Wnt signaling inhibits cementoblast differentiation and promotes proliferation

Department of Periodontology and Endodontology, Tohoku University Graduate School of Dentistry, 4-1 Seiryo-machi Aoba, Sendai, Japan.
Bone (Impact Factor: 3.97). 06/2009; 44(5):805-12. DOI: 10.1016/j.bone.2008.12.029
Source: PubMed


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.

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    • "The pattern of Wnt responding cells in the periodontium has been mapped (Rooker et al. 2010; Lim, Liu, Cheng, Williams, et al. 2014): X-gal +ve cells populate the periodontal ligament space and decorate the surfaces of the alveolar bone (Fig. 2B). Cementoblasts covering the dentin surface are also Wnt responsive, as shown by GFP immunostaining in tissue sections from Axin2 CreERT2/+ ;R26 mTmG/+ mice (Fig. 2C, D and see Nemoto et al. 2009). From these data, one can assume that endogenous Wnt signaling is active in the adult periodontium. "
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    ABSTRACT: A new field of dental medicine seeks to exploit nature's solution for repairing damaged tissues, through the process of regeneration. Most adult mammalian tissues have limited regenerative capacities, but in lower vertebrates, the molecular machinery for regeneration is an elemental part of their genetic makeup. Accumulating data suggest that the molecular pathways responsible for the regenerative capacity of teleosts, amphibians, and reptiles have fallen into disuse in mammals but that they can be "jumpstarted" by the selective activation of key molecules. The Wnt family of secreted proteins constitutes one such critical pathway: Wnt proteins rank among the most potent and ubiquitous stem cell self-renewing factors, with tremendous potential for promoting human tissue regeneration. Wnt reporter and lineage-tracing strains of mice have been employed to create molecular maps of Wnt responsiveness in the craniofacial tissues, and these patterns of Wnt signaling colocalize with stem/progenitor populations in the rodent incisor apex, the dental pulp, the alveolar bone, the periodontal ligament, the cementum, and oral mucosa. The importance of Wnt signaling in both the maintenance and healing of these craniofacial tissues is summarized, and the therapeutic potential of Wnt-based strategies to accelerate healing through activation of endogenous stem cells is highlighted. © International & American Associations for Dental Research 2015.
    Journal of dental research 08/2015; DOI:10.1177/0022034515599772 · 4.14 Impact Factor
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    • "Recent studies in vivo have reported that constitutive stabilization of βcatenin in dental mesenchyme leads to excessive cementum formation [14,15], and that disruption of Wnt/β-catenin signaling in dental mesenchyme arrests the differentiation of cementoblasts [16], suggesting that canonical Wnt/β-catenin signaling is required for cementum formation. In addition, studies in vitro have demonstrated that Wnt/β-catenin signaling up-regulates differentiation and proliferation in rat/mouse dental follicle cells [17] [18] and murine cementoblasts [19], respectively, suggesting the involvement of Wnt/β-catenin signaling in cementogenesis. "
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    ABSTRACT: Wnt signaling regulates multiple cellular events such as cell proliferation, differentiation, and apoptosis through β-catenin-dependent canonical and β-catenin-independent noncanonical pathways. Canonical Wnt/β-catenin signaling can promote the differentiation of dental follicle cells, putative progenitor cells for cementoblasts, osteoblasts, and periodontal ligament cells, toward a cementoblast/osteoblast phenotype during root formation, but little is known about the biological significance of noncanonical Wnt signaling in this process. We identified the expression of Wnt5a, a representative noncanonical Wnt ligand, in tooth root lining cells (i.e. precementoblasts/cementoblasts) and dental follicle cells during mouse tooth root development, as assessed by immunohistochemistry. Silencing expression of the Wnt5a gene in a dental follicle cell line resulted in enhancement of the Wnt3a (a representative canonical Wnt ligand)-mediated increase in alkaline phosphatase (ALP) expression. Conversely, treatment with recombinant Wnt5a inhibited the increase in ALP expression, suggesting that Wnt5a signaling functions as a negative regulator of canonical Wnt-mediated ALP expression of dental follicle cells. Wnt5a did not affect the nuclear translocation of β-catenin as well as β-catenin-mediated transcriptional activation of T-cell factor (Tcf) triggered by Wnt3a, suggesting that Wnt5a inhibits the downstream part of the β-catenin-Tcf pathway. These findings suggest the existence of a feedback mechanism between canonical and noncanonical Wnt signaling during the differentiation of dental follicle cells. Copyright © 2015. Published by Elsevier Inc.
    Experimental Cell Research 06/2015; 336(1). DOI:10.1016/j.yexcr.2015.06.013 · 3.25 Impact Factor
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    • "Sr, activating the ERK1/2 pathway, favored the phosphorylation of PPARγ and its degradation, thereby explaining the significant decrease of PPARγ2 protein observed under Sr treatment and the less dramatic inhibition of the PPARγ2 gene expression. Cyclin D1 is an important cell cycle regulator, promoting proliferation in cell types including epithelial cells, cementoblasts and human MMCs [41] [42] [43] via an ERK1/2 signaling pathway [44]. Moreover, in fibroblasts cultured in adipogenic medium, Fu M. et al. (2005) [21] demonstrated that cyclin D1 inhibits the PPARγ activity by inducing a histone deacetylase (HDAC) activity that favors a transcriptionally inactive chromatin. "
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    ABSTRACT: Adequate protein intake during development is critical to ensure optimal bone gain and to attain a higher peak bone mass later on. We hypothesized that the quality of the dietary protein is of prime importance for bone physiology during moderate protein restriction. The target population was growing Balb/C mice. We compared two protein restricted diets (6% of total energy as protein), one based on soy (LP-SOY) and one based on casein (LP-CAS). For comparison, a normal protein soy-based control group (NP-SOY) and a low protein group receiving an anabolic daily parathyroid hormone (PTH) 1-34 injection (LP-SOY + PTH) were included in the protocol. After 8 weeks, LP-SOY mice had reduced body weights related to a lower lean mass whereas LP-CAS mice were not different from the NP-SOY group. LP-SOY mice were characterized by lower femoral cortical thickness, bone volume, trabecular number and thickness and increased medullar adiposity when compared to both the LP-CAS and NP-SOY groups. However, the dietary intervention had no effect on the vertebral parameters. The negative effect of the LP-SOY diet was correlated to an impaired bone formation as shown by the reduced P1NP serum level as well as the reduced osteoid surfaces and bone formation rate in the femur. PTH injection in LP-SOY mice had no effect on total weight or lean mass, but improved all bone parameters at both femoral and vertebral sites, suggesting that amino acid deficiency was not the primary reason for degraded bone status in mice consuming soy protein. In conclusion, our study showed that under the same protein restriction (6% of energy), a soy diet leads to impaired bone health whereas a casein diet has little effect when compared to a normal protein control.
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