Periodontal Ligament Fibroblasts Sustain Destructive Immune Modulators of Chronic Periodontitis

In-vitro effects of different hyaluronic acids on periodontal biofilm-immune cell interaction

Introduction

Recent studies have demonstrated a positive role of hyaluronic acid (HA) on periodontal clinical outcomes. This in-vitro study aimed to investigate the impact of four different HAs on interactions between periodontal biofilm and immune cells.

Methods

The four HAs included: high-molecular-weight HA (HHA, non-cross-linked), low-molecular-weight HA (LHA), oligomers HA (OHA), and cross-linked high-molecular-weight HA (CHA). Serial experiments were conducted to verify the influence of HAs on: (i) 12-species periodontal biofilm (formation and pre-existing); (ii) expression of inflammatory cytokines and HA receptors in monocytic (MONO-MAC-6) cells and periodontal ligament fibroblasts (PDLF) with or without exposure to periodontal biofilms; (iii) generation of reactive oxygen species (ROS) in MONO-MAC-6 cells and PDLF with presence of biofilm and HA.

Results

The results indicated that HHA and CHA reduced the bacterial counts in a newly formed (4-h) biofilm and in a pre-existing five-day-old biofilm. Without biofilm challenge, OHA triggered inflammatory reaction by increasing IL-1β and IL-10 levels in MONO-MAC cells and IL-8 in PDLF in a time-dependent manner, whereas CHA suppressed this response by inhibiting the expression of IL-10 in MONO-MAC cells and IL-8 in PDLF. Under biofilm challenge, HA decreased the expression of IL-1β (most decreasing HHA) and increased IL-10 levels in MONO-MAC-6 cells in a molecular weight dependent manner (most increasing CHA). The interaction between HA and both cells may occur via ICAM-1 receptor. Biofilm stimulus increased ROS levels in MONO-MAC-6 cells and PDLF, but only HHA slightly suppressed the high generation of ROS induced by biofilm stimulation in both cells.

Conclusion

Overall, these results indicate that OHA induces inflammation, while HHA and CHA exhibit anti-biofilm, primarily anti-inflammatory, and antioxidant properties in the periodontal environment.

Unraveling Divergent Transcriptomic Profiles: A Comparative Single-Cell RNA Sequencing Study of Epithelium, Gingiva, and Periodontal Ligament Tissues

The periodontium comprising periodontal ligament (PDL), gingiva, and epithelium play crucial roles in maintaining tooth integrity and function. Understanding tissue cellular composition and gene expression is crucial for illuminating periodontal pathophysiology. This study aimed to identify tissue-specific markers via scRNA-Seq. Primary human PDL, gingiva, and epithelium tissues (n = 7) were subjected to cell hashing and sorting. scRNA-Seq library preparation using 10× Genomics protocol and Illumina sequencing was conducted. The analysis was performed using Cellranger (v3.1.0), with downstream analysis via R packages Seurat (v5.0.1) and SCORPIUS (v1.0.9). Investigations identified eight distinct cellular clusters, revealing the ubiquitous presence of epithelial and gingival cells. PDL cells evolved in two clusters with numerical superiority. The other clusters showed varied predominance regarding gingival and epithelial cells or an equitable distribution of both. The cluster harboring most cells mainly consisted of PDL cells and was present in all donors. Some of the other clusters were also tissue-inherent, while the presence of others was environmentally influenced, revealing variability across donors. Two clusters exhibited genetic profiles associated with tissue development and cellular integrity, respectively, while all other clusters were distinguished by genes characteristic of immune responses. Developmental trajectory analysis uncovered that PDL cells may develop after epithelial and gingival cells, suggesting the inherent PDL cell-dominated cluster as a final developmental stage. This single-cell RNA sequencing study delineates the hierarchical organization of periodontal tissue development, identifies tissue-specific markers, and reveals the influence of environmental factors on cellular composition, advancing our understanding of periodontal biology and offering potential insights for therapeutic interventions.

Revealing Genetic Dynamics: scRNA-seq Unravels Modifications in Human PDL Cells across In Vivo and In Vitro Environments

The periodontal ligament (PDL) is a highly specialized fibrous tissue comprising heterogeneous cell populations of an intricate nature. These complexities, along with challenges due to cell culture, impede a comprehensive understanding of periodontal pathophysiology. This study aims to address this gap, employing single-cell RNA sequencing (scRNA-seq) technology to analyze the genetic intricacies of PDL both in vivo and in vitro. Primary human PDL samples (n = 7) were split for direct in vivo analysis and cell culture under serum-containing and serum-free conditions. Cell hashing and sorting, scRNA-seq library preparation using the 10x Genomics protocol, and Illumina sequencing were conducted. Primary analysis was performed using Cellranger, with downstream analysis via the R packages Seurat and SCORPIUS. Seven distinct PDL cell clusters were identified comprising different cellular subsets, each characterized by unique genetic profiles, with some showing donor-specific patterns in representation and distribution. Formation of these cellular clusters was influenced by culture conditions, particularly serum presence. Furthermore, certain cell populations were found to be inherent to the PDL tissue, while others exhibited variability across donors. This study elucidates specific genes and cell clusters within the PDL, revealing both inherent and context-driven subpopulations. The impact of culture conditions-notably the presence of serum-on cell cluster formation highlights the critical need for refining culture protocols, as comprehending these influences can drive the creation of superior culture systems vital for advancing research in PDL biology and regenerative therapies. These discoveries not only deepen our comprehension of PDL biology but also open avenues for future investigations into uncovering underlying mechanisms.

Lactobacillus reuteri for chronic periodontitis: focus on underlying mechanisms and future perspectives

Chronic periodontitis is a common oral disorder caused by pathogenic bacteria. Despite the wide use of antibiotics as the conventional adjunctive treatment, the challenges of increased antibiotic resistance and limited therapeutic effect receive considerable attention and the developments of alternative treatments gain increasing consideration. Growing evidence showed that Lactobacillus reuteri (LR) may represent a promising alternative adjunct for chronic periodontitis. It can attenuate inflammation and reduce tissue disruption. LR-assisted treatment has been shown to be effective and relatively safe in multiple clinical trials, and accumulating evidence suggests its significant biological roles. In the current review, we focus on capturing the underlying mechanisms of LR involved in chronic periodontitis, thereby representing a scientific foundation for LR-assisted therapy. Furthermore, we point out the challenges and future directions for further clinical trials to improve the clinical applicability for LR.

The impact of arthritogenic viruses in oral tissues

Arthritis and periodontitis are inflammatory diseases that share several immunopathogenic features. The expansion in the study of virus-induced arthritis has shed light on how this condition could impact other parts of the human body, including the mouth. Viral arthritis is an inflammatory joint disease caused by several viruses, most notably the alphaviruses Chikungunya virus (CHIKV), Sindbis virus (SINV), Ross River virus (RRV), Mayaro virus (MAYV), and O'nyong'nyong virus (ONNV). These viruses can induce an upsurge of matrix metalloproteinases and immune-inflammatory mediators such as Interleukin-6 (IL6), IL-1β, tumor necrosis factor, chemokine ligand 2, and receptor activator of nuclear factor kappa-B ligand in the joint and serum of infected individuals. This can lead to the influx of inflammatory cells to the joints and associated muscles as well as osteoclast activation and differentiation, culminating in clinical signs of swelling, pain, and bone resorption. Moreover, several data indicate that these viral infections can affect other sites of the body, including the mouth. The human oral cavity is a rich and diverse microbial ecosystem, and viral infection can disrupt the balance of microbial species, causing local dysbiosis. Such events can result in oral mucosal damage and gingival bleeding, which are indicative of periodontitis. Additionally, infection by RRV, CHIKV, SINV, MAYV, or ONNV can trigger the formation of osteoclasts and upregulate pro-osteoclastogenic inflammatory mediators, interfering with osteoclast activation. As a result, these viruses may be linked to systemic conditions, including oral manifestations. Therefore, this review focuses on the involvement of alphavirus infections in joint and oral health, acting as potential agents associated with oral mucosal inflammation and alveolar bone loss. The findings of this review demonstrate how alphavirus infections could be linked to the comorbidity between arthritis and periodontitis and may provide a better understanding of potential therapeutic management for both conditions.

