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J Dent Res 86(9):873-877, 2007
© 2007 International and American Associations for Dental Research

RESEARCH REPORT
Biological

Inhibition of SFRP1 Reduces Severity of Periodontitis

C.H. Li, and S. Amar*

Department of Periodontology & Oral Biology, Goldman School of Dental Medicine, Boston University, 650 Albany Street, X-343, Boston, MA 02118, USA

* corresponding author, samar{at}bu.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS & METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Porphyromonas gingivalis (P. gingivalis) is implicated as a major pathogen in periodontitis, a common infectious disease characterized by the inflammation and destruction of periodontal tissues. Secreted frizzled-related protein 1 (SFRP1) modulates apoptosis in different cell types. To characterize the roles of SFRP1 in periodontitis, we used a P. gingivalis-induced murine periodontitis model. Inflammatory responses were measured by morphometric and histomorphometric analysis, apoptosis assay, and immunohistochemistry. We found that P. gingivalis-infected mouse periodontal tissues expressed significantly more SFRP1 compared with those of control mice. Also, in P. gingivalis-infected animals, more apoptosis of inflammatory cells, fibroblasts, and bone-lining cells was observed compared with controls. Antibody experiments aimed at inhibiting SFRP1 expression in periodontitis resulted in a reduction of periodontal breakdown, inflammatory cell infiltrate, osteoclastogenesis, and apoptosis of inflammatory cells and fibroblasts. The results of our studies suggest that SFRP1 may be involved in the development of periodontitis, since inhibiting SFRP1 resulted in reduced periodontal breakdown.

KEY WORDS: experimental periodontitis • alveolar bone loss • Porphyromonas gingivalis (P. gingivalis) • secreted frizzled-related protein 1 (SFRP1)


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS & METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Periodontitis is a bacterial plaque-induced inflammatory disease characterized by destruction of the periodontium, involving downgrowth of epithelium and loss of alveolar bone (Williams, 1990; Socransky and Haffajee, 1992). Porphyromonas gingivalis (P. gingivalis), a Gram-negative, black-pigmented anaerobe, has been implicated as a predominant pathogen associated with periodontitis (Lamont and Jenkinson, 1998; Socransky et al., 1998). The pathogenicity of P. gingivalis could result from contributions of many potential virulence factors, including lipopolysaccharide, fimbriae, and various enzymes (Holt et al., 1999; Zhou et al., 2005). In studying the pathogenesis of periodontitis, we chose a well-accepted murine model, in which disease is induced by P. gingivalis and which features measurable alveolar bone loss (Baker et al., 1994; Kimura et al., 2000).

Wingless/int (Wnt) proteins, a family of secreted proteins, regulate many aspects of cell growth, differentiation, function, and death by increasing the stability and transcriptional activity of ß-catenin (canonical pathway) (Logan and Nusse, 2004). Recent evidence has shown that canonical Wnt signaling plays an important role in the regulation of bone development and remodeling, and also in the pathophysiology of diseases characterized by dysregulated bone maintenance (Westendorf et al., 2004; Bodine and Komm, 2006; Krishnan et al., 2006). Overall, bone mass is regulated by the balance between the activities of osteoblastic bone-forming and osteoclastic bone-resorbing cells. Moreover, Wnt signaling is negatively regulated by secreted frizzled related proteins (SFRPs), a family of antagonists of the Wnt signaling pathway (Jones and Jomary, 2002; Kawano and Kypta, 2003). Furthermore, a recent study has shown that the secreted frizzled related protein-1 (SFRP1) controls osteoblast and osteocyte apoptosis (Bodine et al., 2005). Collectively, these findings suggested that SFRP1 might play a role in alveolar bone loss in periodontitis. The goal of this study was to investigate the potential role of SFRP1 in periodontitis.


