Human embryonic stem cells: mother of all cell and tissue types

Exploring the origins of neurodevelopmental proteasomopathies associated with cardiac malformations: are neural crest cells central to certain pathological mechanisms?

Neurodevelopmental proteasomopathies constitute a recently defined class of rare Mendelian disorders, arising from genomic alterations in proteasome-related genes. These alterations result in the dysfunction of proteasomes, which are multi-subunit protein complexes essential for maintaining cellular protein homeostasis. The clinical phenotype of these diseases manifests as a syndromic association involving impaired neural development and multisystem abnormalities, notably craniofacial anomalies and malformations of the cardiac outflow tract (OFT). These observations suggest that proteasome loss-of-function variants primarily affect specific embryonic cell types which serve as origins for both craniofacial structures and the conotruncal portion of the heart. In this hypothesis article, we propose that neural crest cells (NCCs), a highly multipotent cell population, which generates craniofacial skeleton, mesenchyme as well as the OFT of the heart, in addition to many other derivatives, would exhibit a distinctive vulnerability to protein homeostasis perturbations. Herein, we introduce the diverse cellular compensatory pathways activated in response to protein homeostasis disruption and explore their potential implications for NCC physiology. Altogether, the paper advocates for investigating proteasome biology within NCCs and their early cranial and cardiac derivatives, offering a rationale for future exploration and laying the initial groundwork for therapeutic considerations.

A novel method to reconstruct epithelial tissue using high-purity keratinocyte lineage cells induced from human embryonic stem cells

The treatment of oral mucosa defect such as autologous oral mucosa caused by resection of oral mucosa carcinoma is still not ideal in clinical practice. However, Tissue engineering gives us the possibility to solve this problem. As we all know, Human embryonic stem cells (hESCs) have the ability to give rise to various cell types. We can take advantage of the totipotency of human embryonic stem cells to acquire keratinocytes. Directing the epithelial differentiation of hESCs can provide seed cells for the construction of epithelium tissue by tissue engineering. But, how to get high purity keratinocytes by induced stem cells then Applied to tissue engineering mucosa is an important challenge. We described a novel method to directly induce hESCs to differentiate into keratinocytes. Retinoic acid, ascorbic acid, and bone morphogenetic protein induced hESCs to differentiate into cells that highly expressed cytokeratin (CK)14. Our findings suggest that the retinoic acid, ascorbic acid and bone morphogenetic proteins induced hESCs to form high purity keratinocyte cell populations. In addition, we found that the highly pure keratinocyte populations reconstructed artificial tissue resembling epithelial tissue when inoculated in vitro on a biological scaffold.

Advances and challenges in stem cell culture

Stem cells (SCs) hold great promise for cell therapy, tissue engineering, and regenerative medicine as well as pharmaceutical and biotechnological applications. They have the capacity to self-renew and the ability to differentiate into specialized cell types depending upon their source of isolation. However, use of SCs for clinical applications requires a high quality and quantity of cells. This necessitates large-scale expansion of SCs followed by efficient and homogeneous differentiation into functional derivatives. Traditional methods for maintenance and expansion of cells rely on two-dimensional (2-D) culturing techniques using plastic culture plates and xenogenic media. These methods provide limited expansion and cells tend to lose clonal and differentiation capacity upon long-term passaging. Recently, new approaches for the expansion of SCs have emphasized three-dimensional (3-D) cell growth to mimic the in vivo environment. This review provides a comprehensive compendium of recent advancements in culturing SCs using 2-D and 3-D techniques involving spheroids, biomaterials, and bioreactors. In addition, potential challenges to achieve billion-fold expansion of cells are discussed.

Potential applications of keratinocytes derived from human embryonic stem cells

Although skin grafting is one of the most advanced cell therapy technique, wide application of skin substitutes is hampered by the difficulty in securing sufficient amount of epidermal substitute. Additionally, in understanding the progression of skin aging and disease, and in screening the cosmetic and pharmaceutical products, there is lack of a satisfactory human skin-specific in vitro model. Recently, human embryonic stem cells (hESCs) have been proposed as an unlimited and reliable cell source to obtain almost all cell types present in the human body. This review focuses on the potential off-the-shelf use of hESC-derived keratinocytes for future clinical applications as well as a powerful in vitro skin model to study skin function and integrity, host-pathogen interactions and disease pathogenesis. Furthermore, we discuss the industrial applications of hESC-derived keratinized multi-layer epithelium which provides a human-like test platform for understanding disease pathogenesis, evaluation of new therapeutic modalities and assessment of the safety and efficacy of skin cosmetics and therapeutics. Overall, we conclude that the hESC-derived keratinocytes have great potential for clinical, research and industrial applications.

Development of circadian oscillators in neurosphere cultures during adult neurogenesis

Circadian rhythms are common in many cell types but are reported to be lacking in embryonic stem cells. Recent studies have described possible interactions between the molecular mechanism of circadian clocks and the signaling pathways that regulate stem cell differentiation. Circadian rhythms have not been examined well in neural stem cells and progenitor cells that produce new neurons and glial cells during adult neurogenesis. To evaluate circadian timing abilities of cells undergoing neural differentiation, neurospheres were prepared from the mouse subventricular zone (SVZ), a rich source of adult neural stem cells. Circadian rhythms in mPer1 gene expression were recorded in individual spheres, and cell types were characterized by confocal immunofluorescence microscopy at early and late developmental stages in vitro. Circadian rhythms were observed in neurospheres induced to differentiate into neurons or glia, and rhythms emerged within 3–4 days as differentiation proceeded, suggesting that the neural stem cell state suppresses the functioning of the circadian clock. Evidence was also provided that neural stem progenitor cells derived from the SVZ of adult mice are self-sufficient clock cells capable of producing a circadian rhythm without input from known circadian pacemakers of the organism. Expression of mPer1 occurred in high frequency oscillations before circadian rhythms were detected, which may represent a role for this circadian clock gene in the fast cycling of gene expression responsible for early cell differentiation.

