Characterization of intrastriatal recombinant adeno-associated virus-mediated gene transfer of human tyrosine hydroxylase and human GTP-cyclohydrolase I in a rat model of Parkinson's disease

Routes of administration for adeno-associated viruses carrying gene therapies for brain diseases

Gene therapy is a powerful tool to treat various central nervous system (CNS) diseases ranging from monogenetic diseases to neurodegenerative disorders. Adeno-associated viruses (AAVs) have been widely used as the delivery vehicles for CNS gene therapies due to their safety, CNS tropism, and long-term therapeutic effect. However, several factors, including their ability to cross the blood-brain barrier, the efficiency of transduction, their immunotoxicity, loading capacity, the choice of serotype, and peripheral off-target effects should be carefully considered when designing an optimal AAV delivery strategy for a specific disease. In addition, distinct routes of administration may affect the efficiency and safety of AAV-delivered gene therapies. In this review, we summarize different administration routes of gene therapies delivered by AAVs to the brain in mice and rats. Updated knowledge regarding AAV-delivered gene therapies may facilitate the selection from various administration routes for specific disease models in future research.

An efficient rAAV vector for protein expression in cortical parvalbumin expressing interneurons

Recombinant adeno-associated viruses (rAAV) are extensively used in both research and clinical applications. Despite significant advances, there is a lack of short promoters able to drive the expression of virus delivered genes in specific classes of neurons. We designed an efficient rAAV vector suitable for the rAAV-mediated gene expression in cortical interneurons, mainly in the parvalbumin expressing cells. The vector includes a short parvalbumin promoter and a specialized poly(A) sequence. The degree of conservation of the parvalbumin gene adjoining non-coding regions was used in both the promoter design and the selection of the poly(A) sequence. The specificity was established by co-localizing the fluorescence of the virus delivered eGFP and the antibody for a neuronal marker. rAAV particles were injected in the visual cortex area V1/V2 of adult rats (2-4 months old). Neurons expressing the virus delivered eGFP were mainly positive for interneuronal markers: 66.5 ± 2.8% for parvalbumin, 14.6 ± 2.4% for somatostatin, 7.1 ± 1.2% for vasoactive intestinal peptide, 2.8 ± 0.6% for cholecystokinin. Meanwhile, only 2.1 ± 0.5% were positive for CaMKII, a marker for principal cells in the cortex. The efficiency of the construct was verified by optogenetic experiments: the expression of the virus delivered ChR2 channels was sufficient to evoke by blue light laser high frequency bursts of action potentials in putative fast spiking neurons. We conclude that our promoter allows highly specific expression of the rAAV delivered cDNAs in cortical interneurons with a strong preference for the parvalbumin positive cells.

Levodopa-induced dyskinesia: a historical review of Parkinson's disease, dopamine, and modern advancements in research and treatment

Over the past two decades, animal models of Parkinson's disease (PD) have helped to determine the plausible underlying mechanism of levo-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia following L-DOPA treatment. However, our understanding of the mechanisms related to this phenomenon remains incomplete. The purpose of this manuscript is to provide a comprehensive review of treatment protocols used for assessing the occurrence of L-DOPA-induced dyskinesia, L-DOPA absorption, distribution, drug/food interaction, and discuss current strategies and future directions. This review offers a historical perspective using L-DOPA in animal models of PD and the occurrence of L-DOPA-induced dyskinesia.

Computationally Guided Intracerebral Drug Delivery via Chronically Implanted Microdevices

Treatments for neurologic diseases are often limited in efficacy due to poor spatial and temporal control over their delivery. Intracerebral delivery partially overcomes this by directly infusing therapeutics to the brain. Brain structures, however, are nonuniform and irregularly shaped, precluding complete target coverage by a single bolus without significant off-target effects and possible toxicity. Nearly complete coverage is crucial for effective modulation of these structures. We present a framework with computational mapping algorithms for neural drug delivery (COMMAND) to guide multi-bolus targeting of brain structures that maximizes coverage and minimizes off-target leakage. Custom-fabricated chronic neural implants leverage rational fluidic design to achieve multi-bolus delivery in rodents through a single infusion of radioactive tracer (Cu-64). The resulting spatial distributions replicate computed spatial coverage with 5% error in vivo, as detected by positron emission tomography. COMMAND potentially enables accurate, efficacious targeting of discrete brain regions.

Adeno-Associated Virus Technologies and Methods for Targeted Neuronal Manipulation

Cell-type-specific expression of molecular tools and sensors is critical to construct circuit diagrams and to investigate the activity and function of neurons within the nervous system. Strategies for targeted manipulation include combinations of classical genetic tools such as Cre/loxP and Flp/FRT, use of cis-regulatory elements, targeted knock-in transgenic mice, and gene delivery by AAV and other viral vectors. The combination of these complex technologies with the goal of precise neuronal targeting is a challenge in the lab. This report will discuss the theoretical and practical aspects of combining current technologies and establish best practices for achieving targeted manipulation of specific cell types. Novel applications and tools, as well as areas for development, will be envisioned and discussed.

