p38 MAP kinase is required for Wnt3a-mediated osterix expression independently of Wnt-LRP5/6-GSK3ß signaling axis in dental follicle cells.

Wnt3a is a secreted glycoprotein that activates the glycogen synthase kinase-3ß (GSK3ß)/ß-catenin signaling pathway through low-density-lipoprotein receptor-related protein (LRP)5/6 co-receptors. Wnt3a has been implicated in periodontal development and homeostasis, as well as in cementum formation. Recently, we have reported that Wnt3a increases alkaline phosphatase expression through the induction of osterix (Osx) expression in dental follicle cells, a precursor of cementoblasts. However, the molecular mechanism by which Wnt3a induces Osx expression is still unknown. In this study, we show that Wnt3a-induced Osx expression was inhibited in the presence of p38 mitogen-activated protein kinase (MAPK) inhibitors (SB203580 and SB202190) at gene and protein levels, as assessed by real-time PCR and immunocytohistochemistry, respectively. Pretreatment of cells with Dickkopf-1, a potent canonical Wnt antagonist binding to LRP5/6 co-receptors, did not influence Wnt3a-mediated p38 MAPK phosphorylation, suggesting that Wnt3a activates p38 MAPK through LRP5/6-independent signaling. On the other hand, pretreatment with p38 MAPK inhibitors had no effects on the phosphorylated status of GSK3ß and ß-catenin as well as ß-catenin nuclear translocation, but inhibited Wnt3a-mediated ß-catenin transcriptional activity. These findings suggest that p38 MAPK modulates canonical Wnt signaling at the ß-catenin transcriptional level without any crosstalk with the Wnt3a-mediated LRP5/6-GSK3ß signaling axis and subsequent ß-catenin nuclear translocation. These findings expand our knowledge of the mechanisms controlling periodontal development and regeneration.

Metabotropic glutamate receptor 1 promotes cementoblast proliferation via MAP kinase signaling pathways.

PURPOSE/AIM: Glutamate is one of the signaling molecules responsible for transmission in the central nervous system. Periodontal ligament (PDL) cells were recently reported to express metabotropic glutamate receptors (mGluRs). However, the functions of mGluR signaling in PDL cells or PDL-related cells remain largely unknown. The aim of this study was to investigate the expression and function of mGluRs in PDL-related cells. MATERIALS AND METHODS: OCCM-30 cells, immortalized murine cementoblasts, were stimulated with l-glutamate or mGluRs antagonists. The cells' proliferative response was evaluated using a colorimetric assay and gene expression was assessed using real-time polymerase chain reaction. The nuclear translocation of cyclin D1 was evaluated by immunohistochemistry. RESULTS: l-Glutamate promoted the proliferation of OCCM-30 cells, which expressed mGluR1, but not mGluR5. Dihydroxyphenylglycine (DHPG), an agonist of group I mGluRs (mGluR1 and mGluR5), also promoted cell proliferation, and this was inhibited by LY456236, an mGluR1 antagonist. DHPG increased the expression of cyclin D1, a key regulator of cell proliferation, and its nuclear translocation. DHPG also increased the expression of Bcl2A1, an antiapoptotic oncogene and simultaneously reduced the expression of Bax, a pro-apoptotic marker. Furthermore, the DHPG-induced proliferation of OCCM-30 cells was reduced by pretreatment with SB203580, SP600125, and PD98059, inhibitors of p38, JNK, and ERK1/2, respectively. CONCLUSIONS: These findings indicate that activation of mGluR1 expressed by OCCM-30 cells induces cell proliferation in a manner that is dependent on mitogen-activated protein kinase pathways and that cyclin D1 and Bcl2A1/Bax may be involved. Our results provide useful information for elucidating the mechanisms underlying cementum homeostasis and regeneration.

Extracellular ß-NAD(+) inhibits interleukin-1-induced matrix metalloproteinase-1 and -3 expression on human gingival fibroblasts.

