Therapeutic potentials for glial cell line-derived neurotrophic factor (GDNF) based upon pharmacological activities in the CNS

Failure of Glial Cell-Line Derived Neurotrophic Factor (GDNF) in Clinical Trials Orchestrated By Reduced NR4A2 (NURR1) Transcription Factor in Parkinson's Disease. A Systematic Review

Parkinson’s disease (PD) is one of the most common neurodegenerative maladies with unforeseen complex pathologies. While this neurodegenerative disorder’s neuropathology is reasonably well known, its etiology remains a mystery, making it challenging to aim therapy. Glial cell-line derived neurotrophic factor (GDNF) remains an auspicious therapeutic molecule for treating PD. Neurotrophic factor derived from glial cell lines is effective in rodents and nonhuman primates, but clinical findings have been equivocal. Laborious exertions have been made over the past few decades to improve and assess GDNF in treating PD (clinical studies). Definitive clinical trials have, however, failed to demonstrate a survival advantage. Consequently, there seemed to be a doubt as to whether GDNF has merit in the potential treatment of PD. The purpose of this cutting edge review is to speculate as to why the clinical trials have failed to meet the primary endpoint. We introduce a hypothesis, “Failure of GDNF in clinical trials succumbed by nuclear receptor-related factor 1 (Nurr1) shortfall.” We demonstrate how Nurr1 binds to GDNF to induce dopaminergic neuron synthesis. Due to its undisputable neuro-protection aptitude, we display Nurr1 (also called Nr4a2) as a promising therapeutic target for PD.

Amantadine: reappraisal of the timeless diamond-target updates and novel therapeutic potentials

The aim of the current review was to provide a new, in-depth insight into possible pharmacological targets of amantadine to pave the way to extending its therapeutic use to further indications beyond Parkinson's disease symptoms and viral infections. Considering amantadine's affinities in vitro and the expected concentration at targets at therapeutic doses in humans, the following primary targets seem to be most plausible: aromatic amino acids decarboxylase, glial-cell derived neurotrophic factor, sigma-1 receptors, phosphodiesterases, and nicotinic receptors. Further three targets could play a role to a lesser extent: NMDA receptors, 5-HT3 receptors, and potassium channels. Based on published clinical studies, traumatic brain injury, fatigue [e.g., in multiple sclerosis (MS)], and chorea in Huntington's disease should be regarded potential, encouraging indications. Preclinical investigations suggest amantadine's therapeutic potential in several further indications such as: depression, recovery after spinal cord injury, neuroprotection in MS, and cutaneous pain. Query in the database http://www.clinicaltrials.gov reveals research interest in several further indications: cancer, autism, cocaine abuse, MS, diabetes, attention deficit-hyperactivity disorder, obesity, and schizophrenia.

Nigrostriatal neurons in rat express the glial cell line-derived neurotrophic factor receptor subunit c-RET

The substantia nigra neurons expressing c-RET, a glial cell line-derived neurotrophic factor (GDNF) receptor intracellular tyrosine kinase subunit, were investigated in rats by using a double labeling method which combined retrograde horseradish peroxidase (HRP) labeling after injection into the striatum with immunohistochemistry to c-RET. It was revealed that the distribution of c-RET-immunoreactive neurons and HRP-labeled nigrostriatal neurons overlapped. Numerous double-labeled HRP/c-RET neurons were found in the substantia nigra pars compacta with predominate distribution ipsilateral to the injected striatum. Semiquantitative cell count indicated that a large percentage (97%) of HRP-labeled neurons showed c-RET immunoreactivity. Furthermore, double-labeled HRP/c-RET ones constituted only 61% of total c-RET-immunoreactive neurons in the substantia nigra ipsolateral to the injected striatum. Taken together with previous observations on glial cell line-derived neurotrophic factor in the basal ganglia, this study provides evidence that the c-RET protein may mediate biological activity of GDNF family ligands in most of projecting neurons in the substantia nigra pars compacta where the dopaminergic neurons are numerously distributed. Specially, it suggests that c-RET-mediating signaling cascades may play important roles in neuron-glial interaction that support and sustain nigrostriatal neuronal circuits in the basal ganglia.

GDNF delivery for Parkinson's disease

The mainstays of Parkinson's disease (PD) treatment remain symptomatic, including initial dopamine replacement and subsequent deep brain stimulation, however, neither of these approaches is neuroprotective. Neurotrophic factors - proteins that activate cell signalling pathways regulating neuronal survival, differentiation, growth and regeneration - represent an alternative for treating dopaminergic neurons in PD but are difficult to administer clinically because they do not pass through the blood-brain barrier. Glial cell line-derived neurotrophic factor (GDNF) has potent neurotrophic effects particularly but not exclusively on dopaminergic neurons; in animal models of PD, it has consistently demonstrated both neuroprotective and neuroregenerative effects when provided continuously, either by means of a viral vector or through continuous infusion either into the cerebral ventricles (ICV) or directly into the denervated putamen. This led to a human PD study in which GDNF was administered by monthly bolus intracerebroventricular injections, however, no clinical benefit resulted, probably because of the limited penetration to the target brain areas, and instead significant side effects occurred. In an open-label study of continuous intraputamenal GDNF infusion in five patients (one unilaterally and four bilaterally), we reported excellent tolerance, few side effects and clinical benefit evident within three months of the commencement of treatment. The clinical improvement was sustained and progressive, and by 24-months patients demonstrated a 57 and 63% improvement in their off-medication motor and activities of daily living UPDRS subscores, respectively, with clear benefit in dyskinesias. The benefit was associated with a significant increase in putamenal 18F-dopa uptake on positron emission tomography (PET), and in one patient coming to autopsy after 43 months of unilateral infusion there was evident increased tyrosine hydroxylase immunopositive nerve fibres in the infused putamen. A second open trial in 10 patients using unilateral intraputamenal GDNF infusions has also demonstrated a greater than 30% bilateral benefit in both on- and off-medication scores at 24 weeks. Based on our 6-month results, a randomized controlled clinical trial was conducted to confirm the open-label results, however, GDNF infusion over 6-months did not confer the predetermined level of clinical benefit to patients with PD despite increased 18F-dopa uptake surrounding the catheter tip. It is possible that technical differences between this trial and the positive open label studies contributed to this negative outcome.

