Glial cell line-derived neurotrophic factor protects dopaminergic neurons from 6-hydroxydopamine toxicity in vitro

Alpha-Synuclein drives NURR1 and NLRP3 Inflammasome dysregulation in Parkinson's disease: From pathogenesis to potential therapeutic strategies

Parkinson's disease (PD), a progressive neurodegenerative disorder, is characterized by the loss of dopaminergic neurons and pathological aggregation of α-synuclein (α-Syn). Emerging evidence highlights the interplay between genetic susceptibility, neuroinflammation, and transcriptional dysregulation in driving PD pathogenesis. This review brings together the latest information on three important players: α-Syn, the transcription factor Orphan nuclear receptor (NURR1), and the NOD-like receptor 3 (NLRP3) inflammasome. Pathogenic α-syn aggregates cause damage to neurons by disrupting mitochondria and lysosomes and spreading in a way similar to prion proteins. They also turn on the NLRP3 inflammasome, which is a key player in neuroinflammation. NLRP3-driven release of pro-inflammatory cytokines exacerbates neurodegeneration and creates a self-sustaining inflammatory milieu. Meanwhile, reduced NURR1 activity, a pivotal modulator of dopaminergic neuron survival and development, exposes neurons to oxidative stress, neuroinflammation, and α-Syn toxicity, hence exacerbating disease progression. So, targeting this trio exhibits transformative potential against PD pathogenesis.

Current Experimental Studies of Gene Therapy in Parkinson's Disease

Parkinson's disease (PD) was characterized by late-onset, progressive dopamine neuron loss and movement disorders. The progresses of PD affected the neural function and integrity. To date, most researches had largely addressed the dopamine replacement therapies, but the appearance of L-dopa-induced dyskinesia hampered the use of the drug. And the mechanism of PD is so complicated that it's hard to solve the problem by just add drugs. Researchers began to focus on the genetic underpinnings of Parkinson's disease, searching for new method that may affect the neurodegeneration processes in it. In this paper, we reviewed current delivery methods used in gene therapies for PD, we also summarized the primary target of the gene therapy in the treatment of PD, such like neurotrophic factor (for regeneration), the synthesis of neurotransmitter (for prolong the duration of L-dopa), and the potential proteins that might be a target to modulate via gene therapy. Finally, we discussed RNA interference therapies used in Parkinson's disease, it might act as a new class of drug. We mainly focus on the efficiency and tooling features of different gene therapies in the treatment of PD.

Protection of cultured dopamine neurons from MPP(+) requires a combination of neurotrophic factors

Parkinson's disease is a progressive neurodegenerative disorder, caused in part by the loss of dopamine (DA) neurons in the substantia nigra (SN). Neurotrophic factors have been shown to increase the basal survival of DA neurons in vitro, as well as to protect the neurons from some toxins under certain in vitro conditions and in animal models. Although these factors have often been tested individually, they have rarely been studied in combinations. We therefore examined the effect of such combinations after acute exposure to the toxin 1-methyl-4-phenylpyridinium (MPP(+) ) using dissociated postnatal rat midbrain cultures isolated from SN and ventral tegmental area (VTA). We found that significant loss of DA neurons in the SN occurred with an LC50 of between 1 and 10 μm, whereas the LC50 of DA neurons from the VTA was approximately 1000-fold higher. We did not observe neuroprotection against MPP(+) by individual exposure to glial cell-line derived neurotrophic factor (GDNF), brain derived neurotrophic factor (BDNF), transforming growth factor beta (TGFβ), basic fibroblast growth factor (FGF-2) or growth/differentiation factor 5 (GDF5) at concentrations of 100 or 500 ng/mL. Combinations of two, three or four neurotrophic factors were also ineffective. However, when the SN cultures were exposed to a combination of all five neurotrophic factors, each at a concentration of 100 ng/mL, we observed a 30% increase in DA neuron survival in the presence of 10 and 500 μm MPP(+) . These results may be relevant to the use of neurotrophic factors as therapeutic treatments for Parkinson's disease.

Current Neurogenic and Neuroprotective Strategies to Prevent and Treat Neurodegenerative and Neuropsychiatric Disorders

The adult central nervous system is commonly known to have a very limited regenerative capacity. The presence of functional stem cells in the brain can therefore be seen as a paradox, since in other organs these are known to counterbalance cell loss derived from pathological conditions. This fact has therefore raised the possibility to stimulate neural stem cell differentiation and proliferation or survival by either stem cell replacement therapy or direct administration of neurotrophic factors or other proneurogenic molecules, which in turn has also originated regenerative medicine for the treatment of otherwise incurable neurodegenerative and neuropsychiatric disorders that take a huge toll on society. This may be facilitated by the fact that many of these disorders converge on similar pathophysiological pathways: excitotoxicity, oxidative stress, neuroinflammation, mitochondrial failure, excessive intracellular calcium and apoptosis. This review will therefore focus on the most promising achievements in promoting neuroprotection and neuroregeneration reported to date.

Viral vector delivery of neurotrophic factors for Parkinson's disease therapy

Parkinson's disease (PD) is a neurodegenerative disorder characterised by the progressive loss of midbrain dopaminergic neurons, which causes motor impairments. Current treatments involve dopamine replacement to address the disease symptoms rather than its cause. Factors that promote the survival of dopaminergic neurons have been proposed as novel therapies for PD. Several dopaminergic neurotrophic factors (NTFs) have been examined for their ability to protect and/or restore degenerating dopaminergic neurons, both in animal models and in clinical trials. These include glial cell line-derived neurotrophic factor, neurturin, cerebral dopamine neurotrophic factor and growth/differentiation factor 5. Delivery of these NTFs via injection or infusion to the brain raises several practical problems. A new delivery approach for NTFs involves the use of recombinant viral vectors to enable long-term expression of these factors in brain cells. Vectors used include those based on adenoviruses, adeno-associated viruses and lentiviruses. Here we review progress to date on the potential of each of these four NTFs as novel therapeutic strategies for PD, as well as the challenges that have arisen, from pre-clinical analysis to clinical trials. We conclude by discussing recently-developed approaches to optimise the delivery of NTF-carrying viral vectors to the brain.

