Project Two: Mechanisms Underlying Differential Efficacy of DM1 Therapeutics

Project Leader: Eric T. Wang Ph.D., University of Florida

The therapeutic landscape for myotonic dystrophy type 1 (DM1) has advanced dramatically in the past five years, but conflicting observations about the metabolism of expanded CUG mRNA (transcription, export, turnover, and translation) present challenges for how to interpret results from clinical trials and direct future therapeutic strategies. Fully understanding these fundamental pathophysiological mechanisms in DM1 has been severely limited due to lack of an animal model containing repeat lengths reflective of human disease states and expressed with appropriate spatiotemporal dynamics. To address this problem, we have developed a new mouse DM1 model, which expresses very large CTG repeats within the native mouse Dmpk gene, that display disease features including nuclear foci, splicing defects, myotonia, and myopathy. By using this model, the strengths/weaknesses of leading therapeutic strategies will be assessed that will help us to focus clinical efforts on those with greatest potential. Three therapeutic platforms (ASOs, siRNAs, PMOs) are in, or are rapidly advancing toward, clinical trials in DM1. Since mutant DMPK RNA sequesters MBNL proteins to form nuclear foci, these agents either degrade DMPK transcripts or release MBNL protein from nuclear foci. While initial results are encouraging, there is vigorous debate surrounding the strengths/weaknesses of each strategy. The aims of this project are to: 1) clarify mechanisms regulating the life cycle of expanded Dmpk mRNA, and study the effects of expanded CUG repeats on transcription, turnover, subcellular localization, and translation of host Dmpk mRNA; 2) compare three major therapeutic strategies (ASOs, siRNA,  PMOs) and elucidate mechanisms, strengths and limitations of each using validated skeletal muscle readouts; 3) evaluate several therapeutic strategies to test the hypothesis that such approaches can rescue splicing defects in skeletal, cardiac and/or smooth muscle.