell contacts that enabled splitting or merging between cells and cell clusters, consequently reducing the efficiency of clonal colony formation. High cell-to-cell variability in migration responses to ECM surfaces elicited differential focal adhesion formation and E-cadherin expression within cells and colonies. This resulted in variability within focal adhesions and further loss of E-cadherin expression by hiPSCs.

Conclusions

Migration is an important factor affecting hiPSC colony-forming patterns. Regulation of migratory behavior can be an effective way to improve the expansion of hiPSCs while improving the process of clonal colony formation. We believe that this investigation provides a valuable method for understanding cell phenotypes and heterogeneity during colony formation in culture.

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hiPSC colony-forming patterns were dependent on migratory behavior on different ECM surfaces.

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Colony formation without splitting during migration improved efficiency of clonal colony formation.

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Variability in migration behavior elicited differential cytoskeletal formation and E-cadherin expression.

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Our method is valuable for understanding cell phenotypes and heterogeneity during colony formation.

Enhanced Function of Induced Pluripotent Stem Cell-Derived Endothelial Cells Through ESM1 Signaling

The mortality rate for (cardio)‐vascular disease is one of the highest in the world, so a healthy functional endothelium is of outmost importance against vascular disease. In this study, human induced pluripotent stem (iPS) cells were reprogrammed from 1 ml blood of healthy donors and subsequently differentiated into endothelial cells (iPS‐ECs) with typical EC characteristics. This research combined iPS cell technologies and next‐generation sequencing to acquire an insight into the transcriptional regulation of iPS‐ECs. We identified endothelial cell‐specific molecule 1 (ESM1) as one of the highest expressed genes during EC differentiation, playing a key role in EC enrichment and function by regulating connexin 40 (CX40) and eNOS. Importantly, ESM1 enhanced the iPS‐ECs potential to improve angiogenesis and neovascularisation in in vivo models of angiogenesis and hind limb ischemia. These findings demonstrated for the first time that enriched functional ECs are derived through cell reprogramming and ESM1 signaling, opening the horizon for drug screening and cell‐based therapies for vascular diseases. Therefore, this study showcases a new approach for enriching and enhancing the function of induced pluripotent stem (iPS) cell‐derived ECs from a very small amount of blood through ESM1 signaling, which greatly enhances their functionality and increases their therapeutic potential. Stem Cells2019;37:226–239

Linking a cell-division gene and a suicide gene to define and improve cell therapy safety

Human pluripotent cell lines hold enormous promise for the development of cell-based therapies. Safety, however, is a crucial prerequisite condition for clinical applications. Numerous groups have attempted to eliminate potentially harmful cells through the use of suicide genes¹, but none has quantitatively defined the safety level of transplant therapies. Here, using genome-engineering strategies, we demonstrate the protection of a suicide system from inactivation in dividing cells. We created a transcriptional link between the suicide gene herpes simplex virus thymidine kinase (HSV-TK) and a cell-division gene (CDK1); this combination is designated the safe-cell system. Furthermore, we used a mathematical model to quantify the safety level of the cell therapy as a function of the number of cells that is needed for the therapy and the type of genome editing that is performed. Even with the highly conservative estimates described here, we anticipate that our solution will rapidly accelerate the entry of cell-based medicine into the clinic.

Generation of orthotopically functional salivary gland from embryonic stem cells

Organoids generated from pluripotent stem cells are used in the development of organ replacement regenerative therapy by recapitulating the process of organogenesis. These processes are strictly regulated by morphogen signalling and transcriptional networks. However, the precise transcription factors involved in the organogenesis of exocrine glands, including salivary glands, remain unknown. Here, we identify a specific combination of two transcription factors (Sox9 and Foxc1) responsible for the differentiation of mouse embryonic stem cell-derived oral ectoderm into the salivary gland rudiment in an organoid culture system. Following orthotopic transplantation into mice whose salivary glands had been removed, the induced salivary gland rudiment not only showed a similar morphology and gene expression profile to those of the embryonic salivary gland rudiment of normal mice but also exhibited characteristics of mature salivary glands, including saliva secretion. This study suggests that exocrine glands can be induced from pluripotent stem cells for organ replacement regenerative therapy.

