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.

Microglia from neurogenic and non-neurogenic regions display differential proliferative potential and neuroblast support.

Microglia isolated from the neurogenic subependymal zone (SEZ) and hippocampus (HC) are capable of massive in vitro population expansion that is not possible with microglia isolated from non-neurogenic regions. We asked if this regional heterogeneity in microglial proliferative capacity is cell intrinsic, or is conferred by interaction with respective neurogenic or non-neurogenic niches. By combining SEZ and cerebral cortex (CTX) primary tissue dissociates to generate heterospatial cultures, we find that exposure to the SEZ environment does not enhance CTX microglia expansion; however, the CTX environment exerts a suppressive effect on SEZ microglia expansion.

In vivo intermittent hypoxia elicits enhanced expansion and neuronal differentiation in cultured neural progenitors.

In vitro exposure of neural progenitor cell (NPC) populations to reduced O(2) (e.g. 3% versus 20%) can increase their proliferation, survival and neuronal differentiation.

Ethynyldeoxyuridine (EdU) suppresses in vitro population expansion and in vivo tumor progression of human glioblastoma cells.

Thymidine analogs (TAs) are synthetic nucleosides that incorporate into newly synthesized DNA. Halogenated pyrimidines (HPs), such as bromodeoxyuridine (BrdU), are a class of TAs that can be detected with antibodies and are commonly used for birthdating individual cells and for assessing the proliferative index of cell populations. It is well established that HPs can act as radiosensitizers when incorporated into DNA chains, but they are generally believed not to impair normal cell function in the absence of secondary stressors.

Transplantation of neural stem/progenitor cells into developing and adult CNS.

Neural transplantation has been a long-standing goal for the treatment of neurological injury and disease. The recent discovery of persistent pools of neural stem cells within the adult mammalian brain has re-ignited interest in transplant therapeutics. Since neural stem cells are self-renewing, it may be possible to culture and expand neural stem cells and their progenitor cell progeny to sufficient numbers for use in autologous, self-repair strategies.

Bromodeoxyuridine induces senescence in neural stem and progenitor cells.

Bromodeoxyuridine (BrdU) is a halogenated pyrimidine that incorporates into newly synthesized DNA during the S phase. BrdU is used ubiquitously in cell birthdating studies and as a means of measuring the proliferative index of various cell populations. In the absence of secondary stressors, BrdU is thought to incorporate relatively benignly into replicating DNA chains.

Bromodeoxyuridine inhibits cancer cell proliferation in vitro and in vivo.

The thymidine analog bromodeoxyuridine (BrdU) is incorporated into newly synthesized DNA and has been shown to increase the susceptibility of incorporating cells to ionizing radiation. However, in the absence of secondary stressors, BrdU is thought to substitute relatively benignly for thymidine and is commonly used to "birth-date" proliferative cells. We report a novel antiproliferative effect of BrdU on cancer cells, which is independent of its role in radiosensitization.

Subventricular zone microglia possess a unique capacity for massive in vitro expansion.

Microglia, the resident immune cells of the brain, have recently been hypothesized to play a role both in neuronal diseases and age-related neurogenic decline, and are theorized to be modulators of adult neurogenesis. Current methods for the isolation of microglia from cultured primary brain tissue result in relatively poor yield, requiring a large tissue sample or multiple specimens to obtain a sufficient number of microglia for cell and molecular analysis. We report here a method for the repetitive isolation of microglia from established glial monolayer cultures from which it is possible to expand the initial population of microglia roughly 10,000-fold.

Production of neurospheres from CNS tissue.

The relatively recent discovery of persistent adult neurogenesis has led to the experimental isolation and characterization of central nervous system neural stem cell populations. Protocols for in vitro analysis and expansion of neural stem cells are crucial for understanding their properties and defining characteristics. The methods described here allow for cell and molecular analysis of individual clones of cells--neurospheres--derived from neural stem/progenitor cells.

Using the neurosphere assay to quantify neural stem cells in vivo.

Since their initial description in 1992, neurospheres have appeared in some aspect of more than a thousand published studies. Despite their ubiquitous presence in the scientific literature, there is little consensus regarding the fundamental defining characteristics of neurospheres; thus, there is little agreement about what, if anything, the neurosphere assay can tell us about the relative abundance or behavior of neural stem cells in vivo. In this review we will examine some of the common features of neurospheres, and ask if these features should be interpreted as a proxy for neural stem cells.

Astrocytic stem cells in the adult brain.

The adult mammalian brain harbors a population of neural stem cells (NSCs) that are responsible for persistent neurogenesis in the olfactory system and hippocampus and may also play a role in tumorigenesis. Here, the authors review the evidence that NSCs within the adult brain are a special type of astrocyte. In addition, the authors examine the phylogenetic and ontogenetic relations between this astrocyte stem cell and related members of the astrocyte family.

Microglia instruct subventricular zone neurogenesis.

Microglia are increasingly implicated as a source of non-neural regulation of postnatal neurogenesis and neuronal development. To evaluate better the contributions of microglia to neural stem cells (NSCs) of the subventricular neuraxis, we employed an adherent culture system that models the continuing proliferation and differentiation of the dissociated neuropoietic subventricular tissues. In this model, neuropoietic cells retain the ability to self-renew and form multipotent neurospheres, but progressively lose the ability to generate committed neuroblasts with continued culture.

