Fusobacterium nucleatum exacerbates the progression of pulpitis by regulating the STING-dependent pathway

Comparative analysis of deep dentinal caries microbiota in teeth with normal pulp, reversible pulpitis, symptomatic and asymptomatic irreversible pulpitis

AIM

To characterize the deep dentinal caries microbiota in teeth diagnosed with normal pulp with deep caries (NP), reversible pulpitis (RP), symptomatic irreversible pulpitis (SIP), and asymptomatic irreversible pulpitis (AIP), and to identify potential key pathogens associated with pulpitis progression, exploring their roles in disease advancement.

METHODOLOGY

In this cross-sectional study, we collected 108 dentinal caries samples, categorized into NP (n = 27), RP (n = 27), SIP (n = 27), and AIP (n = 27), according to the American Association of Endodontists' diagnostic criteria. 2 NP samples and 2 RP samples were excluded due to contamination. Samples were processed using Illumina MiSeq high-throughput sequencing. Alpha and beta diversity, taxa abundance differences, co-occurrence network analysis, and functional prediction were evaluated. Correlation analysis between the abundance of bacteria associated with clinical diagnosis, clinical signs, and pulp exposure status was performed with Spearman analysis and the Mantel test.

RESULTS

The bacteriome of deep dentinal caries exhibited statistically significant differences among NP, RP, SIP, and AIP groups. NP and RP showed similar microbial community structures, with comparable alpha diversity, beta diversity, bacterial phenotypes, functions, and network structures. In contrast, AIP and SIP displayed distinct microbial community profiles. AIP was characterized by higher alpha diversity and a greater abundance of gram-negative bacteria, with Propionibacterium and Prevotella_7 identified as bacteria associated with AIP pathogenesis. On the other hand, SIP showed lower alpha diversity and a higher abundance of facultative anaerobes, with Lactobacillus and Limosilactobacillus identified as bacteria associated with SIP pathogenesis. Fusobacterium, Prevotella, Treponema, and Selenomonas were identified as bacteria associated with both AIP and SIP. Compared to NP and RP, the microbial networks in AIP and SIP are more complex and contain more gram-negative endodontic pathogens. These pathogens form complex positive correlations with each other and numerous negative correlations with lactic acid bacteria.

CONCLUSIONS

The bacteriome of deep dentinal caries differs significantly across teeth diagnosed with NP, RP, AIP, and SIP. NP and RP exhibit similar microbial communities, whereas SIP and AIP display distinct microbial profiles.

Identification of pain-related long non-coding RNAs for pulpitis prediction

OBJECTIVES

We investigated the recently generated RNA-sequencing dataset of pulpitis to identify the potential pain-related lncRNAs for pulpitis prediction.

MATERIALS AND METHODS

Differential analysis was performed on the gene expression profile between normal and pulpitis samples to obtain pulpitis-related genes. The co-expressed gene modules were identified by weighted gene coexpression network analysis (WGCNA). Then the hypergeometric test was utilized to screen pain-related core modules. The functional enrichment analysis was performed on the up- and down-regulated genes in the core module of pulpitis pain to explore the underlying mechanisms. A pain-related lncRNA-based classification model was constructed using LASSO. Consensus clustering and gene set variation analysis (GSVA) on the infiltrating immunocytes was used for pulpitis subtyping. miRanda predicts miRNA-target relationship, which was filtered by expression correlation. Hallmark pathway and enrichment analysis was performed to investigate the candidate target pathways of the lncRNAs.

RESULTS

A total of 1830 differential RNAs were identified in pulpitis. WGCNA explored seven co-expressed modules, among which the turquoise module is pain-related with hypergeometric test. The up-regulated genes were significantly enriched in immune response related pathways. Down-regulated genes were significantly enriched in differentiation pathways. Eight lncRNAs in the pain-related module were related to inflammation. Among them, MIR181A2HG was downregulated while other seven lncRNAs were upregulated in pulpitis. The LASSO classification model revealed that MIR181A2HG and LINC00426 achieved outstanding predictive performances with perfect ROC-AUC score (AUC = 1). We differentiated the pulpitis samples into two progression subtypes and MIR181A2HG is a progressive marker for pulpitis. The miRNA-mRNA-lncRNA regulatory network of pulpitis pain was constructed, with GATA3 as a key transcription factor. NF-kappa B signaling pathway is a candidate pathway impacted by these lncRNAs.

CONCLUSIONS

PCED1B-AS1, MIAT, MIR181A2HG, LINC00926, LINC00861, LINC00528, LINC00426 and ITGB2-AS1 may be potential markers of pulpitis pain. A two-lncRNA signature of LINC00426 and MIR181A2HG can accurately predict pulpitis, which could facilitate the molecular diagnosis of pulpitis. GATA3 might regulate these lncRNAs and downstream NF-kappa B signaling pathway.

