Effects of glial cell line-derived neurotrophic factor on developing and mature ventral mesencephalic grafts in oculo

Transplantation of human dental pulp stem cells compensates for striatal atrophy and modulates neuro-inflammation in 3-nitropropionic acid rat model of Huntington's disease

Stem cell-based therapy has recently offered a promising alternative for the remedy of neurodegenerative disorders like Huntington's disease (HD). Herein, we investigated the potential ameliorative effects of implantation of dental pulp stem cells (DPSCs) in 3-nitropropionic acid (3-NP) rat models of HD. In this regard, human DPSCs were isolated, culture-expanded and implanted in rats lesioned with 3-NP. Post-transplantation examinations revealed that DPSCs were able to survive and augment motor skills and muscle activity. Histological analysis showed DPSCs treatment hampered the shrinkage of the striatum along with the inhibition of gliosis and microgliosis in the striatum of 3-NP rat models. We also detected the downregulation of Caspase-3 and pro-inflammatory cytokines such as TNF and IL-1β upon DPSCs grafting. Overall, these findings imply that the grafting of DPSCs could repair motor-skill impairment and induce neurogenesis, probably through the secretion of neurotrophic factors and the modulation of neuroinflammatory response in HD animal models.

Viral Delivery of GDNF Promotes Functional Integration of Human Stem Cell Grafts in Parkinson's Disease

Dopaminergic neurons (DAns), generated from human pluripotent stem cells (hPSCs), are capable of functionally integrating following transplantation and have recently advanced to clinical trials for Parkinson's disease (PD). However, pre-clinical studies have highlighted the low proportion of DAns within hPSC-derived grafts and their inferior plasticity compared to fetal tissue. Here, we examined whether delivery of a developmentally critical protein, glial cell line-derived neurotrophic factor (GDNF), could improve graft outcomes. We tracked the response of DAns implanted into either a GDNF-rich environment or after a delay in exposure. Early GDNF promoted survival and plasticity of non-DAns, leading to enhanced motor recovery in PD rats. Delayed exposure to GDNF promoted functional recovery through increases in DAn specification, DAn plasticity, and DA metabolism. Transcriptional profiling revealed a role for mitogen-activated protein kinase (MAPK)-signaling downstream of GDNF. Collectively, these results demonstrate the potential of neurotrophic gene therapy strategies to improve hPSC graft outcomes.

Morphological and Functional Evidence for Enhanced Growth and Potassium-Evoked Dopamine Release in Striatal Grafts Innervated with a Patchy Growth Pattern. an in Oculo Nigrostriatal Cograft Study

During development of the nigrostriatal dopamine system, a patchy and a diffuse type of striatal innervation pattern can be seen. It has been suggested that when fetal dopaminergic neurons, obtained from the ventral mesencephalon (VM), are grafted adjacent to mature striatal tissue, only the diffuse growth is induced. Intraocular grafting studies have indicated that the dopaminergic growth pattern might be influenced by the age of the target area, the lateral ganglionic eminence (LGE). In this study VM grafts were allowed to innervate LGE grafts of different ages. Fetal VM was implanted next to 2-wk-old or 26-day-old striatal in oculo grafts, and the resulting dopaminergic innervation of the striatal grafts was studied using tyrosine hydroxylase (TH) immunohistochemistry. In striatal grafts receiving innervation at the age of 2 wk in oculo, a patchy TH-immunoreactive growth pattern was found, while in striatal grafts innervated at the age of 26 days mainly the diffuse growth pattern was seen. This implies that grafted striatum reached maturity at approximately 1 mo of age. The age of the dopaminergic neurons at dissection and grafting was also studied concerning the ability to induce patchy growth into mature striatum. Thus, VM dissected from 13- and 18-mm fetuses was implanted to either 4-mo-old LGE (grafted in sequence) or to LGE from the same fetus (grafted simultaneously) as controls. TH-positive innervation of striatal tissue, evaluated 4 wk after implantation of VM, revealed a patchy growth pattern in LGE grafted simultaneously with 13- and 18-mm VM. However, when the striatum was mature at the time of innervation, diffuse growth was observed in striatum innervated by VM dissected from 13-mm fetuses. Interestingly, patchy growth was noted in striatal areas close to VM grafts when the dopaminergic neurons were derived from older fetuses (CRL 18 mm). Furthermore, potassium-induced dopamine release was greater in striatal grafts exhibiting the patchy growth than those showing the diffuse pattern of innervation. In conclusion, patchy dopaminergic growth can be induced in mature striatal tissue by grafting VM from older fetuses. Functionally, potassium-evoked dopamine release is enhanced in dopaminergic patches. These results have implications in terms of finding ways to induce patchy growth when grafting to the mature striatum of patients suffering from Parkinson's disease.

Chemical conversion of mouse fibroblasts into functional dopaminergic neurons

Ectopic expression of lineage-specific transcription factors facilitates the conversion of mammalian somatic cells into dopaminergic (DA) neurons, which is a promising strategy for cell therapy of Parkinson's disease (PD). However, this approach still has some drawbacks limiting its clinical application due to the potential risks of integrating vectors into the host genome. Therefore, it is critical to seek a more desired approach to generate DA neurons derived from mammalian somatic cells. Here, we report that mouse embryonic fibroblasts (MEFs) can be efficiently converted into DA neurons by using small molecules along with specific growth factors. These neuron-like cells generate DA neuronal morphology, and acquire immunocytochemical and calcium imaging special for neuronal electrophysiological profile. More importantly, these converted cells can secrete dopamine, indicating that they are functionally similar to DA neurons. Taken together, our study might provide a promising cell source for treating PD by using chemical approach without introduction of exogenous transcription factors.

Direct conversion of mouse fibroblasts to GABAergic neurons with combined medium without the introduction of transcription factors or miRNAs

Degeneration or loss of GABAergic neurons frequently may lead to many neuropsychiatric disorders such as epilepsy and autism spectrum disorders. So far no clinically effective therapies can slow and halt the progression of these diseases. Cell-replacement therapy is a promising strategy for treatment of these neuropsychiatric diseases. Although increasing evidence showed that mammalian somatic cells can be directly converted into functional neurons using specific transcription factors or miRNAs via virus delivery, the application of these induced neurons is potentially problematic, due to integration of vectors into the host genome, which results in the disruption or dysfunction of nearby genes. Here, we show that mouse fibroblasts could be efficiently reprogrammed into GABAergic neurons in a combined medium composed of conditioned medium from neurotrophin-3 modified Olfactory Ensheathing Cells (NT3-OECs) plus SB431542, GDNF and RA. Following 3 weeks of induction, these cells derived from fibroblasts acquired the morphological and phenotypical GABAerigic neuronal properties, as demonstrated by the expression of neuronal markers including Tuj1, NeuN, Neurofilament-L, GABA, GABA receptors and GABA transporter 1. More importantly, these converted cells acquired neuronal functional properties such as synapse formation and increasing intracellular free calcium influx when treated with BayK, a specific activator of L-type calcium channel. Therefore, our findings demonstrate for the first time that fibroblasts can be directly converted into GABAergic neurons without ectopic expression of specific transcription factors or miRNA. This study may provide a promising cell source for the application of cell replacement therapy in neuropsychiatric disorders.