The role of stem cell therapies in degenerative lumbar spine disease: a review

Degenerative conditions of the lumbar spine are extremely common. Ninety percent of people over the age of 60 years have degenerative change on imaging; however, only a small minority of people will require spine surgery (Hicks et al. Spine (Phila Pa 1976) 34(12):1301-1306, 2009). This minority, however, constitutes a core element of spinal surgery practice. Whilst the patient outcomes from spinal surgeries have improved in recent years, some patients will remain with pain and disability despite technically successful surgery. Advances in regenerative medicine and stem cell therapies, particularly the use of mesenchymal stem cells and allogeneic mesenchymal precursor cells, have led to numerous clinical trials utilising these cell-based therapies to treat degenerative spinal conditions. Through cartilage formation and disc regeneration, fusion enhancement or via modification of pain pathways, stem cells are well suited to enhance spinal surgery practice. This review will focus on the outcomes of lumbar spinal procedures and the role of stem cells in the treatment of degenerative lumbar conditions to enhance clinical practice. The current status of clinical trials utilising stem cell therapies will be discussed, providing clinicians with an overview of the various cell-based treatments likely to be available to patients in the near future.

Stem cells in dermatology

Preclinical and clinical research have shown that stem cell therapy could be a promising therapeutic option for many diseases in which current medical treatments do not achieve satisfying results or cure. This article describes stem cells sources and their therapeutic applications in dermatology today.

Enhanced differentiation of human embryonic stem cells on extracellular matrix-containing osteomimetic scaffolds for bone tissue engineering

Current methods of treating critical size bone defects include autografts and allografts, however, both present major limitations including donor-site morbidity, risk of disease transmission, and immune rejection. Tissue engineering provides a promising alternative to circumvent these shortcomings through the use of autologous cells, three-dimensional scaffolds, and growth factors. We investigated the development of a scaffold with native bone extracellular matrix (ECM) components for directing the osteogenic differentiation of human embryonic stem cells (hESCs). Toward this goal, a microsphere-sintering technique was used to fabricate poly(lactic-co-glycolic acid) (PLGA) scaffolds with optimum mechanical and structural properties. Human osteoblasts (hOBs) were seeded on these scaffolds to deposit bone ECM for 14 days. This was followed by a decellularization step leaving the mineralized matrix intact. Characterization of the decellularized PLGA scaffolds confirmed the deposition of calcium, collagen II, and alkaline phosphatase by osteoblasts. hESCs were seeded on the osteomimetic substrates in the presence of osteogenic growth medium, and osteogenicity was determined according to calcium content, osteocalcin expression, and bone marker gene regulation. Cell proliferation studies showed a constant increase in number for hESCs seeded on both PLGA and ECM-coated PLGA scaffolds. Calcium deposition by hESCs was significantly higher on the osteomimetic scaffolds compared with the control groups. Consistently, immunofluorescence staining demonstrated an increased expression of osteocalcin in hESCs seeded on ECM-coated osteomimetic PLGA scaffolds. Gene expression analysis of RUNX2 and osteocalcin further confirmed osteogenic differentiation of hESCs at the highest expression level on osteomimetic PLGA. These results together demonstrate the potential of PLGA scaffolds with native bone ECM components to direct osteogenic differentiation of hESCs and induce bone formation.

Evaluation of developmental toxicity using undifferentiated human embryonic stem cells

An embryonic stem cell test (EST) has been developed to evaluate the embryotoxic potential of chemicals with an in vitro system. In the present study, novel methods to screen toxic chemicals during the developmental process were evaluated using undifferentiated human embryonic stem (hES) cells. By using surface marker antigens (SSEA-4, TRA-1-60 and TRA-1-81), we confirmed undifferentiated conditions of the used hES cells by immunocytochemistry. We assessed the developmental toxicity of embryotoxic chemicals, 5-fluorouracil, indomethacin and non-embryotoxic penicillin G in different concentrations for up to 7 days. While expressions of the surface markers were not significantly affected, the embryotoxic chemicals influenced their response to pluripotent ES cell markers, such as OCT-4, NANOG, endothelin receptor type B (EDNRB), secreted frizzled related protein 2 (SFRP2), teratocarcinoma-derived growth factor 1 (TDGF1), and phosphatase and tensin homolog (PTEN). Most of the pluripotent ES cell markers were down-regulated in a dose-dependent manner after treatment with embryotoxic chemicals. After treatment with 5-fluorouracil, indomethacin and penicillin G, we observed a remarkable convergence in the degree of up-regulation of development, cell cycle and apoptosis-related genes by gene expression profiles using an Affymetrix GeneChips. Taken together, these results suggest that embryotoxic chemicals have cytotoxic effects, and modulate the expression of ES cell markers as well as development-, cell cycle- and apoptosis-related genes that have pivotal roles in undifferentiated hES cells. Therefore, we suggest that hES cells may be useful for testing the toxic effects of chemicals that could impact the embryonic developmental stage.

Developmental-like bone regeneration by human embryonic stem cell-derived mesenchymal cells

The in vivo osteogenesis potential of mesenchymal-like cells derived from human embryonic stem cells (hESC-MCs) was evaluated in vivo by implantation on collagen/hydroxyapatite scaffolds into calvarial defects in immunodeficient mice. This study is novel because no osteogenic or chondrogenic differentiation protocols were applied to the cells prior to implantation. After 6 weeks, X-ray, microCT, and histological analysis showed that the hESC-MCs had consistently formed a highly vascularized new bone that bridged the bone defect and seamlessly integrated with host bone. The implanted hESC-MCs differentiated in situ to functional hypertrophic chondrocytes, osteoblasts, and osteocytes forming new bone tissue via an endochondral ossification pathway. Evidence for the direct participation of the human cells in bone morphogenesis was verified by two separate assays: with Alu and by human mitochondrial antigen positive staining in conjunction with co-localized expression of human bone sialoprotein in histologically verified regions of new bone. The large volume of new bone in a calvarial defect and the direct participation of the hESC-MCs far exceeds that of previous studies and that of the control adult hMSCs. This study represents a key step forward for bone tissue engineering because of the large volume, vascularity, and reproducibility of new bone formation and the discovery that it is advantageous to not over-commit these progenitor cells to a particular lineage prior to implantation. The hESC-MCs were able to recapitulate the mesenchymal developmental pathway and were able to repair the bone defect semi-autonomously without preimplantation differentiation to osteo- or chondroprogenitors.

