The role of sialoproteins in recognition of bone surface by osteoblasts via integrin

To investigate the roles of collagenous and non-collagenous bone proteins in the early mineralization process by osteoblasts, we have examined the expression of several typical bone proteins (collagen Type I, fibronectin, osteopontin, BSP, osteonectin and osteocalcin) on rat bone marrow derived osteoblastic primary cells (RBMO), using SEM, AFM and laser confocal microscopes. The results suggest that the collagen Type I, osteopontin and BSP play important roles in early biomineralization. To study the roles of these bone proteins at the molecular level, we designed and synthesized the β-peptide (113–125) derived from a conserved sequence of the β subunit of integrins. The β-peptide proved to be a good tool for studying the adhesion properties of bone proteins to integrin by solid phase binding assay of the β-peptide to fibrinogen and fibronectin. The solid phase binding assay suggested that the β-peptide could bind to the collagen Type I and osteopontin. Moreover, the RBMO adhered more strongly to sialoproteins such as osteopontin than to collagen Type I. This suggests that pre-osteoblasts attach to the bone surface and differentiate into osteoblasts by recognizing sialoproteins. This paper reviews our recent results, relating the role of sialoproteins in the recognition of bone surface via integrin by osteoblasts.