A comprehensive study of a 29-capsid AAV library in a non-human primate central nervous system.

Non-human primates (NHPs) are a preferred animal model for optimizing adeno-associated virus (AAV)-mediated CNS gene delivery protocols before clinical trials. In spite of its inherent appeal, it is challenging to compare different serotypes, delivery routes, and disease indications in a well-powered, comprehensive, multigroup NHP experiment. Here, a multiplex barcode recombinant AAV (rAAV) vector-tracing strategy has been applied to a systemic analysis of 29 distinct, wild-type (WT), AAV natural isolates and engineered capsids in the CNS of eight macaques. The report describes distribution of each capsid in 15 areas of the macaques' CNS after intraparenchymal (putamen) injection, or cerebrospinal fluid (CSF)-mediated administration routes (intracisternal, intrathecal, or intracerebroventricular). To trace the vector biodistribution (viral DNA) and targeted tissues transduction (viral mRNA) of each capsid in each of the analyzed CNS areas, quantitative next-generation sequencing analysis, assisted by the digital-droplet PCR technology, was used. The report describes the most efficient AAV capsid variants targeting specific CNS areas after each route of administration using the direct side-by-side comparison of WT AAV isolates and a new generation of rationally designed capsids. The newly developed bioinformatics and visualization algorithms, applicable to the comparative analysis of several mammalian brain models, have been developed and made available in the public domain.

Site-specific modifications to AAV8 capsid yields enhanced brain transduction in the neonatal MPS IIIB mouse.

Mucopolysaccharidosis type IIIB (MPS IIIB) is an autosomal recessive lysosomal disease caused by defective production of the enzyme α-N-acetylglucosaminidase. It is characterized by severe and complex central nervous system degeneration. Effective therapies will likely target early onset disease and overcome the blood-brain barrier. Modifications of adeno-associated viral (AAV) vector capsids that enhance transduction efficiency have been described in the retina. Herein, we describe for the first time, a transduction assessment of two intracranially administered adeno-associated virus serotype 8 variants, in which specific surface-exposed tyrosine (Y) and threonine (T) residues were substituted with phenylalanine (F) and valine (V) residues, respectively. A double-mutant (Y444 + 733F) and a triple-mutant (Y444 + 733F + T494V) AAV8 were evaluated for their efficacy for the potential treatment of MPS IIIB in a neonatal setting. We evaluated biodistribution and transduction profiles of both variants compared to the unmodified parental AAV8, and assessed whether the method of vector administration would modulate their utility. Vectors were administered through four intracranial routes: six sites (IC6), thalamic (T), intracerebroventricular, and ventral tegmental area into neonatal mice. Overall, we conclude that the IC6 method resulted in the widest biodistribution within the brain. Noteworthy, we demonstrate that GFP intensity was significantly more robust with AAV8 (double Y-F + T-V) compared to AAV8 (double Y-F). This provides proof of concept for the enhanced utility of IC6 administration of the capsid modified AAV8 (double Y-F + T-V) as a valid therapeutic approach for the treatment of MPS IIIB, with further implications for other monogenic diseases.

Transgenic mice expressing caspase-6-derived N-terminal fragments of mutant huntingtin develop neurologic abnormalities with predominant cytoplasmic inclusion pathology composed largely of a smaller proteolytic derivative.

Recent studies have implicated an N-terminal caspase-6 cleavage product of mutant huntingtin (htt) as an important mediator of toxicity in Huntington's disease (HD). To directly assess the consequences of such fragments on neurologic function, we produced transgenic mice that express a caspase-6 length N-terminal fragment of mutant htt (N586) with both normal (23Q) and disease (82Q) length glutamine repeats. In contrast to mice expressing N586-23Q, mice expressing N586-82Q accumulate large cytoplasmic inclusion bodies that can be visualized with antibodies to epitopes throughout the N586 protein. However, biochemical analyses of aggregated mutant huntingtin in these mice demonstrated that the inclusion bodies are composed largely of a much smaller htt fragment (terminating before residue 115), with lesser amounts of full-length N586-82Q fragments. Mice expressing the N586-82Q fragment show symptoms typical of previously generated mice expressing mutant huntingtin fragments, including failure to maintain weight, small brain weight and reductions in specific mRNAs in the striatum. Uniquely, these N586-82Q mice develop a progressive movement disorder that includes dramatic deficits in motor performance on the rotarod and ataxia. Our findings suggest that caspase-6-derived fragments of mutant htt are capable of inducing novel HD-related phenotypes, but these fragments are not terminal cleavage products as they are subject to further proteolysis. In this scenario, mutant htt fragments derived from caspase 6, or possibly other proteases, could mediate HD pathogenesis via a 'hit and run' type of mechanism in which caspase-6, or other larger N-terminal fragments, mediate a neurotoxic process before being cleaved to a smaller fragment that accumulates pathologically.