Retinoic acid induces functional c-Ret tyrosine kinase in human neuroblastoma

After the treatment of human neuroblastoma SH-SY5Y cells with retinoic acid for 24 h, the expression of c-Ret receptor tyrosine kinase was greatly elevated. Treatment of SH-SY5Y cells with glial cell line-derived neurotrophic factor under serum-free conditions after incubation of cells with retinoic acid resulted in the phosphorylation of c-Ret receptor tyrosine kinase, with subsequent morphological changes that included formation of neurites and rounding of cell bodies within 24-48 h. The number of neurite-bearing cells decreased with increasing concentrations of mitogen-activated protein kinase-specific and phosphatidylinositol 3-kinase inhibitors. These observations suggest that retinoic acid induces the expression of glial cell line-derived neurotrophic factor-responsive c-Ret receptor tyrosine kinase and that a glial cell line-derived neurotrophic factor-c-Ret receptor tyrosine kinase-induced signal transduction system that might be involved in neurite outgrowth via pathways that include phosphatidylinositol 3-kinase and mitogen-activated protein kinase.

Quantitative analysis of the activation mechanism of the multicomponent growth-factor receptor Ret

Cytokines and growth factors signal by modulating the interactions between multiple receptor components to form an activated receptor complex. The quantitative details of the activation mechanisms of this important class of receptors are not well understood. Using receptor phosphorylation measurements in live cells, as well as mathematical modeling and data fitting, we have characterized the multistep mechanism by which the GDNF-family neurotrophin artemin (ART), together with its co-receptor GDNF-family receptor alpha3 (GFRalpha3), brings about activation of the Ret receptor tyrosine kinase through formation of a pentameric signaling complex: ART-(GFRalpha3)(2)-(Ret)(2). By systematically varying the concentrations of ART and cell-surface GFRalpha3, we establish both the sequence of steps by which the signaling complex forms and the affinities of all the steps, including the two-dimensional affinities of the steps involving protein-protein interactions between membrane-bound species. Our results reveal the ways in which the individual binary interactions involved in the activation of a multicomponent receptor govern the receptor's functional properties.

Glial cell line-derived neurotrophic factor promotes olfactory ensheathing cells migration

Olfactory ensheathing cells (OECs) are a unique type of macroglia with axonal growth-promoting properties. The migrating ability of OECs in CNS is essential for neural regeneration. However, little is known about the extracellular and intracellular factors that regulate OEC migration. In the present study, we examined the effects of glial cell line-derived neurotrophic factor (GDNF) on OECs migration. Initially, the "scratch" migration assay, Boyden chamber assay, and explant migration assay showed that GDNF could promote OECs migration in vitro. Treatment of OECs with GDNF also induced cytoskeleton reorganization and up-regulated expression of cytoskeleton proteins. GDNF-induced OECs migration was demonstrated depending on GFRalpha-1 and Ret receptor, and activation of JNK and Src signaling cascades. Furthermore, GDNF was found to promote implanted OECs migration in a spinal cord hemisection injury model. Together, we report, to our knowledge for the first time, that GDNF stimulate OECs migration in vitro and in vivo.

Glial cell line-derived neurotrophic factor (GDNF) receptor alpha-1 (GFR alpha 1) is highly selective for GDNF versus artemin

To clarify whether glial cell line-derived neurotrophic factor (GDNF) receptor alpha-1 (GFRalpha1), the glycosylphosphatidylinositol (GPI)-linked coreceptor for GDNF, is also a functional coreceptor for artemin (ART), we have studied receptor binding, signaling, and neuronal survival. In cell-free binding studies, GFRalpha1-Ig displayed strong preferential binding to GDNF, though in the presence of soluble RET, weak binding to ART could also be detected. However, using GFRalpha1-transfected NB41A3 cells, ART showed no detectable competition against the binding of (125)I-labeled GDNF. Moreover, ART failed to induce phosphorylation of extracellular signal-related kinase (ERK) and Akt in these cells and was >10(4)-fold less potent than GDNF in stimulating RET phosphorylation. When rat primary dorsal root ganglion (DRG) neurons were used, only the survival promoting activity of GDNF and not that of ART was blocked by an anti-GFRalpha1 antibody. These results indicate that although ART can interact weakly with soluble GFRalpha1 constructs under certain circumstances in vitro, in cell-based functional assays GFRalpha1 is at least 10 000-fold selective for GDNF over ART. The extremely high selectivity of GFRalpha1 for GDNF over ART and the low reactivity of ART for this receptor suggest that GFRalpha1 is not likely to be a functional coreceptor for ART in vivo.

Overexpression of glial cell line-derived neurotrophic factor in the CNS rescues motoneurons from programmed cell death and promotes their long-term survival following axotomy

To study the role of one of the most potent motoneuron (MN) survival factors, glial cell line-derived neurotrophic factor (GDNF) derived from the CNS, we generated transgenic animals overexpressing GDNF under the control of an astrocyte-specific GFAP promoter. In situ hybridization revealed that GDNF was expressed at high levels in astrocytes throughout the brain and spinal cord. We analyzed the effects of CNS-derived GDNF on MN survival during the period of programmed cell death (PCD) and after nerve axotomy. In GFAP-GDNF mice at E15, E18, and P1, the survival of brachial MNs was increased on average by 30%, lumbar MNs by 20%, and thoracic MNs at P1 by 33%. GDNF also prevented MN PCD in several cranial motor nuclei. We demonstrated for the first time that the number of MNs in the mouse abducens nucleus was also increased by 40%, thus extending known MN populations that are responsive to GDNF. Next, we tested if GDNF could support complete and relatively long-term survival of MNs following neonatal facial nerve axotomy. We found that virtually all MNs (91%) in GFAP-GDNF mice survived for up to 18 weeks post-axotomy. This is the longest GDNF-mediated survival of neonatal MNs reported following axotomy. Most of surviving MNs were not atrophic, and MN-specific ChAT and neurofilament immunoreactivity (IR) were preserved. Furthermore, GDNF attenuated axotomy-induced astroglial activation. These data demonstrate that overexpression of GDNF in the CNS has very profound effects on MN survival both during the PCD period and after neuronal injury. GFAP-GDNF mice will be valuable to study the effects of CNS-derived GDNF in mouse models of MN degenerative diseases and axonal regeneration in vivo.

