Glial cell line-derived neurotrophic factor protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity in C57BL/6 mice

Aminochrome decreases NGF, GDNF and induces neuroinflammation in organotypic midbrain slice cultures

Recent evidence shows that aminochrome induces glial activation related to neuroinflammation. This dopamine derived molecule induces formation and stabilization of alpha-synuclein oligomers, mitochondria dysfunction, oxidative stress, dysfunction of proteasomal and lysosomal systems, endoplasmic reticulum stress and disruption of the microtubule network, but until now there has been no evidence of effects on production of cytokines and neurotrophic factors, that are mechanisms involved in neuronal loss in Parkinson's disease (PD). This study examines the potential role of aminochrome on the regulation of NGF, GDNF, TNF-α and IL-1β production and microglial activation in organotypic midbrain slice cultures from P8 - P9 Wistar rats. We demonstrated aminochrome (25 μM, for 24 h) induced reduction of GFAP expression, reduction of NGF and GDNF mRNA levels, morphological changes in Iba1⁺ cells, and increase of both TNF-α, IL-1β mRNA and protein levels. Moreover, aminochrome (25 μM, for 48 h) induced morphological changes in the edge of slices and reduction of TH expression. These results demonstrate neuroinflammation, as well as negative regulation of neurotrophic factors (GDNF and NGF), may be involved in aminochrome-induced neurodegeneration, and they contribute to a better understanding of PD pathogenesis.

Microglia-Mediated Neuroinflammation and Neurotrophic Factor-Induced Protection in the MPTP Mouse Model of Parkinson's Disease-Lessons from Transgenic Mice

Parkinson's disease (PD) is a neurodegenerative disease characterised by histopathological and biochemical manifestations such as loss of midbrain dopaminergic (DA) neurons and decrease in dopamine levels accompanied by a concomitant neuroinflammatory response in the affected brain regions. Over the past decades, the use of toxin-based animal models has been crucial to elucidate disease pathophysiology, and to develop therapeutic approaches aimed to alleviate its motor symptoms. Analyses of transgenic mice deficient for cytokines, chemokine as well as neurotrophic factors and their respective receptors in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD have broadened the current knowledge of neuroinflammation and neurotrophic support. Here, we provide a comprehensive review that summarises the contribution of microglia-mediated neuroinflammation in MPTP-induced neurodegeneration. Moreover, we highlight the contribution of neurotrophic factors as endogenous and/or exogenous molecules to slow the progression of midbrain dopaminergic (mDA) neurons and further discuss the potential of combined therapeutic approaches employing neuroinflammation modifying agents and neurotrophic factors.

Heterotopic mucosal engrafting procedure for direct drug delivery to the brain in mice

Delivery of therapeutics into the brain is impeded by the presence of the blood-brain barrier (BBB) which restricts the passage of polar and high molecular weight compounds from the bloodstream and into brain tissue. Some direct delivery success in humans has been achieved via implantation of transcranial catheters; however this method is highly invasive and associated with numerous complications. A less invasive alternative would be to dose the brain through a surgically implanted, semipermeable membrane such as the nasal mucosa that is used to repair skull base defects following endoscopic transnasal tumor removal surgery in humans. Drug transfer though this membrane would effectively bypass the BBB and diffuse directly into the brain and cerebrospinal fluid. Inspired by this approach, a surgical approach in mice was developed that uses a donor septal mucosal membrane engrafted over an extracranial surgical BBB defect. This model has been shown to effectively allow the passage of high molecular weight compounds into the brain. Since numerous drug candidates are incapable of crossing the BBB, this model is valuable for performing preclinical testing of novel therapies for neurological and psychiatric diseases.

Comparison of GDF5 and GDNF as neuroprotective factors for postnatal dopamine neurons in ventral mesencephalic cultures

