In vitro properties of a newly established medulloblastoma cell line, MCD-1

In vitro models of medulloblastoma: Choosing the right tool for the job

The recently-defined four molecular subgroups of medulloblastoma have required updating of our understanding of in vitro models to include molecular classification and risk stratification features from clinical practice. This review seeks to build a more comprehensive picture of the in vitro systems available for modelling medulloblastoma. The subtype classification and molecular characterisation for over 40 medulloblastoma cell-lines has been compiled, making it possible to identify the strengths and weaknesses in current model systems. Less than half (18/44) of established medulloblastoma cell-lines have been subgrouped. The majority of the subgrouped cell-lines (11/18) are Group 3 with MYC-amplification. SHH cell-lines are the next most common (4/18), half of which exhibit TP53 mutation. WNT and Group 4 subgroups, accounting for 50% of patients, remain underrepresented with 1 and 2 cell-lines respectively. In vitro modelling relies not only on incorporating appropriate tumour cells, but also on using systems with the relevant tissue architecture and phenotype as well as normal tissues. Novel ways of improving the clinical relevance of in vitro models are reviewed, focusing on 3D cell culture, extracellular matrix, co-cultures with normal cells and organotypic slices. This paper champions the establishment of a collaborative online-database and linked cell-bank to catalyse preclinical medulloblastoma research.

Roles of db-cAMP, IBMX and RA in aspects of neural differentiation of cord blood derived mesenchymal-like stem cells

Mesenchymal stem cells (MSCs) have multilineage differentiation potential which includes cell lineages of the central nervous system; hence MSCs might be useful in the treatment of neurodegenerative diseases such as Parkinson's disease. Although mesenchymal stem cells have been shown to differentiate into the neural lineage, there is still little knowledge about the underlying mechanisms of differentiation particularly towards specialized neurons such as dopaminergic neurons. Here, we show that MSCs derived from human umbilical cord blood (MSC^hUCBs) are capable of expressing tyrosine hydroxylase (TH) and Nurr1, markers typically associated with DA neurons. We also found differential phosphorylation of TH isoforms indicating the presence of post-translational mechanisms possibly activating and modifying TH in MSC^hUCB. Furthermore, functional dissection of components in the differentiation medium revealed that dibutyryl-cAMP (db-cAMP), 3-isobutyl-1-methylxanthine (IBMX) and retinoic acid (RA) are involved in the regulation of Nurr1 and Neurofilament-L expression as well as in the differential phosphorylation of TH. We also demonstrate a possible inhibitory role of the protein kinase A signaling pathway in the phosphorylation of specific TH isoforms.

Simultaneous PKC and cAMP activation induces differentiation of human dental pulp stem cells into functionally active neurons

The plasticity of dental pulp stem cells (DPSCs) has been demonstrated by several studies showing that they appear to self-maintain through several passages, giving rise to a variety of cells. The aim of the present study was to differentiate DPSCs to mature neuronal cells showing functional evidence of voltage gated ion channel activities in vitro. First, DPSC cultures were seeded on poly-l-lysine coated surfaces and pretreated for 48h with a medium containing basic fibroblast growth factor and the demethylating agent 5-azacytidine. Then neural induction was performed by the simultaneous activation of protein kinase C and the cyclic adenosine monophosphate pathway. Finally, maturation of the induced cells was achieved by continuous treatment with neurotrophin-3, dibutyryl cyclic AMP, and other supplementary components. Non-induced DPSCs already expressed vimentin, nestin, N-tubulin, neurogenin-2 and neurofilament-M. The inductive treatment resulted in decreased vimentin, nestin, N-tubulin and increased neurogenin-2, neuron-specific enolase, neurofilament-M and glial fibrillary acidic protein expression. By the end of the maturation period, all investigated genes were expressed at higher levels than in undifferentiated controls except vimentin and nestin. Patch clamp analysis revealed the functional activity of both voltage-dependent sodium and potassium channels in the differentiated cells. Our results demonstrate that although most surviving cells show neuronal morphology and express neuronal markers, there is a functional heterogeneity among the differentiated cells obtained by the in vitro differentiation protocol described herein. Nevertheless, this study clearly indicates that the dental pulp contains a cell population that is capable of neural commitment by our three step neuroinductive protocol.

Differential Apaf-1 levels allow cytochrome c to induce apoptosis in brain tumors but not in normal neural tissues

Brain tumors are typically resistant to conventional chemotherapeutics, most of which initiate apoptosis upstream of mitochondrial cytochrome c release. In this study, we demonstrate that directly activating apoptosis downstream of the mitochondria, with cytosolic cytochrome c, kills brain tumor cells but not normal brain tissue. Specifically, cytosolic cytochrome c is sufficient to induce apoptosis in glioblastoma and medulloblastoma cell lines. In contrast, primary neurons from the cerebellum and cortex are remarkably resistant to cytosolic cytochrome c. Importantly, tumor tissue from mouse models of both high-grade astrocytoma and medulloblastoma display hypersensitivity to cytochrome c when compared with surrounding brain tissue. This differential sensitivity to cytochrome c is attributed to high Apaf-1 levels in the tumor tissue compared with low Apaf-1 levels in the adjacent brain tissue. These differences in Apaf-1 abundance correlate with differences in the levels of E2F1, a previously identified activator of Apaf-1 transcription. ChIP assays reveal that E2F1 binds the Apaf-1 promoter specifically in tumor tissue, suggesting that E2F1 contributes to the expression of Apaf-1 in brain tumors. Together, these results demonstrate an unexpected sensitivity of brain tumors to postmitochondrial induction of apoptosis. Moreover, they raise the possibility that this phenomenon could be exploited therapeutically to selectively kill brain cancer cells while sparing the surrounding brain parenchyma.

