Stimulation of interleukin-6 production in human dental pulp cells by peptidoglycans from Lactobacillus casei

Ginsenoside Rb1 alleviates lipopolysaccharide-induced inflammation in human dental pulp cells via the PI3K/Akt, NF-κB, and MAPK signalling pathways

AIM

Among numerous constituents of Panax ginseng, a constituent named Ginsenoside Rb1 (G-Rb1) has been studied to diminish inflammation associated with diseases. This study investigated the anti-inflammatory properties of G-Rb1 on human dental pulp cells (hDPCs) exposed to lipopolysaccharide (LPS) and aimed to determine the underlying molecular mechanisms.

METHODOLOGY

The KEGG pathway analysis was performed after RNA sequencing in G-Rb1- and LPS-treated hDPCs. Reverse-transcription polymerase chain reaction (RT-PCR) and western blot analysis were used for the assessment of cell adhesion molecules and inflammatory cytokines. Statistical analysis was performed with one-way ANOVA and the Student-Newman-Keuls test.

RESULTS

G-Rb1 did not exhibit any cytotoxicity within the range of concentrations tested. However, it affected the levels of TNF-α, IL-6 and IL-8, as these showed reduced levels with exposure to LPS. Additionally, less mRNA and protein expressions of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) were shown. With the presence of G-Rb1, decreased levels of PI3K/Akt, phosphorylated IκBα and p65 were also observed. Furthermore, phosphorylated ERK and JNK by LPS were diminished within 15, 30 and 60 min of G-Rb1 exposure; however, the expression of non-phosphorylated ERK and JNK remained unchanged.

CONCLUSIONS

G-Rb1 suppressed the LPS-induced increase of cell adhesion molecules and inflammatory cytokines, while also inhibiting PI3K/Akt, phosphorylation of NF-κB transcription factors, ERK and JNK of MAPK signalling in hDPCs.

Dissecting specific Wnt components governing osteogenic differentiation potential by human periodontal ligament stem cells through interleukin-6

Periodontal ligament stem cells (PDLSCs) play a significant role on periodontal tissue and alveolar bone homeostasis. During inflammation, interleukin (IL)-6 serves as one of key cytokine players controlling tissue reaction as well as alveolar bone tissue remodeling. It is believed that periodontal tissue inflammation causes periodontium degradation, especially alveolar bone. However, in this study, we show that an inflammatory mediator, IL-6, may serve another direction on alveolar bone homeostasis during inflammatory condition. We found that, IL-6 at 10 and 20 ng/mL was not cytotoxic and dose-dependently exerted beneficial effects on osteogenic differentiation of human PDLSCs (hPDLSCs), as demonstrated by increased alkaline phosphatase activity, mRNA expression of osteogenic markers, and matrix mineralization. The presence of physiological and inflammatory level of IL-6, the osteogenic differentiation potential by hPDLSCs was enhanced by several possible mechanisms including transforming growth factor (TGF), Wnt, and Notch pathways. After in-depth and thorough exploration, we found that Wnt pathway serves as key regulator controlling osteogenic differentiation by hPDLSCs amid the IL-6 presentation. Surprisingly, apart from other mesenchymal stem cells, distinct Wnt components are employed by hPDLSCs, and both canonical and non-canonical Wnt pathways are triggered by different mechanisms. Further validation by gene silencing, treatment with recombinant Wnt ligands, and β-catenin stabilization/translocation confirmed that IL-6 governed the canonical Wnt/β-catenin pathway via either WNT2B or WNT10B and employed WNT5A to activate the non-canonical Wnt pathway. These findings fulfill the homeostasis pathway governing periodontal tissue and alveolar bone regeneration and may serve for further therapeutic regimen design for restoring the tissues.

