Protein kinase-A-dependent osteoprotegerin production on interleukin-1 stimulation in human gingival fibroblasts is distinct from periodontal ligament fibroblasts

Mechanical force application and inflammation induce osteoclastogenesis by independent pathways

OBJECTIVE

To investigate the functional changes of PDL fibroblasts in the presence of mechanical force, inflammation, or a combination of force and inflammation.

MATERIALS AND METHODS

Inflammatory supernatants were prepared by inoculating human neutrophils with Porphyromonas gingivalis. Primary human PDL fibroblasts (PDLF), gingival fibroblasts (GFs), and osteoblasts (Saos2) were then exposed to the inflammatory supernatants. Orthodontic force on the PDLFs was simulated by centrifugation. Analyses included cell proliferation, cell viability, cell cycle, and collagen expression, as well as osteoprotegerin (OPG) and receptor activator of nuclear factor kappa-Β ligand (RANKL) expression.

RESULTS

Mechanical force did not affect PDLF viability, but it increased the metabolic rate compared to resting cells. Force application shifted the PDLF cell cycle to the G0/G1 phase, arresting cell proliferation and leading to elevated collagen production, mild OPG level elevation, and robust RANKL level elevation. Including an inflammatory supernatant in the presence of force did not affect PDLF viability, proliferation, or cytokine expression. By contrast, the inflammatory supernatant increased RANKL expression in GFs, but not in Saos2 cells.

CONCLUSION

Applying mechanical force significantly affects PDLF function. Although inflammation had no effect on PDLF or Saos2 cells, it promoted RANKL expression in GF cells. Within the limitations of the in vitro model, the results suggest that periodontal inflammation and mechanical forces could affect bone catabolism through effects on different cell types, which may culminate in synergistic bone resorption.

Delineating the role of osteoprotegerin as a marker of breast cancer risk among women with a BRCA1 mutation

Women with a pathogenic germline mutation in the BRCA1 gene face a very high lifetime risk of developing breast cancer, estimated at 72% by age 80. Prophylactic bilateral mastectomy is the only effective way to lower their risk; however, most women with a mutation opt for intensive screening with annual MRI and mammography. Given that the BRCA1 gene was identified over 20 years ago, there is a need to identify a novel non-surgical approach to hereditary breast cancer prevention. Here, we provide a review of the emerging preclinical and epidemiologic evidence implicating the dysregulation of progesterone-mediated receptor activator of nuclear factor κB (RANK) signaling in the pathogenesis of BRCA1-associated breast cancer. Experimental studies have demonstrated that RANK inhibition suppresses Brca1-mammary tumorigenesis, suggesting a potential target for prevention. Data from studies conducted among women with a BRCA1 mutation further support this pathway in BRCA1-associated breast cancer development. Progesterone-containing (but not estrogen-alone) hormone replacement therapy is associated with an increased risk of breast cancer in women with a BRCA1 mutation. Furthermore, BRCA1 mutation carriers have significantly lower levels of circulating osteoprotegerin (OPG), the decoy receptor for RANK-ligand (RANKL) and thus endogenous inhibitor of RANK signaling. OPG levels may be associated with the risk of disease, suggesting a role of this protein as a potential biomarker of breast cancer risk. This may improve upon current risk prediction models, stratifying women at the highest risk of developing the disease, and further identify those who may be targets for anti-RANKL chemoprevention. Collectively, the evidence supports therapeutic inhibition of the RANK pathway for the primary prevention of BRCA1-associated breast cancer, which may generate unique prevention strategies (without prophylactic surgery) and enhance quality of life.

The effect of lipoxin A4 on E. coli LPS-induced osteoclastogenesis

Objectives

The objective of the present study was to investigate the effect of lipoxin-type A4 (LXA4) on bacterial-induced osteoclastogenesis.

Material and methods

Human periodontal ligament cells (PDLCs) in coculture with osteoclast precursors (RAW264.7 cells) were exposed to bacterial stimulation with lipopolysaccharide (LPS) to induce inflammation. After 24 h, cells were treated to 100 ng/ml of LXA4 and 50 ng/ml of forymul peptide receptor 2 (FPR2/ALX) receptor antagonist (Boc-2). After 5 days, osteoclastic resorptive activity was assessed on calcium phosphate (CaP) synthetic bone substitute. Additionally, osteoclastic differentiation was evaluated using tartrate-resistant acid phosphatase (TRAP) staining, TRAP enzymatic activity assay, and on the expression of osteoclast-specific genes.

