The high molecular weight fibroblast growth factor-2 isoforms (21,000 mol. wt and 23,000 mol. wt) mediate neurotrophic activity on rat embryonic mesencephalic dopaminergic neurons in vitro

What Can We Learn from FGF-2 Isoform-Specific Mouse Mutants? Differential Insights into FGF-2 Physiology In Vivo

Fibroblast growth factor 2 (FGF-2), ubiquitously expressed in humans and mice, is functionally involved in cell growth, migration and maturation in vitro and in vivo. Based on the same mRNA, an 18-kilo Dalton (kDa) FGF-2 isoform named FGF-2 low molecular weight (FGF-2LMW) isoform is translated in humans and rodents. Additionally, two larger isoforms weighing 21 and 22 kDa also exist, summarized as the FGF-2 high molecular weight (FGF-2HMW) isoform. Meanwhile, the human FGF-2HMW comprises a 22, 23, 24 and 34 kDa protein. Independent studies verified a specific intracellular localization, mode of action and tissue-specific spatiotemporal expression of the FGF-2 isoforms, increasing the complexity of their physiological and pathophysiological roles. In order to analyze their spectrum of effects, FGF-2LMW knock out (ko) and FGF-2HMWko mice have been generated, as well as mice specifically overexpressing either FGF-2LMW or FGF-2HMW. So far, the development and functionality of the cardiovascular system, bone formation and regeneration as well as their impact on the central nervous system including disease models of neurodegeneration, have been examined. This review provides a summary of the studies characterizing the in vivo effects modulated by the FGF-2 isoforms and, thus, offers a comprehensive overview of its actions in the aforementioned organ systems.

FGF-2 isoforms influence the development of dopaminergic neurons in the murine substantia nigra, but not anxiety-like behavior, stress susceptibility, or locomotor behavior

BACKGROUND

Loss of fibroblast growth factor 2 (FGF-2) is responsible for the development of an increased number of dopaminergic (DA) neurons in the murine substantia nigra pars compacta (SNpc). Furthermore, dysregulation of its expression patterns within the central nervous system (CNS) is associated with behavioral abnormalities in mice. Until now, the contributions of the individual FGF-2 isoforms (one low (LMW) and two high molecular weight (HMW) isoforms) in the CNS are elusive.

METHODS

To unravel the specific effects of FGF-2 isoforms, we compared three knockout mouse lines, one only deficient for LMW, one deficient for HMW and another lacking both isoforms, regarding DA neuronal development. With this regard, three time points of ontogenic development of the SNpc were stereologically investigated. Furthermore, behavioral aspects were analyzed in young adult mice, supplemented by corticosterone measurements.

RESULTS

Juvenile mice lacking either LMW or HMW develop equal supernumerary DA neuron numbers in the SNpc. Compensatory increased LMW expression is observed in animals lacking HMW. Meanwhile, no knockout mouse line demonstrated changes in anxiety-like behavior, stress susceptibility, or locomotor behavior.

CONCLUSIONS

Both FGF-2 isoforms crucially influence DA neuronal development in the murine SNpc. However, absence of LMW or HMW alone alters neither anxiety-like nor locomotor behavior, or stress susceptibility. Therefore, FGF-2 is not a determinant and causative factor for behavioral alterations alone, but probably in combination with appropriate conditions, like environmental or genetic factors.

Neuroprotective effects of LMW and HMW FGF2 against amyloid beta toxicity in primary cultured hippocampal neurons

Basic Fibroblast growth factor (FGF2) is important in development and maintenance of central nervous system function. Studies have demonstrated that low molecular weight (LMW) FGF2 is a neuroprotective factor against various insults in vivo and in vitro. In the present study we investigated the neuroprotective effects of high molecular weight (HMW) and LMW FGF2 against amyloid beta-induced neurotoxicity. The results showed that both LMW and HMW FGF2 attenuated the amyloid beta toxicity in the primary cultured hippocampal neurons as measured by WST and LDH release assay. Moreover, the analysis suggested that HMW FGF2 had stronger neuroprotective effect than LMW FGF2. We then demonstrated that LMW and HMW FGF2 activated the ERK and AKT signaling pathways in a similar way. Furthermore, using the ERK inhibitor and AKT inhibitor, we found that the AKT signaling but not ERK signaling pathway was required for the neuroprotective effects of FGF2. Taken together, these results showed the neuroprotective effects of different forms of FGF2 in an AD model and the mechanism underlying the neuroprotection.

Blocking Infralimbic Basic Fibroblast Growth Factor (bFGF or FGF2) Facilitates Extinction of Drug Seeking After Cocaine Self-Administration

Drug exposure results in structural and functional changes in brain regions that regulate reward and these changes may underlie the persistence of compulsive drug seeking and relapse. Neurotrophic factors, such as basic fibroblast growth factor (bFGF or FGF2), are necessary for neuronal survival, growth, and differentiation, and may contribute to these drug-induced changes. Following cocaine exposure, bFGF is increased in addiction-related brain regions, including the infralimbic medial prefrontal cortex (IL-mPFC). The IL-mPFC is necessary for extinction, but whether drug-induced overexpression of bFGF in this region affects extinction of drug seeking is unknown. Thus, we determined whether blocking bFGF in IL-mPFC would facilitate extinction following cocaine self-administration. Rats were trained to lever press for intravenous infusions of cocaine before extinction. Blocking bFGF in IL-mPFC before four extinction sessions resulted in facilitated extinction. In contrast, blocking bFGF alone was not sufficient to facilitate extinction, as blocking bFGF and returning rats to their home cage had no effect on subsequent extinction. Furthermore, bFGF protein expression increased in IL-mPFC following cocaine self-administration, an effect reversed by extinction. These results suggest that cocaine-induced overexpression of bFGF inhibits extinction, as blocking bFGF during extinction permits rapid extinction. Therefore, targeted reductions in bFGF during therapeutic interventions could enhance treatment outcomes for addiction.

