Progress Update: Molecular Mechanism of p38 Kinase-mediated inhibition of DUX4

Update provided by Dr. Vangipurapu
See grant Molecular Mechanism of p38 Kinase-mediated inhibition of DUX4 Gene in Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is a skeletal muscle disorder caused by the de-repression of D4Z4 subunits at 4q35 leading to aberrant DUX4 expression. DUX4 expression has been associated with activation of pathways toxic to muscle tissue leading to muscle cell death. In the current study, we attempted to dissect the molecular basis of DUX4 suppression mediated by p38 MAPK inhibition. To probe the influence of p38 MAPK on DUX4 regulation during early and late myogenic events, we used genetic and pharmacological approaches. Genetic knockout p38a and p38b using CRISPR-Cas9 or treatment with p38a/b inhibitor losmapimod significantly suppressed DUX4 and its target gene mRNA levels during the early myogenesis in vitro, confirming previous observations. However, at later time points, neither genetic nor pharmacological inhibition of p38α/β showed significant inhibition of DUX4 expression, as there is persistent low-level DUX4 expression in knockout/drug treated cells. In xenograft studies, FSHD cells with p38a/b double knockout showed persistent low-level DUX4 target gene expression throughout myogenesis. In summary, our results suggest that while p38a/b MAPK signaling promotes robust DUX4 expression induced early during myogenesis, at later time points there is persistent lower-level expression that is p38-independent. To fully understand the therapeutic potential of p38 inhibition in FSHD, it is necessary determine the mechanism of p38-independent DUX4 expression and its effect on myogenic differentiation and muscle health.

Grant Co-Funding: The Chris Carrino Foundation for FSHD