PGlyRP3 concerts with PPARγ to attenuate DSS-induced colitis in mice

Nutrients may modulate immunity through their transcription factors that act on both metabolic and immunity genes. It has been shown that the transcription factor of lipid ligands PPARγ physically binds the gene promoter of the peptidoglycan recognition protein (PGlyRP3), which showed anti-inflammatory action in vitro. It is hypothesized in the present work that olive oil feeding protects against toxicity of DSS-induced colitis via activation of the lipid transcription factor PPARγ that stimulates the anti-inflammatory PGlyRP3. Results: PGlyRP3 is expressed in mouse colon and up-regulated by olive oil feeding. Olive oil reduced mortality and severity scores of DSS-induced colitis and down-regulated the proinflammatory IL-1b, IL-6 and TNFα genes. This protective effect was accompanied by up-regulation of both PPARγ and PGlyRP3. Inhibition of PPARγ by its antagonist BADGE down-regulated PGlyRP3 and abolished the anti-inflammatory effect of olive oil feeding in this DSS-induced colitis model, reflecting the pivotal role of PPARγ binding nutrition and inflammation. Activation of PGlyRP3 by its ligand peptidoglycan was not responsible for the inflammation caused by peptidoglycan, since neutralization of TLR2 attenuated this inflammatory response without affecting the peptidoglycan-induced PGlyRP3 level. Olive oil activated the IκBα and inhibited NF-κB and cox-2 gene expressions, and p65 nuclear translocation in DSS-colitis mice, reflecting the involvement of the inhibition of NF-κB signaling pathway in the anti-inflammatory olive oil - PPARγ - PGlyRP3 access. This pathway was reactivated by the PPARγ antagonist BADGE. Conclusions: Olive oil regulates by the same transcription factor (PPARγ) both lipid metabolic and immune gene (PGlyRP3) expressions, exerting the anti-inflammatory effect, and protecting against DSS-induced colitis in mice.

Brain-Derived Neurotrophic Factor Inhibits Peptidoglycan-Induced Inflammatory Cytokine Expression in Human Dental Pulp Cells

The aim of this study was to examine the anti-inflammatory effect of brain-derived neurotrophic factor (BDNF) on human dental pulp cells (HDPCs) and identify the intracellular signaling pathway involved. We investigated the effect of BDNF (50 ng/ml) on interleukin (IL)-6 and IL-8 expression in peptidoglycan (PGN)-treated HDPCs. An inhibition assay was performed with MAPK or NF-κB inhibitors to determine the possible signaling pathway. IL-6 and IL-8 mRNA, IL-6 and IL-8 protein, and phosphorylated p38 kinase activity were determined using real-time PCR, ELISA, and Western blot analysis, respectively. BDNF significantly attenuated PGN-induced IL-6 and IL-8 mRNA and protein levels in HDPCs. A p38 inhibitor also inhibited IL-6 and IL-8 mRNA transcription. PGN stimulated phosphorylated p38 kinase activity in HDPCs, which was inhibited by BDNF. Suppression of phosphorylated p38 kinase activity by BDNF in HDPCs inhibited increased IL-6 and IL-8 expression induced by PGN. Our findings suggest that BDNF regulates intracellular signaling molecule activities to exert its anti-inflammatory effect.

Interleukin-6-174G/C Polymorphism Contributes to Periodontitis Susceptibility: An Updated Meta-Analysis of 21 Case-Control Studies

Introduction. Chronic Periodontitis (CP) is suggested to be related to gene variations. Present study aims to quantitatively estimate the association between interleukin-6- (IL-6-) 174G/C polymorphism and CP susceptibility. Materials and Methods. Pubmed, Embase, and Web of Science were searched up to May 2016. The meta-analyses were performed using STATA 12.0. Results. 21 studies were yielded. Significant associations were found under heterozygote comparison and dominant model in studies fulfilling HWE (GC versus GG: OR = 0.690, 95% CI = 0.560–0.849, P = 0.000; CC + GC versus GG: OR = 0.690, 95% CI = 0.568–0.838, P < 0.001); significant associations were found under heterozygote comparison and dominant model in Caucasian studies fulfilling HWE (GC versus GG: OR = 0.752, 95% CI = 0.577–0.980, P = 0.035; CC + GC versus GG: OR = 0.737, 95% CI = 0.576–0.944, P = 0.016); significant associations were found under allele comparison, heterozygote comparison, and dominant model in Brazilian population (C versus G: OR = 0.648, 95% CI = 0.497–0.845, P = 0.001; GC versus GG: OR = 0.621, 95% CI = 0.441–0.876, P = 0.007; CC + GC versus GG: OR = 0.649, 95% CI = 0.470–0.896, P = 0.009). Conclusion. IL-6 174 polymorphism is associated with CP susceptibility. In Brazilian and Caucasian population, IL-6 174 GG genotype plays as a risk factor to CP.

