CONGENITAL MYOPATHIES (CNM): P.143Myostatin as a novel blood based biomarker for antisense oligonucleotide-mediated Dnm2 knockdown to treat myotubular myopathy in mice

Abstract

Centronuclear myopathies (CNM) are non-dystrophic muscle diseases for which no effective therapy is currently available. The most severe form, X-linked CNM, is caused by myotubularin 1 (MTM1) loss-of-function mutations, while the main autosomal dominant form is due to dynamin2 (DNM2) mutations. We previously showed that genetic reduction of DNM2 expression in Mtm1 knockout (Mtm1KO) mice prevents development of muscle pathology. Most recently we have shown that weekly systemic delivery of Dnm2 antisense oligonucleotides (ASOs) into Mtm1KO mice efficiently reduces DNM2 protein level in muscle and prevents the myopathy from developing. In addition, systemic weekly ASO injection into severely affected mice leads to reversal of muscle pathology within two weeks. Here we perform a single injection of ASO into 3-week-old Mtm1KO mice, and complete clinical, histological and molecular analysis of the duration of the effects after a single injection. A single injection of 25mg/kg of ASO targeting DNM2 increased the lifespan, whole body strength, and reduced disease severity in Mtm1KO mice compared to untreated controls. Despite these results, a single injection alone was not sufficient to rescue the disease for the lifespan of the mice, suggesting repeated treatments will be required. Thus, ASO-mediated DNM2 knockdown can efficiently correct muscle defects due to loss of MTM1, providing an attractive therapeutic strategy for this disease. We next analyzed myostatin levels in muscles and blood of Mtm1KO mice. We show myostatin levels in plasma are significantly reduced in Mtm1KO mice, and that treatment by ASOs targeting DNM2 significantly improves myostatin levels in plasma. In addition plasma myostatin levels inversely correlated with the level of DNM2 mRNA in muscles after injection with ASOs. This provides the first evidence of a blood based biomarker that can be used to monitor disease state and rescue in myotubular myopathy mice. With clinical trials for myotubular myopathy currently in progress, these results are of high relevance to the research field.