Biphasic effects of epidermal growth factor on bone nodule formation by isolated rat calvaria cells in vitro

Osteoblast-like cells isolated from fetal rat calvaria (RC) form three-dimensional nodules in vitro having the morphological and immunohistochemical characteristics of bone. When administered continually over 21 days of culture, EGF caused a dose-related inhibition of nodule formation, as well as a reduction in the proportion of mineralized nodules, at concentrations between 10(-12) to 10(-7) M. The same conditions caused an increase in both cell proliferation and saturation density in the cultures, suggesting that decreased nodule formation was not the result of general cell toxicity. Inhibitory concentrations of EGF caused a reversible alteration in cell shape, although changes in protein synthesis were not detectable. Indomethacin (5 X 10(-7) M) did not affect either nodule formation or its inhibition by EGF. When cultures were pretreated for various time periods with 10(-8) M EGF followed by its removal and continued culture in supplemented medium for 21 days, the number of bone nodules formed with brief exposures to EGF (4 hr up to 48 hr) was increased compared to the numbers formed in supplemented medium alone, whereas exposures to EGF of 4 days or longer decreased the number of nodules formed. These data indicate that EGF can either increase or decrease the osteogenic potential of RC cells in vitro depending on the duration of exposure to the factor.