Improved Generation of Induced Pluripotent Stem Cells From Hair Derived Keratinocytes - A Tool to Study Neurodevelopmental Disorders as ADHD

In the last decade, there is an increasing application of induced pluripotent stem cells (iPSCs) for disease modeling. The iPSC technology enables the study of patient-specific neuronal cell lines in vitro to evaluate dysfunction at the cellular level and identify the responsible genetic factors. This approach might be particularly valuable for filling the gap of knowledge at the cellular and molecular levels underlying the pathophysiology of various neurodevelopmental and/or psychiatric disorders, such as attention-deficit hyperactivity disorder (ADHD). However, the invasiveness of skin biopsy or blood withdrawal might represent a major impediment in such protected population. Using hair derived keratinocytes as starting somatic cells circumvents this problem as sample collections can be performed non-invasively. Here we describe an improved, convenient, standardized and effective method to culture and reprogram hair derived keratinocytes from three healthy controls and one ADHD patient into iPSCs, which in turn will be used to generate differentiated neuronal cells. All the cell types were maintained in highly defined, serum-free conditions and showed expression of the respective key marker genes, assessed by both immunocytochemistry and qRT-PCR. The described in vitro personalized neuronal model has its advantage in modeling neurodevelopmental trajectories since it can recapitulate key processes of brain development at the cellular and molecular level and is intended to be used as for example studying ADHD etiopathology.

Engineering the niche for hair regeneration - A critical review

Recent progress in hair follicle regeneration and alopecia treatment necessitates revisiting the concepts and approaches. In this sense, there is a need for shedding light on the clinical and surgical therapies benefitting from nanobiomedicine. From this perspective, this review attempts to recognize requirements upon which new hair therapies are grounded; to underline shortcomings and opportunities associated with recent advanced strategies for hair regeneration; and most critically to look over hair regeneration from nanomaterials and pluripotent stem cell standpoint. It is noteworthy that nanotechnology is able to illuminate a novel path for reprogramming cells and controlled differentiation to achieve the desired performance. Undoubtedly, this strategy needs further advancement and a lot of critical questions have yet to be answered. Herein, we introduce the salient features, the hurdles that must be overcome, the hopes, and practical constraints to engineer stem cell niches for hair follicle regeneration.

Applications of Bioengineered 3D Tissue and Tumor Organoids in Drug Development and Precision Medicine: Current and Future

Over the past decade, advances in biomedical and tissue engineering technologies, such as cell culture techniques, biomaterials, and biofabrication, have driven increasingly widespread use of three-dimensional (3D) cell culture platforms and, subsequently, the use of organoids in a variety of research endeavors. Given the 3D nature of these organoid systems, and the frequent inclusion of extracellular matrix components, these constructs typically have more physiologically accurate cell-cell and cell-matrix interactions than traditional 2D cell cultures. As a result, 3D organoids can serve as better model systems than their 2D counterparts. Moreover, as organoids can be biofabricated from highly functional human cells, they have certain advantages over animal models, being human in nature and more easily manipulated in the laboratory. In this review, we describe such organoid technologies and their deployment in drug development and precision medicine efforts. Organoid technologies are rapidly being developed for these applications and now represent a wide variety of tissue types and diseases. Evidence is emerging that organoids are poised for widespread adoption, not only in academia but also in the pharmaceutical industry and in clinical diagnostic applications, positioning them as indispensable tools in medicine.

