Putting stem cells to work

Embryonic stem cell-derived extracellular vesicles rejuvenate senescent cells and antagonize aging in mice

Aging is a degenerative process that leads to tissue dysfunction and death. Embryonic stem cells (ESCs) have great therapeutic potential for age-related diseases due to their capacity for self-renewal and plasticity. However, the use of ESCs in clinical treatment is limited by immune rejection, tumourigenicity and ethical issues. ESC-derived extracellular vesicles (EVs) may provide therapeutic effects that are comparable to those of ESCs while avoiding unwanted effects. Here, we fully evaluate the role of ESC-EVs in rejuvenation in vitro and in vivo. Using RNA sequencing (RNA-Seq) and microRNA sequencing (miRNA-Seq) screening, we found that miR-15b-5p and miR-290a-5p were highly enriched in ESC-EVs, and induced rejuvenation by silencing the Ccn2-mediated AKT/mTOR pathway. These results demonstrate that miR-15b-5p and miR-290a-5p function as potent activators of rejuvenation mediated by ESC-EVs. The rejuvenating effect of ESC-EVs was further investigated in vivo by injection into aged mice. The results showed that ESC-EVs successfully ameliorated the pathological age-related phenotypes and rescued the transcriptome profile of aged mice. Our findings demonstrate that ESC-EVs treatment can rejuvenate senescence both in vitro and in vivo and suggest the therapeutic potential of ESC-EVs as a novel cell-free alternative to ESCs for age-related diseases.

The Combined Effect of Licorice Extract and Bone Marrow Mesenchymal Stem Cells on Cisplatin-Induced Hepatocellular Damage in Rats

Drug-induced liver damage is a life-threatening disorder, and one major form of it is the hepatotoxicity induced by the drug cisplatin. In folk medicine, Licorice (Glycyrrhiza glabra (is used for detoxification and is believed to be a potent antioxidant. Currently, the magically self-renewable potential of bone marrow mesenchymal stem cells (BM-MSCs) has prompted us to explore their hepatoregenerative capability. The impact of G. glabra extract (GGE) and BM-MSCs alone and, in combination, on protecting against hepatotoxicity was tested on cisplatin-induced liver injury in rats. Hepatic damage, as revealed by liver histopathology and increased levels of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and malondialdehyde (MDA), was elevated in rats by received 7 mg/kg of cisplatin intraperitoneally. The combination of GGE and BM-MSCs returned the enzyme levels to near the normal range. It also improved levels of liver superoxide dismutase (SOD) and glutathione (GSH) and reduced MDA levels. Additionally, it was found that when GGE and BM-MSCs were used together, they significantly downregulated caspase9 (Casp9), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB), and interleukin-1β (IL-1β), which are involved in severe proinflammatory and apoptotic signaling cascades in the liver. Moreover, combining GGE and BM-MSCs led to the normal result of hepatocytes in several examined liver histological sections. Therefore, our findings suggest that GGE may have protective effects against oxidative liver damage and the promising regenerative potential of BM-MSCs.

Molecular Cloning of the Porcine Insulin cDNA Using a Monolayer Culture of Pancreatic Endocrine Cells

Porcine pancreatic endocrine cells are an attractive candidate for islet cell transplantation in view of the immunological properties and structural similarities of porcine insulin to human insulin. We recently established a method of isolation and a primary monolayer culture of porcine pancreatic endocrine cells. In this study, cloning of the porcine insulin cDNA was performed to clarify the genetic background of the purified isolated cells. A homology-based PCR cloning method was employed to determine the sequence using mRNA extracted from the monolayer-forming cells, and the candidate products were then determined by a homology search on the human insulin cDNA. According to the newly identified sequence, rapid amplification of cDNA ends was applied to the 5′ and 3′ ends, and the entire cDNA sequence was determined. Gene and protein expression was confirmed by Northern blotting, immunohistochemistry, and enzyme assay. To examine the transcriptional level, the cultured cells were incubated in a 20 mM D-glucose medium in the presence or absence of 5 μM forskolin. The porcine insulin cDNA exhibited a high homology to the human cDNA and showed 85% matching with the human amino acid sequence. D-Glucose at 20 mM stimulated the insulin secretion and mRNA expression, and further addition of 5 μM forskolin with the glucose was applied as the strongest stimulus in this culture system.

In Vivo Differentiation of Mouse Embryonic Stem Cells into Hepatocytes

Embryonic stem (ES) cells have been regarded as a powerful resource for cell replacement therapy. In recent reports mouse ES cells have been successfully applied in the treatment of spinal cord injury, hereditary myelin disorder of the central nervous system, and diabetes mellitus. Another type of disease that could benefit from the availability of stem cell therapy is liver disease. However, for this potential to be realized, it is necessary to demonstrate the differentiation of ES cells into hepatocytes. To demonstrate the in vivo differentiation potential of mouse ES cells, we injected ES cells into the spleen of immunosuppressed nude mice. Histological analysis of teratomas derived from injected ES cells revealed that some areas contained typical hepatocytes arranged in a sinusoidal structure. The hepatic nature of these cells was further confirmed by showing that transcripts of liver-specific genes were present in the differentiated teratoma using reverse transcriptase-polymerase chain reaction and immunohistochemistry using several liver-specific antibodies including HEP-PAR, phenylalanine hydroxylase, and mouse N-system aminotransferase to identify the respective proteins in the differentiated hepatocytes. This is the first demonstration that mouse ES cells can differentiate in vivo into a mixed population of hepatocytes of varying maturity. This finding extends the potential use of ES cells in the cell replacement therapy by including its possible application for treating liver diseases.