Cervical spinal cord delivery of a rabies G protein pseudotyped lentiviral vector in the SOD-1 transgenic mouse. Invited submission from the Joint Section Meeting on Disorders of the Spine and Peripheral Nerves, March 2004

OBJECT

Lentiviral vectors may constitute a vehicle for long-term therapeutic gene expression in the spinal cord. In amyotrophic lateral sclerosis, spinal cord sclerosis and altered axonal transport pose barriers to therapeutic gene distribution. In the present study the authors characterize gene expression distribution and the behavioral impact of the rabies G (RabG) protein pseudotyped lentiviral vector EIAV.LacZ through cervical spinal cord injection in control and Cu/Zn superoxide dismutase-1 (SOD-1) transgenic mice.

METHODS

Seven-week-old SOD-1 transgenic mice and their wild-type littermates underwent exposure of the cervicomedullary junction and microinjection of RabG.EIAV.LacZ or vehicle. The Basso-Beattie-Bresnahan locomotor score, grip strength meter, and Rotarod assays were used to assess the effects of disease progression, spinal cord microinjection, and lentiviral gene expression. Spinal cords were removed when the mice were in the terminal stage of the disease. The distribution of LacZ gene expression was histologically evaluated and quantified. Direct cervical spinal cord microinjection of RabG.EIAV.LacZ results in extensive central nervous system uptake in SOD-1 transgenic mice; these findings were statistically similar to those in wild-type mice (p > 0.05). Gene expression lasts for the duration of the animal's survival (132 days). The SOD-1 mutation does not prevent retrograde axonal transport of the vector. Three behavioral assays were used to demonstrate that long-term gene expression does not alter sensorimotor function. In comparison with normative data, vector injection and transgene expression do not accelerate disease progression.

CONCLUSIONS

Direct spinal cord injection of RabG.EIAV vectors represents a feasible method for delivering therapeutic genes to upper cervical spinal cord and brainstem motor neurons. Distribution is not affected by the SOD-1 mutation or disease phenotype.

Expression of glial cell line-derived neurotrophic factor mRNA in the human newborn and adult hippocampal formation

Glial cell line-derived neurotrophic factor (GDNF) mRNA-containing neurons were found in normal neonate and adult human hippocampus with a localization pattern consistently similar among different ages. They were numerous in proximal CA1 to CA3 pyramidal layer, granular layer and hilus, and sparse in oriens and molecular layers. The present data provide a map of GDNF-producing neurons in the human archicortex and suggest a role for GDNF in neuronal function throughout life.

Immunohistochemical localization of GDNF in the human hippocampal formation from prenatal life to adulthood

In this study, we examined the immunohistochemical occurrence and distribution of glial cell line-derived neurotrophic factor (GDNF) in autoptic specimens of normal human hippocampus at different ages, from 22 weeks of gestation (w.g.) to adult life. Two different anti-GDNF polyclonal antibodies were used. Western blot analysis on homogenates of human and rat brain and recombinant human GDNF resulted in differential detection of monomeric and dimeric forms of the proteins. The ABC immunohistochemical technique revealed that in the Ammon's horn, numerous positive cell bodies occurred in the pyramidal layer, the majority of them being present in the proximal CA1 and in CA2. Sparse positive neurons could be observed in the stratum oriens and moleculare. In the fascia dentata many granule cells showed a light punctate staining, whereas more heavily labelled neurons occurred in the polymorphic layer and, occasionally, in the molecular layer. The distribution pattern of GDNF-like immunoreactivity appeared consistently similar throughout life stages from 29 w.g. to adult age. However, intensity of labelling and frequency of neuronal cell bodies was highest in the neonate and decreased in adulthood. The present data provide a comprehensive map of the localization of GDNF-like immunoreactive neurons in the human archicortex at developmental ages and in the mature tissue and represent a first step towards the identification of hippocampal neurons which express the protein and/or are responsive to it. They further suggest that GDNF may play a role in the development of intrahippocampal circuitry and in neuronal function and maintenance throughout life.

Topographical localization of glial cell line-derived neurotrophic factor in the human brain stem: an immunohistochemical study of prenatal, neonatal and adult brains

As a step towards the identification of the neuronal populations responsive to glial cell line-derived neurotrophic factor (GDNF) in the human nervous system and their changes with age, this study reports on the immunohistochemical localization of the protein GDNF in the autoptic normal human brain stem of pre- and full-term newborns and adult subjects. Two different anti-GDNF polyclonal antibodies were used. Western blot analysis on homogenates of human and rat brain and recombinant human GDNF resulted in differential detection of monomeric and dimeric forms of the proteins. The ABC immunohistochemical technique on cryostat tissue sections showed an uneven distribution of GDNF-like immunoreactive nerve fibers and terminals and neuronal cell bodies. Immunoreactive elements were mainly localized to the spinal trigeminal, cuneate, solitary, vestibular, and cochlear sensory nuclei, dorsal motor nucleus of the vagus nerve, ventral grey column, hypoglossal nucleus, dorsal and ventrolateral medullary reticular formation, pontine subventricular grey and locus coeruleus, lateral regions of the rostral pontine tegmentum, tectal plate, trochlear nucleus, dorsal and median raphe nuclei, caudal and rostral linear nuclei, cuneiform nucleus, and substantia nigra. Comparison between pre- and full-term newborns and adult subjects revealed changes with age in density of positive innervation and frequency of immunoreactive perikarya. The results obtained provide detailed information on the occurrence of GDNF-like immunoreactive neurons in the human brain stem and suggest that the protein is present in a variety of neuronal systems, which subserve different functional activities, at developmental ages and in adult brains.

