Aggregatibacter actinomycetemcomitans Omp29 is associated with bacterial entry to gingival epithelial cells by F-actin rearrangement

Experimental Inoculation of Aggregatibacter actinomycetemcomitans and Streptococcus gordonii and Its Impact on Alveolar Bone Loss and Oral and Gut Microbiomes

Oral bacteria are implicated not only in oral diseases but also in gut dysbiosis and inflammatory conditions throughout the body. The periodontal pathogen Aggregatibacter actinomycetemcomitans (Aa) often occurs in complex oral biofilms with Streptococcus gordonii (Sg), and this interaction might influence the pathogenic potential of this pathogen. This study aims to assess the impact of oral inoculation with Aa, Sg, and their association (Aa+Sg) on alveolar bone loss, oral microbiome, and their potential effects on intestinal health in a murine model. Sg and/or Aa were orally administered to C57Bl/6 mice, three times per week, for 4 weeks. Aa was also injected into the gingiva three times during the initial experimental week. After 30 days, alveolar bone loss, expression of genes related to inflammation and mucosal permeability in the intestine, serum LPS levels, and the composition of oral and intestinal microbiomes were determined. Alveolar bone resorption was detected in Aa, Sg, and Aa+Sg groups, although Aa bone levels did not differ from that of the SHAM-inoculated group. Il-1β expression was upregulated in the Aa group relative to the other infected groups, while Il-6 expression was downregulated in infected groups. Aa or Sg downregulated the expression of tight junction genes Cldn 1, Cldn 2, Ocdn, and Zo-1 whereas infection with Aa+Sg led to their upregulation, except for Cldn 1. Aa was detected in the oral biofilm of the Aa+Sg group but not in the gut. Infections altered oral and gut microbiomes. The oral biofilm of the Aa group showed increased abundance of Gammaproteobacteria, Enterobacterales, and Alloprevotella, while Sg administration enhanced the abundance of Alloprevotella and Rothia. The gut microbiome of infected groups showed reduced abundance of Erysipelotrichaceae. Infection with Aa or Sg disrupts both oral and gut microbiomes, impacting oral and gut homeostasis. While the combination of Aa with Sg promotes Aa survival in the oral cavity, it mitigates the adverse effects of Aa in the gut, suggesting a beneficial role of Sg associations in gut health.

Aggregatibacter actinomycetemcomitans: From the Oral Cavity to the Heart Valves

Aggregatibacter actinomycetemcomitans (A. actinomycetecomitans) is a Gram-negative bacterial species that is an essential component of the oral microbiota. Due to its aggregative properties, it plays a role in the pathogenesis of human diseases. The presence of the surface proteins Fim, Briae, and microvesicles enables the bacterium to adhere to the epithelial surface and the tooth's surface. The presence of leukotoxin A (LtxA), which plays an important role in the pathogenicity of the bacterium, has been associated with both periodontitis and the etiology of rheumatoid arthritis (RA). A. actinomycetecomitans is also associated with several other systemic diseases and complications, such as endocarditis and different abscesses. In addition to leukotoxin A, A. actinomycetecomitans possesses several different virulence factors, including bacteriocins, chemotaxis inhibitory factors, cytotoxic factors, Fc-binding proteins, immunosuppressive factors, lipopolysaccharide collagenase, fibroblast inhibitory factors, antibiotic resistance determinants, adhesins, invasive factors and factors that inhibit the function of polymorphonuclear leukocytes. The ability of A. actinomycetemcomitans lipopolysaccharide to induce macrophages to secrete the interleukins IL-1, IL-1β, and tumor necrosis factor (TNF) is of considerable importance. The primary etiologic factor in the pathogenesis of periodontal disease is the oral biofilm colonized by anaerobic bacteria. Among these, A. actinomycetemcomitans occupies an important place as a facultative anaerobic bacterium. In addition, A. actinomycetemcomitans possesses many virulence factors that contribute to its potential to cause cancer. This article provides an overview of the virulence factors of A. actinomycetecomitans and its association with various systemic diseases, its oncogenic potential, and the treatment options for infections caused by A. actinomycetecomitans.

