Optimizing Gene Therapy for Respiratory Insufficiency in Duchenne Muscular Dystrophy

PROJECT SUMMARY/ABSTRACT Duchenne muscular dystrophy (DMD) is a devastating X-linked disease with no current cure. DMD is caused by mutations in the gene encoding dystrophin. Dystrophin is a protein necessary for the maintenance of muscle structure and is essential for skeletal and cardiac muscle integrity. As muscle damage progresses, the

respiratory muscles become weak and fibrotic leading to hypoventilation and respiratory insufficiency. Sadly, most patients die from respiratory failure. Further, 1/3 of DMD patients also have neurological manifestations and central nervous system (CNS) pathology. However, the impact of the CNS pathology in the respiratory-

related morbidity in DMD is unknown. Defining the respiratory muscle and neuropathology is essential as novel gene therapies using AAV-microdystrophin (AAV-µDys) for DMD enter clinical trials and become FDA-approved. Several pre-clinical trials with AAV-μDys reveal promising results with dystrophin production resulting in

improved survival and ambulation; however, in these studies the diaphragm was not adequately transduced, and respiratory outcome was not assessed. Thus, there remains a critical need for a therapy that will halt or reverse respiratory disease. In our first aim, we will comprehensively examine breathing and the respiratory motor units

in novel humanized mouse models and compare these to the established mdx DMD mouse model. We will then utilize these DMD mouse models to elucidate the impact of dystrophin deficiency on respiratory neuro-pathology. Finally, we will examine the efficacy of a novel AAV capsid carrying μDys in treating respiratory pathology and

neuro-pathology in the DMD mouse models. The fundamental hypothesis driving this proposal is that dystrophin deficiency in both the respiratory muscles and CNS leads to breathing impairments, and AAV-μDys will correct both the respiratory myopathy and neuropathology. In Aim 1 we will identify the impact of dystrophin deficiency on respiratory function and histopathology in the humanized mouse models of

DMD. In Aim 2, we will perform physiological, histological, transcriptional, and molecular studies to define the impact of dystrophin loss on the respiratory centers and motor neurons of the medulla and cervical spinal cord. Then, we will examine the ability of a novel AAVcc47-µDys to effectively transduce and correct respiratory

muscle and neuro-pathology (Aim 3). The proposed experiments are innovative because the impact of dystrophin deficiency on breathing and neuropathology in humanized mouse models has not been previously examined. Defining this pathology will provide clinically relevant outcome measures for future therapeutic

studies. Finally, the use of the novel AAVcc47 to deliver µDys and target respiratory pathophysiology and neuropathology will provide a much needed therapeutic option for respiratory insufficiency in DMD. Since AAV- µDys gene therapy is already in clinical trials, this work has the strong potential to quickly translate to clinic and

inform and impact the clinical treatment of boys and young men with DMD.