   MATERIALS & METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS & METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Bacteria
For oral infection, silk ligatures that had been soaked in a culture of P. gingivalis (A7436) were prepared. Briefly, the sterile 5-0 silk ligatures were immersed in Schaedler broth containing P. gingivalis supplemented with hemin (5 µg/mL) and menadione (1 µg/mL) in an anaerobic chamber with an atmosphere of 85% N2, 10% H2, and 5% CO2 at 37°C for 2 days.

Mice and Experimental Periodontitis Model
Forty-four 12-week-old male C57BL/6J mice, purchased from the Jackson Laboratory (Bar Harbor, ME, USA), were randomly assigned to either of 2 groups: P. gingivalis-infected and control groups, as previously reported (Li and Amar, 2007). All procedures involving animals were approved by the Institutional Animal Care and Use Committee at Boston University Medical Center. An additional 22 age-, sex-, and strain-matched mice were used for the antibody-blocking experiment. Mice were intraperitoneally anesthetized with a mixture of ketamine (80 mg/kg) and xylazine (10 mg/kg). We induced periodontitis by tying a 5-0 P. gingivalis-soaked silk ligature around the second molar, carefully pushing the ligature into gingival sulcus in the left maxillary quadrant, and knotting it mesio-buccally. The P. gingivalis-soaked ligatures were examined and replaced every other day. Mice in the control group were neither ligated nor infected with bacteria. Individual mice were killed by CO2 overdose on days 0, 3, 7, and 10 after ligature application, for a total of 6 control and 5 experimental mice per time-point.

Blocking SFRP1 with Anti-SFRP1 Antibody
To block the SFRP1 expression in periodontal tissues, 22 mice received gingival injections of either anti-SFRP1 antibody or rabbit normal IgG (Santa Cruz Biotechnology, Santa Cruz, CA, USA) (N = 5 for histomorphometric analysis, N = 6 for morphometry in each group). Each injection consisted of anti-SFRP1 antibody (30 µg) or IgG (30 µg) submucosally to the palatal inter-proximal gingiva between the first and second, and between the second and third molars on days 2, 5, and 6 after ligature application (for a total dose of 90 µg of anti-SFRP1 antibody or of IgG). On day 10, animals were killed, and tissues were collected.

Tissue Specimen Preparation
Following the animals’ death, the palatal bone with intact surrounding tissue from each animal was dissected and fixed in 4% paraformaldehyde for 24 hrs at 4°C. After fixation, the specimens were decalcified in Immunocal (Decal Corporation, Congers, NY, USA) with constant stirring for 14 days at 4°C; Immunocal was changed daily. Cryostat sagittal sections were prepared with a thickness of 5 µm. The sections that were oriented correctly were stained with hematoxylin and eosin (H&E).

Histomorphometric Analysis
Two tissue sections, 40 µm apart, were obtained per animal. Below the cemento-enamel junction (CEJ), 6 fields from each interdental area (3 toward the first molar and 3 toward the second molar) were analyzed. At 100X magnification, epithelial downgrowth (the distance from the CEJ to the apical extent of the junctional epithelium) and alveolar bone loss (the distance between the CEJ and the alveolar bone crest (ABC)) were measured with the use of Image-Pro Plus version 5.0 software (Media Cybernetics, Silver Spring, MD, USA). The results were presented as distance in millimeters. In each field, polymorphonuclear neutrophils (PMN) and mononuclear leukocytes, identified by morphologic characteristics, were quantified at 400X magnification. The number of PMN and mononuclear leukocytes per square millimeter was obtained. We averaged data obtained from these fields to obtain a single number per animal.

Morphometric Analysis
Alveolar bone loss around the second molars was measured by the morphometric method described previously (Klausen et al., 1989). The distance from the CEJ to the ABC was measured at 2 sites per tooth (mesio-palatal and disto-palatal), under a dissecting microscope (30X) with the occlusal face of the molars positioned perpendicular to the base. The results are presented as the distances in millimeters.

Osteoclast Activity
Osteoclasts were quantified as tartrate-resistant acid-phosphatase-positive (TRAP) multinucleated cells at high magnification (400X) (Chiang et al., 1999). The data are presented as number of osteoclasts per square millimeter.

