Astroglia genesis in vitro: Distinct effects of retinoic acid in different phases of neural stem cell differentiation

Institute of Experimental Medicine of Hungarian Academy of Sciences, Budapest, Hungary.
International journal of developmental neuroscience: the official journal of the International Society for Developmental Neuroscience (Impact Factor: 2.58). 07/2009; 27(4):365-75. DOI: 10.1016/j.ijdevneu.2009.02.004
Source: PubMed


In the developing CNS, the manifestation of the macro-glial phenotypes is delayed behind the formation of neurons. The "neurons first--glia second" principle seems to be valid for neural tissue differentiation throughout the neuraxis, but the reasons behind are far from clear. In the presented study, the mechanisms of this timing were investigated in vitro, in the course of the neural differentiation of one cell derived NE-4C neuroectodermal stem and P19 embryonic carcinoma cells. The data demonstrated that astrocyte formation coincided in time with the maturation of postmitotic neurons, but the close vicinity of neurons did not initiate astrocyte formation before schedule. All-trans retinoic acid, a well-known inducer of neuronal differentiation, on the other hand, blocked effectively the astroglia production if present in defined stages of the in vitro neuroectodermal cell differentiation. According to the data, retinoic acid plays at least a dual role in astrogliogenesis: while it is needed for committing neural progenitors for a future production of astrocytes, it prevents premature astrogliogenesis by inhibiting the differentiation of primed glial progenitors.

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    • "Once neural progenitors have been induced to progress to restricted glial progenitors, RA promotes proliferation (Wohl and Weiss, 1998) and can inhibit glial differentiation (Hadinger et al., 2009). Overall, RA is required to induce early progenitors to take a neural fate, whether neuronal or glial, but other factors are necessary to progress astroglial differentiation, a process that RA can inhibit (Hadinger et al., 2009) or promote (Asano et al., 2009). RA can also have an inhibitory effect on mature astrocyte activation, for instance, attenuating the action of lipopolysaccharide (LPS) to induce release of inflammatory chemokines, an action through inhibition of the JAK/STAT pathway (Choi et al., 2005; Kampmann et al., 2008; van Neerven et al., 2010a,b). "
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    ABSTRACT: Retinaldehyde dehydrogenases (RALDH) catalyze the synthesis of the regulatory factor retinoic acid (RA). Cultured astrocytes express several of the RALDH enzyme family, and it has been assumed that this can be extrapolated to astrocytes in vivo. However, this study finds that few astrocytes in the rodent brain express detectable RALDH enzymes, and only when these cells are grown in culture are these enzymes upregulated. Factors controlling the expression of the RALDHs in cultured astrocytes were explored to determine possible reasons for differences between in vitro versus in vivo expression. Retinoids were found to feedback to suppress several of the RALDHs, and physiological levels of retinoids may be one route by which astrocytic RALDHs are maintained at low levels. In the case of RALDH2, in vivo reduction of vitamin A levels in rats resulted in an increase in astrocyte RALDH2 expression in the hippocampus. Other factors though are likely to control RALDH expression. A shift in astrocytic RALDH subcellular localization is a potential mechanism for regulating RA signaling. Under conditions of vitamin A deficiency, RALDH2 protein moved from the cytoplasm to the nucleus where it may synthesize RA at the site of the nuclear RA receptors. Similarly, in conditions of oxidative stress RALDH1 and RALDH2 moved from the cytoplasm to a predominantly nuclear position. Thus, the RALDHs have been revealed to be dynamic in their expression in astrocytes where they may maintain retinoid homeostasis in the brain. © 2012 Wiley Periodicals, Inc.
    Full-text · Article · Dec 2012 · Glia
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    • "The observations suggest that RGl cells represent a more advanced state of neural cell fate commitment in comparison to early embryonic neuroectodermal progenitors. Underlying the assumption, RGl cells – even embryo-derived ones - gave rise readily to astrocytes, in a much shorter term than the investigated early embryonic stem cells [10], [37]. "
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    ABSTRACT: Preferential adhesion of neural stem cells to surfaces covered with a novel synthetic adhesive polypeptide (AK-cyclo[RGDfC]) provided a unique, rapid procedure for isolating radial glia-like cells from both fetal and adult rodent brain. Radial glia-like (RGl) neural stem/progenitor cells grew readily on the peptide-covered surfaces under serum-free culture conditions in the presence of EGF as the only growth factor supplement. Proliferating cells derived either from fetal (E 14.5) forebrain or from different regions of the adult brain maintained several radial glia-specific features including nestin, RC2 immunoreactivity and Pax6, Sox2, Blbp, Glast gene expression. Proliferating RGl cells were obtained also from non-neurogenic zones including the parenchyma of the adult cerebral cortex and dorsal midbrain. Continuous proliferation allowed isolating one-cell derived clones of radial glia-like cells. All clones generated neurons, astrocytes and oligodendrocytes under appropriate inducing conditions. Electrophysiological characterization indicated that passive conductance with large delayed rectifying potassium current might be a uniform feature of non-induced radial glia-like cells. Upon induction, all clones gave rise to GABAergic neurons. Significant differences were found, however, among the clones in the generation of glutamatergic and cathecolamine-synthesizing neurons and in the production of oligodendrocytes.
    Full-text · Article · Dec 2011 · PLoS ONE
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    • "The expression of the early glial/progenitor gene blbp, on the other hand, did not change significantly. The astrocyte marker GFAP, which appeared in normoxic cultures only from the middle of the second induction week (Hádinger et al., 2009), was not induced before schedule by hypoxia (Fig. 6B). "
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    ABSTRACT: Freeze-lesioned regions of the forebrain cortex provide adequate environment for growth of non-differentiated neural progenitors, but do not support their neuron formation. Reduced oxygen supply, among numerous factors, was suspected to impair neuronal cell fate commitment. In the present study, proliferation and differentiation of neural stem/progenitor cells were investigated at different oxygen levels both in vitro and in vivo. Low (1% atmospheric) oxygen supply did not affect the in vitro viability and proliferation of stem cells or the transcription of "stemness" genes but impaired the viability of committed neuronal progenitors and the expression of proneural and neuronal genes. Consequently, the rate of in vitro neuron formation was markedly reduced under hypoxic conditions. In vivo, neural stem/progenitor cells survived and proliferated in freeze-lesioned adult mouse forebrains, but did not develop into neurons. Hypoperfusion-caused hypoxia in lesioned cortices was partially corrected by hyperbaric oxygen treatment (HBOT). HBOT, while reduced the rate of cell proliferation at the lesion site, resulted in sporadic neuron formation from implanted neural stem cells. The data indicate that in hypoxic brain areas, neural stem cells survive and proliferate, but neural tissue-type differentiation can not proceed. Oxygenation renders the damaged brain areas more permissive for tissue-type differentiation and may help the integration of neural stem/progenitor cells.
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