In Vitro-Derived “Neural Stem Cells” Function as Neural Progenitors Without the Capacity for Self-Renewal

NUBP2 deficiency disrupts the centrosome-check point in the brain and causes primary microcephaly

Microcephaly affects 1 in 2,500 babies per year. Primary microcephaly results from aberrant neurogenesis leading to a small brain at birth. This is due to altered patterns of proliferation and/or early differentiation of neurons. Premature differentiation of neurons is associated with defects in the centrosome and/or primary cilia. In this study, we report on the first patients identified with NUBP2 -deficiency and utilize a conditional mouse model to ascertain the molecular mechanisms associated with NUBP2 -deficient primary microcephaly. We identified homozygous NUBP2 variants in these patients who displayed profound primary microcephaly in addition to intrauterine growth restriction, cervical kyphosis, severe contractures of joints, and facial dysmorphia. We then generated a mouse model using Emx1-Cre to ablate Nubp2 from the forebrain. The mice presented with severe microcephaly starting at E18.5. Neurospheres generated from the forebrain of Emx1-Cre; Nubp2 flox/flox conditional deletion mice were used to support the pathogenicity of the patient variants. We show that loss of Nubp2 increases both canonical and non-canonical cell death, but that loss of p53 fails to rescue microcephaly in the mouse model. Examination of neurogenesis in Emx1-Cre; Nubp2 flox/flox mice revealed distinct alterations in proliferation and cellular migration accompanied by supernumerary centrosomes and cilia. We therefore propose that NUBP2 is a novel primary microcephaly-related gene and that the role of Nubp2 in centrosome and cilia regulation is crucial for proper neurogenesis.

TGFβ family signaling in human stem cell self-renewal and differentiation

Human stem cells are undifferentiated cells with the capacity for self-renewal and differentiation into distinct cell lineages, playing important role in the development and maintenance of diverse tissues and organs. The microenvironment of stem cell provides crucial factors and components that exert significant influence over the determination of cell fate. Among these factors, cytokines from the transforming growth factor β (TGFβ) superfamily, including TGFβ, bone morphogenic protein (BMP), Activin and Nodal, have been identified as important regulators governing stem cell maintenance and differentiation. In this review, we present a comprehensive overview of the pivotal roles played by TGFβ superfamily signaling in governing human embryonic stem cells, somatic stem cells, induced pluripotent stem cells, and cancer stem cells. Furthermore, we summarize the latest research and advancements of TGFβ family in various cancer stem cells and stem cell-based therapy, discussing their potential clinical applications in cancer therapy and regeneration medicine.

Neurospheres: a potential in vitro model for the study of central nervous system disorders

Neurogenesis was believed to end after the period of embryonic development. However, the possibility of obtaining an expressive number of cells with functional neuronal characteristics implied a great advance in experimental research. New techniques have emerged to demonstrate that the birth of new neurons continues to occur in the adult brain. Two main rich sources of these cells are the subventricular zone (SVZ) and the subgranular zone of the hippocampal dentate gyrus (SGZ) where adult neural stem cells (aNSCs) have the ability to proliferate and differentiate into mature cell lines. The cultivation of neurospheres is a method to isolate, maintain and expand neural stem cells (NSCs) and has been used extensively by several research groups to analyze the biological properties of NSCs and their potential use in injured brains from animal models. Throughout this review, we highlight the areas where this type of cell culture has been applied and the advantages and limitations of using this model in experimental studies for the neurological clinical scenario.

