Gene therapy of murine motor neuron disease using adenoviral vectors for neurotrophic factors

In vivo gene transfer to cerebral white matter lesions with a recombinant adenovirus vector

Ischemic white matter lesions have been reported in rats after bilateral common carotid ligation (BCAL). Previously, comparing normotensive rats (WKY) with spontaneously hypertensive rats (SHR), we too found that sustained moderate ischemia with spontaneous hypertension accelerated the formation of ischemic white matter lesions. In this study, we explored the feasibility of gene therapy for lesioned white matter by means of an adenovirus vector expressing a reporter gene, LacZ. Using sham-operated and hypoperfused SHR as well as sham-operated and hypoperfused WKY, we demonstrated that (i) adenovirus vectors could deliver a foreign gene into oligodendrocytes and astrocytes in the cerebral white matter; (ii) the transduction efficiency was most effective in SHR after BCAL; and (iii) the level of alpha(V)-integrin was significantly correlated with adenoviral transduction efficiency.

Callosal commissural neurons of Dab1 deficient mutant mouse, yotari

The yotari mouse is an autosomal recessive mutant mouse, caused by mutation of disabled homolog 1 (Dab1) gene. The mutant mouse is recognized by unstable gait and tremor and by early deaths around at the time of weaning. The cytoarchitectures of cerebeller and cerebral cortices and hippocampal formation of the yotari mouse are abnormal. These malformations strikingly resemble those of reeler mouse. In the present study we examined the callosal commissural (CC) neurons of yotari, reeler and normal mice with the injection of recombinant adenovirus into the frontal area 1 (Fr1) to find some possible phenotypes specific for the yotari mouse. The distribution pattern of CC neurons of the yotari was similar to that of the reeler: retrogradely labeled CC neurons were seen throughout all depths of the contralateral Fr1. However, the present statistical analysis revealed that the difference of the mean intracortical position of the CC neurons between the yotari and the reeler is significantly different (Student's t-test), suggesting that the phenotype of the yotari is clearly different from that of the reeler.

In vivo control of NMDA receptor transcript level in motoneurons by viral transduction of a short antisense gene

Glutamate receptors play critical roles in normal and pathological processes. We developed an antisense gene delivery strategy to modulate the NMDA type of glutamate receptor. Using transient transfection in vitro and viral mediated gene transfer in vitro and in vivo, the effect of expression of an antisense gene fragment (60 bp) of the NR1 subunit was tested. Immunoblot analysis showed an antisense-concentration-dependent reduction in the NR1 subunit upon transient co-transfection of a plasmid expressing a sense NR1 gene and a plasmid expressing the antisense fragment into COS-7 cells. After recombination into an adenoviral vector, this antisense fragment reduced the amount of endogenous NR1 protein in PC12 cells. Finally, direct intraparenchymal injection of the viral vector into rat spinal cord resulted in diminished NR1 in motor neurons. Our results demonstrate the efficacy of this approach, which combines antisense with viral gene delivery to control the expression of specific genes in vivo. This approach may also be useful in reducing excitatory neurotransmission in vivo, with implications for the treatment of spinal disorders such as amyotrophic lateral sclerosis or chronic pain.

A possible role for BDNF, NT-4 and TrkB in the spinal cord and muscle of rat subjected to mechanical overload, bupivacaine injection and axotomy

Neurotrophins play a crucial role in the regulation of survival and the maintenance of specific functions for various populations of neurons. Neurotrophin-4 (NT-4) is most abundant in skeletal muscle, and is thought to promote sciatic nerve sprouting, inhibit agrin-induced acetylcholine receptor (AChR) clustering, evoke postsynaptic potentiation and induce mitochondrial proliferation. Using Western blot analysis, immunoprecipitation and immunohistochemistry, we investigated the distribution of NT-4 in slow- and fast-type muscles. We also tested the adaptive response of this protein in the mechanically overloaded muscle, in the regenerating muscle following bupivacaine injection and in the denervated muscle. Additionally, we investigated whether TrkB phosphorylation in the spinal cord and in the sciatic nerve occurs through the interaction with BDNF or NT-4 when the innervating muscle is damaged. Markedly more NT-4 was expressed in fast-type muscles compared with the slow types. TrkB protein was more frequently observed around the edge of myofibers (neuromuscular junction) of the soleus muscle compared with the gastrocnemius muscle. TrkB tyrosine phosphorylation occurred in the spinal cord but not in the sciatic nerve 24 h after bupivacaine injection of the innervating muscle. At the same time, the amount of TrkB co-precipitating with BDNF was markedly increased in the spinal cord. A rapid activation of TrkB (1-8 h) was also observed in the spinal cord after axotomy,while the amount of TrkB co-precipitating with NT-4 was markedly lower after axotomy. These results indicate that NT-4 is preferentially distributed in fast-type muscles. Furthermore, by interacting with BDNF and NT-4, the TrkB in the spinal cord may be important for the survival of motoneurons and outgrowth of injured peripheral axons following muscle damage.

Bcl-2 expression by retrograde transport of adenoviral vectors with Cre-loxP recombination system in motor neurons of mutant SOD1 transgenic mice

We investigated genes expression by retrograde axonal transport of replication-defective adenoviruses carrying genes for LacZ (AdLacZ) and Bcl-2 in motor neurons of transgenic mice expressing mutant human Cu/Zn superoxide dismutase (SOD1) gene containing a substitution of alanine for glycine at position 93. We found that intramuscular injection of AdLacZ into the tongue of mutant SOD1 transgenic mice and their wild-type littermates at various ages results in high expression of the transgene and similar time course of expression in hypoglossal cranial nerve nuclei, suggesting no difference in the behavior of the transgene expression between the two groups. Subsequently, we employed a molecular switching cassette for Bcl-2 designed to express Bcl-2 by Cre-loxP recombination using adenoviral vectors, and examined the COS7 and primary neuronal cells with the mutant SOD1 gene. The overexpression of Bcl-2 in both cells and the neuronal protection against staurosporine-induced apoptosis were observed, after dual infection of adenoviral vectors with cassette for Bcl-2 (AxCALNLBcl-2) and Cre recombinase (AxCANCre). After inoculation of AxCALNLBcl-2 followed by AxCANCre into the tongue of both mutant SOD1 transgenic mice and wild-type littermates, Bcl-2 was detected in both the injection site and the hypoglossal nuclei of brainstems, suggesting that this was the result of retrograde transport of AxCALNLBcl-2 and AxCANCre and expression of Bcl-2 by Cre recombinase in the hypoglossal nuclei. This strategy for delivery of exogenous genes such as Bcl-2 will be useful for studying neuronal death/survival and introducing foreign genes into postmitotic motor neurons, and in gene therapy for motor neuron diseases such as ALS.