Periodontal ligament cells from patients with treated stable periodontitis: Characterization and osteogenic differentiation potential

BACKGROUND AND OBJECTIVE

Periodontal ligament progenitor cells (PDL cells) isolated from patients with inflammatory periodontitis have impaired regenerative capacity, but it is unknown whether this capacity can be recovered upon treatment and stabilization of the periodontal condition. The study aimed to investigate the expression of surface markers and the proliferation and osteogenic potential of PDL cells isolated from patients with treated stable periodontitis (S-PDL cells), periodontally healthy individuals (H-PDL cells), and patients with inflammatory periodontitis (I-PDL cells).

METHODS

H-PDL, I-PDL, and S-PDL cells were isolated from the extracted teeth of individuals who (1) were periodontally healthy, (2) had inflammatory periodontitis, and (3) had treated stable periodontitis, respectively. The expression levels of surface markers and the proliferative and osteogenic capacities of the PDL cells were assessed.

RESULTS

PDL cells derived from all three sources exhibited mesenchymal stem cell (MSC) characteristics. They were positive for MSC-related markers and negative for a hematopoiesis-related marker. However, S-PDL cells had higher proliferation rates, higher expression levels of osteogenic markers, higher alkaline phosphatase activity, and more calcium nodules than I-PDL cells. But all of these parameters remained lower in S-PDL cells than in H-PDL cells.

CONCLUSIONS

S-PDL cells proliferated faster and had greater osteogenic potential than I-PDL cells, although these values remained lower than those in H-PDL cells.

IL-7-Treated Periodontal Ligament Cells Regulate Local Immune Homeostasis by Modulating Treg/Th17 Cell Polarization

Both interleukin (IL)-7 and human periodontal ligament cells (hPDLCs) have immunomodulatory properties. However, their combined effect on CD4⁺T cells has never been studied. In this study, we aimed to investigate the effect of conditioned medium of hPDLCs treated with rhIL-7 on the differentiation of CD4⁺T cells into regulatory T cells/T helper 17 cells (Treg/Th17 cells) and observe the effect of IL-7 on the immunomodulatory properties of PDLCs. After hPDLCs were treated with different concentrations of rhIL-7 for 24 h, the collected supernatants were used to incubate CD4⁺T cells for 3 days. A gamma-secretase inhibitor (DAPT) was used to suppress the activation of the Notch1 signaling pathway. Cell proliferation, apoptosis, and necrosis were determined using the cell counting kit-8 (CCK-8) and flow cytometry (FCM). The expressions of forkhead box P3 (Foxp3) in CD4⁺T cells and transforming growth factor (TGF-β) and IL-6 in the supernatants were determined by ELISA. Reverse transcription-quantitative PCR (RT-qPCR), and the Western blot (WB) determined the mRNA levels and protein expression of various target factors. FCM was used to detect the mean fluorescence intensity of PD-L1 in hPDLCs and to analyze the differentiation of Treg/Th17 cells. Our results showed that IL-7 promoted proliferation and inhibited apoptosis in hPDLCs, promoted the expression of TGF-β, PD-L1, Notch1, Jagged1, and Hes1, and inhibited the levels of hypoxia-inducible factor (HIF)-1α and TCF7, whereas the addition of DAPT effectively reversed these effects. Importantly, we found that the conditioned medium of hPDLCs treated with rhIL-7 promoted the polarization of CD4⁺T cells into Treg cells but had no significant effect on the differentiation of Th17 cells. Our study indicated that treatment of PDLCs with IL-7 can promote the polarization of CD4⁺T cells into Treg cells by modulating the expression of inflammatory factors and signaling molecules through activating the Notch1 signaling pathway, thus participating in the regulation of immune homeostasis in the periodontal microenvironment.

The Expression and Regulatory Roles of Long Non-Coding RNAs in Periodontal Ligament Cells: A Systematic Review

Periodontal ligament (PDL) cells play a pivotal role in periodontal and bone homeostasis and have promising potential for regenerative medicine and tissue engineering. There is compelling evidence that long non-coding RNAs (lncRNAs) are differentially expressed in PDL cells compared to other cell types and that these lncRNAs are involved in a variety of biological processes. This study systematically reviews the current evidence regarding the expression and regulatory functions of lncRNAs in PDL cells during various biological processes. A systematic search was conducted on PubMed, the Web of Science, Embase, and Google Scholar to include articles published up to 1 July 2021. Original research articles that investigated the expression or regulation of lncRNAs in PDL cells were selected and evaluated for a systematic review. Fifty studies were ultimately included, based on our eligibility criteria. Thirteen of these studies broadly explored the expression profiles of lncRNAs in PDL cells using microarray or RNA sequencing. Nineteen studies investigated the mechanisms by which lncRNAs regulate osteogenic differentiation in PDL cells. The remaining 18 studies investigated the mechanism by which lncRNAs regulate the responses of PDL cells to various stimuli, namely, lipopolysaccharide-induced inflammation, tumor necrosis factor alpha-induced inflammation, mechanical stress, oxidative stress, or hypoxia. We systematically reviewed studies on the expression and regulatory roles of lncRNAs in diverse biological processes in PDL cells, including osteogenic differentiation and cellular responses to inflammation, mechanical stress, and other stimuli. These results provide new insights that may guide the development of lncRNA-based therapeutics for periodontal and bone regeneration.

NLRP3 Inflammasome Pharmacological Inhibitors in Glycyrrhiza for NLRP3-Driven Diseases Treatment: Extinguishing the Fire of Inflammation

Inflammation is the tissues’ defense response after the body is stimulated by microbial infection or damage signals, and it is initiated when pattern recognition receptors recognize pathogen-related molecular patterns and danger-related molecular patterns. The hyperactivation of NLRP3 inflammasome, the main driving force of immune outbreaks, is involved in a wide range of inflammatory diseases. Meanwhile, growing evidence has indicated that the development of NLRP3-targeted therapies offers great potential and promise for the treatment of related diseases. The search for and development of efficacious anti-inflammatory prodrugs from natural sources of plants and traditional Chinese medicines (TCMs) have received extensive attention. Glycyrrhiza, an important minister in the kingdom of TCMs, has high activity and a wide range of therapeutic effects. Studies have shown that a variety of active components found in Glycyrrhiza, such as licochalcone A, echinatin, isoliquiritigenin, and glycyrrhizin, produce a wide range of anti-inflammatory effects by discouraging NLRP3 inflammasome activation. Here, we summarize the role and mechanism of the active ingredients in Glycyrrhiza that target the NLRP3 inflammasome and treat related inflammatory diseases. We describe a favorable approach for the development of natural, safe, and efficient drugs that exploit these naturally occurring active ingredients to treat NLRP3-driven diseases.

Establishing a technique for isolation and characterization of human periodontal ligament derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are extensively used in tissue regenerative procedures. One source of MSCs is the periodontal ligament (PDL) of teeth. Isolation of MSCs from extracted teeth is reasonably simple, being less invasive and presenting fewer ethical concerns than does the harvesting of MSC’s from other sites. The objectives of this study were to isolate and characterize the PDL stem cells (PDLSC) from healthy adults’ extracted teeth and then to characterize them by comparing them with bone-marrow derived MSCs (BMMSC).