Microfluidics as efficient technology for the isolation and characterization of stem cells

The recent years have been passed with significant progressions in the utilization of microfluidic technologies for cellular investigations. The aim of microfluidics is to mimic small-scale body environment with features like optical transparency. Microfluidics can screen and monitor different cell types during culture and study cell function in response to stimuli in a fully controlled environment. No matter how the microfluidic environment is similar to in vivo environment, it is not possible to fully investigate stem cells behavior in response to stimuli during cell proliferation and differentiation. Researchers have used stem cells in different fields from fundamental researches to clinical applications. Many cells in the body possess particular functions, but stem cells do not have a specific task and can turn into almost any type of cells. Stem cells are undifferentiated cells with the ability of changing into specific cells that can be essential for the body. Researchers and physicians are interested in stem cells to use them in testing the function of the body's systems and solving their complications. This review discusses the recent advances in utilizing microfluidic techniques for the analysis of stem cells, and mentions the advantages and disadvantages of using microfluidic technology for stem cell research.

A simple, efficient and economical method for isolating and culturing human umbilical cord blood‑derived mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) hold broad therapeutic potential in various diseases, however, it is difficult to produce sufficient numbers of MSCs for clinical application, therefore, improved culture systems are required. The present study aimed to develop a novel method for isolating and culturing human umbilical cord blood‑derived mesenchymal stromal cells (hUCB‑MSCs). A sequential culture method was developed that uses two types of culture media to optimize the isolation and culture of hUCB‑MSCs. First, DMEM supplemented with mesenchymal stem cell growth supplement was used to improve the colony formation and primary culture success rates of hUCB‑MSCs. Then, after removing the heterogeneous cell population, ordinary DMEM was used from the fourth passage. This method obtained hUCB‑MSCs with high culture efficiency and at a greatly reduced cost. The optimal culture conditions were determined and the hUCB‑MSCs were phenotypically characterized after passaging. Taken together, this simple, efficient and economical method can produce a large number of high‑quality hUCB‑MSCs in <1 month, therefore facilitating the future clinical applications of hUCB‑MSCs.

A Simple, Rapid, and Efficient Method for Isolating Mesenchymal Stem Cells from the Entire Umbilical Cord

Several reports have been published on the isolation, culture, and identification of mesenchymal stem cells (MSCs) from different anatomical regions of the umbilical cord (UC). UC is suitable for standardizing methods of MSC isolation because it is a uniform source with high MSC numbers. Although the UC is considered a medical waste after childbirth, ethical issues for its use must be considered. An increased demand for MSCs in regenerative medicine has made scientists prioritize the development of MSC isolation methods. Several research groups are attempting to provide a large number of high-quality MSCs. In this study, we present a modulated explant/enzyme method (MEEM) to isolate the maximum number of MSCs from the entire UC. This method was established for the isolation of MSCs from different anatomical regions of the UC altogether. We could retrieve 6 to 10 million MSCs during 8 to 10 days of primary culture. After three passages, we could obtain 8–10 × 108 cells in 28–30 days. MSCs isolated by this method express CD73, CD90, CD105, and CD44, but they do not express hematopoietic markers CD34 and CD45 or the endothelial marker CD31. The genes SOX2, OCT4, and NANOG are expressed in isolated MSCs. The capacity of these MSCs to differentiate into adipocytes and osteocytes highlights their application in regenerative medicine. This method is simple, reproducible, and cost efficient. Moreover, this method is suitable for the production of a large number of high-quality MSCs from an UC in less than a month, to be used for cell therapy in an 80-kg person.

Neurotoxic effects of AZT on developing and adult neurogenesis

Azidothymidine (AZT) is a synthetic, chain-terminating nucleoside analog used to treat HIV-1 infection. While AZT is not actively transported across the blood brain barrier, it does accumulate at high levels in cerebrospinal fluid, and subsequently diffuses into the overlying parenchyma. Due to the close anatomical proximity of the neurogenic niches to the ventricular system, we hypothesize that diffusion from CSF exposes neural stem/progenitor cells and their progeny to biologically relevant levels of AZT sufficient to perturb normal cell functions. We employed in vitro and in vivo models of mouse neurogenesis in order to assess the effects of AZT on developing and adult neurogenesis. Using in vitro assays we show that AZT reduces the population expansion potential of neural stem/progenitor cells by inducing senescence. Additionally, in a model of in vitro neurogenesis AZT severely attenuates neuroblast production. These effects are mirrored in vivo by clinically-relevant animal models. We show that in utero AZT exposure perturbs both population expansion and neurogenesis among neural stem/progenitor cells. Additionally, a short-term AZT regimen in adult mice suppresses subependymal zone neurogenesis. These data reveal novel negative effects of AZT on neural stem cell biology. Given that the sequelae of HIV infection often include neurologic deficits—subsumed under AIDS Dementia Complex (Brew, 1999)—it is important to determine to what extent AZT negatively affects neurological function in ways that contribute to, or exacerbate, ADC in order to avoid attributing iatrogenic drug effects to the underlying disease process, and thereby skewing the risk/benefit analysis of AZT therapy.

