PPMO treatment improves respiratory function in the<i>mdx</i>mouse model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder caused by dystrophin deficiency. Respiratory complications due to progressive muscle weakness are a major cause of morbidity and mortality in DMD. Exon skipping therapy, mediated here by a cell-penetrating peptide-conjugated phosphorodiamidate morpholino oligomer (PPMO), can potentially restore dystrophin expression in respiratory muscles. However, its ability to treat respiratory pathology has not been studied. Hypothesis: PPMO-mediated exon skipping therapy restores dystrophin expression in respiratory muscles and ameliorates respiratory complications in a mouse model of DMD. Methods: To find if PPMO can alleviate respiratory symptoms in DMD, the male mdx mice (DMD mouse model) were monthly systemically administered 30mg/kg, 50mg/kg and 100mg/kg of PPMO targeting exon 23 of the mouse DMD gene, starting at 2 months of age until they reached 12 months of age. The respiratory function and pulmonary mechanics of the PPMO-treated mice were compared to age-matched male saline-treated WT and mdx mice using whole body plethysmography (WBP) monthly and FlexiVent respectively. WBP was performed at normoxia (FiO 2 : 0.21; N 2 balance) and during a respiratory challenge with hypoxia and hypercapnia (FiCO 2 : 0.07, FiO 2 : 0.10; N 2 balance). Postmortem analysis included immunohistochemistry of respiratory muscles to study the dystrophin expression in muscles. Histological studies on muscles were performed to examine the extent of pathology including immune cell infiltration, muscle regeneration and fibrosis by hematoxylin-eosin and Sirius red staining. Results: Compared to untreated mdx mice, PPMO-treated mice exhibited significant improvement in respiratory function (increased breathing frequency, minute ventilation and tidal volume). Pulmonary mechanics studies show that compared to untreated mdx mice, PPMO-treated mice exhibited increased compliance and reduced resistance and elastance of the respiratory system. Treatment of mdx mice with PPMO resulted in pulmonary mechanics similar to those of WT mice. Dystrophin expression was restored in respiratory muscles, and there was significantly less immune cell infiltration and fibrosis in PPMO-treated mdx mice. Conclusion: Our findings suggest that PPMO-mediated exon skipping therapy improves respiratory function, normalizes respiratory mechanics and improves pathology in mouse model of DMD. Funding: Sarepta Therapeutics, Inc and NHLBI R01HL171282 (MKE) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.