Glial cell line-derived neurotrophic factor attenuates the excitotoxin-induced behavioral and neurochemical deficits in a rodent model of Huntington's disease

New Avenues for the Treatment of Huntington's Disease

Huntington’s disease (HD) is a neurodegenerative disorder caused by a CAG expansion in the HD gene. The disease is characterized by neurodegeneration, particularly in the striatum and cortex. The first symptoms usually appear in mid-life and include cognitive deficits and motor disturbances that progress over time. Despite being a genetic disorder with a known cause, several mechanisms are thought to contribute to neurodegeneration in HD, and numerous pre-clinical and clinical studies have been conducted and are currently underway to test the efficacy of therapeutic approaches targeting some of these mechanisms with varying degrees of success. Although current clinical trials may lead to the identification or refinement of treatments that are likely to improve the quality of life of those living with HD, major efforts continue to be invested at the pre-clinical level, with numerous studies testing novel approaches that show promise as disease-modifying strategies. This review offers a detailed overview of the currently approved treatment options for HD and the clinical trials for this neurodegenerative disorder that are underway and concludes by discussing potential disease-modifying treatments that have shown promise in pre-clinical studies, including increasing neurotropic support, modulating autophagy, epigenetic and genetic manipulations, and the use of nanocarriers and stem cells.

On the Right Track to Treat Movement Disorders: Promising Therapeutic Approaches for Parkinson's and Huntington's Disease

Movement disorders are neurological conditions in which patients manifest a diverse range of movement impairments. Distinct structures within the basal ganglia of the brain, an area involved in movement regulation, are differentially affected for every disease. Among the most studied movement disorder conditions are Parkinson's (PD) and Huntington's disease (HD), in which the deregulation of the movement circuitry due to the loss of specific neuronal populations in basal ganglia is the underlying cause of motor symptoms. These symptoms are due to the loss principally of dopaminergic neurons of the substantia nigra (SN) par compacta and the GABAergic neurons of the striatum in PD and HD, respectively. Although these diseases were described in the 19th century, no effective treatment can slow down, reverse, or stop disease progression. Available pharmacological therapies have been focused on preventing or alleviating motor symptoms to improve the quality of life of patients, but these drugs are not able to mitigate the progressive neurodegeneration. Currently, considerable therapeutic advances have been achieved seeking a more efficacious and durable therapeutic effect. Here, we will focus on the new advances of several therapeutic approaches for PD and HD, starting with the available pharmacological treatments to alleviate the motor symptoms in both diseases. Then, we describe therapeutic strategies that aim to restore specific neuronal populations or their activity. Among the discussed strategies, the use of Neurotrophic factors (NTFs) and genetic approaches to prevent the neuronal loss in these diseases will be described. We will highlight strategies that have been evaluated in both Parkinson's and Huntington's patients, and also the ones with strong preclinical evidence. These current therapeutic techniques represent the most promising tools for the safe treatment of both diseases, specifically those aimed to avoid neuronal loss during disease progression.

Focused ultrasound-induced blood brain-barrier opening enhanced vascular permeability for GDNF delivery in Huntington's disease mouse model

BACKGROUND

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG trinucleotide repeat expansion in the gene encoding the huntingtin (Htt) protein, which results in a protein containing an abnormally expanded polyglutamine (polyQ) sequence. The expanded polyQ in the Htt protein is toxic to brain cells. No therapy exists to delay disease progression.

METHODS

This study describes a gene-liposome system that synergistically applied focused ultrasound (FUS)-blood-brain barrier (BBB) opening for rescuing motor and neuropathological impairments when administered from pre to post-symptomatic transgenic mouse models of HD. DPPC liposomes (LPs) are designed to carry glia cell line-derived neurotrophic factor (GDNF) plasmid DNA (GDNFp) to form a GDNFp-liposome (GDNFp-LPs) complex. Pulsed FUS exposure with microbubbles (MBs) was used to induce BBB opening for non-viral, non-invasive, and targeted gene delivery into the central nervous system (CNS) for therapeutic purposes.

RESULTS

FUS-gene therapy significantly improved motor performance with GDNFp-LPs + FUS treated HD mice equilibrating longer periods in the animal behavior. Reflecting the improvements observed in motor function, GDNF overexpression results in significantly decreased formation of polyglutamine-expanded aggregates, reduced oxidative stress and apoptosis, promoted neurite outgrowth, and improved neuronal survival. Immunoblotting and histological staining further confirmed the neuroprotective effect from delivery of GDNF genes to neuronal cells.

CONCLUSIONS

This study suggests that the GDNFp-LPs plus FUS sonication can provide an effective gene therapy to achieve local extravasation and triggered gene delivery for non-invasive in vivo treatment of CNS diseases.

Widespread Striatal Delivery of GDNF from Encapsulated Cells Prevents the Anatomical and Functional Consequences of Excitotoxicity

Methods

Human ARPE-19 cells engineered to secrete high levels of the glial cell line-derived neurotrophic factor (GDNF) were encapsulated into hollow fiber membranes. The devices were implanted into the rat striatum 1 week prior to striatal quinolinic acid injections. Animals were evaluated using a battery of validated motor tests, and histology was performed to determine the extent of GDNF diffusion and associated prevention of neuronal cell loss and behavioral deficits.

Results

Encapsulated cell-based delivery of GDNF produced widespread distribution of GDNF throughout the entire implanted striatum. Stereological estimates of striatal neuron number and volume of lesion size revealed that GDNF delivery resulted in near complete neuroprotection.

Conclusions

Delivery of neurotrophic molecules such as GDNF using encapsulated cells has reached a technological point where clinical evaluation is justified. Because GDNF has been effective in animal models of Parkinson's disease, stroke, epilepsy, and Huntington's disease, among other debilitating neurodegenerative diseases, encapsulated cell-based delivery of GDNF might represent one innovative means of slowing the neural degeneration seen in a myriad of currently untreatable neurological diseases.

Disease Modification Through Trophic Factor Delivery

Huntington's disease (HD) is characterized by a significant loss of striatal neurons that project to the globus pallidus and substantia nigra, together with loss of cortical projection neurons in varying regions. Mutant huntingtin is suggested to drive the pathogenesis partially by downregulating corticostriatal brain-derived neurotrophic factor (BDNF) levels and signaling. Neurotrophic factors are endogenous peptides that promote the survival and maintenance of neurons. BDNF and other neurotrophic factors have shown neuroprotective benefits in various animal models of neurodegeneration, and are interesting candidates to protect the cell populations that are destined to die in HD. In an attempt to enhance the delivery of neurotrophic factors, several methods have been established to deliver long-term neurotrophic factor gene therapy to human target tissues. This chapter discusses two alternative approaches that have been shown to have potential to deliver neurotrophic factors as a neuroprotective gene therapy for HD. The methods are (1) ex vivo approach where encapsulated cells engineered to express neurotrophic factor are inserted into brain parenchyma or ventricle, and (2) in vivo viral vector therapy, in which viral vector is injected into desired brain area to express gene of interest in the host cells.