Neurotropic growth factors and glycosaminoglycan based matrices to induce dopaminergic tissue formation

Current cell replacement therapies in Parkinson's disease (PD) are limited by low survival of transplanted cell and lacking regeneration of neuronal circuitries. Therefore, bioartificial cell carriers and growth/differentiation factors are applied to improve the integration of transplants and maximize newly generated and/or residual dopaminergic function. In this work, biohybrid poly(ethylene glycol) (starPEG)-heparin hydrogels releasing fibroblast growth factor 2 (FGF-2) and glial-derived neurotrophic factor (GDNF) were used to trigger dopaminergic tissue formation by primary murine midbrain cells in vitro. Matrix-delivered FGF-2 enhanced cell viability while release of GDNF had a pro-neuronal/dopaminergic effect. Combined delivery of both factors from the glycosaminoglycan-based matrices resulted in a tremendous improvement in survival and maturation capacity of dopaminergic neurons as obvious from tyrosine hydroxylase expression and neurite outgrowth. The reported data demonstrate that glycosaminoglycan-based hydrogels can facilitate the administration of neurotrophic factors and are therefore instrumental in potential future treatments of PD.

Tricyclic antidepressant treatment evokes regional changes in neurotrophic factors over time within the intact and degenerating nigrostriatal system

In addition to alleviating depression, trophic responses produced by antidepressants may regulate neural plasticity in the diseased brain, which not only provides symptomatic benefit but also potentially slows the rate of disease progression in Parkinson's disease (PD). Recent in vitro and in vivo data provide evidence that neurotrophic factors such as brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) may be key mediators of the therapeutic response to antidepressants. As such, we conducted a cross-sectional time-course study to determine whether antidepressant-mediated changes in neurotrophic factors occur in relevant brain regions in response to amitriptyline (AMI) treatment before and after intrastriatal 6-hydroxydopamine (6OHDA). Adult male Wistar rats were divided into seven cohorts and given daily injections (i.p.) of AMI (5mg/kg) or saline throughout the duration of the study. In parallel, various cohorts of intact or parkinsonian animals were sacrificed at specific time points to determine the impact of AMI treatment on trophic factor levels in the intact and degenerating nigrostriatal system. The left and right hemispheres of the substantia nigra, striatum, frontal cortex, piriform cortex, hippocampus, and anterior cingulate cortex were dissected, and BDNF and GDNF levels were measured with ELISA. Results show that chronic AMI treatment elicits effects in multiple brain regions and differentially regulates levels of BDNF and GDNF depending on the region. Additionally, AMI halts the progressive degeneration of dopamine (DA) neurons elicited by an intrastriatal 6-OHDA lesion. Taken together, these results suggest that AMI treatment elicits significant trophic changes important to DA neuron survival within both the intact and degenerating nigrostriatal system.

Neural tissue transplantation, repair, and rehabilitation

Transplants of cells and tissues to the central nervous system of adult mammals can, under appropriate conditions, survive, integrate, and function. In particular, the grafted cells can sustain functional recovery in animal models of a range of neurodegenerative conditions including genetic and idiopathic neurodegenerative diseases of adulthood and aging, ischemic stroke, and brain and spinal cord trauma. In a restricted subset of such conditions, cell transplantation has progressed to application in humans in early-stage clinical trials. At the present stage of play, there is clear evidence of clinical efficacy of fetal cell transplants in Parkinson disease (notwithstanding a range of technical difficulties still to be fully resolved), and preliminary claims of promising outcomes in several other severe neurodegenerative conditions, including Huntington disease and stroke. Moreover, the experimental literature is increasingly suggesting that the experience and training of the graft recipient materially affects the functional outcome. For example, environmental enrichment, behavioral activity, and specific training can enhance the recovery process to maximize functional recovery. There are even circumstances where the grafted cells have been demonstrated to restore the neural substrate for new learning. Consequently, it is not sufficient to replace lost cells anatomically; rather, for the grafts to be effective, they need to be integrated functionally into the host circuitry, and the host animal requires training and rehabilitation to maximize function of the reconstructed graft-host circuitry. Such observations require reconsideration of the design of the next generation of clinical trials and subsequent service delivery, to include physiotherapists, cognitive therapists, and rehabilitation experts as core members of the transplant team, along with the neurologists and neurosurgeons that have conventionally led the field.

Directing dopaminergic fiber growth along a preformed molecular pathway from embryonic ventral mesencephalon transplants in the rat brain

To identify guidance molecules to promote long-distance growth of dopaminergic axons from transplanted embryonic ventral mesencephalon (VM) tissue, three pathways were created by expressing green fluorescent protein (GFP), glial cell line-derived neurotrophic factor (GDNF), or a combination of GDNF/GDNF receptor α1 (GFRα1) along the corpus callosum. To generate the guidance pathway, adenovirus encoding these transcripts was injected at four positions along the corpus callosum. In all groups, GDNF adenovirus was also injected on the right side 2.5 mm from the midline at the desired transplant site. Four days later, a piece of VM tissue from embryonic day 14 rats was injected at the transplant site. All rats also received daily subcutaneous injections of N-acetyl-L-cysteinamide (NACA; 100 μg per rat) as well as chondroitinase ABC at transplant site (10 U/ml, 2 μl). Two weeks after transplantation, the rats were perfused and the brains dissected out. Coronal sections were cut and immunostained with antibody to tyrosine hydroxylase (TH) to identify and count dopaminergic fibers in the corpus callosum. In GFP-expressing pathways, TH(+) fibers grew out of the transplants for a short distance in the corpus callosum. Very few TH(+) fibers grew across the midline. However, pathways expressing GDNF supported more TH(+) fiber growth across the midline into the contralateral hemisphere. Significantly greater numbers of TH(+) fibers grew across the midline in animals expressing a combination of GDNF and GFRα1 in the corpus callosum. These data suggest that expression of GDNF or a combination of GDNF and GFRα1 can support the long-distance dopaminergic fiber growth from a VM transplant, with the combination having a superior effect.

