The principles of gene therapy for the nervous system

Gene Therapy Approach with an Emphasis on Growth Factors: Theoretical and Clinical Outcomes in Neurodegenerative Diseases

The etiology of many neurological diseases affecting the central nervous system (CNS) is unknown and still needs more effective and specific therapeutic approaches. Gene therapy has a promising future in treating neurodegenerative disorders by correcting the genetic defects or by therapeutic protein delivery and is now an attraction for neurologists to treat brain disorders, like Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, spinal muscular atrophy, spinocerebellar ataxia, epilepsy, Huntington's disease, stroke, and spinal cord injury. Gene therapy allows the transgene induction, with a unique expression in cells' substrate. This article mainly focuses on the delivering modes of genetic materials in the CNS, which includes viral and non-viral vectors and their application in gene therapy. Despite the many clinical trials conducted so far, data have shown disappointing outcomes. The efforts done to improve outcomes, efficacy, and safety in the identification of targets in various neurological disorders are also discussed here. Adapting gene therapy as a new therapeutic approach for treating neurological disorders seems to be promising, with early detection and delivery of therapy before the neuron is lost, helping a lot the development of new therapeutic options to translate to the clinic.

Liposome-Mediated Gene Transfer into Established CNS Cell Lines, Primary Glial Cells, and in Vivo

Sufficient gene transfer into CNS-derived cells is the most crucial step to develop strategies for gene therapy. In this study liposome-mediated gene transfer using a β-galactosidase (β-GAL) reporter gene was performed in vitro (C6 glioma cells, NT2 neuronal precursor cells, 3T3 fibroblasts, primary glial cells) and in vivo. Using Trypan blue exclusion staining, optimal lipid concentration was observed in the range of 10-12 μg/mL. Under optimal conditions (80,000 cells/16 mm well, incubation overnight, lipid/DNA ratio = 1:18) a high transfection rate was achieved (<9% for C6 cells; <1% for NT2 cells). In primary cultures of glial cells a fair amount of positive stained cells (glial cell) was found, but the transfection efficiency was lower (<0.1%). A “boost-lipofection” markedly increased (twice) lipofection efficiency in C6 cells. Expression of β-GAL reached a maximum after 3-5 days. When the liposome–DNA complexes were injected/infused directly into the brains of adult rats, several weakly stained cells could be observed in the brain region adjacent to the injection site. It is concluded that liposome-mediated gene transfer is an efficient method for gene transfer into CNS cells in vitro, but the transfection efficiency into the rat brain in vivo is far too low and therefore not applicable.

Nonviral gene transfection nanoparticles: function and applications in the brain

In vivo transfer and expression of foreign genes allows for the elucidation of functions of genes in living organisms and generation of disease models in animals that more closely resemble the etiology of human diseases. Gene therapy holds promise for the cure of a number of diseases at the fundamental level. Synthetic "nonviral" materials are fast gaining popularity as safe and efficient vectors for delivering genes to target organs. Not only can nanoparticles function as efficient gene carriers, they also can simultaneously carry diagnostic probes for direct "real-time" visualization of gene transfer and downstream processes. This review has focused on the central nervous system (CNS) as the target for nonviral gene transfer, with special emphasis on organically modified silica (ORMOSIL) nanoparticles developed in our laboratory. These nanoparticles have shown robust gene transfer efficiency in brain cells in vivo and allowed to investigate mechanisms that control neurogenesis as well as neurodegenerative disorders.

Efficient non-viral transfection of adult neural stem/progenitor cells, without affecting viability, proliferation or differentiation

BACKGROUND

Neurogenesis occurs in defined areas of the adult mammalian brain, including the dentate gyrus of the hippocampus. Rat neural stem/progenitor cells isolated from this region retain their multipotency in vitro and in vivo after grafting into the adult brain. Molecular signalling and lineage selection in these cells may be examined using genetic manipulation. However, valid analysis requires that this manipulation should not affect cellular viability, proliferation or differentiation.

METHODS

We screened several transfection protocols to develop a method which met these criteria. We then tested the effects of transfection on viability, proliferation and differentiation into the three neural lineages: neurons, astrocytes and oligodendrocytes.

RESULTS

In initial testing, ExGen500 and FuGene6 efficiently transfected adult neural stem/progenitor cells, in vitro. After optimisation, these agents transfected 16% and 11% of cells, respectively. FuGene6-treated cells did not differ from untransfected cells in their viability or rate of proliferation, whereas these characteristics were significantly reduced following ExGen500 transfection. Importantly, neither agent affected the pattern of differentiation following transfection. Both agents could be used to genetically label cells, and track their differentiation into the three neural lineages, after grafting onto ex vivo organotypic hippocampal slice cultures.

CONCLUSIONS

These data demonstrate that non-viral transfection may be used to genetically manipulate neural stem/progenitor cells, without adversely affecting their growth or perturbing lineage selection. Such a method is valuable for examining the molecular mechanisms of cell fate determination in vitro. Furthermore, this protocol may be exploited in the development of cell-based gene therapy strategies.

In vivo transgene expression using an adenoviral tetracycline-regulated system with neuron-specific enolase promoter

A recombinant adenoviral tetracycline-regulated system with neuron-specific enolase (NSE) promoter was injected stereotaxically into the striatum of rat brains. The efficiency of in vivo transfection was quantified by counting the number of green fluorescent protein (GFP)-positive cells at 3 days, 1 week, and 4 weeks after injection. NeuN immunohistochemistry demonstrated that expression of gammaPKC-GFP was dominant (20-99%) in neuron and expression of gammaPKC-GFP in neuron was significantly higher in pups than adult rats. These results indicate that tetracycline-inhibitable transcription factor (tTA) can drive tetracycline-responsive promoter (TetOp) under the control of NSE promoter, thereby efficiently and selectively expressing gammaPKC-GFP in neurons in vivo.

Neuroprotective role of a proline-rich Akt substrate in apoptotic neuronal cell death after stroke: relationships with nerve growth factor

The Akt signaling pathway contributes to regulation of apoptosis after a variety of cell death stimuli. A novel proline-rich Akt substrate (PRAS) was recently detected and found to be involved in apoptosis. In our study, Akt activation was modulated by growth factors, and treatment with nerve growth factor (NGF) reduced apoptotic cell death after ischemic injury. However, the role of the PRAS pathway in apoptotic neuronal cell death after ischemia remains unknown. Phosphorylated PRAS (pPRAS) and the binding of pPRAS/phosphorylated Akt (pPRAS/pAkt) to 14-3-3 (pPRAS/14-3-3) were detected, and their expression transiently decreased in mouse brains after transient focal cerebral ischemia (tFCI). Liposome-mediated pPRAS cDNA transfection induced overexpression of pPRAS, promoted pPRAS/14-3-3, and inhibited apoptotic neuronal cell death after tFCI. The expression of pPRAS, pPRAS/pAkt, and pPRAS/14-3-3 increased in NGF-treated mice but decreased with inhibition of phosphatidylinositol-3 kinase and the NGF receptor after tFCI. These results suggest that PRAS phosphorylation and its interaction with pAkt and 14-3-3 might play an important role in neuroprotection mediated by NGF in apoptotic neuronal cell death after tFCI.

