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  • 1
    Electronic Resource
    Electronic Resource
    Protein kinase C-mediated functional regulation of dopamine transporter is not achieved by direct phosphorylation of the dopamine transporter protein (2001)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 77 (2001), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Dopaminergic neurotransmission is terminated by the action of the presynaptic dopamine transporter (DAT). It mediates Na+/Cl− -dependent re-uptake of extracellular dopamine (DA) into the cell, and is regarded as a major regulatory mechanism for synaptic transmission. Previous works have documented that protein kinase C (PKC) activator or inhibitor alters DA uptake by DAT, suggesting that PKC phosphorylation plays an important regulatory mechanism in DAT function. Based on the existence of consensus amino acid sequences for PKC phosphorylation, it has been postulated that PKC regulation of DAT is mediated by the direct phosphorylation of DAT protein. In this study, we try to discover whether the functional regulation of DAT by PKC is due to direct phosphorylation of DAT. The PKC null mutant hDAT, where all putative PKC phosphorylation sites are eliminated, has been constructed by the replacement of serine/threonine residues with glycines. The mutation itself showed no effect on the functional activities of DAT. The DA uptake activity of PKC null mutant was equivalent to those of wild-type hDAT (80–110% of wild-type). Phorbol ester activation of PKC inhibited DA uptake of wild-type hDAT by 35%, and staurosphorine blocked the effect of phorbol ester on DA uptake. The same phenomena was observed in PKC null mutant DAT, although no significant phosphorylation was observed by PKC activation. Confocal microscopic analysis using EGFP-fused DAT revealed that the activation of PKC by phorbol ester elicited fluorescent DAT to be internalized into the intracellular space both in wild-type and PKC null mutant DAT in a similar way. These results suggest that PKC-mediated regulation of DAT function is achieved in an indirect manner, such as phosphorylation of a mediator protein or activation of a clathrin-mediated pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2001.00284.x
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  • 2
    Electronic Resource
    Electronic Resource
    In vitro and in vivo analyses of human embryonic stem cell-derived dopamine neurons (2005)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 92 (2005), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Human embryonic stem (hES) cells, due to their capacity of multipotency and self-renewal, may serve as a valuable experimental tool for human developmental biology and may provide an unlimited cell source for cell replacement therapy. The purpose of this study was to assess the developmental potential of hES cells to replace the selectively lost midbrain dopamine (DA) neurons in Parkinson's disease. Here, we report the development of an in vitro differentiation protocol to derive an enriched population of midbrain DA neurons from hES cells. Neural induction of hES cells co-cultured with stromal cells, followed by expansion of the resulting neural precursor cells, efficiently generated DA neurons with concomitant expression of transcriptional factors related to midbrain DA development, such as Pax2, En1 (Engrailed-1), Nurr1, and Lmx1b. Using our procedure, the majority of differentiated hES cells (〉 95%) contained neuronal or neural precursor markers and a high percentage (〉 40%) of TuJ1+ neurons was tyrosine hydroxylase (TH)+, while none of them expressed the undifferentiated ES cell marker, Oct 3/4. Furthermore, hES cell-derived DA neurons demonstrated functionality in vitro, releasing DA in response to KCl-induced depolarization and reuptake of DA. Finally, transplantation of hES-derived DA neurons into the striatum of hemi-parkinsonian rats failed to result in improvement of their behavioral deficits as determined by amphetamine-induced rotation and step-adjustment. Immunohistochemical analyses of grafted brains revealed that abundant hES-derived cells (human nuclei+ cells) survived in the grafts, but none of them were TH+. Therefore, unlike those from mouse ES cells, hES cell-derived DA neurons either do not survive or their DA phenotype is unstable when grafted into rodent brains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.2004.03006.x
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  • 3
    Electronic Resource
    Electronic Resource
    Lithium selectively increases neuronal differentiation of hippocampal neural progenitor cells both in vitro and in vivo (2004)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 89 (2004), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Lithium has been demonstrated to increase neurogenesis in the dentate gyrus of rodent hippocampus. The present study was undertaken to investigate the effects of lithium on the proliferation and differentiation of rat neural progenitor cells in hippocampus both in vitro and in vivo. Lithium chloride (1–3 mm) produced a significant increase in the number of bromodeoxyuridine (BrdU)-positive cells in high-density cultures, but did not increase clonal size in low-density cultures. Lithium chloride at 1 mm (within the therapeutic range) also increased the number of cells double-labeled with BrdU antibody and TuJ1 (a class III β-tubulin antibody) in high-density cultures and the number of TuJ1-positive cells in a clone of low-density cultures, whereas it decreased the number of glial fibrillary acidic protein-positive cells in both cultures. These results suggest that lithium selectively increased differentiation of neuronal progenitors. These actions of lithium appeared to enhance a neuronal subtype, calbindinD28k-positive cells, and involved a phosphorylated extracellular signal-regulated kinase and phosphorylated cyclic AMP response element-binding protein-dependent pathway both in vitro and in vivo. These findings suggest that lithium in therapeutic amounts may elicit its beneficial effects via facilitation of neural progenitor differentiation toward a calbindinD28k-positive neuronal cell type.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2004.02329.x
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  • 4
    Electronic Resource
    Electronic Resource
    Dopaminergic neuronal differentiation from rat embryonic neural precursors by Nurr1 overexpression (2003)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 85 (2003), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In vitro expanded CNS precursors could provide a renewable source of dopamine (DA) neurons for cell therapy in Parkinson's disease. Functional DA neurons have been derived previously from early midbrain precursors. Here we demonstrate the ability of Nurr1, a nuclear orphan receptor essential for midbrain DA neuron development in vivo, to induce dopaminergic differentiation in naïve CNS precursors in vitro. Independent of gestational age or brain region of origin, Nurr1-induced precursors expressed dopaminergic markers and exhibited depolarization-evoked DA release in vitro. However, these cells were less mature and secreted lower levels of DA than those derived from mesencephalic precursors. Transplantation of Nurr1-induced DA neuron precursors resulted in limited survival and in vivo differentiation. No behavioral improvement in apomorphine-induced rotation scores was observed. These results demonstrate that Nurr1 induces dopaminergic features in naïve CNS precursors in vitro. However, additional factors will be required to achieve in vivo function and to unravel the full potential of neural precursors for cell therapy in Parkinson's disease.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2003.01780.x
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