Factors promoting survival of mesencephalic dopaminergic neurons

Identification of Hub Genes and Potential Molecular Pathogenesis in Substantia Nigra in Parkinson's Disease via Bioinformatics Analysis

Parkinson's disease (PD) is the second most common neurodegenerative disease, with significant socioeconomic burdens. One of the crucial pathological features of PD is the loss of dopaminergic neurons in the substantia nigra (SN). However, the exact pathogenesis remains unknown. Moreover, therapies to prevent neurodegenerative progress are still being explored. We performed bioinformatics analysis to identify candidate genes and molecular pathogenesis in the SN of patients with PD. We analyzed the expression profiles, GSE49036 and GSE7621, which included 31 SN tissues in PD samples and 17 SN tissues in healthy control samples, and identified 86 common differentially expressed genes (DEGs). Then, GO and KEGG pathway analyses of the identified DEGs were performed to understand the biological processes and significant pathways of PD. Subsequently, a protein-protein interaction network was established, with 15 hub genes and four key modules which were screened in this network. The expression profiles, GSE8397 and GSE42966, were used to verify these hub genes. We demonstrated a decrease in the expression levels of 14 hub genes in the SN tissues of PD samples. Our results indicated that, among the 14 hub genes, DRD2, SLC18A2, and SLC6A3 may participate in the pathogenesis of PD by influencing the function of the dopaminergic synapse. CACNA1E, KCNJ6, and KCNB1 may affect the function of the dopaminergic synapse by regulating ion transmembrane transport. Moreover, we identified eight microRNAs (miRNAs) that can regulate the hub genes and 339 transcription factors (TFs) targeting these hub genes and miRNAs. Subsequently, we established an mTF-miRNA-gene-gTF regulatory network. Together, the identification of DEGs, hub genes, miRNAs, and TFs could provide better insights into the pathogenesis of PD and contribute to the diagnosis and therapies.

Developmental prefrontal mRNA expression of D2 dopamine receptor splice variants and working memory impairments in rats after early life Interleukin-1β elevation

Long (D2L) and Short (D2S) isoforms of D2 dopamine receptor differ in their biochemical and physiological properties, which could affect functioning of prefrontal cortex. Contribution of distinct D2 dopamine receptor isoforms to cognitive dysfunctions and its developmental regulation are currently not fully elucidated. In the present study, we evaluated developmental mRNA expression of D2S/D2L dopamine receptor isoforms within the rat medial prefrontal cortex (mPFC) in the model of neurodevelopmental cognitive dysfunction. Working memory performance (Y-maze spontaneous alternations) and D2S/D2L mRNA expression in the mPFC (by qRT-PCR) were evaluated in juvenile (P27), adolescent (P42-47) and adult (P75-90) rats after chronic early life treatment with proinflammatory cytokine interleukin (IL)-1β (1 µg/kg i.p. daily P15-21). It was shown that IL-1β elevation during the 3rd week of life leads to working memory deficit originating in juvenile animals and persisting into adulthood. D2S mRNA expression was strongly downregulated during adolescence, and such downregulation was exaggerated in animals injected with IL-1β during P15-21. Early life IL-1β administrations influenced developmental changes in the D2S/D2L mRNA ratio. This measure was found to be decreased in adolescent and adult control (intact and vehicle-treated) rats compared to juvenile control, while in the case of IL-1β-treated animals, the decrease in D2S/D2L ratio was observed only in adulthood but not in adolescence compared to juvenile rats. During the adolescence, D2S mRNA expression was downregulated and D2S/D2L ratio was upregulated in the mPFC of rats treated with IL-1β during the 3rd week of life compared to controls. Based on these data we conclude that changes in the developmental expression of D2 dopamine receptor splice variants within mPFC may underlie long-lasting cognitive deficit associated with neonatal pathology.

Cell reprogramming approaches in gene- and cell-based therapies for Parkinson's disease

Degeneration of dopamine (DA) neurons in the substantia nigra pars compacta is the pathological hallmark of Parkinson's disease (PD). In PD multiple pathogenic mechanisms initiate and drive this neurodegenerative process, making the development of effective treatments challenging. To date, PD patients are primarily treated with dopaminergic drugs able to temporarily enhance DA levels, therefore relieving motor symptoms. However, the drawbacks of these therapies including the inability to alter disease progression are constantly supporting the search for alternative treatment approaches. Over the past years efforts have been put into the development of new therapeutic strategies based on the delivery of therapeutic genes using viral vectors or transplantation of DA neurons for cell-based DA replacement. Here, past achievements and recent advances in gene- and cell-based therapies for PD are outlined. We discuss how current gene and cell therapy strategies hold great promise for the treatment of PD and how the use of stem cells and recent developments in cellular reprogramming could contribute to open a new avenue in PD therapy.

Neurotrophic Enhancers as Therapy for Behavioral Deficits in Rodent Models of Huntington's Disease: Use of Gangliosides, Substituted Pyrimidines, and Mesenchymal Stem Cells

The interest in using neurotrophic factors as potential treatments for neurodegenerative disorders, such as Huntington's disease, has grown in the past decade. A major impediment for the clinical utility of neurotrophic factors is their inability to cross the blood-brain barrier in therapeutically significant amounts. Although several novel mechanisms for delivering exogenous neurotrophins to the brain have been developed, most of them involve invasive procedures or present significant risks. One approach to circumventing these problems is using therapeutic agents that can be administered systemically and have the ability to enhance the activity of neurotrophic factors. This review highlights the use of gangliosides, substituted pyrimidines, and mesenchymal stem cells as neurotrophic enhancers that have significant therapeutic potential while avoiding the pitfalls of delivering exogenous neurotrophic factors through the blood-brain barrier. The review focuses on the potential of these neurotrophic enhancers for treating the behavioral deficits in rodent models of Huntington's disease.

Adaptive cellular stress pathways as therapeutic targets of dietary phytochemicals: focus on the nervous system

During the past 5 decades, it has been widely promulgated that the chemicals in plants that are good for health act as direct scavengers of free radicals. Here we review evidence that favors a different hypothesis for the health benefits of plant consumption, namely, that some phytochemicals exert disease-preventive and therapeutic actions by engaging one or more adaptive cellular response pathways in cells. The evolutionary basis for the latter mechanism is grounded in the fact that plants produce natural antifeedant/noxious chemicals that discourage insects and other organisms from eating them. However, in the amounts typically consumed by humans, the phytochemicals activate one or more conserved adaptive cellular stress response pathways and thereby enhance the ability of cells to resist injury and disease. Examplesof such pathways include those involving the transcription factors nuclear factor erythroid 2-related factor 2, nuclear factor-κB, hypoxia-inducible factor 1α, peroxisome proliferator-activated receptor γ, and forkhead box subgroup O, as well as the production and action of trophic factors and hormones. Translational research to develop interventions that target these pathways may lead to new classes of therapeutic agents that act by stimulating adaptive stress response pathways to bolster endogenous defenses against tissue injury and disease. Because neurons are particularly sensitive to potentially noxious phytochemicals, we focus on the nervous system but also include findings from other cell types in which actions of phytochemicals on specific signal transduction pathways have been more thoroughly studied.

