Parallel induction of the formation of dopamine and its metabolites with induction of tyrosine hydroxylase expression in foetal rat and human cerebral cortical cells by brain-derived neurotrophic factor and glial-cell derived neurotrophic factor

The promise of the TGF-β superfamily as a therapeutic target for Parkinson's disease

A large body of evidence underscore the regulatory role of TGF-β superfamily in the central nervous system. Components of the TGF-β superfamily modulate key events during embryonic brain development and adult brain tissue injury repair. With respect to Parkinson's disease (PD), TGF-ß signaling pathways are implicated in the differentiation, maintenance and synaptic function of the dopaminergic neurons, as well as in processes related to the activation state of astrocytes and microglia. In vitro and in vivo studies using toxin models, have interrogated on the dopaminotrophic and protective role of the TGF-β superfamily members. The evolution of genetic and animal models of PD that more closely recapitulate the disease condition has made possible the dissection of intracellular pathways in response to TGF-ß treatment. Although the first clinical trials using GDNF did not meet their primary endpoints, substantial work has been carried out to reappraise the TGF-β superfamily's clinical benefit.

Norepinephrine upregulates the expression of tyrosine hydroxylase and protects dopaminegic neurons against 6-hydrodopamine toxicity

As a classic neurotransmitter in the brain, norepinephrine (NE) also is an important modulator to other neuronal systems. Using primary cultures from rat ventral mesencephalon (VM) and dopaminergic cell line MN9D, the present study examined the neuroprotective effects of NE and its effects on the expression of tyrosine hydroxylase (TH). The results showed that NE protected both VM cultures and MN9D cells against 6-hydroxydopamine-caused apoptosis, with possible involvement of adrenal receptors. In addition, treatment with NE upregulated TH protein levels in dose- and time-dependent manner. Further experiments to investigate the potential mechanisms underlying this NE-induced upregulation of TH demonstrated a marked increase in protein levels of the brain-derived neurotrophic factor (BDNF) and the phosphorylated extracellular signal-regulated protein kinase 1 and 2 (pERK1/2) in VM cultures treated with NE. In MN9D cells, a significantly increase of TH and pERK1/2 protein levels were observed after their transfection with BDNF cDNA or exposure to BDNF peptides. Treatment of VM cultures with K252a, an antagonist of the tropomyosin-related kinase B, blocked the upregulatory effects of NE on TH, BDNF and pERK1/2. Administration of MEK1 & MEK2 inhibitors also reversed NE-induced upregulation of TH and pERK1/2. Moreover, ChIP assay showed that treatment with NE or BDNF increased H4 acetylation in the TH promoter. These results suggest that the neuroprotection and modulation of NE on dopaminergic neurons are mediated via BDNF and MAPK/ERK pathways, as well as through epigenetic histone modification, which may have implications for the improvement of therapeutic strategies for Parkinson's disease.

Enhanced differentiation of human dopaminergic neuronal cell model for preclinical translational research in Parkinson's disease

Human-derived neuronal cell lines are progressively being utilized in understanding neurobiology and preclinical translational research as they are biologically more relevant than rodent-derived cells lines. The Lund human mesencephalic (LUHMES) cell line comprises human neuronal cells that can be differentiated to post-mitotic neurons and is increasingly being used as an in vitro model for various neurodegenerative diseases. A previously published 2-step differentiation procedure leads to the generation of post-mitotic neurons within 5-days, but only a small proportion (10%) of the total cell population tests positive for tyrosine hydroxylase (TH). Here we report on a novel differentiation protocol that we optimized by using a cocktail of neurotrophic factors, pleiotropic cytokines, and antioxidants to effectively generate proportionately more dopaminergic neurons within the same time period. Visualization and quantification of TH-positive cells revealed that under our new protocol, 25% of the total cell population expressed markers of dopaminergic neurons with the TH-positive neuron count peaking on day 5. These neurons showed spontaneous electrical activity and responded to known Parkinsonian toxins as expected by showing decreased cell viability and dopamine uptake and a concomitant increase in apoptotic cell death. Together, our results outline an improved method for generating a higher proportion of dopaminergic neurons, thus making these cells an ideal neuronal culture model of Parkinson's disease (PD) for translational research.