Loss of dopamine neurons is associated with the motor deficits that occur in Parkinson's disease. Although many drugs have proven to be useful in the treatment of the symptoms of this disease, none has been shown to have a significant impact on the development of the disease. However, we believe that several neurotrophic factors have the potential to reduce its progression. Glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor-β superfamily of neurotrophic factors, has been extensively studied in this regard. Less attention has been paid to growth/differentiation factor 5 (GDF5), another member of the same superfamily. This study compares GDNF and GDF5 in dissociated cultures prepared from ventral mesencephalon and in organotypic co-cultures containing substantia nigra, striatum, and neocortex. We report that both GDNF (10-500 ng/ml) and GDF5 (100-500 ng/ml) promoted the survival of dopamine neurons from the substantia nigra of postnatal rats, although GDNF was considerably more potent than GDF5. In contrast, neither factor had any significant effect on the survival of dopamine neurons from the rat ventral tegmental area. Using organotypic co-cultures, we also compared GDF5 with GDNF as chemoattractants for the innervation of the striatum and the neocortex by dopamine neurons from the substantia nigra. The addition of either GDF5 or GDNF (100-500 ng/ml) caused innervation by dopamine neurons into the cortex as well as the striatum, which did not occur in untreated cultures. Our results are consistent with similar findings suggesting that GDF5, like GDNF, deserves attention as a possible therapeutic intervention for Parkinson's disease.

Pathogenesis-targeted, disease-modifying therapies in Parkinson disease

Parkinson disease is an inexorably progressive neurodegenerative disorder. Multiple attempts have been made to establish therapies for Parkinson disease which provide neuroprotection or disease modification-two related, but not identical, concepts. However, to date, none of these attempts have succeeded. Many challenges exist in this field of research, including a complex multisystem disorder that includes dopaminergic and non-dopaminergic features; poorly understood and clearly multifaceted disease pathogenic mechanisms; a lack of reliable animal models; an absence of effective biomarkers of disease state, progression, and target engagement; and the confounding effects of potent symptomatic therapy. In this article, we will review previous, ongoing, and potential future trials designed to alter the progressive course of the disease from the perspective of the targeted underlying pathogenic mechanisms.

Resveratrol Produces Neurotrophic Effects on Cultured Dopaminergic Neurons through Prompting Astroglial BDNF and GDNF Release

Increasing evidence indicated astroglia-derived neurotrophic factors generation might hold a promising therapy for Parkinson's disease (PD). Resveratrol, naturally present in red wine and grapes with potential benefit for health, is well known to possess a number of pharmacological activities. Besides the antineuroinflammatory properties, we hypothesized the neuroprotective potency of resveratrol is partially due to its additional neurotrophic effects. Here, primary rat midbrain neuron-glia cultures were applied to investigate the neurotrophic effects mediated by resveratrol on dopamine (DA) neurons and further explore the role of neurotrophic factors in its actions. Results showed resveratrol produced neurotrophic effects on cultured DA neurons. Additionally, astroglia-derived neurotrophic factors release was responsible for resveratrol-mediated neurotrophic properties as evidenced by the following observations: (1) resveratrol failed to exert neurotrophic effects on DA neurons in the cultures without astroglia; (2) the astroglia-conditioned medium prepared from astroglia-enriched cultures treated with resveratrol produced neurotrophic effects in neuron-enriched cultures; (3) resveratrol increased neurotrophic factors release in the concentration- and time-dependent manners; (4) resveratrol-mediated neurotrophic effects were suppressed by blocking the action of the neurotrophic factors. Together, resveratrol could produce neurotrophic effects on DA neurons through prompting neurotrophic factors release, and these effects might open new alternative avenues for neurotrophic factor-based therapy targeting PD.

CDNF protects the nigrostriatal dopamine system and promotes recovery after MPTP treatment in mice

Cerebral dopamine neurotrophic factor (CDNF) is a recently discovered protein, which belongs to the evolutionarily conserved CDNF/MANF family of neurotrophic factors. The degeneration of dopamine neurons following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment is well characterized, and efficacy in this model is considered a standard criterion for development of parkinsonian therapies. MPTP is a neurotoxin, which produces parkinsonian symptoms in humans and in C57/Bl6 mice. To date, there are no reports about the effects of CDNF on dopamine neuron survival or function in the MPTP rodent model, a critical gap. Therefore, we studied whether CDNF has neuroprotective and neurorestorative properties for the nigrostriatal dopamine system after MPTP injections in C57/Bl6 mice. We found that bilateral striatal CDNF injections, given 20 h before MPTP, improved horizontal and vertical motor behavior. CDNF pretreatment increased tyrosine hydroxylase (TH) immunoreactivity in the striatum and in the substantia nigra pars reticulata (SNpr), as well as the number of TH-positive cells in substantia nigra pars compacta (SNpc). Posttreatment with CDNF, given 1 week after MPTP injections, increased horizontal and vertical motor behavior of mice, as well as dopamine fiber densities in the striatum and the number of TH-positive cells in SNpc. CDNF did not alter any of the analyzed dopaminergic biomarkers or locomotor behavior in MPTP-untreated animals. We conclude that striatal CDNF administration is both neuroprotective and neurorestorative for the TH-positive cells in the nigrostriatal dopamine system in the MPTP model, which supports the development of CDNF-based treatment for Parkinson's disease.