Mesenchymal stem cells support neuronal fiber growth in an organotypic brain slice co-culture model

Mesenchymal stem cells (MSCs) have been identified as promising candidates for neuroregenerative cell therapies. However, the impact of different isolation procedures on the functional and regenerative characteristics of MSC populations has not been studied thoroughly. To quantify these differences, we directly compared classically isolated bulk bone marrow-derived MSCs (bulk BM-MSCs) to the subpopulation Sca-1(+)Lin(-)CD45(-)-derived MSCs(-) (SL45-MSCs), isolated by fluorescence-activated cell sorting from bulk BM-cell suspensions. Both populations were analyzed with respect to functional readouts, that are, frequency of fibroblast colony forming units (CFU-f), general morphology, and expression of stem cell markers. The SL45-MSC population is characterized by greater morphological homogeneity, higher CFU-f frequency, and significantly increased nestin expression compared with bulk BM-MSCs. We further quantified the potential of both cell populations to enhance neuronal fiber growth, using an ex vivo model of organotypic brain slice co-cultures of the mesocortical dopaminergic projection system. The MSC populations were cultivated underneath the slice co-cultures without direct contact using a transwell system. After cultivation, the fiber density in the border region between the two brain slices was quantified. While both populations significantly enhanced fiber outgrowth as compared with controls, purified SL45-MSCs stimulated fiber growth to a larger degree. Subsequently, we analyzed the expression of different growth factors in both cell populations. The results show a significantly higher expression of brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor in the SL45-MSCs population. Altogether, we conclude that MSC preparations enriched for primary MSCs promote neuronal regeneration and axonal regrowth, more effectively than bulk BM-MSCs, an effect that may be mediated by a higher BDNF secretion.

Laminin-γ1 chain and stress inducible protein 1 synergistically mediate PrPC-dependent axonal growth via Ca2+ mobilization in dorsal root ganglia neurons

Prion protein (PrP(C)) is a cell surface glycoprotein that is abundantly expressed in nervous system. The elucidation of the PrP(C) interactome network and its significance on neural physiology is crucial to understanding neurodegenerative events associated with prion and Alzheimer's diseases. PrP(C) co-opts stress inducible protein 1/alpha7 nicotinic acetylcholine receptor (STI1/α7nAChR) or laminin/Type I metabotropic glutamate receptors (mGluR1/5) to modulate hippocampal neuronal survival and differentiation. However, potential cross-talk between these protein complexes and their role in peripheral neurons has never been addressed. To explore this issue, we investigated PrP(C)-mediated axonogenesis in peripheral neurons in response to STI1 and laminin-γ1 chain-derived peptide (Ln-γ1). STI1 and Ln-γ1 promoted robust axonogenesis in wild-type neurons, whereas no effect was observed in neurons from PrP(C) -null mice. PrP(C) binding to Ln-γ1 or STI1 led to an increase in intracellular Ca(2+) levels via distinct mechanisms: STI1 promoted extracellular Ca(2+) influx, and Ln-γ1 released calcium from intracellular stores. Both effects depend on phospholipase C activation, which is modulated by mGluR1/5 for Ln-γ1, but depends on, C-type transient receptor potential (TRPC) channels rather than α7nAChR for STI1. Treatment of neurons with suboptimal concentrations of both ligands led to synergistic actions on PrP(C)-mediated calcium response and axonogenesis. This effect was likely mediated by simultaneous binding of the two ligands to PrP(C). These results suggest a role for PrP(C) as an organizer of diverse multiprotein complexes, triggering specific signaling pathways and promoting axonogenesis in the peripheral nervous system.

Gene therapy for the treatment of Parkinson's disease: the nature of the biologics expands the future indications

The pharmaceutical industry's development of therapeutic medications for the treatment of Parkinson's disease (PD) endures, as a result of the continuing need for better agents, and the increased clinical demand due to the aging population. Each new drug offers advantages and disadvantages to patients when compared to other medical offerings or surgical options. Deep brain stimulation (DBS) has become a standard surgical remedy for the effective treatment of select patients with PD, for whom most drug regimens have failed or become refractory. Similar to DBS as a surgical option, gene therapy for the treatment of PD is evolving as a future option. In the four different PD gene therapy approaches that have reached clinical trials investigators have documented an excellent safety profile associated with the stereotactic delivery, viral vectors and doses utilized, and transgenes expressed. In this article, we review the clinically relevant gene therapy strategies for the treatment of PD, concentrating on the published preclinical and clinical results, and the likely mechanisms involved. Based on these presentations, we advance an analysis of how the nature of the gene therapy used may eventually expand the scope and utility for the management of PD.

The colayer method as an efficient way to genetically modify mesencephalic progenitor cells transplanted into 6-OHDA rat model of Parkinson's disease

Exogenous cell replacement represents a potent treatment option for Parkinson's disease. However, the low survival rate of transplanted dopaminergic neurons (DA) calls for methodological improvements. Here we evaluated a method to combine transient genetic modification of neuronal progenitor cells with an optimized cell culture protocol prior to intrastriatal transplantation into 6-hydroxydopamine (6-OHDA) unilateral lesioned rats. Plasmid-based delivery of brain-derived neurotrophic factor (BDNF) increases the number of DA neurons, identified by tyrosine hydroxylase immunoreactivity (TH-ir), by 25% in vitro, compared to enhanced green fluorescence protein (EGFP)-transfected controls. However, the nucleofection itself, especially the cell detachment and reseeding procedure, decreases the TH-ir neuron number to 40% compared with nontransfected control cultures. To circumvent this drawback we established the colayer method, which contains a mix of nucleofected cells reseeded on top of an adherent sister culture in a ratio 1:3. In this setup TH-ir neuron number remains high and could be further increased by 25% after BDNF transfection. Comparison of both cell culture procedures (standard and colayer) after intrastriatal transplantation revealed a similar DA neuron survival as seen in vitro. Two weeks after grafting TH-ir neuron number was strongly reduced in animals receiving the standard EGFP-transfected cells (271 ± 62) compared to 1,723 ± 199 TH-ir neurons in the colayer group. In contrast to the in vitro results, no differences in the number of grafted TH-ir neurons were observed between BDNF, EGFP, and nontransfected colayer groups, neither 2 nor 13 weeks after transplantation. Likewise, amphetamine and apomorphine-induced rotational behavior improved similarly over time in all groups. Nevertheless, the colayer protocol provides an efficient way for neurotrophic factor release by transplanted progenitor cells and will help to study the effects of candidate factors on survival and integration of transplanted DA neurons.

Delivery of chemotropic proteins and improvement of dopaminergic neuron outgrowth through a thixotropic hybrid nano-gel

Chemotropic proteins guide neuronal projections to their final target during embryo development and are useful to guide axons of neurons used in transplantation therapies. Site-specific delivery of the proteins however is needed for their application in the brain to avoid degradation and pleiotropic affects. In the present study we report the use of Poly (ethylene glycol)-Silica (PEG-Si) nanocomposite gel with thixotropic properties that make it injectable and suitable for delivery of the chemotropic protein semaphorin 3A. PEG-Si gel forms a functional gradient of semaphorin that enhances axon outgrowth of dopaminergic neurons from rat embryos or differentiated from stem cells in culture. It is not cytotoxic and its properties allowed its injection into the striatum without inflammatory response in the short term. Long term implantation however led to an increase in macrophages and glial cells. The inflammatory response could have resulted from non-degraded silica particles, as observed in biodegradation assays.