Tracing axons in the peripheral nerve using lacZ gene recombinant adenovirus and its application to regeneration of the peripheral nerve

The usefulness of recombinant adenovirus with LacZ to trace axons in the peripheral nervous system was investigated. Recombinant adenovirus with LacZ was applied to the cut end of the tibial nerve in rats. The LacZ gene product (B-galactosidase) filled axons of the tibial nerve, which permitted the continuous long-range tracing of axons. Further, the branching and the direction of the branches could also be examined. Labeled axons in the tibial nerves ran parallel to each other without branching and kept this relative position in the tibial and the sciatic nerve. When the virus was introduced to the regenerating nerve using a silicon tube, the regenerating fibers grew tortuously with short branches in the bulge at the proximal end of the silicon tube. The fibers grew straight in the tube and passed through the bulge at the distal end of the tube without branching. These observations indicate that the LacZ gene recombinant adenovirus is a useful tracer for the study of the peripheral nervous system and of the regeneration processes.

Neuronal Targeting of Cardiotrophin-1 by Coupling with Tetanus Toxin C Fragment

Cardiotrophin-1 (CT-1) is a potent neurotrophic factor for motoneurons but its clinical use in motor neuron diseases is precluded by side effects on the heart and liver. We explored the possibility of targeting CT-1 to neurons by coupling with the tetanus toxin fragment TTC. Genetic fusion proteins between CT-1 or GFP and TTC were produced in Escherichia coli and assayed in vitro. In contrast to uncoupled CT-1 or GFP, TTC-coupled proteins bound with high affinity to cerebral neurons and spinal cord motoneurons and were rapidly internalized. Glia, hepatocytes, or cardiomyocytes did not show detectable binding or uptake of TTC-coupled proteins. Similar to CT-1, TTC-coupled CT-1 induced IL-6 secretion by KB cells, activated Reg-2 gene expression, and promoted motoneuron survival in a dose-dependent manner. In vivo studies will test whether TTC-coupled CT-1 might be targeted to degenerating spinal cord or brain-stem motoneurons and migrate trans-synaptically to cortical motoneurons, which are also affected in amyotrophic lateral sclerosis.

Spinal muscular atrophy: present state

Spinal muscular atrophy (SMA) is a hereditary neurodegenerative disease caused by homozygous deletions or mutations in the SMN1 gene on Chr.5q13. SMA spans from severe Werdnig-Hoffmann disease (SMA 1) to relatively benign Kugelberg-Welander disease (SMA 3). Onset before birth possibly aggravates the clinical course, because immature motoneurons do not show compensatory sprouting and collateral reinnervation, and motor units in SMA 1, in contrast to those in SMA 3, are not enlarged. Genetic evidence indicates that SMN2, a gene 99% identical to SMN1, can attenuate SMA severity: in patients, more SMN2 copies and higher SMN protein levels are correlated with milder SMA. There is evidence that SMN plays a role in motoneuron RNA metabolism, but it has also been linked to apoptosis. Several mouse models with motoneuron disease have been successfully treated with neurotrophic factors. None of these models is, however, homologous to SMA. Recently, genetic mouse models of SMA have been created by introducing human SMN2 transgenes into Smn knockout mice or by targeting the Smn gene knockout to neurons. These mice not only provide important insights into the pathogenesis of SMA but are also crucial for testing new therapeutic strategies. These include SMN gene transfer, molecules capable to up-regulate SMN expression and trophic or antiapoptotic factors.

Partial prevention of cisplatin-induced neuropathy by electroporation-mediated nonviral gene transfer

Cisplatin-induced sensory peripheral neuropathy is the dose-limiting factor for cisplatin chemotherapy. We describe the preventive effect of NT-3 delivery, using direct gene transfer into muscle by in vivo electroporation in a mouse model of cisplatin-induced neuropathy. Cisplatin-induced neuropathy was produced by weekly injections of cisplatin (five injections). Two doses of plasmid DNA encoding murine NT-3 (pCMVNT-3) were tested (5 and 50 microg/animal/injection). Cisplatin-treated mice were given two intramuscular injections. The first injection of pCMVNT-3 was given 2 days before the first injection of cisplatin and the second injection 2 weeks later. Six weeks after the start of the experiment, measurement of NT-3 levels (ELISA) demonstrated significant levels both in muscle and plasma. We observed a smaller cisplatin-related increase in the latency of the sensory nerve action potential of the caudal nerve in pCMVNT-3-treated mice than in controls (p < 0.0001). Mean sensory distal latencies were not different between the 5- and 50- microg/animal/injection groups. Treatment with gene therapy induced only a slight muscle toxicity and no general side effects. Therefore, neurotrophic factor delivery by direct gene transfer into muscle by electroporation is of potential benefit in the prevention of cisplatin-induced neuropathy and of peripheral neuropathies in general.

Charcot-Marie-Tooth disease (CMT): distinctive phenotypic and genotypic features in CMT type 2

Charcot-Marie-Tooth disease (CMT), or hereditary motor and sensory neuropathy (HMSN), includes two main subtypes of CMT1/HMSN I (demyelinating), and CMT2/HMSN II (axonal). Further heterogeneity has been demonstrated by genetic molecular studies, with at least four responsible genes for CMT1. As for CMT2, a mutation in the neurofilament-light (NF-L) gene has been identified in a single family, and other CMT2 loci have been mapped. We propose a clinical classification of the CMT2 phenotypes, and review the features of the identified CMT2 genotypes. The following main subtypes of CMT2 are considered in the phenotype classification: classical CMT2, the variants of CMT2 showing atypical features that may represent either variance in the classical CMT2 phenotype or separate entities; CMT2 plus, i.e. complex forms with involvement of additional neural structures. The recognized CMT2 genotypes include: CMT2A (mapped to chromosome 1p35-36); CMT2B (3q13-22); CMT2C (with vocal cord paresis); CMT2D (7p14); CMT2E, related to a mutation in the NF-L gene on chromosome 8p21; proximal CMT2, or HMSN P (3q13.1); CMT2 with MPZ mutations; autosomal recessive CMT2 (1q21.2-q21.3); agenesis of the corpus callosum with sensorimotor neuronopathy (15q13-q15); CMT2 X-linked with deafness and mental retardation (Xq24-q26). The identified genotypes may correspond to previously described clinical subtypes of CMT2. In particular, classical CMT2 presents in association with NF-L gene mutation, in the only CMT2 family with known gene mutation, and in CMT2A patients. However, the features of classical CMT2 have been paradoxically reported also in families with MPZ mutation, and conversely several CMT2 families are not linked to the known CMT2 loci. Further cloning of the CMT2 genes will ultimately shed light on the pathogenic mechanism(s) implicated in the process of axonal degeneration, shared by the different CMT2 genotypes.