In vivo differentiation potential of buffalo (Bubalus bubalis) embryonic stem cell

Embryonic stem cells (ESCs) derived from inner cell mass (ICM) of mammalian blastocyst are having indefinite proliferation and differentiation capability for any type of cell lineages. In the present study, ICMs of in vitro-derived buffalo blastocysts were cultured into two different culture systems using buffalo fetal fibroblast as somatic cell support and Matrigel as synthetic support to obtain pluripotent buffalo embryonic stem cell (buESC) colonies. Pluripotency of the ESCs were characterised through pluripotency markers whereas, their differentiation capability was assessed by teratoma assay using immuno-compromised mice. Cumulus ooccyte complexes from slaughter house-derived ovaries were subjected to in vitro maturation, in vitro fertilization and in vitro culture to generate blastocysts. Total 262 blastocysts were derived through IVEP with 11.83 % (31/262) hatching rate. To generate buESCs, 15 ICMs from hatched blastocysts were cultured on mitomycin-C-treated homologous fetal fibroblast feeder layer, whereas the leftover 16 ICMs were cultured on extra-cellular matrix (Matrigel). No significant differences were observed for primary ESCs colony formation between two culture systems. Primary colonies as well as passaged ESCs were characterised by alkaline phosphatase staining, karyotyping and expression of transcription-based stem cell markers, OCT-4 and cell surface antigens SSEA-4 and TRA-1-60. Batch of ESCs found positive for pluripotency markers and showing normal karyotype after fifteenth passage were inoculated into eight immuno-compromised mice through subcutaneous and intramuscular route. Subcutaneous route of inoculation was found to be better than intramuscular route. Developed teratomas were excised surgically and subjected to histological analysis. Histological findings revealed presence of all the three germinal layer derivatives in teratoma sections. Presence of germinal layer derivatives were further confirmed by reverse transcriptase-polymerase chain reaction for the presence of differentiation markers like nerve cell adhesion molecule, fetal liver kinase-1 and alpha-feto protein for ectoderm, mesoderm and endoderm, respectively.

A microfluidic traps system supporting prolonged culture of human embryonic stem cells aggregates

The unlimited proliferative and differentiative capacities of embryonic stem cells (ESCs) are tightly regulated by their microenvironment. Local concentrations of soluble factors, cell-cell interactions and extracellular matrix signaling are just a few variables that influence ESC fate. A common method employed to induce ESC differentiation involves the formation of cell aggregates called embryoid bodies (EBs), which recapitulate early stages of embryonic development. EBs are normally formed in suspension cultures, producing heterogeneously shaped and sized aggregates. The present study demonstrates the usage of a microfluidic traps system which supports prolonged EB culturing. The traps are uniquely designed to facilitate cell capture and aggregation while offering efficient gas/nutrients exchange. A finite element simulation is presented with emphasis on several aspects critical to appropriate design of such bioreactors for ESC culture. Finally, human ESC, mouse Nestin-GFP ESC and OCT4-EGFP ESCs were cultured using this technique and demonstrated extended viability for more than 5 days. In addition, EBs developed and maintained a polarized differentiation pattern, possibly as a result of the nutrient gradients imposed by the traps bioreactor. The novel microbioreactor presented here can enhance future embryogenesis research by offering tight control of culturing conditions.

Tissue engineering and regenerative medicine research perspectives for pediatric surgery

Tissue engineering and regenerative medicine research is being aggressively pursued in attempts to develop biological substitutes to replace lost tissue or organs. Remarkable degrees of success have been achieved in the generation of a variety of tissues and organs as a result of concerted contributions by multidisciplinary groups in the field of biotechnology. Engineering of an organ is a complex process which is initiated by appropriate sourcing of cells and their controlled proliferation to achieve critical numbers for seeding on biodegradable scaffolds in order to create cell-scaffold constructs, which are thereafter maintained in bioreactors to generate tissues identical to those required for replacement. Extensive efforts in understanding the characteristics of cells and their interaction with specifically tailored scaffolds holds the key to their attachment, controlled proliferation and differentiation, intercommunication, and organization to form tissues. The demand for tissue-engineered organs is enormous and this technology holds the promise to supply customized organs to overcome the severe shortages that are currently faced by the pediatric patient, especially due to organ-size mismatch. The contemporary state of tissue-engineering technology presented in this review summarizes the advances in the various areas of regenerative medicine and addresses issues that are associated with its future implementation in the pediatric surgical patient.

Anthropological and ethical reflections on the production and use of embryonic stem cells

Stem cells and their potential therapeutic application have generated tremendous public interest, great enthusiasm among researchers and intense commercial interest. There are diverse sources of stem cells. According to their origin and their biological characteristics, they are classified as embryonic stem cells, germline stem cells and tissue stem cells. Until now, the most concrete therapeutic results have come from some adult tissue stem cells, with promising prospects also being offered by umbilical cord stem cells. Regarding embryonic stem cells, there is concern that they would be difficult to control in vivo. Nonetheless, many researchers are still pursuing their potential uses, convinced that they will be useful not only for study, but also for therapy, especially as a result of their high capacity for self-renewal as well as their broad potential for differentiation. This discussion which is eminently scientific in nature, and not lacking in ethical and political repercussions, will not be entered into above all regarding the allocation of available intellectual and economic resources.

