Macrophage exposure to particulate titanium induces phosphorylation of the protein tyrosine kinase lyn and the phospholipases Cγ-1 and Cγ-2

Abstract

A frequent long-term complication of total joint arthroplasty is aseptic loosening, the end result of wear debris production, synovial macrophage activation, inflammatory mediator release, and osteolysis about the implant–bone or cement–bone interface. To elucidate the mechanisms of particle-induced macrophage activation and mediator production, we studied early signal transduction events using J774A.1 macrophages and 3 μm titanium particles. Treating macrophages with herbimycin A or genistein, two inhibitors of protein tyrosine kinases (PTKs), inhibited titanium phagocytosis as well as secretion of tumor necrosis factor-α (TNF-α) and prostaglandin-E 2 (PGE 2) in a dose-dependent manner. Both processes therefore depend on a PTK signaling cascade. Specifically, macrophage exposure to titanium-induced phosphorylation of multiple proteins including the Src kinase Lyn and phospholipase Cγ-1 and Cγ-2. Phosphorylation peaked within 2 min and returned to baseline within 45 min. Similar but not identical phosphorylation patterns were obtained when cells were stimulated with titanium preincubated with serum or albumin, suggesting distinct signal transduction pathways dependent on particle coating.