Collagen-Phagocytosing Ability of Periodontal Osteoblasts at the Bone Surface

Abstract

The collagen-phagocytosing activity of osteoblasts at the alveolar bone-ligament interface of rat mandibular first molars was investigated both histologically and histochemically. Alveolar bones of male Wistar rats (6 months old) were used in this study. Collagen-containing phagosomes appeared in cuboidal osteoblasts aligned on the bone surface. The 5.7% of the osteoblasts exhibiting alkaline phosphatase activity revealed collagen-containing phagosomes, and the collagen fibrils within the phagosomes were at various stages of degradation. In addition, acid phosphatase activity and the immunocytochemical distribution of cathepsin B were found in these collagen-containing phagosomes at similar locations. The presence of both enzymes in the phagosomes suggests that an intracellular degradation of collagen occurs. Therefore, in addition to the osteoblastic functions of synthesizing and secreting bone matrices, osteoblasts are also capable of phagocytosis and the intracellular disintegration of collagen. Our findings suggest that osteoblasts at the alveolar bone-periodontal ligament interface have a collagen-phagocytosing ability and play an important role in the physiological remodeling and metabolic breakdown of collagen fibrils of periodontal ligament without ostoclastic bone remodeling.