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

Transcriptomic features of programmed and inflammatory cell death in gingival tissues

The local gingival tissue environment with homeostasis and tissue-destructive events of periodontitis demonstrates major changes in histological features and biology of the oral/sulcular epithelium, fibroblasts, vascular cells, inflammatory cell infiltration, and alveolar bone.

OBJECTIVE

This study used an experimental periodontitis model to detail the gingival transcriptome related to cell death processes of pyroptosis, necroptosis, ferroptosis, and cuproptosis.

MATERIALS AND METHODS

Healthy Macaca mulatta primates stratified by age, ≤3 years (young), 7-12 years (adolescent), 12-15 years (adult), and 17-23 years (aged), provided gingival tissue biopsies for microarray analysis focused on 257 genes representative of the four cell death processes and bacterial plaque samples for 16S rRNA gene analysis.

RESULTS

Age differences in the profiles of gene expression in healthy tissues were noted for cuproptosis, ferroptosis, necroptosis, and pyroptosis. Major differences were then observed with disease initiation, progression, and resolution also related to the age of the animals. Distinct bacterial families/consortia of species were significantly related to the gene expression differences for the cell death pathways.

CONCLUSIONS

These results emphasized age-associated differences in the gingival tissue molecular response to changes in the quality and quantity of bacteria accumulating with the disease process reflected in regulated cell death pathways that are both physiological and pathophysiological.

PD-1/PD-L1 pathway: A double-edged sword in periodontitis

Periodontitis is a disease caused by infection and immunological imbalance, which often leads to the destruction of periodontal tissue. Programmed death protein 1 (PD-1) and its ligand: programmed death ligand 1 (PD-L1) are important "immune checkpoint" proteins that have a negative regulatory effect on T cells and are targets of immunotherapy. Studies have shown that the expression of PD-1 and PD-L1 in patients with periodontitis is higher than that in healthy individuals. The keystone pathogen Porphyromonas gingivalis (P. gingivalis) is believed to be the main factor driving the upregulation of PD-1/PD-L1. High expression of PD-1/PD-L1 can inhibit the inflammatory response and reduce the destruction of periodontal supporting tissues, but conversely, it can promote the "immune escape" of P. gingivalis, thus magnifying infections. In addition, the PD-1/PD-L1 pathway is also associated with various diseases, such as cancer and Alzheimer's disease. In this review, we discuss the influence and mechanism of the PD-1/PD-L1 pathway as a "double-edged sword" affecting the occurrence and development of periodontitis, as well as its function in periodontitis-related systemic disorders. The PD-1/PD-L1 pathway could be a new avenue for periodontal and its related systemic disorders therapy.

25-hydroxyvitamin D3 generates immunomodulatory plasticity in human periodontal ligament-derived mesenchymal stromal cells that is inflammatory context-dependent

Introduction

Human periodontal ligament-derived mesenchymal stromal cells (hPDL-MSCs) exhibit a tight bi-directional interaction with CD4+ T lymphocytes. The hPDL-MSCs' immunomodulatory abilities are drastically enhanced by pro-inflammatory cytokines via boosting the expression of various immunomediators. 25-hydroxyvitamin D3 (25(OH)D3), the major metabolite of vitamin D3 in the blood, affects both hPDL-MSCs and CD4+ T lymphocytes, but its influence on their interaction is unknown.

Methods

Therefore, primary hPDL-MSCs were stimulated in vitro with tumor necrosis factor (TNF)-α a or interleukin (IL)-1β in the absence and presence of 25(OH)D3 followed by an indirect co-culture with phytohemagglutinin-activated CD4+ T lymphocytes. The CD4+ T lymphocyte proliferation, viability, and cytokine secretion were analyzed. Additionally, the expression of various immunomediators in hPDL-MSCs was investigated, and their implication was verified by using pharmacological inhibitors.

Results

25(OH)D3 significantly counteracted the suppressive effects of IL-1β-treated hPDL-MSCs on CD4+ T lymphocyte proliferation, whereas no effects were observed in the presence of TNF-α. Additionally, 25(OH)D3 significantly increased the percentage of viable CD4+ T lymphocytes via TNF-α- or IL-1β-treated hPDL-MSCs. It also caused a significant decrease in interferon-γ, IL-17A, and transforming growth factor-β productions, which were triggered by TNF-α-treated hPDL-MSCs. 25(OH)D3 significantly decreased the production of various immunomediators in hPDL-MSCs. Inhibition of two of them, prostaglandin E2 and indoleamine-2,3-dioxygenase-1, partially abolished some of the hPDL-MSCs-mediated effects of 25(OH)D3 on CD4+ T lymphocytes.

Conclusion

These data indicate that 25(OH)D3 influences the immunomodulatory activities of hPDL-MSCs. This modulatory potential seems to have high plasticity depending on the local cytokine conditions and may be involved in regulating periodontal tissue inflammatory processes.