Neuroprotective effects and mechanisms of exercise in a chronic mouse model of Parkinson's disease with moderate neurodegeneration

The protective impact of exercise on neurodegenerative processes has not been confirmed, and the mechanisms underlying the benefit of exercise have not been determined in human Parkinson's disease or in chronic animal disease models. This research examined the long-term neurological, behavioral, and mechanistic consequences of endurance exercise in experimental chronic parkinsonism. We used a chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced mouse model of Parkinson's disease with moderate neurodegeneration and examined the effects of treadmill exercise on movement and balance coordination, changes in dopamine neuron biomarkers, mitochondrial functions, and neurotrophic factor activities in the nigrostriatal system. The exercise results were compared with those of the control and sedentary chronic parkinsonian animals. After 18 weeks of exercise training in the chronic parkinsonian mice, we observed a significant deterrence in the loss of neuronal dopamine-producing cells and other functional indicators. The impaired movement and balance incoordination in the chronic parkinsonian mice were also markedly reduced following exercise. Mechanistic investigations revealed that the neuronal and behavioral recovery produced by exercise in the chronic parkinsonian mice was associated with an improved mitochondrial function and an increase in the brain region-specific levels of brain-derived and glial cell line-derived neurotrophic factors. Our findings indicate that exercise not only produces neuronal and mitochondrial protection, it also boosts nigrostriatal neurotrophic factor levels in the chronic parkinsonian mice with moderate neurodegeneration. Therefore, modifying lifestyle with increased exercise activity would be a non-pharmacological neuroprotective approach for averting neurodegenerative processes, as demonstrated in experimental chronic parkinsonism.

Glial cell line-derived neurotrophic factor protects midbrain dopaminergic neurons against lipopolysaccharide neurotoxicity

Aberrant microglia activation causes dopaminergic neuronal loss and nitric oxide produced by microglia plays a critical role in dopaminergic neuronal degeneration. However, no study has determined if GDNF protects dopaminergic neurons via inhibiting nitric oxide generation in Parkinson's disease animal model. We report that GDNF not only reduces lipopolysaccharide-induced degeneration of dopaminergic neurons, suppresses microglia activation and nitric oxide generation, but also reverses the inhibition of phosphoinositide 3-kinase (PI3K) in dopaminergic neurons and microglia. It suggests that the neuroprotective effect of GDNF on dopaminergic neurons may be related to its suppression of microglia activation-mediated nitric oxide via releasing the inhibition of PI3K in both neurons and microglia.

Decreased inflammation and augmented expression of trophic factors correlate with MOG-induced neuroprotection of the injured nigrostriatal system in the murine MPTP model of Parkinson's disease

The response of the immune system during injury of the central nervous system may play a role in protecting neurons. We have previously reported that immunization with MOG 35-55 prior to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced injury of the dopaminergic system promotes less dopamine depletion and less dopaminergic damage of neurons in mice. In this study, we evaluate the influence of MOG immunization on the inflammatory reaction that occurs at the place of injury. C57Bl male mice, 2 and 12 months old, received i.p. injections of MPTP (40 mg/kg) and some groups animals also received an additional injection with myelin oligodendrocyte glycoprotein (MOG) 35-55 in CFA 6 days before MPTP administration. MPTP caused a common inflammatory reaction characterized by microglial activation, infiltration of T cells into the substantia nigra and striatum and increased expression of mRNA encoding pro-inflammatory cytokines (IL-1 beta, TNFalpha, INF gamma) and trophic factors (TGFbeta, GDNF). MOG immunization prior to MPTP administration significantly diminished the microglial reaction and reduced the levels of infiltrating CD8+ lymphocytes. The number of CD4+ T cells remained at the same level as in the MPTP group. Expression of pro-inflammatory cytokines was diminished. The mRNA expression of GDNF was significantly higher in the MOG pretreated mice relative to the MPTP group, both in the 2 month old and 12 month old groups. Since MOG immunization prior to MPTP intoxication appears to prevent nigrostriatal injury, the observed decrease of inflammation and increase of GDNF mRNA expression in the injured areas might represent one of the mechanisms of observed neuroprotection.