Rotating and Neurochemical Activity of Rats Lesioned with Quinolinic Acid and Transplanted with Bone Marrow Mononuclear Cells

Huntington’s disease (HD) is an inherited, neurodegenerative disorder that results from the degeneration of striatal neurons, mainly GABAergic neurons. The study of neurochemical activity has provided reliable markers to explain motor disorders. To treat neurodegenerative diseases, stem cell transplants with bone marrow (BM) have been performed for several decades. In this work we determine the effect of mononuclear bone marrow cell (mBMC) transplantation on the rotational behavior and neurochemical activity in a model of Huntington’s disease in rats. Four experimental groups were organized: Group I: Control animals (n = 5); Group II: Lesion with quinolinic acid (QA) in the striatum (n = 5); Group III: Lesion with QA and transplant with mBMC (n = 5); Group IV: Lesion with QA and transplant with culture medium (Dulbecco’s modified Eagle’s medium (DMEM) injection) (n = 5). The rotational activity induced by D-amphetamine was evaluated and the concentration of the neurotransmitter amino acids (glutamate and GABA) was studied. The striatal cell transplantation decreases the rotations induced by D-amphetamine (p < 0.04, Wilcoxon matched pairs test) and improves the changes produced in the levels of neurotransmitters studied. This work suggests that the loss of GABAergic neurons in the brain of rats lesioned with AQ produces behavioral and neurochemical alterations that can be reversed with the use of bone marrow mononuclear cell transplants.

In Vitro Culture Duration does Not Impact the Ability of Encapsulated Choroid Plexus Transplants to Prevent Neurological Deficits in an Excitotoxin-Lesioned Rat Model of Huntington's Disease

Delivery of neurotrophic molecules to the CNS is a potential treatment strategy for preventing the neuronal loss accompanying many neurological disorders. Choroid plexus (CP) epithelial cells secrete a cocktail of neurotrophic factors, and encapsulated CP transplants are neuroprotective in animal models of stroke and Huntington's disease (HD). Prior to clinical use, it is essential to identify and optimize parameters such as the length of time that transplant products such as encapsulated CP can be maintained. In the present study, neonatal porcine CP was encapsulated within alginate microcapsules and maintained in vitro for 1, 2, or 7 months. The encapsulated cells remained viable (>80%) at all time points and were transplanted unilaterally into the rat striatum. Seven days later, the same animals received unilateral injections of quinolinic acid (QA; 225 nmol) adjacent to the implant site. Separate groups of animals served as controls and received QA alone. After surgery, animals were periodically evaluated for weight loss and were tested for motor function 14 days post-QA. In controls, QA lesions produced a significant loss of body weight and impaired function of the contralateral forelimb. In contrast, implants of CP were potently neuroprotective as rats receiving CP transplants did not lose body weight and were not significantly impaired when tested for motor function. These benefits were independent of the length of time that the cells were held in vitro and demonstrate that the potential potency of alginate encapsulated CP cells can be retained for extremely long periods of time in vitro.

Huntington's Disease: Pathological Mechanisms and Therapeutic Strategies

Huntington's disease (HD) is a devastating neurodegenerative disorder that occurs in patients with a mutation in the huntingtin or IT15 gene. Patients are plagued by early cognitive signs, motor deficits, and psychiatric disturbances. Symptoms are attributed to cell death in the striatum and disruption of cortical–striatal circuitry. Mechanisms of cell death are unclear, but processes involving mitochondrial abnormalities, excitotoxicity, and abnormal protein degradation have been implicated. Many factors likely contribute to neuron death and dysfunction, and this has made it difficult to systematically address the pathology in HD. Pharmaceutical therapies are commonly used in patients to treat disease symptoms. These have limited benefit and do not address the inexorable disease progression. Several neuroprotective therapies are being evaluated in animal models of HD as well as in clinical trials. Similarly, cell replacement strategies such as fetal transplantation have been used in the clinic with minimal success, making future cell replacement strategies such as stem cell therapy uncertain. This review describes the disease pathology in HD and addresses many of the past and emerging therapeutic strategies.

Optimal time for subarachnoid transplantation of neural progenitor cells in the treatment of contusive spinal cord injury

This study aimed to identify the optimal neural progenitor cell transplantation time for spinal cord injury in rats via the subarachnoid space. Cultured neural progenitor cells from 14-day embryonic rats, constitutively expressing enhanced green fluorescence protein, or media alone, were injected into the subarachnoid space of adult rats at 1 hour (acute stage), 7 days (subacute stage) and 28 days (chronic stage) after contusive spinal cord injury. Results showed that grafted neural progenitor cells migrated and aggregated around the blood vessels of the injured region, and infiltrated the spinal cord parenchyma along the tissue spaces in the acute stage transplantation group. However, this was not observed in subacute and chronic stage transplantation groups. O4- and glial fibrillary acidic protein-positive cells, representing oligodendrocytes and astrocytes respectively, were detected in the core of the grafted cluster attached to the cauda equina pia surface in the chronic stage transplantation group 8 weeks after transplantation. Both acute and subacute stage transplantation groups were negative for O4 and glial fibrillary acidic protein cells. Basso, Beattie and Bresnahan scale score comparisons indicated that rat hind limb locomotor activity showed better recovery after acute stage transplantation than after subacute and chronic transplantation. Our experimental findings suggest that the subarachnoid route could be useful for transplantation of neural progenitor cells at the acute stage of spinal cord injury. Although grafted cells survived only for a short time and did not differentiate into astrocytes or neurons, they were able to reach the parenchyma of the injured spinal cord and improve neurological function in rats. Transplantation efficacy was enhanced at the acute stage in comparison with subacute and chronic stages.

