Masaya Nakanishi

Kyoto University, Kyoto, Kyoto-fu, Japan

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Publications (5)20.58 Total impact

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    ABSTRACT: Invasiveness, cellular atypia, and proliferation are hallmarks of malignant gliomas. To effectively target each of these characteristics, it is important to understand their sequence during tumorigenesis. However, because most gliomas are diagnosed at an advanced stage, the chronology of gliomagenesis milestones is not well understood. The aim of the present study was to determine the onset of these characteristics during tumor development. Brain tumor-initiating cells (BTICs) were established by overexpressing H-Ras(V12) in normal neural stem/progenitor cells isolated from the subventricular zone of adult mice harboring a homozygous deletion of the Ink4a/Arf locus. High-grade malignant brain tumors were then created by orthotopic implantation of 10(5) BTICs into the forebrain of 6-week-old wild-type mice. Micewere killed every week for 5 weeks, and tumors were assessed for cellular atypia, proliferation, hemorrhage, necrosis, and invasion. All mice developed highly invasive, hypervascular glioblastoma-like tumors. A 100% penetrance rate and a 4-week median survival were achieved. Tumor cell migration along fiber tracts started within days after implantation and was followed by perivascular infiltration of tumor cells with marked recruitment of reactive host cells. Next, cellular atypia became prominent. Finally, mass proliferation and necrosis were observed in the last stage of the disease. Video monitoring of BTICs in live brain slices confirmed the early onset of migration, as well as the main cell migration patterns. Our results showed that perivascular and intraparenchymal tumor cell migration precede tumor mass formation in the adult brain, suggesting the need for an early and sustained anti-invasion therapy.
    Neoplasia 09/2011; 13(9):784-791. · 5.47 Impact Factor
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    [show abstract] [hide abstract]
    ABSTRACT: Invasiveness, cellular atypia, and proliferation are hallmarks of malignant gliomas. To effectively target each of these characteristics, it is important to understand their sequence during tumorigenesis. However, because most gliomas are diagnosed at an advanced stage, the chronology of gliomagenesis milestones is not well understood. The aim of the present study was to determine the onset of these characteristics during tumor development. Brain tumor-initiating cells (BTICs) were established by overexpressing H-Ras(V12) in normal neural stem/progenitor cells isolated from the subventricular zone of adult mice harboring a homozygous deletion of the Ink4a/Arf locus. High-grade malignant brain tumors were then created by orthotopic implantation of 10(5) BTICs into the forebrain of 6-week-old wild-type mice. Micewere killed every week for 5 weeks, and tumors were assessed for cellular atypia, proliferation, hemorrhage, necrosis, and invasion. All mice developed highly invasive, hypervascular glioblastoma-like tumors. A 100% penetrance rate and a 4-week median survival were achieved. Tumor cell migration along fiber tracts started within days after implantation and was followed by perivascular infiltration of tumor cells with marked recruitment of reactive host cells. Next, cellular atypia became prominent. Finally, mass proliferation and necrosis were observed in the last stage of the disease. Video monitoring of BTICs in live brain slices confirmed the early onset of migration, as well as the main cell migration patterns. Our results showed that perivascular and intraparenchymal tumor cell migration precede tumor mass formation in the adult brain, suggesting the need for an early and sustained anti-invasion therapy.
    Neoplasia (New York, N.Y.) 09/2011; 13(9):784-91. · 5.48 Impact Factor
