Mesencephalic dopaminergic neurons protected by GDNF from axotomy-induced degeneration in the adult brain

The GDNF family members neurturin, artemin and persephin promote the morphological differentiation of cultured ventral mesencephalic dopaminergic neurons

Neurturin (NRTN), artemin (ARTN), persephin (PSPN) and glial cell line-derived neurotrophic factor (GDNF) form a group of neurotrophic factors, also known as the GDNF family ligands (GFLs). They signal through a receptor complex composed of a high-affinity ligand binding subunit, postulated ligand specific, and a common membrane-bound tyrosine kinase RET. Recently, also NCAM has been identified as an alternative signaling receptor. GFLs have been reported to promote survival of cultured dopaminergic neurons. In addition, GDNF treatments have been shown to increase morphological differentiation of tyrosine hydroxylase immunoreactive (TH-ir) neurons. The present comparative study investigated the dose-dependent effects of GFLs on survival and morphological differentiation of TH-ir neurons in primary cultures of E14 rat ventral mesencephalon. Both NRTN and ARTN chronically administered for 5 days significantly increased survival and morphological differentiation of TH-ir cells at all doses investigated [0.1-100 ng/ml], whereas PSPN was found to be slightly less potent with effects on TH-ir cell numbers and morphology at 1.6-100 ng/ml and 6.3-100 ng/ml, respectively. In conclusion, our findings identify NRTN, ARTN and PSPN as potent neurotrophic factors that may play an important role in the structural development and plasticity of ventral mesencephalic dopaminergic neurons.

Differential gene expression after complete spinal cord transection in adult rats: an analysis focused on a subchronic post-injury stage

In an attempt to characterize changes in transcription after a sub-chronic spinal cord injury (SCI), we investigated gene expression profiles using cDNA microarray. Among 7523 genes and expressed sequence tags (ESTs) examined, 444 transcripts, including 218 genes and 226 ESTs, were identified to be either up-regulated (373 of 444) or down-regulated (71 of 444) greater than 2.0-fold in the spinal cord at 14 days after a complete spinal transection at the 11th thoracic level in adult rats. Based on their potential function, these differentially expressed genes were categorized into seven classes which include cell division-related protein, channels and receptors, cytoskeletal elements, extracellular matrix proteins, metalloproteinases and inhibitors, growth-associated molecules, metabolism, intracellular transducers and transcription factors, as well as others. Strong expressional changes were found in all classes revealing the complexity and diversity of gene expression profiles following SCI. We verified array results with RT-PCR for eight genes, Northern blotting for nine genes, and in situ hybridization for one gene and immunohistochemistry for four genes. These analyses confirmed, to a large extent, that the array results have accurately reflected the molecular changes occurring at 14 days post-SCI. Importantly, the current study has identified a number of genes, including annexins, heparin-binding growth-associated protein (HB-GAM), P9ka (S100A4), matrix metalloproteinases, and lysozyme, that may shed new light on SCI-related inflammation, neuroprotection, neurite-outgrowth, synaptogenesis, and astrogliosis. In conclusion, the identification of molecular changes using the large-scale microarray analysis may lead to a better understanding of underlying mechanisms, thus, the development of new repair strategies for SCI.

Motoneurons crave glial cell line-derived neurotrophic factor

This is a commentary on the developmental and therapeutic relevance of recent studies in the glial fibrillary acid protein (GFAP)-glial cell line-derived neurotrophic factor (GDNF) transgenic mouse reported by Zhao et al. (2004). This interesting study demonstrated that increased expression of GDNF in astrocytes increases the number of neighboring motoneurons of certain motoneuron subpopulations by diminishing programmed cell death during development. In addition, astrocyte-derived GDNF was shown to protect facial motoneurons from injury-induced cell death. Since this is the first direct demonstration that secretion of GDNF from astrocytes in the CNS can affect motoneuron development in utero and motoneuron survival after axotomy, novel approaches for motor neuron disease are suggested. The known target neurons that respond to GDNF are reviewed, as are studies using GDNF gene delivery in animal models of amyotrophic lateral sclerosis (ALS). It is postulated that GDNF is a factor to which many motoneurons respond along their whole extent from soma to axon to terminal.

Stroke and TGF-beta proteins: glial cell line-derived neurotrophic factor and bone morphogenetic protein

Recent studies have indicated that proteins in the transforming growth factor-beta superfamily alter damage induced by various neuronal injuries. Of these proteins, glial cell line-derived neurotrophic factor (GDNF) and bone morphogenetic protein-7 (BMP-7) have unique protective and regenerative effects in stroke animals. Delivery of GDNF or BMP-7 to brain tissue reduced cerebral infarction and improved motor functions in stroke animals. Pretreatment with these factors reduced caspase-3 activity and DNA fragmentation in the ischemic brain region, suggesting that antiapoptotic effects are involved. Beside the protective effects, BMP-7 given after stroke improves locomotor function. These regenerative effects of BMP-7 may involve the enhancement of dendritic growth and remodeling. In this review, we illustrate the neuroprotective and neuroregenerative properties of GDNF and BMP-7 and emphasize their therapeutic potential for stroke.

Mice expressing a dominant-negative Ret mutation phenocopy human Hirschsprung disease and delineate a direct role of Ret in spermatogenesis

The Ret receptor tyrosine kinase mediates physiological signals of glial cell line-derived neurotrophic factor (GDNF) family ligands (GFLs) and is essential for postnatal survival in mice. It is implicated in a number of human diseases and developmental abnormalities. Here, we describe our analyses of mice expressing a Ret mutant (RetDN) with diminished kinase activity that inhibits wild-type Ret activity, including its activation of AKT. All RetDN/+ mice died by 1 month of age and had distal intestinal aganglionosis reminiscent of Hirschsprung disease (HSCR) in humans. The RetDN/+ proximal small intestine also had severe hypoganglionosis and reduction in nerve fiber density, suggesting a potential mechanism for the continued gastric dysmotility in postsurgical HSCR patients. Unlike Ret-null mice, which have abnormalities in the parasympathetic and sympathetic nervous systems, the RetDN/+ mice only had defects in the parasympathetic nervous system. A small proportion of RetDN/+ mice had renal agenesis, and the remainder had hypoplastic kidneys and developed tubulocystic abnormalities postnatally. Postnatal analyses of the testes revealed a decreased number of germ cells, degenerating seminiferous tubules,maturation arrest and apoptosis, indicating a crucial role for Ret in early spermatogenesis.

Increased extracellular dopamine concentrations and FosB/ΔFosB expression in striatal brain areas of heterozygous GDNF knockout mice

Glial cell line-derived neurotrophic factor (GDNF) has been shown to be involved in the maintenance of striatal dopaminergic neurons. To study whether reduced levels of endogenous GDNF affect the striatal dopaminergic transmission we estimated the basal extracellular levels of dopamine in vivo, the basal expression of FosB-related proteins in striatal brain areas as well as the effects of acute and repeated cocaine on locomotor activity and dopamine output in mice lacking one GDNF allele (heterozygous GDNF+/- mice). As expected the striatal GDNF protein content was found to be smaller in the GDNF+/- mice than in their wild-type littermates. Unexpectedly the extracellular dopamine concentration in the GDNF+/- mice in the dorsal striatum (CPu) was 2.0-fold, and in the nucleus accumbens (NAc) 1.6-fold the concentration found in the wild-type littermates. Also FosB/DeltaFosB-like immunoreactivity was found to be elevated in the CPu as well as in the core and in the shell of NAc of the GDNF+/- mice as compared with the wild-type mice. This suggests chronic postsynaptic activation of these brain areas and is in line with elevated extracellular dopamine concentrations. Cocaine's effects acutely and after repeated treatment on locomotor activity were similar in the GDNF+/- and the wild-type mice. Neither did cocaine's acute effects on dopamine output differ between the mice of the two strains. Our findings demonstrate that reduced levels of endogenous GDNF induce alterations in dorsal striatal and accumbal dopaminergic transmission, and stress the importance of endogenous GDNF in the regulation of the dopaminergic neurons.

