Milk fat globule epidermal growth factor 8 inhibits periodontitis in non-human primates and its gingival crevicular fluid levels can differentiate periodontal health from disease in humans

The ameliorating role of epithelial cell rests of Malassez in the alleviation of experimentally-induced periodontitis in rats

OBJECTIVE

The present study aimed to investigate the effect of experimentally-induced periodontitis on epithelial cell rests of Malassez (ERM) distribution and its subsequent role in regenerating periodontal ligament (PDL).

DESIGN

The study included 60 rats, aged seven months, randomly and equally divided into two groups: Group I, the control group, and Group II, the experimental group, in which ligature-periodontitis was induced. Ten rats from each group were euthanized at 1, 2, and 4 weeks. For ERM detection, specimens were processed for histological and immunohistochemical examination of cytokeratin-14. Additionally, specimens were prepared for the transmission electron microscope.

RESULTS

Group I demonstrated well-organized PDL fibers with few ERM clumps close to the cervical root portion. In contrast, one week after periodontitis induction, Group II showed marked degeneration, a damaged cluster of ERM cells, narrowing of the PDL space, and early signs of PDL hyalinization. After two weeks, a disorganized PDL was observed with the detection of small ERM clumps enclosing very few cells. After four weeks, PDL fibers were reorganized, and ERM clusters increased significantly. Notably, ERM cells were positive for CK14 in all groups.

CONCLUSION

Early-stage ERM may be affected by periodontitis. However, ERM is capable of recovering its putative role in PDL maintenance.

SIRT6-regulated macrophage efferocytosis epigenetically controls inflammation resolution of diabetic periodontitis

Rationale: Diabetes exacerbates the prevalence and severity of periodontitis, leading to severe periodontal destruction and ultimately tooth loss. Delayed resolution of inflammation is a major contributor to diabetic periodontitis (DP) pathogenesis, but the underlying mechanisms of this imbalanced immune homeostasis remain unclear. Methods: We collected periodontium from periodontitis with or without diabetes to confirm the dysfunctional neutrophils and macrophages in aggravated inflammatory damage and impaired inflammation resolution. Our in vitro experiments confirmed that SIRT6 inhibited macrophage efferocytosis by restraining miR-216a-5p-216b-5p-217 cluster maturation through ''non-canonical'' microprocessor complex (RNA pulldown, RIP, immunostaining, CHIP, Luciferase assays, and FISH). Moreover, we constructed m6SKO mice that underwent LIP-induced periodontitis to explore the in vitro and in vivo effect of SIRT6 on macrophage efferocytosis. Finally, antagomiR-217, a miRNA antagonism, was delivered into the periodontium to treat LIP-induced diabetic periodontitis. Results: We discovered that insufficient SIRT6 as a histone deacetylase in macrophages led to unresolved inflammation and aggravated periodontitis in both human and mouse DP with accumulated apoptotic neutrophil (AN) and higher generation of neutrophil extracellular traps. Mechanistically, we validated that macrophage underwent high glucose stimulation resulting in disturbance of the SIRT6-miR-216/217 axis that triggered impeded efferocytosis of AN through targeting the DEL-1/CD36 axis directly. Furthermore, we demonstrated the inhibitory role of SIRT6 for MIR217HG transcription and identified a non-canonical action of microprocessor that SIRT6 epigenetically hindered the splicing of the primary miR-216/217 via the complex of hnRNPA2B1, DGCR8, and Drosha. Notably, by constructing myeloid-specific deletion of SIRT6 mice and locally delivering antagomir-217 in DP models, we strengthened the in vivo effect of this axis in regulating macrophage efferocytosis and inflammation resolution in DP. Conclusions: Our findings delineated the emerging role of SIRT6 in mediating metabolic dysfunction-associated inflammation, and therapeutically targeting this regulatory axis might be a promising strategy for treating diabetes-associated inflammatory diseases.

Periodontitis induced by orthodontic wire ligature drives oral microflora dysbiosis and aggravates alveolar bone loss in an improved murine model

Aim

To assess the contribution of polymicrobial disruption of host homeostasis to periodontitis progression in orthodontic wire ligation murine model.