Glial cell-line derived neurotrophic factor is essential for electroconvulsive shock-induced neuroprotection in an animal model of Parkinson's disease

Sustained motor improvement in human patients with idiopathic Parkinson's disease has been described following electroconvulsive shock (ECS) treatment. In rats, ECS stimulates the expression of various trophic factors (TFs), some of which have been proposed to exert neuroprotective actions. We previously reported that ECS protects the integrity of the rat nigrostriatal dopaminergic system against 6-hydroxydopamine (6-OHDA)-induced toxicity; in order to shed light into its neuroprotective mechanism, we studied glial cell-line derived neurotrophic factor (GDNF) levels (the most efficient TF for dopaminergic neurons) in the substantia nigra (SN) and striatum of 6-OHDA-injected animals with or without ECS treatment. 6-OHDA injection decreased GDNF levels in the SN control animals, but not in those receiving chronic ECS, suggesting that changes in GDNF expression may participate in the ECS neuroprotective mechanism. To evaluate this possibility, we inhibit GDNF by infusion of GDNF function blocking antibodies in the SN of 6-OHDA-injected animals treated with ECS (or sham ECS). Animals were sacrificed 7 days after 6-OHDA infusion, and the integrity of the nigrostriatal system was studied by tyrosine hydroxylase immunohistochemistry and Cresyl Violet staining. Neuroprotection observed in ECS-treated animals was inhibited by GDNF antibodies in the SN. These results robustly demonstrate that GDNF is essential for the ECS neuroprotective effect observed in 6-OHDA-injected animals.

Chronic deprivation of TrkB signaling leads to selective late-onset nigrostriatal dopaminergic degeneration

The pathological hallmark of Parkinson's disease (PD) is a selective and progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc). In the vast majority of cases the appearance of PD is sporadic, and its etiology remains unknown. Several postmortem studies demonstrate reduced levels of brain-derived neurotrophic factor (BDNF) in the SNc of PD patients. Application of BDNF promotes the survival of DA neurons in PD animal models. Here we show that BDNF signaling via its TrkB receptor tyrosine kinase is important for survival of nigrostriatal DA neurons in aging brains. Immunohistochemistry revealed that the TrkB receptor was expressed in DA neurons located in the SNc and ventral tegmental area (VTA). However, a significant loss of DA neurons occurred at 12-24 months of age only in the SNc but not in the VTA of TrkB hypomorphic mice in which the TrkB receptor was expressed at a quarter to a third of the normal amount. The neuronal loss was accompanied by a decrease in dopaminergic axonal terminals in the striatum and by gliosis in both the SNc and striatum. Furthermore, nigrostriatal DA neurons in the TrkB mutant mice were hypersensitive to the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a mitochondrial complex I inhibitor that selectively kills DA neurons. These results suggest that BDNF-to-TrkB signaling plays an important role in the long-term maintenance of the nigrostriatal system and that its deficiency may contribute to the progression of PD.

Neuroprotective properties of mildronate, a small molecule, in a rat model of Parkinson's disease

Previously, we have found that mildronate [3-(2,2,2-trimethylhydrazinium) propionate dihydrate], a small molecule with charged nitrogen and oxygen atoms, protects mitochondrial metabolism that is altered by inhibitors of complex I and has neuroprotective effects in an azidothymidine-neurotoxicity mouse model. In the present study, we investigated the effects of mildronate in a rat model of Parkinson's disease (PD) that was generated via a unilateral intrastriatal injection of the neurotoxin 6-hydroxydopamine (6-OHDA). We assessed the expression of cell biomarkers that are involved in signaling cascades and provide neural and glial integration: the neuronal marker TH (tyrosine hydroxylase); ubiquitin (a regulatory peptide involved in the ubiquitin-proteasome degradation system); Notch-3 (a marker of progenitor cells); IBA-1 (a marker of microglial cells); glial fibrillary acidic protein, GFAP (a marker of astrocytes); and inducible nitric oxide synthase, iNOS (a marker of inflammation). The data show that in the 6-OHDA-lesioned striatum, mildronate completely prevented the loss of TH, stimulated Notch-3 expression and decreased the expression of ubiquitin, GFAP and iNOS. These results provide evidence for the ability of mildronate to control the expression of an array of cellular proteins and, thus, impart multi-faceted homeostatic mechanisms in neurons and glial cells in a rat model of PD. We suggest that the use of mildronate provides a protective effect during the early stages of PD that can delay or halt the progression of this neurodegenerative disease.

Novel CDNF/MANF family of neurotrophic factors

Current therapeutic interventions for neurodegenerative diseases alleviate only disease symptoms, while treatments that could stop or reverse actual degenerative processes are not available. Parkinson's disease (PD) is a movement disorder with characteristic degeneration of dopaminergic neurons in the midbrain. Few neurotrophic factors (NTFs) that promote survival, maintenance, and differentiation of affected brain neurons are considered as potential therapeutic agents for the treatment of neurodegenerative diseases. Thus, it is important to search and study new NTFs that could also be used in therapy. In this review, we discuss novel evolutionary conserved family of NTFs consisting of two members in the vertebrates, cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF). Invertebrates, including Drosophila and Caenorhabditis have a single protein homologous to vertebrate CDNF/MANF. Characteristic feature of these proteins is eight structurally conserved cysteine residues, which determine the protein fold. The crystal structure analysis revealed that CDNF and MANF consist of two domains; an amino-terminal saposin-like domain that may interact with lipids or membranes, and a presumably unfolded carboxy-terminal domain that may protect cells against endoplasmic reticulum stress. CDNF and MANF protect midbrain dopaminergic neurons and restore motor function in 6-hydroxydopamine rat model of PD in vivo. In line, Drosophila MANF is needed for the maintenance of dopaminergic neurites and dopamine levels in the fly, suggesting that the function of CDNF/MANF proteins is evolutionary conserved. Future studies will reveal the receptors and mode of action of these novel factors, which are potential therapeutic proteins for the treatment of PD.

Signalling mechanisms underlying development and maintenance of dopamine neurons

Majority of the brain dopamine (DA) neurons reside in a distinct area in the midbrain and project axons into the striatum and frontal cortex to control central nervous system (CNS) functions such as movement, motivation and mood. Age-associated specific loss of DA neurons particularly in the midbrain region substantia nigra pars compacta (SNpc) causes Parkinson disease (PD), an incurable condition characterized by rigidity, involuntary and slowed movement affecting about 1% of people over the age of 60 years. Dopamine neurons appear to be one of the most sensitive types of neurons to both intrinsic and extrinsic stressors in the brain. Here we summarize how transcription factors, growth factors and in particular neurotrophic factors are used to make and maintain DA neurons. We also discuss mechanisms that underlie their specific vulnerability and highlight current state of art in drug development.

Guanosine improves motor behavior, reduces apoptosis, and stimulates neurogenesis in rats with parkinsonism

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc) caused by an abnormal rate of apoptosis. Endogenous stem cells in the adult mammalian brain indicate an innate potential for regeneration and possible resource for neuroregeneration in PD. We previously showed that guanosine prevents apoptosis even when administered 48 hr after the toxin 1-methyl-4-phenylpyridinium (MPP(+)). Here, we induced parkinsonism in rats with a proteasome inhibitor. Guanosine treatment reduced apoptosis, increased tyrosine hydroxylase-positive dopaminergic neurons and expression of tyrosine hydroxylase in the SNc, increased cellular proliferation in the SNc and subventricular zone, and ameliorated symptoms. Proliferating cells in the subventricular zone were nestin-positive adult neural progenitor/stem cells. Fibroblast growth factor-2-expressing cells were also increased by guanosine. Thus, guanosine protected cells from apoptosis and stimulated "intrinsic" adult progenitor/stem cells to become dopaminergic neurons in rats with proteasome inhibitor-induced PD. The cellular/molecular mechanisms underlying these effects may open new avenues for development of novel therapeutics for PD.

