Differential expression of neuroD in primary cultures of cerebral cortical neurons

Tinospora cordifolia Induces Differentiation and Senescence Pathways in Neuroblastoma Cells

Children diagnosed with neuroblastomas often suffer from severe side as well as late effects of conventional treatments like chemotherapy and radiotherapy. Recent advances in understanding of molecular pathways involved in cellular differentiation and apoptosis have helped in the development of new therapeutic approach based on differentiation-based therapy of malignant tumours. Natural medicines with their holistic therapeutic approach are known to selectively eliminate cancer cells thus provide a better substitute for the conventional treatment modes. The current study was aimed to investigate the anti-cancer potential of aqueous ethanolic extract of Tinospora cordifolia (TCE) using IMR-32 human neuroblastoma cell line as a model system. TCE is highly recommended in Ayurveda for its general body and metal health-promoting properties. TCE treatment was seen to arrest the majority of cells in G0/G1 phase and modulated the expression of DNA clamp sliding protein (PCNA) and cyclin D1. Further, TCE-treated cells showed differentiation as revealed by their morphology and the expression of neuronal cell specific differentiation markers NF200, MAP-2 and NeuN in neuroblastoma cells. The differentiated phenotype was associated with induction of senescence and pro-apoptosis pathways by enhancing expression of senescence marker mortalin and Rel A subunit of nuclear factor kappa beta (NFkB) along with decreased expression of anti-apoptotic marker, Bcl-xl. TCE exhibited anti-metastatic activity and significantly reduced cell migration in the scratched area along with downregulation of neural cell adhesion molecule (NCAM) polysialylation and secretion of matrix metalloproteinases (MMPs). Our data suggest that crude extract or active phytochemicals from this plant may be a potential candidate for differentiation-based therapy of malignant neuroblastoma cells.

TDP-43 regulates the microprocessor complex activity during in vitro neuronal differentiation

TDP-43 (TAR DNA-binding protein 43) is an RNA-binding protein implicated in RNA metabolism at several levels. Even if ubiquitously expressed, it is considered as a neuronal activity-responsive factor and a major signature for neurological pathologies, making the comprehension of its activity in the nervous system a very challenging issue. TDP-43 has also been described as an accessory component of the Drosha-DGCR8 (DiGeorge syndrome critical region gene 8) microprocessor complex, which is crucially involved in basal and tissue-specific RNA processing events. In the present study, we exploited in vitro neuronal differentiation systems to investigate the TDP-43 demand for the microprocessor function, focusing on both its canonical microRNA biosynthetic activity and its alternative role as a post-transcriptional regulator of gene expression. Our findings reveal a novel role for TDP-43 as an essential factor that controls the stability of Drosha protein during neuronal differentiation, thus globally affecting the production of microRNAs. We also demonstrate that TDP-43 is required for the Drosha-mediated regulation of Neurogenin 2, a master gene orchestrating neurogenesis, whereas post-transcriptional control of Dgcr8, another Drosha target, resulted to be TDP-43-independent. These results implicate a previously uncovered contribution of TDP-43 in regulating the abundance and the substrate specificity of the microprocessor complex and provide new insights into TDP-43 as a key player in neuronal differentiation.

Withania somnifera water extract as a potential candidate for differentiation based therapy of human neuroblastomas

