Induction of chemokines and chemokine receptors CCR2b and CCR4 in authentic human osteoclasts differentiated with RANKL and osteoclast like cells differentiated by MCP‐1 and RANTES

Abstract

Chemokines MCP‐1 and RANTES are induced when authentic bone resorbing human osteoclasts differentiate from monocyte precursors in vitro. In addition, MCP‐1 and RANTES can stimulate the differentiation of cells with the visual appearance of osteoclasts, being multinuclear and positive for tartrate resistance acid phosphatase (TRAP +). We show here that MIP1α is also potently induced by RANKL during human osteoclast differentiation and that this chemokine also induces the formation of TRAP + multinucleated cells in the absence of RANKL. MIP1α was able to overcome the potent inhibition of GM‐CSF on osteoclast differentiation, permitting the cells to pass through to TRAP + multinuclear cells, however these were unable to form resorption pits. Chemokine receptors CCR2b and CCR4 were potently induced by RANKL (12.6‐ and 49‐fold, P = 4.0 × 10⁻⁷ and 4.0 × 10⁻⁸, respectively), while CCR1 and CCR5 were not regulated. Chemokine treatment in the absence of RANKL also induced MCP‐1, RANTES and MIP1α. Unexpectedly, treatment with MCP‐1 in the absence of RANKL resulted in 458‐fold induction of CCR4 (P = 1.0 × 10⁻¹⁰), while RANTES treatment resulted in twofold repression (P = 1.0 × 10⁻⁴). Since CCR2b and CCR4 are MCP‐1 receptors, these data support the existence of an MCP‐1 autocrine loop in human osteoclasts differentiated using RANKL. J. Cell. Biochem.