Growth factor deprivation induces an alternative non-apoptotic death mechanism that is inhibited by Bcl2 in cells derived from neural precursor cells

Although apoptosis has been considered the typical mechanism for physiological cell death, presently alternative mechanisms need to be considered. We previously showed that fibroblast growth factor-2 (FGF2) could act as a survival factor for neural precursor cells. To study the death mechanism activated by the absence of this growth factor, we followed the changes in cell morphology and determined cell viability by staining with several dyes after FGF2 removal from mesencephalic neural-progenitor-cell cultures. The changes observed did not correspond to those associated with apoptosis. After 48 h in the absence of FGF2, cells began to develop vacuoles in their cytoplasm, a phenotype that became very obvious 3-5 days later. Double-membrane vacuoles containing cell debris were observed. Vacuolated cells did not stain with either ethidium bromide or trypan Blue, and did not show chromatin condensations. Nonetheless, during the course of culture, vacuolated cells formed aggregates with highly condensed chromatin and detached from the plate. Neural progenitor cells grown in the presence of FGF2 did not display any of those characteristics. The vacuolated phenotype could be reversed by the addition of FGF2. Typical autophagy inhibitors such as 3-MA and LY294002 inhibited vacuole development, whereas a broad-spectrum caspase inhibitor did not. Interestingly, Bcl-2 overexpression retarded vacuole development. In conclusion, we identified a death autophagy-like mechanism activated by the lack of a specific survival factor that can be inhibited by Bcl2. We propose that anti-apoptotic Bcl2 family members are key molecules controlling death activation independently of the cell degeneration mechanism used.

Encapsulated GDNF-producing C2C12 cells for Parkinson's disease: a pre-clinical study in chronic MPTP-treated baboons

Glial cell line-derived neurotrophic factor (GDNF), a potent neurotrophic factor with restorative effects in a variety of rodent and primate models of Parkinson's disease (PD), could be of therapeutic value to PD. In this study, we show that intraventricular chronic infusion of low doses of GDNF using encapsulated genetically engineered C2C12 cells can exert: (1) transient recovery of motor deficits (hypokinesia); (2) significant protection of intrinsic striatal dopaminergic function in the immediate vicinity of the site of implantation of the capsule in the caudate nucleus, and (3) significant-long-lasting-neurotrophic properties at the nigral level with an increase volume of the cell bodies. These observations confirm the potent neurorestorative potential of GDNF in PD and the safety/efficacy of the encapsulation technology as a means to deliver in situ this neurotrophic cytokine even using an intraventricular approach.

Postischemic administration of Sendai virus vector carrying neurotrophic factor genes prevents delayed neuronal death in gerbils

Sendai virus (SeV) vector-mediated gene delivery of glial cell line-derived neurotrophic factor (GDNF) and nerve growth factor (NGF) prevented the delayed neuronal death induced by transient global ischemia in gerbils, even when the vector was administered several hours after ischemia. Intraventricular administration of SeV vector directed high-level expression of the vector-encoded neurotrophic factor genes, which are potent candidates for the treatment of neurodegenerative diseases. After occlusion of the bilateral carotid arteries of gerbils, SeV vector carrying GDNF (SeV/GDNF), NGF (SeV/NGF), brain-derived neurotrophic factor (SeV/BDNF), insulin-like growth factor-1 (SeV/IGF-1) or vascular endothelial growth factor (SeV/VEGF) was injected into the lateral ventricle. Administration of SeV/GDNF, SeV/NGF or SeV/BDNF 30 min after the ischemic insult effectively prevented the delayed neuronal death of the hippocampal CA1 pyramidal neurons. Furthermore, the administration of SeV/GDNF or SeV/NGF as late as 4 or 6 h after the ischemic insult also prevented the death of these neurons. These results indicate that SeV vector-mediated gene transfer of neurotrophic factors has high therapeutic potency for preventing the delayed neuronal death induced by transient global ischemia, and provides an approach for gene therapy of stroke.

Elevated glial brain-derived neurotrophic factor in Parkinson's diseased nigra

We show the cellular distribution of immunoreactivity (IR) for brain-derived-neurotrophic-factor (BDNF), neurotrophin-3 (NT-3) and tyrosine kinase receptors TRKB and TRKC in idiopathic Parkinson's disease (IPD) and controls at post-mortem. In both groups, nigral neurons, astrocytes, ramified and amoeboid microglia expressed all antigens. Caudate-putamen neurons expressed all antigens except BDNF with similar distribution between groups. In IPD nigra, increased numbers of BDNF-IR and, less frequently, NT-3-IR ramified glia surrounded fragmented neurons, accompanied by BDNF-IR in surrounding neuropil. Amoeboid microglia were abundant only in IPD nigral scars. In IPD, glia might up-regulate neurotrophins in response to signals released from failing nigral neurons.

Pleiotrophin mRNA is highly expressed in neural stem (progenitor) cells of mouse ventral mesencephalon and the product promotes production of dopaminergic neurons from embryonic stem cell-derived nestin-positive cells

Neural stem cells are promising candidates for donor cells in neural transplantation. However, the mechanism by which neural stem cells differentiate into neurons is not well understood. In the present study, a serial analysis of gene expression (SAGE) was carried out to generate a gene file of neural stem (progenitor) cells from the mouse ventral mesencephalon. Among the 15,815 tags investigated, the mRNA of the housekeeping genes (elongation factor 1-alpha, ATPase subunit 6, GAPDH, actin), laminin receptor 1, HSP 70, pleiotrophin, and nestin were highly expressed. Because pleiotrophin (PTN) exhibits mitogenic and trophic effects on neural development and exhibits trophic effects on survival of dopaminergic (DAergic) neurons, we investigated the role of PTN in neurogenesis, especially to DAergic neurons. Here, we show that PTN increased the production of tyrosine hydroxylase (TH)-positive neurons from embryonic stem (ES) cell-derived nestin-positive cells. The expression of Nurr1 mRNA was enhanced by PTN. L-dopa in the culture medium was increased by PTN. This effect was as strong as with sonic hedgehog. Data suggest that PTN mRNA is highly expressed in neural stem (progenitor) cells of mouse ventral mesencephalon, and PTN promotes the production of DAergic neurons from ES cell-derived nestin-positive cells.

Insulin-like growth factor 1 prevents neuronal cell death induced by corticosterone through activation of the PI3k/Akt pathway

Corticosterone (CORT) is well known to induce neuronal damage in various brain regions including the hippocampus, but the precise mechanism(s) of action underlying these effects has yet to be fully established. Insulin-like growth factor-1 (IGF-1) is a trophic factor promoting cell survival by the activation of the phosphatidylinositide 3-kinase (PI3K)/Akt kinase pathway. We report that IGF-1 prevents neuronal cell death induced by CORT, likely via the stimulation of the PI3K/Akt pathway in primary hippocampal cultured neurons. CORT induced neuronal cell death at a minimal concentration of 50 nM. IGF-1 (10 nM) prevented cell death induced by CORT under serum-free conditions. The neuroprotective effect of IGF-1 was accompanied by reversal of the Akt pathway inhibition induced by CORT. The PI3 kinase inhibitor, LY29004, inhibited the neuroprotective effect of IGF-1 whereas the MEK (MAPK kinase) inhibitor PD98059, an upstream blocker of mitogen-activated protein (MAP) kinase, had no effect. These results suggest that IGF-1 can prevent neuronal cell death induced by CORT in hippocampal neurons by modulating the activity of the PI3K/Akt pathway.

Enhanced survival, reinnervation, and functional recovery of intrastriatal dopamine grafts co-transplanted with Schwann cells overexpressing high molecular weight FGF-2 isoforms

Dopaminergic (DA) micrografts were co-transplanted with Schwann cells (SC) overexpressing 18 kDa and 21/23 kDa FGF-2 into the caudate-putamen unit (CPu) of unilaterally 6-hydroxydopamine-lesioned rats. We report here that SC engineered to overexpress FGF-2 promoted DA-graft-induced restoration, whether co-transplanted at the same site or grafted at a second more distant site within the CPu. In addition, the 21/23 kDa FGF-2 isoforms resulted in a significantly better reinnervation and survival of dopaminergic micrografts when compared to the 18-kDa FGF-2 isoform. However, this effect was not that distinct on functional recovery due to, for example, ceiling effects. One main finding of this study was the influence of the gene promotor on DA survival, respectively, vector-mediated trophism. Therefore, comparisons in terms of survival between 18 kDa and higher molecular weight (HMW) FGF-2 are complicated in the mixed grafted experiments. Furthermore, the first demonstration of the presence of the 21/23 kDa FGF-2 isoforms in the nigrostriatal system and their potent neurotrophic in vivo activities, as shown in the present study, suggest (I) a physiological role of these proteins for dopaminergic neurons and (II) a restorative potential under normal as well as regenerative processes. However, FGF-2-mediated effects are more pronounced after co-transplantation with SC/DA cells mixed in one suspension at the same implantation side than in the side-by-side approach with a spatially and temporally separated transplantation of SC (day 1) and DA-cells (day 3). These findings indicate the necessity of direct contact between FGF-2 and DA-neurons, further elucidate the neurotrophic role of FGF-2 for DA-neurons and highlight the differential restorative potentials of its respective isoforms. We propose that administration of HMW FGF-2 may be used to improve function in the rat Parkinson's disease model.

