Myotonic dystrophy (DM1), the most common muscular dystrophy in adults, is caused by an expanded (CTG)n tract in the 3′ UTR of the gene encoding myotonic dystrophy protein kinase (DMPK)1, which results in nuclear entrapment of the 'toxic' mutant RNA and interacting RNA-binding proteins (such as MBNL1) in ribonuclear inclusions2. It is unclear if therapy aimed at eliminating the toxin would be beneficial. To address this, we generated transgenic mice expressing the DMPK 3′ UTR as part of an inducible RNA transcript encoding green fluorescent protein (GFP). We were surprised to find that mice overexpressing a normal DMPK 3′ UTR mRNA reproduced cardinal features of myotonic dystrophy, including myotonia, cardiac conduction abnormalities, histopathology and RNA splicing defects in the absence of detectable nuclear inclusions. However, we observed increased levels of CUG-binding protein (CUG-BP1) in skeletal muscle, as seen in individuals with DM1. Notably, these effects were reversible in both mature skeletal and cardiac muscles by silencing transgene expression. These results represent the first in vivo proof of principle for a therapeutic strategy for treatment of myotonic dystrophy by ablating or silencing expression of the toxic RNA molecules.
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We wish to thank P. Mahadevan and A. Tucker for their insights and continued support. MBNL antibodies were provided by M. Swanson and C. Thornton. Human tissues were provided by J. Puymirat and C. Thornton and purchased from the University of Miami Brain and Tissue Bank. Mouse tissues from other myotonic dystrophy models were provided by J. Puymirat, B. Wieringa and G. Gourdon. Transgenic mice were generated by the University of Wisconsin-Madison Transgenic Core Facility. All studies were done under the auspices of the University of Virginia Animal Care and Use Committee and Institutional Review Board. This work was supported by the Muscular Dystrophy Association and the US National Institute of Arthritis and Musculoskeletal and Skin Diseases.
Transgene expression. (PDF 477 kb)
RNA foci in all three muscle lineages in (CTG)200 mice. (PDF 202 kb)
CUG-BP1 levels elevated in DM1 muscle. (PDF 208 kb)
CUG-BP1 levels increased by toxic RNA. (PDF 288 kb)
Comparison of transgene expression in different mouse models of myotonic dystrophy. (PDF 496 kb)
Model for the splicing balance created by the mutual antagonism between MBNL1 and CUG-BP1 for splicing events. (PDF 429 kb)
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