Biomedical and clinical promises of human pluripotent stem cells for neurological disorders

Neurological disorders are characterized by the chronic and progressive loss of neuronal structures and functions. There is a variability of the onsets and causes of clinical manifestations. Cell therapy has brought a new concept to overcome brain diseases, but the advancement of this therapy is limited by the demands of specialized neurons. Human pluripotent stem cells (hPSCs) have been promised as a renewable resource for generating human neurons for both laboratory and clinical purposes. By the modulations of appropriate signalling pathways, desired neuron subtypes can be obtained, and induced pluripotent stem cells (iPSCs) provide genetically matched neurons for treating patients. These hPSC-derived neurons can also be used for disease modeling and drug screening. Since the most urgent problem today in transplantation is the lack of suitable donor organs and tissues, the derivation of neural progenitor cells from hPSCs has opened a new avenue for regenerative medicine. In this review, we summarize the recent reports that show how to generate neural derivatives from hPSCs, and discuss the current evidence of using these cells in animal studies. We also highlight the possibilities and concerns of translating these hPSC-derived neurons for biomedical and clinical uses in order to fight against neurological disorders.

One-step derivation of mesenchymal stem cell (MSC)-like cells from human pluripotent stem cells on a fibrillar collagen coating

Controlled differentiation of human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) into cells that resemble adult mesenchymal stem cells (MSCs) is an attractive approach to obtain a readily available source of progenitor cells for tissue engineering. The present study reports a new method to rapidly derive MSC-like cells from hESCs and hiPSCs, in one step, based on culturing the cells on thin, fibrillar, type I collagen coatings that mimic the structure of physiological collagen. Human H9 ESCs and HDFa-YK26 iPSCs were singly dissociated in the presence of ROCK inhibitor Y-27632, plated onto fibrillar collagen coated plates and cultured in alpha minimum essential medium (alpha-MEM) supplemented with 10% fetal bovine serum, 50 uM magnesium L-ascorbic acid phosphate and 100 nM dexamethasone. While fewer cells attached on the collagen surface initially than standard tissue culture plastic, after culturing for 10 days, resilient colonies of homogenous spindle-shaped cells were obtained. Flow cytometric analysis showed that a high percentage of the derived cells expressed typical MSC surface markers including CD73, CD90, CD105, CD146 and CD166 and were negative as expected for hematopoietic markers CD34 and CD45. The MSC-like cells derived from pluripotent cells were successfully differentiated in vitro into three different lineages: osteogenic, chondrogenic, and adipogenic. Both H9 hES and YK26 iPS cells displayed similar morphological changes during the derivation process and yielded MSC-like cells with similar properties. In conclusion, this study demonstrates that bioimimetic, fibrillar, type I collagen coatings applied to cell culture plates can be used to guide a rapid, efficient derivation of MSC-like cells from both human ES and iPS cells.

Embryonic stem cells in scaffold-free three-dimensional cell culture: osteogenic differentiation and bone generation

Extracorporeal formation of mineralized bone-like tissue is still an unsolved challenge in tissue engineering. Embryonic stem cells may open up new therapeutic options for the future and should be an interesting model for the analysis of fetal organogenesis. Here we describe a technique for culturing embryonic stem cells (ESCs) in the absence of artificial scaffolds which generated mineralized miromasses. Embryonic stem cells were harvested and osteogenic differentiation was stimulated by the addition of dexamethasone, ascorbic acid, and ß-glycerolphosphate (DAG). After three days of cultivation microspheres were formed. These spherical three-dimensional cell units showed a peripheral zone consisting of densely packed cell layers surrounded by minerals that were embedded in the extracellular matrix. Alizarine red staining confirmed evidence of mineralization after 10 days of DAG stimulation in the stimulated but not in the control group. Transmission electron microscopy demonstrated scorching crystallites and collagenous fibrils as early indication of bone formation. These extracellular structures resembled hydroxyl apatite-like crystals as demonstrated by distinct diffraction patterns using electron diffraction analysis. The micromass culture technique is an appropriate model to form three-dimensional bone-like micro-units without the need for an underlying scaffold. Further studies will have to show whether the technique is applicable also to pluripotent stem cells of different origin.

Ontological aspects of pluripotency and stemness gene expression pattern in the rhesus monkey

Two essential aspects of mammalian development are the progressive specialization of cells toward different lineages, and the maintenance of progenitor cells that will give rise to the differentiated components of each tissue and also contribute new cells as older cells die or become injured. The transition from totipotentiality to pluripotentiality, to multipotentiality, to monopotentiality, and then to differentiation is a continuous process during development. The ontological relationship between these different stages is not well understood. We report for the first time an ontological survey of expression of 45 putative "stemness" and "pluripotency" genes in rhesus monkey oocytes and preimplantation stage embryos, and comparison to the expression in the inner cell mass, trophoblast stem cells, and a rhesus monkey (ORMES6) embryonic stem cell line. Our results reveal that some of these genes are not highly expressed in all totipotent or pluripotent cell types. Some are predominantly maternal mRNAs present in oocytes and embryos before transcriptional activation, and diminishing before the blastocyst stage. Others are well expressed in morulae or early blastocysts, but are poorly expressed in later blastocysts or ICMs. Also, some of the genes employed to induce pluripotent stem cells from somatic cells (iPS genes) appear unlikely to play major roles as stemness or pluripotency genes in normal embryos.

Cell transplantation for articular cartilage defects: principles of past, present, and future practice

As articular cartilage has very limited self-repair capability, the repair and regeneration of damaged cartilage is a major challenge. This review aims to outline the past, present, and future of cell therapies for articular cartilage defect repair. Autologous chondrocyte implantation (ACI) has been used clinically for more than 20 years, and the short, medium, and long-term clinical outcomes of three generation of ACI are extensively overviewed. Also, strategies of clinical outcome evaluation, ACI limitations, and the comparison of ACI clinical outcomes with those of other surgical techniques are discussed. Moreover, mesenchymal stem cells and pluripotent stem cells for cartilage regeneration in vitro, in vivo, and in a few clinical studies are reviewed. This review not only comprehensively analyzes the ACI clinical data but also considers the findings from state-of-the-art stem cell research on cartilage repair from bench and bedside. The conclusion provides clues for the future development of strategies for cartilage regeneration.