The spinal GDNF level is increased after transient spinal cord ischemia in the rat

Glial cell line-derived neurotrophic factor (GDNF) is known as the most potent neurotrophic factor against injury. We have characterized spinal GDNF changes after ischemia to clarify its possible physiological role against ischemic damage. Spinal ischemia in the rat was produced by cross-clamping of the thoracic aorta together with systemic hypotension. The spinal tissue GDNF level was measured by enzyme-linked immunoabsorbent assay (ELISA) and the localization of GDNF in the tissue was examined by immunohistochemistry. GDNF was increased reaching two peaks after ischemia. The first peak was at 2 hrs after onset of recirculation derived from alpha motor neurons. The second GDNF peak was at 72 hrs provided by astrocytes. These data suggest a necessity of GDNF to increase to protect against ischemic damage, and that activated astrocytes may have an important role in maintaining the GDNF level.

Neurotrophic actions of the novel AMPA receptor potentiator, LY404187, in rodent models of Parkinson's disease

Recent developments in the molecular biology and pharmacology of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors has led to the discovery of selective, potent and systemically active AMPA receptor potentiators. These molecules enhance synaptic transmission and evidence suggests that they play important roles in plasticity and cognitive processes. Activation of AMPA receptors also increases neuronal activation and activity-dependent signalling, which may increase brain-derived neurotrophic factor (BDNF) expression and enhance cell proliferation in the brain. We therefore hypothesised that an AMPA receptor potentiator may provide neurotrophic effects in rodent models of Parkinson's disease. In the present studies we report that the potent and selective AMPA receptor potentiator, R,S-N-2-(4-(4-Cyanophenyl)phenyl)propyl 2-propanesulfonamide (LY404187), provides both functional, neurochemical and histological protection against unilateral infusion of 6-hydroxydopamine into the substantia nigra or striatum of rats. The compound also reduced 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced toxicity in mice. Interestingly, we were also able to observe large functional and histological effects when we delayed treatment until after cell death had occurred (3 or 6 days after 6-hydroxydopamine infusion), supporting a neurotrophic mechanism of action. In addition, LY404187 provided a dose-dependent increase in growth-associated protein-43 expression in the striatum. Therefore, we propose that AMPA receptor potentiators offer the potential of a new therapy to halt the progression and perhaps repair the degeneration in Parkinson's disease.

Expression of GDNF and GFR?1 in mouse taste bud cells

GDNF (glial cell line-derived neurotrophic factor) affects the survival and maintenance of central and peripheral neurons. Using an immunocytochemical method, we examined whether the taste bud cells in the circumvallate papillae of normal mice expressed GDNF and its GFR alpha 1 receptor. Using double immunostaining for either of them and NCAM, PGP 9.5, or alpha-gustducin, we additionally sought to determine what type of taste bud cells expressed GDNF or GFR alpha 1, because NCAM is reported to be expressed in type-III cells, PGP 9.5, in type-III and some type-II cells, and alpha-gustducin, in some type-II cells. Normal taste bud cells expressed both GDNF and GFR alpha 1. The percentage of GDNF-immunoreactive cells among all taste bud cells was 31.63%, and that of GFR alpha 1-immunoreactive cells, 83.21%. Confocal laser scanning microscopic observations after double immunostaining showed that almost none of the GDNF-immunoreactive cells in the taste buds were reactive with anti-NCAM or anti-PGP 9.5 antibody, but could be stained with anti-alpha-gustducin antibody. On the other hand, almost all anti-PGP 9.5- or anti-alpha-gustducin-immunoreactive cells were positive for GFR alpha 1. Thus, GDNF-immunoreactive cells did not include type-III cells, but type-II cells, which are alpha-gustducin-immunoreactive; on the other hand, GFR alpha 1-immunoreactive cells included type-II and -III cells, and perhaps type-I cells. We conclude that GDNF in the type-II cells may exert trophic actions on type-I, -II, and -III taste bud cells by binding to their GFR alpha 1 receptors.

Enhancement of Tyrosine Hydroxylase Phosphorylation and Activity by Glial Cell Line-derived Neurotrophic Factor

Although glial cell-line derived neurotrophic factor (GDNF) acts as a potent survival factor for dopaminergic neurons, it is not known whether GDNF can directly alter dopamine synthesis. Tyrosine hydroxylase (TH) is the rate-limiting enzyme for dopamine biosynthesis, and its activity is regulated by phosphorylation on three seryl residues: Ser-19, Ser-31, and Ser-40. Using a TH-expressing human neuroblastoma cell line and rat primary mesencephalic neuron cultures, the present study examined whether GDNF alters the phosphorylation of TH and whether these changes are accompanied by increased enzymatic activity. Exposure to GDNF did not alter the TH protein level in either neuroblastoma cells or in primary neurons. However, significant increases in the phosphorylation of Ser-31 and Ser-40 were detected within minutes of GDNF application in both cell types. Enhanced Ser-31 and Ser-40 phosphorylation was associated with increased TH activity but not dopamine synthesis in neuroblastoma cells, possibly because of the absence of l-aromatic amino acid decarboxylase activity in these cells. In contrast, increased phosphorylation of Ser-31 and Ser-40 was found to enhance dopamine synthesis in primary neurons. Pharmacological experiments show that Erk and protein kinase A phosphorylate Ser-31 and Ser-40, respectively, and that their inhibition blocked both TH phosphorylation and activity. Our results indicate that, in addition to its role as a survival factor for dopaminergic neurons, GDNF can directly increase dopamine synthesis.

Differentiation and tropic/trophic effects of exogenous neural precursors in the adult spinal cord

The fate of exogenous neural stem cells (NSCs) in the environment of the adult nervous system continues to be a matter of debate. In the present study, we report that cells of the murine NSC clone C17.2, when grafted into the lumbar segments of the spinal cord of adult rats, survive and undergo partial differentiation. C17.2 cells migrate avidly toward axonal tracts and nerve roots and differentiate into nonmyelinating ensheathing cells. Notably, C17.2 cells induce the de novo formation of host axon tracts aiming at graft innervation. Differentiation and inductive properties of C17.2 cells are independent of the presence of lesions in the spinal cord. The tropic/trophic interactions of C17.2 NSCs with host axons, the avid C17.2 cell-host axon contacts, and the ensheathing properties of these cells are related to their complex molecular profile, which includes the expression of trophic cytokines and neurotrophins such as glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor, glial growth factor receptors such as ErbB-2; and PASK, the mammalian homologue of the fray gene that is involved in axon ensheathment. These results show that NSCs might not only play a critical supportive role in repairing axonal injury in the adult spinal cord but also can be used as probes for exploring the molecular underpinnings of the regenerative potential of the mature nervous system after injury.

Making connections: the development of mesencephalic dopaminergic neurons

The disorders of two adjacent sets of mesencephalic dopaminergic (MDNs) are associated with two significant health problems: Parkinson's disease and drug addiction. Because of this, a great deal of research has focused on understanding the growth, development and maintenance of MDNs. Many transcription factors and signaling pathways are known to be required for normal MDNs formation, but a unified model of MDN development is still unclear. The long-term goal is to design therapeutic strategies to: (i) nurture and/or heal endogenous MDNs, (ii) replace the affected tissue with exogenous MDNs from in vitro cultivated stem cells and (iii) restore normal connectivity. Recent developmental biology studies show great promise in understanding how MDNs develop both in vivo and in vitro. This information has great therapeutic value and may provide insight into how environmental and genetic factors increase vulnerability to addiction.

