TGF beta 2 and TGF beta 3 are potent survival factors for midbrain dopaminergic neurons

Activation of ionotropic glutamate receptors reduces the production of transforming growth factor-beta2 by developing neurons

Neuronal cultures derived from developing rat cerebral cortex were used to investigate the influence of glutamate receptors on the neuronal production of transforming growth factor-beta2 (TGFbeta2), a multifunctional cytokine that modulates neuronal and glial growth. Long-term exposure (48 h) of cortical neurons to selective antagonists of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors markedly increased TGFbeta2 levels in the culture medium. Conversely, treatment with NMDA or kainate reduced TGFbeta2 to levels below those in untreated cultures. The effect of kainate did not require NMDA receptor activity. Neuronal depolarization with K+ also reduced TGFbeta2 levels by opening voltage-gated L-type Ca2+ channels. Semi-quantitative RT-PCR measurements of neuronal TGFbeta2 mRNA showed that NMDA or AMPA/kainate receptor stimulation reduced TGFbeta2 mRNA levels. These results demonstrate that tonic activation of glutamate-gated cation channels downregulates neuronal expression of the TGFbeta2 gene and provide evidence for a novel mechanism whereby excitatory amino acids could influence the development of glial and neuronal lineages.

The transforming growth factor-betas: structure, signaling, and roles in nervous system development and functions

Transforming growth factor-betas (TGF-betas) are among the most widespread and versatile cytokines. Here, we first provide a brief overview of their molecular biology, biochemistry, and signaling. We then review distribution and functions of the three mammalian TGF-beta isoforms, beta1, beta2, and beta3, and their receptors in the developing and adult nervous system. Roles of TGF-betas in the regulation of radial glia, astroglia, oligodendroglia, and microglia are addressed. Finally, we review the current state of knowledge concerning the roles of TGF-betas in controlling neuronal performances, including the regulation of proliferation of neuronal precursors, survival/death decisions, and neuronal differentiation.

Novel alternative promoters of mouse glial cell line-derived neurotrophic factor gene

We previously isolated cDNA and genomic DNA of the mouse glial cell line-derived neurotrophic factor (GDNF) gene and found that the gene consists of three exons. Recently, it was suggested that an alternative promoter exists within intron 1 of the human GDNF gene, but this has not been confirmed. Novel cDNA clones of the mouse GDNF gene were isolated by 5'-rapid amplification of cDNA ends from postnatal day-14 striatum. A novel exon, containing 351 nucleotides, exists between exon 1 and exon 3 (referred to as exon 2 in our previous report). Luciferase reporter assay showed that a core promoter for the novel exon 2 requires its 5'-untranslated region. Primer extension analysis and reverse transcription-PCR identified another novel transcript that starts 39 bp upstream of exon 3, and the core promoter activity exists within a region containing putative Sp1 sites. Although the core promoters for the novel exons are different from those previously identified, transcripts derived from each promoter coincidentally increased with interleukin-1beta or tumor necrosis factor-alpha stimulation. Gel retardation assays suggested that the NF-kappaB binding site in intron 1 would be involved in the cytokine response of the mouse GDNF gene.

Developmental cell death in dopaminergic neurons of the substantia nigra of mice

Dopaminergic neurons in the substantia nigra pars compacta (SNpc) undergo natural cell death during development in rats. Controversy exists as to the occurrence of this phenomenon in SNpc dopaminergic neurons in the developing mouse. Herein, by using an array of morphologic techniques, we show that many SNpc neurons fulfill the criteria for apoptosis and that the number of apoptotic neurons in the SNpc vary in a time-dependent manner from postnatal day 2 to 32. These dying neurons also show evidence of DNA fragmentation, of activated caspase-3, and of cleavage of beta-actin. Some, but not all of the SNpc apoptotic neurons still express their phenotypic marker tyrosine hydroxylase, confirming their dopaminergic nature. Consistent with the importance of target-derived trophic support in modulating developmental cell death, we demonstrate that destruction of intrinsic striatal neurons by a local injection of quinolinic acid (QA) dramatically enhances the magnitude of SNpc apoptosis and results in a lower number of adult SNpc dopaminergic neurons. Strengthening the apoptotic nature of the observed SNpc developmental cell death, we demonstrate that overexpression of the anti-apoptotic protein Bcl-2 attenuates both natural and QA-induced SNpc apoptosis. The present study provides compelling evidence that developmental neuronal death with a morphology of apoptosis does occur in the SNpc of mice and that this process plays a critical role in regulating the adult number of dopaminergic neurons in the SNpc.

The single intranigral injection of LPS as a new model for studying the selective effects of inflammatory reactions on dopaminergic system

We have injected lipopolysaccharide (LPS) into the nigrostriatal pathway of rats in order to address the role of inflammation in Parkinson's disease (PD). LPS induced a strong macrophage/microglial reaction in Substantia nigra (SN), with a characteristic clustering of macrophage cells around blood-vessels. The SN was far more sensitive than the striatum to the inflammatory stimulus. Moreover, only the dopaminergic neurons of the SN were affected, with no detectable damage to either the GABAergic or the serotoninergic neurons. The damage to the DA neurons in the SN was permanent, as observed 1 year postinjection. Unlike the direct death of dopaminergic neurons caused by agents as MPP(+) or 6-OHDA, LPS seems to cause indirect death due to inflammatory reaction. Therefore, we suggest that the injection of a single dose of LPS within the SN is an interesting model for studying the selective effects of inflammatory reaction on dopaminergic system and also potentially useful for studying PD.

Mutual induction of TGFbeta1 and NGF after treatment with NGF or TGFbeta1 in grafted chromaffin cells of the adrenal medulla

Chromaffin cells have been recognized for their ability to transform into sympathetic ganglion-like cells in response to nerve growth factor (NGF) or to stimulation of other neurotrophic factors. Transforming growth factor beta (TGFbeta) family members have been shown to potentiate the effect of different trophic factors. The aim of this study was to investigate if TGFbeta may influence NGF-induced neuronal transformation and regulation of NGF, TGFbeta1, and their receptors in the adult rat chromaffin tissue after grafting. Intraocular transplantation of adult chromaffin tissue was employed and grafts were treated with TGFbeta1 and/or NGF. Graft survival time was 18 days after which the grafts were processed for TGFbeta luciferase detection assay, NGF enzyme immunoassay, or in situ hybridization. In grafts stimulated with NGF, increased levels of TGFbeta1 and TGFbeta1 mRNA were detected. When grafts instead were treated with TGFbeta1, enhanced levels of NGF protein were found. Furthermore, a positive mRNA signal corresponding to the transforming growth factor II receptor (TbetaRII) was found in the chromaffin cells of the normal adrenal medulla as well as after grafting. No increase of TbetaRII mRNA levels was detected after transplantation or after TGFbeta1 treatment. Instead a reduction of TbetaRII mRNA expression was noted after NGF treatment. NGF stimulation of grafts increased the message for NGF receptors p75 and trkA in the chromaffin transplants. Grafts processed for evaluations of neurite outgrowth were allowed to survive for 28 days and were injected weekly with NGF and/or TGFbeta1. NGF treatment resulted in a robust innervation of the host irides. TGFbeta1 had no additive effect on nerve fiber formation when combined with NGF. Combined treatment of NGF and anti-TGFbeta1 resulted in a significantly larger area of reinnervation. In conclusion, it was found that NGF and TGFbeta1 may regulate the expression of each other's protein in adult chromaffin grafts. Furthermore, TbetaRII mRNA was present in the adult rat chromaffin cells and became downregulated as a result of NGF stimulation. Although no synergistic effects of TGFbeta1 were found on NGF-induced neurite outgrowth, it was found that TGFbeta1 and NGF signaling are closely linked in the chromaffin cells of the adrenal medulla.