Chondrogenic derivatives of embryonic stem cells seeded into 3D polycaprolactone scaffolds generated cartilage tissue in vivo

In spite of recent scientific advances, treatment and repair of cartilage using tissue engineering techniques remains challenging. The major constraint is the limited proliferative capacity of mature autologous chondrocytes used in the tissue engineering approach. This problem can be addressed by using stem cells, which can self-renew with greater proliferative potential. Cartilage tissue engineering using adult mesenchymal stem cells derived from bone marrows has met with limited success. In this study we explored cartilage tissue generation from embryonic stem cells (ESCs). ESCs were induced to differentiate into chondroprogenitors, capable of proliferating and subsequently differentiating into cartilage-producing cells. The chondrogenic cells expressed chondrocyte-specific markers and deposited extracellular matrix proteins, proteoglycans. ESC-derived chondrogenic cells and polycaprolactone scaffolds seeded with these cells implanted in mice (129 SvImJ) generated cartilage tissue in vivo. Postimplant analysis of the retrieved tissues demonstrated cartilage-like tissue formation in 3-4 weeks. The cells of retrieved tissues also expressed the chondrocyte-specific marker collagen II. These findings suggest that ESCs can be used for tissue engineering and cultivation of cartilage tissues.

Compatibility of Embryonic Stem Cells with Biomaterials

Periodontal bone defects and atrophy of the jaws in an aging population are of special concern. Tissue engineering using embryonic stem cells (ESCs) and biomaterials may offer new therapeutic options. The purpose of this study is to evaluate the compatibility of ESCs with biomaterials and the influence of biomaterials on the osteogenic gene expression profile.

Therefore, ESCs are cultured with various biomaterials. The cytocompatibility of murine ESCs is measured regarding the proliferation of the cells on the materials by CyQUANT ® assay, the morphology by scanning electron microscopy, and the influence on the gene expression by real time PCR.

The results show that insoluble collagenous bone matrix, followed by β-tricalciumphosphate, is most suitable for bone tissue engineering regarding cell proliferation, and phenotype. The gene expression analysis indicates that biomaterials do influence the gene expression of ESCs.

Our results provide new insight into the cytocompatibility of ESCs on different scaffolds.

Stem cell-mediated regeneration of the intervertebral disc: cellular and molecular challenge

Regenerative medicine and stem cells hold great promise for intervertebral disc (IVD) disease. The therapeutic implications of utilizing stem cells to repair degenerated discs and treat back pain are highly anticipated by both the clinical and scientific communities. Although the avascular environment of the IVD poses a challenge for stem cell-mediated regeneration, neuroprogenitor cells have been discovered within degenerated discs, allowing scientists to revisit the hostile environment of the IVD as a target for stem cell therapy. Issues now under investigation include the timing of cell delivery and manipulation of stem cells to make them more efficient and adaptive in the IVD niche. This review covers the mechanisms underlying disc degeneration as well as the molecular and cellular challenges involved in directing stem cells to the desired cell type for intradiscal transplantation.

Defined culture conditions of human embryonic stem cells

Human embryonic stem cells (hESCs) are pluripotent cells that have the potential to differentiate into any tissue in the human body; therefore, they are a valuable resource for regenerative medicine, drug screening, and developmental studies. However, the clinical application of hESCs is hampered by the difficulties of eliminating animal products in the culture medium and/or the complexity of conditions required to support hESC growth. We have developed a simple medium [termed hESC Cocktail (HESCO)] containing basic fibroblast growth factor, Wnt3a, April (a proliferation-inducing ligand)/BAFF (B cell-activating factor belonging to TNF), albumin, cholesterol, insulin, and transferrin, which is sufficient for hESC self-renewal and proliferation. Cells grown in HESCO were maintained in an undifferentiated state as determined by using six different stem cell markers, and their genomic integrity was confirmed by karyotyping. Cells cultured in HESCO readily form embryoid bodies in tissue culture and teratomas in mice. In both cases, the cells differentiated into each of the three cell lineages, ectoderm, endoderm, and mesoderm, indicating that they maintained their pluripotency. The use of a minimal medium sufficient for hESC growth is expected to greatly facilitate clinical application and developmental studies of hESCs.

The production and directed differentiation of human embryonic stem cells

Human embryonic stem cells (hESCs) are being rapidly produced from chromosomally euploid, aneuploid, and mutant human embryos that are available from in vitro fertilization clinics treating patients for infertility or preimplantation genetic diagnosis. These hESC lines are an important resource for functional genomics, drug screening, and, perhaps eventually, cell and gene therapy. The methods for deriving hESCs are well established and repeatable and are relatively successful with a ratio of 1:10 to 1:2 new hESC lines produced from 4- to 8-d-old morula and blastocysts and from isolated inner cell mass cell clusters of human blastocysts. The hESCs can be formed and maintained on human somatic cells in humanized serum-free culture conditions and for several passages in cell-free culture systems. The hESCs can be transfected with DNA constructs. Their gene expression profiles are being described and immunological characteristics determined. They may be grown indefinitely in vitro while maintaining their original karyotype and epigenetic status, but this needs to be confirmed from time to time in long-term cultures. hESCs spontaneously differentiate in the absence of the appropriate cell feeder layer, when overgrown in culture and when isolated from the ESC colony. All three major embryonic lineages are produced in differentiating flat attachment cultures and unattached embryoid bodies. Cell progenitors of interest can be identified by markers, expression of reporter genes, and characteristic morphology, and the cells thereafter enriched for progenitor types and further culture to more mature cell types. Directed differentiation systems are well developed for ectodermal pathways that result in neural and glial cells and the mesendodermal pathway for cardiac muscle cells and many other cell types including hematopoietic progenitors and endothelial cells. Directed differentiation into endoderm has been more difficult to achieve, perhaps because of the lack of markers of early progenitors in this lineage. There are reports of enriched cultures of keratinocytes, pigmented retinal epithelium, neural crest cells and motor neurons, hepatic progenitors, and cells that have some markers of gut tissue and pancreatic islet-like cells. The prospects for use of hESC derivatives in regenerative medicine are significant, and there is much optimism for their potential contributions to human regenerative medicine.