A brain microvasculature endothelial cell-specific viral vector with the potential to treat neurovascular and neurological diseases

Gene therapy critically relies on vectors that combine high transduction efficiency with a high degree of target specificity and that can be administered through a safe intravenous route. The lack of suitable vectors, especially for gene therapy of brain disorders, represents a major obstacle. Therefore, we applied an in vivo screening system of random ligand libraries displayed on adeno‐associated viral capsids to select brain‐targeted vectors for the treatment of neurovascular diseases. We identified a capsid variant showing an unprecedented degree of specificity and long‐lasting transduction efficiency for brain microvasculature endothelial cells as the primary target of selection. A therapeutic vector based on this selected viral capsid was used to markedly attenuate the severe cerebrovascular pathology of mice with incontinentia pigmenti after a single intravenous injection. Furthermore, the versatility of this selection system will make it possible to select ligands for additional in vivo targets without requiring previous identification of potential target‐specific receptors.

Simple Purification of Adeno-Associated Virus-DJ for Liver-Specific Gene Expression

Recombinant gene expression using adeno-associated viruses (AAVs) has become a valuable tool in animal studies, as they mediate safe expression of transduced genes for several months. The liver is a major organ of metabolism, and liver-specific expression of a gene can be an invaluable tool for metabolic studies. AAV-DJ is a recombinant AAV generated by the gene shuffling of various AAV serotypes and shares characteristics of AAV2 and AAV8. AAV-DJ contains a heparin-binding domain in its capsid, which suggests that a heparin column could be used for the purification of the AAV. Given that AAV-DJ has been only recently available, relatively little is known about the optimal preparation/purification and application of AAV-DJ. Here, we present a simple large-scale preparation method that can generate 3×10¹³ viral particles for in vivo experiments and demonstrate liver-specific gene expression via systemic injection in mice.

Controlled Striatal DOPA Production From a Gene Delivery System in a Rodent Model of Parkinson's Disease

Conventional symptomatic treatment for Parkinson's disease (PD) with long-term L-3,4-dihydroxyphenylalanine (DOPA) is complicated with development of drug-induced side effects. In vivo viral vector-mediated gene expression encoding tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GCH1) provides a drug delivery strategy of DOPA with distinct advantages over pharmacotherapy. Since the brain alterations made with current gene transfer techniques are irreversible, the therapeutic approaches taken to the clinic should preferably be controllable to match the needs of each individual during the course of their disease. We used a recently described tunable gene expression system based on the use of destabilized dihydrofolate reductase (DD) and generated a N-terminally coupled GCH1 enzyme (DD-GCH1) while the TH enzyme was constitutively expressed, packaged in adeno-associated viral (AAV) vectors. Expression of DD-GCH1 was regulated by the activating ligand trimethoprim (TMP) that crosses the blood-brain barrier. We show that the resulting intervention provides a TMP-dose-dependent regulation of DOPA synthesis that is closely linked to the magnitude of functional effects. Our data constitutes the first proof of principle for controlled reconstitution of dopamine capacity in the brain and suggests that such next-generation gene therapy strategies are now mature for preclinical development toward use in patients with PD.

Oxidative Stress Is Associated with Neuroinflammation in Animal Models of HIV-1 Tat Neurotoxicity

HIV-1 trans-acting protein Tat, an essential protein for viral replication, is a key mediator of neurotoxicity. If Tat oxidant injury and neurotoxicity have been described, consequent neuroinflammation is less understood. Rat caudate-putamens (CPs) were challenged with Tat, with or without prior rSV40-delivered superoxide dismutase or glutathione peroxidase. Tat injection caused oxidative stress. Administration of Tat in the CP induced an increase in numbers of Iba-1- and CD68-positive cells, as well as an infiltration of astrocytes. We also tested the effect of more protracted Tat exposure on neuroinflammation using an experimental model of chronic Tat exposure. SV(Tat): a recombinant SV40-derived gene transfer vector was inoculated into the rat CP, leading to chronic expression of Tat, oxidative stress, and ongoing apoptosis, mainly located in neurons. Intra-CP SV(Tat) injection induced an increase in microglia and astrocytes, suggesting that protracted Tat production increased neuroinflammation. SV(SOD1) or SV(GPx1) significantly reduced neuroinflammation following Tat administration into the CP. Thus, Tat-induced oxidative stress, CNS injury, neuron loss and inflammation may be mitigated by antioxidant gene delivery.

Continuous DOPA synthesis from a single AAV: dosing and efficacy in models of Parkinson's disease

We used a single adeno-associated viral (AAV) vector co-expressing tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GCH1) to investigate the relationship between vector dose, and the magnitude and rate of recovery in hemi-parkinsonian rats. Intrastriatal injections of >1E10 genomic copies (gc) of TH-GCH1 vector resulted in complete recovery in drug-naïve behavior tests. Lower vector dose gave partial to no functional improvement. Stereological quantification revealed no striatal NeuN+ cell loss in any of the groups, whereas a TH-GCH1 dose of >1E11 gc resulted in cell loss in globus pallidus. Thus, a TH-GCH1 dose of 1E10 gc gave complete recovery without causing neuronal loss. Safety and efficacy was also studied in non-human primates where the control vector resulted in co-expression of the transgenes in caudate-putamen. In the TH-GCH1 group, GCH1 expression was robust but TH was not detectable. Moreover, TH-GCH1 treatment did not result in functional improvement in non-human primates.

Overview of gene delivery into cells using HSV-1-based vectors

This overview describes the considerations involved in the preparation and use of a herpes simplex virus type 1 (HSV-1) amplicon as a vector for gene transfer into neurons. Strategies for gene delivery into neurons, either to study the molecular biology of brain function or for gene therapy, must utilize vectors that persist stably in postmitotic cells and that can be targeted both spatially and temporally in the nervous system in vivo. This unit describes the biology of HSV-1 along with a discussion covering development of amplicon and genomic HSV-1 vectors. Advantages and disadvantages of current HSV-1 vectors are presented, and HSV-1 vectors are compared with other vectors for gene transfer into neurons.