Broad specificity of GDNF family receptors GFRalpha1 and GFRalpha2 for GDNF and NTN in neurons and transfected cells

The glial cell line-derived neurotrophic factor (GDNF) family of ligands binds to lipid anchored proteins termed GDNF family receptor (GFR)alphas, and then activates the RET receptor tyrosine kinase, by ligand GFRalpha. The binding of soluble GFRalphas to transfected cells suggested that different GFRalphas were dedicated to particular ligands, with GDNF acting primarily or entirely through GFRalpha1, and neurturin (NTN), through GFRalpha2. More recent evidence has suggested the possibility of cross-talk between these ligands and the two receptors. We examined here whether crosstalk between the GDNF ligands and the GFRalphas is biologically relevant, using midbrain dopaminergic, and parasympathetic, submandibular gland neurons. By biochemical and genetic addition and/or deletion of GFRalpha1 and 2, we show that in both neuronal cell types, robust biological activities of GDNF or NTN can be mediated by either GFRalpha1 or GFRalpha2, although GDNF is slightly more potent in dopaminergic (DA) neurons which normally express GFRalpha1, and NTN in submandibular neurons which normally express GFRalpha2. Throughout the body, GDNF and NTN are likely to have important biological actions on both GFRalpha1- and GFRalpha2-expressing cells.

Implantation of bioactive growth factor-secreting rods enhances fetal dopaminergic graft survival, outgrowth density, and functional recovery in a rat model of Parkinson's disease

One of the drawbacks with fetal ventral mesencephalic (VM) grafts in Parkinson's disease is the limited outgrowth into the host striatum. In order to enhance graft outgrowth, epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) were administered by implantation of bioactive rods to the lateral part of the striatum to support grafted fetal VM implanted to the medial portion of the striatum. The polymer-based bioactive rods allow for a local secretion of neurotrophic factors over a time period of approximately 2 weeks. Moreover, glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor-beta1 (TGFbeta1) were administered using the same technique. Concomitant administration of GDNF and TGFbeta1 was achieved by insertion of one GDNF and one TGFbeta1 rod. This was performed to investigate possible additive effects between GDNF and TGFbeta1. Rotational behavior, outgrowth from and nerve fiber density within the VM graft, and the number of TH-positive cells were studied. Functional compensation by reduction of rotational behavior was significantly enhanced in animals carrying bFGF and GDNF rods in comparison with animals carrying only VM graft. EGF and bFGF significantly increased the innervation density. Moreover, the nerve fiber density within the grafts was significantly enhanced by bFGF. Cell counts showed that a significantly higher number of TH-positive neurons was found in grafts treated with bFGF than that found in GDNF-treated grafts. An additive effect of TGFbeta1 and GDNF was not detectable. These results suggest that bioactive rods is a useful tool to deliver neurotrophic factors into the brain, and since bFGF was a potent factor concerning both functional, immunohistochemical and cell survival results, it might be of interest to use bFGF-secreting rods for enhancing the overall outcome of VM grafts into patients suffering from Parkinson's disease.

Characterization of the dopamine defect in primary cultures of dopaminergic neurons from hypoxanthine phosphoribosyltransferase knockout mice

Lesch-Nyhan disease (LND) is an X-linked metabolic disorder caused by lack of activity of the purine salvage enzyme hypoxanthine phosphoribosyltransferase (HPRT) and characterized by hyperuricemia and debilitating neurological manifestations. The mechanisms underlying the neuropathology are not well understood and the principal neurochemical lesion characterized to date is a deficiency of the dopamine system in the basal ganglia. To facilitate the study of mechanism(s) by which HPRT deficiency causes the dopamine defect, we have compared the survival and dopamine phenotype of primary cultures of dopamine neurons derived from HPRT-deficient mice with the dopaminergic neurons from wild-type mice. The survival of dopaminergic neurons from both sources was promoted to an equal extent by glial cell line-derived neurotrophic factor (GDNF), a potent survival factor for dopamine neurons in vitro. Although the survival of the HPRT-deficient neurons was indistinguishable from that of cells derived from wild-type counterparts, the HPRT-deficient cells demonstrated a persistent deficiency of dopamine content and dopamine uptake with increasing neuritic differentiation, indicating that GDNF does not restore the normal phenotype in HPRT-deficient dopamine neurons despite its well-known protective and regenerative properties in several neurodegeneration models. Nevertheless, the demonstration that GDNF trophic support promotes the survival of these dopaminergic neurons will facilitate gaining a better understanding of the neuropathological mechanisms of LND by allowing a more extensive analysis of the cells central to the Lesch-Nyhan phenotype, the dopaminergic neurons of the basal ganglia.

Patterning of dopaminergic neurotransmitter identity among Caenorhabditis elegans ray sensory neurons by a TGFbeta family signaling pathway and a Hox gene

We have investigated the mechanism that patterns dopamine expression among Caenorhabditis elegans male ray sensory neurons. Dopamine is expressed by the A-type sensory neurons in three out of the nine pairs of rays. We used expression of a tyrosine hydroxylase reporter transgene as well as direct assays for dopamine to study the genetic requirements for adoption of the dopaminergic cell fate. In loss-of-function mutants affecting a TGFbeta family signaling pathway, the DBL-1 pathway, dopaminergic identity is adopted irregularly by a wider subset of the rays. Ectopic expression of the pathway ligand, DBL-1, from a heat-shock-driven transgene results in adoption of dopaminergic identity by rays 3–9; rays 1 and 2 are refractory. The rays are therefore prepatterned with respect to their competence to be induced by a DBL-1 pathway signal. Temperature-shift experiments with a temperature-sensitive type II receptor mutant, as well as heat-shock induction experiments, show that the DBL-1 pathway acts during an interval that extends from two to one cell generation before ray neurons are born and begin to differentiate. In a mutant of the AbdominalB class Hox gene egl-5, rays that normally express EGL-5 do not adopt dopaminergic fate and cannot be induced to express DA when DBL-1 is provided by a heat-shock-driven dbl-1 transgene. Therefore, egl-5 is required for making a subset of rays capable of adopting dopaminergic identity, while the function of the DBL-1 pathway signal is to pattern the realization of this capability.