Effect of glial cell line-derived neurotrophic factor on behavior and key members of the brain serotonin system in mouse strains genetically predisposed to behavioral disorders

The effect of glial cell line-derived neurotrophic factor (GDNF) on behavior and on the serotonin (5-HT) system of a mouse strain predisposed to depressive-like behavior, ASC/Icg (Antidepressant Sensitive Cataleptics), in comparison with the parental "nondepressive" CBA/Lac mice was studied. Within 7 days after acute administration, GDNF (800 ng, i.c.v.) decreased cataleptic immobility but increased depressive-like behavioral traits in both investigated mouse strains and produced anxiolytic effects in ASC mice. The expression of the gene encoding the key enzyme for 5-HT biosynthesis in the brain, tryptophan hydroxylase-2 (Tph-2), and 5-HT1A receptor gene in the midbrain as well as 5-HT2A receptor gene in the frontal cortex were increased in GDNF-treated ASC mice. At the same time, GDNF decreased 5-HT1A and 5-HT2A receptor gene expression in the hippocampus of ASC mice. GDNF failed to change Tph2, 5-HT1A , or 5-HT2A receptor mRNA levels in CBA mice as well as 5-HT transporter gene expression and 5-HT1A and 5-HT2A receptor functional activity in both investigated mouse strains. The results show 1) a GDNF-induced increase in the expression of key genes of the brain 5-HT system, Tph2, 5-HT1A , and 5-HT2A receptors, and 2) significant genotype-dependent differences in the 5-HT system response to GDNF treatment. The data suggest that genetically defined cross-talk between neurotrophic factors and the brain 5-HT system underlies the variability in behavioral response to GDNF.

The cerebrospinal fluid: regulator of neurogenesis, behavior, and beyond

The cerebrospinal fluid (CSF) has attracted renewed interest as an active signaling milieu that regulates brain development, homeostasis, and disease. Advances in proteomics research have enabled an improved characterization of the CSF from development through adulthood, and key neurogenic signaling pathways that are transmitted via the CSF are now being elucidated. Due to its immediate contact with neural stem cells in the developing and adult brain, the CSF's ability to swiftly distribute signals across vast distances in the central nervous system is opening avenues to novel and exciting therapeutic approaches. In this review, we will discuss the development of the choroid plexus-CSF system, and review the current literature on how the CSF actively regulates mammalian brain development, behavior, and responses to traumatic brain injury.

Neurotrophic factors and neurodegenerative diseases: a delivery issue

Neurotrophic factors (NTFs) represent one of the most stimulating challenge in neurodegenerative diseases, due to their potential in neurorestoring and neuroprotection. Despite the large number of proofs-of-concept and evidences of their activity, most of the clinical trials, mainly regarding Parkinson's disease and Alzheimer's disease, demonstrated several failures of the therapeutic intervention. A large number of researches were conducted on this hot topic of neuroscience, clearly evidencing the advantages of NTF approach, but evidencing the major limitations in its application. The inability in crossing the blood-brain barrier and the lack of selectivity actually represent some of the most highlighted limits of NTFs-based therapy. In this review, beside an overview of NTF activity versus the main neuropathological disorders, a summary of the most relevant approaches, from invasive to noninvasive strategies, applied for improving NTF delivery to the central nervous systems is critically considered and evaluated.

Gene therapy for Huntington's disease

Huntington's disease (HD) is a neurodegenerative disease for which there is no cure. Therapies that are efficacious in animal models have to date shown benefit for humans. One potential powerful approach is gene therapy. The ideal method of administration of gene therapy has been hotly debated and viral vectors have provided one method of long-term and wide-spread delivery to the brain. Trophic factors to protect cells from degeneration and RNAi to reduce mutant huntingtin (mHtt) protein expression are 2 main classes of compounds that demonstrate benefit in animal models. This review will examine some commonly used adeno-associated viral (AAV) vectors and discuss some therapies that hold promise for HD.

Adenosine receptors and brain diseases: neuroprotection and neurodegeneration

Adenosine acts in parallel as a neuromodulator and as a homeostatic modulator in the central nervous system. Its neuromodulatory role relies on a balanced activation of inhibitory A(1) receptors (A1R) and facilitatory A(2A) receptors (A2AR), mostly controlling excitatory glutamatergic synapses: A1R impose a tonic brake on excitatory transmission, whereas A2AR are selectively engaged to promote synaptic plasticity phenomena. This neuromodulatory role of adenosine is strikingly similar to the role of adenosine in the control of brain disorders; thus, A1R mostly act as a hurdle that needs to be overcame to begin neurodegeneration and, accordingly, A1R only effectively control neurodegeneration if activated in the temporal vicinity of brain insults; in contrast, the blockade of A2AR alleviates the long-term burden of brain disorders in different neurodegenerative conditions such as ischemia, epilepsy, Parkinson's or Alzheimer's disease and also seem to afford benefits in some psychiatric conditions. In spite of this qualitative agreement between neuromodulation and neuroprotection by A1R and A2AR, it is still unclear if the role of A1R and A2AR in the control of neuroprotection is mostly due to the control of glutamatergic transmission, or if it is instead due to the different homeostatic roles of these receptors related with the control of metabolism, of neuron-glia communication, of neuroinflammation, of neurogenesis or of the control of action of growth factors. In spite of this current mechanistic uncertainty, it seems evident that targeting adenosine receptors might indeed constitute a novel strategy to control the demise of different neurological and psychiatric disorders.

Injectable hydrogels providing sustained delivery of vascular endothelial growth factor are neuroprotective in a rat model of Huntington's disease

Vascular endothelial growth factor (VEGF) is a potent peptide with well-documented pro-angiogenic effects. Recently, it has also become clear that exogenous administration of VEGF is neuroprotective in animal models of central nervous system diseases. In the present study, VEGF was incorporated into a sustained release hydrogel delivery system to examine its potential benefits in a rat model of Huntington's disease (HD). The VEGF-containing hydrogel was stereotaxically injected into the striatum of adult rats. Three days later, quinolinic acid (QA; 225 nmol) was injected into the ipsilateral striatum to produce neuronal loss and behavioral deficits that mimic those observed in HD. Two weeks after surgery, animals were tested for motor function using the placement and cylinder tests. Control animals received either QA alone or QA plus empty hydrogel implants. Behavioral testing confirmed that the QA lesion resulted in significant deficits in the ability of the control animals to use their contralateral forelimb. In contrast, the performance of those animals receiving VEGF was significantly improved relative to controls with only modest motor impairments observed. Stereological counts of NeuN-positive neurons throughout the striatum demonstrated that VEGF implants significantly protected against the loss of striatal neurons induced by QA. These data are the first to demonstrate that VEGF can be used to protect striatal neurons from excitotoxic damage in a rat model of HD.

Treatment of spinal cord injury by transplantation of cells via cerebrospinal fluid

It is very important to probe into the axonal regeneration and functional recovery of central nervous system (CNS) after implantation of cells into cerebrospinal fluid (CSF) for spinal cord injury (SCI). Transplantation of cells via CSF poses great potentials for SCI in clinic. Studies on administration of cells via CSF indicate that the method is safe and convenient. The method is more suitable to treating multiple lesions of the CNS since it does not produce open lesions. However, there are disputes over its promotion effects on axonal regeneration and functional recovery of spinal cord after injury; and some questions, such as the mechanisms of functional recovery of spinal cord, the proper time window of cell transplantation, and cell types of transplantation, still need to be handled. This review summarized the method of cell transplantation via CSF for treatment of SCI.