Mobilization of neural stem cells and generation of new neurons in 6-OHDA-lesioned rats by intracerebroventricular infusion of liver growth factor

Neural stem cells with self-renewal and multilineage potential persist in the subventricular zone of the adult mammalian forebrain. These cells remain relatively quiescent but, under certain conditions, can be stimulated, giving rise to new neurons. Liver growth factor (LGF) is a mitogen for liver cells that shows biological activity in extrahepatic sites and is useful for neuroregenerative therapies. The aim of this study was to investigate the potential neurogenic activity of LGF in the 6-hydroxydopamine rat model of Parkinson's disease. Proliferation was significantly increased in the subventricular zone and denervated striatum of rats receiving ICV LGF infusions, and 25% of the proliferating cells were doublecortin-positive neurons. Doublecortin-positive cells with the morphology of migrating neuroblasts were also observed in the dorsal and ventral regions of the striatum of LGF-infused animals. Moreover, some newly generated cells were neuronal nuclei-positive mature neurons. LGF also stimulated microglia and induced astrogliosis, both phenomena associated with generation and migration of new neurons in the adult brain. In summary, our study shows that LGF stimulates neurogenesis when applied intraventricularly in 6-hydroxydopamine-lesioned rats. Considering that this factor also promotes neuronal migration into damaged tissue, we propose LGF as a novel factor useful for neuronal replacement in neurodegenerative diseases.

Specific vulnerability of substantia nigra compacta neurons

The specific loss of substantia nigra compacta (SNc) neurons in Parkinson's disease (PD) has been the main driving force in initiating research efforts to unravel the apparent SNc-specific vulnerability. Initially, metabolic constraints due to high dopamine turnover have been the main focus in the attempts to solve this issue. Recently, it has become clear that fundamental differences in the molecular signature are adding to the neuronal vulnerability and provide specific molecular dependencies. Here, the different processes that define the molecular background of SNc vulnerability are summarized.

Death receptors and caspases but not mitochondria are activated in the GDNF- or BDNF-deprived dopaminergic neurons

Neurotrophic factors, including glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF), promote survival of midbrain dopaminergic neurons, but the death pathways activated in the dopaminergic neurons by deprivation of these factors are poorly studied. We show here that deprivation of GDNF or BDNF triggers a novel mitochondria-independent death pathway in the cultured embryonic dopaminergic neurons: cytochrome c was not released from the mitochondria to cytosol, proapoptotic protein Bax was not activated, and overexpressed Bcl-xL did not block the death. Caspases were critically required, because the death was completely blocked by caspase inhibitor BAF [boc-aspartyl(OMe)-fluoromethylketone] and overexpression of dominant-negative mutants of caspase-9, -3, and -7 significantly blocked the death. Also, the death receptor pathway was involved, because blockage of caspase-8 or FADD (Fas-associated protein with death domain), an adapter required for caspase-8 activation, inhibited death induced by GDNF or BDNF deprivation. Ligation of Fas by agonistic anti-Fas antibody induced apoptosis in the GDNF- or BDNF-maintained neurons, and inhibition of Fas by Fas-Fc chimera blocked the death of GDNF- or BDNF-deprived neurons, whereas FAIM(L) (long isoform of Fas apoptosis inhibitory molecule) could control the activity of Fas in the dopaminergic neurons.

Induction of human mesenchymal stem cells into dopamine-producing cells with different differentiation protocols

Several reports have shown that human mesenchymal stem cells (MSCs) are capable of differentiating outside the mesenchymal lineage. We sought to induce MSCs to differentiate into dopamine-producing cells for potential use in autologous transplantation in patients with Parkinson's disease (PD). Following cell culture with various combinations of differentiation agents under serum-free defined conditions, different levels of up-regulation were observed in the protein expression of tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. Further analysis of selected differentiation protocols revealed that the induced cells displayed a neuron-like morphology and expressed markers suggesting neuronal differentiation. In addition, there was an increase in Nurr 1, the dopaminergic transcription factor gene, concomitant with a decrease gamma-aminobutyric acid (GABA)ergic marker expression, suggesting a specific dopaminergic direction. Moreover, the induced cells secreted dopamine in response to depolarization. These results demonstrate the great therapeutic potential of human MSCs in PD.

MANF is widely expressed in mammalian tissues and differently regulated after ischemic and epileptic insults in rodent brain

The mesencephalic astrocyte-derived neurotrophic factor (MANF) has been described as a survival factor for dopaminergic neurons in vitro, but its expression in mammalian tissues is poorly known. MANF and a homologous protein, the conserved dopamine neurotrophic factor (CDNF), form a novel evolutionary conserved family of neurotrophic factors. Here we used in situ hybridization and immunohistochemistry to characterize MANF expression in developing and adult mouse. MANF expression was widespread in the nervous system and non-neuronal tissues. In the brain, relatively high MANF levels were detected in the cerebral cortex, hippocampus and cerebellar Purkinje cells. After status epilepticus, Manf mRNA expression was transiently increased in the dentate granule cell layer of hippocampus, thalamic reticular nucleus and in several cortical areas. In contrast, following global forebrain ischemia changes in Manf expression were widespread in the hippocampal formation and more restricted in cerebral cortex. The widespread expression of MANF together with its evolutionary conserved nature and regulation by brain insults suggest that it has important functions both under normal and pathological conditions in many tissue types.

Assessment of stromal-derived inducing activity in the generation of dopaminergic neurons from human embryonic stem cells

Producing dopaminergic (DA) neurons is a major goal of human embryonic stem cell (hESC) research. DA neurons can be differentiated from hESC by coculture with the mouse PA6 stromal cell line; this differentiation-inducing effect is termed stromal-derived inducing activity (SDIA). The molecular and biochemical nature of SDIA is, however, unknown. Various studies have suggested that SDIA involves either a fixation-resistant component located on the PA6 cell surface or factors secreted into the medium by PA6 cells. To address this question, hESC were cocultured with PA6 cells for 12 days and then further differentiated with sonic hedgehog homolog, fibroblast growth factor-8, and glial cell line-derived neurotrophic factor. After 18 days, 34% of cells were tyrosine hydroxylase (TH)+. When PA6 cells were fixed or irradiated, the number of TH+ cells was decreased by threefold, whereas mitomycin-c treatment of feeder cells decreased the number of TH+ cells by 32%. The neural-inducing effect of PA6 cells, as monitored by beta-III-tubulin expression, was minimally affected by mitomycin-c treatment or fixation but was decreased 50% by irradiation. Medium conditioned by PA6 cells was ineffective in differentiating TH+ cells when used alone. Conditioned medium combined with heparin and/or fixed PA6 cells produced TH+ cell differentiation, although less effectively than PA6 cell coculture. Thus, PA6 cell surface activity is required for neural differentiation of hESC, but secreted factors are required for the specific DA neuron-inducing effect. Disclosure of potential conflicts of interest is found at the end of this article.