Characterization of dopaminergic midbrain neurons in a DBH:BDNF transgenic mouse

The neurotrophin brain-derived neurotrophic factor (BDNF) has been implicated in the survival and differentiation of central nervous system neurons, including dopaminergic cells in culture. To determine whether BDNF might play a role in the development of dopaminergic neurons in vivo, we used a previously characterized transgenic mouse (DBH:BDNF) that overexpresses BDNF in adrenergic and noradrenergic neurons as a result of fusion of the BDNF gene to the dopamine beta-hydroxylase (DBH) gene promoter. We quantified dopaminergic neuronal profiles at four midbrain coronal levels and compared DBH:BDNF transgenic animals with wild-type mice of the same genetic background. Analysis of sections immunostained with tyrosine hydroxylase (TH) showed that the mean number of dopaminergic neurons in the four selected midbrain sections was 52% greater (one-way analysis of variance, P < 0.0005) in transgenic mice (2,165 +/- 55 S. E.M., n = 4) than in control mice (1,428 +/- 71 S.E.M., n = 4). The increase in dopaminergic neuron profile count in DBH:BDNF transgenic animals was confirmed by analysis of the pars compacta of the substantia nigra on Nissl-stained sections. Surface area of the reference region of interest containing TH-immunoreactive neurons was similar in transgenic and control mice. Regional analysis of different midbrain areas containing dopaminergic neurons suggested that the increase in cell profile count occurs in a relatively homogeneous manner. Comparison of TH-immunoreactive cell size showed a tendency for smaller neurons in transgenic animals, but the difference was not statistically significant. We conclude that DBH:BDNF transgenic mice show increased number of TH-immunoreactive cells in the midbrain. We propose that BDNF rescues dopaminergic neurons from the perinatal period of developmental cell death as a consequence of increased anterograde transport of the neurotrophin via the coeruleonigral projection.

Signalling by the RET receptor tyrosine kinase and its role in the development of the mammalian enteric nervous system

RET is a member of the receptor tyrosine kinase (RTK) superfamily, which can transduce signalling by glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) in cultured cells. In order to determine whether in addition to being sufficient, RET is also necessary for signalling by these growth factors, we studied the response to GDNF and NTN of primary neuronal cultures (peripheral sensory and central dopaminergic neurons) derived from wild-type and RET-deficient mice. Our experiments show that absence of a functional RET receptor abrogates the biological responses of neuronal cells to both GDNF and NTN. Despite the established role of the RET signal transduction pathway in the development of the mammalian enteric nervous system (ENS), very little is known regarding its cellular mechanism(s) of action. Here, we have studied the effects of GDNF and NTN on cultures of neural crest (NC)-derived cells isolated from the gut of rat embryos. Our findings suggest that GDNF and NTN promote the survival of enteric neurons as well as the survival, proliferation and differentiation of multipotential ENS progenitors present in the gut of E12.5-13.5 rat embryos. However, the effects of these growth factors are stage-specific, since similar ENS cultures established from later stage embryos (E14. 5–15.5), show markedly diminished response to GDNF and NTN. To examine whether the in vitro effects of RET activation reflect the in vivo function(s) of this receptor, the extent of programmed cell death was examined in the gut of wild-type and RET-deficient mouse embryos by TUNEL histochemistry. Our experiments show that a subpopulation of enteric NC undergoes apoptotic cell death specifically in the foregut of embryos lacking the RET receptor. We suggest that normal function of the RET RTK is required in vivo during early stages of ENS histogenesis for the survival of undifferentiated enteric NC and their derivatives.

Developmental regulation of the serotonergic transmitter phenotype in rostral and caudal raphe neurons by transforming growth factor-betas

Serotonergic (5-HT) neurons of the CNS develop as two separate clusters, a rostral and a caudal group, within the brain stem raphe. We show here that the transforming growth factors -beta2 and -beta3 (TGF-beta) and the TGF-beta type II receptor are expressed in the embryonic rat raphe, when 5-HT neurons develop and differentiate. To investigate putative roles of TGF-betas in the regulation of 5-HT neuron development we have generated serum-free cultures isolated either from the rostral or the caudal embryonic rat raphe, respectively. In cultures from the caudal E14 raphe saturating concentrations (5 ng/ml) of TGF-beta2 and -beta3 augmented numbers of tryptophan hydroxylase (TpOH) -immunoreactive neurons and cells specifically taking up 5,7-dihydroxytryptamine (5,7-DHT) by about 1.7-fold over a period of 4 days. Treatment with TGF-betas also increased uptake of 3H-5HT uptake about 1.7-fold. Alterations in 5-HT neuron numbers were due to the induction of serotonergic markers rather than increased survival, as shown by the efficacy of delayed short-term treatments. Comparing rostral and caudal raphe cultures from different embryonic ages suggests that distinct effects of TGF-betas reflect the responsiveness of 5-HT neurons at different ages rather than of different origins.

Bone morphogenetic protein-2 promotes survival and differentiation of striatal GABAergic neurons in the absence of glial cell proliferation

We examined the potential neurotrophic effects of bone morphogenetic protein (BMP)-2 on the survival and differentiation of neurons cultured from the rat developing striatum at embryonic day 16, a period during which the mRNAs for BMP-2 and its receptor subunits (types IA, IB, and II) were detected. BMP-2 exerted potent activity to promote the survival of striatal neurons and increased the number of surviving microtubule-associated protein-2-positive cells by 2.4-fold as compared with the control cultures after 4 days in vitro. Although basic fibroblast growth factor (bFGF) also showed relatively high activity to promote the survival of striatal neurons, transforming growth factor-beta1, -beta2, and -beta3, glial cell line-derived neurotrophic factor, or brain-derived neurotrophic factor promoted their survival weakly. Striatal neurons cultured in the presence of BMP-2 or bFGF possessed extensive neurite outgrowths, the majority of which were GABA-immunoreactive. Inhibition of glial cell proliferation by 5-fluorodeoxyuridine did not affect the capacity of BMP-2 to promote the survival of striatal GABAergic neurons. In contrast, the ability of bFGF to promote the survival of striatal neurons was inhibited significantly by the treatment of cells with 5-fluorodeoxyuridine. All these results suggest that BMP-2 exerts potent neurotrophic effects on the striatal GABAergic neurons in a glial cell-independent manner.

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.

Cellular aspects of trophic actions in the nervous system

During the past three decades the number of molecules exhibiting trophic actions in the brain has increased drastically. These molecules promote and/or control proliferation, differentiation, migration, and survival (sometimes even the death) of their target cells. In this review a comprehensive overview of small diffusible factors showing trophic actions in the central nervous system (CNS) is given. The factors discussed are neurotrophins, epidermal growth factor, fibroblast growth factor, platelet-derived growth factor, insulin-like growth factors, ciliary neurotrophic factor and related molecules, glial-derived growth factor and related molecules, transforming growth factor-beta and related molecules, neurotransmitters, and hormones. All factors are discussed with respect to their trophic actions, their expression patterns in the brain, and molecular aspects of their receptors and intracellular signaling pathways. It becomes evident that there does not exist "the" trophic factor in the CNS but rather a multitude of them interacting with each other in a complicated network of trophic actions forming and maintaining the adult nervous system.