Glial cell line-derived neurotrophic factor is crucial for long-term maintenance of the nigrostriatal system

Glial cell line-derived neurotrophic factor (GDNF) is a potent factor for the ventral mesencephalic dopamine neurons. However, studies on the Gdnf gene deleted (Gdnf(-/-)) mouse have been limited to fetal tissue since these mice die prematurely. To evaluate long-term effects of Gdnf gene deletion, this study involves co-grafts of ventral mesencephalon (VM) and lateral ganglionic eminence (LGE) derived from different Gdnf genotypes. The VM/LGE co-grafts were evaluated at 3, 6, and 12 months for tyrosine hydroxylase (TH) -positive cell survival and nerve fiber formation in the LGE co-transplant, visualized by dopamine- and cyclic AMP-regulated phosphoprotein relative molecular mass 32,000 (DARPP-32) -immunoreactivity. Cell counts revealed no difference in TH-positive neurons between Gdnf genotypes at 3 months postgrafting. At 6 months, a significant reduction in cell number was observed in the Gdnf(-/-) grafts. In fact, in the majority of the Gdnf(-/-) VM/LGE transplant had degenerated. At 12 months, a reduction in cell number was seen in both Gdnf(-/-) and Gdnf(+/-) compared to wild type transplants. In the Gdnf(-/-) grafts, TH-negative inclusion-like structures were present in the cytoplasm of the TH-positive neurons at 3 months. These structures were also found in the Gdnf(+/-) transplants at 12 months, but not in Gdnf(+/+) controls at any time point. In Gdnf(+/+) grafts, TH-positive nerve fiber innervation of the striatal co-grafts was dense and patchy and overlapped with clusters of DARPP-32-positive neurons. This overlap did mismatch in the Gdnf(+/-) grafts, while the TH-positive innervation was sparse in the Gdnf(-/-) transplants and the DARPP-32-positive neurons were widespread distributed. In conclusion, GDNF is essential for long-term maintenance of both the VM TH-positive neurons and for the striatal tissue, and appears crucial for generation of a proper organization of the striatum.

Studies of histogenetic and neurodegenerative processes in the nervous system using heterotopic neurotransplantation

The aim of the present article is to summarize our own experimental and published data on neurotransplantation into ectopic sites such as peripheral nerves (mainly) and the anterior chamber of the eye in rats. The review addresses questions touching on the following problems: the histogenesis and survival of nervous tissue after transplantation, the interaction between transplanted tissues with recipient tissues, assessment of long-term living transplants, simultaneous transplantation of different embryonic rudiments, transplantation of spinal cord ganglia, and the effects of trophic factors on the development of transplants. New data on stem cell transplantation into peripheral nerves are discussed.

Future of cell and gene therapies for Parkinson's disease

The experimental field of restorative neurology continues to advance with implantation of cells or transfer of genes to treat patients with neurological disease. Both strategies have generated a consensus that demonstrates their capacity for structural and molecular brain modification in the adult brain. However, both approaches have yet to successfully address the complexities to make such novel therapeutic modalities work in the clinic. Prior experimental cell transplantation to patients with PD utilized dissected pieces of fetal midbrain tissue, containing mixtures of cells and neuronal types, as donor cells. Stem cell and progenitor cell biology provide new opportunities for selection and development of large batches of specific therapeutic cells. This may allow for cell composition analysis and dosing to optimize the benefit to an individual patient. The biotechnology used for cell and gene therapy for treatment of neurological disease may eventually be as advanced as today's pharmaceutical drug-related design processes. Current gene therapy phase 1 safety trials for PD include the delivery of a growth factor (neurturin via the glial cell line-derived neurotrophic factor receptor) and a transmitter enzyme (glutamic acid decarboxylase and aromatic acid decarboxylase). Many new insights from cell biological and molecular studies provide opportunities to selectively express or suppress factors relevant to neuroprotection and improved function of neurons involved in PD. Future gene and cell therapies are likely to coexist with classic pharmacological therapies because their use can be tailored to individual patients' underlying disease process and need for neuroprotective or restorative interventions.

Effects of glial cell line-derived neurotrophic factor deletion on ventral mesencephalic organotypic tissue cultures

Glial cell line-derived neurotrophic factor (GDNF) is potent for survival and promotion of nerve fibers from midbrain dopamine neurons. It is also known to exert different effects on specific subpopulations of dopamine neurons. In organotypic tissue cultures, dopamine neurons form two diverse nerve fiber growth patterns, targeting the striatum differently. The aim of this study was to investigate the effect of GDNF on the formation of dopamine nerve fibers. Organotypic tissue cultures of ventral mesencephalon of gdnf gene-deleted mice were studied. The results revealed that dopamine neurons survive in the absence of GDNF. Tyrosine hydroxylase immunoreactivity demonstrated, in gdnf knockout and wildtype cultures, nerve fiber formation with two separate morphologies occurring either in the absence or the presence of astrocytes. The outgrowth that occurred in the absence of astrocytes was unaffected by gdnf deletion, whereas nerve fibers guided by the presence of astrocytes were affected in that they reached significantly shorter distances from the gdnf gene-deleted tissue slice, compared to those measured in wildtype cultures. Treatment with GDNF reversed this effect and increased nerve fiber density independent of genotype. Furthermore, migration of astrocytes reached significantly shorter distances from the tissue slice in GDNF knockout compared to wildtype cultures. Exogenous GDNF increased astrocytic migration in gdnf gene-deleted tissue cultures, comparable to lengths observed in wildtype tissue cultures. In conclusion, cultured midbrain dopamine neurons survive in the absence of GDNF, and the addition of GDNF improved dopamine nerve fiber formation - possibly as an indirect effect of astrocytic stimulation.

2-DE profiling of GDNF overexpression-related proteome changes in differentiating ST14A rat progenitor cells

Targeted differentiation of neural progenitor cells (NPCs) is a challenge for treatment of neurodegenerative diseases by cell replacement therapy and cell signalling manipulation. Here, we applied a proteome profiling approach to the rat striatal progenitor model cell line ST14A in order to elucidate cellular differentiation processes. Native cells and cells transfected with the glial cell line-derived neurotrophic factor (GDNF) gene were investigated at the proliferative state and at seven time points up to 72 h after induction of differentiation. 2-DE combined with MALDI-MS was used to create a reference 2-DE-map of 652 spots of which 164 were identified and assigned to 155 unique proteins. For identification of protein expression changes during cell differentiation, spot patterns of triplicate gels were matched to the 2-DE-map. Besides proteins that display expression changes in native cells, we also noted 43 protein-spots that were differentially regulated by GDNF overexpression in more than four time points of the experiment. The expression patterns of putative differentiation markers such as annexin 5 (ANXA5), glucosidase II beta subunit (GLU2B), phosphatidylethanolamine-binding protein 1 (PEBP1), myosin regulatory light chain 2-A (MLRA), NASCENT polypeptide-associated complex alpha (NACA), elongation factor 2 (EF2), peroxiredoxin-1 (PRDX1) and proliferating cell nuclear antigen (PCNA) were verified by Western blotting. The results reflect the large rearrangements of the proteome during the differentiation process of NPCs and their strong modification by neurotrophic factors like GDNF.

