Overexpression of miR-486 improves muscle function in mouse models of RYR1-related diseases

Variants in the ryanodine receptor 1 gene (RYR1) cause several human skeletal muscle disorders, collectively known as RYR1-related diseases (RYR1-RD). Among these, the most frequent congenital myopathy is the central core disease (CCD), characterized by variable clinical manifestations and distinctive histological features such as cores, regions of muscle fibers lacking mitochondria and oxidative enzyme activity, and contractures. In addition, RYR1 variants also are associated with individuals to malignant hyperthermia susceptibility (MHS) that, although almost invariably lacking the histopathological phenotype of a myopathy, is a rare, although potentially lethal, pharmacogenetic disorder triggered by volatile anesthetics and marked by a hypermetabolic state, muscle rigidity and elevated body temperature. While MH crisis can be halted through the administration of Dantrolene, currently, there are no approved treatments for RYR1-related diseases, despite the fact that numerous preclinical studies have been performed on different animal models of these diseases. Among the available preclinical models, two knock-in mouse lines, namely Ryr1Y524S/+ (Ryr1YS/+) and Ryr1I4895T/+ (Ryr1IT/+) mice, carrying either the Y524S or the I4895T RYR1 variants that correspond to human causative Y522S and I4898T RYR1 variants, respectively, are widely used to explore the mechanisms underlying RYR1-RD. Previous research in mdx mice, a preclinical model of muscular dystrophy, demonstrated that the skeletal muscle-specific overexpression of miR-486, a striated muscle-enriched microRNA, mitigates muscle degeneration and ameliorates the dystrophic phenotype. Accordingly, in this study, the hypothesis that skeletal muscle-specific overexpression could yield beneficial effects even in muscles with RYR1 mutations causative for the onset of RYR1-RD, has been verified. To evaluate whether miR-486 overexpression might be a novel potential therapeutic approach for RYR1-RD, two novel compound mouse models were successfully generated by crossing Ryr1IT/+ and Ryr1YS/+ mice with transgenic mice that selectively overexpress miR-486 in skeletal muscle (TgmiR-486/-). The novel mouse lines, referred to as Ryr1IT/miR-486 and Ryr1YS/miR 486, were subjected to different in vivo functional tests to evaluate muscle strength and endurance. Initial histological and molecular analyses on mutated skeletal muscles overexpressing miR-486 were also performed. The results obtained indicate that miR-486 overexpression significantly enhances muscle performance in both Ryr1IT/+ and Ryr1YS/+ mice, suggesting that skeletal muscle-specific overexpression of miR-486 might be considered as a novel promising therapeutic approach for RYR1-RD.