RGD Motif of BSP Functions in Periodontal Development and Maintenance

Objectives: The periodontal attachment complex includes cementum, periodontal ligament (PDL), and alveolar bone. Bone sialoprotein (BSP) is a multifunctional extracellular matrix (ECM) protein present in cementum and bone that promotes cell adhesion and signaling through an RGD integrin-binding motif. Bsp knock-out (KO) mice feature cementum and bone defects, and detachment of PDL. We hypothesized a role for RGD-initiated signaling in this phenotype and generated KAE-knock-in (KAE-KI) mice, replacing the RGD domain with a non-functional KAE sequence, to determine the importance of BSP signaling on dentoalveolar development.
Methods: Mandibles were harvested from KAE-KI and wild-type (WT) mice at 26 days postnatal (dpn) when root formation was complete and analyzed using radiology, microcomputed tomography, histology, immunohistochemistry.
Results: Radiographically and histologically, KAE-KI mice displayed normal molar and incisor teeth, cementum, PDL and alveolar bone structures, compared to WT controls. By H&E staining in histological sections, the PDL spaces of KAE-KI vs. WT mice exhibited trends towards increased cell density. Periostin is an ECM protein associated with PDL organization, and immunostaining indicated disturbed localization of this marker in KAE-KI vs. WT mice. Tartrate resistant acid phosphatase (TRAP) staining revealed 4-fold increase in osteoclastic activity along the alveolar bone surface in KAE-KI mice.
Conclusions: While the RGD motif of BSP is not critical for cementum and alveolar bone formation, the data suggest that it plays a significant role in maintaining the integrity of and remodeling of PDL tissues. Ongoing experiments are focused on detailing the specific role of the RGD motif of BSP in regulating dentoalveolar and skeletal tissues, with potential to apply the knowledge gained toward therapeutic interventions.