Gene delivery and gene therapy with herpes simplex virus-based vectors

The development of efficient means of delivery genes in vivo is essential both for testing gene function in the intact animal and for human gene therapy procedures. A number of viral and non-viral gene delivery methods have been developed for this purpose. Of those herpes simplex virus (HSV)-based vectors have particular advantages for gene delivery to the nervous system including their ability to infect non-dividing neurones and establish asymptomatic latent infections. Moreover, considerable progress has been made, firstly, in disabling HSV vectors so as to prevent the damaging effects of wild type virus and secondly, to ensure long-term expression of the inserted transgene(s). These vectors thus offer a valuable tool for testing gene function in neuronal cells in vivo and may ultimately be safe enough for use in human gene therapy procedures.

Phosphatidylinositol 3-kinase activity in murine motoneuron disease: the progressive motor neuropathy mouse

A murine model of motoneuron disease, the pmn/pmn mouse, shows a reduction in the retrograde transport of fluorescent probes applied directly onto the cut end of sciatic nerve. Brain-derived neurotrophic factor (BDNF), when co-applied with fluorescent tracers, increases the number of retrograde labelled motoneurons. We demonstrate here that spinal cord tissue from pmn/pmn mice had significantly reduced phosphatidylinositol 3-kinase activity and expression in the particulate fraction compared to controls, without changes in the activities or expression of the downstream kinases, protein kinase B/Akt or Erk1. Systemic administration of BDNF augmented phosphatidylinositol 3-kinase specific activity in spinal cord tissue from pmn/pmn and control mice, with a greater elevation in the particulate fractions of pmn/pmn mice than in controls. We examined the effect of inhibitors of phosphatidylinositol 3-kinase and mitogen-activated protein kinase kinase on the retrograde labelling of motoneurons, 24h following the direct application of inhibitors and Fluorogold to the cut end of sciatic nerve in control and pmn/pmn mice (labelling index). The mitogen-activated protein kinase kinase inhibitor PD 98059 had no effect on the labelling index in control or pmn/pmn mice. In the absence of exogenous BDNF, phosphatidylinositol 3-kinase inhibitors reduced the number of labelled motoneurons in control mice, without changing the labelling index in pmn/pmn. Co-application of phosphatidylinositol 3-kinase inhibitors with BDNF to the cut end of sciatic nerve blocked the action of BDNF on retrograde labelling in pmn/pmn mice. These results indicate that the retrograde labelling of motoneurons is mediated by phosphatidylinositol 3-kinase-dependent and -independent pathways. In pmn/pmn mice, phosphatidylinositol 3-kinase activity in spinal neurons is below the level required for optimal retrograde labelling of motoneurons and labelling can be augmented by the administration of growth factors stimulating phosphatidylinositol 3-kinase activity. The data indicate that phosphatidylinositol 3-kinase activity is important in the uptake and/or retrograde transport of substances by motoneurons and is altered in this model of motoneuron diseases.

In vivo adenoviral transduction of the neonatal rat cochlea and middle ear

Virally mediated gene transfer to the adult mammalian ear appears to be a powerful strategy to investigate gene function in the auditory system and to develop new therapeutic treatment for hearing impaired patients. However, there has been little work done in the neonatal middle and inner ear. In this study, a recombinant adenoviral (AdV) vector was used for gene transfer of a beta-galactosidase (beta-gal) reporter gene to the neonatal middle ear and cochlea of 5 day old rats. For transduction of middle ear, AdV was injected through the tympanic membrane into the tympanic cavity. Three and 7 days later, strong expression of beta-gal was observed in epithelial cells of the mucosa, but not in the underlying stroma or mesenchyme. There was little or no infiltration of leukocytes. No expression of beta-gal was detected inside the cochlea or vestibular system. When AdV was injected into the basal turn of the cochlea, high levels of beta-gal expression were observed in cells lining the perilymphatic space and in parts of the spiral ligament 3, 7 and 21 days later. Spiral ganglion cells did not express beta-gal. However, virally mediated gene transfer was observed in some cells of the organ of Corti. A moderate infiltration of leukocytes into the labyrinth was observed, but no vestibular or auditory dysfunction. These results demonstrate that neonatal middle ear and cochlear cells can be successfully transduced with an AdV vector in vivo, without obvious morphological signs of inflammation or cellular damage. AdV vectors provide a tool for investigation of the role of genes in influencing the development of middle and inner ear structures. Virally mediated expression of protective genes could also be used to rescue hair cells or spiral ganglion cells from congenital degeneration or damage.

Reg-2 is a motoneuron neurotrophic factor and a signalling intermediate in the CNTF survival pathway

Cytokines that are related to ciliary neurotrophic factor (CNTF) are physiologically important survival factors for motoneurons, but the mechanisms by which they prevent neuronal cell death remain unknown. Reg-2/PAP I (pancreatitis-associated protein I), referred to here as Reg-2, is a secreted protein whose expression in motoneurons during development is dependent on cytokines. Here we show that CNTF-related cytokines induce Reg-2 expression in cultured motoneurons. Purified Reg-2 can itself act as an autocrine/paracrine neurotrophic factor for a subpopulation of motoneurons, by stimulating a survival pathway involving phosphatidylinositol-3-kinase, Akt kinase and NF-kappaB. Blocking Reg-2 expression in motoneurons using Reg-2 antisense adenovirus specifically abrogates the survival effect of CNTF on cultured motoneurons, indicating that Reg-2 expression is a necessary step in the CNTF survival pathway. Reg-2 shows a unique pattern of expression in late embryonic spinal cord: it is progressively upregulated in individual motoneurons on a cell-by-cell basis, indicating that only a fraction of motoneurons in a given motor pool may be exposed to cytokines. Thus, Reg-2 is a neurotrophic factor for motoneurons, and is itself an obligatory intermediate in the survival signalling pathway of CNTF-related cytokines.

Adenovirus-mediated glial cell line-derived neurotrophic factor gene delivery reduces motor neuron injury after transient spinal cord ischemia in rabbits

OBJECTIVE

Glial cell line-derived neurotrophic factor (GDNF) has protective effects on various injuries involving the central and peripheral nervous systems in vitro and vivo. However, the possible protective effect of GDNF on spinal cord ischemia and the exact mechanism involved in the ameliorative effect of GDNF on ischemic spinal cord injuries are not fully understood. Therefore, we investigated the possible protective effect of the adenovirus-mediated GDNF gene delivery on transient spinal cord ischemia in rabbits.

METHODS

The adenoviral vector (lacZ gene as a control or GDNF gene contained) was injected directly into the lumbar spinal cord via a needle inserted into the dorsal spine 2 days before the animal was subjected to 15 minutes of spinal cord ischemia induced by infrarenal aortic occlusion. In situ terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick-end labeling (TUNEL staining) was performed, and temporal profiles of the GDNF and caspase-3 (caspase-3 is the marker of apoptotic change) immunoreactivity were investigated.

