T.O.1 RNAi therapy for LGMD1A

Abstract

<h2>Abstract</h2> Limb-girdle muscular dystrophy refers to a group of 23 disorders characterized by progressive wasting and weakness of shoulder and hip girdle muscles. The onset and progression of LGMD varies among individuals and genetic subtypes. Pre-clinical studies support that gene therapy is a promising treatment approach for the LGMDs, and importantly one such strategy (for LGMD2D) was recently translated to human clinical trials. Despite the positive direction of LGMD-targeted gene therapies, all strategies to date focused on gene replacement approaches for recessive forms, while treatments for dominant LGMDs have been largely unexplored. This lack of focus on gene therapy for dominant LGMDs arose primarily because these disorders require disease gene knockdown, and the molecular tools to feasibly accomplish this did not exist until recently, with the emergence of RNA interference (RNAi). We hypothesized that patients with dominantly inherited LGMD would benefit from RNAi-mediated reduction of the pathogenic alleles underlying their disease. In this study, we developed the first RNAi-based, pre-clinical treatment for LGMD1A, caused by dominant mutation in one allele of the myotilin (MYOT) gene. To do this, we engineered and delivered MYOT-targeted artificial microRNA (miMYOT) vectors to knockdown mutant MYOT in muscles of an LGMD1A mouse model. Three months after treatment, miMYOT vectors significantly reduced soluble mutant MYOT protein to undetectable levels, and the protein aggregates that are characteristic of LGMD1A were either absent or very small in treated muscles. This reduction was associated with significantly improved muscle mass and whole muscle strength in LGMD1A mice. We are now assessing body wide improvements of miMYOT treatment following global vascular delivery. This work is an important first step toward translating targeted RNAi gene therapy approaches for LGMD1A, and our method could be adapted to impact a large class of dominant muscle disorders.