An update of knowledge on the regulatory role of Treg cells in apical periodontitis

Physical training attenuates systemic cytokine response and tissue damage triggered by apical periodontitis

Apical periodontitis (AP) is a condition characterized by inflammatory and infectious components in the tooth canal. AP affects periradicular tissues and has systemic repercussions. Physical exercise is a structured activity that requires cardiorespiratory function, and can modulate the inflammatory profile in pathological conditions. As a result, this study aimed to determine the effects of aerobic physical training (PT) on the alveolar bone with and without AP, and its systemic inflammatory repercussions. AP was induced in the mandibular first molars, and PT was performed on a treadmill for five consecutive days over four weeks, with progressive increases in speed and activity time. Blood samples were collected to determine serum cytokine levels using immunoassays, and alveolar bone samples were collected for histopathological evaluation, lesion volume and microarchitecture assessment using computed microtomography. Animals with AP had increased pro-inflammatory cytokines levels compared to those without AP; however, these levels were attenuated or restored by PT. Compared to the AP group, the AP + PT group had a smaller lesion volume and greater preservation of the bone trabeculae in the remaining alveolar bone surrounding the lesion. In overall, PT minimized the severity of AP proving to be a valid strategy for individuals undergoing endodontic treatment.

Correlation between PD-1/PD-L1 and RANKL/OPG in chronic apical periodontitis model of Sprague-Dawley rats

Chronic apical periodontitis (CAP) is characterized by inflammation and destruction of the apical periodontium that is of pulpal origin, appearing as an apical radiolucent area, and does not produce clinical symptoms. Little is known about whether the PD-1/PD-L1 ratio is associated with the balance between RANKL and OPG in CAP. The relationship between PD-1/PD-L1 and RANKL/OPG in CAP is investigated in this study. A CAP rat model was established using Sprague-Dawley rats. The pulp chambers were exposed to the oral cavity to allow bacterial contamination. The apical tissues of the bilateral mandibular first molars were analyzed for histological morphology using hematoxylin and eosin (H&E) staining. Immunohistochemistry and qRT-PCR were used to determine the expression of PD-1, PD-L1, OPG, and RANKL mRNA and proteins in periapical tissues and mandibular samples, respectively. The radiological images indicated a poorly defined low-density shadow and alveolar bone resorption after periodontitis induction. Histological analysis revealed an infiltration of inflammatory cells and alveolar bone resorption in the periapical tissues. Mandibular mRNA and periapical protein expression of PD-1, PD-L1, and RANKL was upregulated 7-28 days after periodontitis induction, while the expression of OPG was downregulated. No significant relationship was observed between PD-1/PD-L1 and RANKL/OPG at either mRNA or protein levels in CAP. There is an increased expression of PD-1, PD-L1, and RANKL and a decreased expression of OPG, indicating progression of CAP.

Mouse gingival single-cell transcriptomic atlas identified a novel fibroblast subpopulation activated to guide oral barrier immunity in periodontitis

Periodontitis, one of the most common non-communicable diseases, is characterized by chronic oral inflammation and uncontrolled tooth supporting alveolar bone resorption. Its underlying mechanism to initiate aberrant oral barrier immunity has yet to be delineated. Here, we report a unique fibroblast subpopulation activated to guide oral inflammation (AG fibroblasts) identified in a single-cell RNA sequencing gingival cell atlas constructed from the mouse periodontitis models. AG fibroblasts localized beneath the gingival epithelium and in the cervical periodontal ligament responded to the ligature placement and to the discrete topical application of Toll-like receptor stimulants to mouse maxillary tissue. The upregulated chemokines and ligands of AG fibroblasts linked to the putative receptors of neutrophils in the early stages of periodontitis. In the established chronic inflammation, neutrophils, together with AG fibroblasts, appeared to induce type 3 innate lymphoid cells (ILC3s) that were the primary source of interleukin-17 cytokines. The comparative analysis of Rag2-/- and Rag2-/-Il2rg-/- mice suggested that ILC3 contributed to the cervical alveolar bone resorption interfacing the gingival inflammation. We propose the AG fibroblast-neutrophil-ILC3 axis as a previously unrecognized mechanism which could be involved in the complex interplay between oral barrier immune cells contributing to pathological inflammation in periodontitis.