Cell therapy in Huntington disease

Huntington disease (HD), caused by polyglutamate expansions in the huntingtin protein, is a progressive neurodegenerative disease resulting in cognitive and motor impairments and death. Neuronal dysfunction and degeneration contribute to progressive physiological, motor, cognitive, and emotional disturbances characteristic of HD. A major impetus for research into the treatment of HD has centered on cell therapy strategies to protect vulnerable neuronal cell populations or to replace dysfunctional or dying cells. The work underlying 3 approaches to HD cell therapy includes the potential for self-repair through the manipulation of endogenous stem cells and/or neurogenesis, the use of fetal or stem cell transplantation as a cell replacement strategy, and the administration of neurotrophic factors to protect susceptible neuronal populations. These approaches have shown some promising results in animal models of HD. Although striatal transplantation of fetal-derived cells has undergone clinical assessment since the 1990s, many cell therapy strategies have yet to be applied in the clinic environment. A more thorough understanding of the pathophysiologies underlying HD as well as the response of both endogenous and exogenous cells to the degenerating brain will inform their merit as potential therapeutic agents and enhance the framework by which the success of such strategies are determined.

Neurotrophic factors in neurodegeneration

Neurotrophic factors (NTFs) have the unique potential to support neuronal survival and to augment neuronal function in the injured and diseased nervous system. Numerous studies conducted over the last 20 years have provided evidence for the potent therapeutic potential of NTFs in animal models of neurodegenerative diseases. However, major obstacles for the therapeutic use of NTFs are the inability to deliver proteins across the blood-brain-barrier, and dose-limiting adverse effects resulting from the broad exposure of nontargeted structures to NTFs. Two recent developments have allowed NTFs' promise to be truly tested for the first time: first, recent improvements in viral vectors that allow the targeted delivery of NTFs while providing a long-lasting supply and sufficient therapeutic doses of NTFs; and second, improved animal models developed in recent years. In this review, we will discuss some of the potential therapeutic applications of NTFs in neurodegenerative diseases and the potential contribution of disturbed neurotrophic factor signaling to neurodegenerative diseases.

Neuroprotection by GDNF-secreting stem cells in a Huntington's disease model: optical neuroimage tracking of brain-grafted cells

The use of stem cells for reconstructive or neuroprotective strategies can benefit from new advances in neuroimaging techniques to track grafted cells. In the present work, we analyze the potential of a neural stem cell (NSC) line, which stably expresses the glial cell line-derived neurotrophic factor (GDNF) and the firefly luciferase gene (GDNF/Luc-NSC), for cell therapy in a Huntington's disease mouse model. Our results show that detection of light photons is an effective method to quantify the proliferation rate and to characterize the migration pathways of transplanted NSCs. Intravenous administration of luciferine, the luciferase substract, into the grafted animals allowed the detection of implanted cells in real time by an optical neuroimaging methodology, overpassing the limits of serial histological analyses. We observed that transplanted GDNF/Luc-NSCs survive after grafting and expand more when transplanted in quinolinate-lesioned nude mouse striata than when transplanted in non-lesioned mice. We also demonstrate that GDNF/Luc-NSCs prevent the degeneration of striatal neurons in the excitotoxic mouse model of Huntington's disease and reduce the amphetamine-induced rotational behavior in mice bearing unilateral lesions.

Extensive neuroprotection by choroid plexus transplants in excitotoxin lesioned monkeys

Huntington's disease (HD) results from degeneration of striatal neurons. Choroid plexus (CP) cells secrete neurotrophic factors, and CP transplants are neuroprotective in rat models of HD. To determine if similar neuroprotective effects could be obtained in primates, porcine CP was encapsulated in alginate capsules. PCR confirmed that the CP cells expressed transthyretin and immunocytochemistry demonstrated typical ZO-1 and tubulin staining. In vitro, CP conditioned media enhanced the survival and preserved neurite number and length on serum deprived neurons. Cynomolgus primates were transplanted with CP-loaded capsules into the caudate and putamen followed by quinolinic acid (QA) lesions 1 week later. Control monkeys received empty capsules plus QA. Choroid plexus transplants significantly protected striatal neurons as revealed by stereological counts of NeuN-positive neurons (8% loss vs. 43% in controls) and striatum volume (10% decrease vs. 40% in controls). These data indicate that CP transplants might be useful for preventing the degeneration of neurons in HD.

Viral delivery of glial cell line-derived neurotrophic factor improves behavior and protects striatal neurons in a mouse model of Huntington's disease

Huntington's disease (HD) is a fatal, genetic, neurological disorder resulting from a trinucleotide repeat expansion in the gene that encodes for the protein huntingtin. These excessive repeats confer a toxic gain of function on huntingtin, which leads to the degeneration of striatal and cortical neurons and a devastating motor, cognitive, and psychological disorder. Trophic factor administration has emerged as a compelling potential therapy for a variety of neurodegenerative disorders, including HD. We previously demonstrated that viral delivery of glial cell line-derived neurotrophic factor (GDNF) provides structural and functional neuroprotection in a rat neurotoxin model of HD. In this report we demonstrate that viral delivery of GDNF into the striatum of presymptomatic mice ameliorates behavioral deficits on the accelerating rotorod and hind limb clasping tests in transgenic HD mice. Behavioral neuroprotection was associated with anatomical preservation of the number and size of striatal neurons from cell death and cell atrophy. Additionally, GDNF-treated mice had a lower percentage of neurons containing mutant huntingtin-stained inclusion bodies, a hallmark of HD pathology. These data further support the concept that viral vector delivery of GDNF may be a viable treatment for patients suffering from HD.