Methods

Orthodontic wire rings were inserted between the first and second molars of mice for 18 days for the orthodontic wire ligation mouse model, and Pg injection model and Pg-LPS injection model were used as controls. Alveolar bone loss and periodontal inflammation were analyzed by micro-CT, histological staining and qRT-PCR. Further, pyrosequencing of 16S rRNA gene amplicon was used to analyze the development of oral microorganism dysbiosis in the mice.

Results

Micro-CT, TRAP staining and qRT-PCR showed that orthodontic wire ligation model led to more severe alveolar bone loss than Pg and Pg-LPS models.

H&E staining and qRT-PCR demonstrated that stronger inflammatory response was induced by the orthodontic wire treatment compared to the other models. In addition, pyrosequencing of 16S rRNA gene amplicons revealed that the composition of oral microbiota presented a transition as the disease progressed and significant differences emerged in oral microbiota communities between orthodontic ligature mice and healthy controls. Furthermore, antibiotic treatment decreased both inflammation and alveolar bone loss in response to microbial community dysbiosis. However, no significant difference in bacterial community composition was observed in Pg and Pg-LPS models.

Conclusions

Orthodontic wire ligation drove oral microbial community transitions that mimicked polymicrobial communities characterized by polymicrobial synergy and dysbiosis. Our improved model is suitable for further study of pathogenesis of periodontitis and exploration of corresponding treatment strategies.

Does the RGD region of certain proteins affect metabolic activity?

A better understanding of the role of mineralized tissues and their associated factors in governing whole-body metabolism should be of value toward informing clinical strategies to treat mineralized tissue and metabolic disorders, such as diabetes and obesity. This perspective provides evidence suggesting a role for the arginine-glycine-aspartic acid (RGD) region, a sequence identified in several proteins secreted by bone cells, as well as other cells, in modulating systemic metabolic activity. We focus on (a) two of the SIBLING (small integrin-binding ligand, N-linked glycoprotein) family genes/proteins, bone sialoprotein (BSP) and osteopontin (OPN), (b) insulin-like growth factor-binding protein-1 & 2 (IGFBP-1, IGFBP-2) and (c) developmental endothelial locus 1 (DEL1) and milk fat globule–EGF factor-8 (MFG-E8). In addition, for our readers to appreciate the mounting evidence that a multitude of bone secreted factors affect the activity of other tissues, we provide a brief overview of other proteins, to include fibroblast growth factor 23 (FGF23), phosphatase orphan 1 (PHOSPHO1), osteocalcin (OCN/BGLAP), tissue non-specific alkaline phosphatase (TNAP) and acidic serine aspartic-rich MEPE-associated motif (ASARM), along with known/suggested functions of these factors in influencing energy metabolism.

The Roles of Neutrophils Linking Periodontitis and Atherosclerotic Cardiovascular Diseases

Inflammation plays a crucial role in the onset and development of atherosclerosis. Periodontitis is a common chronic disease linked to other chronic inflammatory diseases such as atherosclerotic cardiovascular disease (ASCVD). The mechanistic pathways underlying this association are yet to be fully understood. This critical review aims at discuss the role of neutrophils in mediating the relationship between periodontitis and ASCVD. Systemic inflammation triggered by periodontitis could lead to adaptations in hematopoietic stem and progenitor cells (HSPCs) resulting in trained granulopoiesis in the bone marrow, thereby increasing the production of neutrophils and driving the hyper-responsiveness of these abundant innate-immune cells. These alterations may contribute to the onset, progression, and complications of atherosclerosis. Despite the emerging evidence suggesting that the treatment of periodontitis improves surrogate markers of cardiovascular disease, the resolution of periodontitis may not necessarily reverse neutrophil hyper-responsiveness since the hyper-inflammatory re-programming of granulopoiesis can persist long after the inflammatory inducers are removed. Novel and targeted approaches to manipulate neutrophil numbers and functions are warranted within the context of the treatment of periodontitis and also to mitigate its potential impact on ASCVD.

Inhibition of sphingosine-1-phosphate receptor 2 attenuated ligature-induced periodontitis in mice

Objectives

Periodontitis is an inflammatory bone loss disease initiated by oral bacterial inflammation. Herein, we determined whether inhibition of sphingosine‐1‐phosphate receptor 2 (S1PR2, a G protein‐coupled receptor) by its specific antagonist, JTE013, could alleviate ligature‐induced periodontitis in mice.