Induction of Midbrain Dopaminergic Neurons from Primate Embryonic Stem Cells by Coculture with Sertoli Cells

The aim of this study was to produce dopaminergic neurons from primate embryonic stem (ES) cells following coculture with mouse Sertoli cells. After 3 weeks of induction, immunostaining revealed that 90% +/- 9% of the colonies contained tyrosine hydroxylase-positive (TH(+)) neurons, and 60% +/- 7% of the tubulin beta III-positive (Tuj III(+)) neurons were TH(+). Reverse transcription-polymerase chain reaction analyses showed that Sertoli-induced neurons expressed midbrain dopaminergic neuron markers, including TH, dopamine transporter, aromatic amino acid decarboxylase (AADC), receptors such as TrkB and TrkC, and transcription factors NurrI and Lmx1b. Neurons that had been differentiated on Sertoli cells were positive for Pax2, En1, and AADC, midbrain-related markers, and negative for dopamine-beta-hydroxylase, a marker of noradrenergic neurons. These Sertoli cell-induced dopaminergic cells can release dopamine when depolarized by high K(+). Sertoli cell-conditioned medium contained glial cell line-derived neurotrophic factor (GDNF) and supported neuronal differentiation. After pretreatment with anti-GDNF antibody, the percentage of Tuj III(+) colonies was reduced to 14%. Thus, GDNF contributed significantly to inducing primate ES cells into dopaminergic neurons. When transplanted into a 6-hydroxydopamine-treated Parkinson's disease model, primate-derived dopaminergic neurons integrated into the mouse striatum. Two weeks after transplantation, surviving TH(+) cells were present. These TH(+) cells survived for 2 months. Therefore, the induction method of coculture ES cells with Sertoli cells provides an unlimited source of primate cells for the study of pathogenesis and transplantation in Parkinson's disease.

Delivery of neurotrophic factors and therapeutic proteins for retinal diseases

Neurotrophic factors have the ability to protect and initiate growth of neurons. In the central nervous system, neurotrophic factors are neuroprotective in a wide range of disease states. Similarly, disease pathologies of the neurosensory retina respond favourably in animal models of retinitis pigmentosa, macular degeneration, glaucoma and others. With advances in drug delivery and cell therapy, an almost universal increase in efficacy is being realised. Now, repeated injections of neurotrophic factors are being replaced by controlled delivery of cell-mediated factor secretion, reducing the number of potential acute side effects. Tissue engineering strategies in conjunction with gene-modulated protein therapy or gene transfer are creating a unique treatment niche and are quickly gaining acclaim in the clinic. This review surveys the founding and current work on neurotrophic factors such as CNTF, BDNF, GDNF, LEDGF, PEDF and others. Ongoing clinical trials and successful preclinical studies are summarised as well.

Dissociation between short-term increased graft survival and long-term functional improvements in Parkinsonian rats overexpressing glial cell line-derived neurotrophic factor

The present study was designed to analyse whether continuous overexpression of glial cell line-derived neurotrophic factor (GDNF) in the striatum by a recombinant lentiviral vector can provide improved cell survival and additional long-term functional benefits after transplantation of fetal ventral mesencephalic cells in Parkinsonian rats. A four-site intrastriatal 6-hydroxydopamine lesion resulted in an 80-90% depletion of nigral dopamine cells and striatal fiber innervation, leading to stable motor impairments. Histological analysis performed at 4 weeks after grafting into the GDNF-overexpressing striatum revealed a twofold increase in the number of surviving tyrosine hydroxylase (TH)-positive cells, as compared with grafts placed in control (green fluorescent protein-overexpressing) animals. However, in animals that were allowed to survive for 6 months, the numbers of surviving TH-positive cells in the grafts were equal in both groups, suggesting that the cells initially protected at 4 weeks failed to survive despite the continued presence of GDNF. Although cell survival was similar in both grafted groups, the TH-positive fiber innervation density was lower in the GDNF-treated grafted animals (30% of normal) compared with animals with control grafts (55% of normal). The vesicular monoamine transporter-2-positive fiber density in the striatum, by contrast, was equal in both groups, suggesting that long-term GDNF overexpression induced a selective down-regulation of TH in the grafted dopamine neurons. Behavioral analysis in the long-term grafted animals showed that the control grafted animals improved their performance in spontaneous motor behaviors to approximately 50% of normal, whereas the GDNF treatment did not provide any additional recovery.

Hydrophobic dipeptide Leu-Ile protects against neuronal death by inducing brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor synthesis

We investigated whether certain hydrophobic dipeptides, Leu-Ile, Leu-Pro, and Pro-Ile, which partially resemble the site on FK506 that binds to immunophilin, could stimulate glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) synthesis in cultured neurons and found only Leu-Ile to be an active dipeptide. Leu-Ile protected against the death of mesencephalic neurons from wild-type mice but not from mice lacking the BDNF or GDNF gene. Next, we examined the effects of i.p. or i.c.v. administration of Leu-Ile on BDNF and GDNF contents. Both types of administration increased the contents of BDNF and GDNF in the striatum of mice. Also, peripheral administration of Leu-Ile inhibited dopaminergic (DA) denervation caused by unilateral injection of 6-hydroxydopamine (6-OHDA) into the striatum of mice. The number of rotations following a methamphetamine challenge was lower in the Leu-Ile-treated group than in the nontreated group. Next, we compared the calcineurin activity and immunosuppressant activity of Leu-Ile with those of FK506. Leu-Ile was not inhibitory toward calcineurin cellular activity in cultured neuronal cells. Furthermore, Leu-Ile did not suppress concanavalin A (ConA)-induced synthesis/secretion of interleukin-2 by cultured spleen cells, suggesting that the immunosuppressant activity of Leu-Ile may be negligible when used as a therapeutic tool for neurodegenerative diseases.