0.1% Nano-silver mediates PD-1/PD-L1 pathway and alleviates chronic apical periodontitis in rats

This study was to investigate whether the programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) and T-helper 17 (Th17)/regulatory T (Treg) balance are associated with chronic apical periodontitis (CAP) relived by 0.1% nano-silver. CAP rat models were established by opening the first molars of the right and left mandible and exposing the pulp cavity to the oral cavity. CAP model was verified by cone-beam computed tomography, X-ray digital radiovisiography, and hematoxylin-eosin (H and E) staining. The rats were randomly divided into the sham, Ca(OH)₂, and 0.1% nano-silver groups (n = 12 in each group) 2 weeks after surgery. The pathological changes in the apical area were detected by H and E staining. PD-1, PD-L1, RORγT, IL-17, and Foxp3 in periapical tissues were detected by qRT-PCR and immunohistochemistry. Th17/Treg and PD-1/PD-L1 were analyzed by flow cytometry. After 7, 14, and 21 days of 0.1% nano-silver treatment, inflammatory cells in the apical region were slightly reduced and inflammatory infiltration was relieved compared with the sham group. RORγT, IL-17, PD-1, and PD-L1 decreased and Foxp3 increased after 7, 14, and 21 days of 0.1% nano-silver treatment compared with the sham group (p < 0.05); however, there were no significant differences with Ca(OH)₂ group (p > 0.05). Flow cytometry revealed that 0.1% nano-silver solution decreased Th17/Treg and PD-1/PD-L1 ratio. 0.1% Nano-silver significantly reduced the inflammation of CAP in rats. PD-1/PD-L1 was included in Th17/Treg balance restored by 0.1% nano-silver.

PD-L1, a Potential Immunomodulator Linking Immunology and Orthodontically Induced Inflammatory Root Resorption (OIIRR): Friend or Foe?

Orthodontically induced inflammatory root resorption (OIIRR) is considered an undesired and inevitable complication induced by orthodontic forces. This inflammatory mechanism is regulated by immune cells that precede orthodontic tooth movement (OTM) and can influence the severity of OIIRR. The process of OIIRR is based on an immune response. On some occasions, the immune system attacks the dentition by inflammatory processes during orthodontic treatment. Studies on the involvement of the PD-1/PD-L1 immune checkpoint have demonstrated its role in evading immune responses, aiming to identify possible novel therapeutic approaches for periodontitis. In the field of orthodontics, the important question arises of whether PD-L1 has a role in the development of OIIRR to amplify the amount of resorption. We hypothesize that blocking of the PD-L1 immune checkpoint could be a suitable procedure to reduce the process of OIIRR during orthodontic tooth movement. This review attempts to shed light on the regulation of immune mechanisms and inflammatory responses that could influence the pathogenesis of OIIRR and to acquire knowledge about the role of PD-L1 in the immunomodulation involved in OIIRR. Possible clinical outcomes will be discussed in relation to PD-L1 expression and immunologic changes throughout the resorption process.

Immunorthodontics: PD-L1, a Novel Immunomodulator in Cementoblasts, Is Regulated by HIF-1α under Hypoxia

Recent studies have revealed that hypoxia alters the PD-L1 expression in periodontal cells. HIF-1α is a key regulator for PD-L1. As hypoxia presents a hallmark of an orthodontically induced microenvironment, hypoxic stimulation of PD-L1 expression may play vital roles in immunorthodontics and orthodontically induced inflammatory root resorption (OIIRR). This study aims to investigate the hypoxic regulation of PD-L1 in cementoblasts, and its interaction with hypoxia-induced HIF-1α expression. The cementoblast (OCCM-30) cells (M. Somerman, NIH, NIDCR, Bethesda, Maryland) were cultured in the presence and absence of cobalt (II) chloride (CoCl2). Protein expression of PD-L1 and HIF-1α as well as their gene expression were evaluated by Western blotting and RT-qPCR. Immunofluorescence was applied to visualize the localization of the proteins within cells. The HIF-1α inhibitor (HY-111387, MedChemExpress) was added, and CRISPR/Cas9 plasmid targeting HIF-1α was transferred for further investigation by flow cytometry analysis. Under hypoxic conditions, cementoblasts undergo an up-regulation of PD-L1 expression at protein and mRNA levels. Silencing of HIF-1α using CRISPR/Cas9 indicated a major positive correlation with HIF-1α in regulating PD-L1 expression. Taken together, these findings show the influence of hypoxia on PD-L1 expression is modulated in a HIF-1α dependent manner. The HIF-1α/PD-L1 pathway may play a role in the immune response of cementoblasts. Thus, combined HIF-1α/PD-L1 inhibition could be of possible therapeutic relevance for OIIRR prevention.

