Chronic metabolic acidosis reversibly inhibits extracellular matrix gene expression in mouse osteoblasts

Abstract

Chronic metabolic acidosis induces net calcium efflux from bone mineral through an increase in osteoclastic resorption and a decrease in osteoblastic matrix deposition and mineralization. To determine the effects of chronic metabolic acidosis on the expression of genes necessary for mineralization, we grew primary bone cells, which are principally osteoblasts, to confluence in neutral pH (7.5) medium and then switched the cells either to a neutral pH or to an acidic pH (7.1) differentiation medium. Cells were harvested for RNA at 4- to 7-day intervals for up to 44 days. By 36 days, there was extensive bone nodule formation and mineralization in cells cultured in neutral medium; however, there was a substantial decrease in nodule formation and mineralization in cells cultured in acidic medium. There was a marked increase in matrix Gla protein RNA and an increase in osteopontin RNA in neutral cultures; however, acidic medium almost completely prevented any increase. In contrast, RNA levels for osteonectin and transforming growth factor-β1 were not altered by chronic acidosis. Additional cells were incubated in acid differentiation medium for 1, 2, or 3 wk and then transferred to neutral medium; in each case, there was recovery of matrix Gla protein RNA and osteopontin RNA expression. Still other cells were incubated in neutral differentiation medium for 1, 2, or 3 wk and then transferred to acid medium; in each case there was inhibition of matrix Gla protein RNA and osteopontin RNA expression. Thus metabolic acidosis appears to specifically inhibit RNA accumulation of certain genes whose products may be essential for formation of mature bone matrix.

Noggin Suppression Enhances in Vitro Osteogenesis and Accelerates in Vivo Bone Formation

“…MC3T3-E1 preosteoblasts were purchased from ATCC (Manassas, VA). Primary osteoblasts were harvested from 5-day-old CD-1 mice as previously described (27). Briefly, calvaria were harvested and parietal bones were trimmed under ϫ2.5 magnification to within 0.5 mm of each fibrous border.…”

In Vivo Modulation of FGF Biological Activity Alters Cranial Suture Fate

“…18 Osteoblast-enriched cell cultures (NRCs) derived from neonatal rat calvaria were established as previously described by Frick and colleagues. 19 First passage cells were used for all experiments.…”

Effect of metabolic and respiratory acidosis on intracellular calcium in osteoblasts

“…Met acidosis increases osteoblastic expression of cyclooxygenase 2 (COX-2) (47) and receptor activator of NF-B ligand (RANKL) (33,35), the latter which interacts with its osteoclastic receptor RANK to stimulate bone resorption. Met acidosis also alters osteoblastic extracellular matrix by decreasing expression of type 1 collagen (7,9,19,20,34,48), osteopontin, and matrix gla protein (31,32), which limits bone formation, and increases secretion of ␤-glucuronidase by osteoclasts (7,19,48), which stimulates bone resorption.…”