There is increasing evidence to show that extracellular ß-nicotinamide adenine dinucleotide (ß-NAD(+)) modulates various biological functions in inflammatory/immune regions. The aim of this study was to determine the effect of ß-NAD(+) on matrix metalloproteinase (MMP) expression on human gingival fibroblasts (hGF), the excess production of which leads to the matrix degradation associated with the pathological processes of periodontitis. The expression of MMP-1 and MMP-3 on hGF was determined by real-time polymerase chain reaction (PCR) and an enzyme-linked immunosorbent assay. The phosphorylated status of mitogen-activated protein (MAP) kinases, extracellular signal-regulated kinase 1/2 (ERK), c-Jun N-terminal kinase (JNK), and p38 and the expression of inhibitor κB (IκB)α were determined by Western blotting. ß-NAD(+) inhibited the expression of MMP-1 and MMP-3 triggered by IL-1α at gene and protein levels. ß-NAD(+) had no significant effect on the IL-1α-induced phosphorylation of ERK1/2, JNK, and p38 and also had no effect on the IL-1α-induced degradation of IκBα relative to the control, suggesting that inhibition by ß-NAD(+) was independent of the MAP kinase and the nuclear factor-κB signaling pathways. Transcripts of NAD(+)-metabolizing enzymes, such as NAD(+)-glycohydrolase, adenosine diphosphate (ADP)-ribosylcyclase, and ADP-ribosyltransferase, were expressed by hGF as assessed by RT-PCR. Experiments using α-NAD(+), which is not a substrate for ADP-ribosylcyclase or ADP-ribosyltransferase, revealed the possible contribution of NAD(+)-glycohydrolase to the inhibition of MMP. This is consistent with the finding that ADP-ribose, an NAD(+)-metabolite by NAD(+)-glycohydrolase, exhibited MMP inhibition similar to ß-NAD(+). The present findings may provide an additional viewpoint to clarify a natural feedback mechanism during the inflammatory process in periodontal tissue.

Wnt5a signaling is a substantial constituent in bone morphogenetic protein-2-mediated osteoblastogenesis.

Wnts are secreted glycoproteins that mediate developmental and post-developmental physiology by regulating cellular processes including proliferation, differentiation, and apoptosis through ß-catenin-dependent canonical and ß-catenin-independent noncanonical pathway. It has been reported that Wnt5a activates noncanonical Wnt signaling through receptor tyrosine kinase-like orphan receptor 2 (Ror2). Although it appears that Wnt5a/Ror2 signaling supports normal bone physiology, the biological significance of noncanonical Wnts in osteogenesis is essentially unknown. In this study, we identified expression of Wnt5a in osteoblasts in the ossification zone of the tibial growth plate as well as bone marrow of the rat tibia as assessed by immunohistochemistry. In addition, we show that osteoblastic differentiation mediated by BMP-2 is associated with increased expression of Wnt5a and Ror2 using cultured pre-osteoblasts, MC3T3-E1 cells. Silencing gene expression of Wnt5a and Ror2 in MC3T3-E1 cells results in suppression of BMP-2-mediated osteoblastic differentiation, suggesting that Wnt5a and Ror2 signaling are of substantial importance for BMP-2-mediated osteoblastic differentiation. BMP-2 stimulation induced phosphorylation of Smad1/5/8 in a similar fashion in both siWnt5a-treated cells and control cells, suggesting that Wnt5a was dispensable for the phosphorylation of Smads by BMP-2. Taken together, our results suggest that Wnt5a/Ror2 signaling appears to be involved in BMP-2-mediated osteoblast differentiation in a Smad independent pathway.

Elevated extracellular calcium increases expression of bone morphogenetic protein-2 gene via a calcium channel and ERK pathway in human dental pulp cells.

