Immunoreactive Localization of Transforming Growth Factor-β Type II Receptor-Positive Cells in Rat Tibiae

To identify the target cells of transforming growth factor-β (TGF-β) in normal bone tissue, we examined TGF-β type II receptor expression using immunohistochemistry, reverse transcription-polymerase chain reaction (RT-PCR), and in situ hybridization in young rat tibiae. In the epiphyseal growth plate, the TGF-β type II receptor cDNA was detected by RT-PCR and, alternatively, the TGF-β type II receptor protein and mRNA expression were observed in the chondrocytes in the lower part of the proliferative cell layer, and in maturative and hypertrophic cell layers by immunohistochemistry and in situ hybridization. Of these, proliferative and maturative chondrocytes, in particular, revealed strong mRNA expression. In the cortical bone area, immunoreactivity for the TGF-β type II receptor was detected in the fibroblastic cells near the osteoblasts on the endosteal surface of cortical bone. In conclusion, our findings suggest that target cells of TGF-β in normal bone tissue could be considered mainly as extracellular matrix-producing chondrocytes and undifferentiated preosteoblasts, and TGF-β may affect matrix production and differentiation of these cells.