Induction of neuronal differentiation of rat muscle-derived stem cells in vitro using basic fibroblast growth factor and ethosuximide

Several studies have demonstrated that basic fibroblast growth factor (bFGF) can induce neural differentiation of mesenchymal stem cells. In this study, we investigated the neural differentiation of muscle-derived stem cells (MDSCs) following treatment with bFGF and ethosuximide, a small molecule used as an anticonvulsant in humans. Stem cells isolated from rat skeletal muscle (rMDSCs) were pre-induced by culturing with 25 ng/mL bFGF for 24 h and then were transferred to a medium supplemented with or without 4 mM ethosuximide. Neuronal differentiation was assessed by immunocytochemical and western blotting analyses of marker expression. Immunocytochemistry of rMDSCs treated with bFGF and ethosuximide identified abundant cells expressing neuronal markers (TuJ1, neuron-specific class III β-tubulin; NeuN, neuronal nuclear antigen; and NF-MH; neurofilament M and H). Olig2 (oligodendrocyte transcription factor 2)-positive cells were also observed, indicating the presence of oligodendrocyte lineage cells. These findings were substantiated by western blotting analysis of marker proteins. In particular, the expression of NeuN and TuJ1 was significantly higher in rMDSCs treated with ethosuximide and bFGF than in cells stimulated with bFGF alone (NeuN, p < 0.05 and TuJ1, p < 0.001). Expression of the astrocyte marker GFAP (glial fibrillary acidic protein) was not detected in this study. Collectively, the results showed that treatment with bFGF and ethosuximide induced effective transdifferentiation of rMDSCs into cells with a neural-like phenotype. Notably, rMDSCs treated with a combination of bFGF plus ethosuximide showed enhanced differentiation compared with cells treated with bFGF alone, implying that ethosuximide may stimulate neuronal differentiation.

Muscle reorganisation through local injection of stem cells in the diaphragm of mdx mice

Background

The diaphragm is the major respiratory muscle affected by Duchenne muscular dystrophy (DMD) and is responsible for causing 80% of deaths. The use of mechanical forces that act on the body or intermittent pressure on the airways improves the quality of life of patients but does not prevent the progression of respiratory failure. Thus, diseases that require tissue repair, such as DMD, represent a group of pathologies that have great potential for cell therapy. The application of stem cells directly into the diaphragm instead of systemic application can reduce cell migration to other affected areas and increase the chances of muscle reorganisation. The mdx mouse is a suitable animal model for this research because its diaphragmatic phenotype is similar to human DMD. Therefore, the aim of this study was to assess the potential cell implantation in the diaphragm muscle after the xenotransplantation of stem cells.

Methods

A total of 9 mice, including 3 control BALB/Cmice, 3 5-month-old mdx mice without stem cell injections and 3 mdx mice injected with stem cells, were used. The animals injected with stem cells underwent laparoscopy so that stem cells from GFP-labelled rabbit olfactory epithelium could be locally injected into the diaphragm muscle. After 8 days, all animals were euthanised, and the diaphragm muscle was dissected and subjected to histological and immunohistochemical analyses.

Results

Both the fresh diaphragm tissue and immunohistochemical analyses showed immunopositive GFP labelling of some of the cells and immunonegativity of myoblast bundles. In the histological analysis, we observed a reduction in the inflammatory infiltrate as well as the presence of a few peripheral nuclei and myoblast bundles.