Dysfunction of dopamine homeostasis: clues in the hunt for novel Parkinson's disease therapies

Parkinson's disease is the second most common neurodegenerative disorder and, at present, has no cure. Both environmental and genetic factors have been implicated in the etiology of the disease; however, the pathogenic pathways leading to neuronal degeneration are still unclear. Parkinson's disease is characterized by the preferential death of a subset of neurons in the mesencephalon that use dopamine as neurotransmitter for synaptic communication. Dopamine is a highly reactive molecule that can lead to cytotoxicity if not properly stored and metabolized. Targeting any of the pathways that tightly control this neurotransmitter holds great therapeutic expectations. In this article we present a comprehensive overview of the cellular pathways that control dopamine fate and discuss potential therapeutic approaches to counteract or slow Parkinson's disease onset and progression.

Liposomes for brain delivery

INTRODUCTION

Development of drug delivery systems for brain delivery is one of the most challenging research topics in pharmaceutical areas, mainly due to the presence of the blood-brain barrier (BBB), which separates the blood from the cerebral parenchyma thus limiting the brain uptake of the majority of therapeutic agents. Among the several carriers, which have been studied to overcome this problem, liposomes have gained increasing attention as promising strategies for brain-targeted drug delivery. The most advantageous features of liposomes are their ability to incorporate and deliver large amounts of drug and the possibility to decorate their surface with different ligands.

AREAS COVERED

The purpose of this review is to explore the different approaches studied to transport and deliver therapeutics and imaging agents to the brain by using liposomes. In the first part of the review, particular attention is paid to describe the anatomy of the BBB and different physiological transport mechanisms available for drug permeation. In the second part, the different strategies for the delivery of a drug to the brain using liposomes are reviewed for each transport mechanism.

EXPERT OPINION

Over the last decade, there have been significant developments concerning liposomal brain delivery systems conjugated with selected ligands with high specificity and low immunogenicity. An universally useful liposomal formulation for brain targeting does not exist but liposome design must be modulated by the appropriate choice of the specific homing device and transport mechanism.

Gene-based therapy of Parkinson's Disease: Translation from animal model to human clinical trial employing convection enhanced delivery

The existing treatment of Parkinson's disease (PD) is directed towards substituting dopamine loss with either dopamine replacement therapy or pharmacological therapies aimed at increasing dopamine at the synapse level. Emerging viable alternatives include the use of cell-based and gene-based therapeutics. In this review, we discuss efforts in developing in vitro and in vivo models and their translation to human clinical trials for gene-based therapy of this distressing and prevalent neurodegenerative disorder. Given the mismatch between expectations from preclinical data and results of human pivotal trials, drug delivery has been identified as the key emerging area for translational research due to limitation of limited efficacy. The chief highlights of the current topic include use of improved delivery methods of gene-based therapeutic agents. Convection-enhanced delivery (CED), an advanced infusion technique with demonstrated utility in ex vivo and in vivo animal models has recently been adopted for PD gene-based therapy trials. Several preclinical studies suggest that magnetic resonance imaging (MRI)-guided navigation for accurately targeting and real time monitoring viral vector delivery (rCED) in future clinical trials involving detection of gene expression and restoration of dopaminergic function loss using pro-drug approach will greatly enhance these PD treatments.

Gene therapy for the treatment of Parkinson's disease: the nature of the biologics expands the future indications

The pharmaceutical industry's development of therapeutic medications for the treatment of Parkinson's disease (PD) endures, as a result of the continuing need for better agents, and the increased clinical demand due to the aging population. Each new drug offers advantages and disadvantages to patients when compared to other medical offerings or surgical options. Deep brain stimulation (DBS) has become a standard surgical remedy for the effective treatment of select patients with PD, for whom most drug regimens have failed or become refractory. Similar to DBS as a surgical option, gene therapy for the treatment of PD is evolving as a future option. In the four different PD gene therapy approaches that have reached clinical trials investigators have documented an excellent safety profile associated with the stereotactic delivery, viral vectors and doses utilized, and transgenes expressed. In this article, we review the clinically relevant gene therapy strategies for the treatment of PD, concentrating on the published preclinical and clinical results, and the likely mechanisms involved. Based on these presentations, we advance an analysis of how the nature of the gene therapy used may eventually expand the scope and utility for the management of PD.

Gene delivery of antioxidant enzymes inhibits human immunodeficiency virus type 1 gp120-induced expression of caspases

Caspases are implicated in neuronal death in neurodegenerative and other central nervous system (CNS) diseases. In a rat model of human immunodeficiency virus type 1 (HIV-1) associated neurocognitive disorders (HAND), we previously characterized HIV-1 envelope gp120-induced neuronal apoptosis by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. In this model, neuronal apoptosis occurred probably via gp120-induced reactive oxygen species (ROS). Antioxidant gene delivery blunted gp120-related apoptosis. Here, we studied the effect of gp120 on different caspases (3, 6, 8, 9) expression. Caspases production increased in the rat caudate-putamen (CP) 6h after gp120 injection into the same structure. The expression of caspases peaked by 24h. Caspases colocalized mainly with neurons. Prior gene delivery of the antioxidant enzymes Cu/Zn superoxide dismutase (SOD1) or glutathione peroxidase (GPx1) into the CP before injecting gp120 there reduced levels of gp120-induced caspases, recapitulating the effect of antioxidant enzymes on gp120-induced apoptosis observed by TUNEL. Thus, HIV-1 gp120 increased caspases expression in the CP. Prior antioxidant enzyme treatment mitigated production of these caspases, probably by reducing ROS levels.