CLINICAL RELEVANCE

This study identified potential pain-related lncRNAs with underlying molecular mechanism analysis for the prediction of pulpitis. The classification model based on lncRNAs will facilitate the early diagnosis of pulpitis.

Guanylate-binding protein 5-mediated autophagy can promote the clearance of intracellular F. nucleatum in dental pulp cells during pulpitis

BACKGROUND

IFN-γ is crucial in induction of inducible cell-autonomous immunity, and IFN-γ signaling pathway is activated in pulpitis. Guanylate-binding proteins (GBPs) are a family of IFN-inducible GTPases and could utilize autophagy or pyroptosis to mitigate infection. GBP5 is abundantly expressed in inflamed pulp and human dental pulp cells (HDPCs). Therefore, we hypothesize that GBP5 in HDPCs exerts an immune-regulatory role in defending against bacterium infection.

METHODS

Fusobacterium nucleatum (F. nucleatum) was used to infect HDPCs, and immunoblotting and qRT-PCR were used to detect pyroptosis and autophagy. Pharmacological or genetic approaches were used to enhance or knock down GBP5 expression in HDPCs. Blood agar plate counting and immunoblotting were used to observe bacteria clearance effect and activation of autophagy. Student's t-test and one-way ANOVA were individually used for comparisons between two and multiple groups. Statistical significance was set at P < 0.05.

RESULTS

Following F. nucleatum infection in HDPCs, the autophagy marker LC3B was significantly upregulated while the mRNA and protein expression levels of p62 were increased. IFN-γ priming significantly inhibited the intracellular survival of F. nucleatum and enhanced the autophagic activity of HDPCs. GBP5 overexpression significantly increased the efficiency of HDPCs in clearing intracellular F. nucleatum and activated autophagic flux in HDPCs, while downregulating GBP5 in HDPCs suppressed autophagic flux.

CONCLUSION

IFN-γ-mediated GBP5 overexpression in HDPCs during F. nucleatum infection exerts an anti-microbial function through autophagy activation.

STING inhibition alleviates bone resorption in apical periodontitis

AIM

The goal of this study was to investigate the potential effects of an immunotherapeutic drug targeting STING to suppress the overreactive innate immune response and relieve the bone defect in apical periodontitis.

METHODOLOGY

We established an apical periodontitis mouse model in Sting-/- and WT mice in vivo. The progression of apical periodontitis was analysed by micro-CT analysis and H&E staining. The expression level and localization of STING in F4/80+ cells were identified by IHC and immunofluorescence staining. RANKL in periapical tissues was tested by IHC staining. TRAP staining was used to detect osteoclasts. To clarify the effect of STING inhibitor C-176 as an immunotherapeutic drug, mice with apical periodontitis were treated with C-176 and the bone loss was identified by H&E, TRAP, RANKL staining and micro-CT. Bone marrow-derived macrophages (BMMs) were isolated from Sting-/- and WT mice and induced to osteoclasts in a lipopolysaccharide (LPS)-induced inflammatory environment in vitro. Moreover, WT BMMs were treated with C-176 to determine the effect on osteoclast differentiation by TRAP staining. The expression levels of osteoclast-related genes were tested using qRT-PCR.

RESULTS

Compared to WT mice, the bone resorption and inflammatory cell infiltration were reduced in exposed Sting-/- mice. In the exposed WT group, STING was activated mainly in F4/80+ macrophages. Histological staining revealed the less osteoclasts and lower expression of osteoclast-related factor RANKL in Sting-/- mice. The treatment of the STING inhibitor C-176 in an apical periodontitis mice model alleviated inflammation progression and bone loss, similar to the effect observed in Sting-/- mice. Expression of RANKL and osteoclast number in periapical tissues were also decreased after C-176 administration. In vitro, TRAP staining showed fewer positive cells and qRT-PCR reflected decreased expression of osteoclastic marker, Src and Acp5 were detected during osteoclastic differentiation in Sting-/- and C-176 treated BMMs.

CONCLUSIONS

STING was activated and was proven to be a positive factor in bone loss and osteoclastogenesis in apical periodontitis. The STING inhibitor C-176 administration could alleviate the bone loss via modulating local immune response, which provided immunotherapy to the treatment of apical periodontitis.

Reexamining the role of Fusobacterium nucleatum subspecies in clinical and experimental studies

The Gram-negative anaerobic species Fusobacterium nucleatum was originally described as a commensal organism from the human oral microbiome. However, it is now widely recognized as a key inflammophilic pathobiont associated with a wide variety of oral and extraoral diseases. Historically, F. nucleatum has been classified into four subspecies that have been generally considered as functionally interchangeable in their pathogenic potential. Recent studies have challenged this notion, as clinical data reveal a highly biased distribution of F. nucleatum subspecies within disease sites of both inflammatory oral diseases and various malignancies. This review details the historical basis for the F. nucleatum subspecies designations and summarizes our current understanding of the similarities and distinctions between these organisms to provide important context for future clinical and laboratory studies of F. nucleatum.