Interplay between mitochondria and reactive oxygen and nitrogen species in metabolic adaptation to hypoxia in facioscapulohumeral muscular dystrophy: potential therapeutic targets

Facioscapulohumeral muscular dystrophy (FSHD) is characterised by descending skeletal muscle weakness and wasting. FSHD is caused by mis-expression of the transcription factor DUX4, which is linked to oxidative stress, a condition especially detrimental to skeletal muscle with its high metabolic activity and energy demands. Oxidative damage characterises FSHD and recent work suggests metabolic dysfunction and perturbed hypoxia signalling as novel pathomechanisms. However, redox biology of FSHD remains poorly understood, and integrating the complex dynamics of DUX4-induced metabolic changes is lacking.Here we pinpoint the kinetic involvement of altered mitochondrial RONS metabolism and impaired mitochondrial function in aetiology of oxidative stress in FSHD. Transcriptomic analysis in FSHD muscle biopsies reveals strong enrichment for pathways involved in mitochondrial complex I assembly, nitrogen metabolism, oxidative stress response and hypoxia signalling. We found elevated ROS levels correlate with increases in steady-state mitochondrial membrane potential in FSHD myogenic cells. DUX4 triggers mitochondrial membrane polarisation prior to oxidative stress generation and apoptosis through mitochondrial ROS, and affects NO· bioavailability via mitochondrial peroxidation. We identify complex I as the primary target for DUX4-induced mitochondrial dysfunction, with strong correlation between complex I-linked respiration and cellular oxygenation/hypoxia signalling activity in environmental hypoxia. Thus, FSHD myogenesis is uniquely susceptible to hypoxia-induced oxidative stress as a consequence of metabolic mis-adaptation. Importantly, mitochondria-targeted antioxidants rescue FSHD pathology more effectively than conventional antioxidants, highlighting the central involvement of disturbed mitochondrial RONS metabolism. This work provides a pathomechanistic model by which DUX4-induced changes in oxidative metabolism impair muscle function in FSHD, amplified when metabolic adaptation to varying O2 tension is required.HighlightsTranscriptomics data from FSHD muscle indicates enrichment for disturbed mitochondrial pathwaysDisturbed RONS metabolism correlates with mitochondrial membrane polarisation and myotube hypotrophyDUX4-induced changes in mitochondrial function precede oxidative stress through mitoROS and affect hypoxia signalling via complex IFSHD is sensitive to environmental hypoxia, which increases ROS levels in FSHD myotubesHypotrophy in hypoxic FSHD myotubes is efficiently rescued with mitochondria-targeted antioxidantsGraphical abstract