RNA-based gene therapies for myotonic dystrophy type 1
|Advisor:||Puymirat, Jack; Rossi, John J.|
|Abstract:||Myotonic dystrophy type 1 (DM1) is a severe neuromuscular disease that ultimately causes loss of mobility and premature death. DM1 is the most common muscular dystrophy in adults with a world wide incidence of 1 affected individual in every 15 000. This disease is of special relevance in the Saguenay and Charlevoix regions in Quebec, where 1 in every 500 individuals is a carrier of the mutation. DM1 is caused by the expansion of an unstable CTG trinucleotide repeat located in 3’UTR of the DMPK (DM protein kinase) gene. However, it has been shown that most DM1 symptoms are related to the nuclear retention of mutant DMPK mRNA. These mutant transcripts bind to nuclear proteins and form foci in DM1 cell nuclei. This is though to be the leading cause of metabolical disruptions and defective alternative splicing of several mRNAs observed in DM1 cells. Our main project objective was to evaluate whether destruction of mutant DMPK mRNA could restore normal phenotype features in DM1 human skeletal myoblasts. The use of three RNA-based approaches: antisense RNAs, ribozymes and shRNAs, all displayed significant reductions in mutant DMPK mRNA. Antisense RNAs and ribozymes, as opposed to shRNAs, allowed specific targeting and destruction of mutant DMPK mRNAs in the nucleus of DM1 myoblasts. This feature thus allows a basal level of DMPK protein expression which is of particular relevance in the advent of developing a gene therapy for DM1. Ribozymes were effective in reducing the number and intensity of foci present in the nucleus of the myoblasts, thus allowing the release of certain CUG-binding proteins. This resulted in restoration of the defective splicing of the insulin receptor mRNA. Antisense RNAs to the DMPK mRNA expressed by an oncoretrovirus restored myoblast fusion, glucose uptake and lowered nuclear levels of CUGBP, an alternative splicing factor. Over expression of hnRNP-H, an alternative splicing factor that we showed could bind to CUG repeats, also reduces expression of CUGBP and restores defective splicing of the insulin receptor. These results reveal for the first time the intricate link between mutant DMPK mRNA nuclear retention, depletion of a CUG-binding protein that is also a splicing factor and exacerbation of related DM1 features. In conclusion, our work has allowed to better define the mechanisms involved in DM1 pathogenesis and has validated the relevance of developing a gene therapy that specifically targets mutant DMPK mRNAs.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||11 April 2018|
|Collection:||Thèses et mémoires|
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