Regulation of Trophic Factor Expression by Innervating Target Regions in Intraocular Double Transplants

Trophic factors have been found to play a significant role both in long-term survival processes and in more rapid and dynamic processes in the brain and spinal cord. However, little is known regarding the regulation of expression of growth factors, and how these proteins interact on a cell-to-cell basis. We have studied protein levels of one growth factor known to affect the noradrenergic innervation of the hippocampal formation, namely brain-derived neurotrophic factor (BDNF). The purpose of the present study was to determine if appropriate innervation or contact between the LC noradrenergic neurons and their target, the hippocampus, affects expression of this growth factor in either brain region. Fetal brain stem tissue, containing the LC, and hippocampal formation were dissected from embryonic day 17 rat fetuses and transplanted together or alone into the anterior chamber of the eye of adult Fisher 344 rats. The tissue was grown together for 6 weeks, after which the animals were sacrificed and ELISAs for BDNF were undertaken. Transplantation to the anterior chamber of the eye increased the expression of BDNF in the hippocampal but not the brain stem tissue, compared with levels observed in fetal and adult rats in vivo. In addition, double grafting with hippocampal tissue more than tripled BDNF levels in brain stem grafts and doubled BDNF levels in the hippocampal portion of double grafts compared with hippocampal single grafts. Triple grafts containing basal forebrain, hippocampus, and brain stem LC tissue increased brain stem and hippocampal BDNF levels even further. Colchicine treatment of LC-hippocampal double grafts gave rise to a significant decrease in hippocampal BDNF levels to levels seen in single hippocampal grafts, while only a partial reduction of BDNF levels was seen in the brain stem portion of the same double grafts treated with colchicine. The findings suggest that an appropriate hippocampal innervation or contact with its target tissues is essential for regulation of BDNF expression in the brain stem, and that retrograde transport of BDNF can occur between double grafted fetal tissues in oculo.

Dampened Amphetamine-Stimulated Behavior and Altered Dopamine Transporter Function in the Absence of Brain GDNF

Midbrain dopamine neuron dysfunction contributes to various psychiatric and neurological diseases, including drug addiction and Parkinson's disease. Because of its well established dopaminotrophic effects, the therapeutic potential of glial cell line-derived neurotrophic factor (GDNF) has been studied extensively in various disorders with disturbed dopamine homeostasis. However, the outcomes from preclinical and clinical studies vary, highlighting a need for a better understanding of the physiological role of GDNF on striatal dopaminergic function. Nevertheless, the current lack of appropriate animal models has limited this understanding. Therefore, we have generated novel mouse models to study conditional Gdnf deletion in the CNS during embryonic development and reduction of striatal GDNF levels in adult mice via AAV-Cre delivery. We found that both of these mice have reduced amphetamine-induced locomotor response and striatal dopamine efflux. Embryonic GDNF deletion in the CNS did not affect striatal dopamine levels or dopamine release, but dopamine reuptake was increased due to increased levels of both total and synaptic membrane-associated dopamine transporters. Collectively, these results suggest that endogenous GDNF plays an important role in regulating the function of dopamine transporters in the striatum.SIGNIFICANCE STATEMENT Delivery of ectopic glial cell line-derived neurotrophic factor (GDNF) promotes the function, plasticity, and survival of midbrain dopaminergic neurons, the dysfunction of which contributes to various neurological and psychiatric diseases. However, how the deletion or reduction of GDNF in the CNS affects the function of dopaminergic neurons has remained unknown. Using conditional Gdnf knock-out mice, we found that endogenous GDNF affects striatal dopamine homeostasis and regulates amphetamine-induced behaviors by regulating the level and function of dopamine transporters. These data regarding the physiological role of GDNF are relevant in the context of neurological and neurodegenerative diseases that involve changes in dopamine transporter function.