The effect of microglia on embryonic dopaminergic neuronal survival in vitro: diffusible signals from neurons and glia change microglia from neurotoxic to neuroprotective

When embryonic dopaminergic neurons are transplanted into the adult brain, approximately 95% die within a few days. To assess whether microglia activated during transplantation might be responsible for this rapid death, we examined the effect of microglia on rat embryonic dopaminergic neurons in vitro. Conditioned medium from 7-day-old microglia was found to decrease the number of dopamine neurons surviving in primary culture, but activation of the microglia with N-formyl-methionyl-leucyl-phenylalanine (FMLP) or Zymosan A did not increase the toxicity of the conditioned medium. We next tested the effect of coculturing microglia and dopaminergic neurons by placing microglia in semipermeable well inserts over the neuronal cultures. The presence of microglia now increased dopaminergic neuronal survival, microglial activation again having no effect. To increase yet further the possible interactions between microglia and neurons, the mesencephalic cells and microglia were mixed together and placed as a tissue in three-dimensional culture, and here again the presence of microglia increased dopaminergic neuronal survival with no effect of activation. Contact of microglia with the mesencephalic cells therefore converted them from being toxic to dopaminergic neurons to promoting their survival. The change in microglial effect from toxic to protective was caused by soluble molecules secreted by cells in the neuronal cultures, as conditioned medium derived from microglia-neuronal cocultures also had a dopaminergic neuron survival effect, indicating that microglia in cocultures behave differently from microglia removed from neuronal and glial influence. Microglia cocultured with either neurons or astrocytes downregulated inducible nitric oxide synthase (iNOS), indicating a decrease in the production of nitric oxide and possibly other toxic molecules. These findings indicate that in their natural environment, microglia are likely to be beneficial for the survival of embryonic dopaminergic grafts.

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.

Recovery of chronic parkinsonian monkeys by autotransplants of carotid body cell aggregates into putamen

We have studied the effect of unilateral autografts of carotid body cell aggregates into the putamen of MPTP-treated monkeys with chronic parkinsonism. Two to four weeks after transplantation, the monkeys initiated a progressive recovery of mobility with reduction of tremor and bradykinesia and restoration of fine motor abilities on the contralateral side. Apomorphine injections induced rotations toward the side of the transplant. Functional recovery was accompanied by the survival of tyrosine hydroxylase-positive (TH-positive) grafted glomus cells. A high density of TH-immunoreactive fibers was seen reinnervating broad regions of the ipsilateral putamen and caudate nucleus. The nongrafted, contralateral striatum remained deafferented. Intrastriatal autografting of carotid body tissue is a feasible technique with beneficial effects on parkinsonian monkeys; thus, this therapeutic approach could also be applied to treat patients with Parkinson's disease.

Effects of transforming growth factor-beta (isoforms 1-3) on amyloid-beta deposition, inflammation, and cell targeting in organotypic hippocampal slice cultures

The transforming growth factor-beta (TGF-beta) family consists of three isoforms and is part of a larger family of cytokines regulating differentiation, development, and tissue repair. Previous work from our laboratory has shown that TGF-beta1 can increase amyloid-beta protein (Abeta) immunoreactive (Abetair) plaque-like deposits in rat brain. The aim of the current study was to evaluate all three isoforms of TGF-beta for their ability to affect the deposition and neurotoxicity of Abeta in an organotypic, hippocampal slice culture model of Abeta deposition. Slice cultures were treated with Abeta either with or without one of the TGF-beta isoforms. All three isoforms can increase Abeta accumulation (over Abeta treatment alone) within the slice culture, as determined by ELISA. However, there are striking differences in the pattern of Abetair among the three isoforms of TGF-beta. Isoforms 1 and 3 produced a cellular pattern of Abeta staining that colocalizes with GS lectin staining (microglia). TGF-beta2 produces dramatic Abeta staining of pyramidal neurons in layers CA1-CA2. In addition to cellular Abeta staining, plaque-like deposits are increased by all of the TGF-betas. Although no gross toxicity was observed, morphological neurodegenerative changes were seen in the CA1 region when the slices were treated with Abeta plus TGF-beta2. Our results demonstrate important functional differences among the TGF-beta isoforms in their ability to alter the cellular distribution and degradation of Abeta. These changes may be relevant to the pathology of Alzheimer's disease (AD).

Glial cell line-derived neurotrophic factor requires transforming growth factor-beta for exerting its full neurotrophic potential on peripheral and CNS neurons

Numerous studies have suggested that glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic molecule. We show now on a variety of cultured neurons including peripheral autonomic, sensory, and CNS dopaminergic neurons that GDNF is not trophically active unless supplemented with TGF-beta. Immunoneutralization of endogenous TGF-beta provided by serum or TGF-beta-secreting cells, as e.g., neurons, in culture abolishes the neurotrophic effect of GDNF. The dose-response relationship required for the synergistic effect of GDNF and TGF-beta identifies 60 pg/ml of either factor combined with 2 ng/ml of the other factor as the EC50. GDNF/TGF-beta signaling employs activation of phosphatidylinositol-3 (PI-3) kinase as an intermediate step as shown by the effect of the specific PI-3 kinase inhibitor wortmannin. The synergistic action of GDNF and TGF-beta involves protection of glycosylphosphatidylinositol (GPI)-linked receptors as shown by the restoration of their trophic effects after phosphatidylinositol-specific phospholipase C-mediated hydrolysis of GPI-anchored GDNF family receptor alpha. The biological significance of the trophic synergism of GDNF and TGF-beta is underscored by colocalization of the receptors for TGF-beta and GDNF on all investigated GDNF-responsive neuron populations in vivo. Moreover, the in vivo relevance of the TGF-beta/GDNF synergism is highlighted by the co-storage of TGF-beta and GDNF in secretory vesicles of a model neuron, the chromaffin cell, and their activity-dependent release. Our results broaden the definition of a neurotrophic factor by incorporating the possibility that two factors that lack a neurotrophic activity when acting separately become neurotrophic when acting in concert. Moreover, our data may have a substantial impact on the treatment of neurodegenerative diseases.

Dopamine D1 and D2 receptor-mediated acute and long-lasting behavioral effects of glial cell line-derived neurotrophic factor administered into the striatum

To determine the differences in behavioral effects between intrastriatal and intracerebroventricular glial cell-derived neurotrophic factor (GDNF) administration, spontaneous locomotor activity was measured after intrastriatal or intracerebroventricular injection of GDNF (10 microg) in normal adult rats with implanted guide cannulae. In addition, the distribution of GDNF after intracerebral injection was studied immunohistochemically. Intrastriatal administration of GDNF significantly increased rearing behavior 3-4 h after injection. Increases in all three aspects of locomotor activity (motility, locomotion, and rearing) were most pronounced 3 days after intrastriatal injection, and they lasted for several days. This hyperactivity was blocked by the selective dopamine D1 receptor antagonist SCH22390 and by the selective D2 receptor antagonist raclopride at doses of the dopamine receptor antagonists, which by themselves did not affect spontaneous locomotor activity. These results suggest that GDNF has both acute and long-lasting pharmacological effects on dopamine neurons in adult animals and stimulates locomotor activity by activating both dopamine D1 and D2 receptors. On the other hand, intracerebroventricular administration of the same dose of GDNF failed to increase locomotor activity at any time during the test period (12 days). The immunohistochemical study demonstrated widespread distribution of GDNF in the entire body of the striatum within 24 h after intrastriatal injection. It also revealed deep penetration of GDNF from the ventricular space into the brain parenchyma after intracerebroventricular injection. GDNF-immunoreactive neuronal cell bodies were seen in the ipsilateral substantia nigra pars compacta most frequently 6 h after intrastriatal injection. The number of such cell bodies after intracerebroventricular administration, on the other hand, was much lower than that seen after intrastriatal administration. Taken together, these data suggest that intrastriatal administration of GDNF is an effective approach for affecting DA transmission. Long-lasting behavior effects are mediated via dopamine D1 and D2 receptors. Higher doses of GDNF would probably be needed using the intracerebroventricular route as compared to intraparenchymal delivery to exert effects on the nigrostriatal system in Parkinson's disease patients.