Methods

The PDL tissue was scraped from the roots of freshly extracted teeth to enzymatically digest using collagenase. The cells were sub-cultured. Flow-cytometric analysis for the MSC surface-markers CD105, CD73, CD166, CD90, CD34, CD45 and HLA-DR was performed. To confirm the phenotype, total RNA was extracted to synthesize cDNA and which was then subjected to RT-PCR. The gene-expression for Oct4A, Sox2, NANOG and GAPDH was determined by gel-electrophoresis. To assess their multilineage potential, cells were cultured with osteogenic, chondrogenic and adipogenic medium and then stained by Alizarin-red, Alcian-blue and Oil-Red-O respectively. MSCs from the bone-marrow were processed similarly to serve as controls.

Results

The cells isolated from extracted teeth expanded successfully. On flow-cytometric analysis, the cells were positive for CD73, CD90, CD105, CD166 and negative for CD34, CD45 and HLA-DR. The PDLSCs expressed Oct4A, Sox2, and NANOG mRNA with GAPDH expression. Cells cultured in the osteogenic, chondrogenic and adipogenic media stained positive for Alizarin-red, Alcian-blue and Oil- Red-O respectively. The surface marker expression and the trilineage differentiation characteristics were comparable to those of the BMMSCs.

Conclusions

The periodontal ligament tissue of extracted teeth is a potential source of therapeutically useful MSCs. Harvesting them is not invasive and are a promising source of MSC as the PDLSCs showed characteristics similar to those of the highly regarded MSC’s derived from bone-marrow.

The Potential Roles of Dec1 and Dec2 in Periodontal Inflammation

Periodontal inflammation is a common inflammatory disease associated with chronic inflammation that can ultimately lead to alveolar attachment loss and bone destruction. Understanding autophagy and pyroptosis has suggested their significant roles in inflammation. In recent years, studies of differentiated embryo-chondrocyte expressed genes 1 and 2 (Dec1 and Dec2) have shown that they play important functions in autophagy and in pyroptosis, which contribute to the onset of periodontal inflammation. In this review, we summarize recent studies on the roles of clock genes, including Dec1 and Dec2, that are related to periodontal inflammation and other diseases.

CTHRC1 Knockdown Promotes Inflammatory Responses Partially by p38 MAPK Activation in Human Periodontal Ligament Cells

Collagen triple helix repeat containing 1 (CTHRC1), a secreted glycoprotein, is widely expressed in many tissues. It has been recently defined as a novel marker for rheumatoid arthritis (RA), a systemic inflammatory disorder. However, the precise role of CTHRC1 in other chronic inflammatory diseases, like periodontal disease, remains unclear. This research aimed to explore the presence of CTHRC1 in periodontal inflammation, determine the precise role in inflammatory response modulation in periodontal ligament cells (PDLCs), and explore its underlying mechanisms. In vivo gingival crevicular fluid (GCF) and gingivae were obtained from healthy people and chronic periodontitis patients. Maxillary tissues of mice with or without ligature-induced periodontitis were immunostained for CTHRC1. In vitro human PDLCs were treated with tumor necrosis factor alpha (TNF-α) to mimic the inflammatory environment. Small interfering RNA (siRNA) was used to silence CTHRC1. SB203580 was used to inhibit the p38 mitogen-activated protein kinase (MAPK) pathway. CTHRC1 was highly expressed in GCF and gingival tissues of periodontitis patients. Animal models also revealed the same tendency. CTHRC1 knockdown promoted inflammatory cytokine production and activated the p38 MAPK signaling pathway in PDLCs. Inhibiting the p38 MAPK signaling pathway partially attenuated the inflammatory responses. This study revealed that CTHRC1 was highly expressed in periodontitis and suggested that CTHRC1 might play an important role in modulating periodontal inflammation.

Tissue Engineering for Periodontal Ligament Regeneration: Biomechanical Specifications

The periodontal biomechanical environment is very difficult to investigate. By the complex geometry and composition of the periodontal ligament (PDL), its mechanical behavior is very dependent on the type of loading (compressive versus tensile loading; static versus cyclic loading; uniaxial versus multiaxial) and the location around the root (cervical, middle, or apical). These different aspects of the PDL make it difficult to develop a functional biomaterial to treat periodontal attachment due to periodontal diseases. This review aims to describe the structural and biomechanical properties of the PDL. Particular importance is placed in the close interrelationship that exists between structure and biomechanics: the PDL structural organization is specific to its biomechanical environment, and its biomechanical properties are specific to its structural arrangement. This balance between structure and biomechanics can be explained by a mechanosensitive periodontal cellular activity. These specifications have to be considered in the further tissue engineering strategies for the development of an efficient biomaterial for periodontal tissues regeneration.

Dec2 attenuates autophagy in inflamed periodontal tissues

INTRODUCTION

Transcriptional regulation of autophagy depends on the transcription factors coordinated inflammatory feedback mechanism. Here, we provide a comprehensive functional characterization of periodontal ligament fibroblasts (PDLFs) treated with Porphyromonas gingivalis lipopolysaccharide (LPS), aiming to reveal previously unappreciated biological changes and to investigate how a transcription factor differentiated embryonic chondrocytes 2 (Dec2)-deficient environment influences the function of autophagy in nflamed human PDLFs.

METHODS

A Dec2-deficient (Dec2KO) experimental periodontal inflammation mouse model and treatment with P. gingivalis LPS were employed to examine the role of autophagy in PDLFs using hematoxylin and eosin staining and immunohistochemistry in vivo. A Dec2 small interfering RNA (siRNA) was used to modulate autophagy, and the effect of autophagy on the Dec2 pathway was explored using real-time polymerase chain reaction and western blot analysis in vitro.

RESULTS

LPS-treated human PDLFs (HPDLFs) induced autophagy, as demonstrated by the enhanced levels of microtubule-associated protein 1 light chain 3-II (LC3-II) and the induction of ATG5, Beclin1, and Dec2. Compared with a scrambled siRNA, a Dec2 siRNA triggered the detrimental influences of LPS and markedly enhanced autophagy expression in inflamed HPDLFs. The expression of phosphorylated ERK was increased and levels of phosphorylated mammalian target of rapamycin (mTOR) were decreased after exposure to LPS in Dec2 siRNA transfected HPDLFs. The Dec2KO model exhibited that P. gingivalis in Dec2 deficient conditions increases the inflammation of PDLFs by regulating autophagy.

CONCLUSIONS

These results demonstrate that a Dec2 deficiency can alleviate LPS-induced inflammation via the ERK/mTOR signaling pathway by regulating autophagy, conceivably delivering a novel approach for the detection of periodontal treatments.

Application of specialized pro-resolving mediators in periodontitis and peri-implantitis: a review

Scaling and root planning is a key element in the mechanical therapy used for the eradication of biofilm, which is the major etiological factor for periodontitis and peri‐implantitis. However, periodontitis is also a host mediated disease, therefore, removal of the biofilm without adjunctive therapy may not achieve the desired clinical outcome due to persistent activation of the innate and adaptive immune cells. Most recently, even the resident cells of the periodontium, including periodontal ligament fibroblasts, have been shown to produce several inflammatory factors in response to bacterial challenge. With increased understanding of the pathophysiology of periodontitis, more research is focusing on opposing excessive inflammation with specialized pro‐resolving mediators (SPMs). This review article covers the major limitations of current standards of care for periodontitis and peri‐implantitis, and it highlights recent advances and prospects of SPMs in the context of tissue reconstruction and regeneration. Here, we focus primarily on the role of SPMs in restoring tissue homeostasis after periodontal infection.