Striatal pleiotrophin overexpression provides functional and morphological neuroprotection in the 6-hydroxydopamine model.

Neurotrophic factors are integrally involved in the development of the nigrostriatal system and in combination with gene therapy, possess great therapeutic potential for Parkinson's disease (PD). Pleiotrophin (PTN) is involved in the development, maintenance, and repair of the nigrostriatal dopamine (DA) system. The present study examined the ability of striatal PTN overexpression, delivered via psueudotyped recombinant adeno-associated virus type 2/1 (rAAV2/1), to provide neuroprotection and functional restoration from 6-hydroxydopamine (6-OHDA). Striatal PTN overexpression led to significant neuroprotection of tyrosine hydroxylase immunoreactive (THir) neurons in the substantia nigra pars compacta (SNpc) and THir neurite density in the striatum, with long-term PTN overexpression producing recovery from 6-OHDA-induced deficits in contralateral forelimb use. Transduced striatal PTN levels were increased threefold compared to adult striatal PTN expression and approximated peak endogenous developmental levels (P1). rAAV2/1 vector exclusively transduced neurons within the striatum and SNpc with approximately half the total striatal volume routinely transduced using our injection parameters. Our results indicate that striatal PTN overexpression can provide neuroprotection for the 6-OHDA lesioned nigrostriatal system based upon morphological and functional measures and that striatal PTN levels similar in magnitude to those expressed in the striatum during development are sufficient to provide neuroprotection from Parkinsonian insult.

Regulated protein expression for in vivo gene therapy for neurological disorders: progress, strategies, and issues.

The field of in vivo gene therapy has matured to the point where there are numerous clinical trials underway including late-stage clinical trials. Several viral vectors are especially efficient and support lifetime protein expression in the brain and a number of clinical trials are underway for various progressive or chronic neurological disorders including Parkinson's disease, Alzheimer's disease, and Batten's disease. To date, however, none of the vectors in clinical use have any direct way to reverse or control their transgene product in the event continued protein expression should become problematic. Several schemes that use elements within the vector design have been developed that allow an external drug or pro-drug to alter ongoing protein expression after in vivo gene transfer. The most promising and most studied regulated protein expression methods for in vivo gene transfer are reviewed. In addition, potential scientific and clinical advantages of transgene regulation for gene therapy are discussed.

Differential transduction following basal ganglia administration of distinct pseudotyped AAV capsid serotypes in nonhuman primates.

We examined the transduction efficiency of different adeno-associated virus (AAV) capsid serotypes encoding for green fluorescent protein (GFP) flanked by AAV2 inverted terminal repeats in the nonhuman primate basal ganglia as a prelude to translational studies, as well as clinical trials in patients with Parkinson's disease (PD). Six intact young adult cynomolgus monkeys received a single 10 microl injection of AAV2/1-GFP, AAV2/5-GFP, or AAV2/8-GFP pseudotyped vectors into the caudate nucleus and putamen bilaterally in a pattern that resulted in each capsid serotype being injected into at least four striatal sites. GFP immunohistochemistry revealed excellent transduction rates for each AAV pseudotype. Stereological estimates of GFP+ cells within the striatum revealed that AAV2/5-GFP transduces significantly higher number of cells than AAV2/8-GFP (P < 0.05) and there was no significant difference between AAV2/5-GFP and AAV2/1-GFP (P = 0.348). Consistent with this result, Cavalieri estimates revealed that AAV2/5-GFP resulted in a significantly larger transduction volume than AAV2/8-GFP (P < 0.05). Each pseudotype transduced striatal neurons effectively [>95% GFP+ cells colocalized neuron-specific nuclear protein (NeuN)]. The current data suggest that AAV2/5 and AAV2/1 are superior to AAV2/8 for gene delivery to the nonhuman primate striatum and therefore better candidates for therapeutic applications targeting this structure.

α-Synuclein expression in rat substantia nigra suppresses phospholipase D2 toxicity and nigral neurodegeneration.