Growth/differentiation factor 5 and glial cell line-derived neurotrophic factor enhance survival and function of dopaminergic grafts in a rat model of Parkinson's disease

Growth/differentiation factor 5 is a member of the transforming growth factor beta superfamily, which has neurotrophic and neuroprotective effects on dopaminergic neurons both in vitro and in vivo. Here we investigate the effects of growth/differentiation factor 5 on foetal mesencephalic grafts transplanted into a rat model of Parkinson's disease, and compare them with those of glial cell line-derived neurotrophic factor. Mesencephalic tissue was suspended in solutions containing either growth/differentiation factor 5 or glial cell line-derived neurotrophic factor prior to transplantation into the left striatum of rats with 6-hydroxydopamine lesions of the left medial forebrain bundle. Both proteins enhanced graft-induced compensation of amphetamine-stimulated rotations. Positron emission tomography studies showed that both neurotrophins increased graft-induced recovery of striatal binding of [11C]RTI-121, a marker for dopaminergic nerve terminals. Post mortem analysis at 8 weeks after transplantation showed that both neurotrophins significantly increased the survival of grafted dopaminergic neurons. This study shows that growth/differentiation factor 5 is at least as effective as glial cell line-derived neurotrophic factor in enhancing the survival and functional activity of mesencephalic grafts, and thus is an important candidate for use in the treatment of Parkinson's disease.

The non-synaptic expression of transforming growth factor-beta 2 is neurally regulated and varies between skeletal muscle fibre types

In adult skeletal muscles, transforming growth factor-beta 2 is restricted to the postsynaptic domain of the neuromuscular junction. The various putative functions of this transforming growth factor-beta 2 predict different patterns of transforming growth factor-beta 2 expression in denervated muscles. We therefore denervated rat tibialis anterior, extensor digitorum longus and soleus muscles and examined the expression of transforming growth factor-beta 2 using semi-quantitative reverse-transcription polymerase chain reaction and immunohistochemistry. Denervation up-regulated transforming growth factor-beta 2 expression extrasynaptically with little or no effect on synaptic expression. The up-regulation was detectable by one day, had become significant by three days and remained elevated for at least two weeks. This proves that the transforming growth factor-beta 2 associated with the neuromuscular junction is not under neural control and is consistent with transforming growth factor-beta 2 being a trophic factor for motoneurons. This pattern of transforming growth factor-beta 2 expression is similar to that described for other proteins associated with the neuromuscular junction, notably the acetylcholine receptor subunit genes. However, in contrast to the acetylcholine receptor subunit genes, the extent of up-regulation of transforming growth factor-beta 2 varied between fibre types, with the glycolytic IIB fibres being less affected than other fibre types.

TGF-beta receptors-I and -II immunoexpression in Alzheimer's disease: a comparison with aging and progressive supranuclear palsy

The transforming growth factor-betas (TGF-betas) influence cell survival, and TGF-beta2 shows increased immunoexpression in neurofibrillary tangle-bearing neurons and reactive glia in Alzheimer's disease (AD) and progressive supranuclear palsy (PSP). We compared immunohistochemical expression of TGF-beta type I (RI) and type II (RII) receptors in eight patients with AD, eight controls and three cases of progressive supranuclear palsy. Mild intraneuronal immunoreactivity for the RI receptor was observed in all cases. Intraneuronal TGF-beta RII receptor immunoexpression was more common in all groups, and its frequency did not differ between groups. We observed increased immunoreactivity for both RI and RII subtypes in reactive glia in the AD frontal cortex (RI: U = 0.5, p = 0.002; and RII: U = 9.000, p = 0.006) and parahippocampal gyrus (RI: U = 9.500, p = 0.013; RII: U = 14.5, p = 0.05) compared to control cases. We conclude that TGF-beta RI and II immunoreactivity is increased in reactive glia in AD and progressive supranuclear palsy, and RI immunoreactivity may occasionally be increased in neurons in cases with advanced AD.

Developmental regulation of neuronal K+ channels by target-derived TGF beta in vivo and in vitro

The functional expression of Ca2+-activated K+ channels (KCa) in developing chick ciliary ganglion (CG) neurons requires interactions with target tissues and preganglionic innervation. Here, we show that the stimulatory effects of target tissues are mediated by an isoform of TGFbeta. Exposure of cultured CG neurons to TGFbeta1, but not TGFbeta2 or TGFbeta3, caused robust stimulation of KCa. The KCa stimulatory effects of target tissue extracts were blocked by a neutralizing pan-TGFbeta antiserum but not by specific TGFbeta2 or TGFbeta3 antisera. Intraocular injection of TGFbeta1 caused robust stimulation of KCa, whereas intraocular injection of pan-TGFbeta antiserum inhibited expression of KCa in CG neurons developing in vivo. The effects of TGFbeta1 were potentiated by beta-neuregulin-1, a differentiation factor expressed in preganglionic neurons.

Survival factors and apoptosis

This chapter will explore the role of survival factors in suppression of apoptosis, and illustrate how survival signals play a critical role in the survival of both normal and tumor cells. Survival factors necessary for the development and maintenance of the nervous system and hemopoietic system will be surveyed. This will be followed by a detailed discussion of the role of insulin-like growth factor I (IGF-I) and its receptor in suppression of apoptosis. The importance of survival signals from the IGF-IR for development and tumorigenesis will be discussed, and results of a mutational analysis of the receptor to assign domains necessary for suppression of apoptosis will be summarized. Finally, a discussion of the signal transduction pathways involved in survival factor-signaling will review the roles played by PI-3 kinase and AKT and speculate on how activation of these kinases by survival factors might regulate the apoptotic pathway.

Neurturin exerts potent actions on survival and function of midbrain dopaminergic neurons

Glial cell line-derived neurotrophic factor (GDNF) exhibits potent effects on survival and function of midbrain dopaminergic (DA) neurons in a variety of models. Although other growth factors expressed in the vicinity of developing DA neurons have been reported to support survival of DA neurons in vitro, to date none of these factors duplicate the potent and selective actions of GDNF in vivo. We report here that neurturin (NTN), a homolog of GDNF, is expressed in the nigrostriatal system, and that NTN exerts potent effects on survival and function of midbrain DA neurons. Our findings indicate that NTN mRNA is sequentially expressed in the ventral midbrain and striatum during development and that NTN exhibits survival-promoting actions on both developing and mature DA neurons. In vitro, NTN supports survival of embryonic DA neurons, and in vivo, direct injection of NTN into the substantia nigra protects mature DA neurons from cell death induced by 6-OHDA. Furthermore, administration of NTN into the striatum of intact adult animals induces behavioral and biochemical changes associated with functional upregulation of nigral DA neurons. The similarity in potency and efficacy of NTN and GDNF on DA neurons in several paradigms stands in contrast to the differential distribution of the receptor components GDNF Family Receptor alpha1 (GFRalpha1) and GFRalpha2 within the ventral mesencephalon. These results suggest that NTN is an endogenous trophic factor for midbrain DA neurons and point to the possibility that GDNF and NTN may exert redundant trophic influences on nigral DA neurons acting via a receptor complex that includes GFRalpha1.