Neurotrophic factors: from neurodevelopmental regulators to novel therapies for Parkinson's disease

Neuroprotection and neuroregeneration are two of the most promising disease-modifying therapies for the incurable and widespread Parkinson's disease. In Parkinson's disease, progressive degeneration of nigrostriatal dopaminergic neurons causes debilitating motor symptoms. Neurotrophic factors play important regulatory roles in the development, survival and maintenance of specific neuronal populations. These factors have the potential to slow down, halt or reverse the loss of nigrostriatal dopaminergic neurons in Parkinson's disease. Several neurotrophic factors have been investigated in this regard. This review article discusses the neurodevelopmental roles and therapeutic potential of three dopaminergic neurotrophic factors: glial cell line-derived neurotrophic factor, neurturin and growth/differentiation factor 5.

Challenges and promises in the development of neurotrophic factor-based therapies for Parkinson's disease

Parkinson's disease (PD) is a chronic movement disorder typically coupled to progressive degeneration of dopaminergic neurons in the substantia nigra (SN). The treatments currently available are satisfactory for symptomatic management, but the efficacy tends to decrease as neuronal loss progresses. Neurotrophic factors (NTFs) are endogenous proteins known to promote neuronal survival, even in degenerating states. Therefore, the use of these factors is regarded as a possible therapeutic approach, which would aim to prevent PD or to even restore homeostasis in neurodegenerative disorders. Intriguingly, although favorable results in in vitro and in vivo models of the disease were attained, clinical trials using these molecules have failed to demonstrate a clear therapeutic benefit. Therefore, the development of animal models that more closely reproduce the mechanisms known to underlie PD-related neurodegeneration would be a major step towards improving the capacity to predict the clinical usefulness of a given NTF-based approach in the experimental setting. Moreover, some adjustments to the design of clinical trials ought to be considered, which include recruiting patients in the initial stages of the disease, improving the efficacy of the delivery methods, and combining synergetic NTFs or adding NTF-boosting drugs to the already available pharmacological approaches. Despite the drawbacks on the road to the use of NTFs as pharmacological tools for PD, very relevant achievements have been reached. In this article, we review the current status of the potential relevance of NTFs for treating PD, taking into consideration experimental evidence, human observational studies, and data from clinical trials.

Increased antiparkinson efficacy of the combined administration of VEGF- and GDNF-loaded nanospheres in a partial lesion model of Parkinson's disease

Current research efforts are focused on the application of growth factors, such as glial cell line-derived neurotrophic factor (GDNF) and vascular endothelial growth factor (VEGF), as neuroregenerative approaches that will prevent the neurodegenerative process in Parkinson’s disease. Continuing a previous work published by our research group, and with the aim to overcome different limitations related to growth factor administration, VEGF and GDNF were encapsulated in poly(lactic-co-glycolic acid) nanospheres (NS). This strategy facilitates the combined administration of the VEGF and GDNF into the brain of 6-hydroxydopamine (6-OHDA) partially lesioned rats, resulting in a continuous and simultaneous drug release. The NS particle size was about 200 nm and the simultaneous addition of VEGF NS and GDNF NS resulted in significant protection of the PC-12 cell line against 6-OHDA in vitro. Once the poly(lactic-co-glycolic acid) NS were implanted into the striatum of 6-OHDA partially lesioned rats, the amphetamine rotation behavior test was carried out over 10 weeks, in order to check for in vivo efficacy. The results showed that VEGF NS and GDNF NS significantly decreased the number of amphetamine-induced rotations at the end of the study. In addition, tyrosine hydroxylase immunohistochemical analysis in the striatum and the external substantia nigra confirmed a significant enhancement of neurons in the VEGF NS and GDNF NS treatment group. The synergistic effect of VEGF NS and GDNF NS allows for a reduction of the dose by half, and may be a valuable neurogenerative/neuroreparative approach for treating Parkinson’s disease.

Neurotrophic and neuroprotective efficacy of intranasal GDNF in a rat model of Parkinson's disease

Glial cell line-derived neurotrophic factor (GDNF) exerts neurotrophic and neuroprotective effects on substantia nigra (SN) dopamine neurons and has great therapeutic potential for Parkinson's disease (PD). Hindering this potential is the fact that GDNF cannot cross the blood-brain barrier. The aim of this study was to assess the effects of GDNF administered by the intranasal route in normal rats, and in the unilateral 6-hydroxydopamine (6-OHDA) model of PD. In the first study, rats received single intranasal doses of 50-μg GDNF in phosphate-buffered saline (PBS) or cationic liposomes, but no 6-OHDA. In the second study, rats were nasally administered 10, 50 or 150 μg of GDNF in PBS or cationic liposomes 1h before injection of 6-OHDA. All groups were sacrificed 3-4 weeks later. Both intranasal GDNF treatments induced a neurotrophic effect in the SN insofar as the number of tyrosine hydroxylase (TH)-positive neurons was significantly higher than in controls given intranasal PBS liposomes. Dopamine cell counts were also higher in the intact SN of 6-OHDA-lesioned rats compared to controls given PBS liposomes. Most importantly, intranasal GDNF provided significant neuroprotective efficacy indicated by greater TH immunostaining density in the lesioned versus intact SN of rats given single 50-μg doses of GDNF in PBS, or 150-μg doses of liposomal GDNF, compared to lesioned rats given PBS liposomes. Three 50-μg doses given at daily intervals (1 day before, 1h before, and 1 day after 6-OHDA) provided even greater protection than single 150-μg doses. Multiple doses at short intervals may therefore provide greater neuroprotection than single bolus doses. These results demonstrate both a neurotrophic effect of intranasal GDNF in the intact SN as well as neuroprotective efficacy in the unilateral 6-OHDA model, supporting pursuit of this approach as a potential treatment for PD.