Adenovirus-mediated gene transfer into the brain stem to examine cardiovascular function: role of nitric oxide and Rho-kinase

The central nervous system plays an important role in the regulation of blood pressure via the sympathetic nervous system. Abnormal regulation of the sympathetic nerve activity is involved in the pathophysiology of hypertension. In particular, the brain stem, including the nucleus tractus solitarii (NTS) and the rostral ventrolateral medulla (RVLM), is a key site that controls and maintains blood pressure via the sympathetic nervous system. Nitric oxide (NO) is a unique molecule that influences sympathetic nerve activity. Rho-kinase is a downstream effector of the small GTPase, Rho, and is implicated in various cellular functions. We developed a technique to transfer adenovirus vectors encoding endothelial nitric oxide synthase and dominant-negative Rho-kinase into the NTS or the RVLM of rats in vivo. We applied this technique to hypertensive rats to explore the physiological significance of NO and Rho-kinase.

The magnocellular neuronal phenotype: cell-specific gene expression in the hypothalamo-neurohypophysial system

The magnocellular oxytocin (OT) and vasopressin (VP) neurons of the hypothalamo-neurohypophysial system are exceptional cell biological models to study mechanisms of cell-specific gene expression and neurosecretion of neuropeptides in the central nervous system. Single cell differential gene expression experiments have further defined these phenotypes by identifying novel and distinct regulatory molecules in these neurons. Transgenic mouse studies have led to the intergenic region (IGR) hypothesis, which states that the DNA sequences between the OT- and VP-genes contain critical enhancer sites for their cell-specific expression. The recent cloning and sequencing of the human IGR, and its comparison with the mouse IGR sequence has identified conserved sequences as putative, cell-specific enhancer sites which are now being evaluated by biolistic transfections of organotypic hypothalamic cultures. With these data, it is possible to target the gene expression of specific molecules to magnocellular neurons both in vivo and in vitro, in order to perturb and/or visualize neurosecretory and other processes.

Cationic liposome-mediated GDNF gene transfer after spinal cord injury

Glial cell line-derived neurotrophic factor (GDNF) has been shown to protect cranial and spinal motoneurons, which suggests potential uses of GDNF in the treatment of spinal cord injury (SCI) and motor neuron disease. We examined neuroprotective effect of cationic liposome-mediated GDNF gene transfer in vivo on axonal regeneration and locomotor function recovery after SCI in adult rats. The mixture of DC-Chol liposomes and recombinant plasmid pEGFP-GDNF cDNA was injected after SCI. RT-PCR confirmed the increased expression of GDNF mRNA in the injected areas at 7 days after injection. The expression of EGFP-GDNF was observed in the cells around the injection locus by fluorescence microscope at least 4 weeks after injection. Four weeks after GDNF gene transfer, regeneration of the corticospinal tracts was assessed using anterograde tract tracing. There are more HRP labeling of corticospinal tract axons across the lesion in GDNF group compared with control group. In GDNF group, the maximum distance these labeled axons extended varied in different animals and ranged from 5 mm to approximately 9 mm from the lesion. In control group, no HRP labeled axons extended caudal to the lesion. The locomotion function of hindlimbs of rats was evaluated using inclined plane test and BBB locomotor scores. The locomotion functional scores in GDNF group were higher than that in control group within 1-4 weeks after SCI (p < 0.05). These data demonstrate that in vivo transfer of GDNF cDNA can promote axonal regeneration and enhance locomotion functional recovery, suggesting that cationic liposome-mediated delivery of GDNF cDNA may be a practical gene transfer method for traumatic SCI treatment.

Characterization of lentiviral vector-mediated gene transfer in adult mouse brain

Lentiviral vectors are promising tools for gene transfer into the central nervous system. We have characterized in detail transduction with human immunodeficiency virus type 1 (HIV-1)-derived vectors encoding enhanced green fluorescent protein (eGFP) in the adult mouse brain. Different brain regions such as the striatum, hippocampus, and the lateral ventricle were targeted. The eGFP protein was transported anterogradely in the nigrostriatal pathway, but we have found no evidence of transport of the lentiviral vector particle. The performance levels of the different generations of packaging and transfer plasmid were compared. Omission of the accessory genes from the packaging plasmid resulted in a modest decrease in transgene expression. Inclusion of the woodchuck hepatitis posttranscriptional regulatory element, on the one hand, and the central polypurine tract and termination sequences, on the other hand, in the transfer vector each resulted in a 4- to 5-fold increase in transgene expression levels. Combination of both elements enhanced expression levels more than the sum of the individual components, suggesting a synergistic effect. In the serum of mice injected with lentiviral vectors a humoral response to vector proteins was detected, but this did not compromise transgene expression. Immune response to the transgene was found only in a minority of the animals.

Vasopressin gene expression: experimental models and strategies

The intergenic region (IGR) separating the genes for vasopressin (VP) and oxytocin (OT) has been shown to be critical for the cell-specific expression of these peptide genes in hypothalamic neurons. To date, the most relevant information about the putative cis-elements in the IGR that might determine cell-specific gene expression has come from studies in transgenic models. As a first step toward increasing the efficiency of the IGR sequence deletion studies in transgenic animals, a comparative genomics approach comparing the IGR sequence in humans versus mice was used to identify conserved sequences that might be candidate regulatory elements. The nucleotide sequence of the IGR between the human VP and OT genes was determined and compared to the mouse IGR, and 26 conserved sequences in three distinct clusters were found. These conserved sequences and motifs may be important for the cell-specific expression of the VP and OT genes. However, before further significant progress can be made, a "high-throughput" method for the analysis of deletion constructs in relevant cell types in vitro is needed. It is proposed here that organotypic culture models combined with the use of particle-mediated gene transfer methods may provide an effective, general strategy for the study of cell-specific expression in the central nervous system.

Effect of immunity on gene delivery into anterior horn motor neurons by live attenuated herpes simplex virus vector

Efficient and prolonged foreign gene expression has been demonstrated in the bilateral anterior horn motor neurons of the spinal cord by intramuscular inoculation with attenuated herpes simplex virus (HSV) expressing latency associated transcript promoter-driven beta-galactosidase (betaH1). To examine the effect of immunity on the gene delivery, betaH1 was applied in rats immunized subcutaneously or intramuscularly with the parent HF strain. Rats were immunized subcutaneously with HF strain and 28 days later when the high antibody titer was maintained, betaH1 was inoculated into the right gastrocnemius muscle. Second, 35 days after inoculation with HF strain into the right gastrocnemius muscle, betaH1 was inoculated at the same site. In both ways of immunization, immunity did not abolish or prevent the transgene expression in the anterior horn motor neurons, but attenuated the range and the number of the beta-galactosidase-positive neurons from about 85% to 50-65% on 28 days after inoculation with betaH1. However, beta-galactosidase activity was observed in a wide range of the bilateral anterior horn motor neurons without significant pathological changes. These findings support the feasibility of the attenuated HSV vector in gene delivery into the central nervous system, even in the presence of immunity.

