Expression of Adhesion Molecules during Tooth Resorption in Feline Teeth: A Model System for Aggressive Osteoclastic Activity

Tooth resorption, a common feline dental problem, is often initiated at the cemento-enamel junction and hence is called cat 'neck' lesion. Studies have demonstrated that osteoclasts/odontoclasts are increased and activated at resorption sites, and that areas of resorption are partly repaired by formation of tissues resembling bone, cementum, and possibly dentin. However, the cellular/molecular mechanisms/factors involved in resorption and repair are unknown. In this study of tissues from cats with 'neck' lesions, we used specific antibodies and immunohistochemical analyses to examine adhesion molecules associated with mineralized tissues, bone sialoprotein (BSP) and osteopontin (OPN), and a cell-surface receptor linked with these molecules, α _vβ₃, for their localization in these lesions. In addition, to determine general cellular activity during repair, we performed in situ hybridization using a type I collagen riboprobe.

Results showed OPN localized to resorption fronts and reversal lines, while BSP was localized to reversal lines. However, some osteoclasts and odontoblasts "sat" on mineralized surfaces not associated with OPN. The cell-surface receptor, α_vβ ₃, was localized to surfaces of osteoclasts/odontoclasts. Type I collagen mRNA was expressed where osteoblasts attempted to repair mineralized tissue. In contrast, odontoblasts did not express mRNA for type I collagen. This study suggests that osteoclastic resorption is the predominant activity in 'neck' lesions and that this activity was accompanied, at least in part, by increased concentrations of OPN and an associated integrin, α _vβ₃, at resorption sites. Lack of collagen expression by odontoblasts indicates that odontoblasts do not play an active role in attempts at repair.