Roles for the TGFβ superfamily in the development and survival of midbrain dopaminergic neurons

The adult midbrain contains 75% of all dopaminergic neurons in the CNS. Within the midbrain, these neurons are divided into three anatomically and functionally distinct clusters termed A8, A9 and A10. The A9 group plays a functionally non-redundant role in the control of voluntary movement, which is highlighted by the motor syndrome that results from their progressive degeneration in the neurodegenerative disorder, Parkinson's disease. Despite 50 years of investigation, treatment for Parkinson's disease remains symptomatic, but an intensive research effort has proposed delivering neurotrophic factors to the brain to protect the remaining dopaminergic neurons, or using these neurotrophic factors to differentiate dopaminergic neurons from stem cell sources for cell transplantation. Most neurotrophic factors studied in this context have been members of the transforming growth factor β (TGFβ) superfamily. In recent years, an intensive research effort has focused on understanding the function of these proteins in midbrain dopaminergic neuron development and their role in the molecular architecture that regulates the development of this brain region, with the goal of applying this knowledge to develop novel therapies for Parkinson's disease. In this review, the current evidence showing that TGFβ superfamily members play critical roles in the regulation of midbrain dopaminergic neuron induction, differentiation, target innervation and survival during embryonic and postnatal development is analysed, and the implications of these findings are discussed.

NURR1 in Parkinson disease--from pathogenesis to therapeutic potential

In Parkinson disease (PD), affected midbrain dopamine (DA) neurons lose specific dopaminergic properties before the neurons die. How the phenotype of DA neurons is normally established and the ways in which pathology affects the maintenance of cell identity are, therefore, important considerations. Orphan nuclear receptor NURR1 (NURR1, also known as NR4A2) is involved in the differentiation of midbrain DA neurons, but also has an important role in the adult brain. Emerging evidence indicates that impaired NURR1 function might contribute to the pathogenesis of PD: NURR1 and its transcriptional targets are downregulated in midbrain DA neurons that express high levels of the disease-causing protein α-synuclein. Clinical and experimental data indicate that disrupted NURR1 function contributes to induction of DA neuron dysfunction, which is seen in early stages of PD. The likely involvement of NURR1 in the development and progression of PD makes this protein a potentially interesting target for therapeutic intervention.

Trophic factor gene therapy for Parkinson's disease

Parkinson's disease (PD) is a chronic and progressive neurodegenerative movement disorder for which there is presently no cure. Pharmacological remedies targeting the dopaminergic network are relatively effective at ameliorating motor deficits, especially in the early stages of the disease, but none of these therapies are curative and many generate their own problems. Recent advances in PD research have demonstrated that gene delivery of trophic factors, glial cell line-derived neurotrophic factor (GDNF) and neurturin, in particular, can provide structural and functional recovery in rodent and nonhuman primate models of PD. Similar success has been gleaned in open-label clinical trials, although this has yet to be realized in double-blinded analyses. This work reviews the field of trophic factor gene delivery for PD.

Brain targeting of nerve growth factor using poly(butyl cyanoacrylate) nanoparticles

The nerve growth factor (NGF) is essential for the survival of both peripheral ganglion cells and central cholinergic neurons in the basal forebrain. The accelerated loss of central cholinergic neurons during Alzheimer's disease may be a determinant cause of dementia, and this observation may suggest a possible therapeutic benefit from treatment with NGF. In recent years, convincing data have been published involving neurotrophic factors for the modulation of dopaminergic transmission within the brain and concerning the ability of NGF to prevent the degeneration of dopaminergic neurons. In this connection, the administration of NGF may slow down the progression of Parkinson's disease. However, NGF, as well as other peptidic neurotrophic factors, does not significantly penetrate the blood-brain barrier (BBB) from the circulation. Therefore, any clinical usefulness of NGF as a potential CNS therapy will depend on the use of a suitable carrier system that enhances its transport through the BBB. The present study investigates brain delivery of NGF adsorbed on poly(butyl cyanoacrylate) (PBCA) nanoparticles coated with polysorbate 80 and the pharmacological efficacy of this delivery system in the model of acute scopolamine-induced amnesia in rats as well as in the model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinsonian syndrome. As shown by the passive avoidance reflex (PAR) test, the intravenous administration of the nanoparticle-bound NGF successfully reversed scopolamine-induced amnesia and improved recognition and memory. This formulation also demonstrated a significant reduction of the basic symptoms of Parkinsonism (oligokinesia, rigidity, tremor). In addition, the efficient transport of NGF across the BBB was confirmed by direct measurement of NGF concentrations in the murine brain. These results demonstrate that the PBCA nanoparticles coated with polysorbate 80 are an effective carrier system for the transport of NGF to the central nervous system across the BBB following intravenous injection. This approach may improve the NGF-based therapy of age-related neurodegenerative diseases.

Antiparkinsonian effect of nerve growth factor adsorbed on polybutylcyanoacrylate nanoparticles coated with polysorbate-80

The study examined the antiparkinsonian effect of nerve growth factor adsorbed on the surface of polybutylcyanoacrylate nanoparticles coated with polysorbate-80 surfactant. The parkinsonian syndrome in C57B1/6 mice was provoked by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The basic symptoms of the parkinsonian syndrome decreased under the action of the nerve growth factor adsorbed on nanoparticles coated with polysorbate-80, which was seen from decreased rigidity and increased locomotor activity compared to control mice receiving with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine alone. This effect of nerve growth factor on nanoparticles persisted after 7 and 21 days after single injection of the neurotoxin. These data attest to the possibility of using nanoparticles prepared from amphiphilic polymers and coated with polysorbate-80 for the delivery of nerve growth factor into the brain during systemic treatment.

Some aspects of astroglial functions and aluminum implications for neurodegeneration

The present decade had witnessed an unprecedented attention focused on glial cells as a result of their unusual physiological roles that are being unraveled. It is now known that, rather than being a mere supporter of neurons, astroglia are actively involved in their modulation. The aluminum hypothesis seems to have been laid to rest, probably due to contradictory epidemiological reports on it as a causative factor of neurodegenerative diseases. Surprisingly, newer scientific evidences continue to appear and recent findings have implicated astrocytes as the principal target of its toxic action. In view of the likely detrimental effects of the interaction between these two infamous partners in neuroscience on neurons and nervous system, we have reviewed some aspects of glia-neuron interaction and discussed the implications of aluminum-impaired astrocytic functions on neurodegeneration. Because sporadic causes still account for the majority of the neurodegenerative diseases of which Alzheimer's disease is the most prominent, it has been suggested that neurotoxicologists should not relent in screening for the environmental agents, such as aluminum, and that considerable attention should be given to glial cells in view of the likely implications of environmental toxicants on their never-imagined newly reported roles in the central nervous system (CNS).