Results

We found that stimulation of in the osteoclasts with LPS-stimulated PDLCs induced a significant increase in tartrate-resistant acid phosphatase (TRAP) positive cells, higher resorptive activity, and enhanced expression of specific genes. Meanwhile, LXA4-treatment exhibited strong anti-inflammatory activity, and was able to reverse these inflammatory effects.

Conclusions

We conclude that (1) PDLCs are a potential target for treating bacterial-induced bone resorption in patients with periodontal disease, and (2) LXA4 is a suitable candidate for such therapy.

Clinical relevance

The results prove that lipoxins have a protective role in bacterial-induced periodontal inflammation and alveolar bone resorption, which can be translated into a clinical beneficial alterative treatment.

Porphyromonas gulae Activates Unprimed and Gamma Interferon-Primed Macrophages via the Pattern Recognition Receptors Toll-Like Receptor 2 (TLR2), TLR4, and NOD2

Porphyromonas gulae is an anaerobic, Gram-negative coccobacillus that has been associated with periodontal disease in companion animals. The aims of this study were to analyze the ligation of pattern recognition receptors by P. gulae and the subsequent activation of macrophages. Exposure of HEK cells transfected with Toll-like receptors (TLRs) or NOD-like receptors to P. gulae resulted in the ligation of TLR2, TLR4, and NOD2. The effects of this engagement of receptors were investigated by measuring the synthesis of nitric oxide (NO), CD86 expression, and inflammatory cytokine production by wild-type, TLR2^-/-, and TLR4^-/- macrophages. The addition of P. gulae to unprimed and gamma interferon (IFN-γ)-primed (M1 phenotype) macrophages significantly increased the surface expression of CD86, but only M1 macrophages produced nitric oxide. P. gulae-induced expression of CD86 on unprimed macrophages was dependent on both TLR2 and TLR4, but CD86 expression and NO production in M1 macrophages were only TLR2 dependent. P. gulae induced an increase in secretion of interleukin-1α (IL-1α), IL-1β, IL-6, IL-12p70, IL-13, tumor necrosis factor alpha (TNF-α), granulocyte colony-stimulating factor (G-CSF), monocyte chemoattractant protein 1 (MCP-1), and macrophage inflammatory protein 1α (MIP-1α) by M1 macrophages compared to that by unprimed controls. Among these cytokines, secretion of IL-6 and TNF-α by M1 macrophages was dependent on either TLR2 or TLR4. Our data indicate that TLR2 and TLR4 are important for P. gulae activation of unprimed macrophages and that activation and effector functions induced in M1 macrophages by P. gulae are mainly dependent on TLR2. In conclusion, P. gulae induces a strong TLR2-dependent inflammatory M1 macrophage response which may be important in establishing the chronic inflammation associated with periodontal disease in companion animals.

Differentiated embryonic chondrocytes 1 expression of periodontal ligament tissue and gingival tissue in the patients with chronic periodontitis

OBJECTIVE

To evaluate the DEC1 expression of periodontal ligament tissue and gingival tissue in the patients with chronic periodontitis.

METHODS

20 non-smoking patients with chronic periodontitis and 20 healthy individuals were enrolled. Periodontal ligament tissue and gingival tissue samples from healthy subjects were collected during teeth extraction for orthodontic reason or the third molar extraction. The parallel samples from patients with chronic periodontitis were obtained during periodontal flap operations or teeth extraction as part of periodontal treatment. The DEC1 expression and the alkaline phosphatase (ALP) activity of both the periodontal ligament tissue and gingival tissue were determined by Western blot, Immunohistochemistry and ALP Detection Kit.

RESULTS

The DEC1 expression of periodontal ligament tissue in the patients with chronic periodontitis decreased significantly along with the decreased ALP activity. On the contrary, the DEC1 expression of gingival tissue in the patients with chronic periodontitis increased significantly. Further study found that the DEC1 expression of gingival tissue increased mainly in the suprabasal layer of gingival epithelial cells but decreased in the gingival connective tissue of the patients with chronic periodontitis.

CONCLUSION

The DEC1 expression decreases in the periodontal ligament tissue which is related to the osteogenic capacity, whereas the DEC1 expression increases in the suprabasal layer of gingival epithelial cells which are involved in immune inflammatory response in the patients with chronic periodontitis. The findings provide a new target to explore the pathology and the therapy of periodontitis.

