Single-cell RNA sequencing in facioscapulohumeral muscular dystrophy disease etiology and development.

Facioscapulohumeral muscular dystrophy (FSHD) is characterized by sporadic de-repression of the transcription factor DUX4 in skeletal muscle. DUX4 activates a cascade of muscle disrupting events, eventually leading to muscle atrophy and apoptosis. Yet, how sporadic DUX4 expression leads to the generalized muscle wasting remains unclear. Transcriptome analyses have systematically been challenged by the majority of nuclei being DUX4neg, weakening the DUX4 transcriptome signature. Moreover, DUX4 has been shown to be expressed in a highly dynamic burst-like manner, likely resulting in the detection of the downstream cascade of events long after DUX4 expression itself has faded. Identifying the FSHD transcriptome in individual cells and unraveling the cascade of events leading to FSHD development may therefore provide important insights in the disease process. We employed single-cell RNA sequencing, combined with pseudotime trajectory modeling, to study FSHD disease etiology and cellular progression in human primary myocytes. We identified a small FSHD-specific cell population in all tested patient-derived cultures and detected new genes associated with DUX4 de-repression. We furthermore generated an FSHD cellular progression model, reflecting both the early burst-like DUX4 expression as well as the downstream activation of various FSHD-associated pathways, which allowed us to correlate DUX4 expression signature dynamics with that of regulatory complexes, thereby facilitating the prioritization of epigenetic targets for DUX4 silencing. Single-cell transcriptomics combined with pseudotime modeling thus holds valuable information on FSHD disease etiology and progression that can potentially guide biomarker and target selection for therapy.

Transgenic zebrafish model of DUX4 misexpression reveals a developmental role in FSHD pathogenesis.

Facioscapulohumeral dystrophy type 1 (FSHD-1) is the most common autosomal dominant form of muscular dystrophy with a prevalence of ∼1 in 8000 individuals. It is considered a late-onset form of muscular dystrophy and leads to asymmetric muscle weakness in the facial, scapular, trunk and lower extremities. The prevalent hypothesis on disease pathogenesis is explained by misexpression of a germ line, primate-specific transcription factor DUX4-fl (double homeobox 4, full-length isoform) linked to the chromosome 4q35. In vitro and in vivo studies have demonstrated that very low levels of DUX4-fl expression are sufficient to induce an apoptotic and/or lethal phenotype, and therefore modeling of the disease has proved challenging. In this study, we expand upon our previously established injection model of DUX4 misexpression in zebrafish and describe a DUX4-inducible transgenic zebrafish model that better recapitulates the expression pattern and late onset phenotype characteristic of FSHD patients. We show that an induced burst of DUX4 expression during early development results in the onset of FSHD-like phenotypes in adulthood, even when DUX4 is no longer detectable. We also utilize our injection model to study long-term consequences of DUX4 expression in those that fail to show a developmental phenotype. Herein, we introduce a hypothesis that DUX4 expression during developmental stages is sufficient to induce FSHD-like phenotypes in later adulthood. Our findings point to a developmental role of DUX4 misexpression in the pathogenesis of FSHD and should be factored into the design of future therapies.

Early-Onset Infantile Facioscapulohumeral Muscular Dystrophy: A Timely Review.

Facioscapulohumeral muscular dystrophy (FSHD)-the worldwide third most common inherited muscular dystrophy caused by the heterozygous contraction of a 3.3 kb tandem repeat (D4Z4) on a chromosome with a 4q35 haplotype-is a progressive genetic myopathy with variable onset of symptoms, distribution of muscle weakness, and clinical severity. While much is known about the clinical course of adult FSHD, data on the early-onset infantile phenotype, especially on the progression of the disease, are relatively scarce. Contrary to the classical form, patients with infantile FSHD more often have a rapid decline in muscle wasting and systemic features with multiple extramuscular involvements. A rough correlation between the phenotypic severity of FSHD and the D4Z4 repeat size has been reported, and the majority of patients with infantile FSHD obtain a very short D4Z4 repeat length (one to three copies, EcoRI size 10-14 kb), in contrast to the classical, slowly progressive, form of FSHD (15-38 kb). With the increasing identifications of case reports and the advance in genetic diagnostics, recent studies have suggested that the infantile variant of FSHD is not a genetically separate entity but a part of the FSHD spectrum. Nevertheless, many questions about the clinical phenotype and natural history of infantile FSHD remain unanswered, limiting evidence-based clinical management. In this review, we summarize the updated research to gain insight into the clinical spectrum of infantile FSHD and raise views to improve recognition and understanding of its underlying pathomechanism, and further, to advance novel treatments and standard care methods.