Erythropoietin and GDNF enhance ventral mesencephalic fiber outgrowth and capillary proliferation following neural transplantation in a rodent model of Parkinson's disease

Low dopaminergic cell survival and suboptimal fiber reinnervation are likely major contributing factors for the limited benefits of neural transplantation in Parkinson's disease (PD) patients. Glial cell lined-derived neurotrophic factor (GDNF) has been shown to enhance dopaminergic cell survival and fiber outgrowth of the graft site as well as promote behavioral recovery in rodent models of PD, while erythropoietin (EPO) can produce dopaminergic neuroprotective effects against 6-hydroxydopamine (6-OHDA) exposure on cultured neurons and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice. The aim of this study was to determine if fetal ventral mesencephalic (FVM) tissue exposed to hibernation media containing a combination of GDNF and EPO could enhance dopaminergic graft survival, striatal reinnervation and functional recovery in a 6-OHDA rodent model of PD. FVM tissue was dissected from 14-day-old rat fetuses and placed for 6 days in hibernation media alone, and in hibernation media that received either a daily administration of GDNF, EPO or a combination of GDNF and EPO. Following hibernation, FVM cells were transplanted as a single cell suspension into the striatum of unilateral 6-OHDA-lesioned rats. Rotational behavioral assessment revealed animals that received FVM tissue exposed to GDNF, EPO or the combination of both drugs had accelerated functional recovery. Immunohistochemical and stereological assessment revealed a significant increase in graft fiber density and angiogenesis into the graft when compared with control. These findings suggest that the hibernation of FVM tissue in a combination of GDNF and EPO can enhance graft efficacy and may have important implications for tissue preparation protocols for clinical neural transplantation in PD.

Characterization of organotypic ventral mesencephalic cultures from embryonic mice and protection against MPP toxicity by GDNF

We characterized organotypic ventral mesencephalic (VM) cultures derived from embryonic day 12 (E12) mice (CBL57/bL6) in terms of number of dopaminergic neurons, cell soma size and dopamine production in relation to time in vitro and tested the effects of 1-methyl-4-phenylpyridinium (MPP(+)) and glial derived neurotrophic factor (GDNF) to validate this novel culture model. Dopamine production and dopaminergic neuron soma size increased dramatically with time in vitro, whereas the number of dopamine neurons declined by approximately 30% between week 1 and week 2, which was further reduced after week 4. GDNF treatment (100 ng/mL) increased dopaminergic neuron soma size (up to 43%) and DOPAC production (approximately three-fold), but not the number of dopamine neurons in control cultures. One-week-old cultures were more vulnerable to MPP(+), than three-week-old cultures. The EC(50) for dopamine depletion after 2 days exposure and 15 days of recovery were 0.6 and 7 microm, respectively. Both pre-treatment and post-treatment with GDNF are important to obtain maximal protection against MPP(+) toxicity. In one-week-old cultures (5 microm MPP(+), 2 days) GDNF provided potent neuroprotection with dopamine contents reaching control levels and number of tyrosine hydroxylase (TH)(+) cells up to 80% of control, but in three-week-old cultures (10 microm MPP(+), 2 days) the protective potential of GDNF was markedly reduced. Long recovery periods after MPP(+) exposure are required to distinguish between reversible or irreversible toxic and/or trophic effects.

Development of the dopaminergic neurons in the rodent brainstem

The loss of dopaminergic (DA) neurons in the ventral midbrain is the principal cause of Parkinson's disease. The search for candidate molecules that promote the genesis and survival capacities of DA neurons is a major area of investigation and hope. A better characterization of the developmental pathways that govern the specification, differentiation, and survival of these neurons will be essential in devising therapies aimed to rescue or replace midbrain DA neurons in Parkinson's patients. In this brief review, we will discuss the major steps in the normal development of midbrain DA neurons.

Interleukin-6 induces glutathione in hippocampal cells

The cytokine interleukin-6 (IL-6) increases the levels of the physiological antioxidant glutathione (GSH) in peripheral organ systems such as liver tissue. Only little evidence exists about the actions of this cytokine on GSH in neuronal cell systems despite its possible neuroprotective effects. Therefore, we here characterized the effects of IL-6 on GSH in clonal hippocampal HT22 cells and in rat neuronal primary hippocampal cells. Our results demonstrate significant increases of GSH under most conditions after treatment with IL-6 in a time range of 1 to 48 h (HT22 cells) and 1 to 72 h (primary rat neuronal hippocampal cells). Further studies with an IL-6 antibody strongly support the specificity of the effects. These results suggest that IL-6 plays a substantial role in the regulation of GSH in hippocampal cells.

Neurotrophic and neuroprotective effects of the neuregulin glial growth factor-2 on dopaminergic neurons in rat primary midbrain cultures

Glial growth factor-2 (GGF2) and other neuregulin (NRG) isoforms have been shown to play important roles in survival, migration, and differentiation of certain neural and non-neural cells. Because midbrain dopamine (DA) cells express the NRG receptor, ErbB4, the present study examined the potential neurotrophic and/or neuroprotective effects of GGF2 on cultured primary dopaminergic neurons. Embryonic day 14 rat mesencephalic cell cultures were maintained in serum-free medium and treated with GGF2 or vehicle. The number of tyrosine hydroxylase-positive (TH+) neurons and high-affinity [3H]DA uptake were assessed at day in vitro (DIV) 9. Separate midbrain cultures were treated with 100 ng/mL GGF2 on DIV 0 and exposed to the catecholamine-specific neurotoxin 6-hydroxydopamine (6-OHDA) on DIV 4. GGF2 treatment significantly increased DA uptake, the number of TH+ neurons, and neurite outgrowth when compared to the controls in both the serum-free and the 6-OHDA-challenged cultures. Furthermore, three NRG receptors were detected in the midbrain cultures by western blot analysis. Immunostaining for glial fibrillary acidic protein revealed that GGF2 also weakly promoted mesencephalic glial proliferation in the midbrain cultures. These results indicate that GGF2 is neurotrophic and neuroprotective for developing dopaminergic neurons and suggest a role for NRGs in repair of the damaged nigrostriatal system that occurs in Parkinson's disease.