Neurotrophic factors in Parkinson's disease are regulated by exercise: Evidence-based practice

We carried out a qualitative review of the literature on the influence of forced or voluntary exercise in Parkinson's Disease (PD)-induced animals, to better understand neural mechanisms and the role of neurotrophic factors (NFs) involved in the improvement of motor behavior. A few studies indicated that forced or voluntary exercise may promote neuroprotection, through upregulation of NF expression, against toxicity of drugs that simulate PD. Forced training, such as treadmill exercise and forced-limb use, adopted in most studies, in addition to voluntary exercise on a running wheel are suitable methods for NFs upregulation.

Current Neurogenic and Neuroprotective Strategies to Prevent and Treat Neurodegenerative and Neuropsychiatric Disorders

The adult central nervous system is commonly known to have a very limited regenerative capacity. The presence of functional stem cells in the brain can therefore be seen as a paradox, since in other organs these are known to counterbalance cell loss derived from pathological conditions. This fact has therefore raised the possibility to stimulate neural stem cell differentiation and proliferation or survival by either stem cell replacement therapy or direct administration of neurotrophic factors or other proneurogenic molecules, which in turn has also originated regenerative medicine for the treatment of otherwise incurable neurodegenerative and neuropsychiatric disorders that take a huge toll on society. This may be facilitated by the fact that many of these disorders converge on similar pathophysiological pathways: excitotoxicity, oxidative stress, neuroinflammation, mitochondrial failure, excessive intracellular calcium and apoptosis. This review will therefore focus on the most promising achievements in promoting neuroprotection and neuroregeneration reported to date.

Increased antiparkinson efficacy of the combined administration of VEGF- and GDNF-loaded nanospheres in a partial lesion model of Parkinson's disease

Current research efforts are focused on the application of growth factors, such as glial cell line-derived neurotrophic factor (GDNF) and vascular endothelial growth factor (VEGF), as neuroregenerative approaches that will prevent the neurodegenerative process in Parkinson’s disease. Continuing a previous work published by our research group, and with the aim to overcome different limitations related to growth factor administration, VEGF and GDNF were encapsulated in poly(lactic-co-glycolic acid) nanospheres (NS). This strategy facilitates the combined administration of the VEGF and GDNF into the brain of 6-hydroxydopamine (6-OHDA) partially lesioned rats, resulting in a continuous and simultaneous drug release. The NS particle size was about 200 nm and the simultaneous addition of VEGF NS and GDNF NS resulted in significant protection of the PC-12 cell line against 6-OHDA in vitro. Once the poly(lactic-co-glycolic acid) NS were implanted into the striatum of 6-OHDA partially lesioned rats, the amphetamine rotation behavior test was carried out over 10 weeks, in order to check for in vivo efficacy. The results showed that VEGF NS and GDNF NS significantly decreased the number of amphetamine-induced rotations at the end of the study. In addition, tyrosine hydroxylase immunohistochemical analysis in the striatum and the external substantia nigra confirmed a significant enhancement of neurons in the VEGF NS and GDNF NS treatment group. The synergistic effect of VEGF NS and GDNF NS allows for a reduction of the dose by half, and may be a valuable neurogenerative/neuroreparative approach for treating Parkinson’s disease.

Roles for the TGFβ superfamily in the development and survival of midbrain dopaminergic neurons

The adult midbrain contains 75% of all dopaminergic neurons in the CNS. Within the midbrain, these neurons are divided into three anatomically and functionally distinct clusters termed A8, A9 and A10. The A9 group plays a functionally non-redundant role in the control of voluntary movement, which is highlighted by the motor syndrome that results from their progressive degeneration in the neurodegenerative disorder, Parkinson's disease. Despite 50 years of investigation, treatment for Parkinson's disease remains symptomatic, but an intensive research effort has proposed delivering neurotrophic factors to the brain to protect the remaining dopaminergic neurons, or using these neurotrophic factors to differentiate dopaminergic neurons from stem cell sources for cell transplantation. Most neurotrophic factors studied in this context have been members of the transforming growth factor β (TGFβ) superfamily. In recent years, an intensive research effort has focused on understanding the function of these proteins in midbrain dopaminergic neuron development and their role in the molecular architecture that regulates the development of this brain region, with the goal of applying this knowledge to develop novel therapies for Parkinson's disease. In this review, the current evidence showing that TGFβ superfamily members play critical roles in the regulation of midbrain dopaminergic neuron induction, differentiation, target innervation and survival during embryonic and postnatal development is analysed, and the implications of these findings are discussed.