Dux4 induces cell cycle arrest at G1 phase through upregulation of p21 expression.

It has been implicated that Dux4 plays crucial roles in development of facioscapulohumeral dystrophy. But the underlying myopathic mechanisms and related down-stream events of this retrogene were far from clear. Here, we reported that overexpression of Dux4 in a cell model TE671 reduced cell proliferation rate, and increased G1 phase accumulation. We also determined the impact of Dux4 on p53/p21 signal pathway, which controls the checkpoint in cell cycle progression. Overexpression of Dux4 increased p21 mRNA and protein level, while expression of p53, phospho-p53 remained unchanged. Silencing p21 rescued Dux4 mediated proliferation defect and cell cycle arrest. Furthermore, we demonstrated that enhanced Dux4 expression increased p21 promoter activity and elevated expression of Sp1 transcription factor. Mutation of Sp1 binding site decreased dux4 induced p21 promoter activation. Chromatin immunoprecipitation (ChIP) assays confirmed the Dux4-induced binding of Sp1 to p21 promoter in vivo. These results suggest that Dux4 might induce proliferation inhibition and G1 phase arrest through upregulation of p21.

Therapeutic Approaches in Facioscapulohumeral Muscular Dystrophy.

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common types of muscular dystrophy, affecting roughly one in 8000 individuals. The complex underlying genetics and poor mechanistic understanding has caused a bottleneck in therapeutic development. Until the discovery of DUX4 and its causal role in FSHD, most trials were untargeted with limited results. Emerging approaches can learn from these early trials to increase their chance of success. Here, we explore the evolution of FSHD clinical trials from nonspecific anabolic or anti-inflammatory/oxidant strategies to cutting-edge molecular therapies targeting DUX4, and we discuss the importance of clinical outcome measures. With combined advances across multiple facets of FSHD research, the field is now poised to accelerate the process of therapeutic discovery and testing.

Facioscapulohumeral muscular dystrophy.

PURPOSE OF REVIEW: Knowledge of the pathogenetic mechanisms in facioscapulohumeral muscular dystrophy is still scattered, but has recently been advanced through novel developments on the genetic scientific front. RECENT FINDINGS: The present brief review highlights some recent studies on the pathogenesis of facioscapulohumeral muscular dystrophy pointing to major involvement of muscle development pathways and possibly vascular development pathways as well, which feeds into ideas about homeobox-related transcriptional dysregulation, which was originally suggested, based on the apparent descending order of muscle weakness. SUMMARY: The present findings and observations set a broad agenda for further research and possible therapeutic targets.

[First facioscapulohumeral muscular dystrophy prenatal diagnosis in a Bulgarian family].

Facioscapulohumeral muscular dystrophy (FSHD) is the third most common myopathy. It is characterized by progressive descendent involvement of facial, shoulder girdle, truncal and lower extremities muscles. FSHD locus was mapped on the terminal part of the long arm of chromosome 4 (4q35). The disease is caused by a deletion of an integral number of tandem D4Z4 repeats and dimension of the pathological fragments < or = 38kb. Prenatal diagnosis of FSHD is possible but it is potentially difficult because of the big amount and high quality of DNA required. Hereby we describe the first prenatal tests performed for a Bulgarian family.

[Clinical and genetical features of Japanese early-onset facioscapulohumeral muscular dystrophy].

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant form of muscular dystrophy characterized by progressive weakness and wasting of the facial, shoulder-girdle and upper arm muscles. The gene locus for FSHD is mapped to the subtelomeric region of chromosome 4q35, in which smaller EcoRI fragments (10 to 33 kb) are detected in most families by Southern blot analysis. The purpose of this study is to clarify the frequency and clinical/genetical features of early-onset FSHD in Japanese patients with 4q35-FSHD. In a series of 231 patients from 145 families with 4q35-FSHD, there were 31 patients (13.4%; male: female = 12:19) of 29 families (20%) with early-onset FSHD, 16 of whom were sporadic. Genetic analysis revealed that they had significantly smaller sized EcoRI fragments (range, 10 to 23 kb; mean 14.1 kb) than the other patients (range, 12 to 33 kb; mean 19.6 kb) (p < 0.001, U-test). All patients with the smallest EcoRI fragments (10 to 11 kb) were sporadic cases with early onset. Mental retardation (10/11) and epilepsy (4/11) was often observed in them, but not in the other patients. In early-onset FSHD, tongue muscle involvement (8/31) and swallowing disturbance (2/31), which has been regarded as exclusion criteria of FSHD, were also present. The onset of gait disturbance was significantly earlier (mean age = 11.9) in early-onset FSHD compared to the other group (mean age = 28.7). All patients with early-onset FSHD showed gait disturbance before 28 years of age. In conclusion, Japanese early-onset FSHD patients tend to have large gene deletions on chromosome 4q35, and show severe and variable phenotypes.