NAIP protects the nigrostriatal dopamine pathway in an intrastriatal 6-OHDA rat model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder of the basal ganglia, associated with the inappropriate death of dopaminergic neurons of the substantia nigra pars compacta (SNc). Here, we show that adenovirally mediated expression of neuronal apoptosis inhibitor protein (NAIP) ameliorates the loss of nigrostriatal function following intrastriatal 6-OHDA administration by attenuating the death of dopamine neurons and dopaminergic fibres in the striatum. In addition, we also addressed the role of the cysteine protease caspase-3 activity in this adult 6-OHDA model, because a role for caspases has been implicated in the loss of dopamine neurons in PD, and because NAIP is also a reputed inhibitor of caspase-3. Although caspase-3-like proteolysis was induced in the SNc dopamine neurons of juvenile rats lesioned with 6-OHDA and in adult rats following axotomy of the medial forebrain bundle, caspase-3 is not induced in the dopamine neurons of adult 6-OHDA-lesioned animals. Taken together, these results suggest that therapeutic strategies based on NAIP may have potential value for the treatment of PD.

In vivo protein expression from mRNA delivered into adult rat brain

The expression of proteins after local mRNA delivery has a great potential for analysis of protein function in vivo. To explore the feasibility of such a technique within the central nervous system (CNS), we delivered luciferase-encoding mRNA into the rat brain. The tissue distribution and stability of injected mRNA were analyzed using in situ detection and Northern hybridization, while luciferase expression was measured by enzymatic assay. Following intracerebral injection of lipofectin-complexed mRNA, expression of luciferase was detectable as early as 1 h, was maximal at 2-3 h, but was below the level of detection by 24 h. The extent of luciferase expression correlated with the amount of mRNA delivered. Luciferase expression was higher when lipofectin-complexed rather than naked mRNA was injected. In addition, the luciferase expression increased significantly by adding a 50 nt-long poly(A) tail to the 3'-end of the mRNA. Delivering mRNA to the cerebral cortex or hippocampus resulted in measurable luciferase activity at the injection sites but not in adjacent areas. Accordingly, the luciferase mRNA was also localized to the injection site, and the amount of intact transcript was significantly higher at 3 h compared to 24 h after injection. These results demonstrate that in vivo mRNA delivery is a feasible technique for immediate, transient overexpression of desired proteins in the CNS and, therefore, can serve as a model system to study the neurobiological effects of specific proteins.

Serotonergic gene expression and depression: implications for developing novel antidepressants

The development and configuration of several neural networks is dependent on the actions of serotonin (5-HT) acting through multiple hetero- and autoreceptor subtypes. During early brain development 5-HT modulates morphogenetic activities, such as neural differentiation, axon outgrowth, and synaptic modeling. In the adult brain, midbrain raphe serotonergic neurons project to a variety of brain regions and modulate a wide range of physiological functions. Several lines of evidence indicate that genetically determined variability in serotonergic gene expression, as it has been documented for the 5-HT transporter, influences temperamental traits and may lead to psychopathological conditions with increased anxiety, depression, and aggression. Investigation of the regulation of serotonergic gene transcription and its impact on neuronal development, synaptic plasticity, and neurogenesis spur interest to identify serotonergic gene-related molecular factors underlying disease states and to develop more effective antidepressant treatment strategies. Gene targeting strategies have increasingly been integrated into investigations of brain function and along with the fading dogma of a limited capacity of neurons for regeneration and reproducibility, it is realized that gene transfer techniques using efficient viral vectors in conjunction with neuron-selective transcriptional control systems may also be applicable to complex disorders of the brain. Given the fact that the 5-HT system continues to be an important target for drug development and production, novel strategies aiming toward the modification of 5-HT function at the level of gene expression are likely to be exploited by enterprises participating actively in the introduction of alternative therapeutic approaches.

Therapeutic potential of neurotrophic factors and neural stem cells against ischemic brain injury

Development of neuronal and glial cells and their maintenance are under control of neurotrophic factors (NTFs). An exogenous administration of NTFs protects extremely sensitive brain tissue from ischemic damage. On the other hand, it is now known that neural stem cells are present in normal adult brain, and have a potential to compensate and recover neural functions that were lost due to ischemic stroke. These stem cells are also under control of NTFs to differentiate into a certain species of neural cells. Thus, the purpose of this review is to summarize the present understanding of the role of NTFs in normal and ischemic brain and the therapeutic potential of NTF protein itself or gene therapy, and then to summarize the role of NTFs in stem cell differentiation and a possible therapeutic potential with the neural stem cells against ischemic brain injury.

Nonviral glial cell-derived neurotrophic factor gene transfer enhances survival of cultured dopaminergic neurons and improves their function after transplantation in a rat model of Parkinson's disease

Transplantation of dopaminergic fetal mesencephalic tissue into the striatum is currently being developed for treatment of patients with advanced Parkinson's disease. Ethical concerns regarding the use of human fetal tissue, and the limited availability as well as poor survival and differentiation of dopaminergic neurons after transplantation have reduced the extent and outcome of this approach so far. With the purpose of finding means to increase the yield of dopaminergic neurons in transplants, and to reduce the amount of fetal tissue needed for each transplanted patient, we transfected rat fetal ventral mesencephalic (VM) tissue grown as organotypic free-floating roller tube (FFRT) cultures with a vector encoding human glial cell-derived neurotrophic factor (hGDNF). For transfer of an episomal expression vector (pRep7-GDNF8) a nonviral, nonliposomal cationic transfection technique was applied and optimized. Recombinant hGDNF expression resulted in a higher number of TH-positive neurons in the cultures as measured 6 days after transfection. Ventral mesencephalic cultures expressing hGDNF were then grafted into the striatum of unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats. Grafting of genetically modified VM cultures resulted in earlier functional recovery compared with grafting nontransfected cultures. We conclude that organotypic free-floating roller tube cultures can be successfully transfected to produce hGDNF with effects on TH-expressing neurons in vitro and functional effects after grafting in a rat Parkinson's disease model.