Interleukin-6 concentration changes in plasma and saliva in bisphosphonate-related osteonecrosis of the jaws

AIM

To determine the plasma and saliva levels of IL-6 in patients with bisphosphonate-related osteonecrosis of the jaws (BRONJ) and to investigate whether there is a correlation between more advanced stages of BRONJ and levels of IL-6.

MATERIAL AND METHODS

We studied three groups: group 1 consisted of 30 patients with BRONJ due to intravenous bisphosphonates (ivBP), group 2 consisted of 25 patients treated with ivBP but without BRONJ, and group 3 consisted of 15 healthy controls. In each case, we assayed plasma and saliva IL-6 samples using an ELISA test.

RESULTS

Significantly, higher IL-6 values were found in both saliva and plasma in group 1 vs groups 2 and 3 (P < 0.01). Group 1 showed no differences in plasma or saliva IL-6 according to patient gender (P > 0.05), type of tumor, BRONJ location, etiology of BRONJ, or disease stage (P > 0.05). We found higher plasma and saliva IL-6 values in the more advances stages of BRONJ, although the differences were not statistically significant.

CONCLUSIONS

Plasma and saliva IL-6 values were higher in our patients with BRONJ than in controls and therefore might be a useful tool for monitoring the severity of BRONJ.

Anti-inflammatory effect of catechin on cultured human dental pulp cells affected by bacteria-derived factors

Catechins (bioactive polyphenols in green tea) are known to exhibit potent anti-inflammatory properties. However, the anti-inflammatory effects of catechins on inflamed dental pulp tissue are not known. In this study, we investigated the effect of epigallocatechin-3-gallate (EGCG) and epicatechin gallate (ECG), the major components of green tea catechins, on the expression of pro-inflammatory cytokines and adhesion molecules in human dental pulp cells stimulated with bacteria-derived factors such as lipopolysaccharide (LPS) and peptidoglycan (PG). The expression of interleukin (IL)-6 and of IL-8 was examined using the reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assays. The expression of intercellular adhesion molecule-1 (ICAM-1) and of vascular cell adhesion molecule-1 (VCAM-1) on dental pulp cells was analyzed using flow cytometry. The presence of EGCG and ECG significantly reduced, in a concentration-dependent manner, the expression of IL-6 and IL-8 in dental pulp cells exposed to LPS or PG. Increased expression of ICAM-1 and VCAM-1 on the dental pulp cells in response to bacterial components was also decreased by treatment with EGCG and ECG. These findings suggest that green tea catechins may prevent the exacerbation of pulpitis.

Roles of TLR2, TLR4, NOD2, and NOD1 in Pulp Fibroblasts

Pulp fibroblasts express various pro-inflammatory mediators leading to marked infiltration of inflammatory cells in the progression of pulpitis. We hypothesized that pulp fibroblasts play roles in the recognition of invaded caries-related bacteria and the subsequent innate immune responses. We found clear expressions of TLR2, NOD1, and NOD2 and a faint expression of TLR4 in human dental pulp fibroblasts (HDPF) by RT-PCR and flow cytometry. We also observed that various pro-inflammatory mediators, including cytokines, chemokines, adhesion molecules, prostaglandin E2 and its key enzyme COX-2, not iNOS or caspase-1, were markedly up-regulated by stimulation with these TLR and NOD agonists. More over, the NOD2 agonist acted synergistically with the TLR2, not the TLR4, agonist to stimulate the production of pro-inflammatory mediators in HDPF. These findings indicate that TLR2, TLR4, NOD2, and NOD1 in HDPF are functional receptors, and NOD2 is a modulator of signals transmitted through TLR2 in pulpal immune responses, leading to progressive pulpitis.

Expression of nucleotide-binding oligomerization domain 2 in normal human dental pulp cells and dental pulp tissues

INTRODUCTION

The nucleotide-binding oligomerization domain (NOD) proteins belong to a distinct family of proteins that are implicated in the intracellular recognition of bacterial components. NOD2 appears to be a sensor of bacterial peptidoglycans because it recognizes a minimal motif present in all peptidoglycans. The interaction of NOD2 with downstream signaling molecules ultimately results in the activation of NF-kappaB and production of inflammatory mediators in innate immunity. As such, NOD2 may play an important role in the detection of bacterial pathogens and the initiation of inflammation within the dental pulp. This study was designed to evaluate the expression of NOD2 in normal human dental pulp cells (HDPCs) and human pulp tissues.

