PDGFRα-Positive B Cells Are Neural Stem Cells in the Adult SVZ that Form Glioma-like Growths in Response to Increased PDGF Signaling

Can adult neural stem cells create new brains? Plasticity in the adult mammalian neurogenic niches: realities and expectations in the era of regenerative biology

Since the first experimental reports showing the persistence of neurogenic activity in the adult mammalian brain, this field of neurosciences has expanded significantly. It is now widely accepted that neural stem and precursor cells survive during adulthood and are able to respond to various endogenous and exogenous cues by altering their proliferation and differentiation activity. Nevertheless, the pathway to therapeutic applications still seems to be long. This review attempts to summarize and revisit the available data regarding the plasticity potential of adult neural stem cells and of their normal microenvironment, the neurogenic niche. Recent data have demonstrated that adult neural stem cells retain a high level of pluripotency and that adult neurogenic systems can switch the balance between neurogenesis and gliogenesis and can generate a range of cell types with an efficiency that was not initially expected. Moreover, adult neural stem and precursor cells seem to be able to self-regulate their interaction with the microenvironment and even to contribute to its synthesis, altogether revealing a high level of plasticity potential. The next important step will be to elucidate the factors that limit this plasticity in vivo, and such a restrictive role for the microenvironment is discussed in more details.

Is HCMV a tumor promoter?

Human cytomegalovirus (HCMV) is a beta-herpesvirus that causes persistent infection in humans and can cause severe disease in fetuses and immunocompromised individuals. Although HCMV is not currently causally implicated in human cancer, emerging evidence suggests that HCMV infection and expression may be specifically associated with human malignancies including malignant glioma, colon, and prostate cancer. In addition, multiple investigators have demonstrated that HCMV can dysregulate signaling pathways involved in initiation and promotion of malignancy, including tumor suppressor, mitogenic signaling, inflammatory, immune regulation, angiogenesis and invasion, and epigenetic mechanisms. This review highlights some of the recent evidence that HCMV might play a role in modulating the tumor microenvironment as well as in the initiation and promotion of tumor cells themselves.

SHP-2/PTPN11 mediates gliomagenesis driven by PDGFRA and INK4A/ARF aberrations in mice and humans

Recent collaborative efforts have subclassified malignant glioblastomas into 4 clinical relevant subtypes based on their signature genetic lesions. Platelet-derived growth factor receptor α (PDGFRA) overexpression is concomitant with a loss of cyclin-dependent kinase inhibitor 2A (CDKN2A) locus (encoding P16INK4A and P14ARF) in a large number of tumors within one subtype of glioblastomas. Here we report that activation of PDGFRα conferred tumorigenicity to Ink4a/Arf-deficient mouse astrocytes and human glioma cells in the brain. Restoration of p16INK4a but not p19ARF suppressed PDGFRα-promoted glioma formation. Mechanistically, abrogation of signaling modules in PDGFRα that lost capacity to bind to SHP-2 or PI3K significantly diminished PDGFRα-promoted tumorigenesis. Furthermore, inhibition of SHP-2 by shRNAs or pharmacological inhibitors disrupted the interaction of PI3K with PDGFRα, suppressed downstream AKT/mTOR activation, and impaired tumorigenesis of Ink4a/Arf-null cells, whereas expression of an activated PI3K mutant rescued the effect of SHP-2 inhibition on tumorigenicity. PDGFRα and PDGF-A are coexpressed in clinical glioblastoma specimens, and such co-expression is linked with activation of SHP-2/AKT/mTOR signaling. Together, our data suggest that in glioblastomas with Ink4a/Arf deficiency, overexpressed PDGFRα promotes tumorigenesis through the PI3K/AKT/mTOR-mediated pathway regulated by SHP-2 activity. These findings functionally validate the genomic analysis of glioblastomas and identify SHP-2 as a potential target for treatment of glioblastomas.

Brain abnormalities and glioma-like lesions in mice overexpressing the long isoform of PDGF-A in astrocytic cells

Background

Deregulation of platelet-derived growth factor (PDGF) signaling is a hallmark of malignant glioma. Two alternatively spliced PDGF-A mRNAs have been described, corresponding to a long (L) and a short (S) isoform of PDGF-A. In contrast to PDGF-A(S), the PDGF-A(L) isoform has a lysine and arginine rich carboxy-terminal extension that acts as an extracellular matrix retention motif. However, the exact role of PDGF-A(L) and how it functionally differs from the shorter isoform is not well understood.

Methodology/Principal Findings

We overexpressed PDGF-A(L) as a transgene under control of the glial fibrillary acidic protein (GFAP) promoter in the mouse brain. This directs expression of the transgene to astrocytic cells and GFAP expressing neural stem cells throughout the developing and adult central nervous system. Transgenic mice exhibited a phenotype with enlarged skull at approximately 6-16 weeks of age and they died between 1.5 months and 2 years of age. We detected an increased number of undifferentiated cells in all areas of transgene expression, such as in the subependymal zone around the lateral ventricle and in the cerebellar medulla. The cells stained positive for Pdgfr-α, Olig2 and NG2 but this population did only partially overlap with cells positive for Gfap and the transgene reporter. Interestingly, a few mice presented with overt neoplastic glioma-like lesions composed of both Olig2 and Gfap positive cell populations and with microvascular proliferation, in a wild-type p53 background.

Conclusions

Our findings show that PDGF-A(L) can induce accumulation of immature cells in the mouse brain. The strong expression of NG2, Pdgfr-α and Olig2 in PDGF-A(L) brains suggests that a fraction of these cells are oligodendrocyte progenitors. In addition, accumulation of fluid in the subarachnoid space and skull enlargement indicate that an increased intracranial pressure contributed to the observed lethality.

Developmental profiling of postnatal dentate gyrus progenitors provides evidence for dynamic cell-autonomous regulation

The dentate gyrus of the hippocampus is one of the most prominent regions in the postnatal mammalian brain where neurogenesis continues throughout life. There is tremendous speculation regarding the potential implications of adult hippocampal neurogenesis, though it remains unclear to what extent this ability becomes attenuated during normal aging, and what genetic changes in the progenitor population ensue over time. Using defined elements of the nestin promoter, we developed a transgenic mouse that reliably labels neural stem and early progenitors with green fluorescent protein (GFP). Using a combination of immunohistochemical and flow cytometry techniques, we characterized the progenitor cells within the dentate gyrus and created a developmental profile from postnatal day 7 (P7) until 6 months of age. In addition, we demonstrate that the proliferative potential of these progenitors is controlled at least in part by cell-autonomous cues. Finally, to identify what may underlie these differences, we performed stem cell-specific microarrays on GFP-expressing sorted cells from isolated P7 and postnatal day 28 (P28) dentate gyrus. We identified several differentially expressed genes that may underlie the functional differences that we observe in neurosphere assays from sorted cells and differentiation assays at these different ages. These data suggest that neural progenitors from the dentate gyrus are differentially regulated by cell-autonomous factors that change over time.

