Notch - a possible mediator between Epstein-Barr virus infection and bone resorption in apical periodontitis

Herpes simplex virus type 1 in periapical pathoses: Systematic review and meta-analysis

OBJECTIVES

The objective of this systematic review and meta-analysis of observational studies was to assess whether herpes simplex virus type 1 (HSV-1) can infect endodontic periapical lesions.

MATERIALS AND METHODS

Studies with cross-sectional design investigating HSV-1 in periapical tissues of patients with symptomatic and asymptomatic acute and chronic apical periodontitis were searched through MEDLINE, Scopus, Embase, Web of Science, and Google Scholar. Pooled HSV-1 prevalence proportion with 95% confidence interval (95CI) in periapical lesions was assessed with both fixed-effect and random-effects models, with/without adjustment for study quality and publication bias. Result robustness was investigated through sensitivity and subgroup analyses.

RESULTS

Literature search, performed twice, provided 84 items, and eight remained for the meta-analysis; globally, there were 194 patients mostly adults. The pooled HSV-1 prevalence proportions, assessed with various methods, were 6.9% (95CI, 3.8-11.3%, fixed-effect); 6.8% (95CI, 3.6-11.0%, random-effects); 8.1% (95CI, 4.4-14.5%, quality-adjusted); and 4.8% (95CI, 2.0-11.4%; adjusted for small-study effect).

CONCLUSIONS

The results indicated that HSV-1 can colonize the periapical tissues of 3%-11% patients with periapical diseases. Such data do not imply a causative role of HSV-1 in disease development and advancement. Well-designed and large-sized prospective cohort studies should be added in the literature panorama.

[Research Progress in the Molecular Regulatory Mechanisms of Alveolar Bone Restoration]

Alveolar bone, the protruding portion of the maxilla and the mandible that surrounds the roots of teeth, plays an important role in tooth development, eruption, and masticatory performance. In oral inflammatory diseases, including apical periodontitis, periodontitis, and peri-implantitis, alveolar bone defects cause the loosening or loss of teeth, impair the masticatory function, and endanger the physical and mental health of patients. However, alveolar bone restoration is confronted with great clinical challenges due to the the complicated effect of the biological, mechanical, and chemical factors in the oral microenvironment. An in-depth understanding of the underlying molecular regulatory mechanisms will contribute to the exploration of new targets for alveolar bone restoration. Recent studies have shown that Notch, Wnt, Toll-like receptor (TLR), and nuclear factor-κB (NF-κB) signaling pathways regulate the proliferation, differentiation, apoptosis, and autophagy of osteoclasts, osteoblasts, osteocytes, periodontal ligament cells, macrophages, and adaptive immune cells, modulate the expression of inflammatory mediators, affect the balance of the receptor activator for nuclear factor-κB ligand/receptor activator for nuclear factor-κB/osteoprotegerin (RANKL/RANK/OPG) system, and ultimately participate in alveolar bone restoration. Additionally, alveolar bone restoration involves AMP-activated protein kinase (AMPK), phosphatidyl inositol 3-kinase/protein kinase B (PI3K/AKT), Hippo/YAP, Janus kinase/signal transducer and activator of transcription (JAK/STAT), and transforming growth factor β (TGF-β) signaling pathways. However, current studies have failed to construct mature molecular regulatory networks for alveolar bone restoration. There is an urgent need for further research on the molecular regulatory mechanisms of alveolar bone restoration by using new technologies such as single-cell transcriptome sequencing and spatial transcriptome sequencing.

Involvement of the Notch signaling system in alveolar bone resorption

The Notch pathway is an evolutionarily preserved signaling pathway involved in a variety of vital cell functions. Additionally, it is one of the key regulators of inflammation, and controls the differentiation and function of different cells. Moreover, it was found to be involved in skeletal development and bone remodeling process. This review provides an overview of the involvement of the Notch signaling pathway in the pathogenesis of alveolar bone resorption in different forms of pathological conditions such as apical periodontitis, periodontal disease, and peri-implantitis. In vitro and in vivo evidence have confirmed the involvement of Notch signaling in alveolar bone homeostasis. Nonetheless, Notch signaling system, along with complex network of different biomolecules are involved in pathological process of bone resorption in apical periodontitis, periodontitis, and peri-implantitis. In this regard, there is a substantial interest to control the activity of this pathway in the treatment of disorders associated with its dysregulation. This review provides knowledge on Notch signaling and outlines its functions in alveolar bone homeostasis and alveolar bone resorption. Further investigations are needed to determine whether inhibition of the Notch signaling pathways might be beneficial and safe as a novel approach in the treatment of these pathological conditions.