Microfabrication-based modulation of embryonic stem cell differentiation

Embryonic stem (ES) cells form spontaneous aggregates during differentiation, and cell-cell communication in the aggregates plays an important role in differentiation. The development of a controlled differentiation scheme for ES cells has been hindered by the lack of a reliable method to produce uniform aggregate sizes. Conventional techniques, such as hanging drop and suspension cultures, do not allow precise control over size of ES cell aggregates. To surmount this problem, we microfabricated adhesive stencils to make mouse ES (mES) cell aggregates of specific sizes ranging from 100 microm to 500 microm in diameter. With this technique, we studied the effect of the initial aggregate size on ES cell differentiation. After 20 days of induction of differentiation, we analyzed the stem cell populations using gene and protein expression assays as well as biochemical functions. Notably, we found that germ layer differentiation depends on the initial size of the ES cell aggregate. Among the ES cell aggregate sizes tested, the aggregates with 300 microm diameter showed similar differentiation profiles of three germ layers as embryoid bodies made using the "hanging drop" technique. The smaller (100 microm) aggregates showed the increased expression of ectodermal markers compared to the larger (500 microm) aggregates, while the 500 microm aggregates showed the increased expression of mesodermal and endodermal markers compared to the 100 microm aggregates. These results indicate that the initial size of the aggregate is an important factor for ES cell differentiation, and can affect germ layer selection as well as the extent of differentiation.

The Use of Stem Cells’ Hematopoietic Stimulating Factors Therapy Following Spinal Cord Injury

Spinal cord injury (SCI) remains one of the most devastating conditions in medicine, particularly due to the loss of productive life years and the high economic burden it places on our society. There are limited therapeutic options available to reduce the morbidity and mortality related to SCI. However, recent work with stem cells in repairing SCI appears to be promising, making this one of the most exciting frontiers in medicine. A brief review of the mechanisms of SCI is presented. Stem cells from a variety of sources have shown effectiveness in improving motor function after SCI in animals. The pre-clinical use of stem cells in SCI and methods of delivery are discussed. The potential use of granulocyte-colony stimulating factor (G-CSF) to increase the number of stem cells engrafting at the site of injury in order to improve neurological and motor function recovery following SCI is introduced. G-CSF, through stimulation of lymphohemopoietic stem cells in peripheral blood, can potentially cause repopulation of the SCI region with neural progenitor cells. This allows for improved functional outcomes. More pre-clinical and translational research exploring this possibility is required.

Totipotency, twinning, and ensoulment at fertilization

From fertilization to approximately the sixteenth day of development, human embryonic cells are said to have the capacities of totipotency and monozygotic twinning, both of which are problematic to a theory of ensoulment at fertilization. In this article I will address the problems which these capacities pose to such a theory and present an interpretation of the biological data which renders ensoulment at fertilization more plausible. I will then argue that not only is an ensoulment theory consistent with current biological data on the human embryo, but it may offer an explanation for the phenomencon of monozygotic twinning.

Generation of embryonic stem cell lines from mouse blastocysts developed in vivo and in vitro: relation to Oct-4 expression

Embryonic stem (ES) cells are the source of all embryonic germ layer tissues. Oct-4 is essential for their pluripotency. Sincein vitroculture may influence Oct-4 expression, we investigated to what extent blastocysts culturedin vitrofrom the zygote stage are capable of expressing Oct-4 and generating ES cell lines. We comparedin vivowithin vitroderived blastocysts from B6D2 mice with regard to Oct-4 expression in inner cell mass (ICM) outgrowths and blastocysts. ES cells were characterized by immunostaining for alkaline phosphatase (ALP), stage-specific embryonic antigen-1 (SSEA-1) and Oct-4. Embryoid bodies were made to evaluate the ES cells’ differentiation potential. ICM outgrowths were immunostained for Oct-4 after 6 days in culture. A quantitative real-time PCR assay was performed on individual blastocysts. Of thein vitroderived blastocysts, 17% gave rise to ES cells vs 38% of thein vivoblastocysts. Six-day old outgrowths fromin vivodeveloped blastocysts expressed Oct-4 in 55% of the cases vs 31% of thein vitroderived blastocysts. The amount of Oct-4 mRNA was significantly higher for freshly collectedin vivoblastocysts compared toin vitrocultured blastocysts.In vitrocultured mouse blastocysts retain the capacity to express Oct-4 and to generate ES cells, be it to a lower level thanin vivoblastocysts.

Skeletal myogenesis by human embryonic stem cells

We have examined the myogenic potential of human embryonic stem (hES) cells in a xeno-transplantation animal model. Here we show that precursors differentiated from hES cells can undergo myogenesis in an adult environment and give rise to a range of cell types in the myogenic lineage. This study provides direct evidences that hES cells can regenerate both muscle and satellite cells in vivo and are another promising cell type for treating muscle degenerative disorders in addition to other myogenic cell types.

From teratocarcinomas to embryonic stem cells and beyond: a history of embryonic stem cell research

We are currently facing an unprecedented level of public interest in research on embryonic stem cells, an area of biomedical research that until recently was small, highly specialized and of limited interest to anyone but experts in the field. Real and imagined possibilities for the treatment of degenerative and other diseases are of special interest to our rapidly ageing population; real and imagined associations of stem cells to cloning, embryos and reproduction stir deeply held beliefs and prejudices. The conjunction of these factors could explain the recent sudden interest in embryonic stem cells but we ought to remember that this research has a long and convoluted history, and that the findings described today in the scientific and popular press are firmly grounded in research that has been going on for several decades. Here I briefly recapitulate this fascinating history.