Growth factor enhanced retroviral gene transfer to the adult central nervous system

The use of viral vectors for gene delivery into mammalian cells provides a new approach in the treatment of many human diseases. The first viral vector approved for human clinical trials was murine leukemia virus (MLV), which remains the most commonly used vector in clinical trials to date. However, the application of MLV vectors is limited since MLV requires cells to be actively dividing in order for transduction and therefore gene delivery to occur. This limitation precludes the use of MLV for delivering genes to the adult CNS, where very little cell division is occurring. However, we speculated that this inherent limitation of ML V may be overcome by utilizing the known mitogenic effect of growth factors on cells of the CNS. Specifically, an in vivo application of growth factor to the adult brain, if able to induce cell division, could enhance MLV-based gene transfer to the adult brain. We now show that an exogenous application of basic fibroblast growth factor induces cell division in vivo. Under these conditions, where cells of the adult brain are stimulated to divide, MLV-based gene transfer is significantly enhanced. This novel approach precludes any vector modifications and provides a simple and effective way of delivering genes to cells of the adult brain utilizing MLV-based retroviral vectors.

Helper-dependent adenovirus vectors: their use as a gene delivery system to neurons

Recombinant adenovirus vectors have provided a major advance in gene delivery systems for post-mitotic neurons. However, the use of these first generation vectors has been limited due to the onset of virally mediated effects on cellular function and viability. In the present study we have used primary cultures of cerebellar granule neurons to examine the efficacy and cytotoxic effects of a helper-dependent adenovirus vector (hdAd) in comparison with a first generation vector. Our results demonstrate that the hdAd system provides equally efficient infectivity with significantly reduced toxicity in comparison to first generation vectors. Neurons transduced with a high titre of a first generation vector exhibited a time-dependent shut down in global protein synthesis and impaired physiological function as demonstrated by a loss of glutamate receptor responsiveness. This was followed by an increase in the fraction of TUNEL-positive cells and a loss of neuronal survival. In contrast, hdAds could be used at titres that transduce >85% of neurons with little cytotoxic effect: cellular glutamate receptor responses and rates of protein synthesis were indistinguishable from uninfected controls. Furthermore, cell viability was not significantly affected for at least 7 days after infection. At excessive viral titres, however, infection with hdAd did cause moderate but significant changes in cell function and viability in primary neuronal cultures. Thus, while these vectors are remarkably improved over first generation vectors, these also have limitations with respect to viral effects on cellular function and viability. Gene Therapy (2000) 7, 1200-1209.

Long-term gene expression in the anterior horn motor neurons after intramuscular inoculation of a live herpes simplex virus vector

To clarify the feasibility of the herpes simplex virus (HSV) vector in expressing the foreign gene in the motor neuron, we inoculated a live attenuated HSV expressing beta-galactosidase (beta-gal) activity under a latency-associated transcript promoter in the right gastrocnemius muscle of rats. Expression of beta-gal activity was observed 5 days after inoculation in the bilateral anterior horn cells of the spinal cord that innervates the inoculation muscle. However, the spread of beta-gal activity was not observed in the inoculation muscle. Without significant pathological changes, the spread of beta-gal-expressing neurons was observed in the lumbosacral spinal cord until 14 days after inoculation with staining concentrated in the anterior horn cells. Ninety percent of the anterior horn motor neurons expressed beta-gal activity with expression continuing to at least 182 days after inoculation. Thus beta-gal activity was expressed in the bilateral anterior horn cells at the lumbosacral spinal cord that innervates the inoculated muscle for a long time, possibly a life-long period. This indicates that this recombinant HSV vector system to motor neurons may further improve the understanding and treatment of neurological diseases in motor neurons of the spinal cord.

Dopa-producing astrocytes generated by adenoviral transduction of human tyrosine hydroxylase gene: in vitro study and transplantation to hemiparkinsonian model rats

Astrocytes secreting a large amount of 3,4-dihydroxyphenylalanine (dopa) were generated by adenoviral transduction of the human tyrosine hydroxylase (TH) gene. After characterizing in vitro, the effect of transplantation of these astrocytes to the striatum of hemiparkinsonian model rats was investigated. Subconfluent cortical astrocytes were infected by replication-defect adenovirus type 5 carrying the human TH-1 gene or the LacZ reporter gene under the promoter of the glial fibrillary acidic protein (AdexGFAP-HTH-1, AdexGFAP-NL-LacZ). Dopa secretion was not evident at 3 days after the transduction of the HTH-1 gene but it increased from 7 days up to at least 4 months. The secretion was substrate (tyrosine)-dependent, and was enhanced by loading tetrahydrobioputerin (BH4) concentration-dependently. One-third of the hemiparkinsonian model rats, that were transplanted the HTH-1 gene-transduced astrocytes or introduced the direct injection of the viral vector to the striatum, showed a reduction of methamphetamine-induced rotations for at least 6 weeks. Apomorphine-induced rotation was decreased to the 50% level of the control's, but the reduction was obtained equally by the transplantation of HTH-1 gene-transduced or LacZ reporter gene-transduced astrocytes, or by the introduction of HTH-1 or LacZ gene carrying adenovirus. Treatment with FK506 for 3 weeks improved the late-phase apomorphine-induced rotations following the introduction of the HTH-1 gene carrying adenovirus. Histological examination revealed that, in animals that showed a reduction of methamphetamine-rotation, the TH positive astrocytes-like cells were distributed widely in the host striatum for at least 4 weeks. The number of TH positive astrocytes-like cells and their immunoreactivity decreased after 6 weeks when OX-41 positive microglias/macrophages were infiltrated. Data indicate that the adenoviral transduction of the human TH gene to astrocytes and its introduction to the striatum is a promising approach for the treatment of Parkinson's disease. However, the further technical improvements are required to optimize the adenoviral gene delivery, such as the control of viral toxicity and the regulation of the immune response.

Liposome-mediated NGF gene transfection following neuronal injury: potential therapeutic applications

We have systematically investigated the therapeutic potential of cationic liposome-mediated neurotrophic gene transfer for treatment of CNS injury. Following determination of optimal transfection conditions, we examined the effects of dimethylaminoethane-carbamoyl-cholesterol (DC-Chol) liposome-mediated NGF cDNA transfection in injured and uninjured primary septo-hippocampal cell cultures and rat brains. In in vitro studies, we detected an increase of NGF mRNA in cultures 1 day after transfection. Subsequent ELISA and PC12 cell biological assays confirmed that cultured cells secreted soluble active NGF into the media from day 2 after gene transfection. Further experiments showed that such NGF gene transfection reduced the loss of chol- ine acetyltransferase (ChAT) activity in cultures following calcium-dependent depolarization injury. In in vivo studies, following intraventricular injections of NGF cDNA complexed with DC-Chol liposomes, ELISA detected nine- to 12-fold increases of NGF in rat CSF. Further studies showed that liposome/NGF cDNA complexes could attenuate the loss of cholinergic neuronal immunostaining in the rat septum after traumatic brain injury (TBI). Since deficits in cholinergic neurotransmission are a major consequence of TBI, our studies demonstrate for the first time that DC-Chol liposome-mediated NGF gene transfection may have therapeutic potential for treatment of brain injury.