Continuous dopaminergic stimulation: clinical aspects and experimental bases

In patients with Parkinson disease, pulsatile administration of dopaminergic drugs is associated with motor fluctuations and dyskinesias. By contrast, treatments that provide more continuous dopaminergic stimulation are associated with less intense motor complications. This can be achieved by using drugs with longer half-lives, delayed release formulations, and routes of administration that permit continuous delivery. The mechanisms by which different modes of dopaminergic treatment (pulsatile or continuous) determine the motor response are not fully understood. However, the use of experimental models of parkinsonism has helped understand the motor complications associated with pulsatile dopamine replacement. These studies have provided important insights into the biochemical and molecular changes in the basal ganglia in response to continuous stimulation. In addition, these models have facilitated the development of new treatments that may stabilize the motor response and the biochemical alterations in the basal ganglia to provide more efficient forms of continuous dopaminergic stimulation in patients with Parkinson disease.

Production of recombinant adeno-associated viral vectors and use in in vitro and in vivo administration

Adeno-associated virus is a nonpathogenic human virus that has been developed into a gene-delivery vector due to its high efficiency of infection for many different cell types and its ability to persist and lead to long-term gene expression. This unit describes efficient methods to generate high-titer, research-grade, adenovirus-free recombinant single-stranded and self-complementary adeno-associated virus in various serotypes, along with methods to quantify the viral vectors. Two detailed methods are provided for viral vector delivery into the rodent brain and spinal cord, and for histological detection of transgene expression of GFP.

Design of a single AAV vector for coexpression of TH and GCH1 to establish continuous DOPA synthesis in a rat model of Parkinson's disease

Preclinical efficacy of continuous delivery of 3,4-dihydroxyphenylalanine (DOPA) with adeno-associated viral (AAV) vectors has recently been documented in animal models of Parkinson's disease (PD). So far, all studies have utilized a mix of two monocistronic vectors expressing either of the two genes, tyrosine hydroxylase (TH) and GTP cyclohydrolase-1 (GCH1), needed for DOPA production. Here, we present a novel vector design that enables efficient DOPA production from a single AAV vector in rats with complete unilateral dopamine (DA) lesions. Functional efficacy was assessed with drug-induced and spontaneous motor behavioral tests where vector-treated animals showed near complete and stable recovery within 1 month. Recovery of motor function was associated with restoration of extracellular DA levels as assessed by online microdialysis. Histological analysis showed robust transgene expression not only in the striatum but also in overlying cortical areas. In globus pallidus, we noted loss of NeuN staining, which might be due to different sensitivity in neuronal populations to transgene expression. Taken together, we present a single AAV vector design that result in efficient DOPA production and wide-spread transduction. This is a favorable starting point for continued translation toward a therapeutic application, although future studies need to carefully review target region, vector spread and dilution with this approach.

HIV-1 Tat neurotoxicity: a model of acute and chronic exposure, and neuroprotection by gene delivery of antioxidant enzymes

HIV-associated neurocognitive disorder (HAND) is an increasingly common, progressive disease characterized by neuronal loss and progressively deteriorating CNS function. HIV-1 gene products, particularly gp120 and Tat elicit reactive oxygen species (ROS) that lead to oxidant injury and cause neuron apoptosis. Understanding of, and developing therapies for, HAND requires accessible models of the disease. We have devised experimental approaches to studying the acute and chronic effects of Tat on the CNS. We studied acute exposure by injecting recombinant Tat protein into the caudate-putamen (CP). Ongoing Tat expression, which more closely mimics HIV-1 infection of the brain, was studied by delivering Tat-expression over time using an SV40-derived gene delivery vector, SV(Tat). Both acute and chronic Tat exposure induced lipid peroxidation and neuronal apoptosis. Finally, prior administration of recombinant SV40 vectors carrying antioxidant enzymes, copper/zinc superoxide dismutase (SOD1) or glutathione peroxidase (GPx1), protected from Tat-induced apoptosis and oxidative injury. Thus, injection of recombinant HIV-1 Tat and the expression vector, SV(Tat), into the rat CP cause respectively acute or ongoing apoptosis and oxidative stress in neurons and may represent useful animal models for studying the pathogenesis and, potentially, treatment of HIV-1 Tat-related damage.

The degenerating substantia nigra as a susceptible region for gene transfer-mediated inflammation

Parkinson's disease (PD) is characterized by the progressive degeneration of neurons in the substantia nigra pars compacta (SN). The naïve SN is highly susceptible to inflammation. In addition, microglial activation in the degenerating SN displays distinct characteristics that increase the reactivity of the region towards inflammatory stimuli. On the other hand, gene therapy for PD has recently move forward into clinical settings, with PD being the neurodegenerative disorder with the highest number of Phase I/II gene therapy clinical trials approved and completed. These clinical trials are not targeting the SN, but this region is a certain candidate for future gene therapy interventions. Here, the unique immune-related properties of the degenerating SN in the context of a putative gene therapy intervention are reviewed. Several variables affecting the host response to gene delivery such as vector type and dosage, age and stage of disease of patients, and method of gene delivery and transgene used are discussed. Finally, approaches to diminish the risk of immune-mediated toxicity by gene transfer in the SN are presented.

