Osteopontin mediates macrophage chemotaxis via alpha sub(4) and alpha sub(9) integrins and survival via the alpha sub(4) integrin

Osteopontin (OPN) is highly expressed by macrophages and plays a key role in the pathology of several chronic inflammatory diseases including atherosclerosis and the foreign body reaction. However, the molecular mechanism behind OPN regulation of macrophage functions is not well understood. OPN is a secreted molecule and interacts with several integrins via two domains: the RGD sequence binding to alpha sub(v)-containing integrins, and the SLAYGLR sequence binding to alpha sub(4) beta sub(1), alpha sub(4) beta sub(7), and alpha sub(9) beta sub(1) integrins. Here we determined the role of OPN in macrophage survival, chemotaxis, and activation state. For survival studies, OPN treated-bone marrow derived macrophages (BMDMs) were challenged with growth factor withdrawal and neutralizing integrin antibodies. We found that survival in BMDMs is mediated primarily through the alpha sub(4) integrin. In chemotaxis studies, we observed that migration to OPN was blocked by neutralizing alpha sub(4) and alpha sub(9) integrin antibodies. Further, OPN did not affect macrophage activation as measured by IL-12 production. Finally, the relative contributions of the RGD and the SLAYGLR functional domains of OPN to leukocyte recruitment were evaluated in an in vivo model. We generated chimeric mice expressing mutated forms of OPN in myeloid-derived leukocytes, and found that the SLAYGLR functional domain of OPN, but not the RGD, mediates macrophage accumulation in response to thioglycollate-elicited peritonitis. Collectively, these data indicate that alpha sub(4) and alpha sub(9) integrins interacting with OPN via the SLAYGLR domain play a key role in macrophage biology by regulating migration, survival, and accumulation. J. Cell. Biochem. 114: 1194-1202, 2013. copyright 2012 Wiley Periodicals, Inc.