PROBE 2023 guidelines for reporting observational studies in endodontics: Explanation and elaboration

Observational studies play a critical role in evaluating the prevalence and incidence of conditions or diseases in populations as well as in defining the benefits and potential hazards of health-related interventions. There are currently no reporting guidelines for observational studies in the field of Endodontics. The Preferred Reporting Items for study Designs in Endodontology (PRIDE) team has developed and published new reporting guidelines for observational-based studies called the 'Preferred Reporting items for OBservational studies in Endodontics (PROBE) 2023' guidelines. The PROBE 2023 guidelines were developed exclusively for the speciality of Endodontics by integrating and adapting the 'STrengthening the Reporting of OBservational studies in Epidemiology (STROBE)' checklist and the 'Clinical and Laboratory Images in Publications (CLIP)' principles. The recommendations of the Guidance for Developers of Health Research Reporting Guidelines were adhered to throughout the process of developing the guidelines. The purpose of this document is to serve as a guide for authors by providing an explanation for each of the items in the PROBE 2023 checklist along with relevant examples from the literature. The document also offers advice to authors on how they can address each item in their manuscript before submission to a journal. The PROBE 2023 checklist is freely accessible and downloadable from the PRIDE website (http://pride-endodonticguidelines.org/probe/).

TMT-based quantitative proteomics analysis reveals the role of Notch signaling in FAdV-4-infected LMH cell

Fowl adenovirus serotype 4 (FAdV-4) is recognized as a pathogen that causes hydropericardium syndrome. Irrespective of the pathway used by the virus to invade the chicken, the pathological characteristics of the disease include degeneration and necrosis of hepatocytes, formation of intranuclear inclusions, as well as inflammatory cell infiltration. Liver dysfunction constitutes one of the critical factors leading to death. Therefore, it is vital to investigate the virus-mediated severe pathological liver damage to further understand the pathogenesis of FAdV-4. Here, proteomics, a tandem mass tag (TMT)-based approach to directly analyze protein expression, was used to determine the protein expression during FAdV-4 proliferation in leghorn male hepatoma (LMH) cells. We identified 177 differentially expressed proteins associated with various biological processes and pathways. The functional enrichment analysis revealed that FAdV-4 could downregulate some signaling pathways in LMH cells, including NOD-like receptor signaling, RIG-I-like receptor signaling, NF-κB signaling, TNF signaling pathway, and Notch signaling, FoxO signaling, PI3K-Akt signaling, and autophagy. The results of proteomics screening suggested an association between FAdV-4 infection and Notch signaling in LMH in vitro, indicating that Notch signaling regulated the expression of inflammatory cytokines and interferons but not viral replication in LMH cells. These data contributed to the understanding of the immunopathogenesis and inflammopathogenesis of FAdV-4 infection and also provided valuable information for the further analysis of the molecular mechanisms underlying viral pathogenesis.

Role of PI3K in the bone resorption of apical periodontitis

BACKGROUND

Phosphoinositide 3-kinase (PI3K) is located within cells, and is involved in regulating cell survival, proliferation, apoptosis and angiogenesis. The purpose of this study was to investigate the role of PI3K in the process of bone destruction in apical periodontitis, and provide reference data for the treatment of this disease.

METHODS

The relative mRNA expression of PI3K, Acp5 and NFATc1 in the normal human periodontal ligament and in chronic apical periodontitis were analyzed by real-time quantitative polymerase chain reaction (RT-qPCR). A mouse model of apical periodontitis was established by root canal exposure to the oral cavity, and HE staining was used to observe the progress of apical periodontitis. Immunohistochemical staining was used to detect the expression of PI3K and AKT in different stages of apical periodontitis, while enzymatic histochemical staining was used for detection of osteoclasts. An Escherichia coli lipopolysaccharide (LPS)-mediated inflammatory environment was also established at the osteoclast and osteoblast level, and osteoclasts or osteoblasts were treated with the PI3K inhibitor LY294002 to examine the role of PI3K in bone resorption.