Neurotrophic factor-α1 prevents stress-induced depression through enhancement of neurogenesis and is activated by rosiglitazone

Major depressive disorder is often linked to stress. Although short-term stress is without effect in mice, prolonged stress leads to depressive-like behavior, indicating that an allostatic mechanism exists in this difference. Here we demonstrate that mice after short-term (1 h per day for 7 days) chronic restraint stress (CRS), do not display depressive-like behavior. Analysis of the hippocampus of these mice showed increased levels of neurotrophic factor-α1 (NF-α1; also known as carboxypeptidase E, CPE), concomitant with enhanced fibroblast growth factor 2 (FGF2) expression, and an increase in neurogenesis in the dentate gyrus. In contrast, after prolonged (6 h per day for 21 days) CRS, mice show decreased hippocampal NF-α1 and FGF2 levels and depressive-like responses. In NF-α1-knockout mice, hippocampal FGF2 levels and neurogenesis are reduced. These mice exhibit depressive-like behavior that is reversed by FGF2 administration. Indeed, studies in cultured hippocampal neurons reveal that NF-α1 treatment directly upregulates FGF2 expression through extracellular signal-regulated kinase-Sp1 signaling. Thus, during short-term CRS, hippocampal NF-α1 expression is upregulated and has a key role in preventing the onset of depressive-like behavior through enhanced FGF2-mediated neurogenesis. To evaluate the therapeutic potential of this pathway, we examined, rosiglitazone (Rosi), a PPARγ agonist, which has been shown to have antidepressant activity in rodents and humans. Rosi upregulates FGF2 expression in a NF-α1-dependent manner in hippocampal neurons. Mice fed Rosi show increased hippocampal NF-α1 levels and neurogenesis compared with controls, thereby indicating the antidepressant action of this drug. Development of drugs that activate the NF-α1/FGF2/neurogenesis pathway can offer a new approach to depression therapy.

A nuclear odyssey: fibroblast growth factor-2 (FGF-2) as a regulator of nuclear homeostasis in the nervous system

Nuclear localization of classical growth factors is a well-known phenomenon but still remains a molecular and cellular conundrum. Fibroblast growth factor-2 (FGF-2) is an excellent example of a protein which functions as an extracellular molecule involved in canonical receptor tyrosine kinase signaling as well as displaying intracellular functions. Paracrine and nuclear functions are two important sides of the same protein. FGF-2 is expressed in isoforms with different molecular weights from one mRNA species. In rodents, all of these isoforms become imported to the nucleus. In this review, we discuss structural and functional aspects of FGF-2 isoforms in the nervous system. The nuclear odyssey of FGF-2 is reflected by nuclear dynamics, localization to nuclear bodies such as nucleoli, binding to chromatin and engagement in various protein interactions. Recently discovered molecular partnerships of the isoforms shed light on their nuclear functions, thereby greatly extending our knowledge of the multifaceted functions of FGF-2.

FGF-2 deficiency does not influence FGF ligand and receptor expression during development of the nigrostriatal system

Secreted proteins of the fibroblast growth factor (FGF) family play important roles during development of various organ systems. A detailed knowledge of their temporal and spatial expression profiles, especially of closely related FGF family members, are essential to further identification of specific functions in distinct tissues. In the central nervous system dopaminergic neurons of the substantia nigra and their axonal projections into the striatum progressively degenerate in Parkinson's disease. In contrast, FGF-2 deficient mice display increased numbers of dopaminergic neurons. In this study, we determined the expression profiles of all 22 FGF-ligands and 10 FGF-receptor isoforms, in order to clarify, if FGF-2 deficiency leads to compensatory up-regulation of other FGFs in the nigrostriatal system. Three tissues, ventral mesencephalon (VM), striatum (STR) and as reference tissue spinal cord (SC) of wild-type and FGF-2 deficient mice at four developmental stages E14.5, P0, P28, and adult were comparatively analyzed by quantitative RT-PCR. As no differences between the genotypes were observed, a compensatory up-regulation can be excluded. Moreover, this analysis revealed that the majority of FGF-ligands (18/22) and FGF-receptors (9/10) are expressed during normal development of the nigrostriatal system and identified dynamic changes for some family members. By comparing relative expression level changes to SC reference tissue, general alterations in all 3 tissues, such as increased expression of FGF-1, -2, -22, FgfR-2c, -3c and decreased expression of FGF-13 during postnatal development were identified. Further, specific changes affecting only one tissue, such as increased FGF-16 (STR) or decreased FGF-17 (VM) expression, or two tissues, such as decreased expression of FGF-8 (VM, STR) and FGF-15 (SC, VM) were found. Moreover, 3 developmentally down-regulated FGFs (FGF-8b, FGF-15, FGF-17a) were functionally characterized by plasmid-based over-expression in dissociated E11.5 VM cell cultures, however, such a continuous exposure had no influence on the yield of dopaminergic neurons in vitro.