Neuroblastoma is an aggressive childhood disease of the sympathetic nervous system. Treatments are often ineffective and have serious side effects. Conventional therapy of neuroblastoma includes the differentiation agents. Unlike chemo-radiotherapy, differentiation therapy shows minimal side effects on normal cells, because normal non-malignant cells are already differentiated. Keeping in view the limited toxicity of Withania somnifera (Ashwagandha), the current study was aimed to investigate the efficacy of Ashwagandha water extract (ASH-WEX) for anti-proliferative potential in neuroblastoma and its underlying signalling mechanisms. ASH-WEX significantly reduced cell proliferation and induced cell differentiation as indicated by morphological changes and NF200 expression in human IMR-32 neuroblastoma cells. The induction of differentiation was accompanied by HSP70 and mortalin induction as well as pancytoplasmic translocation of the mortalin in ASH-WEX treated cells. Furthermore, the ASH-WEX treatment lead to induction of neural cell adhesion molecule (NCAM) expression and reduction in its polysialylation, thus elucidating its anti-migratory potential, which was also supported by downregulation of MMP 2 and 9 activity. ASH-WEX treatment led to cell cycle arrest at G0/G1 phase and increase in early apoptotic population. Modulation of cell cycle marker Cyclin D1, anti-apoptotic marker bcl-xl and Akt-P provide evidence that ASH-WEX may prove to be a promising phytotherapeutic intervention in neuroblatoma related malignancies.

Ion channels and ionotropic receptors in human embryonic stem cell derived neural progenitors

Human neural progenitor cells differentiated from human embryonic stem cells offer a potential cell source for studying neurodegenerative diseases and for drug screening assays. Previously, we demonstrated that human neural progenitors could be maintained in a proliferative state with the addition of leukemia inhibitory factor and basic fibroblast growth factor. Here we demonstrate that 96 h after removal of basic fibroblast growth factor the neural progenitor cell culture was significantly altered and cell replication halted. Fourteen days after the removal of basic fibroblast growth factor, most cells expressed microtubule-associated protein 2 and TUJ1, markers characterizing a post-mitotic neuronal phenotype as well as neural developmental markers Cdh2 and Gbx2. Real-time PCR was performed to determine the ionotropic receptor subunit expression profile. Differentiated neural progenitors express subunits of glutamatergic, GABAergic, nicotinic, purinergic and transient receptor potential receptors. In addition, sodium and calcium channel subunits were also expressed. Functionally, virtually all the hNP cells tested under whole-cell voltage clamp exhibited delayed rectifier potassium channel currents and some differentiated cells exhibited tetrodotoxin-sensitive, voltage-dependent sodium channel current. Action potentials could also be elicited by currents injection under whole-cell current clamp in a minority of cells. These results indicate that removing basic fibroblast growth factor from the neural progenitor cell cultures leads to a post-mitotic state, and has the capability to produce excitable cells that can generate action potentials, a landmark characteristic of a neuronal phenotype. This is the first report of an efficient and simple means of generating human neuronal cells for ionotropic receptor assays and ultimately for electrically active human neural cell assays for drug discovery.

The chick optic tectum developmental stages. A dynamic table based on temporal- and spatial-dependent histogenetic changes: A structural, morphometric and immunocytochemical analysis

Development is often described as temporal sequences of developmental stages (DSs). When tables of DS are defined exclusively in the time domain they cannot discriminate histogenetic differences between different positions along a spatial reference axis. We introduce a table of DSs for the developing chick optic tectum (OT) based on time- and space-dependent changes in quantitative morphometric parameters, qualitative histogenetic features and immunocytochemical pattern of several developmentally active molecules (Notch1, Hes5, NeuroD1, β-III-Tubulin, synaptotagmin-I and neurofilament-M). Seven DSs and four transitional stages were defined from ED2 to ED12, when the basic OT cortical organization is established, along a spatial developmental gradient axis extending between a zone of maximal and a zone of minimal development. The table of DSs reveals that DSs do not only progress as a function of time but also display a spatially organized propagation along the developmental gradient axis. The complex and dynamic character of the OT development is documented by the fact that several DSs are simultaneously present at any ED or any embryonic stage. The table of DSs allows interpreting how developmental cell behaviors are temporally and spatially organized and explains how different DSs appear as a function of both time and space. The table of DSs provides a reference system to characterize the OT corticogenesis and to reliably compare observations made in different specimens.