Analysis of gene expression in Parkinson's disease: possible involvement of neurotrophic support and axon guidance in dopaminergic cell death

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra. We have studied alterations in gene expression in the substantia nigra, the caudate nucleus and putamen of four PD patients and four matched controls using custom designed Agilent microarrays. To gain insight into changes in gene expression during early stages of dopaminergic neurodegeneration, we selectively investigated the relatively spared parts of the PD substantia nigra, and correlated gene expression changes with alterations in neuronal density. We identified changes in the expression of 287 transcripts in the substantia nigra, 16 transcripts in the caudate nucleus and four transcripts in the putamen. For selected transcripts, transcriptional alterations were confirmed with qPCR on a larger set of seven PD cases and seven matched controls. We detected concerted changes in functionally connected groups of genes. In the PD substantia nigra, we observed strong evidence for a reduction in neurotrophic support and alterations in axon guidance cues. As the changes occur in relatively spared parts of the PD substantia nigra, they suggest novel disease mechanisms involving neurotrophic support and axon guidance in early stages of cellular stress events, ultimately leading to dopaminergic cell death in PD.

Tripchlorolide protects against MPTP-induced neurotoxicity in C57BL/6 mice

Many current studies of Parkinson's disease (PD) suggest that inflammation is involved in the neurodegenerative process. Tripchlorolide (TW397), a traditional Chinese herbal compound with anti-inflammatory and immunosuppressive properties, has been shown to protect dopaminergic neurons against, and restore their function after, the neurotoxicity induced by 1-methyl-4-phenylpyridinium ions in vitro. This study was designed to investigate the effect of TW397 in vivo in the PD model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned C57BL/6 mice. In the animals that received vehicle-only (i.e., no TW397) treatment with MPTP i.p. injection, the survival ratios of tyrosine hydroxylase-immunoreactive (TH-IR) neurons in the substantia nigra pars compacta and TH-IR fibres in the striatum were only 59 and 13%, respectively, compared with the normal controls. Intriguingly, in conjunction with MPTP, treatment with TW397, 1 microg/kg for 16 days, once per day, dramatically improved the survival rate of the TH-IR neurons and TH-IR fibres to 80 and 43% of the control. The treatment with TW397 also significantly improved the level of dopamine in the substantia nigra and striatum to 157 and 191%, respectively, of the MPTP- plus vehicle-treated group. In addition, in MPTP-treated animals the rota-rod performances of those treated with 0.5 or 1 microg/kg TW397 were significantly improved, by approximately 2- and 3-fold, respectively, relative to vehicle-treated animals. The neuroprotective effect of TW397 was coincident with an attenuated astroglial response within the striatum. These data demonstrate a neuroprotective action of TW397 in vivo against MPTP toxicity, with important implications for the treatment of PD.

MPTP-induced deficits in striatal synaptic plasticity are prevented by glial cell line-derived neurotrophic factor expressed via an adeno-associated viral vector

This study determined the consequences of dopamine denervation of the striatum on synaptic plasticity and prevention of these changes with gene therapy using an adeno-associated viral vector (AAV) expressing glial cell line-derived neurotrophic factor (GDNF). C57BL6/J mice were injected with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP); long-term depression (LTD) or potentiation (LTP) were measured in vitro. Fast-scan cyclic voltammetry measured electrically released dopamine from a functionally relevant pool in these same striatal slices. After MPTP, dopamine release and uptake were greatly diminished, and LTP and LTD were blocked in the striatal slices. The loss of plasticity resulted directly from the loss of dopamine since its application rescued synaptic plasticity. Striatal GDNF expression via AAV, before MPTP, significantly protected against the loss of dopamine and prevented the blockade of corticostriatal LTP. These data demonstrate that dopamine plays a role in supporting several forms of striatal plasticity and that GDNF expression via AAV prevents the loss of dopamine and striatal plasticity caused by MPTP. We propose that impairment of striatal plasticity after dopamine denervation plays a role in the symptomology of Parkinson's disease and that AAV expression of neurotrophic factors represents a tenable approach to protecting against or slowing these neurobiological deficits.