Materials and Methods

C57BL/6 mice were placed with silk ligatures at the left maxillary second molar to induce experimental periodontitis. Mice were treated with JTE013 or control vehicle (dimethyl sulfoxide, DMSO) oral topically on the ligatures once daily. After 15 days of treatment, RNA was extracted from the lingual mucosal tissues to quantify IL‐1β, IL‐6, and TNF mRNA levels in the tissues. Alveolar bone loss was determined by micro‐computed tomography. Sagittal periodontal tissue sections were cut and stained by hematoxylin and eosin (H&E) for general histology, or stained by tartrate‐resistant acid phosphatase (TRAP) for osteoclasts.

Results

Treatment with JTE013 attenuated ligature‐induced alveolar bone loss compared with DMSO treatment. Treatment with JTE013 reduced IL‐1β, IL‐6, and TNF mRNA levels in murine gingival mucosal tissues, inhibited leukocyte infiltration in the periodontal tissues, and decreased the number of osteoclasts in the periodontal tissues compared with controls.

Conclusion

Oral topical administration of JTE013 alleviated periodontal inflammatory bone loss induced by ligature placement in mice.

Current understanding of periodontal disease pathogenesis and targets for host-modulation therapy

Recent advances indicate that periodontitis is driven by reciprocally reinforced interactions between a dysbiotic microbiome and dysregulated inflammation. Inflammation is not only a consequence of dysbiosis but, via mediating tissue dysfunction and damage, fuels further growth of selectively dysbiotic communities of bacteria (inflammophiles), thereby generating a self-sustained feed-forward loop that perpetuates the disease. These considerations provide a strong rationale for developing adjunctive host-modulation therapies for the treatment of periodontitis. Such host-modulation approaches aim to inhibit harmful inflammation and promote its resolution or to interfere directly with downstream effectors of connective tissue and bone destruction. This paper reviews diverse strategies targeted to modulate the host periodontal response and discusses their mechanisms of action, perceived safety, and potential for clinical application.

Histone Lys demethylase KDM3C demonstrates anti-inflammatory effects by suppressing NF-κB signaling and osteoclastogenesis

Histone Lys-specific demethylases (KDMs) play a key role in many biological processes through epigenetic mechanisms. However, the role of KDMs in inflammatory responses to oral bacterial infection is poorly understood. Here, we show a novel regulatory role of KDM3C in inflammatory responses to oral bacterial infection. KDM3C expression is transiently suppressed in human and mouse macrophages exposed to LPS from Porphyromonas gingivalis (Pg LPS). Loss of KDM3C in both human and mouse macrophages led to notable induction of proinflammatory cytokines in response to Pg LPS stimulation. Also, KDM3C depletion led to strong induction of p65 phosphorylation and accelerated nuclear translocation in cells exposed to Pg LPS. Kdm3C knockout (KO) in mice led to increased alveolar bone destruction upon induction of experimental periodontitis or pulp exposure compared with those of the wild-type (WT) littermates. The Kdm3C KO mice also revealed an increased number of osteoclasts juxtaposed to the bony lesions. We also confirmed enhanced osteoclastogenesis by bone marrow-derived macrophages isolated from the Kdm3C KO compared with the WT controls. These findings suggest an anti-inflammatory function of KDM3C in regulating the inflammatory responses against oral bacterial infection through suppression of NF-κB signaling and osteoclastogenesis.-Lee, J. Y., Mehrazarin, S., Alshaikh, A., Kim, S., Chen, W., Lux, R., Gwack, Y., Kim, R. H., Kang, M. K. Histone Lys demethylase KDM3C demonstrates anti-inflammatory effects by suppressing NF-κB signaling and osteoclastogenesis.

An experimental murine model to study periodontitis

Periodontal disease (PD) is a common dental disease associated with the interaction between dysbiotic oral microbiota and host immunity. It is a prevalent disease, resulting in loss of gingival tissue, periodontal ligament, cementum and alveolar bone. PD is a major form of tooth loss in the adult population. Experimental animal models have enabled the study of PD pathogenesis and are used to test new therapeutic approaches for treating the disease. The ligature-induced periodontitis model has several advantages as compared with other models, including rapid disease induction, predictable bone loss and the capacity to study periodontal tissue and alveolar bone regeneration because the model is established within the periodontal apparatus. Although mice are the most convenient and versatile animal models used in research, ligature-induced periodontitis has been more frequently used in large animals. This is mostly due to the technical challenges involved in consistently placing ligatures around murine teeth. To reduce the technical challenge associated with the traditional ligature model, we previously developed a simplified method to easily install a bacterially retentive ligature between two molars for inducing periodontitis. In this protocol, we provide detailed instructions for placement of the ligature and demonstrate how the model can be used to evaluate gingival tissue inflammation and alveolar bone loss over a period of 18 d after ligature placement. This model can also be used on germ-free mice to investigate the role of human oral bacteria in periodontitis in vivo. In conclusion, this protocol enables the mechanistic study of the pathogenesis of periodontitis in vivo.

