Abstract :
[en] Facioscapulohumeral muscular dystrophy (FSHD) is linked to chromatin opening and DNA hypomethylation at the D4Z4 repeat array in the 4q35 subtelomeric region. The open chromatin facilitates the expression of the DUX4 gene located in the last D4Z4 unit flanked by a polyA signal. The DUX4 protein is a potent transcription factor that initiates a deregulation cascade affecting many genes and that causes the disease.
We have previously compared the proteome of primary FSHD and control myotubes at day 4 of differentiation (Tassin et al. 2012). FSHD myotubes presented a disturbance of two major caveolar proteins: PTRF (cavin-1) and MURC (cavin-4). Caveolae are membrane nanodomains, considered as a subset of lipid rafts, enriched in cholesterol and sphingolipids. They play a major role in signal transduction for in many biological processes. Caveolae contain the muscle specific caveolin (caveolin-3) and small clusters of GPI-anchor proteins, also increased in FSHD myotubes. The extracellular protein AHNAK, a member of the dysferlin protein complex, is also slightly increased in FSHD myotubes. Caveolin-3, MG53 and dysferlin interact as well as PTRF and MG53 suggesting a link to the plasma membrane repair affected in dysferlinopathies (Cai et al. 2009; Zhu et al. 2011).
To evaluate the FSHD caveolar defect, we investigate some proteins of the membrane repair complex and cavins (PTRF, SDPR, SRBC, MURC) by western-blot and immunofluorescence. We will also study their putative relocations with a lipid raft tracer: the FITC-conjugated cholera toxin B subunit. We perform these experiments on iC2C12-DUX4 myoblasts (kindly provided by Prof. M. Kyba), human primary or immortalized mosaïc myoblasts (Prof. G. Butler-Browne and Prof. D. Laoudj-Chenivesse) in proliferation or differentiation.
If caveolar dysfunction can be shown in FSHD, deregulation of MURC and PTRF that are essential for skeletal muscle membrane stability could lead to deregulation of many cellular processes. In addition, if a link with DUX4 can be demonstrated, these proteins could be used as additional FSHD biomarkers. Identification of FSHD biomarkers and their validation is essential to assess the therapeutic approach developed by our laboratory i.e. antisense tools targeting the DUX4 mRNA and preventing protein expression.