Immunohistochemistry
Immunohistochemical staining for SFRP1 was performed as we have described previously (Han and Amar, 2004). At high magnification (400X), SFRP1-positive inflammatory cells, fibroblasts, and bone-lining cells (defined as flattened cells lining the bone surface with ovoid-shaped nuclei) were quantified based on morphological criteria. The data are presented as the number of each cell type per square millimeter.

Apoptosis Assay
Apoptotic inflammatory cells, fibroblasts, and bone-lining cells were detected by TUNEL assay, with the use of an in situ cell death detection kit (Roche Diagnostics, Indianapolis, IN, USA), performed according to the manufacturer’s instructions. At high magnification (400X), TUNEL-positive inflammatory cells, fibroblasts, and bone-lining cells were counted based on morphological criteria. The data are presented as a percentage of apoptotic cells related to the total cell counts in the same field of analysis.

Statistical Analysis
All measurements were performed twice in a blind fashion and one week apart. Intra-examiner variation was found to be less than 5%. All values were expressed as mean ± SEM. Analysis was performed by Student’s t test.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS & METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Experimental Periodontitis Model
Our previous study demonstrated that the P. gingivalis-induced periodontitis model used here is a reliable murine model, which showed site-specific, time-dependent epithelial downgrowth, alveolar bone loss (Fig. 1AGo), and inflammation (Li and Amar, 2007). Additionally, the osteoclast activity observed was consistent with the progression of an inflammatory front. Furthermore, alveolar bone loss could be quantified accurately by any of 3 alveolar bone analyses, including histomorphometry, morphometry, and micro-computed tomography. On the basis of the evidence, we chose this model to investigate the role of SFRP1 in periodontitis for this study.


Figure 1
Figure 1
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  		Figure 1. Alveolar bone loss and SFRP1 expression in the P. gingivalis-induced murine periodontitis model. (A) Morphometric images for alveolar bone loss on day 10 in the control and the infected animals. (B–D) Quantification of SFRP1-immunopositive cells identified by immunohistochemical staining: (B) inflammatory cells, (C) fibroblasts, and (D) bone-lining cells. Data represent mean values ± SEM (N = 6 for the control group, N = 5 for the infected group at each time-point). *Statistically significant at p < 0.05 by Student’s t test.

 
    SFRP1 Expression
There was no detectable SFRP1 expression in the controls (Figs. 1B, 1C, 1DGo). In contrast, in the P. gingivalis-infected group, the number of SFRP1-positive inflammatory cells was significantly increased at day 3; maximal expression was observed at day 7 (Fig. 1BGo). The SFRP1-positive fibroblasts and bone-lining cells were detectable only at day 7 (Figs. 1C, 1DGo).

    Apoptosis
In the P. gingivalis-infected group, the number of apoptotic inflammatory cells significantly increased from day 3, peaked at day 7, and remained higher at day 10 compared with the controls (Fig. 2AGo). In addition, the number of apoptotic fibroblasts significantly increased, also peaking at day 7 compared with the control animals (Fig. 2BGo). Similarly, apoptosis of bone-lining cells peaked at day 7 (Fig. 2CGo).


Figure 2
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  		Figure 2. Apoptosis of cell types in P. gingivalis-induced murine model. (A) Inflammatory cells, (B) fibroblasts, and (C) bone-lining cells were analyzed and quantified, then represented as percentages of apoptotic cells relative to the total cell counts in the same field of analysis by TUNEL assay. Data represent mean values ± SEM (N = 6 for the control group, N = 5 for the infected group at each time-point). *,{dagger}, and {ddagger} = statistically significant at p < 0.05, p < 0.01, and p < 0.001, respectively.