Cell transplantation and genetic engineering: new approaches to cardiac pathology

The remarkable progress in experimental cell transplantation, stem cell biology and genetic engineering promise new therapy and hopefully a cure for patients with end stage heart failure. Engineering of viable cardiac grafts with the potential to grow and remodel will provide new solutions to the serious problems of heart donor shortage. The ability to replace the injured heart muscle will have a dramatic influence on medicine, especially with the increasing number of patients with heart failure. This innovative research, now tested in human patients, still faces significant problems that need to be solved before it can be considered as an established therapeutic tool. The present review will focus on selected topics related to the promise and obstacles associated with cell transplantation, with and without genetic manipulation, for myocardial repair.

Tissue-engineering approaches for axonal guidance

Owing to the profound impact of nervous system damage, extensive studies have been carried out aimed at facilitating axonal regeneration following injury. Tissue engineering, as an emerging and rapidly growing field, has received extensive attention for nervous system axonal guidance. Numerous engineered substrates containing oriented extracellular matrix molecules, cells or channels have displayed potential of supporting axonal regeneration and functional recovery. Most attempts are focused on seeking new biomaterials, new cell sources, as well as novel designs of tissue-engineered neuronal bridging devices, to generate safer and more efficacious neuronal tissue repairs.

Cell therapies for type 1 diabetes mellitus

Type 1 diabetes is caused by autoimmune destruction of pancreatic beta-cells and is characterised by absolute insulin insufficiency. The monocellular nature of this disease and endocrine action of insulin make this disease an excellent candidate for cellular therapy. Furthermore, precedent for cellular therapies has been set by successful cadaveric whole pancreas and islet transplantation. In order to expand the supply of cells to meet current and future needs, several novel cell sources have been proposed, including human beta-cells or islets expanded in culture, islet xenografts and pancreatic ductal progenitor cells. Surrogate beta-cells derived from hepatocytes, intestinal K cells or non-endodermal cell types have also been suggested. Stem cells found in bone marrow and umbilical cord blood have been used extensively to repopulate the haematopoietic system and offer the possibility of autologous transplantation. Recent studies have suggested that these stem cells may also have a broader capacity to differentiate, possibly into beta-cells. Stem cells from embryonic sources, such as human embryonic stem and embryonic germ cells, have the ability to proliferate extensively in culture and have an inherent developmental plasticity that may make them a potentially unlimited source of cells that can sense glucose and produce mature insulin. The wide range of proposed cell sources and our increasingly clear picture of pancreatic development suggest that novel cellular therapies might one day compete with non-cellular glucose sensing and insulin delivery devices.

Non-hematopoietic human bone marrow contains long-lasting, pluripotential mesenchymal stem cells

Mesenchymal stem cells (MSC) are considered as potential agents for reconstructive and gene-targeting therapies since they differentiate into various cell-lineages, exhibit an extended survival once injected into a host, and can easily be transfected with engineered DNA. MSC are essentially isolated from hematopoietic bone marrow (BM), a process that is rather invasive and may raise ethical concerns. In an attempt to find an alternative source, we evaluated whether non-hematopoietic (nh)BM recovered from femoral heads of patients undergoing hip arthroplasty contained MSC. Ex vivo, 99% of nhBM cells were CD45(+) leukocytes. After culture, leukocytes were replaced by a homogeneous layer of adherent CD45(-) CD14(-) CD34(-) CD11b(-) CD90(+) HLA-ABC(+) cells. Culture doubling time (mean = 4 days, range 1.6-6.7 days) was not correlated with patient age (27-81 years, n = 16). Amplified cultures supported long-term hematopoiesis, and could be differentiated in vitro into adipocytes and chondrocytes. Moreover, a small fraction of nhBM cells spontaneously expressed MyoD1 and formed myotubes, suggesting that myogenic differentiation also occurred. nhBM contained clonogenic cells whose frequency (1/13,000), doubling time (2.1 days), and maximal amplification (up to 10(6)-fold) were not age-related. All 14 clones analyzed (from five patients, ages 27-78 years) differentiated into at least one mesenchymal lineage, and 66% were bipotential (n = 8/12), or tripotential (n = 2/3). In conclusion, nhBM contains pluripotential mesenchymal progenitors which are similar to hematopoietic BM-derived MSC, and whose biological functions are not altered by aging. Furthermore, if MSC-based therapies hold their promises, nhBM may become the source of choice for responding to the increasing demand for MSC.

Genesis of embryonic stem cells

Embryonic stem (ES) cells are permanent pluripotent stem cell lines established from pre-implantation mouse embryos. There is currently great interest in the potential therapeutic applications of analogous cells derived from human embryos. The isolation of ES cells is commonly presented as a straightforward transfer of cells in the early embryo into culture. In reality, however, continuous expansion of pluripotent cells does not occur in vivo, and in vitro is the exception rather than the norm. Both genetic and epigenetic factors influence the ability to derive ES cells. We have tracked the expression of a key marker and determinant of pluripotency, the transcription factor Oct-4, in primary cultures of mouse epiblasts and used this to assay the effect of experimental manipulations on the maintenance of a pluripotent cell compartment. We find that expression of Oct-4 is often lost prior to overt cytodifferentiation of the epiblast. The rate and extent of Oct-4 extinction varies with genetic background. We report that treatment with the MAP kinase/ERK kinase inhibitor PD98059, which suppresses activation of the mitogen-activated protein kinases Erk1 and Erk2, results in increased persistence of Oct-4-expressing cells. Oct-4 expression is also relatively sustained in cultures of diapause embryos and of isolated inner cell masses. Combination of all three conditions allowed the derivation of germline-competent ES cells from the normally refractory CBA mouse strain. These findings suggest that the genesis of an ES cell is a relatively complex process requiring epigenetic modulation of key gene expression over a brief time-window. Procedures that extend this time-window and/or directly regulate the critical genes should increase the efficiency of ES cell derivation.