METHODS

Human pulp tissue samples were collected from freshly extracted human wisdom teeth, and HDPCs were prepared from the explants of normal human dental pulp tissues. Nested reverse-transcription polymerase chain reaction (Nested RT-PCR) and Western blotting were performed to detect the expression of NOD2 messenger RNA and protein, respectively. Immunohistochemical staining was used to determine the distribution of NOD2 in the pulp tissues.

RESULTS

The NOD2 messenger RNA and protein were present in normal human dental pulp tissues, with most NOD2 protein expression being localized to odontoblasts and some pulp vascular endothelial cells. In contrast, HDPCs only showed a low level of NOD2 protein expression.

CONCLUSIONS

Our results suggest that NOD2 protein expressed in HDPCs and pulp tissues may play an important role in dental immune defense.

The effects of tumor necrosis factor-alpha, interleukin-1beta, interleukin-6, and transforming growth factor-beta1 on pulp fibroblast mediated collagen degradation

Dental pulp destruction is believed to be regulated, in part, by the matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs). Cytokines are believed to be important in the pathogenesis of pulpitis. This study examined the effects that TNF-alpha, IL-1beta, IL-6, and TGF-beta1 have on the collagen degradation mediated by pulp fibroblasts utilizing a cell-mediated collagen degradation assay. Reverse transcriptase-polymerase chain reaction, Western blot analyses, and zymography were utilized to examine multiple MMPs and TIMPs. The collagen degradation mediated by these cells was stimulated by these cytokines. TNF-alpha, IL-1beta, and IL-6 increased the mRNA and/or protein expression of MMP-1, MMP-2, and MMP-3. TGF-beta1 decreased MMP-1 mRNA expression, while only slightly affecting the MMP-2 and MMP-3 mRNA and/or protein. These cytokines did not affect the expression of TIMP-1 or TIMP-2. These results suggest that these cytokines affect pulp destruction, in part, by differentially regulating the MMPs and TIMPs.

Cytokine signalling in rat pulp interstitial fluid and transcapillary fluid exchange during lipopolysaccharide-induced acute inflammation

The dental pulp consists of loose connective tissue encased in rigid dentinal walls. Because of its topography the tissue has low interstitial compliance and limited capacity to expand during fluid volume changes. Due to limitations regarding access to interstitial fluid, basic knowledge on transcapillary fluid transport parameters is lacking for this organ. The scope of this project was dual: first we aimed at establishing a method for isolation of pulp interstitial fluid (IF), and second we applied the method in rats subjected to lipopolysaccharide (LPS)-induced endotoxaemia. The aim was to measure colloid osmotic pressure (COP) and pro-inflammatory cytokines in the pulp IF during acute inflammation. Fluid volumes and pulpal blood flow (PBF) were measured to obtain more information about microcirculatory changes that take place in this pulpitis model. By centrifugation of incisor pulp at 239 g we were able to extract fluid representative for IF. Pulp IF had a relative high control COP (approximately 83% of plasma COP) and was similar to plasma COP 3 h after LPS challenge. The pulp exhibited a high content of IF (0.60 +/- 0.03 ml (g wet weight)(-1)) and a vascular volume of 0.03 +/- 0.01 ml (g w.w.)(-1) No differences were observed in the distribution of fluid volumes after 1.5 and 3 h LPS exposure. PBF and systemic blood pressure dropped significantly after LPS administration. PBF remained low whereas systemic blood pressure was re-established during the 3-h period, implying organ dysfunction. There was a differential pattern of cytokine expression in pulp IF and serum with cytokines such as IL-1alpha, IL-1beta and TNF-alpha locally produced, whereas others such as IFN-gamma and IL-6 were produced systemically and probably spilled over to the pulp IF after LPS exposure. Our findings show that pulp IF can be isolated by centrifugation and that this method is useful when studying fluid balance and extracellular signalling mechanisms in the dental pulp in normal and pathological conditions.