From Cells to Environment: Exploring the Interplay between Factors Shaping Bone Health and Disease

The skeletal system is an extraordinary structure that serves multiple purposes within the body, including providing support, facilitating movement, and safeguarding vital organs. Moreover, it acts as a reservoir for essential minerals crucial for overall bodily function. The intricate interplay of bone cells plays a critical role in maintaining bone homeostasis, ensuring a delicate balance. However, various factors, both intrinsic and extrinsic, can disrupt this vital physiological process. These factors encompass genetics, aging, dietary and lifestyle choices, the gut microbiome, environmental toxins, and more. They can interfere with bone health through several mechanisms, such as hormonal imbalances, disruptions in bone turnover, direct toxicity to osteoblasts, increased osteoclast activity, immune system aging, impaired inflammatory responses, and disturbances in the gut-bone axis. As a consequence, these disturbances can give rise to a range of bone disorders. The regulation of bone's physiological functions involves an intricate network of continuous processes known as bone remodeling, which is influenced by various intrinsic and extrinsic factors within the organism. However, our understanding of the precise cellular and molecular mechanisms governing the complex interactions between environmental factors and the host elements that affect bone health is still in its nascent stages. In light of this, this comprehensive review aims to explore emerging evidence surrounding bone homeostasis, potential risk factors influencing it, and prospective therapeutic interventions for future management of bone-related disorders.

Mouse gingival single-cell transcriptomic atlas: An activated fibroblast subpopulation guides oral barrier immunity in periodontitis

Periodontitis, one of the most common non-communicable diseases, is characterized by chronic oral inflammation and uncontrolled tooth supporting alveolar bone resorption. Its underlying mechanism to initiate aberrant oral barrier immunity has yet to be delineated. Here, we report a unique fibroblast subpopulation activated to guide oral inflammation (AG fibroblasts) identified in a single-cell RNA sequencing gingival cell atlas constructed from the mouse periodontitis models. AG fibroblasts localized beneath the gingival epithelium and in the cervical periodontal ligament responded to the ligature placement and to the discrete application of Toll-like receptor stimulants to mouse maxillary tissue. The upregulated chemokines and ligands of AG fibroblasts linked to the putative receptors of neutrophils in the early stages of periodontitis. In the established chronic inflammation, neutrophils together with AG fibroblasts appeared to induce type 3 innate lymphoid cells (ILC3s) that were the primary source of interleukin-17 cytokines. The comparative analysis of Rag2-/- and Rag2γc-/- mice suggested that ILC3 contributed to the cervical alveolar bone resorption interfacing the gingival inflammation. We propose that AG fibroblasts function as a previously unrecognized surveillant to initiate gingival inflammation leading to periodontitis through the AG fibroblast-neutrophil-ILC3 axis.

Prevention and repair of orthodontically induced root resorption using ultrasound: a scoping review

INTRODUCTION

This review summarizes the available recent literature on different mechanisms and parameters of pulsed ultrasound (US) that have been used during orthodontic treatments to prevent and repair root resorption.

AREAS COVERED

A literature search was conducted between January (2002) and September (2022) in the following databases: PubMed, Google-Scholar, Embase and The-Cochrane-Library. After exclusions, a total of 19 papers were included in the present review. The most used US parameters with positive outcomes were frequency of 1.5 MHz, pulse repetition frequency of 1000 Hz, output intensity of 30 mW/cm2, duration of application of 20 mins and total number sessions were 14 with a repetition interval of 1day. The suggested mechanisms induced by US were alteration of cementoblasts, osteoblasts, osteoclasts, alkaline-phosphatase (ALP), runt-related-gene-2 (Runx2), osteoprotegerin (OPG), type-I-collagen (Col-I), C-telopeptide-type-I-collagen (CTX-I), hepatocyte-growth-factor (HGF), bone morphogenetic protein-2 (BMP-2), cyclooxygenase-2 (Cox-2), calcium (Ca2+), receptor activator of nuclear factor-kappa-B ligand (RANKL), and receptor activator of nuclear factor-kappa-B (RANK).

