Low level DUX4 expression disrupts myogenesis through deregulation of myogenic gene expression

Abstract

Loss of silencing of the DUX4 gene on chromosome 4 causes facioscapulohumeral muscular dystrophy. While high level DUX4 expression induces apoptosis, the effects of low level DUX4 expression on human myogenic cells are not well understood. Low levels and sporadic expression of DUX4 have been reported in FSHD biopsy samples and myoblast cultures. Here, we show that a large set of human myogenic genes is rapidly deregulated by DUX4, including MYOD1 and MYF5, which are efficiently repressed even by low, non-toxic levels of DUX4. Human myoblasts modified to express low nontoxic levels of DUX4 were significantly impaired from differentiating into myotubes in vitro. Surprisingly, inhibition of differentiation does not require the transcriptional activation domain, thus is likely a feature of all mammalian DUX genes. DUX4 does not bind near the MYF5 gene, but has a prominent ChIP-seq peak within the MYF5 −118 kb enhancer. We find that when DUX4 binds at this site, it directs enhancer activity towards a nearby transcriptional start site for a noncoding nonfunctional RNA we name DIME (DUX4-induced MYF5 enhancer) transcript. These data highlight the anti-myogenic properties of DUX4 in human myogenic progenitor cells, and provide an example of enhancer disruption in the downregulation of MYF5.

DUX4 Signalling in the Pathogenesis of Facioscapulohumeral Muscular Dystrophy

“…DUX4 expression has been demonstrated to downregulate genes involved in myogenesis, such as those coding for MyoD, myogenin, desmin, and Pax7; Myf5 expression levels, on the other hand, were increased by DUX4 [55]. Low levels of DUX4 expression decreased muscle differentiation in vitro, as confirmed by a reduction in myosin heavy chain (MyHC)-positive fibers [55,76]. This DUX4-induced suppression of myogenic genes is found in both murine and human in vitro models [55,76,77].…”

“…Low levels of DUX4 expression decreased muscle differentiation in vitro, as confirmed by a reduction in myosin heavy chain (MyHC)-positive fibers [55,76]. This DUX4-induced suppression of myogenic genes is found in both murine and human in vitro models [55,76,77]. Furthermore, DUX4 decreased myogenic gene expression in satellite cells, which not only reduced their proliferation but also impaired the differentiation and fusion of myotubes derived from them [77].…”

Genome wide analysis of gene expression changes in skin from patients with type 2 diabetes

“…This gene rapidly downregulates the transcription factor Myogenic Differentiation 1 (MyoD), resulting in impaired myogenic differentiation and muscle regeneration [68]. Low expression of DUX4 impairs myogenesis through a reduction in myogenic gene expression [69]. DUX4L9 expression impairs myofibrillogenesis and potentially has a role in controlling muscle cell differentiation through association with type III intermediate filament protein desmin [70,71].…”

Transgenic mice expressing tunable levels of DUX4 develop characteristic facioscapulohumeral muscular dystrophy-like pathophysiology ranging in severity

“…Many of these DUX4 target genes, including germline-specific genes, cleavage-stage genes, and immune system regulators, are not normally expressed in healthy myogenic cells [24,26,33,34]. In addition, DUX4-FL expression ultimately initiates a cascade of numerous potentially detrimental events including the disruption of proteostasis, nonsense-mediated decay, and mRNA splicing mechanisms [21,36,37], altered myogenesis [38][39][40][41], and induction of apoptosis [7,21,[42][43][44]. These DUX4-mediated changes, either alone or in combination, lead to progressive muscle cell death and ultimately pathology [20,45].…”