Importance of Dexamethasone in Mineralised Matrix Production in Saos-2 Cells.

Objectives: A mature osteoblast-like human osteosarcoma cell line, Saos-2, was selected as a model to study the effects of osteogenic media components on the production of mineralised matrix in vitro. A combination of ß-glycerophosphate (ß-Gly), dexamethasone (Dex) and ascorbic acid (Asc) is routinely used to induce osteogenic differentiation and mineral production by cells, where ß-Gly acts as an organic phosphate ion source for mineral deposition, Dex induces osteoblastic differentiation and Asc is involved in collagen-I synthesis, required for extracellular matrix production. The aim of this study was to determine whether Dex was necessary to stimulate relatively differentiated Saos-2 cells to synthesise mineralised bone matrix.
Methods: Cells were exposed to different combinations of osteogenic media containing 1% ß-Gly (0.2 g/ml), 1% Dex (10^-6M) and 0.5% Asc (10 mg/ml) for 7 days. Cells were counted, and the mineralised matrix production was measured using alizarin red staining. The gene expression of osteocalcin, a late marker for bone formation and collagen-I was analysed using reverse transcription PCR.
Results: Addition of Dex did not significantly affect the expression of osteocalcin, collagen-I or mineral deposition of Saos-2 cells. Treatment of cells with ß-Gly increased the production of mineralised matrix by approximately 94% and decreased cell numbers by 63% compared with the cells receiving no ß-Gly supplementation. Asc did not have a significant impact on the mineral deposition, but upregulated the expression of collagen-I.
Conclusions: Our results suggested that Dex does not play role in the osteogenic behaviour of the Saos-2 cell line. However, ß-Gly and Asc appear to have an impact on the amount of matrix produced and collagen-I expressed respectively. Further analysis using quantitative wavelength-dispersive X-ray spectroscopy of the deposited matrix is necessary to exclude the possibility of dystrophic mineralisation in the absence of Dex.