Intracisternal rSV40 administration provides effective pan-CNS transgene expression

Potential genetic treatments for many generalized central nervous system (CNS) diseases require transgene expression throughout the CNS. Using oxidant stress and apoptosis caused by HIV-1 envelope gp120 as a model, we studied pan-CNS neuroprotective gene delivery into the cisterna magna (CM). Recombinant SV40 vectors carrying Cu/Zn superoxide dismutase or glutathione peroxidase were injected into rat CMs following intraperitoneal administration of mannitol. Sustained transgene expression was seen in neurons throughout the CNS. On challenge, 8 weeks later with gp120 injected into the caudate putamen, significant neuroprotection was documented. Thus, intracisternal administration of antioxidant-carrying rSV40 vectors may be useful in treating widespread CNS diseases such as HIV-1-associated neurocognitive disorders characterized by oxidative stress.

Gene transfer to the cerebellum

There are several diseases for which gene transfer therapy to the cerebellum might be practicable. In these studies, we used recombinant Tag-deleted SV40-derived vectors (rSV40s) to study gene delivery targeting the cerebellum. These vectors transduce neurons and microglia very effectively in vitro and in vivo, and so we tested them to evaluate gene transfer to the cerebellum in vivo. Using a rSV40 vector carrying human immunodeficiency virus (HIV)-Nef with a C-terminal FLAG epitope, we characterized the distribution, duration, and cell types transduced. Rats received test and control vectors by stereotaxic injection into the cerebellum. Transgene expression was assessed 1, 2, and 4 weeks later by immunostaining of serial brain sections. FLAG epitope-expressing cells were seen, at all times after vector administration, principally detected in the Purkinje cells of the cerebellum, identified as immunopositive for calbindin. Occasional microglial cells were tranduced; transgene expression was not detected in astrocytes or oligodendrocytes. No inflammatory or other reaction was detected at any time. Thus, SV40-derived vectors can deliver effective, safe, and durable transgene expression to the cerebellum.

Adeno-associated viral gene delivery in neurodegenerative disease

The advent of viral gene therapy technology has contributed greatly to the study of a variety of medical conditions, and there is increasing promise for clinical translation of gene therapy into human treatments. Adeno-associated viral (AAV) vectors provide one of the more promising approaches to gene delivery, and have been used extensively over the last 20 years. Derived from nonpathogenic parvoviruses, these vectors allow for stable and robust expression of desired transgenes in vitro and in vivo. AAV vectors efficiently and stably transduce neurons, with some strains targeting neurons exclusively in the brain. Thus, AAV vectors are particularly useful for neurodegenerative diseases, which have led to numerous preclinical studies and several human trials of gene therapy in patients with Parkinson's disease, Alzheimer's disease, and pediatric neurogenetic disorders. Here, we describe an efficient and reliable method for the production and purification of AAV serotype 2 vectors for both in vitro and in vivo applications.

Development of advanced therapies based on viral vector-mediated overexpression of therapeutic molecules and knockdown of disease-related genes for Parkinson’s disease

The last decade witnessed the translation of several gene-based therapeutic approaches from experimental studies to early clinical trials. Studies targeting the treatment of Parkinson’s disease (PD) were among the forefront of trials in the CNS. In this article, we overview three major strategies for the treatment of PD: the enzyme-replacement strategies are based on well-defined principles of functional restoration and are well suited for treatment of patients with advanced disease who would typically experience complications due to side effects of pharmacotherapy. Neurotrophic factor delivery, on the other hand, aims to delay the disability and eventually modifiy disease progression. Finally, we present an outlook to a completely new way of interfering with the disease process, which is taking advantage of recently discovered RNAi mechanisms in cells. Gene therapy is now becoming a reality in the clinics and developments in the next decade will help uncover the true potential of this approach for not only the treatment of PD patients, but also many other neurological disorders.

The vesicular glutamate transporter-1 upstream promoter and first intron each support glutamatergic-specific expression in rat postrhinal cortex

Multiple applications of direct gene transfer into neurons require restricting expression to glutamatergic neurons, or specific subclasses of glutamatergic neurons. Thus, it is desirable to develop and analyze promoters that support glutamatergic-specific expression. The three vesicular glutamate transporters (VGLUTs) are found in different populations of neurons, and VGLUT1 is the predominant VGLUT in the neocortex, hippocampus, and cerebellar cortex. We previously reported on a plasmid (amplicon) Herpes Simplex Virus vector that contains a VGLUT1 promoter. This vector supports long-term expression in VGLUT1-containing glutamatergic neurons in rat postrhinal (POR) cortex, but does not support expression in VGLUT2-containing glutamatergic neurons in the ventral medial hypothalamus. This VGLUT1 promoter contains both the VGLUT1 upstream promoter and the VGLUT1 first intron. In this study, we begin to isolate and analyze the glutamatergic-specific regulatory elements in this VGLUT1 promoter. We show that the VGLUT1 upstream promoter and first intron each support glutamatergic-specific expression. We isolated a small, basal VGLUT1 promoter that does not support glutamatergic-specific expression. Next, we fused either the VGLUT1 upstream promoter or the first intron to this basal promoter. The VGLUT1 upstream promoter or the first intron, fused to the basal promoter, each supported glutamatergic-specific expression in POR cortex.

