Abstract 4142024: MicroRNA 486 is Myogenic and Remodels Dystrophic Transcriptome in Limb-Girdle Muscular Dystrophy Type 2B (Dysferlinopathy)

Introduction: Dysferlinopathy, a subgroup within muscular dystrophies, is an autosomal recessive myopathy that entails a spectrum of progressive muscle degeneration with a pathogenic mechanism of impaired sarcolemma. Its genetic etiology is rooted in mutations in the DYSF gene at Chromosome 2p13. The DYSF gene encodes for dysferlin, a type II transmembrane protein prominently expressed in skeletal muscle and cardiac tissue. Dysferlin plays a pivotal role in calcium-dependent membrane repair and regulate macrophage activation in skeletal muscles. MicroRNAs (miRNAs), highly conserved non-coding RNA transcripts under 25 nucleotides, modulate translational repression via mRNA degradation. Reduced expression of miR-486, a muscle enriched miRNA, has been correlated with the disease severity in Duchenne muscular dystrophy. However, the expression level of miR-486 and its role has not been elucidated in dysferlinopathy. Hypothesis: We hypothesized that miR-486 expression is differentially expressed in dysferlin-deficient skeletal muscle, function as a regulator of cell cycle kinetics, differentiation, and is essential for the sarcolemma repair machinery. Methods: Tissue expression analysis of miR-486 was performed across ten mice tissues. Subsequently, miR-486 was overexpressed and silenced in both wild type and dysferlin deficient murine myoblasts (C2C12 cells) via cellular transfection (n=3). Differential expression of miR-486 levels and various cell cycle genes were validated using qRT-PCR. Myoblast fusion assay, along with immunohistochemistry was undertaken to determine cellular differentiation. Bioinformatics approach was undertaken for pathway analysis of miR486 in dystrophic muscles. Results: We confirmed that miR486 is myogenic, demonstrated by highest expression in skeletal muscles. We found reduced expression of miR486 by more than two folds in dysferlin-deficient myoblasts compared to the wild-type. Overexpression of miR-486 increased Ki-67 and MCM2 expression in wild-type myoblasts, indicating its pro-proliferative role. Conclusion: The results thus far suggest that dysferlinopathy is associated with aberrant expression of miR-486, which plays a role in regulating myoblast proliferation. We are currently focused on elucidating how miR-486 influences myoblast differentiation and characterizing the underlying molecular mechanisms by quantifying the gene expression changes driven by modulation of miR-486.