GFRalpha1 is an essential receptor component for GDNF in the developing nervous system and kidney

Glial cell line-derived neurotrophic factor (GDNF) is a distant member of the TGFbeta protein family that is essential for neuronal survival and renal morphogenesis. We show that mice who are deficient in the glycosyl-phosphatidyl inositol (GPI) -linked protein GFRalpha1 (GDNFRalpha) display deficits in the kidneys, the enteric nervous system, and spinal motor and sensory neurons that are strikingly similar to those of the GDNF- and Ret-deficient mice. GFRalpha1-deficient dopaminergic and nodose sensory ganglia neurons no longer respond to GDNF or to the structurally related protein neurturin (NTN) but can be rescued when exposed to GDNF or neurturin in the presence of soluble GFRalpha1. In contrast, GFRalpha1-deficient submandibular parasympathetic neurons retain normal response to these two factors. Taken together with the available genetic and biochemical data, these findings support the idea that GFRalpha1 and the transmembrane tyrosine kinase Ret are both necessary receptor components for GDNF in the developing kidney and nervous system, and that GDNF and neurturin can mediate some of their activities through a second receptor.

GDNF is abundant in the adult rat gut

Glial derived neurotrophic factor (GDNF) is essential for the development of the enteric nervous system (ENS). Although previous work has measured GDNF mRNA levels, little is known about the concentration of GDNF protein produced in developing or adult tissues. The aim of this study was to quantitate the concentration of GDNF protein in various tissues of the developing and adult rat and in adult human gut. A two site antibody immunoassay was used to quantitate GDNF using recombinant rat GDNF as a standard. In the adult rat gastrointestinal tract the intestine contained the highest concentration of GDNF while the stomach and esophagus have the lowest concentrations. The isolated muscular wall of the intestine has approximately four times the GDNF concentration of the intact intestine. Other tissues with smooth muscle such as the aorta and urinary bladder contain moderate GDNF concentrations. In contrast, GDNF is barely detectable in the adult kidney and liver. High concentrations of GDNF were also detected in human colon and jejunum. As development proceeds in the rat, there is a tendency for the concentration of GDNF to increase in the intestine but decrease in other tissues. Treatment of the jejunum with the cationic surfactant benzyldimethyltetradecylammonium chloride (BAC) results in an increase in the number of smooth muscle cells, a decrease in myenteric neurons, and an increase in the concentration of GDNF in homogenates of intestine. The observations that GDNF concentrations are high in the adult intestine suggest that this growth factor may be important for the maintenance of the adult ENS.

Case-control study of the D2 dopamine receptor gene and smoking status in lung cancer patients

BACKGROUND

Interindividual differences in the structure and expression of the dopamine receptor genes affect dopamine availability and may be the genetic basis for variation in vulnerability to tobacco smoking. In this study, prevalences of polymorphisms in the TaqIA allele (A1 and A2) and the TaqIB allele (B1 and B2) of the D2 dopamine receptor gene in 157 lung cancer case patients and 126 control subjects were determined to assess whether individuals homozygous or heterozygous for the less common A1 and B1 alleles are more vulnerable to nicotine addiction.

METHODS

Case and control subjects were accrued from an ongoing epidemiologic study. Blood samples were collected from them and subjected to molecular genetic analyses. Subjects were interviewed to obtain relevant information. Current and former smokers were administered a questionnaire to quantify their addiction to nicotine.

RESULTS

The combined B1B2 genotypes appeared to be more prevalent in ever smokers than in never smokers among case patients (30.3% versus 13.3%; two-sided P = .233) and among control subjects (30.9% and 0%; two-sided P = .02); statistically significant differences were not observed among those with A1 genotypes. Statistically significant correlations between the presence of the A1 and B1 alleles were observed (r = .73 for case subjects and r = .76 for control subjects; two-sided P<.001). Individuals with rarer genotypes reported having been substantially younger at the time of smoking initiation (statistically significant for both A1 and B1) and having attempted to quit smoking fewer times (statistically significant for only A1).

CONCLUSION

Variant alleles of the D2 dopamine receptor gene may play a role in determining nicotine addiction, although the associations between the at-risk genotypes and measures of nicotine addiction were not entirely consistent.

Persephin, a novel neurotrophic factor related to GDNF and neurturin

A novel neurotrophic factor named Persephin that is approximately 40% identical to glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) has been identified using degenerate PCR. Persephin, like GDNF and NTN, promotes the survival of ventral midbrain dopaminergic neurons in culture and prevents their degeneration after 6-hydroxydopamine treatment in vivo. Persephin also supports the survival of motor neurons in culture and in vivo after sciatic nerve axotomy and, like GDNF, promotes ureteric bud branching. However, in contrast to GDNF and NTN, persephin does not support any of the peripheral neurons that were examined. Fibroblasts transfected with Ret and one of the coreceptors GFRalpha-1 or GFRalpha-2 do not respond to persephin, suggesting that persephin utilizes additional, or different, receptor components than GDNF and NTN.

Bone morphogenetic proteins and their receptors: potential functions in the brain

Transforming growth factors-beta (TGF-betas), activins, and bone morphogenetic proteins (BMPs) comprise an evolutionarily well-conserved group of proteins controlling a number of cell differentiation, cell growth, and morphogentic processes during development. The superfamily of TGFbeta-related genes include over 25 members in mammals several of which are expressed in the growing nervous system and serve important functions in regionalizing the early CNS. Cultured nerve cells show different responses to these factors. Recent developments have revealed that TGFbetas, activins, and BMPs selectively signal to the responding cells via different hetero-oligomeric complexes of type I and type II serine/threonine kinase receptors. The adult brain exhibits specific expression patterns of some of these receptors suggesting neuronal functions not only during development but also in the mature brain. In particular, the brain is expressing high levels of bone morphogenetic protein receptor type II (BMPR-II), activin receptor type I (ActR-I), and activin receptor type IIA (ActR-II). This indicates that osteogenic protein-1 (OP-1/BMP-7), BMP-2, and BMP-4 as well as activins may serve functions for brain neurons. Expression of the receptors partially overlaps in populations of neurons and has been shown to be regulated by brain lesions. This suggests that brain neurons may use receptors BMPR-II and ActR-I to sense the presence of BMPs. This may form a system parallel to the neurotrophin Trk tyrosine kinase receptors regulating neuroplasticity and brain repair. The presence of BMPs in brain is not well studied, but preliminary in situ data indicate that the BMP relatives growth/differentiation factor (GDF)-1 and GDF-10 are distinctly but differentially expressed at high levels in neurons expressing BMPR-II and ActR-I. The receptors mediating responses to these two GDFs remain, however, to be defined. Finally, recent data show that the signal from the activated type I serine/threonine kinase receptor is directly transduced to the nucleus by Smad proteins that become incorporated into transcriptional complexes. Preliminary in situ hybridization observations demonstrate the existence of different Smad mRNAs. It is concluded that BMPs and their signaling systems may comprise a novel pathway for control of neural activity and offer means for pharmacological interventions rescuing brain neurons.