Differential effects of growth/differentiation factor 5 and glial cell line-derived neurotrophic factor on dopaminergic neurons and astroglia in cultures of embryonic rat midbrain

Parkinson's disease is characterized by the progressive degeneration of midbrain dopaminergic neurons. Several studies have examined the effects of the dopaminergic neurotrophins growth/differentiation factor 5 (GDF5) and glial cell line-derived neurotrophic factor (GDNF) on these neurons in vitro. However, there is little information regarding their effects on astroglial cells. Here, the effects of GDF5 and GDNF on dopaminergic neuronal and astroglial survival and differentiation in embryonic rat midbrain cultures were examined. Both GDF5 and GDNF enhanced the survival and differentiation of dopaminergic neurons. GDF5 significantly increased the survival of astroglial cells, whereas GDNF had no significant effect on these cells. The possible involvement of astroglia in the dopaminergic neurotrophic effect induced by GDF5 was investigated by examining the effect of GDF5 on the survival of dopaminergic neurons in glia-depleted midbrain cultures. There was no significant difference between the survival of dopaminergic neurons in glia-depleted cultures treated with GDF5 and that in mixed cell cultures treated with GDF5, suggesting that GDF5 acts directly on dopaminergic neurons in exerting its neurotrophic effect. GDF5 and GDNF have been established as potent neurotrophic factors for dopaminergic neurons. However, the effects of adding a combination of these neurotrophins to midbrain cultures have not been previously examined. The present study found that combined treatment with GDF5 and GDNF significantly increased the survival of dopaminergic neurons in cultures compared with that in cultures treated with either neurotrophin alone. This was an additive effect, indicating that these neurotrophins act on separate subpopulations of dopaminergic neurons.

Early transplantation of an encapsulated glial cell line—derived neurotrophic factor—producing cell demonstrating strong neuroprotective effects in a rat model of Parkinson disease

Object. Glial cell line—derived neurotrophic factor (GDNF) has been shown to confer neuroprotective effects on dopaminergic neurons. The authors investigated the effects of GDNF on 6-hydroxydopamine (6-OHDA)—treated dopaminergic neurons in vitro and in vivo.

Methods. First, the authors examined how 1, 10, or 100 ng/ml of GDNF, administered to cells 24 hours before, simultaneously with, or 2 or 4 hours after 6-OHDA was added, affected dopaminergic neurons. In a primary culture of E14 murine ventral mesencephalic neurons, earlier treatment with the higher dosage of GDNF suppressed 6-OHDA—induced loss of dopaminergic neurons better than later treatment. Next, the authors examined whether continuous infusion of GDNF at earlier time points would demonstrate a greater neuroprotective effect in a rat model of Parkinson disease (PD). They established a human GDNF-secreting cell line, called BHK-GDNF, and encapsulated the cells into hollow fibers. The encapsulated cells were unilaterally implanted into the striatum of adult rats 1 week before; simultaneously with; or 1, 2, or 4 weeks after 6-OHDA was given to induce lesions of the same striatum. With the earlier transplantation of a BHK-GDNF capsule, there was a significant reduction in the number of amphetamine-induced rotations displayed by the animals. Rats that had received earlier implantation of BHK-GDNF capsules displayed more tyrosine hydroxylase—positive neurons in the substantia nigra pars compacta and a tendency for glial proliferation in the striatum.

Conclusions. These neuroprotective effects may be related to glial proliferation and signaling via the GDNF receptor α1. The results of this study support a role for this grafting technique in the treatment of PD.

Effects of 6-hydroxydopamine on primary cultures of substantia nigra: specific damage to dopamine neurons and the impact of glial cell line-derived neurotrophic factor

6-Hydroxydopamine (6-OHDA)-induced loss of dopamine (DA) neurons has served to produce an animal model of DA neuron loss in Parkinson's disease. We report here the use of 6-OHDA to produce an in vitro model of this phenomena using dissociated cultures prepared from neonatal rat mesencephalon. Cultures were exposed to 6-OHDA (40-100 microm, 15 min) in an antioxidant medium, and DA and GABA neurons evaluated by immunocytochemistry. 6-OHDA induced morphological and biochemical signs of cell death in DA neurons within 3 h, followed by loss of tyrosine hydroxylase immunoreactive neurons within 2 days. In substantia nigra (SN) cultures, DA neurons were much more affected by 6-OHDA than were GABA neurons. In contrast, DA neurons from the ventral tegmental area were only lost at higher, non-specific concentrations of 6-OHDA. The effects of 6-OHDA on nigral DA neurons were blocked by inhibitors of high affinity DA transport and by z-DEVD-fmk (150 microm), a caspase inhibitor. Glial cell line-derived neurotrophic factor (GDNF) treatment reduced TUNEL labeling 3 h after 6-OHDA exposure, but did not prevent loss of DA neurons at 48 h. Thus, 6-OHDA can selectively destroy DA neurons in post-natal cultures of SN, acting at least in part by initiating caspase-dependent apoptosis, and this effect can be attenuated early but not late by GDNF.

Generation of embryonic stem cells and transgenic mice expressing green fluorescence protein in midbrain dopaminergic neurons

We have generated embryonic stem (ES) cells and transgenic mice with green fluorescent protein (GFP) inserted into the Pitx3 locus via homologous recombination. In the central nervous system, Pitx3-directed GFP was visualized in dopaminergic (DA) neurons in the substantia nigra and ventral tegmental area. Live primary DA neurons can be isolated by fluorescence-activated cell sorting from these transgenic mouse embryos. In culture, Pitx3-GFP is coexpressed in a proportion of ES-derived DA neurons. Furthermore, ES cell-derived Pitx3-GFP expressing DA neurons responded to neurotrophic factors and were sensitive to DA-specific neurotoxin N-4-methyl-1, 2, 3, 6-tetrahydropyridine. We anticipate that the Pitx3-GFP ES cells could be used as a powerful model system for functional identification of molecules governing mDA neuron differentiation and for preclinical research including pharmaceutical drug screening and transplantation. The Pitx3 knock-in mice, on the other hand, could be used for purifying primary neurons for molecular studies associated with the midbrain-specific DA phenotype at a level not previously feasible. These mice would also provide a useful tool to study DA fate determination from embryo- or adult-derived neural stem cells.