Injury and strain-dependent dopaminergic neuronal degeneration in the substantia nigra of mice after axotomy or MPTP

We studied the effects of axotomy or neurotoxin on the survival of substantia nigra pars compacta (SNpc) neurons in two strains of mice, FVB/N or C57BL/6. Fluoro gold (FG) was injected into both striata of the mice to retrogradely label the nigrostriatal neuronal population. Ten days later, these neurons were axotomized in the medial forebrain bundle (MFB) unilaterally or N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was administered intraperitonealy for 2 days to produce bilateral degeneration. MFB transection or MPTP administration produced a progressive loss of FG-labeled and tyrosine hydroxylase immunolabeled (TH+) neurons in both strains. Relative to control, 72% of SNpc neurons died 4 weeks after axotomy in C57BL/6 mice and 50% died after axotomy in FVB/N mice. MPTP resulted in death of 80% of SNpc neurons in C57BL/6 mice but only 40% in the FVB strain 4 weeks after MPTP administration. In this more sensitive strain, MPTP cell death was associated with positive staining for terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and nuclear condensation. In contrast, no TUNEL staining was detected in SNpc after MPTP in FVB/N mice. Further, while similar kinetics and extent of cell death accompanied axotomy, axotomy-induced cell death was TUNEL negative in both FVB/N and C57BL/6 mice. Double staining for TUNEL and microtubule associated protein 2 confirmed that the majority of the TUNEL positive cells were neurons. These data indicate that genetic factors and the type of lesion play an important role in determining death of dopaminergic neurons after injury.

Effect of glial cell line‐derived neurotrophic factor (GDNF) co‐transplantation with fetal ventral mesencephalic cells (VMC) on functional restoration in 6‐hydroxydopamine (6‐OHDA) lesioned rat model of Parkinson's disease: neurobehavioral, neurochemical and immunohistochemical studies

Among trophic factors already known, glial cell line-derived neurotrophic factor (GDNF) and other members of its family have potent and specific action on dopaminergic neurons. In the present investigation an attempt has been made to validate the role of GDNF co-transplantation with fetal ventral mesencephalic cells (VMC) on functional viability and restoration using neurobehavioral, neurochemical and immunohistochemical parameters at 6 weeks post-transplantation in 6-hydroxydopamine (6-OHDA) lesioned rat model of Parkinson's disease (PD). A significant restoration (P<0.01) in D-amphetamine induced rotations, spontaneous and apomorphine induced locomotor activity in rats co-transplanted with VMC and GDNF was observed as compared to VMC alone transplanted rats. Level of dopamine (DA), 3,4-dihydroxy-phenyl acetic acid (DOPAC) and dopamine D2 (DA-D2) receptors in the caudate putamen (CPu) were significantly (P<0.001) restored in co-transplanted group as compared to VMC transplanted or GDNF administered animals. The functional viability of transplanted VMC was confirmed by tyrosine hydroxylase (TH) expression and quantification of TH-positive cells by image analysis revealed a significant restoration in TH-IR fibers density as well as TH-IR neurons counts in co-transplanted animals over VMC transplanted animals. Results suggest that co-transplantation of VMC and GDNF may be a better approach towards functional restoration in 6-OHDA lesioned rat model of Parkinson's disease.

Mitogenic effect of glial cell line-derived neurotrophic factor is dependent on the activation of p70S6 kinase, but independent of the activation of ERK and up-regulation of Ret in SH-SY5Y cells

Glial cell line-derived neurotrophic factor (GDNF) activates c-Ret tyrosine kinase and several downstream intracellular pathways; the biological effects caused by the activation of each of these pathways, however, remain to be elucidated. Here we report the ability of GDNF to induce proliferation, rather than differentiation, of neuroblastoma cells (SH-SY5Y) by targeting the signaling pathway responsible for mediating this proliferative effect. GDNF induces the phosphorylation of Akt and p70S6 kinase (p70S6K) in SH-SY5Y cells in which Ret protein expression is relatively low. Interestingly, treating SH-SY5Y cells with retinoic acid greatly increases Ret protein levels and GDNF-induced Ret tyrosine phosphorylation, but does not affect the mitogenic action of GDNF and the activation of the Akt/p70S6K pathway. In contrast, the activation of the ERK pathway and the resulting induction of immediate-early genes parallel the increases in Ret protein levels. Rapamycin, a specific inhibitor of p70S6K activation by the mammalian target of rapamycin, completely prevents GDNF-induced proliferation and activation of p70S6K. These results suggest that GDNF promotes cell proliferation via the activation of p70S6K, independent of the ERK signaling pathway, and that GDNF activates the Akt/p70S6K pathway more efficiently than the ERK pathway in the cells in which Ret expression is low.

Glial cell line neurotrophic factor-family receptor alpha-1 is present in central neurons with distinct phenotypes

Glial cell line neurotrophic factor(GDNF) is a potent survival factor for several types of neurons. GDNF binds with high affinity to the GDNF-family receptor alpha-1 (GFRalpha-1) which is expressed in different brain areas. In the present study, by using anatomical techniques, we document the phenotypic diversity among GFRalpha-1 expressing neurons in the CNS. GFRalpha-1 expression was found in GABA (gamma-aminobutyric acid)-containing neurons distributed in the cortex, reticular thalamic nucleus and septum. While high expression of GFRalpha-1 was often observed in cholinergic motoneurons in the spinal cord, very few septal cholinergic neurons were found to express GFRalpha-1. GFRalpha-1 transcripts were also detected in catecholaminergic neurons in the periventricular hypothalamic nucleus, dorsal raphe nucleus and locus ceruleus. Within the raphe nucleus, GFRalpha-1 expression was prominent in many serotonergic neurons and in few neurons containing the enzyme nitric oxide synthase. As GFRalpha-1 is activated by GDNF and GDNF-related neurotrophic factors, the widespread distribution of GFRalpha-1 in neurons with different phenotypes indicates that the neuronal activity of these neurons is likely to be affected by GDNF and GDNF-related neurotrophic factors. This would result in the regulation of diverse neuronal pathways in the adult brain. Published by Elsevier Science Ltd on behalf of IBRO.

Electro-acupuncture improves behavior and upregulates GDNF mRNA in MFB transected rats

Low and high frequency electro-acupuncture (EA) stimulation was used in rats that had been lesioned by medial forebrain bundle transection. Behavioral tests showed that both low and high frequency EA stimulation significantly reduced the amphetamine-induced rotation 2 weeks after the lesion but only high frequency EA improved the rotational behavior at 4 weeks. Analysis of the dopamine content in the striatum did not show any significant change after EA. In situ hybridization showed that high frequency EA stimulation up-regulated the glial cell line-derived neurotrophic factor (GDNF) mRNA in both sides of the globus pallidus, while low frequency EA only affected the unlesioned side. It suggests that the retrograde nourishment of GDNF to the dopaminergic neurons and the balanced activity of different nuclei in the basal ganglia circuit after EA may contribute to the behavioral improvement in these rats, which might be the factors that underlie the effectiveness of EA in the treatment of Parkinson's disease.

Complications of a trophic xenotransplant approach in parkinsonian monkeys

Various restorative cell transplantation strategies have been investigated to substitute for lost dopamine (DA) neurons or to enhance DA synthesis in Parkinson's disease. Intracerebral implantation of engineered cells encapsulated in a semipermeable polymer membrane constitutes one way to deliver bioactive substances unable to cross the blood-brain barrier while avoiding the need for long-term immunosuppression. Glial cell line-derived neurotrophic factor (GDNF) has shown trophic effects on DA neurons but effective and sustained delivery within the brain parenchyma remains problematic. The long-term efficacy and late complications of a xenotransplant approach utilizing GDNF-expressing encapsulated baby hamster kidney (BHK) cells were examined. Each of five MPTP-lesioned parkinsonian cynomolgus monkeys received five devices containing active or inert cells grafted bilaterally in the striatum in a two-stage procedure 9 months apart and animals were sacrificed 4 months later for analyses. No definite motor benefit was observed, DA levels were comparable between GDNF- and control cell-implanted striata, and tyrosine hydroxylase (TH) immunoreactivity in the substantia nigra showed no consistent recovery. Cell viability and GDNF synthesis in the explanted devices were negligible. The brain tissue surrounding all implants showed an intense immune reaction with prominent "foreign body" inflammatory infiltrates. Membrane biophysics, the cell type used, and the extended period of time the devices remained in situ may have contributed to the negative outcome and should be addressed in future investigations using this approach.