RESULTS

The expression of PI3K, Acp5 and NFATc1 genes in chronic apical periodontitis sample groups was significantly increased relative to healthy periodontal ligament tissue (P < 0.05). Mouse apical periodontitis was successfully established and bone resorption peaked between 2 and 3 weeks (P < 0.05). The expression of PI3K and Akt increased with the progression of inflammation, and reached a peak at 14 days (P < 0.05). The gene and protein expression of PI3K, TRAP and NFATc1 in osteoclasts were significantly increased (P < 0.05) in the E. coli LPS-mediated inflammatory microenvironment compared to the normal control group. Meanwhile in osteoblasts, the gene and protein expression of PI3K, BMP-2 and Runx2 were significantly reduced (P < 0.05) in the inflammatory microenvironment. With the addition of LY294002, expressions of bone resorption-related factors (TRAP, NFATc1) and bone formation-related factors (BMP-2, Runx2) significantly decreased (P < 0.05).

CONCLUSIONS

Under the inflammatory environment induced by LPS, PI3K participates in the occurrence and development of chronic apical periodontitis by regulating the proliferation and differentiation of osteoclasts and osteoblasts.

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.

Ex vivo study of IL-6 expression and function in immune cell subsets from human periapical lesions

AIM

Even though IL-6 is a key inflammatory cytokine in periapical lesions (PLs), its function in stable periapical disease is unknown. Therefore, the aim of this study was to investigate following: first, the ex vivo production of IL-6 by clinically different PLs; next, subsets of immune cells expressing IL-6 in PLs according to their inflammatory status and finally, modulatory effect of IL-6 on T-cell cytokine production in cell cultures.

METHODOLOGY

Inflammatory cells were isolated from a total of 95 human PLs. Detection of IL-6⁺ cells within the myeloid and lymphoid populations was performed by multicolour flow cytometry. ELISA and FlowCytomix Microbeads Assay were used to measure cytokine levels in culture supernatants. To study the role of IL-6 in PLs, mononuclear cells (MNC) from symptomatic (Sy) or asymptomatic (Asy) PLs were treated with IL-6 or Tocilizumab, an IL-6R blocking antibody. The differences between groups were tested by unpaired t-test, Mann-Whitney or Friedman tests.

RESULTS

The levels of IL-6 in PL MNC culture supernatants were significantly higher compared to total PL cells and PL granulocytes (p<0.001). MNC from Sy PLs produced significantly hihger levels of IL-6 than MNC from Asy PLs (p<0.001). Flow cytometry analysis showed that NKT cells, CD8⁺ T cells and M2 macrophages (MØ), were dominant IL-6⁺ cells, in contrast to CD4⁺ T cells. However, CD8⁺ and CD4⁺ T cells contributed the most to IL-6 production. IL-6^hi producing MNC cultures had higher levels of Th1 (IFN-γ), Th17 (IL-17A), Tfh (IL-21) and RANKL, whereas Th2 (IL-4) and Tregs cytokines (IL-10, TGF-β) were lower, compared to IL-6^low producing cultures. Exogenous IL-6 stimulated 17A, IL-21 and RANKL, independently of PL activation status, but decreased IFN-γ, IL-4 and IL-33 levels in IL-6^hi producing cultures. Tocilizumab increased IL-10 and TGF-β in IL-6^low producing cultures. All differences were p<0.05.

CONCLUSIONS

Most immune cells from Sy PLs expressed higher levels of IL-6 compared to Asy PLs, which correlated with IL-6 production in culture. Analysis of cytokines suggested a dominant pro-inflammatory T-cell response and osteodestructive function of IL-6 in PLs judging by Th17/Tfh cell activation, Tregs inhibition and increased RANKL/OPG ratio. Excessive IL-6 production decreased Th1/Th2 responses.

Herpesviruses in Periodontitis: An Umbrella Review

BACKGROUND

Despite numerous studies indicating a high prevalence of herpesviruses in both apical and marginal periodontitis samples, their exact role in the pathogenesis of a periodontal disease is still unclear.

OBJECTIVE

This umbrella review aimed to summarize data on herpesviruses detection in marginal periodontitis (MP) and apical periodontitis of endodontic origin (APEO) samples.