RESULTS

In the control rabbit, the majority of motor neurons showed selective cell death at 7 days of reperfusion. Immunocytochemistry showed that in situ TUNEL staining was selectively detected at 2 days of reperfusion in motor neuron nuclei. GDNF and caspase-3 were selectively induced in the motor neuron cells at 8 hours of reperfusion. In the GDNF-treated group, a large population of motor neuron cells was still surviving at 7 days after having been subjected to 15 minutes of ischemia. Unlike the control group, the GDNF-treated group expressed GDNF persistently. Induction of TUNEL staining and immunoreactivity for caspase-3 were greatly reduced by the GDNF treatment.

CONCLUSION

These results suggest that the reduction in motor neuron death by GDNF was greatly associated with a reduction in DNA fragmentation and apoptotic signals of the caspase-3 cascade; they further suggest a great potential for gene therapy for paraplegic patients in the future.

Novel drug development for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) has become an increasingly attractive area for the pharmaceutical industry, the most experimentally tractable of the neurodegenerative diseases. Mechanisms underlying cell death in ALS are likely to be important in more common but more complex disorders. Riluzole, the only drug launched for treatment ALS is currently undergoing industrial trials for Alzheimer's, Parkinson's, Huntington disease, stroke and head injury. Other compounds in Phase III testing for ALS (mecamserin, xaliproden, gabapentin) are also in trials for other neurodegenerative disorders. Mechanisms of action of these advanced compounds are limited to glutamate antagonism, direct or indirect growth factor activity, as well as GABA agonism and interaction with calcium channels. A broader range of mechanisms is represented by compounds in Phase I trials: glutamate antagonism (dextramethorphan/p450 inhibitor; talampanel), growth factors (leukemia inhibiting factor; IL-1 receptor; encapsulated cells secreting CNTF) and antioxidants (TR500, a glutathione-repleting agent; recombinant superoxide dismutase; procysteine.) An even broader range of mechanisms is being explored in preclinical discovery programs. Recognition of the difficulties associated with delivery of protein therapeutics to the CNS has led to development of small molecules interacting either with neurotrophin receptors or with downstream intracellular signalling pathways. Other novel drug targets include caspaces, protein kinases and other molecules influencing apoptosis. High-throughput screens of large libraries of small molecules yield lead compounds that are subsequently optimized by chemists, screened for toxicity, and validated before a candidate is selected for clinical trials. The net is cast wide in early discovery efforts, only about 1% of which result in useful drugs at the end of a decade-long process. Successful discovery and development of novel drugs will increasingly depend on collaborative efforts between the academy and industry.

Partial functional recovery of paraplegic rat by adenovirus-mediated gene delivery of constitutively active MEK1

Spinal cord injury in adult mammals results in little axonal regeneration, although the mechanism of regeneration failure still remains elusive. Recent research has revealed that activation of the extracellular-signal-regulated kinases (ERKs) plays an important role in the neurite outgrowth. In the present study, we constructed a replication-defective adenovirus vector carrying mutated form of MEK1 (CA-MEK virus), which constitutively activate ERK pathway, and investigated its effect on thoracic spinal cord injury model in young adult rats as well as neurite outgrowth in vitro. In rat pheocromocytoma cell line PC12 cells, CA-MEK virus infection induced sustained activation of ERKs and stimulated neurite outgrowth in the absence of neurotrophic factors. In rat spinal cord transection model, injection of CA-MEK virus into the completely transected spinal cord efficiently activated ERKs in the supraspinal neurons and induced axonal regeneration across the transection site, which was confirmed by anterograde labeling with wheat-germ-agglutinin conjugated peroxidase (WGA-HRP). Spinal cord evoked potentials (SCEP) showed that these regenerated axons were electroconductive. Most importantly, CA-MEK virus-treated rats showed significant recovery of hind limb function 2 weeks after operation compared to the control rats treated with no virus or LacZ virus. These results suggest that adenovirus-mediated CA-MEK gene transduction offers a novel strategy for the gene therapy of spinal cord injury.

Riluzole prolongs survival and delays muscle strength deterioration in mice with progressive motor neuronopathy (pmn)

The neuroprotective drug riluzole (Rilutek) is a sodium channel blocker and anti-excitotoxic drug which is marketed for the treatment of amyotrophic lateral sclerosis (ALS). Previous studies have shown that riluzole prolongs survival of transgenic mice harboring the mutated form of Cu,Zn-superoxide dismutase found in familial forms of the human disease. In this study we have examined the effect of treatment with riluzole in mice suffering from progressive motor neuronopathy (pmn), a hereditary autosomal recessive wasting disease which shares some symptoms of ALS. These mutants display hind limb weakness starting during the 3rd week of life and leading to paralysis and death during the 7th week of life. Daily treatment with 8 mg/kg of riluzole by oral route significantly retarded the appearance of paralysis, increased life span and improved motor performance on grip test and electromyographic results in the early stage of the disease. There was no effect of riluzole on weight gain. These data demonstrate that riluzole significantly prolongs life span, retards the onset of paralysis and slows the evolution of functional parameters connected with muscle strength in the pmn mouse model of motor neuron disease.

Retargeting of adenoviral vectors to neurons using the Hc fragment of tetanus toxin

The Hc fragment of tetanus toxin (Hc) retains the specific nerve cell binding and transport properties of the holotoxin, but lacks any toxicity. We are investigating the potential for utilising its neurotropism for targeted gene delivery to the central nervous system. Previously we reported the use of Hc-polylysine conjugates for selective gene transfer into neuronal cells in vitro. However, as attempts to apply these constructs in vivo were not successful, we have extended these studies to modification of the tropism of adenoviral vectors. Either Hc-polylysine conjugates or the Fab fragment of a neutralising anti-knob antibody covalently bound to Hc were attached to the virus. Infection of neuronal and non-neuronal cell lines with retargeted virus showed highly increased neuronal cell selectivity, but no significant enhancement of gene delivery into these cells. High concentrations of free Hc blocked the infectivity of the retargeted vector efficiently. Intramuscular injection of retargeted virus into mouse tongues resulted in selective gene transfer to the neurons of the hypoglossal nucleus, where no pathological changes were observed. As differentiated neurons do not undergo cell division, appropriate vectors carrying a thymidine kinase gene, which allows selective elimination of dividing cells, may be exploitable for the treatment of tumours of the central nervous system. The demonstrated suitability of the Hc fragment of tetanus toxin as targeting moiety for viral vectors also indicates a potential for gene therapy of inherited neurodegenerative diseases such as spinal muscular atrophy.

Cellular transplants as sources for therapeutic agents

Soluble factors normally produced by cells of the human body are of increasing importance as potential therapeutic agents. Although considerable progress has been made in understanding the etiology and pathogenesis of disease, in developing animal models and newer experimental therapeutics, few discoveries have been translated into clinically effective ways of delivering the multiple therapeutic agents obtained from living mammalian cells. This review examines the use of transplanted cells as alternatives to conventional delivery systems to deliver a variety of protein based therapeutic agents. The chapter begins with a set of questions to establish the complexity and challenges of this form of drug delivery. The following section focuses the discussion on our understanding of genetic engineering, tissue engineering, and some areas of developmental biology as they relate to the development of this nascent field. Much of the discussion has a neuro/endocrine emphasis. The chapter ends by listing the basic ingredients needed to push the use of transplanted cells toward medical practice and some general comments about future developments.

