Daunorubicin reduces MBNL1 sequestration caused by CUG-repeat expansion and rescues cardiac dysfunctions in a Drosophila model of myotonic dystrophy.

M Chakraborty,Michel Ney,Chantal Sellier,B Llamusi,R Artero,Pascal Villa,Nicolas Charlet-Berguerand

doi:10.1242/dmm.032557

Abstract

ABSTRACTMyotonic dystrophy (DM) is a dominantly inherited neuromuscular disorder caused by expression of mutant myotonin-protein kinase (DMPK) transcripts containing expanded CUG repeats. Pathogenic DMPK 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 Muscleblind (Mbl), the Drosophila MBNL 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 Mbl sequestration in Drosophila 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.

Highlights

Myotonic dystrophy type 1 [DM type 1 (DM1); Online Mendelian Inheritance of Man (OMIM) 160900] is the most common muscular dystrophy in adults (Harper, 2001; Smith and Gutmann, 2016)
Muscleblind is sufficient to rescue the cardiac dysfunctions and reduced survival caused by expanded CUG repeats To understand the role of Mbl in cardiac dysfunction induced by expanded CUG repeat expression, we generated recombinant flies that simultaneously expressed 250 pure CUG repeats and either Mbl isoform C (MblC; the best evolutionary conserved Mbl isoform in Drosophila) or green fluorescent protein (GFP), as control
Heart dysfunctions, including systolic and diastolic dysfunction, arrhythmia and reduced contractility, in DM1 model flies expressing GFP were identical to DM1 flies (Fig. S1) and were similar to the previously reported alterations (Chakraborty et al, 2015), indicating that the expression of the GFP reporter is innocuous in heart

Summary

Introduction

Myotonic dystrophy type 1 [DM1; Online Mendelian Inheritance of Man (OMIM) 160900] is the most common muscular dystrophy in adults (Harper, 2001; Smith and Gutmann, 2016). The third type of cardiac dysfunction observed in DM1, rarer, is mechanical diastolic and/or systolic dysfunction that can progress to combined systolic and diastolic heart failure (Phillips and Harper, 1997; Mathieu et al, 1999; Lazarus et al, 2002; Groh et al, 2008). The genetic cause of DM1 is an expansion of CTG repeats in the 3′UTR of the DMPK gene (Brook et al, 1992; Fu et al, 1992; Mahadevan et al, 1992) This microsatellite expansion is transcribed into mutant DMPK mRNA that contains hundreds to thousands of CUG repeats that are toxic through dysfunction of at least two RNA-binding proteins. As a result of disrupting the function of these proteins, various mis-regulations in RNA metabolism have been described in individuals with DM1, some of which are associated with specific symptoms of the disease (Mankodi et al, 2002; Savkur et al, 2001; Tang et al, 2012; Fugier et al, 2011; Freyermuth et al, 2016)

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