Selective glial cell line-derived neurotrophic factor production in adult dopaminergic carotid body cells in situ and after intrastriatal transplantation

Glial cell line-derived neurotrophic factor (GDNF) exerts a notable protective effect on dopaminergic neurons in rodent and primate models of Parkinson's disease (PD). The clinical applicability of this therapy is, however, hampered by the need of a durable and stable GDNF source allowing the safe and continuous delivery of the trophic factor into the brain parenchyma. Intrastriatal carotid body (CB) autografting is a neuroprotective therapy potentially useful in PD. It induces long-term recovery of parkinsonian animals through a trophic effect on nigrostriatal neurons and causes amelioration of symptoms in some PD patients. Moreover, the adult rodent CB has been shown to express GDNF. Here we show, using heterozygous GDNF/lacZ knock-out mice, that unexpectedly CB dopaminergic glomus, or type I, cells are the source of CB GDNF. Among the neural or paraneural cells tested, glomus cells are those that synthesize and release the highest amount of GDNF in the adult rodent (as measured by standard and in situ ELISA). Furthermore, GDNF expression by glomus cells is maintained after intrastriatal grafting and in CB of aged and parkinsonian 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated animals. Thus, glomus cells appear to be prototypical abundant sources of GDNF, ideally suited to be used as biological pumps for the endogenous delivery of trophic factors in PD and other neurodegenerative diseases.

Glial cell line-derived neurotrophic factor promotes the arborization of cultured striatal neurons through the p42/p44 mitogen-activated protein kinase pathway

Glial cell line-derived neurotrophic factor (GDNF) promotes the survival or differentiation of several types of neurons. This study examines GDNF-induced signal transduction and biological effects in cultured striatal neurons. Results show that GDNF addition to striatal cultures transiently increased the protein levels of phosphorylated p42/p44, but did not change the levels of phosphorylated Akt. GDNF effects on phosphorylated p42/p44 levels were blocked by the mitogen-activated protein kinase (MAPK) pathway specific inhibitors (PD98059 and U0126). Activation of the p42/p44 MAPK pathway by GDNF led to an increase in the degree of dendritic arborization and axon length of both GABA- and calbindin-positive neurons but had no effect on their survival and maturation. These GDNF-mediated effects were suppressed in the presence of the inhibitor of the MAPK pathway (PD98059). Furthermore, the addition of the phosphatidylinositol 3-kinase pathway specific inhibitor (LY294002) blocked GDNF-mediated striatal cell differentiation suggesting that the basal activity of this pathway is needed for the effects of GDNF. Our results indicate that treatment of cultured striatal cells with GDNF specifically activates the p42/p44 MAPK pathway, leading to an increase in the arborization of GABA- and calbindin-positive neurons.

Pharmaceutical, cellular and genetic therapies for Huntington's disease

HD (Huntington's disease) is a devastating neurodegenerative disorder caused by a polyglutamine expansion in the gene encoding the huntingtin protein. Presently, there is no known cure for HD and existing symptomatic treatments are limited. However, recent advances have identified multiple pathological mechanisms involved in HD, some of which have now become the focus of therapeutic intervention. In this review, we consider progress made towards developing safe and effective pharmaceutical-, cell- and genetic-based therapies, and discuss the extent to which some of these therapies have been successfully translated into clinical trials. These new prospects offer hope for delaying and possibly halting this debilitating disease.

Lentiviral gene delivery of GDNF into the striatum of R6/2 Huntington mice fails to attenuate behavioral and neuropathological changes

Transgenic R6/2 mice, which express exon 1 of the human mutant Huntington disease gene, develop behavioral and neuropathological changes that bear some resemblance to the human disease. Several studies have shown that elevated glial cell line-derived neurotrophic factor (GDNF) levels can exert neuroprotective effects in animal models of Huntington disease that are based on intrastriatal injections of excitotoxins. Therefore, the aim of the present study was to examine whether intrastriatal delivery of the GDNF gene by lentivirus (LV-GDNF) could provide structural and functional protection in R6/2 transgenic mice. Four- to 5-week-old mice were left untreated or alternatively received intrastriatal injections of either LV-GDNF or the same viral vector encoding green fluorescent protein (GFP) (LV-GFP) as a control. During the 4-week follow-up period, there was the expected deterioration in performance of the R6/2 mice in paw clasping, rotarod, and open field tests, and the LV-GDNF treated mice showed no improvement over controls. ELISA showed that the LV-GDNF-injected animals had a significant increase in GDNF level in the striatum, and immunohistochemical analysis revealed that GDNF was also overexpressed in brain regions receiving striatal projections. However, GDNF overexpression had no effect on the neuropathological changes examined. Thus, there were no significant differences in the number of EM-48-positive intraneuronal huntingtin inclusions, number of BrdU-positive cells and size of striatal neuronal cross-sectional area. These results suggest that intrastriatal lentiviral vector transfer of GDNF, performed at 5 weeks of age, does not ameliorate neurological and behavioral impairments in the R6/2 transgenic mice model of HD. Further studies are, however, needed to investigate if GDNF given at earlier time points is beneficial.

AAV-mediated gene delivery of BDNF or GDNF is neuroprotective in a model of Huntington disease

Huntington disease (HD) is a neurodegenerative disorder that results in the progressive loss of GABAergic medium spiny projection neurons in the striatum. Neurotrophic factors have demonstrated neuroprotective actions on striatal neurons, suggesting that increased neurotrophic factor expression may prevent or reduce neuronal loss in the HD brain. We investigated whether enhanced expression of brain-derived neurotrophic factor (BDNF) or glial cell line-derived neurotrophic factor (GDNF), achieved by adeno-associated viral (AAV) vector-mediated gene delivery, could protect striatal neurons in the quinolinic acid (QA) rodent model of HD. Adult Wistar rats received unilateral intrastriatal injections of AAV-BDNF, AAV-GDNF, AAV-GFP, or PBS. Three weeks later, the rats were lesioned with QA, a toxin that induces striatal neuron death by an excitotoxic process. Both AAV-BDNF and AAV-GDNF significantly reduced the loss of both NeuN- and calbindin-immunopositive striatal neurons 2 weeks after lesion compared to controls. AAV-BDNF also provided significant neurotrophic support to NOS-immunopositive striatal interneurons, while AAV-GDNF-treated rats demonstrated significant protection of parvalbumin-immunopositive striatal interneurons compared to controls. These results indicate that AAV-mediated gene transfer of BDNF or GDNF into the striatum provides neuronal protection in a rodent model of HD.

Cabergoline stimulates synthesis and secretion of nerve growth factor, brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor by mouse astrocytes in primary culture

Neuroprotection is the primary concern in patients with newly diagnosed Parkinson's disease. The D2/weak D1 dopamine agonist cabergoline elicits neuroprotection by antioxidation and scavenging free radicals, and may protect neurons by up-regulating endogenous neurotrophic factors synthesis in the brain. In primary cultured mouse astrocytes, cabergoline 37 micromol/l immediately elevated concentrations of nerve growth factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor (GDNF) in culture medium, reaching 9.9-, 2.6- and 30-fold, respectively, of control levels at 16 h. Relative mRNA levels were 3.0-, 1.5- and 1.9-fold, respectively, of controls at 3 h. These effects may be mediated partly by the dopamine D2 receptor. Cabergoline may be a good candidate for an inducer of GDNF, which may have neuroprotective and neurorestorative properties in dopaminergic nigral neurons.

