Adenovirus-mediated transgene expression in nonhuman primate brain

Gene replacement therapies for inherited disorders of neurotransmission: Current progress in succinic semialdehyde dehydrogenase deficiency

Neurodevelopment is a highly organized and complex process involving lasting and often irreversible changes in the central nervous system. Inherited disorders of neurotransmission (IDNT) are a group of genetic disorders where neurotransmission is primarily affected, resulting in abnormal brain development from early life, manifest as neurodevelopmental disorders and other chronic conditions. In principle, IDNT (particularly those of monogenic causes) are amenable to gene replacement therapy via precise genetic correction. However, practical challenges for gene replacement therapy remain major hurdles for its translation from bench to bedside. We discuss key considerations for the development of gene replacement therapies for IDNT. As an example, we describe our ongoing work on gene replacement therapy for succinic semialdehyde dehydrogenase deficiency, a GABA catabolic disorder.

Beyond Gene Inactivation: Evolution of Tools for Analysis of Serotonergic Circuitry

In the brain, serotonin (5-hydroxytryptamine, 5-HT) controls a multitude of physiological and behavioral functions. Serotonergic neurons in the raphe nuclei give rise to a complex and extensive network of axonal projections throughout the whole brain. A major challenge in the analysis of these circuits is to understand how the serotonergic networks are linked to the numerous functions of this neurotransmitter. In the past, many studies employed approaches to inactivate different genes involved in serotonergic neuron formation, 5-HT transmission, or 5-HT metabolism. Although these approaches have contributed significantly to our understanding of serotonergic circuits, they usually result in life-long gene inactivation. As a consequence, compensatory changes in serotonergic and other neurotransmitter systems may occur and complicate the interpretation of the observed phenotypes. To dissect the complexity of the serotonergic system with greater precision, approaches to reversibly manipulate subpopulations of serotonergic neurons are required. In this review, we summarize findings on genetic animal models that enable control of 5-HT neuronal activity or mapping of the serotonergic system. This includes a comparative analysis of several mouse and rat lines expressing Cre or Flp recombinases under Tph2, Sert, or Pet1 promoters with a focus on specificity and recombination efficiency. We further introduce applications for Cre-mediated cell-type specific gene expression to optimize spatial and temporal precision for the manipulation of serotonergic neurons. Finally, we discuss other temporally regulated systems, such as optogenetics and designer receptors exclusively activated by designer drugs (DREADD) approaches to control 5-HT neuron activity.

Gene therapy of the central nervous system: general considerations on viral vectors for gene transfer into the brain

The last decade has nourished strong doubts on the beneficial prospects of gene therapy for curing fatal diseases. However, this climate of reservation is currently being transcended by the publication of several successful clinical protocols, restoring confidence in the appropriateness of therapeutic gene transfer. A strong sign of this present enthusiasm for gene therapy by clinicians and industrials is the market approval of the therapeutic viral vector Glybera, the first commercial product in Europe of this class of drug. This new field of medicine is particularly attractive when considering therapies for a number of neurological disorders, most of which are desperately waiting for a satisfactory treatment. The central nervous system is indeed a very compliant organ where gene transfer can be stable and successful if provided through an appropriate strategy. The purpose of this review is to present the characteristics of the most efficient virus-derived vectors used by researchers and clinicians to genetically modify particular cell types or whole regions of the brain. In addition, we discuss major issues regarding side effects, such as genotoxicity and immune response associated to the use of these vectors.

Efficient gene delivery and selective transduction of astrocytes in the mammalian brain using viral vectors

Astrocytes are now considered as key players in brain information processing because of their newly discovered roles in synapse formation and plasticity, energy metabolism and blood flow regulation. However, our understanding of astrocyte function is still fragmented compared to other brain cell types. A better appreciation of the biology of astrocytes requires the development of tools to generate animal models in which astrocyte-specific proteins and pathways can be manipulated. In addition, it is becoming increasingly evident that astrocytes are also important players in many neurological disorders. Targeted modulation of protein expression in astrocytes would be critical for the development of new therapeutic strategies. Gene transfer is valuable to target a subpopulation of cells and explore their function in experimental models. In particular, viral-mediated gene transfer provides a rapid, highly flexible and cost-effective, in vivo paradigm to study the impact of genes of interest during central nervous system development or in adult animals. We will review the different strategies that led to the recent development of efficient viral vectors that can be successfully used to selectively transduce astrocytes in the mammalian brain.

Combining glial cell line-derived neurotrophic factor gene delivery (AdGDNF) with L-arginine decreases contusion size but not behavioral deficits after traumatic brain injury

Our laboratory has previously demonstrated that viral administration of glial cell line-derived neurotrophic factor (AdGDNF), one week prior to a controlled cortical impact (CCI) over the forelimb sensorimotor cortex of the rat (FL-SMC) is neuroprotective, but does not significantly enhance recovery of sensorimotor function. One possible explanation for this discrepancy is that although protected, neurons may not have been functional due to enduring metabolic deficiencies. Additionally, metabolic events following TBI may interfere with expression of therapeutic proteins administered to the injured brain via gene therapy. The current study focused on enhancing the metabolic function of the brain by increasing cerebral blood flow (CBF) with l-arginine in conjunction with administration of AdGDNF immediately following CCI. An adenoviral vector harboring human GDNF was injected unilaterally into FL-SMC of the rat immediately following a unilateral CCI over the FL-SMC. Within 30min of the CCI and AdGDNF injections, some animals were injected with l-arginine (i.v.). Tests of forelimb function and asymmetry were administered for 4weeks post-injury. Animals were sacrificed and contusion size and GDNF protein expression measured. This study demonstrated that rats treated with AdGDNF and l-arginine post-CCI had a significantly smaller contusion than injured rats who did not receive any treatment, or injured rats treated with either AdGDNF or l-arginine alone. Nevertheless, no amelioration of behavioral deficits was seen. These findings suggest that AdGDNF alone following a CCI was not therapeutic and although combining it with l-arginine decreased contusion size, it did not enhance behavioral recovery.

