Expression of the H- and L-subunits of ferritin in bone marrow macrophages of patients with osteoarthritis

Abstract

Osteoarthritis is a disease characterized by an increase in the production of reactive oxygen species (ROS) in afflicted joints. Excess iron, due to its role in the production of ROS and crystal deposition in the joints, is implicated in the disease progression of osteoarthritis. Ferritin is a major regulator of the bioavailability of iron, and its functions are determined largely by the combination of H- and L-subunits present in its outer protein shell. The purpose of the study was to investigate the expression of the H- and L-subunits of ferritin in bone marrow macrophages of osteoarthritis patients. The cytokine profiles were assessed as cytokines play an important role in the expression of the ferritin subunits. The H-subunit of ferritin in the bone marrow macrophages was significantly higher (P value = 0.035) in the osteoarthritis patients compared with the controls (107.84; 69.25–167.94 counts/μm2; n= 7 versus 71.07; 58.56–86.26 counts/μm2; n= 19). A marginally significant increase (P value = 0.059) was shown for the expression of the L-subunit in the osteoarthritis patients compared with the controls (133.03; 104.04–170.10 counts/μm2; n= 7 versus 104.23; 91.53–118.70 counts/μm2; n= 19). The osteoarthritis and control groups had comparable C-reactive protein, as well as proinflammatory and anti-inflammatory cytokine concentrations. The major exception was for transforming growth factor-β (TGF-β), which was higher (P value = 0.014) in the plasma of the osteoarthritis patients (16.69; 13.09–21.28 ng/mL; n= 7 versus 8.60; 6.34–11.67 ng/mL; n= 19). Up-regulation of the ferritin subunits decreases the levels of bioavailable iron and provides protection against the unwarranted production of ROS and crystal deposition. A role for TGF-β in the up-regulation of the expression of the H-subunit, and possibly the L-subunit, of ferritin is postulated in osteoarthritis.