Transcription factors in the development of midbrain dopamine neurons

The development of midbrain dopamine (DA) neurons follows a number of stages marked by distinct events. After preparation of the region by signals that provide induction and patterning, at least two cascades of transcription factors contribute to the fully matured midbrain DA systems. One cascade involving the nuclear receptor Nurr1 is required to synthesize the neurotransmitter DA; the enzyme tyrosine hydroxylase (TH) depends on it. The other cascade involves homeobox genes. Lmx1b and engrailed genes are expressed before the genesis of DA neurons and maintain their expression in these neurons. Lmx1b drives Ptx3, which is the latest transcription factor known to be induced. Its induction coincides with that of TH. Disruption of the function of Ptx3 affects the formation of the substantia nigra (SN) and alters the anatomical organization of the midbrain DA systems. While each cascade contributes to a specific aspect of DA neurons, both cascades are required for survival during development, indicating that the maintenance of DA neurons is delicately dependent on the appropriate activity of multiple transcriptional cascades.

Intravitreal injections of neurotrophic factors and forskolin enhance survival and axonal regeneration of axotomized beta ganglion cells in cat retina

Some retinal ganglion cells in adult cats survive axotomy for two months and regenerate their axons when a peripheral nerve is transplanted to the transected optic nerve. However, regenerated retinal ganglion cells were fewer than 4% of the total retinal ganglion cell population in the intact retina. The present study examined the effects of intravitreal injections of neurotrophic factors (brain-derived neurotrophic factor, ciliary neurotrophic factor, basic fibroblast growth factor, glial cell-derived neurotrophic factor, neurotrophin 4), first on the survival of axotomized cat retinal ganglion cells within 2 weeks, and then on axonal regeneration of the retinal ganglion cells for 2 months after peripheral nerve transplantation. We tested first enhancement of the survival by one of the factors, and then one or two of them supplemented with forskolin, which increases intracellular cAMP. Single injections of 0.5 microg or 1 microg brain-derived neurotrophic factor, 1 microg ciliary neurotrophic factor, or 1 microg glial cell-derived neurotrophic factor significantly increased total numbers of surviving retinal ganglion cells; 1.6-1.8 times those in control retinas. Identification of retinal ganglion cell types with Lucifer Yellow injections revealed that the increase of surviving beta cells was most conspicuous: 2.5-fold (brain-derived neurotrophic factor) to 3.6-fold (ciliary neurotrophic factor). A combined injection of 1 microg brain-derived neurotrophic factor, 1 microg ciliary neurotrophic factor, and 0.1 mg forskolin resulted in a 4.7-fold increase of surviving beta cells, i.e. 50% survival on day 14. On the axonal regeneration by peripheral nerve transplantation, a combined injection of brain-derived neurotrophic factor, ciliary neurotrophic factor, and forskolin resulted in a 3.4-fold increase of beta cells with regenerated axons. The increase of regenerated beta cells was mainly due to the enhancing effect of neurotrophic factors on their survival, and possibly to a change of retinal ganglion cell properties by cAMP to facilitate their axonal regeneration.

Glial cell line-derived neurotrophic factor contributes to delayed inflammatory hyperalgesia in adjuvant rat pain model

Neurotrophic factors, such as nerve growth factor and brain-derived neurotrophic factor, are members of the structurally related neurotrophin family that play important roles in pain modulation. Although there are also indications for the involvement of glial cell line-derived neurotrophic factor (GDNF), it is unclear whether and how GDNF is involved in inflammatory pain. In the present study, we studied the expression pattern of GDNF in dorsal root ganglia (DRG) and spinal cord, using confocal microscopy. We demonstrate that GDNF is well associated with nonpeptidergic pain pathway and that GDNF could possibly be anterogradely transported from DRG neurons to superficial spinal cord dorsal horn. We also studied the dynamic changes of GDNF expression in rats during chronic inflammation using injection of complete Freund's adjuvant as a model of chronic pain. We found that GDNF was down-regulated in both dorsal root ganglia and spinal cords 2 weeks after arthritis induction. To assess the impact of this down-regulation on pain transmission, we used a function-blocking antibody against GDNF delivered intrathecally in the same chronic-pain animal models. Injection of this antibody to GDNF produced no immediate effect, but decreased the delayed, bilateral hyperalgesia induced from a unilateral injection of complete Freund's adjuvant. The effect of this antibody coincided with the down-regulation of GDNF immunoreactivity in response to inflammation, suggesting that GDNF supports biochemical changes that contribute to hyperalgesia.

Direct brain infusion of glial cell line-derived neurotrophic factor in Parkinson disease

Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor with restorative effects in a wide variety of rodent and primate models of Parkinson disease, but penetration into brain tissue from either the blood or the cerebro-spinal fluid is limited. Here we delivered GDNF directly into the putamen of five Parkinson patients in a phase 1 safety trial. One catheter needed to be repositioned and there were changes in the magnetic resonance images that disappeared after lowering the concentration of GDNF. After one year, there were no serious clinical side effects, a 39% improvement in the off-medication motor sub-score of the Unified Parkinson's Disease Rating Scale (UPDRS) and a 61% improvement in the activities of daily living sub-score. Medication-induced dyskinesias were reduced by 64% and were not observed off medication during chronic GDNF delivery. Positron emission tomography (PET) scans of [(18)F]dopamine uptake showed a significant 28% increase in putamen dopamine storage after 18 months, suggesting a direct effect of GDNF on dopamine function. This study warrants careful examination of GDNF as a treatment for Parkinson disease.

A genomewide scan for attention-deficit/hyperactivity disorder in an extended sample: suggestive linkage on 17p11

Attention-deficit/hyperactivity disorder (ADHD [MIM 143465]) is a common, highly heritable neurobehavioral disorder of childhood onset, characterized by hyperactivity, impulsivity, and/or inattention. As part of an ongoing study of the genetic etiology of ADHD, we have performed a genomewide linkage scan in 204 nuclear families comprising 853 individuals and 270 affected sibling pairs (ASPs). Previously, we reported genomewide linkage analysis of a "first wave" of these families composed of 126 ASPs. A follow-up investigation of one region on 16p yielded significant linkage in an extended sample. The current study extends the original sample of 126 ASPs to 270 ASPs and provides linkage analyses of the entire sample, using polymorphic microsatellite markers that define an approximately 10-cM map across the genome. Maximum LOD score (MLS) analysis identified suggestive linkage for 17p11 (MLS=2.98) and four nominal regions with MLS values >1.0, including 5p13, 6q14, 11q25, and 20q13. These data, taken together with the fine mapping on 16p13, suggest two regions as highly likely to harbor risk genes for ADHD: 16p13 and 17p11. Interestingly, both regions, as well as 5p13, have been highlighted in genomewide scans for autism.

Increase in secretion of glial cell line-derived neurotrophic factor from glial cell lines by inhibitors of vacuolar ATPase

Glial cell line-derived neurotrophic factor (GDNF) was reported to be effective for treating subjects with neurodegenerative diseases such as Parkinson's disease. In search of finding a compound which promotes GDNF secretion, we found that concanamycin A (ConA), a vacuolar ATPase (V-type ATPase) inhibitor purified from Streptomyces diastatochromogens, enhanced GDNF secretion from glioma cells. The rat glioma cell line, C6, and the human glioma cell lines, U87MG and T98G, abundantly expressed GDNF mRNA, and secreted GDNF into culture media, and this event was potently enhanced by a Ca(2+) ionophore and by phorbol ester, as noted in other cells. ConA concentration dependently and potently increased GDNF release from C6, U87MG and T98G cells into culture media. In addition, ConA enhanced GDNF secretion from astrocyte primary cultures prepared from the human fetus with the same potency seen in glioma cell lines. Likewise, another V-type ATPase inhibitor, bafilomycinA1 facilitated GDNF release from C6, U87MG and T98G glioma cells, in a concentration-dependent manner. The potencies of these V-type ATPase inhibitors in enhancing GDNF secretion were consistent with those which inhibited V-type ATPase activity. These results suggest that blockade of V-type ATPase potently stimulates the secretion of GDNF from glial cells. The V-type ATPase inhibitors may be beneficial to use for the treatment of diseases in which increase in GDNF could be effective.

Intravenous TAT-GDNF is protective after focal cerebral ischemia in mice

BACKGROUND AND PURPOSE

Delivery of therapeutic proteins into tissues and across the blood-brain barrier is severely limited by their size and biochemical properties. The 11-amino acid human immunodeficiency virus TAT protein transduction domain is able to cross cell membranes and the blood-brain barrier, even when coupled with larger peptides. The present studies were done to evaluate whether TAT-glial line-derived neurotrophic factor (GDNF) fusion protein is protective in focal cerebral ischemia.