Loss of Dec1 prevents autophagy in inflamed periodontal ligament fibroblast

Periodontal ligament fibroblasts (PDLFs) are integral to the homeostasis of periodontal tissue. The transcription factor Dec1 functions to modulate Porphyromonas gingivalis-induced periodontal inflammation. Here, we aimed to characterize the Dec1-mediated autophagy in PDLFs under inflammatory conditions. Human PDLFs were subjected to an inflammatory environment using P. gingivalis Lipopolysaccaride (LPS) along with Dec1 siRNA in vitro. Quantitative real-time polymerase chain reaction and Western blot analyses were used to evaluate the expression levels of autophagy-related genes and their upstream AKT/mTOR signaling pathways. An experimental P. gingivalis-treated Dec1 knockout (Dec1KO) mouse model was used to confirm the expression of autophagy in PDLFs in vivo. Treatment with P. gingivalis LPS induced the expression of ATG5, Beclin1 and microtubule-associated protein 1 light chain 3 (LC3) and elevated the expression of pro-inflammatory cytokine IL-1β and Dec1 in human PDLFs. Knockdown of Dec1 partly reversed the detrimental influences of LPS on these autophagy markers in human PDLFs. The inhibition of autophagy with Dec1 siRNA suppressed the inflammatory effect of AKT/mTOR signaling pathways following treatment with P. gingivalis LPS. P. gingivalis-treated Dec1KO mice partly reduced autophagy expression. These findings suggest that a Dec1 deficiency can modulate the interaction between autophagy and inflammation in PDLFs.

Osteoprotegerin is sensitive to actomyosin tension in human periodontal ligament fibroblasts

Periodontal ligament fibroblasts (PdLFs) are an elongated cell type in the periodontium with matrix and bone regulatory functions which become abnormal in periodontal disease (PD). Here we found that the normally elongated and oriented PdLF nucleus becomes rounded and loses orientation in a mouse model of PD. Using in vitro micropatterning of cultured primary PdLF cell shape, we show that PdLF elongation correlates with nuclear elongation and the presence of thicker, contractile F-actin fibers. The rounded nuclei in mouse PD models in vivo are, therefore, indicative of reduced actomyosin tension. Inhibiting actomyosin contractility by inhibiting myosin light chain kinase, Rho kinase or myosin ATPase activity, in cultured PdLFs each consistently reduced messenger RNA levels of bone regulatory protein osteoprotegerin (OPG). Infection of cultured PdLFs with two different types of periodontal bacteria (Porphyromonas gingivalis and Fusobacterium nucleatum) failed to recapitulate the observed nuclear rounding in vivo, upregulated nonmuscle myosin II phosphorylation and downregulated OPG. Collectively, our results add support to the hypothesis that PdLF contractility becomes decreased and contributes to disease progression in PD.

A comparison of acyl-moieties for noncovalent functionalization of PLGA and PEG-PLGA nanoparticles with a cell-penetrating peptide

Noncovalent functionalization with acylated cell-penetrating peptides achieves an efficient cellular uptake of PLGA and PEG-PLGA nanoparticles.

Autophagy, One of the Main Steps in Periodontitis Pathogenesis and Evolution

Periodontitis represents a complex inflammatory disease that compromises the integrity of the tooth-supporting tissue through the interaction of specific periodontal pathogens and the host's immune system. Experimental data help to outline the idea that the molecular way towards periodontitis initiation and progression presents four key steps: bacterial infection, inflammation, oxidative stress, and autophagy. The aim of this review is to outline the autophagy involvement in the pathogenesis and evolution of periodontitis from at least three points of view: periodontal pathogen invasion control, innate immune signaling pathways regulation and apoptosis inhibition in periodontal cells. The exact roles played by reactive oxygen species (ROS) inside the molecular mechanisms for autophagy initiation in periodontitis still require further investigation. However, clarifying the role and the mechanism of redox regulation of autophagy in the periodontitis context may be particularly beneficial for the elaboration of new therapeutic strategies.

Cannabinoid type-2 receptor agonist, inverse agonist, and anandamide regulation of inflammatory responses in IL-1β stimulated primary human periodontal ligament fibroblasts

OBJECTIVE

The aim of this study is to understand the role of cannabinoid type 2 receptor (CB2R) during periodontal inflammation and to identify anti-inflammatory agents for the development of drugs to treat periodontitis (PD).

BACKGROUND

Cannabinoid type 2 receptor is found in periodontal tissue at sites of inflammation/infection. Our previous study demonstrated anti-inflammatory responses in human periodontal ligament fibroblasts (hPDLFs) via CB2R ligands.

METHODS

Anandamide (AEA), HU-308 (agonist), and SMM-189 (inverse agonist) were tested for effects on IL-1β-stimulated cytokines, chemokines, and angiogenic and vascular markers expressed by hPDLFs using Mesoscale Discovery V-Plex Kits. Signal transduction pathways (p-c-Jun, p-ERK, p-p-38, p-JNK, p-CREB, and p-NF-kB) were investigated using Cisbio HTRF kits. ACTOne and Tango™ -BLA functional assays were used to measure cyclic AMP (cAMP) and β-arrestin activity.

RESULTS

IL-1β stimulated hPDLF production of 18/39 analytes, which were downregulated by the CB2R agonist and the inverse agonist. AEA exhibited pro-inflammatory and anti-inflammatory effects. IL-1β increased phosphoproteins within the first hour except p-JNK. CB2R ligands attenuated p-p38 and p-NFĸB, but a late rise in p-38 was seen with HU-308. As p-ERK levels declined, a significant increase in p-ERK was observed later in the time course by synthetic CB2R ligands. P-JNK was significantly affected by SMM-189 only, while p-CREB was elevated significantly by CB2R ligands at 180 minutes. HU-308 affected both cAMP and β-arrestin pathway. SMM-189 only stimulated cAMP.

CONCLUSION

The findings that CB2R agonist and inverse agonist may potentially regulate inflammation suggest that development of CB2R therapeutics could improve on current treatments for PD and other oral inflammatory pathologies.

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.

Lipoxin suppresses inflammation via the TLR4/MyD88/NF-κB pathway in periodontal ligament cells

Objective

The objective of the present study was to evaluate the anti‐inflammatory effects of lipoxin A4 (LXA4) for the treatment of periodontitis in an in vitro model.

Methods

Human PDLCs were challenged with Escherichia coli (E. coli) lipopolysaccharide (LPS) to evoke an inflammatory response. This was done either in monoculture or in coculture with THP‐1, a monocytic cell line. Thereafter, cytokine expression was measured by ELISA, with or without LXA4. In addition, the effects of LXA4 were analyzed on the TLR‐MyD88‐NF‐κB (TMN)‐mediated intracellular signal pathway using immunocytochemistry.

Results

In response to LPS, the level of the pro‐inflammatory cytokine tumor necrosis factor alpha increased, whereas the anti‐inflammatory cytokine interleukin‐4 decreased significantly (p < .05). These effects were consistently reversed when LPS‐challenged PDLCs were also treated with LXA4. The results in the coculture system were comparable to the monoculture. Immunohistochemistry and quantitative assessment confirmed the importance of the TMN signal pathway in these processes.

Conclusion

These results corroborate earlier findings that PDLCs play an important role in inflammation. Moreover, LXA4 might offer new approaches for the therapeutic treatment of periodontal disease.