Embryonic Stem Cells: Similarities and Differences Between Human and Murine Embryonic Stem Cells

The derivation of murine embryonic stem (mES) cell lines was reported for the first time in 1981 (Nature, 1981; 292:154-156; Proc Natl Acad Sci U S A, 1981; 78:7634-7638), and they have since proved to be a very useful tool with which to study mammalian development, which is characterized by pluripotency and differentiation. About 20 years later, the successful generation of human embryonic stem (hES) cell lines was described (Science, 1998; 282:1145-1147). Although mES and hES are derived from mammals, they cannot be looked at as being one and the same. While basic information for hES can be derived from mES, such information does not correspond on a one-to-one basis. This review gives an overview of the characteristics of embryonic stem cells with the main focus on the similarities and differences between human and mES cells.

Future and applications of cloning

The birth of viable offspring from somatic cell nuclear transfer (SCNT) in mammals caused a major re-examination of the understanding of the commitment of cells to specific tissue lineages during differentiation. The questions of whether cells undergo dedifferentiation or transdifferentiation during the development of offspring and how these changes are controlled is a source of ongoing debate that is yet to be resolved. Irrespective of the outcome of this debate, it is clear that cloning using SCNT has a place and purpose in the future of research and animal breeding. The future uses of SCNT could include the production of transgenic mice, the production of transgenic livestock and assisting with the re-establishment of endangered species. Human medicine also would benefit from future use of SCNT because it would allow the production of patient-specific embryonic stem cells.

Osteogenic differentiation within intact human embryoid bodies result in a marked increase in osteocalcin secretion after 12 days of in vitro culture, and formation of morphologically distinct nodule-like structures

Osteogenic lineages derived from human embryonic stem cells hold much promise for clinical application in bone regeneration, in addition to providing a useful research model in developmental biology, and for pharmacological and cytotoxicity screening of bone-related biomaterials and drugs in vitro. Previously, osteogenic differentiation of human embryonic stem cells was achieved through dissociation of embryoid bodies by trypsinization, prior to culture with osteogenesis-promoting medium. This study therefore attempted a new approach: that is to achieve osteogenesis within intact human embryoid bodies. After 22 days of culture in osteogenesis-promoting medium comprising a cocktail of ascorbic acid, beta-glycerophosphate and dexamethasone, the attached embryoid bodies exhibited much cellular outgrowth and migration, and formed morphologically distinct nodule-like structures. These were somewhat similar to osteogenic nodules formed by mesenchymal stem cells, as reported by previous studies. Immunohistochemical staining and RT-PCR analysis confirmed the presence of osteogenic cells within these nodule-like structures. Additionally, the quantitative assay of osteocalcin secretion demonstrated a rapid sharp increase in osteocalcin expression on day 12 of in vitro culture, which could suggest the appearance of differentiated osteoblasts from day 12 onwards. Future work will attempt to investigate whether other cytokines, growth factors and chemical compounds could further enhance osteogenesis within intact human embryoid bodies.

Factors influencing stem cell differentiation into the hepatic lineage in vitro

A major area of research in transplantation medicine is the potential application of stem cells in liver regeneration. This would require well-defined and efficient protocols for directing the differentiation of stem cells into the hepatic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying hepatogenesis and liver metabolism. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for newly developed biomaterials and drugs, could also utilize protocols developed for the hepatic differentiation of stem cells. Hence, this review critically examines the various strategies that could be employed to direct the differentiation of stem cells into the hepatic lineage in vitro.

Update on the use of stem cells for cardiac disease

Major advances have recently been made in our understanding of stem cell biology, and in the application of stem cells to treat cardiac disease. Resident cardiac stem cells have now been described and the long-accepted paradigm of the adult mammalian heart as an organ without regenerative capacity has been questioned. Various stem-cell-based approaches for ameliorating cardiac disease have been shown to be beneficial in animal models and are now being trialled in humans, with several phase I clinical studies already completed. Although these clinical studies lacked adequate placebo controls, they have consistently shown promising results. If confirmed by larger phase II/III trials, it is possible that within a few years a powerful new therapeutic option may be available for the burgeoning number of patients suffering from myocardial ischaemia and/or other cardiac disorders.

Single inner cell masses yield embryonic stem cell lines differing in lifr expression and their developmental potential

The unique differentiation potential of inner cell mass derived embryonic stem cells together with their outstanding self-renewal capacity makes them a desirable source for somatic cell therapy of human diseases. Somatic cells are gained by in vitro differentiation of embryonic stem cells, however, the differentiation potential of embryonic stem cells varied even between isogenic cell lines. Variable differentiation potentials may either be a consequence of an inherent inhomogeneity of gene expression in the inner cell mass or may have technical reasons. To understand variations in the differentiation potential, we generated pairs of isogenic, monozygotic twin, and single inner cell mass derived clonal embryonic stem cell lines, and demonstrate that they differentially express the leukaemia inhibitory factor receptor gene. Variations of leukaemia inhibitory factor receptor protein levels are already evident in the inner cell mass and predispose the cardiomyogenic potential of embryonic stem cell lines in a Janus activated kinase dependent manner. Thus, a single inner cell mass may give rise to embryonic stem cell lines with different developmental potentials.

Directing stem cell differentiation into the chondrogenic lineage in vitro

A major area in regenerative medicine is the application of stem cells in cartilage tissue engineering and reconstructive surgery. This requires well-defined and efficient protocols for directing the differentiation of stem cells into the chondrogenic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying chondrogenesis and cartilaginous tissue biology. The development of pharmacokinetic and cytotoxicity/genotoxicity screening tests for cartilage-related biomaterials and drugs could also utilize protocols developed for the chondrogenic differentiation of stem cells. Hence, this review critically examines the various strategies that could be used to direct the differentiation of stem cells into the chondrogenic lineage in vitro.

Incorporating protein transduction domains (PTD) within recombinant ‘fusion’ transcription factors. A novel strategy for directing stem cell differentiation?