Activation of phosphatidylinositol-linked D1-like receptor modulates FGF-2 expression in astrocytes via IP3-dependent Ca2+ signaling

Fibroblast growth factor-2 (FGF-2) is predominantly synthesized and secreted by astrocytes in adult brain. Our previous study showed that activation of classical dopamine receptor D(1) or D(2) elicits FGF-2 biosynthesis and secretion in astrocytes. Here, we report that astrocytic FGF-2 expression is also regulated by phosphatidylinositol (PI)-linked D(1)-like receptor. SKF83959, a selective PI-linked D(1)-like receptor agonist, upregulates the levels of FGF-2 protein in striatal astrocyte cultures in classical dopamine D(1) and D(2) receptor-independent manner. The conditional medium derived from SKF83959-activated astrocytes promoted the number of TH(+) neurons in vitro. Treatment of astrocytes with SKF83959 increased intracellular calcium in two phases. Inhibition of intracellular calcium oscillation by inositol 1,4,5-triphosphate (IP3) inhibitors blocked the SKF83959-induced increase in FGF-2 expression. Moreover, intraperitoneal administration of SKF83959 reversed l-methyl-4-phenyl-l,2,3,6-tetrahydropypridine (MPTP)-induced reduction in FGF-2 expression in both the striatum and ventral midbrain and resulted in marked protection of dopaminergic neurons from MPTP-induced neurotoxicity. These results indicate that IP3/Ca(2+)/calmodulin-dependent protein kinase is an uncharted intracellular signaling pathway that is crucial for the regulation of FGF-2 synthesis in astrocytes. PI-linked D(1)-like receptor plays an important role in the regulation of astrocytic FGF-2 expression and neuroprotection which may provide a potential target for the drug discovery in Parkinson's disease.

High molecular weight FGF2: the biology of a nuclear growth factor

Fibroblast growth factor 2 (FGF2) is one of the most studied growth factors to date. Most attention has been dedicated to the smallest, 18 kDa FGF2 variant that is released by cells and acts through activation of cell-surface FGF-receptor tyrosine kinases. There are, however, several higher molecular weight (HMW) variants of FGF2 that rarely leave their producing cells, are retained in the nucleus and act independently of FGF-receptors (FGFR). Despite significant evidence documenting the expression and intracellular trafficking of HMW FGF2, many important questions remain about the physiological roles and mechanisms of action of HMW FGF2. In this review, we summarize the current knowledge about the biology of HMW FGF2, its role in disease and areas for future investigation.

Chronic antidepressant treatments increase basic fibroblast growth factor and fibroblast growth factor-binding protein in neurons

One of the mechanisms proposed for antidepressant drugs is the enhancement of synaptic connections and plasticity in the hippocampus and cerebral cortex. Fibroblast growth factor 2 (FGF2) is a growth factor essential for the proper formation of synaptic connections in the cerebral cortex, maturation and survival of catecholamine neurons, and neurogenesis. In this report, we attempted to establish a correlation between antidepressant treatments and FGF2 expression in the cerebral cortex and hippocampus, two brain areas relevant for depression. Desipramine (DMI, 10mg/kg) or fluoxetine (FLU, 5mg/kg) was injected acutely (single injection) or chronically (daily injection for two weeks) in adult rats. Chronic, but not acute, antidepressant treatments increase FGF2 immunoreactivity in neurons of the cerebral cortex and in both astrocytes and neurons of the hippocampus. FGF2 immunoreactivity in the cortex was increased mainly in the cytoplasm of neurons of layer V. Western blot analyses of nuclear and cytosolic extracts from the cortex revealed that both antidepressants increase FGF2 isoforms in the cytosolic extracts and decrease accumulation of FGF2 immunoreactivity in the nucleus. To characterize the anatomical and cellular specificity of antidepressants, we examined FGF-binding protein (FBP), a secreted protein that acts as an extracellular chaperone for FGF2 and enhances its activity. DMI and FLU increased FBP immunoreactivity in both cortical and hippocampal neurons. Our data suggest that FGF2 and FBP may participate in the plastic responses underlying the clinical efficacy of antidepressants.

Gene expression profiling of major depression and suicide in the prefrontal cortex of postmortem brains

Genome-wide gene expression analysis using DNA microarray has a great advantage to identify the genes or specific molecular cascades involved in mental diseases, including major depression and suicide. In the present study, we conducted DNA microarray analysis of major depression using postmortem prefrontal cortices. The gene expression patterns were compared between the controls and subjects with major depression. As a result, 99 genes were listed as the differentially expressed genes in major depression, of which several genes such as FGFR1, NCAM1, and CAMK2A were of interest. Gene ontology analysis suggested an overrepresentation of genes implicated in the downregulation or inhibition of cell proliferation. The present results may support the hypothesis that major depression is associated with impaired cellular proliferation and plasticity. Comparison between the controls and suicide victims with major depression, bipolar disorder, or schizophrenia was also conducted in the present study. Two genes, CAD and ATP1A3, were differentially expressed in the three comparisons in the same direction. Interestingly, these two genes were also included in the differentially expressed 99 genes in major depression. It may be worth investigating the genes in relation to suicide or major depression.