Differentiation of human bone marrow stem cells into cells with a neural phenotype: diverse effects of two specific treatments

Background

It has recently been demonstrated that the fate of adult cells is not restricted to their tissues of origin. In particular, it has been shown that bone marrow stem cells can give rise to cells of different tissues, including neural cells, hepatocytes and myocytes, expanding their differentiation potential.

Results

In order to identify factors able to lead differentiation of stem cells towards cells of neural lineage, we isolated stromal cells from human adult bone marrow (BMSC). Cells were treated with: (1) TPA, forskolin, IBMX, FGF-1 or (2) retinoic acid and 2-mercaptoethanol (BME). Treatment (1) induced differentiation into neuron-like cells within 24 hours, while a longer treatment was required when using retinoic acid and BME. Morphological modifications were more dramatic after treatment (1) compared with treatment (2). In BMSC both treatments induced the expression of neural markers such as NF, GFAP, TUJ-1 and neuron-specific enolase. Moreover, the transcription factor Hes1 increased after both treatments.

Conclusion

Our study may contribute towards the identification of mechanisms involved in the differentiation of stem cells towards cells of neural lineage.

Proliferation and death of conditionally immortalized neural cells from murine neocortex: p53 alters the ability of neuron-like cells to re-enter the cell cycle

Neurons are distinctive in that they are generally considered to be permanently post-mitotic cells. The oncoprotein p53 is a key regulator in neuronal development, notably in cell proliferation and neuronal death. We hypothesize that p53 maintains the post-mitotic characteristic of differentiated neurons. New lines of conditionally immortalized cortical cells were generated to test this hypothesis. Populations of cells were obtained from the neocortices of dual transgenic mice that were null for p53 and expressed a temperature-sensitive SV40 large T antigen. At a permissive temperature (32 degrees C), the cells continued to proliferate and most expressed nestin and proteins associated with glia. At a non-permissive temperature (39 degrees C), the cells expressed cytoskeletal proteins associated with differentiated neurons such as microtubule associated protein 2 and neurofilament 200. Under permissive conditions, both p53(+/-) and p53(-/-) cells exhibited similar cycling behaviors; the length of the cell cycle was 13-15 h and >85% of the cells were actively cycling. In non-permissive conditions, most p53(+/-) cells stopped dividing, whereas the p53(-/-) cells continued to proliferate. The survival of the cells also differed. In the non-permissive conditions, many p53(+/-) cells died following treatment with a neurotoxin (ethanol, 400 mg/dl), whereas the p53(-/-) cells did not. After re-introduction to the permissive conditions, both cell lines expressed neuron-like characteristics, but only the p53(-/-) cells retained their ability to cycle. Therefore, p53-mediated activities appear to be involved in the proliferation, survival, and post-mitotic nature of neuron-like cells.

AF5, a CNS cell line immortalized with an N-terminal fragment of SV40 large T: growth, differentiation, genetic stability, and gene expression

Central nervous system progenitor cells that are self-renewing in culture and also differentiate under controlled conditions are potentially useful for developmental studies and for cell-based therapies. We characterized growth and plasticity properties and gene expression in a rat mesencephalic cell line, AF5, that was immortalized with an N-terminal fragment of SV40 large T (T155g). For over 150 population doublings in culture, the growth rate of AF5 cells remained steady, the cells remained responsive to bFGF, and telomerase activity and telomere lengths were unchanged. While karyotype analyses revealed some chromosomal abnormalities, these were also unchanged over time; additionally, no mutations in p53 gene sequences were found, and wild-type p53 activation was normal. AF5 cells produced PDGF, TGFbeta1, TGFbeta2, and bFGF. Similar to primary progenitor cells, AF5 cells retained their plasticity in culture; they could be propagated in an undifferentiated state as "neurospheres" in serum-free media or as adherent cultures in serum-containing media, and they differentiated when allowed to become confluent. Adherent subconfluent actively growing cultures expressed a marker for immature neurons, nestin, while few cells expressed the mature neuronal cell marker betaIII-tubulin. Confluent cultures ceased growing, developed differentiated morphologies, contained few or no nestin-expressing cells, and acquired betaIII-tubulin expression. Global gene expression was examined using a 15,000 gene microarray, comparing exponential growth with and without bFGF stimulation, and the differentiated state. The AF5 cell line exhibited stable genetic and growth properties over extended periods of time, while retaining the ability to differentiate in vitro. These data suggest that the AF5 cell line may be useful as an in vitro model system for studies of neural differentiation.

In vitro differentiation of human marrow stromal cells into early progenitors of neural cells by conditions that increase intracellular cyclic AMP

Human marrow stromal cells (hMSCs) are multipotential stem cells that can be differentiated into bone, cartilage, fat, and muscle. In the experiments here, we found that undifferentiated cultures of hMSCs express some markers characteristic of neural cells such as microtubule-associated protein 1B (MAP1B), neuron-specific tubulin (TuJ-1), neuron-specific enolase (NSE), and vimentin. By treating hMSCs with 0.5 mM isobutylmethylxanthine (IBMX)/1 mM dibutyryl cyclic AMP (dbcAMP) for 6 days, about 25% of the hMSCs differentiated into cells with a typical neural cell morphology and with increased levels of both NSE and vimentin. The data suggested that the hMSCs may have been differentiated into early progenitors of neural cells in vitro under conditions that increase the intracellular level of cAMP.