AGE-RELATED-CHANGES IN BONE-FORMATION OSTEOBLASTIC CELL-PROLIFERATION, AND DIFFERENTIATION DURING POSTNATAL OSTEOGENESIS IN HUMAN CALVARIA

We have determined the age-related changes in the growth characteristi cs and expression of the osteoblast phenotype in human calvaria osteob lastic cells in relation with histologic indices of bone formation dur ing postnatal calvaria osteogenesis. Histomorphometric analysis of nor mal calvaria samples obtained from 36 children, aged 3 to 18 months, s howed an age-related decrease in the extent of bone surface covered wi th osteoblasts and newly synthesized collagen, demonstrating a progres sive decline in bone formation during postnatal calvaria osteogenesis. Immunohistochemical analysis showed expression of type I collagen, bo ne sialoprotein, and osteonectin in the matrix and osteoblasts, with n o apparent age-related change during postnatal calvaria osteogenesis. Cells isolated from human calvaria displayed characteristics of the os teoblast phenotype including alkaline phosphatase (ALP) activity, oste ocalcin (OC) production, expression of bone matrix proteins, and respo nsiveness to calciotropic hormones. The growth of human calvaria osteo blastic cells was high at 3 months of age and decreased with age, as a ssessed by (H-3)-thymidine incorporation into DNA. Thus, the age-relat ed decrease in bone formation is associated with a decline in osteobla stic cell proliferation during human calvaria osteogenesis. In contras t, ALP activity and OC production increased with age in basal conditio ns and in response to 1,25(OH)(2) Vitamin D-3, suggesting a reciprocal relationship between cell growth and expression of phenotypic markers during human postnatal osteogenesis, Finally, we found that human cal varia osteoblastic cells isolated from young individuals with high bon e formation activity in vivo and high growth potential in vitro had th e ability to form calcified nodular bone-like structures in vitro in t he presence of ascorbic acid and beta-glycerophosphate, providing a ne w model to study human osteogenesis in vitro. (C) 1997 Wiley-Liss, Inc .