Expression of cartilage-derived retinoic acid-sensitive protein during healing of the rat tooth-extraction socket

Cartilage-derived retinoic acid sensitive protein (CD-RAP) is a recently de scribed, cartilage-specific protein. During early healing of the tooth-extr action socket,. cells express both chondrogenic and osteogenic cell markers , but no cartilage is formed. Cartilaginous collagen type II protein, a maj or constituent of hyaline cartilage, has not been detected in the healing s ocket, although type IX collagen, which coats these fibres, has been detect ed transiently in early socket healing. This study investigated the spatial and temporal expression of CD-RAP and various osteoblast cell markers, i.e ., alkaline phosphatase, osteopontin, osteonectin and osteocalcin, during h ealing. Immunolocalization of these proteins was determined in the rat toot h socket at 3, 4, 5, 6, 7, 8, 10 and 14 days after extraction. CD-RAP was e xpressed by preosteoblast cells maximally at 6, 7, and 8 days after extract ion. Fully differentiated osteoblasts expressed osteocalcin, a specific ost eoblast marker. Preosteoblasts and fibroblasts did not express osteocalcin. On double immunofluorescent staining, some preosteoblasts coexpressed CD-R AP (indicative of chondrogenic differentiation), and either alkaline phosph atase or osteopontin (markers of osteogenic stem-cell maturation). There wa s no colocalization between osteopontin and osteonectin. CD-RAP was unique amongst the cell markers used in that it was expressed by preosteoblasts, b ut not by osteoblasts lining the newly formed trabeculae. CD-RAP may have a n important role in osteoblast cell differentiation during bone healing. (C ) 1999 Elsevier Science Ltd. All rights reserved.