Conclusion

We were able to implant stem cells into the diaphragm via local injection, which promoted moderate muscle reorganisation. The presence of myoblast bundles cannot be attributed to stem cell incorporation because there was no immunopositive labelling in this structure. It is believed that the formation of the bundles may have been stimulated by cellular signalling mechanisms that have not yet been elucidated.

TGF-β family signaling in stem cells

BACKGROUND

The diversity of cell types and tissue types that originate throughout development derives from the differentiation potential of embryonic stem cells and somatic stem cells. While the former are pluripotent, and thus can give rise to a full differentiation spectrum, the latter have limited differentiation potential but drive tissue remodeling. Additionally cancer tissues also have a small population of self-renewing cells with stem cell properties. These cancer stem cells may arise through dedifferentiation from non-stem cells in cancer tissues, illustrating their plasticity, and may greatly contribute to the resistance of cancers to chemotherapies.

SCOPE OF REVIEW

The capacity of the different types of stem cells for self-renewal, the establishment and maintenance of their differentiation potential, and the selection of differentiation programs are greatly defined by the interplay of signaling molecules provided by both the stem cells themselves, and their microenvironment, the niche. Here we discuss common and divergent roles of TGF-β family signaling in the regulation of embryonic, reprogrammed pluripotent, somatic, and cancer stem cells.

MAJOR CONCLUSIONS

Increasing evidence highlights the similarities between responses of normal and cancer stem cells to signaling molecules, provided or activated by their microenvironment. While TGF-β family signaling regulates stemness of normal and cancer stem cells, its effects are diverse and depend on the cell types and physiological state of the cells.

GENERAL SIGNIFICANCE

Further mechanistic studies will provide a better understanding of the roles of TGF-β family signaling in the regulation of stem cells. These basic studies may lead to the development of a new therapeutic or prognostic strategies for the treatment of cancers. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

The adult mouse dentate gyrus contains populations of committed progenitor cells that are distinct from subependymal zone neural stem cells

There is currently a debate as to whether or not a neural stem cell (NSC) exists in the adult mammalian hippocampus. Clonal colony-forming assays allow single cells to cells to be evaluated for stem cell properties: self-renewal and multipotentiality. In these in vitro assays, single cells from the subependymal zone (SEZ) of the adult lateral ventricle yield large colonies which self-renew and are multipotential, while single cells from the adult dentate gyrus (DG) produce small, unipotent, and nonself-renewing colonies. We find that multipotential and long-term self-renewing colonies can be isolated only from the early embryonic hippocampus, before the formation of the DG. No movement of progenitors from the postnatal SEZ to the newly forming DG subgranular zone is detected and adult DG colonies in vitro originate from the embryonic hippocampal primordium. These data support a model where embryonic hippocampal NSCs change their properties as the organism ages. When adult DG spheres are cocultured with embryonic brain slices, self-renewal (but not multipotentiality) is restored and maintained for several passages off of slices. Adult clonal DG spheres grown on embryonic brain slices or transplanted into brains of neonatal mice do not give rise to neurons. Neurons arise from separate, small clones that are approximately 10 times more frequent than sphere colonies in vitro and may be responsible for maintaining neurogenesis in the adult in vivo. We propose that there are separate glial and neuronal clones in the adult hippocampus, with glial progenitors being the most proliferative in culture.

Stem cells in microfluidics

Microfluidic techniques have been recently developed for cell-based assays. In microfluidic systems, the objective is for these microenvironments to mimic in vivo surroundings. With advantageous characteristics such as optical transparency and the capability for automating protocols, different types of cells can be cultured, screened, and monitored in real time to systematically investigate their morphology and functions under well-controlled microenvironments in response to various stimuli. Recently, the study of stem cells using microfluidic platforms has attracted considerable interest. Even though stem cells have been studied extensively using bench-top systems, an understanding of their behavior in in vivo-like microenvironments which stimulate cell proliferation and differentiation is still lacking. In this paper, recent cell studies using microfluidic systems are first introduced. The various miniature systems for cell culture, sorting and isolation, and stimulation are then systematically reviewed. The main focus of this review is on papers published in recent years studying stem cells by using microfluidic technology. This review aims to provide experts in microfluidics an overview of various microfluidic systems for stem cell research.