GFRalpha-2 and GFRalpha-3 are two new receptors for ligands of the GDNF family

The receptor for glial cell line-derived neurotrophic factor (GDNF) consists of GFRalpha-1 and Ret. Neurturin is a GDNF-related neurotrophin whose receptor is presently unknown. Here we report that neurturin can bind to either GFRalpha-1 or GFRalpha-2, a novel receptor related to GFRalpha-1. Both GFRalpha-1 and GFRalpha-2 mediate neurturin-induced Ret phosphorylation. GDNF can also bind to either GFRalpha-1 or GFRalpha-2, and activate Ret in the presence of either binding receptor. Although both ligands interact with both receptors, cells expressing GFRalpha-1 bind GDNF more efficiently than neurturin, while cells expressing GFRalpha-2 bind neurturin preferentially. Cross-linking and Ret activation data also suggest that while there is cross-talk, GFRalpha-1 is the primary receptor for GDNF and GFRalpha-2 exhibits a preference for neurturin. We have also cloned a cDNA that apparently codes for a third member of the GFRalpha receptor family. This putative receptor, designated GFRalpha-3, is closely related in amino acid sequence and is nearly identical in the spacing of its cysteine residues to both GFRalpha-1 and GFRalpha-2. Analysis of the tissue distribution of GFRalpha-1, GFRalpha-2, GFRalpha-3, and Ret by Northern blot reveals overlapping but distinct patterns of expression. Consistent with a role in GDNF function, the GFRalphas and Ret are expressed in many of the same tissues, suggesting that GFRalphas mediate the action of GDNF family ligands in vivo.

Cloning and structural organization of the gene encoding the mouse glial cell line-derived neurotrophic factor, GDNF

cDNA for glial cell line-derived neurotrophic factor (GDNF) was cloned from mouse neonatal brain by the method of 5'-rapid amplification of cDNA end (5'-RACE), and the sequence of it's 5'-untranslated region (5'-UTR) was determined. The mouse GDNF gene was then isolated from a genomic library and analyzed for its nucleotide sequence. In vitro translation analysis indicated that the second ATG codon in an open reading frame is the translation start point. Structural analysis of the isolated clones showed that the GDNF gene was separated into three exons and the actual translation start point was present in the second exon. RNA blot hybridization analysis indicated that the GDNF mRNA is approximately 4.5 kb long. The transcriptional start site in the GDNF gene was determined and a typical TATA box sequence was found in the promoter region. On the other hand, the gene expression of GDNF in C6 glioma cells was transiently induced by treatment with phorbol myristate acetate (PMA), but not by forskolin.

TGF-beta in the central nervous system: potential roles in ischemic injury and neurodegenerative diseases

The Transforming Growth Factor-betas (TGF-beta) are a group of multifunctional proteins whose cellular sites of production and action are widely distributed throughout the body, including the central nervous system (CNS). Within the CNS, various isoforms of TGF-beta are produced by both glial and neural cells. When evaluated in either cell culture or in vivo models, the various isoforms of TGF-beta have been shown to have potent effects on the proliferation, function, or survival of both neurons and all three glial cell types, astrocytes, microglia and oligodendrocytes. TGF-beta has also been shown to play a role in several forms of acute CNS pathology including ischemia, excitotoxicity and several forms of neurodegenerative diseases including multiple sclerosis, Parkinson's disease, AIDS dementia and Alzheimer's disease.

Expression of the glial cell line-derived neurotrophic factor gene in rat brain after transient MCA occlusion

Change of the glial cell line-derived neurotrophic factor (GDNF) gene expression in rat brain was examined after transient middle cerebral artery (MCA) occlusion of adult rats. Northern blot analysis showed that the mRNA began to be induced in the occluded MCA from 1 h of reperfusion with a peak at 3 h, and almost diminished by 1 day of reperfusion. Immunohistochemical analysis with brain sections showed an expression of GDNF-like immunoreactivity in neurons of the cerebral cortex and caudate after 90 min of ischemia in a similar way to the mRNA, but the staining was more disseminated and stronger in the cerebral cortex than the caudate. No glial cell was stained in the brain sections. The present results indicate that the GDNF gene was expressed in an early stage of reperfusion in neuronal cells of the MCA territory, but that the staining property was different between in the cerebral cortex and caudate.

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

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

Transforming growth factor beta 1 transduced mouse prostate reconstitutions: I. Induction of neuronal phenotypes

BACKGROUND

We previously showed that retroviral transduction of transforming growth factor beta 1 (TGF-beta 1) induces focally hyperplastic lesions resembling benign prostatic hyperplasia (BPH) and an increase in the number of ganglion-like cells in the mouse prostate reconstitution (MPR) model in vivo. In the present study we further characterize the neuronal phenotypes induced by TGF-beta 1 retroviral transduction in MPRs.

METHODS

Computer-assisted morphometric analysis was used to evaluate neuronal density. Neuronal cell markers, including neurofilament, neuron-specific enolase, tyrosine hydroxylase, choline acetyltransferase, L-met enkaphaline, and serotonin, were detected by immunostaining.

RESULTS

A fourfold increase in neuronal density was observed in TGF-beta 1 retrovirus-transduced MPRs. The relative frequencies of neuronal subtypes remained similar, with catecholaminergic and cholinergic neurons presenting as the most abundant. We found no evidence of infection of neurons; therefore, increased neuronal density was likely due to paracrine activities.

CONCLUSIONS

Our results suggest that enforced TGF-beta 1 expression leads to growth and/or survival of both catecholaminergic and cholinergic neuronal cells in mouse prostate reconstitutions.

Growth/differentiation factor 5 protects nigrostriatal dopaminergic neurones in a rat model of Parkinson's disease

Growth/differentiation factor 5 (GDF5), a novel member of the transforming growth factor beta superfamily, promotes the survival of dopaminergic neurones in vitro. We present here the first evidence for a neuroprotective action of GDF5 in vivo. We investigated the effects of intracerebral administration of GDF5 on a rat model of Parkinson's disease. GDF5 was administered just above the substantia nigra and into the lateral ventricle immediately before ipsilateral injection of 6-hydroxydopamine into the medial forebrain bundle. GDF5 prevented the development of amphetamine-induced rotations and preserved the integrity of striatal dopaminergic nerve terminals, as measured by positron emission tomography. Post-mortem studies showed that GDF5 spared dopamine levels in the striatum and tyrosine hydroxylase positive neurones in the midbrain. This study suggests that GDF5 has potential for the treatment of Parkinson's disease.

Amelioration of brain edema by topical application of glial cell line-derived neurotrophic factor in reperfused rat brain

Glial cell line-derived neurotrophic factor (GDNF) was applied topically on the brain surface of reperfused rat brain after 90 min of transient middle cerebral artery occlusion. In contrast to the cases treated with vehicle, a formation of brain edema was greatly reduced at 2 days by the treatment with GDNF. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick end labeling (TUNEL) staining was also markedly reduced in the cases with GDNF treatment both at 1 and 2 days of reperfusion. However, amelioration of the induction of immunoreactive 70 kDa heat shock protein was only a minimum by the GDNF treatment. The present results suggest that the treatment with GDNF has a significant effect on ameliorating brain edema formation after transient focal brain ischemia, and the effect is greatly associated with the reduction of TUNEL staining, but minimally with that of stress response of cells.