Application of embryonic and adult stem cells in regenerative medicine will require efficient protocols for directing stem cell differentiation into well-defined lineages. The use of exogenous cytokines, growth factors, or extracellular matrix substratum, will obviously require extended durations of in vitro culture. With autologous adult stem cells, this could delay transplantation to the patient, as well as alter the immunogenicity of the cultured autologous cells. Genetic modulation to direct stem cell differentiation would obviate prolonged durations of in vitro culture; but there are overwhelming safety concerns with regards to the application of recombinant DNA technology in human clinical therapy. A novel alternative would be to incorporate protein transduction domains (PTD) into recombinant transcription factors that play important roles in somatic differentiation. Such protein-engineered transcription factors will then have the ability to translocate across the cell membrane and be internalized within the cytosol, thereby acting as paracrine signaling molecules. Upon internalization, the recombinant transcription factors would only have a limited active half-life, so that their effects are only transient. However, this could provide sufficient stimulus for initiating stem cell differentiation into a required lineage.

Potential utility of cell-permeable transcription factors to direct stem cell differentiation

Application of embryonic and adult stem cells in regenerative medicine will require efficient protocols for directing stem cell differentiation into well-defined lineages. Differentiation induced by exogenous cytokines, growth factors, or extracellular matrix components will require extended in vitro culture that would delay autologous transplantation and may well alter the immunogenicity of cultured cells. Genetic modulation to direct stem cell differentiation may obviate prolonged culture, but safety concerns preclude clinical application of genetically altered cells in the foreseeable future A novel alternative would be to incorporate protein transduction domains (PTDs) into recombinant transcription factors that play important roles in somatic differentiation. Such protein-engineered transcription factors would then have the ability to translocate across the cell membrane and be internalized within the cytosol, where they would act as paracrine signaling molecules. Upon internalization, the recombinant transcription factors would only have a limited active half-life, so that their effects may only be transient. However, this could provide sufficient stimulus for initiating stem cell differentiation into a required lineage.

Ultrastructure of human embryonic stem cells and spontaneous and retinoic acid-induced differentiating cells

Ultrastructural and immunohistochemical studies of 4 groups of cells-(human embryonic stem cells (hES), embryoid bodies (EB), and spontaneously and retinoic acid (RA)-induced differentiating cells)-were carried out to investigate their detailed phenotype. Immunohistochemically, the EB cells showed strong immunoreactivity for CD34, CD117, and nestin. Differentiating cells expressed pancytokertin, vimentin, CD31, CD56, GFAP, nestin, and NeuN as well as CD34, and c-Kit. However, synaptophysin and neurofilaments were not present in these same differentiating cells. Transmission electron microscopy showed that hES and EB cells were very similar to germ cells or cells of the inner cell mass. Spontaneously and RA-induced differentiating cells exhibited epithelial, mesenchymal, endodermal, and neuronal phenotypes. The perikarya of the neuronal cells had rich RERs (Nissl substance) and long cytoplasmic processes filled with numerous neural tubules. However, neither synaptic junctions nor synaptic vesicles were developed. In our study, RA treatment with brain-derived growth factor and TGFalpha in neuron differentiation medium induced not only neuronal differentiation but also pluripotential differentiation. Full neuronal differentiation did not occur after 2 weeks in culture, as no synaptic junctions and synaptic vesicles developed.

Changing genetic world of IVF, stem cells and PGD. C. Embryogenesis and the differentiation of the haemopoietic system

In this final review, attention is focused on the formation of several haemopoietic systems and their genetic markers. Very early haemopoietic precursors have been identified in mesoderm and yolk sac, as interactions arise between haemopoietic stem cells (HSC) and mesenchymal stem cells (MSC). The foundation cell for the haemopoietic system has not been identified, although several candidate cells carrying specific markers have been recognized and are highly pluripotent. Haemangioblasts were proposed as the founder haemopoietic stem cell. They may be the source of pluripotent haemopoietic cells formed in blastocyst injection chimaeras, a characteristic typical of ES cells. Their role as the founder cell of haemopoietic and mesenchymal tissues is discussed.

Human embryonic stem cells: towards therapies for cardiac disease. Derivation of a Dutch human embryonic stem cell line

Cell transplantation is being discussed as a potential therapy for multiple disorders caused by loss or malfunction of single or at most a few cell types. These include diabetes, Parkinson's disease and myocardial infarction or cardiac failure. However, it is not yet clear whether cells from adult tissues ('adult stem cells') or embryos ('embryonic stem cells') will prove to be the most appropriate replacement cells; most likely, each disease will have its own preferred source. This study presents the background to this discussion and the current state of research in replacement of cardiac tissue, with focus on recent developments using human embryonic stem cells. It also describes a new human embryonic stem cell (HESC) line, NL-HESC1, the first to be derived in the Netherlands, and shows that it forms cardiac cells in a manner comparable with that of hES2 and hES3 cells grown in the same laboratory.

Derivation characteristics and perspectives for mammalian pluripotential stem cells

Pluripotential stem cells have been derived in mice and primates from preimplantation embryos, postimplantation embryos and bone marrow stroma. Embryonic stem cells established from the inner cell mass of the mouse and human blastocyst can be maintained in an undifferentiated state for a long time by continuous passage on embryonic fibroblasts or in the presence of specific inhibitors of differentiation. Pluripotential stem cells can be induced to differentiate into all the tissues of the body and are able to colonise tissues of interest after transplantation. In mouse models of disease, there are numerous examples of improved tissue function and correction of pathological phenotype. Embryonic stem cells can be derived by nuclear transfer to establish genome-specific cell lines and, in mice, it has been shown that embryonic stem cells are more successfully reprogrammed for development by nuclear transfer than somatic cells. Pluripotential stem cells are a very valuable research resource for the analysis of differentiation pathways, functional genomics, tissue engineering and drug screening. Clinical applications may include both cell therapy and gene therapy for a wide range of tissue injury and degeneration. There is considerable interest in the development of pluripotential stem cell lines in many mammalian species for similar research interests and applications.