Gene expression profiling of pulpal tissue reveals the molecular complexity of dental caries

High-throughput characterisation of the molecular response of pulpal tissue under carious lesions may contribute to improved future diagnosis and treatment. To identify genes associated with this process, oligonucleotide microarrays containing approximately 15,000 human sequences were screened using pooled total RNA isolated from pulpal tissue from both healthy and carious teeth. Data analysis identified 445 genes with 2-fold or greater difference in expression level, with 85 more abundant in health and 360 more abundant in disease. Subsequent gene ontological grouping identified a variety of processes and functions potentially activated or down-modulated during caries. Validation of microarray results was obtained by a combination of real-time and semi-quantitative PCR for selected genes, confirming down-regulation of Dentin Matrix Protein-1 (DMP-1), SLIT 2, Period-2 (PER 2), Period-3 (PER 3), osteoadherin, Glypican-3, Midkine, activin receptor interacting protein-1 (AIP 1), osteoadherin and growth hormone receptor (GHR), and up-regulation of Adrenomedullin (ADM), Interleukin-11 (IL-11), Bone sialoprotein (BSP), matrix Gla protein (MGP), endothelial cell growth factor-1 (ECGF 1), inhibin beta A and orosomucoid-1 (ORM 1), in diseased pulp. Real-time PCR analyses of ADM and DMP-1 in a panel of healthy and carious pulpal tissue and also in immune system cells highlighted the heterogeneity of caries and indicated increased expression of ADM in neutrophils activated by bacterial products. In contrast, DMP-1 was predominantly expressed by cells native to healthy pulpal tissue. This study has greatly extended our molecular knowledge of dental tissue disease and identified involvement of genes previously unassociated with this process.

Proinflammatory cytokine profiles in pulp fibroblasts stimulated with lipopolysaccharide and methyl mercaptan

Pulpal disease is intimately associated with the immune system's response to bacteria products. Clinical pathology is mediated in part by the production of pyrogenic cytokines, especially interleukin (IL)-1, tumor necrosis factor (TNF)-alpha, and IL-6. Methyl mercaptan (CH3SH), a volatile sulfur compound produced by anaerobic Gram-negative bacteria, has been shown to contribute to the production of IL-1 by human mononuclear cells. In this report, we investigated the production of IL-1, TNF-alpha, and IL-6 by human pulp fibroblasts when stimulated for various periods of time with lipopolysaccharide (LPS) with or without the presence of CH3SH. We found that LPS and CH3SH had no effect on the production of IL-1 or TNF-alpha. However, LPS stimulated IL-6 production, and this production was augmented when CH3SH was present. We conclude that the volatile sulfur compound CH3SH plays a role in activation and modulation of the immune response through its role in production of IL-6.

Pulp biology: progress during the past 25 years

During the past 25 years there has been a rapid expansion in our knowledge of the dentine and pulp complex. This paper provides representative examples of important advances that researchers have made in this field. Topics to be considered include: differentiation of odontoblasts, dentine matrix proteins, extent of odontoblast processes, pulpal stem cells, apoptosis, interstitial fluid pressure in normal and inflamed pulps, class II antigen-presenting cells of the pulp, cytokines, antibodies, pulpal calcifications, tertiary dentine and pulpal inflammation associated with bacterial contamination of exposed dentine beneath restorations.

Differential regulation of interleukin-6 and inducible cyclooxygenase gene expression by cytokines through prostaglandin-dependent and -independent mechanisms in human dental pulp fibroblasts

Increased levels of interleukin-1 (IL)-1, tumor necrosis factor-alpha (TNF-alpha), IL-6, and prostaglandin E2 (PGE2) have been detected in inflamed pulp tissue. To gain further insight into the molecular pathogenesis of pulpitis, we investigated the effects of IL-1alpha or TNF-alpha and PGE2, either alone or in combination on IL-6 and cyclooxygenase (COX)-2 messenger RNA (mRNA) production in cultured human dental pulp (HDP) fibroblasts. Exposure of HDP fibroblasts to IL-1alpha or TNF-alpha resulted in elevated levels of IL-6 (approximately 3.4 to approximately 10.4-fold) and COX-2 (approximately 5 to approximately 6.2-fold) mRNA. Simultaneous addition of IL-1alpha and PGE2 or TNF-alpha and PGE2 to the cultures significantly reduced the cytokine-induced IL-6 mRNA synthesis ranging from 45% to 65%. However, indomethacin enhanced the cytokine-stimulated IL-6 mRNA synthesis by approximately 1.7 to approximately 3.4-fold. This action could be reversed by exogenous PGE2. In contrast, PGE2 or indomethacin failed to modify the stimulatory effect of IL-1alpha or TNF-alpha on COX-2 gene expression. Because excessive levels of IL-6 and prostaglandins have been connected with the pathogenesis of several inflammatory diseases, our results suggest the involvement of HDP fibroblasts in the development of pulpitis via producing IL-6 and COX-2. Furthermore, expression of IL-6 and COX-2 genes in this cell seems to be differentially regulated by cytokines through prostaglandin-dependent and -independent pathways.