Brain cancer stem cells: current status on glioblastoma multiforme

Glioblastoma multiforme (GBM), an aggressive brain tumor of astrocytic/neural stem cell origin, represents one of the most incurable cancers. GBM tumors are highly heterogeneous. However, most tumors contain a subpopulation of cells that display neural stem cell characteristics in vitro and that can generate a new brain tumor upon transplantation in mice. Hence, previously identified molecular pathways regulating neural stem cell biology were found to represent the cornerstone of GBM stem cell self-renewal mechanism. GBM tumors are also notorious for their resistance to radiation therapy. Notably, GBM "cancer stem cells" were also found to be responsible for this radioresistance. Herein, we will analyze the data supporting or not the cancer stem cell model in GBM, overview the current knowledge regarding GBM stem cell self-renewal and radioresistance molecular mechanisms, and discuss the potential therapeutic application of these findings.

Epigenetic regulation of aging stem cells

The function of adult tissue-specific stem cells declines with age, which may contribute to the physiological decline in tissue homeostasis and the increased risk of neoplasm during aging. Old stem cells can be 'rejuvenated' by environmental stimuli in some cases, raising the possibility that a subset of age-dependent stem cell changes is regulated by reversible mechanisms. Epigenetic regulators are good candidates for such mechanisms, as they provide a versatile checkpoint to mediate plastic changes in gene expression and have recently been found to control organismal longevity. Here, we review the importance of chromatin regulation in adult stem cell compartments. We particularly focus on the roles of chromatin-modifying complexes and transcription factors that directly impact chromatin in aging stem cells. Understanding the regulation of chromatin states in adult stem cells is likely to have important implications for identifying avenues to maintain the homeostatic balance between sustained function and neoplastic transformation of aging stem cells.

Phosphorylation state of Olig2 regulates proliferation of neural progenitors

The bHLH transcription factors that regulate early development of the central nervous system can generally be classified as either antineural or proneural. Initial expression of antineural factors prevents cell cycle exit and thereby expands the pool of neural progenitors. Subsequent (and typically transient) expression of proneural factors promotes cell cycle exit, subtype specification, and differentiation. Against this backdrop, the bHLH transcription factor Olig2 in the oligodendrocyte lineage is unorthodox, showing antineural functions in multipotent CNS progenitor cells but also sustained expression and proneural functions in the formation of oligodendrocytes. We show here that the proliferative function of Olig2 is controlled by developmentally regulated phosphorylation of a conserved triple serine motif within the amino-terminal domain. In the phosphorylated state, Olig2 maintains antineural (i.e., promitotic) functions that are reflected in human glioma cells and in a genetically defined murine model of primary glioma.

The central nervous system-restricted transcription factor Olig2 opposes p53 responses to genotoxic damage in neural progenitors and malignant glioma

High-grade gliomas are notoriously insensitive to radiation and genotoxic drugs. Paradoxically, the p53 gene is structurally intact in the majority of these tumors. Resistance to genotoxic modalities in p53-positive gliomas is generally attributed to attenuation of p53 functions by mutations of other components within the p53 signaling axis, such as p14(Arf), MDM2, and ATM, but this explanation is not entirely satisfactory. We show here that the central nervous system (CNS)-restricted transcription factor Olig2 affects a key posttranslational modification of p53 in both normal and malignant neural progenitors and thereby antagonizes the interaction of p53 with promoter elements of multiple target genes. In the absence of Olig2 function, even attenuated levels of p53 are adequate for biological responses to genotoxic damage.

PDGF induced microRNA alterations in cancer cells

Platelet derived growth factor (PDGF) regulates gene transcription by binding to specific receptors. PDGF plays a critical role in oncogenesis in brain and other tumors, regulates angiogenesis, and remodels the stroma in physiologic conditions. Here, we show by using microRNA (miR) arrays that PDGFs regulate the expression and function of miRs in glioblastoma and ovarian cancer cells. The two PDGF ligands AA and BB affect expression of several miRs in ligand-specific manner; the most robust changes consisting of let-7d repression by PDGF-AA and miR-146b induction by PDGF-BB. Induction of miR-146b by PDGF-BB is modulated via MAPK-dependent induction of c-fos. We demonstrate that PDGF regulates expression of some of its known targets (e.g. cyclin D1) through miR alterations and identify the epidermal growth factor receptor (EGFR) as a new PDGF-BB target. We show that its expression and function are repressed by PDGF-induced miR-146b and that mir-146b and EGFR correlate inversely in human glioblastomas. We propose that PDGF-regulated gene transcription involves alterations in non-coding RNAs and provide evidence for a miR-dependent feedback mechanism balancing growth factor receptor signaling in cancer cells.

Persistent roles of signal transduction of platelet-derived growth factor B in genesis, growth, and anaplastic transformation of gliomas in an in-vivo serial transplantation model

We previously reported that retrovirally transduced platelet-derived growth factor-B (PDGFB) in glial progenitors of the rat cerebral white matter, subventricular zone, or brain stem induced malignant brain tumors closely resembling human glioblastoma (GBM). While human GBMs may progress over the period of several months to a few years, prospective, long-term in-vivo observation of histological changes of the tumor tissues is not feasible in these models, because the animals undergo rapid tumor progression and mortality within approximately 1 month. We thus performed successive, long-term in-vivo transplantation of the PDGFB-induced tumor cells into the rat cerebrum. Primary retroviral transduction of PDGFB in the glial progenitors of the rat basal ganglia induced malignant glioma resembling human GBM or anaplastic oligodendroglioma (AOL) consisting of relatively monomorphous tumor cells expressing markers for the oligodendrocyte lineage. In the course of long-term successive transplantation, tumor cells presented pleomorphism as well as focal GFAP expression. This suggests that secondary chromosomal aberration and dysregulation of gene expression following accelerated cell cycle by PDGFB stimulation would induce morphological and immunophenotypic changes in tumor cells. Furthermore, while the primary tumors contained only a minor fraction of proviral GFP-expressing or hemagglutinin-expressing cells, most tumor cells came to express these proviral genes in the course of serial transplantation suggesting a persistent role of PDGFB-expressing cells in maintenance and growth of the tumors. This model would be useful for investigation of the long-term effects of PDGFB stimulation in glioma tissues on anaplastic evolution.

Brain tumor-initiating cells and cells of origin in glioblastoma

Glioblastoma Multiforme (GBM) is the most malignant and devastating primary brain tumour with a median survival of ∼12–16 months. Although recent large scale sequencing projects have shed considerable light into the complexity of the disease, there remains much to be elucidated in the hopes of generating effective therapeutic strategies. Although these studies investigate the mutations and expression of bulk tumour they have limits with respect to cell of origin and the concept of brain tumour initiating cells (BTIC). Current research has challenged the old paradigm of the stochastic model as recent evidence suggests that a subset of cancer cells within a tumor is responsible for tumor initiation, maintenance, and resistance to therapy. To gain a better understanding of the different compartment of cells that GBM comprise of require careful and elegant experiments. In addition to studying GBM, exploring the role of normal neural stem cells and progenitors cells is essential to partially explain whether these GBM BTIC behave similarly or differently then their non transformed counterparts. Here we discuss the recent literature between the two models, candidate regions of glioma genesis, candidate cells of origin for GBM, and possible therapeutic avenues to explore.

