Basic fibroblast growth factor promotes the survival of embryonic ventral mesencephalic dopaminergic neurons--I. Effects in vitro

Temporo-spatial expression of bFGF and TGFbeta2 in embryonic dopaminergic grafts in a rat model of Parkinson's disease

In the present study we analyzed the temporo-spatial expression pattern of basic fibroblast growth factor (bFGF) and transforming growth factor beta 2 (TGFbeta2) in embryonic dopaminergic transplants in the 6-hydroxydopamine rat model of Parkinson's disease. The grafts differentiated for 1, 2, 4 and 8 weeks, respectively and were then analyzed using antibodies directed against tyrosine hydroxylase, bFGF and TGFbeta2. At all time points investigated, grafts contained tyrosine hydroxylase immunoreactive neurons. One week after transplantation the grafts displayed no immunoreactivity for bFGF and TGFbeta2. In more mature grafts (starting at 2 weeks post transplantation) bFGF and TGFbeta2 immunoreactivity became detectable within the graft and at the graft-host interface but was restricted only to astrocytes. In the striatum surrounding the graft, a transient increase of TGFbeta2 immunoreactive astrocytic processes was observed between 1 and 2 weeks after transplantation. This temporo-spatial expression pattern of TGFbeta2 immunoreactive astrocytes suggests that the upregulation of TGFbeta2 is more likely due to the trauma imposed by the transplantation procedure than to an intrinsic differentiation program. Lack of both bFGF and TGFbeta2 expression in grafted dopaminergic neurons compared to their normal expression in the adult rat substantia nigra indicates that these transplanted neurons do not develop their complete physiological phenotype. Together with the observed deficiency in astrocytic bFGF early after grafting this may be responsible for the poor survival of grafted embryonic dopaminergic cells.

Activated macrophages and microglia induce dopaminergic sprouting in the injured striatum and express brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor

Nigrostriatal dopaminergic neurons undergo sprouting around the margins of a striatal wound. The mechanism of this periwound sprouting has been unclear. In this study, we have examined the role played by the macrophage and microglial response that follows striatal injury. Macrophages and activated microglia quickly accumulate after injury and reach their greatest numbers in the first week. Subsequently, the number of both cell types declines rapidly in the first month and thereafter more slowly. Macrophage numbers eventually cease to decline, and a sizable group of these cells remains at the wound site and forms a long-term, highly activated resident population. This population of macrophages expresses increasing amounts of glial cell line-derived neurotrophic factor mRNA with time. Brain-derived neurotrophic factor mRNA is also expressed in and around the wound site. Production of this factor is by both activated microglia and, to a lesser extent, macrophages. The production of these potent dopaminergic neurotrophic factors occurs in a similar spatial distribution to sprouting dopaminergic fibers. Moreover, dopamine transporter-positive dopaminergic neurites can be seen growing toward and embracing hemosiderin-filled wound macrophages. The dopaminergic sprouting that accompanies striatal injury thus appears to result from neurotrophic factor secretion by activated macrophages and microglia at the wound site.

Therapeutic potential of nerve growth factors in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative syndrome which primarily affects dopamine-producing neurons of the substantia nigra, resulting in poverty and slowness of movement, instability of gait and posture, and tremor at rest in individuals with the disease. While symptoms of the disease can be effectively managed for several years with available drugs, the syndrome is progressive and the efficacy of standard drugs wanes with time. One experimental approach to therapy is to use natural and synthetic molecules which promote survival and growth of dopaminergic neurons, so-called 'neurotrophic factors', to stabilise the diminishing population of dopaminergic neurons and stimulate compensation and growth in these cells. In this review, we examine the available evidence on 29 molecules with neurotrophic properties for dopaminergic neurons. The properties of these molecules provide ample reasons for optimism that a neurotrophic strategy can be developed that would provide a significant treatment option for patients with PD. While the search continues for even more specific, potent and long lasting agents, the single greatest challenge is the development of techniques for targeted delivery of these molecules.

