Sonic hedgehog and FGF8: inadequate signals for the differentiation of a dopamine phenotype in mouse and human neurons in culture

Complementation of dopaminergic signaling by Pitx3-GDNF synergy induces dopamine secretion by multipotent Ntera2 cells

Human teratocarcinoma cell line Ntera2 (NT2) expresses dopamine signals and has shown its safe profile for clinical applications. Attempts to restore complete dopaminergic (DAergic) phenotype enabling these cells to secrete dopamine have not been fully successful so far. We applied a blend of gene transfer techniques and a defined medium to convert NT2 cells to fully DAergic. The cells were primarily engineered to overexpress the Pitx3 gene product and then cultured in a growth medium supplemented with knockout serum and retinoic acid to form embroid bodies (EBs). Trypsinization of EB colonies produced single cells ready for differentiation. Neuronal/DAergic induction was promoted by applying conditioned medium taken from engineered human astrocytomas over-secreting glial cell-derived neurotrophic factor (GDNF). Immunocytochemistry, reverse-transcription and real-time polymerase chain reaction analyses confirmed significantly induced expression of molecules involved in dopamine signaling and metabolism including tyrosine hydroxylase, Nurr1, dopamine transporter, and aromatic acid decarboxylase. High-performance liquid chromatography analysis indicated release of dopamine only from a class of fully differentiated cells expressing Pitx3 and exposed to GDNF. In addition, Pitx3 and GDNF additively promoted in vitro neuroprotection against Parkinsonian toxin. One month after transplantation to the striatum of 6-OHDA-leasioned rats, differentiated NT2 cells survived and induced significant increase in striatal volume. Besides, cell implantation improved motor coordination in Parkinson's disease (PD) rat models. Our findings highlight the importance of Pitx3-GDNF interplay in dopamine signaling and indicate that our strategy might be useful for the restoration of DAergic fate of NT2 cells to make them clinically applicable toward cell replacement therapy of PD.

Fibroblast Growth Factor-2 alone as an efficient inducer for differentiation of human bone marrow mesenchymal stem cells into dopaminergic neurons

Background

The reported efficiency of differentiation of human bone marrow derived Mesenchymal Stem Cells (hBM MSC) into dopaminergic neurons with different inducers is found to vary. Thus, in the current study we have investigated the response of hBM MSC to some of the neuronal inducers and their combinations. Neuronal differentiation inducing agents Fibroblastic Growth Factor 2 (FGF2), Sonic Hedge Hog (Shh), Fibroblastic Growth Factor 8 (FGF8) & All Trans Retinoic Acid (ATRA) were used either singly or in varied combinations.

Results

The differentiated and undifferentiated hBM MSC were characterized in terms of morphology, expression of cell markers at transcriptional and translational levels, amount of dopamine secreted by the cells in the media and changes in cell membrane potential by calcium ions imaging. Induced hBM MSC revealed neuron like morphology and expressed cellular markers suggesting neuronal differentiation with all the inducing agents. However, upon quantitative analysis through qPCR, cells induced with FGF2 were found to show maximum expression of tyrosine hydroxylase (TH) by 47.5 folds. Immunofluorescence analysis of differentiated and undifferentiated cells also revealed expression of nestin, neurofilament, microtubule associated protein- 2, beta tubulin III and TH in differentiated cells, at translational level. This data was supported by immunoblotting analysis. Further, ELISA study also supported the release of dopamine by cultures induced with FGF2. When the cells were depolarised with KCl solution, those induced with Shh & FGF8 showed maximum calcium ion trafficking, followed by the cells induced with FGF2 only.

Conclusions

We conclude that hBM MSC can be coaxed to differentiate efficiently into dopaminergic neurons in the presence of a very simple media cocktail containing only one main inducer like FGF2 and thus contribute towards cellular therapy in Parkinson's and other related disorders. These dopaminergic neurons are also functionally active, as shown by calcium ion trafficking.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-014-0083-1) contains supplementary material, which is available to authorized users.