The physiological and pharmacological role of basic fibroblast growth factor in the dopaminergic nigrostriatal system

Basic fibroblast growth factor (FGF-2) is a physiological relevant neurotrophic factor in the nigrostriatal system and hence a promising candidate for the establishment of alternative therapeutic strategies in Parkinson's disease. FGF-2 and its high-affinity receptors (FGFR) display an expression in the developing, postnatal, and adult substantia nigra (SN) and in the striatum. Exogenous application promoted survival, neurite outgrowth and protection from neurotoxin-induced death of dopaminergic (DA) neurons both in vitro and in vivo. In animal models of Parkinson's disease, co-transplantation of fetal DA cells with FGF-2 expressing cells increased survival and functional integration of the grafted DA neurons resulting in improved behavioral performance. Analyzing the physiological function of the endogenous FGF-2 system during development and after neurotoxin-induced lesion revealed for the DA neurons of the SNpc a dependence on FGFR3 signaling during development. In addition, in the absence of FGF-2 an increased number of DA neurons was found, whereas enhanced levels of FGF-2 resulted in a reduced DA cell density. Following neurotoxin-induced lesion of DA neurons, FGF-2-deleted mice displayed a higher extent of DA neuron death whereas in FGF-2 overexpressing mice more DA neurons were protected. According to the data, FGF-2 seems to promote DA neuron survival via FGFR3 during development, whereas absence of this ligand could be compensated by other members of the FGF family. In contrast, in the adult organism, FGF-2 cannot be compensated by other factors under lesion conditions suggesting a central role for this molecule in the nigrostriatal system.

Fibroblast growth factor (FGF)-2 and FGF receptor 3 are required for the development of the substantia nigra, and FGF-2 plays a crucial role for the rescue of dopaminergic neurons after 6-hydroxydopamine lesion

Basic fibroblast growth factor (FGF-2) is involved in the development and maintenance of the nervous system. Exogenous administration of FGF-2 increased dopaminergic (DA) graft survival in different animal models of Parkinson's disease. To study the physiological function of the endogenous FGF-2 system, we analyzed the nigrostriatal system of mice lacking FGF-2, mice overexpressing FGF-2, and FGF-receptor-3 (FGFR3)-deficient mice both after development and after 6-hydroxydopamine lesion. FGFR3-deficient mice (+/-) displayed a reduced number of DA neurons compared with the respective wild type. Whereas absence of FGF-2 led to significantly increased numbers of DA neurons, enhanced amount of the growth factor in mice overexpressing FGF-2 resulted in less tyrosine hydroxylase expression and a reduced DA cell density. The volumes of the substantia nigra were enlarged in both FGF-2(-/-) and in FGF-2 transgenic mice, suggesting an important role of FGF-2 for the establishment of the proper number of DA neurons and a normal sized substantia nigra during development. In a second set of experiments, the putative relevance of endogenous FGF-2 after neurotoxin application was investigated regarding the number of rescued DA neurons after partial 6-OHDA lesion. Interestingly, the results after lesion were directly opposed to the results after development: significantly less DA neurons survived in FGF-2(-/-) mice compared with wild-type mice. Together, the results indicate that FGFR3 is crucially involved in regulating the number of DA neurons. The lack of FGF-2 seems to be (over)compensated during development, but, after lesion, compensation mechanisms fail. The transgenic mice showed that endogenous FGF-2 protects DA neurons from 6-OHDA neurotoxicity.

Nucleofection is the most efficient nonviral transfection method for neuronal stem cells derived from ventral mesencephali with no changes in cell composition or dopaminergic fate

Neuronal progenitor cells (NPCs) play an important role in potential regenerative therapeutic strategies for neurodegenerative diseases, such as Parkinson disease. However, survival of transplanted cells is, as yet, limited, and the identification of grafted cells in situ remains difficult. The use of NPCs could be more effective with regard to a better survival and maturation when transfected with one or more neurotrophic factors. Therefore, we investigated the possibility of transfecting mesencephalic neuronal progenitors with different constructs carrying neurotrophic factors or the expression reporters enhanced green fluorescence protein (EGFP) and red fluorescent protein (DsRed). Different techniques for transfection were compared, and the highest transfection rate of up to 47% was achieved by nucleofection. Mesencephalic neuronal progenitors survived the transfection procedure; 6 hours after transfection, viability was approximately 40%, and the transfected cells differentiated into, for example, tyrosine hydroxylase-positive neurons. Within the group of transfected cells, many progenitors and several neurons were found. To provide the progenitor cells with a neurotrophic factor, different isoforms of fibroblast growth factor-2 were introduced. To follow the behavior of the transfected cells in vitro, functional tests such as the cell viability assay (water-soluble tetrazolium salt assay [WST-1]) and the cell proliferation assay (5-bromo-2'-deoxyuridine-enzyme-linked immunosorbent assay) were performed. In addition, these transfected NPCs were viable after transplantation, expressed tyrosine hydroxylase in vivo, and could easily be detected within the host striatum because of their EGFP expression. This study shows that genetic modification of neural progenitors could provide attractive perspectives for new therapeutic concepts in neurodegenerative diseases.

Hippocampal FGF-2 and FGFR1 mRNA expression in major depression, schizophrenia and bipolar disorder

INTRODUCTION

FGF-2 is important for stem cell proliferation, neocortical development and adult neuronal survival and growth. Reduced frontal cortical FGF-2 expression is described in major depression and is attenuated by antidepressants. We determined the distribution of hippocampal FGF-2 and its receptor (FGFR1) mRNA in post-mortem brains of people who suffered from major depression, bipolar disorder and schizophrenia and those of controls.

METHODS

FGF-2 and FGFR1 mRNA were measured within hippocampal CA1, CA4 regions and the dentate gyrus (DG), using in situ hybridization. Within hippocampal regions, cellular staining was compared between diagnostic groups, using repeated measures analysis of variance.

RESULTS

The density of FGF-2 mRNA+ cells in CA4 was reduced in depression compared to controls. The percentage of FGFR1 mRNA+ cells was higher in depression (CA1 and CA4) and schizophrenia (CA4) than in controls. FGFR1 mRNA expression was higher in depression than in the other groups in CA1, CA4 and DG. Overall FGF-2 mRNA expression was higher in DG than in CA1 and CA4.