Transplanted human embryonic stem cells as biological ‘catalysts’ for tissue repair and regeneration

Human embryonic stem cells have tremendous potential in the newly emerging field of regenerative medicine. Recently, it was demonstrated that the rescue of lethal cardiac defects in Id knockout mutant mouse embryos was not due to the transplanted cells giving rise to functional new tissues within the defective embryonic heart. Instead, there is indirect evidence that the observed therapeutic effect was due to various secreted factors emanating from the transplanted cells. This therefore, introduces the exciting prospect of utilizing human embryonic stem cells as biological 'catalysts' to promote tissue repair and regeneration in transplantation therapy. However, the immunological barrier against allogenic transplantation, as well as the teratogenic potential of human embryonic stem cells poses major technical challenges. A possible strategy to overcome the immunological barrier may be to impose a temporary regimen of immunosuppressive drugs followed by their gradual withdrawal, once adequate tissue regeneration has been achieved. Other more novel alternatives include the use of microencapsulation to block interaction with the transplant recipient's immune system, and co-transplantation with bone marrow-derived mesenchymal stem cells, which have been demonstrated to possess immuno-suppressive properties. The teratogenic potential of human embryonic stem cells could possibly be alleviated by directing the differentiation of these cells to specific lineages prior to transplantation, or through mitotic inactivation (gamma irradiation or mitomycin C exposure). Co-transplantation with autologous adult stem cells may represent a novel strategy to further enhance the 'catalytic' effects of human embryonic stem cells. The various factors secreted by human embryonic stem cells could then have a concentrated localized effect on relatively large numbers of co-transplanted autologous adult stem cells, which may in turn lead to enhanced repair and regeneration of the damaged tissue or organ. Moreover, there is also a possibility that synergistic interactions between the co-transplanted human embryonic stem cells and autologous adult stem cells, may somehow produce signals for the recruitment and migration of additional endogenous adult stem cells within the recipient (i.e. peripheral blood circulation, bone marrow), which could further enhance organ/tissue regeneration. Hence, the potential use of human embryonic stem cells as biological 'catalysts' to stimulate tissue repair and regeneration, appears to hold tremendous promise in the field of regenerative medicine. This new therapeutic strategy needs to thoroughly investigated, in view of its potentially important clinical applications.

Establishment and characterization of new human embryonic stem cell lines

Human embryonic stem cells (hESC), with their ability to differentiate into all cell types in the human body, are likely to play a very important therapeutic role in a variety of neurodegenerative and life-threatening disorders in the near future. Although more than 120 different human embryonic stem cell lines have been reported worldwide, only a handful are currently available for researchers, which limits the number of studies that can be performed. This study reports the isolation, establishment and characterization of new human embryonic stem cell lines, as well as their differentiation potential into variety of somatic cell types. Blastocyst-stage embryos donated for research after assisted reproductive techniques were used for embryonic stem cell isolation. A total of 31 blastocysts were processed either for immunosurgery or direct culture methods for inner cell mass isolation. A total of nine primary stem cell colonies were isolated and of these, seven cell lines were further expanded and passaged. Established lines were characterized by their cellular and colony morphology, karyotypes and immunocytochemical properties. They were also successfully cryopreserved/thawed and showed similar growth and cellular properties upon thawing. When induced to differentiate in vitro, these cells formed a variety of somatic cell lineages including cells of endoderm, ectoderm and mesoderm origin. There is now an exponentially growing interest in stem cell biology as well as its therapeutic applications for life-threatening human diseases. However, limited availability of stem cell lines as well as financial or ethical limitations restrict the number of research projects. The establishment of new hESC lines may create additional potential sources for further worldwide and nationwide research on stem cells.

Directing stem cells into the keratinocyte lineage in vitro

A major area of research in regenerative medicine is the potential application of stem cells in skin grafting and tissue engineering. This would require well defined and efficient protocols for directing the commitment and differentiation of stem cells into the keratinocyte lineage, together with their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying skin tissue biology, as well as facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmacokinetic and cytotoxicity/genotoxicity screening tests for skin-related biomaterials and drugs could also utilize protocols developed for the commitment and differentiation of stem cells into the keratinocyte lineage. Hence, this review critically examines the various strategies that could be employed to direct the commitment and differentiation of stem cells into the keratinocyte lineage in vitro.

Chromatin remodeling and stem cell theory of relativity

The field of stem cell biology is currently being redefined. Stem cell (hematopoietic and non-hematopoietic) differentiation has been considered hierarchical in nature, but recent data suggest that there is no progenitor/stem cell hierarchy, but rather a reversible continuum. The stem cell (hematopoietic and non-hematopoietic) phenotype, the total differentiation capacity (hematopoietic and non-hematopoietic), gene expression as well as other stem cell functional characteristics (homing, receptor and adhesion molecule expression) vary throughout a cell-cycle transit widely. This seems to be dependent on shifting chromatin and gene expression with cell-cycle transit. The published data on DNA methylation, histone acetylation, and also RNAi, the major regulators of gene expression, conjoins very well and provides an explanation for the major issues of stem cell biology. Those features of stem cells mentioned above can be rather difficult to apprehend when a classical hierarchy biology view is applied, but they become clear and easier to understand once they are correlated with the underlining epigenetic changes. We are entering a new era of stem cell biology the era of "chromatinomics." We are one step closer to the practical use of cellular therapy for degenerative diseases.

Cryopreservation of adherent human embryonic stem cells

Standard human embryonic stem (HES) cell cryopreservation methodologies, including slow freezing and vitrification of colonies in suspension, are plagued by poor viability and high differentiation rates upon recovery. To facilitate research studies and clinical applications of HES cells, we have developed a cryopreservation technique based on stabilizing HES colonies adherent to or embedded in a Matrigel matrix. This method increases cell viability by over an order of magnitude compared with cryopreservation in suspension and reduces differentiation. Loading adherent HES cells with the disaccharide trehalose prior to cryopreserving in a dimethylsulfoxide-containing cryoprotectant solution further improves cell viability under certain conditions. Our proposed approach has the potential to reduce the time required to amplify frozen stocks of HES cells, minimize risk of clonal selection during freeze-thaw cycles, and facilitate storage of HES cell clone libraries.