Embryonic stem cells generated by nuclear transfer of human somatic nuclei into rabbit oocytes

To solve the problem of immune incompatibility, nuclear transplantation has been envisaged as a means to produce cells or tissues for human autologous transplantation. Here we have derived embryonic stem cells by the transfer of human somatic nuclei into rabbit oocytes. The number of blastocysts that developed from the fused nuclear transfer was comparable among nuclear donors at ages of 5, 42, 52 and 60 years, and nuclear transfer (NT) embryonic stem cells (ntES cells) were subsequently derived from each of the four age groups. These results suggest that human somatic nuclei can form ntES cells independent of the age of the donor. The derived ntES cells are human based on karyotype, isogenicity, in situ hybridization, PCR and immunocytochemistry with probes that distinguish between the various species. The ntES cells maintain the capability of sustained growth in an undifferentiated state, and form embryoid bodies, which, on further induction, give rise to cell types such as neuron and muscle, as well as mixed cell populations that express markers representative of all three germ layers. Thus, ntES cells derived from human somatic cells by NT to rabbit eggs retain phenotypes similar to those of conventional human ES cells, including the ability to undergo multilineage cellular differentiation.

Recent advances in stem cell neurobiology

1. Neural stem cells can be cultured from the CNS of different mammalian species at many stages of development. They have an extensive capacity for self-renewal and will proliferate ex vivo in response to mitogenic growth factors or following genetic modification with immortalising oncogenes. Neural stem cells are multipotent since their differentiating progeny will give rise to the principal cellular phenotypes comprising the mature CNS: neurons, astrocytes and oligodendrocytes. 2. Neural stem cells can also be derived from more primitive embryonic stem (ES) cells cultured from the blastocyst. ES cells are considered to be pluripotent since they can give rise to the full cellular spectrum and will, therefore, contribute to all three of the embryonic germ layers: endoderm, mesoderm and ectoderm. However, pluripotent cells have also been derived from germ cells and teratocarcinomas (embryonal carcinomas) and their progeny may also give rise to the multiple cellular phenotypes contributing to the CNS. In a recent development, ES cells have also been isolated and grown from human blastocysts, thus raising the possibility of growing autologous stem cells when combined with nuclear transfer technology. 3. There is now an emerging recognition that the adult mammalian brain, including that of primates and humans, harbours stem cell populations suggesting the existence of a previously unrecognised neural plasticity to the mature CNS, and thereby raising the possibility of promoting endogenous neural reconstruction. 4. Such reports have fuelled expectations for the clinical exploitation of neural stem cells in cell replacement or recruitment strategies for the treatment of a variety of human neurological conditions including Parkinson's disease (PD), Huntington's disease, multiple sclerosis and ischaemic brain injury. Owing to their migratory capacity within the CNS, neural stem cells may also find potential clinical application as cellular vectors for widespread gene delivery and the expression of therapeutic proteins. In this regard, they may be eminently suitable for the correction of genetically-determined CNS disorders and in the management of certain tumors responsive to cytokines. Since large numbers of stem cells can be generated efficiently in culture, they may obviate some of the technical and ethical limitations associated with the use of fresh (primary) embryonic neural tissue in current transplantation strategies. 5. While considerable recent progress has been made in terms of developing new techniques allowing for the long-term culture of human stem cells, the successful clinical application of these cells is presently limited by our understanding of both (i) the intrinsic and extrinsic regulators of stem cell proliferation and (ii) those factors controlling cell lineage determination and differentiation. Although such cells may also provide accessible model systems for studying neural development, progress in the field has been further limited by the lack of suitable markers needed for the identification and selection of cells within proliferating heterogeneous populations of precursor cells. There is a further need to distinguish between the committed fate (defined during normal development) and the potential specification (implying flexibility of fate through manipulation of its environment) of stem cells undergoing differentiation. 6. With these challenges lying ahead, it is the opinion of the authors that stem-cell therapy is likely to remain within the experimental arena for the foreseeable future. In this regard, few (if any) of the in vivo studies employing neural stem cell grafts have shown convincingly that behavioural recovery can be achieved in the various model paradigms. Moreover, issues relating to the quality control of cultured cells and their safety following transplantation have only begun to be addressed. 7. While on the one hand cell biotechnologists have been quick to realise the potential commercial value, human stem cell research and its clinical applications has been the subject of intense ethical and legislative considerations. The present chapter aims to review some recent aspects of stem cell research applicable to developmental neurobiology and the potential applications in clinical neuroscience.

Embryonic stem cells: new possible therapy for degenerative diseases that affect elderly people

The capacity of embryonic stem (ES) cells for virtually unlimited self renewal and differentiation has opened up the prospect of widespread applications in biomedical research and regenerative medicine. The use of these cells would overcome the problems of donor tissue shortage and implant rejection, if the cells are made immunocompatible with the recipient. Since the derivation in 1998 of human ES cell lines from preimplantation embryos, considerable research is centered on their biology, on how differentiation can be encouraged toward particular cell lineages, and also on the means to enrich and purify derivative cell types. In addition, ES cells may be used as an in vitro system not only to study cell differentiation but also to evaluate the effects of new drugs and the identification of genes as potential therapeutic targets. This review will summarize what is known about animal and human ES cells with particular emphasis on their application in four animal models of human diseases. Present studies of mouse ES cell transplantation reveal encouraging results but also technical barriers that have to be overcome before clinical trials can be considered.