EXPERT OPINION

Understanding mechanisms and deciding which parameters of US that can be used during orthodontic treatment to prevent and repair root resorption is a great challenge. This work summarizes all the available data that can aid this process and suggest that US is an effective noninvasive method not only in prevention and repairing of orthodontic induced root resorption but also in accelerating teeth movement.

Double-Edged Sword Effect of Pyroptosis: The Role of Caspase-1/-4/-5/-11 in Different Levels of Apical Periodontitis

The study was to investigate the effect of canonical and noncanonical pyroptosis in apical periodontitis. Proteins' profiles of human apical periodontitis tissue were analyzed by label-free proteomics. Immunofluorescence was used to detect proteins related to pyroptosis in human apical periodontitis tissues and experimental apical periodontitis models. A dual experimental apical periodontitis model with both smaller (mandible) and larger (maxilla) bone lesions was established. THP-1-derived macrophages were stimulated with P. gingivalis lipopolysaccharide in vitro with or without the caspase-1/-4/-5 inhibitor Ac-FTDL-CMK. Propidium iodide staining, lactic dehydrogenase release and Western blot were applied to evaluate cell death and the protein expression. Caspase-1/-4/-5 were expressed in human apical periodontitis tissues. Caspase-1/-11 were involved in bone loss in experimental apical periodontitis. Caspase-1/-11 inhibitors reduced bone loss in larger lesions (maxilla) but accelerated bone loss in smaller lesions (mandible). Caspase-1/-4/-5 inhibitors also showed double-edged sword effects on propidium iodide staining and lactic dehydrogenase release in vitro. The expression of cleaved-caspase-1/-4/-5, mature interluekin-1β and gasdermin D N-terminal domain increased in THP-1-derived macrophages after lipopolysaccharide stimulation but decreased after treatment with Ac-FTDL-CMK. Pyroptosis contributed to apical periodontitis and excited a double-edged sword effect in inducing bone loss in vivo and cell death in vitro.

Mechanisms of bone remodeling and therapeutic strategies in chronic apical periodontitis

Chronic periapical periodontitis (CAP) is a typical oral disease in which periodontal inflammation caused by an odontogenic infection eventually leads to bone loss. Uncontrolled infections often lead to extensive bone loss around the root tip, which ultimately leads to tooth loss. The main clinical issue in the treatment of periapical periodontitis is the repair of jawbone defects, and infection control is the first priority. However, the oral cavity is an open environment, and the distribution of microorganisms through the mouth in jawbone defects is inevitable. The subversion of host cell metabolism by oral microorganisms initiates disease. The presence of microorganisms stimulates a series of immune responses, which in turn stimulates bone healing. Given the above background, we intended to examine the paradoxes and connections between microorganisms and jaw defect repair in anticipation of new ideas for jaw defect repair. To this end, we reviewed the microbial factors, human signaling pathways, immune cells, and cytokines involved in the development of CAP, as well as concentrated growth factor (CGF) and stem cells in bone defect repair, with the aim of understanding the impact of microbial factors on host cell metabolism to inform the etiology and clinical management of CAP.

