The adult human brain harbors multipotent perivascular mesenchymal stem cells

Blood vessels and adjacent cells form perivascular stem cell niches in adult tissues. In this perivascular niche, a stem cell with mesenchymal characteristics was recently identified in some adult somatic tissues. These cells are pericytes that line the microvasculature, express mesenchymal markers and differentiate into mesodermal lineages but might even have the capacity to generate tissue-specific cell types. Here, we isolated, purified and characterized a previously unrecognized progenitor population from two different regions in the adult human brain, the ventricular wall and the neocortex. We show that these cells co-express markers for mesenchymal stem cells and pericytes in vivo and in vitro, but do not express glial, neuronal progenitor, hematopoietic, endothelial or microglial markers in their native state. Furthermore, we demonstrate at a clonal level that these progenitors have true multilineage potential towards both, the mesodermal and neuroectodermal phenotype. They can be epigenetically induced in vitro into adipocytes, chondroblasts and osteoblasts but also into glial cells and immature neurons. This progenitor population exhibits long-term proliferation, karyotype stability and retention of phenotype and multipotency following extensive propagation. Thus, we provide evidence that the vascular niche in the adult human brain harbors a novel progenitor with multilineage capacity that appears to represent mesenchymal stem cells and is different from any previously described human neural stem cell. Future studies will elucidate whether these cells may play a role for disease or may represent a reservoir that can be exploited in efforts to repair the diseased human brain.

Identification of molecules derived from human fibroblast feeder cells that support the proliferation of human embryonic stem cells

The majority of human embryonic stem cell lines depend on a feeder cell layer for continuous growth in vitro, so that they can remain in an undifferentiated state. Limited knowledge is available concerning the molecular mechanisms that underlie the capacity of feeder cells to support both the proliferation and pluripotency of these cells. Importantly, feeder cells generally lose their capacity to support human embryonic stem cell proliferation in vitro following long-term culture. In this study, we performed large-scale gene expression profiles of human foreskin fibroblasts during early, intermediate and late passages using a custom DNA microarray platform (NeuroStem 2.0 Chip). The microarray data was validated using RT-PCR and virtual SAGE analysis. Our comparative gene expression study identified a limited number of molecular targets potentially involved in the ability of human neonatal foreskin fibroblasts to serve as feeder cells for human embryonic stem cell cultures. Among these, the C-KIT, leptin and pigment epithelium-derived factor (PEDF) genes were the most interesting candidates.

Critical issues of clinical human embryonic stem cell therapy for brain repair

Embryonic stem cells (ESCs) provide hope as a potential regenerative therapy for neurological conditions such as Parkinson's disease and spinal cord injury. Currently, ESC-based nervous system repair faces several problems. One major hurdle is related to problems in generating large and defined populations of the desired types of neurons from human ESCs (hESCs). Moreover, survival of grafted hESC-derived cells has varied and functional recovery in recipient animals has often been disappointing. Importantly, in clinical trials, adverse effects after surgery, including tumors or vigorous immune reactions, must be avoided. Here we highlight attempts to overcome these hurdles with hESCs intended for central nervous system repair. We focus on hESC-derived dopamine-producing neurons that can be grafted in Parkinson's disease and identify critical experiments that need to be conducted before clinical trials can occur.

Midbrain expression of Delta-like 1 homologue is regulated by GDNF and is associated with dopaminergic differentiation