Donor cells for nuclear cloning: many are called, but few are chosen

The few viable clones obtained at the end of a typical cloning experiment are genetic copies of the donor cell genome of a non-reproductive (somatic) or embryonic cell used for nuclear transfer. Nuclear totipotency has to be reestablished by erasing epigenetic constraints imposed on the donor genome during differentiation in a process which involves active chromatin remodeling. Various donor cell types and cell cycle combinations have proven to be capable of generating cloned offspring. However, an ideal nuclear donor may have not yet been found. This review summarizes current theoretical aspects of donor cell selection. It focuses on the impact of genetic and epigenetic differences between donor cell types on successful mammalian cloning.

Glucose-responsive insulin-producing cells from stem cells

Recent success with immunosuppression following islet cell transplantation offers hope that a cell transplantation treatment for type 1 (juvenile) diabetes may be possible if sufficient quantities of safe and effective cells can be produced. For the treatment of type 1 diabetes, the two therapeutically essential functions are the ability to monitor blood glucose levels and the production of corresponding and sufficient levels of mature insulin to maintain glycemic control. Stem cells can replicate themselves and produce cells that take on more specialized functions. If a source of stem cells capable of yielding glucose-responsive insulin-producing (GRIP) cells can be identified, then transplantation-based treatment for type 1 diabetes may become widely available. Currently, stem cells from embryonic and adult sources are being investigated for their ability to proliferate and differentiate into cells with GRIP function. Human embryonic pluripotent stem cells, commonly referred to as embryonic stem (ES) cells and embryonic germ (EG) cells, have received significant attention owing to their broad capacity to differentiate and ability to proliferate well in culture. Their application to diabetes research is of particular promise, as it has been demonstrated that mouse ES cells are capable of producing cells able to normalize glucose levels of diabetic mice, and human ES cells can differentiate into cells capable of insulin production. Cells with GRIP function have also been derived from stem cells residing in adult organisms, here referred to as endogenous stem cell sources. Independent of source, stem cells capable of producing cells with GRIP function may provide a widely available cell transplantation treatment for type 1 diabetes.

The commercialization of human stem cells: ethical and policy issues

The first stage of the human embryonic stem (ES) cell research debate revolved around fundamental questions, such as whether the research should be done at all, what types of research may be done, who should do the research, and how the research should be funded. Now that some of these questions are being answered, we are beginning to see the next stage of the debate: the battle for property rights relating to human ES cells. The reason why property rights will be a key issue in this debate is simple and easy to understand: it costs a great deal of money to do this research, to develop new products, and to implement therapies; and private companies, researchers, and health professionals require returns on investments and reimbursements for goods and services. This paper considers arguments for and against property rights relating to ES cells defends the following points: (1) It should be legal to buy and sell ES cells and products. (2) It should be legal to patent ES cells, products, and related technologies. (3) It should not be legal to buy, sell, or patent human embryos. (4) Patents on ES cells, products, and related technologies should not be excessively broad. (5) Patents on ES cells, products, and related technologies should be granted only when applicants state definite, plausible uses for their inventions. (6) There should be a research exemption in ES cell patenting to allow academic scientists to conduct research in regenerative medicine. (7) It may be appropriate to take steps to prevent companies from using patents in ES cells, products, and related technologies only to block competitors. (8) As the field of regenerative medicine continues to develop, societies should revisit issues relating to property rights on a continuing basis in order to develop policies and develop regulations to maximize the social, medical, economic, and scientific benefits of ES cell research and product development.

Neural stem cells spontaneously express dopaminergic traits after transplantation into the intact or 6-hydroxydopamine-lesioned rat

The ability to differentiate neural stem cells (NSCs) into dopamine neurons is fundamental to their role in cell replacement therapies for neurodegenerative disorders such as Parkinson's disease. We show here that when a clonal line (C17.2) of undifferentiated NSCs is transplanted into the intact or 6-hydroxydopamine-lesioned striatum, cells withdraw from the cell cycle (BrdU(-)), migrate extensively in the host striatum, and express markers associated with neuronal (beta-tubulin III(+), NSE(+), NeuN(+)) but not glial (GFAP(-), MBP(-), A2B5(-)) differentiation. Importantly, by 2-5 weeks postgrafting, in the majority of these transplants, nearly all engrafted cells express the dopamine-synthesizing enzymes tyrosine hydroxylase and aromatic L-amino decarboxylase, sometimes resulting in changes in motor behavior. In contrast, no NSCs stain for dopamine-beta-hydroxylase, choline acetyltransferase, glutamic acid decarboxylase, or serotonin. We conclude that, following transplantation into the intact or 6-hydroxydopamine-lesioned rat, the adult brain contains intrinsic cues sufficient to direct the specific expression of dopaminergic traits in immature multipotential neural stem cells.

Embryonic stem cells

The capacity of embryonic stem cells for virtually unlimited self-renewal and differentiation capacity has opened up the prospect of widespread applications in biomedical research and regenerative medicine. For the latter, the cells provide hope that it will be possible to overcome the problems of donor tissue shortage and also, by making the cells immunocompatible with the recipient, implant rejection. Four years after the first derivation of human pluripotent cell lines from pre-implantation embryos, a great deal has been learnt about their biology and how differentiation can be encouraged towards particular cell lineages. However, considerable research is needed, not least into means to enrich and purify derivative cell lineages, before clinical trials can be considered.

Does hereditary metabolic disease modulate senescence and ageing?