We present genetic evidence that an in vivo role of α-synuclein (α-syn) is to inhibit phospholipase D2 (PLD2), an enzyme that is believed to participate in vesicle trafficking, membrane signaling, and both endo- and exocytosis. Overexpression of PLD2 in rat substantia nigra pars compacta (SNc) caused severe neurodegeneration of dopamine (DA) neurons, loss of striatal DA, and an associated ipsilateral amphetamine-induced rotational asymmetry. Coexpression of human wild type α-syn suppressed PLD2 neurodegeneration, DA loss, and amphetamine-induced rotational asymmetry. However, an α-syn mutant defective for inhibition of PLD2 in vitro also failed to inhibit PLD toxicity in vivo. Further, reduction of PLD2 activity in SNc, either by siRNA knockdown of PLD2 or overexpression of α-syn, both produced an unusual contralateral amphetamine-induced rotational asymmetry, opposite to that seen with overexpression of PLD2, suggesting that PLD2 and α-syn were both involved in DA release or reuptake. Finally, α-syn coimmunoprecipitated with PLD2 from extracts prepared from striatal tissues. Taken together, our data demonstrate that α-syn is an inhibitor of PLD2 in vivo, and confirm earlier reports that α-syn inhibits PLD2 in vitro. Our data also demonstrate that it is possible to use viral-mediated gene transfer to study gene interactions in vivo.

In vivo RNAi-mediated alpha-synuclein silencing induces nigrostriatal degeneration.

Two small-interfering RNAs (siRNAs) targeting alpha-synuclein (alpha-syn) and three control siRNAs were cloned in an adeno-associated virus (AAV) vector and unilaterally injected into rat substantia nigra pars compacta (SNc). Reduction of alpha-syn resulted in a rapid (4 week) reduction in the number of tyrosine hydroxylase (TH) positive cells and striatal dopamine (DA) on the injected side. The level of neurodegeneration induced by the different siRNAs correlated with their ability to downregulate alpha-syn protein and mRNA in tissue culture and in vivo. Examination of various SNc neuronal markers indicated that neurodegeneration was due to cell loss and not just downregulation of DA synthesis. Reduction of alpha-syn also resulted in a pronounced amphetamine induced behavioral asymmetry consistent with the level of neurodegeneration. In contrast, none of the three control siRNAs, which targeted genes not normally expressed in SNc, showed evidence of neurodegeneration or behavioral asymmetry, even at longer survival times. Moreover, co-expression of both rat alpha-syn and alpha-syn siRNA partially reversed the neurodegenerative and behavioral effects of alpha-syn siRNA alone. Our data show that alpha-syn plays an important role in the rat SNc and suggest that both up- and downregulation of wild-type alpha-syn expression increase the risk of nigrostriatal pathology.

The phosphorylation state of Ser-129 in human alpha-synuclein determines neurodegeneration in a rat model of Parkinson disease.

Studies have shown that alpha-synuclein (alpha-syn) deposited in Lewy bodies in brain tissue from patients with Parkinson disease (PD) is extensively phosphorylated at Ser-129. We used recombinant Adeno-associated virus (rAAV) to overexpress human wild-type (wt) alpha-syn and two human alpha-syn mutants with site-directed replacement of Ser-129 to alanine (S129A) or to aspartate (S129D) in the nigrostriatal tract of the rat to investigate the effect of Ser-129 phosphorylation state on dopaminergic neuron pathology. Rats were injected with rAAV2/5 vectors in the substantia nigra pars compacta (SNc) on one side of the brain; the other side remained as a nontransduced control. The level of human wt or mutant alpha-syn expressed on the injected side was about four times the endogenous rat alpha-syn. There was a significant reduction of dopaminergic neurons in the SNc and dopamine (DA) and tyrosine hydroxylase (TH) levels in the striatum of all S129A-treated rats as early as 4 wk postinjection. Nigral DA pathology occurred more slowly in the wt-injected animals, but by 26 wk the wt alpha-syn group lost nigral TH neurons equivalent to the mutated S129A group at 8 wk. In stark contrast, we did not observe any pathological changes in S129D-treated animals. Therefore, the nonphosphorylated form of S129 exacerbates alpha-syn-induced nigral pathology, whereas Ser-129 phosphorylation eliminates alpha-syn-induced nigrostriatal degeneration. This suggests possible new therapeutic targets for Parkinson Disease.

