FUNCTIONAL-CHARACTERIZATION OF PROSTAGLANDIN E(2) INDUCIBLE OSTEOGENIC COLONY-FORMING-UNITS IN CULTURES OF CELLS ISOLATED FROM THE NEONATALRAT CALVARIUM

Prostaglandin E(2) (PGE(2)) increases the number of mineralized nodule s that form in cultures of rat calvarial (RC) cells. The purpose of ou r study was to characterize PGE(2)-inducible osteogenic colony forming units (CFU-Os) by determining their number, the cell populations from which they were released, their specific responsive period to PGE(2), and their proliferating and differentiating characteristics under the stimulation of PGE,. Limiting dilution analysis was used to determine the number of PGE(2)-inducible CFU-Os. Sequential digestion of intact rat parietal bones with collagenase isolated 5 subpopulations of RC c ells that were used to estimate the cell populations where PGE(2)-indu cible CFU-Os resided. The responsive period of PGE(2)-inducible CFU-Os to PGE(2) was evaluated by treating cultures of mixed RC cells for al l possible combinations of days 1-10, 11-20, and 21-30. PGE(2) effects on proliferation and differentiation of CFU-Os were evaluated by comp aring the DNA synthesis and AP activity in subpopulations I and IV on days 3, 6, and 9. Results showed: (i) PGE(2)-inducible CFU-Os represen t 0.27% of cells in the mixed RC population, (2) the majority of deter mined and PGE(2)-inducible CFU-Os were found in the subpopulations rel eased during the 60-100 min digestion periods, (3) the response of PGE (2)-inducible CFU-Os is limited to the first 10 days of culture, and ( 4) PGE(2)-stimulated nodule formation is associated with an early incr ease in DNA synthesis and a sustained increase in alkaline phosphatase activity. We conclude that, functionally, PGE(2)-inducible CFU-Os are slowly proliferating AP negative cells primarily found in the subpopu lations III-V. PGE, stimulates them to proliferate and become AP+, and function as determined CFU-Os to form mineralized nodules in vitro. ( C) 1996, Wiley-Liss, Inc.