Why the study?
The role of p38 in regulating DUX4 at different myogenic stages had not been investigated, despite p38 inhibitors being tested in clinical trials for facioscapulohumeral muscular dystrophy.
Does p38 inhibition reduce DUX4 and DUX4 target gene expression during different stages of myogenesis in FSHD models?
Does p38 inhibition reduce DUX4 and DUX4 target gene expression during different stages of myogenesis in FSHD models?
While p38 is critical for DUX4 expression during early myogenesis, a significant level of DUX4 expression later in myogenesis is independent of p38α/β activity, potentially explaining the failure of losmapimod to suppress DUX4 targets in clinical trials.
Facioscapulohumeral muscular dystrophy (FSHD) is a degenerative muscle disease caused by loss of epigenetic silencing and ectopic reactivation of the embryonic double homeobox protein 4 gene (DUX4) in skeletal muscle. The p38 MAP kinase inhibitor losmapimod is currently being tested in FSHD clinical trials due to the finding that p38 inhibition suppresses DUX4 expression in preclinical models. However, the role of p38 in regulating DUX4 at different myogenic stages has not been investigated. We used genetic and pharmacologic tools in FSHD patient-derived myoblasts/myocytes to explore the temporal role of p38 in differentiation-induced DUX4 expression. Deletion of MAPK14/11 or inhibition of p38α/β caused a significant reduction in early differentiation-dependent increases in DUX4 and DUX4 target gene expression. However, in MAPK14/11 knockout cells, there remains a differentiation-associated increase in DUX4 and DUX4 target gene expression later in differentiation. Furthermore, pharmacologic inhibition of p38α/β only partially decreased DUX4 and DUX4 target gene expression in late differentiating myotubes. In xenograft studies, p38α/β inhibition by losmapimod failed to suppress DUX4 target gene expression in late FSHD xenografts. Our results show that while p38 is critical for DUX4 expression during early myogenesis, later in myogenesis a significant level of DUX4 expression is independent of p38α/β activity.
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Vangipurapu et al. (2024) studied Facioscapulohumeral muscular dystrophy. p38 MAPK inhibition (losmapimod or CRISPR knockout) vs. Vehicle or unmodified/Cas9 control was evaluated on DUX4 and DUX4 target gene expression.
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