Stem cells in genetic myelin disorders

The genetic myelin disorders are a range of diseases that manifest with severe neurological problems, often from infancy. It has been postulated for some time that stem cells might be an effective treatment for these disorders, primarily as agents to restore dysfunctional or lost myelin. Stem cells, however, may offer a wider range of therapeutic potential, for instance as vehicles to replace abnormal enzymes or genes, or to provide trophic support for residual CNS tissue. This article will review several of the more common genetic myelin disorders and currently available therapies, including bone marrow transplantation for adrenoleukodystrophy. Specific stem cell subtypes and their relevance to potential therapeutic use will be discussed and stem cell transplantation in animal model studies will also be reviewed.

Neural progenitors of the postnatal and adult mouse forebrain retain the ability to self-replicate, form neurospheres, and undergo multipotent differentiation in vivo

Somatic stem cells are reservoirs to replace lost cells or damaged tissue. Cells with neural stem cell (NSC) characteristics can be isolated from the postnatal mammalian brain into adulthood and expanded as neurospheres. We addressed the ability of these in vitro expanded putative NSCs to retain progenitor characteristics in vivo, in analogy to hematopoietic stem cells. When transplanted in utero, both postnatal and adult neural progenitors colonize host brains and contribute neurons and glia. In stark contrast to what has been reported when transplanted in postnatal hosts, epidermal growth factor-expanded cells also remain self-replicating and multipotent in vivo over many months and can be serially transplanted into multiple hosts. Surprisingly, embryonically transplanted NSCs remain in the neurogenic regions in adult hosts, where they express progenitor cell markers and continue to proliferate even after 6 months without tumor formation. These data indicate that spherogenic cells of the postnatal and adult mammalian brain retain their potential in vitro and in vivo throughout the life of the organism and beyond transplantation, which has important implications for cell replacement strategies.

Towards personalized cell-replacement therapies for brain repair

The inability of the CNS to efficiently repair damage caused by trauma and neurodegenerative or demyelinating diseases has underlined the necessity for developing novel therapeutic strategies. Cell transplantation to replace lost neurons and the grafting of myelinating cells to repair demyelinating lesions are promising approaches for treating CNS injuries and demyelination. In this review, we will address the prospects of using stem cells or myelinating glial cells of the PNS, as well as olfactory ensheathing cells, in cell-replacement therapies. The recent generation of induced pluripotent stem cells from adult somatic cells by introduction of three or four genes controlling ‘stemness’ and their subsequent differentiation to desired phenotypes, constitutes a significant advancement towards personalized cell-replacement therapies.

Use of human neural tissue for the generation of progenitors

Accumulating evidence suggests that a better understanding of normal human brain stem cells and tumor stem cells (TSCs) will have profound implications for treating central nervous system disease during the next decade. Neurosurgeons routinely resect excess surgical tissue containing either normal brain stem cells or TSCs. These cells are immediately available for expansion and use in basic biological assays, animal implantation, and comparative analysis studies. Although normal stem cells have much slower kinetics of expansion than TSCs, they are easily expandable and can be frozen for future use in stem cell banks. This nearly limitless resource holds promise for understanding the basic biology of normal brain stem cells and TSCs, which will likely direct the next major shift in therapeutics for brain tumors, brain and spinal cord injury, and neurodegenerative disease. This report reviews the progress that has been made in harvesting and expanding both normal and tumor-derived stem cells and emphasizes the integral role neurosurgeons will play in moving the neural stem cell field forward.