Dental pulp cells, which have been shown to share phenotypical features with osteoblasts, are capable of differentiating into odontoblast-like cells and generating a dentin-like mineral structure. Elevated extracellular Ca(2+)Ca(2+)(o) has been implicated in osteogenesis by stimulating the proliferation and differentiation of osteoblasts; however, the role of Ca(2+)(o) signaling in odontogenesis remains unclear. We found that elevated Ca(2+)(o) increases bone morphogenetic protein (BMP)-2 gene expression in human dental pulp cells. The increase was modulated not only at a transcriptional level but also at a post-transcriptional level, because treatment with Ca(2+) increased the stability of BMP-2 mRNA in the presence of actinomycin D, an inhibitor of transcription. A similar increase in BMP-2 mRNA level was observed in other human mesenchymal cells from oral tissue; periodontal ligament cells and gingival fibroblasts. However, the latter cells exhibited considerably lower expression of BMP-2 mRNA compared with dental pulp cells and periodontal ligament cells. The BMP-2 increase was markedly inhibited by pretreatment with an extracellular signal-regulated kinase (ERK) inhibitor, PD98059, and partially inhibited by the L-type Ca(2+) channels inhibitor, nifedipine. However, pretreatment with nifedipine had no effect on ERK1/2 phosphorylation triggered by Ca(2+), suggesting that the Ca(2+) influx from Ca(2+) channels may operate independently of ERK signaling. Dental pulp cells do not express the transcript of Ca(2+)-sensing receptors (CaSR) and only respond slightly to other cations such as Sr(2+) and spermine, suggesting that dental pulp cells respond to Ca(2+)(o) to increase BMP-2 mRNA expression in a manner different from CaSR and rather specific for Ca(2+)(o) among cations.

Extracellular calcium increases fibroblast growth factor 2 gene expression via extracellular signal-regulated kinase 1/2 and protein kinase A signaling in mouse dental papilla cells.

We previously reported that elevated extracellular calcium (Ca2+) levels increase bone morphogenetic protein 2 expression in human dental pulp (hDP) cells. However, it is unknown whether extracellular Ca2+ affects the expression of other growth factors such as fibroblast growth factor 2 (FGF2). The present study aimed to examine the effect of extracellular Ca2+ on FGF2 gene expression in hDP and immortalized mouse dental papilla (mDP) cells. Cells were stimulated with 10 mM CaCl2 in the presence or absence of cell signaling inhibitors. FGF2 gene expression was assessed using real-time polymerase chain reaction. The phosphorylation status of signaling molecules was examined by Western blotting. Extracellular Ca2+ increased FGF2 gene expression in mDP and hDP cells. Gene expression of the calcium-sensing receptor and G protein-coupled receptor family C group 6 member A, both of which are extracellular Ca2+ sensors, was not detected. Ca2+-mediated Fgf2 expression was reduced by pretreatment with the protein kinase A (PKA) inhibitor H-89 or extracellular signal-regulated kinase (ERK) 1/2 inhibitor PD98059 but not by pretreatment with the protein kinase C inhibitor GF-109203X or p38 inhibitor SB203580. Extracellular Ca2+ increased PKA activity and ERK1/2 phosphorylation. Ca2+-induced PKA activity decreased by pretreatment with PD98059. These findings indicate that elevated extracellular Ca2+ levels led to increased Fgf2 expression through ERK1/2 and PKA in mDP cells and that this mechanism may be useful for designing regenerative therapies for dentin.

Calcium phosphate particles induce interleukin-8 expression in a human gingival epithelial cell line via the nuclear factor-κB signaling pathway.

BACKGROUND: Dental calculus is calcified plaque composed primarily of calcium phosphate mineral salts, and there is a clear association between the presence of calculus and the initiation/progression of periodontitis. However, it is still inconclusive whether dental calculus can be a direct causative factor. The authors examined the effect of nano/microsized calcium phosphate particles, which may be generated in the process of early precipitation and/or dissolution of calcium phosphate mineral, on the expression of interleukin (IL)-8 in human gingival epithelial cells. METHODS: Primary human gingival epithelial cells and/or a human gingival carcinoma cell line (Ca9-22) were stimulated with calcium phosphate particles. Gene and protein levels were assessed by real-time polymerase chain reaction analysis and enzyme-linked immunosorbent assay, respectively. The activity of nuclear factor (NF)-κB signaling was measured by an immunofluorescence assay to evaluate NF-κB p65 nuclear translocation. RESULTS: The results show that nano/microsized particles stimulate IL-8 expression in human gingival epithelial cells at gene and protein levels. The activity to induce IL-8 expression depends on the particle size: particles with a diameter of 200 nm are more effective than those of 40-nm and 5-µm diameters. Calcium phosphate particles (diameter 200 nm) stimulated NF-κB activity. Pretreatment with BMS-345541, an NF-κB signaling inhibitor, inhibited the particle-mediated IL-8 gene induction, suggesting a requirement for the NF-κB signaling pathway. CONCLUSION: These findings suggest that calcium phosphate particles, which may be related to calculus development, may act as a direct causative factor in the pathogenesis of gingival epithelium.