 
Blocking Expression of SFRP1 in Periodontitis Model
    Inflammatory Responses and SFRP1 Expression
To investigate the role of SFRP1 in periodontitis, we injected anti-SFRP1 antibody into the palatal inter-proximal gingiva between the first and second, and between the second and third molars. SFRP1 expression was significantly reduced in the anti-SFRP1 antibody-injected group compared with the IgG-injected group (TableGo). Histomorphometric analysis showed that the group treated with anti-SFRP1 antibody clearly exhibited significantly less epithelial downgrowth (TableGo) and alveolar bone loss (data not shown) than did the IgG-injected group. Similarly, analysis of morphometric data also showed a significant reduction of alveolar bone loss on mesio-palatal sites of second molars in the anti-SFRP1 antibody group compared with the IgG-injected group (TableGo, Fig. 3Go). Measurements of alveolar bone loss at disto-palatal sites showed patterns similar to those at the mesio-palatal site (data not shown). In addition, the numbers of osteoclasts were significantly reduced in animals that received anti-SFRP1 antibody compared with IgG-injected animals (TableGo). A significant reduction of PMN and mononuclear leukocyte infiltrates was also observed in the group injected with anti-SFRP1 antibody, compared with the IgG-injected group (TableGo).


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  		Table. Inflammatory Responses, Apoptosis, and SFRP1 Expression in an Antibody Experiment
 

Figure 3
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  		Figure 3. Localized treatment with anti-SFRP1 antibody reduced alveolar bone loss in the P. gingivalis-induced periodontitis model. Representative macroscopic image of alveolar bone after de-fleshing viewed from the palatal side on day 10. Animals were treated with either IgG or anti-SFRP1 antibody.

 
    Apoptosis
A significant decrease in inflammatory cell apoptosis was observed in the group injected with anti-SFRP1 antibody compared with the IgG-injected group (TableGo). Fibroblast apoptosis followed a trend similar to that seen for inflammatory cell apoptosis (TableGo). Apoptosis of bone-lining cells was also reduced in the anti-SFRP1 antibody-injected group compared with the IgG-injected group, but this involved a relatively small number of cells (TableGo).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS & METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
To assess the effect of SFRP1 inhibition in the inflammatory process, we used a P. gingivalis-induced murine periodontitis model. This model was found to be consistent with other animal models and the human appearance of chronic periodontitis (Adams et al., 1979; Rowe and Bradley, 1981). Our results demonstrated that, in periodontal tissues of P. gingivalis-infected animals, significant SFRP1 expression, as well as more apoptosis of inflammatory cells, fibroblasts, and bone-lining cells, was observed compared with controls. Additionally, inhibition of SFRP1 expression led to a significant reduction in P. gingivalis-induced inflammation, epithelial downgrowth, and alveolar bone loss. Also, a significant reduction in osteoclastogenesis and apoptosis of both inflammatory cells and fibroblasts was observed.

Consistent with the current literature (Pycroft et al., 2002), our study did not disclose any apoptosis in control animals, mostly because, at that stage, the turnover rate is very slow. However, congruent with the findings of Achong et al.(2003), in response to P. gingivalis-soaked ligatures, a phase of acute inflammation with maximum PMN infiltration was observed at day 7, followed by a more chronic inflammation phase with apical migration of the junctional epithelium, loss of connective tissue, and alveolar bone loss at day 10. Our apoptosis and SFRP1 expression data paralleled the inflammation phases, peaking at day 7 and being maintained at day 10.

Analysis of recent data demonstrated that the receptor activator of NF{kappa}B ligand (RANKL) is markedly induced in inflammatory cells of persons with periodontitis (Liu et al., 2003) and in osteoblasts exposed to P. gingivalis infection (Okahashi et al., 2004). Furthermore, Wnt family members have been found to regulate osteoclast formation and bone resorption, through down-regulation of RANKL (Spencer et al., 2006). This led to the proposition that, in osteoblasts, Wnt signaling markedly promotes osteoprotegerin (OPG) expression, a major inhibitor of osteoclast differentiation (Glass et al., 2005). Other observations have suggested that bone turnover is regulated by the interactions of RANKL and OPG (Khosla, 2001). In the present study, the inhibition of SFRP1 expression decreased periodontal tissue destruction, as measured by both epithelial downgrowth and alveolar bone loss. Inhibition of SFRP1 also led to a reduction of the inflammatory infiltrate. Consistent with these findings, the number of osteoclasts around the alveolar bone surface also decreased after SFRP1 inhibition. Our results agree with those from previous studies reporting that Wnt/ß-catenin signaling controls osteoclast differentiation (Holmen et al., 2005), such that the extent of alveolar bone loss can be altered by a change in the RANKL/OPG signaling axis.