RET signaling does not modulate MPTP toxicity but is required for regeneration of dopaminergic axon terminals

Activation of the RET (rearranged during transfection) receptor by glial cell-line-derived neurotrophic factor (GDNF) has been identified as an important differentiation and survival factor for dopaminergic neurons of the midbrain in preclinical experiments. These encouraging results have led to clinical trials of GDNF in patients with Parkinson's disease, which have resulted in conflicting findings. To investigate the potential benefit of Ret-dependent signaling on the challenged dopaminergic system, we tested the effect of tissue-selective ablation of the Ret gene on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity in mice, the most widely used animal model for Parkinson's disease. Ablation of Ret did not modify the MPTP-induced loss of dopaminergic neurons in the substantia nigra pars compacta and the dopaminergic innervation of the striatum at 14 days. However, Ret ablation abolished the regeneration of dopaminergic fibers and terminals, as well as the partial recovery of striatal dopamine concentrations, that was observed in control mice between days 14 and 90 after MPTP treatment. We therefore conclude that RET signaling has no influence on the survival of dopaminergic neurons in the MPTP model of Parkinson's disease but rather facilitates the regeneration of dopaminergic axon terminals.

Protection of dopaminergic neurons by electroconvulsive shock in an animal model of Parkinson’s disease

Electroconvulsive shock (ECS) improves motor function in Parkinson's disease. In rats, ECS stimulates the expression of various factors some of which have been proposed to exert neuroprotective actions. We have investigated the effects of ECS on 6-hydroxydopamine (6-OHDA)-injected rats. Three weeks after a unilateral administration of 6-OHDA, 85-95% nigral dopaminergic neurons are lost. Chronic ECS prevented this cell loss, protect the nigrostriatal pathway (assessed by FloroGold retrograde labeling) and reduce motor impairment in 6-OHDA-treated animals. Injection of 6-OHDA caused loss of expression of glial cell-line derived neurotrophic factor (GDNF) in the substantia nigra. Chronic ECS completely prevented this loss of GDNF expression in 6-OHDA-treated animals. We also found that protected dopaminergic neurons co-express GDNF receptor proteins. These results strongly suggest that endogenous changes in GDNF expression may participate in the neuroprotective mechanism of ECS against 6-OHDA induced toxicity.

Absence of Ret signaling in mice causes progressive and late degeneration of the nigrostriatal system

Support of ageing neurons by endogenous neurotrophic factors such as glial cell line–derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) may determine whether the neurons resist or succumb to neurodegeneration. GDNF has been tested in clinical trials for the treatment of Parkinson disease (PD), a common neurodegenerative disorder characterized by the loss of midbrain dopaminergic (DA) neurons. BDNF modulates nigrostriatal functions and rescues DA neurons in PD animal models. The physiological roles of GDNF and BDNF signaling in the adult nigrostriatal DA system are unknown. We generated mice with regionally selective ablations of the genes encoding the receptors for GDNF (Ret) and BDNF (TrkB). We find that Ret, but not TrkB, ablation causes progressive and adult-onset loss of DA neurons specifically in the substantia nigra pars compacta, degeneration of DA nerve terminals in striatum, and pronounced glial activation. These findings establish Ret as a critical regulator of long-term maintenance of the nigrostriatal DA system and suggest conditional Ret mutants as useful tools for gaining insights into the molecular mechanisms involved in the development of PD.

What does a neuron need to survive? Our body produces its own survival factors for neurons, so-called neurotrophic factors, which have additional roles in neuron differentiation, growth, and function. Declining production of a neurotrophic factor or impaired signal transduction in ageing neurons may contribute to pathological neurodegeneration in humans. Glial cell line–derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) have been suggested as survival factors for midbrain dopaminergic neurons, a group of neurons primarily affected in Parkinson disease.

To investigate the physiological requirements for GDNF and BDNF to establish and maintain an important output pathway of these neurons—the nigrostriatal pathway—in the intact brain, we generated mutant mice with regionally selective ablations of the receptors for these survival factors, Ret (receptor of GDNF and related family members) or TrkB (BDNF receptor). Surprisingly, these mice survive to adulthood and show normal development and maturation of the nigrostriatal system. However, in ageing mice, ablation of Ret leads to a progressive and cell-type–specific loss of substantia nigra pars compacta neurons and their projections into the striatum. Our findings establish Ret and subsequent downstream effectors as critical regulators of long-term maintenance of the nigrostriatal system.

Ret, a receptor for glial cell line-derived neurotrophic factor, selectively regulates long-term maintenance of the nigrostriatal dopaminergic system.

Neural stem cell transplantation and melatonin treatment in a 6-hydroxydopamine model of Parkinson's disease

Melatonin has multiple roles including neuroprotection. Melatonin signaling involves diverse targets including two G-protein-coupled receptors, MT(1) and MT(2), which have both been localized to the nigrostriatal pathway. Previous studies in our laboratory demonstrated preservation of tyrosine hydroxylase immunoreactivity, following chronic treatment with a physiological dose of melatonin, in the 6-hydroxydopamine rat model of Parkinson's disease. Additionally, we reported the presence of the melatonin MT(1) receptor subtype in cultured C17.2 neural stem cells (NSCs). In the present study, we examined the effects of C17.2 NSC transplantation on dopaminergic denervation following 6-hydroxydopamine lesioning in the rat striatum. Moreover, based on our detection of the MT(1) in these cells, we examined the effects of combined C17.2 NSC transplantation and melatonin treatment, following striatal lesioning. Behavioral studies indicated a marked inhibition of apomorphine-induced rotations in lesioned animals that received C17.2 NSC transplantation, melatonin, or the combined regimen. In addition, these treatments resulted in a significant protection of tyrosine hydroxylase immunoreactivity in the striatum and substantia nigra of lesioned animals, when compared with untreated controls. Lesioned animals treated with C17.2 NSCs, melatonin or a combination of both agents exhibited no significant differences in the number of tyrosine hydroxylase-positive cells in the substantia nigra or ventral tegmental area ipsilateral or contralateral to the lesioned striatum. These findings suggest that stem cell therapy and concomitant use of neuroprotective agents such as melatonin could be a viable approach in Parkinson's disease.

Tissue distribution of Ret, GFRalpha-1, GFRalpha-2 and GFRalpha-3 receptors in the human brainstem at fetal, neonatal and adult age

Occurrence and localization of receptor components of the glial cell line-derived neurotrophic factor (GDNF) family ligands, the Ret receptor tyrosine kinase and the GDNF family receptor (GFR) alpha-1 to -3, were examined by immunohistochemistry in the normal human brainstem at fetal, neonatal, and adult age. Immunoreactive elements were detectable at all examined ages with uneven distribution and consistent pattern for each receptor. As a rule, the GFRalpha-1 and GFRalpha-2 antisera produced the most abundant and diffuse tissue labelling. Immunoreactive perikarya were observed within sensory and motor nuclei of cranial nerves, dorsal column nuclei, olivary nuclear complex, reticular formation, pontine nuclei, locus caeruleus, raphe nuclei, substantia nigra, and quadrigeminal plate. Nerve fibers occurred within gracile and cuneate fasciculi, trigeminal spinal tract and nucleus, facial, trigeminal, vestibular and oculomotor nerves, solitary tract, medial longitudinal fasciculus, medial lemniscus, and inferior and superior cerebellar peduncles. Occasionally, glial cells were stained. Age changes were appreciable in the distribution pattern of each receptor. On the whole, in the grey matter, labelled perikarya were more frequently observed in pre- and perinatal than in adult specimens; on the other hand, in discrete regions, nerve fibers and terminals were abundant and showed a plexiform arrangement only in adult tissue; finally, distinct fiber systems in the white matter were immunolabelled only at pre- and perinatal ages. The results obtained suggest the involvement of Ret and GFRalpha receptors signalling in processes subserving both the organization of discrete brainstem neuronal systems during development and their functional activity and maintenance in adult life.