Up-regulated ferritin in periodontitis promotes inflammatory cytokine expression in human periodontal ligament cells through transferrin receptor via ERK/P38 MAPK pathways

OBJECTIVE

Ferritin, an iron-binding protein, is ubiquitous and highly conserved; it plays a crucial role in inflammation, which is the main symptom of periodontitis. Full-length cDNA library analyses have demonstrated abundant expression of ferritin in human periodontal ligament. The aims of the present study were to explore how ferritin is regulated by local inflammation, and to investigate its functions and mechanisms of action in the process of periodontitis.

METHODS

Human gingival tissues were collected from periodontitis patients and healthy individuals. Experimental periodontitis was induced by ligature of second molars in mice. The expression of ferritin light polypeptide (FTL) and ferritin heavy polypeptide (FTH) were assessed by immunohistochemistry. Meanwhile, after stimulating human periodontal ligament cells (HPDLCs) with P. gingivalis-lipopolysaccharide (LPS), interleukin (IL)-6, and tumor necrosis factor-α (TNF-α), the expression of FTH and FTL were measured. Then, IL-6 and IL-8 were measured after incubation with different concentrations of apoferritin (iron-free ferritin) and several intracellular signaling pathway inhibitors, or after knockdown of the transferrin receptor.

RESULTS

Both FTH and FTL were substantially higher in inflamed periodontal tissues than in healthy tissues. The location of the elevated expression correlated well with the extent of inflammatory infiltration. Moreover, expression of FTH and FTL were enhanced after stimulation with P. gingivalis-LPS, IL-6, TNF-α. Apoferritin induced the production of IL-6 and IL-8 in a dose-dependent manner partly through binding to the transferrin receptor and activating ERK/P38 signaling pathways in HPDLCs.

CONCLUSIONS

Ferritin is up-regulated by inflammation and exhibits cytokine-like activity in HPDLCs inducing a signaling cascade that promotes expression of pro-inflammatory cytokines associated with periodontitis.

Involvement of interleukin‑23 induced by Porphyromonas endodontalis lipopolysaccharide in osteoclastogenesis

Periapical lesions are characterized by the destruction of periapical bone, and occur as a result of local inflammatory responses to root canal infection by microorganisms including Porphyromonas endodontalis (P. endodontalis). P. endodontalis and its primary virulence factor, lipopolysaccharide (LPS), are associated with the development of periapical lesions and alveolar bone loss. Interleukin-23 (IL-23) is critical in the initiation and progression of periodontal disease via effects on peripheral bone metabolism. The present study investigated the expression of IL-23 in tissue where a periapical lesion was present, and the effect of P. endodontalis LPS on the expression of IL-23 in periodontal ligament (PDL) cells. Reverse transcription- quantitative polymerase chain reaction and immunohistochemistry revealed increased levels of IL-23 expression in tissue with periapical lesions compared with healthy PDL tissue. Treatment with P. endodontalis LPS increased the expression of IL-23 in the SH-9 human PDL cell line. BAY11-7082, a nuclear factor κB inhibitor, suppressed P. endodontalis LPS-induced IL-23 expression in SH-9 cells. Treatment of RAW264.7 cells with conditioned medium from P. endodontalis LPS-treated SH-9 cells promoted osteoclastogenesis. By contrast, RAW264.7 cells treated with conditioned medium from IL-23-knockdown SH-9 cells underwent reduced levels of osteoclastogenesis. The results of the present study indicated that the expression of IL-23 in PDL cells induced by P. endodontalis LPS treatment may be involved in the progression of periapical lesions via stimulation of the osteoclastogenesis process.

Chronic stress accelerates ligature-induced periodontitis by suppressing glucocorticoid receptor-α signaling

Periodontitis is a common chronic inflammatory disease. Recent studies have shown that chronic stress (CS) might modulate periodontal disease, but there are few models of CS-induced periodontitis, and the underlying mechanisms are unclear. The present study established a rat model of periodontitis associated with CS induced by nylon thread ligatures. The severity of periodontitis was evaluated in this model by radiographic and pathological examination. The inflammatory reaction indicated by the elevated serum levels of interleukin (IL)-1β, IL-6 and IL-8 was assessed by enzyme-linked immunosorbent assay. Toll-like receptor-4 (TLR4) and glucocorticoid receptor-α (GR-α) expressions were detected by reverse transcriptase-PCR and western blotting. Open-field tests and serum corticosterone were used to evaluate CS. The results showed that CS induced behavioral changes and increased corticosterone levels of the animals with periodontitis. CS stimulation markedly increased alveolar bone loss, periodontal pocket depth and the number of plaques. It also enhanced the inflammatory reaction. These results suggest that CS accelerated the ligature-induced pathological changes associated with periodontitis. Further analysis of the mechanisms involved showed that GR-α expression was significantly downregulated in periodontal tissues of the animals undergoing CS. Blocking GR-α signaling in lipopolysaccharide and corticosteroid-treated human periodontal ligament fibroblast cells in vitro significantly upregulated the expression of p-Akt (protein kinase B) and TLR4, promoted nuclear factor-κB activity and increased levels of IL-1β, IL-6 and IL-8. This research suggests that CS might accelerate the pathological progression of periodontitis by a GR-α signaling-mediated inflammatory response and that this may be a potential therapeutic target for the treatment of periodontal disease, particularly in patients with CS.

Expression of programmed death 1 ligand 1 on periodontal tissue cells as a possible protective feedback mechanism against periodontal tissue destruction

Programmed death 1 ligand 1 (PD-L1) is a negative co-stimulatory molecule in immune responses. Previous reports have indicated that inflammatory cytokines can upregulate the expression of PD-L1 in tumor cells, which in turn suppresses host immune responses. Periodontitis is characterized by persistent inflammation of the periodontium, which is initiated by infection with oral bacteria and results in damage to cells and the matrices of the periodontal connective tissues. In the present study, the expression and function of PD-L1 in periodontal tissue destruction were examined. Periodontal ligament cells (PDLCs) were stimulated by inflammatory cytokines and periodontal pathogens. The expression and function of PD-L1 on the surface of PDLCs was investigated using flow cytometry in vitro. Periodontal disease was induced by the injection of Porphyromonas gingivalis in mouse models. The expression levels of PD-L1 in the periodontal tissues of the mice were analyzed using flow cytometry and immunohistochemistry. PD-L1 was inducibly expressed on the PDLCs by the inflammatory cytokines and periodontal pathogens. The inflammation-induced expression of PD-L1 was shown to cause the apoptosis of activated T lymphocytes and improve the survival of PDLCs. Furthermore, in the mouse model of experimental periodontitis, the expression of PD-L1 in severe cases of periodontitis was significantly lower, compared with that in mild cases. By contrast, no significant differences were observed between the healthy control and severe periodontitis groups. The results of the present study showed that the expression of PD-L1 may inhibit the destruction of periodontal tissues, indicating the involvement of a possible protective feedback mechanism against periodontal infection.

Transglutaminase 2 up-regulation is associated with RANKL/OPG pathway in cultured HPDL cells and THP-1-differentiated macrophages

Recent evidence emphasized that transglutaminase 2 (TG2), a protein cross-linking enzyme, may play a role in the early phase of inflammation. High levels of TG2 have been associated with the constitutive activation of nuclear factor-kappa B (NF-κB) that is considered the main regulator of inflammation. In this context, the receptor activator of NF-kappa B ligand (RANKL) and receptor activator of NF-κB have extensive functions in the regulation of cytokine secretion associated with different pathological conditions. The human periodontal ligament (HPDL) cells, which express and secrete osteoprotegerin (OPG) and RANKL, represent an useful "ex vivo" model for monitoring cell response in inflammatory microenvironments, such as periodontitis-dependent tissue response. Thus, we evaluated TG2 expression and alterations in RANKL/OPG ratio occurring in cultured HPDL cells. The HPDL cells were obtained from patients with chronic periodontitis (CP) and healthy subjects. We observed the up-regulation of some inflammatory markers, such as IL-6, TNF-α, and HMGB-1, and at the same time an increase in TG2 mRNA levels in HPDL cells from CP patients compared with healthy subjects. We found a positive correlation between RANKL/OPG ratio and TG2 mRNA levels in HPDL cells from CP patients. In the parallel experiments, we demonstrated that TG2 inhibition reduced RANKL expression in both HPDL cells from CP patients and monocytes differentiated to macrophages by tetradecanoyl phorbol acetate treatment. Given the RANKL key role in NF-κB pathway and the observed up-regulation of pro-inflammatory cytokines, our data suggest that TG2 may be involved in molecular mechanisms of inflammatory response occurring in periodontal disease.

