Protein kinase A activation inhibits DUX4 gene expression in myotubes from patients with facioscapulohumeral muscular dystrophy

Abstract

Facioscapulohumeral muscular dystrophy (FSHD) is among the most prevalent of the adult-onset muscular dystrophies. FSHD causes a loss of muscle mass and function, resulting in severe debilitation and reduction in quality of life. Currently, only the symptoms of FSHD can be treated, and such treatments have minimal benefit. The available options are not curative, and none of the treatments address the underlying cause of FSHD. The genetic, epigenetic, and molecular mechanisms triggering FSHD are now quite well-understood, and it has been shown that expression of the transcriptional regulator () is necessary for disease onset and is largely thought to be the causative factor in FSHD. Therefore, we sought to identify compounds suppressing expression in a phenotypic screen using FSHD patient-derived muscle cells, a zinc finger and SCAN domain-containing 4 (ZSCAN4)-based reporter gene assay for measuring DUX4 activity, and ∼3,000 small molecules. This effort identified molecules that reduce gene expression and hence DUX4 activity. Among those, β-adrenergic receptor agonists and phosphodiesterase inhibitors, both leading to increased cellular cAMP, effectively decreased expression by>75% in cells from individuals with FSHD. Of note, we found that cAMP production reduces expression through a protein kinase A-dependent mode of action in FSHD patient myotubes. These findings increase our understanding of how expression is regulated in FSHD and point to potential areas of therapeutic intervention.

DUX4 Signalling in the Pathogenesis of Facioscapulohumeral Muscular Dystrophy

“…This effect of DUX4 on global histone acetylation appears to be conserved, as the murine homologue Dux induces a similar phenomenon [99]. It is possible that the involvement of p300/CBP explains how strategies that aim to increase intracellular cyclic adenosine monophosphate (cAMP) levels could inhibit DUX4-mediated toxicity, given that cAMP signalling is a known regulator of p300/CBP activity [84,100,101].…”

Lymphocytes contribute to DUX4 target genes in FSHD muscle biopsies

“…This suggests a ubiquity in DUX4 target gene activation regardless of cell type, indicating that processes altered in myogenic cells in FSHD may similarly be altered in FSHD immune cells. As DUX4 and its target genes likely contribute to FSHD progression and are targets for potential therapeutics 49–51 , this suggests a role for the immune system, as well as muscle cells, in contributing to DUX4-mediated pathology in FSHD.…”

“…Such a finding requires confirmation with paired blood samples and muscle biopsies, beyond the scope of this proof-of-principle study. Moreover, many putative FSHD therapeutics in development target DUX4 and target gene expression 49,51,55,56 . We have shown that DUX4 and its target genes are robustly expressed in FSHD blood cells in a manner correlated with pathological muscle changes, thus anti-DUX4 therapy may be easily monitored for dose-titration by blood cell based DUX4 expression assessment.…”

Consequences of epigenetic derepression in facioscapulohumeral muscular dystrophy

“…However, in none of the trials salbutamol proved to benefit the physical performance of the patient group in comparison to the control group. Nevertheless, a recent study using β2AR agonists salbutamol and formoterol in FSHD myotube cultures showed that both drugs were able to reduce the expression of well‐known DUX4 target genes ZSCAN4 , TRIM43 , MBD3L2 , and LEUTX , and to induce the production of cAMP . cAMP, an ATP derivate, is a second messenger crucial for many biological process such as transport of hormones, ion channel regulation and protein kinase activation like the protein kinase A (PKA) .…”