Hereditary metabolic diseases in the context of evolutionary biology elicit interesting questions about ageing and senescence: Will persons successfully treated for inborn errors of metabolism, age and die prematurely because of compromised longevity? Because some unhealthy longevity has its origins in germline and somatic mutational processes, and in an inability to withstand metabolic stress, are there lessons to be learned about senescence from hereditary metabolic disease? Why are ageing, senescence and death necessary for Homo sapiens and how do they happen? These questions form the theme upon which several variations are played during the course of this essay. The theory of the disposable soma recognizes genomic and environmental events, well-seasoned by Chance, as determinants of ageing and senescence. Together, they cause the somatic damage that results in death. Genomics will reveal genes involved in longevity, both healthy and unhealthy. There will be schedules of gene expression behind our life-history traits. As in the field of hereditary metabolic disease, analogous genetic enquiries about ageing can be formulated. For example, how will heterozygotes age? Will association studies in centenarians reveal 'longevity genes'? Will disparate longevity in sib pairs reveal genetic factors? If there are 'ageing' mutations, of what types and with what effects? Will these initiatives lead to healthier longevity? A deeper question yet remains: why has human biology invested so greatly in grandparenthood?

New names for old disciplines

Since the completion of the human genome map, genomics, proteomics and pharmacogenomics have become popular headings. In this review some 40 years of development in research and laboratory diagnosis of inborn errors of metabolism are summarized. It is shown that collaborative approaches of clinicians, geneticists, pathologists, biochemists and molecular biologists have contributed significantly to the (prenatal) diagnosis, genetic counselling and prevention of simple gene disorders, and in some instances to successful treatment. DNA technology widens the range to predictive risk testing for multifactorial disorders manifesting in adulthood. This offers new perspectives for potential patients and their close relatives, but also poses new psychosocial and ethical problems. Despite high expectations of new technologies in the development of new medicines for multifactorial disorders, examples of previous studies on the molecular etiology and pathogenesis of monogenic diseases indicate that a long way is ahead of us. Also the treatment of rare disorders and equal access to cure and care in the Third World need great attention.

Embryonic stem cells as an in vitro model for mutagenicity, cytotoxicity and embryotoxicity studies: present state and future prospects

Primary cultures or established cell lines of vertebrates are commonly used to analyse the mutagenic, embryotoxic or teratogenic potential of environmental factors, drugs and xenobiotics in vitro. However, these cellular systems do not include developmental processes from early embryonic stages up to terminally differentiated cell types. An alternative approach has been offered by permanent lines of pluripotent stem cells of embryonic origin, such as embryonic carcinoma (EC), embryonic stem (ES) and embryonic germ (EG) cells. The undifferentiated stem cell lines are characterized by nearly unlimited self-renewal capacity and have been shown to differentiate in vitro into cells of all three primary germ layers. Pluripotent embryonic stem cell lines recapitulate cellular developmental processes and gene expression patterns of early embryogenesis during in vitro differentiation, data which are summarized in this review. In addition, recent studies are presented which investigated mutagenic, cytotoxic and embryotoxic effects of chemical substances using in vitro systems of pluripotent embryonic stem cells. Furthermore, an outlook is given on future molecular technologies using embryonic stem cells in developmental toxicology and embryotoxicology.

Chondrocytic differentiation of mesenchymal stem cells sequentially exposed to transforming growth factor-beta1 in monolayer and insulin-like growth factor-I in a three-dimensional matrix

This study evaluated chondrogenesis of mesenchymal progenitor stem cells (MSCs) cultured initially under pre-confluent monolayer conditions exposed to transforming growth factor-beta1 (TGF-beta1), and subsequently in three-dimensional cultures containing insulin-like growth factor I (IGF-I). Bone marrow aspirates and chondrocytes were obtained from horses and cultured in monolayer with 0 or 5 ng of TGF-beta 1 per ml of medium for 6 days. TGF-beta 1 treated and untreated cultures were distributed to three-dimensional fibrin disks containing 0 or 100 ng of IGF-I per ml of medium to establish four treatment groups. After 13 days, cultures were assessed by toluidine blue staining, collagen types I and II in situ hybridization and immunohistochemistry, proteoglycan production by [35S]-sulfate incorporation, and disk DNA content by fluorometry. Mesenchymal cells in monolayer cultures treated with TGF-beta1 actively proliferated for the first 4 days, developed cellular rounding, and formed cell clusters. Treated MSC cultures had a two-fold increase in medium proteoglycan content. Pretreatment of MSCs with TGF-beta1 followed by exposure of cells to IGF-I in three-dimensional culture significantly increased the formation of markers of chondrocytic function including disk proteoglycan content and procollagen type II mRNA production. However, proteoglycan and procollagen type II production by MSC's remained lower than parallel chondrocyte cultures. MSC pretreatment with TGF-beta1 without sequential IGF-I was less effective in initiating expression of markers of chondrogenesis. This study indicates that although MSC differentiation was less than complete when compared to mature chondrocytes, chondrogenesis was observed in IGF-I supplemented cultures, particularly when used in concert with TGF-beta1 pretreatment.

Mammalian cloning: advances and limitations

For many years, researchers cloning mammals experienced little success, but recent advances have led to the successful cloning of several mammalian species. However, cloning by the transfer of nuclei from adult cells is still a hit-and-miss procedure, and it is not clear what technical and biological factors underlie this. Our understanding of the molecular basis of reprogramming remains extremely limited and affects experimental approaches towards increasing the success rate of cloning. Given the future practical benefits that cloning can offer, the time has come to address what should be done to resolve this problem.