Olfactory ensheathing cell transplantation restores functional deficits in rat model of Parkinson's disease: a cotransplantation approach with fetal ventral mesencephalic cells

Different strategies have been worked out to promote survival of transplanted fetal ventral mesencephalic cells (VMCs) using trophic and nontrophic support. Olfactory ensheathing cells (OECs) express high level of growth factors including NGF, bFGF, GDNF, and NT3, which are known to play important role in functional restoration or neurodegeneration. In the present investigation, an attempt has been made to study functional restoration in 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease (PD) following cotransplantation of VMC and OECs (cultured from olfactory bulb, OB) in striatal region. The functional restoration was assessed using neurobehavioral, neurochemical, and immunohistochemical approach. At 12 weeks, post-transplantation, a significant recovery (P < 0.001) in D-amphetamine induced circling behavior (73%), and spontaneous locomotor activity (SLA, 81%) was evident in cotransplanted animals when compared with 6-OHDA-lesioned animals. A significant restoration (P < 0.001) in [3H]-spiperone binding (77%), dopamine (DA) (82%) and 3,4-dihydroxy phenyl acetic acid (DOPAC) level (75%) was observed in animals cotransplanted with OECs and VMC in comparison to lesioned animals. A significantly high expression and quantification of tyrosine hydroxylase (TH)-positive cells in cotransplanted animals further confirmed the supportive role of OECs in viability of transplanted dopaminergic cells, which in turn may be helping in functional restoration. This was further substantiated by our observation of enhanced TH immunoreactivity and differentiation in VMC cocultured with OECs under in vitro conditions as compared to VMC alone cultures. The results suggest that cotransplantation of OECs and VMC may be a better approach for functional restoration in 6-OHDA-induced rat model of Parkinson's disease.

Overexpression of glial cell line-derived neurotrophic factor induces genes regulating migration and differentiation of neuronal progenitor cells

The glial cell line-derived neurotrophic factor (GDNF) is involved in the development and maintenance of neural tissues. Mutations in components of its signaling pathway lead to severe migration deficits of neuronal crest stem cells, tumor formation, or ablation of the urinary system. In animal models of Parkinson's disease, GDNF has been recognized to be neuroprotective and to improve motor function when delivered into the cerebral ventricles or into the substantia nigra. Here, we characterize the network of 43 genes induced by GDNF overproduction of neuronal progenitor cells (ST14A), which mainly regulate migration and differentiation of neuronal progenitor cells. GDNF down-regulates doublecortin, Paf-ah1b (Lis1), dynamin, and alpha-tubulin, which are involved in neocortical lamination and cytoskeletal reorganization. Axonal guidance depends on cell-surface molecules and extracellular matrix proteins. Laminin, Mpl3, Alcam, Bin1, Id1, Id2, Id3, neuregulin1, the ephrinB2-receptor, neuritin, focal adhesion kinase (FAK), Tc10, Pdpk1, clusterin, GTP-cyclooxygenase1, and follistatin are genes up-regulated by GDNF overexpression. Moreover, we found four key enzymes of the cholesterol-synthesis pathway to be down-regulated leading to decreased farnesyl-pyrophospate production. Many proteins are anchored by farnesyl-derivates at the cell membrane. The identification of these GDNF-regulated genes may open new opportunities for directly influencing differentiation and developmental processes of neurons.

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

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

Toward full restoration of synaptic and terminal function of the dopaminergic system in Parkinson's disease by stem cells

New therapeutic nonpharmacological methodology in Parkinson's disease (PD) involves cell and synaptic renewal or replacement to restore function of neuronal systems, including the dopaminergic (DA) system. Using fetal DA cell therapy in PD patients and laboratory models, it has been demonstrated that functional motor deficits associated with parkinsonism can be reduced. Similar results have been observed in animal models with stem cell-derived DA neurons. Evidence obtained from transplanted PD patients further shows that the underlying disease process does not destroy transplanted fetal DA cells, although degeneration of the host nigrostriatal system continues. The optimal DA cell regeneration system would reconstitute a normal neuronal network capable of restoring feedback-controlled release of DA in the nigrostriatal system. The success of cell therapy for PD is limited by access to preparation and development of highly specialized dopaminergic neurons found in the A9 and A10 region of the substantia nigra pars compacta as well as the technical and surgical steps associated with the transplantation procedure. Recent laboratory work has focused on using stem cells as a starting point for deriving the optimal DA cells to restore the nigrostriatal system. Ultimately, understanding the cell biological principles necessary for generating functional DA neurons can provide many new avenues for better treatment of patients with PD.

Neurospheres modified to produce glial cell line-derived neurotrophic factor increase the survival of transplanted dopamine neurons

Glial cell line-derived neurotrophic factor (GDNF) has been shown to increase the survival of dopamine neurons in a variety of in vitro and in vivo model systems. Therefore, it constitutes an important therapeutic protein with the potential to ameliorate dopamine neuronal degeneration in Parkinson's disease or to support dopamine neuronal replacement strategies. However, biophysical and practical considerations present obstacles for the direct delivery of the GDNF protein to CNS neurons. Here we show that rodent neural precursor cells isolated and expanded in culture as neurospheres (NS) can be genetically modified to express green fluorescent protein (GFP) or to release GDNF using lentiviral constructs. GDNF-NS increased the fibre outgrowth of primary embryonic dopamine neurons in cocultures, showing that the protein was released in biologically significant quantities. Furthermore, after transplantation into the 6-hydroxydopamine-lesioned rat striatum, GDNF-NS significantly increased the survival of cografted primary dopamine neurons. However, this was not reflected in behavioural recovery in these animals. We found that, by 6 weeks, few cells expressed GDNF or GFP, suggesting either that transgene expression was down-regulated over time or that the cells died. This may explain the initial effects on dopamine neuronal survival within the graft but the lack of long-term effect on subsequent fibre outgrowth and behaviour. Providing sustained levels of neural precursor-mediated transgene expression can be achieved following transplantation in the future; this approach may prove beneficial as an alternative therapeutic strategy in the cell-based management of Parkinson's disease.

Additive effect of glial cell line-derived neurotrophic factor and neurotrophin-4/5 on rat fetal nigral explant cultures

Transplantation of embryonic dopaminergic neurons is an experimental therapy for Parkinson's disease, but limited tissue availability and suboptimal survival of grafted dopaminergic neurons impede more widespread clinical application. Glial cell line-derived neurotrophic factor (GDNF) and neurotrophin-4/5 (NT-4/5) exert neurotrophic effects on dopaminergic neurons via different receptor systems. In this study, we investigated possible additive or synergistic effects of combined GDNF and NT-4/5 treatment on rat embryonic (embryonic day 14) nigral explant cultures grown for 8 days. Contrary to cultures treated with GDNF alone, cultures exposed to NT-4/5 and GDNF+NT-4/5 were significantly larger than controls (1.6- and 2.0-fold, respectively) and contained significantly more protein (1.6-fold). Treatment with GDNF, NT-4/5 and GDNF+NT-4/5 significantly increased dopamine levels in the culture medium by 1.5-, 2.5- and 4.7-fold, respectively, compared to control levels, and the numbers of surviving tyrosine hydroxylase-immunoreactive neurons increased by 1.7-, 2.1-, and 3.4-fold, respectively. Tyrosine hydroxylase enzyme activity was moderately increased in all treatment groups compared to controls. Counts of nigral neurons containing the calcium-binding protein, calbindin-D28k, revealed a marked increase in these cells by combined GDNF and NT-4/5 treatment. Western blots for neuron-specific enolase suggested an enhanced neuronal content in cultures after combination treatment, whereas the expression of glial markers was unaffected. The release of lactate dehydrogenase into the culture medium was significantly reduced for GDNF+NT-4/5-treated cultures only. These results indicate that combined treatment with GDNF and NT4/5 may be beneficial for embryonic nigral donor tissue either prior to, or in conjunction with, intrastriatal transplantation in Parkinson's disease.