Neurotrophic factors in Huntington's disease

Huntington's disease is a neurodegenerative disorder characterized by the selective loss of striatal neurons and, to a lesser extent, cortical neurons. The neurodegenerative process is caused by the mutation of huntingtin gene. Recent studies have established a link between mutant huntingtin, excitotoxicity and neurotrophic factors. Neurotrophic factors prevent cell death in degenerative processes but they can also enhance growth and function of neurons that are affected in Huntington's disease. The endogenous regulation of the expression of neurotrophic factors and their receptors in the striatum and its connections can be important to protect striatal cells and maintains basal ganglia connectivity. The administration of exogenous neurotrophic factors, in animal models of Huntington's disease, has been used to characterize the trophic requirements of striatal and cortical neurons. Neurotrophins, glial cell line-derived neurotrophic factor family members and ciliary neurotrophic factor have shown a potent neuroprotective effects on different neuronal populations of the striatum. Furthermore, they are also useful to maintain the integrity of the corticostriatal pathway. Thus, these neurotrophic factors may be suitable for the development of a neuroprotective therapy for neurodegenerative disorders of the basal ganglia.

GFAP knockout mice have increased levels of GDNF that protect striatal neurons from metabolic and excitotoxic insults

In response to injury and degeneration, astrocytes hypertrophy, extend processes, and increase production of glial fibrillary acidic protein (GFAP), an intermediate filament protein located within their cytoplasm. The present study tested the hypothesis that GFAP expression alters the vulnerability of neurons to excitotoxic and metabolic insult induced by 3-nitroproprionic acid (3-NP), an irreversible inhibitor of mitochondrial complex II activity or the excitotoxin quinolinic acid (QA). In this respect, adult GFAP knockout mice (KO) and wild-type control mice (WT) received unilateral intrastriatal injections of 3-NP (200 nmol/microl) or QA (100 nmol/microl) and were killed 1, 2, or 4 weeks later. Lesion volume and neuronal counts were quantified using unbiased stereologic principles. For both QA and 3-NP lesions, a significant decrease in lesion volume and an increase in striatal projection neurons were seen in GFAP KO mice compared with WT mice. Enzyme-linked immunoassay analysis revealed increased basal levels of glial cell derived neurotrophic factor (GDNF) relative to WT mice. In contrast, no differences were observed in the expression of ciliary neurotrophic factor or nerve growth factor. These data strongly suggest that the expression of GFAP is implicated with the production of GDNF to a degree that confers neuroprotection after an excitotoxic or metabolic insult.

Structural and functional neuroprotection in a rat model of Huntington's disease by viral gene transfer of GDNF

Huntington's disease (HD) is an autosomal dominant disorder caused by an expanded polyglutamine (CAG) tract at the IT15 locus on chromosome 4. These excessive repeats lead to the degeneration of striatal and cortical neurons resulting in a devastating cognitive, psychiatric, and motor disorder for which no treatments are available. Neurotrophic factors support the viability of striatal neurons suggesting that they might prevent the inevitable neural degeneration and its accompanying functional decline associated with HD. The present study investigated whether glial cell line-derived neurotrophic factor (GDNF) delivered by an adeno associated virus could provide structural and functional neuroprotection in a rat model of HD. Lewis rats received bilateral injections of either AAV-GDNF (n = 12) or AAV-green fluorescence protein (AAV-GFP, n = 12) into the striatum followed 2 weeks later by chronic subcutaneous infusions of the mitochondrial toxin, 3-nitropropionic acid (3-NP, 38 mg/kg). All rats underwent 4 weeks of behavioral testing and were then sacrificed. Following 3-NP, the performance by AAV-GFP-treated rats on a raised platform motor task deteriorated while the performance by AAV-GDNF-treated rats was near normal (P < 0.001). AAV-GDNF-treated rats also received better scores on a blinded semi-quantitative neurological scale compared to rats receiving AAV-GFP (P < 0.001). Histological analyses supported our behavioral findings. 3-NP-treated rats receiving AAV-GDNF displayed 70% more NeuN-immunoreactive neurons compared to 3-NP-treated rats receiving AAV-GFP (P = 0.002). Similar findings were seen with dopamine-and-adenosine-3'5'-monophosphate-regulated phosphoprotein (DARPP-32) staining. These data indicate that the viral-mediated gene transfer of GDNF into the striatum provides neuroanatomical and behavioral protection in a rodent model of HD.

Dissemination and proliferation of neural stem cells on the spinal cord by injection into the fourth ventricle of the rat: a method for cell transplantation

We examined the distribution of hippocampus-derived neural stem cells on the spinal cord surface for up to 3 weeks following injection through the fourth ventricle. The injected cells were disseminated as tiny spots on the pia mater of the spinal cord and proliferated into large cell-clusters. On both the dorsal and ventral side, cell clusters increased in number rapidly up to 5 days after injection and thereafter decreased gradually due to the coalition of neighbouring clusters. Concomitantly, individual cell clusters continuously increased in size, occupying almost 50% of the spinal cord surface. Cell attachment was usually found around blood vessels, along which cells invaded into the spinal cord. In the injured site, cells migrated into the lesion and were integrated into the spinal cord tissue, some of which had differentiated into astrocytes 1-2 weeks after injection. BrdU-uptake experiments demonstrated that the transplanted cells proliferated within the host cerebrospinal fluid. These results indicate that application of neural stem cells through the ventricle is an effective method to disseminate cells all over the spinal cord and that they can migrate and be integrated into the injured spinal cord.

Brain sites of movement disorder: genetic and environmental agents in neurodevelopmental perturbations

In assessing and assimilating the neurodevelopmental basis of the so-called movement disorders it is probably useful to establish certain concepts that will modulate both the variation and selection of affliction, mechanisms-processes and diversity of disease states. Both genetic, developmental and degenerative aberrations are to be encompassed within such an approach, as well as all deviations from the necessary components of behaviour that are generally understood to incorporate "normal" functioning. In the present treatise, both conditions of hyperactivity/hypoactivity, akinesia and bradykinesia together with a constellation of other symptoms and syndromes are considered in conjunction with the neuropharmacological and brain morphological alterations that may or may not accompany them, e.g. following neonatal denervation. As a case in point, the neuroanatomical and neurochemical points of interaction in Attention Deficit and Hyperactivity disorder (ADHD) are examined with reference to both the perinatal metallic and organic environment and genetic backgrounds. The role of apoptosis, as opposed to necrosis, in cell death during brain development necessitates careful considerations of the current explosion of evidence for brain nerve growth factors, neurotrophins and cytokines, and the processes regulating their appearance, release and fate. Some of these processes may possess putative inherited characteristics, like alpha-synuclein, others may to greater or lesser extents be endogenous or semi-endogenous (in food), like the tetrahydroisoquinolines, others exogenous until inhaled or injested through environmental accident, like heavy metals, e.g. mercury. Another central concept of neurodevelopment is cellular plasticity, thereby underlining the essential involvement of glutamate systems and N-methyl-D-aspartate receptor configurations. Finally, an essential assimilation of brain development in disease must delineate the relative merits of inherited as opposed to environmental risks not only for the commonly-regarded movement disorders, like Parkinson's disease, Huntington's disease and epilepsy, but also for afflictions bearing strong elements of psychosocial tragedy, like ADHD, autism and Savantism.

