Transcriptional profiling of bone marrow stromal cells in response to Porphyromonas gingivalis secreted products

Microbial-stem cell interactions in periodontal disease

Periodontitis is initiated by hyper-inflammatory responses in the periodontal tissues that generate dysbiotic ecological changes within the microbial communities. As a result, supportive tissues of the tooth are damaged and periodontal attachment is lost. Gingival recession, formation of periodontal pockets with the presence of bleeding, and often suppuration and/or tooth mobility are evident upon clinical examination. These changes may ultimately lead to tooth loss. Mesenchymal stem cells (MSCs) are implicated in controlling periodontal disease progression and have been shown to play a key role in periodontal tissue homeostasis and regeneration. Evidence shows that MSCs interact with subgingival microorganisms and their by-products and modulate the activity of immune cells by either paracrine mechanisms or direct cell-to-cell contact. The aim of this review is to reveal the interactions that take place between microbes and in particular periodontal pathogens and MSCs in order to understand the factors and mechanisms that modulate the regenerative capacity of periodontal tissues and the ability of the host to defend against putative pathogens. The clinical implications of these interactions in terms of anti-inflammatory and paracrine responses of MSCs, anti-microbial properties and alterations in function including their regenerative potential are critically discussed based on literature findings. In addition, future directions to design periodontal research models and study ex vivo the microbial-stem cell interactions are introduced.

The Effects of Porphyromonas gingivalis on Inflammatory and Immune Responses and Osteogenesis of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are increasingly used in tissue regeneration, not only because of their multilineage differentiation ability, but also because of their immunomodulatory function, which allows them to play a role in the inflammatory milieu, especially in periodontitis. Porphyromonas gingivalis (P. gingivalis) is an important pathogen associated with the progression of periodontitis. Heterogeneous MSC sources show differences in their inflammatory-immune responsiveness and osteogenesis capabilities when exposed to P. gingivalis and its virulence factors. This article reviews the promoted inflammatory and immune responses of periodontal ligament stem cells, which are potential pitfalls in bone regeneration. MSCs from other sources showed contradictory inflammatory and immune reactions in the few studies on this topic. We also summarize the mechanisms involved in the inflammatory, immune responses and osteogenic potential of MSCs exposed to P. gingivalis and its virulence factors to inform an improved utilization of MSCs in regenerative therapies for periodontitis.

Toll-Like Receptors and Dental Mesenchymal Stromal Cells

Dental mesenchymal stromal cells (MSCs) are a promising tool for clinical application in and beyond dentistry. These cells possess multilineage differentiation potential and immunomodulatory properties. Due to their localization in the oral cavity, these cells could sometimes be exposed to different bacteria and viruses. Dental MSCs express various Toll-like receptors (TLRs), and therefore, they can recognize different microorganisms. The engagement of TLRs in dental MSCs by various ligands might change their properties and function. The differentiation capacity of dental MSCs might be either inhibited or enhanced by TLRs ligands depending on their nature and concentrations. Activation of TLR signaling in dental MSCs induces the production of proinflammatory mediators. Additionally, TLR ligands alter the immunomodulatory ability of dental MSCs, but this aspect is still poorly explored. Understanding the role of TLR signaling in dental MSCs physiology is essential to assess their role in oral homeostasis, inflammatory diseases, and tissue regeneration.

Salivary proteotypes of gingivitis tolerance and resilience

Aim

This study aimed to characterize the salivary proteome during the induction and resolution of gingival inflammation in the course of human experimental gingivitis (EG), and to cluster the proteomic profiles based on the clinically defined “slow” and “fast” response patterns.

Materials and Methods

A total of 50 unstimulated whole saliva were obtained from the EG model which was induced over 21 days (days 0, 7, 14 and 21), followed by a two‐week resolution phase (day 35). Label‐free quantitative proteomics using liquid chromatography–tandem mass spectrometry was applied. Regulated proteins were subject to Gene Ontology enrichment analysis.

Results

A total of 804 human proteins were quantified by ≥ 2 peptides. Principal component analysis depicted significant differences between “fast” and “slow” responders. Despite gingival and plaque scores being similar at baseline among the two groups, “fast” responders presented with 48 proteins that were at > 4‐fold higher levels than “slow” responders. These up‐regulated proteins showed enrichment in “antigen presentation” and “proteolysis.”

Conclusions

Together, these findings highlight the utility of integrative systems‐level quantitative proteomic approaches to unravel the molecular basis of “salivary proteotypes” associated with gingivitis dubbed as “fast” and “slow” responders. Hence, these differential responses may help prognosticate individual susceptibility to gingival inflammation.