Efficient CNS gene delivery by intravenous injection

We administered recombinant SV40-derived viral vectors (rSV40s) intravenously to mice with or without prior intraperitoneal injection of mannitol to deliver transgenes to the central nervous system (CNS). We detected transgene-expressing cells (mainly neurons) most prominently in the cortex and spinal cord; prior intraperitoneal mannitol injection increased CNS gene delivery tenfold. Intravenous injection of rSV40s, particularly with mannitol pretreatment, resulted in extensive expression of multiple transgenes throughout the CNS.

Role of CCR5 and its ligands in the control of vascular inflammation and leukocyte recruitment required for acute excitotoxic seizure induction and neural damage

Chemokines may play a role in leukocyte migration across the blood-brain barrier (BBB) during neuroinflammation and other neuropathological processes, such as epilepsy. We investigated the role of the chemokine receptor CCR5 in seizures. We used a rat model based on intraperitoneal kainic acid (KA) administration. Four months before KA injection, adult rats were given femoral intramarrow inoculations of SV (RNAiR5-RevM10.AU1), which carries an interfering RNA (RNAi) against CCR5, plus a marker epitope (AU1), or its monofunctional RNAi-carrying homologue, SV(RNAiR5). This treatment lowered expression of CCR5 in circulating cells. In control rats, seizures induced elevated expression of CCR5 ligands MIP-1α and RANTES in the microvasculature, increased BBB leakage and CCR5(+) cells, as well as neuronal loss, inflammation, and gliosis in the hippocampi. Animals given either the bifunctional or the monofunctional vector were largely protected from KA-induced seizures, neuroinflammation, BBB damage, and neuron loss. Brain CCR5 mRNA was reduced. Rats receiving RNAiR5-bearing vectors showed far greater repair responses: increased neuronal proliferation, and decreased production of MIP-1α and RANTES. Controls received unrelated SV(BUGT) vectors. Decrease in CCR5 in circulating cells strongly protected from excitotoxin-induced seizures, BBB leakage, CNS injury, and inflammation, and facilitated neurogenic repair.

Gene therapy for Parkinson's disease

The once fantastic theoretical concept that patients with Parkinson's disease (PD) would receive gene therapy in an attempt to alleviate their symptoms and potentially modify the course of their disease has become a reality. On the basis of positive preclinical data, four different gene therapy approaches are currently in Phase I or Phase II clinical trials. Some approaches are intended to increase levels of endogenous dopamine or enhance the function of the prodrug levodopa. Others are intended to normalize basal ganglia circuitry by reducing the PD-related overactivity of specific brain structures such as the subthalamic nucleus. Each is intended for symptomatic benefit. Finally, gene delivery of trophic factors that not only augment dopaminergic function but are potentially disease modifying has a strong preclinical database and are also in clinical trials. Each of these approaches is discussed in the present review.

Optimization of continuous in vivo DOPA production and studies on ectopic DA synthesis using rAAV5 vectors in Parkinsonian rats

Viral vector-mediated gene transfer is emerging as a novel therapeutic approach with clinical utility in treatment of Parkinson's disease. Recombinant adeno-associated viral (rAAV) vector in particular has been utilized for continuous l-3,4 dihydroxyphenylalanine (DOPA) delivery by expressing the tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GCH1) genes which are necessary and sufficient for efficient synthesis of DOPA from dietary tyrosine. The present study was designed to determine the optimal stoichiometric relationship between TH and GCH1 genes for ectopic DOPA production and the cellular machinery involved in its synthesis, storage, and metabolism. For this purpose, we injected a fixed amount of rAAV5-TH vector and increasing amounts of rAAV5-GCH1 into the striatum of rats with complete unilateral dopamine lesion. After 7 weeks the animals were killed for either biochemical or histological analysis. We show that increasing the availability of 5,6,7,8-tetrahydro-l-biopterin (BH4) in the same cellular compartment as the TH enzyme resulted in better efficiency in DOPA synthesis, most likely by hindering inactivation of the enzyme and increasing its stability. Importantly, the BH4 synthesis from ectopic GCH1 expression was saturable, yielding optimal TH enzyme functionality between GCH1 : TH ratios of 1 : 3 and 1 : 7.

A rat model of human immunodeficiency virus 1 encephalopathy using envelope glycoprotein gp120 expression delivered by SV40 vectors

Human immunodeficiency virus 1 (HIV-1) encephalopathy is thought to result in part from the toxicity of HIV-1 envelope glycoprotein gp120 for neurons. Experimental systems for studying the effects of gp120 and other HIV proteins on the brain have been limited to the acute effects of recombinant proteins in vitro or in vivo in simian immunodeficiency virus-infected monkeys. We describe an experimental rodent model of ongoing gp120-induced neurotoxicity in which HIV-1 envelope is expressed in the brain using an SV40-derived gene delivery vector, SV(gp120). When it is inoculated stereotaxically into the rat caudate putamen, SV(gp120) caused a partly hemorrhagic lesion in which neuron and other cell apoptosis continues for at least 12 weeks. Human immunodeficiency virus gp120 is expressed throughout this time, and some apoptotic cells are gp120 positive. Malondialdehyde and 4-hydroxynonenal assays indicated that there was lipid peroxidation in these lesions. Prior administration of recombinant SV40 vectors carrying antioxidant enzymes, copper/ zinc superoxide dismutase or glutathione peroxidase, was protective against SV(gp120)-induced oxidative injury and apoptosis. Thus, in vivo inoculation of SV(gp120) into the rat caudate putamen causes ongoing oxidative stress and apoptosis in neurons and may therefore represent a useful animal model for studying the pathogenesis and treatment of HIV-1 envelope-related brain damage.