Modulation of tyrosine hydroxylase expression by melatonin in human SH-SY5Y neuroblastoma cells

We have previously reported in vivo preservation of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis, following treatment with physiological doses of melatonin, in a 6-hydroxydopamine model of Parkinson's disease. Based on these findings, we postulated that melatonin would similarly modulate the expression of TH in vitro. Therefore, using human SH-SY5Y neuroblastoma cells which can differentiate into dopaminergic neurons following treatment with retinoic acid, we first examined whether these cells express melatonin receptors. Subsequently, the physiological dose-dependent effects of melatonin on TH expression were examined in both undifferentiated and differentiated cells. The novel detection of the G protein-coupled melatonin MT(1) receptor in SH-SY5Y cells by RT-PCR was confirmed by sequencing and Western blotting. In addition, following treatment of SH-SY5Y cells with melatonin (0.1-100 nM) for 24h, Western analysis revealed a significant increase in TH protein levels. A biphasic response, with significant increases in TH protein at 0.5 and 1 nM melatonin and a reversal at higher doses was seen in undifferentiated cells; whereas in differentiated cells, melatonin was effective at doses of 1 and 100 nM. These findings suggest a physiological role for melatonin in modulating TH expression, possibly via the MT(1) receptor.

Rapid down-regulation of Ret following exposure of dopaminergic neurons to neurotoxins

The survival and functional maintenance of vertebrate neurons depends on the availability of specific neurotrophic factors. We studied the influence of neurotrophic support on responses of dopaminergic neurons to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, a neurotoxin known to damage the nigrostriatal dopaminergic pathway in humans and other mammals. Treatment of mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine caused decreases in levels of Ret, a tyrosine kinase receptor for glial cell line-derived neurotrophic factor (GDNF) in the striatum, under the condition in which tyrosine hydroxylase was moderately decreased and the GDNF family receptor alpha1, another receptor of GDNF that is the ligand-binding subunit, were unaffected. Down-regulation of Ret was also observed in dopamine-producing PC12 cells undergoing apoptosis induced by rotenone, another toxic substance for dopaminergic neurons, while other cellular components were not affected. Ret was also extremely vulnerable to other apoptotic inducing conditions. Taken together, these results indicate that Ret, an important signal molecule in dopaminergic neurons, may be down-regulated in the early stages of neuronal degeneration caused by various neurotoxic substances, and may lead to reduced neurotrophic influences.

Modification of the number and phenotype of striatal dopaminergic cells by carotid body graft

In non-human primates, striatal tyrosine hydroxylase-immunoreactive (TH-ir) cells are increased in number after dopamine depletion and in response to trophic factor delivery. As carotid body cells contain the dopaminotrophic glial cell line-derived neurotrophic factor (GDNF), we evaluated the number, morphology and neurochemistry of these TH-ir cells, in the anterior and posterior striatum of five monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) which received a graft of carotid body cell aggregates (CBCA) (n = 3) or sham surgery (n = 2), and six MPTP-monkeys that were sacrificed 6 months and 3 years after the last MPTP dose [MPTP I (n = 3) and MPTP II (n = 3), respectively]. Three intact monkeys served as controls. A disability rating scale was used for the assessment of parkinsonism in all lesioned animals, both before and after surgery. For the neurochemical examination, tissue sections were double-labelled with antibodies to TH, dopamine transporter, dopa decarboxylase-67, vesicular monoamine transporter 2, glutamic acid decarboxylase -67, calbindin, parvalbumin, calretinin, neuronal nitric oxide synthase and GDNF. Only animals receiving CBCA graft showed a moderate but significant recovery of parkinsonism that persisted 12 months after the graft. The grafted striatum contained the greatest TH-ir cell density (120.4 +/- 10.3 cells/100 mm2), while the control striatum displayed the lowest (15.4 +/- 6.8 cells/100 mm2), and MPTP I, MPTP II and sham-operated monkeys showed a similar intermediate value (66.1 +/- 6.2, 58.3 +/- 17.2 and 57.7 +/- 7.0 cells/100 mm2, respectively). In addition, in the post-commissural striatum, only CBCA graft induced a significant increase in the TH-ir cell density compared to control animals (47.9 +/- 15.9 and 7.9 +/- 3.2, respectively). Phenotypically, TH-ir cells were striatal dopaminergic interneurons. However, in the grafted animals, the phenotype was different from that in control, MPTP and sham-operated monkeys, with the appearance of TH/GDNF-ir cells and the emergence of two TH-ir subpopulations of different size as the two main differentiating features. Our data confirm and extend previous studies demonstrating that striatal CBCA grafts produce a long-lasting motor recovery of MPTP-monkeys along with an increase in the number and phenotype changes of the striatal TH-ir interneurons, probably by the action of the trophic factors contained in carotid body cells. The increased number of striatal TH-ir cells observed in the grafted striatum may contribute to the improvement of parkinsonism observed after the graft.

Tissue distribution of neurturin, persephin and artemin in the human brainstem at fetal, neonatal and adult age

The occurrence of the glial cell line-derived neurotrophic factor (GDNF) family ligands neurturin (NTN), persephin (PSP), and artemin (ART) was examined by immunohistochemistry in the normal human brainstem at pre-, perinatal and adult age. Immunolabelled neurons were unevenly distributed and each trophin had a consistent distribution pattern. As a rule, the NTN antiserum produced the most abundant and diffuse tissue labelling, whereas the lowest density of positive elements was observed after ART immunostaining. Labelling for NTN, PSP, and ART occurred at all examined ages. For each trophin, neuronal perikarya were observed within sensory and motor nuclei of cranial nerves, dorsal column nuclei, olivary nuclear complex, reticular formation, pontine nuclei, locus caeruleus, raphe nuclei, substantia nigra, and quadrigeminal plate. Nerve fibers occurred within gracile and cuneate fasciculi, trigeminal spinal tract and nucleus, oculomotor and facial nerves, solitary tract, vestibular nerve, medial longitudinal fasciculus, medial and lateral lemnisci, and inferior and superior cerebellar peduncles. Age changes were detected in the distribution pattern for each trophin. On the whole, in the grey matter, labelled perikarya were more frequently observed in pre- and perinatal than in adult specimens; on the other hand, in discrete regions, nerve fibers and terminals were abundant and showed a definite arrangement only in adult tissue; finally, distinct fiber systems in the white matter were immunolabelled only at pre- and perinatal ages. The results support the concept of a trophic involvement of NTN, PSP, and ART in the development, functional activity and maintenance of a variety of human brainstem neuronal systems.

