Deregulations of miR-1 and its target Multiplexin promote dilated cardiomyopathy associated with myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy. It is caused by the excessive expansion of non-coding CTG repeat, which when transcribed affect functions of RNA-binding factors. Specifically, MBNL1 is sequestered in nuclear foci while CELF1 is stabilised, with adverse effects on alternative splicing, processing and stability of a large set of muscular and cardiac transcripts. Among these effects, inefficient processing and down-regulation of muscle- and heart-specific miRNA, miR-1, has been reported in DM1 patients, but the impact of reduced miR-1 on DM1 pathogenesis was unknown. Here, we used Drosophila DM1 models to explore miR-1 involvement in cardiac dysfunction in DM1. We found that miR-1 down-regulation in the heart led to dilated cardiomyopathy (DCM), a DM1-associated phenotype. We then combined in silico screening for miR-1 targets with transcriptional profiling of DM1 cardiac cells to identify miR-1 target genes with potential roles in DCM. We identified Multiplexin (Mp) as a new cardiac miR-1 target involved in DM1. Mp and its human ortholog Col15A1 were both highly enriched in cardiac cells of DCM-developing DM1 flies and in heart samples from DM1 patients with DCM, respectively. Importantly, when overexpressed in the heart, Mp induced DCM, whereas its attenuation ameliorated the DCM phenotype in aged DM1 flies. Reduced levels of miR-1 and consecutive up-regulation of its target Mp/Col15A1 are thus critical in DM1-associated DCM.