Neuroprotective effects of vascular endothelial growth factor (VEGF) upon dopaminergic neurons in a rat model of Parkinson's disease

Vascular endothelial growth factor (VEGF) has previously been shown to display neuroprotective effects following ischemia, suggesting that VEGF may potentially be applied as a neuroprotective agent for the treatment of other neurological diseases. In this study, we investigated the neuroprotective capacity of VEGF in a model of Parkinson's disease. VEGF was found to be neuroprotective against cell death of primary E14 murine ventral mesencephalic neurons induced by 6-hydroxydopamine (6-OHDA) treatment in vitro. Further, rats receiving a continuous infusion of VEGF into the striatum via encapsulated hVEGF-secreting cells (baby hamster kidney-VEGF) displayed a significant decrease in amphetamine-induced rotational behavior and a significant preservation of tyrosine hydroxylase-positive neurons and fibers compared with control animals. VEGF likely functions via direct mechanisms by signaling through the neuropilin receptor expressed upon dopaminergic neurons in response to 6-OHDA treatment. Further, VEGF is likely to promote neuroprotection indirectly by activating the proliferation of glia and by promoting angiogenesis. Our results support a potential neuroprotective role for VEGF in the treatment of Parkinson's disease.

Effect of 6-hydroxydopamine on striatal GDNF and nigral GFRα1 and RET mRNAs in the adult rat

Exogenous GDNF as well as vectors containing the gene for this trophic factor has been shown to be neuroprotective in animal models of Parkinson's disease. We therefore investigated whether changes in striatal GDNF protein and nigral mRNA levels of its co-receptors GFRalpha1 and RET occur in response to lesions of dopamine (DA) neurons and examined the temporal profile of these changes as they relate to the loss of dopaminergic markers. Rats were lesioned with 6-hydroxydopamine and sacrificed 3 h to 60 days post-infusion. DA tissue levels in the striatum and tyrosine hydroxylase immunoreactivity in the substantia nigra (SN) and ventral tegmental area (VTA) were used to determine the size of the lesions. GDNF protein was measured in the striatum using radioimmunocytochemistry. In situ hybridization was used to determine alterations in the mRNAs of RET and GFRalpha1 in the SN and VTA. We observed no persistent changes in GDNF protein in the striatum in response to 6-hydroxydopamine over the 60-day observation period, suggesting that compensatory changes in this trophic factor do not occur in response to injury. Dramatic decreases in RET and GFRalpha1 were observed in both SN and VTA that were generally correlated with the loss of TH protein and striatal DA content, strongly suggesting that these receptors are located on DA neurons and that the protective effect of GDNF reflects a direct action of the trophic factor on these neurons.

Effects of GDNF on 6-OHDA-induced death in a dopaminergic cell line: modulation by inhibitors of PI3 kinase and MEK

Parkinson's disease is a neurodegenerative disorder associated with the selective death of dopaminergic neurons. Glial cell line-derived neurotrophic factor (GDNF) can protect dopaminergic neurons in several parkinsonian models. We used the dopaminergic cell line MN9D to explore the mechanisms underlying GDNF-mediated protection against the neurotoxin 6-hydroxydopamine (6-OHDA). MN9D cell viability was decreased 24 hr after a 15-min exposure to 6-OHDA (50-1000 microM) as revealed by staining with Hoechst reagent and Trypan blue. The addition of GDNF (10 ng/ml) before, during, and after exposure to 6-OHDA significantly increased the number of viable cells as assessed by Hoechst staining. In contrast, 6-OHDA-induced cell membrane damage was unaffected as measured by Trypan blue exclusion. The PI3K specific inhibitor LY294002 (10-50 microM) blocked GDNF-mediated protection against nuclear condensation, as did the MAPK kinase (MEK) inhibitor U0126 (5- 20 microM). These studies suggest that GDNF can protect dopaminergic cells against some but not all aspects of 6-OHDA-induced toxicity by acting through both PI3K and MAPK signaling pathways.

Glial cell line-derived neurotrophic factor-supplemented hibernation of fetal ventral mesencephalic neurons for transplantation in Parkinson disease: long-term storage

OBJECT

Transplantation of fetal dopaminergic tissue is being investigated in animal models and clinical trials for its potential as a treatment for advanced Parkinson disease. At the same time, the availability of fetal tissue is limited, making its storage time prior to transplantation a key practical issue. Although it results in a smaller percentage of surviving cells. a longer storage time enables fetal tissue obtained over several days to be pooled for transplantation in a recipient. Glial cell line-derived neurotrophic factor (GDNF) has been shown to improve survival of human dopaminergic tissue that has been stored prior to transplantation. The objective of this study was to evaluate the effects on fetal dopaminergic tissue of GDNF-supplemented hibernation for extended periods of 6 to 15 days.

METHODS

The ventral mesencephalon (VM) was harvested in a total of 27 14-day-old rat fetuses, and three VMs were cultured immediately (fresh control group). The remaining 24 VMs were divided sagittally along the midline to yield 48 equal pieces of hemimesencephalon. Twenty-four pieces were stored with GDNF-supplemented hibernation medium for 6, 9, 12, or 15 days, and the 24 "partner" hemimesencephalon pieces were stored in control hibernation medium for the same periods of time. Tissue was cultured for 48 hours and processed for tyrosine hydroxylase (TH) immunoreactivity and double-stained with cresyl violet. Cell counts for all cultures and the percentage of TH-immunoreactive cells were obtained. The percentage of TH-immunoreactive cells for the fresh control group was 6.3 +/- 0.5%. The percentage of TH-immunoreactive cells in cultures derived from tissue stored in GDNF-supplemented medium was significantly increased at 6 and 9 days posthibernation compared with the fresh control group and the "partner" groups stored in hibernation medium only. No significant increase in the percentage of TH-immunoreactive cells was observed in the 12- and 15-day groups.

CONCLUSIONS

In this study the authors have demonstrated that fetal dopaminergic tissue can be safely stored for up to 9 days in GDNF-supplemented hibernation medium. Furthermore, the percentage of TH-immunoreactive cells is significantly increased after 6 and 9 days of storage in this medium, improving the yield of TH-immunoreactive cells prior to transplantation. These observations have practical clinical implications for collecting fetal dopaminergic cells and improving their survival after transplantation.

