Systemic MyoAAV-saRNA delivery activates endogenous utrophin and rescues dystrophic pathology in mdx mice

Therapeutic activation of endogenous utrophin, a homolog of dystrophin, represents a mutation-agnostic therapeutic strategy with considerable potential for treating Duchenne muscular dystrophy (DMD). However, the large size of current dCas9-based activation systems hinders efficient adeno-associated virus (AAV) delivery, and the long-term feasibility and therapeutic durability of such treatments remain uncertain. To overcome these limitations, we developed a muscle-targeted utrophin activation platform based on small activating RNA (saRNA), termed MyoAAV-saRNA.

Screening of a panel of saRNAs targeting the Utrn promoter identified Utrophin-257 as the most effective variant, capable of inducing more than a 3.7-fold increase in dystrophin mRNA expression in vitro. This candidate was subsequently packaged into AAV vectors for systemic administration.

Following intravenous delivery of MyoAAV 2A-saRNA-257 in mdx mouse models, significant upregulation of utrophin mRNA was observed. This activation led to functional improvements, including partial restoration of the sarcolemma, histopathological amelioration (reduced centronucleation, inflammation, and fibrosis), and enhanced muscle strength.

Collectively, these preclinical findings establish MyoAAV-saRNA as a promising and translatable platform for utrophin induction, highlighting its therapeutic potential for DMD.