Immunohistochemical Localization of SPARC (osteonectin) and Denatured Collagen and Their Relationship to Remodelling in Rat Dental Tissues

To study this relationship, specific antibodies were used to determine the distribution of these proteins in mature rat dental tissues. Staining for SPARC with affinity-purified polyclonal antibodies was prominent throughout molar and incisor ligaments, endosteal tissue, dental pulp and muscle. More moderate staining was observed in other soft tissues including the lamina propria of gingiva, whereas the staining of demineralized bone was weak and in dentine was barely detectable. A monoclonal antibody (MBP 322), raised against a denatured form of a small collagenous bone protein, reacted strongly with osteoblastic cells but more moderately with alveolar bone. A strong reaction, indicative of unfolded collagen, was also evident throughout the dental pulp and molar ligament, whereas in the incisor ligament staining was largely restricted to the tooth-related half. Moderate staining with this antibody was also observed in other soft tissues and in dentine. The monoclonal antibody also stained the nuclei of certain cells; notably, whereas most of the fibroblasts in the tooth-related half of the incisor ligament were stained strongly, only occasional nuclei of fibroblasts in the molar ligament and in the bone-related half of the incisor ligament showed immunoreactivity. The differential staining of nuclei provides evidence for phenotypic differences between fibroblast populations within these tissues. The prominence of SPARC in the ligament tissues is consistent with their embryonic characteristics, whereas unfolded collagen recognized by the MBP 322 antibody may indicate sites of rapid collagen remodelling.