Animal models for inherited peripheral neuropathies: chances to find treatment strategies?

Mutations in four identified genes (peripheral myelin protein 22, P(0), connexin 32, and the early growth response 2 zinc finger protein) are the cause for several forms of inherited peripheral neuropathies that are still incurable disorders. Some forms of these disorders are well mimicked by engineered or spontaneous rodent mutants that might be instrumental for developing treatment strategies. This review focusses on common pathways of pathogenesis of the disorders and emphasizes strategies that might be suitable to ameliorate disease expression.

Analysis of organ physiology in transgenic mice

The increasing availability of transgenic mouse models of gene deletion and human disease has mandated the development of creative approaches to characterize mouse phenotype. The mouse presents unique challenges to phenotype analysis because of its small size, habits, and inability to verbalize clinical symptoms. This review describes strategies to study mouse organ physiology, focusing on the cardiovascular, pulmonary, renal, gastrointestinal, and neurobehavioral systems. General concerns about evaluating mouse phenotype studies are discussed. Monitoring and anesthesia methods are reviewed, with emphasis on the feasibility and limitations of noninvasive and invasive procedures to monitor physiological parameters, do cannulations, and perform surgical procedures. Examples of phenotype studies are cited to demonstrate the practical applications and limitations of the measurement methods. The repertoire of phenotype analysis methods reviewed here should be useful to investigators involved in or contemplating the use of mouse models.

Approach to gene therapy of glycogenosis type II (Pompe disease)

Pompe disease is a generalized lysosomal glycogenosis affecting essentially the skeletal muscles and the heart. It is due to the deficiency of acid alpha-glucosidase, also called acid maltase, involved in glycogen degradation by the cleavage of alpha-1,4 and alpha-1,6 glycosidic linkages. The severe infantile, milder juvenile, and late-onset or adult forms are associated under the generic name of glycogenoses type II. The clinical picture can differ according to these variants, forming a clinical spectrum from cardiorespiratory failure with early death in the infantile variant to late muscular weakness or respiratory problems in the adult variant. Enzymatic pre- and postnatal diagnoses and mutation characterization are available. Different therapeutic attempts have been conceived and some of them have come to clinical trials. Several pilot studies have demonstrated the feasibility of gene therapy and remarkable advances have been realized. Of particular interest, strategies for gene therapy in a generalized disease like Pompe disease must be accompanied by the secretion and uptake of the corrective enzyme by more distant cells or tissues in order to obtain efficient results. Preliminary positive results have been obtained in animal models, and new approaches with improvements in the access to muscle and heart, in the efficacy and innocuity of vectors, and in the clinical evolution are proposed. Gene therapy is a promising strategy for Pompe disease. However, several steps must be explored before this method becomes clinically successful.

Extensive sprouting of sensory afferents and hyperalgesia induced by conditional expression of nerve growth factor in the adult spinal cord

Genetic transfer of growth-promoting molecules was proposed as a potential strategy to modify the nonpermissive nature of the adult CNS to induce axonal regeneration. To evaluate whether overexpression of neurotrophins or cellular adhesion molecules would effect axonal plasticity, adenoviruses encoding fibroblast growth factor-2 (FGF-2/Adts), nerve growth factor (NGF/Adts), neurotrophin-3, and the cell adhesion molecules N-cadherin and L1 were injected into the dorsal horn of the adult spinal cord. Transgene expression was primarily localized to astrocytes in the dorsal horn and motor neurons within the ventral horn. Overexpression of these factors, with the exception of NGF/Adts, failed to increase axonal sprouting. Eight days after NGF/Adts injections, axonal sprouting within the dorsal horn was apparent, and after 4 weeks, extensive spouting was observed throughout the entire dorsal horn, extending into the ventral horn and the white matter of the lateral funiculus. These axons were identified primarily as a subpopulation of nociceptive fibers expressing calcitonin gene-related peptide and substance-P. Behavioral analysis revealed thermal hyperalgesia and perturbation of accurate paw placement on grid-walking tasks for both FGF-2- and NGF-treated animals. These results indicate that the administration of growth-promoting molecules can induce robust axonal plasticity of normal adult primary sensory neurons into areas of transgene expression, causing significant alterations in behavioral responses. This observation also indicates that gene transfer protocols that aim to reconstruct diseased or injured pathways should also be designed to prevent the sprouting of the normal circuitry from adjacent unaffected neurons.

Early and selective loss of neuromuscular synapse subtypes with low sprouting competence in motoneuron diseases

The addition or loss of synapses in response to changes in activity, disease, or aging is a major aspect of nervous system plasticity in the adult. The mechanisms that affect the turnover and maintenance of synapses in the adult are poorly understood and are difficult to investigate in the brain. Here, we exploited a unique anatomical arrangement in the neuromuscular system to determine whether subtypes of synapses can differ in anatomical plasticity and vulnerability. In three genetic mouse models of motoneuron disease of diverse origin and severity, we observed a gradual and selective loss of synaptic connections that begun long before the onset of clinical deficits and correlated with the timing of disease progression. A subgroup of fast-type (fast-fatiguable) neuromuscular synapses was highly vulnerable and was lost very early on. In contrast, slow-type synapses resisted up to the terminal phase of the disease. Muscle-specific differences were also evident. Similar selective losses were detected in aged mice. These selective vulnerability properties of synapses coincided with hitherto unrecognized major differences in stimulus-induced anatomical plasticity that could also be revealed in healthy mice. Using paralysis and/or growth-associated protein 43 overexpression to induce synaptic sprouting, we found that slow-type, disease-resistant synapses were particularly plastic. In contrast, fast-type synapses with the highest vulnerability failed to exhibit any stimulus-induced change. The results reveal pronounced subtype specificity in the anatomical plasticity and susceptibility to loss of neuromuscular synapses and suggest that degenerative motoneuron diseases involve a common early pathway of selective and progressive synaptic weakening also associated with aging.

