Effects of TGF-beta 2 on mineral resorption in cultured embryonic mouse long bones; 45Ca release and osteoclast differentiation and migration.

To study the effects of transforming growth factor beta 2 (TGF-beta 2) on bone resorption, cultures of 17-day-old foetal mouse metatarsal long bones were used. The long bone rudiments were cultured for 5 days in medium supplemented with 10% rat serum. The effects of TGF-beta 2 were studied at concentrations of 1, 4, and 10 ng/ml. At all concentrations TGF-beta 2 caused a significant reduction in osteoclastic resorption measured as release of 45Ca from prelabelled bones. The same long bones were subsequently used for histological evaluations. Pre-osteoclasts and osteoclasts were identified as tartrate resistant acid phosphatase (TRAP) positive cells in the mineralized diaphysis, the periosteum around the diaphysis, and the perichondrium around the cartilaginous ends. The distribution of TRAP-positive cells over the three compartments showed that TGF-beta 2 inhibited the migration of TRAP-positive cells from the periosteum into the mineralized diaphysis in a dose dependent manner. In addition, TGF-beta 2 had a biphasic effect on TRAP cell differentiation, as 1 ng/ml increased, but 4 ng/ml and higher decreased TRAP cell numbers. We conclude that TGF-beta 2 is a potent regulator of osteoclastic bone resorption, by modulating both osteoclast migration and osteoclast differentiation.