Myositis-specific autoantibodies recognising Mi2 also target the AIRE protein at a shared PHD zinc finger.

OBJECTIVES

In patients with dermatomyositis with anti-Mi2 autoantibodies, autoantibodies can enter muscle cells, leading to the aberrant expression of genes normally repressed by the Mi2/nucleosome remodelling and deacetylation (NuRD) complex. However, the mechanism by which autoantibodies interfere with Mi2/NuRD function remains unclear. This study aimed to identify additional autoantibodies in anti-Mi2-positive patients and the epitopes recognised by these autoantibodies.

METHODS

Phage immunoprecipitation sequencing (PhIP-Seq) was used to screen sera from patients with anti-Mi2 autoantibody-positive myositis. Enzyme-linked immunosorbent assays (ELISAs) and luciferase immunoprecipitation system (LIPS) immunoassays were used to detect autoantibodies in sera from healthy controls, patients with myositis, and those with other autoimmune diseases.

RESULTS

PhIP-Seq identified autoantibodies recognising the autoimmune regulator (AIRE) in sera from anti-Mi2 autoantibody-positive patients. Both anti-AIRE and anti-Mi2 autoantibodies predominantly recognised a homologous region containing the plant homeodomain zinc finger type I (PHD1), which is critical for AIRE and Mi2/NuRD function. ELISA and LIPS showed that anti-Mi2 autoantibody-positive patients were positive for anti-AIRE autoantibodies, whereas AIRE reactivity was largely absent in healthy comparators, anti-Mi2 autoantibody-negative myositis, and other autoimmune diseases. Affinity-purified anti-Mi2 autoantibodies recognised both Mi2 and AIRE by ELISA, whereas anti-Mi2-depleted fractions did not recognise either protein.

CONCLUSIONS

Autoantibodies targeting Mi2 recognise AIRE at a shared PHD1 epitope - a conserved motif found in numerous transcriptional regulators. These findings support a model in which anti-Mi2 autoantibodies disrupt the Mi2/NuRD complex, and potentially other PHD1-containing proteins, by interfering with chromatin binding, although further studies are needed to directly demonstrate this mechanism in vivo.