METHODS

Anesthetized male C57BL/6j mice were submitted to intraluminal thread occlusion of the middle cerebral artery. Reperfusion was initiated 30 minutes later by thread retraction. Laser Doppler flow was monitored during the experiments. TAT-GDNF, TAT-GFP (0.6 nmol each), or vehicle was intravenously applied over 10 minutes immediately after reperfusion. After 3 days (30 minutes of ischemia), animals were reanesthetized and decapitated. Brain injury was evaluated by histochemical stainings.

RESULTS

Immunocytochemical experiments confirmed the presence of TAT-GDNF protein in the brains of fusion protein-treated nonischemic control animals 3 to 4 hours after TAT fusion protein delivery. TAT-GDNF significantly reduced the number of caspase-3-immunoreactive and DNA-fragmented cells and increased the number of viable neurons in the striatum, where disseminated tissue injury was observed, compared with TAT-GFP- or vehicle-treated animals.

CONCLUSIONS

Our results demonstrate that TAT fusion proteins are powerful tools for the treatment of focal ischemia when delivered both before and after an ischemic insult. This approach may be of clinical interest because such fusion proteins can be intravenously applied and reach the ischemic brain regions. This approach may therefore offer new perspectives for future strategies in stroke therapy.

Radiation and regeneration: behavioral improvement and GDNF expression after Gamma Knife radiosurgery in the 6-OHDA rodent model of hemi-parkinsonism

BACKGROUND

Recent research has demonstrated that the adult mammalian CNS is capable of regeneration. This regeneration is often initiated as a response to thermal, chemical or mechanical injury. The effects of radiation on the mammalian CNS have also been found to aid in certain regeneration processes.

METHOD

In our project we examined the potential therapeutic value of radiation induced regeneration of diseased mammalian rat CNS. Eleven Sprague-Dawley rats with 6-hydroxy-dopamine (6-OHDA) induced hemi-parkinsonism were treated in the Leksell Gamma Knife using a single 4 mm collimator shot targeted to the ipsilateral (parkinsonian) caudate-putamen complex. A maximum dose of 140 Gy was used to create a necrotic lesion. Animals were tested behaviorally using the apomorphine-induced rotational behavior model before and up to 6 months after radiosurgery. Histochemical analysis was performed 2 weeks, 1 month and 4 months after radiosurgery. Histological sections were obtained and immunohistochemistry was performed for glial cell line derived neurotrophic factor (GDNF).

FINDINGS

The rotational behavior for 11/11 animals (100%) was found to initially worsen at 2 weeks and 4 weeks after radiosurgery before a statistically highly significant reduction in apomorphine induced rotations was observed at 2, 3, and 4 months after radiosurgery (83% reduction by month four; p < 0.0001). For 2/11 animals the rotational behavior almost disappeared indicating near-abolition of parkinsonian behavior. On histological examination, the lesions were easily identified as areas of necrosis about 4 mm in diameter. The region immediately adjacent to the lesion was found to have highly positive expression of GDNF indicating high activity in dopamine-regenerating processes.

INTERPRETATION

In this preliminary study we demonstrated that radiosurgical lesioning with the Gamma Knife into the striatum of hemi-parkinsonian animals resulted in significant behavioral improvement of signs of parkinsonism. Since GDNF expression is tightly linked to the dopaminergic system, we conclude that focused radiation is potentially capable of inducing regeneration of dopaminergic pathways in the adult CNS. Further studies with dose deescalation and molecular biological characterization of the regeneration cascades are necessary to gain access to potential clinical value of our observations.

Sendai virus vector-mediated gene transfer of glial cell line-derived neurotrophic factor prevents delayed neuronal death after transient global ischemia in gerbils

We have developed a cytoplasmic replicating virus vector of Sendai virus (SeV) that infects and replicates in most mammalian cells, including neurons, and directs high-level gene expression. To investigate the protective effect of SeV vector-mediated gene transfer of glial cell line-derived neurotrophic factor (GDNF) on the delayed neuronal death caused by transient global ischemia in gerbils, SeV vectors carrying either GDNF (SeV/GDNF) or enhanced green fluorescent protein gene (SeV/GFP) were stereotaxically microinjected into the lateral ventricle. Four days after injection, occlusion of the bilateral common carotid arteries for 5 min produced transient global forebrain ischemia. Treatment with SeV/GDNF significantly decreased the delayed neuronal death of the hippocampal CA1 pyramidal neurons observed 6 days after the operation. TUNEL staining demonstrated that SeV/GDNF treatment markedly reduced the number of apoptotic cells in the hippocampal CA1 neurons, indicating that SeV/GDNF treatment prevented apoptosis. Furthermore, delayed neuronal death on the contralateral side of the hippocampal CA1 was also prevented to a similar extent as that on the ipsilateral side. These results suggest that SeV/GDNF prevents the delayed neuronal death induced by ischemia and is potentially useful for gene therapy for stroke.

Interactions of cyclic adenosine monophosphate, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor treatment on the survival and growth of postnatal mesencephalic dopamine neurons in vitro

The survival of rat postnatal mesencephalic dopamine (DA) neurons in dissociated cell cultures was studied by examining the combinatorial effects of dibutyryl cyclic adenosine monophosphate (db-cAMP), glial cell line-derived neurotrophic factor (GDNF), and brain-derived neurotrophic factor (BDNF), as well as selective inhibitors of protein kinase A (PKA), and mitogen-activated protein kinase (MAPK). Postnatal DA neurons were maintained for 14 days in vitro, and were identified by immunohistochemistry using tyrosine hydroxylase antibody. The survival and growth of DA neurons was significantly increased by the inclusion of either >100 microM db-cAMP or 10 microM Forskolin plus 100 microM IBMX in the culture medium. Neither 10-50 ng/ml GDNF nor 50 ng/ml BDNF alone significantly increased DA neuron survival in vitro. However, the combined use of GDNF and BDNF did increase DA neuron survival, and the addition of either db-cAMP or IBMX/Forskolin to media containing these neurotrophins markedly increased DA neuron survival and growth. The cAMP inhibitor Rp-cAMP, the cAMP-dependent protein kinase A inhibitor H89, and the MAP kinase (MAPK) pathway inhibitor PD98059 significantly reduced the survival of DA neurons when applied alone in the absence of added growth factors. Application of GDNF plus BDNF, or db-cAMP significantly protected the DA neurons from the deleterious effects on survival of either 20 microM H89 or 20 microM PD 98059. The results suggest that BDNF, GDNF, and cAMP produce convergent signals to activate PKA and MAPK pathways which are involved in the survival of postnatal mesencephalic DA neurons in vitro.

Neurotrophic factors for the investigation and treatment of movement disorders

Neurotrophic factors (NFs) are proteins that enhance neuronal survival, differentiation, neurotransmitter function and resistance to neurotoxins and lesions. For these reasons the NFs are considered as a new potential therapeutic tool for the treatment of neurodegenerative disorders, a group of diseases that produce the most important cause for disability in the Western world. Some NFs prevent or even reverse the behavioral, biochemical, pharmacological and histological abnormalities observed in several in vitro and in vivo models of neurodegenerative disorders, namely Parkinson's disease. Several NFs have been investigated in primate models of neurological disorders and some of them have been used for patients with these diseases. The results so far obtained in humans have been disappointing for several reasons, including technical problems for delivery, unbearable side effects or lack of efficacy. Future approaches for the use of NFs in humans should include the following: (1) Investigation of the putative compounds in animal models more related to the pathophysiology of each disease, such as in genetic models of neurodegenerative diseases; (2) New methods of delivery including genetic engineering by viral vectors and administration through implantable devices; (3) More precise methods of continuous response evaluation, including the novel neuroimaging techniques; (4) Investigation of the effects of behavioral stimulation and conventional pharmacotherapy on the metabolism of NFs.

XIB4035, a novel nonpeptidyl small molecule agonist for GFRalpha-1

We investigated the agonistic activities of N(4)-(7-chloro-2-[(E)-2-(2-chloro-phenyl)-vinyl]-quinolin-4-yl)-N(1),N(1)-diethyl-pentane-1,4-diamine (XIB4035), at the glial cell line-derived neurotrophic factor (GDNF) family receptoralpha-1(GFRalpha-1) in Neuro-2A cells, a mouse neuroblastoma cell line which is a suitable model for investigating functions mediated through GFRalpha-1. XIB4035 concentration-dependently inhibited [(125)I]GDNF binding in Neuro-2A cells with an IC(50) of 10.4 microM. GDNF induced autophosphorylation of Ret protein, and promoted neurite outgrowth in Neuro-2A cells. XIB4035, like GDNF, induced Ret autophosphorylation in the Neuro-2A cells. Moreover, XIB4035 promoted neurite outgrowth in a concentration-dependent manner. These results show that XIB4035 may act as an agonist at GFRalpha-1 receptor complex, and mimic neurotrophic effects of GDNF in Neuro-2A cells. This is an interesting finding showing that a nonpeptidyl small molecule is capable of inducing activation of a receptor that normally bind a relatively large protein ligand such as GDNF.

