AntimiR treatment corrects myotonic dystrophy primary cell defects across several CTG repeat expansions with a dual mechanism of action.

Abstract

This study evaluated therapeutic antimiRs in primary myoblasts from patients with myotonic dystrophy type 1 (DM1). DM1 results from unstable CTG repeat expansions in the <i>DMPK</i> gene, leading to variable clinical manifestations by depleting muscleblind-like splicing regulator protein MBNL1. AntimiRs targeting natural repressors miR-23b and miR-218 boost MBNL1 expression but must be optimized for a better pharmacological profile in humans. In untreated cells, miR-23b and miR-218 were up-regulated, which correlated with CTG repeat size, supporting that active MBNL1 protein repression synergizes with the sequestration by CUG expansions in <i>DMPK</i>. AntimiR treatment improved RNA toxicity readouts and corrected regulated exon inclusions and myoblast defects such as fusion index and myotube area across CTG expansions. Unexpectedly, the treatment also reduced <i>DMPK</i> transcripts and ribonuclear foci. A leading antimiR reversed 68% of dysregulated genes. This study highlights the potential of antimiRs to treat various DM1 forms across a range of repeat sizes and genetic backgrounds by mitigating MBNL1 sequestration and enhancing protein synthesis.