Involvement of caspase-like proteinases in apoptosis of neuronal PC12 cells and primary cultured microglia induced by 6-hydroxydopamine

Activation of proteolytic enzymes, including the caspase family of proteinases, is a feature characteristic of the apoptotic program. In the present study, we examined a potential role of intracellular proteinases in the death of neuronal PC12 and primary cultured rat microglial cells induced by 6-hydroxydopamine (6-OHDA). In both neuronal PC12 and microglial cells, 6-OHDA (10-200 microM) induced apoptosis in a dose-dependent manner as judged by the DNA break. The 6-OHDA was ineffective in Bcl-2-overexpressing neuronal PC12 cells. Pretreatment of these cells with two caspase inhibitors, acetyl-Try-Val-Ala-Asp-aldehyde and acetyl-Asp-Glu-Val-Asp-aldehyde, prevented the 6-OHDA-induced apoptosis. Pepstatin A and leupeptin, potent inhibitors of aspartic and cysteine proteinases, respectively, partly inhibited the apoptosis of microglia but not neuronal PC12 cells. In contrast, GBR12935, a dopamine uptake inhibitor, significantly inhibited the apoptotic death of neuronal PC12 cells but not microglia. These results suggest that mechanisms by which 6-OHDA induces apoptosis in these two cell types are distinct; 6-OHDA incorporated into neuronal PC12 cells and its metabolites may activate the caspase-like enzymes, whereas oxidative metabolites of the agent produced extracellularly may activate the caspase and the endosomal/lysosomal proteolytic systems in microglia.

Optimal effectiveness of BDNF for fetal nigral transplants coincides with the ontogenic appearance of BDNF in the striatum

Transplantation of fetal nigral dopamine neurons into the caudate and putamen of Parkinson's disease patients produces limited symptomatic relief. One approach to augment the outgrowth and function of nigral grafts includes exposure of the graphs to neurotrophic factors; however, the temporal requirements for optimizing these actions are unknown. The present study characterized the ontogeny of brain-derived neurotrophic factor (BDNF) in the rat striatum and used this information to define and evaluate three distinct periods of BDNF infusion into fetal nigral grafts transplanted into the striatum of rats with experimental Parkinson's disease. At postnatal day 1 (P1), BDNF and dopamine were measured at 17 and 27% of peak levels, respectively, that occurred at P27 for both. Both compounds showed their greatest surge between P7 and P20, increasing from 40% to approximately 95% of peak levels. Exogenous BDNF infused into transplants during weeks 1 and 2 after the transplantation, which coincide with the developmental period embryonic day 14 (E14)-P7 for transplanted tissue, did not improve rotational behavior or enhance fiber outgrowth of transplanted dopamine neurons. Delaying the BDNF infusion until transplanted tissue was approximately P8-P21 greatly enhanced the effect on rotational behavior and doubled the area of dopamine fiber outgrowth from the transplants. Delaying the infusion until transplanted tissue was approximately P36-P49 failed to augment fiber outgrowth and decreased the behavioral function of transplants. Thus, the optimal effect of exogenous BDNF on the development of dopamine neurons in fetal nigral transplants occurs at a postnatal age when endogenous dopamine and BDNF show the greatest increases during the normal development of the striatum.

Enhancement of graft survival and sensorimotor behavioral recovery in rats undergoing transplantation with dopaminergic cells exposed to glial cell line-derived neurotrophic factor

OBJECT

The goal of this study was to investigate the ability of fetal dopaminergic neurons to improve complex sensorimotor behavior.

METHODS

The authors obtained ventral mesencephalic tissue from 14-day-old rat fetuses. The cells were exposed to glial cell line-derived neurotrophic factor (GDNF) prior to transplantation into rats with unilateral 6-hydroxydopamine lesions of the dopaminergic nigrostriatal pathway. Animals that received 400,000 cells exposed to GDNF demonstrated significant improvement in contralateral forelimb function and showed improvement in rotational behavior faster than animals that received cells not exposed to GDNF. Increasing the number of implanted cells to 800,000 exposed to GDNF did not result in any additional improvement in functional recovery.

CONCLUSIONS

As neural grafting procedures in the nervous system evolve and genetically engineered cells or stem cells replace fetal tissue, crucial questions about cell number and trophic regulation will need to be addressed. This study demonstrates that grafting of 400,000 cells exposed to GDNF before transplantation has a beneficial effect in the restoration of complex sensorimotor behavior.

Partial purification of a pramipexole-induced trophic activity directed at dopamine neurons in ventral mesencephalic cultures

We previously demonstrated that media conditioned by exposure to ventral mesencephalic (VM) cultures in the presence of pramipexole (PPX) and other drugs with dopamine (DA) D3 properties, increased the growth and survival of DA neurons in recipient VM cultures. This trophic activity was heat-labile and not present in parietal cortex cultures or cultures pretreated with the DA neuron toxin MPP+. In an effort to begin to identify the protein(s) responsible for this trophic effect, we compared the conditioned media from normal VM cultures, VM cultures incubated with PPX, and VM cultures pretreated with MPP+ and treated with PPX. Neutralization studies using anti-GDNF and anti-BDNF failed to reduce the conditioned media transfer effect, and Millipore Ultrafree centrifugation studies placed the mol.wt. of the activity around 30 kDa. SDS separation revealed three potential bands of interest. A 35-kDa band was present in normal cultures, increased in PPX-incubated cultures, and absent in MPP+-pretreated/PPX-incubated cultures. This conforms to the effect the protein concentrates used to produce these gels had on the growth of DA neurons in VM cultures. Since VM cultures grown in neural basal media, which inhibits the growth of glia, still responded to PPX in a dose-dependent fashion, the trophic activity may be a DA autotrophic factor. However, the gels also revealed two bands at approximately 31 and 55 kDa that were reduced by exposure to PPX and present in MPP+-pretreated cultures. The possibility that these are neuroinhibitory factors that are also regulated by PPX therefore cannot be ruled out.