Expression of full-length and truncated trkB in human striatum and substantia nigra neurons: implications for Parkinson's disease

Brain derived neurotrophic factor (BDNF) is a potent mediator of cell survival and differentiation and can reverse neuronal injury associated with Parkinson's disease (PD). Tropomyosin receptor kinase B (trkB) is the high affinity receptor for BDNF. There are two major trkB isoforms, the full-length receptor (trkB.tk(+)) and the truncated receptor (trkB.t1), that mediate the diverse, region specific functions of BDNF. Both trkB isoforms are widely distributed throughout the brain, but the isoform specific distribution of trkB.t1 and trkB.tk(+) to human neurons is not well characterized. Therefore, we report the regional and neuronal distribution of trkB.tk(+) and trkB.t1 in the striatum and substantia nigra pars compacta (SNpc) of human autopsy tissues from control and PD cases. In both PD and control tissues, we found abundant, punctate distribution of trkB.tk(+) and trkB.t1 proteins in striatum and SNpc neurons. In PD, trkB.tk(+) is decreased in striatal neurites, increased in striatal somata, decreased in SNpc somata and dendrites, and increased in SNpc axons. TrkB.t1 is increased in striatal somata, decreased in striatal axons, and increased in SNpc distal dendrites. We believe changes in trkB isoform distribution and expression levels may be markers of pathology and affect the neuronal response to BDNF.

Maternal treadmill exercise during pregnancy decreases anxiety and increases prefrontal cortex VEGF and BDNF levels of rat pups in early and late periods of life

In a previous study we demonstrated that, regular aerobic exercise during pregnancy decreased maternal deprivation induced anxiety. The purpose of this study is to investigate whether the positive effects of maternal exercise on the male and female offspring's early and late period of life. Half of the test subjects in each group were evaluated when they were 26 days old, and the other half were evaluated when they were 4 months old. The anxiety levels of maternally exercised groups were less than the control groups in both sexes and in both prepubertal and adult periods. The locomotor activity more increased in females. The prefrontal VEGF and BDNF levels were greater for both age groups and sexes in the maternally exercised group compared to control group. Moreover, there was a strong positive correlations between prefrontal cortex BDNF levels and results of open field tests; and VEGF levels and results of elevated plus maze tests. There was no difference in serum corticosterone levels between groups. These results indicate that maternal exercise during pregnancy may protect the pups from anxiety in early and late periods of life, and affects the prefrontal cortex positively.

Truncated TrkB: beyond a dominant negative receptor

BDNF activates trkB receptors to regulate neuronal survival, differentiation, and proliferation. Mutations in the BDNF gene, altered BDNF expression, and altered trkB expression are associated with degenerative and psychiatric disorders. The full-length trkB receptor (trkB.tk(+)) undergoes autophosphorylation to activate intracellular signaling pathways. The truncated trkB receptor (trkB.t1) is abundantly expressed in the brain but lacks the catalytic tyrosine kinase domain. TrkB.t1 is a dominant-negative receptor that inhibits trkB.tk(+) signaling. While this is an important function of trkB.t1, it is only one of its many functions. TrkB.t1 sequesters and translocate BDNF, induces filopodia and neurite outgrowth, stimulates intracellular signaling cascades, regulates Rho GTPase signaling, and modifies cytoskeletal structures. TrkB.t1 is an active signaling molecule with regulatory effects on neurons and astrocytes.

Neuronal activity regulates expression of tyrosine hydroxylase in adult mouse substantia nigra pars compacta neurons