Live cell imaging of X chromosome reactivation during somatic cell reprogramming

Generation of induced pluripotent stem cells (iPSCs) with naive pluripotency is important for their applications in regenerative medicine. In female iPSCs, acquisition of naive pluripotency is coupled to X chromosome reactivation (XCR) during somatic cell reprogramming, and live cell monitoring of XCR is potentially useful for analyzing how iPSCs acquire naive pluripotency. Here we generated female mouse embryonic stem cells (ESCs) that carry the enhanced green fluorescent protein (EGFP) and humanized Kusabira-Orange (hKO) genes inserted into an intergenic site near either the Syap1 or Taf1 gene on both X chromosomes. The ESC clones, which initially expressed both EGFP and hKO, inactivated one of the fluorescent protein genes upon differentiation, indicating that the EGFP and hKO genes are subject to X chromosome inactivation (XCI). When the derived somatic cells carrying the EGFP gene on the inactive X chromosome (Xi) were reprogrammed into iPSCs, the EGFP gene on the Xi was reactivated when pluripotency marker genes were induced. Thus, the fluorescent protein genes inserted into an intergenic locus on both X chromosomes enable live cell monitoring of XCI during ESC differentiation and XCR during reprogramming. This is the first study that succeeded live cell imaging of XCR during reprogramming.

Bringing cultured meat to market: Technical, socio-political, and regulatory challenges in cellular agriculture

BACKGROUND

Cultured meat forms part of the emerging field of cellular agriculture. Still an early stage field it seeks to deliver products traditionally made through livestock rearing in novel forms that require no, or significantly reduced, animal involvement. Key examples include cultured meat, milk, egg white and leather. Here, we focus upon cultured meat and its technical, socio-political and regulatory challenges and opportunities.

SCOPE AND APPROACH

The paper reports the thinking of an interdisciplinary team, all of whom have been active in the field for a number of years. It draws heavily upon the published literature, as well as our own professional experience. This includes ongoing laboratory work to produce cultured meat and over seventy interviews with experts in the area conducted in the social science work.

KEY FINDINGS AND CONCLUSIONS

Cultured meat is a promising, but early stage, technology with key technical challenges including cell source, culture media, mimicking the in-vivo myogenesis environment, animal-derived and synthetic materials, and bioprocessing for commercial-scale production. Analysis of the social context has too readily been reduced to ethics and consumer acceptance, and whilst these are key issues, the importance of the political and institutional forms a cultured meat industry might take must also be recognised, and how ambiguities shape any emergent regulatory system.

New Turns for High Efficiency Knock-In of Large DNA in Human Pluripotent Stem Cells

The groundbreaking CRISPR technology is revolutionizing biomedical research with its superior simplicity, high efficiency, and robust accuracy. Recent technological advances by a coupling CRISPR system with various DNA repair mechanisms have further opened up new opportunities to overcome existing challenges in knocking-in foreign DNA in human pluripotent stem cells, including embryonic stem cells (ESC) and induced pluripotent stem cells (iPSC). In this review, we summarized the very recent development of CRISPR-based knock-in strategies and discussed the results obtained as well as potential applications in human ESC and iPSC.

Zero-dimensional, one-dimensional, two-dimensional and three-dimensional biomaterials for cell fate regulation

The interaction of biological cells with artificial biomaterials is one of the most important issues in tissue engineering and regenerative medicine. The interaction is strongly governed by physical and chemical properties of the materials and displayed with differentiated cellular behaviors, including cell self-renewal, differentiation, reprogramming, dedifferentiation, or transdifferentiation as a result. A number of engineered biomaterials with micro- or nano-structures have been developed to mimic structural components of cell niche and specific function of extra cellular matrix (ECM) over past two decades. In this review article, we briefly introduce the fabrication of biomaterials and their classification into zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) ones. More importantly, the influence of different biomaterials on inducing cell self-renewal, differentiation, reprogramming, dedifferentiation, and transdifferentiation was discussed based on the progress at 0D, 1D, 2D and 3D levels, following which the current research limitations and research perspectives were provided.

Organoid technology for brain and therapeutics research

Brain is one of the most complex organs in human. The current brain research is mainly based on the animal models and traditional cell culture. However, the inherent species differences between humans and animals as well as the gap between organ level and cell level make it difficult to study human brain development and associated disorders through traditional technologies. Recently, the brain organoids derived from pluripotent stem cells have been reported to recapitulate many key features of human brain in vivo, for example recapitulating the zone of putative outer radial glia cells. Brain organoids offer a new platform for scientists to study brain development, neurological diseases, drug discovery and personalized medicine, regenerative medicine, and so on. Here, we discuss the progress, applications, advantages, limitations, and prospects of brain organoid technology in neurosciences and related therapeutics.