Prospects for the treatment of Parkinson's disease using neurotrophic factors

Parkinson's disease (PD) is a debilitating neurodegenerative condition that is characterised by a progressive loss of dopaminergic neurones of the substantia nigra pars compacta (SNpc) and the presence of alpha-synuclein cytoplasmic inclusions (Lewy bodies). Cardinal symptoms include tremor, bradykinesia, and rigidity, although cognitive and autonomic disturbances are not uncommon. Pharmacological treatment targeting the dopaminergic network is relatively effective at ameliorating these symptoms, especially in the early stages of the disease, but none of these therapies are curative and they generate their own problems. As dopaminergic neuronal death in PD occurs in a gradual manner, it is amenable to treatments that can either protect remaining dopaminergic neurones or prevent death of those neurones that have begun to die. Use of neurotrophic factors is a potential candidate, as various factors have been shown to increase dopaminergic neuronal survival in culture and promote survival and axonal growth in animal models of PD. Glial cell line-derived neurotrophic factor (GDNF) is currently the most effective substance that has been intensively studied and shown to have a specific 'dopaminotrophic' effect. This review will therefore focus on studies that have investigated GDNF and discuss the potential for neurotrophic factor treatment in PD.

Cell implantation therapies for Parkinson's disease using neural stem, transgenic or xenogeneic donor cells

A new therapeutic neurological and neurosurgical methodology involves cell implantation into the living brain in order to replace intrinsic neuronal systems, that do not spontaneously regenerate after injury, such as the dopaminergic (DA) system affected in Parkinson's disease (PD) and aging. Current clinical data indicate proof of principle for this cell implantation therapy for PD. Furthermore, the disease process does not appear to negatively affect the transplanted cells, although the patient's endogenous DA system degeneration continues. However, the optimal cells for replacement, such as highly specialized human fetal dopaminergic cells capable of repairing an entire degenerated nigro-striatal system, cannot be reliably obtained or generated in sufficient numbers for a standardized medically effective intervention. Xenogeneic and transgenic cell sources of analogous DA cells have shown great utility in animal models and some promise in early pilot studies in PD patients. The cell implantation treatment discipline, using cell fate committed fetal allo- or xenogeneic dopamine neurons and glia, is currently complemented by research on potential stem cell derived DA neurons. Understanding the cell biological principles and developing methodology necessary to generate functional DA progenitors is currently our focus for obtaining DA cells in sufficient quantities for the unmet cell transplantation need for patients with PD and related disorders.

Neuroimmunophilin ligand enhances neurite outgrowth and effect of fetal dopamine transplants

Neuroimmunophilin ligands have been shown to enhance neurite outgrowth in several neuronal systems in culture, including primary dopaminergic neurons from fetal ventral mesencephalon. We investigated the ability of neuroimmunophilin ligands to enhance outgrowth of transplanted fetal dopamine neurons in vivo. Rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopamine system were transplanted with rat embryonic day 14 ventral mesencephalon into the striatum, then treated orally with a neuroimmunophilin ligand (15mg/kg) or vehicle once per day for 14 days. All transplanted animals regained dopamine function over a 10 week behavioral test period, as indicated by decrease and reversal of amphetamine-induced rotation. In addition, neuroimmunophilin ligand-treated animals showed a more pronounced motor response during the first 10min after amphetamine injection, possibly reflecting increased striatal reinnervation or increased functional capacity. At post-mortem analyses, neuroimmunophilin ligand-treated rats showed a significantly higher density of tyrosine hydroxylase-positive fibers reinnervating the lesioned striatum, both immediately surrounding the transplant (92% of unlesioned density in neuroimmunophilin-treated rats vs 67% of unlesioned levels in vehicle-treated rats) and at some distance from the transplant/host interface. The number of tyrosine hydroxylase-positive cells within the transplants was not different between groups. This study demonstrates that short-term oral administration of a neuroimmunophilin ligand can enhance neurite outgrowth from fetal dopamine neuronal transplants.

Immunophilin ligands and GDNF enhance neurite branching or elongation from developing dopamine neurons in culture

Neurotrophic effects of immunophilin ligands have been shown in animal models of peripheral and central nervous system insult. To investigate the specific growth-promoting effects of these compounds, we examined the effects of various immunophilin ligands on primary dopamine (DA) neurons in culture and compared these with a well-known DA trophic factor, glial cell line-derived neurotrophic factor (GDNF). In neuronal cultures from Embryonic Day 14 ventral mesencephalon, enhanced elongation of DA neurites was observed with immunophilin ligands, which inhibited the phosphatase activity of calcineurin (FK506 and cyclosporin A) when compared to vehicle-treated cultures. This elongation was also observed with GDNF, known to exert its trophic effects through phosphorylation-dependent pathways. In contrast, immunophilin ligands that do not inhibit calcineurin (rapamycin and V-10,367) increased branching of DA neurites, suggesting that elongation is dependent upon maintained phosphorylation while branching is not. In addition, both V-10,367 and rapamycin antagonized the elongation effects of FK506 and induced branching. The antagonism of elongation (and reappearance of branching) illustrates the intrinsic abilities of developing DA neurons to either elongate or branch, but not both. We show that the immunophilin FKBP12 (12-kDa FK506-binding protein) is expressed in ventral mesencephalic neuronal cultures and colocalizes with DA neurons. This work elucidates the specific growth-promoting effects by which GDNF and immunophilin ligands modify developmental growth processes of DA neurons, via their interactions with intracellular targets.