Glial cell line-derived neurotrophic factor improves intrastriatal graft survival of stored dopaminergic cells

Glial cell line-derived neurotrophic factor, the newest member of the transforming growth factor-beta superfamily, has been shown to promote the survival and differentiation of dopaminergic neurons in the ventral mesencephalon. Glial cell line-derived neurotrophic factor has been implicated in both the in vitro and in vivo recovery of mesencephalic dopaminergic cells challenged with the neurotoxins 1-methyl-4-phenylpyridinium and 6-hydroxydopamine. Previous studies have shown increased survival of intrastriatally transplanted dopaminergic cells when followed by infusion of neurotrophic factors such as basic fibroblast growth factor, brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor. However, the effects of glial cell line-derived neurotrophic factor co-administered with dopaminergic cells prior to implantation in the host striatum have not been studied. In the present study, the hypothesis was that treating fetal ventral mesencephalic tissue containing the dopaminergic substantia nigra with glial cell line-derived neurotrophic factor either during storage or at the time of transplantation, would enhance grafted dopaminergic cell survival and functional reinnervation of the host striatum in the unilaterally 6-hydroxydopamine-lesioned rat. To test this hypothesis, two experiments were performed. In the first experimental group (n = 7), fetal ventral mesencephalons from embryonic day 14 rats were maintained in hibernation medium containing glial cell line-derived neurotrophic factor (1 migrogram/ml) at 4 degrees C for six days prior to dissociation and stereotactic implantation into the host striatum: the control group (n = 5) received tissue hibernated without glial cell line-derived neurotrophic factor. The second experimental group (n = 8) received fresh fetal ventral mesencephalic tissue treated with glial cell line-derived neurotrophic factor (0.2 microgram/microliter) while the control group (n = 5) received the fresh graft with no glial cell line-derived neurotrophic factor. Transplantation success was assessed by behavioural analysis (rotometry) and tyrosine hydroxylase immunohistochemistry. Cell counts of tyrosine hydoxylase-stained sections revealed a statistically significant increase in tyrosine hydroxylase-positive neurons in grafts exposed to glial cell line-derived neurotrophic factor during hibernation as compared to control grafts. In addition, there was a statistically significant enhancement of fibre density in the glial cell line-derived neurotrophic factor hibernation graft group as compared to the glial cell line-derived neurotrophic factor fresh graft group. Behavioural analysis three weeks post-grafting exhibited a statistically significant decrease in amphetamine-induced rotations in animals transplanted with glial cell line-derived neurotrophic factor grafts as compared to control grafts. These findings suggest that storing dopaminergic cells in a glial cell line-derived neurotrophic factor-containing medium prior to transplantation increases graft survival, graft derived fibre outgrowth, and behavioural recovery in the adult host. This observation has potential implications for enhancing the efficacy of neural transplantation in the treatment of Parkinson's disease.

Apoptotic cell death of cultured cerebral cortical neurons induced by withdrawal of astroglial trophic support

Peripheral neurons which depend on NGF for their survival undergo apoptosis after NGF deprivation. However, a convenient in vitro method for assessing the programmed cell death of the central neurons has not been established, because the dependence of particular central neurons on neurotrophic factors has been clarified only for small populations of neurons. Based on the fact that cortical neurons survive in culture for many weeks in the presence of astroglial cells, we have established an in vitro cell death model in which the neurons die through apoptosis. Cortical neurons were maintained on a cover slip for 1 week on top of astroglial cells, and then cell death was induced by separation of the neurons from the astroglial cells. The cortical neurons died within 2-4 days. Nuclei of the dying neurons showed the morphological features of apoptosis, and DNA fragmentation was observed by the TUNEL method and by in situ nick translation (ISNT) staining. The cell death was significantly suppressed by neurotrophic factors, NT-3, NT-4, BDNF, and GDNF, but not by NGF. The neuronal survival was prolonged, as in the case of peripheral neurons, by bFGF, elevated potassium, cAMP, forskolin, and metabotropic glutamate receptor agonist. The cell death was inhibited by inhibitors of interleukin-1 beta-converting enzyme and CPP32. CPP32-like proteolytic activity was increased prior to the appearance of apoptotic cells. These results suggest that cortical neurons die after separation from glial cells through apoptosis caused by deprivation of neurotrophic factors produced by the astroglial cells.