It has previously been reported that Wnt signaling mediates leukocyte-inflammatory responses. Activation of Wnt decreased transendothelial migration of monocytes, which was associated with monocyte adherence to endothelial cells (Tickenbrock et al., 2006). Thus, it is reasonable to suggest that Wnt-regulated impeded migration may also have been involved in the reduction of inflammatory cell infiltration that we observed after anti-SFRP1 antibody treatment. Additionally, disease severity of periodontitis is ultimately determined by host immune response, notably via inflammatory cells and fibroblasts, which express several cytokines that influence disease progression (Seymour et al., 1993). Current studies have revealed that macrophages are responsible for apoptosis of LPS-induced osteoblasts and periodontal ligament (PDL) cells (Thammasitboon et al., 2006). Moreover, recent studies have also indicated that PDL fibroblasts exhibit special functions for the repair and regeneration of alveolar bone, and thereby play a role in preventing bone resorption (Murakami et al., 1999). Consistent with these findings, our results demonstrated that blocking SFRP1 expression resulted in reducing both inflammatory cell infiltrates into periodontal tissues and the extent of apoptosis of inflammatory cells and fibroblasts. Together, these may largely explain the observed reduction in breakdown of periodontal tissues in mice treated with anti-SFRP1 antibody.

Previous studies have demonstrated that SFRP1 is a negative modulator of osteoblast survival (Bodine et al., 2005). Moreover, an in vivo study has been reported in which loss of SFRP1 enhanced osteoblast proliferation, differentiation, and function; it also led to an increase in bone mass and suppressed apoptosis of osteoblasts and osteocytes (Bodine et al., 2004). Analysis of our data did not contradict these findings, although, in our study, treatment with anti-SFRP1 did not dramatically decrease the apoptosis of bone-lining cells. However, loss of SFRP1 may still have augmented the activity of mature osteoblasts. Supporting our findings, others have reported that SFRP1 can regulate biological function in both autocrine and paracrine fashions (Bodine and Komm, 2006).

However, the picture may be more complex than this. It was recently reported that SFRP1 binds directly to RANKL, where it can negatively regulate RANKL-dependent osteoclastogenesis (Hausler et al., 2004). Interestingly, SFRP1 regulates the Wnt signaling pathway by binding to Wnt and/or Fz, but it can also bind to RANKL. This suggests that, in regulating bone homeostasis, modulation of the RANKL level and the RANKL/OPG ratio, rather than the deletion of RANKL, has the greatest effect on osteoclasts. Thus, interfering with SFRP1 expression may alter both osteoblast and osteoclast differentiation and function, with the net result being reduction of alveolar bone loss. In our study, the expression of SFRP1 may represent a compensatory mechanism to regulate osteoclastogenesis in the context of periodontitis. Further study is needed to dissect the mechanisms related to SFRP1 that modulate periodontitis progression.

In summary, our results indicate that SFRP1 is expressed in inflammatory cells and bone cells associated with a P. gingivalis murine periodontitis model, whereas SFRP1 inhibition leads to reduced periodontitis severity. Inhibition of SFRP1 might represent an important therapeutic target in periodontitis for the decrease of inflammatory cell infiltrate and bone resorption.


   ACKNOWLEDGMENTS
 
This study was supported by National Institute of Dental and Craniofacial Research grant R01 DE15989 to S. Amar.