Somatic gene therapy in animal models of Parkinson's disease

Gene therapy in Parkinson's disease (PD) emerged about 10 years ago but until now, no clinical trials are under way, because most approaches have failed to show long-term therapeutic effects in PD animal models and because safety concerns precluded the use in humans so far. This review tries to give an overview on the development of different strategies in gene therapy in PD animal models and point out new and possibly more successful directions, including the transplantation of neural precursor cells and pig tissue.

The influence of interleukin-1 receptor antagonist transgene on spiral ganglion neurons

The cytokine interleukin-1beta (IL-1) has been shown to induce the secretion of NGF and GDNF in several types of neuronal populations. IL-1 has also been shown to mediate immune response following trauma or presence of foreign antigens. We investigated the influence of an IL-1 antagonist on the survival of spiral ganglion neurons in inner ears in which hair cells have been eliminated. We used a replication-deficient adenoviral vector containing the human IL-1 receptor antagonist (IL-1ra) cDNA. Guinea pigs were bilaterally deafened with ototoxic drugs. One week later their left cochleae were inoculated with the IL-1ra vector, designated Ad.IL-1ra. The vector was delivered by injection through the cochlear round window. IL-1ra protein levels within the perilymph of Ad.IL-1ra-injected animals were measured with ELISA and found to be significantly elevated compared to our controls. Spiral ganglion cell counts in experimental ears revealed a lower density of neurons after Ad.IL-1ra inoculation. Taken together, the data suggest that the Ad.IL-1ra-infected cochlear cells synthesized the transgenic human IL-1ra protein, which was then secreted by the cells into the perilymph, resulting in an accelerated neuronal degeneration in hair cell-depleted ears.

Cell-specific gene expression in oxytocin and vasopressin magnocellular neurons

The oxytocin (OT) and vasopressin (VP) expressing magnocellular neurons in the hypothalamic-neurohypophysial system (HNS) have been the most studied of all the neuroendocrine cell-types. Despite this, our understanding of the mechanisms that underly the cell-specific expression of the peptide genes in these neurons has remained obscure. Part of the reason for this may be related to the close apposition of the OT and VP genes in the chromosomal locus, the genes being separated by as little as 3.5 kb in the mouse, and their interactions which are critical for cell-specific expression of the genes. Recent studies using intact rat OT and VP constructs in transgenic mice, and rat and mouse VP genes with CAT inserts in exon III as reporters in transgenic rats and mice, respectively, have suggested the presence of cell-specific enhancer elements in the 3' downstream (intergenic region, IGR) region of the VP gene. Evidence in favor of this view is presented from transgenic mouse studies on the expression of mouse OT- and VP-CAT gene constructs. Oxytocin and vasopressin phenotypes in the magnocellular neuronal population have traditionally been assessed by either immunocytochemical or in situ hybridization histochemical methods leading to the view that these genes are never coexpressed. However, more sensitive methods show that most OT cells also express some VP mRNA, and most VP cells contain some OT mRNA. A third phenotype containing equivalent levels of both OT and VP mRNA can also be found under some conditions, thereby complicating our analysis of cell-specificity. A continuing problem hindering studies of the regulation of OT and VP gene expression in neurons, is the absence of an appropriate cell line to examine these issues. We have found that stationary slice-explant cultures allow for excellent preservation of highly differentiated magnocellular neurons in long-term culture, and that these cultures can be used for physiological and pharmacological studies and analysis of gene expression.

Oligodendrocyte-specific gene expression in mouse brain: use of a myelin-forming cell type-specific promoter in an adeno-associated virus

To explore the feasibility of cell type-specific gene expression in oligodendrocytes as a possible therapeutic approach for demyelinating diseases, the cell specificity, tissue specificity, and duration of gene expression were investigated using recombinant adeno-associated viral vectors (rAAV) carrying a green fluorescence protein (GFP) gene. Recombinant AAV vectors carrying either the myelin basic protein (MBP) promoter (rAAV-MBP-GFP) or the cytomegalovirus (CMV) immediate early promoter (rAAV-CMV-GFP) were semistereotactically injected into the brain of C57BL/6J mice. Injection of the rAAV-MBP-GFP vector into or near the corpus callosum resulted in high levels of GFP expression in white matter regions. Double immunostaining with cell- specific markers proved that these GFP-expressing cells were oligodendrocytes. Injection of the rAAV- MBP-GFP vector into gray matter rarely produced GFP expression. In contrast, injection of the rAAV-CMV-GFP vector resulted in few GFP-expressing cells in the white matter, with most of the GFP-expressing cells being neurons located in the cerebral cortex along the needle track. The expression of the GFP driven by the MBP promoter persisted for at least 3 months.

Gene therapy for cerebrovascular disease

OBJECTIVE

To review the principles of and the experimental and clinical results of gene therapy for cerebrovascular disease.

METHODS

Literature review.

RESULTS

Vectors for gene transfer into the brain or into the cerebral vasculature include naked plasmid deoxyribonucleic acid, cationic liposomes, and viruses such as adenovirus, retrovirus, adeno-associated virus, and herpes simplex virus. Experiments using these vectors showed that intra- or perivascular application to systemic arteries can lead to transfection and expression of a foreign transgene in the adventitia and the endothelium. Intrathecal administration can lead to transfection and foreign transgene expression in leptomeningeal cells as well as in fibroblasts of blood vessel adventitia. Biological effects demonstrated thus far include increased nitric oxide production by transfection of cerebral arterial adventitia with adenovirus expressing nitric oxide synthase. Adenoviruses carrying foreign genes have been used to decrease neuronal damage in cerebral ischemia and to decrease blood pressure in spontaneously hypertensive rats. Vectors and therapeutic applications for gene therapy are evolving rapidly.

CONCLUSION

Gene therapy for cerebrovascular disease is likely to have clinical application in the near future and will have a major impact on neurosurgery. Neurosurgeons will need to be aware of the literature in this area.