Improving adenovirus based gene transfer: strategies to accomplish immune evasion

Adenovirus (Ad) based gene transfer vectors continue to be the platform of choice for an increasing number of clinical trials worldwide. In fact, within the last five years, the number of clinical trials that utilize Ad based vectors has doubled, indicating growing enthusiasm for the numerous positive characteristics of this gene transfer platform. For example, Ad vectors can be easily and relatively inexpensively produced to high titers in a cGMP compliant manner, can be stably stored and transported, and have a broad applicability for a wide range of clinical conditions, including both gene therapy and vaccine applications. Ad vector based gene transfer will become more useful as strategies to counteract innate and/or pre-existing adaptive immune responses to Ads are developed and confirmed to be efficacious. The approaches attempting to overcome these limitations can be divided into two broad categories: pre-emptive immune modulation of the host, and selective modification of the Ad vector itself. The first category of methods includes the use of immunosuppressive drugs or specific compounds to block important immune pathways, which are known to be induced by Ads. The second category comprises several innovative strategies inclusive of: (1) Ad-capsid-display of specific inhibitors or ligands; (2) covalent modifications of the entire Ad vector capsid moiety; (3) the use of tissue specific promoters and local administration routes; (4) the use of genome modified Ads; and (5) the development of chimeric or alternative serotype Ads. This review article will focus on both the promise and the limitations of each of these immune evasion strategies, and in the process delineate future directions in developing safer and more efficacious Ad-based gene transfer strategies.

AAV-GAD gene for rat models of neuropathic pain and Parkinson's disease

The introduction of therapeutic genes to neurons by genetic modification has potential as an effective treatment for CNS disorders for all that a successful clinical application has not yet been fully implemented. In this paper, we will discussed the role of AAV vectors with the GAD65 gene for animal models of PD and neuropathic pain. AAV vector is one of the most attractive gene delivery vehicles for direct introduction of therapeutic genes into the CNS in the treatment of neurological diseases. GAD65 is present as a membrane-associated form in synapses and is primarily involved in producing synaptic gamma-aminobutyric acid (GABA) for vesicular release. We constructed rAAV-GAD65 expressing rat GAD65 and demonstrated that rat Parkinsonian symptoms can be significantly improved concomitantly with the production of GAD65. We also demonstrated rAAV-GAD65 as a successful gene delivery vehicle in a chronic pain model by administrating rAAV-GAD65 to DRGs because GABA driven by GAD is a major inhibitory neurotransmitter in the dorsal horn of the spinal cord and also plays an important role in the ventral horn. We believe that AAV vectors can be excellent candidates for gene therapy of neurological diseases.

Preclinical development of gene therapy for Parkinson's disease

Multiple targets and pathways may be amenable to the development of gene therapy approaches for Parkinson's disease. This article discusses some of the cellular and brain circuit pathways relevant to Parkinson's disease that would be clinically amenable to gene therapy. Approaches could be classified according to two main categories, i.e. symptomatic vs. neuroprotective/neurorestorative strategies. Examples of the different possibilities currently in development are given and feature both dopaminergic and non-dopaminergic symptomatic treatments of parkinsonian symptoms and/or L-DOPA-induced side effects, anti-apoptotic neuroprotective strategies and growth-factor delivery for neuroprotection/neurorestoration. While gene therapy has been mostly used so far for enhancing the expression of the target gene, the use of dominant negative or siRNA opens new possibilities. This, combined with the key feature of gene delivery that offers access to intracellular signalling pathways, is likely to further expand the number of proposed targets to be studied.

Viral vectors for in vivo gene transfer in Parkinson's disease: properties and clinical grade production

Because Parkinson's disease is a progressive degenerative disorder that is mainly confined to the basal ganglia, gene transfer to deliver therapeutic molecules is an attractive treatment avenue. The present review focuses on direct in vivo gene transfer vectors that have been developed to a degree that they have been successfully used in animal model of Parkinson's disease. Accordingly, the properties of recombinant adenovirus, recombinant adeno-associated virus, herpes simplex virus, and lentivirus are described and contrasted. In order for viral vectors to be developed into clinical grade reagents, they must be manufactured and tested to precise regulatory standards. Indeed, clinical lots of viral vectors can be produced in compliance with current Good Manufacturing Practices (cGMPs) regulations using industry accepted manufacturing methodologies, manufacturing controls, and quality systems. The viral vector properties themselves combined with physiological product formulations facilitate long-term storage and direct in vivo administration.

The "perivascular pump" driven by arterial pulsation is a powerful mechanism for the distribution of therapeutic molecules within the brain

We investigated the movement of interstitially infused macromolecules within the central nervous system (CNS) in rats with high and low blood pressure (BP)/heart rate and in rats euthanized immediately before infusion (no heart action). Adeno-associated virus 2 (AAV2), fluorescent liposomes, or bovine serum albumin was infused into rat striatum (six hemispheres per group) by convection-enhanced delivery (CED). After infusion, distribution volumes were evaluated. The rats with high BP/heart rate displayed a significantly larger distribution of the infused molecules within the injected site and more extensive transport of those molecules to the globus pallidus. This difference was particularly apparent for AAV2, for which a 16.5-fold greater distribution of viral capsids was observed in the rats with high BP/heart rate than in the rats with no heartbeat. Similar results were observed for liposomes, despite their larger diameter. The distribution of all infused molecules in all rats that had low or no blood flow was confined to the space around brain blood vessels. These findings show that fluid circulation within the CNS through the perivascular space is the primary mechanism by which viral particles and other therapeutic agents administered by CED are spread within the brain and that cardiac contractions power this process.