Grade C Molar-Incisor Pattern Periodontitis in Young Adults: What Have We Learned So Far?

Grade C molar-incisor pattern periodontitis (C-MIP) is a disease that affects specific teeth with an early onset and aggressive progression. It occurs in systemically healthy patients, mostly African descendants, at an early age, with familial involvement, minimal biofilm accumulation, and minor inflammation. Severe and rapidly progressive bone loss is observed around the first molars and incisors. This clinical condition has been usually diagnosed in children and young adults with permanent dentition under 30 years of age. However, this disease can also affect the primary dentition, which is not as frequently discussed in the literature. Radiographic records have shown that most patients diagnosed in the permanent dentition already presented disease signs in the primary dentition. A hyperresponsive immunological profile is observed in local (gingival crevicular fluid-GCF) and systemic environments. Siblings have also displayed a heightened inflammatory profile even without clinical signs of disease. A. actinomycetemcomitans has been classified as a key pathogen in C-MIP in both dentitions. Scaling and root planning associated with systemic antibiotics is the current gold standard to treat C-MIP, leading to GCF biomarker reduction, some systemic inflammatory response modulation and microbiome profile changes to a healthy-site profile. Further studies should focus on other possible disease-contributing risk factors.

Illuminating the oral microbiome: cellular microbiology

Epithelial cells line mucosal surfaces such as in the gingival crevice and provide a barrier to the ingress of colonizing microorganisms. However, epithelial cells are more than a passive barrier to microbial intrusion, and rather constitute an interactive interface with colonizing organisms which senses the composition of the microbiome and communicates this information to the underlying cells of the innate immune system. Microorganisms, for their part, have devised means to manipulate host cell signal transduction pathways to favor their colonization and survival. Study of this field, which has become known as cellular microbiology, has revealed much about epithelial cell physiology, bacterial colonization and pathogenic strategies, and innate host responses.

Current concepts in the pathogenesis of periodontitis: from symbiosis to dysbiosis

The primary etiological agent for the initiation and progression of periodontal disease is the dental plaque biofilm which is an organized aggregation of microorganisms residing within a complex intercellular matrix. The non-specific plaque hypothesis was the first attempt to explain the role of the dental biofilm in the pathogenesis of periodontal diseases. However, the introduction of sophisticated diagnostic and laboratory assays has led to the realisation that the development of periodontitis requires more than a mere increase in the biomass of dental plaque. Indeed, multispecies biofilms exhibit complex interactions between the bacteria and the host. In addition, not all resident microorganisms within the biofilm are pathogenic, since beneficial bacteria exist that serve to maintain a symbiotic relationship between the plaque microbiome and the host's immune-inflammatory response, preventing the emergence of pathogenic microorganisms and the development of dysbiosis. This review aims to highlight the development and structure of the dental plaque biofilm and to explore current literature on the transition from a healthy (symbiotic) to a diseased (dysbiotic) biofilm in periodontitis and the associated immune-inflammatory responses that drive periodontal tissue destruction and form mechanistic pathways that impact other systemic non-communicable diseases.

Lactobacilli Attenuate the Effect of Aggregatibacter actinomycetemcomitans Infection in Gingival Epithelial Cells