OLIG2 is differentially expressed in pediatric astrocytic and in ependymal neoplasms

The bHLH transcription factor, OLIG2, is universally expressed in adult human gliomas and, as a major factor in the development of oligodendrocytes, is expressed at the highest levels in low-grade oligodendroglial tumors. In addition, it is functionally required for the formation of high-grade astrocytomas in a genetically relevant murine model. The pediatric gliomas have genomic profiles that are different from the corresponding adult tumors and accordingly, the expression of OLIG2 in non-oligodendroglial pediatric gliomas is not well documented within specific tumor types. In the current study, the pattern of OLIG2 expression in a spectrum of 90 non-oligodendroglial pediatric gliomas varied from very low levels in the ependymomas (cellular and tanycytic) to high levels in pilocytic astrocytoma, and in the diffuse-type astrocytic tumors (WHO grades II–IV). With dual-labeling, glioblastoma had the highest percentage of OLIG2 expressing cells that were also Ki-67 positive (mean = 16.3%) whereas pilocytic astrocytoma WHO grade I and astrocytoma WHO grade II had the lowest (0.9 and 1%, respectively); most of the Ki-67 positive cells in the diffuse-type astrocytomas (WHO grade II–III) were also OLIG2 positive (92–94%). In contrast to the various types of pediatric astrocytic tumors, all ependymomas WHO grade II, regardless of site of origin, showed at most minimal OLIG2 expression, suggesting that OLIG2 function in pediatric gliomas is cell lineage dependent.

Human glioblastoma-initiating cells invade specifically the subventricular zones and olfactory bulbs of mice after striatal injection

In patients with glioblastoma multiforme, recurrence is the rule despite continuous advances in surgery, radiotherapy and chemotherapy. Within these malignant gliomas, glioblastoma stem cells or initiating cells have been recently described, and they were shown to be specifically involved in experimental tumorigenesis. In this study, we show that some human glioblastoma cells injected into the striatum of immunodeficient nude mice exhibit a tropism for the subventricular zones. There and similarily to neurogenic stem cells, these subventricular glioblastoma cells were then able to migrate toward the olfactory bulbs. Finally, the glioblastoma cells isolated from the adult mouse subventricular zones and olfactory bulbs display high tumorigenicity when secondary injected in a new mouse brain. Together, these data suggest that neurogenic zones could be a reservoir for particular cancer-initiating cells.

Aging of the subventricular zone neural stem cell niche: evidence for quiescence-associated changes between early and mid-adulthood

Stem cells can exist in either active or quiescent states. In the aging hippocampus, adult neural stem cells (aNSCs) shift into a quiescent state, contributing to age-related reductions in hippocampal neurogenesis. Here, we focused on the subventricular zone (SVZ) stem cell niche of the adult forebrain, asking to what extent quiescence-associated changes in aNSCs are initiated between early and middle-age. Immunohistochemical and label retention experiments revealed that the overall output of the SVZ stem cell system was already highly decreased in middle-aged mice (12-months-old) compared with young adult mice (2-month-old), as measured by reduced marker expression for multiple neural precursor sub-populations and diminished addition of SVZ-derived neuroblasts to the olfactory bulbs (OBs). These changes were associated with significant cytological aberrations within the SVZ niche, including an overall atrophy of the SVZ and accumulation of large lipid droplets within ependymal cells, which are key support cells of the SVZ niche. Importantly, the reduced output of the middle-aged SVZ stem cell system correlated with quiescence-associated changes in middle-aged aNSCs. Specifically, while tissue culture experiments showed that young adult and middle-aged forebrains possessed equal numbers of neurosphere-forming aNSCs, the middle-aged neurospheres exhibited differences in their in vitro properties, and middle-aged aNSCs in vivo divided less frequently. These findings demonstrate that aNSCs begin undergoing quiescence-associated changes between early and mid-adulthood in the mouse SVZ, and serve as a useful framework for further studies aimed at defining the early events involved in aging-associated quiescence of aNSCs.

Energy metabolism in adult neural stem cell fate

The adult mammalian brain contains a population of neural stem cells that can give rise to neurons, astrocytes, and oligodendrocytes and are thought to be involved in certain forms of memory, behavior, and brain injury repair. Neural stem cell properties, such as self-renewal and multipotency, are modulated by both cell-intrinsic and cell-extrinsic factors. Emerging evidence suggests that energy metabolism is an important regulator of neural stem cell function. Molecules and signaling pathways that sense and influence energy metabolism, including insulin/insulin-like growth factor I (IGF-1)-FoxO and insulin/IGF-1-mTOR signaling, AMP-activated protein kinase (AMPK), SIRT1, and hypoxia-inducible factors, are now implicated in neural stem cell biology. Furthermore, these signaling modules are likely to cooperate with other pathways involved in stem cell maintenance and differentiation. This review summarizes the current understanding of how cellular and systemic energy metabolism regulate neural stem cell fate. The known consequences of dietary restriction, exercise, aging, and pathologies with deregulated energy metabolism for neural stem cells and their differentiated progeny will also be discussed. A better understanding of how neural stem cells are influenced by changes in energy availability will help unravel the complex nature of neural stem cell biology in both the normal and diseased state.

PDGF-B-driven gliomagenesis can occur in the absence of the proteoglycan NG2

BACKGROUND

In the last years, the transmembrane proteoglycan NG2 has gained interest as a therapeutic target for the treatment of diverse tumor types, including gliomas, because increases of its expression correlate with dismal prognosis. NG2 has been shown to function as a co-receptor for PDGF ligands whose aberrant expression is common in gliomas. We have recently generated a glioma model based on the overexpression of PDGF-B in neural progenitors and here we investigated the possible relevance of NG2 during PDGF-driven gliomagenesis.

METHODS

The survival curves of NG2-KO mice overexpressing PDGF-B were compared to controls by using a Log-rank test. The characteristics of tumors induced in NG2-KO were compared to those of tumors induced in wild type mice by immunostaining for different cell lineage markers and by transplantation assays in adult mice.

RESULTS

We showed that the lack of NG2 does not appreciably affect any of the characterized steps of PDGF-driven brain tumorigenesis, such as oligodendrocyte progenitor cells (OPC) induction, the recruitment of bystander OPCs and the progression to full malignancy, which take place as in wild type animals.

CONCLUSIONS

Our analysis, using both NG2-KO mice and a miRNA based silencing approach, clearly demonstrates that NG2 is not required for PDGF-B to efficiently induce and maintain gliomas from neural progenitors. On the basis of the data obtained, we therefore suggest that the role of NG2 as a target molecule for glioma treatment should be carefully reconsidered.