Safety of direct administration of AAV2(CU)hCLN2, a candidate treatment for the central nervous system manifestations of late infantile neuronal ceroid lipofuscinosis, to the brain of rats and nonhuman primates

Late infantile neuronal ceroid lipofuscinosis (LINCL), a pediatric autosomal recessive neurodegenerative lysosomal storage disorder, results from mutations in the CLN2 gene and consequent deficiency in tripeptidyl-peptidase I (TPP-I) and progressive destruction of neurons. We have previously demonstrated that CNS gene transfer of AAV2(CU)hCLN2 (an AAV2-based vector expressing the human CLN2 cDNA) in rats and nonhuman primates mediates long-term TPP-I expression in the CNS neurons [Sondhi, D., Peterson, D.A., Giannaris, E.L., Sanders, C.T., Mendez, B.S., De, B., Rostkowski, A., Blancard, B., Bjugstad, K., Sladek, J.R., Redmond, D.E., Leopold, P.L., Kaminsky, S.M., Hackett, N.R., and Crystal, R.G. (2005). Gene Ther. 12, 1618-1632]. The present study tests the hypothesis that direct CNS administration of a clinical-grade AAV2(CU)hCLN2 vector to the CNS of rats and nonhuman primates at doses scalable to humans has a long-term safety profile acceptable for initiating clinical trials. Fischer 344 rats were injected bilaterally via the striatum with 2 x 10(10) particle units (PU) of AAV2(CU)hCLN2, using saline as a control. At 13, 26, and 52 weeks, vector and phosphate-buffered salineinjected rats were killed (n = 6 per time point), and blood, brain, and distant organs were assessed. There were no biologically significant differences between control and vector groups for complete blood count, serum chemistry, and neutralizing anti-AAV2 antibody levels. CNS administration of AAV2 CUhCLN2 did not result in any pathological changes in the brain that were attributable to the vector, although microscopic changes were observed along the track consistent with needle trauma. A total dose of 3.6 x 10(10) or 3.6 x 10(11) PU of AAV2(CU)hCLN2 was administered to the CNS of African Green monkeys at 12 locations, targeting the caudate nucleus, hippocampus, and overlying cortices. Monkeys (n = 3 at each dose) were killed 1, 13, 26, or 52 weeks after injection. Controls included sham-injected, saline-injected, and AAV2(CU)Null-injected (3.6 x 10(11) PU) monkeys. There were no biologically significant differences among vector-injected and control groups in any parameter of the general assessment, complete blood count, or serum chemistry assessed at multiple time points after vector administration. Importantly, no abnormal behavior was observed in any group in videotaped neurological assessment, where behaviors were quantified before administration and at multiple time points afterward. Histopathological examination of the CNS demonstrated that 1 week after administration, AAV2(CU)hCLN2 produced transient minor white matter edema with reactive glial cells in the corona radiata of the cerebrum along the injection track and in the surrounding white matter. This abnormality was not observed at 13, 26, or 52 weeks. Together with the long-term gene expression after gene transfer, these findings supported the initiation of clinical trials to assess the safety of AAV2(CU)hCLN2 administration to individuals with LINCL.

Ex vivo gene delivery of GDNF using primary astrocytes transduced with a lentiviral vector provides neuroprotection in a rat model of Parkinson's disease

Astrocytes are, as normal constituents of the brain, promising vehicles for ex vivo gene delivery to the central nervous system. In the present study, we have used a lentiviral vector encoding glial cell line-derived neurotrophic factor (GDNF) to transduce rat-derived primary astrocytes, in order to evaluate their potential for long-term transgene expression in vivo and neuroprotection in a rat model of Parkinson's disease. Following transplantation of GDNF-transduced astrocytes to the intact striatum, the level of released GDNF was 2.93 +/- 0.28 ng/mg tissue at 1 week post-grafting, reduced to 0.42 +/- 0.12 ng/mg tissue at 4 weeks, and thereafter was maintained at this level throughout the experiment (12 weeks; 0.53 +/- 0.068 ng/mg tissue). Similarly, grafting to the substantia nigra (SN) resulted in a significant overexpression of GDNF ( approximately 0.20 ng/mg tissue) at 1 week. Intact animals receiving transplants of GDNF-transduced astrocytes displayed an increased contralateral turning (5.39 +/- 1.19 turns/min) in the amphetamine-induced rotation test, which significantly correlated with the GDNF tissue levels measured in the striatum, indicating a stimulatory effect of GDNF on the dopaminergic function. Transplantation of GDNF-transduced astrocytes to the SN 1 week prior to an intrastriatal 6-hydroxydopamine lesion provided a significant protection of nigral tyrosine hydroxylase-positive cells. By contrast, when the cells were transplanted to the striatum, the level of released GDNF was not sufficient to rescue the striatal fibers and, hence, to protect the nigral dopaminergic neurons. Overall, our results suggest that genetically modified astrocytes expressing GDNF can provide neuroprotection in a rat model of Parkinson's disease following transplantation to the SN.

Gene therapy in Parkinson?s disease

Gene therapy in Parkinson's disease appears to be at the brink of the clinical study phase. Future gene therapy protocols will be based on a substantial amount of preclinical data regarding the use of ex vivo and in vivo genetic modifications with the help of viral or non-viral vectors. To date, the supplementation of neurotrophic factors and substitution for the dopaminergic deficit have formed the focus of trials to achieve relief in animal models of Parkinson's disease. Newer approaches include attempts to influence detrimental cell signalling pathways and to inhibit overactive basal ganglia structures. Nevertheless, current models of Parkinson's disease do not mirror all aspects of the human disease, and important issues with respect to long-term protein expression, choice of target structures and transgenes and safety remain to be solved. Here, we thoroughly review available animal data of gene transfer in models of Parkinson's disease.