Dopamine receptors in human embryonic stem cell neurodifferentiation

We tested whether dopaminergic drugs can improve the protocol for in vitro differentiation of H9 human embryonic stem cells (hESCs) into dopaminergic neurons. The expression of 5 dopamine (DA) receptor subtypes (mRNA and protein) was analyzed at each protocol stage (1, undifferentiated hESCs; 2, embryoid bodies [EBs]; 3, neuroepithelial rosettes; 4, expanding neuroepithelium; and 5, differentiating neurons) and compared to human fetal brain (gestational week 17-19). D2-like DA receptors (D2, D3, and D4) predominate over the D1-like receptors (D1 and D5) during derivation of neurons from hESCs. D1 was the receptor subtype with the lowest representation in each protocol stage (Stages 1-5). D1/D5-agonist SKF38393 and D2/D3/D4-agonist quinpirole (either alone or combined) evoked Ca(2+) responses, indicating functional receptors in hESCs. To identify when receptor activation causes a striking effect on hESC neurodifferentiation, and what ligands and endpoints are most interesting, we varied the timing, duration, and drug in the culture media. Dopaminergic agonists or antagonists were administered either early (Stages 1-3) or late (Stages 4-5). Early DA exposure resulted in more neuroepithelial colonies, more neuronal clusters, and more TH(+) clusters. The D1/D5 antagonist SKF83566 had a strong effect on EB morphology and the expression of midbrain markers. Late exposure to DA resulted in a modest increase in TH(+) neuron clusters (∼75%). The increase caused by DA did not occur in the presence of dibutyryl cAMP (dbcAMP), suggesting that DA acts through the cAMP pathway. However, a D2-antagonist (L741) decreased TH(+) cluster counts. Electrophysiological parameters of the postmitotic neurons were not significantly affected by late DA treatment (Stages 4-5). The mRNA of mature neurons (VGLUT1 and GAD1) and the midbrain markers (GIRK2, LMX1A, and MSX1) were lower in hESCs treated by DA or a D2-antagonist. When hESCs were neurodifferentiated on PA6 stromal cells, DA also increased expression of tyrosine hydroxylase. Although these results are consistent with DA's role in potentiating DA neurodifferentiation, dopaminergic treatments are generally less efficient than dbcAMP alone.

Characterization of Porcine Ventral Mesencephalic Precursor Cells following Long-Term Propagation in 3D Culture

The potential use of predifferentiated neural precursor cells for treatment of a neurological disorder like Parkinson's disease combines stem cell research with previous experimental and clinical transplantation of developing dopaminergic neurons. One current obstacle is, however, the lack of ability to generate dopaminergic neurons after long-term in vitro propagation of the cells. The domestic pig is considered a useful nonprimate large animal model in neuroscience, because of a better resemblance of the larger gyrencephalic pig brain to the human brain than the commonly used brains of smaller rodents. In the present study, porcine embryonic (28–30 days), ventral mesencephalic precursor cells were isolated and propagated as free-floating neural tissue spheres in medium containing epidermal growth factor and fibroblast growth factor 2. For passaging, the tissue spheres were cut into quarters, avoiding mechanical or enzymatic dissociation in order to minimize cellular trauma and preserve intercellular contacts. Spheres were propagated for up to 237 days with analysis of cellular content and differentiation at various time points. Our study provides the first demonstration that porcine ventral mesencephalic precursor cells can be long-term propagated as neural tissue spheres, thereby providing an experimental 3D in vitro model for studies of neural precursor cells, their niche, and differentiation capacity.

Expansion and characterization of ventral mesencephalic precursor cells: Effect of mitogens and investigation of FA1 as a potential dopaminergic marker

Methods for identification and in vitro expansion of ventral mesencephalic dopaminergic precursor cells are of interest in the search for transplantable neurons for cell therapy in Parkinson's disease (PD). We investigated the potential use of fibroblast growth factor 2 (FGF2) and fibroblast growth factor 8 (FGF8) for expansion of such dopaminergic precursor cells, and fetal antigen-1 (FA1), a secreted neuronal protein of unknown function, as a non-invasive dopaminergic marker. Tissue from embryonic day (ED) 12 rat ventral mesencephalon was dissociated mechanically and cultured for 4 days in the presence of FGF2, FGF8, or without mitogens (control). After mitogen withdrawal and addition of 0.5% bovine serum, cells were differentiated for 6 days. Before differentiation, significantly more cells incorporated BrdU in cultures exposed to FGF2 (19-fold; P < 0.001) and FGF8 (3-fold; P < 0.05) compared to controls. After differentiation, biochemical analyses showed significantly more dopamine and FA1 in conditioned medium from both FGF2 and FGF8 expanded cultures than in controls. Correspondingly, numbers of tyrosine hydroxylase (TH)- and FA1-immunoreactive cells had increased 16-fold (P < 0.001) and 2.1-fold (P < 0.001), respectively in the FGF2 group and 10-fold (P < 0.001) and 1.8-fold (P < 0.05), respectively in the FGF8 group. In conclusion, the present procedure allows efficient expansion and differentiation of dopaminergic precursor cells and provides novel evidence of FGF8 as a mitogen for these cells. Furthermore, FA1 was identified as a potential supplementary non-invasive marker of cultured dopaminergic neurons.