Effects of sevoflurane on primary neuronal cultures of embryonic rats

BACKGROUND AND OBJECTIVE

Commonly used anaesthetics can cause neurodegeneration in the developing brain. Sevoflurane, a widely used substance in paediatric anaesthesia, has not been analysed thus far. This study was carried out to investigate the effects of sevoflurane on neuronal cell viability.

METHODS

Primary cortical neuronal cultures were prepared from Wistar rat embryos (E18), kept in 100 microl Gibco-Neurobasal-A medium and exposed to 4 and 8 Vol.% sevoflurane for up to 48 h. Cell viability was assessed using the methyltetrazolium assay and was related to untreated controls. To evaluate the role of gamma-aminobutyric acid type A receptors, untreated cells were preincubated with the receptor antagonists gabazine or picrotoxin and were subsequently exposed to 8 Vol.% sevoflurane and the receptor antagonist. Cell viability was assessed and compared with that of sevoflurane-treated controls.

RESULTS

Up to 6 (8 Vol.%) and 12 h (4 Vol.%) of exposure to sevoflurane, cell viability was equal when compared with untreated controls. Only longer exposure times led to significantly lowered cell viability. After 12 h of exposure, no significant differences in cell viability were found between these two series. Cell viability of cultures treated with sevoflurane and the receptor antagonists showed no significant differences when compared with sevoflurane-exposed controls.

CONCLUSION

These results suggest that sevoflurane does not cause neurodegeneration in primary cortical neurons of the rat following clinically relevant exposure times and concentrations.

Mass-spectrometric characterization of phospholipids and their primary peroxidation products in rat cortical neurons during staurosporine-induced apoptosis

The molecular diversity of phospholipids is essential for their structural and signaling functions in cell membranes. In the current work, we present, the results of mass spectrometric characterization of individual molecular species in major classes of phospholipids -- phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), phosphatidylserine (PtdSer), phosphatidylinositol (PtdIns), sphingomyelin (CerPCho), and cardiolipin (Ptd(2)Gro) -- and their oxidation products during apoptosis induced in neurons by staurosporine (STS). The diversity of molecular species of phospholipids in rat cortical neurons followed the order Ptd(2)Gro > PtdEtn >> PtdCho >> PtdSer > PtdIns > CerPCho. The number of polyunsaturated oxidizable species decreased in the order Ptd(2)Gro >> PtdEtn > PtdCho > PtdSer > PtdIns > CerPCho. Thus a relatively minor class of phospholipids, Ptd(2)Gro, was represented in cortical neurons by the greatest variety of both total and peroxidizable molecular species. Quantitative fluorescence HPLC analysis employed to assess the oxidation of different classes of phospholipids in neuronal cells during intrinsic apoptosis induced by STS revealed that three anionic phospholipids -- Ptd(2)Gro >> PtdSer > PtdIns -- underwent robust oxidation. No significant oxidation in the most dominant phospholipid classes -- PtdCho and PtdEtn -- was detected. MS-studies revealed the presence of hydroxy-, hydroperoxy- as well as hydroxy-/hydroperoxy-species of Ptd(2)Gro, PtdSer, and PtdIns. Experiments in model systems where total cortex Ptd(2)Gro and PtdSer fractions were incubated in the presence of cytochrome c (cyt c) and H(2)O(2), confirmed that molecular identities of the products formed were similar to the ones generated during STS-induced neuronal apoptosis. The temporal sequence of biomarkers of STS-induced apoptosis and phospholipid peroxidation combined with recently demonstrated redox catalytic properties of cyt c realized through its interactions with Ptd(2)Gro and PtdSer suggest that cyt c acts as a catalyst of selective peroxidation of anionic phospholipids yielding Ptd(2)Gro and PtdSer peroxidation products. These oxidation products participate in mitochondrial membrane permeability transition and in PtdSer externalization leading to recognition and uptake of apoptotic cells by professional phagocytes.