Neurotrophic and neuroprotective effects of tripchlorolide, an extract of Chinese herb Tripterygium wilfordii Hook F, on dopaminergic neurons

It has been reported recently that the immunosuppressant FK506 produced neurotrophic and neuroprotective effects on dopaminergic neurons in vitro and in vivo. We investigated whether tripchlorolide, an immunosuppressive extract of Chinese herb Tripterygium wilfordii Hook F, could exert similar neurotrophic and neuroprotective effects similar to those of FK506. It was found that tripchlorolide promoted axonal elongation and protected dopaminergic neurons from a neurotoxic lesion induced by 1-methyl-4-phenylpyridinium ion (MPP+) at concentrations of as low as 10(-12) to 10(-8) M. In situ hybridization study revealed that tripchlorolide stimulated brain-derived neurotrophic factor (BDNF) mRNA expression. In vivo administration of tripchlorolide (1 microg/kg, ip) for 28 days effectively attenuated the rotational behavior challenged by D-amphetamine in the model rats by transection of the medial forebrain bundle. In addition, tripchlorolide treatment (0.5 or 1 microg/kg/day for 28 days) increased the survival of dopaminergic neurons in substantia nigra pars compacta by 50 and 67%, respectively. Moreover, tripchlorolide markedly prevented the decrease in amount of dopamine in the striatum of model rats. Taken together, our data provide the first evidence that tripchlorolide acts as a neuroprotective molecule that rescues MPP+ or axotomy-induced degeneration of dopaminergic neurons, which may imply its therapeutic potential for Parkinson's disease. The underlying mechanism may be relevant to its neurotrophic effect and its efficacy in stimulating the expression of BDNF.

Long-term striatal overexpression of GDNF selectively downregulates tyrosine hydroxylase in the intact nigrostriatal dopamine system

Sustained neurotrophic factor treatment in neurodegenerative disorders such as Parkinson's disease is likely to affect both degenerating and intact neurons. To investigate the effect of long-term glial cell line-derived neurotrophic factor (GDNF) overexpression on intact nigrostriatal dopamine neurons, we injected a recombinant lentiviral vector encoding GDNF, or green fluorescent protein, in the right striatum of young adult rats. Thirteen months after viral injection GDNF levels were 4.5 ng/mg tissue in the striatum and 0.9 ng/mg in the substantia nigra as measured by ELISA, representing a 25-100-fold increase above control vector- or nontransduced tissue. GDNF overexpression significantly reduced tyrosine hydroxylase mRNA levels (by 39-72%) in the substantia nigra and ventral tegmental area neurons, and the optical density of tyrosine hydroxylase-immunoreactive innervation in the striatum was reduced by 25-52% with the most prominent reductions appearing caudally. No significant reduction was seen in striatal vesicular monoamine transporter 2-immunoreactivity or [3H]mazindole binding autoradiography to dopamine uptake sites, two other presynaptic markers in dopamine axon terminals. The striatal D1 and D2 receptor binding as determined by [3H]SCH23390 and [3H]spiperone binding, respectively, was unaltered relative to the intact side in both treatment groups. Preproenkephalin mRNA levels in postsynaptic striatal neurons, which increase upon removal of striatal dopamine, were also unaffected by the GDNF treatment. Taken together our findings indicate that sustained GDNF administration to intact nigrostriatal dopamine neurons selectively reduces tyrosine hydroxylase expression, without altering striatal dopamine transmission to the extent that compensatory changes in several other components related to dopamine storage and signalling occur.

Glial cell line-derived neurotrophic factor released by synthetic guidance channels promotes facial nerve regeneration in the rat

Regeneration of the human facial nerve after lesion is often limited, leading to severe functional impairments, in particular when repair is delayed for several months, when cross-facial nerve grafts have to be performed, or in elderly patients. To improve the outcome, the potential accelerating and maturating effects of the neurotrophic factors glial cell line-derived neurotrophic factor (GDNF) and neurotrophin-3 (NT-3) on nerve regeneration were assessed using an axotomy model of the rat facial nerve. One-centimeter-long synthetic guidance channels releasing the neurotrophic factors over several weeks were used to bridge an 8 mm nerve gap, a distance that does not allow regeneration in the absence of growth factors. Nerve cables regenerated in the presence of GDNF showed a large number of myelinated axons 6 weeks after grafting (871 +/- 373, n = 5), whereas only 106 +/- 86 (n = 5) myelinated axons were counted in the presence of NT-3. Retrograde labeling with fluorogold revealed 981 +/- 450 (n = 5) and 53 +/- 38 (n = 5) retrogradely labeled motoneurons in the facial nucleus in the presence of GDNF and NT-3, respectively. No regenerated axons or retrogradely labeled cells were observed in the absence of growth factors (n = 6). These results demonstrate that GDNF, as previously described for the sciatic nerve, a mixed sensory and motor nerve, is also very efficient in promoting regeneration of the facial nerve, an essentially pure motor nerve. GDNF may therefore be useful in improving facial nerve regeneration in the clinic.

Bimodal upregulation of glial cell line-derived neurotrophic factor (GDNF) in the neonatal rat brain following ischemic/hypoxic injury

In order to delineate the spatial and temporal patterns of glial cell line-derived neurotrophic factor (GDNF) expression following ischemic/hypoxic injury in immature and neonatal brain, GDNF protein levels and immunocytochemistry were studied in rats subjected to a modified Levine procedure. Significant upregulation of GDNF protein occurred in a bimodal fashion in the damaged left cerebral cortex and hippocampus, while the levels in the right cerebral hemisphere of both control and ischemic groups remained relatively unchanged. Immunocytochemical studies indicated that the early rise in GDNF levels was most likely to be related to enhanced neuronal release of GDNF. The second rise was probably related to progressive astrogliosis that occurred in response to injury. In contrast to the lack of GDNF expression among astrocytes in normal mature brains, reactive astrocytes in the neonate appear to possess a ready capacity to express GDNF. Spatial and temporal changes in the pattern of GDNF expression following injury, as determined in this study may provide insight into the functions of GDNF in vivo and into possible therapeutic approaches toward prevention of damage or rescue of neurons following brain injury.

TGFbeta induces GDNF responsiveness in neurons by recruitment of GFRalpha1 to the plasma membrane

We have previously shown that the neurotrophic effect of glial cell line-derived neurotrophic factor (GDNF) in vitro and in vivo requires the presence of transforming growth factor (TGF)beta. Using primary neurons (chick E8 ciliary) we show that the combination of GDNF plus TGFbeta promotes survival, whereas the single factors do not. This cooperative effect is inhibited by blocking the extracellular signal-regulated kinase (ERK)/MAPK pathway, but not by interfering with the PI3 kinase signaling cascade. Although there is no functional GDNF signaling in the absence of TGFbeta, pretreatment with TGFbeta confers GDNF responsiveness to the cells. This is not due to upregulation of GDNF receptors mRNA and protein, but to TGFbeta-induced recruitment of the glycosyl-phosphatidylinositol-anchored GDNF receptor (GFR)alpha1 to the plasma membrane. This is supported by the fact that GDNF in the presence of a soluble GFRalpha1 can promote survival in the absence of TGFbeta. Our data suggest that TGFbeta is involved in GFRalpha1 membrane translocation, thereby permitting GDNF signaling and neurotrophic effects.

