p38 alpha Regulates Expression of DUX4 in a Model of Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is caused by the loss of repression at the D4Z4 locus leading to aberrant double homeobox 4 (DUX4) expression in skeletal muscle. Activation of this early embryonic transcription factor results in the expression of its target genes causing muscle fiber death. Although progress toward understanding the signals driving DUX4 expression has been made, the factors and pathways involved in the transcriptional activation of this gene remain largely unknown. Here, we describe the identification and characterization of p38 alpha as a novel regulator of DUX4 expression in FSHD myotubes. By using multiple highly characterized, potent, and specific inhibitors of p38 alpha/beta, we show a robust reduction of DUX4 expression, activity, and cell death across patient-derived FSHD1 and FSHD2 lines. RNA-seq profiling reveals that a small number of genes are differentially expressed upon p38 alpha/beta inhibition, the vast majority of which are DUX4 target genes. Our results reveal a novel and apparently critical role for p38 alpha in the aberrant activation of DUX4 in FSHD and support the potential of p38 alpha/beta inhibitors as effective therapeutics to treat FSHD at its root cause. SIGNIFICANCE STATEMENT Using patient-derived facioscapulohumeral muscular dystrophy (FSHD) myotubes, we characterize the pharmacological relationships between p38 alpha/beta inhibition, double homeobox 4 (DUX4) expression, its downstream transcriptional program, and muscle cell death. p38 alpha/beta inhibition results in potent and specific DUX4 downregulation across multiple genotypes without significant effects in the process of myogenesis in vitro. These findings highlight the potential of p38 alpha/beta inhibitors for the treatment of FSHD, a condition that today has no approved therapies.