Chemotactic response of osteoblastlike cells to transforming growth factor beta

Transforming growth factor beta (TGF-beta) has multiple effects on bone cell metabolism in vitro but its exact role in bone remodeling still needs to be defined. Here we demonstrate that TGF-beta is chemotactic for osteoblastlike cells from fetal rat calvariae and osteoblastlike ROS 17/2.8 osteosarcoma cells. Maximal chemotaxis occurred at 5-15 pg/ml of TGF-beta and was observed with TGF-beta 1 and TGF-beta 2 at equivalent concentrations. Conditioned medium from osteoblastlike cells containing latent TGF-beta failed to stimulate chemotactic migration. However, chemotactic activity was observed in conditioned medium that had been transiently acidified. Since acidification is known to activate TGF-beta, these results suggest that only active TGF-beta is capable of inducing a chemotactic response. Preincubation of osteoblastlike cells with TGF-beta in concentrations from 10 pg/ml to 1 ng/ml for 48 h abolished a subsequent chemotactic response of these cells to TGF-beta, indicating that TGF-beta-induced chemotaxis is a transient phenomenon. Since TGF-beta may be released from the bone matrix and/or activated during bone resorption, the chemotactic activity of TGF-beta for osteoblastlike cells may be important for the recruitment of osteoblastlike cells to sites of bone remodeling.