Differential expression of fibroblast growth factor receptor-1, -2, and -3and syndecan-1, -2, and -4 in neonatal rat mandibular condyle and calvariaduring osteogenic differentiation in vitro

Fibroblast growth factors (FGFs) play important roles in the control of ske letal cell growth and differentiation. To identify the mechanisms of regula tion of FGF actions during chondrogenesis and osteogenesis, we investigated , by immunohistochemistry, the spatiotemporal expression of the high-affini ty FGF receptors (FGFR-1, -2, and -3) and coreceptors (syndecans-1, -2, and -4) in newborn rat condyle and calvaria during chondrogenesis and osteogen esis in vitro. During chondrogenesis at 4 days of culture, condyle chondroc ytes showed weak FGFR-1, FGFR-2, and syndecan-1 immunoreactivity; stronger syndecan-2 expression; and marked FGFR-3 and syndecan-4 immunolabeling. At a later stage (i.e,, 9 days of culture), FGFR-1, -2, and -3 were coexpresse d with syndecan-4 in chondrocytes. Condyle progenitor cells located in the condyle perichondrium initially expressed strong syndecan-2 and -4 and weak syndecan-1 labeling, whereas no FGFR was detectable. When these cells diff erentiated into osteoblasts, they expressed syndecan-2 and -4 coincidently with FGFR-1, -2, and -3 at 9 days of culture. In newborn rat calvaria, synd ecan-1, -2, and -4 were coexpressed mainly with FGFR-1 and -2 in osteoblast s, in the two models, treatment with FGF-2 (100 ng/mL) at 4-9 days of cultu re increased cell growth and decreased glycosaminoglycan or collagen synthe sis, respectively, suggesting interactions of FGF-2 with distinct FGFRs and syndecans during chondrogenesis and osteogenesis, The coincident or distin ct spatiotemporal expression pattern of FGFRs and syndecans in chondrocytes , progenitor cells, and osteoblasts represents a dynamic mechanism by which FGF effects on skeletal cells may be controlled in a coordinate manner dur ing cartilage and bone formation in vitro. (C) 1999 by Elsevier Science Inc . All rights reserved.