mTOR Signaling in the Regulation of CD4+ T Cell Subsets in Periodontal Diseases

Periodontal disease results from the inflammatory infiltration by the microbial community which is marked through tooth mobility and alveolar bone resorption. The inflammation in periodontal disease is mediated by CD4⁺ T cells through cytokine secretion and osteoclastogenetic activity. Historically, the inflammatory model in periodontal disease is described through disruption of the balance between two subsets of T helper cells which are T-helper type 1 (Th1) and T-helper type 2 (Th2). However, more and more studies have found that apart from subsets of helper T cells, regulatory T-cells and Th17 cells are also involved in the pathogenesis of periodontal diseases. Growing evidence proves that helper T cells differentiation, activation, and subset determination are under the strong impact of mTOR signaling. mTOR signaling could promote Th1 and Th17 cell differentiation and inhibit Treg commitment through different mTOR complexes, therefore we anticipate a regulation effect of mTOR signaling on periodontal diseases by regulating CD4⁺ T cell subsets. This review aims to integrate the topical researches about the role of different types of Th cells in the pathogenesis of periodontal diseases, as well as the regulation of mTOR signaling in the specification and selection of Th cell commitment.

A Systematic Review and Meta-Analysis on Multiple Cytokine Gene Polymorphisms in the Pathogenesis of Periodontitis

Aim

Periodontitis is an inflammatory disease that destroys both soft and hard periodontal tissues. However, a complex periodontal cytokine network remains unclear. This systematic review explored multiple cytokine gene polymorphisms in the pathogenesis of periodontitis.

Material and Methods

A systematic search was performed using the databases from previous publications, which indicated the association between cytokine polymorphisms and periodontitis pathogenesis. Meta-analysis was conducted using fixed or randomized models to calculate the significance of multiple cytokine polymorphisms. A total of 147 articles were analyzed with polymorphisms in 12 interleukins [Th1 (IL-2, IFN-γ, and TNF-α), Th2 (IL-4 and IL-13), Th17 (IL-1α, IL-1β, IL-6, and IL-17), and Treg cytokines (IL-10 and TGF-β)]. Doi plot was used to probe the occurrence of publication bias.

Results

The polymorphisms of IL-2 and TNF-α of Th1 cytokine family may be associated with the pathogenesis or the prevention of periodontitis risk, while the polymorphism of IFN-γ is not related to periodontitis risk. The polymorphisms for IL-4 and IL-13 of Th2 cytokine family are not found to be associated with the pathogenesis of periodontitis. For the polymorphisms of the members of Th17 cytokine family, different IL-1α polymorphisms may have inverse actions in the pathogenesis of periodontitis. IL-1β is a noteworthy cytokine biomarker in periodontitis development and progression. IL-6 may have a protective function in the inflammatory responses of periodontitis, and IL-17 has a weak relationship the inflammatory responses. The polymorphisms for the members of Treg cell cytokines may have a protective function against periodontitis risk. LFK indexes show the major asymmetry due to publication bias.

Conclusion

IL-1β is a notable cytokine biomarker in periodontitis risk. Treg cytokines favor an anti-inflammatory and protective environment. Further data are needed to confirm the present conclusion due to publication bias.

Oral Osteomicrobiology: The Role of Oral Microbiota in Alveolar Bone Homeostasis

Osteomicrobiology is a new research field in which the aim is to explore the role of microbiota in bone homeostasis. The alveolar bone is that part of the maxilla and mandible that supports the teeth. It is now evident that naturally occurring alveolar bone loss is considerably stunted in germ-free mice compared with specific-pathogen-free mice. Recently, the roles of oral microbiota in modulating host defense systems and alveolar bone homeostasis have attracted increasing attention. Moreover, the mechanistic understanding of oral microbiota in mediating alveolar bone remodeling processes is undergoing rapid progress due to the advancement in technology. In this review, to provide insight into the role of oral microbiota in alveolar bone homeostasis, we introduced the term “oral osteomicrobiology.” We discussed regulation of alveolar bone development and bone loss by oral microbiota under physiological and pathological conditions. We also focused on the signaling pathways involved in oral osteomicrobiology and discussed the bridging role of osteoimmunity and influencing factors in this process. Finally, the critical techniques for osteomicrobiological investigations were introduced.