Macrophages: A communication network linking Porphyromonas gingivalis infection and associated systemic diseases

Porphyromonas gingivalis (P. gingivalis) is a Gram-negative anaerobic pathogen that is involved in the pathogenesis of periodontitis and systemic diseases. P. gingivalis has recently been detected in rheumatoid arthritis (RA), cardiovascular disease, and tumors, as well as Alzheimer’s disease (AD), and the presence of P. gingivalis in these diseases are correlated with poor prognosis. Macrophages are major innate immune cells which modulate immune responses against pathogens, however, multiple bacteria have evolved abilities to evade or even subvert the macrophages’ immune response, in which subsequently promote the diseases’ initiation and progression. P. gingivalis as a keystone pathogen of periodontitis has received increasing attention for the onset and development of systemic diseases. P. gingivalis induces macrophage polarization and inflammasome activation. It also causes immune response evasion which plays important roles in promoting inflammatory diseases, autoimmune diseases, and tumor development. In this review, we summarize recent discoveries on the interaction of P. gingivalis and macrophages in relevant disease development and progression, such as periodontitis, atherosclerosis, RA, AD, and cancers, aiming to provide an in-depth mechanistic understanding of this interaction and potential therapeutic strategies.

PD-L1 Up-Regulation in Prostate Cancer Cells by Porphyromonas gingivalis

Chronic inflammation is known to contribute to various human cancers. Porphyromonas gingivalis (P. gingivalis), is a gram-negative oral keystone pathogen that may cause severe periodontitis and expresses several virulence factors to affect the host immune system. Periodontitis is a chronic infectious disease that while progression, may cause loss of attachment and destruction of the tooth supporting tissues. Prostate cancer is one of the most common malignancies in men. Increasing evidence links periodontitis with prostate cancer, however the mechanisms explaining this relationship remain unclear. The aim of this study was to investigate the expression and signaling pathway of programmed death ligand 1 (PD-L1) in a prostate cancer cell line after infection with P. gingivalis and stimulation with P. gingivalis components to reveal the mechanism of tumor-induced immune evasion associated with bacterial infection in the tumor environment. Prostate cancer cells were infected with different concentrations of viable P. gingivalis and treated with different concentrations of heat-killed P. gingivalis and P. gingivalis cell components, including the total membrane fraction, inner membrane fraction, outer membrane fraction, cytosolic fraction and peptidoglycan (PGN). Chemical inhibitors were used to block different important molecules of signaling pathways to assess the participating signal transduction mechanisms. PD-L1 expression was detected by Western blot after 24 h of infection. PD-L1 was demonstrated to be upregulated in prostate cancer cells after infection with viable and with heat-killed P. gingivalis membrane fractions. Also isolated PGN induced PD-L1 up-regulation. The upregulation was mediated by the NOD1/NOD2 signaling pathway. No upregulation could be detected after treatment of the cells with P. gingivalis lipopolysaccharide (LPS). These results indicate, that chronic inflammatory disease can contribute to tumor immune evasion by modifying the tumor microenvironment. Thus, chronic infection possibly plays an essential role in the immune response and may promote the development and progression of prostate cancer.

Immunorthodontics: Role of HIF-1α in the Regulation of (Peptidoglycan-Induced) PD-L1 Expression in Cementoblasts under Compressive Force

Patients with periodontitis undergoing orthodontic therapy may suffer from undesired dental root resorption. The purpose of this in vitro study was to investigate the molecular mechanisms resulting in PD-L1 expression of cementoblasts in response to infection with Porphyromonas gingivalis (P. gingivalis) peptidoglycan (PGN) and compressive force (CF), and its interaction with hypoxia-inducible factor (HIF)-1α molecule: The cementoblast (OCCM-30) cells were kinetically infected with various concentrations of P. gingivalis PGN in the presence and absence of CF. Western blotting and RT-qPCR were performed to examine the protein expression of PD-L1 and HIF-1α as well as their gene expression. Immunofluorescence was applied to visualize the localization of these proteins within cells. An HIF-1α inhibitor was added for further investigation of necroptosis by flow cytometry analysis. Releases of soluble GAS-6 were measured by ELISA. P. gingivalis PGN dose dependently stimulated PD-L1 upregulation in cementoblasts at protein and mRNA levels. CF combined with P. gingivalis PGN had synergistic effects on the induction of PD-L1. Blockade of HIF-1α inhibited the P. gingivalis PGN-inducible PD-L1 protein expression under compression, indicating an HIF-1α dependent regulation of PD-L1 induction. Concomitantly, an HIF-1α inhibitor decreased the GAS-6 release in the presence of CF and P. gingivalis PGN co-stimulation. The data suggest that PGN of P. gingivalis participates in PD-L1 up-regulation in cementoblasts. Additionally, the influence of compressive force on P. gingivalis PGN-induced PD-L1 expression occurs in HIF-1α dependently. In this regard, HIF-1α may play roles in the immune response of cementoblasts via immune-inhibitory PD-L1. Our results underline the importance of molecular mechanisms involved in bacteria-induced periodontics and root resorption.