Implants of polymer-encapsulated genetically modified cells releasing glial cell line-derived neurotrophic factor improve survival, growth, and function of fetal dopaminergic grafts

Neural transplantation as an experimental therapy for Parkinsonian patients has been shown to be effective in several clinical trials. Further benefit, however, may be expected if the grafting is combined with a treatment of neurotrophic factors thus improving the survival and growth of grafted embryonic dopaminergic neurons. Continuous trophic support may be needed and therefore requires the long-term delivery of neurotrophic factors to the brain. We demonstrate here that the implantation of polymer-encapsulated cells genetically engineered to continuously secrete glial cell line-derived neurotrophic factor to the adult rat striatum improves dopaminergic graft survival and function. Near complete compensation of 6-hydroxydopamine-induced rotation was already achieved within 3 weeks postgrafting in rats that received glial cell line-derived neurotrophic factor-releasing capsules in addition to dopaminergic cell grafts of cultured tissue. Rats without trophic factor supply showed only little recovery at the same time point and sham grafted rats showed no recovery. The number of tyrosine hydroxylase-immunoreactive cells per graft was increased 2.6-fold in the presence of glial cell line-derived neurotrophic factor 6 weeks postgrafting. Similarly, tyrosine hydroxylase-immunoreactive fibers around the graft were increased by 53%. Moreover, these fibers showed a preferential growth towards the trophic factor-releasing capsule. Taken together, these results provide evidence that encapsulated genetically engineered cells are an effective means of long-term trophic factor supply into the adult rat brain and that the delivery of glial cell line-derived neurotrophic factor can sustain dopaminergic graft function and survival.

Distribution of fibroblast growth factor (FGF)-2 and FGF receptor-1 messenger RNA expression and protein presence in the mid-trimester human fetus

Fibroblast growth factors (FGF) are known to have key roles in embryonic growth and morphogenesis, but their presence and contributions to fetal development are unclear. In particular, little information exists as to the relevance of FGF and their specific receptors to human fetal development. We studied the anatomical distribution of messenger RNA encoding FGF-2 and one of its high affinity receptors, FGFR1, using in situ hybridization in a variety of human fetal tissues in early second trimester. Corresponding protein distributions were determined by immunohistochemistry. Both FGF-2 and FGFR1 mRNA and proteins were found to be present in every organ and tissue examined, but with defined cellular localizations. In skeletal muscle, both FGF-2 and FGFR1 mRNA and peptides were present in differentiated fibers, and both co-localized to proliferating chondrocytes of the epiphyseal growth plate. FGF-2 and FGFR1 mRNA and peptides were also present within cardiac or gastrointestinal smooth muscle. Within the gastrointestinal tract FGF-2 mRNA and peptide were located in the submucosal tissue, whereas FGFR1 was expressed within the overlying mucosa. Similarly, in skin, FGF-2 was expressed within the dermis whereas FGFR1 mRNA and peptide were most apparent in the stratum germinativum of the epidermis. In kidney and lung, FGFR1 mRNA was located in the tubular and alveolar epithelia respectively, whereas FGF-2 was expressed in both epithelial and mesenchymal cell populations. Both growth factor and receptor were widespread in both neuroblasts and glioblasts in the cerebral cortex of the brain. Immunoreactivity for FGF-2 and FGFR1 was seen in all vascular endothelial cells of major vessels and capillaries. Within the skin, kidney, lung, and intestine FGF-2 immunoreactivity was found in basement membranes underlying epithelia, and was associated with the extracellular matrix and plasma membranes of many cell types. The results show that FGF-2 and one of its receptors are widely expressed anatomically in the mid-trimester human fetus.

