Effect of extracellular calcium on the gene expression of bone morphogenetic protein-2 and -4 of normal human bone cells

Abstract

A high extracellular calcium level inhibits the formation of osteoclast-like cells and stimulates osteoblastic proliferation, indicating that extracellular calcium plays an important role in the process of bone remodeling. The present study examined the effects of a high extracellular calcium level on mRNA levels of bone morphogenetic protein (BMP)-2 and -4, which are well-documented osteoinductive proteins, and the differentiation of normal human mandible-derived bone cells in vitro. High extracellular calcium significantly increased cell proliferation at an optimal dose of 0.4 mM CaCl₂ added to control medium containing 1.8 mM CaCl₂. The addition of 0.1–0.4 mM CaCl₂ markedly increased the mRNA levels of BMP-2 and -4 following incubation for 0.5 and 24 h as evaluated by reverse transcription–polymerase chain reaction. While an increased extracellular calcium level (addition of 0.1–1.2 mM CaCl₂) failed to increase alkaline phosphatase activity and osteocalcin secretion, it did significantly increase type I collagen synthesis, monitored by the production of procollagen type I carboxy-terminal peptide. These results indicate that the extracellular calcium level regulates BMPs and type I collagen synthesis in osteoblastic cells.