P.104Skeletal muscle reduction of Dnm2 with antisense oligonucleotides in myotubular myopathy

Abstract

Centronuclear myopathies (CNM) are a group of severe muscle diseases for which no effective therapy is currently available. The most severe and neonatal X-linked form is known as myotubular myopathy and caused by loss-of-function mutations in Myotubularin (MTM1), while the main autosomal dominant form is due to mutations in Dynamin 2 (DNM2). We previously showed that genetic reduction of DNM2 expression in Mtm1 knockout (Mtm1KO) mice prevents development of muscle pathology. We are now investigating skeletal muscle targeting of Dnm2 reduction in mice. Indeed specific muscle isoforms are expressed during muscle maturation and in adulthood, through alternative splicing. A single intraperitoneal injection of 25mg/kg of antisense oligonucleotides targeting the total pool of Dnm2 increased the lifespan, whole body strength, and reduced disease severity in Mtm1KO mice, however a single injection alone was not sufficient to rescue the disease for the lifespan of the mice. Repeated injections of ASO was able to revert the disease phenotype in mice within 2 weeks, and the effects lasted several months after the final injection. ASO was still detected in skeletal muscles at this time point, but not in key tissues such as the liver, which may explain in part the longterm improvement in the myopathic phenotype. New ligand-conjugated antisense (LICA) oligonucleotides targeting Dnm2 are now being tested in Mtm1KO mice for potency and efficacy. ASO-mediated Dnm2 knockdown can efficiently correct skeletal muscle defects due to loss of MTM1, providing an attractive therapeutic strategy for this disease. Effective muscle targeting will be an important step in translation of this approach to the clinic for patients.