Cationic liposome-mediated DNA transfection in organotypic explant cultures of the ventral mesencephalon

We have examined the potential of cationic liposomes as a tool for approaches to gene therapy in the CNS. Our previous work has shown that cationic liposomes formulated from 3 beta-[N-(N',N'-dimethylaminoethane)carbamoyl] cholesterol (DC-Chol) and dioleoyl-L-alpha-phosphatidylethanolamine (DOPE) could achieve high transfection levels in a neuronal cell line (McQuillin et al. Neuroreport 1997; 8: 1481-1484). We therefore wished to assess transfection efficiencies in organotypic cultures from the brain with a reporter plasmid expressing E. coli beta-galactosidase in order to mimic an in vivo model. Explant cultures were generated according to the method of Stoppini et al (J Neurosci Meth 1991; 37: 173-182) with slight modifications. Brain slices were maintained on transparent porous membranes and were observed to maintain their intrinsic connectivity and cytoarchitecture to a large degree over periods of up to 6 weeks in culture. CNS tissue was obtained from rats at birth or 5 days after birth. After transfection beta-galactosidase expression was detected in cells of both neuronal and non-neuronal morphology. Control cultures were exposed to liposome alone and a plasmid that had the beta-galactosidase gene insert removed. Only low levels of endogenous beta-galactosidase reactivity were seen in these control cultures. DC-Chol/DOPE-mediated transfection was confirmed using a RT-PCR protocol capable of differentiating between untranscribed plasmid DNA and RNA generated from the transfected vector. These results suggest that cationic liposomes, particularly DC-Chol/DOPE liposomes, will be useful as delivery agents for gene transfer to CNS cells in vitro and possibly in vivo.

Gene transfer to the brain: emerging therapeutic strategy in psychiatry?

In the past 5 years, gene transfer strategies have increasingly been integrated into investigations of brain function with focus on cellular and molecular mechanisms of neuronal development, plasticity, and degeneration. These techniques are also under study as prospective treatment strategies for neurodegenerative disorders including Parkinson's and Alzheimer's disease. There has been considerable progress in the development of efficient and safe viral vectors for the delivery of transgenes directly to brain cells, and of transplantation techniques for neuronal, nonneuronal, and progenitor cells that have been genetically modified to release therapeutic gene products in the brain. New insights into the structure and organization of gene promoters and associated regulatory elements indicate a high degree of modularity and the design of a recombinant transcriptional apparatus that may allow developmental regulation and tissue-restricted expression to avoid unwanted side effects of the gene product, as well as the modulation of its expression by administered drugs in a therapeutic setting, is now an achievable goal. Based on an improved understanding of technologies that allow the addition, alteration, or elimination of individual genes to create transgenic animal models, constitutive or conditional gene knockout strategies are likely to increase our knowledge of which gene products are involved in the etiology and pathophysiology of psychiatric disorders, such as schizophrenia. Paralleling the refinement of gene transfer techniques and the fading dogma of a limited capacity of neurons for regeneration, reproducibility, and plasticity, it is currently being realized that gene therapy may also be applicable to genetically complex, non-mendelian disorders. While the concept of therapeutic gene transfer in severe neurodegenerative and psychiatric disorders is still in its theoretical infancy, the technical prerequisites are being developed at an extraordinary pace, thus raising not only modest hopes for a beneficial application of these novel treatment strategies in some forms of chronic-progressive, consistently debilitating, and treatment-refractory psychosis, but also intensifying widespread ethical implications and public concerns regarding its potential for enhancement of normal CNS function.

Adeno-associated virus-mediated gene transfer to the brain: duration and modulation of expression

Adeno-associated virus (AAV) is a promising vector for central nervous system (CNS) gene transfer, but a number of issues must be addressed if AAV is to be used for widespread delivery throughout the CNS. Our aim was to test the effect of dose, route of delivery, and hydroxyurea treatment on brain expression of beta-galactosidase activity after cerebral inoculation with an rAAV-lacZ vector (rAAV-beta-gal). We also wished to test whether an immune response appeared against the vector and the transgene product. We found in BALB/c mice that beta-Gal expression increased during the first 2 months after inoculation, then decreased slightly by 4 months, and continued out to 6, 12, and 15 months in single animals. Cerebral injection produced localized beta-Gal expression that did not diffuse to other regions despite a fivefold increase in injection volume. Intraventricular injection resulted in negligible transduction. Antibodies to AAV capsid protein and beta-Gal appeared at low levels at 2 and 4 months, but correlated poorly with beta-Gal expression and did not prevent readministration of rAAV-beta-gal. Hydroxyurea treatment did not result in increased transduction in vivo. We conclude that our study confirms rAAV vectors as having considerable potential for CNS gene transfer; however, several important problems must be addressed if this vector system is to be used for long-term transduction of the entire brain. Sustained, regulatable expression will be needed if rAAV is to be used in the treatment of chronic CNS disease. The difficulty in delivering AAV to diverse regions of the brain is an important problem that must be overcome if these vectors are to be used for anything beyond localized transduction.

Suppression of inflammation by dexamethasone prolongs adenoviral vector-mediated transgene expression in the facial nucleus of the rat

Adenoviral vector directed gene transfer to rat facial motoneurons occurs efficiently following intra-parenchymal injection of relatively high dosages (> or =10(7) pfu per injection) of a prototype first generation adenoviral vector. However, high level of transgene expression, as observed during the first week following administration of the adenoviral vector, declines during the second and third weeks and is associated with a local inflammatory response. In the present study rats were treated with dexamethasone to suppress the inflammatory response that occurs following administration of a first generation adenoviral vector and the effect of dexamethasone treatment on the duration of transgene expression was studied. Dexamethasone-treated rats displayed a reduced infiltration of macrophages and intra-parenchymal T-cells were not detectable at 14 days post-infusion of the viral vector. Transduced astrocytes persisted following treatment with dexamethasone, whereas only a few transduced motoneurons survived. In conclusion, suppression of inflammation by dexamethasone has a beneficial effect on the survival of transduced astroglial cells but exerts only moderate protection on transduced facial motoneurons.

The role of neuronal growth factors in neurodegenerative disorders of the human brain

Recent evidence suggests that neurotrophic factors that promote the survival or differentiation of developing neurons may also protect mature neurons from neuronal atrophy in the degenerating human brain. Furthermore, it has been proposed that the pathogenesis of human neurodegenerative disorders may be due to an alteration in neurotrophic factor and/or trk receptor levels. The use of neurotrophic factors as therapeutic agents is a novel approach aimed at restoring and maintaining neuronal function in the central nervous system (CNS). Research is currently being undertaken to determine potential mechanisms to deliver neurotrophic factors to selectively vulnerable regions of the CNS. However, while there is widespread interest in the use of neurotrophic factors to prevent and/or reduce the neuronal cell loss and atrophy observed in neurodegenerative disorders, little research has been performed examining the expression and functional role of these factors in the normal and diseased human brain. This review will discuss recent studies and examine the role members of the nerve growth factor family (NGF, BDNF and NT-3) and trk receptors as well as additional growth factors (GDNF, TGF-alpha and IGF-I) may play in neurodegenerative disorders of the human brain.