Improved survival of embryonic porcine dopaminergic neurons in coculture with a conditionally immortalized GDNF-producing hippocampal cell line

Transplantation of embryonic nigral tissue is used as an experimental therapy for patients with Parkinson's disease but is hampered by a limited survival rate of dopaminergic neurons. Glial cell line-derived neurotrophic factor (GDNF) is a potent survival factor for nigrostriatal dopaminergic neurons, and the present in vitro study aimed at improving the survival of dopaminergic neurons in porcine mesencephalic brain slice cultures by adding transfected, immortalized, temperature-sensitive GDNF-releasing HiB5 cells (HiB5-GDNF). Embryonic (E27/28) porcine ventral mesencephalic brain slices were placed on membrane inserts in six-well plates with serum-containing medium, and HiB5-GDNF, nontransfected HiB5 cells (HiB5-control), or green fluorescent protein-producing HiB5 cells (HiB5-GFP) were seeded onto each tissue slice. The concentration of GDNF in the coculture medium was 0.49 +/- 0.13 ng/ml at day 9 and 0. 22 +/- 0.05 ng/ml at day 19 (mean +/- SEM) as measured by GDNF ELISA. The decrease in release of GDNF over time was paralleled by a gradual reduction in the number of HiB5-GFP cells expressing the reporter gene (EGFP). At day 12, HPLC analysis revealed that medium from HiB5-GDNF cocultures contained 2.0 times more dopamine than medium from HiB5-control cocultures. At day 21 there was 1.6 times more dopamine. Similar results were obtained for the dopamine metabolite 3,4-dihydroxyphenylacetic acid. At day 21, cell counts showed that HiB5-GDNF cocultures contained 1.5 times more tyrosine hydroxylase immunoreactive neurons than HiB5-control cocultures, which must be compared with a 1.8 fold increase after chronic treatment with rhGDNF (10 ng/ml). In conclusion, the better survival of HiB5-GDNF cocultures is promising for the generation of effective cell lines for local delivery of neurotrophic factors to intracerebral nigral grafts.

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.

Glial cell line-derived neurotrophic factor is essential for postnatal survival of midbrain dopamine neurons

Glial cell line-derived neurotrophic factor (GDNF) is one of the most potent trophic factors that have been identified for midbrain dopamine (DA) neurons. Null mutations for trophic factor genes have been used frequently for studies of the role of these important proteins in brain development. One problem with these studies has been that often only prenatal development can be studied because many of the knockout strains, such as those with GDNF null mutations, will die shortly after birth. In this study, we looked at the continued fate of specific neuronal phenotypes from trophic factor knockout mice beyond the time that these animals die. By transplanting fetal neural tissues from GDNF -/-, GDNF +/-, and wild-type (WT) mice into the brain of adult wild-type mice, we demonstrate that the continued postnatal development of ventral midbrain dopamine neurons is severely disturbed as a result of the GDNF null mutation. Ventral midbrain grafts from -/- fetuses have markedly reduced DA neuron numbers and fiber outgrowth. Moreover, DA neurons in such transplants can be "rescued" by immersion in GDNF before grafting. These findings suggest that postnatal survival and/or phenotypic expression of ventral mesencephalic DA neurons is dependent on GDNF. In addition, we present here a strategy for studies of maturation and even aging of tissues from trophic factor and other knockout animals that do not survive past birth.

Exposure of foetal mesencephalic cells to bone morphogenetic protein-2 enhances the survival of dopaminergic neurones in rat striatal grafts

The transplantation of foetal mesencephalic cells (FMC) into the brain striatal system is an emerging treatment for Parkinson's disease, despite of the relatively poor survival of implanted cells. The ability of neurotrophic factors to regulate neurone survival and differentiation suggests they could be used to enhance the success of cerebral grafts. We analyzed the effect of pre-treatment of FMC suspensions with bone morphogenetic protein-2 (BMP-2) (50 ng/ml) prior to grafting into the striatum of 6-hydroxydopamine lesioned rats. The viability of a FMC suspension was enhanced in vitro by BMP-2. Four weeks after transplantation, the number of dopaminergic neurones was higher and their morphology more developed in grafts pre-treated with BMP-2, compared with non-pre-treated grafts and rats showed a significant reduction in the turning behaviour test. Thus, the pre-treatment of FMCs with BMP-2 should be considered, together with other neurotrophic factors, as a procedure for transplantational treatment of Parkinson's disease.

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

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

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

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

Lack of effect of short-term depletion of plasma complement C3 on the survival of syngeneic dopaminergic neurons following grafting into the intact rat striatum

Metabolically compromised cells may be subject to complement-mediated cytotoxicity. The aim of this study was to clarify to what extent plasma complement C3 might contribute to the low survival (5-20%) of grafted dopaminergic neurons. The survival of intrastriatal cell suspension grafts of syngeneic dopaminergic, tyrosine hydroxylase (TH)-containing neurons was compared in rats subjected to short-term i.v. treatment with 1) cobra venom factor (CVF), or 2) placebo treatment. Depletion of plasma complement C3 by CVF was confirmed by crossed immunoelectrophoresis. With 159 +/- 37 (mean +/- SEM) TH-immunoreactive and 154 + /- 40 TH mRNA-expressing neurons in the CVF-treated rats (n = 9), and 117 +/- 34 TH-immunoreactive and 160 +/- 49 TH mRNA-expressing neurons in placebo rats (n = 6), the CVF treatment did not increase the survival of the grafted dopaminergic neurons. Similarly, CVF had no apparent effect on the astroglial, microglial, or oligodendroglial cell response within and around the graft. The data indicate that depletion of plasma complement C3 at the time of grafting has no effect on the long-term survival of syngeneic ventral mesencephalic dopaminergic neuronal grafts.

Differential effects of glial cell line-derived neurotrophic factor and neurturin on developing and adult substantia nigra dopaminergic neurons

Neurturin (NTN) and glial cell line-derived neurotrophic factor (GDNF), two members of the GDNF family of growth factors, exert very similar biological activities in different systems, including the substantia nigra. Our goal in the present work was to compare their function and define whether nonoverlapping biological activities on midbrain dopaminergic neurons exist. We first found that NTN and GDNF are differentially regulated during postnatal development. NTN mRNA progressively decreased in the ventral mesencephalon and progressively increased in the striatum, coincident with a decrease in GDNF mRNA expression. This finding suggested distinct physiological roles for each factor in the nigrostriatal system. We therefore examined their function in ventral mesencephalon cultures and found that NTN promoted survival comparable with GDNF, but only GDNF induced sprouting and hypertrophy of developing dopaminergic neurons. We subsequently examined the ability of NTN to prevent the 6-hydroxydopamine-induced degeneration of adult dopaminergic neurons in vivo. Fibroblasts genetically engineered to deliver high levels of GDNF or NTN were grafted supranigrally. NTN was found to be as potent as GDNF at preventing the death of nigral dopaminergic neurons, but only GDNF induced tyrosine hydroxylase staining, sprouting, or hypertrophy of dopaminergic neurons. In conclusion, our results show selective survival-promoting effects of NTN over wider survival, neuritogenic, and hypertrophic effects of GDNF on dopaminergic neurons in vitro and in vivo. Such differences are likely to underlie unique roles for each factor in postnatal development and may ultimately be exploited in the treatment of Parkinson's disease.