METHODS

The study protocol has been drafted a priori and registered to the International Prospective Register of Systematic Reviews (PROSPERO) (CRD42020215922). The literature search was conducted using the following electronic databases: Clarivate Analytics' Web of Science, Scopus, PubMed and Cochrane Database of Systematic Reviews, from inception to October 2020, with no language restrictions. Systematic reviews with or without meta-analysis that evaluated the association between the occurrence of herpesviruses and different forms of periodontal diseases were included. Other types of studies, including narrative reviews, were excluded. Two reviewers independently performed a literature search, data extraction, and quality assessment of included studies. Any disagreements or doubts were resolved by a third reviewer. The quality of the reviews was assessed using the AMSTAR 2 tool (A measurement tool to assess systematic reviews).

RESULTS

Six systematic reviews were included in the current review. One was graded as high quality, another one was graded as moderate quality, whereas the other four were graded as critically low-quality reviews. The presence of herpesviruses in subgingival samples was associated with an increased risk of MP, supported by the corresponding meta-analyses. Although the association was strong (OR > 3.0), the confidence intervals were wide, heterogeneity was significant, and studies were of small sample size. In addition, publication bias was detected. Contrary, data from systematic reviews that assessed APEO and herpesviruses did not show any significant associations.

CONCLUSIONS

Low-quality studies with high uncertainty suggest a strong association between herpesviruses and MP, but not with APEO.

The human oral virome: Shedding light on the dark matter

Mediators of the initiation, development, and recurrence of periodontitis include the oral microbiome embedded in subgingival plaque and the host immune response to a dysbiosis within this dynamic and complex microbial community. Although mediators have been studied extensively, researchers in the field have been unable to fully ascribe certain clinical presentations of periodontitis to their nature. Emergence of high-throughput sequencing technologies has resulted in better characterization of the microbial oral dysbiosis that extends beyond the extensively studied putative bacterial periodontopathogens to a shift in the oral virome composition during disease conditions. Although the biological dark matter inserted by retroviruses was once believed to be nonfunctional, research has revealed that it encodes historical viral-eukaryotic interactions and influences host development. The objective of this review is to evaluate the proposed association of herpesviruses to the etiology and pathogenesis of periodontal disease and survey the highly abundant prokaryotic viruses to delineate their potential roles in biofilm dynamics, as well as their interactions with putative bacterial periodontopathogens and eukaryotic cells. The findings suggest that potential novel periodontal therapies targeting or utilizing the oral virome can alleviate certain clinical presentations of periodontitis. Perhaps it is time to embrace the viral dark matter within the periodontal environment to fully comprehend the pathogenesis and systemic implications of periodontitis.

Impact of Notch signalling molecules and bone resorption regulators on clinical parameters in periodontitis

BACKGROUND AND OBJECTIVE

Notch signalling cascade has recently been connected to alveolar bone resorption in periodontitis. Hence, the present cross-sectional study aimed to analyze the expression of Notch signalling pathway (Notch 1, Notch 2, Jagged 1, Hes 1, Hey 1) and periodontitis-related (tumor necrosis factor alpha- TNF-α, interleukin 17-IL-17, receptor activator of nuclear factor-kappa B ligand-RANKL, osteoprotegerin-OPG) molecules and correlate it with clinical parameters in aggressive (AP) and chronic (CP) periodontitis. Additionally, the aforementioned markers' expression was evaluated in periodontitis patients with different RANKL/OPG ratios.

MATERIAL AND METHODS

Eighty patients were enrolled either in AP or CP group. Clinical attachment level (CAL), bleeding on probing (BOP), periodontal probing depth (PPD) and plaque index (PI) were recorded for each patient. Total RNA was extracted from gingival crevicular fluid samples. Relative gene expression of investigated markers was determined by reverse transcriptase-real-time polymerase chain reaction.

RESULTS

Significantly higher values of PPD were observed in AP compared to CP (P = .010). Negative correlations between OPG and CAL, and OPG and PI, were found in AP (P = .045, P = .006, respectively), while Hey 1 and PI had a positive correlation (P = .049). In multivariate linear regression analysis, OPG and Notch 2 were predictors of CAL in AP group. TNF-α and IL-17 were higher in RANKL predominant than in OPG predominant cases (P = .007, P = .001, respectively). In RANKL predominant lesions Notch 1 and Jagged 1 were down-regulated in AP compared to CP patients (P = .010, P = .025, respectively).

CONCLUSION

The present study demonstrated that changes in Notch 2 expression affected CAL in AP cases hence this molecule could be considered as a contributor to alveolar bone loss. In RANKL-activated settings, the down-regulation of Notch 1 might participate in more severe bone resorption in AP.