Positron emission tomography imaging demonstrates correlation between behavioral recovery and correction of dopamine neurotransmission after gene therapy.

In vivo gene transfer using viral vectors is an emerging therapy for neurodegenerative diseases with a clinical impact recently demonstrated in Parkinson's disease patients. Recombinant adeno-associated viral (rAAV) vectors, in particular, provide an excellent tool for long-term expression of therapeutic genes in the brain. Here we used the [(11)C]raclopride [(S)-(-)-3,5-dichloro-N-((1-ethyl-2-pyrrolidinyl)methyl)-2-hydroxy-6-methoxybenzamide] micro-positron emission tomography (PET) technique to demonstrate that delivery of the tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GCH1) enzymes using an rAAV5 vector normalizes the increased [(11)C]raclopride binding in hemiparkinsonian rats. Importantly, we show in vivo by microPET imaging and postmortem by classical binding assays performed in the very same animals that the changes in [(11)C]raclopride after viral vector-based enzyme replacement therapy is attributable to a decrease in the affinity of the tracer binding to the D(2) receptors, providing evidence for reconstitution of a functional pool of endogenous dopamine in the striatum. Moreover, the extent of the normalization in this non-invasive imaging measure was highly correlated with the functional recovery in motor behavior. The PET imaging protocol used in this study is fully adaptable to humans and thus can serve as an in vivo imaging technique to follow TH + GCH1 gene therapy in PD patients and provide an additional objective measure to a potential clinical trial using rAAV vectors to deliver l-3,4-dihydroxyphenylanaline in the brain.

Striatal readministration of rAAV vectors reveals an immune response against AAV2 capsids that can be circumvented.

Recombinant adeno-associated virus (rAAV) expresses no viral genes after transduction. In addition, because the brain is relatively immunoprivileged, intracranial rAAV transduction may be immunologically benign due to a lack of antigen presentation. However, preexposure to AAV allows neutralizing antibodies (nAbs) to block brain transduction and rAAV readministration in the brain leads to an inflammatory response in the second-injection site. In this study, we replicate our striatal rAAV2/2-GDNF readministration results and extend this effect to a second transgene, green fluorescent protein (GFP). Unlike rAAV2/2-GDNF readministration, striatal rAAV2/2-GFP readministration leads to a loss of transgene in the second site in the absence of detectable circulating nAbs. In order to determine whether the transgene or the AAV2 capsid is the antigenic stimulus in brain for the immune response in the second site, we readministered rAAV2/2-GFP using two different rAAV serotypes (rAAV2/2 followed by rAAV2/5). In this case, there was no striatal inflammation or transgene loss detected in the second-injection site. In addition, striatal readministration of rAAV2/5-GFP also resulted in no detectable immune response. Furthermore, delaying rAAV2/2 striatal readministration to a 11-week interval abrogated the immune response in the second-injection site. Finally, while striatal readministration of rAAV2/2 leads to significant loss of transgene in the second-injection site, this effect is not due to loss of vector genomes as determined by quantitative real-time PCR. We conclude that intracellular processing of AAV capsids after transduction is the immunogenic antigen and capsid serotypes that are processed more quickly than rAAV2/2 are less immunogenic.

Tight Long-term dynamic doxycycline responsive nigrostriatal GDNF using a single rAAV vector.

Glial cell line-derived neurotrophic factor (GDNF) gene transfer is being developed as a treatment for Parkinson's disease (PD). Due to the potential for side effects, external transgene regulation should enhance this strategy's safety profile. Here, we demonstrate dynamic control during long-term expression of GDNF using a recombinant adeno-associated virus (rAAV)-based bicistronic tetracycline (tet)-off construct. Nigrostriatal GDNF overexpression induces body weight alterations in rodents, enabling longitudinal in vivo tracking of GDNF expression after nigral vector delivery. Regulated GDNF expression was highly sensitive to dietary doxycycline (DOX), displaying undetectable striatal GDNF levels at serum DOX levels below those required for antimicrobial activity. However, in the absence of DOX, striatal GDNF levels exceeded levels required for efficacy in PD models. We also demonstrate the absence of a series of known GDNF-associated side effects when using direct intrastriatal vector delivery. Therefore, this single rAAV vector system meets most of the requirements for an experimental reagent for treatment of PD.

Nigrostriatal rAAV-mediated GDNF overexpression induces robust weight loss in a rat model of age-related obesity.