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.

RET is dispensable for maintenance of midbrain dopaminergic neurons in adult mice

Glial cell-line derived neurotrophic factor (GDNF)-mediated RET tyrosine kinase signaling is implicated in the survival of several PNS and CNS neuronal populations that are important in the pathogenesis of several disorders including Parkinson's disease and drug addiction. However, it has been difficult to study these processes and the physiological importance of this pathway in adult mice because of the neonatal lethality of Gdnf and Ret null mice. We report successful creation of RET conditional reporter mice to investigate postnatal physiologic roles of RET and monitor the fate of RET-expressing cell types. To delete RET specifically in dopaminergic neurons and determine the physiologic requirement of RET in the maintenance of substantia nigra compacta (SNC) and ventral tegmental area (VTA), we bred the RET conditional mice with mice that specifically express Cre from the dopamine transporter (Dat) locus. A detailed morphometric and biochemical analysis including dopaminergic neuron number and size in SNC and VTA, and fiber density in the striatum and nucleus accumbens, and dopamine levels indicate that RET is not required for providing global trophic support to midbrain dopaminergic neurons in adult mice. Furthermore, RET deficiency in these neurons does not cause major sensorimotor abnormalities. Hence our results support the idea that RET signaling is not critical for the normal physiology of the SNC and VTA in adult mice.

Glia cell number modulates sensitivity to MPTP in mice

Free radical damage has been shown to play a significant role in the pathogenesis of a number of neurodegenerative diseases including Parkinson's disease. One model of experimental parkinsonism is the loss of substantia nigra cells following administration of MPTP. Previously, it has been shown that a number of inbred strains of mice have differential responses to this toxin, and this difference is dependent on glial cells. In this study, the number of glial cells in the substantia nigra pars compacta of C57Bl/6J (MPTP-sensitive) and Swiss Webster (MPTP-resistant) strains of mice was examined. The C57Bl/6J mice have an approximately 50% lower number of GFAP+ and S-100beta glial cells than the Swiss Webster mice. C57Bl/6J mice have a 25% increased number of resident nonactivated microglial cells. To determine whether this difference in cell number has functional significance, we used an in vitro SN culture system that allowed us to manipulate the number of glial cells. When C57Bl/6 neurons were grown on a glial mat plated with twice the number of cells, we were able to rescue the MPTP-sensitive neurons from toxin-induced cell death. This suggests that the number of glial cells in the SNpc may be an important factor in the survival of dopaminergic neurons following exposure to xenobiotics.

Environmental enrichment in adulthood eliminates neuronal death in experimental Parkinsonism

Idiopathic Parkinson's disease (PD) affects 2% of adults over 50 years of age. PD patients demonstrate a progressive loss of dopamine neurons in the substantia nigra pars compacta (SNpc). One model that recapitulates the pathology of PD is the administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Here we show that exposure to an enriched environment (EE) (a combination of exercise, social interactions and learning) or exercise alone during adulthood, totally protects against MPTP-induced Parkinsonism. Furthermore, changes in mRNA expression would suggest that increases in glia-derived neurotrophic factors, coupled with a decrease of dopamine-related transporters (e.g. dopamine transporter, DAT; vesicular monoamine transporter, VMAT2), contribute to the observed neuroprotection of dopamine neurons in the nigrostriatal system following MPTP exposure. This non-pharmacological approach presents significant implications for the prevention and/or treatment of PD.

The MPTP model of Parkinson's disease

The biochemical and cellular changes that occur following administration of 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) are remarkably similar to that seen in idiopathic Parkinson's disease (PD). In this review, we detail the molecular activities of this compound from peripheral intoxication through its various biotransformations. In addition, we detail the interplay that occurs between the different cellular compartments (neurons and glia) that eventually consort to kill substantia nigra pars compacta (SNpc) neurons.