Affymetrix GeneChip technology and quantitative real-time PCR (Q-PCR) were used to examine changes in gene expression in the adult murine substantia nigra pars compacta (SNc) following lentiviral glial cell line-derived neurotrophic factor (GDNF) delivery in adult striatum. We identified several genes that were upregulated after GDNF treatment. Among these, the gene encoding the transmembrane protein Delta-like 1 homologue (Dlk1) was upregulated with a greater than 4-fold increase in mRNA encoding this protein. Immunohistochemistry with a Dlk1-specific antibody confirmed the observed upregulation with increased positive staining of cell bodies in the SNc and fibers in the striatum. Analysis of the developmental regulation of Dlk1 in the murine ventral midbrain showed that the upregulation of Dlk1 mRNA correlated with the generation of tyrosine hydroxylase (TH)-positive neurons. Furthermore, Dlk1 expression was analyzed in MesC2.10 cells, which are derived from embryonic human mesencephalon and capable of undergoing differentiation into dopaminergic neurons. We detected upregulation of Dlk1 mRNA and protein under conditions where MesC2.10 cells differentiate into a dopaminergic phenotype (41.7+/-7.1% Dlk1+ cells). In contrast, control cultures subjected to default differentiation into non-dopaminergic neurons only expressed very few (3.7+/-1.3%) Dlk1-immunopositive cells. The expression of Dlk1 in MesC2.10 cells was specifically upregulated by the addition of GDNF. Thus, our data suggest that Dlk1 expression precedes the appearance of TH in mesencephalic cells and that levels of Dlk1 are regulated by GDNF.

"NeuroStem Chip": a novel highly specialized tool to study neural differentiation pathways in human stem cells

Background

Human stem cells are viewed as a possible source of neurons for a cell-based therapy of neurodegenerative disorders, such as Parkinson's disease. Several protocols that generate different types of neurons from human stem cells (hSCs) have been developed. Nevertheless, the cellular mechanisms that underlie the development of neurons in vitro as they are subjected to the specific differentiation protocols are often poorly understood.

Results

We have designed a focused DNA (oligonucleotide-based) large-scale microarray platform (named "NeuroStem Chip") and used it to study gene expression patterns in hSCs as they differentiate into neurons. We have selected genes that are relevant to cells (i) being stem cells, (ii) becoming neurons, and (iii) being neurons. The NeuroStem Chip has over 1,300 pre-selected gene targets and multiple controls spotted in quadruplicates (~46,000 spots total). In this study, we present the NeuroStem Chip in detail and describe the special advantages it offers to the fields of experimental neurology and stem cell biology. To illustrate the utility of NeuroStem Chip platform, we have characterized an undifferentiated population of pluripotent human embryonic stem cells (hESCs, cell line SA02). In addition, we have performed a comparative gene expression analysis of those cells versus a heterogeneous population of hESC-derived cells committed towards neuronal/dopaminergic differentiation pathway by co-culturing with PA6 stromal cells for 16 days and containing a few tyrosine hydroxylase-positive dopaminergic neurons.

Conclusion

We characterized the gene expression profiles of undifferentiated and dopaminergic lineage-committed hESC-derived cells using a highly focused custom microarray platform (NeuroStem Chip) that can become an important research tool in human stem cell biology. We propose that the areas of application for NeuroStem microarray platform could be the following: (i) characterization of the expression of established, pre-selected gene targets in hSC lines, including newly derived ones, (ii) longitudinal quality control for maintained hSC populations, (iii) following gene expression changes during differentiation under defined cell culture conditions, and (iv) confirming the success of differentiation into specific neuronal subtypes.

Tyrosine hydroxylase expression is unstable in a human immortalized mesencephalic cell line--studies in vitro and after intracerebral grafting in vivo

We have studied the stability of the dopaminergic phenotype in a conditionally immortalized human mesencephalic cell line, MESC2.10. Even though MESC2.10 cells exhibit features of dopaminergic neurons in vitro, none of the cells expressed tyrosine hydroxylase (TH) after transplantation into a rat model of Parkinson's disease. We examined whether this is caused by cell death or loss of transmitter phenotype. Cells were cultured in differentiation medium, then harvested and replated into the same medium where they continued to express TH, whereas replated cells fed medium lacking differentiation factors (dibutyryl cAMP and glial cell line-derived neurotrophic factor) did not. Interestingly, cultures grown in the absence of differentiation factors could regain TH expression once exposed to differentiation medium. Our data suggest that TH expression in vitro is inducible in neurons derived from the MESC2.10 cell line and that the dopaminergic phenotype of these cells in vivo might be unstable.

