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Gene replacement therapy to ameliorate respiratory system dysfunction in a pre-clinical model of Duchenne muscular dystrophy
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Date
2025
Authors
Slyne, Aoife D.
Journal Title
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Publisher
University College Cork
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Abstract
Duchenne muscular dystrophy (DMD) is a life-limiting X-linked disorder, characterised by neuromuscular dysfunction secondary to dystrophin deficiency. The absence of the structural protein dystrophin in DMD leads to severe and progressive skeletal muscle remodelling and dysfunction, which extends to the respiratory muscles, with deleterious consequences for respiratory system performance. There is a progressive decline in respiratory muscle and pulmonary function with disease progression in DMD, with premature death ultimately occurring due to ventilatory insufficiency leading to cardio-respiratory failure. There is currently no cure for this devastating disease. Comprehensive studies on the control of breathing across the natural history of disease are lacking in DMD and animal models of dystrophinopathies. Additionally, ongoing pre-clinical and clinical studies overlook the impact of interventional strategies on the respiratory control system. We examined the respiratory control network in a pre-clinical model of DMD, the mdx mouse, across the natural history of the disease. Given that DMD is a genetic disease, we assessed the potential of a gene replacement therapy to ameliorate respiratory system dysfunction in mdx mice.
Wild-type and mdx mice were studied at two timepoints; 4-months of age (early dystrophic disease) and 16-months of age (advanced dystrophic disease). We assessed ventilation and metabolism in conscious mice during normoxia and chemostimulation with hypoxic-hypercapnia. We measured inspiratory pressure, ventilation and obligatory (diaphragm, intercostal and parasternal) and accessory (sternomastoid, cleidomastoid, scalene and trapezius) respiratory muscle EMG activities in anaesthetised spontaneously breathing mice in vivo. Obligatory and accessory muscle form, function and cytokine concentrations were assessed. Interventional studies consisted of a single, systemic, clinically relevant, therapeutic dose of AAV-microdystrophin gene therapy. Two months following treatment, ventilation and metabolism, obligatory (diaphragm) and accessory (scalene) respiratory muscle form, and diaphragm muscle function were assessed.
Despite obligatory and accessory muscle dysfunction, including inflammation, structural remodelling, weakness and reduced EMG activity, peak inspiratory pressure-generating capacity and ventilation are preserved in early disease. Obligatory and accessory muscle dysfunction progressively declines with advanced disease, with the emergence of reduced peak inspiratory pressure-generating capacity. While there was evidence of progressive accessory muscle dysfunction, more profound remodelling was seen in the diaphragm muscle comparing early and advanced dystrophic disease. A therapeutic dose of AAV-microdystrophin gene therapy is insufficient to correct respiratory muscle remodelling and dysfunction in mdx mice.
In conclusion, peak inspiratory performance is compensated in early dystrophic disease. A progressive decline in diaphragm and extra-diaphragmatic muscle form, function and control contributes to respiratory system compromise in advanced disease. We reason that further loss of compensation afforded by accessory muscles likely contributes to end-stage respiratory failure. Gene replacement studies indicate that further work is required to determine optimal therapeutic targeting of respiratory muscles. These data have relevance to the development of interventional strategies designed to alleviate respiratory muscle dysfunction to protect and improve breathing in human dystrophinopathies.
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Keywords
Duchenne muscular dystrophy , Mdx , Breathing , Diaphragm , Accessory muscles of breathing , Inspiratory pressure , EMG , Muscle structure and function , Cytokines , AAV gene therapy , Microdystrophin
Citation
Slyne, A. D. 2025. Gene replacement therapy to ameliorate respiratory system dysfunction in a pre-clinical model of Duchenne muscular dystrophy. PhD Thesis, University College Cork.