The potential use of stem cells in multiple sclerosis: an overview of the preclinical experience

The reported neurodegeneration process in multiple sclerosis may explain the lack of efficacy of the currently used immunomodulating modalities and the irreversible axonal damage, which results in accumulating disability. Efforts for neuroprotective treatments have not been, so far, successful in clinical studies in other CNS diseases. Therefore, for MS, the use of stem cells may provide a logical solution, since these cells can migrate locally into the areas of white matter lesions (plaques) and have the potential to support local neurogenesis and rebuilding of the affected myelin. This may be achieved both by support of the resident CNS stem cells repertoire and by differentiation of the transplanted cells into neurons and myelin-producing cells (oligodendrocytes). Stem cells were also shown to possess immunomodulating properties, inducing systemic and local suppression of the myelin-targeting autoimmune lymphocytes. Several types of stem cells (embryonic and adult) have been described and extensively studied in animal models of CNS diseases. In this review, we summarize the experience with the use of different types of stem cells in the animal models of MS (EAE) and we describe the advantages and disadvantages of each stem cell type for future clinical applications in MS.

The neurosphere assay, a method under scrutiny

OBJECTIVES

The aim of this review is to provide an overview of the fundamental features of the neurosphere assay (NSA), which was initially described in 1992, and has since been used not only to detect the presence of stem cells in embryonic and adult mammalian neural tissues, but also to study their characteristics in vitro. Implicit in this review is a detailed examination of the limitations of the NSA, and how this assay is most accurately and appropriately used. Finally we will point out criteria that should be challenged to design alternative ways to overcome the limits of this assay.

METHODS

NSA is used to isolate putative neural stem cells (NSCs) from the central nervous system (CNS) and to demonstrate the critical stem cell attributes of proliferation, extensive self-renewal and the ability to give rise to a large number of differentiated and functional progeny. Nevertheless, the capability of neural progenitor cells to form neurospheres precludes its utilisation to accurately quantify bona fide stem cell frequency based simply on neurosphere numbers. New culture conditions are needed to be able to distinguish the activity of progenitor cells from stem cells.

CONCLUSION

A commonly used, and arguably misused, methodology, the NSA has provided a wealth of information on precursor activity of cells derived from the embryonic through to the aged CNS. Importantly, the NSA has contributed to the demise of the 'no new neurogenesis' dogma, and the beginning of a new era of CNS regenerative medicine. Nevertheless, the interpretations arising from the utilisation of the NSA need to take into consideration its limits, so as not to be used beyond its specificity and sensitivity.

Use of stem cells for the treatment of multiple sclerosis

The reported evidence of neurodegeneration in multiple sclerosis (MS) may explain the lack of efficacy of the currently used immunomodulating modalities and the irreversible axonal damage, which results in accumulating disability. To date, efforts for neuroprotective treatments have not been successful in clinical studies in other CNS diseases. Therefore, for MS, the use of stem cells may provide a logical solution, since these cells can migrate locally into the areas of white-matter lesions (plaques) and have the potential to support local neurogenesis and rebuilding of the affected myelin. This is achieved both by support of the resident CNS stem cell repertoire and by differentiation of the transplanted cells into neurons and myelin-producing cells (oligodendrocytes). Stem cells were also shown to possess immunomodulating properties, inducing systemic and local suppression of the myelin-targeting autoimmune lymphocytes. Several types of stem cells (embryonic and adult) have been described and extensively studied in animal models of CNS diseases and the various models of MS (experimental autoimmune encephalomyelitis [EAE]). In this review, we summarize the experience with the use of different types of stem cells in CNS disease models, focusing on the models of EAE and describe the advantages and disadvantages of each stem cell type for future clinical applications in MS.

Separation and enrichment of neural stem cells using segregation in an expanded bed

An expanded bed system has been developed for a novel application in which the separation and enrichment of neural stem cells from a sample containing a mixture of stem and progenitor cells is achieved based on the difference in the sizes of the aggregates of these types of cells. Inert Sephadex beads and flocculated yeast cells were used as experimental controls and references. The characteristics of the separation of neural stem cell aggregates based on size are similar to those achieved with flocculated yeast where cell-to-cell aggregation controls the pattern of size separation different from those of inert Sephadex beads.