Striatal delivery of dopamine (DA) by midbrain substantia nigra pars compacta (SNc) neurons is vital for motor control and its depletion causes the motor symptoms of Parkinson's disease. While membrane potential changes or neuronal activity regulates tyrosine hydroxylase (TH, the rate limiting enzyme in catecholamine synthesis) expression in other catecholaminergic cells, it is not known whether the same occurs in adult SNc neurons. We administered drugs known to alter neuronal activity to mouse SNc DAergic neurons in various experimental preparations and measured changes in their TH expression. In cultured midbrain neurons, blockade of action potentials with 1 μM tetrodotoxin decreased TH expression beginning around 20 h later (as measured in real time by green fluorescent protein (GFP) expression driven off TH promoter activity). By contrast, partial blockade of small-conductance, Ca(2+) -activated potassium channels with 300 nM apamin increased TH mRNA and protein between 12 and 24 h later in slices of adult midbrain. Two-week infusions of 300 nM apamin directly to the adult mouse midbrain in vivo also increased TH expression in SNc neurons, measured immunohistochemically. Paradoxically, the number of TH immunoreactive (TH+) SNc neurons decreased in these animals. Similar in vivo infusions of drugs affecting other ion-channels and receptors (L-type voltage-activated Ca(2+) channels, GABA(A) receptors, high K(+) , DA receptors) also increased or decreased cellular TH immunoreactivity but decreased or increased, respectively, the number of TH+ cells in SNc. We conclude that in adult SNc neurons: (i) TH expression is activity-dependent and begins to change ∼20 h following sustained changes in neuronal activity; (ii) ion-channels and receptors mediating cell-autonomous activity or synaptic input are equally potent in altering TH expression; and (iii) activity-dependent changes in TH expression are balanced by opposing changes in the number of TH+ SNc cells.

Neurochemical characterization of tyrosine hydroxylase-immunoreactive interneurons in the developing rat cerebral cortex

Understanding the development of cortical interneuron phenotypic diversity is critical because interneuron dysfunction has been implicated in several neurodevelopmental disorders. Here, tyrosine hydroxylase (TH)-immunoreactive neurons in the developing and adult rat cortex were characterized in light of findings regarding interneuron neurochemistry and development. Cortical TH-immunoreactive neurons were first observed 2 weeks postnatally and peaked in number 3 weeks after birth. At subsequent ages, the number of these cell profiles was gradually reduced, and they were seen less frequently in adults. No DNA fragmentation or active caspase 3 was observed in cortical TH cells at any age examined, eliminating cell death as an explanation for the decrease in cell number. Although cortical TH cells reportedly fail to produce subsequent catecholaminergic enzymes, we found that the majority of these cells at all ages contained phosphorylated TH, suggesting that the enzyme may be active and producing L-DOPA as an end-product. Morphological criteria and colocalization of some TH cells with glutamic acid decarboxylase suggest that these cells are interneurons. Previously, parvalbumin, somatostatin, and calretinin were demonstrated in non-overlapping subsets of interneurons. Cortical TH neurons colocalized with calretinin but not with parvalbumin or somatostatin. These findings suggest that the transitory increase in TH cell number is not due to cell death but possibly due to alterations in the amount of detectable TH present in these cells, and that at least some cortical TH-producing interneurons belong to the calretinin-containing subset of interneurons that originate developmentally in the caudal ganglionic eminence.

Interaction between BDNF Val66Met and dopamine transporter gene variation influences anxiety-related traits

The involvement in neural plasticity and the mediation of effects of repeated stress exposure and long-term antidepressant treatment on hippocampal neurogenesis supports a critical role of brain-derived neurotrophic factor (BDNF) in the pathophysiology of affective and other stress-related disorders. A previously reported valine to methionine substitution at amino-acid position 66 (BDNF Val66Met) seems to account for memory disturbance and hippocampal dysfunction. In the present study, we evaluated the impact of the BDNF Val66Met polymorphism on individual differences in personality traits in a sample of healthy volunteers in relation to other common gene variants thought to be involved in the pathophysiology of affective disorders, such as the serotonin transporter promoter polymorphism (5-HTTLPR) and a variable number of tandem repeat polymorphism of the dopamine transporter gene (DAT VNTR). Personality traits were assessed using the NEO personality inventory (NEO-PI-R) and Tridimensional Personality Questionnaire (TPQ). There was a significant DAT VNTR-dependent association between NEO-PI-R Neuroticism and the BDNF Val66Met polymorphism. Among individuals with at least one copy of the DAT 9-repeat allele, carriers of the BDNF Met allele exhibited significantly lower Neuroticism scores than noncarriers. This interaction was also observed for TPQ Harm Avoidance, a personality dimension related to Neuroticism. Our results support the notion that allelic variation at the BDNF locus--in interaction with other gene variants--influences anxiety- and depression-related personality traits.