Evaluation of milk fat globule-epidermal growth factor-factor VIII and IL-1β levels in gingival crevicular fluid and saliva in periodontal disease and health

The aim of this study is to determine the levels of MFG-E8 and interleukin (IL)-1β in saliva and gingival crevicular fluid (GCF) associated with periodontal health and disease. Whole saliva and GCF samples were obtained from systemically healthy participants who were either periodontally healthy (n = 24) or suffered from gingivitis (n = 25) or chronic periodontitis (n = 25). Full-mouth clinical periodontal measurements, including bleeding on probing, probing depth, gingival index, plaque index, and clinical attachment level were also recorded. Enzyme-linked immunosorbent assay was used to estimate MFG-E8 and IL-1β levels in the samples. Analysis of variance, Kruskal-Wallis tests, and Pearson correlation tests were used to analyse the data statistically. The total level of MFG-E8 in GCF was significantly higher in the healthy group than in the other two groups (P = 0.01). Salivary MFG-E8 levels did not differ significantly among the groups. There were negative correlations between the level of MFG-E8 in GCF and probing depth (P = 0.03), bleeding on probing (P = 0.001), plaque index (P = 0.003), and gingival index (P = 0.003). The total level of IL-1β in GCF was significantly lower in the healthy group than in the groups with gingivitis and chronic periodontitis (P < 0.001). Salivary IL-1β levels showed significant differences across all three groups (P < 0.001). The level of MFG-E8 in GCF was higher in the healthy group than in the periodontal disease groups. Furthermore, there was no difference between gingivitis and periodontitis groups. The relationship between MFG-E8 and periodontal status should be further investigated.

DEL-1-Regulated Immune Plasticity and Inflammatory Disorders

In contrast to traditional immune cell-centered viewpoints, recent studies suggest that tissues are not passive recipients of immunity but have a 'regulatory say' over the host inflammatory response. Identification of tissue-derived homeostatic molecules regulating immune plasticity is seminal for understanding the inherent regulatory potential of different organs in the immune response. DEL-1 (developmental endothelial locus-1) is a secreted multidomain protein interacting with integrins and phospholipids and regulates, depending on its expression location, distinct stages of the host inflammatory response (from myelopoiesis over leukocyte recruitment to efferocytosis and resolution of inflammation). Here we synthesize recent evidence of DEL-1 as an exemplar local regulatory factor in the context of tissue immune plasticity and inflammatory disorders (such as periodontitis, multiple sclerosis, and pulmonary disorders), and discuss its potential as a therapeutic agent.

DEL-1 promotes macrophage efferocytosis and clearance of inflammation

Resolution of inflammation is essential for tissue homeostasis and a promising approach to inflammatory disorders. Here we found that DEL-1, a secreted protein inhibiting leukocyte-endothelial adhesion and inflammation initiation, also functions as a non-redundant downstream effector in inflammation clearance. In human and murine periodontitis, waning of inflammation correlated with DEL-1 upregulation, whereas resolution of experimental periodontitis failed in DEL-1 deficiency. This concept was mechanistically substantiated in acute monosodium urate crystal-induced inflammation, where the pro-resolution function of DEL-1 was attributed to effective apoptotic neutrophil clearance (efferocytosis). DEL-1-mediated efferocytosis induced liver-X-receptor-dependent macrophage reprogramming to pro-resolving phenotype and was required for optimal production of at least certain specific pro-resolving mediators. Experiments in transgenic mice with cell-specific overexpression of DEL-1 linked its anti-leukocyte recruitment action to endothelial-derived DEL-1 and its efferocytic/pro-resolving action to macrophage-derived DEL-1. Thus, the compartmentalized expression of DEL-1 facilitates distinct homeostatic functions in an appropriate context that can be harnessed therapeutically.