Expression of Periodontal Ligament Fibroblast-specific Gene, PDLs22 During Development of Periodontal Ligament, Alveolar Bone and Cementum

Ji, Suk; Kim, Byung Ock; Kim, Heung Joong; Kim, Sung Mi; Park, Joo Cheol

Abstract

Identifying specific factors and/or mechanism regulating development of periodontal tissue will provide important information as to which molecules and cells are required for regulation of periodontal tissue lost as a consequence of disease. The origin and location of cementoblast and osteoblast precursor cells in adult periodontal tissues is not definitely known but it has been suggested that tooth related periodontal ligament may be the source of cementoblasts and the bone-related periodontal ligament for osteoblasts. However, little is known of the molecular mechanism controlling PDL function. PDL-specific protein; PDLs22 had been previously identified as a novel protein isolated from cultured human PDL fibroblasts using subtraction hybridization between human gingival fibroblasts and PDL fibroblasts. The aim of this study was to examine the functional characterization of PDLs22 in differentiation of periodontal ligament, alveolar bone and cementum. Human osteocalcin (OC), osteonectin (ON) and PDLs22 mRNA were detected by reverse transcription polymerase chain reaction (RT-PCR) in primary cell cultures of periodontal ligament fibroblast during mineral nodule formation in vitro. And the localization of PDLs22 in rat tissues was detected by polyclonal antibody against PDLs22 by means of immunohistochemical staining. The results were as follows: 1. PDL cells were capable of producing mineral-like nodules in vitro. 2. PDLs22 mRNA was expressed in the initial stages whereas it was not expressed in the calcification stage, during mineral nodule formation of PDL cells in vitro. 3. PDLs22 protein was expressed in external dental epithelium and stellate reticulum during crown formation stage, and was continued in external dental epithelium of Hertwig's epithelial sheath. Also PDLs22 protein was strongly expressed in the bone and cementum-related side of the PDL and weakly expressed in the middle of PDL. In the developing bone, PDLs22 protein is only expressed in preosteoblast not osteocyte and osteoblast. The results suggest PDLs22 is important mediator of epithelial-mesenchymal reaction in development of PDL, alveolar bone and cementum and is related to initial differentiation of cementum and alveolar bone.