Rescue of lesioned adult rat spinal motoneurons by adenoviral gene transfer of glial cell line-derived neurotrophic factor

Glial cell line-derived neurotrophic factor (GDNF) has been shown to protect cranial and spinal motoneurons, that suggests potential uses of GDNF in the treatment of spinal cord injury and motor neuron diseases. We examined neuroprotective effect of human GDNF encoded by an adenovirus vector (AxCAhGDNF) on the death of lesioned adult rat spinal motoneurons. The seventh cervical segment (C7) ventral and dorsal roots and dorsal root ganglia of adult Fisher 344 rats were avulsed, and AxCAhGDNF, AxCALacZ (adenovirus encoding beta-galactosidase gene) or PBS was inoculated in C7 vertebral foramen. One week after the avulsion and treatment with AxCALacZ, the animals showed expression of beta-galactosidase activity in lesioned spinal motoneurons. Animals avulsed and treated with AxCAhGDNF showed intense immunolabeling for GDNF in lesioned spinal motoneurons and expression of virus-induced human GDNF mRNA transcripts in the lesioned spinal cord tissue. Nissl-stained cell counts revealed that the treatment with AxCAhGDNF significantly prevented the loss of lesioned ventral horn motoneurons 2 to 8 weeks after avulsion, as compared to AxCALacZ or PBS treatment. Furthermore, the AxCAhGDNF treatment ameliorated choline acetyltransferase immunoreactivity in the lesioned motoneurons after avulsion. These results indicate that the adenovirus-mediated gene transfer of GDNF may prevent the degeneration of motoneurons in adult humans with spinal cord injury and motor neuron diseases.

Development of pharmacological agents for targeting neurotrophins and their receptors

Neurotrophins comprise a family of protein growth factors that control the survival, growth, and/or differentiation of neurons and several other cell populations derived from the neuroectoderm. Neurotrophins and their receptors are important targets for the therapy of human disease, with potential applications ranging from the treatment of chronic or acute neurodegeneration to pain and cancer. Neurotrophins have been used clinically but are poor pharmacological agents. Consequently, approaches to develop pharmacological agents that target neurotrophins, their receptors or neurotrophin signaling pathways have been attempted.

Adenoviral and adeno-associated viral transfer of genes to the peripheral nervous system

Targeted expression of foreign genes to the peripheral nervous system is interesting for many applications, including gene therapy of neuromuscular diseases, neuroanatomical studies, and elucidation of mechanisms of axonal flow. Here we describe a microneurosurgical technique for injection of replication-defective viral vectors into dorsal root ganglia (DRG). Adenovirus- and adeno-associated virus-based vectors with transcriptional competence for DRG neurons led to expression of the gene of interest throughout the first neuron of the sensory system, from the distal portions of the respective sensory nerve to the ipsilateral nucleus gracilis and cuneatus, which contains the synapses to the spinothalamic tracts. Use of Rag-1 ablated mice, which lack all B and T lymphocytes, allowed for sustained expression for periods exceeding 100 days. In immunocompetent mice, long-term (52 days) expression was achieved with similar efficiency by using adeno-associated viral vectors. DRG injection was vastly superior to intraneural injection into the sciatic nerve, which mainly transduced Schwann cells in the vicinity of the site of inoculation site but only inefficiently transduced nerve fibers, whereas i.m. injection did not lead to any significant expression of the reporter gene in nerve fibers. The versatile and efficient transduction of genes of interest should enable a wide variety of functional studies of peripheral nervous system pathophysiology.

Neurotrophin-3 levels in cerebrospinal fluid from children with bacterial meningitis, viral meningitis, or encephalitis

Neurotrophin-3 levels were measured in the cerebrospinal fluid of 35 patients with bacterial meningitis, viral meningitis, or encephalitis by two-site enzyme immunoassay. Elevated cerebrospinal fluid levels of neurotrophin-3 were demonstrated in 8 of 18 patients with bacterial meningitis. Follow-up examination of the eight patients at the convalescent stage showed diminished cerebrospinal fluid levels of neurotrophin-3. In contrast, none of the 17 patients with viral meningitis or encephalitis showed an elevation of neurotrophin-3 levels in cerebrospinal fluid. No relationships were observed between neurotrophin-3 levels and cerebrospinal fluid cell numbers, cerebrospinal fluid protein levels, serum C-reactive protein concentrations, or outcome in bacterial meningitis. Since neurotrophin-3 is involved in the survival of neurons and the modulation of the immune system, neurotrophin-3 could play a neuroprotective or immunomodulatory role in bacterial meningitis.

Effects of testosterone on the development of a sexually dimorphic neuromuscular system in ciliary neurotrophic factor receptor knockout mice

Motoneurons in the spinal nucleus of the bulbocavernosus (SNB) innervate the perineal muscles, bulbocavernosus (BC), and levator ani (LA). Testosterone regulates the survival of SNB motoneurons and BC/LA muscles during perinatal life. Previous findings suggest that effects of testosterone on this system may be mediated by trophic factors-in particular, by a factor acting through the ciliary neurotrophic factor alpha-receptor (CNTFRalpha). To test the role of CNTFRalpha in the response of the developing SNB system to testosterone, CNTFRalpha +/+ and -/- mice were treated with testosterone propionate (TP) or oil during late embryonic development. BC/LA muscle size and SNB motoneuron number were evaluated on the day of birth. Large sex differences in BC and LA muscle size were present in newborn mice of both genotypes, but muscle volumes were reduced in CNTFRalpha -/- animals relative to same-sex, wild-type controls. Prenatal testosterone treatment completely eliminated the sex difference in BC/LA muscle size in wild-type animals, and eliminated the effect of the CNTFRalpha gene deletion on muscle size in males. However, the effect of TP treatment on BC and LA muscle sizes was blunted in CNTFRalpha -/- females. SNB motoneuron number was sexually dimorphic in oil-treated, wild-type mice. In contrast, there was no sex difference in SNB motoneuron number in oil-treated, CNTFRalpha knockout mice. Prenatal treatment with testosterone did not increase SNB motoneuron number in CNTFRalpha -/- mice, but also did not significantly increase SNB motoneuron number in newborn wild-type animals. These findings confirm the absence of a sex difference in SNB motoneuron number in CNTFRalpha -/- mice. Moreover, the CNTFRalpha gene deletion influences perineal muscle development and the response of the perineal muscles to testosterone. Prenatal TP treatment of CNTFRalpha -/- males overcomes the effects of the gene deletion on the BC and LA muscles without a concomitant effect on SNB motoneuron number.

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.

Comparative analysis of motoneuron loss and functional deficits in PMN mice: implications for human motoneuron disease

We have investigated the correlation between functional and morphological deficits in PMN mice, an animal model of human motoneuron disease. Electrophysiologic investigations showed first abnormalities, i.e. reduction of M-response amplitudes, already at postnatal d 13 when the disease was not yet phenotypically apparent, and when motoneuron and motor axon numbers were still normal. After d 27, a loss of more than 30% of motoneuron axons and cell bodies was detectable in the phrenic nerve and facial nucleus, respectively. At that stage, PMN mice showed severe functional and electrophysiological deficits. At later stages of the disease when still more than 50% of motor axons and at least 60% of motoneuron cell bodies were present, the distal compound muscle action potential amplitude decreased by more than 95% in small foot muscles after sciatic nerve stimulation. We conclude that functional deficits precede structural deficits in this animal model of human motoneuron disease. Our findings are in agreement with the concept of the 'sick motoneuron' in this animal model of motoneuron disease rather than the idea of progressive loss of motoneurons resulting in disease only after a significant number of motoneurons has degenerated.