Tracing axons of peripheral nerves in rats: a potential technique to study the equine recurrent laryngeal nerve

To study the fascicular anatomy of peripheral nerves, three different groups of retrograde axonal tracers were evaluated: fluorophores, horseradish peroxidase conjugated to subunit B of cholera toxin (CT-HRP), and adeno-associated virus (AAV). The hindlimb nerves in rats served as a model to identify the most efficient tracer in regard to labeling axons within peripheral nerves. The rat's tibial and common peroneal nerves were injected with the different tracers and the sciatic nerve was subsequently examined for evidence of labeled axons. The CT-HRP clearly provided the best results in this rat model. Subsequently, CT-HRP was injected into the recurrent laryngeal nerve (RLN) of two horses in order to identify the location and distribution pattern of the RLN axons within the course of the cervical vagus nerve trunk. No labeling could be observed in either of the two horses.

NMDA-evoked consumption and recovery of mitochondrially targeted aequorin suggests increased Ca2+ uptake by a subset of mitochondria in hippocampal neurons

Activation of NMDA receptors produces large increases in cytosolic Ca(2+) that are taken up into mitochondria. We used recombinant aequorin targeted to mitochondria to report changes in matrix Ca(2+) in rat hippocampal neurons in culture. Upon binding Ca(2+), aequorin emits a photon in a one-shot reaction that consumes the indicator. Here we show that stimulation with NMDA produced a mitochondrial Ca(2+) response that rapidly inactivated. However, following a 30-min recovery period the response was restored, suggesting the presence of a pool of indicator that was not exposed to high Ca(2+) during the initial stimulus. We speculate that aequorin distant from the Ca(2+) source was protected from microdomains of high Ca(2+) near the plasmalemma and that this aequorin moved, either by movement of individual mitochondria or via the mitochondrial tubular network, to replenish consumed indicator during the recovery time. A large Ca(2+) increase in a subset of mitochondria could produce local changes in energy metabolism, regional Ca(2+) buffering, and foci that initiate neurotoxic processes.

Altered distribution of mitochondria impairs calcium homeostasis in rat hippocampal neurons in culture

The specificity of Ca2+ signals is conferred in part by limiting changes in cytosolic Ca2+ to subcellular domains. Mitochondria play a major role in regulating Ca2+ in neurons and may participate in its spatial localization. We examined the effects of changes in the distribution of mitochondria on NMDA-induced Ca2+ increases. Hippocampal cultures were treated with the microtubule-destabilizing agent vinblastine, which caused the mitochondria to aggregate and migrate towards one side of the neuron. This treatment did not appear to decrease the energy status of mitochondria, as indicated by a normal membrane potential and pH gradient across the inner membrane. Moreover, electron microscopy showed that vinblastine treatment altered the distribution but not the ultrastructure of mitochondria. NMDA (200 micro m, 1 min) evoked a greater increase in cytosolic Ca2+ in vinblastine-treated cells than in untreated cells. This increase did not result from impaired Ca2+ efflux, enhanced Ca2+ influx, opening of the mitochondrial permeability transition pore or altered function of endoplasmic reticulum Ca2+ stores. Ca2+ uptake into mitochondria was reduced by 53% in vinblastine-treated cells, as reported by mitochondrially targeted aequorin. Thus, the distribution of mitochondria maintained by microtubules is critical for buffering Ca2+ influx. A subset of mitochondria close to a Ca2+ source may preferentially regulate Ca2+ microdomains, set the threshold for Ca2+-induced toxicity and participate in local ATP production.

Controlled transgene expression by E1-E4-defective adenovirus vectors harbouring a "tet-on" switch system

BACKGROUND

The "tet switch system" was originally described under the tet-off configuration with its components encoded by two separate plasmids. Since then, many virus vectors harbouring tet-off components have been designed and their regulation by tetracycline is widely reported. On the contrary, tet-on regulation by viral vectors is poorly documented.

METHODS

E1-E4-defective adenoviruses harbouring either rtTA or the luciferase gene under a minimal inducible promoter (TK* or CMV*) or both components in a single genome were produced. Using either a double or a single virus strategy, induction of luciferase expression was investigated in various cell lines, in mice muscle and in rat brain.

RESULTS

Over 400-fold induction can be reached with PC12 and NHA cells using a double virus strategy. Comparison of the background activity of different minimal inducible promoters revealed a significant difference between TK* and CMV* promoters both with the cell culture and the in vivo experiments. Interestingly, a single virus strategy permitted an induction exceeding 600-fold with human astrocyte primary cells. Moreover, the E1-E4-defective adenovirus-mediated tet-on system can be quickly switched off and turned back on again. Depending on the cell line, the level of rtTA derived by the single virus strategy differed, resulting in different efficiencies. Experiments performed in rat striatum and mouse muscle confirmed the importance of rtTA expression and minimal promoter used on both doxycycline-independent expression and induction efficiency. Under appropriated rtTA expression, a 32-fold induction is observed in mouse muscle.

CONCLUSIONS

In the recombinant adenovirus context, the CMV* but not the TK* promoter is sensitive to transcriptional interference resulting in high doxycycline-independent expression. By paying attention to the rtTA expression, moderate and high induction can be obtained in vivo and in vitro accordingly.

Visualizing selective neural pathways with WGA transgene: combination of neuroanatomy with gene technology

Functional logic employed by the nervous system for information processing resides mainly in the wiring patterns among specific types of neurons. Therefore, detailed knowledge on neuronal networks is essential for understanding a wide range of brain functions. A powerful and long-awaited method for analyzing the neuronal connectivity patterns would be to deliver tracers selectively to specific types of neurons and at the same time to label transsynaptically their axonal target neurons. For this purpose, we took advantage of a unique property of plant lectin, wheat germ agglutinin (WGA), which has been used as a transsynaptic tracer in classical neuroanatomical studies. We developed a novel genetic strategy that employs WGA cDNA as a transgene, for the visualization of selective and functional neural pathways in the nervous system. In this article, I will introduce several examples of neural pathways visualized with the WGA transgene and discuss about its further refinement and applications.