Probiotics may be considered as an additional strategy to achieve a balanced microbiome in periodontitis. However, the mechanisms underlying the use of probiotics in the prevention or control of periodontitis are still not fully elucidated. This in vitro study aimed to evaluate the effect of two commercially available strains of lactobacilli on gingival epithelial cells (GECs) challenged by Aggregatibacter actinomycetemcomitans. OBA-9 GECs were infected with A. actinomycetemcomitans strain JP2 at an MOI of 1:100 and/or co-infected with Lactobacillus acidophilus La5 (La5) or Lacticaseibacillus rhamnosus Lr32 (Lr32) at an MOI of 1:10 for 2 and 24 h. The number of adherent/internalized bacteria to GECs was determined by qPCR. Production of inflammatory mediators (CXCL-8, IL-1β, GM-CSF, and IL-10) by GECs was determined by ELISA, and the expression of genes encoding cell receptors and involved in apoptosis was determined by RT-qPCR. Apoptosis was also analyzed by Annexin V staining. There was a slight loss in OBA-9 cell viability after infection with A. actinomycetemcomitans or the tested probiotics after 2 h, which was magnified after 24-h co-infection. Adherence of A. actinomycetemcomitans to GECs was 1.8 × 107 (± 1.2 × 106) cells/well in the mono-infection but reduced to 1.2 × 107 (± 1.5 × 106) in the co-infection with Lr32 and to 6 × 106 (± 1 × 106) in the co-infection with La5 (p < 0.05). GECs mono-infected with A. actinomycetemcomitans produced CXCL-8, GM-CSF, and IL-1β, and the co-infection with both probiotic strains altered this profile. While the co-infection of A. actinomycetemcomitans with La5 resulted in reduced levels of all mediators, the co-infection with Lr32 promoted reduced levels of CXCL-8 and GM-CSF but increased the production of IL-1β. The probiotics upregulated the expression of TLR2 and downregulated TLR4 in cells co-infected with A. actinomycetemcomitans. A. actinomycetemcomitans-induced the upregulation of NRLP3 was attenuated by La5 but increased by Lr32. Furthermore, the transcription of the anti-apoptotic gene BCL-2 was upregulated, whereas the pro-apoptotic BAX was downregulated in cells co-infected with A. actinomycetemcomitans and the probiotics. Infection with A. actinomycetemcomitans induced apoptosis in GECs, whereas the co-infection with lactobacilli attenuated the apoptotic phenotype. Both tested lactobacilli may interfere in A. actinomycetemcomitans colonization of the oral cavity by reducing its ability to interact with gingival epithelial cells and modulating cells response. However, L. acidophilus La5 properties suggest that this strain has a higher potential to control A. actinomycetemcomitans-associated periodontitis than L. rhamnosus Lr32.

Enhancing production of herpes simplex virus type 1 in oral epithelial cells by co-infection with Aggregatibacter actinomycetemcomitans

BACKGROUND/PURPOSE

The association between herpetic/bacterial co-infection and periodontal diseases has been reported. However, how interactions between herpesviruses and periodontal bacteria dampen periodontal inflammation is still unclear. This study determined effects of co-infection with oral bacteria, including Streptococcus sanguinis, Fusobacterium nucleatum or Aggregatibacter actinomycetemcomitans, in herpes simplex virus type 1 (HSV-1)-infected oral epithelial cells.

METHODS

Cell viability was determined by detection the activity of mitochondrial dehydrogenase. Viral production was measured using the plaque assay. Levels of bacterial and viral DNA were determined by real-time polymerase chain reaction. Secretion of interleukin (IL)-6 and IL-8 was measured using the enzyme-linked immunosorbent assay.

RESULTS

Viability was not further reduced by bacterial co-infection in HSV-1-infected cells. Co-infection with HSV-1 and S. sanguinis or F. nucleatum reduced the viral yield whereas co-infection with HSV-1 and A. actinomycetemcomitans significantly enhanced the viral yield in oral epithelial cells. The enhancing effect of A. actinomycetemcomitans was not affected by bacterial heat-inactivation. Co-infection with HSV-1/A. actinomycetemcomitans increased intracellular levels of both viral and bacterial DNA. Secretion of IL-6 and IL-8 stimulated by A. actinomycetemcomitans infection was partly reduced by co-infection with HSV-1 in oral epithelial cells.

CONCLUSION

In contrast to S. sanguinis and F. nucleatum, A. actinomycetemcomitans enhanced the yield of HSV-1. Either HSV-1 or A. actinomycetemcomitans may be benefited from co-infection, in aspects of increases in production of viral and bacterial DNA as well as reductions in cytokine secretion. These findings echoed with previous clinical studies showing co-infection of HSV and A. actinomycetemcomitans in patients with aggressive periodontitis.

