Signal-Regulated Protein Kinases/Protein Kinase B-p53-BH3–Interacting Domain Death Agonist Pathway Regulates Gingipain-Induced Apoptosis in Osteoblasts

Gingipains may be one of the key virulence factors of Porphyromonas gingivalis to impair cognition and enhance blood-brain barrier permeability: An animal study

AIM

Blood-brain barrier (BBB) disorder is one of the early findings in cognitive impairments. We have recently found that Porphyromonas gingivalis bacteraemia can cause cognitive impairment and increased BBB permeability. This study aimed to find out the possible key virulence factors of P. gingivalis contributing to the pathological process.

MATERIALS AND METHODS

C57/BL6 mice were infected with P. gingivalis or gingipains or P. gingivalis lipopolysaccharide (P. gingivalis LPS group) by tail vein injection for 8 weeks. The cognitive behaviour changes in mice, the histopathological changes in the hippocampus and cerebral cortex, the alternations of BBB permeability, and the changes in Mfsd2a and Cav-1 levels were measured. The mechanisms of Ddx3x-induced regulation on Mfsd2a by arginine-specific gingipain A (RgpA) in BMECs were explored.

RESULTS

P. gingivalis and gingipains significantly promoted mice cognitive impairment, pathological changes in the hippocampus and cerebral cortex, increased BBB permeability, inhibited Mfsd2a expression and up-regulated Cav-1 expression. After RgpA stimulation, the permeability of the BBB model in vitro increased, and the Ddx3x/Mfsd2a/Cav-1 regulatory axis was activated.

CONCLUSIONS

Gingipains may be one of the key virulence factors of P. gingivalis to impair cognition and enhance BBB permeability by the Ddx3x/Mfsd2a/Cav-1 axis.

Periodontitis as a promoting factor of T2D: current evidence and mechanisms

Periodontitis is an infectious disease caused by an imbalance between the local microbiota and host immune response. Epidemiologically, periodontitis is closely related to the occurrence, development, and poor prognosis of T2D and is recognized as a potential risk factor for T2D. In recent years, increasing attention has been given to the role of the virulence factors produced by disorders of the subgingival microbiota in the pathological mechanism of T2D, including islet β-cell dysfunction and insulin resistance (IR). However, the related mechanisms have not been well summarized. This review highlights periodontitis-derived virulence factors, reviews how these stimuli directly or indirectly regulate islet β-cell dysfunction. The mechanisms by which IR is induced in insulin-targeting tissues (the liver, visceral adipose tissue, and skeletal muscle) are explained, clarifying the influence of periodontitis on the occurrence and development of T2D. In addition, the positive effects of periodontal therapy on T2D are overviewed. Finally, the limitations and prospects of the current research are discussed. In summary, periodontitis is worthy of attention as a promoting factor of T2D. Understanding on the effect of disseminated periodontitis-derived virulence factors on the T2D-related tissues and cells may provide new treatment options for reducing the risk of T2D associated with periodontitis.

Porphyromonas gingivalis-Helicobacter pylori co-incubation enhances Porphyromonas gingivalis virulence and increases migration of infected human oral keratinocytes

Background

Porphyromonas gingivalis is part of the subgingival biofilm and a keystone species in the development of periodontitis. Interactions between P.gingivalis and other bacteria in biofilms have been shown to affect bacterial virulence. Helicobacter pylori also inhabits the subgingival biofilm, but the consequences of interactions there with P.gingivalis remain unknown. Here, we investigated how the pre-incubation of P.gingivalis with H.pylori affects P.gingivalis virulence.

Methods

We assayed P.gingivalis internalization by oral keratinocytes (OKs), hemagglutination and biofilm formation to identify alterations in virulence after pre-incubation with H. pylori. Also, we evaluated viability and migration of OKs infected with P. gingivalis, as well as the role of toll-like receptor 4 (TLR4).   In addition, we quantified the mRNA of genes associated with P.gingivalis virulence.

Results

Pre-incubation of P.gingivalis with H.pylori enhanced P.gingivalis biofilm formation, bacterial internalization into OKs and hemagglutination. Infection with pre-incubated P.gingivalis increased OK migration in a manner dependent on the O-antigen and linked to  increased expression of the gingipain RgpB. Also, OK TLR4 participates in these events, because upon TLR4 knock-down, pre-incubated P.gingivalis no longer stimulated OK migration.