Extracellular adenosine triphosphate induces IDO and IFNγ expression of human periodontal ligament cells through P2 X7 receptor signaling

BACKGROUND

Mechanical stimuli induce the release of adenosine triphosphate into the extracellular environment by human periodontal ligament cells (hPDLCs). Extracellular adenosine triphosphate (eATP) plays the role in both inflammation and osteogenic differentiation. eATP involves in immunosuppressive action by increasing immunosuppressive molecules IDO and IFNγ expression on immune cells. However, the role of eATP on the immunomodulation of hPDLCs remains unclear. This study aimed to examine the effects of eATP on the IDO and IFNγ expression of hPDLCs and the participation of purinergic P₂ receptors in this phenomenon.

METHODS

hPDLCs were treated with eATP. The mRNA and protein expression of indoleamine-pyrrole 2,3-dioxygenase (IDO) and interferon-gamma (IFNγ) were determined. The role of the purinergic P₂ receptor was determined using calcium chelator (EGTA) and PKC inhibitor (PKCi). Chemical inhibitors (KN62 and BBG), small interfering RNA (siRNA), and P₂ X₇ receptor agonist (BzATP) were used to confirm the involvement of P₂ X₇ receptors on IDO and IFNγ induction by hPDLCs.

RESULTS

eATP significantly enhanced mRNA expression of IDO and IFNγ. Moreover, eATP increased kynurenine which is the active metabolite of tryptophan breakdown catalyzed by the IDO enzyme and significantly induced IFNγ protein expression. EGTA and PKCi reduced eATP-induced IDO and IFNγ expressions by hPDLCs, confirming the role of calcium signaling. Chemical P₂ X₇ inhibitors (KN62 and BBG) and siRNA targeting the P₂ X₇ receptor significantly inhibited the eATP-induced IDO and IFNγ production. Correspondingly, BzATP markedly increased IDO and IFNγ expression.

CONCLUSION

eATP induced immunosuppressive function of hPDLCs by promoting IDO and IFNγ production via P₂ X₇ receptor signaling. eATP may become a promising target for periodontal regeneration by modulating immune response and further triggering tissue healing.

Mucosal circadian rhythm pathway genes altered by aging and periodontitis

As circadian processes can impact the immune system and are affected by infections and inflammation, this study examined the expression of circadian rhythm genes in periodontitis.

METHODS

Macaca mulatta were used with naturally-occurring and ligature-induced periodontitis. Gingival tissue samples were obtained from healthy, diseased, and resolved sites in four groups: young (≤3 years), adolescent (3-7 years), adult (12-26) and aged (18-23 years). Microarrays targeted circadian rhythm (n = 42), inflammation/tissue destruction (n = 11), bone biology (n = 8) and hypoxia pathway (n = 7) genes.

RESULTS

The expression of many circadian rhythm genes, across functional components of the pathway, was decreased in healthy tissues from younger and aged animals, as well as showing significant decreases with periodontitis. Negative correlations of the circadian rhythm gene levels with inflammatory mediators and tissue destructive/remodeling genes were particularly accentuated in disease. A dominance of positive correlations with hypoxia genes was observed, except HIF1A, that was uniformly negatively correlated in health, disease and resolution.

CONCLUSIONS

The chronic inflammation of periodontitis exhibits an alteration of the circadian rhythm pathway, predominantly via decreased gene expression. Thus, variation in disease expression and the underlying molecular mechanisms of disease may be altered due to changes in regulation of the circadian rhythm pathway functions.

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.

Overexpression of PD-L1 in gingival basal keratinocytes reduces periodontal inflammation in a ligature-induced periodontitis model

Background

The immune checkpoint programmed cell death 1 (PD‐1): PD‐1 ligand 1 (PD‐L1) pathway plays a crucial role in maintaining immune tolerance and preventing tissue damages by excessive immune responses. PD‐L1 is physiologically expressed and upregulated in keratinocytes (KCs) in the oral cavity. We here investigated the contribution of PD‐L1 that was overexpressed in gingival basal KCs in a ligature‐induced periodontitis model.

Methods

Wild‐type (WT) BALB/c and K14/PD‐L1 transgenic (tg) mice, in which PD‐L1 was overexpressed in basal KCs under control of the keratin 14 promoter, were used. To induce periodontitis, a 9‐0 silk ligature was placed around the upper right second molar, and lipopolysaccharide from Porphyromonas gingivalis was applied on the suture. Gingival tissues were collected on day 7, after which histological analyses were performed, including by hematoxylin and eosin and tartrate‐resistant acid phosphate staining (TRAP) and quantitative PCR for proinflammatory cytokines and bone metabolism‐related genes. Alveolar bone loss at 7 weeks after ligature placement was assessed by micro‐computed tomography analysis.

Results

PD‐L1 was overexpressed in the basal KCs of all gingival epithelia in K14/PD‐L1tg mice. Early ligature‐induced periodontal inflammation, as assessed based on histological changes, elevation of proinflammatory cytokine (IL‐1β, IL‐6, TNF‐α) expression, periodontal ligament degeneration, and osteoclastogenesis as assessed by Rankl and Opg expression and TRAP+ cells, was markedly impaired in K14/PD‐L1tg mice. Alveolar bone resorption at a late time point was also clearly minimized in K14/PD‐L1tg mice.

