Development of fibrosis in FSHD muscle

Development of fibrosis and its impact on muscle regeneration in FSHD muscle
Céline Lancelot, Gilles Carnac, Denis Nonclercq, Paul Delrée, Dalila Laoudj-Chenivesse, Alexandra Belayew, Frédérique Coppée
1 Laboratory of Molecular Biology, UMONS, Mons, Belgium; 2 Laboratory of Physiology and experimental medicine, INSERM U1046, Montpellier, France; 3 Laboratory of Histology, UMONS, Mons, Belgium; 4 Pathology and Genetic Institute , IPG, Gosselies, Belgium.

After muscle injury, quiescent satellite cells or recruited mesenchymal stem cells are activated and divide to provide myoblasts that repair the damaged muscle fibers. Despite the significant muscle damage, low muscle regeneration is observed in facioscapulohumeral dystrophy (FSHD) compared to other muscular dystrophies. The extracellular matrix (ECM) is a major component of the satellite cell niche that can also recruit other muscle progenitor cells after muscle damage. Affected FSHD muscles present an extensive fibrosis even in areas with histologically normal fibers. We hypothesized that modifications in the ECM composition of FSHD muscles are contributing to the observed low muscle regeneration.

We observed an early thickening of ECM in areas without histological abnormalities of affected FSHD muscles. Indeed, our preliminary data suggest in vitro and in vivo deregulations of some ECM components produced by myoblasts. As fibroblasts produce most components of the ECM, alterations of resident fibroblasts in FSHD muscles could contribute to the pathology. In order to characterize components of the ECM in FSHD muscles we established fibroblast and myoblast primary cultures from control and FSHD muscle biopsies.
The cells were purified by magnetic sorting with 50-nm superparamagnetic particles that are conjugated to highly specific antibodies against a particular antigen on the fibroblast or myoblast surface. The identity of our cultures was confirmed by immunofluorescence detection of specific cell markers (desmin, vimentin, collagen I and CD90).

This material will allow us to determine whether fibrosis is an early event in FSHD and could contribute to the incorrect response of progenitor muscle cells. We will also investigate whether the ECM deregulations in FSHD could affect muscle regeneration. Finally, we will evaluate whether the causative gene(s) of FSHD (DUX4) and its homologue involved in muscle regeneration (DUX4c) could be involved in early fibrosis.