Background and Objectives: Duchenne Muscular Dystrophy (DMD) is one of the most severe disorders of muscle degeneration, caused by mutations in the dystrophin gene. The absence of dystrophin leads to progressive muscle degeneration, chronic inflammation, and fibrosis. While clinical trials indicate the potential benefits of microdystrophin (μDys) gene therapy, remaining issues include the need to increase muscle stem cells, maintain regenerative capacity and promote slow-type oxidative myofiber specification. Therefore, there remains an urgent need for approaches that address the full suite of pathophysiological features in DMD, including loss of muscle strength, endurance, regenerative capacity, myogenesis program dysfunction and restoration of the satellite cells.
AUF1 is an mRNA binding protein that binds repeated AU-rich elements (AREs) located in the 3’-untranslated region. AREs target mRNAs for rapid degradation, stabilization, and/or increased translation. The key regulators of muscle satellite cell activation and maintenance, myogenesis and oxidative metabolism are encoded by ARE-mRNAs that are regulated by AUF1. Moreover, AUF1 gene therapy strongly increases skeletal muscle expression of the dystrophin homolog utrophin, which can functionally substitute for dystrophin.
Results: We show that one-month-old mdx DMD mice administered AAV8.tMCK.AUF1 demonstrate strongly increased physical endurance and strength compared to mdx controls which is durably retained at 6 months at study completion. AUF1 gene therapy increased satellite cell population, utrophin and dystrophin associated protein complex expression, and improved diaphragm and limb skeletal muscle integrity.
Because AUF1 and µDys gene therapies act through distinct mechanisms, we tested a tandem AAV8.AUF1/AAV8.μDys approach. μDys combined with AUF1 demonstrated superior muscle function, strength and endurance compared to AUF1 or μDys therapy alone. Furthermore, the μDys/AUF1 combination demonstrated superior muscle morphology, protection of muscle from atrophy following muscle injury and durably increased exercise endurance.
Conclusions: These results provide compelling evidence that AUF1 mono- or μDys combination gene therapy may offer an alternative improved approach to treat DMD.