Chemotactic response of mesenchymal cells, fibroblasts and osteoblast-like cells to bone Gla protein.

Bone gla protein (BGP) and decarboxylated bone gla protein (dBGP) were tested for chemotactic activity against stage 24 chick limb bud mesenchymal cells, chick embryonic muscle-derived fibroblasts, murine Balb/C 3T3 cells, and two lines of rat osteosarcoma cells, ROS-17/2.8 and -25/1. Both BGP and dBGP were potent chemoattractants for all the cell types except 3T3 cells. The dose response curves were bell-shaped, with maximal chemotactic response ranging from 5 pg/ml for ROS 25/1 cells to 10 ng/ml for the stage 24 limb bud cells. dBGP was equally potent a chemoattractant as BGP for all cell types tested indicating that the gamma-carboxylation of the glutamic acid residues is not required for chemotactic activity. Given this chemotactic capability, it is possible that BGP acts in bone remodelling by attracting osteogenic cells to the sites of bone resorption where BGP may be liberated or exposed.