| Summary: | Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by the loss of upper and lower motor neurons, with no effective treatment to date. Only 5-10% of ALS cases are familial, of which 20% are caused by missense mutations in the gene encoding Cu/Zn superoxide dismutase 1 (SOD I). Although ALS has a multi-factorial aetiology, oxidative stress is hypothesized to be one of the key pathogenic mechanisms. It is thus proposed that manipulation of the expression of anti- oxidant genes may serve as a therapeutic strategy for the protection of motor neurons. It has been previously found that three specific anti-oxidant genes (PTGR 1 /L TB4DH - prostaglandin reductase I / leukotriene B4 12-hydroxydehydrogenase, PRDX3 - peroxiredoxin 3, and NRF2 - nuclear factor erythroid 2-related factor 2) are down- regulated in the presence of mutant SOD 1. The main aim of this project is to alter the expression of the target genes using viral vectors and study the effect on the vulnerability of cells expressing mutant SOD I both in vitro and in vivo. Lentiviral vectors expressing each of the three target genes were tested in the NSC34 cell line (hybrid cell line of mouse motor neurons and neuroblastoma), and the oxidative stress levels as well as cell survival was measured in wild type cells and cells stably expressing the human SOD I gene incorporating the ALS-causing G93A mutation. In the ALS tissue culture model, stable over-expression was achieved, and two of the genes showed cytoprotective properties. Virally delivered PTGR I exhibited no significant effect on oxidation stress levels or cell survival, and as such this gene was not investigated further. However, cells over-expressing either PRDX3 or NRF2 showed a significant decrease in endogenous oxidation stress levels by 40% and 50% respectively compared to controls, whereas cell survival was increased by 30%. These two genes were taken forward to the ALS mouse model, in which intramuscular injections of adeno-associated virus serotype 6 expressing either of the target genes were administered at a pre-symptornatic stage. Behavioural tests and quantitative readouts of motor function allowed the investigation of this therapeutic strategy. However no significant effect was seen in survival, disease onset or disease progression. Quantification of the efficiency of viral delivery showed that only 5% of the lumbar motor neurons were transduced through retrograde transport accounting for the absence of a therapeutic effect. These results suggest that such a delivery is not sufficient to induce a therapeutic effect, and a more widespread CNS delivery is needed.
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