Induction of dopaminergic neurons from growth factor expanded neural stem/progenitor cell cultures derived from human first trimester forebrain

Multipotent stem/progenitor cells derived from human first trimester forebrain can be expanded as free-floating aggregates, so called neurospheres. These cells can differentiate into neurons, astrocytes and oligodendrocytes. In vitro differentiation protocols normally yield gamma-aminobutyric acid-immunoreactive neurons, whereas only few tyrosine hydroxylase (TH) expressing neurons are found. The present report describes conditions under which 4-10% of the cells in the culture become TH immunoreactive (ir) neurons within 24h. Factors including acidic fibroblast growth factor (aFGF) in combination with agents that increase intracellular cyclic AMP and activate protein kinase C, in addition to a substrate that promotes neuronal differentiation appear critical for efficient TH induction. The cells remain THir after trypsinization and replating, even when their subsequent culturing takes place in the absence of inducing factors. Consistent with a dopaminergic phenotype, mRNAs encoding aromatic acid decarboxylase, but not dopamine-beta-hydroxylase were detected by quantitative real time RT-PCR. Ten weeks after the cells had been grafted into the striatum of adult rats with unilateral nigrostriatal lesions, only very few of the surviving human neurons expressed TH. Our data suggest that a significant proportion of expandable human neural progenitors can differentiate into TH-expressing cells in vitro and that they could be useful for drug and gene discovery. Additional experiments, however, are required to improve the survival and phenotypic stability of these cells before they can be considered useful for cell replacement therapy in Parkinson's disease.

Stem cell therapy for Parkinson?s disease: where do we stand?

A major neuropathological feature of Parkinson's disease (PD) is the loss of nigrostriatal dopaminergic neuron. Patients exhibit motor symptoms, including bradykinesia, rigidity, and tremor. Neural grafting has been reported to restore striatial dopaminergic neurotransmission and induce symptomatic relief. The major limitation of cell replacement therapy for PD is the shortage of suitable donor tissue. The present review describes the possible sources of cells, including embryonic stem cells and somatic adult stem cells, both of which potentially could be used in cell therapy for PD, and discusses the advantages and disadvantages of each cell type.

Soluble CD40 ligand induces selective proliferation of lymphoma cells in primary mantle cell lymphoma cell cultures

Interaction between CD40 and the CD40 ligand (CD40L) is critical for the survival and proliferation of B cells during immunopoiesis. However, the role of CD40L in the pathogenesis of malignant lymphomas is ambiguous. Primary mantle cell lymphoma (MCL) cells were cultured in the presence of recombinant human CD40L trimer (huCD40LT), and a significant time- and dose-dependent induction of DNA synthesis was observed in thymidine incorporation assays (n = 7, P <.04). The maximal rate of DNA synthesis was reached at huCD40LT doses of 100 ng/mL and above after 4 days of culture, but a significant increase of DNA synthesis was detected already at doses of 1 ng/mL (P =.03). HuCD40LT never inhibited the basal level of DNA synthesis. These findings established 400 ng/mL of huCD40LT for 4 days as standard conditions in the system. Under these conditions, huCD40LT significantly increased the proportion of cells in the S/G(2)/M phases of the cell cycle in 4 of 7 studied cases, while the fraction of apoptotic cells remained unchanged (n = 7). HuCD40LT also induced expression of CD80/B7-1, CD86/B7-2, and CD95/Fas and up-regulated the expression of HLA-DR (n = 6). With the use of bromodeoxyuridine incorporation in triple-color flow cytometric analysis, it was found that huCD40LT induced cell-cycle progression in light chain-restricted cells only, of which a median of 14% (range, 0.5% to 29%; n = 4) returned to G(0/1) phase DNA content after bromodeoxyuridine incorporation, demonstrating completion of at least one cell cycle in the presence of huCD40LT. Thus, primary clonal MCL cells are activated and can proliferate in the presence of huCD40LT as a single agent.