Carnosol, a component of rosemary (Rosmarinus officinalis L.) protects nigral dopaminergic neuronal cells

Carnosol, a major component of Rosmarinus officinalis, is a phenolic diterpene that has potent antioxidant and anti-inflammatory activities. In this study, we investigated the protective effects of carnosol on rotenone-induced neurotoxicity in cultured dopaminergic cells. Results showed that cell viability was significantly improved with carnosol through downregulation of caspase-3. Furthermore, carnosol significantly increased the tyrosine hydroxylase, Nurr1, and extracellular signal-regulated kinase 1/2. These results suggest that carnosol may have potential as a possible compound for the development of new agents to treat Parkinson's disease.

Glial cell line-derived neurotrophic factor (GDNF) is required for differentiation of pontine noradrenergic neurons and patterning of central respiratory output

Genetic mutations affecting signaling by glial cell line-derived neurotrophic factor (GDNF) perturb development of breathing in mice and are associated with congenital central hypoventilation syndrome in humans. However, the role of GDNF in development of brainstem neurons that control breathing is largely unknown. The present study demonstrates that genetic loss of GDNF decreases the number of tyrosine hydroxylase (TH) neurons in the pontine A5 noradrenergic cell group, a major source of inhibitory input to the medullary respiratory pattern generator. This phenotype is associated with a significant increase in the frequency of central respiratory output recorded from the fetal medulla-spinal cord in vitro. In dissociate cultures of the A5 region from rat embryos, GDNF increases TH cell number and neurite growth without affecting total neuronal survival or proliferation of TH neurons. These effects of GDNF are inhibited by function blocking antibodies against endogenous brain-derived neurotrophic factor (BDNF), indicating that GDNF requires BDNF as a cofactor to stimulate differentiation of A5 neurons. Our findings demonstrate that GDNF is required for development of pontine noradrenergic neurons in vivo and indicate that defects in the A5 cell group may contribute to the effects of genetic disruption of GDNF signaling on respiratory control.

Differential effects of growth/differentiation factor 5 and glial cell line-derived neurotrophic factor on dopaminergic neurons and astroglia in cultures of embryonic rat midbrain

Parkinson's disease is characterized by the progressive degeneration of midbrain dopaminergic neurons. Several studies have examined the effects of the dopaminergic neurotrophins growth/differentiation factor 5 (GDF5) and glial cell line-derived neurotrophic factor (GDNF) on these neurons in vitro. However, there is little information regarding their effects on astroglial cells. Here, the effects of GDF5 and GDNF on dopaminergic neuronal and astroglial survival and differentiation in embryonic rat midbrain cultures were examined. Both GDF5 and GDNF enhanced the survival and differentiation of dopaminergic neurons. GDF5 significantly increased the survival of astroglial cells, whereas GDNF had no significant effect on these cells. The possible involvement of astroglia in the dopaminergic neurotrophic effect induced by GDF5 was investigated by examining the effect of GDF5 on the survival of dopaminergic neurons in glia-depleted midbrain cultures. There was no significant difference between the survival of dopaminergic neurons in glia-depleted cultures treated with GDF5 and that in mixed cell cultures treated with GDF5, suggesting that GDF5 acts directly on dopaminergic neurons in exerting its neurotrophic effect. GDF5 and GDNF have been established as potent neurotrophic factors for dopaminergic neurons. However, the effects of adding a combination of these neurotrophins to midbrain cultures have not been previously examined. The present study found that combined treatment with GDF5 and GDNF significantly increased the survival of dopaminergic neurons in cultures compared with that in cultures treated with either neurotrophin alone. This was an additive effect, indicating that these neurotrophins act on separate subpopulations of dopaminergic neurons.