Fusion of neural stem cells in culture.

An important issue in stem cell biology relates to mechanisms of cellular plasticity. Specifically, could any observed multipotency of, e.g.

In vitro-derived "neural stem cells" function as neural progenitors without the capacity for self-renewal.

Hematopoietic stem cells have been defined by their ability to self-renew and successfully reconstitute hematopoiesis throughout the life of a transplant recipient. Neural stem cells (NSCs) are believed to exist in the regenerating regions of the brain in adult mice: the subependymal zone (SEZ) of the lateral ventricles (LVs) and the hippocampal dentate gyrus. Cells from the SEZ can be cultured to generate neurospheres or multipotent astrocytic stem cells (MASCs), both of which demonstrate the stem cell qualities of multipotency and self-renewal in vitro.

Mesenchymal stem cells spontaneously express neural proteins in culture and are neurogenic after transplantation.

Reports of neural transdifferentiation of mesenchymal stem cells (MSCs) suggest the possibility that these cells may serve as a source for stem cell-based regenerative medicine to treat neurological disorders. However, some recent studies controvert previous reports of MSC neurogenecity. In the current study, we evaluate the neural differentiation potential of mouse bone marrow-derived MSCs.

Neuron-to-astrocyte transition: phenotypic fluidity and the formation of hybrid asterons in differentiating neurospheres.

To the extent that their fate choice and differentiation processes can be understood and manipulated, neural stem cells represent a promising therapeutic tool for a variety of neuropathologies. We have previously shown that mature astrocytes possess neural stem cell attributes, and can give rise to neurons through the formation of multipotent neurosphere clones. Here we show that relatively mature neurons generated from neurospheres derived from postnatal subependymal zone or cerebellar cortex undergo a phenotypic transformation into astrocytes that coincides with the appearance of a nonfused, hybrid cell type that shares the morphology, antigenicity, and physiology of both neurons and astrocytes.

Ionizing radiation enhances the engraftment of transplanted in vitro-derived multipotent astrocytic stem cells.

The subependymal zone (SEZ) is a region of persistent neurogenesis in the adult mammalian brain containing a neural stem cell (NSC) pool that continuously generates migratory neuroblasts that travel in chains through the rostral migratory stream (RMS) to the olfactory bulb (OB), where they differentiate and functionally integrate into existing neural circuitry. NSCs can be isolated from the SEZ and cultured to generate either neurospheres (NSs) or multipotent astrocytic stem cells (MASCs), with both possessing the stem cell characteristics of multipotency and self-renewal. NSs and MASCs home to the SEZ after transplantation into the lateral ventricle (LV) and contribute to neuroblast migration, with minimal engraftment into the OB observed in the adult mouse.

GM1-ganglioside-mediated activation of the unfolded protein response causes neuronal death in a neurodegenerative gangliosidosis.

GM1-ganglioside (GM1) is a major sialoglycolipid of neuronal membranes that, among other functions, modulates calcium homeostasis. Excessive accumulation of GM1 due to deficiency of lysosomal beta-galactosidase (beta-gal) characterizes the neurodegenerative disease GM1-gangliosidosis, but whether the accumulation of GM1 is directly responsible for CNS pathogenesis was unknown. Here we demonstrate that activation of an unfolded protein response (UPR) associated with the upregulation of BiP and CHOP and the activation of JNK2 and caspase-12 leads to neuronal apoptosis in the mouse model of GM1-gangliosidosis.

Bone marrow transdifferentiation in brain after transplantation: a retrospective study.

Background: End-organ repair by adult haemopoietic stem cells is under great scrutiny with investigators challenging the notion of these cells' plasticity. Some investigations of animals and short-term human bone marrow transplants suggest that bone marrow can repair brain. We looked for evidence of clinically relevant marrow-derived restorative neurogenesis: long-term, multilineage, neural engraftment that is not the result of cell-fusion events.

Neural trans-differentiation potential of hepatic oval cells in the neonatal mouse brain.

Although the existence of the hepatic oval cell (HOC), the liver stem cell has been known for almost 70 years, little is known about the potential for this adult stem cell to trans-differentiate into cells of other tissues. While their origin remains enigmatic, HOCs share many similarities with hematopoietic stem cells. Recent studies have revealed that a small percentage of HOCs can arise from a bone marrow-derived stem cell source.

Astrocytes as stem cells: nomenclature, phenotype, and translation.

Recently discovered multipotent astrocytic stem cells are discussed in light of current nomenclature for glial precursor and lineage-associated cells in the developing, postnatal, and adult mammalian brain. Defining the phenotype of any immature cell in the nervous system is a challenge, and a position is stated that includes the need for categorizing cells within a continuum of differentiation potential. The possibility for dedifferentiating glial cells into clonogenic stem-like cells offers numerous possibilities for translating knowledge and technology from this subfield of stem cell biology to regenerative medicine.

Transplantation of an indigenous neural stem cell population leading to hyperplasia and atypical integration.

Astrocytes exhibit neural stem cell characteristics in vitro by generating multipotent clones of cells. In order to see if normal cues are present in vivo that can direct these astrocytes to generate cells of neuronal lineage, the astrocytes were transplanted into the persistently neurogenic mouse subependymal zone/rostral migratory stream. Grafted astrocytes assumed migratory profiles, joined chains of indigenous neuroblasts, and migrated into the olfactory bulb.