Profiling Serum Antibodies Against Muscle Antigens in Facioscapulohumeral Muscular Dystrophy Finds No Disease-Specific Autoantibodies

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.

Elevated plasma complement components in facioscapulohumeral dystrophy

“…It is notable that evidence in FSHD exists for engagement of each of the three activation pathways as well as the amplification loop. Although serum antibodies against antigens expressed in FSHD muscle have not been identified (29), the classical pathway could be engaged by natural antibody recognition of neoepitopes expressed on injured myocytes or the release of intracellular components that engage C1q (30). The lectin pathway can similarly be activated by pattern recognition engagement of factors generated during injury (31).…”

The FSHD jigsaw: are we placing the tiles in the right position?

“…Tissue and circulating markers received little attention compared to image biomarkers, and no reliable biomarkers have been identified. Several groups found alterations in the circulating levels of several pro-inflammatory and regulatory cytokines (IL6) [33,34] or miRNAs that is, (miR-206) [35][36][37][38] and unsuccessfully investigated for the presence of disease-specific antibodies [39]. These molecules showed no disease specificity weakening their relevance for FSHD.…”

Outcome Measures in Facioscapulohumeral Muscular Dystrophy Clinical Trials

“…Clearly more studies with larger sample sizes, longitudinal evaluation, and increased diversity of disease severity are needed to verify the value of these biomarkers as outcome measures in FSHD studies. Notably, a recent study profiling serum antibody against muscle antigens in 138 FSHD patients did not find any disease-specific autoantibodies compared to control subjects [ 149 ]. DUX4 -related microRNA signatures in both FSHD skeletal muscles and serum have also been recently investigated [ 150 ].…”