LOX-1 expressed in cultured rat chondrocytes mediates oxidized LDL-induced cell death-possible role of dephosphorylation of Akt.

The oxidative changes of lipids in cartilage proceed with ageing and with the grade of osteoarthritis. To clarify the role of oxidatively modified lipids in articular cartilage in osteoarthritis, here, we investigated lectin-like oxidized LDL receptor (LOX-1) in rat cultured articular chondrocytes. LOX-1 expression was detectable in basal culture condition and enhanced by the treatment of oxidized LDL and interleukin-1beta. DiI-labeled oxidized LDL was bound and ingested by chondrocytes via LOX-1. Oxidized LDL dose-dependently reduced chondrocyte viability, inducing non-apoptotic cell death, which was again suppressed by anti-LOX-1 antibody treatment. Oxidized LDL reduced the amount of phosphorylated Akt, a substrate of PI3 kinase via LOX-1. Consistently, the PI3 kinase inhibitor, LY294002, decreased cell viability dose-dependently, and the PI3 kinase activator, IGF-I, reversed the effect of oxidized LDL on the cell death. LOX-1 might be involved in the pathogenesis of osteoarthritis, inducing chondrocyte death through PI3 kinase/Akt pathway.

Lectin-like oxidized low-density lipoprotein receptor 1 mediates leukocyte infiltration and articular cartilage destruction in rat zymosan-induced arthritis.

OBJECTIVE: The relationship between rheumatoid arthritis and atherosclerosis has been recognized for >20 years. This study aimed to elucidate the roles of oxidized low-density lipoprotein (ox-LDL; one of the main pathogenic factors of atherosclerosis) and its endothelial receptor, lectin-like ox-LDL receptor 1 (LOX-1), in arthritic joints using a rat zymosan-induced arthritis (ZIA) model. METHODS: LOX-1 expression and ox-LDL accumulation in arthritic joints were detected by immunohistochemistry using specific mouse anti-LOX-1 and anti-ox-LDL monoclonal antibodies, respectively. To elucidate the effects of the expressed LOX-1 on arthritis, ZIA rats were treated with anti-LOX-1 antibody or normal mouse IgG. The severity of arthritis was analyzed by joint swelling. Cell infiltration, synovial hyperplasia, and proteoglycan losses were also determined by histologic scoring. Proinflammatory cytokine and nitrite levels in serum and joint fluid were also measured. RESULTS: Immunohistochemical study of ZIA demonstrated LOX-1 expression on synovial endothelium and postcapillary venules at 6 hours after the induction of inflammation, with maximum expression detected at 24 hours. LOX-1 was also expressed weakly on both joint cartilage and synovium. Ox-LDL, a ligand of LOX-1, was also detected in articular chondrocytes. Administration of anti-LOX-1 antibody, which blocks LOX-1 activity, suppressed joint swelling (by 33.5%), leukocyte infiltration, and joint nitrite accumulation at 24 hours, as well as cartilage destruction at 7 days, compared with control rats. CONCLUSION: LOX-1 induction in arthritic joints might play a role in promoting joint inflammation and cartilage destruction by mediating leukocyte infiltration into the arthritic joints of ZIA rats.