Received February 7, 2007; Last revision April 2, 2007; Accepted May 9, 2007


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS & METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Adams RA, Zander HA, Polson AM (1979). Cell populations in the transseptal fiber region before, during and after experimental periodontitis in squirrel monkeys. J Periodontol 50:7–12.[ISI][Medline]

Achong R, Nishimura I, Ramachandran H, Howell TH, Fiorellini JP, Karimbux NY (2003). Membrane type (MT) 1-matrix metalloproteinase (MMP) and MMP-2 expression in ligature-induced periodontitis in the rat. J Periodontol 74:494–500.[ISI][Medline]

Baker PJ, Evans RT, Roopenian DC (1994). Oral infection with Porphyromonas gingivalis and induced alveolar bone loss in immunocompetent and severe combined immunodeficient mice. Arch Oral Biol 39:1035–1040.[ISI][Medline]

Bodine PV, Komm BS (2006). Wnt signaling and osteoblastogenesis. Rev Endocr Metab Disord 7:33–39.[ISI][Medline]

Bodine PV, Zhao W, Kharode YP, Bex FJ, Lambert AJ, Goad MB, et al. (2004). The Wnt antagonist secreted frizzled-related protein-1 is a negative regulator of trabecular bone formation in adult mice. Mol Endocrinol 18:1222–1237.[Abstract/Free Full Text]

Bodine PV, Billiard J, Moran RA, Ponce-de-Leon H, McLarney S, Mangine A, et al. (2005). The Wnt antagonist secreted frizzled-related protein-1 controls osteoblast and osteocyte apoptosis. J Cell Biochem 96:1212–1230.[ISI][Medline]

Chiang CY, Kyritsis G, Graves DT, Amar S (1999). Interleukin-1 and tumor necrosis factor activities partially account for calvarial bone resorption induced by local injection of lipopolysaccharide. Infect Immun 67:4231–4236.[Abstract/Free Full Text]

Glass DA, Bialek P, Ahn JD, Starbuck M, Patel MS, Clevers H, et al. (2005). Canonical Wnt signaling in differentiated osteoblasts controls osteoclast differentiation. Dev Cell 8:751–764.[ISI][Medline]

Han X, Amar S (2004). Secreted frizzled-related protein 1 (SFRP1) protects fibroblasts from ceramide-induced apoptosis. J Biol Chem 279:2832–2840.[Abstract/Free Full Text]

Hausler KD, Horwood NJ, Chuman Y, Fisher JL, Ellis J, Martin TJ, et al. (2004). Secreted frizzled-related protein-1 inhibits RANKL-dependent osteoclast formation. J Bone Miner Res 19:1873–1881.[ISI][Medline]

Holmen SL, Zylstra CR, Mukherjee A, Sigler RE, Faugere MC, Bouxsein ML, et al. (2005). Essential role of beta-catenin in postnatal bone acquisition. J Biol Chem 280:21162–21168.[Abstract/Free Full Text]

Holt SC, Kesavalu L, Walker S, Genco CA (1999). Virulence factors of Porphyromonas gingivalis. Periodontol 2000 20:168–238.

Jones SE, Jomary C (2002). Secreted frizzled-related proteins: searching for relationships and patterns. Bioessays 24:811–820.[ISI][Medline]

Kawano Y, Kypta R (2003). Secreted antagonists of the Wnt signaling pathway. J Cell Sci 116(Pt 13):2627–2634.[Abstract/Free Full Text]

Khosla S (2001). Minireview: the OPG/RANKL/RANK system. Endocrinology 142:5050–5055.[Abstract/Free Full Text]

Kimura S, Nagai A, Onitsuka T, Koga T, Fujiwara T, Kaya H, et al. (2000). Induction of experimental periodontitis in mice with Porphyromonas gingivalis-adhered ligatures. J Periodontol 71:1167–1173.[ISI][Medline]

Klausen B, Evans RT, Sfintescu C (1989). Two complementary methods of assessing periodontal bone level in rats. Scand J Dent Res 97:494–499.[ISI][Medline]