A glial cell line-derived neurotrophic factor-secreting clone of the Schwann cell line SCTM41 enhances survival and fiber outgrowth from embryonic nigral neurons grafted to the striatum and to the lesioned substantia nigra

We have developed a novel Schwann cell line, SCTM41, derived from postnatal sciatic nerve cultures and have stably transfected a clone with a rat glial cell line-derived neurotrophic factor (GDNF) construct. Coculture with this GDNF-secreting clone enhances in vitro survival and fiber growth of embryonic dopaminergic neurons. In the rat unilateral 6-OHDA lesion model of Parkinson's disease, we have therefore made cografts of these cells with embryonic day 14 ventral mesencephalic grafts and assayed for effects on dopaminergic cell survival and process outgrowth. We show that cografts of GDNF-secreting Schwann cell lines improve the survival of intrastriatal embryonic dopaminergic neuronal grafts and improve neurite outgrowth into the host neuropil but have no additional effect on amphetamine-induced rotation. We next looked to see whether bridge grafts of GDNF-secreting SCTM41 cells would promote the growth of axons to their striatal targets from dopaminergic neurons implanted orthotopically into the 6-OHDA-lesioned substantia nigra. We show that such bridge grafts increase the survival of implanted embryonic dopaminergic neurons and promote the growth of axons through the grafts to the striatum.

GDNF increases the density of cells containing calbindin but not of cells containing calretinin in cultured rat and human fetal nigral tissue

Among the dopaminergic neurons in substantia nigra pars compacta and in the ventral tegmental area, subpopulations express the calcium-binding proteins calbindin (CB) and calretinin (CR), and the CB-containing neurons are supposed to be less prone to degeneration in Parkinson's disease. Glial cell line-derived neurotrophic factor (GDNF) is a potent survival factor for nigrostriatal dopaminergic neurons. Using free-floating roller-tube (FFRT) cultures derived from fetal rat (E14) ventral mesencephalon we found that GDNF (10 ng/ml) significantly increased the number of surviving tyrosine hydroxylase (TH)-immunoreactive neurons. The possible effects of GDNF treatment on CB-immunoreactive (CB-ir) and CR-ir neurons in such cultures were examined in the present study. The neuronal cell densities were measured by quantifying the numbers of CB-ir and CR-ir neurons in areas of sections through the most extensive parts of the spherical cultures. In 4-day-old and 8-day-old cultures GDNF treatment increased the density of CB-ir neurons by 50% and 59%, respectively. Partial co-existence of TH and CB was shown using the method of double immunolabeling. The density of CR-containing neurons was unaffected by GDNF treatment as confirmed by Western blotting for CR. Parallel effects of GDNF treatment were obtained for cultures of human fetal ventral mesencephalon (8 weeks postconception). In conclusion, our findings identify GDNF as a potent factor for fetal rat and human nigral CB-ir neurons able to promote their survival in culture. Referring to a suggested neuroprotective role of CB, the results may be of relevance in the context of neuronal transplantation of patients suffering from severe Parkinson's disease.

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.

Glial cell line-derived neurotrophic factor improves survival of dopaminergic neurons in transplants of fetal ventral mesencephalic tissue

This study was designed to determine whether or not an exogenous source of glial cell line-derived neurotrophic factor (GDNF) could be delivered continuously into the denervated/transplanted striatum and stimulate the survival, growth, and function of fetal ventral mesencephalic tissue transplants. Adult male rats with unilateral 6-hydroxydopamine lesions received transplants of fetal ventral mesencephalic tissue into the denervated striatum. Immediately thereafter, osmotic pumps [Alzet 2002, 0.5 microliter/h] were attached to intracerebral cannula and either a citrate buffer alone [control] or r-methuGDNF [dissolved in sodium citrate buffer to a concentration of 0.45 microgram/microliter] was infused into a site approximately 1.0 mm lateral to the transplant for a 2-week period; one group of lesioned animals did not receive transplants but was infused with GDNF. The effect of GDNF on tyrosine hydroxylase-positive (TH+) fiber outgrowth from transplants was variable, and image analysis revealed no significant difference between the GDNF and citrate groups. In contrast, the mean number of TH+ cells bodies in transplants infused with GDNF [2,037 +/- 149, n = 8] vs citrate [663 +/- 160, n = 8] was statistically significant (P < 0.001); cell counts were made in every third brain section [35 micrometer]. Similarly, transplants infused with GDNF showed an over-compensatory effect to amphetamine-induced rotational behavior that was significantly lower than that observed in transplanted animals receiving citrate buffer infusions. Infusions of GDNF into the denervated striatum alone had no significant effect on amphetamine-induced rotational behavior or on TH fiber morphology in the lesioned striatum. Thus, a continuous infusion of GDNF can improve the survivability of dopaminergic neurons in transplants of fetal ventral mesencephalic tissue.

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

OBJECT

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

METHODS

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

CONCLUSIONS

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

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

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

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

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

Intrastriatal glial cell line-derived neurotrophic factor promotes sprouting of spared nigrostriatal dopaminergic afferents and induces recovery of function in a rat model of Parkinson's disease

The ability of intrastriatally-administered glial cell line-derived neurotrophic factor to induce reinnervation and functional recovery in the partially-lesioned nigrostriatal dopamine system was explored in rats subjected to an axon terminal lesion induced by injection of 6-hydroxydopamine into the striatum. Glial cell line-derived neurotrophic factor was administered as multiple intrastriatal injections (10 x 5 micrograms) over a three-week period starting four weeks after the 6-hydroxydopamine injection, i.e. at the time when the acute phase of degeneration of the nigral dopamine neurons is complete. In the control group the lesion induced a 75-90% reduction of the dopaminergic innervation in the dorsolateral striatum (assessed by [3H]N-[1-(2-benzo(b)thiopenyl)cyclohexyl]piperidine-labelled dopamine uptake sites), and an approximately 50% reduction in the number of tyrosine hydroxylase-positive cell bodies in the central part of the substantia nigra, accompanied by a significant impairment in spontaneous motor behaviour, as assessed by a forelimb stepping test. In the glial cell line-derived neurotrophic factor-treated animals striatal [3H]N-[1-(2-benzo(b)thiopenyl)cyclohexyl]piperidine binding was restored to 70-95% of normal and contralateral forelimb stepping was completely normalized. The extent of striatal denervation in the individual lesioned and treated animals was well correlated with the performance of the affected limb in the stepping test. These results show that intrastriatal glial cell line-derived neurotrophic factor can stimulate substantial axonal sprouting and reinnervation of the partially deafferated striatum to a degree sufficient to reverse the lesion-induced deficit in spontaneous motoric behaviour, indicating that a direct action of glial cell line-derived neurotrophic factor on spared dopaminergic afferents in the striatum may be important for functional recovery in the rat Parkinson model.

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

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