CONCLUSIONS

We found raised measures of FGFR1 mRNA+ in major depression and, less so, in schizophrenia, along with reduced FGF-2 mRNA density in depression. Perturbations of FGF regulation could be relevant to the pathogenesis of both disorders as FGF-2 and FGFR1 are implicated in normal hippocampal synaptology, stem cell recruitment, and connectivity, and are modulated by corticosteroids.

Apomorphine-induced activation of dopamine receptors modulates FGF-2 expression in astrocytic cultures and promotes survival of dopaminergic neurons

Apomorphine (APO), a potent D1/D2 dopamine receptor agonist, is currently used as an antiparkinsonian drug. We have shown previously that APO stimulates synthesis and release of multiple trophic factors, such as brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF), in both mesencephalic and striatal neurons, thereby effectively preventing dopaminergic neuron loss in vitro. The present study was designed to investigate the effects of APO on fibroblast growth factor-2 (FGF-2) expression and regulation in astrocytes, and furthermore, to identify signaling mechanisms underlying these effects. Here, we show that FGF-2 expression is robustly induced in cultured astrocytes in response to APO. FGF-2 expression was proportional to APO concentration and time-dependent. Conversely, treatment with S-APO, a derivative of R-APO lacking DA receptor agonist activity, did not alter FGF-2 levels. APO treatment resulted in enhanced cytosol FGF-2 immunoreactivity, export of high MW forms of FGF-2 to the cytoplasm from the nucleus and increased extracellular release of FGF-2. Interestingly, both high and low MW forms of FGF-2 were detectable in conditioned medium of APO-treated cultures. This APO-induced effect was correlated with activation of D1 and D2 receptors, as it could be either mimicked by dopamine receptor agonists (SKF38393, quinpirole) or partially blocked by antagonists (SCH23390, SKF83566, haloperidol). Activation of the D1 receptor preferentially increased PKA activity, whereas activation of the D2 receptor only promoted phosphorylation of MAPK. Importantly, APO-modulated FGF-2 expression was independent of Akt/phosphoinositide 3-kinase signaling. These data suggest that APO can enhance biosynthesis and release of FGF-2 through activation of dopamine receptors in striatal astrocytes. Both cAMP/PKA and MEK/MAPK signaling cascades are major steps mediating this process.

Dopaminergic properties and function after grafting of attached neural precursor cultures

Generation of dopaminergic (DA) neurons from multipotent embryonic progenitors represents a promising therapeutical strategy for Parkinson's disease (PD). Aim of the present study was the establishment of enhanced cell culture conditions, which optimize the use of midbrain progenitor cells in animal models of PD. In addition, the progenitor cells were characterized during expansion and differentiation according to morphological and electrophysiological criteria and compared to primary tissue. Here, we report that CNS precursors can be expanded in vitro up to 40-fold and afterwards be efficiently differentiated into DA neurons. After 4-5 days under differentiation conditions, more than 70% of the neurons were TH+, equivalent to 30% of the total cell population. Calcium imaging revealed the presence of calcium-permeable AMPA receptors in the differentiated precursors which are capable to contribute to many developmental processes. The overall survival rate, degree of reinnervation and the behavioral performance after transplantation of 4 days in-vitro-differentiated cells were similar to results after direct grafting of E14 ventral mesencephalic cells, whereas after shorter or longer differentiation periods, respectively, less effects were achieved. Compared to the amount of in-vitro-generated DA neurons, the survival rate was only 0.8%, indicating that these cells are very vulnerable. Our results suggest that expanded and differentiated DA precursors from attached cultures can survive microtransplantation and integrate within the striatum in terms of behavioral recovery. However, there is only a short time window during in vitro differentiation, in which enough cells are already differentiated towards a DA phenotype and simultaneously not too mature for implantation. However, additional factors and/or genetical manipulation of these expanded progenitors will be required to increase their in vivo survival in order to improve both the ethical and the technical outlook for the use of fetal tissue in clinical transplantation.

Shedding light into the role of BDNF in the pharmacotherapy of Parkinson's disease

Parkinson's disease (PD) is a chronic, neurodegenerative disease with a 1% incidence in the population over 55 years of age. Movement impairments represent undoubtedly the hallmark of the disorder; however, extensive evidence implicates cognitive deficits as concomitant peculiar features. Brain-derived neurotrophic factor (BDNF) colocalizes with dopamine neurons in the substantia nigra, where dopaminergic cell bodies are located, and it has recently garnered attention as a molecule crucial for cognition, a function that is also compromised in PD patients. Thus, due to its colocalization with dopaminergic neurons and its role in cognition, BDNF might possess a dual role in PD, both as a neuroprotective molecule, since its inhibition leads to loss of nigral dopaminergic neurons, and as a neuromodulator, as its enhanced expression ameliorates cognitive processes. In this review, we discuss the mechanism of action of established as well as novel drugs for PD with a particular emphasis to those interfering with BDNF biosynthesis.

Amphetamine induces dendritic growth in ventral tegmental area dopaminergic neurons in vivo via basic fibroblast growth factor

Dopaminergic neurons of the ventral tegmental area are implicated in the physiology of reward, and long-lasting changes in their function induced by exposure to psychostimulant drugs are related to the pathophysiology of drug abuse. It is not known, however, whether such changes are accompanied by morphological changes in these neurons. We characterized and labeled cells in slices containing the ventral tegmental area using whole-cell electrophysiological methods. Injections of saline or amphetamine were given to rats on postnatal days 10, 12 and 14 and individual neurons were examined one to four weeks later. We show that repeated exposure to amphetamine induces substantial dendritic growth of ventral tegmental area dopaminergic neurons in vivo. Furthermore, we show, by immuno-neutralization of endogenous basic fibroblast growth factor, that the amphetamine-induced increase in astrocytic basic fibroblast growth factor in the ventral tegmental area is essential for these morphological changes. We propose that the amphetamine-induced elaboration of the dendritic arbor of dopaminergic neurons leads to their increased excitability and contributes to compulsive drug-seeking and relapse.