The differentiation potential of human foetal neuronal progenitor cells in vitro

Previously, this laboratory has shown that human foetal progenitor cells derived from ventral mesencephalon (VM) can be developmentally directed towards a dopaminergic lineage. In the present study, the effects are reported of several as yet untested differentiation/survival factors on the controlled conversion of neural progenitor cells to dopaminergic neurons. Positive immunoreactivity to tyrosine hydroxylase (TH) and raised levels of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), secreted into culture medium, were used to indicate the presence of the dopaminergic neuronal phenotype, i.e., active TH. Incubation with retinoic acid (RA) (0.5 microM) lead to an increase in the number of cultured cells showing positive immunoreactivity for the neuronal marker, microtubule-associated protein (MAP)-2ab. A concomitant increase in TH-positive immunoreactivity was also demonstrated. The brain-derived neurotrophic factor (BDNF) (50 ng/ml), glial-derived neurotrophic factor (GDNF) (10 ng/ml) and interleukin-1 beta (IL-1 beta) (10 ng/ml) also had positive effects in promoting neural progenitor cell differentiation towards the dopaminergic phenotype in the presence of dopamine (10 microM) and forskolin (Fsk) (10 microM). There was no synergy in this effect when progenitor cells were incubated with all of these agents simultaneously. The trans-differentiation potential of the progenitor cells to be directed towards other neurotransmitter phenotypic lineages was also investigated. It was found that, with the right cocktails of agents, serotonin (Ser) (75 microM), acidic fibroblast growth factor (aFGF) (10 ng/ml), BDNF (50 ng/ml) and forskolin (10 microM), these same cells could be directed down the serotonergic cell lineage pathway (as judged by the appearance of tryptophan hydroxylase (TPH) positive immunoreactivity, and synthesis of 5-HT and its metabolites, secreted into the culture medium). However, no cocktail containing noradrenaline (10 nM-500 microM), BDNF (50 ng/ml) and forskolin (10 microM) was found which promoted differentiation towards the noradrenergic cell phenotype as judged by the absence of any TH or D beta H positive immunoreactivity, and no formation of 3,4-dihydroxyphenylethyleneglycol (DOPEG), the principal metabolite of noradrenaline. The controlled trans-differentiation potential of these cell could pave the way for development and harvesting of large numbers of neurons of the appropriate neurotransmitter phenotype for future transplantation therapies for the treatment of neurodegenerative diseases such as Parkinson's disease (PD) and Alzheimer's disease.

Tyrosine hydroxylase induction by basic fibroblast growth factor and cyclic AMP analogs in striatal neural stem cells: role of ERK1/ERK2 mitogen-activated protein kinase and protein kinase C

Neural stem cells (NSC) with self-renewal and multilineage potential are considered good candidates for cell replacement of damaged nervous tissue. In vitro experimental conditions can differentiate these cells into specific neuronal phenotypes. In the present study, we describe the combined effect of basic fibroblast growth factor (bFGF) and dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP) on the differentiation of fetal rat striatal NSC into tyrosine hydroxylase-positive cells. Tyrosine hydroxylase induction was accompanied by the activation of ERK1/ERK2 mitogen-activated protein kinase and was inhibited by the ERK1/ERK2 pathway blocker PD98059, suggesting that ERK activation may be important for this process. In addition, protein kinase C (PKC) was shown to be required for tyrosine hydroxylase protein expression. The inhibition of PKC by staurosporin, as well as its downregulation, decreased the ability of bFGF+dbcAMP to generate tyrosine hydroxylase-positive cells. Moreover, the PKC activator phorbol 12-myristate 13-acetate (PMA) together with bFGF and dbcAMP led to a significant increase in phospho-ERK1/ERK2 levels, and the percentage of beta-tubulin III-positive cells that expressed tyrosine hydroxylase increased by 3.5-fold. PMA also promoted the phosphorylation of the cyclic AMP response element binding protein that might contribute to the increase in tyrosine hydroxylase-positive cells observed in bFGF+dbcAMP+PMA-treated cultures. From these results, we conclude that the manipulation in vitro of NSC from rat fetal striatum with bFGF, cyclic AMP analogs, and PKC activators promotes the generation of tyrosine hydroxylase-positive neurons.