Bone morphogenetic proteins: neurotrophic roles for midbrain dopaminergic neurons and implications of astroglial cells

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor beta (TGF-beta) superfamily that have been implicated in tissue growth and remodelling. Recent evidence suggests that several BMPs are expressed in the developing and adult brain. Specifically, we show that BMP 2 and BMP 6 are expressed in the developing midbrain floor of the rat. We studied potential neurotrophic effects of BMPs on the in vitro survival, transmitter uptake and protection against MPP+ toxicity of mesencephalic dopaminergic neurons cultured from the embryonic midbrain floor at embryonic day (E) 14. At 10 ng/ml and under serum-free conditions, most BMPs promoted the survival of dopaminergic neurons visualized by tyrosine hydroxylase immunocytochemistry during an 8-day culture period, but to varying extents (relative potencies: BMP 6 = 12 > 2, 4, 7). BMPs 6 and 12 were as effective as fibroblast growth factor-2 (FGF-2) and glial cell line-derived neurotrophic factor, promoting survival 1.7-fold compared with controls. BMPs 9 and 11 were not effective. Dose-response curves revealed an EC50 for BMPs 2, 6 and 12 of 2 ng/ml. BMPs 2, 4, 6, 7, 9 and 12 also promoted DNA synthesis and astroglial cell differentiation, visualized by 5-bromodeoxyuridine (BrdU) incorporation and glial fibrillary acidic protein (GFAP) immunocytochemistry respectively. Suppression of cell proliferation and subsequent maturation of GFAP-positive cells by 5-fluorodeoxyuridine or aminoadipic acid abolished the neuron survival-promoting effect of BMP 2. This suggests that BMPs, like other non-TGF-beta factors affecting dopaminergic neuron survival, act indirectly, probably by stimulating the synthesis and/or release of glial-derived trophic factors. BMP 6 and BMP 7 also increased the uptake of [3H]dopamine without affecting the uptake of [3H]5-hydroxytryptamine and [3H]GABA, underscoring the specificity of the trophic effect. We conclude that several BMPs share a neurotrophic capacity for dopaminergic midbrain neurons with other members of the TGF-beta superfamily, but act indirectly, possibly through glial cells.

Neurons promote macrophage proliferation by producing transforming growth factor-beta2

The infiltration of bone marrow-derived macrophages into the CNS contributes to growth and reactions of microglia during development or after brain injury. The proliferation of microglial cells is stimulated by colony-stimulating factor 1 (CSF-1), an astrocyte-produced growth factor that acts on mononuclear phagocytes. In the present study, we have shown, using an in vitro model system, that rodent neurons obtained from the developing cerebral cortex produce a soluble factor that strongly enhances the proliferation of macrophages cultured in the presence of CSF-1. Both macrophages isolated from the developing brain and those from the adult bone marrow were stimulated. Kinetic analyses of [3H]thymidine incorporation into macrophages indicated that their response to the neuron-derived factor involved a shortening of the cycle of proliferating cells. The effect of neurons on macrophages was blocked in the presence of antibodies neutralizing transforming growth factor-beta2 (TGF-beta2), whereas recombinant TGF-beta2 stimulated macrophage proliferation in the presence of CSF-1. Neuronal secretion of TGF-beta2 was confirmed by reverse transcription-PCR detection of TGF-beta2 transcripts and immunodetection of the protein within neurons and in their culture medium. In situ hybridization and immunohistochemical experiments showed neuronal expression of TGF-beta2 in sections of cerebral cortex obtained from 6-d-old rats, an age at which extensive developmental recruitment of macrophages occurs in this cerebral region. Altogether, our results provide direct evidence that neurons have the capacity to promote brain macrophage proliferation and demonstrate the role of TGF-beta2 in this neuronal function.

Bone morphogenetic proteins in the nervous system

Bone morphogenetic proteins (BMPs) are a rapidly expanding subclass of the transforming growth factor superfamily. BMP ligands and receptor subunits are present throughout neural development within discrete regions of the embryonic brain and within neural crest-derived pre- and post-migratory zones. BMPs initially inhibit the formation of neuroectoderm during gastrulation while, within the neural tube, they act as gradient morphogens to promote the differentiation of dorsal cell types and intermediate cell types throughout co-operative signaling. In the peripheral nervous system, BMPs act as instructive signals for neuronal lineage commitment and promote graded stages of neuronal differentiation. By contrast, within the CNS, these same factors promote astroglial lineage elaboration from embryonic subventricular zone progenitor cells, with concurrent suppression of the neuronal or oligodendroglial lineages, or both. In addition, BMPs act on more lineage-restricted embryonic CNS progenitor cells to promote regional neuronal survival and cellular differentiation. Furthermore, these versatile cytokines induce selective apoptosis of discrete rhombencephalic neural crest-associated cellular populations. These observations suggest that the BMPs exhibit a broad range of cellular and context-specific effects during multiple stages of neural development.

Activin exerts a neurotrophic effect on cultured hippocampal neurons

Activin is a member of the transforming growth factor (TGF)-beta superfamily, which comprises a growing list of multifunctional proteins that serve as regulators of cell proliferation and differentiation. Recently, activin was shown to regulate the neurotransmitter phenotype in peripheral neurons. It is also a potent survival factor for neurogenic clonal cell lines, retinal neurons and midbrain dopaminergic neurons. We have studied the effect of activin on hippocampal cells which show abundant expression of activin receptors or binding sites. Exposure of primary cultures of rat hippocampal neurons to activin supported neuronal survival. This neurotrophic action of activin was blocked by treatment with the tyrosine kinase inhibitor genistein or the protein kinase C inhibitor calphostin C. However, the Ca2+/calmodulin kinase inhibitor KN-62 had no effect. Nicardipine, a blocker of the L-type Ca2+ channel, also inhibited the neurotrophic effect of activin. Furthermore, activin potentiated the depolarization-induced elevation in intracellular Ca2+ concentration ([Ca2+]i). The neurotrophic effect and the potentiation of depolarization-induced increase of [Ca2+]i caused by activin were completely abolished by the protein synthesis inhibitor cycloheximide. These results suggest that activin supports neuronal survival by increasing the expression of voltage-dependent Ca2+ channel through the action of a tyrosine kinase and of protein kinase C, but not of Ca2+/calmodulin kinase.

Bone morphogenetic proteins induce astroglial differentiation of oligodendroglial-astroglial progenitor cells

We have used bipotent postnatal cortical oligodendroglial-astroglial progenitor cells (O-2As) to examine the role of inductive signals in astroglial lineage commitment. O-2A progenitor cells undergo progressive oligodendroglial differentiation when cultured in serum-free medium, but differentiate into astrocytes in medium supplemented with FBS. We now report that the bone morphogenetic proteins (BMPs), a major subclass of the transforming growth factor beta (TGFbeta) superfamily, promote the selective, dose-dependent differentiation of O-2As into astrocytes with concurrent suppression of oligodendroglial differentiation. This astroglial-inductive action is not sanctioned by other members of the TGFbeta superfamily. Astroglial differentiation requires only very brief initial exposure to the BMPs and is accompanied by increased cellular survival and accelerated exit from cell cycle. Dual-label immunofluorescence microscopy documents that O-2A progenitor cells express a complement of BMP type I and type II receptor subunits required for signal transduction. Furthermore, expression of BMP2 in vivo reaches maximal levels during the period of gliogenesis. These results suggest that the BMPs act as potent inductive factors in postnatal glial lineage commitment that initiate a stable program of astroglial differentiation.