Analysis of TGFbeta3 gene expression and protein levels in human bone and serum

Recent data indicate that TGFbeta3, one member of the TGFbeta-isoforms, has an important role in bone remodeling. Up to date little is known about the expression and regulation of TGFbeta3 in man. We established a highly specific ELISA for quantitative measurement of TGFbeta3 in bone and blood samples and a RT-PCR in combination with HPLC for detection and quantification of TGFbeta3 mRNA in 89 human bone samples. Levels of TGFbeta3 protein ranged between 30 and 66 pg/mg bone (mean 36,6 +/-1,03 pg/mg) and between 30 and 1910 pg/ml in serum (mean 128.9+/-38.9 pg/ml). TGFbeta3 mRNA expression as well as protein levels in serum and in bone declined age dependently. No specific load- or site-specific distribution of TGFbeta3 mRNA expression or protein content was detected at different sites indicating an absence of mechanical regulation. Protein levels of TGFbeta3 in serum correlated with TGFbeta3 mRNA expression in bone (p= 0.0027; r=0.49). By contrast, TGFbeta3 protein levels stored in the bone matrix were not related to TGFbeta3 mRNA reflecting the long term process of TGFbeta3 deposition during bone remodeling. Notably TGFbeta3 serum levels were highly correlated with IGF-I and osteocalcin levels in serum. We conclude that TGFbeta3 in man circulates in significant amounts which appears to be representative for TGFbeta3 expression in bone tissue and may be in part derived from bone. The high correlation of TGFbeta3 with IGF-I suggests parallel systemic principles of regulation.