Progress in transduction of cerebellar Purkinje cells in vivo using viral vectors

Expression of a foreign gene in cerebellar Purkinje cells in vivo is a powerful method for exploring the pathophysiology of the cerebellum. Although using developmental engineering many gene-modified mice have been generated, this approach is time-consuming and requires a lot of effort for crossing different lines of mice, genotyping and maintenance of animals. If a gene of interest can be transferred to and efficiently expressed in Purkinje cells of developing and mature animals, it saves much time, effort and money. Recent advances in viral vectors have markedly contributed to selective and efficient gene transfer to Purkinje cells in vivo. There are two approaches for selective gene expression in Purkinje cells: one is to take advantage of the viral tropism for Purkinje cells, which includes the tropism of adeno-associated virus and the vesicular stomatitis virus glycoprotein (VSV-G)-pseudotyped lentivirus. Another method, which might be used in combination with the first one, is utilization of a Purkinje-cell-specific promoter. Focusing mainly on these points, recent progress in viral-vector-mediated transduction of Purkinje cells in vivo is reviewed.

HIV-1 gp120 neurotoxicity proximally and at a distance from the point of exposure: protection by rSV40 delivery of antioxidant enzymes

Toxicity of HIV-1 envelope glycoprotein (gp120) for substantia nigra (SN) neurons may contribute to the Parkinsonian manifestations often seen in HIV-1-associated dementia (HAD). We studied the neurotoxicity of gp120 for dopaminergic neurons and potential neuroprotection by antioxidant gene delivery. Rats were injected stereotaxically into their caudate-putamen (CP); CP and (substantia nigra) SN neuron loss was quantified. The area of neuron loss extended several millimeters from the injection site, approximately 35% of the CP area. SN neurons, outside of this area of direct neurotoxicity, were also severely affected. Dopaminergic SN neurons (expressing tyrosine hydroxylase, TH, in the SN and dopamine transporter, DAT, in the CP) were mostly affected: intra-CP gp120 caused approximately 50% DAT+ SN neuron loss. Prior intra-CP gene delivery of Cu/Zn superoxide dismutase (SOD1) or glutathione peroxidase (GPx1) protected SN neurons from intra-CP gp120. Thus, SN dopaminergic neurons are highly sensitive to HIV-1 gp120-induced neurotoxicity, and antioxidant gene delivery, even at a distance, is protective.

Scientific rationale for the development of gene therapy strategies for Parkinson's disease

The ever-evolving understanding of the neuronal systems involved in Parkinson's disease together with the recent advances in recombinant viral vector technology has led to the development of several gene therapy applications that are now entering into clinical testing phase. To date, four fundamentally different approaches have been pursued utilizing recombinant adeno-associated virus and lentiviruses as vectors for delivery. These strategies aim either to restore the lost brain functions by substitution of enzymes critical for synthesis of neurotransmitters or neurotrophic factors as a means to boost the function of remaining neurons in the diseased brain. In this review we discuss the differences in mechanism of action and describe the scientific rationale behind the currently tested gene therapy approaches for Parkinson's disease in some detail and pinpoint their individual unique strengths and weaknesses.

Future of cell and gene therapies for Parkinson's disease

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

Targeted overexpression of human alpha-synuclein triggers microglial activation and an adaptive immune response in a mouse model of Parkinson disease

Microglial activation and adaptive immunity have been implicated in the neurodegenerative processes in Parkinson disease. It has been proposed that these responses may be triggered by modified forms of alpha-synuclein (alpha-SYN), particularly nitrated species, which are released as a consequence of dopaminergic neurodegeneration. To examine the relationship between alpha-SYN, microglial activation, and adaptive immunity, we used a mouse model of Parkinson disease in which human alpha-SYN is overexpressed by a recombinant adeno-associated virus vector, serotype 2 (AAV2-SYN); this overexpression leads to slow degeneration of dopaminergic neurons. Microglial activation and components of the adaptive immune response were assessed using immunohistochemistry; quantitative polymerase chain reaction was used to examine cytokine expression. Four weeks after injection, there was a marked increase in CD68-positive microglia and greater infiltration of B and T lymphocytes in the substantia nigra pars compacta of the AAV2-SYN group than in controls. At 12 weeks, CD68 staining declined, but B- and T-cell infiltration persisted. Expression of proinflammatory cytokines was enhanced, whereas markers of alternative activation (i.e. arginase I and interleukins 4 and 13) were not altered. Increased immunoreactivity for mouse immunoglobulin was detected at all time points in the AAV2-SYN animals. These data show that overexpression of alpha-SYN alone, in the absence of overt neurodegeneration, is sufficient to trigger neuroinflammation with both microglial activation and stimulation of adaptive immunity.