Corticostriatopallidal neuroprotection by adenovirus-mediated ciliary neurotrophic factor gene transfer in a rat model of progressive striatal degeneration

Ciliary neurotrophic factor (CNTF) is a potent protective factor for striatal neurons in animal models of Huntington's disease (HD). Clinical application of this potential therapeutic still requires the design and optimization of delivery systems. In the case of HD, spatial spread in the vast volume occupied by the striatum and long-term delivery of the factor are particular challenges for these systems. We explored the potential of adenovirus-mediated gene transfer to fulfill these requirements by studying the functional and anatomical effects of single-site striatal delivery of CNTF recombinant vectors in a rat model of HD. In an initial series of experiments, unilateral injections of CNTF adenovirus were performed in rats 10, 30, or 90 d before a 5 d neurotoxic treatment with systemic 3-nitropropionic acid (3NP). Preservation of striatal neurons was observed at all time points, demonstrating temporally extended neuroprotective effects of the CNTF adenovirus. In a second series of experiments, bilateral injections of CNTF adenovirus were performed in the medial aspect of the striatum 10 d before starting 3NP intoxication. Despite placement of the CNTF-producing vector outside the lateral striatal area susceptible to lesion, massive protection of corticostriatopallidal circuits was observed, associated with significant behavioral benefits. This spatial spread of neuroprotection is discussed with reference to the retrograde transport of the adenovirus vector and the anterograde transport of the transgenic CNTF. Overall, adenovirus-mediated CNTF gene transfer appears to be a potentially useful delivery system for widespread, long-term circuit neuroprotection in HD patients.

Astrocyte delivery of glial cell line-derived neurotrophic factor in a mouse model of Parkinson's disease

Primary astrocytes were genetically modified ex vivo to express recombinant glial cell line-derived neurotrophic factor (GDNF) and subsequently were tested for their ability to provide neuroprotection to dopaminergic neurons in a 6-hydroxydopamine (6-OHDA) mouse model of Parkinson's disease. A replication-defective retrovirus was constructed, which contained the rat GDNF sequence and a sequence encoding a beta-galactosidase (beta-gal)/neomycin phosphotransferase fusion protein, linked via an internal ribosomal entry site. Murine astrocytes transduced with this vector secreted GDNF into the culture media at the rate of 115 +/- 34 pg/24 h/10(5) cells and expressed cytoplasmic beta-gal, whereas control nontransduced astrocytes were negative for GDNF production and cytoplasmic beta-gal expression. Mice that received implants of GDNF-producing astrocytes into the striatum or nigra displayed elevated levels of GDNF compared to mice that received control nontransduced astrocytes. In addition, tissue content of GDNF was increased bilaterally and in brain regions both proximal and distal to the graft, even though astrocyte migration away from the graft site did not occur. Importantly, GDNF-producing astrocytes provided marked neuroprotection of nigral dopaminergic perikarya, and partial protection of striatal dopaminergic fibers, when implanted into the midbrain 6 days prior to a retrograde 6-OHDA lesion, as assessed by tyrosine hydroxylase immunohistochemistry. Similarly, GDNF-producing astrocytes prevented the acquisition of amphetamine-induced rotational behavior in 6-OHDA-treated mice and completely prevented dopamine depletion within the substantia nigra, as assessed by high-performance liquid chromatography. These results indicate that continuous exposure to low levels of GDNF provided by transgenic astrocytes provides marked neuroprotection of nigral dopaminergic neurons. (c)2002 Elsevier Science (USA).

Stem cells in the treatment of Parkinson's disease

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

NMDA-induced calcium loads recycle across the mitochondrial inner membrane of hippocampal neurons in culture

Mitochondria sequester N-methyl-D-aspartate (NMDA)-induced Ca(2+) loads and regulate the shape of intracellular Ca(2+) concentration ([Ca(2+)](i)) responses in neurons. When isolated mitochondria are exposed to high [Ca(2+)](,) Ca(2+) enters the matrix via the uniporter and returns to the cytosol by Na(+)/Ca(2+) exchange. Released Ca(2+) may re-enter the mitochondrion recycling across the inner membrane dissipating respiratory energy. Ca(2+) recycling, the continuous uptake and release of Ca(2+) by mitochondria, has not been described in intact neurons. Here we used single-cell microfluorimetry to measure [Ca(2+)](i) and mitochondrially targeted aequorin to measure matrix Ca(2+) concentration ([Ca(2+)](mt)) to determine whether Ca(2+) recycles across the mitochondrial inner membrane in intact neurons following treatment with NMDA. We used ruthenium red and CGP 37157 to block uptake via the uniporter and release via Na(+)/Ca(2+) exchange, respectively. As predicted by the Ca(2+) recycling hypothesis, blocking the uniporter immediately following challenge with 200 microM NMDA produced a rapid and transient increase in cytosolic Ca(2+) without a corresponding increase in matrix Ca(2+). Blocking mitochondrial Ca(2+) release produced the opposite effect, depressing cytosolic Ca(2+) levels and prolonging the time for matrix Ca(2+) levels to recover. The Ca(2+) recycling hypothesis uniquely predicts these reciprocal changes in the Ca(2+) levels between the two compartments. Ca(2+) recycling was not detected following treatment with 20 microM NMDA. Thus Ca(2+) recycling across the inner membrane was more pronounced following treatment with a high relative to a low concentration of NMDA, consistent with a role in Ca(2+)-dependent neurotoxicity.

Viral-based gene transfer to the mammalian CNS for functional genomic studies

A fundamental problem in neuroscience has been the creation of suitable in vivo model systems to study basic neurological phenomena and pathology of the central nervous system (CNS). Somatic cell genetic engineering with viral vectors provides a versatile tool to model normal brain physiology and a variety of neurological diseases.