Adult human bone marrow stromal spheres express neuronal traits in vitro and in a rat model of Parkinson's disease

Adult human bone marrow stromal cells (hMSCs) grown in suspension culture gave rise to spheres of neural progenitor (NP) cells, capable of expressing both dopaminergic (DA) and GABAergic (GABA) traits. After transplantation into the Parkinsonian rat, human NPs and neurons were present at 2 weeks. Although no DA neurons appeared to survive transplantation, there were abundant GABA neurons present in the graft. By 4 weeks, however, all cells had died. Finding ways to prolong survival and promote the appropriate neurotransmitter phenotype is essential if hMSCs are to be clinically useful.

Influence of retinoic acid and lithium on proliferation and dopaminergic potential of human NT2 cells

Our laboratory is working with the human NTera2/D1 (NT2) cell line, which has properties similar to those of progenitor cells in the central nervous system (CNS). These neural-like precursor cells can differentiate into all three major lineages, neurons, astrocytes, and oligodendrocytes. The pure neuronal population, hNT neurons, possess characteristics of dopamine (DA) cells. First, we analyzed whether the retinoic acid (RA)-treated hNT neurons and the NT2 precursor cells expressed two transcription factors required for development of the midbrain DA neurons. We report that NT2 cells endogenously expressed Engrailed-1 and Ptx3, whereas RA-treated hNT neurons did not express Engrailed-1 or Ptx3. Next we examined the influence of lithium treatment on Engrailed-1 and Ptx3 as well as another critical transcription factor, Nurr1. Previous research has shown that lithium can mimic the Wnt pathway, which is important for the induction of these transcription factors. Finally, we investigated the effect of lithium treatment on the viability and proliferation of NT2 cells, because lithium has been shown to stimulate neurogenesis in adult neural precursors. Lithium treatment increased the viability and proliferation of NT2 cells. The expression of transcription factors essential for the induction and maintenance of the DA phenotype was not increased in NT2 after lithium treatment. We conclude that the NT2 cell line is an excellent in vitro model system for studying the influence of pharmalogical agents on proliferation, differentiation, and apoptosis of a human neural progenitor cell line.

Delivery of sonic hedgehog or glial derived neurotrophic factor to dopamine-rich grafts in a rat model of Parkinson's disease using adenoviral vectors Increased yield of dopamine cells is dependent on embryonic donor age

The poor survival of dopamine grafts in Parkinson's disease is one of the main obstacles to the widespread application of this therapy. One hypothesis is that implanted neurons, once removed from the embryonic environment, lack the differentiation factors needed to develop the dopaminergic phenotype. In an effort to improve the numbers of dopamine neurons surviving in the grafts, we have investigated the potential of adenoviral vectors to deliver the differentiation factor sonic hedgehog or the glial cell line-derived neurotrophic factor GDNF to dopamine-rich grafts in a rat model of Parkinson's disease. Adenoviral vectors containing sonic hedgehog, GDNF, or the marker gene LacZ were injected into the dopamine depleted striatum of hemiparkinsonian rats. Two weeks later, ventral mesencephalic cell suspensions were prepared from embryos of donor ages E12, E13, E14 or E15 and implanted into the vector-transduced striatum. Pre-treatment with the sonic hedgehog vector produced a three-fold increase in the numbers of tyrosine hydroxylase-positive (presumed dopaminergic) cells in grafts derived from E12 donors, but had no effect on E13-E15 grafts. By contrast, pre-treatment with the GDNF vector increased yields of dopamine cells in grafts derived from E14 and E15 donors but had no effect on grafts from younger donors. The results indicate that provision of both trophic and differentiation factors can enhance the yields of dopamine neurons in ventral mesencephalic grafts, but that the two factors differ in the age and stage of embryonic development at which they have maximal effects.