S100A4 upregulation suppresses tissue ossification and enhances matrix degradation in experimental periodontitis models

AIM

S100A4, also known as fibroblast-specific protein 1 or metastasin 1, is not only highly expressed in growth-stimulated cultured cells and metastatic tumor cells, but also in the periodontal ligament. The aim of this study was to investigate the roles of S100A4 in the pathogenesis of periodontitis and its regulatory mechanisms in inflammatory milieu.

METHODS

Experimental periodontitis was induced in rats by submarginal silk ligatures. TRAP activity and S100A4 expression in periodontal ligaments were examined using immunohistochemistry and immunofluorescence methods. IL-1β-treated human periodontal ligament cells (hPDLCs) were used as in vitro model of experimental periodontitis. S100A4 mRNA and protein were assessed using qRT-PCR and Western blot, respectively. hPDLCs were transfected with either S100A4 overexpression plasmids or shRNAs plasmids. The mineralization in hPDLCs was evaluated with a 12-d osteogenic induction assay, and the expression of ALP, OCN, MMP-2 and MMP-13 was analyzed by qRT-PCR.

RESULTS

In the periodontal ligaments of rats with experimental periodontitis, TRAP activity and S100A4 protein staining were considerably more intense compared with those in the control rats. Treatment of hPDLCs with IL-1β (10, 50 and 100 ng/mL) dose-dependently increased the mRNA and protein levels of S100A4. Transfection with shRNAs markedly increased mineralized nodule formation and the osteogenic-related markers ALP and OCN levels in hPDLCs, whereas the overexpression of S100A4 significantly reduced mineralized nodule formation, and increased the matrix degradation enzymes MMP-2 and MMP-13 levels in hPDLCs.

CONCLUSION

S100A4 is upregulated in the experimental rat periodontitis and in IL-1β-treated hPDLCs, where S100A4 suppresses osteogenic differentiation and enhances matrix degradation. Thus, S100A4 is a potential target for the treatment of periodontitis.

Association between plasma leptin level and systemic inflammatory markers in patients with aggressive periodontitis

Background:

Increasing evidence supports an association between periodontitis and systemic diseases. Leptin is involved both in the energy metabolism and inflammatory processes and is suggested to be a link between periodontal infection and systemic health. The present study aimed to evaluate the peripheral leptin concentration in patients with aggressive periodontitis (AgP) and to explore the relationship between leptin and systemic inflammation.

Methods:

Ninety patients with AgP visiting the Clinic of the Periodontology Department, Peking University School and Hospital of Stomatology between July 2001 and May 2006, and 44 healthy controls (staff and student volunteers in the same institute) were recruited. Plasma levels of leptin and inflammatory cytokines including interleukin (IL)-1β, IL-6, tumor necrosis factor-α (TNF-α) and C-reactive protein (CRP) were measured by enzyme-linked immunosorbent assay. Correlation and multiple linear regression analysis were performed to analyze the association between plasma leptin level and other variables.

Results:

Plasma leptin level of AgP group was significantly higher than that of the control group (19.7 ± 4.4 ng/ml vs. 7.5 ± 1.3 ng/ml, P < 0.01). After controlling for age, gender, and body mass index, positive correlation was observed between plasma leptin concentration and log-transformed levels of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α and CRP), and the partial correlation coefficients ranged from 0.199 to 0.376 (P < 0.05). Log-transformed IL-1β and IL-6 levels entered the final regression model (standardized β were 0.422 and 0.461 respectively, P < 0.01).

Conclusions:

Elevated plasma leptin concentration may be associated with increased systemic levels of inflammatory markers in AgP patients.

Study of the association between the interleukin-1 β c.3954C>T polymorphism and periodontitis in a population sample from Bahia, Brazil

BACKGROUND

Periodontitis is an inflammatory disease characterized by the loss of connective tissue and alveolar bone. Different factors are associated with the onset and prognosis of this disease, both environmental and genetic. The latter particularly relate to molecules secreted as a function of the host immune response, such as pro-inflammatory cytokines. Studies indicate that the polymorphism c. 3954C > T in the interleukin-1 β encoding gene (IL1B) can be considered as an aggravating factor in the periodontitis condition.

AIMS

This study aimed to evaluate whether there is an association between the IL1B c. 3954C > T gene polymorphism and the prevalence of periodontitis in the population from Vitória da Conquista-Bahia, Brazil.

MATERIALS AND METHODS

A total of 347 subjects (134 cases and 213 controls) who provided epithelial tissue of the oral cavity and saliva samples for DNA extraction and quantification of IL1B, respectively, were selected. Genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism followed by electrophoresis in agarose gel. The evaluation of the cytokine concentration was performed by enzyme-linked immunosorbent assay.

STATISTICAL ANALYSIS

Statistical calculations involved in this work include Chi-square test, Fisher Exact test, Mann-Whitney and Kruskal-Wallis tests.

RESULTS

Our findings revealed that: (i) No statistically significant relationship between periodontitis and the polymorphism studied was observed; (ii) no significant difference between the concentrations of IL1B in saliva between the case and control subjects and between the genotypes of these individuals and the concentrations of this cytokine.

CONCLUSIONS

We conclude that, in the sample evaluated, the IL1B c. 3954C > T polymorphism did not present as an etiological factor for periodontitis.

Porphyromonas gingivalis promotes the cell cycle and inflammatory cytokine production in periodontal ligament fibroblasts

OBJECTIVE

The infection of Porphyromonas gingivalis (P. gingivalis) modulates host immune-inflammatory responses and destructs homeostasis of normal cell cycle, thereby leading to periodontal tissue destruction. Human periodontal ligament fibroblasts (PDLFs) are key players in the host immune responses and periodontal tissue regeneration. The aim of the present study was to discover the effects of P. gingivalis infection on the cell cycle and inflammatory cytokine production in PDLFs.

DESIGN

P. gingivalis infection model into PDLFs was established. The effect of P. gingivalis on the cell proliferation and cell cycle were detected by MTT and flow cytometry. The p21, cyclin D1 and cyclin E mRNA expression, p21 protein expression, as well as IL-6 and IL-8 protein levels were analyzed by RT-qPCR, Western blot and ELISA, respectively.

RESULTS

P. gingivalis promoted proliferation and G1 phase of PDLFs. G1 phase promotion was associated with the decreased level of p21 and the up-regulation of cyclin D1 at 6h, and with the increased level of cyclin E at 12h. Simultaneously, the immune-inflammatory response of PDLFs was initiated by P. gingivalis during the initial stage of infection, including the increased expressions of IL-6 and IL-8.

CONCLUSION

We confirmed that the infection of P. gingivalis could modulate the expression of PDLF genes, which control cell cycle and inflammatory cytokine production. Thus, P. gingivalis may contribute to the proliferation and inflammation of periodontal tissue.

