Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB079

Poster Communications

Chronic Intermittent Hypoxia Enhances Respiratory Muscle Weakness in Dystrophin-deficient mdx Mice

D. P. Burns1, S. E. Drummond1, L. Sheeran2, A. Coiscaud1, C. O'Hehir1, D. Edge2, K. D. O'Halloran1

1. Physiology, School of Medicine, University College Cork, Cork, Ireland. 2. Physiology, School of Medicine, Trinity Biomedical Sciences Institute, Trinity College Dublin, the University of Dublin, Dublin, Ireland.

Sleep-disordered breathing (SDB) is a prominent feature of neuromuscular disease. Boys with Duchenne muscular dystrophy (DMD) experience nocturnal desaturation during sleep as a result of obstructive and central apnoea. We have previously described maladaptive changes in respiratory muscle structure and function in rodent models of chronic intermittent hypoxia (CIH), a hallmark feature of SDB driving many pathologies. We hypothesized that CIH exacerbates respiratory muscle dysfunction in muscular dystrophy. We sought to explore the effects of CIH on diaphragm muscle in wild-type (WT) and dystrophin-deficient mdx mice. Six-week-old male WT (n=9) and mdx (n=9) mice were exposed to CIH, consisting of alternating bouts of hypoxia (90s; 5-6.5% O2 at the nadir) and normoxia (210s; 21% O2) for 12 cycles per hour, 8 hours per day for 14 days. WT (n=9) and mdx (n=9) sham animals were exposed to normoxia in parallel. Diaphragm muscle was excised and functional capacity was examined ex vivo. Diaphragm muscle structure was examined along with the expression of inflammatory-, redox-, autophagy- and mitophagy-related genes. Data were statistically compared by two-way ANOVA with Bonferroni post hoc test. P<0.05 was considered statistically significant. Substantial muscle weakness was observed in dystrophic diaphragm compared with WT diaphragm. Exposure to CIH elicited significant muscle weakness in the diaphragm of WT mice. In mdx mice, exposure to CIH resulted in further weakness in the compromised diaphragm. Mdx diaphragm had significantly increased area of mononuclear cell infiltration, increased muscle fibre central nucleation, increased number of muscle fibres expressing embryonic myosin and elevated collagen content compared with WT. CIH significantly decreased mononuclear cell infiltration and central nucleation in mdx diaphragm. There was elevated expression of NF-kB, TNF-a, Nrf2, NOX-2, atrogin-1 and PARK2 mRNA in mdx diaphragm compared with WT. CIH increased the expression of BNIP3 and PINK1 in mdx diaphragm. Our findings demonstrate that exposure to CIH exacerbates diaphragm muscle weakness in the mdx model of muscular dystrophy. Since SDB is a feature of DMD, we reason that SDB may accelerate respiratory insufficiency in DMD. An understanding of the pathogenic factors driving CIH-induced muscle weakness in mdx may help inform therapeutic strategies that may have relevance to DMD boys.

Where applicable, experiments conform with Society ethical requirements