Neuroprotective immunity: T cell-derived glutamate endows astrocytes with a neuroprotective phenotype

A well-controlled T cell response to CNS injury may result in increased neuronal survival. However, the precise mechanism of T cell-induced neuroprotection is unknown. In this study, we report the unexpected finding that during culture of T cells, high levels of glutamate accumulate, which are efficiently cleared if T cells are cocultured with astrocytes. The T cell-derived glutamate elicits in turn, the release of neuroprotective thiols (cysteine, glutathione, and cysteinyl-glycine) and lactate from astrocytes. Media obtained from astrocytes conditioned in the presence of T cells reduce neuronal apoptosis induced by oxidative stress in primary neuronal cultures from 48 +/- 14 to 9 +/- 4% (p < 0.001). Inhibition of glutamate-dependent signaling during astrocyte-T cell cocultivation by a glutamate uptake inhibitor, l-aspartic acid beta-hydroxamate, abolishes this neuroprotective effect. The ability of astrocytes to clear extracellular glutamate is impaired under conditions of oxidative stress. We demonstrate that T cells, via secreted cytokines, restore glutamate clearance capacity of astrocytes under oxidative conditions. Furthermore, under normoxic conditions, glutamate-buffering capacity of astrocytes is increased upon cocultivation with T cells. It is known that, following CNS injury, astrocytes can respond with beneficial or destructive effects on neurons. However, the context and signaling mechanisms for this dual astrocytic response are unknown. Our results implicate T cells as potential determinants of the context that elicits a protective role for astrocytes in the damaged CNS.

Autologous transplants of Adipose-Derived Adult Stromal (ADAS) cells afford dopaminergic neuroprotection in a model of Parkinson's disease

Adult adipose contains stromal progenitor cells with neurogenic potential. However, the stability of neuronal phenotypes adopted by Adipose-Derived Adult Stromal (ADAS) cells and whether terminal neuronal differentiation is required for their consideration as alternatives in cell replacement strategies to treat neurological disorders is largely unknown. We investigated whether in vitro neural induction of ADAS cells determined their ability to neuroprotect or restore function in a lesioned dopaminergic pathway. In vitro-expanded naïve or differentiated ADAS cells were autologously transplanted into substantia nigra 1 week after an intrastriatal 6-hydroxydopamine injection. Neurochemical and behavioral measures demonstrated neuroprotective effects of both ADAS grafts against 6-hydroxydopamine-induced dopaminergic neuron death, suggesting that pre-transplantation differentiation of the cells does not determine their ability to survive or neuroprotect in vivo. Therefore, we investigated whether equivalent protection by naïve and neurally-induced ADAS grafts resulted from robust in situ differentiation of both graft types into dopaminergic fates. Immunohistological analyses revealed that ADAS cells did not adopt dopaminergic cell fates in situ, consistent with the limited ability of these cells to undergo terminal differentiation into electrically active neurons in vitro. Moreover, re-exposure of neurally-differentiated ADAS cells to serum-containing medium in vitro confirmed ADAS cell phenotypic instability (plasticity). Lastly, given that gene expression analyses of in vitro-expanded ADAS cells revealed that both naïve and differentiated ADAS cells express potent dopaminergic survival factors, ADAS transplants may have exerted neuroprotective effects by production of trophic factors at the lesion site. ADAS cells may be ideal for ex vivo gene transfer therapies in Parkinson's disease treatment.

The role of BETA2/NeuroD1 in the development of the nervous system

BETA2/NeuroD1 is a member of the basic helix-loop-helix (bHLH) transcription factor family, which has been shown to play a major role in development of the nervous system and formation of the endocrine system. Gain-of-function studies have indicated that BETA2/NeuroD1 is important for the neurogenesis of Xenopus embryos and several neurogenic cell lines. Disruption of the gene encoding BETA2/NeuroD1 leads to severe abnormalities of the developing mouse central nervous system as well as the peripheral nervous system. The focus of this article is on the recent progress in understanding the role of BETA2/NeuroD1 in the development of the nervous system.

