Wnt signaling inhibits cementoblast differentiation and promotes proliferation.
Cementoblasts, tooth root lining cells, are responsible for laying down cementum on the root surface, a process that is indispensable for establishing a functional periodontal ligament. Cementoblasts share phenotypical features with osteoblasts. Wnt signaling has been implicated in increased bone formation by controlling mesenchymal stem cell or osteoblastic cell functions; however the role of Wnt signaling on cementogenesis has not been examined. In this study, we have identified a consistent expression profile of Wnt signaling molecules in cementoblasts, in vitro by RT-PCR. Exposure of cells to LiCl, which promotes canonical Wnt signaling by inhibiting GSK-3beta, increased beta-catenin nuclear translocation and up-regulated the transcriptional activity of a canonical Wnt-responsive promoters, suggesting that an endogenous canonical Wnt pathway functions in cementoblasts. Activation of endogenous canonical Wnt signaling with LiCl suppressed alkaline phosphatase (ALP) activity and expression of genes associated with cementum function; ALP, bone sialoprotein (BSP), and osteocalcin (OCN). Exposure to Wnt3a, as a representative canonical Wnt member, also inhibited the expression of ALP, BSP, and OCN gene. This effect was accompanied by decreased gene expression of Runx2 and Osterix and by increased gene expression of lymphoid enhancer factor-1. Pretreatment with Dickkopf (Dkk)-1, a potent canonical Wnt antagonist, which binds to a low-density lipoprotein-receptor-related protein (LRP)-5/6 co-receptor, attenuated the suppressive effects of Wnt3a on mRNA expression of Runx2 and OCN on cementoblasts. These findings suggest that canonical Wnt signaling inhibits cementoblast differentiation via regulation of expression of selective transcription factors. Wnt3a also increased the expression of cyclin D1, known as a cell cycle regulator, as well as cell proliferation. In conclusion, these observations suggest that Wnt signaling inhibits cementoblast differentiation and promotes cell proliferation. Elucidating the role of Wnt in controlling cementoblast function will provide new tools needed to improve on existing periodontal regeneration therapies.
Department of Periodontology and Endodontology, Tohoku University Graduate School of Dentistry, 4-1 Seiryo-machi Aoba, Sendai, Japan. e-nemoto@umin.ac.jp
Eiji
E
Nemoto
Yohei
Y
Koshikawa
Sousuke
S
Kanaya
Masahiro
M
Tsuchiya
Masato
M
Tamura
Martha J
MJ
Somerman
Hidetoshi
H
Shimauchi
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects*; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects*; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics; D019938:Cyclin D1 / Q000235:genetics; D003739:Dental Cementum / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D018021:Lithium Chloride / Q000494:pharmacology; D051379:Mice; D008856:Microscopy, Fluorescence; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D000076182:Sp7 Transcription Factor; D014157:Transcription Factors / Q000235:genetics; D051153:Wnt Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D060508:Wnt3 Protein; D060509:Wnt3A Protein; D051176:beta Catenin / Q000378:metabolism
D050659:Core Binding Factor Alpha 1 Subunit; D000076182:Sp7 Transcription Factor; C479466:Sp7 protein, mouse; D014157:Transcription Factors; D051153:Wnt Proteins; D060508:Wnt3 Protein; D060509:Wnt3A Protein; C555511:Wnt3a protein, mouse; D051176:beta Catenin; D019938:Cyclin D1; D000469:Alkaline Phosphatase; D018021:Lithium Chloride