Engquist, E. N. | bioRxiv Science

bioRxiv2025

Mitochondrial Respiratory Chain Function is crucial for Muscle Toxicity in Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is driven by DUX4-induced toxicity, yet the pathomechanisms remain unclear. Here, we identify persistent transcriptional suppression of the mitochondrial respiratory chain and metabolic rewiring in FSHD muscle biopsies and myotubes. Using DUX4-inducible human myogenic cells, we show that DUX4 target gene activation is accompanied by mitochondrial function impairment and Caspase 9-mediated apoptosis. Reverse electron transfer (RET) at complex I is the dominant oxidative stress generating mechanism in FSHD muscle cells. RET-driven mitochondrial reactive oxygen species (mitoROS) are the trigger for oxidative stress and apoptosis, which is a unique feature of FSHD mitochondria. Pharmacological inhibition of RET suppresses mitoROS, reduces Caspase 9 activation, and rescues abnormal myogenesis in FSHD cell lines. Importantly, DUX4 is non-toxic in oxidative phosphorylation-deficient human myogenic cells. Our findings identify the mitochondrial respiratory chain as a key mediator of DUX4 toxicity and highlight RET inhibition as a potential therapeutic approach for FSHD. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=136 SRC="FIGDIR/small/690559v1_ufig1.gif" ALT="Figure 1"> View larger version (48K): org.highwire.dtl.DTLVardef@254927org.highwire.dtl.DTLVardef@1e5c67forg.highwire.dtl.DTLVardef@4ace42org.highwire.dtl.DTLVardef@12b710e_HPS_FORMAT_FIGEXP M_FIG (Created with BioRender.com) C_FIG

biochemistry↗

bioRxiv2025

CEBPβ regulates myoblast proliferation and myogenic differentiation during human myogenesis and rescues defective differentiation in FSHD

CCAAT enhancer binding protein {beta} (CEBPB) is a member of the bZIP transcription factor family and is expressed in many cell types. Whilst CEBPB has been shown to regulate the function of murine satellite cells, the resident skeletal muscle stem cell, however little is known of its role in human myogenesis and muscle disease. We report that CEBPB is expressed in proliferating human myoblasts but swiftly down-regulated upon myogenic differentiation. Interestingly, either over-expression or knock-down of CEBPB inhibit the proliferation rate of human myoblasts. Down-regulation of CEBPB upon myogenic differentiation is then necessary for subsequent myogenic differentiation and fusion into multinucleated myotubes. In the muscle disease context, CEBPB protein levels are increased in myoblasts derived from facioscapulohumeral muscular dystrophy (FSHD) patients. Knock-down of CEBPB in FSHD myoblasts improves myogenic differentiation. In summary, we show that CEBPB is a regulator of human myogenesis and altered CEBPB expression may contribute to defective myogenesis in FSHD.

cell biology↗

bioRxiv2021

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{middle dot} 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. HighlightsO_LITranscriptomics data from FSHD muscle indicates enrichment for disturbed mitochondrial pathways C_LIO_LIDisturbed RONS metabolism correlates with mitochondrial membrane polarisation and myotube hypotrophy C_LIO_LIDUX4-induced changes in mitochondrial function precede oxidative stress through mitoROS and affect hypoxia signalling via complex I C_LIO_LIFSHD is sensitive to environmental hypoxia, which increases ROS levels in FSHD myotubes C_LIO_LIHypotrophy in hypoxic FSHD myotubes is efficiently rescued with mitochondria-targeted antioxidants C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=107 SRC="FIGDIR/small/459509v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@16ae1a8org.highwire.dtl.DTLVardef@517caorg.highwire.dtl.DTLVardef@5d0734org.highwire.dtl.DTLVardef@183ef50_HPS_FORMAT_FIGEXP M_FIG C_FIG

pathology↗