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.

Neuroprotection by neurotrophins and GDNF family members in the excitotoxic model of Huntington's disease

Huntington's disease is a neurodegenerative disorder characterized by a selective degeneration of striatal projection neurons, which deal with choreic movements. Neuroprotective therapy could be achieved with the knowledge of the specific trophic requirements of these neuronal populations. Thus, the induction of endogenous trophic response or the exogenous administration of neurotrophic factors may help to prevent or stop the progression of the illness. Excitotoxicity has been implicated in the etiology of Huntington's disease, because intrastriatal injection of glutamate receptor agonists reproduces some of the neuropathological features of this disorder. Activation of glutamate receptors in the striatum differentially regulates the expression of neurotrophins, glial cell line-derived neurotrophic factor (GDNF), neurturin, and their receptors in the striatum and in its connections, cortex, and substantia nigra, showing a selective trophic response against excitotoxic insults. Transplantation of cells genetically engineered to release neurotrophic factors in the striatum has been used to study the neuroprotective effects of neurotrophin and GDNF family members in the excitotoxic model of Huntington's disease. Neurotrophins (brain-derived neurotrophic factor [BDNF], neurotrophin-3, and neurotrophin-4) protected striatal projection neurons against quinolinic or kainic acid treatment. However, GDNF family members showed a more specific action. Neurturin only protected gamma-aminobutyric acid (GABA)/enkephalinergic neurons that project to the external segment of the globus pallidus, whereas GDNF exerts its effects on GABA/substance P positive neurons, which project to the substantia nigra pars compacta and the internal segment of the globus pallidus. In conclusion, the trophic requirements of each population of striatal projection neurons are due to a complex interaction between several neurotrophic factors, such as neurotrophins and GDNF family members, which can be modified, in different pathological conditions. Moreover, these neurotrophic factors may be able to provide selective protection for basal ganglia circuits, which are affected in striatonigral degenerative disorders, such as Huntington's disease or multisystem atrophy.

Excitatory amino acids differentially regulate the expression of GDNF, neurturin, and their receptors in the adult rat striatum

Glial cell line-derived neurotrophic factor (GDNF) family ligands are important regulators of neuronal development and maintenance of the connectivity in the basal ganglia and show neuroprotective activities in several paradigms of brain injury. The mRNAs of two members of this family, GDNF and neurturin, and also their receptors have been detected in the basal ganglia. In the present work, we analyzed the time course changes in the expression of these neurotrophic factors and receptors in the adult rat striatum, induced by quinolinate or kainate excitotoxicity. Our results show that stimulation of NMDA or non-NMDA receptors induced different effects on the mRNA levels analyzed. Expression of GDNF and its preferred receptor, GDNF family receptor-alpha1 (GFRalpha1), was transiently up-regulated by quinolinate and kainate, but with differing intensity and temporal pattern. Immunohistochemical analysis showed that, although GDNF and GFRalpha1 were initially localized in neurons, excitotoxicity induced the expression of these proteins in astrocyte-like cells. Neurturin mRNA levels were only up-regulated after quinolinate injection, whereas quinolinate or kainate injection did not modify GFRalpha2 mRNA. The mRNA for the common receptor, c-Ret, was up-regulated by both agonists with similar temporal pattern but with differing intensity. Immunohistochemical analysis showed that c-Ret protein was located on neurons. These changes in mRNA levels and protein localization of GDNF family components could reflect an endogenous trophic response of striatal cells to different excitotoxic insults.

Striatopallidal neurons are selectively protected by neurturin in an excitotoxic model of Huntington's disease

Excitotoxicity has been involved in the pathogenesis of several neurodegenerative disorders. Using intrastriatal quinolinic acid (QUIN) injection as an animal model of Huntington's disease, we attempt to identify the neurotransmitter phenotype of striatal projection neurons protected by neurturin (NRTN). Control or NRTN-secreting cell lines were grafted in the striatum before QUIN injection and striatal projection neurons were examined by retrograde Fluorogold labeling and in situ hybridization. Intrastriatal grafting of NRTN-secreting cell line selectively prevented the loss of striatopallidal neurons and also the decrease in the mRNA levels for their markers (glutamic acid decarboxylase 67 and preproenkephalin) induced by QUIN, without affecting striatonigral neurons. Thus, our findings show that NRTN is a selective neuroprotective factor for striatopallidal neurons, suggesting that it might be a candidate for the treatment of movement disorders in which this neuronal population is affected.

New method for transplantation of neurosphere cells into injured spinal cord through cerebrospinal fluid in rat

Here we report a novel method of supplying cultured neurosphere cells to the injured spinal cord, by injection of cells into the cerebrospinal fluid (CSF) through the fourth ventricle or cisterna magna. Hippocampus-derived neurosphere cells, isolated from a transgenic rat fetus expressing green fluorescent protein, were transplanted into the CSF of a rat with spinal cord injury. It was found that injected cells were extensively transported by CSF within the subarachnoidal space, and survived as clusters on the pial surface of the spinal cord. The most notable finding was that a large number of injected cells migrated into the lesion site and integrated into the injured spinal cord tissues.