Regulation of c-Ret, GFRalpha1, and GFRalpha2 in the substantia nigra pars compacta in a rat model of Parkinson's disease

Glial cell line-derived neurotrophic factor (GDNF) family members have been proposed as candidates for the treatment of Parkinson's disease because they protect nigral dopaminergic neurons against various types of insult. However, the efficiency of these factors depends on the availability of their receptors after damage. We evaluated the changes in the expression of c-Ret, GFRalpha1, and GFRalpha2 in the substantia nigra pars compacta in a rat model of Parkinson's disease by in situ hybridization. Intrastriatal injection of 6-hydroxydopamine (6-OHDA) transiently increased c-Ret and GFRalpha1 mRNA levels in the substantia nigra pars compacta at 1 day postlesion. At later time points, 3 and 6 days, the expression of c-Ret and GFRalpha1 was downregulated. GFRalpha2 expression was differentially regulated, as it decreased only 6 days after 6-OHDA injection. Triple-labeling studies, using in situ hybridization for the GDNF family receptors and immunohistochemistry for neuronal or glial cell markers, showed that changes in the expression of c-Ret, GFRalpha1, and GFRalpha2 in the substantia nigra pars compacta were localized to neurons. In conclusion, our results show that nigral neurons differentially regulate the expression of GDNF family receptors as a transient and compensatory response to 6-OHDA lesion.

Glial cell line-derived neurotrophic factor up-regulates GTP-cyclohydrolase I activity and tetrahydrobiopterin levels in primary dopaminergic neurones

Glial cell line-derived neurotrophic factor (GDNF) protects dopaminergic neurones against toxic and physical damage. In addition, GDNF promotes differentiation and structural integrity of dopaminergic neurones. Here we show that GDNF can support the function of primary dopaminergic neurones by triggering activation of GTP-cyclohydrolase I (GTPCH I), a key enzyme in catecholamine biosynthesis. GDNF stimulation of primary dopaminergic neurones expressing both tyrosine 3-monooxygenase and GTPCH I resulted in a dose-dependent doubling of GTPCH I activity, and a concomitant increase in tetrahydrobiopterin levels whereas tyrosine 3-monooxygenase activity was not altered. Actinomycin D, asan inhibitor of de novo biosynthesis, abolished any GDNF-mediated up-regulation of GTPCH I activity. However, GTPCH I mRNA levels in primary dopaminergic neurones were not altered by GDNF treatment, suggesting that the mode of action for that up-regulation is not directly connected to the regulation of GTPCH I transcription. We conclude that GDNF, in addition to its action in structural differentiation, also promotes differentiation regarding expression and enzymatic activity of a crucial component in the dopaminergic biosynthetic pathway.

Cationic liposome-mediated GDNF gene transfer after spinal cord injury

Glial cell line-derived neurotrophic factor (GDNF) has been shown to protect cranial and spinal motoneurons, which suggests potential uses of GDNF in the treatment of spinal cord injury (SCI) and motor neuron disease. We examined neuroprotective effect of cationic liposome-mediated GDNF gene transfer in vivo on axonal regeneration and locomotor function recovery after SCI in adult rats. The mixture of DC-Chol liposomes and recombinant plasmid pEGFP-GDNF cDNA was injected after SCI. RT-PCR confirmed the increased expression of GDNF mRNA in the injected areas at 7 days after injection. The expression of EGFP-GDNF was observed in the cells around the injection locus by fluorescence microscope at least 4 weeks after injection. Four weeks after GDNF gene transfer, regeneration of the corticospinal tracts was assessed using anterograde tract tracing. There are more HRP labeling of corticospinal tract axons across the lesion in GDNF group compared with control group. In GDNF group, the maximum distance these labeled axons extended varied in different animals and ranged from 5 mm to approximately 9 mm from the lesion. In control group, no HRP labeled axons extended caudal to the lesion. The locomotion function of hindlimbs of rats was evaluated using inclined plane test and BBB locomotor scores. The locomotion functional scores in GDNF group were higher than that in control group within 1-4 weeks after SCI (p < 0.05). These data demonstrate that in vivo transfer of GDNF cDNA can promote axonal regeneration and enhance locomotion functional recovery, suggesting that cationic liposome-mediated delivery of GDNF cDNA may be a practical gene transfer method for traumatic SCI treatment.

Dopaminergic neuroprotection and regeneration by neurturin assessed by using behavioral, biochemical and histochemical measurements in a model of progressive Parkinson's disease

Trophic effects of neurturin, a member of the glial cell line-derived neurotrophic factor-family, have been demonstrated on mesencephalic dopaminergic neurons, suggesting its therapeutic potential for Parkinson's disease. This study was designed to test the neuroprotective and regenerative effects of an intrastriatal injection of neurturin based on behavioral, neurochemical and histochemical changes in a rat model of progressive Parkinson's disease. An extensive and progressive dopaminergic lesion was unilaterally made by intrastriatal convection-enhanced delivery of 6-hydroxydopamine (6-OHDA), in which 20 microg of 6-OHDA dissolved in 20 microl of vehicle was infused at a rate of 0.2 microl/min. For neuroprotection study, recombinant human neurturin (5 microg in 5 microl of vehicle) was stereotaxically injected into the unilateral striatum. The 6-OHDA lesion was made on the ipsilateral side 3 days after the neurturin treatment. Tyrosine hydroxylase (TH)-immunoreactive neurons of the substantia nigra were protected from progressive degeneration in the neurturin-treated animals compared with the vehicle-treated animals 2 and 8 weeks after the 6-OHDA lesion. Eight weeks after the 6-OHDA lesion, dopamine concentration significantly increased in the striatum of neurturin-treated animals with improvement of methamphetamine-induced rotation behavior. For neuroregeneration study, 5 microg of neurturin was injected into the striatum 12 weeks after the 6-OHDA lesion. Four weeks after neurturin or vehicle injection, there were no significant differences in the survival of nigral TH-immunoreactive neurons between the groups. However, TH-immunoreactive fibers were thicker and more abundant in the striatum of the neurturin-treated rats compared to those of the control group, suggesting neurturin-induced growth of the dopaminergic axons. Striatal dopamine levels also significantly increased in the neurturin-treated rats compared with those in the control group of rats, accompanied by the recovery of methamphetamine-induced rotation in the neurturin-treated rats. In conclusion, an intrastriatal injection of neurturin is a useful method to protect nigral dopaminergic neurons from extensive cell death in a model of progressive Parkinson's disease, as well as to promote the axonal regeneration and dopaminergic function.

Therapeutic time window of adenovirus-mediated GDNF gene transfer after transient middle cerebral artery occlusion in rat

The time dependent influence of adenovirus-mediated glial cell line-derived neurotrophic factor (GDNF) gene (Ad-GDNF) was examined after 90 min of transient middle cerebral artery occlusion (MCAO) in rats. Treatment with Ad-GDNF significantly reduced the infarct volume when immediately administered after the reperfusion, but became insignificant when administered at 1 h after the reperfusion as were the cases treated with vehicle- and adenoviral vector containing the E. coli lacZ gene (Ad-LacZ)-treated groups. The protective effect of GDNF was related to the significant reduction of the number of TUNEL positive cells as well as immunohistochemical positive cells for active caspase-3 but not -9. These results showed that exogenous GDNF gene transfer successfully reduced the infarct size in a time-dependant manner by suppressing active caspase-3 but not active caspase-9. However, the therapeutic time window was shorter than the effect of GDNF protein itself previously reported.

Lentivirally delivered glial cell line-derived neurotrophic factor increases the number of striatal dopaminergic neurons in primate models of nigrostriatal degeneration

The primate striatum contains tyrosine hydroxylase (TH)-immunoreactive (ir) neurons, the numbers of which are augmented after dopamine depletion. Glial cell line-derived neurotrophic factor (GDNF) strongly modulates the viability and phenotypic expression of dopamine ventral mesencephalic neurons. The effect of GDNF on TH-ir neurons intrinsic to the striatum has yet to be investigated. In the present study, stereological counts of TH-ir striatal neurons in aged and parkinsonian nonhuman primates revealed that GDNF delivered via a lentiviral vector (lenti-) further increased the number of these cells. Aged monkeys treated with lenti-GDNF displayed an eightfold increase in TH-ir neurons relative to lenti-beta-galactosidase-treated monkeys. Unilateral 1-methyl-4-phenyl- 1,2,3,6-tetrahydropyridine treatment alone in young monkeys resulted in a bilateral eightfold increase in TH-ir striatal cells. This effect was further magnified sevenfold on the side of lenti-GDNF treatment. These cells colocalized with the neuronal marker neuronal-specific nuclear protein. Some of these cells colocalized with GDNF-ir, indicating that an alteration in phenotype may occur by the direct actions of this trophic factor. Thus, GDNF may mediate plasticity in the dopamine-depleted primate brain, which may serve to compensate for cell loss by converting striatal neurons to a dopaminergic phenotype.