Neurofibromatosis-1 regulates neuroglial progenitor proliferation and glial differentiation in a brain region-specific manner

Recent studies have shown that neuroglial progenitor/stem cells (NSCs) from different brain regions exhibit varying capacities for self-renewal and differentiation. In this study, we used neurofibromatosis-1 (NF1) as a model system to elucidate a novel molecular mechanism underlying brain region-specific NSC functional heterogeneity. We demonstrate that Nf1 loss leads to increased NSC proliferation and gliogenesis in the brainstem, but not in the cortex. Using Nf1 genetically engineered mice and derivative NSC neurosphere cultures, we show that this brain region-specific increase in NSC proliferation and gliogenesis results from selective Akt hyperactivation. The molecular basis for the increased brainstem-specific Akt activation in brainstem NSCs is the consequence of differential rictor expression, leading to region-specific mammalian target of rapamycin (mTOR)/rictor-mediated Akt phosphorylation and Akt-regulated p27 phosphorylation. Collectively, these findings establish mTOR/rictor-mediated Akt activation as a key driver of NSC proliferation and gliogenesis, and identify a unique mechanism for conferring brain region-specific responses to cancer-causing genetic changes.

The utility and limitations of neurosphere assay, CD133 immunophenotyping and side population assay in glioma stem cell research

The newly proposed glioma stem cell (GSC) hypothesis may re-model the way we diagnose and treat the tumor, which highlights the need for a complete knowledge on the genetic and epigenetic "blueprints" of GSCs. To identify the true "stemness" signatures, pure GSC populations are primarily needed. Reliable in vitro methods enriching for GSCs and thereby identifying the key stem-like characteristics constitute the preliminary step forward. We discuss in this review the current widely used methods for enriching and isolating GSCs, namely neurosphere assay, CD133 Immunophenotyping and side population assay, and detail their limitations and potential pitfalls that could complicate interpretation of corresponding results.

Glial progenitors in the brainstem give rise to malignant gliomas by platelet-derived growth factor stimulation

Glial progenitors in the white matter and the subventricular zone are the major population of cycling cells in the postnatal central nervous system, and thought to be candidates for glioma-initiating cells. However, less is known about the dividing cell populations in the brainstem than those in the cerebrum, leading to the lag of basic understanding of brainstem gliomas. We herein demonstrate much fewer cycling glial progenitors exist in the brainstem than in the cerebrum. We also show that infecting brainstem glial progenitors with PDGFB-green fluorescent protein (GFP)-expressing retrovirus induced tumors that closely resembled human malignant gliomas. Of note, brainstem tumors grew more slowly than cerebral tumors induced by the same retrovirus, and >80% tumor cells in the brainstem consisted of GFP-positive, infected progenitors while GFP-positive cells in the cerebral tumors were <20%. These indicate that cerebral tumors progressed rapidly by recruiting resident progenitors via paracrine mechanism whereas brainstem tumors grew more slowly by clonal expansion of the infected population. The cerebral and brainstem glial progenitors similarly showed reversible dedifferentiation upon PDGF stimulation in vitro and did not show the intrinsic difference in terms of the responsiveness to PDGF. We therefore suggest that slower, monoclonal progression pattern of the brainstem tumors is at least partly due to the environmental factors including the cell density of the glial progenitors. Together, these findings are the first implications regarding the cell-of-origin and the gliomagenesis in the brainstem.

Cuprizone-induced demyelination in CNP::GFP transgenic mice

Cuprizone (bis-cyclohexanone oxaldihydrazone) was previously shown to induce demyelination in white matter enriched brain structures. In the present study we used the cuprizone demyelination model in transgenic mice expressing the enhanced green fluorescent protein (GFP) under the 2'-3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) promoter. The use of these particular transgenic mice allows easy detection of cells belonging to the entire oligodendroglial (OLG) lineage, ranging from OLG precursors to mature myelinating OLGs. We were able to evaluate the precise extent of oligodendroglial cell damage and recovery within the murine adult central nervous system (CNS) after inducing demyelination by acute cuprizone intoxication. A generalized loss of GFP+ cells was observed after cuprizone exposure and correlated with a decline in myelin basic protein (MBP) expression. OLGs were depleted in many brain areas that were previously thought to be unaffected by cuprizone treatment. Thus, in addition to the well-known cuprizone effects on the medial corpus callosum, we also found a loss of GFP+ cells in most brain structures, particularly in the caudatus putamen, cortex, anterior commissure, olfactory bulb, hippocampus, optic chiasm, brainstem, and cingulum. Loss of GFP+ cells was accompanied by extensive astrogliosis and microglial activation, although neurons were not affected. Interestingly, cuprizone-treated animals showed both activation of GFAP expression and a higher proliferation rate in subventricular zone cells. A week after cuprizone removal from the diet, GFP+ oligodendroglial cells began repopulating the damaged structures. GFP expression precedes that of MBP and allows OLG detection before myelin restoration.

Identification of a Chr 11 quantitative trait locus that modulates proliferation in the rostral migratory stream of the adult mouse brain

Neuron production takes place continuously in the rostral migratory stream (RMS) of the adult mammalian brain. The molecular mechanisms that regulate progenitor cell division and differentiation in the RMS remain largely unknown. Here, we surveyed the mouse genome in an unbiased manner to identify candidate gene loci that regulate proliferation in the adult RMS. We quantified neurogenesis in adult C57BL/6J and A/J mice, and 27 recombinant inbred lines derived from those parental strains. We showed that the A/J RMS had greater numbers of bromodeoxyuridine-labeled cells than that of C57BL/6J mice with similar cell cycle parameters, indicating that the differences in the number of bromodeoxyuridine-positive cells reflected the number of proliferating cells between the strains. AXB and BXA recombinant inbred strains demonstrated even greater variation in the numbers of proliferating cells. Genome-wide mapping of this trait revealed that chromosome 11 harbors a significant quantitative trait locus at 116.75 +/- 0.75 Mb that affects cell proliferation in the adult RMS. The genomic regions that influence RMS proliferation did not overlap with genomic regions regulating proliferation in the adult subgranular zone of the hippocampal dentate gyrus. On the contrary, a different, suggestive locus that modulates cell proliferation in the subgranular zone was mapped to chromosome 3 at 102 +/- 7 Mb. A subset of genes in the chromosome 11 quantitative trait locus region is associated with neurogenesis and cell proliferation. Our findings provide new insights into the genetic control of neural proliferation and an excellent starting point to identify genes critical to this process.

