Method: Calcein double labeling were used to define formation rates of the alveolar bone on three different interfaces: periosteal, endosteal and PDL separately. Adeno-virus Cre was injected into Rosa 26 PDL regions to determine whether progenitor cells in PDL contribute alveolar bone formation. An X-gal stain assay was used to trace Osx-lacZ signal distributions in PDL, and alveolar bone regions. Sclerostin antibodies, blocking SOST (a potent inhibitor of Wnt-b-catenin) was subcutaneously injected to one-month-old periostin KO mice, which display severe periodontal like phenotype such as defects in PDL and alveolar bone, for 8-weeks. Radiographs, MicroCT, histology, FITC stain, X-gal stain, SEM, and immuno-histochemistry were utilized for phenotypic analyses.
Result: 1) The alveolar-bone formation rate varied in different interfaces with the PDL-alveolar bone interface highest (4.79±0.03um/day), followed by the periosteal-alveolar bone interface (2.29±0.18um/day) and the endosteal-alveolar bone interface (1.52±0.13um/day); 2) there was an expression gradient of OSX in the PDL region with the PDL-alveolar bone interface highest; 3) The cell lineage study showed lacZ positive osteocytes in the PDL-alveolar interface; 4) SEM and FITC stained images demonstrated that PDL cells form alveolar bone; and 5) Treatment of periostin mice with Sclerostin antibodies for knocking sclerostin function in bone cells not only rescued alveolar bone phenotypes but also greatly improved PDL phenotype in periostin-null mice.
Conclusion: Our in vivo studies demonstrated that PDL progenitor cells directly contribute bone formation in PDL-alveolar-bone interface; and that alveolar-bone cells have a positive feedback on PDL morphology and homeostasis in vivo.