Expression of the Ste20-like kinase SLK during embryonic development and in the murine adult central nervous system

Cell growth and terminal differentiation are controlled by complex signaling cascades that regulate the expression of specific subsets of genes controlling cell fate and morphogenic processes. We have recently cloned and characterized a novel Ste20-like kinase termed SLK (Sabourin et al., Mol. Cel. Biol. 20 (2000) 684). However, the specific function of SLK is poorly understood. To gain further insights into the role of SLK we have characterized its activity, expression and distribution in the CNS during embryonic development and in the adult brain. Although SLK is expressed ubiquitously in adult tissues, our results show that it is expressed preferentially in neuronal lineages during development. We find that SLK is preferentially expressed in the neurons and neuroepithelium of the developing embryo and can be detected at 10.5 and 12.5 days post-coitum (dpc) in the forebrain, midbrain and hindbrain of the developing CNS. At later stages (14.5 dpc), SLK is expressed in the hypothalamus region, all layers of the neural tube, dorsal root ganglion and in the proliferating ependymal layers. Surprisingly, following middle cerebral artery occlusion, SLK expressing neuronal cells are lost and SLK is localized to phagocytic macrophages/microglia. These results suggest a functional role for SLK in early neuronal development as well as in the adult CNS.

REST-VP16 activates multiple neuronal differentiation genes in human NT2 cells

The RE1-silencing transcription factor (REST)/neuron-restrictive silencer factor (NRSF) can repress transcription of a battery of neuronal differentiation genes in non-neuronal cells by binding to a specific consensus DNA sequence present in their regulatory regions. However, REST/NRSF(-/-) mice suggest that the absence of REST/NRSF-dependent repression alone is not sufficient for the expression of these neuronal differentiation genes and that the presence of other promoter/enhancer-specific activators is required. Here we describe the construction of a recombinant transcription factor, REST-VP16, by replacing repressor domains of REST/NRSF with the activation domain of a viral activator VP16. In transient transfection experiments, REST-VP16 was found to operate through RE1 binding site/neuron-restrictive enhancer element (RE1/NRSE), activate plasmid-encoded neuronal promoters in various mammalian cell types and activate cellular REST/NRSF target genes, even in the absence of factors that are otherwise required to activate such genes. Efficient expression of REST-VP16 through adenoviral vectors in NT2 cells, which resemble human committed neuronal progenitor cells, was found to cause activation of multiple neuronal genes that are characteristic markers for neuronal differentiation. Thus, REST-VP16 could be used as a unique tool to study neuronal differentiation pathways and neuronal diseases that arise due to the deregulation of this process.

Expression of neuroD/BETA2 in mitotic and postmitotic neuronal cells during the development of nervous system

NeuroD/BETA2, a basic helix-loop-helix transcription factor, has been shown to play a role in tissue-specific differentiation of pancreatic and enteroendocrine cells. To gain further insight into the function of neuroD/BETA2 in the nervous system development, we examined the expression pattern of neuroD/BETA2 during embryonic and postnatal development by using in situ hybridization. Dynamic changes of neuroD/BETA2 expression in the central nervous system were observed during embryogenesis, especially in telencephalon, hippocampus, cerebellum, spinal cord, and olfactory epithelium. Moderate level of expression was also detected in developing pancreas in early embryogenesis. Although the neuroD/BETA2 expression in cerebellum and hippocampus increased over time, expression in cerebral cortex, spinal cord, as well as in fetal pancreas gradually decreased as embryogenesis proceeded. High level of the neuroD/BETA2 expression in developing cerebellum and hippocampus persisted throughout postnatal development and remained at a stable level in the adult brain. Interestingly, neuroD/BETA2 expression was detected not only in postmitotic but also in mitotic cells, as was evident in its expression in external granular layer of cerebellum and granule cells of the dentate gyrus during postnatal development. This observation suggests that neuroD/BETA2 may have a unique role in proliferation, differentiation, or both, of granule cells of cerebellum and dentate gyrus.