백악모세포가 법랑모세포의 세포사멸에 미치는 영향

Abstract

Tooth development is complex processes in which epithelial- mesenchymal interactions play pivotal roles in controling tooth and periodontium formation. After crown formation, Hertwig's epithelial root sheath (HERS) is formed from ectodermally-derived internal and external enamel epithelium, and play important roles in root dentin formation and cementogenesis. HERS cells eventually dissociates from the root surface to form the epithelial rests of Malassez (ERM), and some of them undergo apotosis. HERS breaks up into epithelial cords at the very beginning of cementogenesis. However, it is not clear yet whether HERS cells simply undergo apoptosis or whether other mechanisms contribute to their reduction and apoptosis. Our hypothesis is that developing cementoblasts can affect the cellular changes of HERS cells including apoptosis during root formation. HERS cells are derived from ameloblast lineage cells. To identify the role of cementoblasts in HERS cell apotosis, we evaluated the effects of cementoblasts on the apoptosis of ameloblasts using co-culture system between cementoblastic OCCM-30 and ameloblastic ALCs. A transwell co-culture system, comet assay, TUNEL staining, and DNA fragmentation assay were used to detect the interplay between ameloblasts and cementoblasts as well as the apoptosis of ameloblasts. The expression of apoptosis related genes was evaluated by RT-PCR and western blot analysis. Cementoblasts increased genomic DNA fragmentation of ameloblasts in our co-culture system. TUNEL and comet assay showed more apoptotic cells in co-cultured ameloblasts with cementoblasts than normal ameloblasts. However, cementoblasts couldn't facilitate the apoptosis of oral epithelial cells (KB) as seen in ameloblasts. During the co-culture, Fas expression was increased in co-cultured ameloblasts compare with the normal ameloblasts while FasL expression was increased in cementoblasts after co-culture. Treatment of Kp7-6, Fas antagonist, showed reduction of apoptosis in co-cultured ameloblasts. These data suggest that cementoblast facilitates the apoptosis of HERS cells and this apoptosis might be related to Fas-FasL pathway during root formation.

Keywords: HERS, apoptosis, cementoblast, ameloblast, root formation