Neuroprotection through delivery of glial cell line-derived neurotrophic factor by neural stem cells in a mouse model of Parkinson's disease

Neural stem cells (NSCs) have been proposed as tools for treating neurodegeneration because of their capacity to give rise to cell types appropriate to the structure in which they are grafted. In the present work, we explore the ability of NSCs to stably express transgenes and locally deliver soluble molecules with neuroprotective activity, such as glial cell line-derived neurotrophic factor (GDNF). NSCs engineered to release GDNF engrafted well in the host striatum, integrated and gave rise to neurons, astrocytes, and oligodendrocytes, and maintained stable high levels of GDNF expression for at least 4 months. The therapeutic potential of intrastriatal GDNF-NSCs grafts was tested in a mouse 6-hydroxydopamine model of Parkinson's disease. We found that GDNF-NSCs prevented the degeneration of dopaminergic neurons in the substantia nigra and reduced behavioral impairment in these animals. Thus, our results demonstrate that NSCs efficiently express therapeutic levels of GDNF in vivo, suggesting a use for NSCs engineered to release neuroprotective molecules in the treatment of neurodegenerative disorders, including Parkinson's disease.

Bcl-2 and GDNF Delivered by HSV-Mediated Gene Transfer Act Additively to Protect Dopaminergic Neurons from 6-OHDA-Induced Degeneration

Previous studies have demonstrated that either the neurotrophin glial-derived neurotrophic factor (GDNF) or the antiapoptotic peptide Bcl-2 delivered into striatum by a viral vector protects dopaminergic neurons of the substantia nigra in vivo from degeneration induced by the administration of the neurotoxin 6-hydroxydopamine (6-OHDA). In this study we used recombinant, replication-incompetent, genomic herpes simplex virus-based vectors to deliver the genes coding for Bcl-2 and GDNF into rat substantia nigra (SN) 1 week prior to 6-OHDA injection into the striatum. Vector-mediated expression of either Bcl-2 or GDNF alone each resulted in a doubling in cell survival as measured by retrograde labeling with fluorogold (FG) and a 50% increase in tyrosine hydroxylase-immunoreactive (TH-IR) neurons in the lesioned SN compared to the unlesioned side. Gene transfer of Bcl-2 and GDNF were equivalent in this effect. Coadministration of the Bcl-2-expressing vector with the GDNF-expressing vector improved the survival of lesioned SN neurons as measured by FG labeling by 33% and by the expression of TH-IR by 15%. These results suggest that the two factors delivered together act in an additive fashion to improve DA cell survival in the face of 6-OHDA toxicity.

Intravitreal adenoviral gene transfer evokes an immune response in the retina that is directed against the heterologous lacZ transgene product but does not limit transgene expression

Recombinant E1-deleted adenoviral vectors (DeltaE1-Ad) are promising tools for in vivo gene transfer into the mammalian CNS including the retina. However, the duration of transgene expression is limited, and this limitation has partly been attributed to an immune response directed against vector-derived proteins. Here, we employed immunocytochemistry to assess the immune response to intravitreously injected DeltaE1-Ad encoding the lacZ gene or various neurotrophins (NTs). beta-Galactosidase was expressed by retinal cells for up to 4 weeks. Following intravitreal inoculation of AdCMV-lacZ, microglial and T cells were detected with a panel of antibodies in the retinal cell layers after 2 days (D2). The inflammatory response reached a maximum between D7 and D14. In contrast, no immune response was seen following injection of Ad encoding NTs. Yet, like with Ad-CMV-lacZ, their expression was also limited to approximately 4 weeks. Thus, beta-galactosidase seems to trigger a host immune response following intravitreal adenoviral lacZ gene transfer, but immune responses are not the cause of limited NT transgene expression from the CMV promoter in the inner retina.

Quantitative analysis of transgene protein, mRNA, and vector DNA following injection of an adenoviral vector harboring glial cell line-derived neurotrophic factor into the primate caudate nucleus

Gene therapy for neurodegenerative diseases relies on stable expression of a vector-mediated transgene in the human central nervous system (CNS). In nonhuman primate CNS, transgene expression has been primarily assessed using descriptive histological methods. Here, we quantified the expression of a human glial cell line-derived neurotrophic factor (hGDNF) transgene using an ELISA specific for hGDNF protein and real-time quantitative RT-PCR and PCR for hGDNF mRNA and vector DNA, respectively. Transgene expression was assessed 1 week after injection of an E1-, E3-deleted adenovirus harboring hGDNF into the caudate nucleus of St. Kitts green monkey. We found that 57-147 million and 116-771 million copies of hGDNF mRNA and vector DNA, respectively, were present per 10,000 copies of the beta-actin gene. In the same sites, 40-152 pg of hGDNF protein per milligram of tissue was measured. Comparisons of these measures among monkeys demonstrated variable vector DNA and protein levels, but consistent mRNA levels at one-third of the level of vector DNA. This suggests that local responses to the vector play a role in the level of transgene expression and that high levels of vector DNA do not necessarily predict a high level of transgene protein. However, the results of this study do show that neuroprotective levels of GDNF transgene expression can be achieved following injection of an adenoviral vector into nonhuman primate caudate. Moreover, these assays provide quantitative methods for evaluating and comparing viral vectors in primate CNS.

The future of gene therapy for stroke

New diagnostic and treatment strategies are being developed for stroke. Gene therapy has several potential advantages over classical pharmacologic therapy. Direct administration of DNA into the brain offers the advantage of producing high concentrations of therapeutic agents in a relatively localized environment. Gene transfer also provides longer duration of effect than traditional drug therapy. Recent studies indicate that gene transfer can produce functional proteins in brain parenchyma and cerebral blood vessels after stroke. In animal models, gene transfer may reduce effects of cerebral ischemia or subarachnoid hemorrhage. This review summarizes some current methods of gene transfer to the brain and recent progress that may lead to gene therapy for stroke.

