RESUMEN
Facioscapulohumeral muscular dystrophy (FSHD) is one of the most prevalent adult muscular dystrophies. The common clinical signs usually appear during the second decade of life but when the first molecular dysregulations occur is still unknown. Our aim was to determine whether molecular dysregulations can be identified during FSHD fetal muscle development. We compared muscle biopsies derived from FSHD1 fetuses and the cells derived from some of these biopsies with biopsies and cells derived from control fetuses. We mainly focus on DUX4 isoform expression because the expression of DUX4 has been confirmed in both FSHD cells and biopsies by several laboratories. We measured DUX4 isoform expression by using qRT-PCR in fetal FSHD1 myotubes treated or not with an shRNA directed against DUX4 mRNA. We also analyzed DUX4 downstream target gene expression in myotubes and fetal or adult FSHD1 and control quadriceps biopsies. We show that both DUX4-FL isoforms are already expressed in FSHD1 myotubes. Interestingly, DUX4-FL expression level is much lower in trapezius than in quadriceps myotubes, which is confirmed by the level of expression of DUX4 downstream genes. We observed that TRIM43 and MBD3L2 are already overexpressed in FSHD1 fetal quadriceps biopsies, at similar levels to those observed in adult FSHD1 quadriceps biopsies. These results indicate that molecular markers of the disease are already expressed during fetal life, thus opening a new field of investigation for mechanisms leading to FSHD.
Asunto(s)
Proteínas de Homeodominio/genética , Fibras Musculares Esqueléticas/metabolismo , Distrofia Muscular Facioescapulohumeral/embriología , Distrofia Muscular Facioescapulohumeral/genética , Adulto , Células Cultivadas , Femenino , Feto , Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/metabolismo , Humanos , Masculino , Persona de Mediana Edad , Desarrollo de Músculos , Fibras Musculares Esqueléticas/patología , Distrofia Muscular Facioescapulohumeral/patología , Isoformas de Proteínas/genética , Músculo Cuádriceps/embriología , Músculo Cuádriceps/metabolismo , Isoformas de ARN/genética , Isoformas de ARN/metabolismo , ARN Interferente Pequeño/genética , Proteínas Represoras/genética , Proteínas Represoras/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Músculos Superficiales de la Espalda/embriología , Músculos Superficiales de la Espalda/metabolismoRESUMEN
OBJECTIVE: Facioscapulohumeral muscular dystrophy (FSHD) is linked to either contraction of D4Z4 repeats on chromosome 4 or to mutations in the SMCHD1 gene, both of which result in the aberrant expression of the transcription factor DUX4. However, it is still difficult to correlate these genotypes with the phenotypes observed in patients. Because we have recently shown that mice with disrupted Fat1 functions exhibit FSHD-like phenotypes, we have investigated the expression of the human FAT1 gene in FSHD. METHODS: We first analyzed FAT1 expression in FSHD adult muscles and determined whether FAT1 expression was driven by DUX4. We next determined FAT1 expression levels in 64 muscles isolated from 16 control fetuses. These data were further complemented with analysis of Fat1 expression in developing mouse embryos. RESULTS: We demonstrated that FAT1 expression is independent of DUX4. Moreover, we observed that (1) in control fetal human biopsies or in developing mouse embryos, FAT1 is expressed at lower levels in muscles that are affected at early stages of FSHD progression than in muscles that are affected later or are nonaffected; and (2) in adult muscle biopsies, FAT1 expression is lower in FSHD muscles compared to control muscles. INTERPRETATION: We propose a revised model for FSHD in which FAT1 levels might play a role in determining which muscles will exhibit early and late disease onset, whereas DUX4 may worsen the muscle phenotype.