Affiliations: [a] Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands
| [b] Department of Biomolecular Chemistry, Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| [c] Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| [d] Department of Internal Medicine and Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
Correspondence to: Anna Greco, MD, Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Reinier Postlaan 4, 6525 GC, Nijmegen, The Netherlands. P.O. Box 9101, 6500 HB Nijmegen, The Netherlands. Tel.: +31 68 71 17 452; Fax: +31 24 354 1122; E-mail: [email protected].
Abstract: Background:FSHD is caused by specific genetic mutations resulting in activation of the Double Homeobox 4 gene (DUX4). DUX4 targets hundreds of downstream genes eventually leading to muscle atrophy, oxidative stress, abnormal myogenesis, and muscle inflammation. We hypothesized that DUX4-induced aberrant expression of genes triggers a sustained autoimmune response against skeletal muscle cells. Objective:This study aimed at the identification of autoantibodies directed against muscle antigens in FSHD. Moreover, a possible relationship between serum antibody reactivity and DUX4 expression was also investigated. Methods:FSHD sera (N = 138, 48±16 years, 48% male) and healthy control sera (N = 20, 47±14 years, 50% male) were analyzed by immunoblotting for antibodies against several skeletal muscle protein extracts: healthy muscle, FSHD muscle, healthy and FSHD myotubes, and inducible DUX4 expressing myoblasts. In addition, DUX4 expressing myoblasts were analyzed by immunofluorescence with FSHD and healthy control sera. Results:The results showed that the reactivity of FSHD sera did not significantly differ from that of healthy controls, with all the tested muscle antigen extracts. Besides, the immunofluorescent staining of DUX4-expressing myoblasts was not different when incubated with either FSHD or healthy control sera. Conclusion:Since the methodology used did not lead to the identification of disease-specific autoantibodies in the FSHD cohort, we suggest that autoantibody-mediated pathology may not be an important disease mechanism in FSHD. Nevertheless, it is crucial to further unravel if and which role the immune system plays in FSHD pathogenesis. Other innate as well as adaptive immune players could be involved in the complex DUX4 cascade of events and could become appealing druggable targets.