Apoptosis Transcriptional Profile Induced by Porphyromonas gingivalis HmuY

This study aimed at evaluating the transcriptional profile of apoptosis-related genes after in vitro stimulation of peripheral blood mononuclear cells (PBMCs) derived from individuals with periodontitis (P) and healthy nonperiodontitis (NP) control subjects with P. gingivalis HmuY protein. PBMCs from the P and NP groups were stimulated with HmuY P. gingivalis protein, and the expression of genes related to apoptosis was assessed by custom real-time polymerase chain reaction array (Custom RT2 PCR Array). Compared with the NP group, the P group showed low relative levels of apoptosis-related gene expression, downregulated for FAS, FAS ligand, TNFSF10 (TRAIL), BAK1, CASP9, and APAF1 after P. gingivalis HmuY protein stimulation. Furthermore, the P group exhibited low levels of relative gene expression, downregulated for CASP7 when the cells were not stimulated. Our data suggest that P. gingivalis HmuY protein might participate differently in the modulation of the intrinsic and extrinsic apoptosis pathways.

The Regulatory Role of the Oral Commensal Streptococcus mitis on Human Monocytes

Streptococcus mitis colonizes all niches of the human oral cavity from early infancy and throughout life. Monocytes patrol blood vessels, lymphoid and non-lymphoid tissues and migrate into infected tissue where they participate in the inflammatory cascade and immune regulation. Here, we studied the effect of S. mitis on monocytes. Transcriptome analysis of monocytes exposed to S. mitis (SmMo) revealed increased transcription of chemotactic factors (CCL2, CCL3, CCL20, CXCL1, CXCL2) and cytokines (IL1A, IL1B, IL6, IL23, IL36G, TNF), indicating that S. mitis may trigger recruitment of leucocytes and initiate inflammation. Increased transcription in SmMo of IL1B, IL6 and IL23 indicated that S. mitis may participate in the induction of Th17 responses and agreed with our earlier findings of S. mitis-mediated memory Th17 reactivity. Furthermore, S. mitis inhibited tetanus toxoid-specific CD4 T cell proliferation. This can be due to the increased secretion of IL-10 and expression of PD-L1 that was observed in SmMo. PGE2 can modulate IL-10 and PD-L1 expression, concomitant with that of CCR7, IL-12 and IL-23 that also were changed. This, along with increased SmMo transcription of PTGS2 (COX2) and PTGER4 (EP4), pointed to a role of PGE2. Measurement of PGE2 secretion by SmMo showed indeed a marked increase, and chemical inhibition of PGE2 production lowered the PD-L1 expression on SmMo. In conclusion, our findings show that S. mitis may trigger immune modulation by recruiting immune cells to the site of infection, while at the same time dampening the severity of the response through expression of IL-10, PGE2 and PD-L1.

Triggering receptor expressed on myeloid cells in the pathogenesis of periodontitis: potential novel treatment strategies

INTRODUCTION

Periodontal diseases are polymicrobial inflammatory disorders of the tissue, ligament, and bone structures supporting teeth. Periodontitis (inflammation with corresponding loss of attachment) affects 40-50% of adults. Recently, members of the Triggering Receptor on Myeloid Cell (TREM) family have been studied to determine their relationship to these diseases. Areas covered: TREM-1 is a receptor expressed on the surface of PMNs, monocytes, macrophages, dendritic cells, vascular smooth muscle cells, and keratinocytes upregulated in the presence of periodontal inflammation. TREM-1 expression can be upregulated by oral bacterium Porphyromonas gingivalis that can be abrogated by a sub-antimicrobial dose of doxycycline. When cleaved from the cell surface, a soluble form of TREM-1 (sTREM-1) can be used as a biomarker of inflammation and might also provide a link between oral and systemic inflammation. While less understood, TREM-2 has a role in osteoclastogenesis which could contribute to the alveolar bone destruction seen in more advanced periodontitis. Expert commentary: Additional studies to simulate biofilm microenvironment in TREM research are warranted. Longitudinal studies determining TREM-1, sTREM-1, and TREM-2 levels in tissues over time and progression of periodontal diseases would provide valuable information in the role of TREM receptors as indicators of or contributors to the disease process.

Porphyromonas gingivalis can invade periodontal ligament stem cells

Background

Porphyromonas gingivalis is strongly associated with the development, progression, severity and recurrence of periodontitis. Periodontal ligament stem cells (PDLSCs) play an important role in the maintenance of periodontal tissue self-renewal and repair. The purpose of this study was to investigate the ability of P. gingivalis to infect PDLSCs using an in vitro monolayer model.

Methods

We separated and cultured primary PDLSCs using the tissue block with limiting dilution method. The efficiency of P. gingivalis (ATCC 33277) infection of PDLSCs was measured using agar plate culture and quantitative polymerase chain reaction (q-PCR) methods. PDLSCs infected with P. gingivalis were also observed by transmission electron microscopy.

