Gene Therapy for Respiratory Pathology in Duchenne Muscular Dystrophy

Introduction: Duchenne muscular dystrophy (DMD) is an X-linked severe neuromuscular disorder, caused by a lack of dystrophin which results in progressive muscular degeneration. As the disease progresses, patients develop respiratory insufficiency and ultimately die from cardiorespiratory failure. Adeno-associated viral (AAV) gene therapy is an FDA approved therapy for the treatment of DMD. However, the impact of this gene therapy on respiratory function remains unclear. This study aims to utilize a systemic injection of AAV carrying a microdystrophin (μDys) to target and treat respiratory pathology in a mouse model of DMD. Methods: Three groups of mice were studied: mdx mice treated with saline (n=16), mdx mice treated with AAV-μDys (n=16) and wild type (WT) control mice treated with saline (n=16). All groups received therapy systemically through a tail vein injection. Whole body plethysmography (WBP) at 8 weeks of age and every 2 months until 56 weeks of age to assess respiratory function at baseline during normoxia (FiO2: 0.21; N2 balance) and during a respiratory challenge with hypoxia and hypercapnia (FiCO2: 0.07, FiO2: 0.10; N2 balance). Strength testing was performed. In a subgroup of mice (n=8 per group), postmortem studies were performed at 16 weeks of age and included diaphragm muscle strength, histological analysis of the diaphragm, tongue, and tibialis anterior to assess for muscle fiber regeneration, presence of dystrophin and fibrosis. Results:mdx mice treated with AAV-μDys did not show a significant difference in respiratory parameters during normoxia throughout the study. However, at 48 weeks of age, the AAV-μDys treated mdx mice started to exhibit an increased tidal volume, minute ventilation, peak inspiratory flow, and peak expiratory flow during the respiratory challenge when compared with saline treated mdx mice. Ex vivo diaphragm muscle function did not show a difference in muscle strength between AAV and saline treated mdx mice 2 months post-treatment. Hematoxylin and eosin staining showed a decreased cellular infiltration in the diaphragm, tongue, and tibialis anterior, Sirus red staining revealed decreased fibrosis, and immunohistochemistry showed the presence of dystrophin in the mdx mice treated with AAV-μDys group when compared with mdx mice treated with saline. Conclusion: Overall, these data indicate that AAV gene therapy enhances respiratory pathology and structural muscle pathologyin mdx mice. Ongoing studies will examine the ability of gene therapy to improve ex vivo diaphragm function, persistence of dystrophin protein expression and enhancement of muscle structure several months following AAV-μDys administration.

Duke Scholars

Author Mai ElMallah Pediatrics, Pulmonary and Sleep Medicine