Intraventricular administration of glial cell line-derived neurotrophic factor (GDNF) in primate and humans to study Parkinson's disease (PD) has revealed the potential for GDNF to induce weight loss. Our previous data indicate that bilateral continuous hypothalamic GDNF overexpression via recombinant adeno-associated virus (rAAV) results in significant failure to gain weight in young rats and weight loss in aged rats. Based on these previous results, we hypothesized that because the nigrostriatal tract passes through the lateral hypothalamus, motor hyperactivity mediated by nigrostriatal dopamine (DA) may have been responsible for the previously observed effect on body weight. In this study, we compared bilateral injections of rAAV2/5-GDNF in hypothalamus versus substantia nigra (SN) in aged Brown-Norway X Fisher 344 rats. Nigrostriatal GDNF overexpression resulted in significantly greater weight loss than rats treated in hypothalamus. The nigral or hypothalamic GDNF-induced weight loss was unrelated to motor activity levels of the rats, though some of the weight loss could be attributed to a transient reduction in food intake. Forebrain DA levels did not account for the observed effects on body weight, although GDNF-induced increases in nucleus accumbens DA may have partially contributed to this effect in the hypothalamic GDNF-treated group. However, only nigrostriatal GDNF overexpression induced activation of phosphorylated extracellular signal-regulated kinase (p-ERK) in a small population of corticotrophin-releasing factor [corticotrophin-releasing hormone (CRH)] neurons located specifically in the medial parvocellullar division (MPD) of the paraventricular nucleus of the hypothalamus. Activation of these hypothalamic CRH neurons likely accounted for the observed metabolic effects leading to weight loss in obese rats.

Alterations of the gut microbiota with antibiotics protects dopamine neuron loss and improve motor deficits in a pharmacological rodent model of Parkinson's disease.

Parkinson's disease (PD) is a debilitating condition resulting in motor and non-motor symptoms affecting approximately 10 million people worldwide. Currently, there are no pharmacological treatments that can cure the condition or effectively halt its progression. The focus of PD research has been primarily on the neurobiological basis and consequences of dopamine (DA) neuron degeneration given that the loss of DA neurons projecting from the substantia nigra to the dorsal striatum results in the development of cardinal PD motor symptoms. Alternatively, gastrointestinal dysfunction is well recognized in PD patients, and often occurs prior to the development of motor symptoms. The gut microbiota, which contains thousands of bacterial species, play important roles in intestinal barrier integrity and function, metabolism, immunity and brain function. Pre-clinical and clinical studies suggest an important link between alterations in the composition of the gut microbiota and psychiatric and neurological conditions, including PD. Several reports have documented gut dysbiosis and alterations in the composition of the gut microbiota in PD patients. Therefore, the goal of this study was to explore the contribution of the gut microbiota to the behavioral and neurochemical alterations in a rodent toxin model of DA depletion that reproduces the motor symptoms associated with PD. We observed that chronic treatment of adult rats with non-absorbable antibiotics ameliorates the neurotoxicity of 6-hydroxydopamine (6-OHDA) in a unilateral lesion model. Specifically, immunohistochemistry against the dopaminergic neuron marker tyrosine hydroxylase (TH) showed an attenuation of the degree of 6-OHDA-induced dopaminergic neuron loss in antibiotic treated animals compared to control animals. In addition, we observed a reduction in the expression of pro-inflammatory markers in the striatum of antibiotic-treated animals. The degree of motor dysfunction after 6-OHDA was also attenuated in antibiotic-treated animals as measured by paw-rearing measurements in the cylinder test, forepaw stepping test, and ipsilateral rotations observed in the amphetamine-induced rotation test. These results implicate the gut microbiota as a potential contributor to pathology in the development of PD. Further studies are necessary to understand the specific mechanisms involved in transducing alterations in the gut microbiota to changes in dopaminergic neuron loss and motor dysfunction.

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.

Neonatal intraperitoneal or intravenous injections of recombinant adeno-associated virus type 8 transduce dorsal root ganglia and lower motor neurons.

