Objective: To assess the expression and processing of a disintegrin and metalloproteinase, ADAM 12 (meltrin-alpha), in the formation of multinuclear cells. Methods. In situ hybridization, immunohistochemical staining, and Western blotting of interface membrane around loosened total hip replacement implants. Macrophage-colony stimulating factor (M-CSF) and receptor activator of nuclear factor-kappaB ligand (RANKL) costimulation of human monocytes followed by FACS, immunofluorescence staining, Western blotting, and bone resorption assay.
Results: ADAM 12 mRNA-containing mononuclear cells were often seen in a close spatial relationship with ADAM 12-positive multinuclear cells. Morphometric analysis of ADAM 12 disclosed that 53% +/- 2% of all interface cells were ADAM 12-positive compared to 5% +/- 1% in controls (p < 0.001). M-CSF and RANKL were richly present in interface tissue around loosening implants. Upon M-CSF and RANKL costimulation of human monocytes in vitro, the ADAM 12 staining pattern changed over time, and ADAM 12-positive cells formed large mono-, bi-, and multinuclear cells at Day 7 and many multinuclear giant cells and/or osteoclasts at Day 14. Western blot disclosed 90 kDa latent ADAM 12L but also the metalloproteinase-cleaved, fusion-active 60 kDa form transiently just before the burst of fusion.
Conclusion: ADAM 12, well recognized for participation in cell-cell fusion in myoblast formation, is upregulated and processed upon formation of multinuclear giant cells and osteoclasts. It may play a role in formation of giant cells and osteoclasts around loosened total hip replacement implants.