Stem Cells Engineered During Different Stages of Reprogramming Reveal Varying Therapeutic Efficacies

Stem cells are emerging as promising treatment strategies for several brain disorders and pathologies. In this study, we explored the potential of creating induced pluripotent stem cell-derived neural stem cells (ipNSC) by using either unmodified or gene-modified somatic cells and tested their fate and therapeutic efficacies in vitro and in vivo. We show that cells engineered in somatic state lose transgene-expression during the neural induction process, which is partially restored by histone deacetylase inhibitor treatment whereas cells engineered at the ipNSC state have sustained expression of transgenes. In vivo, bimodal mouse and human ipNSCs engineered to express tumor specific death-receptor ligand and suicide-inducing therapeutic proteins have profound anti-tumor efficacy when encapsulated in synthetic extracellular matrix and transplanted in mouse models of resected-glioblastoma. This study provides insights into using somatic cells for treating CNS disorders and presents a receptor-targeted cancer therapeutic approach for brain tumors. Stem Cells 2018;36:932-942.

Ten years of progress and promise of induced pluripotent stem cells: historical origins, characteristics, mechanisms, limitations, and potential applications

The discovery of induced pluripotent stem cells (iPSCs) by Shinya Yamanaka in 2006 was heralded as a major breakthrough of the decade in stem cell research. The ability to reprogram human somatic cells to a pluripotent embryonic stem cell-like state through the ectopic expression of a combination of embryonic transcription factors was greeted with great excitement by scientists and bioethicists. The reprogramming technology offers the opportunity to generate patient-specific stem cells for modeling human diseases, drug development and screening, and individualized regenerative cell therapy. However, fundamental questions have been raised regarding the molecular mechanism of iPSCs generation, a process still poorly understood by scientists. The efficiency of reprogramming of iPSCs remains low due to the effect of various barriers to reprogramming. There is also the risk of chromosomal instability and oncogenic transformation associated with the use of viral vectors, such as retrovirus and lentivirus, which deliver the reprogramming transcription factors by integration in the host cell genome. These challenges can hinder the therapeutic prospects and promise of iPSCs and their clinical applications. Consequently, extensive studies have been done to elucidate the molecular mechanism of reprogramming and novel strategies have been identified which help to improve the efficiency of reprogramming methods and overcome the safety concerns linked with iPSC generation. Distinct barriers and enhancers of reprogramming have been elucidated, and non-integrating reprogramming methods have been reported. Here, we summarize the progress and the recent advances that have been made over the last 10 years in the iPSC field, with emphasis on the molecular mechanism of reprogramming, strategies to improve the efficiency of reprogramming, characteristics and limitations of iPSCs, and the progress made in the applications of iPSCs in the field of disease modelling, drug discovery and regenerative medicine. Additionally, this study appraises the role of genomic editing technology in the generation of healthy iPSCs.

Efficient production of erythroid, megakaryocytic and myeloid cells, using single cell-derived iPSC colony differentiation

Hematopoietic differentiation of human induced pluripotent stem cells (iPSCs) provide opportunities not only for fundamental research and disease modelling/drug testing but also for large-scale production of blood effector cells for future clinical application. Although there are multiple ways to differentiate human iPSCs towards hematopoietic lineages, there is a need to develop reproducible and robust protocols. Here we introduce an efficient way to produce three major blood cell types using a standardized differentiation protocol that starts with a single hematopoietic initiation step. This system is feeder-free, avoids EB-formation, starts with a hematopoietic initiation step based on a novel single cell-derived iPSC colony differentiation and produces multi-potential progenitors within 8-10 days. Followed by lineage-specific growth factor supplementation these cells can be matured into well characterized erythroid, megakaryocytic and myeloid cells with high-purity, without transcription factor overexpression or any kind of pre-purification step. This standardized differentiation system provides a simple platform to produce specific blood cells in a reproducible manner for hematopoietic development studies, disease modelling, drug testing and the potential for future therapeutic applications.