Upregulated Leptin in Periodontitis Promotes Inflammatory Cytokine Expression in Periodontal Ligament Cells

BACKGROUND

Imbalance or disruption in the expression of inflammatory mediators contributes greatly to the breakdown of the periodontal supporting tissues. Leptin, through binding to its receptor (obesity-related leptin and leptin receptor [OBR]), has potent effects on immunity and inflammation. However, to date, researchers only indicated a role of leptin in periodontitis. No direct or valid evidence exists about how leptin and its receptor are regulated by local inflammation, what effects they have, and the underlying mechanisms.

METHODS

Experimental periodontitis was induced by ligation of mandibular second molars in beagle dogs. The expression of leptin, OBR, and interleukin (IL)-1β was examined by immunohistochemistry. Meanwhile, recombinant human IL-1β was used to stimulate human periodontal ligament cells (hPDLCs) in vitro, and mRNA and protein levels of leptin were measured using real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Then, mRNA and protein levels of IL-6 and IL-8 were measured using real-time PCR and ELISA, after stimulation with various concentrations of leptin, knocking down all or only the long form of OBR (OBRb) by small interfering RNA and incubation with multiple intracellular signaling pathway inhibitors, respectively.

RESULTS

Leptin and OBR increased substantially in inflammatory periodontal tissues, which correlated well with the extent of inflammatory infiltration, and was a result of the upregulation in resident cells themselves. A high dose of leptin could induce the expression of mRNA and protein of IL-6 and IL-8 in hPDLCs through binding with OBRb and activating different intracellular signaling pathways.

CONCLUSION

Upregulated leptin and OBR in periodontitis stimulated proinflammatory cytokine expression in PDL cells to additionally promote local inflammation.

C-reactive protein expression is up-regulated in apical lesions of endodontic origin in association with interleukin-6

INTRODUCTION

C-reactive protein (CRP) is the prototype component of acute-phase proteins induced ultimately by interleukin (IL)-6 in the liver, but it is unknown whether periradicular tissues locally express CRP. The present study aimed to identify whether CRP messenger RNA synthesis occurs in situ within apical lesions of endodontic origin (ALEOs) and healthy periodontal ligament and its association with IL-6 and to determine their protein levels and tissue localization.

METHODS

Patients with asymptomatic apical periodontitis and healthy volunteers presenting at the School of Dentistry, University of Chile, Santiago, Chile, were enrolled. ALEOs and healthy teeth were obtained and processed for either immunohistochemistry and double immunofluorescence to assess IL-6 and CRP tissue localization, whereas healthy periodontal ligaments were processed as controls for real-time reverse-transcription polymerase chain reaction for their RNA expression levels and multiplex assay to determine their protein levels. Statistic analysis was performed using the unpaired t test or Mann-Whitney test according to data distribution and Pearson correlation.

RESULTS

IL-6 and CRP were synthesized in ALEOs, whereas their RNA expression and protein levels were significantly higher when compared with healthy periodontal ligament. IL-6 and CRP immunolocalized to the inflammatory cells, vascular endothelial cells, and mesenchymal cells. Both, IL-6 and CRP colocalized in ALEOs, and a positive correlation was found between their expression levels (P < .05).

CONCLUSIONS

IL-6 and CRP messenger RNA are constitutively expressed in periodontal ligament and up-regulated in ALEOs along with higher protein levels. Given their pleiotropic effects, IL-6 and CRP protein levels in apical tissues might partially explain the development and progression of ALEOs as well as potentially asymptomatic apical periodontitis-associated systemic low-grade inflammation.

Chronic stress enhances progression of periodontitis via α1-adrenergic signaling: a potential target for periodontal disease therapy

This study assessed the roles of chronic stress (CS) in the stimulation of the sympathetic nervous system and explored the underlying mechanisms of periodontitis. Using an animal model of periodontitis and CS, the expression of tyrosine hydroxylase (TH) and the protein levels of the α1-adrenergic receptor (α1-AR) and β2-adrenergic receptor (β2-AR) were assessed. Furthermore, human periodontal ligament fibroblasts (HPDLFs) were stimulated with lipopolysaccharide (LPS) to mimic the process of inflammation. The proliferation of the HPDLFs and the expression of α1-AR and β2-AR were assessed. The inflammatory-related cytokines interleukin (IL)-1β, IL-6 and IL-8 were detected after pretreatment with the α1/β2-AR blockers phentolamine/propranolol, both in vitro and in vivo. Results show that periodontitis under CS conditions enhanced the expression of TH, α1-AR and β2-AR. Phentolamine significantly reduced the inflammatory cytokine levels. Furthermore, we observed a marked decrease in HPDLF proliferation and the increased expression of α1-ARfollowing LPS pretreatment. Pretreatment with phentolamine dramatically ameliorated LPS-inhibited cell proliferation. In addition, the blocking of α1-ARsignaling also hindered the upregulation of the inflammatory-related cytokines IL-1β, IL-6 and IL-8. These results suggest that CS can significantly enhance the pathological progression of periodontitis by an α1-adrenergic signaling-mediated inflammatory response. We have identified a potential therapeutic target for the treatment of periodontal disease, particularly in those patients suffering from concurrent CS.

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.

Osteoimmunological mechanisms involved in orthodontically and bacterially induced periodontal stress

BACKGROUND AND OBJECTIVE

Orthodontic tooth movement is known to cause sterile inflammation of the periodontal ligament (PDL). It may also be accompanied by pathological effects of external apical root resorption, with interindividual differences in the incidence and extent of resorption. An involvement of autoimmunological mechanisms is currently under discussion. This study aimed to improve our understanding of similarities between the inflammatory mechanisms underlying the pathophysiology of periodontitis and root resorption.

MATERIALS AND METHODS

Human PDL cells were stimulated with interleukin (IL)-1β/IL-17A/IFN-γ, or left non-stimulated. Their potential for phagocytosis was then evaluated by incubation with dextran or E. coli or S. aureus particles, followed by flow cytometric and immunohistochemical analysis. Real-time polymerase chain reaction (PCR) was used to analyze receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) expression in PDL cells. Verification was obtained in vivo by studying IL-17A, RANKL, and OPG expression in biopsies of inflamed periodontal tissues and in biopsies of rat maxillae with mechanically induced root resorption. Statistical analysis included Wilcoxon's rank sum test to analyze gene expression data and one-way ANOVA in conjunction with Tukey's post hoc test to analyze flow cytometric data.

RESULTS

PDL cells phagocytosed foreign particles under both inflammatory and non-inflammatory conditions. Furthermore, IL-17A significantly downregulated RANKL expression while significantly upregulating OPG expression in PDL cells. These immunomodulatory cytokines were also demonstrable in both inflammatorily altered periodontal tissues and root resorption lacunae, while the incidence of IL-7A was strikingly variable in resorption areas.

CONCLUSION

PDL cells were demonstrated to effect phagocytosis and to express immunomodulatory molecules, which proves their capability of participating in periodontal osteoimmunological processes. The development of root resorption and periodontitis appears to be governed by similar pathophysiological mechanisms.

A challenge with Porphyromonas gingivalis differentially affects the osteoclastogenesis potential of periodontal ligament fibroblasts from periodontitis patients and non-periodontitis donors

AIM

Porphyromonas gingivalis (Pg) may cause an immune-inflammatory response in host cells leading to bone degradation by osteoclasts. We investigated the osteoclast-inducing capacity of periodontal ligament fibroblasts from periodontitis patients and non-periodontitis donors after a challenge with viable Pg.