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    ABSTRACT: The cancer stem cell (CSC) model, in which a small population of cells within a tumor possesses the ability to self-renew and recon-stitute the phenotype of primary tumor, has gained wide accep-tance based on evidence over the past decade. It has also been reported that cancer cell lines contain a CSC subpopulation. How-ever, phenotypic differences between CSCs and non-CSCs in cancer cell lines are not better defined than in primary tumors. Further-more, some cell lines do not have a CSC population, revealed as a side population and expression of CD133. Thus, the identification of CSCs in cancer cell lines remains elusive. Here, we investigated the CSC hierarchy within HCT116 colon cancer cells, which do not have a CD133-positive subpopulation. We examined the expres-sion of alternative CSC markers epithelial specific antigen (ESA) and CD44 in floating-sphere-derived cells, which are known to be the cells of enriching CSCs. Sphere-derived HCT116 cells exhibited heterogeneous expression of ESA and CD44. The two major subpopulations of HCT116 sphere cells (ESA low CD44) ⁄ low and ESA high CD44 high) exhibited a biological ⁄ proliferative hierarchy of sphere-forming and soft agar colony-forming activity. However, there was no difference between the two subpopulations in the incidence of xenograft tumors. When ESA low CD44) ⁄ low cells were allowed to aggregate and re-form floating-spheres, the biologi-cal ⁄ proliferative hierarchy of parental HCT116 spheres was recon-stituted, in terms of ESA and CD44 expression. Thus, HCT116 cells have plasticity when they are set in floating-spheres, suggesting that maintenance of the HCT116 cell line conforms to a stochastic model, not a CSC model.
    Cancer Science 12/2009; 100(12):2275-2282. · 3.48 Impact Factor
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    ABSTRACT: Microglia are believed to play an important role in the regulation of phagocytosis, neuronal survival, neuronal cell death, and inflammation. Recent studies have demonstrated that microglia are multipotential stem cells that give rise to neurons, astrocytes, and oligodendrocytes. However, the functional properties of neurons derived from microglia are poorly understood. In this study, we investigated the possibility that microglia differentiate into functional neurons. Immunocytochemical study demonstrated that microtubule-associated protein 2 (MAP2)-positive cells were derived from microglia under differentiation conditions. Intracellular Ca(2+) imaging study demonstrated that KCl caused no significant changes in [Ca(2+)](i) in microglia, whereas it caused a remarkable increase in [Ca(2+)](i) in microglia-derived cells. Furthermore, electrophysiological study demonstrated that the spike waveform, firing rate, and tetrodotoxin sensitivity of extracellular action potentials evoked by 4-aminopyridine from microglia-derived MAP2-positive cells were nearly identical to those from cultured cortical neurons. These results suggest that microglia-derived MAP2-positive cells possess properties of functional neurons.
    Biochemical and Biophysical Research Communications 05/2008; 368(4):971-6. · 2.41 Impact Factor
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    ABSTRACT: Neural stem/progenitor cells (NSPCs) proliferate and differentiate depending on their intrinsic properties and local environment. It has been recognized that astrocytes promote neurogenic differentiation of NSPCs, suggesting the importance of cell-cell interactions between glial cells and NSPCs. Recent studies have demonstrated that microglia, one type of glial cells, play an important role in neurogenesis. However, little is known about how activated microglia control the proliferation and differentiation of NSPCs. In this study, we investigated the possibility that microglia-derived soluble factors regulate the behaviour of NSPCs. To this end, NSPCs and microglial cultures were obtained from rat embryonic day 16 subventricular zone (SVZ) and rat postnatal 1 day cortex, respectively, and the conditioned medium from microglia was prepared. Microglial-conditioned medium had no significant effect on the proliferation of NSPCs. In contrast, it increased the percentage of cells positive for a marker of astrocytes, glial fibrillary acidic protein (GFAP) during differentiation. The induction of astrocytic differentiation by microglial-conditioned medium was reduced by the inhibition of the Janus kinase/signal transducer and activation of transcription (JAK/STAT) and mitogen-activated protein kinase (MAPK) pathways. Furthermore, microglia-derived interleukin (IL)-6 and leukaemia inhibitory factor (LIF) were identified as essential molecules for this astrocytic differentiation using neutralizing antibodies and recombinant cytokines. Our results suggest that microglia as well as astrocytes contribute to the integrity of the local environment of NSPCs, and at least IL-6 and LIF released by activated microglia promote astrocytic differentiation of NSPCs via the activation of the JAK/STAT and MAPK pathways.
    European Journal of Neuroscience 03/2007; 25(3):649-58. · 3.75 Impact Factor