Glial cell line-derived neurotrophic factor-supplemented hibernation of fetal ventral mesencephalic neurons for transplantation in Parkinson disease: long-term storage

OBJECT

Investigation of fetal dopaminergic tissue transplantation is being conducted in animal models and clinical trials as a potential treatment for advanced Parkinson disease (PD). Because the availability of fetal tissue is limited, however, the duration of its storage prior to transplantation is a key practical issue. Longer storage times may enable fetal tissue obtained over several days to be pooled together for transplantation in a recipient. Glial cell line-derived neurotrophic factor (GDNF) has been shown to improve survival of stored human dopaminergic tissue prior to transplantation. The objective of this study was to evaluate GDNF-supplemented hibernation of fetal dopaminergic tissue for extended periods of 6 to 15 days.

METHODS

A total of 27 rat ventral mesencephalons (VMs) were obtained in gestation Day 14 rat fetuses, and three were cultured immediately (fresh-culture control group). The remaining 24 VMs were divided sagittally along the midline to form 48 equal pieces of hemimesencephalons. Twenty-four pieces were stored with GDNF-supplemented hibernation medium for 6, 9, 12, or 15 days, and the 24 "partner" hemimesencephalons were stored in control hibernation medium for the same periods of time. Tissue was cultured for 48 hours and processed for tyrosine hydroxylase (TH) immunoreactivity and cresyl violet. Cell counts for all cultures and percentage of TH-immunoreactive cells were obtained. The percentage of TH-positive cells for the fresh control group was 6.3 +/- 0.5%; that measured in cultures derived from tissue hibernated in GDNF-supplemented medium was significantly increased at 6 and 9 days posthibernation compared with the fresh-culture control group and the partner groups stored in hibernation medium only. No significant increase in percentage of TH-immunoreactive cells was observed in the 12- and 15-day hibernation groups.

CONCLUSIONS

In summary the authors found that fetal dopaminergic tissue can safely be stored up to 9 days in GDNF-supplemented hibernation medium. Furthermore the percentage of TH-immunoreactive cells is significantly increased after 6 and 9 days of storage in this medium, improving the yield of TH-positive cells prior to transplantation. These observations may have important clinical implications for collecting fetal dopaminergic cells and improving their survival after transplantation.

Signaling pathways mediate the neuroprotective effects of GDNF

We show that the glial cell line-derived neurotrophic factor (GDNF) activates the PI3K/Akt-signaling pathway in human neuroblastoma cells that express functional Ret-receptor complexes. Consistent with this finding we show PI3K-dependent Bad-inactivation by binding to 14-3-3 proteins in response to GDNF. Using differential display techniques we detected several cDNA clones differentially expressed after treatment with GDNF or 6-OHDA.

Temporal changes in the neurotrophic environment of the denervated striatum as determined by the survival and outgrowth of grafted fetal dopamine neurons

There is growing evidence that the neurotrophic environment of the denervated striatum may change with time following a lesion of the nigrostriatal pathway in young adult rats. To test this hypothesis, we implanted fetal dopamine grafts into the striatum at several different time points relative to the nigrostriatal pathway lesion and allowed the grafts to integrate with the host for a period of 1 month; subsequently, we observed the function and morphology of the dopamine grafts. Fetal grafts were implanted at the following time points relative to the lesion: 1 week before (-1 Week), at the same time (Week 0), 1 week after (1 Week), 4 weeks after (4 Weeks), or 12 weeks after (12 Weeks). Amphetamine-induced rotational behavior was assessed 4 weeks after grafting for all groups. Rotational scores indicate that grafts for the 1 Week group showed the greatest reversal of amphetamine-induced rotational behavior that was also significantly greater than the scores for the -1 Week group. Morphological analysis revealed that grafts in the Week 0, 1 Week and 4 Weeks groups showed a significantly larger area of tyrosine hydroxylase-positive (TH+) fiber outgrowth than in the -1 Week group, while fiber outgrowth for the 12 Weeks group was significantly lower than for the 1 Week group. Cell count analysis for TH+ neurons within the graft indicate a significantly greater number of TH+ neurons in grafts for the 1 Week group than in grafts for the -1 Week. The results of this study suggest that neurotoxic lesions may induce a compensatory increase in neurotrophic activity within the denervated striatum of young rats that is conducive to the survival and outgrowth of fetal dopamine grafts. These data also correlate well with reports that the expression of several specific dopaminergic neurotrophic factors within the striatum increase following a neurotoxic lesion of the nigrostriatal pathway in young adult rats.

Differential effects of glucocorticoids and gonadal steroids on glutathione levels in neuronal and glial cell systems

The aim of the present study was to investigate the short- and long-term effects of glucocorticoids [corticosterone (CORT), dexamethasone (DEX), 6-methylprednisolone (6-MP)] and gonadal steroids [17beta-estradiol (E(2)), progesterone (PROG), testosterone (TEST)] on the levels of the antioxidant glutathione (GSH) in different cell systems of the CNS (neuronal hippocampal HT22 cells, primary hippocampal and neocortical brain cells, and C(6) glioma cells). In HT22 cells, steroids exerted mainly long-term effects. Significant increases of GSH levels were detectable after a 24 hr treatment with 10(-7) M of DEX (122% +/- 5%), 6-MP (208% +/- 32%), E(2) (134% +/- 10%), and TEST (155% +/- 17%). A significant decrease occurred after incubation with PROG for 24 hr (79% +/- 9%). In primary hippocampal cultures, a 24 hr treatment with DEX (140% +/- 8%), E(2) (123% +/- 6%), and PROG (118% +/- 5%) led to significant increases of the GSH levels, whereas, in neocortical primary cultures, only an incubation with E(2) increased GSH (149% +/- 8%). In C(6) cells, hormone treatment led to both significant short-term (1 hr: CORT 114% +/- 5%, DEX 90% +/- 3%, E(2) 88% +/- 3%; 3 hr: DEX 115% +/- 5%, E(2) 122% +/- 6%, TEST 78% +/- 4%) and significant long-term (24 hr: CORT 74% +/- 4%, 6-MP 84% +/- 5%, E(2) 115% +/- 6%, PROG 91% +/- 4%, TEST 116% +/- 5%) effects. In summary, we were able to demonstrate differential effects of steroids on GSH levels in different cellular CNS models, showing an important influence of steroids and especially E(2) on antioxidative cellular functions in neuronal and glial cells.

