Differential in vitro phenotype pattern, transforming growth factor-β₁ activity and mRNA expression of transforming growth factor-β₁ in Apert osteoblasts

Abstract 

The phenotype of Apert osteoblasts differs from that of normal osteoblasts in the accumulation of macromolecules in the extracellular matrix. Apert osteoblasts increase type I collagen, fibronectin and glycosaminoglycans secretion compared with normal osteoblasts. Because the extracellular matrix macromolecule accumulation is greatly modulated by transforming growth factor-β₁, we examined the ability of normal and Apert osteoblasts to secrete transforming growth factor-β₁ by CCL-64 assay and to produce transforming growth factor-β₁ by analysis of the mRNA expression of transforming growth factor-β₁. Northern blot analysis revealed an increased amount of transforming growth factor-β₁ mRNA expression in Apert osteoblasts compared with normal ones. Moreover, the level of the active transforming growth factor-β₁ isoform was higher in Apert than in normal media. In pathologic cells, the increase in transforming growth factor-β₁ gene expression was associated with a parallel increase in the factor secreted into the medium. The level of transforming growth factor-β₁ was decreased by the addition of basic fibroblast growth factor. Transforming growth factor-β₁ is controlled temporally and spatially during skeletal tissue development and produces complex stimulatory and inhibitory changes in osteoblast functions. We hypothesise that in vitro differences between normal and Apert osteoblasts may be correlated to different transforming growth factor-β₁ cascade patterns, probably due to an altered balance between transforming growth factor-β₁ and basic fibroblast growth factor.