Gene therapy trials in the ovine model of McArdle's disease
Howell, J.Mc.C., Pari, G., Fletcher, S., Wilton, S., Davies, L.J., Lloyd, F., Nalbantoglu, J., Collins, T., DiMauro, S., Kakulas, B.A. and Karpati, G. (2001) Gene therapy trials in the ovine model of McArdle's disease. In: 2nd Meeting of the Australasian Gene Therapy Society, 27 - 29 April 2001, Sydney, Australia.
McArdle’s disease is an autosomal recessive metabolic myopathy characterised by a deficiency in muscle glycogen phosphorylase and results in exercise intolerance, rhabdomyolysis and recurring myoglobinuria. Sustained disabling weakness may also occur late in the course of the disease. At present, no satisfactory treatment is available for this disorder. There are three mammalian isoenzymes of glycogen phosphorylase (muscle, brain and liver forms) which are encoded by different loci. The brain and muscle isoforms are expressed in foetal muscle, whereas the muscle isoform is expressed during the late phases of muscle differentiation and is the only isoform present in adult skeletal muscle. McArdle’s disease is caused by genetic defects in the muscle-specific isoform resulting in either the absence or decreased levels of muscle glycogen phosphorylase, with minimal or no detectable enzymatic activity.
A sheep model of McArdle’s disease, characterised by diminished exercise tolerance and impaired glycogen degradation has been described. Studies revealed the absence of glycogen phosphorylase cytochemical activity in the muscle fibres. A splice site mutation in the myophosphorylase gene results in the loss of eight bases at the 5’ end of exon 20 of the transcript. This deletion disrupts the reading frame, thereby removing the last 31 residues of the myophosphorylase.
We report results from trials in which a first generation adenovirus, expressing the (a) human muscle phosphorylase gene driven by the Rous Sarcoma virus promoter (ADV myophos) or (b) Lac Z reporter gene with a cytomegalovirus promoter (ADV Lac Z) was injected into the semitendinosus muscle of affected lambs at sites with or without prior injection of notexin. Ten days after injection of ADVmyophos alone, there was an approximately 10-fold increase in glycogen phosphorylase activity when compared to levels from uninjected muscle. Similar results were seen at 30 days, with a slight decrease at 60 days. Combining notexin and ADV myophos resulted in 40 times the glycogen phosphorylase activity at 10 days, however, at 30 and 60 days results were similar to those obtained for ADV myophos alone. When either notexin or ADV LacZ alone were injected, average glycogen phosphorylase activity was comparable to that from ADV myophos only sites. Phosphorylase expression was not seen in uninjected muscle but was evident at sites injected with notexin. This is likely to be due to upregulation of another ovine phosphorylase isoform and is currently being investigated.
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|Murdoch Affiliation:||School of Veterinary and Biomedical Sciences|
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