Calcium-mediated increased expression of fibroblast growth factor-2 acts through NF-κB and PGE2/EP4 receptor signaling pathways in cementoblasts.

We reported previously that cementoblasts are provided with sensing mechanisms for extracellular Ca2+ and that elevated extracellular Ca2+ increases fibroblast growth factor-2 (FGF-2) gene and protein expression levels via a cyclic AMP/protein kinase A (PKA) dependent pathway. In the present study, we found that stimulation of murine cementoblasts with 10 mM CaCl2 induced cyclooxygenase-2 (COX-2) gene expression and prostaglandin E2 (PGE2) biosynthesis. NS-398, a COX-2 inhibitor, significantly reduced CaCl2-induced increase in Fgf-2 gene expression, indicating that PGE2 synthesized by COX-2 may be involved in FGF-2 induction. The inhibitory effect of NS-398 was restored completely by the addition of PGE2 receptor 4 (E-prostanoid receptor 4, called EP4) agonist, but not agonists for EP1, EP2, and EP3. Furthermore, EP4 antagonist significantly reduced CaCl2-induced Fgf-2 induction, suggesting that it is mediated by EP4 activation. However, stimulation with EP4 agonist alone in the absence of CaCl2 had no effect on the Fgf-2 induction, indicating that EP4 signaling alone is not sufficient. CaCl2 also upregulated gene expression levels of Ep4 and Cox-2, as well as Fgf-2 and induction of these genes was abolished by pretreatment with BMS-345541, a nuclear factor-κB (NF-κB) inhibitor, indicating that NF-κB signaling triggered by CaCl2 is indispensable for FGF-2 induction. Furthermore, CaCl2-induced Fgf-2 induction was synergistically enhanced by the addition of EP4 agonist. This indicates that the signaling triggered via CaCl2 and its combination with EP4 agonist may be useful as a novel strategy for periodontal regeneration.

Nanohydroxyapatite increases BMP-2 expression via a p38 MAP kinase dependent pathway in periodontal ligament cells.

OBJECTIVE: Bone morphogenetic protein (BMP)-2 promotes the osteoblastic differentiation of human periodontal ligament (PDL) cells, which play a pivotal role in periodontal regeneration. Recently, nano-sized hydroxyapatite (nano-HA) has been highlighted due to its advantageous features over micro-sized materials. DESIGN AND RESULTS: We investigated the effect of nano-HA on BMP-2 expression in human PDL cells. Real time PCR analysis revealed that the expression of BMP-2 increased upon stimulation with nano-HA in dose- and time-dependent manners. An immunofluorescence assay demonstrated the synthesis of BMP-2 proteins. Concentrations of Ca(2+) as well as phosphate (Pi) in culture supernatants were unchanged, suggesting that nano-HA functioned as a nanoparticle rather than as a possible source for releasing Ca(2+) and/or Pi extracellularly, which were shown to also enhance the expression of BMP-2. Nano-HA-induced BMP-2 expression was dependent on the p38 MAP kinase pathway because increases in BMP-2 expression were inhibited by treatment with SB203580, a p38 inhibitor, and phosphorylation of p38 was detected by Western blotting. CONCLUSIONS: This novel mechanism of nano-HA will be important for the rational design of future periodontal regeneration.

Extracellular calcium increases fibroblast growth factor 2 gene expression via extracellular signal-regulated kinase 1/2 and protein kinase A signaling in mouse dental papilla cells