Expression of glial cell line-derived neurotrophic factor induced by transient forebrain ischemia in rats

This study examined the expression of glial cell line-derived neurotrophic factor (GDNF) mRNA and the cellular localization of GDNF production in rats subjected to transient forebrain ischemia induced by four-vessel occlusion. Transient forebrain ischemia induced GDNF mRNA expression in the hippocampus from 3 h to 3 days after the ischemic episode, with peak expression at 6 h. The GDNF mRNA increase in the cerebral cortex was similar to that in the hippocampus, whereas no increase in GDNF mRNA was observed in the striatum and brainstem. Western blot analysis showed that GDNF in the hippocampal CA1 region was increased slightly from 3 to 24 h after the ischemia, and then subsequently declined to below the baseline level. In the hippocampus, GDNF was evenly produced in pyramidal neurons of both sham-operated rats and normal rats, as determined by immunohistochemistry. Interestingly, we found that ischemia-induced reactive astrocytes, as well as surviving neurons, produced GDNF in 3-7 days after the ischemia. On the other hand, in other regions, such as the cerebral cortex, striatum, and brainstem, there was no change in GDNF-positive cells secondary to ischemia. These findings suggest that expression of GDNF mRNA is regulated in part via ischemia-induced neuronal degeneration. They also suggest that ischemia-induced reactive astrocytes may produce GDNF to protect against neuronal death. Therefore, GDNF may play an important role in ischemia-induced neuronal death in the 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.

Protection of nigral neurons by GDNF-engineered marrow cell transplantation

Marrow stromal cells, which have many characteristics of stem cells, populate various non-hematopoietic tissues including the brain. In the present study, the cDNA for the dopaminergic neurotrophic factor Glial Cell Line-Derived Neurotrophic Factor (GDNF) was delivered using marrow cells in the mouse 1-Methyl-4-phenyl-1,2,3,6-tetrahydro-pyridine (MPTP) model of Parkinson's disease. Following cross-sex intravenous bone marrow transplantation with male donor cells that had been transduced with GDNF (GDNF-BMT) or with non-manipulated marrow (Control-BMT), female recipient mice were subjected to systemic MPTP injections. Eight weeks after neurotoxin exposure, more tyrosine hydroxylase immunoreactive nigral neurons and striatal terminal density were observed in the GDNF-BMT mice compared with the Control-BMT group. In addition, following the expected initial behavioral hyperactivity in both groups, a significant difference in motor activity was detected between the two groups. GDNF immunoreactive male donor marrow derived cells were detected in the brains of GDNF-BMT mice but not in controls. These data indicate that marrow derived cells that seed the brain can express biologically active gene products and, therefore, can function as effective vehicles for therapeutic gene transfer to the brain.

Glial cell line-derived neurotrophic factor (GDNF) gene delivery protects dopaminergic terminals from degeneration

Previously, we observed that injection of an adenoviral (Ad) vector expressing glial cell line-derived neurotrophic factor (GDNF) into the striatum, but not the substantia nigra (SN), prior to a partial 6-OHDA lesion protects dopaminergic (DA) neuronal function and prevents the development of behavioral impairment in the aged rat. This suggests that striatal injection of AdGDNF maintains nigrostriatal function either by protecting DA terminals or by stimulating axonal sprouting to the denervated striatum. To distinguish between these possible mechanisms, the present study examines the effect of GDNF gene delivery on molecular markers of DA terminals and neuronal sprouting in the aged (20 month) rat brain. AdGDNF or a control vector coding for beta-galactosidase (AdLacZ) was injected unilaterally into either the striatum or the SN. One week later, rats received a unilateral intrastriatal injection of 6-OHDA on the side of vector injection. Two weeks postlesion, rats injected with AdGDNF into either the striatum or the SN exhibited a reduction in the area of striatal denervation and increased binding of the DA transporter ligand [(125)I]IPCIT in the lesioned striatum compared to control animals. Furthermore, injections of AdGDNF into the striatum, but not the SN, increased levels of tyrosine hydroxylase mRNA in lesioned DA neurons in the SN and prevented the development of amphetamine-induced rotational asymmetry. In contrast, the level of T1 alpha-tubulin mRNA, a marker of neuronal sprouting, was not increased in lesioned DA neurons in the SN following injection of AdGDNF either into the striatum or into the SN. These results suggest that GDNF gene delivery prior to a partial lesion ameliorates damage caused by 6-OHDA in aged rats by inhibiting the degeneration of DA terminals rather than by inducing sprouting of nigrostriatal axons.