A rapid assay for glial cell line-derived neurotrophic factor and neurturin based on transfection of cells with tyrosine hydroxylase promoter-luciferase construct

Glial cell line-derived neurotrophic factor (GDNF), a potent survival and trophic factor for various neuronal cells, has been measured by assaying its bioactivity based on neurite outgrowth or cell proliferation. We describe herein a sensitive and simple non-radioactive quantitative bioassay for GDNF family proteins based on their ability to induce tyrosine hydroxylase (TH) gene expression. Human neuroblastoma SK-N-MC cells were stably transfected with expression constructs of c-ret and with a luciferase reporter gene driven by 2 kb of the rat TH gene promoter region. In the presence of GDNF, luciferase activity increased with 20 h of incubation. A dose-dependent increase in luciferase activity was observed in the presence of GDNF between 1 and 300 ng/ml. This assay was also applicable for the quantification of the bioactivity of neurturin, another member of the GDNF family showing an even more sensitive profile of dose dependency than GDNF. Typical culture media were applicable in this assay. This method can be easily applied to numerous samples of conditioned medium in a short time.

Neurotrophic factors for the investigation and treatment of movement disorders

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

Heparin facilitates glial cell line-derived neurotrophic factor signal transduction

Glial cell-line neurotrophic factor (GDNF), a neurotrophic factor with heparin binding affinity, promotes the survival and differentiation of a variety of neuronal cells including dopaminergic neuron. The effect of heparin on GDNF signaling was investigated based on the expression of the tyrosine hydroxyrase (TH) gene in neurobalstoma cells. Up-regulation of TH gene mRNA by GDNF was enhanced by co-administration of heparin. This facilitation by heparin was particularly evident at suboptimal levels of GDNF, which was consistent with the luciferase assay using TH gene promoter. Pretreatment with heparitinase decreased TH promoter activity in the absence of heparin. Phosphorylation of extracellular regulated kinase was increased in the presence of heparin, although tyrosine phosphorylation of Ret receptor tyrosine kinase was not affected by heparin. Expression of early response genes such as c-fos or Egr1 increased and sustained in the presence of heparin more than that without heparin. These results indicate that interaction with glycosaminoglycans such as heparin affects GDNF signal transduction positively.

Glial cell line-derived neurotrophic factor up-regulates the expression of tyrosine hydroxylase gene in human neuroblastoma cell lines

The role of glial cell line-derived neurotrophic factor (GDNF) in the survival of dopaminergic neurons has been well documented, but its effect on dopamine biosynthesis remains to be elucidated. In this study, the effect of GDNF on the gene expression of tyrosine hydroxylase (TH), the rate-limiting enzyme of dopamine biosynthesis, was investigated. We found that GDNF elevated the expression of the TH gene at both mRNA and protein levels in TGW cells, a human neuroblastoma cell line. GDNF significantly enhances the transcription rate of the TH gene as actinomycin D prevented the induction of TH mRNA and GDNF increased the activity of the TH promoter. In addition, GDNF exerts a relatively weak but significant effect on the stability of TH mRNA, because GDNF delayed the degradation of TH mRNA and strengthened a special TH mRNA/protein interaction known to be relevant with TH mRNA stability. By comparing several human neurogenic cell lines, we found that GDNF-induced TH expression was only observed in the cells possessing Ret protein and coincided with the expression levels. Taken together, these results indicate that GDNF up-regulates the expression of the TH gene by promoting the transcription of the TH gene and the stability of TH mRNA with the Ret receptor dependency in some neuroblastoma cell lines. Thus, GDNF exerts its neurotrophic role not only in promoting cells survival, but also in affecting dopamine biosynthesis.

Stem cells in the treatment of Parkinson's disease

Stem cells have been suggested as candidate therapeutic tools for neurodegenerative disorders, given their ability to give rise to the appropriate cell types after grafting in vivo. In this review I summarize some of the evidence currently available concerning two approaches for the treatment of Parkinson's disease: (1) The generation of dopaminergic neurons from embryonic stem cells, multipotent stem cells, and neuronal progenitor cells for cell replacement therapy. (2) The engineering of multipotent stem cells to release glial cell-line derived neurotrophic factor, a potent neurotrophic factor for dopaminergic neurons, in a neuroprotective and neuroregenerative approach to the treatment of Parkinson's disease.