Abstract We previously reported that elevated extracellular calcium (Ca2+) levels increase bone morphogenetic protein 2 expression in human dental pulp (hDP) cells. However, it is unknown whether extracellular Ca2+ affects the expression of other growth factors such as fibroblast growth factor 2 (FGF2). Objective: The present study aimed to examine the effect of extracellular Ca2+ on FGF2 gene expression in hDP and immortalized mouse dental papilla (mDP) cells. Materials and Methods: Cells were stimulated with 10 mM CaCl2 in the presence or absence of cell signaling inhibitors. FGF2 gene expression was assessed using real-time polymerase chain reaction. The phosphorylation status of signaling molecules was examined by Western blotting. Results: Extracellular Ca2+ increased FGF2 gene expression in mDP and hDP cells. Gene expression of the calcium-sensing receptor and G protein-coupled receptor family C group 6 member A, both of which are extracellular Ca2+ sensors, was not detected. Ca2+-mediated Fgf2 expression was reduced by pretreatment with the protein kinase A (PKA) inhibitor H-89 or extracellular signal-regulated kinase (ERK) 1/2 inhibitor PD98059 but not by pretreatment with the protein kinase C inhibitor GF-109203X or p38 inhibitor SB203580. Extracellular Ca2+ increased PKA activity and ERK1/2 phosphorylation. Ca2+-induced PKA activity decreased by pretreatment with PD98059. Conclusions: These findings indicate that elevated extracellular Ca2+ levels led to increased Fgf2 expression through ERK1/2 and PKA in mDP cells and that this mechanism may be useful for designing regenerative therapies for dentin.

Elevated extracellular calcium increases fibroblast growth factor-2 gene and protein expression levels via a cAMP/PKA dependent pathway in cementoblasts.

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. Elevated levels of extracellular Ca(2+) have been implicated in osteogenesis by stimulating the proliferation and differentiation of osteoblasts; however, the role of extracellular Ca(2+) signaling in cementogenesis has not been examined. Using RT-PCR, we found that elevated levels of extracellular Ca(2+) increase fibroblast growth factor (FGF)-2 gene expression with a peak at 6h. Pretreatment with a protein kinase A (PKA) inhibitor, H89, or an adenylate cyclase inhibitor, MDL-12,330A, inhibited Ca(2+)-stimulated Fgf-2 expression. In contrast, pretreatment with the protein kinase C (PKC) inhibitor GF-109203X or the phospholipase C (PLC) inhibitor U73122 did not affect the expression of Fgf-2 transcripts, suggesting that the increase in Fgf-2 expression was dependent on the PKA but not the PLC/PKC signaling pathway. Treatment with an activator of adenylate cyclase, forskolin, or a cell-permeable analog of cAMP, 8-Br-cAMP, enhanced Ca(2+)-stimulated Fgf-2 expression, but a single treatment with forskolin or 8-Br-cAMP did not, suggesting that cAMP generation is indispensable but not sufficient for Ca(2+)-stimulated FGF2 expression. Next, we examined the cation specificity of the putative receptor and showed that treatment with trivalent/divalent inorganic ions, Ca(2+), Gd(3+), Sr(2+), or Al(3+), caused a dose-dependent increase in Fgf-2 mRNA levels in a cAMP-dependent fashion, whereas Mg(2+) and the organic ions neomycin and spermine had no effect on Fgf-2 gene expression levels. These findings suggest that an extracellular Ca(2+)-sensing mechanism is present in cementoblasts and its activation leads to FGF-2 stimulation in a cAMP/PKA dependent fashion. Understanding the pathway regulating key genes involved in modulating the regeneration of oral tissues will assist in designing regenerative therapies based on reliable biological principles.

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.

Expression of CD13/aminopeptidase N on human gingival fibroblasts and up-regulation upon stimulation with interleukin-4 and interleukin-13.

