The Pathogenic Effects of Fusobacterium nucleatum on the Proliferation, Osteogenic Differentiation, and Transcriptome of Osteoblasts

The influence of microorganisms on bone homeostasis in apical periodontitis

OBJECTIVE

This review aims to provide an overview of the role of microorganisms in the onset and progression of periapical diseases, particularly regarding their effects on bone homeostasis.

DESIGN

The search for this narrative review was conducted in PubMed, Web of Science and Google Scholar using relevant keywords, including checking reference lists of journal articles by hand searching.

RESULTS

Microorganisms directly promote osteoclasts through pathways such as nuclear factor-κB (NF-κB) and extracellular regulated protein kinases (ERK), while inhibiting osteoblasts function by interfering with the wingless-related integration site (Wnt)/β-catenin pathway in the periapical area. Moreover, microorganisms indirectly regulate periapical bone homeostasis by inducing programmed cell death and modulating the immune microenvironment through the activation of innate immunity via pattern-recognition receptors (PRRs) and subsequent cascades of responses. Among these microorganisms, Enterococcus faecalis, Porphyromonas gingivalis and Fusobacterium nucleatum play significant roles.

CONCLUSION

Microorganisms regulate pathways such as NF-ĸB and Wnt/β-catenin, as well as programmed cell death and the immune microenvironment in the periapical area, thereby disrupting bone homeostasis.

[Research progress on the regulatory cell death of osteoblasts in periodontitis]

Periodontitis is a chronic inflammatory disease characterized by progressive destruction of alveolar bone. The most critical mechanism underlying alveolar bone destruction is the imbalance of bone homeostasis, where osteoblast-mediated bone matrix synthesis plays an important role in regulating bone homeostasis. Regulated cell death is instrumental in both the inflammatory microenvironment and the regulation of bone homeostasis. Chronic inflammation, oxidative stress, and other factors can be directly involved in mitochondrial and death receptor-mediated signaling pathways, modulating B-cell lymphoma 2 family proteins and cysteine aspartic acid specific protease (caspase) activity, thereby affecting osteoblast apoptosis and alveolar bone homeostasis. Chronic inflammation and cellular damage induce osteoblast necroptosis via the RIPK1/RIPK3/MLKL signaling pathway, exacerbating the inflammatory response and accelerating alveolar bone destruction. Stimuli such as pathogenic microorganisms and cellular injury may also activate caspase-1-dependent or independent signaling pathways and gasdermin D family proteins, promoting osteoblast pyroptosis and releasing pro-inflammatory cytokines to mediate alveolar bone damage. Iron overload and lipid peroxidation in periodontitis can trigger ferroptosis in osteoblasts, impacting their survival and function, ultimately leading to bone homeostasis imbalance. This article focuses on the mechanism of periodontal disease affecting bone homeostasis through regulatory cell death, aiming to provide research evidence for the treatment of periodontitis and alveolar bone homeostasis imbalance.

Fusobacterium nucleatum infection modulates the transcriptome and epigenome of HCT116 colorectal cancer cells in an oxygen-dependent manner

Fusobacterium nucleatum, a gram-negative oral bacterium, has been consistently validated as a strong contributor to the progression of several types of cancer, including colorectal (CRC) and pancreatic cancer. While previous in vitro studies have shown that intracellular F. nucleatum enhances malignant phenotypes such as cell migration, the dependence of this regulation on features of the tumor microenvironment (TME) such as oxygen levels are wholly uncharacterized. Here we examine the influence of hypoxia in facilitating F. nucleatum invasion and its effects on host responses focusing on changes in the global epigenome and transcriptome. Using a multiomic approach, we analyze epigenomic alterations of H3K27ac and global transcriptomic alterations sustained within a hypoxia and normoxia conditioned CRC cell line HCT116 at 24 h following initial infection with F. nucleatum. Our findings reveal that intracellular F. nucleatum activates signaling pathways and biological processes in host cells similar to those induced upon hypoxia conditioning in the absence of infection. Furthermore, we show that a hypoxic TME favors F. nucleatum invasion and persistence and therefore infection under hypoxia may amplify malignant transformation by exacerbating the effects induced by hypoxia alone. These results motivate future studies to investigate host-microbe interactions in tumor tissue relevant conditions that more accurately define parameters for targeted cancer therapies.

Polymethylmethacrylate-hydroxyapatite antibacterial and antifungal activity against oral bacteria: An in vitro study

Objective

Reconstruction of alveolar bone defects resulting from aging, trauma, ablative surgery or pathology, remains a significant clinical challenge. The objective of this study was to investigate the antibacterial and antifungal activities of mixed polymethylmethacrylate-hydroxyapatite (PMMA-HA) against oral microorganisms. Our findings could provide valuable insights into the prospective application of PMMA-HA as a synthetic bone graft material to manage alveolar bone defects via tissue engineering.