Discussion

We provide here for the first time insight to the consequences of direct interaction between P.gingivalis and H.pylori. In doing so, we shed light on the mechanism by which H. pylori presence in the oral cavity increases the severity or progression of periodontitis.

Effect of Enterococcus faecalis OG1RF on human calvarial osteoblast apoptosis

Background

Enterococcus faecalis is a dominant pathogen in the root canals of teeth with persistent apical periodontitis (PAP), and osteoblast apoptosis contributes to imbalanced bone remodelling in PAP. Here, we investigated the effect of E. faecalis OG1RF on apoptosis in primary human calvarial osteoblasts. Specifically, the expression of apoptosis-related genes and the role of anti-apoptotic and pro-apoptotic members of the BCL-2 family were examined.

Methods

Primary human calvarial osteoblasts were incubated with E. faecalis OG1RF at multiplicities of infection corresponding to infection time points. Flow cytometry, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay, caspase-3/-8/-9 activity assay, polymerase chain reaction (PCR) array, and quantitative real-time PCR were used to assess osteoblast apoptosis.

Results

E. faecalis infection increased the number of early- and late-phase apoptotic cells and TUNEL-positive cells, decreased the mitochondrial membrane potential (ΔΨm), and activated the caspase-3/-8/-9 pathway. Moreover, of all 84 apoptosis-related genes in the PCR array, the expression of 16 genes was upregulated and that of four genes was downregulated in the infected osteoblasts. Notably, the mRNA expression of anti-apoptotic BCL2 was downregulated, whereas that of the pro-apoptotic BCL2L11, HRK, BIK, BMF, NOXA, and BECN1 and anti-apoptotic BCL2A1 was upregulated.

Conclusions

E. faecalis OG1RF infection triggered apoptosis in human calvarial osteoblasts, and BCL-2 family members acted as regulators of osteoblast apoptosis. Therefore, BCL-2 family members may act as potential therapeutic targets for persistent apical periodontitis.

Protective Effects of Polydatin on Reproductive Injury Induced by Ionizing Radiation

The reproductive system is vulnerable to ionizing radiation, which is a hot research topic at present. We tested the effect of polydatin on spermatocytes(GC-1 cells) after X-ray irradiation. The reproductive damage model of C.elegans was established by 60Coγ-ray, and the protective effect of polydatin on reproductive damage caused by ionizing radiation was evaluated. We quantified the ROS levels of GC-1 cells and C.elegans after irradiation with polydatin and evaluated the anti-apoptosis effect of polydatin at proper concentration. Differential genes of C.elegans reproductive damage were screened out from transcriptome sequencing results and comparable GEO datasets. It was proved that 100μM polydatin significantly reduced the apoptosis of GC-1 cells induced by 2 Gy X-ray. In addition, the longevity, reproductive capacity, germ cell apoptosis and spawning and hatching capacity of polydatin were tested. The results showed that 100 μM polydatin content significantly increased the influence of 50 Gy 60Coγ-ray on reproductive capacity of C.elegans. Quantitative analysis of mRNA and protein levels of apoptosis-related genes and reproductive-related genes by qRT-PCR and Western blotcon firmed that polydatin with appropriate dosage had good protective effects on reproductive damage caused by radiation, which laid a foundation for the application research of polydatin in radiation protection.

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.

Intracellular Porphyromonas gingivalis Promotes the Proliferation of Colorectal Cancer Cells via the MAPK/ERK Signaling Pathway

