Objectives: Osteopontin (OPN) is a non-traditional pro-inflammatory cytokine and is involved in muscle regeneration and inflammation. The aim of this study was to investigate the expression of OPN in skeletal muscle and serum of patients with IIMs.
Methods: 45 patients with IIMs (27 with PM and 18 with DM) were included in the study. Patients received initial prednisone therapy (1-1.5 mg/kg/day) without other immunosuppressive agents. Muscle biopsies were taken before start of treatment and serum samples were collected from each patient before and after corticosteroid treatment. The expression of OPN in skeletal muscle was using immunofluorescence staining and western blotting. Serum OPN levels were detected by enzyme-linked immunosorbent assays (ELISA).
Results: OPN expression was increased in muscle samples from IIM patients compared to control muscle. The serum level of OPN was significantly higher in IIM patients than in controls. Moreover, the serum concentrations in the DM subgroup were significantly higher compared to the PM groups. Serum OPN levels positively correlated with creatinine kinase (CK), C-reactive protein (CRP) in PM and DM patients, respectively. After corticosteroid treatment, serum OPN levels decreased significantly in steroid responders compared to baseline, but no significant decrease was observed in steroid non-responders.
Conclusions: OPN is increased in patients with DM and PM, both in muscle and serum. OPN may play an important role in the pathogenesis of IIMs. Moreover, serum OPN may be a potential biomarker for this illness, and changes in serum OPN may provide an index of therapeutic efficacy.