Methods: The expression of Cyr61 and NF-kB pathway molecules was examined by Western blotting. CCL2 expression was assessed by Northern blotting and enzyme-linked immunosorbent assay (ELISA). Interaction between NF-kB and Cyr61 promoter was evaluated by electrophoretic mobility shift assay (EMSA). In rat CIA, osteoblastic expression of Cyr61 was examined by immunohistochemistry and disease progression was assessed by clinical, radiographic, and histologic examinations.
Results: EGCG inhibits cytokine-stimulated Cyr61 expression in human bone marrow-derived osteoblasts and U2OS cells. In U2OS, EGCG attenuates mTOR/rictor/Akt/NF-κB activation induced by oncostatin M(OSM), and suppresses OSM/Cyr61-stimulated CCL2 expressions. Co-distribution of CD68+ macrophages and Cyr61+ osteoblasts in osteolytic areas was obvious in CIA model. Clinical, radiographic, and immunohistochemical analyses revealed that administration of EGCG markedly diminished the severity of CIA, macrophage infiltration, and the number of Cyr61-synthesizing osteoblasts.
Conclusions: By modulating the mTOR/rictor/Akt/NF-κB pathway, EGCG attenuated Cyr61 production in osteoblastic cells and in turn diminished macrophage chemotaxis. Our data support the therapeutic potential of EGCG on arthritis.