Expression of glial cell line-derived neurotrophic factor (GDNF) in the developing human fetal brain

GDNF expression was examined immunocytochemically in developing human fetal brains obtained from aborted fetuses ranging from 7 to 39 weeks in gestational age. At 7-8 weeks, strong immunoreactivity was noted within radial glial processes, glia limitans and choroid plexus of the telencephalic vesicle. By 10 weeks, ependymal cells, primitive matrix cells and early developing cortical plate neurons showed positive staining. By 15-16 weeks, migrating neurons in the subventricular and intermediate zones and in the cortical plate were strongly positive for GDNF. The glia limitans of the cerebral cortex and subependymal astrocytes remained positive at this time. As fetal age increased, GDNF expression shifted to neurons and glial cells in the deeper structures of the brain. The most prominent GDNF staining was observed in the cytoplasm and dendrites of Purkinje cells of the cerebellum by 25 weeks and thereafter. Pyramidal neurons of the CA1 region and granule cells of the dentate fascia of the hippocampus, neurons of the entorhinal cortex, and scattered neurons within the brain stem, medulla and spinal cord all showed strong GDNF staining by 25-35 weeks. Widespread GDNF expression in neuronal and non-neuronal cells with distinct developmental shifts suggests that GDNF may play a critical role in the survival, differentiation and maintenance of neurons at different stages of development in the developing human fetal brain.

Prospects for the treatment of Parkinson's disease using neurotrophic factors

Parkinson's disease (PD) is a debilitating neurodegenerative condition that is characterised by a progressive loss of dopaminergic neurones of the substantia nigra pars compacta (SNpc) and the presence of alpha-synuclein cytoplasmic inclusions (Lewy bodies). Cardinal symptoms include tremor, bradykinesia, and rigidity, although cognitive and autonomic disturbances are not uncommon. Pharmacological treatment targeting the dopaminergic network is relatively effective at ameliorating these symptoms, especially in the early stages of the disease, but none of these therapies are curative and they generate their own problems. As dopaminergic neuronal death in PD occurs in a gradual manner, it is amenable to treatments that can either protect remaining dopaminergic neurones or prevent death of those neurones that have begun to die. Use of neurotrophic factors is a potential candidate, as various factors have been shown to increase dopaminergic neuronal survival in culture and promote survival and axonal growth in animal models of PD. Glial cell line-derived neurotrophic factor (GDNF) is currently the most effective substance that has been intensively studied and shown to have a specific 'dopaminotrophic' effect. This review will therefore focus on studies that have investigated GDNF and discuss the potential for neurotrophic factor treatment in PD.

Differentiation of embryonic stem cell-derived dopaminergic neurons is enhanced by survival-promoting factors

Here, we describe the generation of viable and dopamine-producing neurons derived from pluripotent mouse embryonic stem cells. Neurotrophic factors in combination with survival-promoting factors, such as interleukin-1beta, glial cell line-derived neurotrophic factor, neurturin, transforming growth factor-beta(3) and dibutyryl-cyclic AMP, significantly enhanced Nurr1 and tyrosine hydroxylase (TH) mRNA levels, whereas En-1, mash-1 and dopamine-2-receptor mRNA levels were not upregulated. In parallel, mRNA levels of the anti-apoptotic gene bcl-2 were found to be upregulated at terminal stages. Double immunofluorescence analysis revealed increased numbers of TH- and dopamine transporter-, but not gamma-aminobutyric acid- and serotonin-positive neurons in relation to synaptophysin-labeled cells by survival-promoting factors. Moreover, high-performance liquid chromatography analysis showed detectable levels of intracellular dopamine. We conclude that survival-promoting factors enhance differentiation, survival and maintenance of dopaminergic neurons derived from embryonic stem cells.

Sustained extracellular signal-regulated kinase activation by 6-hydroxydopamine: implications for Parkinson's disease

Although the toxin 6-hydroxydopamine (6-OHDA) is utilized extensively in animal models of Parkinson's disease, the underlying mechanism of its toxic effects on dopaminergic neurons is not completely understood. We examined the effects of 6-OHDA on the CNS-derived tyrosine hydroxylase expressing B65 cell line, with particular attention to the regulation of the extracellular signal-regulated protein kinases (ERK). 6-OHDA elicited a dose-dependent cytotoxicity in B65 cells. Toxic doses of 6-OHDA also elicited a biphasic pattern of ERK phosphorylation with a prominent sustained phase, a pattern that differed from that observed with hydrogen peroxide (H(2)O(2)) treatment. 6-OHDA-elicited ERK phosphorylation was blocked by PD98059, an inhibitor of the upstream mitogen activated protein kinase kinase (MEK) that phosphorylates and activates ERK. PD98059 also conferred protection against 6-OHDA cytotoxicity, but did not affect H(2)O(2) toxicity in B65 cells. These results suggest that ERK activation plays a direct mechanistic role in 6-OHDA toxicity, rather than representing a protective compensatory response, and raise the possibility that abnormal patterns of ERK activation may contribute to dopaminergic neuronal cell death.

Regulation of serotonin transporter gene expression in human glial cells by growth factors

The aims of this study were to identify monoamine transporters expressed in human glial cells, and to examine the regulation of their expression by stress-related growth factors. The expression of serotonin transporter mRNA was detected by reverse transcriptase-polymerase chain reaction in normal human astrocytes, whereas the dopamine transporter (DAT) and the norepinephrine transporter (NET) were not detected. The cDNA sequence of the "glial" serotonin transporter in astrocytes was consistent with that reported for the "neuronal" serotonin transporter (SERT). Moreover, we also demonstrated SERT expression in glial fibrillary acidic protein-positive cells by immunocytochemical staining in normal human astrocytes. Serotonin transporter gene expression was also detected in glioma-derived cell lines (A172, KG-1-C and KGK). Addition of basic fibroblast growth factor (bFGF) or epidermal growth factor (EGF) for 2 days increased serotonin transporter gene expression in astrocytes and JAR (human choriocarcinoma cell line). Basic fibroblast growth factor, but not epidermal growth factor, increased specific [3H]serotonin uptake in astrocytes in a time (1-4 days)- and concentration (20-100 ng/ml)-dependent manner. The expression of genes for basic fibroblast growth factor and epidermal growth factor receptors was detected in astrocytes. These findings suggest that the expression of the serotonin transporter in human glial cells is positively regulated by basic fibroblast growth factor.