Immune system modulates the function of adult neural stem cells

New neurons are continuously produced in most, if not all, mammals. This Neurogenesis occurs only in discrete regions of the adult brain: the subventricular zone (SVZ) and the subgranular zone (SGZ). In these areas, there are neural stem cells (NSCs), multipotent and selfrenewing, which are regulated by a number of molecules and signaling pathways that control their cell fate choices, survival and proliferation rates. It was believed that growth and morphogenic factors were the unique mediators that controlled NSCs in vivo. Recently, chemokines and cytokines have been identified as important regulators of NSCs functions. Some of the most studied immunological effectors are leukemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF), interferon-gamma (IFN-γ), insulin-like growth factor-1 (IGF-1), tumor necrosis factor alpha (TNF-α), and the chemokines MCP-1 and SDF-1. These substances exert a considerable regulation on proliferation, cell-fate choices, migration and survival of NSCs. Hence, the immune system is emerging as an important regulator of neurogenic niches in the adult brain, but further studies are necessary to fully establish the biological meaning of these neural effects.

Molecular chaperone alphaB-crystallin is expressed in the human fetal telencephalon at midgestation by a subset of progenitor cells

Alphab-crystallin (CRYAB) is a small heat shock protein with a chaperoning activity that is present in the postnatal healthy human brain in oligodendrocytes and in a few astrocytes. The involvement of CRYAB in cell differentiation, proliferation, signaling, cytoskeletal assembly, and apoptosis in various model systems has suggested that it might also play a role in the developing human brain. We analyzed the distribution and the levels of this molecular chaperone in healthy and polygenetically compromised (Down syndrome [DS]) human telencephalon at midgestation. We demonstrate that CRYAB is expressed in a temporospatial pattern by numerous radial glial cells and some early oligodendrocyte progenitors, including dividing cells, as well as a few astroglial cells in both healthy and DS fetal brains. We also found abundant phosphorylation of CRYAB at Ser-59, which mediates its antiapoptotic and cytoskeletal functions. There was only marginal phosphorylation at Ser-45.In contrast to our earlier study in young DS subjects, upregulation of phosphorylated CRYAB occurred rarely in DS fetuses. The distribution, the timing of appearance, and the results of colocalization studies suggest that CRYAB assists in the biological processes associated with developmental remodeling/differentiation and proliferation of select subpopulations of progenitor cells in human fetal brain at midgestation.

A novel role for the Receptor for Advanced Glycation End-products in neural progenitor cells derived from adult SubVentricular Zone

The Receptor for Advanced Glycation End-products (RAGE) is a member of the immunoglobulin superfamily of cell surface receptors which interacts with a wide range of ligands, such as High-Mobility Group Box-1 (HMGB-1), S100B, advanced glycation end-products (AGEs). Here we provided evidence for the restricted expression of RAGE in the undifferentiated neural stem/progenitor cells of mouse adult SubVentricular Zone (SVZ) neurogenic region and adult SVZ-derived neurospheres. Additionally, RAGE ligands stimulated both proliferation and neuronal differentiation of SVZ-derived neural progenitor cells (NPC) in vitro. NF-kappaB nuclear translocation occurred upon RAGE activation in SVZ-derived neurospheres and its blockade (by SN-50) or its absence (in p50(-/-) derived NPC) resulted in the inhibition of the ligand-mediated effects on neuronal differentiation. These novel findings delineate an interesting scenario where the RAGE-NF-kappaB axis may contribute to regulate adult neural stem/progenitor cell function in physiological and possibly pathological conditions where this axis is upregulated.

T cells enhance stem-like properties and conditional malignancy in gliomas

Background

Small populations of highly tumorigenic stem-like cells (cancer stem cells; CSCs) can exist within, and uniquely regenerate cancers including malignant brain tumors (gliomas). Many aspects of glioma CSCs (GSCs), however, have been characterized in non-physiological settings.

Methods

We found gene expression similarity superiorly defined glioma “stemness”, and revealed that GSC similarity increased with lower tumor grade. Using this method, we examined stemness in human grade IV gliomas (GBM) before and after dendritic cell (DC) vaccine therapy. This was followed by gene expression, phenotypic and functional analysis of murine GL26 tumors recovered from nude, wild-type, or DC-vaccinated host brains.

Results

GSC similarity was specifically increased in post-vaccine GBMs, and correlated best to vaccine-altered gene expression and endogenous anti-tumor T cell activity. GL26 analysis confirmed immune alterations, specific acquisition of stem cell markers, specifically enhanced sensitivity to anti-stem drug (cyclopamine), and enhanced tumorigenicity in wild-type hosts, in tumors in proportion to anti-tumor T cell activity. Nevertheless, vaccine-exposed GL26 cells were no more tumorigenic than parental GL26 in T cell-deficient hosts, though they otherwise appeared similar to GSCs enriched by chemotherapy. Finally, vaccine-exposed GBM and GL26 exhibited relatively homogeneous expression of genes expressed in progenitor cells and/or differentiation.

Conclusions

T cell activity represents an inducible physiological process capable of proportionally enriching GSCs in human and mouse gliomas. Stem-like gliomas enriched by strong T cell activity, however, may differ from other GSCs in that their stem-like properties may be disassociated from increased tumor malignancy and heterogeneity under specific host immune conditions.

Brain tumor stem cells

Since the end of the ‘no-new-neuron’ theory, emerging evidence from multiple studies has supported the existence of stem cells in neurogenic areas of the adult brain. Along with this discovery, neural stem cells became candidate cells being at the origin of brain tumors. In fact, it has been demonstrated that molecular mechanisms controlling self-renewal and differentiation are shared between brain tumor stem cells and neural stem cells and that corruption of genes implicated in these pathways can direct tumor growth. In this regard, future anticancer approaches could be inspired by uncovering such redundancies and setting up treatments leading to exhaustion of the cancer stem cell pool. However, deleterious effects on (normal) neural stem cells should be minimized. Such therapeutic models underline the importance to study the cellular mechanisms implicated in fate decisions of neural stem cells and the oncogenic derivation of adult brain cells. In this review, we discuss the putative origins of brain tumor stem cells and their possible implications on future therapies.

Cholera toxin regulates a signaling pathway critical for the expansion of neural stem cell cultures from the fetal and adult rodent brains

Background

New mechanisms that regulate neural stem cell (NSC) expansion will contribute to improved assay systems and the emerging regenerative approach that targets endogenous stem cells. Expanding knowledge on the control of stem cell self renewal will also lead to new approaches for targeting the stem cell population of cancers.

Methodology/Principal Findings

Here we show that Cholera toxin regulates two recently characterized NSC markers, the Tie2 receptor and the transcription factor Hes3, and promotes the expansion of NSCs in culture. Cholera toxin increases immunoreactivity for the Tie2 receptor and rapidly induces the nuclear localization of Hes3. This is followed by powerful cultured NSC expansion and induction of proliferation both in the presence and absence of mitogen.

Conclusions/Significance

Our data suggest a new cell biological mechanism that regulates the self renewal and differentiation properties of stem cells, providing a new logic to manipulate NSCs in the context of regenerative disease and cancer.