Intrastriatal injection of sonic hedgehog reduces behavioral impairment in a rat model of Parkinson's disease

Sonic hedgehog (Shh), a member of hedgehog (hh) family of signaling molecules, is necessary for normal axial patterning and cellular differentiation in the developing central nervous system. Shh also promotes the survival of fetal dopaminergic neurons and protects cultures of fetal midbrain dopaminergic neurons from the toxic effects of N-methyl-4-phenylpyridinium (MPP(+)), a neurotoxin that selectively injures nigral dopaminergic neurons. The mRNA expression of Shh and its putative receptor in the adult brain indicates an important role of Shh in the mature nervous system in addition to its roles during embryogenesis. In this study we examined the behavioral and anatomical effects of intrastriatal injection of singly myristoylated wild-type human Sonic hedgehog N-terminal fragment (Shh-M) in a rat model of Parkinson's disease (PD). Five groups of rats received a series of four intrastriatal injections of Shh-M (180 ng, 540 ng, or 4.275 microg per injection), glial cell line-derived neurotrophic factor (GDNF) (1 microg/injection), or vehicle on days 1, 3, 5, and 8. On day 4, the animals received an intrastriatal injection of 15 microg 6-hydroxydopamine (6-OHDA) free base. Intrastriatal administration of Shh (180 ng/injection) twice before and after a single intrastriatal injection of 6-OHDA reduced apomorphine- and amphetamine-induced rotation and forelimb akinesia and partially preserved dopaminergic axons in the striatum. This is the first demonstration in vivo that Shh reduces behavioral deficits induced by intrastriatal 6-OHDA lesion and suggests that Shh may be useful in the treatment of disorders that affect the nigrostriatal system, such as PD.

Neuroprotective effect of interleukin-6 and IL6/IL6R chimera in the quinolinic acid rat model of Huntington's syndrome

Ciliary neurotrophic factor prevents behavioural deficits and striatal degeneration in rat and primate models of Huntington's disease. Interleukin-6, another member of the cytokine family, and the chimeric molecule (IL6/IL6R) in which interleukin-6 and its soluble receptor are fused, have been shown to exert trophic action on various neuronal populations in the central nervous system. Therefore, we investigated the neuroprotective effect of these two molecules in the quinolinic acid model of Huntington's disease. LacZ-, interleukin-6- and IL6/IL6R-expressing lentiviral vectors were stereotaxically injected into the striatum of Wistar rats. Three weeks later the animals were lesioned through the intrastriatal injection of 180 nmol of quinolinic acid. The extent of the striatal damage was significantly diminished in the rats that had been treated with interleukin-6 or IL6/IL6R. The neuroprotective effect was, however, more pronounced with the IL6/IL6R chimera than with interleukin-6 as indicated by the volume of the lesions (38.6 +/- 10% in the IL6/IL6R group, 63.3 +/- 3.6% in the IL-6 group and 84.3 +/-2.9% in the control group). Quantitative analysis of striatal interneurons further demonstrated that the IL6/IL6R chimera is more neuroprotective than IL-6 on ChAT- and NADPH-d-immunoreactive neurons. These results suggest that the IL6/IL6R chimera is a potential treatment for Huntington's disease.

Riluzole stimulates nerve growth factor, brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor synthesis in cultured mouse astrocytes

Riluzole is an antiexcitotoxic agent used for the treatment of amyotrophic lateral sclerosis, and reported to have neuroprotective effects in animal models of Parkinson's disease, Huntington's disease and brain ischemia. We investigated the effects of riluzole on synthesis of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) in cultured mouse astrocytes. The protein and mRNA levels were measured by enzyme-linked immunosorbent assay and semiquantitative reverse transcription-polymerase chain reaction, respectively. Treatment with riluzole at 100 microg/ml (426 microM) for 24 h increased the contents of NGF, BDNF, and GDNF in the culture medium 109-fold, 2.0-fold and 3.1-fold over the control, respectively. The drug-induced relative mRNA levels of NGF, BDNF, and GDNF were 7.3-fold at 2 h, 2.1-fold at 4 h, and 1.9-fold at 2 h, respectively. These results indicate that riluzole stimulates synthesis of NGF, BDNF and GDNF in cultured astrocytes. Riluzole might exert neuroprotective effects, at least in part, via stimulation of neurotrophic factors.

Neuroprotection of striatal neurons against kainate excitotoxicity by neurotrophins and GDNF family members

Neurotrophic factors are regarded as potential therapeutic tools in neurodegenerative disorders. Here, we analysed the protective effects of brain-derived neurotrophic factor, neurotrophin-3, glial cell line-derived neurotrophic factor and neurturin against the excitotoxic damage induced by kainate in striatal neurons in vitro and in vivo. Our results show that the decrease in the number of cultured striatal calbindin-positive neurons induced by kainate was prevented by treatment with any of these factors. To characterize their protective effects in vivo, cell lines overexpressing brain-derived neurotrophic factor, neurotrophin-3, glial cell line-derived neurotrophic factor or neurturin were grafted into the striatum. We found that the numbers of striatal projection neurons (calbindin-positive) and striatal interneurons (parvalbumin- or choline acetyltransferase-positive) were differentially decreased after kainate lesion. These neurotrophic factors prevented the loss of striatal projection neurons and interneurons with differing efficiency: brain-derived neurotrophic factor was the most efficient, whereas neurturin was the least. Our findings show that brain-derived neurotrophic factor, neurotrophin-3, glial cell line-derived neurotrophic factor and neurturin have specific neuroprotective profiles in striatal neurons and indicate that they are specific modulators of the survival of distinct subsets of striatal neurons in pathophysiological conditions.

Neuroprotective effect of a CNTF-expressing lentiviral vector in the quinolinic acid rat model of Huntington's disease

Neurodegenerative diseases represent promising targets for gene therapy approaches provided effective transfer vectors. In the present study, we evaluated the effectiveness of LacZ-expressing lentiviral vectors with two different internal promoters, the mouse phosphoglycerate kinase 1 (PGK) and cytomegalovirus (CMV), to infect striatal cells. The intrastriatal injection of lenti-beta-Gal vectors lead to 207, 400 +/- 11,500 and 303,100 +/- 4,300 infected cells in adult rats, respectively. Importantly, the beta-galactosidase activity was higher in striatal extracts from PGK-LacZ-injected animals as compared to CMV-LacZ animals. The efficacy of the system was further examined with a potential therapeutic gene for the treatment of Huntington's disease, the human ciliary neurotrophic factor (CNTF). PGK-LacZ- or PGK-CNTF-expressing viruses were stereotaxically injected into the striatum of rats, 3 weeks later the animals were unilaterally lesioned with 180 nmol of quinolinic acid (QA). Control animals displayed 148 +/- 43 apomorphine-induced rotations ipsilateral to the lesion 5 days postlesion as compared to 26 +/- 22 turns/45 min in the CNTF-treated group. The extent of the striatal damage was significantly diminished in the CNTF-treated rats as indicated by the 52 +/- 9.7% decrease of the lesion volume and the sparing of DARPP-32, ChAT and NADPH-d neuronal populations. These results further establish that lentiviruses may represent an efficient gene delivery system for the screening of therapeutic molecules in Huntington's disease.