Human fibroblast-derived cell lines have characteristics of embryonic stem cells and cells of neuro-ectodermal origin

Fibroblasts are the most ubiquitous cells in complex organisms. They are the main cells of stromal tissue and play an important role in repair and healing of damaged organs. Here we report new data-initially serendipitous findings-that fibroblast-derived cell line (human fetal lung derived cells, MRC-5) have the morphology, growth rate and gene expression pattern characteristic of embryonic stem cells and cells of neuro-ectodermal origin. We have developed a serum-free culture system to maintain these cells in proliferative state. We discovered that, at proliferative state, these cells express transcription factors of pluripotent cells, OCT-3/4 and REX-1, and embryonic cell surface antigens SSEA-1, SSEA-3, and SSEA-4, as well as TRA-1-60 and TRA-1-81. In addition to embryonic cell markers, the fibroblasts expressed neuroectodermal genes: Musashi-1, nestin, medium neurofilament, and beta-III tubulin. RT-PCR data revealed that mesencephalic transcription factors, Nurr-1 and PTX-3, were also expressed in MRC-5 cells, and that these cells could be induced to express tyrosine hydroxylase (TH). Expression of TH followed down-regulation of genes associated with cell proliferation, OCT-3/4, REX-1, and beta-catenin. These data indicate that the cells commonly known as fibroblasts have some of the characteristics of stem cells, and can be induced to become neuroectodermal cells and perhaps even mature neurons.

The generation of dopaminergic neurons by human neural stem cells is enhanced by Bcl-XL, both in vitro and in vivo

Progress in stem cell biology research is enhancing our ability to generate specific neuron types for basic and applied studies and to design new treatments for neurodegenerative diseases. In the case of Parkinson's disease (PD), alternative human dopaminergic (DAergic) neurons other than primary fetal tissue do not yet exist. One possible source could be human neural stem cells (hNSCs), although the yield in DAergic neurons and their survival are very limited. [see figure]. In this study, we found that Bcl-X(L) enhances (one-to-two orders of magnitude) the capacity for spontaneous dopaminergic differentiation of hNSCs, which then exceeds that of cultured human ventral mesencephalic tissue. Bcl-X(L) also enhanced total neuron generation by hNSCs, but to a lower extent. Neuronal phenotypes other than DA were not affected by Bcl-X(L), indicating an exquisitely specific effect on DAergic neurons. In vivo, grafts of Bcl-X(L)-overexpressing hNSCs do generate surviving human TH+ neurons in the adult rat 6-OH-dopamine lesioned striatum, something never seen when naive hNSCs were transplanted. Most of the data obtained here in terms of the effects of Bcl-X(L) are consistent with an enhanced survival type of mechanism and not supportive of induction, specification, or proliferation of DAergic precursors. From this in vitro and in vivo evidence, we conclude that enhancing Bcl-X(L) expression is important to obtain human DAergic neurons from hNSCs. These findings may facilitate the development of drug-screening and cell-replacement activities to discover new therapeutic strategies for PD.

Serotonergic-like progenitor cells propagated from neural stem cells in vitro: survival with SERT protein expression following implantation into brains of mice lacking SERT

Neural stem cells (NSCs) obtained from the midbrain region of embryonic (E14) mice were initially cultured with basic fibroblast growth factor (bFGF), Sonic hedgehog, and FGF-8 in a serum-free N-2 culture medium to foster differentiation into a serotonergic-like phenotype. During the initial differentiating phase, these progenitor cells expressed En1, Pax3, and Pax5 mRNA. Subsequently, a single serotonin [5-hydroxytryptamine (5-HT)] and tryptophan hydroxylase-positive clone was isolated, which gave rise to cells that developed serotonergic properties. Sixty percent of these progenitor cells expressed the serotonin transporter (SERT), as indicated by specific ligand binding of [125I]-RTI-55. To further evaluate SERT functionality, we showed that these progenitor cells possessed specific [3H]-5-HT uptake activity. Implantation of the serotonergic-like progenitors into the hippocampus of adult mice genetically lacking SERT was followed by migration of these cells into adjacent brain regions, and survival of the cells at 8 weeks was accompanied by a gradual increase in density of SERT protein expression, which was not found in vehicle-injected, control mice. These findings suggest that this serotonergic-like NSC model will be a useful contribution to the development of cell biotechnology in regard to the expression of missing genes such as SERT in the adult brain.