Effects of chronic substance P treatment and intracranial fetal grafts on learning after hippocampal kainic acid lesions

The purpose of this experiment was to investigate whether the neurokinin substance P (SP) can enhance adaptive graft effects on learning and memory functions in animals with lesions of the hippocampus. Adult male Wistar rats received a bilateral kainic acid (KA) lesion of the dorsal hippocampus. One week postlesion, bilateral grafts of fetal hippocampal tissue suspension were applied into the damaged region in half of the animals, whereas the other half received sham transplants (physiological saline). Animals of the control group received a bilateral sham lesion of the hippocampus and sham transplants. One week after transplantation surgery, the rats were tested in the place version of the Morris water maze over a period of 9 weeks. Then they were tested for SP-induced conditioned place preference and on a step-through inhibitory avoidance task. All animals received IP injections of either SP (5 or 50 micrograms/kg) or the SP vehicle (0.5 ml/kg). The treatment with SP or the vehicle was begun 1 week after transplantation and was performed 5 days a week over a period of 10 weeks. During behavioral tests in the water maze and avoidance task, application of the substances was performed 5 h after testing. For the conditioned place preference test, the conditioning trials were performed immediately after drug administration; the test trials were given 24 h later. Chronic administration of 50 micrograms/kg SP, but not 5 micrograms/ kg SP, was found to improve water maze performance in lesioned animals with and without grafts. Unexpectedly, the lesion group with the graft without additional SP treatment was not superior to the lesion group devoid of the graft in this task. The rats without lesions of the hippocampus still showed a conditioned place preference to 50 micrograms/kg SP after 9 weeks of repeated SP applications. In the inhibitory avoidance task, the grafts facilitated retention performance independent of whether SP treatment was given. The morphological analysis of the transplants revealed higher graft volumes and a higher diameter of large pyramidal neurons (> 10 microns) in rats chronically treated with 50 micrograms/kg SP.

Glial cell line-derived neurotrophic factor (GDNF) gene expression in the human brain: a post mortem in situ hybridization study with special reference to Parkinson's disease

Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor for dopaminergic neurons. Since dopaminergic neurons degenerate in Parkinson's disease, this factor is a potential therapeutical tool that may save dopaminergic neurons during the pathological process. Moreover, a reduced GDNF expression may be involved in the pathophysiology of the disease. In this study, we tested whether altered GDNF production may participate in the mechanism of cell death in this disease. GDNF gene expression was analyzed by in situ hybridization using riboprobes corresponding to a sequence of the exon 2 human GDNF gene. Experiments were performed on tissue sections of the mesencephalon and the striatum from 8 patients with Parkinson's disease and 6 control subjects matched for age at death and for post mortem delay. No labelling was observed in either group of patients. This absence of detectable expression could not be attributed to methodological problems as a positive staining was observed using the same probes for sections of astroglioma biopsies from human adults and for sections of a newborn infant brain obtained at post-mortem. These data suggest that GDNF is probably expressed at a very low level in the adult human brain and its involvement in the pathophysiology of Parkinson's disease remains to be demonstrated. GDNF may represent a powerful new therapeutic agent for Parkinson's disease, however.

Inhibitors of type IV phosphodiesterases reduce the toxicity of MPTP in substantia nigra neurons in vivo

The neuropathology of Parkinson's disease is characterized by the degeneration of dopaminergic neurons in the substantia nigra. We have recently shown that the activation of protein kinase A improves the survival of dopaminergic neurons in culture and, furthermore, protects them from the dopaminergic neurotoxin, 1-methyl-4-phenylpyridinium ion (MPP+) in vitro. We have now analysed the potential of phosphodiesterase inhibitors to increase cAMP levels in dopaminergic neurons, to improve their survival in culture and to protect them from the toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in vivo. Increasing intracellular cAMP with phosphodiesterase type IV-specific inhibitors enhanced the survival of dopaminergic neurons in culture. Inhibitors of other phosphodiesterase types were not active. In vivo, phosphodiesterase type IV inhibitors reduced the MPTP-induced dopamine depletion in the striatum of C57BL/6 mice. Furthermore, the loss of tyrosine hydroxylase-immunopositive neurons in the substantia nigra of these animals was diminished. After Nissl staining, a similar reduction of the MPTP-induced loss of neurons was observed in the substantia nigra. The protective effect of protein kinase A activation did not appear to be due to the blocking of MPP+ uptake into dopaminergic neurons. This was not decreased after treatment with forskolin or 8-(4-chlorophenylthio)-cAMP. Thus, protein kinase A regulates the survival and differentiation of dopaminergic substantia nigra neurons in vivo, implicating a therapeutic potential for substances which regulate cAMP turnover in these neurons.