New therapeutic approaches to Parkinson's disease including neural transplants

Parkinson's disease (PD) is a common neurodegenerative disorder of the brain and typically presents with a disorder of movement. The core pathological event underlying the condition is the loss of the dopaminergic nigrostriatal pathway with the formation of alpha-synuclein positive Lewy bodies. As a result, drugs that target the degenerating dopaminergic network within the brain work well at least in the early stages of the disease. Unfortunately, with time these therapies fail and produce their own unique side-effect profile, and this, coupled with the more diffuse pathological and clinical findings in advancing disease, has led to a search for more effective therapies. In this review, the authors will briefly discuss the emerging new drug therapies in PD before concentrating on a more detailed discussion on the state of cell therapies to cure PD.

Gene profiling the response to kainic acid induced seizures

Kainic acid activates non-N-methyl-d-aspartate (NMDA) glutamate receptors where it increases synaptic activity resulting in seizures, neurodegeneration, and remodeling. We performed microarray analysis on rat hippocampal tissue following kainic acid treatment in order to study the signaling mechanisms underlying these diverse processes in an attempt to increase our current understanding of mechanisms contributing to such fundamental processes as neuronal protection and neuronal plasticity. The kainic acid-treated rats used in our array experiments demonstrated severe seizure behavior that was also accompanied by neuronal degeneration which is suggested by fluoro-jade B staining and anti-caspase-3 immunohistochemistry. The gene profile revealed 36 novel kainic acid regulated genes along with additional genes previously reported. The functional roles of these novel genes are discussed. These genes mainly have roles in transcription and to a lesser extent have roles in cell death, extracellular matrix remodeling, cell cycle progression, neuroprotection, angiogenesis, and synaptic signaling. Gene regulation was confirmed via quantitative real time polymerase chain reaction and in situ hybridization.

Differentially promoted peripheral nerve regeneration by grafted Schwann cells over-expressing different FGF-2 isoforms

Artificial nerve grafts are needed to reconstruct massive defects in the peripheral nervous system when autologous nerve grafts are not available in sufficient amounts. Nerve grafts containing Schwann cells display a suitable substrate for long-distance regeneration. We present here a comprehensive analysis of the in vivo effects of different isoforms of fibroblast growth factor-2 (FGF-2) on peripheral nerve regeneration across long gaps. FGF-2 isoforms were provided by grafted, genetically modified Schwann cells over-expressing 18-kDa-FGF-2 and 21-/23-kDa-FGF-2, respectively. Functional tests evaluated motor and sensory recovery. Additionally, morphometrical analyses of regenerated nerves were performed 3 and 6 months after grafting. Distinct regeneration promoting effects of the different FGF-2 isoforms were found. 18-kDa-FGF-2 mediated inhibitory effects on the grade of myelination of regenerating axons, whereas 21-/23-kDa-FGF-2 mediated early recovery of sensory functions and stimulation of long-distance myelination of regenerating axons. The results contribute to the development of new therapeutic strategies in peripheral nerve repair.

Fibroblast growth factor-20 promotes the differentiation of Nurr1-overexpressing neural stem cells into tyrosine hydroxylase-positive neurons

Stem cells are currently considered as alternative cell resources for restorative transplantation strategies in Parkinson's disease. However, the mechanisms that induce differentiation of a stem cell toward the dopaminergic phenotype are still partly unknown thus hampering the production of dopaminergic neurons from stem cells. In the past, FGF-20 has been found to promote the survival of ventral mesencephalic (VM) dopaminergic (DA) neurons in culture. We hereby provide evidence that FGF-20, a growth factor of the FGF family, is expressed in the adult and 6-OHDA-lesioned striatum and substantia nigra, but is not expressed by VM glia or DA neurons, suggesting that FGF-20 may work on DA neurons in a paracrine- or target-derived manner. We also found that co-culture of Nurr1-NSCs with Schwann cells overexpressing FGF-20 induced the acquisition of a neuronal morphology by the NSCs and the expression of tyrosine hydroxylase (TH) as assessed by immunocytochemistry, cell ELISA, and Western blot analysis. RT-PCR showed, that both, Schwann cells and Nurr1-NSCs (differentiated or not), expressed the FGF-1 receptor suggesting that both direct and indirect actions of FGF-20 are possible. We show that differentiated Nurr1 cells retained both neuronal morphology and TH expression after transplantation into the striatum of 6-OHDA-lesioned postnatal or adult rats, but that neuritogenesis was only observed after postnatal grafts. Thus, our results suggest that FGF-20 promotes the differentiation of Nurr1-NSCs into TH-positive neurons and that additional factors are required for the efficient differentiation of DA neurons in the adult brain.

