Interfering with the transcription deregulation cascades in fshd

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disorder with a prevalence of 7/100,000 birth. It is characterized by an antero-posterior and often asymmetric progression of muscle weakness first affecting the face, the scapulae and the foot dorsiflexors. FSHD is linked to contraction of the D4Z4 repeat array in 4q35. We have identified the double homebox 4 (DUX4) gene within each D4Z4 unit and shown its expression in FSHD but not healthy primary myoblasts or muscle biopsies. We found the stable mRNAs comprising the full DUX4 ORF derived from the most distal unit and unexpectedly extended within the flanking pLAM region that provided an intron and a polydenylation signal. Other groups recently showed this signal was required on the contracted allele to develop FSHD. The DUX4 protein is a transcription factor that directly activates or inhibits many genes, some of wich encode other transcription factors with other target genes ect. The resulting deregulation cascade causes muscle atrophy and differentiation defects, inflammation and oxidative stress wich are key features of the disease. By differential proteome studies of FSHD versus healthy myotubes. We could identify additional FSHD biomarkers induced by DUX4. We have also characterized the homologous DUX4c gene 42-kb centromeric of the D4Z4 locus. It is expressed in healthy muscles, is increased in DMD and FSHD, and causes human myoblast proliferation. We now found that DUX4 expression in human myoblast cultures induced atrophic myotubes and E3 ubiquitin typical of muscle atrophy. In contrast DUX4c expression induced disorganized myotubes with large clusters of myonuclei . These atrophic/disorganized phenotypes are typical of FSHD primary myotube cultures. Inhibition of DUX4 or DUX4c expression should prevent the gene deregulation cascade and restore a healthy myotube phenotype. With this aim we used antisense approaches in human myoblast cultures to either induce mRNA destruction by RNA interference (siRNAs) or affect splicing by specific antisense oligomers. Decrease in DUX4 or DUX4c protein expression was confirmed by immunodetection on western blot and the biomarkers and myotube phenotypes changed as expected. These strategies seem promising and contribute to future development of therapeutic approaches for FSHD. We aknowledge funding from the AFM. CV and SC held FRIA (Belgium) graduate fellowships, AT and EA were post-doctoral FNRS (Belgium) associates.