Immunohistochemical localization of glial cell line-derived neurotrophic factor in the human central nervous system

Glial cell line-derived neurotrophic factor, initially purified from the rat glial cell line B49, has the ability to promote the survival and differentiation of various types of neurons in the central and peripheral nervous systems. In the present study, to evaluate the physiological role of glial cell line-derived neurotrophic factor in the central nervous system, we investigated the cellular and regional distribution of glial cell line-derived neurotrophic factor immunoreactivity in autopsied control human brains and spinal cords using a polyclonal glial cell line-derived neurotrophic factor-specific antibody. On western blot analysis, the antibody reacted with recombinant human glial cell line-derived neurotrophic factor, and recognized a single band at a molecular weight of approximately 34,000 in human brain homogenates. Glial cell line-derived neurotrophic factor immunoreactivity was observed mainly in the neuronal somata, dendrites and axons. In the telencephalon, diencephalon and brainstem, the cell bodies and proximal processes of several neuronal subtypes were immunostained with punctate dots. Furthermore, immunopositive nerve fibers were also observed, and numerous axons were intensely immunolabeled in the internal segment of the globus pallidus and the pars reticulata of the substantia nigra. In the cerebellum, the most conspicuous immunostaining was found in the Purkinje cells, in which the somata and dendrites were strongly immunolabeled. Intense immunoreactivity was also detected in the posterior horn of the spinal cord. In addition to the neuronal elements, immunopositive glial cell bodies and processes were observed in various regions. Our results suggest that glial cell line-derived neurotrophic factor is widely localized, but can be found selectively in certain neuronal subpopulations of the human central nervous system. Glial cell line-derived neurotrophic factor may regulate the maintenance of neuronal functions under normal circumstances.

Protection by synergistic effects of adenovirus-mediated X-chromosome-linked inhibitor of apoptosis and glial cell line-derived neurotrophic factor gene transfer in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson's disease

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces clinical, biochemical, and neuropathological changes reminiscent of those occurring in idiopathic Parkinson's disease (PD). Here we show that a peptide caspase inhibitor, N-benzyloxy-carbonyl-val-ala-asp-fluoromethyl ketone, or adenoviral gene transfer (AdV) of a protein caspase inhibitor, X-chromosome-linked inhibitor of apoptosis (XIAP), prevent cell death of dopaminergic substantia nigra pars compacta (SNpc) neurons induced by MPTP or its active metabolite 1-methyl-4-phenylpyridinium in vitro and in vivo. Because the MPTP-induced decrease in striatal concentrations of dopamine and its metabolites does not differ between AdV-XIAP- and control vector-treated mice, this protection is not associated with a preservation of nigrostriatal terminals. In contrast, the combination of adenoviral gene transfer of XIAP and of the glial cell line-derived neurotrophic factor to the striatum provides synergistic effects, rescuing dopaminergic SNpc neurons from cell death and maintaining their nigrostriatal terminals. These data suggest that a combination of a caspase inhibitor, which blocks death, and a neurotrophic factor, which promotes the specific function of the rescued neurons, may be a promising strategy for the treatment of PD.

Glial cell line-derived neurotrophic factor concentration dependently improves disability and motor activity in MPTP-treated common marmosets

Glial cell line-derived neurotrophic factor (GDNF) has previously reduced motor deficits and preserved nigral dopamine neurones in rhesus monkeys with a unilateral MPTP-induced lesion of substantia nigra. We now report on the ability of GDNF to reverse motor deficits induced by parenteral administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to common marmosets resulting in bilateral degeneration of the nigrostriatal pathway. Prior to GDNF administration, all MPTP-treated animals showed akinesia or bradykinesia, rigidity, postural instability and tremor. Intraventricular injection of GDNF (10, 100 or 500 microg) at 9 and 13 weeks post MPTP treatment resulted in a concentration dependent improvement in locomotor activity and motor disability which became significant after administration of 100 and 500 microg of GDNF. The most prominent improvements were in alertness, checking movements, and posture. It is concluded that intraventricular GDNF administration improves bilateral Parkinsonian motor disability following MPTP treatment and this may reflect an action of GDNF on remaining nigral dopaminergic neurones.

