Mdx mice have a defect in autophagy that is restored by rapamycin‐loaded nanoparticle treatment

Abstract

Duchenne Muscular Dystrophy (DMD) is genetic disorder caused by mutations in dystrophin, a cytoskeletal protein in muscles, leading to progressive muscle wasting and ultimately death in the second or third decade of life. The current standard of care for DMD patients is corticosteroid therapy which slows down the natural progression of the disease but causes unwanted side effects. Our lab's previous studies of therapeutics in an in vivo DMD model has demonstrated that mdx mice treated with rapamycin‐loaded nanoparticles showed an increase in strength that was not observed with oral rapamycin treatment. Because rapamycin is known to induce autophagy, we assayed for autophagy in mdx mice treated with rapamycin‐loaded nanoparticles. Western blot analysis of LC3B‐II, the processed form of a protein used in autophagy, suggests that there is a previously unknown defect in autophagy in mdx mice, as shown by a lack of LC3 3B‐II accumulation after blockade of autophagic flux by colchicine (Fig. 1A). Rapamycin nanoparticle treatment rescues autophagy to levels comparable to the control (Fig. 1B), suggesting that defective autophagy may contribute to the physical manifestations of muscular dystrophy in mdx mice and that restoration to normal levels may lead to the observed strength increase. Supported by NIH grant (R01 AR056223 to S.A.W.).