PLAGL2 regulates Wnt signaling to impede differentiation in neural stem cells and gliomas

A hallmark feature of glioblastoma is its strong self-renewal potential and immature differentiation state, which contributes to its plasticity and therapeutic resistance. Here, integrated genomic and biological analyses identified PLAGL2 as a potent protooncogene targeted for amplification/gain in malignant gliomas. Enhanced PLAGL2 expression strongly suppresses neural stem cell (NSC) and glioma-initiating cell differentiation while promoting their self-renewal capacity upon differentiation induction. Transcriptome analysis revealed that these differentiation-suppressive activities are attributable in part to PLAGL2 modulation of Wnt/beta-catenin signaling. Inhibition of Wnt signaling partially restores PLAGL2-expressing NSC differentiation capacity. The identification of PLAGL2 as a glioma oncogene highlights the importance of a growing class of cancer genes functioning to impart stem cell-like characteristics in malignant cells.

Integrated molecular genetic profiling of pediatric high-grade gliomas reveals key differences with the adult disease

PURPOSE

To define copy number alterations and gene expression signatures underlying pediatric high-grade glioma (HGG).

PATIENTS AND METHODS

We conducted a high-resolution analysis of genomic imbalances in 78 de novo pediatric HGGs, including seven diffuse intrinsic pontine gliomas, and 10 HGGs arising in children who received cranial irradiation for a previous cancer using single nucleotide polymorphism microarray analysis. Gene expression was analyzed with gene expression microarrays for 53 tumors. Results were compared with publicly available data from adult tumors.

RESULTS

Significant differences in copy number alterations distinguish childhood and adult glioblastoma. PDGFRA was the predominant target of focal amplification in childhood HGG, including diffuse intrinsic pontine gliomas, and gene expression analyses supported an important role for deregulated PDGFRalpha signaling in pediatric HGG. No IDH1 hotspot mutations were found in pediatric tumors, highlighting molecular differences with adult secondary glioblastoma. Pediatric and adult glioblastomas were clearly distinguished by frequent gain of chromosome 1q (30% v 9%, respectively) and lower frequency of chromosome 7 gain (13% v 74%, respectively) and 10q loss (35% v 80%, respectively). PDGFRA amplification and 1q gain occurred at significantly higher frequency in irradiation-induced tumors, suggesting that these are initiating events in childhood gliomagenesis. A subset of pediatric HGGs showed minimal copy number changes.

CONCLUSION

Integrated molecular profiling showed substantial differences in the molecular features underlying pediatric and adult HGG, indicating that findings in adult tumors cannot be simply extrapolated to younger patients. PDGFRalpha may be a useful target for pediatric HGG, including diffuse pontine gliomas.

Deciphering the oligodendrogenic program of neural progenitors: cell intrinsic and extrinsic regulators

In the developing and adult CNS, neural stem/progenitor cells (NSPCs) and oligodendroglial progenitor cells (OPCs) follow an oligodendrogenic process with the aim of myelinating axons. This process is to a high degree regulated by an oligodendrogenic program (OPr) composed of intrinsic and extrinsic factors that modulate the different steps required for NSPCs to differentiate into myelinating oligodendrocytes. Even though NSPCs and OPCs are present in the diseased CNS and have the capacity to generate oligodendrocytes, sparse remyelination of axons constitutes a major constraint in therapies toward multiple sclerosis (MS) and spinal cord injury (SCI). Lack of pro-oligodendrogenic factors and presence of anti-oligodendrogenic activities are thought to be the main reasons for this limitation. Thus, molecular and cellular strategies aiming at remyelination and at targeting such pro- and anti-oligodendrogenic mechanisms are currently under investigation. The present review summarizes the current knowledge on the OPr; it implements our own findings on mesenchymal stem cell-derived pro-oligodendroglial factors and on the role of p57/kip2 in oligodendroglial differentiation. Moreover, it describes molecular and cellular approaches for the development of future therapies toward remyelination.

The nuclear receptor tailless induces long-term neural stem cell expansion and brain tumor initiation

Malignant gliomas are the most common primary brain tumors, and are associated with frequent resistance to therapy as well as poor prognosis. Here we demonstrate that the nuclear receptor tailless (Tlx), which in the adult is expressed exclusively in astrocyte-like B cells of the subventricular zone, acts as a key regulator of neural stem cell (NSC) expansion and brain tumor initiation from NSCs. Overexpression of Tlx antagonizes age-dependent exhaustion of NSCs in mice and leads to migration of stem/progenitor cells from their natural niche. The increase of NSCs persists with age, and leads to efficient production of newborn neurons in aged brain tissues. These cells initiate the development of glioma-like lesions and gliomas. Glioma development is accelerated upon loss of the tumor suppressor p53. Tlx-induced NSC expansion and gliomagenesis are associated with increased angiogenesis, which allows for the migration and maintenance of brain tumor stem cells in the perivascular niche. We also demonstrate that Tlx transcripts are overexpressed in human primary glioblastomas in which Tlx expression is restricted to a subpopulation of nestin-positive perivascular tumor cells. Our study clearly demonstrates how NSCs contribute to brain tumorgenesis driven by a stem cell-specific transcription factor, thus providing novel insights into the histogenesis and molecular pathogenesis of primary brain tumors.

Polysialic acid neural cell adhesion molecule (PSA-NCAM) is an adverse prognosis factor in glioblastoma, and regulates olig2 expression in glioma cell lines

BACKGROUND

Glioblastoma multiforme (GBM) is the most aggressive and frequent brain tumor, albeit without cure. Although patient survival is limited to one year on average, significant variability in outcome is observed. The assessment of biomarkers is needed to gain better knowledge of this type of tumor, help prognosis, design and evaluate therapies. The neurodevelopmental polysialic acid neural cell adhesion molecule (PSA-NCAM) protein is overexpressed in various cancers. Here, we studied its expression in GBM and evaluated its prognosis value for overall survival (OS) and disease free survival (DFS).

METHODS

We set up a specific and sensitive enzyme linked immunosorbent assay (ELISA) test for PSA-NCAM quantification, which correlated well with PSA-NCAM semi quantitative analysis by immunohistochemistry, and thus provides an accurate quantitative measurement of PSA-NCAM content for the 56 GBM biopsies analyzed. For statistics, the Spearman correlation coefficient was used to evaluate the consistency between the immunohistochemistry and ELISA data. Patients' survival was estimated by using the Kaplan-Meier method, and curves were compared using the log-rank test. On multivariate analysis, the effect of potential risk factors on the DFS and OS were evaluated using the cox regression proportional hazard models. The threshold for statistical significance was p = 0.05.

RESULTS

We showed that PSA-NCAM was expressed by approximately two thirds of the GBM at variable levels. On univariate analysis, PSA-NCAM content was an adverse prognosis factor for both OS (p = 0.04) and DFS (p = 0.0017). On multivariate analysis, PSA-NCAM expression was an independent negative predictor of OS (p = 0.046) and DFS (p = 0.007). Furthermore, in glioma cell lines, PSA-NCAM level expression was correlated to the one of olig2, a transcription factor required for gliomagenesis.

CONCLUSION

PSA-NCAM represents a valuable biomarker for the prognosis of GBM patients.