Rapid differentiation of NT2 cells in Sertoli–NT2 cell tissue constructs grown in the rotating wall bioreactor

Cell replacement therapy is of great interest as a long-term treatment of neurodegenerative diseases such as Parkinson's disease (PD). We have previously shown that Sertoli cells (SC) provide neurotrophic support to transplants of dopaminergic fetal neurons and NT2N neurons, derived from the human clonal precursors cell line NTera2/D1 (NT2), which differentiate into dopaminergic NT2N neurons when exposed to retinoic acid. We have created SC-NT2 cell tissue constructs cultured in the high aspect ratio vessel (HARV) rotating wall bioreactor. Sertoli cells, NT2, and SC plus NT2 cells combined in starting ratios of 1:1, 1:2, 1:4 and 1:8 were cultured in the HARV in DMEM with 10% fetal bovine serum and 1% growth factor reduced Matrigel for 3 days, without retinoic acid. Conventional, non-HARV, cultures grown in the same culture medium were used as controls. The presence of tyrosine hydroxylase (TH) was assessed in all culture conditions. Sertoli-neuron-aggregated-cell (SNAC) tissue constructs grown at starting ratios of 1:1 to 1:4 contained a significant amount of TH after 3 days of culture in the HARV. No TH was detected in SC HARV cultures, or SC, NT2 or SC-NT2 conventional co-cultures. Quantitative stereology of immunolabled 1:4 SNAC revealed that approximately 9% of NT2 cells differentiate into TH-positive (TH+) NT2N neurons after 3 days of culture in the HARV, without retinoic acid. SNAC tissue constructs also released dopamine (DA) when stimulated with KCl, suggesting that TH-positive NT2N neurons in the SNAC adopted a functional dopaminergic phenotype. SNAC tissue constructs may be an important source of dopaminergic neurons for neuronal transplantation.

Tyrosine hydroxylase induction by basic fibroblast growth factor and cyclic AMP analogs in striatal neural stem cells: role of ERK1/ERK2 mitogen-activated protein kinase and protein kinase C

Neural stem cells (NSC) with self-renewal and multilineage potential are considered good candidates for cell replacement of damaged nervous tissue. In vitro experimental conditions can differentiate these cells into specific neuronal phenotypes. In the present study, we describe the combined effect of basic fibroblast growth factor (bFGF) and dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP) on the differentiation of fetal rat striatal NSC into tyrosine hydroxylase-positive cells. Tyrosine hydroxylase induction was accompanied by the activation of ERK1/ERK2 mitogen-activated protein kinase and was inhibited by the ERK1/ERK2 pathway blocker PD98059, suggesting that ERK activation may be important for this process. In addition, protein kinase C (PKC) was shown to be required for tyrosine hydroxylase protein expression. The inhibition of PKC by staurosporin, as well as its downregulation, decreased the ability of bFGF+dbcAMP to generate tyrosine hydroxylase-positive cells. Moreover, the PKC activator phorbol 12-myristate 13-acetate (PMA) together with bFGF and dbcAMP led to a significant increase in phospho-ERK1/ERK2 levels, and the percentage of beta-tubulin III-positive cells that expressed tyrosine hydroxylase increased by 3.5-fold. PMA also promoted the phosphorylation of the cyclic AMP response element binding protein that might contribute to the increase in tyrosine hydroxylase-positive cells observed in bFGF+dbcAMP+PMA-treated cultures. From these results, we conclude that the manipulation in vitro of NSC from rat fetal striatum with bFGF, cyclic AMP analogs, and PKC activators promotes the generation of tyrosine hydroxylase-positive neurons.

Induction and specification of midbrain dopaminergic cells: focus on SHH, FGF8, and TGF-?