The physiological and pharmacological role of basic fibroblast growth factor in the dopaminergic nigrostriatal system

Basic fibroblast growth factor (FGF-2) is a physiological relevant neurotrophic factor in the nigrostriatal system and hence a promising candidate for the establishment of alternative therapeutic strategies in Parkinson's disease. FGF-2 and its high-affinity receptors (FGFR) display an expression in the developing, postnatal, and adult substantia nigra (SN) and in the striatum. Exogenous application promoted survival, neurite outgrowth and protection from neurotoxin-induced death of dopaminergic (DA) neurons both in vitro and in vivo. In animal models of Parkinson's disease, co-transplantation of fetal DA cells with FGF-2 expressing cells increased survival and functional integration of the grafted DA neurons resulting in improved behavioral performance. Analyzing the physiological function of the endogenous FGF-2 system during development and after neurotoxin-induced lesion revealed for the DA neurons of the SNpc a dependence on FGFR3 signaling during development. In addition, in the absence of FGF-2 an increased number of DA neurons was found, whereas enhanced levels of FGF-2 resulted in a reduced DA cell density. Following neurotoxin-induced lesion of DA neurons, FGF-2-deleted mice displayed a higher extent of DA neuron death whereas in FGF-2 overexpressing mice more DA neurons were protected. According to the data, FGF-2 seems to promote DA neuron survival via FGFR3 during development, whereas absence of this ligand could be compensated by other members of the FGF family. In contrast, in the adult organism, FGF-2 cannot be compensated by other factors under lesion conditions suggesting a central role for this molecule in the nigrostriatal system.

How to make a mesodiencephalic dopaminergic neuron

Dopaminergic neurons located in the ventral mesodiencephalon are essential for the control of voluntary movement and the regulation of emotion, and are severely affected in neurodegenerative diseases such as Parkinson's disease. Recent advances in molecular biology and mouse genetics have helped to unravel the mechanisms involved in the development of mesodiencephalic dopaminergic (mdDA) neurons, including their specification, migration and differentiation, as well as the processes that govern axonal pathfinding and their specific patterns of connectivity and maintenance. Here, we follow the developmental path of these neurons with the goal of generating a molecular code that could be exploited in cell-replacement strategies to treat diseases such as Parkinson's disease.

Fibroblast growth factor (FGF)-2 and FGF receptor 3 are required for the development of the substantia nigra, and FGF-2 plays a crucial role for the rescue of dopaminergic neurons after 6-hydroxydopamine lesion

Basic fibroblast growth factor (FGF-2) is involved in the development and maintenance of the nervous system. Exogenous administration of FGF-2 increased dopaminergic (DA) graft survival in different animal models of Parkinson's disease. To study the physiological function of the endogenous FGF-2 system, we analyzed the nigrostriatal system of mice lacking FGF-2, mice overexpressing FGF-2, and FGF-receptor-3 (FGFR3)-deficient mice both after development and after 6-hydroxydopamine lesion. FGFR3-deficient mice (+/-) displayed a reduced number of DA neurons compared with the respective wild type. Whereas absence of FGF-2 led to significantly increased numbers of DA neurons, enhanced amount of the growth factor in mice overexpressing FGF-2 resulted in less tyrosine hydroxylase expression and a reduced DA cell density. The volumes of the substantia nigra were enlarged in both FGF-2(-/-) and in FGF-2 transgenic mice, suggesting an important role of FGF-2 for the establishment of the proper number of DA neurons and a normal sized substantia nigra during development. In a second set of experiments, the putative relevance of endogenous FGF-2 after neurotoxin application was investigated regarding the number of rescued DA neurons after partial 6-OHDA lesion. Interestingly, the results after lesion were directly opposed to the results after development: significantly less DA neurons survived in FGF-2(-/-) mice compared with wild-type mice. Together, the results indicate that FGFR3 is crucially involved in regulating the number of DA neurons. The lack of FGF-2 seems to be (over)compensated during development, but, after lesion, compensation mechanisms fail. The transgenic mice showed that endogenous FGF-2 protects DA neurons from 6-OHDA neurotoxicity.

Survival of DA neurons is independent of CREM upregulation in absence of CREB

cAMP response element binding protein (CREB) and the related factors CREM (cAMP response element modulator) and ATF1 (activation transcription factor 1) are bZIP-domain-containing transcription factors activated through cAMP and other signaling pathways. The disruption of CREB function in developing and mature neurons affects their development and survival when associated with loss of CREM. Since dopaminergic (DA) neurons are affected in several neurological diseases, we generated CREB conditional mutants in DA neurons by using a newly generated transgenic Cre line targeting the dopaminergic system (DATCre). Here we report the generation and analysis of mutant mice lacking CREB in DA neurons (CREB(DATCre) mutants). During adulthood, lack of CREB leads to a partial loss of DA neurons. Since CREM is upregulated in absence of CREB, we have introduced this mutation in a CREM-/- genetic background to assess a compensatory role of CREM. Additional inactivation of CREM does not lead to a more severe phenotype.

Verification of functional AAV-mediated neurotrophic and anti-apoptotic factor expression

The use of viral vectors for gene delivery offer many advantages for both basic research and therapeutic application through the continuous expression of a gene product within a target region. It is vital however that any gene product is correctly expressed in a biologically active form, and this should be confirmed prior to large scale in vivo studies. Using adeno-associated viral (AAV) vectors to direct the expression of either a neurotrophic factor or an anti-apoptotic protein, we have developed a range of in vitro assays to verify functional transgenic protein expression. Brain-derived neurotropic factor (BDNF) activity was confirmed by demonstrating enhanced generation of GABAergic neurons in embryonic (E15) striatal cultures and AAV-mediated glial-derived neurotrophic factor (GDNF) function using an assay for dopaminergic differentiation of embryonic (E14) ventral mesencephalic cultures. To assess functional anti-apoptotic factor expression we designed cell-survival assays, using embryonic cortical cultures to confirm Bcl-x(L) activity and the HT1080 cell-line for X-linked inhibitor of apoptosis protein (XIAP) activity following AAV-mediated expression. This study demonstrates that the use of functional assays provides valuable confirmation of desired biotherapeutic expression prior to extensive investigation with new gene delivery vectors.

GDNF applied to the MPTP-lesioned nigrostriatal system requires TGF-beta for its neuroprotective action

GDNF is a potent neurotrophic factor for nigrostriatal dopaminergic neurons in vitro and in animal models of Parkinson's disease (PD), but has largely failed when tested in therapeutic applications in human PD. We report here that GDNF requires transforming growth factor-beta (TGF-beta) to elicit its neurotrophic activity. Lesioning the mouse nigrostriatal system with MPTP significantly upregulates striatal TGF-beta2 mRNA levels. As expected, GDNF protects against the destructive effects of MPTP, including losses of TH-ir nigral neurons, striatal dopamine and TH-ir fibers. Application of antibodies neutralizing all three TGF-beta isoforms to the MPTP-lesioned striatum abolishes the neurotrophic effect of GDNF. We show that TGF-beta antibodies are not toxic and do not interfere with retrograde transport of iodinated GDNF, suggesting that TGF-beta antibodies do not impair internalization and retrograde trafficking of GDNF. We conclude that striatal TGF-beta may be essential for permitting exogenous GDNF to act as a neuroprotective factor.

Estrogen and the development and protection of nigrostriatal dopaminergic neurons: concerted action of a multitude of signals, protective molecules, and growth factors

The nigrostriatal dopamine system comprises the dopaminergic neurons located in the ventral midbrain, their axonal connections to the forebrain, and their direct cellular target cells in the striatal complex, i.e. GABAergic neurons. The major function of the nigrostriatal dopaminergic unit is the coordination and fine tuning of motor functions at the extrapyramidal level. Numerous biologically active factors including different types of growth factors (neurotrophins, members of the TGFbeta family, IGFs) and peptide/steroid hormones have been identified in the past to be implicated in the regulation of developmental aspects of this neural system. Some of these developmentally active determinants have in addition been found to play a crucial role in the mediation of neuroprotection concerning dopaminergic neurons. Estrogen was identified as such a compound interfering with embryonic neuronal differentiation and cell survival. The physiological mechanisms underlying these effects are very complex and include interactions with other developmental signals (growth factors), inflammatory processes as well as apoptotic events, but also require the activation of nonneuronal cells such as astrocytes. It appears that estrogen is assuming control over or at least influences a multitude of developmental and protective cellular mechanisms rather than taking over the part of a singular protagonist.