BACKGROUND AND OBJECTIVES: Aminopeptidase N (APN)/CD13 is a multifunctional ectoenzyme that is involved in anti-inflammatory reactions, control of immune reactions and differentiation of many cellular systems. Here, we hypothesized that CD13/APN would be expressed on human gingival fibroblasts (hGF) and would contribute to the regulation of immune responses in periodontal tissue. METHODS AND RESULTS: CD13/APN was expressed on hGF at the mRNA and protein levels as determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and flow cytometry, respectively. Enzymatic activities accompanying the expression were assessed by colorimetrical analysis using the synthetic substrate Leu-p-nitroanilide. We examined the possible regulation of CD13/APN expression on hGF in response to T cell-derived cytokines. T helper (Th) 2 cell type cytokines such as interleukin-4 and interleukin-13, but not interleukin-2 or interleukin-15, preferentially increased the expression of proteins as well as the enzymatic activities of CD13/APN in a dose-dependent manner. Receptors for these cytokines, the interleukin-4 receptor alpha chain, interleukin-13 receptor alpha1 chain, and interleukin-2R common gamma chain, were expressed on hGF assessed by RT-PCR or flow cytometry. hGF exhibited inhibitory effects for formyl-methionyl-leucyl-phenylalanine (FMLP)-induced polymorphonuclear leukocyte-activation that was evaluated by Mac-1 expression, and this inhibitory effect was partially recovered by pre-treatment with the APN-specific inhibitor bestatin. CONCLUSIONS: These findings suggested that CD13/APN expressed by hGF could contribute to the anti-inflammatory response in periodontal tissue, and may be involved in disease processes mediated by Th2 cells.

Retinoic acid is a potential negative regulator for differentiation of human periodontal ligament cells.

BACKGROUND AND OBJECTIVES: Retinoic acid (RA) exerts a wide variety of effects on development, cellular differentiation and homeostasis in various tissues. However, little is known about the effects of RA on the differentiation of periodontal ligament cells. In this study, we investigated whether RA can affect the dexamethasone-induced differentiation of periodontal ligament cells. METHODS AND RESULTS: Human periodontal ligament cells were differentiated via culturing in the presence of dexamethasone, ascorbic acid, and beta-glycerophosphate for mineralized nodule formation, as characterized by von Kossa staining. Continuous treatment with all-trans-RA inhibited the mineralization in a dose-dependent manner, with complete inhibition over 1 microm RA. Other RA analogs, 9-cis-RA and 13-cis-RA, were also effective. Furthermore, addition of RA for just the first 4 days completely inhibited the mineralization; however, as RA was added at later stages of culture, the inhibitory effect was diminished, suggesting that RA had a phase-dependent inhibition of mineralization. RA receptor (RAR)-alpha agonist (AM-580), but not retinoid X receptor agonist (methoprene acid), inhibited the mineralization, and reverse transcription-polymerase chain reaction analysis revealed that RAR-alpha was expressed on the cells, suggesting that RAR-alpha was involved in the inhibitory mechanism. This inhibition was accompanied by inhibition of alkaline phosphatase activity; however, neither expression of platelet-derived growth factor (PDGF) receptor-alpha, PDGF receptor-beta, or epidermal growth factor (EGF) receptor, nor phosphorylation of extracellular signal-regulated kinases triggered by PDGF-ascorbic acid or PDGF-BB was changed, as assessed by flow cytometry or western blot analyses. CONCLUSIONS: These findings suggest that RA is a potential negative regulator for differentiation of human periodontal ligament cells.

Porphyromonas gingivalis lipopolysaccharides induce maturation of dendritic cells with CD14+CD16+ phenotype.

Primary immune responses are initiated by dendritic cells (DC) that inform naive T helper cells about invading pathogens. DC undergo sequential events leading to irreversible maturation upon bacterial stimulation. To investigate the responses of DC during periodontal infection, we studied the effects of LPS from Porphyromonas gingivalis on DC. DC generated from human peripheral monocytes by culture with IL-4 and GM-CSF were incubated with P. gingivalis LPS (Pg LPS) or Escherichia coli LPS (Ec LPS). Flow cytometry and real-time quantitative RT-PCR analysis revealed that Pg LPS, but not Ec LPS, preferentially up-regulated CD14 and CD16 expression at protein and mRNA levels. Furthermore, Pg LPS preferentially induced the secretion of soluble CD14. CD1a, HLA-DR and CD54 were highly expressed on DC stimulated with both kinds of LPS; however, CD40, CD80, CD83 and CD86 expression on Pg LPS-stimulated DC was lower than on Ec LPS-stimulated DC. With regard to IL-6, IL-8, IL-10, IL-12 and RANTES production from DC and allogeneic T cell proliferation, Pg LPS was a weaker stimulator than Ec LPS. These results suggested that Pg LPS triggers maturation of DC with unique characteristics, which exhibited weak immunostimulatory activity and may contribute to induction of chronic inflammation at the site of periodontal infection.