Effects of 6-hydroxydopamine on primary cultures of substantia nigra: specific damage to dopamine neurons and the impact of glial cell line-derived neurotrophic factor

6-Hydroxydopamine (6-OHDA)-induced loss of dopamine (DA) neurons has served to produce an animal model of DA neuron loss in Parkinson's disease. We report here the use of 6-OHDA to produce an in vitro model of this phenomena using dissociated cultures prepared from neonatal rat mesencephalon. Cultures were exposed to 6-OHDA (40-100 microm, 15 min) in an antioxidant medium, and DA and GABA neurons evaluated by immunocytochemistry. 6-OHDA induced morphological and biochemical signs of cell death in DA neurons within 3 h, followed by loss of tyrosine hydroxylase immunoreactive neurons within 2 days. In substantia nigra (SN) cultures, DA neurons were much more affected by 6-OHDA than were GABA neurons. In contrast, DA neurons from the ventral tegmental area were only lost at higher, non-specific concentrations of 6-OHDA. The effects of 6-OHDA on nigral DA neurons were blocked by inhibitors of high affinity DA transport and by z-DEVD-fmk (150 microm), a caspase inhibitor. Glial cell line-derived neurotrophic factor (GDNF) treatment reduced TUNEL labeling 3 h after 6-OHDA exposure, but did not prevent loss of DA neurons at 48 h. Thus, 6-OHDA can selectively destroy DA neurons in post-natal cultures of SN, acting at least in part by initiating caspase-dependent apoptosis, and this effect can be attenuated early but not late by GDNF.

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

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

Expression of the fibroblast growth factor-2 isoforms and the FGF receptor 1–4 transcripts in the rat model system of Parkinson's disease

Basic fibroblast growth factor (FGF)-2 occurs in different isoforms representing different translation products of a single mRNA. We have previously shown that the high molecular weight FGF-2 isoforms (21, 23 kD) stimulated survival- and neurite-promoting activities and protective effects on cultured embryonic dopaminergic (DA) neurons of the substantia nigra (Neuroscience 100 (2000) 73). In this study the expression of FGF-2 isoforms in the striatum and substantia nigra was analyzed by Western blot in adult intact rats and following complete unilateral 6-hydroxydopamine (6-OHDA) lesion. In intact rats, all three FGF-2 isoforms (18, 21, 23 kD) are expressed. Neurotoxin-mediated lesion of nigral DA neurons revealed no change of the FGF-2 isoform expression pattern in the nigrostriatal system. Additionally, the FGF receptors 1, 2 and 3 are expressed in these tissues and displayed no alterations after 6-OHDA injection as demonstrated by RT-PCR. The presence of all three FGF-2 isoforms and the FGFR 1-3, together with the previous demonstrated neurotrophic effects of FGF-2 on dopaminergic neurons, suggest a physiological function of the FGF-2 isoforms in the nigrostriatal system.

6-hydroxydopamine induces dopaminergic cell degeneration via a caspase-9-mediated apoptotic pathway that is attenuated by caspase-9dn expression

This study showed that primary dopaminergic neurons or the dopaminergic cell line MN9D, when exposed to 15 min of the parkinsonian toxin 6-hydroxydopamine (6-OHDA) in the range of 30-100 microM, underwent delayed degeneration and exhibited hallmarks of apoptosis. These results, along with the absence of any increase in lactate dehydrogenase (LDH) release from the degenerated cells, imply that apoptosis was the dominant mode of cell death. Moreover, a distinct elevation in the measured cellular activities of caspase-9 and -3 but not of caspase-8 points to the caspase-9/caspase-3 cascade as the predominant apoptotic pathway in the degeneration of dopaminergic neurons and MN9D cells. In addition, the presence of caspase-9 or -3 peptide inhibitors but not of caspase-8 inhibitor attenuated cell death significantly, supporting the notion that only the intrinsic apoptotic pathway is utilized to achieve cell death. Finally, overexpression of a mutant caspase-9 with dominant negative phenotype (caspase-9dn) in MN9D cells and primary dopaminergic neurons via the adenovirus and adenoassociated virus gene delivery system, respectively, conferred marked increases in tolerance to the toxicity of 6-OHDA. These results point to the intrinsic caspase-9/caspase-3 cascade as the predominant signaling pathway underlying dopaminergic cell death induced by 6-OHDA and suggest that gene delivery of caspase-9dn can attenuate this pathway and its degenerative consequences.

Basic fibroblast growth factor isoforms promote axonal elongation and branching of adult sensory neurons in vitro

Synthesis of the multifunctional cytokine basic fibroblast growth factor (FGF-2) is up-regulated after sciatic nerve lesion. In this study, the effects of low and high molecular weight FGF-2 isoforms on axonal elongation and branching of dissociated rat sensory neurons derived from adult lumbar dorsal root ganglia were investigated. These neurons express FGF receptor (FGFR) type I in the cytoplasmic/membrane compartment and in nuclear speckles. FGF-2 isoforms increase the number of axonal branches in cultures obtained from control rats, but do not promote axonal elongation. In response to a preconditioning lesion, i.e. transection of the sciatic nerve 1 week before culture, the axonal length of ipsilateral lumbar sensory neurons increases two-fold when compared with non-lesioned control rats, and this response is significantly enhanced by FGF-2 isoforms but not by nerve growth factor (NGF). Neurons dissociated from ganglia located contralaterally to the lesion exhibit a smaller increase in axon elongation (30%). The stimulating effects of FGF-2 isoforms on axon growth are fully blocked, and the enhanced regeneration of prelesioned neurons is reduced by the FGFR inhibitor SU5402 suggesting an involvement of endogenous FGF signaling in response to a lesion. The present data support a direct neurotrophic role of the 18 kD and 23 kD FGF-2 isoforms on adult axonal regeneration which may be of therapeutic value in the treatment of peripheral nerve lesions. Furthermore, evidence is provided for an enhanced regenerative capacity not only of preaxotomized neurons but also of homonymous non-axotomized neurons.