Systematic differences in time of dopaminergic neuron origin between normal mice and homozygous weaver mutants

Immunocytochemical labeling for tyrosine hydroxylase and [3H]thymidine autoradiography were combined in wild-type mice and in mice homozygous for the weaver mutant gene (wv) to see whether the neurogenetic patterns of midbrain dopaminergic neurons was normal in the mutants and whether the degeneration of dopaminergic neurons was linked to their time of origin. Dams of wild-type and homozygous weaver mice were injected with [3H]thymidine on embryonic days (E) 11-E12, E12-E13, E13-E14, and E14-E15 to label neurons in the retrorubral field, the substantia nigra pars compacta, the ventral tegmental area, and the interfascicular nucleus as they were being generated. The quantitatively determined time of origin profiles indicated that wv/wv mice have the same time span of neurogenesis as +/+ mice (E10 to E14), but have significant deficits in the proportion of late-generated neurons in each dopaminergic population. In the retrorubral field and substantia nigra, weaver homozygotes had substantial losses of dopaminergic neurons and had a greater deficit in the proportion of neurons generated late while, in the ventral tegmental area and interfascicular nucleus, there were slight losses of dopaminergic neurons and only slight deficits in the proportion of late-generated neurons. These findings lead to the conclusion that the weaver gene is specifically targeting dopaminergic neurons that are generated late, mainly on E13 and E14.

Specific effects of platelet derived growth factor (PDGF) on fetal rat and human dopaminergic neurons in vitro

The neurotrophic effects of the BB isoform of platelet-derived growth factor (PDGF) on rat and human fetal mesencephalic dopaminergic neurons have been characterized in vitro. A dose-response analysis demonstrated maximal responses at 30 ng/ml of PDGF-BB. This concentration resulted in a marked increase in the survival and neurite outgrowth from rat and human tyrosine hydroxylase-(TH) positive, presumed dopaminergic neurons after 7 days in vitro. The effects of PDGF-BB on survival of TH-positive neurons were comparable to those of brain-derived neurotrophic factor (BDNF), whereas neurite outgrowth was more pronounced after addition of BDNF. The combination of BDNF and PDGF-BB yielded no additive effects. Double immunohistochemical staining of rat cultures demonstrated PDGF beta-receptors on about 90% of the TH-positive neurons. PDGF-BB treatment of rat mesencephalic cultures induced an upregulation of c-fos and TH mRNA with maximal levels after 0.5-2 h as assessed by quantitative PCR analysis. An increased number of Fos protein-positive cells was detected immunohistochemically after 4 h of PDGF-BB treatment. The present results provide further evidence for specific and direct effects of PDGF-BB on gene expression, survival and neurite outgrowth of mesencephalic dopaminergic neurons of rat and human origin.

Novel therapeutic directions for Parkinson's disease

Problems associated with the long-term use of L-dopa to treat Parkinson's disease have prompted considerable interest in developing alternative therapeutic strategies for this disorder. Newer approaches have included dopamine-cell transplantation, genetic manipulation of striatal cells in situ and the localized administration of trophic factors to injured neurons in the substantia nigra. These studies not only offer promise for treating Parkinson's disease, but also provide insights into properties of the nigrostriatal system that may eventually help to prevent neuronal degeneration.

Stimulation of zif/268 gene expression by basic fibroblast growth factor in primary rat striatal cultures

The presence of basic fibroblast growth factor (bFGF) in the basal ganglia, and its known neurotrophic activity, has created interest in its possible role as an agent to attenuate striatal neurodegeneration. However, little information is available on the mechanisms through which bFGF might exert a long-term influence on striatal function. Primary cultures of embryonic rat striatal neurones were used to ascertain whether bFGF can alter the pattern of striatal gene expression. Treatment of cultures with bFGF (500 pM) resulted in a dramatic increase in the levels of zif/268 mRNA within 45 min. This induction was attenuated by the tyrosine kinase inhibitor genistein (100 microM), but not by its inactive structural analogue genistin (100 microM). The induction of zif/268 mRNA was found to occur in non-neuronal cells, with no increase in mRNA levels being observed in neurones. A similar induction was noted for another putative transcription factor, jun B, although no induction of the related factor jun D could be detected. These results show that bFGF can induce immediate-early gene expression in striatal cultures, and therefore that this may provide a mechanism, mediated by non-neuronal cells, which allows bFGF to cause a long-term change in striatal neurochemistry.

Fibroblast growth factors: structure-activity on dopamine neurons in vitro

We investigated the effect of neurotrophic factors on dopamine (DA) cells in vitro. At concentrations of nanograms/c.c. basic fibroblast growth factor (bFGF) is a more potent DA-trophic agent than brain derived neurotrophic factor (BDNF) or epidermal growth factor (EGF) in fetal mid brain neurons. In these cells, bFGF produces a greater increase of DA levels and percentage of cells positive for tyrosine hydroxylase (TH+) than BDNF and EGF. Acidic fibroblast growth factor (aFGF) was not tested in fetal DA cells since aFGF requires heparin for its effect and fetal mid brain cultures do not grow well in the presence of a high concentration of heparin. We further investigated the effect of bFGF and aFGF, and two of their analogs, in catecholamine rich human neuroblastoma cells NB69. In these cells aFGF, at concentrations of picograms/c.c., increases DA levels, while its analogs, E118 and super short, have no effect. Acidic FGF also increases norepinephrine levels, the number of TH+ cells, and the percentage of TH+ with respect to the total number of nuclei. Basic fibroblast growth factor (bFGF) produced similar, but less potent effects. Acidic FGF was active only in the presence of heparin; the effect of bFGF was independent of heparin. FGFs are promising drugs for the treatment of PD, though further investigations with these compounds should be performed before their use in clinical trials.