Targeting lower motor neurons (LMNs) for gene delivery could be useful for disorders such as spinal muscular atrophy and amyotrophic lateral sclerosis. LMNs reside in the ventral gray matter of the spinal cord and send axonal projections to innervate skeletal muscle. Studies have used intramuscular injections of adeno-associated virus type 2 (AAV2) to deliver viral vectors to LMNs via retrograde transport. However, treating large areas of the spinal cord in a human would require numerous intramuscular injections, thereby increasing viral titer and risk of immune response. New AAV serotypes, such as AAV8, have a dispersed transduction pattern after intravenous or intraperitoneal injection in neonatal mice, and may transduce LMNs by retrograde transport or through entry into the nervous system. To test LMN transduction after systemic injection, we administered recombinant AAV8 (rAAV8) carrying the green fluorescent protein (GFP) gene by intravenous or intraperitoneal injection to neonatal mice on postnatal day 1. Tissues were harvested 5 and 14 days postinjection and analyzed by real-time polymerase chain reaction and GFP immunohistochemistry to assess the presence of AAV genomes and GFP expression, respectively. Spinal cords were positive for AAV genomes at both time points. GFP immunohistochemistry revealed infrequent labeling of LMNs across all time points and injection routes. Somewhat surprisingly, there was extensive labeling of fibers in the dorsal horns and columns, indicating dorsal root ganglion transduction across all time points and injection routes. Our data suggest that systemic injection of rAAV8 is not an effective delivery route to target lower motor neurons, but could be useful for targeting sensory pathways in chronic pain.

Recombinant adeno-associated virus-mediated global anterograde delivery of glial cell line-derived neurotrophic factor to the spinal cord: comparison of rubrospinal and corticospinal tracts in the rat.

Amyotrophic lateral sclerosis (ALS) is characterized by progressive loss of spinal lower motoneurons. Gene delivery is a promising strategy to deliver therapeutic molecules to these vulnerable cells. However, definition of an optimal route of delivery capable of accessing neurons over a considerable extent of the neuraxis represents a significant logistical problem. Intramuscular vector injections are not ideal as this approach would involve hundreds of injections to completely treat an ALS patient and also would be dependent on retrograde transport of the viral platform of choice. Alternatively, upper motoneurons could deliver trophic factors over considerable distances by anterograde transport after a relatively localized intracerebral injection. To test this approach, the present study was designed to compare the corticospinal (CST) and rubrospinal (RST) tracts for their ability to transport recombinant adeno-associated virus serotype 5 (rAAV5)-derived green fluorescent protein (GFP) or glial cell line-derived neurotrophic factor (GDNF) to the spinal cord. Unilateral injections of rAAV5-GFP into the red nucleus (RN) or motor cortex of normal rats produced GFP-positive fibers in the appropriate descending tracts extending to the lumbar spinal cord. For both tracts, GFP-positive axonal projections into the spinal gray matter were consistently observed. GDNF immunohistochemistry demonstrated that confirmed RN injections resulted in GDNF-positive fibers projecting into spinal gray matter as seen in the GFP group. In contrast, confirmed cortical rAAV5-GDNF injections resulted in less evident staining in spinal cord. Spinal cord GDNF levels were elevated at distances up to 72 mm from the injection sites, and confirmed that RST-related GDNF transport to spinal cord surpassed CST-associated delivery.

Unexpected off-targeting effects of anti-huntingtin ribozymes and siRNA in vivo.

Gene transfer strategies to reduce levels of mutant huntingtin (mHtt) mRNA and protein by targeting human Htt have shown therapeutic promise in vivo. Previously, we have reported that a specific, adeno-associated viral vector (rAAV)-delivered short-hairpin RNA (siHUNT-2) targeting human Htt mRNA unexpectedly decreased levels of striatal-specific transcripts in both wild-type and R6/1 transgenic HD mice. The goal of this study was to determine whether the siHUNT-2-mediated effect was due to adverse effects of RNA interference (RNAi) expression in the brain. To this end, we designed two catalytically active hammerhead ribozymes directed against the same region of human Htt mRNA targeted by siHUNT-2 and delivered them to wild-type and R6/1 transgenic HD mice. After 10 weeks of continuous expression, these ribozymes, like siHUNT-2, negatively impacted the expression of a subset of genes in the striatum. This effect was independent of rAAV transduction and specific to the targeting of a unique sequence in human Htt mRNA. After consideration of the known potential RNAi-specific toxic mechanisms, only cleavage of an unintended RNA target can account for the data reported herein. Thus, long-term rAAV-mediated RNAi in the brain does not, in and of itself, negatively affect striatal gene expression. These findings have important implications in the development of therapeutic RNAi for the treatment of neurological disease.

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.