Daunorubicin reduces MBNL1 titration by expanded CUG repeat RNA and rescues cardiac dysfunctions in a <i>Drosophila</i> model of myotonic dystrophy

Abstract

Myotonic dystrophy (DM) is a dominantly inherited neuromuscular disorder caused by expression of mutant myotonin-protein kinase (<i>DMPK</i>) transcripts containing expanded CUG repeats. Pathogenic <i>DMPK</i> RNA sequesters the muscleblind-like (MBNL) proteins, causing alterations in metabolism of various RNAs. Cardiac dysfunction represents the second most common cause of death in DM type 1 (DM1) patients. However, the contribution of MBNL sequestration in DM1 cardiac dysfunction is unclear. We overexpressed <i>Muscleblind</i> (<i>Mbl</i>), the <i>Drosophila</i><i>MBNL</i> orthologue, in cardiomyocytes of DM1 model flies and observed a rescue of heart dysfunctions, which are characteristic of these model flies and resemble cardiac defects observed in patients. We also identified a drug - daunorubicin hydrochloride - that directly binds to CUG repeats and alleviates <i>Mbl</i> sequestration in <i>Drosophila</i> DM1 cardiomyocytes, resulting in mis-splicing rescue and cardiac function recovery. These results demonstrate the relevance of Mbl sequestration caused by expanded-CUG-repeat RNA in cardiac dysfunctions in DM1, and highlight the potential of strategies aimed at inhibiting this protein-RNA interaction to recover normal cardiac function.