The role of pathological miRNAs in Duchenne and Becker Muscular Dystrophy


Pre-Clinical Research

Poster Number: 227


Alyson Fiorillo, PhD, Children's National Hospital, Nikki McCormack, PhD, Children's National Research Institute, Christopher Tully, MS, Children’s National Medical Center, Kelsey Calabrese, University of Maryland, Chris Heier, PhD, Children's National Medical Center

Chronic inflammation is a major driver of Duchenne Muscular Dystrophy (DMD) disease and inflammation persists even after patients are treated with FDA-approved dystrophin restoration therapies. Thus, there is an urgent need for pre-clinical dystrophy models that dissect the molecular underpinnings of chronic inflammation to inform current and future treatment regimens. miRNAs play a key role in regulating inflammatory signaling. Our laboratory has characterized two miRNA panels that are elevated in dystrophic muscle collectively referred to as inflamma-miRs. A subset of inflamma-miRs bind to the dystrophin 3′ untranslated region (UTR) and reduce dystrophin protein in DMD exon skipping therapies, Becker Muscular Dystrophy (BMD), and inflammatory myositis. We identified NF-kB consensus elements in the promoter/enhancer regions of inflamma-miRs, and demonstrated inflammation drives inflamma-miR expression, reducing dystrophin, further activating inflammatory signaling, and causing a self-sustaining pathological feedback loop. Supporting inflamma-miR regulation via NF-kB, we show treatment with the anti-inflammatory drug vamorolone reduces inflamma-miRs in DMD model (mdx) mice and our preliminary data shows in low-dystrophin expressing bmd mice created by our lab, vamorolone reduces inflamm-miRs and increases dystrophin protein levels by 50%. These data also suggest inflamma-miR reduction can increase expression of truncated dystrophin isoforms (e.g., exon skipping/BMD). Interestingly, two inflamma-miRs (miR-146a, miR-142-3p) resemble viral RNA, the natural ligand for Toll-like receptor 7 (TLR7). Several reports show “viral like” miRNAs act as novel TLR7 ligands. In vitro, we show miR-146a and miR-142-3p bind to TLR7 and activate pro-inflammatory cytokine secretion, while either mutation of uridine-rich regions of miRNAs or CRISPR-mediated deletion of TLR7 prevents activation. While in a healthy state TLR7 expression is confined to immune cells, we find TLR7 is inappropriately expressed in diseased muscle suggesting inflamed muscle is primed to sense viral-like miRNAs. Collectively, our data provide evidence for targeting dystrophin-targeting inflamma-miRs as a therapeutic mechanism to increase dystrophin in combination with exon skipping in DMD or as a stand-alone therapy in BMD. Further, they suggest that inflamma-miR-TLR7 interactions could serve as a novel therapeutic target to “turn off” the pathological inflammatory feedback loop in dystrophic muscle.