An immunohistochemical study of osteoprotegerin in the human dental pulp

This study investigated the expression of osteoprotegerin (OPG) in healthy and inflamed dental pulps. Histological sections 7 microm thick of 47 teeth, either caries-free or affected by gross caries, were used. Sections were stained with hematoxylin-eosin, and other sections of the same specimen were subjected to the avidin-biotin peroxidase complex immunohistochemical procedure for detection of OPG. The study focused on the coronal pulp that was divided into peripheral and central regions. In the peripheral pulp healthy and inflamed specimens showed high OPG immunoreactivity of the odontoblastic layer. When no inflammation was present in the central pulp OPG immunoreactivity was light. Fibroblasts and endothelial cells showed immunoreactivity ranging from none to intense. When inflammation was present in the central pulp the chronic inflammatory cells showed intense immunoreactivity.

Effect of systemic penicillin on pain in untreated irreversible pulpitis

OBJECTIVE

The purpose of this prospective, randomized, double-blind study was to determine the effect of penicillin on pain in untreated teeth diagnosed with irreversible pulpitis.

STUDY DESIGN

Forty emergency patients participated, and each had a clinical diagnosis of an irreversible pulpitis. Patients randomly received a 7-day oral dose (28 capsules, 500 mg each, to be taken every 6 hours) of either penicillin or a placebo control in a double-blind manner. No endodontic treatment was performed. Each patient also received ibuprofen; acetaminophen with codeine (30 mg); and a 7-day diary to record pain, percussion pain, and number and type of pain medication taken.

RESULTS

The administration of penicillin did not significantly (P >.05) reduce pain, percussion pain, or the number of analgesic medications taken by patients with untreated irreversible pulpitis. The majority of patients with untreated irreversible pulpitis had significant pain and required analgesics to manage this pain.

CONCLUSION

Penicillin should not be prescribed for untreated irreversible pulpitis because penicillin is ineffective for pain relief.

Expression of osteoprotegerin (osteoclastogenesis inhibitory factor) in cultures of human dental mesenchymal cells and epithelial cells

Osteoprotegerin (OPG)/osteoclastogenesis inhibitory factor (OCIF) inhibits osteoclast differentiation, activity, and survival; therefore OPG/OCIF may regulate the resorption of dental hard tissues, such as alveolar bone, cementum, and dentin. To investigate this issue, reverse transcriptase-polymerase chain reaction using specific primers for OPG/OCIF was performed with total RNAs isolated from human gingival keratinocytes (HGKs), human gingival fibroblasts (HGFs), human periodontal ligament cells (HPDLs), and human pulp cells (HPCs) in culture. PCR products were found in HGFs, HPDLs, and HPCs, but not in HGKs, and the DNA sequence of these products was 100% identical to the reported sequence of the OPG gene. Northern blot analyses also showed that HGFs, HPDLs, and HPCs, but not HGKs, expressed OPG/OCIF transcripts of approximately 2.5 kb. Interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) increased OPG/OCIF mRNA levels in a dose-and time-dependent manner in HPDL. After 12 h of treatment, IL-1beta at 3 ng/ml and TNF-alpha at 3 ng/ml increased OPG/OCIF mRNA expression by 190% and 110%, respectively, with a maximal effect. The stimulatory effects of IL-1beta and TNF-alpha were also seen in HPC. However, IL-6 and transforming growth factor-beta had little effect on OPG/OCIF mRNA levels in HPDL. These findings suggest that OPG/OCIF synthesized by dental mesenchymal cells locally regulates the resorption of dental hard tissues through cytokines.