Results

We assessed stem cell properties including cell morphology, clone formation, growth activity, cell surface antigens and multiple differentiation capacity. The infection rates of P. gingivalis in PDLSC at MOIs of 50, 100, 200, and 500 were 5.83%, 8.12%, 7.77% and 7.53% according to the agar plate culture method. By q-PCR, the efficiencies of P. gingivalis infection of PDLSCs at MOIs of 50, 100, 200, and 500 were 6.74%, 10.56%, 10.36% and 9.78%, respectively. Overall, the infection efficiency based on q-PCR was higher than that according to agar plate culture. Using transmission electron microscopy, we verified that P. gingivalis (ATCC 33277) could infect and invade PDLSCs after 2 h of incubation, and endocytic vacuoles were not found surrounding the internalized bacteria.

Conclusions

In conclusion, our data demonstrate that P. gingivalis can invade PDLSCs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-017-0950-5) contains supplementary material, which is available to authorized users.

Secretome of gingival epithelium in response to subgingival biofilms

Periodontitis is the chronic inflammatory destruction of periodontal tissues as a result of bacterial biofilm formation on the tooth surface. Proteins secreted by the gingival epithelium challenged by subgingival biofilms represent an important initial response for periodontal inflammation. The aim of this in vitro study was to characterize the whole secreted proteome of gingival epithelial tissue challenged by subgingival biofilms, and to evaluate the differential effects of the presence of the red-complex species in the biofilm. Multi-layered human gingival epithelial cultures were challenged with a 10-species in vitro biofilm model or its seven-species variant excluding the red complex. Liquid chromatography-tandem mass spectrometry for label-free quantitative proteomics was applied to identify and quantify the secreted epithelial proteins in the culture supernatant. A total of 192 proteins were identified and quantified. The biofilm challenge resulted in more secreted proteins being downregulated than upregulated. Even so, presence of the red complex in the biofilm was responsible for much of this downregulatory effect. Over 24 h, the upregulated biological processes were associated with inflammation and apoptosis, whereas the downregulated processes were associated with the disruption of epithelial tissue integrity and impairment of tissue turnover. Over 48 h, negative regulation of several metabolic processes and degradation of various molecular complexes was further intensified. Again, many of these biological regulations were attributed to the presence of the red complex. In conclusion, the present study provides the secreted proteome profile of gingival epithelial tissue to subgingival biofilms, and identifies a significant role for the red-complex species in the observed effects.

Quantitative proteomics reveal distinct protein regulations caused by Aggregatibacter actinomycetemcomitans within subgingival biofilms

Periodontitis is an infectious disease that causes the inflammatory destruction of the tooth-supporting (periodontal) tissues, caused by polymicrobial biofilm communities growing on the tooth surface. Aggressive periodontitis is strongly associated with the presence of Aggregatibacter actinomycetemcomitans in the subgingival biofilms. Nevertheless, whether and how A. actinomycetemcomitans orchestrates molecular changes within the biofilm is unclear. The aim of this work was to decipher the interactions between A. actinomycetemcomitans and other bacterial species in a multi-species biofilm using proteomic analysis. An in vitro 10-species "subgingival" biofilm model, or its derivative that included additionally A. actinomycetemcomitans, were anaerobically cultivated on hydroxyapatite discs for 64 h. When present, A. actinomycetemcomitans formed dense intra-species clumps within the biofilm mass, and did not affect the numbers of the other species in the biofilm. Liquid chromatography-tandem mass spectrometry was used to identify the proteomic content of the biofilm lysate. A total of 3225 and 3352 proteins were identified in the biofilm, in presence or absence of A. actinomycetemcomitans, respectively. Label-free quantitative proteomics revealed that 483 out of the 728 quantified bacterial proteins (excluding those of A. actinomycetemcomitans) were accordingly regulated. Interestingly, all quantified proteins from Prevotella intermedia were up-regulated, and most quantified proteins from Campylobacter rectus, Streptococcus anginosus, and Porphyromonas gingivalis were down-regulated in presence of A. actinomycetemcomitans. Enrichment of Gene Ontology pathway analysis showed that the regulated groups of proteins were responsible primarily for changes in the metabolic rate, the ferric iron-binding, and the 5S RNA binding capacities, on the universal biofilm level. While the presence of A. actinomycetemcomitans did not affect the numeric composition or absolute protein numbers of the other biofilm species, it caused qualitative changes in their overall protein expression profile. These molecular shifts within the biofilm warrant further investigation on their potential impact on its virulence properties, and association with periodontal pathogenesis.