Immunomodulation and neuroprotection with mesenchymal bone marrow stem cells (MSCs): a proposed treatment for multiple sclerosis and other neuroimmunological/neurodegenerative diseases

Bone marrow (BM) derived mesenchymal stem cells (MSCs) (non-hematopoietic, stromal cells) can differentiate under certain circumstances into cells from various neuronal and glial type lineages; they also exert immunomodulatory effects. For potential clinical applications, BM-MSCs offer significant practical advantages over other types of stem cells, since they can be obtained from the adult BM (the patient himself being the donor) and can be easily cultured and expanded posing in parallel a very low risk for development of malignancies. We have shown that BM-MSCs cultured with a cocktail of growth factors (containing FGF and BDNF) differentiate into neuronal/glial lineage cells with a predominance of cells expressing astrocytes' markers. BM-MSCs were effective in suppression of chronic EAE in mice and induced neuroprotection, preserving most of the axons in the CNS of successfully-treated animals. Histopathological studies revealed that MSCs could efficiently migrate into the CNS inflamed tissue (both when administered intravenously and intraventricularly) and differentiated into cells expressing neural-glial lineage markers. Our preclinical results indicate that bone marrow can provide a source of stem cells with a potential for migration into inflamed CNS tissue and differentiation into cells expressing neuronal and glial cell markers. Such an approach may provide a feasible and practical way for in situ immunomodulation, neuroprotection and possibly remyelination/regeneration in diseases like multiple sclerosis. We therefore developed a explorative protocol for the evaluation of this therapeutic approach in a small group of patients with MS and other neurodegenerative diseases.

Increased dentate neurogenesis after grafting of glial restricted progenitors or neural stem cells in the aging hippocampus

Neurogenesis in the dentate gyrus (DG) declines severely by middle age, potentially because of age-related changes in the DG microenvironment. We hypothesize that providing fresh glial restricted progenitors (GRPs) or neural stem cells (NSCs) to the aging hippocampus via grafting enriches the DG microenvironment and thereby stimulates the production of new granule cells from endogenous NSCs. The GRPs isolated from the spinal cords of embryonic day 13.5 transgenic F344 rats expressing human alkaline phosphatase gene and NSCs isolated from embryonic day 9 caudal neural tubes of Sox-2:EGFP transgenic mice were expanded in vitro and grafted into the hippocampi of middle-aged (12 months old) F344 rats. Both types of grafts survived well, and grafted NSCs in addition migrated to all layers of the hippocampus. Phenotypic characterization revealed that both GRPs and NSCs differentiated predominantly into astrocytes and oligodendrocytic progenitors. Neuronal differentiation of graft-derived cells was mostly absent except in the dentate subgranular zone (SGZ), where some of the migrated NSCs but not GRPs differentiated into neurons. Analyses of the numbers of newly born neurons in the DG using 5'-bromodeoxyuridine and/or doublecortin assays, however, demonstrated considerably increased dentate neurogenesis in animals receiving grafts of GRPs or NSCs in comparison with both naïve controls and animals receiving sham-grafting surgery. Thus, both GRPs and NSCs survive well, differentiate predominantly into glia, and stimulate the endogenous NSCs in the SGZ to produce more new dentate granule cells following grafting into the aging hippocampus. Grafting of GRPs or NSCs therefore provides an attractive approach for improving neurogenesis in the aging hippocampus. Disclosure of potential conflicts of interest is found at the end of this article.

Stem Cells Need Chemical Solutions

Stem cell research finds itself at a critical juncture, having presented a promise and potential that has thus far gone substantially unrealized. Chemical science has technology and expertise that can solve some of these shortcomings. Recruiting chemical scientists to collaborate with stem cell biologists will advance significantly efforts to understand normal development of and achieve therapeutic applications using stem cells.