Cell-fate decisions along the dorsoventral and anterior-posterior axis of the neural tube are dictated by factors from signaling and organizing centers. According to the prevailing notion, the formation of mesencephalic dopaminergic neurons is directed by diffusable signals from the notochord, floor plate, and isthmic organizer. Sonic hedgehog (Shh), secreted by the notochord and floor plate, and fibroblast growth factor (FGF) 8, secreted by the isthmus, are thought to be key molecules involved in the development of midbrain dopaminergic neurons. During the last decade, the introduction of elegant explant culture systems and the generation of transgenic and mutant mice have greatly contributed to a better understanding of the molecular signals that direct the induction and specification of midbrain dopaminergic neurons. In this context, experimental evidence has challenged the dominant roles of Shh and FGF8 in dopaminergic neuron development. Additional molecules have been identified as being required for the generation of mesencephalic dopaminergic neurons, particularly members of the transforming growth factor beta superfamily.

TGF-beta promotes survival on mesencephalic dopaminergic neurons in cooperation with Shh and FGF-8

Impaired neuronal survival is a key event in the development of degenerative diseases, such as Parkinson's disease (PD). Here we show that transforming growth factor beta (TGF-beta) acts directly on rat E14 midbrain dopaminergic neurons in vitro, its survival-promoting effect being not mediated by BDNF, NT-3, or GDNF. Treatment with TGF-beta, sonic hedgehog (Shh), or fibroblast growth factor-8 (FGF8) significantly increased number of tyrosine hydroxylase (TH)-immunoreactive neurons after 7 days, whereas application of these factors added together further increased number of TH-positive neurons, compared to single-factor treatments. Neutralization of endogenous TGF-beta, Shh, or FGF8 significantly reduced number of dopaminergic neurons. TGF-beta treatment decreased number of apoptotic cells, having no effect on cell proliferation. Neutralization of TGF-beta in vivo during chick E6-10 resulted in reduced number of midbrain dopaminergic neurons. The results suggest that TGF-beta is required for survival of mesencephalic dopaminergic neurons acting in cooperation with Shh and FGF8.

High Titer Retroviral Gene Transduction to Neural Progenitor Cells for Establishment of Donor Cells for Neural Transplantation to Parkinsonian Model Rats

Neural progenitor cells (NPCs) are expected to be useful donor sources for cell transplantation therapy in Parkinson's disease. However, control of the differentiational lineage, especially into dopaminergic neurons, is still difficult. Thus, genetic modification of NPCs to produce l-dopa is potentially useful. The present study prepared high titer retrovirus carrying human tyrosine hydroxylase-1 (HTH-1) gene. HTH-1 gene could be efficiently transduced into NPCs obtained from the E12.5 rat mesencephalon. This retroviral gene transduction caused no apparent changes in survival, proliferation, or differentiation. In vitro, HTH-1 gene-transduced NPCs released little l-dopa and addition of tetrahydrobiopterin, the cofactor of tyrosine hydroxylase, was required for production of l-dopa. In vivo, three of seven hemi-parkinsonian model rats that received HTH-1 gene-transduced donor NPCs achieved functional recovery. High titer retroviral vector for gene transduction could be used to prepare NPCs for transplantation to hemi-parkinsonian model rats. However, functional recovery after transplantation of HTH-1 gene-transduced NPCs was incomplete.

Studies on the differentiation of dopaminergic traits in human neural progenitor cells in vitro and in vivo

The development of cell replacement therapies for the treatment of neurodegenerative disorders such as Parkinson's disease (PD) may depend upon the successful differentiation of human neural stem/progenitor cells into dopamine (DA) neurons. We show here that primary human neural progenitors (HNPs) can be expanded and maintained in culture both as neurospheres (NSPs) and attached monolayers where they develop into neurons and glia. When transplanted into the 6-hydroxydopamine-lesioned rat striatum, undifferentiated NSPs survive longer (60% graft survival at 8-16 weeks vs. 30% graft survival at 8-13 weeks) and migrate farther than their attached counterparts. While both NSP and attached cells continue to express neuronal traits after transplantation, the spontaneous expression of differentiated transmitter-related traits is not observed in either cell type. However, following predifferentiation in culture using a previously described cocktail of reagents, approximately 25% of HNPs can permanently express the DA enzyme tyrosine hydroxylase (TH), even following replating and removal of the DA differentiation cocktail. When these predifferentiated HNPs are transplanted into the brain, however, TH staining is not observed, either because expression is lost or TH-expressing cells preferentially die. Consistent with the latter view is a decrease in total cell survival and migration, and an enhanced glial response in these grafts. In contrast, we found that the overall survival of HNPs is improved when cells engraft near blood vessels or CSF compartments or when they are placed into an intact unlesioned brain, suggesting that there are factors, as yet unidentified, that can better support the development of engrafted HNPs.