Adenovirus-mediated in vivo gene transfer in guinea pig middle ear mucosa

This article describes a study designed to assess the feasibility of using recombinant adenovirus for delivering therapeutic peptides in vivo in the guinea pig middle ear cleft. A recombinant adenoviral vector AdCMVsp1 LacZ containing the Escherichia coli beta-galactosidase was injected into the middle ear space. Qualitative assessment of cell middle ear transfection was performed on day 2 by light microscopy study, after injecting a multiplicity of infection (MOI) ranging from 0 to 1000. At an MOI of 30, 30% of the promontory area epithelial cells were stained. An MOI of 50 stained 60% of the cells and an MOI of 100 or more stained more than 90% of the cells. The duration of cell transfection was studied after injecting an MOI of 50. The percentage of stained cells was 60% on day 2, 10% on day 7, and 0% on day 14. Middle ear mucosal inflammation, consisting of a granulocytic infiltrate, was observed when an MOI above 50 was used. Even at a high MOI (500), no staining could be found in the cochlea, in the facial nerve, in the brain, or in visceral organs. These data suggest that recombinant adenovirus vectors can be used to transfer genes in the middle ear. This method appears to be safe, and may be envisaged as a short-duration treatment to transfer genes in vivo in the treatment of middle ear diseases.

Neurometabolic disease

Advances in knowledge of neurometabolic disease continues. Of great interest to the neurologist are the definitions of the molecular defects in Niemann-Pick C disease, Refsum disease, and five of the disorders of peroxisome biogenesis, including rhizomelic chondrodysplasia punctata. Duplication of the proteolipid protein gene is the most common molecular abnormality in Pelizaeus Merzbacher disease. Therapies for guanidinoacetate methyltransferase deficiency and for 3-phosphoglycerated dehydrogenase deficiency appear promising. Animal models have been developed for X-linked adrenoleukodystrophy, metachromatic leukodystrophy and Zellweger syndrome and will aid in the understanding of pathogenesis and the evaluation of therapy.

Manipulation of gene expression in the mammalian nervous system: application in the study of neurite outgrowth and neuroregeneration-related proteins

A fundamental issue in neurobiology entails the study of the formation of neuronal connections and their potential to regenerate following injury. In recent years, an expanding number of gene families has been identified involved in different aspects of neurite outgrowth and regeneration. These include neurotrophic factors, cell-adhesion molecules, growth-associated proteins, cytoskeletal proteins and chemorepulsive proteins. Genetic manipulation technology (transgenic mice, knockout mice, viral vectors and antisense oligonucleotides) has been instrumental in defining the function of these neurite outgrowth-related proteins. The aim of this paper is to provide an overview of the above-mentioned four approaches to manipulate gene expression in vivo and to discuss the progress that has been made using this technology in helping to understand the molecular mechanisms that regulate neurite outgrowth. We will show that work with transgenic mice and knockout mice has contributed significantly to the dissection of the function of several proteins with a key role in neurite outgrowth and neuronal survival. Recently developed viral vectors for gene transfer in postmitotic neurons have opened up new avenues to analyze the function of a protein following local expression in naive adult rodents. The initial results with viral vector-based gene transfer provide a conceptual framework for further studies on genetic therapy of neuroregeneration and neurodegenerative diseases.

Adenoviral vector-mediated GDNF gene therapy in a rodent lesion model of late stage Parkinson's disease

A recombinant adenoviral vector encoding the human glial cell line-derived neurotrophic factor (GDNF) gene (Ad-GDNF) was used to express the neurotrophic factor GDNF in the unilaterally 6-hydroxydopamine (6-OHDA) denervated substantia nigra (SN) of adult rats ten weeks following the 6-OHDA injection. 6-OHDA lesions significantly increased apomorphine-induced (contralateral) rotations and reduced striatal and nigral dopamine (DA) levels by 99% and 70%, respectively. Ad-GDNF significantly (P < 0.01) decreased (by 30-40%) apomorphine-induced rotations in lesioned rats for up to two weeks following a single injection. Locomotor activity, assessed 7 days following the Ad-GDNF injection, was also significantly (P < 0.05) increased (by 300-400%). Two weeks after the Ad-GDNF injection, locomotor activity was still significantly increased compared to the Ad-beta-gal-injected 6-OHDA lesioned (control) group. Additionally, in Ad-GDNF-injected rats, there was a significant decrease (10-13%) in weight gain which persisted for approximately two weeks following the injection. Consistent with the behavioral changes, levels of DA and the metabolite dihydroxyphenylacetic acid (DOPAC) were elevated (by 98% and 65%, respectively) in the SN, but not the striatum of Ad-GDNF-injected rats. Overall, a single Ad-GDNF injection had significant effects for 2-3 weeks following administration. These results suggest that virally delivered GDNF promotes the recovery of nigral dopaminergic tone (i.e.: increased DA and DOPAC levels) and improves behavioral performance (i.e.: decreased rotations, increased locomotion) in rodents with extensive nigrostriatal dopaminergic denervation. Moreover, our results suggest that viral delivery of trophic factors may be used eventually to treat neurodegenerative diseases such as Parkinson's disease.

Gene expression induced by cerebral ischemia: an apoptotic perspective

The flow of new information on gene expression related to apoptosis has been relentless in the last several years. This has also been the case with respect to gene expression after cerebral ischemia. Many of genes associated with an apoptotic mode of cell death have now been studied in the context of experimental cerebral ischemia from the immediate early genes through modulating genes such as bcl-2 to genes in the final execution phase such as interleukin-1β converting enzyme (ICE)-related proteases. It was impossible to adequately cite all primary reports on these subjects. However, many excellent reviews have appeared in the last year, which together, cover all these areas of interest. In this review, we have elected to cite only reports published since January 1996 and use an extensive collection of reviews (indicated in italics) to guide the reader to the earlier literature. Our intent is to provide the reader with a timely and useful analysis of the current state of the art. It is hoped that this approach does not cause offense with our colleagues whose contributions before 1996 laid the foundation for much of this work.

In vivo adenovirus-mediated gene transfer and the expression in ischemic and reperfused rat brain

In an attempt to study whether ischemic brain could express a foreign gene in vivo, a replication-defective adenoviral vector containing the Escherichia coli lacZ gene was directly injected into the ischemic or reperfused cerebral cortex of rat, and temporal and spatial profiles of the exogenous gene expression were compared with that of the control brain. Right middle cerebral artery (MCA) of rat was continuously occluded by an insertion of nylon thread for 2 days, or only transiently occluded for 90 min and then the blood flow was restored for 21 days. The adenoviral vector was administered just after the MCA occlusion or reperfusion in the case of continuous ischemia and reperfusion, respectively. Adenoviral vector was transferred into the continuous ischemic brain, and the lacZ gene was expressed until 2 days of the occlusion in the cerebral cortex of the occluded MCA territory with the number of expressing cells smaller and the staining just weaker than that of the control brain. In contrast, expression of the lacZ gene was not or only minimally observed in the reperfused brain until 2 days. However, the expression dramatically exploded at 7 days of reperfusion at a level similar to that of the control, and the expression diminished by 21 days. A few neurons in the ipsilateral thalamus, hypothalamus, and basal ganglia, and in the contralateral cerebral cortex expressed the lacZ gene at 7 days after reperfusion, a phenomenon similar to the case of the control. The majority of brain cells that expressed the lacZ gene were neurons, and a part (5-10%) were astroglial cells. Traumatic injury and immunological response in the brain were minimal both in the cases of control and ischemia/reperfusion. The present study shows an effective gene transfer and the expression in neural cells of ischemic and reperfused brains in vivo, and suggests a great potential of the gene therapy for ischemic stroke patients in the future.

