Transforming growth factor beta (TGF-beta) levels in the conditioned media of human bone cells: relationship to donor age, bone volume, and concentration of TGF-beta in human bone matrix in vivo.

Transforming growth factor-beta (TGF-beta) is thought to play an important role in human bone remodeling. In the present study, we examined constitutive differences in TGF-beta levels in primary bone cell cultures from the iliac crest of 112 women, aged 28-79 years. TGF-beta1 was the major TGF-beta isoform in the conditioned media, as determined by neutralizing TGF-beta activity with specific antibodies against TGF-beta1-3 in the mink lung cell bioassay, and by enzyme-linked immunoassay (ELISA). TGF-beta1 levels in the conditioned media did not change with donor age. There was a lack of association between TGF-beta levels in vitro and the concentration of matrix-associated TGF-beta in vivo. TGF-beta1 levels failed to be associated with the local trabecular bone volume in the complete study population (r = +0.15, p = 0.16, n = 89). A significant association between TGF-beta1 levels and bone volume was present in premenopausal women (r = +0.39, p = 0.02, n = 33), but was largely accounted for by the two samples with the highest TGF-beta concentrations. In conclusion, our data suggest that TGF-beta1 is the major TGF-beta isoform produced by human bone cells in vitro, and that the constitutive secretion of TGF-beta by bone cells does not change with age. Whether constitutive differences in TGF-beta secretion may be a determinant of human bone mass remains to be clarified in further studies.