Genetic analysis of the roles of Hh, FGF8, and nodal signaling during catecholaminergic system development in the zebrafish brain

CNS catecholaminergic neurons can be distinguished by their neurotransmitters as dopaminergic or noradrenergic and form in distinct regions at characteristic embryonic stages. This raises the question of whether all catecholaminergic neurons of one transmitter type are specified by the same set of factors. Therefore, we performed genetic analyses to define signaling requirements for the specification of distinct clusters of catecholaminergic neurons in zebrafish. In mutants affecting midbrain- hindbrain boundary (MHB) organizer formation, the earliest ventral diencephalic dopaminergic neurons appear normal. However, after 2 d of development, we observed fewer cells than in wild types, which suggests that the MHB provides proliferation or survival factors rather than specifying ventral diencephalic dopaminergic clusters. In hedgehog (Hh) pathway mutants, the formation of catecholaminergic neurons is affected only in the pretectal cluster. Surprisingly, neither fibroblast growth factor 8 (FGF8) alone nor in combination with Hh signaling is required for specification of early developing dopaminergic neurons. We analyzed the formation of prosomeric territories in the forebrain of Hh and Nodal pathway mutants to determine whether the absence of specific dopaminergic clusters may be caused by early patterning defects ablating corresponding parts of the CNS. In Nodal pathway mutants, ventral diencephalic and pretectal catecholaminergic neurons fail to develop, whereas both anatomical structures form at least in part. This suggests that Nodal signaling is required for catecholaminergic neuron specification. In summary, our results do not support the previously suggested dominant roles for sonic hedgehog and Fgf8 in specification of the first catecholaminergic neurons, but instead indicate a novel role for Nodal signaling in this process.

Making and repairing the mammalian brain--in vitro production of dopaminergic neurons

Midbrain dopamine (DA) neurons play an essential role in modulating motor control, and their degeneration is the hallmark feature of Parkinson's disease (PD). In vitro production of DA neurons provides insight into the mechanisms that control cell fate choice, and offers an alternative to the use of fetal tissue for experimental cell replacement in PD. Here we will review the advantages and disadvantages of the various renewable cell sources and protocols tested, and discuss their relevance for basic studies and for cell therapy.

SHH and FGF8 play distinct roles during development of noradrenergic neurons in the locus coeruleus of the zebrafish

Several signaling pathways have been implicated in the development of dopaminergic and serotonergic neurons. Here, we analyzed the formation of noradrenergic (NAergic) cells in the locus coeruleus (LC) of zebrafish. In the sonic hedgehog (shh) mutant, cells positive for tyrosine hydroxylase, a marker for putative NAergic cells in the LC were reduced. Similarly, the inhibition of translation of all hh genes and the perturbation of Shh signaling by forskolin resulted in a decrease in the number of cells. Conversely, when SHH was overexpressed, an increase in number was observed. Thus, Shh is involved in maintaining the appropriate number of cells in the LC. While elevated levels of bone morphogenetic protein 4 (BMP4) did not attenuate tyrosine hydroxylase-positive cells, exogenous fibroblast growth factor 8 (FGF8) rescued NAergic neurons in the acerebellar (ace) mutant, providing direct in vivo evidence that Fgf8 is required for the induction of NAergic neurons in the LC.

Treatment of neural injury with marrow stromal cells

We describe our preclinical studies on the use of bone-marrow stromal cells (MSC; an uncharacterised mixed population of plastic-adherent cells) in the treatment of neural injury. These cells obtained from donor rats or human beings have been directly transplanted into brain or administered intra-arterially or intravenously. MSC selectively target injured tissue and promote functional recovery. Signals that target inflammatory cells to injured tissue probably direct MSC to injury sites. Although some MSC express proteins typical of neural cells, the possibility that benefit is derived by replacement of infarcted tissue with differentiated MSC is highly unlikely. MSC activate endogenous restorative responses in injured brain, which include angiogenesis, neurogenesis, and synaptogenesis. Given the robust therapeutic benefit of these cells in the treatment of experimental neural injury, and the fact that MSC have been used in the treatment of other human disease, there is justification for further preclinical studies leading to clinical trials for the treatment of neural injury such as stroke.