Transforming Growth Factor β Is Required for Differentiation of Mouse Mesencephalic Progenitors into Dopaminergic Neurons In Vitro and In Vivo: Ectopic Induction in Dorsal Mesencephalon

Tissue engineering is a prerequisite for cell replacement as therapeutic strategy for degenerative diseases, such as Parkinson's disease. In the present study, we investigated regional identity of mesencephalic neural progenitors and characterized their development toward ventral mesencephalic dopaminergic neurons. We show that neural progenitors from ventral and dorsal mouse embryonic day 12 mesencephalon exhibit regional identity in vitro. Treatment of ventral midbrain dissociated neurospheres with transforming growth factor beta (TGF-beta) increased the number of Nurr1- and tyrosine hydroxylase (TH)-immunoreactive cells, which can be further increased when the spheres are treated with TGF-beta in combination with sonic hedgehog (Shh) and fibroblast growth factor 8 (FGF8). TGF-beta differentiation signaling is TGF-beta receptor-mediated, involving the Smad pathway, as well as the p38 mitogen-activated protein kinase pathway. In vivo, TGF-beta2/TGF-beta3 double-knockout mouse embryos revealed significantly reduced numbers of TH labeled cells in ventral mesencephalon but not in locus coeruleus. TH reduction in Tgfbeta2(-/-)/Tgfbeta3(+/-) was higher than in Tgf-beta2(+/-)/Tgf-beta3(-/-). Most importantly, TGF-beta may ectopically induce TH-immunopositive cells in dorsal mesencephalon in vitro, in a Shh- and FGF8-independent manner. Together, the results clearly demonstrate that TGF-beta2 and TGF-beta3 are essential signals for differentiation of midbrain progenitors toward neuronal fate and dopaminergic phenotype.

BIG news in alcohol addiction: new findings on growth factor pathways BDNF, insulin, and GDNF

In recent years, it has become clear that growth factors are not only critical for the development of the central nervous system (CNS) but may also be important contributors to other neuronal functions in the adult brain. This symposium, presented at the 2005 RSA meeting, discussed evidence to support the hypothesis that alterations in growth factor pathways produce dramatic changes in the effects of alcohol on the CNS. The 4 speakers showed that the behavioral effects of alcohol in the adult are regulated by 3 growth factors, insulin, glial cell line-derived neurotrophic factor (GDNF), and brain-derived neurotrophic factor (BDNF). Dr. Wolf from the Heberlein laboratory presented findings obtained from genetic manipulations in Drosophila melanogaster, demonstrating that the insulin pathway controls sensitivity to the intoxicating effects of alcohol. Marian Logrip from the Ron and Janak laboratories presented evidence obtained in rodents that low concentrations of alcohol increase the expression of BDNF in the brain to regulate alcohol consumption. Dr. Pandey showed that amygdalar BDNF regulates alcohol's anxiolytic effects and preference. Finally, Dr. Janak presented evidence that increases in the expression of GDNF in the midbrain reduce alcohol self-administration in rats.

Strategies to unravel molecular codes essential for the development of meso-diencephalic dopaminergic neurons

Understanding the development of neuronal systems has become an important asset in the attempt to solve complex questions about neuropathology as found in Parkinson's disease, schizophrenia and other complex neuronal diseases. The development of anatomical and functional divergent structures in the brain is achieved by a combination of early anatomical patterning and highly coordinated neuronal migration and differentiation events. Fundamental to the existence of divergent structures in the brain is the early region-specific molecular programming. Neuronal progenitors located along the neural tube can still adapt many different identities. Their exact position in the developing brain, however, determines early molecular specification by region-specific signalling molecules. These signals determine time and region-specific expression of early regulatory genes, leading to neuronal differentiation. Here, we focus on a well-described neuronal group, the meso-diencephalic dopaminergic neurons, of which heterogeneity based on anatomical position could account for the difference in vulnerability of specific subgroups as observed in Parkinson's disease. The knowledge of their molecular coding helps us to understand how the meso-diencephalic dopaminergic system is built and could provide clues that unravel mechanisms associated with the neuropathology in complex diseases such as Parkinson's disease.

Intrastriatal Infusion of Liver Growth Factor Stimulates Dopamine Terminal Sprouting and Partially Restores Motor Function in 6-Hydroxydopamine-lesioned Rats

Liver growth factor (LGF) is a mitogen for liver cells that shows biological activity in extrahepatic sites and may be useful for neuroregenerative therapies. The aim of this work was to investigate the effects of the intrastriatal (IS) infusion of LGF in the 6-hydroxydopamine rat model of Parkinson's disease. Tyrosine hydroxylase-positive innervation was significantly increased in the dopamine-denervated striatum of rats receiving intrastriatal LGF infusions (160 ng/day/rat × 15 days) as compared with a vehicle-infused group. There was no evidence of dopaminergic neurogenesis in the striatum or substantia nigra in any experimental group at the times studied. However, in those animals undergoing IS-LGF infusion for 48 hr, we found a significant increase in both microglial proliferation and in the number of microglial cells that acquired the ameboid morphology. This is characteristic of activated microglia/macrophages that has been reported to play an important role in dopamine terminal sprouting. In summary, our study shows that IS infusion of LGF stimulates the outgrowth of tyrosine hydroxylase-positive terminals in the striatum of 6-hydroxydopamine-treated rats. As apomorphine-induced rotational behavior was also reduced in these animals, we propose LGF as a novel factor that, when delivered to the striatum, may be useful in the treatment of Parkinson's disease.

Striatal expression of GDNF and differential vulnerability of midbrain dopaminergic cells

Glial cell line-derived neurotrophic factor (GDNF) is a member of the transforming growth factor-beta superfamily that when exogenously administrated exerts a potent trophic action on dopaminergic (DA) cells. Although we know a lot about its signalling mechanisms and pharmacological effects, physiological actions of GDNF on the adult brain remain unclear. Here, we have used morphological and molecular techniques, and an experimental model of Parkinson's disease in rats, to investigate whether GDNF constitutively expressed in the adult mesostriatal system plays a neuroprotective role on midbrain DA cells. We found that although all midbrain DA cells express both receptor components of GDNF (GFRalpha1 and Ret), those in the ventral tegmental area (VTA) and rostromedial substantia nigra (SNrm) also contain GDNF but not GDNFmRNA. The levels of GDNFmRNA are significantly higher in the ventral striatum (vSt), the target region of VTA and SNrm cells, than in the dorsal striatum (dSt), the target region of DA cells in the caudoventral substantia nigra (SNcv). After fluoro-gold injection in striatum, VTA and SNrm DA cells show triple labelling for tyrosine hydroxylase, GDNF and fluoro-gold, and after colchicine injection in the lateral ventricle, they become GDNF-immunonegative, suggesting that GDNF in DA somata comes from their striatal target. As DA cells in VTA and SNrm are more resistant than those in SNcv to intracerebroventricular injection of 6-OHDA, as occurs in Parkinson's disease, we can suggest that the fact that they project to vSt, where GDNF expression is significantly higher than in the dSt, is a neuroprotective factor involved in the differential vulnerability of midbrain DA neurons.