Gene therapy with herpes simplex virus vectors: progress and prospects for clinical neuroscience

Gene delivery to the nervous system represents perhaps the ultimate challenge of gene therapy in view of the complexity of this system, the wide variety of intractable neurological diseases, and the need to deliver the gene to nondividing cells. Although a variety of systems for such gene delivery are under development, herpes simplex virus has unique advantages in terms of its large genome size and its ability to naturally enter a latent state in neuronal cells. Considerable progress has been made in the effective disablement of this virus while retaining its ability to deliver genes and in producing long-term expression of the foreign gene. It is likely that these viruses may ultimately be of use in human gene therapy procedures for otherwise intractable neurological diseases such as Parkinson's disease.

GDNF and NGF family members and receptors in human fetal and adult spinal cord and dorsal root ganglia

We describe the expression of mRNA encoding ligands and receptors of members of the GDNF family and members of the neurotrophin family in the adult human spinal cord and dorsal root ganglia (DRG). Fetal human spinal cord and ganglia were investigated for the presence of ligands and receptors of the neurotrophin family. Tissues were collected from human organ donors and after routine elective abortions. Messenger RNA was found encoding RET, GFR alpha-1, BDNF, trkB, and trkC in the adult human spinal cord and BDNF, NT-3, p75, trkB, and trkC in the fetal human spinal cord. The percentage of adult human DRG cells expressing p75, trkA, trkB, or trkC was 57, 46, 29, and 24%, respectively, and that of DRG cells expressing RET, GFR alpha-1, GFR alpha-2, or GFR alpha-3 was 79, 20, 51, and 32%, respectively. GFR alpha-2 was expressed selectively in small, GFR alpha-3 principally in small and GFR alpha-1 and RET in both large and small adult human DRG neurons. p75 and trkB were expressed by a wide range of DRG neurons while trkA was expressed in most small diameter and trkC primarily in large DRG neurons. Fetal DRG cells were positive for the same probes as adult DRG cells except for NT-3, which was only found in fetal DRG cells. Messenger RNA species only expressed at detectable levels in fetal but not adult spinal cord tissues included GDNF, GFR alpha-2, NT-3, and p75. Notably, GFR alpha-2, which is expressed in the adult rat spinal cord, was not found in the adult human spinal cord.

Viral vectors for gene therapy in Parkinson's disease

The ability of transplanted neurons from aborted foetuses to produce some therapeutic benefit in Parkinson's disease makes this disease an obvious target for the development of gene therapy procedures which involve delivering the same factors as are provided by the foetal neurons but using a reagent which could be produced in large amounts in a standardised manner. This approach could involve both the delivery of the gene encoding tyrosine hydroxylase to boost dopamine production or the delivery of genes encoding neurotrophic factors such as GDNF to promote the survival of dopaminergic neurons. A variety of different viral and non-viral methods for achieving such gene delivery has been described. These are discussed together with the particular advantages of herpes simplex virus-based vectors which have the potential to deliver multiple therapeutic genes in a single virus vector.

Gene delivery and gene therapy with herpes simplex virus-based vectors

The development of efficient means of delivery genes in vivo is essential both for testing gene function in the intact animal and for human gene therapy procedures. A number of viral and non-viral gene delivery methods have been developed for this purpose. Of those herpes simplex virus (HSV)-based vectors have particular advantages for gene delivery to the nervous system including their ability to infect non-dividing neurones and establish asymptomatic latent infections. Moreover, considerable progress has been made, firstly, in disabling HSV vectors so as to prevent the damaging effects of wild type virus and secondly, to ensure long-term expression of the inserted transgene(s). These vectors thus offer a valuable tool for testing gene function in neuronal cells in vivo and may ultimately be safe enough for use in human gene therapy procedures.

Immunohistochemical localization of glial cell line-derived neurotrophic factor family receptor alpha-1 in the rat brain: confirmation of expression in various neuronal systems

The localization of glial cell line-derived neurotrophic factor (GDNF) family receptor alpha-1 (GFRalpha-1) was investigated in rat brain by immunohistochemistry using a polyclonal antibody against a specific sequence of the rat protein. For raising the antisera in rabbits, we synthesized the oligopeptide SDVFQQVEHISKGN that corresponds to residues 139 to 152 of rat GFRalpha-1. On immunospot assay, 0.5 microg/ml of an affinity-purified antibody was capable of detecting 7.8 pmol of the rat GFRalpha-1 oligopeptides. When rat brain homogenates were examined by Western blots, the antibody revealed two main bands with molecular weights of approximately 47 kDa and 53 kDa, corresponding to the known sizes of GFRalpha-1. Immunohistochemistry in rat brain demonstrated that GFRalpha-1-like immunoreactivity was present in neurons but not in glial cells. The localization of GFRalpha-1-like immunoreactivity was largely consistent with that of the corresponding GFRalpha-1 mRNA. Positive neurons were distributed widely in various brain regions, but were particularly abundant in such regions as the olfactory bulb, diagonal band, substantia innominata, zona incerta, substantia nigra, cerebellar cortex, nuclei of the cranial nerves including auditory system and spinal motoneurons. The present study showed that GFRalpha-1 in the normal central nervous system is expressed preferentially in certain multiple neuronal systems that include cholinergic system as well as dopaminergic system and motor neurons. As GFRalpha-1 protein was found in numerous brain structures, GDNF family ligands may have therapeutic application not only in degenerative diseases affecting in specific nervous systems, such as Parkinson's disease, amyotrophic lateral sclerosis and multiple system atrophy, but in diffusely damaging diseases like cerebrovascular diseases.

