| 2902 Role of Osteopontin in Macrophage Chemotaxis | ||
|
J. SODEK1, B. ZHU2, A. PAES DA SILVA2, M. BANSAL2, A. BANSAL2, G.K. HUNTER3, and H.A. GOLDBERG4, 1University of Toronto, CIHR Group in Matrix Dynamics, Faculty of Dentistry, Canada, 2University of Toronto, 3University of Western Ontario, London, Canada, 4University of Western Ontario, Faculty of Dentistry, London, Canada Chemotaxis of macrophages is a critical part of the cellular immune response in which osteopontin (OPN) has a major role. Thus, previous studies have shown that OPN acts as a chemoattractant for macrophages and is required for G-protein-receptor-coupled chemotaxis of peritoneal macrophages to fMLP. However, different post-translationally modified (PTM) forms of OPN appear to mediate these effects. Objectives: To elucidate the forms of OPN that regulate macrophage chemotaxis and the mechanisms involved. Methods: Chemotaxis of murine macrophage RAW264.7 cells and peritoneal macrophages from OPN+/+ and OPN-/- mice were analyzed in Transwell chambers. The effects of different forms of OPN were tested for their ability to promote chemotaxis and to rescue fMLP-mediated chemotaxis. Results: Native PTM-OPN (nOPN), recombinant (rOPN), RGD-mutated recombinant (rOPNm) and amino-terminal fragments of OPN all induced macrophage chemotaxis and their effects were blocked by anti-CD44 antibodies. These results indicate that chemotaxis of macrophages by OPN is mediated by the CD44 receptor and that modification of the OPN is not required. In contrast only PTM-OPN (nOPN), as a substratum or in culture medium at high concentration, could rescue the impaired migration of OPN-/- macrophages to fMLP. Although the rescue appeared to involve the avb3 receptor, neither vitronectin nor bone sialoprotein could rescue the OPN-/- cells, indicating selectivity for PTM-OPN. That CSF-1, which signals through a protein tyrosine kinase (PTK) receptor, could also rescue fMLP-induced chemotaxis of OPN-/- cells suggested that signalling through integrins or PTK receptors can circumvent the impaired chemotaxis, possibly through the activation of PI3-kinase. Impaired chemotaxis of OPN-/- macrophages appears to involve CD44 expression, which is reduced in OPN-/- cells, since CD44+/- macrophages show a similar profile of impaired chemotaxis. Conclusions: These studies have shown that different forms of OPN can both directly and indirectly regulate chemotaxis of macrophages through interactions involving the CD44 receptor. | ||
| Seq #307 - Osteoclast Differentiation and Function 8:00 AM-9:30 AM, Saturday, 13 March 2004 Hawaii Convention Center 315 | ||
|
Back to the Mineralized Tissue Program
| ||