Angiogenic factors stimulate growth of adult neural stem cells

BACKGROUND

The ability to grow a uniform cell type from the adult central nervous system (CNS) is valuable for developing cell therapies and new strategies for drug discovery. The adult mammalian brain is a source of neural stem cells (NSC) found in both neurogenic and non-neurogenic zones but difficulties in culturing these hinders their use as research tools.

METHODOLOGY/PRINCIPAL FINDINGS

Here we show that NSCs can be efficiently grown in adherent cell cultures when angiogenic signals are included in the medium. These signals include both anti-angiogenic factors (the soluble form of the Notch receptor ligand, Dll4) and pro-angiogenic factors (the Tie-2 receptor ligand, Angiopoietin 2). These treatments support the self renewal state of cultured NSCs and expression of the transcription factor Hes3, which also identifies the cancer stem cell population in human tumors. In an organotypic slice model, angiogenic factors maintain vascular structure and increase the density of dopamine neuron processes.

CONCLUSIONS/SIGNIFICANCE

We demonstrate new properties of adult NSCs and a method to generate efficient adult NSC cultures from various central nervous system areas. These findings will help establish cellular models relevant to cancer and regeneration.

Transcriptional profiles of CD133+ and CD133- glioblastoma-derived cancer stem cell lines suggest different cells of origin

Glioblastoma multiforme (GBM) is paradigmatic for the investigation of cancer stem cells (CSC) in solid tumors. Growing evidence suggests that different types of CSC lead to the formation of GBM. This has prompted the present comparison of gene expression profiles between 17 GBM CSC lines and their different putative founder cells. Using a newly derived 24-gene signature, we can now distinguish two subgroups of GBM: Type I CSC lines display "proneural" signature genes and resemble fetal neural stem cell (fNSC) lines, whereas type II CSC lines show "mesenchymal" transcriptional profiles similar to adult NSC (aNSC) lines. Phenotypically, type I CSC lines are CD133 positive and grow as neurospheres. Type II CSC lines, in contrast, display (semi-)adherent growth and lack CD133 expression. Molecular differences between type I and type II CSC lines include the expression of extracellular matrix molecules and the transcriptional activity of the WNT and the transforming growth factor-beta/bone morphogenetic protein signaling pathways. Importantly, these characteristics were not affected by induced adherence on laminin. Comparing CSC lines with their putative cells of origin, we observed greatly increased proliferation and impaired differentiation capacity in both types of CSC lines but no cancer-associated activation of otherwise silent signaling pathways. Thus, our data suggest that the heterogeneous tumor entity GBM may derive from cells that have preserved or acquired properties of either fNSC or aNSC but lost the corresponding differentiation potential. Moreover, we propose a gene signature that enables the subclassification of GBM according to their putative cells of origin.

Diverse roles of the vasculature within the neural stem cell niche

An interdependent relationship between the vascular and nervous systems begins during the earliest stages of development and persists through the mammalian lifespan. Accordingly, the process of adult neurogenesis involves the coordinated response of both systems to maintain a specialized microenvironment (niche) that tips the scale towards maintenance or regeneration, as needed. Understanding the nature and regulation of this balance will provide a foundation on which the potential for molecular- and stem cell-based therapies can be developed to treat prevalent CNS diseases and disorders. The vasculature is cited as a prominent feature within the adult subventricular zone and subgranular zone, known adult neural stem cell niches, helping to retain neural stem and progenitor cell potential. The vascular compartment within the neural stem cell niche has the unique opportunity to not only regulate neural stem and progenitor cells through direct contact with, and paracrine signaling from, endothelial and mural cells that make up blood vessels, but also integrates systemic signals into the local microenvironment via distribution of soluble factors from blood circulation to regulate stem cell niche behavior. Understanding the intricate role that the vasculature plays to influence neural stem cells in the context of niche regulation will help to bridge the gap from bench to bedside for the development of regeneration-based therapies for the CNS.

Gliomagenesis and the use of neural stem cells in brain tumor treatment

The role of neural stem cells (NSCs) in both the physiological and pathological processes in the brain has been refined through recent studies within the neuro-oncological field. Alterations in NSC regulatory mechanisms may be fundamental for the development and progression of malignant gliomas. A subpopulation of cells within the tumor known as brain tumor stem cells (BTSCs) have been shown to share key properties with NSCs. The BTSC hypothesis has significantly contributed to a potential understanding as to why brain tumors hold such dismal prognosis. On the other hand, the normal NSCs possess the capacity to migrate extensively towards the tumor bulk as well as to lingering neoplastic regions of the brain. The tropism of NSCs towards brain tumors may provide an additional tool for the treatment of brain cancer. The creation of potential therapies through the use of NSCs has been studied and includes the delivery of gene products to specific locations of the central nervous system selectively targeting malignant brain tumor cells and maximizing the efficiency of their delivery. Here, the proposed mechanisms of how brain tumors emerge, the molecular pathways interrupted in NSC pathogenesis and the most recent preclinical results in the use of NSCs for glioma treatment are reviewed.

Integrated genomic analysis identifies clinically relevant subtypes of glioblastoma characterized by abnormalities in PDGFRA, IDH1, EGFR, and NF1

The Cancer Genome Atlas Network recently cataloged recurrent genomic abnormalities in glioblastoma multiforme (GBM). We describe a robust gene expression-based molecular classification of GBM into Proneural, Neural, Classical, and Mesenchymal subtypes and integrate multidimensional genomic data to establish patterns of somatic mutations and DNA copy number. Aberrations and gene expression of EGFR, NF1, and PDGFRA/IDH1 each define the Classical, Mesenchymal, and Proneural subtypes, respectively. Gene signatures of normal brain cell types show a strong relationship between subtypes and different neural lineages. Additionally, response to aggressive therapy differs by subtype, with the greatest benefit in the Classical subtype and no benefit in the Proneural subtype. We provide a framework that unifies transcriptomic and genomic dimensions for GBM molecular stratification with important implications for future studies.

Developmental cues and persistent neurogenic potential within an in vitro neural niche

Background

Neurogenesis, the production of neural cell-types from neural stem cells (NSCs), occurs during development as well as within select regions of the adult brain. NSCs in the adult subependymal zone (SEZ) exist in a well-categorized niche microenvironment established by surrounding cells and their molecular products. The components of this niche maintain the NSCs and their definitive properties, including the ability to self-renew and multipotency (neuronal and glial differentiation).

Results

We describe a model in vitro NSC niche, derived from embryonic stem cells, that produces many of the cells and products of the developing subventricular zone (SVZ) and adult SEZ NSC niche. We demonstrate a possible role for apoptosis and for components of the extracellular matrix in the maintenance of the NSC population within our niche cultures. We characterize expression of genes relevant to NSC self-renewal and the process of neurogenesis and compare these findings to gene expression produced by an established neural-induction protocol employing retinoic acid.

