Genome-wide Mechanosensitive MicroRNA (MechanomiR) Screen Uncovers Dysregulation of Their Regulatory Networks in the mdm Mouse Model of Muscular Dystrophy

Muscular dystrophies (MDs) are a heterogeneous group of genetic and neuromuscular disorders, which result in severe loss of motor ability and skeletal muscle mass and function. Aberrant mechanotransduction and dysregulated-microRNA pathways are often associated with the progression of MD. Here, we hypothesized that dysregulation of mechanosensitive microRNAs (mechanomiRs) in dystrophic skeletal muscle plays a major role in the progression of MD. To test our hypothesis, we performed a genome-wide expression profile of anisotropically regulated mechanomiRs and bioinformatically analyzed their target gene networks. We assessed their functional roles in the advancement of MD using diaphragm muscles from mdm (MD with myositis) mice, an animal model of human tibial MD (titinopathy), and their wild-type littermates. We were able to show that ex vivo anisotropic mechanical stretch significantly alters the miRNA expression profile in diaphragm muscles from WT and mdm mice; as a result, some of the genes associated with MDs are dysregulated in mdm mice due to differential regulation of a distinct set of mechanomiRs. Interestingly, we found a contrasting expression pattern of the highly expressed let-7 family mechanomiRs, let-7e-5p and miR-98-5p, and their target genes associated with the extracellular matrix and TGF-beta pathways, respectively, between WT and mdm mice. Gain-and loss-of-function analysis of let-7e-5p in myocytes isolated from the diaphragms of WT and mdm mice confirmed Col1a1, Col1a2, Col3a1, Col24a1, Col27a1, Itga1, Itga4, Scd1, and Thbs1 as target genes of let-7e-5p. Furthermore, we found that miR-98 negatively regulates myoblast differentiation. Our study therefore introduces additional biological players in the regulation of skeletal muscle structure and myogenesis that may contribute to unexplained disorders of MD.