Effects of GDNF on 6-OHDA-induced death in a dopaminergic cell line: modulation by inhibitors of PI3 kinase and MEK

Parkinson's disease is a neurodegenerative disorder associated with the selective death of dopaminergic neurons. Glial cell line-derived neurotrophic factor (GDNF) can protect dopaminergic neurons in several parkinsonian models. We used the dopaminergic cell line MN9D to explore the mechanisms underlying GDNF-mediated protection against the neurotoxin 6-hydroxydopamine (6-OHDA). MN9D cell viability was decreased 24 hr after a 15-min exposure to 6-OHDA (50-1000 microM) as revealed by staining with Hoechst reagent and Trypan blue. The addition of GDNF (10 ng/ml) before, during, and after exposure to 6-OHDA significantly increased the number of viable cells as assessed by Hoechst staining. In contrast, 6-OHDA-induced cell membrane damage was unaffected as measured by Trypan blue exclusion. The PI3K specific inhibitor LY294002 (10-50 microM) blocked GDNF-mediated protection against nuclear condensation, as did the MAPK kinase (MEK) inhibitor U0126 (5- 20 microM). These studies suggest that GDNF can protect dopaminergic cells against some but not all aspects of 6-OHDA-induced toxicity by acting through both PI3K and MAPK signaling pathways.

Differential intranuclear localization of fibroblast growth factor-2 isoforms and specific interaction with the survival of motoneuron protein

Fibroblast growth factor 2 (FGF-2) is an important modulator of cell growth and differentiation and a neurotrophic factor. FGF-2 occurs in isoforms, at a low molecular weight of 18,000 and at least two high molecular weight forms (21,000 and 23,000), representing alternative translation products from a single mRNA. In addition to its role as an extracellular ligand, FGF-2 localizes to the nuclei of cells. Here we show differential localization of the 18- and 23-kDa isoforms in the nuclei of rat Schwann cells. Whereas the 18-kDa isoform was found in the nucleoli, nucleoplasm, and Cajal bodies, the 23-kDa isoform localized in a punctuate pattern and associates with mitotic chromosomes suggesting different functional roles of the isoforms. Moreover, we show here that the 23-kDa FGF-2 isoform co-immunoprecipitates specifically with the survival of motor neuron protein (SMN). SMN is an assembly and recycling factor of the splicing machinery and locates to the cytoplasm, the nucleoplasm, and nuclear gems, where it co-localizes with 23-kDa FGF-2. Patients with spinal muscular atrophy suffer from fatal degeneration of motoneurons because of mutations and deletions of the gene for the SMN protein.

Antidepressant treatments induce the expression of basic fibroblast growth factor in cortical and hippocampal neurons

New experimental evidence suggests that the mechanism of action of antidepressants includes the induction of neurotrophic factor synthesis in selected brain areas. The present study is aimed at establishing whether prolonged antidepressant treatments increase the expression of basic fibroblast growth factor (FGF2), a polypeptide growth factor that has a broad neurotrophic activity in the adult central nervous system. Rats received a single dose or long-term (3 weeks) administration of desipramine (DMI), fluoxetine (FLU), and mianserin (MIA), then were sacrificed at 5 and 24 h after the last injection. RNase protection assay and Western blot analysis revealed that all antidepressant drugs elicited an anatomically specific increase in FGF2 mRNA and protein. The increase in FGF2 mRNA after a single injection was seen only at 5 h after the injection and was restricted to the entorhinal cortex, whereas the effect of the long-term treatments lasted up to 24 h and occurred in the entire cortex and hippocampus. Immunohistochemical analysis of FGF2 immunoreactivity was carried out to investigate which cell types responded to the antidepressant treatments. DMI and MIA increased FGF2 proteins predominantly in neurons of layer V throughout the cerebral cortex and in some neurofilament-positive cells of the hippocampus. FLU increased FGF2 immunoreactivity mainly in neurofilament-positive cells of the hippocampus. These findings may explain the therapeutic efficacy of antidepressants in affective disorders.

Distinctive effects of rat fibroblast growth factor-2 isoforms on PC12 and Schwann cells

Fibroblast growth factor-2 (FGF-2) is an important modulator of cell growth and differentiation and stimulates cell survival of various cells including neurons. Rat FGF-2 occurs in three isoforms, a low molecular weight 18 kD and two high molecular weight forms (21, 23 kD), representing alternative translation products from a single mRNA. The 18 kD isoform shows mainly cytoplasmatic localization, whereas the 21/23 kD FGF-2 are localized in the nucleus. In addition, the FGF-2 isoforms are differentially regulated in the sensory ganglia and peripheral nerve following nerve injury and in the adrenal medulla during post-natal development and after hormonal stimuli. The distinct intracellular distribution and differential regulation of the different FGF-2 isoforms indicate that they have unique biological roles, however, little is known about the biological effects of the high molecular weight FGF-2 isoforms. Immortalized Schwann cells and PC12 cells, which stably overexpress the different FGF-2 isoforms, showed that the different endogenous-overexpressed FGF-2 isoforms lead to dramatic modifications in cell proliferation and survival, when tested in serum-free and serum-containing medium. In contrast, application of recombinant FGF-2 isoforms on normal PC12 and immortalized Schwann cells results in similar biological effects on the proliferation and survival of the cells. Furthermore, we investigated the potential regulatory effects of endogenous-overexpressed and exogenous-applied FGF-2 isoforms on the mRNA level of the FGF-2 receptors and, additionally, on the tyrosin hydroxylase mRNA expression in PC12 cells.