Adenoviral cardiotrophin-1 gene transfer protects pmn mice from progressive motor neuronopathy

Cardiotrophin-1 (CT-1), an IL-6-related cytokine, causes hypertrophy of cardiac myocytes and has pleiotropic effects on various other cell types, including motoneurons. Here, we analyzed systemic CT-1 effects in progressive motor neuronopathy (pmn) mice that suffer from progressive motoneuronal degeneration, muscle paralysis, and premature death. Administration of an adenoviral CT-1 vector to newborn pmn mice leads to sustained CT-1 expression in the injected muscles and bloodstream, prolonged survival of animals, and improved motor functions. CT-1-treated pmn mice showed a significantly reduced degeneration of facial motoneuron cytons and phrenic nerve myelinated axons. The terminal innervation of skeletal muscle, grossly disturbed in untreated pmn mice, was almost completely preserved in CT-1-treated pmn mice. The remarkable neuroprotection conferred by CT-1 might become clinically relevant if CT-1 side effects, including cardiotoxicity, could be circumvented by a more targeted delivery of this cytokine to the nervous system.

Experimental models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a chronic neurodegenerative disease characterized by the progressive loss of motor neurons, leading to profound weakness and eventual death of affected individuals. For the vast majority of patients with ALS, the etiology of the disorder is unknown, and although multiple clinical trials of various therapeutic agents have been undertaken, truly effective therapy is not currently available for the disease. The selection of treatments used in ALS clinical trials frequently has its basis in promising data obtained from experimental model systems in which the proposed agent has shown some effect in protecting motor neurons from a particular insult. The likelihood of a successful clinical outcome for a given treatment in ALS would therefore depend on two principal factors, including the similarity of the model to the disease and the biologic action of the potential therapeutic agent. Partly because early experimental models of ALS failed to replicate the disease process, treatment success in these models did not carry over into human trials. Recently, however, a variety of newer model systems have been developed and utilized to investigate motor neuron degeneration as related to ALS. For example, in this issue, Corse et al. use a rat spinal cord organotypic slice subjected to glutamate excitotoxicity as a model system to test the effectiveness of neurotrophic factors in preventing motor neuron degeneration. This review will assess the strengths and weaknesses of differing ALS model systems that have been used to preclinically test potential drug efficacy in ALS.

Mechanical and excitotoxic lesion of motoneurons: effects of neurotrophins and ciliary neurotrophic factor on survival and regeneration

Mechanical lesion of peripheral nerves leads to extensive death of corresponding motoneurons in newborn rodents. The extent of cell death can be significantly reduced by neurotrophic factors. These molecules are produced by glial and neuronal cells and play an important role in supporting survival and regeneration of various neuronal populations in the central nervous system, in particular after mechanical, excitotoxic and ischemic insults. In addition, factors such as ciliary neurotrophic factor and neurotrophin-3 influence glial cell proliferation and survival. We have investigated the role of neurotrophic factors on motoneurons, both in cell culture and after axotomy in vivo. Moreover, the role of excitatory neurotransmission in modulating dendritic architecture of these cells was analyzed. Our data suggest that motoneurons are a suitable model for investigating the complex functional and morphological changes after brain lesion and for the identification of new therapeutic strategies to influence survival and functional recovery under such circumstances.

Neuron-restrictive silencer elements mediate neuron specificity of adenoviral gene expression

Neuron-restrictive silencer elements (NRSEs) were used to target the gene expression of adenoviral vectors specifically to neuron cells in the central nervous system. By generating adenoviral constructs in which NRSE sequences were placed upstream from the ubiquitous phosphoglycerate kinase promoter, the specificity of expression of a luciferase reporter gene was tested in both cell lines and primary cultures. Whereas transgene expression was negligible in nonneuronal cells following infection with an adenovirus containing 12 NRSEs, neuronal cells strongly expressed luciferase when infected with the same adenovirus. The NRSEs restricted expression of the luciferase gene to neuronal cells in vivo when adenoviruses were injected both intramuscularly into mice and intracerebrally into rats. This NRSE strategy may avoid side effects resulting from the ectopic expression of therapeutic genes in the treatment of neurological diseases. In particular, it may allow the direct transfection of motor neurons without promoting transgene expression within inoculated muscles or the secretion of transgene products into the bloodstream.

Peripheral nerve graft and neurotrophic factors enhance neuronal survival and expression of nitric oxide synthase in Clarke's nucleus after hemisection of the spinal cord in adult rat

The present study examined the effects of peripheral nerve (PN) graft and neurotrophic factors on the expression of nitric oxide synthase (NOS) and the survival of Clarke's nucleus (CN) neurons at the first lumbar spinal segment (L1) 15 days after hemisection of the spinal cord at T11. Normal intact CN neurons did not express NOS. Forty-one percent of the ipsilateral CN neurons survived after hemisection at T11, and 48% of the surviving neurons expressed NOS. Transplantation of PN graft at the lesion site promoted the survival of CN neurons to 71% and increased the expression of NOS to 70%. Continuous infusion of brain-derived neurotrophic factor, ciliary neurotrophic factor, and neurotrophic-3, but not glial cell-derived neurotrophic factor, at the lesion site enhanced the survival of CN neurons to about 65%. Among the surviving neurons about 70% were NOS-positive. These results indicated that transplantation of autologous PN graft or continuous infusion of neurotrophic factors could enhance the survival of axotomized CN neurons. In addition, the survival-promoting function of the neurotrophic agents was coincided with the upregulation of the expression of NOS. However, whether the upregulation of NOS expression in injured CN neurons is related to the rescue function or is a side effect of the neurotrophic factors is not clear and needed further investigation.

Loss of distal axons and sensory Merkel cells and features indicative of muscle denervation in hindlimbs of P0-deficient mice

Mice lacking the major Schwann cell myelin component P0 show a severe dysmyelination with pathological features reminiscent of the Déjérine-Sottas syndrome in humans. Previous morphological and electrophysiological studies on these mice did not only demonstrate a compromised myelination and myelin maintenance, but were suggestive of an impairment of axons as well. Here, we studied the axonal pathology in P0-deficient mice by quantitative electron microscopy. In addition, we investigated epidermal receptor end organs by immunocytochemistry and muscle pathology by histochemistry. In proximal sections of facial and femoral nerves, axon calibers were significantly reduced, whereas the number of myelin-competent axons was not diminished in 5- and 17-month-old P0-deficient mice. However, in distal branches of the femoral and sciatic nerve (digital nerves innervating the skin of the first toe) the numbers of myelin-competent axons were reduced by 70% in 6-month-old P0-deficient mice. Immunolabeling of foot pads revealed a corresponding loss of Merkel cells by 75%, suggesting that survival of these cells is dependent on the presence or maintenance of their innervating myelinated axons. In addition, quadriceps and gastrocnemius muscles showed pathological features indicative of denervation and axonal sprouting. These findings demonstrate that loss of an important myelin component can initiate degenerative mechanisms not only in the Schwann cell but also in the distal portions of myelinated axons, leading to the degeneration of specialized receptor end organs and impairment of muscle innervation.