Direct binding of GTP cyclohydrolase and tyrosine hydroxylase: regulatory interactions between key enzymes in dopamine biosynthesis

The signaling functions of dopamine require a finely tuned regulatory network for rapid induction and suppression of output. A key target of regulation is the enzyme tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis, which is activated by phosphorylation and modulated by the availability of its cofactor, tetrahydrobiopterin. The first enzyme in the cofactor synthesis pathway, GTP cyclohydrolase I, is activated by phosphorylation and inhibited by tetrahydrobiopterin. We previously reported that deficits in GTP cyclohydrolase activity in Drosophila heterozygous for mutant alleles of the gene encoding this enzyme led to tightly corresponding diminution of in vivo tyrosine hydroxylase activity that could not be rescued by exogenous cofactor. We also found that the two enzymes could be coimmunoprecipitated from tissue extracts and proposed functional interactions between the enzymes that extended beyond provision of cofactor by one pathway for another. Here, we confirm the physical association of these enzymes, identifying interacting regions in both, and we demonstrate that their association can be regulated by phosphorylation. The functional consequences of the interaction include an increase in GTP cyclohydrolase activity, with concomitant protection from end-product feedback inhibition. In vivo, this effect would in turn provide sufficient cofactor when demand for catecholamine synthesis is greatest. The activity of tyrosine hydroxylase is also increased by this interaction, in excess of the stimulation resulting from phosphorylation alone. Vmax is elevated, with no change in Km. These results demonstrate that these enzymes engage in mutual positive regulation.

Sustained striatal ciliary neurotrophic factor expression negatively affects behavior and gene expression in normal and R6/1 mice

Huntington's disease (HD) is a neurodegenerative disorder caused by an elongation of CAG repeats in the HD gene, which encodes a mutant copy of huntingtin with an expanded polyglutatmine repeat. Individuals who are affected by the disease suffer from motor, cognitive, and emotional impairments. Levels of certain striatal-enriched mRNAs decrease in both HD patients and transgenic HD mice prior to the development of motor symptoms and neuronal cell death. Ciliary neurotrophic factor (CNTF) has been shown to protect neurons against chemically induced toxic insults in vitro and in vivo. To test the hypothesis that CNTF might protect neurons from the negative effects of the mutant huntingtin protein in vivo, CNTF was continuously expressed following transduction of the striatum by recombinant adeno-associated viral vectors (rAAV2). Wild-type and R6/1 HD transgenic (R6/1) mice that received bilateral or unilateral intrastriatal injections of rAAV2-CNTF experienced weight loss. The CNTF-treated R6/1 HD transgenic mice experienced motor impairments at an earlier age than expected compared with age-matched control R6/1 HD transgenic animals. CNTF also caused abnormal behavior in WT mice. In addition to behavioral impairments, in situ hybridization showed that, in both WT and R6/1 mice, CNTF expression caused a significant decrease in the levels of striatal-enriched transcripts. Overall, continuous expression of striatal CNTF at the dose mediated by the expression cassette used in this study was detrimental to HD and wild-type mice.

Overview of gene delivery into cells using HSV-1-based vectors

This overview describes the considerations involved in the preparation and use of herpes simplex virus type 1 (HSV-1) as a vector for gene transfer into neurons. Strategies for gene delivery into neurons, either to study the molecular biology of brain function or for gene therapy, must utilize vectors that persist stably in postmitotic cells and that can be targeted both spatially and temporally in the nervous system in vivo. This unit describes the biology of HSV-1 along with a discussion covering development of amplicon and genomic HSV-1 vectors. Advantages and disadvantages of current HSV-1 vectors are presented, and HSV-1 vectors are compared with other vectors for gene transfer into neurons.

Production of recombinant adeno-associated viral vectors

Adeno-associated virus is a nonpathogenic human virus that has been developed into a gene-delivery vector due to its high efficiency of infection for many different cell types and its ability to persist and lead to long-term gene expression. This unit describes efficient methods to generate high-titer, research-grade, adenovirus-free recombinant single-stranded and self-complementary adeno-associated virus in various serotypes, along with methods to quantify the viral vectors.

Advances in gene therapy for movement disorders

After nearly 20 years of preclinical experimentation with various gene delivery approaches in animal models of Parkinson's disease (PD), clinical trials are finally underway. The risk/benefit ratio for these procedures is now generally considered acceptable under approved protocols. The current vehicle for gene delivery to the human brain is recombinant adeno-associated viral vector, which is nonpathogenic and non-self-amplifying. Candidate genes tested in PD patients encode 1) glutamic acid decarboxylase, which is injected into the subthalamic nucleus to catalyze biosynthesis of the inhibitory neurotransmitter gamma-aminobutyric acid and so essentially mimic deep brain stimulation of this nucleus; 2) aromatic l-amino acid decarboxylase, which converts l-dopa to dopamine; and 3) neurturin, a member of the glial cell line-derived neurotrophic factor family. Unraveling the genetic underpinnings of PD could allow gene therapy to go beyond modulating neurotransmission or providing trophic effects to dopaminergic neurons by delivering a specific missing or defective gene. For example, the parkin gene (PARK2) is linked to recessively inherited PD due to loss of function mutations; it prevents alpha-synuclein-induced degeneration of nigral dopaminergic neurons in rats and nonhuman primates. On the other hand, for dominantly inherited Huntington's disease (HD), in which an expanded polyglutamine tract imparts to the protein huntingtin a toxic gain of function, repressing expression of the mutant allele in the striatum using RNA interference technology mitigates pathology and delays the phenotype in a mouse model. Here we review the current state of preclinical and clinical gene therapy studies conducted in PD and HD.

Production of recombinant adeno-associated viral vectors for in vitro and in vivo use

Adeno-associated virus is a nonpathogenic human virus that has been developed into a gene-delivery vector due to its high efficiency of infection in many different cell types and its ability to persist and lead to long-term gene expression. The vector is also a valuable tool in molecular biology experiments. This unit describes efficient methods to generate high-titer, research-grade, adenovirus-free, recombinant single-stranded and self-complementary adeno-associated virus in various serotypes, along with methods to quantify the viral vectors.