Krishnan V, Bryant HU, Macdougald OA (2006). Regulation of bone mass by Wnt signaling. J Clin Invest 116:1202–1209.[ISI][Medline]

Lamont RJ, Jenkinson HF (1998). Life below the gum line: pathogenic mechanisms of Porphyromonas gingivalis. Microbiol Mol Biol Rev 62:1244–1263.[Abstract/Free Full Text]

Li CH, Amar S (2007). Morphometric, histomorphometric and microcomputed tomographic analysis of periodontal inflammatory lesions in a murine model. J Periodontol 78:1120–1128.[ISI][Medline]

Liu D, Xu JK, Figliomeni L, Huang L, Pavlos NJ, Rogers M, et al. (2003). Expression of RANKL and OPG mRNA in periodontal disease: possible involvement in bone destruction. Int J Mol Med 11:17–21.[ISI][Medline]

Logan CY, Nusse R (2004). The Wnt signaling pathway in development and disease. Annu Rev Cell Dev Biol 20:781–810.[ISI][Medline]

Murakami S, Takayama S, Ikezawa K, Shimabukuro Y, Kitamura M, Nozaki T, et al. (1999). Regeneration of periodontal tissues by basic fibroblast growth factor. J Periodontal Res 34:425–430.[ISI][Medline]

Okahashi N, Inaba H, Nakagawa I, Yamamura T, Kuboniwa M, Nakayama K, et al. (2004). Porphyromonas gingivalis induces receptor activator of NF-kappaB ligand expression in osteoblasts through the activator protein 1 pathway. Infect Immun 72:1706–1714.[Abstract/Free Full Text]

Pycroft JM, Hann A, Moxham BJ (2002). Apoptosis in the connective tissues of the periodontal ligament and gingivae of rat incisor and molar teeth at various stages of development. Connect Tissue Res 43:265–279.[ISI][Medline]

Rowe DJ, Bradley LS (1981). Quantitative analyses of osteoclasts, bone loss and inflammation in human periodontal disease. J Periodontal Res 16:13–19.[ISI][Medline]

Seymour GJ, Gemmell E, Reinhardt RA, Eastcott J, Taubman MA (1993). Immunopathogenesis of chronic inflammatory periodontal disease: cellular and molecular mechanisms. J Periodontal Res 28:478–486.[ISI][Medline]

Socransky SS, Haffajee AD (1992). The bacterial etiology of destructive periodontal disease: current concepts. J Periodontol 63(4 Suppl):322–331.[ISI][Medline]

Socransky SS, Haffajee AD, Cugini MA, Smith C, Kent RL (1998). Microbial complexes in subgingival plaque. J Clin Periodontol 25:134–144.[ISI][Medline]

Spencer GJ, Utting JC, Etheridge SL, Arnett TR, Genever PG (2006). Wnt signalling in osteoblasts regulates expression of the receptor activator of NFkappaB ligand and inhibits osteoclastogenesis in vitro. J Cell Sci 119(Pt 7):1283–1296.[Abstract/Free Full Text]

Thammasitboon K, Goldring SR, Boch JA (2006). Role of macrophages in LPS-induced osteoblast and PDL cell apoptosis. Bone 38:845–852.[Medline]

Tickenbrock L, Schwable J, Strey A, Sargin B, Hehn S, Baas M, et al. (2006). Wnt signaling regulates transendothelial migration of monocytes. J Leukoc Biol 79:1306–1313.[Abstract/Free Full Text]

Westendorf JJ, Kahler RA, Schroeder TM (2004). Wnt signaling in osteoblasts and bone diseases. Gene 341:19–39.[ISI][Medline]

Williams RC (1990). Periodontal disease. N Engl J Med 322:373–382.[ISI][Medline]

Zhou Q, Desta T, Fenton M, Graves DT, Amar S (2005). Cytokine profiling of macrophages exposed to Porphyromonas gingivalis, its lipopolysaccharide, or its FimA protein. Infect Immun 73:935–943.[Abstract/Free Full Text]





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