Viral vectors in the treatment of Parkinson's disease

Parkinson's disease is an obvious target for the development of gene therapy procedures which could involve both the delivery of the gene encoding tyrosine hydroxylase to boost dopamine production or the delivery of genes encoding neurotrophic factors such as GDNF to promote the survival of dopaminergic neurons. A variety of different viral and nonviral methods for achieving such gene delivery are described together with the particular advantages of herpes simplex virus-based vectors which have the potential to deliver multiple therapeutic genes in a single virus vector.

Distribution and retrograde transport of trophic factors in the central nervous system: functional implications for the treatment of neurodegenerative diseases

Neurotrophins play a crucial role in the maintenance, survival and selective vulnerability of various neuronal populations within the normal and diseased brain. Several families of growth promoting substances have been identified within the central nervous system (CNS) including the superfamily of nerve growth factor related neurotrophin factors, glial derived neurotrophic factor (GDNF) and ciliary neurotrophic factor (CNTF). In addition, other non-neuronal growth factors such as fibroblast growth factor (FGF) have also been identified. This article reviews the trophic anatomy of these factors within the CNS. Intraventricular and intraparenchymal injections of exogenous nerve growth factor result in retrograde labeling mainly within the cholinergic basal forebrain. Distribution of brain derived neurotrophic factor (BDNF) following intraventricular injection is minimal due to the binding to the trkB receptor along the ventricular wall. In contrast, intraparenchymal injections of BDNF results in widespread retrograde transport throughout the CNS. BDNF has also been shown to be transported anterogradely within the CNS. Infusion of GDNF into the CNS results in retrograde transport limited to the nigrostriatal pathway. Hippocampal injections of NT-3 retrogradely label mainly basal forebrain neurons. Retrograde transport of radiolabeled CNTF has only been observed in sensory neurons of the sciatic nerve. Following intraventricular and intraparenchymal infusion of radiolabeled bFGF, retrograde neuronal labeling was found in the telecephalon, diencephalon, mesencephalon and pons. In contrast retrograde labeling for aFGF was found only in the hypothalamus and midbrain. Since select neurotrophins traffic anterogradely and retrogradely within the nervous system, these proteins could be used to treat neurological diseases such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis.

GDNF expression is increased in denervated human skeletal muscle

Glial cell line derived neurotrophic factor (GDNF) is a potent trophic factor for several subpopulations of neurons including motor neurons. Two different transcripts of the GDNF gene (GDNF633 and GDNF555) have been detected in various tissues, including skeletal muscle. Denervation leads to an upregulation of GDNF633 in rat skeletal muscle, indicating that GDNF is involved in the response of skeletal muscle to denervation and possibly in reinnervation. To determine the role of GDNF in human neuromuscular disease, we investigated the expression of both transcripts in normal and denervated muscle and in muscle biopsies from Duchenne muscular dystrophy patients. GDNF expression levels were analyzed by competitive RT-PCR in 38 muscle specimens. Levels of both transcripts were significantly elevated in denervated muscle compared to normal and dystrophic muscle. Morphometric analysis of muscle-fiber calibers and its correlation to GDNF expression revealed that higher levels of GDNF were expressed in rapidly-progressive neurogenic atrophy, including four amyotrophic lateral sclerosis (ALS) cases, compared to cases of chronic atrophy. In dystrophic muscle, transcript levels were not significantly altered compared to normal controls. These data indicate that denervation, but not dystrophy, enhances GDNF expression in human skeletal muscle. Thus, the increase of GDNF expression is part of the reaction of human skeletal muscle to denervation caused by motor nerve lesion. GDNF might act on regenerating nerve fibers during muscle fiber reinnervation.

Topographical distribution of [125I]-glial cell line-derived neurotrophic factor in unlesioned and MPTP-lesioned rhesus monkey brain following a bolus intraventricular injection

The present study determined the topographical distribution profile for [125I]-glial cell line-derived neurotrophic factor in unlesioned and MPTP-lesioned (unilateral intracarotid injection) rhesus monkeys following an intraventricular injection. Autoradiographic analysis showed that following a bolus intraventricular injection, there was widespread distribution of [125I]-glial cell line-derived neurotrophic factor throughout the ventricular system (walls of lateral, third, and fourth ventricles and aqueduct), with some accumulation at the lateral ventricle injection site, possibly associated with the ependymal cell layer. In both unlesioned and MPTP-lesioned monkeys, there was labelling of the cerebral cortex, substantia nigra/ventral tegmental area and sequestration of [125I]-glial cell line-derived neurotrophic factor adjacent to the hippocampal formation, globus pallidus, ventral to and in the substantia nigra. However, [125I]-glial cell line-derived neurotrophic factor did not appear to diffuse readily or accumulate in the caudate-putamen even though there was some penetration away from the ventricular walls. Throughout the brain, there was also substantial non-parenchymal labelling of [125I]-glial cell line-derived neurotrophic factor, possibly associated with extracellular matrix components, meninges and vasculature due to the heparin binding properties of glial cell line-derived neurotrophic factor. In addition to the extensive loss of tyrosine hydroxylase immunoreactivity within the substantia nigra, there was also decreased accumulation of [125I]-glial cell line-derived neurotrophic factor and reduced glial cell line-derived neurotrophic factor immunoreactivity ipsilateral to the lesion. Microscopic analysis showed that glial cell line-derived neurotrophic factor immunoreactivity was associated with upper cortical layers including a high density of immunoreactivity at the surface of the cortex (meningeal, pial layer, vasculature) and around the ventricular walls (with some cellular labelling and labelling of vasculature). Moderate staining was observed in nigral cells contralateral to the MPTP-lesion, whereas only minimal levels of that glial cell line-derived neurotrophic factor immunoreactivity were detected ipsilateral to the lesion. This study shows that intraventricularly injected glial cell line-derived neurotrophic factor accumulates not only around the ventricular walls, but also in specific brain regions in which sub-populations of cells are more readily accessible than others. The presence of cells labelled with [125I] and immunopositive for glial cell line-derived neurotrophic factor in the substantia nigra indicates that these cells are a target for the trophic factor following intraventricular administration. Thus, the behavioral improvement observed in MPTP-lesioned monkeys following an intraventricular injection of glial cell line-derived neurotrophic factor is likely the result of activation of nigral cells.

