THE EFFECTS OF FIBROBLAST GROWTH-FACTOR-II ON HUMAN NEONATAL CALVARIAOSTEOBLASTIC CELLS ARE DIFFERENTIATION STAGE-SPECIFIC

Fibroblast growth factors (FGFs) appear to play an important role in h uman cranial osteogenesis. We therefore investigated the effects of re combinant human FGF-2 (rhFGF-2) on human calvaria (HC) osteoblastic ce lls. Immunocytochemical analysis showed that confluent HC cells expres s both FGF receptors -1 and -2. In short-term culture, rhFGF-2 (0.1-10 0 ng/ml, 2-5 days) increased HC cell growth and decreased alkaline pho sphatase (ALP) activity and type I collagen (ColI) synthesis, as evalu ated by P1CP levels. When HC cells were induced to differentiate in lo ng-term culture in the presence of 50 mu g/ml ascorbic acid and 3 mM p hosphate, HC cells initially proliferated, then ALP activity and ColI synthesis decreased and calcium content in the extracellular matrix in creased. Continuous treatment with rhFGF-2 (50 ng/ml) for 1-28 days, o r a transient rhFGF-2 treatment for 1-7 days, slightly increased DNA s ynthesis at 7 days, whereas a late treatment for 8-28 days had no effe ct on cell growth. The continuous and transient treatments with rhFGF- 2 decreased ALP activity, ColI synthesis, and matrix mineralization. T his was associated with a transient fall in osteocalcin (OC) productio n at 7 days. In contrast, the late rhFGF-2 treatment for 8-28 days onl y slightly inhibited ALP activity and increased matrix mineralization. In addition, both continuous and late treatments with rhFGF-2 increas ed OC production in more mature cells at 3-4 weeks of culture. We also found that the early and late treatments with rhFGF-2 had opposite ef fects on transforming growth factor beta 2 production in proliferating cells and more mature cells. The results show that rhFGF-2 slightly s timulates cell growth and reduces the expression of osteoblast markers in less mature cells, whereas it induces OC production and matrix min eralization in more mature cells, indicating that the effects of FGF-2 are differentiation stage specific and that FGF-2 may modulate HC ost eogenesis by acting at distinct stages of cell maturation.