Chemotactic response of osteoblastlike cells to transforming growth factorβ

Transforming growth factor β (TGF‐β) 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‐β 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‐β and was observed with TGF‐β₁ and TGF‐β₂ at equivalent concentrations. Conditioned medium from osteoblastlike cells containing latent TGF‐β 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‐β, these results suggest that only active TGF‐β is capable of inducing a chemotactic response. Preincubation of osteoblastlike cells with TGF‐β in concentrations from 10 pg/ml to 1 ng/ml for 48 h abolished a subsequent chemotactic response of these cells to TGF‐β, indicating that TGF‐β‐induced chemotaxis is a transient phenomenon. Since TGF‐β may be released from the bone matrix and/or activated during bone resorption, the chemotactic activity of TGF‐β for osteoblastlike cells may be important for the recruitment of osteoblastlike cells to sites of bone remodeling.