Glial cell line-derived neurotrophic factor attenuates the locomotor hypofunction and striatonigral neurochemical deficits induced by chronic systemic administration of the mitochondrial toxin 3-nitropropionic acid

The present study investigated whether glial cell line-derived neurotrophic factor prevents the progressive striatal degeneration induced by chronic systemic administration of the mitochondrial toxin, 3-nitropropionic acid. In addition, the effects of delayed treatment with glial cell line-derived neurotrophic factor on toxin-induced behavioural and neurochemical deficits were determined. Locomotor activity in rats infused with 3-nitropropionic acid (15 mg/kg/day, for four weeks) via subcutaneous osmotic minipumps was considerably reduced compared to control rats. However, in rats given a single intracerebroventricular injection of 100 micrograms of glial cell line-derived neurotrophic factor, locomotor activity was significantly higher than in rats injected with the vehicle, an effect that was most pronounced at the onset of toxin infusion. Consistent with a protective or restorative effect in this model of striatal neurodegeneration, toxin-induced deficits in markers of neurotransmitter function were attenuated by glial cell line-derived neurotrophic factor. Thus, [3H]GABA uptake and [3H]tiagabine/GABA uptake sites in striatal target tissues (globus pallidus and substantia nigra), as well as [3H]choline uptake, choline acetyltransferase activity and dopamine receptor binding in the striatum were decreased by the toxin and restored to varying degrees by glial cell line-derived neurotrophic factor administration. As with locomotor abnormalities, effects on neurochemical deficits were most prominent when glial cell line-derived neurotrophic factor was given at the start of toxin infusion, but remained significantly higher than in the vehicle-injected rats when given up to two weeks after. Substance P, dynorphin A and [Met]enkephalin levels in the striatal target tissues also were reduced by 3-nitropropionic acid. The results show that glial cell line-derived neurotrophic factor protects striatal neurons from slow excitotoxic cell death resulting from energy deprivation, secondary to mitochondrial dysfunction. Moreover, they suggest that glial cell line-derived neurotrophic factor may be a viable therapeutic agent for slowly progressive central nervous system disorders, like Huntington's disease, that may be caused by secondary excitotoxicity resulting from abnormal energy utilization.

Adenoviral vector-mediated GDNF gene therapy in a rodent lesion model of late stage Parkinson's disease

A recombinant adenoviral vector encoding the human glial cell line-derived neurotrophic factor (GDNF) gene (Ad-GDNF) was used to express the neurotrophic factor GDNF in the unilaterally 6-hydroxydopamine (6-OHDA) denervated substantia nigra (SN) of adult rats ten weeks following the 6-OHDA injection. 6-OHDA lesions significantly increased apomorphine-induced (contralateral) rotations and reduced striatal and nigral dopamine (DA) levels by 99% and 70%, respectively. Ad-GDNF significantly (P < 0.01) decreased (by 30-40%) apomorphine-induced rotations in lesioned rats for up to two weeks following a single injection. Locomotor activity, assessed 7 days following the Ad-GDNF injection, was also significantly (P < 0.05) increased (by 300-400%). Two weeks after the Ad-GDNF injection, locomotor activity was still significantly increased compared to the Ad-beta-gal-injected 6-OHDA lesioned (control) group. Additionally, in Ad-GDNF-injected rats, there was a significant decrease (10-13%) in weight gain which persisted for approximately two weeks following the injection. Consistent with the behavioral changes, levels of DA and the metabolite dihydroxyphenylacetic acid (DOPAC) were elevated (by 98% and 65%, respectively) in the SN, but not the striatum of Ad-GDNF-injected rats. Overall, a single Ad-GDNF injection had significant effects for 2-3 weeks following administration. These results suggest that virally delivered GDNF promotes the recovery of nigral dopaminergic tone (i.e.: increased DA and DOPAC levels) and improves behavioral performance (i.e.: decreased rotations, increased locomotion) in rodents with extensive nigrostriatal dopaminergic denervation. Moreover, our results suggest that viral delivery of trophic factors may be used eventually to treat neurodegenerative diseases such as Parkinson's disease.

Studies on neuroprotective and regenerative effects of GDNF in a partial lesion model of Parkinson's disease

Intrastriatal 6-hydroxydopamine injections in rats induce partial lesions of the nigrostriatal dopamine (DA) system which are accompanied by a delayed and protracted degeneration of DA neurons within the substantia nigra. By careful selection of the dose and placement of the toxin it is possible to obtain reproducible and regionally defined partial lesions which are well correlated with stable functional deficits, not only in drug-induced behaviors but also in spontaneous motoric and sensorimotoric function, which are analogous to the symptoms seen in patients during early stages of Parkinson's disease. The intrastriatal partial lesion model has proved to be particularly useful for studies on the mechanisms of action of neurotrophic factors since it offers opportunities to investigate both protection of degenerating DA neurons during the acute phases after the lesion and stimulation of regeneration and functional recovery during the chronic phase of the postlesion period when a subset of the spared nigral DA neurons persist in an atrophic and dysfunctional state. In the in vivo experiments performed in this model glial cell line-derived neurotrophic factor (GDNF) has been shown to exert neurotrophic effects both at the level of the cell bodies in the substantia nigra and at the level of the axon terminals in the striatum. Intrastriatal administration of GDNF appears to be a particularly effective site for induction of axonal sprouting and regeneration accompanied by recovery of spontaneous sensorimotor behaviors in the chronically lesioned nigrostriatal dopamine system.