Acute direct adenoviral vector cytotoxicity and chronic, but not acute, inflammatory responses correlate with decreased vector-mediated transgene expression in the brain

The potential utility of adenoviruses for the treatment of chronic neurological disease is controversial due to reports of vector-associated toxicity, inflammation, and transient transgene expression. To focus upon the mechanism by which transgene expression is lost, we injected increasing doses [1 x 10(6) to 1 x 10(9) infectious units (iu)] of a first-generation adenovirus vector expressing beta-galactosidase into the brains of immune-competent adult rats. Transgene expression was evaluated simultaneously with acute neuronal and glial cell cytotoxicity, and acute and chronic inflammation using immunohistochemistry, at 3 and 30 days post-vector administration. Our results show a clear threshold effect of viral dose upon the amount of transgene expression persisting by 30 days after vector administration. Below 10(8) iu, transgene expression remained stable over the 30-day period. Following infection of more than 10(8) iu, the extent of transgene expression at 30 days was inversely correlated with increasing viral dose. The severity of acute inflammation increased proportionally with increasing vector dose from 10(6) to 10(9) infectious units. In contrast, acute vector-mediated cytotoxicity and chronic inflammation were observed only above the threshold level of vector dose. Above 10(8) iu both the extent of the acute toxicity and the severity of the chronic inflammation were inversely correlated with transgene expression at 30 days. Thus, our data suggest that both an acute loss of cells through direct vector-mediated toxicity and the elicitation of chronic inflammation (but not acute inflammation) may account for the decline in transduction persistence at high vector doses.

Towards a neuroprotective gene therapy for Parkinson's disease: use of adenovirus, AAV and lentivirus vectors for gene transfer of GDNF to the nigrostriatal system in the rat Parkinson model

During the last few years, recombinant viral vectors derived from adenovirus (Ad), adeno-associated virus (AAV) or lentivirus (LV) have been developed into highly effective vehicles for gene transfer to the adult central nervous system. In recent experiments, in the rat model of Parkinson's disease, all three vector systems have been shown to be effective for long-term delivery of glial cell line-derived neurotrophic factor (GDNF) at biologically relevant levels in the nigrostriatal system. Injection of the GDNF encoding vectors into either striatum or substantia nigra thus makes it possible to obtain a regionally restricted over-expression of GDNF within the nigrostriatal system that is sufficient to block the toxin-induced degeneration of the nigral dopamine neurons. Injection of GDNF vectors in the striatum, in particular, is effective not only in rescuing the cell bodies in the substantia nigra, but also in preserving the nigrostriatal projection and a functional striatal dopamine innervation in the rat Parkinson model. Long-term experiments using AAV-GDNF and LV-GDNF vectors show, moreover, that sustained GDNF delivery over 3-6 months can promote regeneration and significant functional recovery in both 6-OHDA-lesioned rats and MPTP-lesioned monkeys. The impressive efficacy of the novel AAV and LV vectors in rodent and primate Parkinson models suggests that the time may now be ripe to explore these vector systems as tools for neuroprotective treatments in patients with Parkinson's disease.

Gene therapy for amyotrophic lateral sclerosis and other motor neuron diseases

There are several incurable diseases of motor neuron degeneration, including amyotrophic lateral sclerosis (ALS), primary lateral sclerosis, hereditary spastic hemiplegia, spinal muscular atrophy, and bulbospinal atrophy. Advances in gene transfer techniques coupled with new insights into molecular pathology have opened promising avenues for gene therapy aimed at halting disease progression. Nonviral preparations and recombinant adenoviruses, adeno-associated viruses, herpesviruses, and lentiviruses may ultimately transduce sufficient numbers of cerebral, brainstem, and spinal cord neurons for therapeutic applications. This could be accomplished by direct injection, transduction of lower motor neurons via retrograde transport after intramuscular injection, or cell-based therapies. Studies using transgenic mice expressing mutant superoxide dismutase 1 (SOD1), a model for one form of ALS, established that several proteins were neuroprotective, including calbindin, bcl-2, and growth factors. These same molecules promoted neuronal survival in other injury models, suggesting general applicability to all forms of ALS. Potentially correctable genetic lesions have also been identified for hereditary spastic hemiplegia, bulbospinal atrophy, and spinal muscular atrophy. Finally, it may be possible to repopulate lost corticospinal and lower motor neurons by transplanting stem cells or stimulating native progenitor populations. The challenge ahead is to translate these basic science breakthroughs into workable clinical practice.

Development of an adenoviral vector for intracerebral delivery of the dopamine D(2) receptor

The age-related loss of striatal dopamine D(2) receptors (D(2)R) has been observed in numerous species, including rodents, monkeys, and man, and is partly responsible for impaired motor function in aged mammals. We have developed an adenoviral vector designed for intracerebral transfer of cDNA for D(2)R. Results of in vitro studies demonstrated that the vector produced abundant message for D(2)R and that the vector was membrane bound and capable of binding appropriate ligand. Results of in vivo studies provided clear evidence of D(2)R production when injected into the striatum of rats. The D(2)R produced were capable of binding appropriate ligand. In addition, evidence of functional receptors was produced by demonstrating apomorphine-induced rotational behavior in rats receiving a unilateral injection of the vector. Despite these successes, we have been unable to demonstrate improvement in the motor behavior of aged rats receiving bilateral injections of the vector. A major problem with this vector as with similar adenoviral vectors is the loss of expression beginning 3-5 days after injection to undetectable levels at 21 days. Because of the lack of motor functional effects in aged rats and the loss of expression of the vector, other strategies for development of the vector are being pursued. Regarding functional effects, we have examined the feasibility of manipulating hippocampal acetylcholine (ACh) release through D(2)R manipulation to improve memory performance. Using microdialysis, we have demonstrated in vivo in rats that treatment with a D(2)R agonist increases hippocampal ACh release while treatment with a D(2)R antagonist attentuates this effect as well as impairs performance in a complex maze task. In addition, a D(2)R null mutant mouse is being used to examine possible therapeutic effects of the vector. These mice show specific motor deficits. Recent studies using positron emission tomography have also demonstrated the feasibility of in vivo imaging of the vector. Thus, use of adenoviral vectors specific for neurotransmitter receptors can provide a highly useful research tool for examining age-related alterations in behavioral function and a possible strategy for therapeutic intervention.