MATERIALS AND METHODS

PDLFs from periodontitis patients (n = 8) and non-periodontitis donors (n = 7) were incubated for 6 h with or without viable Pg and subsequently co-cultured with osteoclast precursors from peripheral blood mononuclear cells (PBMCs). The number of multinucleated tartrate-resistant acid phosphatase-positive cells was determined at 21 days. Expression of osteoclastogenesis-associated genes was assessed after infection of PDLFs mono-cultures and in PDLFs-PBMCs co-cultures. Resorption activity was analysed on bone slices.

RESULTS

Pg induced the expression of osteoclastogenesis-associated genes by PDLFs. After bacterial challenge the formation of osteoclast-like cell was decreased in co-cultures of PBMCs with non-periodontitis PDLFs, but not with PDLFs from periodontitis patients.

CONCLUSION

PDLFs from sites free of periodontitis respond to an infection with Pg by tempering formation of osteoclast-like cells, probably promoting clearance of the infection. PDLFs from periodontitis sites are desensitized to a Pg challenge in terms of their osteoclast-inducing capacity.

Gingival fibroblasts from periodontitis patients exhibit inflammatory characteristics in vitro

OBJECTIVE

Gingival fibroblasts (GFs) are an important regulatory cell type in the progression of periodontitis. This study aimed to compare the expression levels of genes associated with inflammation, extracellular matrix degradation and bone destruction in GFs isolated from healthy and periodontitis subjects in the absence and presence of Porphyromonas gingivalis.

DESIGNS

Primary GFs from healthy (n=10) and periodontitis subjects (n=10) were stimulated in vitro with viable P. gingivalis ATCC 49417 and 3 clinical isolates of P. gingivalis with type II fimbriae from one healthy subject (KUMC-H1) and two periodontitis patients (KUMC-P1, -P2). The mRNA expression of proinflammatory cytokines (interleukin (IL)-6, IL-8, IL-1B), anti-inflammatory cytokines (IL-4, IL-10), matrix metalloproteinase (MMP)-1 and 2, tissue inhibitor matrix metalloproteinase (TIMP)-3 and osteoprotegerin (OPG) were assessed using real-time PCR. The levels of IL-6, IL-1β and TIMP-3 protein were measured by an enzyme-linked immunosorbent assay.

RESULTS

The mRNA expression of IL-6, IL-1B and TIMP-3 was higher in the periodontitis group compared with the healthy group, whereas IL-4 expression was higher in the healthy group both in the absence and presence of the P. gingivalis strains. The expression levels of IL-6, IL-1β and TIMP-3 protein were also higher in the periodontitis group in the absence and/or presence of the P. gingivalis strains. There was inter-strain variability among P. gingivalis strains in the ability to induce expression of the proinflammatory cytokines, MMPs and OPG and in the ability to degrade IL-6 protein.

CONCLUSION

High expression of proinflammatory cytokines and TIMP-3 and low expression of IL-4 can be a signature of GFs associated with periodontitis.

Resolvin D1 protects periodontal ligament

Resolution agonists are endogenous mediators that drive inflammation to homeostasis. We earlier demonstrated in vivo activity of resolvins and lipoxins on regenerative periodontal wound healing. The goal of this study was to determine the impact of resolvin D1 (RvD1) on the function of human periodontal ligament (PDL) fibroblasts, which are critical for wound healing during regeneration of the soft and hard tissues around teeth. Primary cells were cultured from biopsies obtained from three individuals free of periodontal diseases. Peripheral blood mononuclear cells were isolated by density gradient centrifugation from whole blood of healthy volunteers. PGE2, leukotriene B4 (LTB4), and lipoxin A4 (LXA4) in culture supernatants were measured by ELISA. The direct impact of RvD1 on PDL fibroblast proliferation was measured and wound closure was analyzed in vitro using a fibroblast culture "scratch assay." PDL fibroblast function in response to RvD1 was further characterized by basic FGF production by ELISA. IL-1β and TNF-α enhanced the production of PGE2. Treatment of PDL cells and monocytes with 0.1-10 ng/ml RvD1 (0.27-27 M) reduced cytokine induced production of PGE2 and upregulated LXA4 production by both PDL cells and monocytes. RvD1 significantly enhanced PDL fibroblast proliferation and wound closure as well as basic FGF release. The results demonstrate that anti-inflammatory and proresolution actions of RvD1 with upregulation of arachidonic acid-derived endogenous resolution pathways (LXA4) and suggest resolution pathway synergy establishing a novel mechanism for the proresolution activity of the ω-3 docosahexaenoic acid-derived resolution agonist RvD1.

Peri-implant crestal bone loss: a putative mechanism

Purpose. The immunological mechanisms of peri-implant crestal bone loss have, hitherto, not been elucidated. We hypothesized that bacterial products from the microgap cause upregulation of cytokines in otherwise healthy peri-implant cells, which results in osteoclast formation and, ultimately, in bone resorption. Materials and Methods. We used RT-PCR and ELISA to assay mediators of osteoclastogenesis in rat and human macrophages (r-and hMO); bone marrow derived stromal cells (r-and hBMCs); and human gingival fibroblasts (hGF)—with or without stimulation by LPS. TRAP positive multinucleate cells were assessed for their resorptive ability. Results. We show that IL-1α, IL-1β, and IL-6 were expressed by all examined cell types, and TNF-α was upregulated in hGF. Secretion of IL-1α and IL-1β proteins was stimulated in hMO by LPS, and IL-6 protein secretion was highly stimulated in hBMCs and hGF. Both LPS and RANKL stimulated macrophages to form osteoclast-like TRAP positive cells, which resorbed calcium phosphate substrates. Conclusion. Taken together, the results of our study support the hypothesis that bacterial endotoxins upregulate enhanced mediators of osteoclastogenesis in resident cells found in the healthy peri-implant compartment and that the local synergistic action of cytokines secreted by such cells results in the genesis of resorptively active osteoclasts.

MiR-17 modulates osteogenic differentiation through a coherent feed-forward loop in mesenchymal stem cells isolated from periodontal ligaments of patients with periodontitis

Chronic inflammatory diseases, such as rheumatoid arthritis and periodontitis, are the most common causes of bone tissue destruction. Recently, human periodontal ligament tissue-derived mesenchymal stem cells (PDLSCs), a population of multipotent stem cells, have been used to reconstruct tissues destroyed by chronic inflammation. However, the impact of the local inflammatory microenvironment on tissue-specific stem cells and the mechanisms controlling the effects of the local inflammatory environment remain poorly understood. In this study, we found that the multidifferentiation potential of mesenchymal stem cells (MSCs) isolated from periodontitis-affected periodontal ligament tissue (P-PDLSCs) was significantly lower than that of MSCs isolated from healthy human periodontal ligament tissue (H-PDLSCs). Inflammation in the microenvironment resulted in an inhibition of miR-17 levels, and a perturbation in the expression of miR-17 partly reversed the differentiation potential of PDLSCs in this microenvironment. Furthermore, inflammation in the microenvironment promoted the expression of Smad ubiquitin regulatory factor one (Smurf1), an important negative regulator of MSC osteogenic differentiation. Western blotting and 3' untranslated regions (3'-UTR) reporter assays confirmed that Smurf1 is a direct target of miR-17 in PDLSCs. Our data demonstrate that excessive inflammatory cytokine levels, miR-17, and Smurf1 were all involved in a coherent feed-forward loop. In this circuit, inflammatory cytokines led to direct activation of Smurf1 and downregulation of miR-17, thereby increasing degradation of Smurf1-mediated osteoblast-specific factors. The elucidation of the molecular mechanisms governing MSC osteogenic differentiation in a chronic inflammatory microenvironment could provide us with a better knowledge of chronic inflammatory disorder and improve stem cell-mediated inflammatory bone disease therapy.