Human bone marrow osteoprogenitors express estrogen receptor-alpha and bone morphogenetic proteins 2 and 4 mRNA during osteoblastic differentiation

Understanding the mechanisms that control the proliferation and commitment of human stem cells into cells of the osteogenic lineage for the preservati on of skeletal structure is of basic importance in bone physiology. This st udy examines some aspects of the differentiation in vitro of human bone mar row fibroblastic cells cultured in the absence (basal media) or presence of 1 nM dexamethasone and 50 mu g/ml ascorbate for 6, 10, 14, and 21 days. No rthern blot analysis and in situ hybridisation with digoxygenin-labelled ri boprobes for Type I collagen, osteocalcin, bone morphogenetic proteins 2 (B MP-2), and 4 (BMP-4) and the estrogen receptor alpha (ER alpha), together w ith immunocytochemical analysis of ER alpha expression and histochemical st aining of alkaline phosphatase was performed. In basal media, alkaline phos phatase activity and collagen expressions were detected at day 6, ER alpha from day 10 and osteocalcin from day 10. In the presence of dexamethasone a nd ascorbate, cell proliferation and alkaline phosphatase were markedly sti mulated over 10 to 14 days with a dramatic increase in the temporal express ion of Type I collagen, ER alpha, and osteocalcin mRNAs in these cultures. Northern blot analysis showed cells cultured in basal media, expressed the highest levels of the mRNA for each marker protein at day 14, whereas in th e presence of ascorbate and dexamethasone, the highest levels for alkaline phosphatase, ER alpha, osteocalcin, BMP-2, and BMP-4 were observed at day 2 1. ER alpha, BMP-2, and BMP-4 expression were found to correlate temporally with induction of the osteoblast phenotype as determined by alkaline phosp hatase, collagen, and osteocalcin expression. These results give additional information on the development of the osteoblast phenotype from early fibr oblastic stem cells and on the biological factors involved in this process. These studies suggest a role for estrogen and BMP-2 and -4 in the differen tiation of osteoprogenitor cells. J. Cell. Biochem. 75:382-392, 1999. (C) 1 999 Wiley-Liss, Inc.