Conclusion

Overexpression of PD‐L1 in gingival basal keratinocytes in K14/PD‐L1tg mice reduces periodontal inflammation and alveolar bone resorption in a ligature‐induced periodontitis model.

LPS stimulates gingival fibroblasts to express PD-L1 via the p38 pathway under periodontal inflammatory conditions

OBJECTIVE

The overall aim of this research was to investigate the differences in the expression of programmed death ligand 1 (PD-L1) in human gingival fibroblasts (HGFs) between a periodontal healthy group and a periodontal inflammatory group. and explore the possible mechanism involved.

METHODS

Differences in PD-L1 mRNA and protein expression in HGFs from a periodontal healthy group and a periodontal inflammatory group were examined by qPCR and western blotting, respectively, and were further tested after lipopolysaccharide (LPS) stimulation in both groups. The effects of a p38 pathway inhibitor on the changes in p38 phosphorylation levels and PD-L1 expression after LPS stimulation were investigated in both groups.

RESULTS

PD-L1 mRNA and protein levels in HGFs in the periodontal inflammatory group were significantly higher than those in the periodontal healthy group (p < 0.05). After 10 μg/mL LPS stimulation, PD-L1 mRNA levels in HGFs from both groups increased significantly (p < 0.05), peaking at 4 h, and the peak was significantly higher in the periodontal inflammatory group than in the periodontal healthy group (p < 0.05). However, PD-L1 protein expression was upregulated only in the inflammatory group (p < 0.05). Inhibition of the p38 pathway in HGFs decreased p38 phosphorylation in both groups (p < 0.05) but this treatment reversed the LPS-induced increase in PD-L1 mRNA and protein levels only in the inflammatory group (p < 0.05).

CONCLUSION

In the periodontal inflammatory state, the expression of PD-L1 in HGFs is more easily activated, and may be influenced by the p38 pathway.

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.

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.

Continuing Effect of Cytokines and Toll-Like Receptor Agonists on Indoleamine-2,3-Dioxygenase-1 in Human Periodontal Ligament Stem/Stromal Cells

Transplanted mesenchymal stem/stromal cells (MSCs) are a promising and innovative approach in regenerative medicine. Their regenerative potential is partly based upon their immunomodulatory activities. One of the most investigated immunomediators in MSCs, such as in periodontal ligament-derived MSCs (hPDLSCs), is indoleamine-2,3-dioxygenase-1 (IDO-1) which is upregulated by inflammatory stimuli, like cytokines. However, there are no data concerning continuing IDO-1 expression in hPDLSCs after the removal of inflammatory stimuli, such as cytokines and toll-like receptor (TLR) agonist-2 and TLR-3. Hence, primary hPDLSCs were stimulated with interleukin (IL)-1β, tumor necrosis factor (TNF)-α, interferon (IFN)-γ, TLR-2 agonist Pam3CSK4 or TLR-3 agonist Poly I/C. IDO-1 gene and protein expression and its enzymatic activity were measured up to five days after removing any stimuli. IL-1β- and TNF-α-induced IDO-1 expression and enzymatic activity decreased in a time-dependent manner after cessation of stimulation. IFN-γ caused a long-lasting effect on IDO-1 up to five days after removing IFN-γ. Both, TLR-2 and TLR-3 agonists induced a significant increase in IDO-1 gene expression, but only TLR-3 agonist induced significantly higher IDO-1 protein expression and enzymatic activity in conditioned media (CM). IDO-1 activity of Poly I/C- and Pam3CSK4-treated hPDLSCs was higher at one day after removal of stimuli than immediately after stimulation and declined to basal levels after five days. Among all tested stimuli, only IFN-γ was able to induce long-lasting IDO-1 expression and activity in hPDLSCs. The high plasticity of IDO-1 expression and its enzymatic activity in hPDLSCs due to the variable cytokine and virulence factor milieu and the temporal-dependent responsiveness of hPDLSCs may cause a highly dynamic potential of hPDLSCs to modulate immune responses in periodontal tissues.

Understanding Inflammasomes and PD-1/PD-L1 Crosstalk to Improve Cancer Treatment Efficiency

Inflammasomes and immune checkpoints have been shown to participate in carcinogenesis, cancer growth and response to treatment. Thus, targeting cytokines resulting from inflammasome activation, such as interleukin (IL)-1β, has emerged as a new tool in the therapeutic arsenal. Moreover, the use of checkpoint inhibitors such as anti-PD-1 or anti-PD-L1 has revolutionized the treatment of some cancer patients. However, inflammasome activation and consecutive cytokine release only occurs in some chemotherapeutic treatments and immune checkpoint inhibitors only work for a restricted number of patients, thus limiting the use of therapies targeting these pathways. Expanding knowledge about the inefficiency of these therapies recently brought forward the hypothesis of targeting both pathways. In this review, we provide an overview of the crosstalk between inflammasomes and programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) that might explain how these two pathways are mutually dependent, and perhaps why targeting only one of them leads to inefficiency of cancer treatment in some patients.