Glial cell line-derived neurotrophic factor-levodopa interactions and reduction of side effects in parkinsonian monkeys

Glial cell line-derived neurotrophic factor (GDNF) stimulates the nigrostriatal dopaminergic pathway and improves motor functions in animal models of parkinsonism. Sinemet is currently the most widely used drug for treating Parkinson's disease. The present study has evaluated GDNF-Sinemet interactions in parkinsonian rhesus monkeys. Both GDNF and Sinemet, when given alone, significantly improved total parkinsonian scores. The response to Sinemet did not change after intracerebroventricular vehicle injections. In contrast, there was a functional interaction between GDNF and levodopa. When comparing the levodopa dose response before and after GDNF treatment, significant behavioral improvements were seen after trophic factor administration at every levodopa dose level except 500 mg. Adverse responses to Sinemet treatment alone in parkinsonian animals included vomiting, dykinesias, dystonias, and stereotypic movements. Combined GDNF-Sinemet treatment significantly reduced the occurrence of these levodopa-induced side effects, with a >90% decrease in adverse responses seen at the mid-Sinemet (250 mg levodopa-25 mg carbidopa) dose level. The only side effect from GDNF treatment was a transitory weight loss. Thus, combined GDNF-Sinemet treatment could be of therapeutic value in treating parkinsonism, by producing a greater functional response and by mitigating adverse responses to Sinemet treatment.

Glial cell line-derived neurotrophic factor attenuates behavioural deficits and regulates nigrostriatal dopaminergic and peptidergic markers in 6-hydroxydopamine-lesioned adult rats: comparison of intraventricular and intranigral delivery

The effects of intranigrally- or intraventricularly-administered glial cell line-derived neurotrophic factor were tested on low dose (0.05 mg/kg) apomorphine-induced rotations and tyrosine hydroxylase activity in the substantia nigra and striatum of stable 6-hydroxydopamine-lesioned rats. In addition, we determined if 6-hydroxydopamine lesions in the absence or presence of treatment affected neuropeptide (substance P, met-enkephalin, dynorphin) content in the striatum. Glial cell line-derived neurotrophic factor, when administered intranigrally, prevented apomorphine-induced rotational behaviour for 11 weeks following a single injection. In comparison, intraventricularly-administered glial cell line-derived neurotrophic factor produced a transient reduction in rotational behaviour that lasted for two to three weeks following a single injection. We also show that rotational behaviour is reduced following each subsequent intraventricular injection of glial cell line-derived neurotrophic factor given every six weeks, a time-point when baseline rotation deficits were re-established. Intranigrally- or intraventricularly-administered glial cell line-derived neurotrophic factor significantly reduced weight gain in all 6-hydroxydopamine-lesioned rats in this study. Following behavioural analysis where a confirmed improvement of behaviour was established, tissues were dissected for neurochemical analysis. In lesioned rats with intranigral injections of administered glial cell line-derived neurotrophic factor, significant increases of nigral, but not striatal tyrosine hydroxylase activity were measured. Additionally, 6-hydroxydopamine lesions significantly increased striatal dynorphin (61-139%) and met-enkephalin (81-139%), but not substance P levels. In these rats, intranigrally-administered glial cell line-derived neurotrophic factor injections reversed lesion-induced increases in nigral dynorphin A levels and increased nigral dopamine levels, but did not alter nigral met-enkephalin or substance P levels nor striatal dopamine levels. In lesioned rats with intraventricular injections of glial cell line-derived neurotrophic factor, tyrosine hydroxylase ispilateral to the lesion was increased in the substantia nigra, but not in the striatum. Intraventricularly-administered glial cell line-derived neurotrophic factor did not reverse lesion-induced increases in nigral dynorphin A or met-enkephalin levels nor did glial cell line-derived neurotrophic factor affect substance P levels in the striatum. These results suggest that in an animal model of Parkinson's disease, the neurotrophic factor glial cell line-derived neurotrophic factor reverses behavioural consequences of 6-hydroxydopamine administration, an effect that may involve both dopaminergic and peptidergic neurotransmission.

Intracerebroventricular glial cell line-derived neurotrophic factor improves motor function and supports nigrostriatal dopamine neurons in bilaterally 6-hydroxydopamine lesioned rats

In order to evaluate the efficacy of glial cell line-derived neurotrophic factor (GDNF) in a model of advanced Parkinson's disease, we studied rats with extensive bilateral lesions of the nigrostriatal pathway. Adult male F344 rats were injected bilaterally into the medial forebrain bundle with the neurotoxin 6-hydroxydopamine. Locomotor ability as measured by total distance traveled in an open field over 20 min, as well as von Frey hair testing of sensorimotor neglect, was monitored weekly. Rats demonstrating severe motor impairment and sensorimotor neglect were used for this study and were sorted to achieve similar average behavioral scores between the two treatment groups. After 2 weeks of pretesting, the rats received 250 microg GDNF or vehicle injected into the right lateral cerebral ventricle. Three weeks later, an additional 500 microg GDNF or vehicle was injected into the contralateral ventricle. The rats were monitored for another 2 weeks prior to sacrifice. Behavioral results indicated that von Frey hair scores were inconsistent between tests for each rat and were unchanged following GDNF treatment. However, GDNF recipients demonstrated significant improvement in locomotor ability compared to vehicle recipients. High-pressure liquid chromatography-electrochemical detection analysis of neurotransmitter levels revealed a significant increase in dopamine content within the substantia nigra and ventral tegmenta, but not the striata, of GDNF-treated rats. Further, immunohistochemical staining of tissues from matched pairs of rats revealed increased numbers of tyrosine hydroxylase-positive ventral mesencephalic neurons in one of the two pairs of rats examined. These results suggest that intracerebroventricular GDNF administration improves motor ability and supports nigrostriatal dopaminergic neurons in a model of severe Parkinson's disease.

