Idiopathic inflammatory myopathies and the classical NF-κB complex: Current insights and implications for therapy

The idiopathic inflammatory myopathies (IIM) comprise a heterogeneous group of muscle diseases. The three best-studied subgroups are dermatomyositis (DM), polymyositis (PM) and sporadic inclusion body myositis (IBM). The latter represents a steroid-refractory condition. PM and IBM are characterized by a cell-mediated immune response directed against non-necrotic fibers expressing Major Histocompatibility Complex class I (MHC class I). IBM presents with additional degenerative features, including rimmed vacuoles and depositions of aberrant proteins. DM is a complement-mediated endotheliopathy often accompanied by characteristic skin manifestations. The ubiquitously expressed transcription factor NF-κB is considered essential for the development of auto-immunity. This review describes data gathered so far concerning the distribution of the classical heterodimer p65/p50 and its inhibitor I-κBα in IIM skeletal muscle. Data suggest that the NF-κB complex plays a role in the endotheliopathy characterizing DM and might be involved in myofiber regeneration, and appoint CD4+ and CD68+ mononuclear cells with a more prominent role than previously assumed. Fragmentary knowledge of the immunopathogenesis of IIM hampers the development of therapeutic strategies suited to all patient groups. Unravelling the precise involvement of NF-κB subunits in IIM immunopathogenesis can shed new light onto the etiology of these diseases and may offer a novel therapeutic target.