PD-L1 correlates with chemokines and cytokines in gingival crevicular fluid from healthy and diseased sites in subjects with periodontitis

Objective

PD-L1 is an immune checkpoint molecule that regulates immune and inflammatory responses. While cells of periodontal tissues express PD-L1, its presence in GCF is not known. The purpose of this study was to measure the PD-L1 values in GCF and correlate values with the presence of chemokine and cytokine values from periodontally diseased subjects and periodontally healthy subjects.

Results

PD-L1 values (pg/30 s), determined in triplicate using a fluorescent microparticle-based immunoassay ranged from 0.04–31.65 pg/30 s. PD-L1 correlated with 15 out of 22 chemokine and cytokine responses. In 85 healthy sites in 31 subjects, PD-L1 values were negatively correlated with IL6, CXCL8, IL10, and CCL3 values. In 53 diseased sites in 20 subjects, PD-L1 values were positively correlated with CCL11, CSF2, IFNG, IL1A, IL1B, IL2, IL7, IL15, and CCL5 values and negatively correlated with IL12A and IL5 values. Gene ontology (GO) annotations identified roles of PD-L1 in Th1 and Th2 activation and T-cell exhaustion signaling canonical pathways. PD-L1 values were correlated with the expression of chemokines and cytokines, which likely regulates immune cell trafficking and protects the periodontium from uncontrolled immune responses to pathogens and inflammation-induced tissue damage.

Emerging role of exosomes in craniofacial and dental applications

Exosomes, a specific subgroup of extracellular vesicles that are secreted by cells, have been recognized as important mediators of intercellular communication. They participate in a diverse range of physiological and pathological processes. Given the capability of exosomes to carry molecular cargos and transfer bioactive components, exosome-based disease diagnosis and therapeutics have been extensively studied over the past few decades. Herein, we highlight the emerging applications of exosomes as biomarkers and therapeutic agents in the craniofacial and dental field. Moreover, we discuss the current challenges and future perspectives of exosomes in clinical applications.

Cytokines Differently Define the Immunomodulation of Mesenchymal Stem Cells from the Periodontal Ligament

Human periodontal ligament stem cells (hPDLSCs) play an important role in periodontal tissue homeostasis and regeneration. The function of these cells in vivo depends largely on their immunomodulatory ability, which is reciprocally regulated by immune cells via cytokines, particularly interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-1β. Different cytokines activate distinct signaling pathways and might differently affect immunomodulatory activities of hPDLSCs. This study directly compared the effect of IFN-γ, TNF-α, or IL-1β treated primary hPDLSCs on allogenic CD4⁺ T lymphocyte proliferation and apoptosis in an indirect co-culture model. The effects of IFN-γ, TNF-α, and IL-1β on the expression of specific immunomodulatory factors such as intoleamine-2,3-dioxygenase-1 (IDO-1), prostaglandin E₂ (PGE₂), and programmed cell death 1 ligand 1 (PD-L1) and ligand 2 (PD-L2) in hPDLSCs were compared. The contribution of different immunomodulatory mediators to the immunomodulatory effects of hPDLSCs in the indirect co-culture experiments was assessed using specific inhibitors. Proliferation of CD4⁺ T lymphocytes was inhibited by hPDLSCs, and this effect was strongly enhanced by IFN-γ and IL-1β but not by TNF-α. Apoptosis of CD4⁺ T lymphocytes was decreased by hPDLSCs per se. This effect was counteracted by IFN-γ or IL-1β. Additionally, IFN-γ, TNF-α, and IL-1β differently regulated all investigated immunomediators in hPDLSCs. Pharmacological inhibition of immunomediators showed that their contribution in regulating CD4⁺ T lymphocytes depends on the cytokine milieu. Our data indicate that inflammatory cytokines activate specific immunomodulatory mechanisms in hPDLSCs and the expression of particular immunomodulatory factors, which underlies a complex reciprocal interaction between hPDLSCs and CD4⁺ T lymphocytes.