Glial cell line-derived neurotrophic factor induces the dopaminergic and cholinergic phenotype and increases locomotor activity in aged Fischer 344 rats

Glial cell line-derived neurotrophic factor has been shown to affect dopaminergic and cholinergic neuron markers and functions in young rats. However, it is not known if the response to exogenous glial cell line-derived neurotrophic factor is augmented during normal aging. Thus, the effects of chronic intraventricular infusions of glial cell line-derived neurotrophic factor were determined in young adult (three-months-old) and aged (24-months-old) Fischer 344 (F344) male rats. The effects of glial cell line-derived neurotrophic factor were compared to the effects of the neurotrophin nerve growth factor. Growth factors were administered at a dose of 10 mg/day for 14 days. Locomotor activity and weight changes were also examined in all rats. Aged F344 rats showed significantly reduced (by 75-80%) locomotor activity compared to young rats. In glial cell line-derived neurotrophic factor-treated aged and young rats there was significantly increased (242% and 149%, respectively) locomotor activity measured at seven days. There was also a significant increase in locomotor activity measured 14 days after the start of infusion. Both glial cell line-derived neurotrophic factor and nerve growth factor reduced weight gain by 10% in young and old F344 rats. Two weeks following the start of nerve growth factor or glial cell line-derived neurotrophic factor administration the brains were used for neurochemical analyses. Glial cell line-derived neurotrophic factor significantly increased tyrosine hydroxylase activity in the substantia nigra and striatum of aged rats and in the substantia nigra of young rats. Nerve growth factor treatment did not significantly affect tyrosine hydroxylase activity. However, glial cell line-derived neurotrophic factor and nerve growth factor increased choline acetyltransferase activity in the septum, hippocampus, striatum and cortex of aged rats and in the hippocampus and striatum of young rats to a comparable degree. These findings indicate that specific dopaminergic and cholinergic neuron populations remain responsive to glial cell line-derived neurotrophic factor during the life span of the rat and may be involved in maintaining phenotypic expression within multiple neuronal populations. Additionally, the glial cell line-derived neurotrophic factor-induced up-regulation of brain neurotransmitter systems may be responsible for increased locomotor activity in F344 rats.

Glial cell line-derived neurotrophic factor: distribution and pharmacology in the rat following a bolus intraventricular injection

Glial cell line-derived neurotrophic factor (GDNF) has been shown to increase dopaminergic parameters in vitro and in vivo and can reduce parkinsonian behaviors in animal models of the disease. This study determined the potential of the lateral ventricle as an administration route for GDNF by examining the distribution and neurochemical consequences of a single intraventricular injection. Autoradiographic analysis showed that intraventricularly administered [125I]GDNF was distributed throughout the ventricular system at 1 and 24 h following injection. The cerebral cortex, septum, diagonal band, fimbria, striatum, hippocampus, hypothalamus, substantia nigra/ventral tegmental area, and cerebellum were also labeled. At 7 days, there was still labeling throughout the ventricular system, hypothalamus, substantia nigra, and cerebellum. Twenty-four hours following an intrastriatal injection of [125I]GDNF, label was observed in the substantia nigra/ventral tegmental area, demonstrating retrograde transport. The neurochemical effects of intraventricularly administered GDNF (0.1-100 micrograms) at 7 days post injection were also examined. GDNF significantly increased striatal (approximately 28%) and nigral (up to 40%) dopamine, as well as regulated the dopamine metabolites homovanillic acid and dihydroxyphenylacetic acid. Dopamine levels were unchanged in the frontal cortex. Dopamine content was significantly increased in the hypothalamus (up to 35%), an increase which may contribute to the inhibition of weight gain seen after administration of GDNF. Additionally, dopamine turnover was decreased or unchanged across the brain regions analyzed, which may indicate that in unlesioned rats, intraventricularly administered GDNF stimulates the synthesis and storage of dopamine. This study shows that intraventricularly injected GDNF can access basal ganglia structures, most notably the midbrain dopamine cell body region, and remains present in this area for at least 7 days following a single administration. GDNF differentially increases dopaminergic tone within a variety of brain structures, including the nigrostriatal pathway. These data support the potential effectiveness of intraventricular administered GDNF as a treatment for Parkinson's disease.

Germline mutations in glial cell line-derived neurotrophic factor (GDNF) and RET in a Hirschsprung disease patient

Hirschsprung disease (HSCR), or congenital aganglionic megacolon, is the most common cause of congenital bowel obstruction with an incidence of 1 in 5000 live births. HSCR may be inherited as a single gene disorder with reduced penetrance or as a multigenic trait. HSCR mutations have been identified in the RET receptor tyrosine kinase, endothelin-B receptor (EDNRB) and its physiological ligand, endothelin 3 (EDN3). Although RET's ligand has remained elusive, it is expected to be an extracellular neurotrophic molecule expressed in the developing gut and kidney mesenchyme, based on the phenotypes of intestinal aganglionosis and renal agenesis observed in homozygous RET knockout (Ret -/-) mice. The glial cell line-derived neurotrophic factor (GDNF) is such a molecule. Recently, mice carrying two null alleles for Gdnf were shown to exhibit phenotypes remarkably similar to Ret-/- animals. We screened 106 unrelated HSCR patients for mutations in GDNF by direct sequencing. We identified one familial mutation in a HSCR patient with a known de novo RET mutation and malrotation of the gut. No haplotype sharing was evident in any of 36 HSCR kindreds typed for microsatellite markers surrounding GDNF on human chromosome 5p. Our data suggest that GDNF is a minor contributor to human HSCR susceptibility and that loss of its function in enteric neurogenesis may be compensated for by other neurotrophic factors or via other pathways. However, it may be that in rare instances, RET and GDNF mutations act in concert to produce an enteric phenotype.