Respiratory Dysfunction in a novel mouse model of Duchenne Muscular Dystrophy.

Abstract

Duchenne muscular dystrophy (DMD) is the most common genetic disease in adolescent males. It is caused by a loss of dystrophin protein, necessary for skeletal and cardiac muscle fiber membrane integrity, linking the sarcolemma to the extracellular matrix. Without dystrophin, muscle fibers are unable to maintain structure, with each contraction and relaxation leading to progressive muscle weakness. Weakness of the diaphragm results in respiratory failure for patients in early adulthood. For over 30 years, the mdx mouse which lacks dystrophin expression has served as a relevant model for DMD. However, the genotype of the mdx mouse does not reflect that of the patient population.Recently, a new mouse model harboring a human mutation in the dystrophin gene (DMD) was introduced into the mdx mouse (hDMD/Δ52;mdx) to better recapitulate a common genotype in patients. Since respiratory pathology is a significant cause of morbidity and mortality in DMD, this study sought to characterize the respiratory pathology in a novel DMD model – the hDMD/Δ52;mdx ‐ and further investigate the mdx mouse, using C57BL/6J mice as wildtype controls. The hypothesis driving this work is that the hDMD/Δ52;mdx mouse has greater respiratory deficiency compared to the mdx mouse. Whole body plethysmography (WBP) was used to assess respiration at baseline and during a challenge with hypercapnic and hypoxic conditions (FiCO2: 0.07, FiO2: 0.10; nitrogen balance). While exposed to normoxic air (FiO2: 0.21; nitrogen balance) the hDMD/Δ52;mdx was indistinguishable from either control at each time point. However, during the respiratory challenge the hDMD/Δ52;mdx mice had reduced frequency and minute ventilation by 6 months, which continued to decline at 12 months compared to the C57B/6J mice. Post mortem immunohistochemical studies of the neuromuscular junctions within the diaphragm showed that hDMD/Δ52;mdx and mdx mice had reduced overlap between presynaptic and postsynaptic endplates. Myofiber atrophy, fibrosis, and myofiber regeneration were also observed in the diaphragms of both mouse models. In conclusion, the hDMD/Δ52;mdx exhibits moderate respiratory pathology, and serves as a relevant animal model to study the impact of novel therapies on respiratory function.Support or Funding InformationDuke Department of Pediatrics Derfner Grant; R01 HD099486‐01; 1R21NS098131‐01