Role of periodontal ligament fibroblasts in osteoclastogenesis: a review

During the last decade it has become clear that periodontal ligament fibroblasts may contribute to the in vitro differentiation of osteoclasts. We surveyed the current findings regarding their osteoclastogenesis potential. Periodontal ligament fibroblasts have the capacity to select and attract osteoclast precursors and subsequently to retract and enable migration of osteoclast precursors to the bone surface. There, fusion of precursors takes place, giving rise to osteoclasts. The RANKL-RANK-osteoprotegerin (OPG) axis is considered crucial in this process. Periodontal ligament fibroblasts produce primarily OPG, an osteoclastogenesis-inhibitory molecule. However, they may be influenced in vivo by direct or indirect interactions with bacteria or by mechanical loading. Incubation of periodontal ligament fibroblasts with bacteria or bacterial components causes an increased expression of RANKL and other osteoclastogenesis-stimulating molecules, such as tumor necrosis factor-α and macrophage-colony stimulating factor. Similar results are observed after the application of mechanical loading to these fibroblasts. Periodontal ligament fibroblasts may be considered to play an important role in the remodelling of alveolar bone. In vitro experiments have demonstrated that periodontal ligament fibroblasts adapt to bacterial and mechanical stimuli by synthesizing higher levels of osteoclastogenesis-stimulating molecules. Therefore, they probably contribute to the enhanced osteoclast formation observed during periodontitis and to orthodontic tooth movement.

Inflammatory mediators in the pathogenesis of periodontitis

Periodontitis is a chronic inflammatory condition of the periodontium involving interactions between bacterial products, numerous cell populations and inflammatory mediators. It is generally accepted that periodontitis is initiated by complex and diverse microbial biofilms which form on the teeth, i.e. dental plaque. Substances released from this biofilm such as lipopolysaccharides, antigens and other virulence factors, gain access to the gingival tissue and initiate an inflammatory and immune response, leading to the activation of host defence cells. As a result of cellular activation, inflammatory mediators, including cytokines, chemokines, arachidonic acid metabolites and proteolytic enzymes collectively contribute to tissue destruction and bone resorption. This review summarises recent studies on the pathogenesis of periodontitis, with the main focus on inflammatory mediators and their role in periodontal disease.

Periodontal fibroblasts modulate proliferation and osteogenic differentiation of embryonic stem cells through production of fibroblast growth factors

BACKGROUND

Periodontal ligament fibroblasts (PLFs) maintain homeostasis of periodontal ligaments by producing paracrine factors that affect various functions of stem-like cells. It is hypothesized that PLFs induce proliferation and differentiation of stem cells more effectively than gingival fibroblasts (GFs) and skin fibroblasts (SFs).

METHODS

PLFs and GFs were isolated from extracted teeth and cultured in the presence and absence of osteogenesis-inducing factors. Mouse embryonic stem (mES) cells and SFs were purchased commercially. mES cells were incubated with culture supernatants of these fibroblasts or cocultured directly with the cells. Proliferation and mineralization in mES cells were determined at various times of incubation. Immunostaining and polymerase chain reaction were performed. The activity of mitogen-activated protein kinase and alkaline phosphatase (ALP) was also measured.

RESULTS

In cocultures, PLFs stimulated proliferation of mES cells more effectively than GFs or SFs. Similarly, the addition of culture supernatant of PLFs induced the most prominent proliferation of mES cells, and this was significantly inhibited by treatment with antibody against fibroblast growth factor (FGF)4 or the c-Jun N-terminal kinase inhibitor SP600125 (anthra[1,9-cd]pyrazol-6(2H)-one). Supplementation with culture supernatant from the fibroblasts induced osteogenic differentiation of mES cells in the order PLFs > GFs > SFs. These activities of PLFs were related to their potential to produce osteogenic markers, such as ALP and runt-related transcription factor-2 (Runx2), and to secrete FGF7. Pretreatment of mES cells with the extracellular signal-regulated kinase inhibitor PD98059 [2-(2-amino-3-methyoxyphenyl)-4H-1-benzopyran-4-one] or SP600125 clearly attenuated mineralization induced by culture supernatant of PLF with attendant decreases in mRNA levels of Runx2, bone sialoprotein, osteocalcin, and osteopontin.

CONCLUSION

PLFs regulate the proliferation and osteogenic differentiation of mES cells more strongly than GFs and SFs via the secretion of FGF through a mechanism that involves mitogen-activated protein kinase-mediated signaling.

