Dose-dependent microdystrophin expression enhancement in cardiac muscle by a cardiac specific regulatory element

Duchenne muscular dystrophy (DMD) is an X-linked recessive disease that affects 1:5,000 live male births and is characterized by muscle wasting. By the age of 13 years, affected individuals are often wheelchair bound and suffer from respiratory and cardiac failure, which results in premature death. Although the administration of corticosteroids and ventilation can relieve the symptoms and extend the patients' lifespan, currently no cure exists for DMD. Among the different approaches under preclinical and clinical testing, gene therapy, using adeno-associated viral (AAV) vectors, is one of the most promising. In this study, we delivered intravenously AAV9 vectors expressing the microdystrophin MD1 (ΔR4-R23/ΔCT) under control of the synthetic muscle-specific promoter Spc5-12 and assessed the effect of adding a cardiac-specific cis-regulatory module (designated as CS-CRM4) on its expression profile in skeletal and cardiac muscles. Results show that Spc5-12 promoter, in combination with an AAV serotype that has high tropism for the heart, drives high MD1 expression levels in cardiac muscle in mdx mice. The additional regulatory element CS-CRM4 can further improve MD1 expression in cardiac muscles, but its effect is dose dependent and enhancement becomes evident only at lower vector doses.