Methods

HA powder was obtained from the Center for Ceramics in Indonesia and PMMA granules were obtained from HiMedia Laboratories; these were prepared in 20:80, 30:70, and 40:60 ratios. The antibacterial diffusion method was then performed against Staphylococcusaureus, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Fusobacterium nucleatum, while the antifungal diffusion method was used to test against Candida albicans. Standardized protocols were used for microbial culturing and inhibition zones were measured with digital calipers. Statistical analyses included one-way ANOVA and Kruskal-Wallis tests, supplemented by post-hoc Tukey HSD tests.

Results

A PMMA-HA scaffold with a 20:80 ratio demonstrated the highest antibacterial activity against S. aureus, A. actinomycetemcomitans, P. gingivalis, and F. nucleatum. This was followed by the 30:70 and 40:60 ratios in terms of antibacterial activity. Statistical significance was achieved with p < 0.05 in comparison to controls. However, none of the PMMA-HA ratios showed antifungal activity against C. albicans.

Conclusion

PMMA-HA scaffolds have significant activity against bacteria, but not against fungi.

Immunomodulatory functions of microorganisms in tissue regenerative healing

External pathogenic microorganisms and commensal microorganisms in the body have either harmful or beneficial impacts on the regenerative repair of tissues, and the immune system plays a crucial regulatory role in this process. This review summarises our current understanding of microorganism-immune system interactions, with a focus on how these interactions impact the renewal and repair ability of tissues, including skin, bone, gut, liver, and nerves. This review concludes with a discussion of the mechanisms by which microbes act on various types of immune cells to affect tissue regeneration, offers potential strategies for using microbial therapies to enhance the regenerative repair function of tissues, and suggest novel therapeutic approaches for regenerative medicine. STATEMENT OF SIGNIFICANCE: Microbiological communities have crucial impacts on human health and illness by participating in energy collection and storage and performing various metabolic processes. External pathogenic microorganisms and commensal microorganisms in the body have either harmful or beneficial impacts on the regenerative repair of tissues, and the immune system plays a critical regulatory role in this process. This study reviews the important correlation between microorganisms and the immune system and investigates the mechanism of various microorganism that participate in the regeneration and repair of tissues and organs by modulating immune system.

"Medicine food homology" plants promote periodontal health: antimicrobial, anti-inflammatory, and inhibition of bone resorption

"Medicine food homology" (MFH) is a term with a lengthy history. It refers to the fact that a lot of traditional natural products have both culinary and therapeutic benefits. The antibacterial, anti-inflammatory and anticancer effects of MFH plants and their secondary metabolites have been confirmed by numerous research. A bacterially generated inflammatory illness with a complicated pathophysiology, periodontitis causes the loss of the teeth's supporting tissues. Several MFH plants have recently been shown to have the ability to prevent and treat periodontitis, which is exhibited by blocking the disease's pathogens and the virulence factors that go along with them, lowering the host's inflammatory reactions and halting the loss of alveolar bone. To give a theoretical foundation for the creation of functional foods, oral care products and adjuvant therapies, this review has especially explored the potential medicinal benefit of MFH plants and their secondary metabolites in the prevention and treatment of periodontitis.

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.

Outer Membrane Vesicles From Fusobacterium nucleatum Switch M0-Like Macrophages Toward the M1 Phenotype to Destroy Periodontal Tissues in Mice