Restorative effects of GDNF on striatal dopamine release in rats treated with neurotoxic doses of methamphetamine

Repeated methamphetamine (METH) administration to animals can result in long-lasting decreases in striatal dopamine (DA) release and content. Glial cell line-derived neurotrophic factor (GDNF) has pronounced effects on dopaminergic systems in vivo, including neuroprotective effects against METH. The present experiments were designed to examine the ability of GDNF to reverse, or accelerate recovery from, METH-induced alterations in striatal DA release. Male Fischer-344 rats were administered METH (5 mg/kg, s.c.) or saline 4 times in one day at 2-hour intervals. Seven days later the animals were anesthetized and given a single injection of 10 microg GDNF, or vehicle, into the right striatum. Three weeks later microdialysis experiments were carried out in both the right and left striata to examine basal and evoked levels of DA and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). In animals treated with METH followed by vehicle 7 days later, there were significant reductions in potassium- and amphetamine-evoked overflow of DA, and in basal levels of DOPAC and HVA, compared to control animals. In rats treated with METH followed 7 days later with GDNF, there were significant increases in potassium- and amphetamine-evoked overflow of DA on the right, GDNF-treated, side of the brain compared to the left side. Basal levels of DOPAC and HVA were also elevated on the GDNF-treated side of the brain. These results suggest that GDNF can accelerate recovery of dopaminergic release processes in the striatum of rats treated with neurotoxic doses of METH.

Development of an antibody against a 40,000 mol. wt brain injury-derived neurotrophic peptide-binding protein and identification of a 40,000 mol. wt brain injury-derived neurotrophic peptide-binding protein in hippocampal neurons

Brain injury-derived neurotrophic peptide is a 13-amino acid peptide derived from a 15,000 mol. wt neurotrophic factor released from sites of mechanical injury in neonatal rat brain. This peptide promotes survival of septal cholinergic neurons and mesencephalic dopaminergic neurons, and protects hippocampal neurons from glutamate-induced neurotoxicity. In this study, we have developed a monoclonal antibody against a brain injury-derived neurotrophic peptide-binding protein by immunizing mice with septal synaptosomes from five-week-old rat brain. Monoclonal antibodies were screened for inhibition of the binding of a 125I-labeled analogue of brain injury-derived neurotrophic peptide to rat brain synaptosomes. The monoclonal antibody 6A22 suppressed the biological activity of brain injury-derived neurotrophic peptide and abolished the protective effect of the neurotrophic peptide against glutamate-induced neurotoxicity. This monoclonal antibody recognized a 40,000 mol. wt brain injury-derived neurotrophic peptide-binding protein, which was also identified by cross-linking experiments. Immunohistochemical studies showed that the 6A22 antibody bound to the cell surfaces of a subpopulation (about 60%) of hippocampal neurons in culture. These results are consistent with the possibility that the 40,000 mol. wt protein belongs to brain injury-derived neurotrophic peptide receptors.

Transplantation of fetal kidney tissue reduces cerebral infarction induced by middle cerebral artery ligation

The authors, and others, have recently reported that intracerebral administration of glial cell line-derived neurotrophic factor (GDNF) or osteogenic protein-1 protects against ischemia-induced injury in the cerebral cortex of adult rats. Because these trophic factors are highly expressed in the fetal, but not adult, kidney cortex, the possibility that transplantation of fetal kidney tissue could serve as a cellular reservoir for such molecules and protect against ischemic injury in cerebral cortex was examined. Fetal kidneys obtained from rat embryos at gestational day 16, and adult kidney cortex, were dissected and cut into small pieces. Adult male Sprague-Dawley rats were anesthetized with chloral hydrate and placed in a stereotactic apparatus. Kidney tissues were transplanted into three cortical areas adjacent to the right middle cerebral artery (MCA). Thirty minutes after grafting, the right MCA was transiently ligated for 90 minutes. Twenty-four hours after the onset of reperfusion, animals were evaluated behaviorally. It was found that the stroke animals that received adult kidney transplantation developed motor imbalance. However, animals that received fetal kidney grafts showed significant behavioral improvement. Animals were later sacrificed and brains were removed for triphenyltetrazolium chloride staining, Pax-2 immunostaining, and GDNF mRNA expression. It was noted that transplantation of fetal kidney but not adult kidney tissue greatly reduced the volume of infarction in the cerebral cortex. Fetal kidney grafts showed Pax-2 immunoreactivity and GDNF mRNA in the host cerebral cortex. In contrast, GDNF mRNA expression was not found in the adult kidney grafts. Taken together, our data indicate that fetal kidney transplantation reduces ischemia/reperfusion-induced cortical infarction and behavioral deficits in adult rats, and that such tissue grafts could serve as an unique cellular reservoir for trophic factor application to the brain.