Adaptive response to electrical pulse stimulation is impaired in FSHD myotubes by DUX4 gene network activation

Facioscapulohumeral dystrophy (FSHD) is one of the most common muscular dystrophies with no effective treatment. The disease is linked to abnormal derepression of DUX4 embryonic transcription factor in skeletal muscle, but at very low frequency. How this relates to the disease process and the exact nature of functional defects of FSHD muscle cells remain obscure. We used electrical pulse stimulation (EPS) substituting motor neuron activation to perform quantitative structural, functional, and gene expression analyses of in vitro differentiated control and FSHD skeletal myocytes. We found that EPS effectively stimulated muscle contractile gene expression and contractility activation in control cells, which are impaired in FSHD patient cells. This is accompanied by exacerbated organizational differences of sarcomeric striation. Importantly, this FSHD patient cell phenotype was confirmed in engineered mutant cells carrying D4Z4 repeat contraction and SMCHD1 mutation. Notably, FSHD patient/mutant cells fail to activate musclin/OSTN, an exercise-responsive muscle-protective myokine. Overexpression of LEUTX, a major downstream DUX4 target, was sufficient to recapitulate this phenotype, indicating that the phenotype is linked to DUX4 gene network activation. The results demonstrate DUX4-induced cell intrinsic functional defects of FSHD muscle cells in adaptive response to electrical stimulation, suggesting the possible activity-stimulated pathological mechanism of FSHD.