Porphyromonas gingivalis (P. gingivalis) is a keystone pathogen in periodontitis. However, several clinical studies have revealed an enrichment of P. gingivalis in the stool samples and colorectal mucosa of colorectal cancer patients. Thus, the goal of this study was to determine whether P. gingivalis can promote colorectal cancer progression in vitro. We established an acute infection model (24 h, multiplicity of infection =100) of P. gingivalis invasion of colorectal cancer cells to study the alterations induced by P. gingivalis in the proliferation and cell cycle of colorectal cancer cells. We observed that P. gingivalis can adhere and invade host cells a few hours after infection. Once invaded, P. gingivalis significantly promoted colorectal cancer cell proliferation, and the percentage of S phase cells was increased in the cell cycle assay. However, KDP136, a gingipain-deficient mutant of P. gingivalis 33277, showed a decreased ability to promote colorectal cancer cell proliferation, indicating that gingipain is associated with colorectal cancer cell proliferation. Furthermore, we extracted RNA from colorectal cancer cells for high-throughput sequencing analysis and reconfirmed the results by quantitative polymerase chain reaction and western blot analyses. The results suggested that the MAPK/ERK signaling pathway is significantly activated by P. gingivalis, while these changes were not observed for KDP136. In conclusion, P. gingivalis can invade cells and promote the proliferation of colorectal cancer cells by activating the MAPK/ERK signaling pathway. Gingipain is an essential virulence factor in this interaction.

Gingipains promote RANKL-induced osteoclastogenesis through the enhancement of integrin β3 in RAW264.7 cells

As a crucial virulence factor of Porphyromonas gingivalis, gingipains play an important role in periodontal destruction. This study aimed to investigate the effect of gingipains on osteoclastogenesis. We used RAW264.7 cells as osteoclast precursors in our study. In experimental groups, cells were treated with gingipains and/or receptor activator of nuclear factor-κB ligand (RANKL). Tartrate-resistant acid phosphatase (TRAP) activity staining assay showed osteoclast precursors and RANKL-induced mature osteoclasts were increased in a gingipains dose-dependent manner. Real-time reverse transcription polymerase chain reaction analysis demonstrated that gingipains upregulated osteoclastic genes including the protease cathepsin K (Ctsk), matrix metalloprotein 9 (Mmp9), nuclear factor of activated T cells 1 (Nfatc1) and acid phosphatase 5, tartrate resistant (Acp5) in a time-dependent manner. Western blotting assays presented upregulated expressions of TNF receptor-activating factor 6 (TRAF6) and integrin β3 induced by gingipains and RANKL compared to RANKL alone. Enhanced integrin-related signaling was also demonstrated by elevated phosphorylations of FAK and paxillin compared to control. Moreover, the pit resorption assays showed that gingipains augmented bone resorptive function of osteoclasts induced by RANKL. When we used Cilengitide to block integrin αvβ3, gingipains reversed the reduction of formation and resorptive function in RANKL-induced osteoclasts, as they enhanced integrin αvβ3 levels more than RANKL treatment alone. In conclusion, our data suggest that gingipains augmented the differentiation and function of mature osteoclasts induced by RANKL through the increase in integrin αvβ3.

Gingipains disrupt F-actin and cause osteoblast apoptosis via integrin β1

BACKGROUND AND OBJECTIVE

The aim of this study was to explore the cellular mechanisms underlying gingipain-caused changes in cell morphology and apoptosis of osteoblasts.

MATERIAL AND METHODS

Human calvarial osteoblasts and mouse osteoblasts MC3T3-E1 were treated with gingipain extracts from Porphyromonas gingivalis stain W83. Apoptosis was detected with annexin V and propidium iodide flow cytometry analysis or terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling staining. F-actin was determined by immunostaining. Western blotting was used to detect protein expression. Knocking down and overexpressing approaches were used to determine the role of integrin β1.

RESULTS

Osteoblasts exposed to gingipain extracts displayed increased apoptosis, accompanied by loss of F-actin integrity and cell shrinkage. The effects of gingipain extracts were abolished by the cysteine protease inhibitor N-tosyl-l-lysyl chloromethyl-ketone. Notably, gingipain extracts resulted in reduction of integrin β1, accompanied by diminished active RhoA whereas without effect on the total RhoA. Knockdown of integrin β1 resembled those seen in gingipain-treated osteoblasts. By contrast, the effects of gingipain extracts were abrogated by either overexpression of integrin β1 or presence of RhoA agonist CN03.

CONCLUSION

Gingipain-induced F-actin disruption and apoptosis are mediated by the degradation of integrin β1 and inhibition of RhoA activity, which account for osteoblast apoptosis.