Abstract
Immune cells are involved in the pathogenesis of osteoarthritis (OA). CD4(+) T cells were activated during the onset of OA and induced macrophage inflammatory protein (MIP)-1γ expression and subsequent osteoclast formation. We evaluated the effects of local knockdown of MIP-1γ in a mouse OA model induced by anterior cruciate ligament transection. The mouse macrophage cell lines and osteoclast-like cells generated from immature hematopoietic monocyte/macrophage progenitors of murine bone marrow were cocultured with either receptor activator of NFκB ligand (RANKL) or CD4(+) T cells. The levels of MIP-1γ and RANKL in cells and mice were examined by enzyme-linked immunosorbent assay (ELISA). The osteoclastogenesis was evaluated using tartrate-resistant acid phosphatase and cathepsin K staining. OA was induced in one hind-leg knee joint of B6 mice. Lentiviral vector encoding MIP-1γ small hairpin RNA (shRNA) and control vector were individually injected intra-articularly into the knee joints, which were histologically assessed for manifestations of OA. The expression of MIP-1γ and matrix metalloproteinase (MMP)-13 and the infiltration of CD4(+) T cells, macrophages, and osteoclastogenesis in tissues were examined using immunohistochemistry. CD4(+) T cells were involved in OA by inducing MIP-1γ expression in osteoclast progenitors and the subsequent osteoclast formation. Neutralizing MIP-1γ with a specific antibody abolishes RANKL-stimulated and CD4(+) T-cell-stimulated osteoclast formation. MIP-1γ levels were significantly higher in synovium and the chondro-osseous junction of joints 90 days postsurgery. The number of infiltrated CD4(+) T cells and macrophages and IL-1β expression were reduced in the synovial tissues of mice treated with MIP-1γ shRNA. Histopathological examinations revealed that mice treated with MIP-1γ shRNA had less severe OA than control mice had, as well as decreased osteoclast formation and MMP-13 expression. Locally inhibiting MIP-1γ expression may ameliorate disease progression and provide a new OA therapy.