Cerebellar proteoglycans regulate sonic hedgehog responses during development

Sonic hedgehog promotes proliferation of developing cerebellar granule cells. As sonic hedgehog is expressed in the cerebellum throughout life it is not clear why proliferation occurs only in the early postnatal period and only in the external granule cell layer. We asked whether heparan sulfate proteoglycans might regulate sonic hedgehog-induced proliferation and thereby contribute to the specialized proliferative environment of the external granule cell layer. We identified a conserved sequence within sonic hedgehog that is essential for binding to heparan sulfate proteoglycans, but not for binding to the receptor patched. Sonic hedgehog interactions with heparan sulfate proteoglycans promote maximal proliferation of postnatal day 6 granule cells. By contrast, proliferation of less mature granule cells is not affected by sonic hedgehog-proteoglycan interactions. The importance of proteoglycans for proliferation increases during development in parallel with increasing expression of the glycosyltransferase genes, exostosin 1 and exostosin 2. These data suggest that heparan sulfate proteoglycans, synthesized by exostosins, may be critical determinants of granule cell proliferation.

Stem cells in the treatment of Parkinson's disease

Stem cells have been suggested as candidate therapeutic tools for neurodegenerative disorders, given their ability to give rise to the appropriate cell types after grafting in vivo. In this review I summarize some of the evidence currently available concerning two approaches for the treatment of Parkinson's disease: (1) The generation of dopaminergic neurons from embryonic stem cells, multipotent stem cells, and neuronal progenitor cells for cell replacement therapy. (2) The engineering of multipotent stem cells to release glial cell-line derived neurotrophic factor, a potent neurotrophic factor for dopaminergic neurons, in a neuroprotective and neuroregenerative approach to the treatment of Parkinson's disease.

Induction of a dopaminergic phenotype in cultured striatal neurons by bone morphogenetic proteins

In the present study, we examined whether the bone morphogenetic proteins (BMPs), which are important in the developmental specification of transmitter type in certain classes of neurons, might also play a role in signaling the differentiation of a dopaminergic (DA) phenotype. We found that BMP-2, -4 and -6 were each capable of inducing, in a dose and time dependent manner, moderate levels of the DA enzyme tyrosine hydroxylase (TH) in cultured neurons from the mouse embryonic striatum. In contradistinction to other TH-inducing agents, BMPs initiated de novo TH expression without the required synergy of exogenous growth factors or co-activating substances and in neurons presumably aged (E16) beyond the critical period for induction. However, the appearance of TH in induced cells was short-lived (24 h) and could not be prolonged by repeated supplementation with the BMPs. Inhibitors of the mitogen-activated protein kinase (MAPK/ERK) signaling pathway, PD98059 and apigenin, did not prevent TH induction by BMP-4, as they did other TH inducing agents, indicating that the MAPK/ERK pathway does not mediate BMPs effects on TH expression. We conclude that BMP-2, -4 and -6 can be added to the expanding inventory of agents capable of inducing TH, making them potentially important in the specification of a DA phenotype in stem/precursor cells for the treatment of Parkinson's disease.

Differentiation of human dopamine neurons from an embryonic carcinomal stem cell line

Previous studies from this laboratory have demonstrated that fibroblast growth factor 1 together with a number of co-activator molecules (dopamine, TPA, IBMX/forskolin), will induce the expression of the catecholamine biosynthetic enzyme tyrosine hydroxylase (TH) in 10% of human neurons (hNTs) derived from the NT2 cell line [10]. In the present study, we found that TH induction was increased to nearly 75% in hNTs when cells were permitted to age 2 weeks in culture prior to treatment with the differentiation cocktail. This high level of TH expression was sustained 7 days after removal of the differentiating agents from the media. Moreover, the induced TH present in these cells was enzymatically active, resulting in the production of low levels of dopamine (DA) and its metabolite DOPAC. These findings suggest that hNTs may provide an important tissue culture model for the study of factors regulating TH gene expression in human neurons. Moreover, hNTs may serve, in vivo, as a source of human DA neurons for use in transplantation therapies.