Protein kinase D3 regulates the expression of the immunosuppressive protein, PD‑L1, through STAT1/STAT3 signaling

Oral squamous cell carcinoma (OSCC) is capable of constructing a favorable immune escape environment through interactions of cells with cells and of cells with the environment. Programmed death ligand-1 (PD-L1) is a well-recognized inhibitor of anti-tumor immunity that plays an important role in tumor immune escape. However, the molecular mechanisms regulating PD-L1 expression are not yet fully understood. In this study, to investigate the role of protein kinase D3 (PKD3) in the regulation of PD-L1 expression, the expression and correlation of PKD3 and PD-L1 were first analyzed by the immunostaining of human OSCC tissue sections, cell experiments and TCGA gene expression databases. The expression levels of PKD3 and PD-L1 were found to be significantly higher in OSCC cells than in normal tissues or cells. In addition, the expression levels of PKD3 and PD-L1 were found to be significantly positively correlated. Subsequently, it was found that the levsel of PD-L1 expression decreased following the silencing of PKD3 and that the ability of interferon (IFN)-γ to induce PD-L1 expression was also decreased in OSCC. The opposite phenomenon occurred following the overexpression of PKD3. It was also found that the phosphorylation of signal transducer and activator of transcription (STAT)1/STAT3 was reduced by the knockdown of PKD3 in OSCC. Moreover, the expression level of PD-L1 was decreased after the use of siRNA to knockdown STAT1 or STAT3. On the whole, the findings of this study confirm that PKD3 regulates the expression of PD-L1 induced by IFN-γ by regulating the phosphorylation of STAT1/STAT3. These findings broaden the understanding of the biological function of PKD3, suggesting that PKD is a potential therapeutic target for OSCC.

Immunomodulatory properties of dental tissue-derived mesenchymal stem cells: Implication in disease and tissue regeneration

Mesenchymal stem cells (MSCs) are considered as an attractive tool for tissue regeneration and possess a strong immunomodulatory ability. Dental tissue-derived MSCs can be isolated from different sources, such as the dental pulp, periodontal ligament, deciduous teeth, apical papilla, dental follicles and gingiva. According to numerous in vitro studies, the effect of dental MSCs on immune cells might depend on several factors, such as the experimental setting, MSC tissue source and type of immune cell preparation. Most studies have shown that the immunomodulatory activity of dental MSCs is strongly upregulated by activated immune cells. MSCs exert mostly immunosuppressive effects, leading to the dampening of immune cell activation. Thus, the reciprocal interaction between dental MSCs and immune cells represents an elegant mechanism that potentially contributes to tissue homeostasis and inflammatory disease progression. Although the immunomodulatory potential of dental MSCs has been extensively investigated in vitro, its role in vivo remains obscure. A few studies have reported that the MSCs isolated from inflamed dental tissues have a compromised immunomodulatory ability. Moreover, the expression of some immunomodulatory proteins is enhanced in periodontal disease and even shows some correlation with disease severity. MSC-based immunomodulation may play an essential role in the regeneration of different dental tissues. Therefore, immunomodulation-based strategies may be a very promising tool in regenerative dentistry.

HBD3 Induces PD-L1 Expression on Head and Neck Squamous Cell Carcinoma Cell Lines

Human β-defensin 3 (HBD3) is an antimicrobial peptide up-regulated in the oral tissues of individuals with head and neck squamous cell carcinomas (HNSCC) and oral squamous cell carcinomas (SCC) and present in high concentrations in their saliva. In this study, we determined if HBD3 contributes to HNSCC pathogenesis by inducing programmed death-ligand 1 (PD-L1) expression on HNSCC cell lines. For this, SCC cell lines SCC4, SCC15, SCC19, SCC25, and SCC99 (5.0 × 10⁴ viable cells) were used. Cells were incubated with IFNγ (0.6 µM) and HBD3 (0.2, 2.0, or 20.0 µM) for 24 h. Cells alone served as controls. Cells were then treated with anti-human APC-CD274 (PD-L1) and Live/Dead Fixable Green Dead Cell Stain. Cells treated with an isotype antibody and cells alone served as controls. All cell suspensions were analyzed in a LSR II Violet Flow Cytometer. Cytometric data was analyzed using FlowJo software. Treatment with IFNγ (0.6 µM) increased the number of cells expressing PD-L1 (p < 0.05) with respect to controls. Treatment with HBD3 (20.0 µM) also increased the number of cells expressing PD-L1 (p < 0.05) with respect to controls. However, treatment with IFNγ (0.6 µM) was not significantly different from treatment with HBD3 (20.0 µM) and the numbers of cells expressing PD-L1 were similar (p = 1). Thus, HBD3 increases the number of cells expressing PD-L1. This is a novel concept, but the role HBD3 contributes to HNSCC pathogenesis by inducing PD-L1 expression in tumors will have to be determined.

The detailed distribution of T cell subpopulations in immune-stable renal allograft recipients: a single center study

Background

Most renal allograft recipients reach a stable immune state (neither rejection nor infection) after transplantation. However, the detailed distribution of overall T lymphocyte subsets in the peripheral blood of these immune-stable renal transplant recipients remains unclear. We aim to identify differences between this stable immune state and a healthy immune state.

Methods

In total, 103 recipients underwent renal transplantation from 2012 to 2016 and received regular follow-up in our clinic. A total of 88 of these 103 recipients were enrolled in our study according to the inclusion and exclusion criteria. A total of 47 patients were 1 year post-transplantation, and 41 were 5 years post-transplantation. In addition, 41 healthy volunteers were recruited from our physical examination clinic. Detailed T cell subpopulations from the peripheral blood were assessed via flow cytometry. The parental frequency of each subset was calculated and compared among the diverse groups.