Basic fibroblast growth factor increases dopaminergic graft survival and function in a rat model of Parkinson's disease

The clinical use of fetal neural grafts as an intracerebral source of dopamine for patients with Parkinson's disease has met with limited success. Since basic fibroblast growth factor (bFGF) enhances the survival and growth of dopaminergic neurons in vitro, we explored whether cells genetically modified to produce bFGF would improve the functional efficacy of dopaminergic neurons implanted into rats with experimental Parkinson's disease. Results show that bFGF-producing cells grafted together with fetal dopamine neurons have potent growth-promoting effects on the implanted neurons in vivo. Moreover, rats implanted with such co-grafts display the most pronounced behavioural improvements post-grafting. These findings not only provide insight into the function of bFGF in situ, but also suggest an approach for enhancing the survival and function of dopamine neurons grafted into the damaged brain.

Neuroblast cell death in ovo and in culture: interaction of ethanol and neurotrophic factors

We used two experimental paradigms to examine the influence of the neurotrophins, NGF, EGF, and bFGF on normal neuroblast survival and also after ethanol insult. In the first paradigm, chick embryos received in ovo at embryonic day 1 and 2 (E1 and E2) saline (control) ethanol (10mg/50 microliters/day), NGF (50 ng/50 microliters/day), or EGF (25 ng/50 microliters/day), or ethanol+NGF or EGF. At E3, cultures were prepared from whole embryos separately from each group. At C2, all cultures were labeled with [3H]thymidine and assessed for effects or neuronal survival. In the second paradigm, cultures were prepared from 3-day-old whole embryos and at C0, cultures were treated with either ethanol (50 mM) alone, NGF (50 ng/ml) alone, EGF (25 ng/ml) alone, bFGF (50 ng/ml) alone, or were treated concomitantly with ethanol plus one of the neurotrophins; control had only the culture medium, DMEM + 5% FBS. We obtained the following findings. 1) Cultures derived from embryos treated with either of the three neurotrophins exhibited a higher neuronal survival as compared to controls (1st paradigm). 2) The survival-promoting effect was also observed when the neurotrophins were added directly to the cultures (2nd paradigm). 3) As reported previously, cultures derived from ethanol-treated embryos exhibited a marked decline in neuronal survival as compared to controls. 4) All three neurotrophins attenuated the decline in neuronal survival produced by ethanol. The 'rescuing' effects of the neurotrophins support our early hypothesis that ethanol administration during early neurogenesis interferes with microenvironmental trophic signals essential for neuroblast survival and differentiation.

Behavioural consequences of neural transplantation

Neural grafts can reverse many functional deficits associated with brain damage, whether of traumatic, toxic, neurodegenerative or genetic origin. In some model systems recovery can be partial or complete; whereas in others the grafts have limited effects or may actually cause further dysfunction. In order to devise rational and effective transplantation strategies it is necessary to understand the mechanisms by which grafts exert their functional effects. Several alternatives have been proposed, and these include non-specific consequences of surgery, acute diffuse neurotrophic and growth mechanisms, chronic diffuse release of deficient neurochemicals, bridging tissues for host regeneration, diffuse reinnervation of the host brain, and reciprocal graft-host reconnection. These alternative mechanisms are not necessarily exclusive in any particular situation, and all have been seen to apply in different model systems.