Conclusions

The in vitro NSC niche shows an identity that is distinct from the neurally induced embryonic cells that were used to derive it. Molecular and cellular components found in our in vitro NSC niche include NSCs, neural progeny, and ECM components and their receptors. Establishment of the in vitro NSC niche occurs in conjunction with apoptosis. Applications of this culture system range from studies of signaling events fundamental to niche formation and maintenance as well as development of unique NSC transplant platforms to treat disease or injury.

Cerebellar stem cells act as medulloblastoma-initiating cells in a mouse model and a neural stem cell signature characterizes a subset of human medulloblastomas

Cells with stem cell properties have been isolated from various areas of the postnatal mammalian brain, most recently from the postnatal mouse cerebellum. We show here that inactivation of the tumor suppressor genes Rb and p53 in these endogenous neural stem cells induced deregulated proliferation and resistance to apoptosis in vitro. Moreover, injection of these cells into mice formed medulloblastomas. Medulloblastomas are the most common malignant brain tumors of childhood, and despite recent advances in treatment they are associated with high morbidity and mortality. They are highly heterogeneous tumors characterized by a diverse genetic make-up and expression profile as well as variable prognosis. Here, we describe a novel ontogenetic pathway of medulloblastoma that significantly contributes to understanding their heterogeneity. Experimental medulloblastomas originating from neural stem cells preferentially expressed stem cell markers Nestin, Sox2 and Sox9, which were not expressed in medulloblastomas originating from granule-cell-restricted progenitors. Furthermore, the expression of these markers identified a subset of human medulloblastomas associated with a poorer clinical outcome.

Harvey Cushing's attempt at the first human pituitary transplantation

BACKGROUND

This case study illustrates Harvey Cushing's pioneering work in pituitary transplantation in the early 20th century and the essential relationship between laboratory research and clinical practice. In 1911, a 48 year-old man presented at Johns Hopkins Hospital with bitemporal hemianopsia, hypothermia, hypersomnolence, decreased libido, polydypsia and polyuria.

INVESTIGATION

A review of the Johns Hopkins Hospital surgical records from 1896-1912 on a patient with hypopituitarism secondary to a suprasellar mass, in whom the first documented pituitary gland transplantation was performed.

DIAGNOSIS

A diagnosis of hypopituitarism was made. Postmortem examination revealed a cystic cavity lined with squamous epithelium.

MANAGEMENT

The patient was treated with whole-gland pituitary extract, which improved his symptoms only temporarily. Cushing transplanted a pituitary gland obtained from a spontaneously aborted fetus into the cerebral cortex of the patient, who showed marked improvement of his somnolence and confusion, whereas his polyuria and polydypsia persisted. A recurrence of symptoms after 6 weeks prompted Cushing to attempt a second transplant of a fetal pituitary gland, without improvement. The patient resumed hormonal supplementation with whole-gland pituitary extract, but died a month after the second transplant from respiratory complications.

Orphan nuclear receptor TLX activates Wnt/beta-catenin signalling to stimulate neural stem cell proliferation and self-renewal

The nuclear receptor TLX (also known as NR2E1) is essential for adult neural stem cell self-renewal; however, the molecular mechanisms involved remain elusive. Here we show that TLX activates the canonical Wnt/beta-catenin pathway in adult mouse neural stem cells. Furthermore, we demonstrate that Wnt/beta-catenin signalling is important in the proliferation and self-renewal of adult neural stem cells in the presence of epidermal growth factor and fibroblast growth factor. Wnt7a and active beta-catenin promote neural stem cell self-renewal, whereas the deletion of Wnt7a or the lentiviral transduction of axin, a beta-catenin inhibitor, led to decreased cell proliferation in adult neurogenic areas. Lentiviral transduction of active beta-catenin led to increased numbers of type B neural stem cells in the subventricular zone of adult brains, whereas deletion of Wnt7a or TLX resulted in decreased numbers of neural stem cells retaining bromodeoxyuridine label in the adult brain. Both Wnt7a and active beta-catenin significantly rescued a TLX (also known as Nr2e1) short interfering RNA-induced deficiency in neural stem cell proliferation. Lentiviral transduction of an active beta-catenin increased cell proliferation in neurogenic areas of TLX-null adult brains markedly. These results strongly support the hypothesis that TLX acts through the Wnt/beta-catenin pathway to regulate neural stem cell proliferation and self-renewal. Moreover, this study suggests that neural stem cells can promote their own self-renewal by secreting signalling molecules that act in an autocrine/paracrine mode.

microRNAs in gliomas: small regulators of a big problem

Gliomas are the most common form of primary brain tumors and are associated with a poor clinical outcome. The molecular mechanisms that contribute to gliomagenesis have become increasingly clear in recent years, yet much remains to be learned. This is particularly true for the role of microRNAs in gliomagenesis, as an appreciation for the significance of aberrant miRNA expression in human cancer has only emerged in the last 5 years. It is now evident that microRNAs regulate a wide variety of tumorigenic processes including cellular proliferation, differentiation, angiogenesis, invasion, and apoptosis. Here we review the current state of knowledge related to the role of microRNAs in glial tumor development. This is a rapidly evolving field and it is likely that we have only begun to appreciate the involvement of microRNAs in relation to glioma formation, and the therapeutic potential of microRNAs to improve outcome for glioma patients.

Signaling in malignant astrocytomas: role of neural stem cells and its therapeutic implications

Malignant astrocytomas are infiltrative and aggressive brain tumors. Conventional forms of therapy have not been effective in controlling this incurable disease. Recent advances in understanding the molecular biology of these tumors have revealed potential mechanisms by which astrocytoma cells undergo tumor initiation, progression, and maintenance, as well as possible avenues for targeted therapeutics. Studies on the role of neural stem cells as cells of origin and tumor-propagating cells have also greatly increased our understanding of the biology and clinical behavior of these tumors. An integrated view of the genetics, signal transduction, and cell biology of astrocytomas, as well as clinical data from patients, will provide a more useful approach in designing novel therapies for this devastating disease.

Combinations of genetic mutations in the adult neural stem cell compartment determine brain tumour phenotypes

It has been suggested that intrinsic brain tumours originate from a neural stem/progenitor cell population in the subventricular zone of the post-natal brain. However, the influence of the initial genetic mutation on the phenotype as well as the contribution of mature astrocytes to the formation of brain tumours is still not understood. We deleted Rb/p53, Rb/p53/PTEN or PTEN/p53 in adult subventricular stem cells; in ectopically neurografted stem cells; in mature parenchymal astrocytes and in transplanted astrocytes. We found that only stem cells, but not astrocytes, gave rise to brain tumours, independent of their location. This suggests a cell autonomous mechanism that enables stem cells to generate brain tumours, whereas mature astrocytes do not form brain tumours in adults. Recombination of PTEN/p53 gave rise to gliomas whereas deletion of Rb/p53 or Rb/p53/PTEN generated primitive neuroectodermal tumours (PNET), indicating an important role of an initial Rb loss in driving the PNET phenotype. Our study underlines an important role of stem cells and the relevance of initial genetic mutations in the pathogenesis and phenotype of brain tumours.