Periodontitis is a chronic inflammatory oral disease that affects nearly 50% of all adults. Fusobacterium nucleatum (F. nucleatum) is known to be involved in the formation and development of periodontitis. Outer membrane vesicles (OMVs) harboring toxic bacterial components are continuously released during F. nucleatum growth and regulate the extent of the inflammatory response by controlling the functions of immune and non-immune cells in tissues. Macrophages are important immune cells in periodontal tissue that resist pathogen invasion and play an important role in the pathophysiological process of periodontitis. However, the role of the interaction between F. nucleatum OMVs and macrophages in the occurrence and development of periodontitis has not been studied. The purpose of this study was to clarify the effect of F. nucleatum OMVs on the polarization of macrophages and the roles of this specific polarization and F. nucleatum OMVs in the pathophysiology of periodontitis. The periodontitis model was established by inducing ligation in C57BL/6 mice as previously described. Micro-CT, RT-qPCR, hematoxylin-eosin (H&E) and tartrate acid phosphatase (TRAP) staining assays were performed to analyze the periodontal tissue, alveolar bone loss, number of osteoclasts and expression of inflammatory factors in gingival tissue. The changes in the state and cytokine secretion of bone marrow-derived macrophages (BMDMs) stimulated by F. nucleatum OMVs were observed in vivo by confocal microscopy, flow cytometry, Western blot and ELISA. Mouse gingival fibroblasts (MGFs) were isolated and then cocultured with macrophages. The effects of F. nucleatum OMVs on the proliferation and apoptosis of MGFs were analyzed by flow cytometry and lactate dehydrogenase (LDH) assays. The periodontitis symptoms of mice in the F. nucleatum OMVs + ligation group were more serious than those of mice in the simple ligation group, with more osteoclasts and more inflammatory factors (IL-1β, IL-6, and TNF-α) being observed in their gingival tissues. M0 macrophages transformed into M1 macrophages after the stimulation of BMDMs with F. nucleatum OMVs, and the M1 macrophages then released more inflammatory cytokines. Analysis of the coculture model showed that the MGF apoptosis and LDH release in the inflammatory environment were increased by F. nucleatum OMV treatment. In conclusion, F. nucleatum OMVs were shown to aggravate periodontitis, alveolar bone loss and the number of osteoclasts in an animal model of periodontitis. F. nucleatum OMVs promoted the polarization of macrophages toward the proinflammatory M1 phenotype, and the inflammatory environment further aggravated the toxicity of F. nucleatum OMVs on MGFs. These results suggest that M1 macrophages and F. nucleatum OMVs play roles in the occurrence and development of periodontitis.

Enterococcus faecalis OG1RF induces apoptosis in MG63 cells via caspase-3/-8/-9 without activation of caspase-1/GSDMD

OBJECTIVE

Regulated cell death is key in the pathogenesis of persistent apical periodontitis. Here, we investigated the mechanisms of regulated cell death in osteoblast-like MG63 cells infected with Enterococcus faecalis OG1RF.

MATERIALS AND METHODS

MG63 cells were infected with live E. faecalis OG1RF at the indicated multiplicity of infection for the indicated infection time. We evaluated the cells by flow cytometry, terminal deoxynucleotidyl transferase dUTP nick end labelling assay and lactate dehydrogenase release analysis; measured the activity of caspase-1/-3/-8/-9 and the release of interleukin-1β; and determined the expression of apoptosis-associated proteins and gasdermin D by apoptosis antibody array and Western blotting.

RESULTS

Enterococcus faecalis OG1RF reduced the mitochondrial membrane potential of the infected cells, increased the percentage of apoptotic and terminal deoxynucleotidyl transferase dUTP nick end labelling-positive cells, and enhanced lactate dehydrogenase release. The expression of caspase-3 and survivin and the activity of caspase-3/-8/-9 were upregulated, while the expression of death receptor 6 was downregulated. The activity of caspase-1/gasdermin D and the release of interleukin-1β remained unaltered.

CONCLUSION

Enterococcus faecalis OG1RF induced both intrinsic and extrinsic MG63 cell apoptosis via caspase-3/-8/-9 activation but did not activate the pyroptotic pathway regulated by caspase-1/gasdermin D.

Regulation of Anti-Apoptotic SOD2 and BIRC3 in Periodontal Cells and Tissues

The aim of the study was to clarify whether orthodontic forces and periodontitis interact with respect to the anti-apoptotic molecules superoxide dismutase 2 (SOD2) and baculoviral IAP repeat-containing protein 3 (BIRC3). SOD2, BIRC3, and the apoptotic markers caspases 3 (CASP3) and 9 (CASP9) were analyzed in gingiva from periodontally healthy and periodontitis subjects by real-time PCR and immunohistochemistry. SOD2 and BIRC3 were also studied in gingiva from rats with experimental periodontitis and/or orthodontic tooth movement. Additionally, SOD2 and BIRC3 levels were examined in human periodontal fibroblasts incubated with Fusobacterium nucleatum and/or subjected to mechanical forces. Gingiva from periodontitis patients showed significantly higher SOD2, BIRC3, CASP3, and CASP9 levels than periodontally healthy gingiva. SOD2 and BIRC3 expressions were also significantly increased in the gingiva from rats with experimental periodontitis, but the upregulation of both molecules was significantly diminished in the concomitant presence of orthodontic tooth movement. In vitro, SOD2 and BIRC3 levels were significantly increased by F. nucleatum, but this stimulatory effect was also significantly inhibited by mechanical forces. Our study suggests that SOD2 and BIRC3 are produced in periodontal infection as a protective mechanism against exaggerated apoptosis. In the concomitant presence of orthodontic forces, this protective anti-apoptotic mechanism may get lost.