Aggregatibacter actinomycetemcomitans Outer Membrane Proteins 29 and 29 Paralogue Induce Evasion of Immune Response

Aggregatibacter actinomycetemcomitans (Aa) is abundant within the microbial dysbiotic community of some patients with periodontitis. Aa outer membrane protein 29 (OMP29), a member of the OMPA family, mediates the invasion of Aa to gingival epithelial cells (GECs). This study evaluated the effect of OMP29 and its paralogue OMP29^par on the response of GECs to Aa. The omp29 or/and omp29^par deletion mutants AaΔ29, AaΔ29P, and AaΔ29Δ29P were constructed, and recombinant Aa OMP29^His was obtained. Microarray analysis and the evaluation of cxcl-8 gene expression were performed to examine the response of GECs line OBA-09 to Aa and its mutants. The expression of cxcl-8 and its product CXCL-8 was examined in LPS-stimulated OBA-09 cells with Aa OMP29^His. Proteomics analysis showed that the deletion of omp29 led to overexpression of both OMP29^par and another membrane protein OMP39, the expression of which was further increased in AaΔ29Δ29P. OBA-09 cells challenged with AaΔ29Δ29P exhibited a higher expression of cxcl-8 in comparison to wildtype Aa strain AaD7S or single-deletion mutants AaΔ29 or AaΔ29P. LPS-stimulated OBA-09 cells challenged with Aa OMP29^His showed reduced expressions of cxcl-8 and its product CXCL-8. OBA-09 cells challenged with AaΔ29Δ29P in comparison to Aa strain AaD7S resulted in higher expressions of genes involved in apoptosis and inflammatory response such as bcl2, birc3, casp3, c3, ep300, fas, fosb, grb2, il-1α, il-1β, il-6, cxcl-8, nr3c1, prkcq, socs3, and tnfrsf1β and reduced expressions of cd74, crp, faslg, tlr1, and vcam1. The results suggested a novel strategy of Aa, mediated by OMP29 and OMP29^par, to evade host immune response by inhibiting CXCL-8 expression and modulating the genes involved in apoptosis and inflammatory response in GECs. Pending further confirmation, the strategy might interfere with the recruitment of neutrophils and dampen the host inflammatory response, leading to a more permissive subgingival niche for bacterial growth.

Modulation of host cellular responses by gram-negative bacterial porins

The outer membrane of a gram-negative bacteria encapsulates the plasma membrane thereby protecting it from the harsh external environment. This membrane acts as a sieving barrier due to the presence of special membrane-spanning proteins called "porins." These porins are β-barrel channel proteins that allow the passive transport of hydrophilic molecules and are impermeable to large and charged molecules. Many porins form trimers in the outer membrane. They are abundantly present on the bacterial surface and therefore play various significant roles in the host-bacteria interactions. These include the roles of porins in the adhesion and virulence mechanisms necessary for the pathogenesis, along with providing resistance to the bacteria against the antimicrobial substances. They also act as the receptors for phage and complement proteins and are involved in modulating the host cellular responses. In addition, the potential use of porins as adjuvants, vaccine candidates, therapeutic targets, and biomarkers is now being exploited. In this review, we focus briefly on the structure of the porins along with their important functions and roles in the host-bacteria interactions.