The response of human and rat fetal ventral mesencephalon in culture to the brain-derived neurotrophic factor treatment

Brain-derived neurotrophic factor (BDNF) has been shown to increase the survival of dopaminergic neurons in rodent mesencephalic cultures. The mRNAs of BDNF and trkB receptor have been found to be expressed in the substantia nigra of rat. In this study, the action of BDNF was studied on the survival and transmitter-specific differentiation of dopaminergic neurons of fetal human CNS aged 9-10-week in vitro. Dopaminergic neuron viability and phenotypic expression were monitored by tyrosine hydroxylase (TH) immunohistochemistry and measurement of dopamine (DA) content with HPLC, respectively. After seven days of treatment with BDNF there were 2.2-fold greater number of TH+ neurons surviving than in untreated cultures. Although very low levels of DA were detectable in human tissue, considerable amounts of DA was found in the culture medium from around 13 days in vitro (DIV), indicating that DA in human fetal tissue tended to be synthesised and released into the incubation medium more readily than from cultured rat fetal tissue during the same period. The content of DA in the BDNF-treated cultures was approximately double that of untreated cultures after 7 days. In rat fetal tissue, the capacity of each TH+ neuron to produce DA was not changed in the BDNF-treated cultures (7 DIV) compared with control cultures, suggesting that BDNF does not up-regulate the production of DA but rather acts to reduce cell death rates. Ciliary neurotrophic factor (CNTF) treatment of rat mesencephalic culture failed to improve the period of survival of fetal dopaminergic neurons and had no effect on the production of DA in cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative effect of alpha-MSH and b-FGF on neurite extension of fetal rat spinal cord neurons in culture

Basic fibroblast growth factor (b-FGF) and alpha melanocyte stimulating hormone (alpha-MSH) were tested for their ability to promote axonal elongation on E14 fetal rat spinal cord cell culture, and to support cell survival. A similar development of neurite was observed in alpha-MSH treated cultures or in control cultures, with an axonal length ranging from 87.50 microns to 195.60 microns on day 3. Complete cell death occurred after 6 days of incubation. Whatever the concentration of b-FGF used (0.312-2.5 ng/ml), a significant increase (1.2- to 1.4-fold) in neurite length was observed, with neuronal survival up to 9 days.

Basic fibroblast growth factor induces c-fos expression in primary cultures of rat striatum

Basic fibroblast growth factor (bFGF) is present in the rat striatum in vivo, where evidence suggests it may have a long-term trophic role in supporting the survival of striatal neurones. To examine the possibility that these effects of bFGF might be mediated by induction of neuronal gene expression, we have investigated the ability of bFGF to stimulate expression of the immediate-early gene c-fos in primary cultures of embryonic rat striatum. The basal levels of c-fos mRNA were low in both neurones and glia in culture. Application of 500 pM bFGF resulted, within 45 min, in a 11-fold increase in the c-fos hybridisation signal in the non-neuronal cells. No significant induction of c-fos mRNA was detected in the striatal neurones at this time. The induction in non-neuronal cells was blocked by the tyrosine kinase inhibitor genistein (100 microM), but not by its inactive structural analogue genistin (100 microM). These results represent a novel mechanism whereby bFGF can exert prolonged effects on striatal function, and indicate that the increases in striatal c-fos gene expression induced by bFGF occur primarily in non-neuronal cells.

Fibroblast growth factors: activities and significance of non-neurotrophin neurotrophic growth factors

Although first characterized by virtue of their ability to stimulate endothelial cell proliferation in vitro and angiogenesis in vivo, the fibroblast growth factors are now also well recognized for their neurotrophic activities. Understanding the physiological significance of these multifunctional, virtually ubiquitous and pluripotential molecules, however, remains enigmatic. Recent advances describing their molecular, biochemical and biological characteristics has led to a better understanding of their role in the central nervous system.

Basic fibroblast growth factor promotes the survival of embryonic ventral mesencephalic dopaminergic neurons--II. Effects on nigral transplants in vivo

The clinical potential of transplants of fetal dopaminergic neurons is limited by the fact that the percentage of cells surviving in such grafts is in general quite low. This report investigates the use of basic fibroblast growth factor administration (given either as a pretreatment or by repeated intrastriatal infusions) to promote the survival and behavioural efficacy of embryonic dopamine-rich nigral transplants in rats. Pretreatment of the graft tissue by brief incubation with basic fibroblast growth factor increased the survival of tyrosine hydroxylase-immunoreactive (presumed dopaminergic) neurons in the grafts in comparison to control grafts, and accelerated the recovery in the transplanted animals in tests of drug-induced rotational asymmetry. However, the clear advantage seen in the rotation test conducted three weeks after transplantation had disappeared by nine weeks. The moderate effects of pretreatment were markedly enhanced by repeated intrastriatal infusion of basic fibroblast growth factor into the host animals over 20 days following transplantation. This resulted in > 100% increase in the number of dopaminergic neurons surviving in the grafts, and was accompanied by a significantly greater recovery of the rats' rotational asymmetries which persisted over the full nine weeks of testing. However, the repeated intracerebral infusions induced an inflammatory reaction in the striatum, and the associated trauma both complicates the interpretation of the mechanism of observed recovery and compromises the utility of this route of basic fibroblast growth factor administration for promoting graft survival.