Novel Roles of Nestin in Bone, Cementum and Root Dentin

Objectives: Nestin is an intermediate filament protein and a marker of bone and odontoblast cells, although its function in tooth and bone formation is largely unknown. We previously reported that osterix (Osx) was essential for alveolar bone, cellular cementum and root (but not crown) dentin formation, although detail mechanism was not fully understood. The goal of this study is to determine whether nestin is a target molecule of osterix during postnatal bone and tooth development.
Methods: The multiple approaches combining X-ray, uCT, backscattered and acid-etched casted SEM, FITC-Confocal microscope, immunohistochemistry, TRAP and Toluidine blue stain were used to study Osx conditional knockout (cKO) mice (by crossing Osx-loxP and 2.3 Col 1 Cre together) and nestin KO mice.
Results: 1) Osx-cKO mice displayed a severe root dentin and cementum phenotype, in which nestin levels were greatly decreased; 2) nestin KO newborn pups exhibited no apparent difference from the control pups but developed a delayed molar eruption (Fig 1, A) with reduced TRAP in the osteoclast cells; 3) nestin KO mice also developed expanded predentin and short, thin root, in which dentin tubes were irregular, thin and short (Fig 1, B, C); 4) nestin KO mice exhibited a small cellular cementum mass with sharp reductions in DMP1, BSP and OPN plus great increases in biglycan expression (Fig 2); and 5) nestin KO mice developed defective alveolar bone, including reduced bone volume and a defect in maturation from osteoblasts to osteocytes (Fig 3). Taken together, nestin KO, similar to the Osx-cKO mice, displays a defect in alveolar bone, cellular cementum and molar root dentin during postnatal development.
Conclusions: Nestin, one of key molecules downstream of osterix, plays a critical role in postnatal bone, root and cellular cementum development.