Adenoviral vectors for in vivo gene delivery to oligodendrocytes: transgene expression and cytopathic consequences

Replication defective viral vectors provide a potentially useful means of gene transfer to oligodendrocytes and thus for studying the pathogenesis of white matter disease. In this study we have examined the expression pattern of E1/E3 deleted adenoviral vectors expressing the reporter gene LacZ (AdlacZ) as a means of establishing the value of these vectors for gene delivery to oligodendrocytes in adult rat white matter. Our results indicate that although such an approach can be used to induce transgene expression in oligodendrocytes, it is complicated by both immunogenic and cytopathic effects. Thus, in normal animals, injection of DeltaE1/E3 adenoviral vectors was associated with a robust immune response that led to a lack of expression by 40 days after injection. In order to overcome this complication, virus was injected into the white matter of immuno-deficient athymic rats. These experiments indi- cated that even in the absence of a T cell response high viral titres of DeltaE1/E3 adenoviral vectors had a profound cytopathic effect leading to death of oligodendrocytes and hence demyelination. A similar cytopathic effect was demonstrated using an adenoviral vector expressing the neurocytokine ciliary neurotrophic factor (AdCNTF). As the titre of injected virus was decreased there was a significant decrease in the number of transgene expressing cells. These experiments therefore indicated that in immunodeficient recipients there is a narrow window of virus titre that results in a high rate of infectivity and expression without significant cytopathic consequences. At higher viral titres the cytopathic effects include oligodendrocyte death and demyelination, while at lower titres there is a significant decrease in the efficiency of the number of cells expressing the transgene.

Neurotrophic factors and neuro-muscular disease: II. GDNF, other neurotrophic factors, and future directions

This is the second of two reviews in which we discuss the essential aspects of neurotrophic factor neurobiology, the characteristics of each neurotrophic factor, and their clinical relevance to neuromuscular diseases. The previous paper reviewed the neurotrophin family and neuropoietic cytokines. In the present article, we focus on the GDNF family and other neurotrophic factors and then consider future approaches that may be utilized in neurotrophic factor treatment.

Intramuscular grafts of myoblasts genetically modified to secrete glial cell line-derived neurotrophic factor prevent motoneuron loss and disease progression in a mouse model of familial amyotrophic lateral sclerosis

Effects of ex vivo GDNF gene delivery on the degeneration of motoneurons were studied in the G1H transgenic mouse model of familial ALS carrying a human superoxide dismutase (SOD1) with a Gly93Ala mutation (Gurney et al., 1994). Retroviral vectors were made to produce human GDNF or E. coli beta-galactosidase (beta-Gal) by transient transfection of the Phoenix cell line and used to infect primary mouse myoblasts. In 6-week-old G1H mice, 50,000 myoblasts per muscle were injected bilaterally into two hindlimb muscles. Untreated G1H and wild-type mice served as additional controls. At 17 weeks of age, 1 week before sacrifice, these muscles were injected with fluorogold (FG) to retrogradely label spinal motoneurons that maintained axonal projections to the muscles. There were significantly more large FG-labeled alpha motoneurons at 18 weeks in GDNF-treated G1H mice than in untreated and beta-Gal-treated G1H mice. A morphometric study of motoneuron size distribution showed that GDNF shifted the size distribution of motoneurons toward larger cells compared with control G1H mice, although the average size and number of large motoneurons in GDNF-treated mice were less than that in wild-type mice. GDNF also prolonged the onset of disease, delayed the deterioration of performance in tests of motor behavior, and slowed muscle atrophy. Quantitative, real-time RT-PCR and PCR showed persistence of transgene mRNA and DNA in muscle for up to 12 weeks postgrafting. These observations demonstrate that ex vivo GDNF gene therapy in a mouse model of FALS promotes the survival of functional motoneurons, suggesting that a similar approach might delay the progression of neurodegeneration in ALS.

Antiglutamate therapy of ALS--which is the next step?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease which was thought to be untreatable for a long time. However, recent evidence in men indicates that antiglutamatergic strategies are the first to have an influence on its pathogenesis and slow down the disease process. Since the effect of the drugs is still small, this progress cannot only be seen as a success of the present but most also be acknowledged as a starting point for the future. How will these future studies look like? They will have to take into account that ALS presumably has a long preclinical period and they will use a number of novel compounds and treatment strategies which have recently been shown to be effective in a transgenic animal model. This also implies that we are likely to use combination therapies and have to try to treat patients early. The latter will be necessarily connected with the demand for a novel clinical attitude to the diagnosis of the disease.

Adenoviral gene therapy of the Tay-Sachs disease in hexosaminidase A-deficient knock-out mice

The severe neurodegenerative disorder, Tays-Sachs disease, is caused by a beta-hexosaminidase alpha-subunit deficiency which prevents the formation of lysosomal heterodimeric alpha-beta enzyme, hexosaminidase A (HexA). No treatment is available for this fatal disease; however, gene therapy could represent a therapeutic approach. We previously have constructed and characterized, in vitro, adenoviral and retroviral vectors coding for alpha- and beta-subunits of the human beta-hexosaminidases. Here, we have determined the in vivo strategy which leads to the highest HexA activity in the maximum number of tissues in hexA -deficient knock-out mice. We demonstrated that intravenous co-administration of adenoviral vectors coding for both alpha- and beta-subunits, resulting in preferential liver transduction, was essential to obtain the most successful results. Only the supply of both subunits allowed for HexA overexpression leading to massive secretion of the enzyme in serum, and full or partial enzymatic activity restoration in all peripheral tissues tested. The enzymatic correction was likely to be due to direct cellular transduction by adenoviral vectors and/or uptake of secreted HexA by different organs. These results confirmed that the liver was the preferential target organ to deliver a large amount of secreted proteins. In addition, the need to overexpress both subunits of heterodimeric proteins in order to obtain a high level of secretion in animals defective in only one subunit is emphasized. The endogenous non-defective subunit is otherwise limiting.

Group D adenoviruses infect primary central nervous system cells more efficiently than those from group C

Group C adenovirus-mediated gene transfer to central nervous system cells is inefficient. We found that wild-type group D viruses, or recombinant adenovirus type 2 (Ad2) (group C) modified to contain Ad17 (group D) fiber, were more efficient in infecting primary cultures of neurons. Together with studies on primary vascular endothelial cells and tissue culture cell lines, our results indicate that there is not a universally applicable adenovirus serotype for use as a gene transfer vector.