Strategies for directing the differentiation of stem cells into the osteogenic lineage in vitro

A major area in regenerative medicine is the application of stem cells in bone reconstruction and bone tissue engineering. This will require well-defined and efficient protocols for directing the differentiation of stem cells into the osteogenic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages on transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying osteogenesis and bone development, and facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for bone-related biomaterials and drugs could also use protocols developed for the osteogenic differentiation of stem cells. This review critically examines the various strategies that could be used to direct the differentiation of stem cells into the osteogenic lineage in vitro.

Significant variations in differentiation properties between independent mouse ES cell lines cultured under defined conditions

Mouse embryonic stem (ES) cells are isolated from the inner cell mass (ICM)/epiblast of preimplantation embryos and are widely used in cell differentiation studies. We have previously observed differences in transcript and antigen expression following differentiation of ES cells lines in vitro. We have investigated this further by comparing the differentiation characteristics of five independently derived ES cell lines cultured and differentiated under defined conditions. Undifferentiated ES cell lines exhibited similar morphology and antigen/transcript marker expression. However, upon differentiation in monolayer culture by LIF withdrawal, only two of the lines expressed similar germ layer transcript profiles, and these were significantly altered compared to differentiation in serum-supplemented media. Neurofilament-68k was the only transcript marker common to all cell lines, however, induction of neuroectoderm lineages using 1 microM all-trans retinoic acid (RA) resulted in significant variations in cell number and morphology between the lines. Furthermore, neurons were only formed from clones of the two cell lines that exhibited similar transcript profiles, although the morphology was different between the two. We conclude that the independent ES cell lines in this study differ in their response to alterations in culture conditions in vitro, and the use of an appropriate cell line enables relatively homogeneous neuronal populations to be achieved in monolayer culture under defined conditions.

Stem cells today: A. Origin and potential of embryo stem cells

The study of embryo stem cells began in 1963, initially using disaggregates of cleaving rabbit and mouse embryos. Their differentiation in vitro was modest, and usually curtailed at best to the formation of trophectoderm cells, which attached to plastic. Rabbit morulae and blastocysts adhered more readily, trophectoderm forming a sheet of cells which was overgrown by stem cells from inner cell mass. Whole-blastocyst cultures on collagen-coated surfaces produced a pile of cells, and its outgrowths included neural, blood, neuronal, phagocytic and many other types of cell. When inner cell mass was freed and cultured intact or as cell disaggregates, lines of embryo stem cells (ES) were established which possessed good rates of cleavage, and immense stability in their secretion of enzymes, morphology and chromosomal complement. Developmental capacities of single mouse embryo stem cells were measured by injecting one or more into a recipient blastocyst, and extent of colonization in resulting chimaeras measured their pluripotency. In mouse, cell clumps were termed embryoid bodies, which produced similar outgrowths as in rabbit. Component cells again differentiated widely, depending to a limited extent on their exposure to various cytokines or substrates. Markers for differentiation or pluripotency were established, which revealed how neural, cardiac, haematological and other ES lines could be established in vitro. These have proved useful to study early differentiation and their use in grafting to sick recipients. Displaying similar properties, human ES cells emerged in the late 1990s. Models for the clinical use of ES cells showed how they colonized rapidly, travelled to target tissues via fetal pathways, differentiated and colonized target organs. No signs of inflammation or tissue damage were noted; injured tissues could be repaired including remyelination, and no cancers were formed. ES cells offer wide therapeutic potentials for humans, although extensive clinical trials are still awaited.

Tissue engineering and cell based therapies, from the bench to the clinic: the potential to replace, repair and regenerate

The field of Regenerative Biology as it applies to Regenerative Medicine is an increasingly expanding area of research with hopes of providing therapeutic treatments for diseases and/or injuries that conventional medicines and even new biologic drug therapies cannot effectively treat. Extensive research in the area of Regenerative Medicine is focused on the development of cells, tissues and organs for the purpose of restoring function through transplantation. The general belief is that replacement, repair and restoration of function is best accomplished by cells, tissues or organs that can perform the appropriate physiologic/metabolic duties better than any mechanical device, recombinant protein therapeutic or chemical compound. Several strategies are currently being investigated and include, cell therapies derived from autologous primary cell isolates, cell therapies derived from established cell lines, cell therapies derived from a variety of stem cells, including bone marrow/mesenchymal stem cells, cord blood stem cells, embryonic stem cells, as well as cells tissues and organs from genetically modified animals. This mini-review is not meant to be exhaustive, but aims to highlight clinical applications for the four areas of research listed above and will address a few key advances and a few of the hurdles yet to be overcome as the technology and science improve the likelihood that Regenerative Medicine will become clinically routine.

Directed neuronal differentiation of human embryonic stem cells

Background

We have developed a culture system for the efficient and directed differentiation of human embryonic stem cells (HESCs) to neural precursors and neurons.

HESC were maintained by manual passaging and were differentiated to a morphologically distinct OCT-4⁺/SSEA-4^- monolayer cell type prior to the derivation of embryoid bodies. Embryoid bodies were grown in suspension in serum free conditions, in the presence of 50% conditioned medium from the human hepatocarcinoma cell line HepG2 (MedII).

Results

A neural precursor population was observed within HESC derived serum free embryoid bodies cultured in MedII conditioned medium, around 7–10 days after derivation. The neural precursors were organized into rosettes comprised of a central cavity surrounded by ring of cells, 4 to 8 cells in width. The central cells within rosettes were proliferating, as indicated by the presence of condensed mitotic chromosomes and by phosphoHistone H3 immunostaining. When plated and maintained in adherent culture, the rosettes of neural precursors were surrounded by large interwoven networks of neurites. Immunostaining demonstrated the expression of nestin in rosettes and associated non-neuronal cell types, and a radial expression of Map-2 in rosettes. Differentiated neurons expressed the markers Map-2 and Neurofilament H, and a subpopulation of the neurons expressed tyrosine hydroxylase, a marker for dopaminergic neurons.

Conclusion

This novel directed differentiation approach led to the efficient derivation of neuronal cultures from HESCs, including the differentiation of tyrosine hydroxylase expressing neurons. HESC were morphologically differentiated to a monolayer OCT-4⁺ cell type, which was used to derive embryoid bodies directly into serum free conditions. Exposure to the MedII conditioned medium enhanced the derivation of neural precursors, the first example of the effect of this conditioned medium on HESC.