Results

The demographics and baseline characteristics of every group were analyzed. The frequency of total T cells (CD3+) was decreased in the renal allograft recipients. No difference in the variation of the CD4+, CD8+, and activated (HLA-DR+) T cell subsets was noted among the diverse groups. Regarding T cell receptor (TCR) markers, significant reductions were found in the proportion of γδ T cells and their Vδ2 subset in the renal allograft recipients. The proportions of both CD4+ and CD8+ programmed cell death protein (PD) 1+ T cell subsets were increased in the renal allograft recipients. The CD27+CD28+ T cell proportions in both the CD4+ and CD8+ populations were significantly decreased in the allograft recipients, but the opposite results were found for both CD4+ and CD8+ CD27-CD28- T cells. An increased percentage of CD4+ effector memory T cells and a declined fraction of CD8+ central memory T cells were found in the renal allograft recipients.

Conclusion

Limited differences in general T cell subsets (CD4+, CD8+, and HLA-DR+) were noted. However, obvious differences between renal allograft recipients and healthy volunteers were identified with TCR, PD1, costimulatory molecules, and memory T cell markers.

Detection of Exosomal PD-L1 RNA in Saliva of Patients With Periodontitis

Periodontitis is the most prevalent inflammatory disease of the periodontium, and is related to oral and systemic health. Exosomes are emerging as non-invasive biomarker for liquid biopsy. We here evaluated the levels of programmed death-ligand 1 (PD-L1) mRNA in salivary exosomes from patients with periodontitis and non-periodontitis controls. The purposes of this study were to establish a procedure for isolation and detection of mRNA in exosomes from saliva of periodontitis patients, to characterize the level of salivary exosomal PD-L1, and to illustrate its clinical relevance. Bioinformatics analysis suggested that periodontitis was associated with an inflammation gene expression signature, that PD-L1 expression positively correlated with inflammation in periodontitis based on gene set enrichment analysis (GSEA) and that PD-L1 expression was remarkably elevated in periodontitis patients versus control subjects. Exosomal RNAs were successfully isolated from saliva of 61 patients and 30 controls and were subjected to qRT-PCR. Levels of PD-L1 mRNA in salivary exosomes were higher in periodontitis patients than controls (P < 0.01). Salivary exosomal PD-L1 mRNA showed significant difference between the stages of periodontitis. In summary, the protocols for isolating and detecting exosomal RNA from saliva of periodontitis patients were, for the first time, characterized. The current study suggests that assay of exosomes-based PD-L1 mRNA in saliva has potential to distinguish periodontitis from the healthy, and the levels correlate with the severity/stage of periodontitis.

Comparative Analysis of Gene Expression Patterns for Oral Epithelium-Related Functions with Aging

Epithelial cells and functions of the epithelium are critical to the health of the oral cavity. We used a nonhuman primate model to profile the transcriptome of gingival tissues in health across the lifespan and hypothesized that in older animals, epithelial-related transcriptome patterns would reflect epithelial cells that are aggressively responsive to the surrounding environment and less able to modulate and resolve the noxious challenge from the bacteria. Rhesus monkeys (n = 34) with a healthy periodontium were distributed into four groups: ≤3 years (young), 3-7 years (adolescent), 12-16 years (adult), and 18-23 years (aged), and a buccal gingival sample from the premolar/molar region of each animal was obtained. RNA was subjected to a microarray analysis (GeneChip^® Rhesus Macaque Genome Array, Affymetrix), and 336 genes examined that are linked to epithelium and epithelial cell functions categorized into 9 broad functional groups: extracellular matrix and cell structure; extracellular matrix remodeling enzymes; cell adhesion molecules, cytoskeleton regulation; inflammatory response; growth factors; kinases/cell signaling; cell surface receptors; junction associated molecules; autophagy/apoptosis; antimicrobial peptides; and transcription factors. Total of 255 genes displayed a normalized signal >100, and differences across the age groups were observed primarily in extracellular matrix and cell structure, cell adhesion molecules, and cell surface receptor gene categories with elevations in the aged tissues. Keratins 2, 5, 6B, 13, 16, 17 were all significantly increased in healthy-aged tissues versus adults, and keratins 1 and 2 were significantly decreased in young animals. Approximately 15 integrins are highly expressed in the gingival tissues across the age groups with only ITGA8, ITGAM (CD11b), and ITGB2 significantly increased in the aged tissues. Little impact of aging on desmosomal/hemidesmosomal genes was noted. These results suggest that healthy gingival aging has a relatively limited impact on the broader functions of the epithelium and epithelial cells, with some effects on genes for extracellular matrix and cell adhesion molecules (e.g., integrins). Thus, while there is a substantial impact of aging on immune system targets even in healthy gingiva, it appears that the epithelial barrier remains reasonably molecularly intact in this model system.