Lipopolysaccharide-induced indoleamine 2,3-dioxygenase expression in the periodontal ligament

BACKGROUND AND OBJECTIVE

Indoleamine 2,3-dioxygenase (IDO) is a tryptophan-oxidizing enzyme with immune-inhibitory effects. The aim of this study was to investigate the expression of IDO by lipopolysaccharide (LPS), a component of gram-negative bacteria, in human periodontal ligament (PDL) cells.

MATERIAL AND METHODS

Human PDL cells and gingival fibroblasts (GFs) were prepared from explants of human PDLs and from gingival tissues of clinically healthy donors, respectively. Real-time RT-PCR, western blotting and the IDO enzyme assay were performed to determine the expression of IDO following LPS treatment of cells. LPS was injected into mice tail veins to evaluate the effects of LPS in vivo in the maxillary first molar. Immunofluorescence staining and histological analysis were followed to localize IDO in mouse PDL.

RESULTS

The level of expression of IDO mRNA in primary human PDL cells after LPS treatment was increased in a dose-dependent manner, reaching a peak 8 h after LPS treatment. The expression and activities of IDO protein were significantly increased in comparison with those of the control. In addition, the increased production of kynurenine in culture medium was observed 72 h after LPS treatment. In the immunofluorescence findings, stronger immunoreactivities were shown in PDL than in gingival tissues in the maxillae. In accordance with the immunofluorescence findings, LPS treatment induced a strong up-regulation of IDO mRNA in human PDL cells, whereas human GFs showed only a weak response to LPS.

CONCLUSION

These results clearly show that IDO was induced by LPS in primary human PDL cells, suggesting that PDL might be involved in the regulation of oral inflammatory disease.

Role of periodontal pathogenic bacteria in RANKL-mediated bone destruction in periodontal disease

Accumulated lines of evidence suggest that hyperimmune responses to periodontal bacteria result in the destruction of periodontal connective tissue and alveolar bone. The etiological roles of periodontal bacteria in the onset and progression of periodontal disease (PD) are well documented. However, the mechanism underlying the engagement of periodontal bacteria in RANKL-mediated alveolar bone resorption remains unclear. Therefore, this review article addresses three critical subjects. First, we discuss earlier studies of immune intervention, ultimately leading to the identification of bacteria-reactive lymphocytes as the cellular source of osteoclast-induction factor lymphokine (now called RANKL) in the context of periodontal bone resorption. Next, we consider (1) the effects of periodontal bacteria on RANKL production from a variety of adaptive immune effector cells, as well as fibroblasts, in inflamed periodontal tissue and (2) the bifunctional roles (upregulation vs. downregulation) of LPS produced from periodontal bacteria in a RANKL-induced osteoclast-signal pathway. Future studies in these two areas could lead to new therapeutic approaches for the management of PD by down-modulating RANKL production and/or RANKL-mediated osteoclastogenesis in the context of host immune responses against periodontal pathogenic bacteria.

Internal prostaglandin synthesis augments osteoprotegerin production in human gingival fibroblasts stimulated by lipopolysaccharide

Periodontitis is an inflammatory bone disease caused by Gram-negative anaerobic bacteria. Osteoclast differentiation is regulated by the balance between receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG). The purpose of this study was to examine the mechanism of OPG production in human gingival fibroblasts (HGF) stimulated by lipopolysaccharide (LPS) from periodontopathic bacteria. The expressions of Toll-like receptor 2 (TLR-2) and TLR-4 in HGF were examined using flow-cytometry. HGF were stimulated with whole cell extracts or LPS from Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis with or without polymyxin B, a LPS inhibitor. In addition, HGF were stimulated with LPS, prostaglandin E(2) (PGE(2)), various agonists of PGE receptors (EP1, EP2, EP3 and EP4 agonists) with or without indomethacin (IND), a prostaglandin synthesis inhibitor. OPG and PGE(2) production was measured using an enzyme-linked immunosorbent assay (ELISA). HGF expressed both TLR-2 and TLR-4. Both A. actinomycetemcomitans and P. gingivalis LPS augmented OPG expression in HGF. Whole cell extracts from A. actinomycetemcomitans and P. gingivalis augmented OPG production by HGF; the augmentation was suppressed by polymyxin B. IND suppressed OPG production in LPS-stimulated HGF. PGE(2) stimulated HGF to produce OPG. EP1 and EP2 agonists, but not EP3 and EP4 agonists, increased OPG production by HGF. These results suggest that LPS-induced OPG production by HGF is regulated via EP1 and/or EP2 receptors by endogenously generated PGE(2).