Self-inactivating lentiviral vectors with enhanced transgene expression as potential gene transfer system in Parkinson's disease

Glial cell line-derived neurotrophic factor (GDNF) is able to protect dopaminergic neurons against various insults and constitutes therefore a promising candidate for the treatment of Parkinson's disease. Lentiviral vectors that infect quiescent neuronal cells may allow the localized delivery of GDNF, thus avoiding potential side effects related to the activation of other brain structures. To test this hypothesis in a setting ensuring both maximal biosafety and optimal transgene expression, a self-inactivating (SIN) lentiviral vector was modified by insertion of the posttranscriptional regulatory element of the woodchuck hepatitis virus, and particles were produced with a multiply attenuated packaging system. After a single injection of 2 microl of a lacZ-expressing vector (SIN-W-LacZ) in the substantia nigra of adult rats, an average of 40.1 +/- 6.0% of the tyrosine hydroxylase (TH)-positive neurons were transduced as compared with 5.0 +/- 2.1% with the first-generation lentiviral vector. Moreover, the SIN-W vector expressing GDNF under the control of the mouse phosphoglycerate kinase 1 (PGK) promoter was able to protect nigral dopaminergic neurons after medial forebrain bundle axotomy. Expression of hGDNF in the nanogram range was detected in extracts of mesencephalon of animals injected with an SIN-W-PGK-GDNF vector, whereas it was undetectable in animals injected with a control vector. Lentiviral vectors with enhanced expression and safety features further establish the potential use of these vectors for the local delivery of bioactive molecules into defined structures of the central nervous system.

Differential effects of glial cell line-derived neurotrophic factor (GDNF) in the striatum and substantia nigra of the aged Parkinsonian rat

Injection of an adenoviral (Ad) vector encoding human glial cell line-derived neurotrophic factor (GDNF) protects dopaminergic (DA) neurons in the substantia nigra (SN) of young rats. As Parkinson's disease occurs primarily in aged populations, we examined whether chronic biosynthesis of GDNF, achieved by adenovirus-mediated delivery of a GDNF gene (AdGDNF), can protect DA neurons and improve DA-dependent behavioral function in aged (20 months) rats with progressive 6-OHDA lesions of the nigrostriatal projection. Furthermore, the differential effects of injecting AdGDNF either near DA cell bodies in the SN or at DA terminals in the striatum were compared. AdGDNF or control vector was injected unilaterally into either the striatum or SN. One week later, rats received a unilateral intrastriatal injection of 6-OHDA on the same side as the vector injection. AdGDNF injection into either the striatum or SN significantly reduced the loss of FG labelled DA neurons 5 weeks after lesion (P </= 0.05). However, only striatal injections of AdGDNF protected against the development of behavioral deficits characteristic of unilateral DA depletion. Striatal AdGDNF injections also reduced tyrosine hydroxylase fiber loss and increased amphetamine-induced striatal Fos expression. These results demonstrate that increased levels of striatal, but not nigral, GDNF biosynthesis prevents DA neuronal loss and protects DA terminals from 6-OHDA-induced damage, thereby maintaining DA function in the aged rat.

Lentiviral gene transfer to the nonhuman primate brain

Lentiviral vectors infect quiescent cells and allow for the delivery of genes to discrete brain regions. The present study assessed whether stable lentiviral gene transduction can be achieved in the monkey nigrostriatal system. Three young adult Rhesus monkeys received injections of a lentiviral vector encoding for the marker gene beta galatosidase (beta Gal). On one side of the brain, each monkey received multiple lentivirus injections into the caudate and putamen. On the opposite side, each animal received a single injection aimed at the substantia nigra. The first two monkeys were sacrificed 1 month postinjection, while the third monkey was sacrificed 3 months postinjection. Robust incorporation of the beta Gal gene was seen in the striatum of all three monkeys. Stereological counts revealed that 930,218; 1,192,359; and 1,501,217 cells in the striatum were beta Gal positive in monkeys 1 (n = 2) and 3 (n = 1) months later, respectively. Only the third monkey had an injection placed directly into the substantia nigra and 187,308 beta Gal-positive cells were identified in this animal. The injections induced only minor perivascular cuffing and there was no apparent inflammatory response resulting from the lentivirus injections. Double label experiments revealed that between 80 and 87% of the beta Gal-positive cells were neurons. These data indicate that robust transduction of striatal and nigral cells can occur in the nonhuman primate brain for up to 3 months. Studies are now ongoing testing the ability of lentivirus encoding for dopaminergic trophic factors to augment the nigrostriatal system in nonhuman primate models of Parkinson's disease.

Inflammatory responses and their impact on beta-galactosidase transgene expression following adenovirus vector delivery to the primate caudate nucleus

An E1, E3 deleted adenovirus vector, serotype 5, carrying the marker gene LacZ was bilaterally microinfused into the caudate nuclei of 10 St Kitts green monkeys. The location and number of cells expressing transgene and host immunologic response were evaluated at 1 week (n = 2) and 1 month (n = 8) following vector infusion. A large number of cells expressed beta-galactosidase in some monkeys, exceeding 600000 in one monkey, but no expression was seen in three of 10. All monkeys had positive adenoviral antibody titers before vector infusion, indicating the possibility of previous exposure to some adenovirus, but only one showed a significant increase in titer afterwards. Inflammatory cell markers revealed an inverse correlation between transgene expression and the extent of inflammatory response. Dexamethasone administered immediately before and for 8 days following vector delivery, however, had no effect on transgene expression. The demonstration of significant inflammatory responses in the brain of some individual primates, including demyelination, indicates the need for new generations of adenovirus vectors, or the successful suppression of inflammatory responses, before this vector is suitable for non-cytotoxic clinical applications in the CNS.