HMGB1, a new proinflammatory molecule of interest in polymyositis and dermatomyositis patients

Background

Polymyositis (PM) and dermatomyositis (DM) are chronic inflammatory muscle disorders of unknown origin. The ubiquitously expressed nuclear protein high mobility group box chromosomal protein 1 (H MGB1) will, when released extracellularly, act as a potent proinflammatory molecule.

Objective

To investigate H MGB1 expression in muscle tissue from PM and DM patients with and without inflammatory infiltrates present in their muscle biopsy.

Methods

Muscle biopsy specimens from 10 patients (6 PM, 4 DM) with and 14 patients (8 PM, 6 DM) without inflammatory cell infiltrates and 8 healthy controls were investigated. H MGB1 expression was studied by immunohistochemical staining.

Results

Patients with inflammatory cell infiltrates show H MGB1 staining mainly with a cytoplasmic localization in vascular endothelial cells, infiltrating rounded mononuclear cells of macrophage-like morphology for all patients and in muscle fibres in 6 of 10 patients. In patients without inflammatory infiltrates, H MGB1 was detected in 3 of 14 patients, all with DM, in endothelial cells with a cytoplasmic manner, there was no H MGB1 expression in the muscle fibres. No cytoplasmic or nuclear H MGB1 expression was found in the muscle tissue specimens from healthy controls.

Conclusion

H MGB1 was detected in muscle biopsies from PM and DM patients with inflammatory cell infiltrates. H MGB1 could play a role in maintaining the chronic inflammation. The major cell source of H MGB1 production in myositis seems to be the mononuclear inflammatory cells. H MGB1 could be a molecule of potential interest for new targeted therapy in myositis.