Wnt/β-catenin signaling suppresses DUX4 expression and prevents apoptosis of FSHD muscle cells

Facioscapulohumeralmuscular dystrophy is a dominantly inheritedmyopathy associated with chromatin relaxation of the D4Z4 macrosatellite array on chromosome 4. DUX4 is encoded within each unit of the D4Z4 array where it is normally transcriptionally silenced and packaged as constitutive heterochromatin. Truncation of the array to less than 11 D4Z4 units (FSHD1) or mutations in SMCHD1 (FSHD2) results in chromatin relaxation and a small percentage of culturedmyoblasts from these individuals exhibit infrequent bursts of DUX4 expression. There are no cellular or animal models to determine the trigger of the DUX4 producing transcriptional burstsandtherehasbeenafailure to date to detect the protein in significantnumbers of cellsfromFSHD-affected individuals. Here, we demonstrate for the first time that myotubes generated from FSHD patients express sufficientamountsofDUX4toundergoDUX4-dependentapoptosis.Weshowthat activation of theWnt/-catenin signaling pathway suppresses DUX4 transcription in FSHD1 and FSHD2 myotubes and can rescue DUX4-mediated myotube apoptosis. In addition, reduction of mRNA transcripts from Wnt pathway genes β-catenin, Wnt3A and Wnt9b results in DUX4 activation. We propose that Wnt/β-catenin signaling is important for transcriptional repression of DUX4 and identify a novel group of therapeutic targets for the treatment of FSHD.