[Marseille welcomes the FSHD Society International Research Conference]. / Le colloque annuel de la FSHD Society s'invite à Marseille.

TITLE: Le colloque annuel de la FSHD Society s'invite à Marseille. ABSTRACT: Les 19 et 20 juin 2019, la conférence internationale sur la recherche dans la dystrophie facio-scapulo-humérale (FSHD) a eu lieu à Marseille. La rencontre rassemblant 180 participants, médecins, scientifiques et patients était organisée au Palais du Pharo à Marseille. Ce site historique emblématique surplombant le Vieux Port et faisant face à Notre Dame de la Garde a été construit dans la seconde moitié du XIXe siècle par Napoléon III pour son épouse, l'impératrice Eugénie.

The activatory long non-coding RNA DBE-T reveals the epigenetic etiology of facioscapulohumeral muscular dystrophy.

Facioscapulohumeral muscular dystrophy (FSHD) is a neuromuscular disorder often considered to be the third most common muscular dystrophy. Deletions reducing the copy number of the D4Z4 repeat in the distal end of the 4q arm are the main genetic cause of the disease. The recently highlighted research has identified a transcriptional activatory long non-coding RNA involved in the disease that acts through the recruitment of ASH1L, a protein belonging to the Trithorax family.

Decreased proliferation kinetics of mouse myoblasts overexpressing FRG1.

Although recent publications have linked the molecular events driving facioscapulohumeral muscular dystrophy (FSHD) to expression of the double homeobox transcription factor DUX4, overexpression of FRG1 has been proposed as one alternative causal agent as mice overexpressing FRG1 present with muscular dystrophy. Here, we characterize proliferative defects in two independent myoblast lines overexpressing FRG1. Myoblasts isolated from thigh muscle of FRG1 transgenic mice, an affected dystrophic muscle, exhibit delayed proliferation as measured by decreased clone size, whereas myoblasts isolated from the unaffected diaphragm muscle proliferated normally. To confirm the observation that overexpression of FRG1 could impair myoblast proliferation, we examined C2C12 myoblasts with inducible overexpression of FRG1, finding increased doubling time and G1-phase cells in mass culture after induction of FRG1 and decreased levels of pRb phosphorylation. We propose that depressed myoblast proliferation may contribute to the pathology of mice overexpressing FRG1 and may play a part in FSHD.

Testing the position-effect variegation hypothesis for facioscapulohumeral muscular dystrophy by analysis of histone modification and gene expression in subtelomeric 4q.

Facioscapulohumeral muscular dystrophy (FSHD) is a unique dominant disorder involving shortening of an array of tandem 3.3 kb repeats. This copy-number polymorphic repeat, D4Z4, is present in arrays at both 4q35 and 10q26, but only 4q35 arrays with one to 10 copies of the repeat are linked to FSHD. The most popular model for how the 4q35 array-shortening causes FSHD is that it results in a loss of postulated D4Z4 heterochromatinization, which spreads proximally, leading to overexpression of FSHD genes in cis. This would be similar to a loss of position-effect variegation (PEV) in Drosophila. To test for the putative heterochromatinization, we quantitated chromatin immunoprecipitation with an antibody for acetylated histone H4 that discriminates between constitutive heterochromatin and unexpressed euchromatin. Contrary to the above model, H4 acetylation levels of a non-repeated region adjacent to the 4q35 and 10q26 D4Z4 arrays in normal and FSHD lymphoid cells were like those in unexpressed euchromatin and not constitutive heterochromatin. Also, these control and FSHD cells displayed similar H4 hyperacetylation (like that of expressed genes) at the 5' regions of 4q35 candidate genes FRG1 and ANT1. Contrary to the loss-of-PEV model and a recent report, there was no position-dependent increase in transcript levels from these genes in FSHD skeletal muscle samples compared with controls. Our results favor a new model for the molecular genetic etiology of FSHD, such as, differential long-distance cis looping that depends upon the presence of a 4q35 D4Z4 array with less than a threshold number of copies of the 3.3 kb repeat.