Regulated expression of the diphtheria toxin A gene in human glioma cells using prokaryotic transcriptional control elements

Because accurate regulation of toxin gene expression is critical for safe and effective gene therapy applications, the authors have examined the regulation of diphtheria toxin A (DTA) fragment expression in human glioma cell lines using two transcriptional control systems derived from Escherichia coli: the tetracycline (Tet) system and the lactose (Lac) system. The Tet system includes a tetracycline-controlled transactivator (tTA), a tTA-responsive minimum human cytomegalovirus (hCMV) promoter controlling the expression of the DTA gene, and tetracycline as an allosteric inhibitor. The Lac system includes the lac repressor (lacR), a lacR-regulated Rous sarcoma virus-long terminal repeat (RSV-LTR) promoter controlling the expression of the DTA gene, and isopropyl-thio-beta-D-galactoside (IPTG) as an allosteric inducer. Expression plasmids encoding either tTA or lacR were transfected into U-87MG and U-343MG glioma cells along with the responsive DTA plasmid. Cell killing was monitored by the ability of the toxin to abolish protein synthesis and was quantitated using a luciferase reporter gene. In the Tet system, tumor cell killing could be regulated by tetracycline up to 120-fold. In contrast, only a twofold IPTG-dependent regulation was obtained using the Lac system because of an incomplete repression of DTA expression in the uninduced state. Replacement of the RSV-LTR promoter with the heavy metal-inducible mouse metallothionein-1 promoter in the lacR-responsive unit, as well as the generation of a clonal glioma cell line expressing lacR, did not significantly enhance regulation of DTA in the Lac system. In conclusion, this study demonstrates that the Tet system is of potential use in gene therapy applications in which regulated expression of a therapeutic gene is an important issue.

Gene therapy for central nervous system injury: the use of cationic liposomes: an invited review

This paper briefly reviews general principles of gene therapy with emphasis on the therapeutic potential of cationic liposome-mediated neurotrophin gene transfer to treat central nervous system (CNS) injury. Current developments in studies of gene therapy for CNS injury are both impressive and promising. Ex vivo gene transfer into the CNS is relatively mature in animal studies following more than a decade of experimental studies. In vivo gene transfer into the CNS has gained more attention recently. Although progress has been made using viral vectors, rapid advances in transfection technologies employing cationic liposomes, together with the relatively low toxicity of these nonviral vector systems, suggest that liposomes may have significant potential for clinical applications. Although many investigators have recognized that gene therapy may be useful for treatment of certain genetic defect diseases or cancer, gene therapy for CNS injury is relatively novel. In contrast to genetic defect disorders, temporary induction of transgenes may have therapeutic applications for CNS injuries such as stroke and trauma. Employing gene transfer techniques to achieve therapeutically useful levels of expression of neurotrophins in the CNS could provide a new strategy for treatment of the traumatically injured CNS.

Microtubule-mediated transport of incoming herpes simplex virus 1 capsids to the nucleus

Herpes simplex virus 1 fuses with the plasma membrane of a host cell, and the incoming capsids are efficiently and rapidly transported across the cytosol to the nuclear pore complexes, where the viral DNA genomes are released into the nucleoplasm. Using biochemical assays, immunofluorescence, and immunoelectron microscopy in the presence and absence of microtubule depolymerizing agents, it was shown that the cytosolic capsid transport in Vero cells was mediated by microtubules. Antibody labeling revealed the attachment of dynein, a minus end-directed, microtubule-dependent motor, to the viral capsids. We propose that the incoming capsids bind to microtubules and use dynein to propel them from the cell periphery to the nucleus.

Gene therapy for Parkinson's disease: an approach to the prevention or palliation of levodopa-associated motor complications

Gene therapy holds considerable potential for the treatment of central nervous system disease. The introduction of functional genes into the brain of patients with Parkinson's disease may, for example, prove useful as a means to replace a defective gene, introduce a potentially neuroprotective or neurorestorative protein, or permit the physiological delivery of a deficient neurotransmitter. Recent observations suggest that the oral administration of currently available dopaminomimetics to relatively advanced parkinsonian patients leads to nonphysiologic intermittent stimulation of striatal neurons that express dopamine receptors. Resultant activation of signal transduction pathways from these dopaminergic receptors on medium-sized GABAergic neurons apparently induces long-term potentiation of adjacent glutamatergic receptors of the N-methyl-D-aspartate subtype. The effects of dopaminergic drugs thus become modified in ways that favor the clinical appearance of response fluctuations and peak-dose dyskinesias. In parkinsonian models was well as in patients with Parkinson's disease, continuous dopaminergic replacement tends to prevent or alleviate these adverse effects. By continuously maintaining appropriate cerebral dopamine concentrations, molecular techniques which stimulate an increase in the intrastriatal activity of tyrosine hydroxylase, the rate-limiting enzyme for dopamine synthesis, might be expected to palliate parkinsonian symptoms with less risk of the disabling consequences of current therapy. Clinical study of these approaches could also serve as initial, relatively simple, proof-of-principle evaluations of the safety and efficacy of genetic approaches to the treatment of basic disease processes in Parkinson's disease and related neurodegenerative disorders.

Transient gene transfer to neurons and glia: analysis of adenoviral vector performance in the CNS and PNS

In this paper a detailed protocol is presented for neuroscientists planning to start work on first generation recombinant adenoviral vectors as gene transfer agents for the nervous system. The performance of a prototype adenoviral vector encoding the bacterial lacZ gene as a reporter was studied, following direct injection in several regions of the central and peripheral nervous system. The distribution of the cells expressing the transgene appears to be determined by natural anatomical boundaries and possibly by the degree of myelinization of a particular brain region. In highly myelinated areas with a compact cellular structure (e.g. the cortex and olfactory bulb) the spread of the viral vector is limited to the region close to the injection needle, while in areas with a laminar structure (e.g. the hippocampus and the eye) more widespread transgene expression is observed. Retrograde transport of the viral vector may serve as an attractive alternative route of transgene delivery. A time course of expression of beta-galactosidase in neural cells in the facial nucleus revealed high expression during the first week after AdLacZ injection. However, a significant decline in transgene expression during the second and third week was observed. This may be caused by an immune response against the transduced cells or by silencing of the cytomegalovirus promoter used to drive transgene expression. Taken together, the data underscore that for each application of adenoviral vectors as gene transfer agents in the nervous system it is important to examine vector spread in and infectability of the neural structure that is subject to genetic modification.