Developmental potential of somatic stem cells in mammalian adults

Traditionally, somatic tissue-derived stem cells of mammalian adults have been viewed as pluripotent precursors capable of lifelong maintenance of cellular compartments typical of the tissue in which they reside. However in recent years, in vitro cultures and in vivo transplantation assays have indicated that adult somatic stem cell of various species are capable of adopting multiple fates. Bone marrow cells can give rise to a wide array of phenotypes, including blood, endothelial, bone, cartilage, fat, tendon, lung, liver, muscle, marrow stroma, and even brain cells. Conversely, neural stem cells as well as progenitors present in the muscle may contribute to blood cell production, indicating that adult stem cells present in numerous tissues may generate multiple cell types even of different dermal origin. Therefore, the developmental potential of adult somatic stem cells might be reassessed, although the mechanisms that ultimately lead to determination of cell fate are not completely defined. The successful long-term culturing and expansion of somatic adult stem cells together with their intrinsic versatility leads to future hope of stem cell therapeutic use in a wide spectrum of diseases and disorders of several, even not easily accessible, tissues.

Cloning of an Endangered Species (Bos gaurus) Using Interspecies Nuclear Transfer

Approximately 100 species become extinct a day. Despite increasing interest in using cloning to rescue endangered species, successful interspecies nuclear transfer has not been previously described, and only a few reports of in vitro embryo formation exist. Here we show that interspecies nuclear transfer can be used to clone an endangered species with normal karyotypic and phenotypic development through implantation and the late stages of fetal growth. Somatic cells from a gaur bull (Bos gaurus), a large wild ox on the verge of extinction, (Species Survival Plan < 100 animals) were electrofused with enucleated oocytes from domestic cows. Twelve percent of the reconstructed oocytes developed to the blastocyst stage, and 18% of these embryos developed to the fetal stage when transferred to surrogate mothers. Three of the fetuses were electively removed at days 46 to 54 of gestation, and two continued gestation longer than 180 (ongoing) and 200 days, respectively. Microsatellite marker and cytogenetic analyses confirmed that the nuclear genome of the cloned animals was gaurus in origin. The gaur nuclei were shown to direct normal fetal development, with differentiation into complex tissue and organs, even though the mitochondrial DNA (mtDNA) within all the tissue types evaluated was derived exclusively from the recipient bovine oocytes. These results suggest that somatic cell cloning methods could be used to restore endangered, or even extinct, species and populations.

Stem cell generation and choice of fate: role of cytokines and cellular microenvironment

Hematopoietic stem cells (HSC) have provided a model for the isolation, enrichment and transplantation of stem cells. Gene targeting studies in mice have shown that expression of the thrombopoietin receptor (TpoR) is linked to the accumulation of HSCs capable to generate long-term blood repopulation when injected into irradiated mice. The powerful increase in vivo in HSC numbers by retrovirally transduced HOX4B, a homeotic gene, along with the role of the TpoR, suggested that stem cell fate, renewal, differentiation and number can be controlled. The discovery of the precise region of the mouse embryo where HSCs originate and the isolation of supporting stromal cell lines open the possibility of identifying the precise signals required for HSC choice of fate. The completion of human genome sequencing coupled with advances in gene expression profiling using DNA microarrays will enable the identification of key genes deciding the fate of stem cells. Downstream from HSCs, multipotent hematopoietic progenitor cells appear to co-express a multiplicity of genes characteristic of different blood lineages. Genomic approaches will permit the identification of the select group of genes consolidated by the commitment of these multipotent progenitors towards one or the other of the blood lineages. Studies with neural stem cells pointed to the unexpected plastic nature of these cells. Isolation of stem cells from multiple tissues may suggest that, providing the appropriate environment/ signal, tissues could be regenerated in the laboratory and used for transplantation. A spectacular example of influence of the environment on cell fate was revealed decades ago by using mouse embryonic stem cells (ES). Injected into blastocysts, ES cells contribute to the formation of all adult tissues. Injected into adult mice, ES cells become cancer cells. After multiple passages as ascites, when injected back into the blastocyst environment, ES- derived cancer cells behaved again as ES cells. More recently, the successful cloning of mammals and reprogramming of transferred nuclei by factors in the cytoplasm of oocytes turned back the clock by showing that differentiated nuclei can be "re-booted" to generate again the stem cells for different tissues.

Neurons from stem cells: Implications for understanding nervous system development and repair

Neurodegenerative diseases cost the economies of the developed world billions of dollars per annum. Given ageing population profiles and the increasing extent of this problem, there has been a surge of interest in neural stem cells and in neural differentiation protocols that yield neural cells for therapeutic transplantation. Due to the oncogenic potential of stem cells a better characterisation of neural differentiation, including the identification of new neurotrophic factors, is required. Stem cell cultures undergoing synchronous in vitro neural differentiation provide a valuable resource for gene discovery. Novel tools such as microarrays promise to yield information regarding gene expression in stem cells. With the completion of the yeast, C. elegans, Drosophila, human, and mouse genome projects, the functional characterisation of genes using genetic and bioinformatic tools will aid in the identification of important regulators of neural differentiation.Key words: neural differentiation, neural precursor cell, brain repair, central nervous system repair, CNS.

Gene therapy approaches for modulating bone regeneration

Following injury, bone has the ability to regenerate itself to a form and function nearly indistinguishable from the pre-injury state. However, if the injury is beyond a critical limit, recovery will not occur without therapeutic interventions. Autografts and implants with banked bone continue as the treatments of choice, although each exhibits limitations and liabilities. Alternatives have included the utilization of bone-graft substitutes that may incorporate bone derivatives and soluble signaling molecules such as mitogens and morphogens. In addition, an evolving treatment modality, gene therapy, offers an exciting avenue for bone regeneration. This review presents some of the current concepts for developing a rational gene therapy approach in bone regeneration.