Expression of virulence factors under different environmental conditions in Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is a facultative anaerobic Gram-negative bacterium associated with periodontal diseases, especially aggressive periodontitis. The virulence factors of this pathogen, including adhesins, exotoxins, and endotoxin, have been extensively studied. However, little is known about their gene expression mode in the host. Herein, we investigated whether culture conditions reflecting in vivo environments, including serum and saliva, alter expression levels of virulence genes in the strain HK1651, a JP2 clone. Under aerobic conditions, addition of calf serum (CS) into a general medium induced high expression of two outer membrane proteins (omp100 and omp64). The high expression of omp100 and omp64 was also induced by an iron-limited medium. RNA-seq analysis showed that the gene expressions of several factors involved in iron acquisition were increased in the CS-containing medium. When HK1651 was grown on agar plates, genes encoding many virulence factors, including the Omps, cytolethal distending toxin, and leukotoxin, were differentially expressed. Then, we investigated their expression in five other A. actinomycetemcomitans strains grown in general and CS-containing media. The expression pattern of virulence factors varied among strains. Compared with the other five strains, HK1561 showed high expression of omp29 regardless of the CS addition, while the gene expression of leukotoxin in HK1651 was higher only in the medium without CS. HK1651 showed reduced biofilm in both CS- and saliva-containing media. Coaggregation with Fusobacterium nucleatum was remarkably enhanced using HK1651 grown in the CS-containing medium. Our results indicate that the expression of virulence factors is altered by adaptation to different conditions during infection.

Nanoscale observation of PM2.5 incorporated into mammalian cells using scanning electron-assisted dielectric microscope

PM2.5 has been correlated with risk factors for various diseases and infections. It promotes tissue injury by direct effects of particle components. However, effects of PM2.5 on cells have not been fully investigated. Recently, we developed a novel imaging technology, scanning electron-assisted dielectric-impedance microscopy (SE-ADM), which enables observation of various biological specimens in aqueous solution. In this study, we successfully observed PM2.5 incorporated into living mammalian cells in culture media. Our system directly revealed the process of PM2.5 aggregation in the cells at a nanometre resolution. Further, we found that the PM2.5 aggregates in the intact cells were surrounded by intracellular membrane-like structures of low-density in the SE-ADM images. Moreover, the PM2.5 aggregates were shown by confocal Raman microscopy to be located inside the cells rather than on the cell surface. We expect our method to be applicable to the observation of various nanoparticles inside cells in culture media.

Mast cells exhibit intracellular microbicidal activity against Aggregatibacter actinomycetemcomitans

BACKGROUND AND OBJECTIVE

Several studies have demonstrated that mast cells are equipped with versatile tools to combat and kill bacteria. Additionally, mast cells produce and secrete a variety of mediators, which either regulate the host's immune system or directly attack bacteria. In this study, the intracellular microbicidal capacity of mast cells against Aggregatibacter actinomycetemcomitans was evaluated.

METHODS

Murine mast cells were challenged in vitro with A actinomycetemcomitans for 3, 5, 10, and 24 hours. Subsequently, the colony-forming units were counted. Additionally, the production and release of nitric oxide and hydrogen peroxide were analyzed by DAF-FM diacetate, the Griess reaction, and the Amplex Red kit, respectively. Cell death was evaluated using FITC Annexin V and propidium iodide staining.

RESULTS

Mast cells are able to efficiently eliminate periodontopathogen, with best results after 10 hours of intracellular challenge. The production/release of nitric oxide-and to a lesser extent of hydrogen peroxide-by mast cells was in agreement with its microbicidal capacity. Ninety percent of the mast cells  maintained their cellular viability even after 24 hours of bacterial challenge.

CONCLUSIONS

This is-to the best of our knowledge-the first report to describe the intracellular microbicidal activity of mast cells against A actinomycetemcomitans, concerning the production and release of potentially bactericidal substances. Further, the low number of cell deaths confirms that the decreased number of colony-forming units was due to the higher antimicrobial activity of mast cells. The results highlight the importance of these cells in the defense mechanisms of biofilm-induced periodontal disease.

Distinct Signaling Pathways Between Human Macrophages and Primary Gingival Epithelial Cells by Aggregatibacter actinomycetemcomitans

In aggressive periodontitis, the dysbiotic microbial community in the subgingival crevice, which is abundant in Aggregatibacter actinomycetemcomitans, interacts with extra- and intracellular receptors of host cells, leading to exacerbated inflammation and subsequent tissue destruction. Our goal was to understand the innate immune interactions of A. actinomycetemcomitans with macrophages and human gingival epithelial cells (HGECs) on the signaling cascade involved in inflammasome and inflammatory responses. U937 macrophages and HGECs were co-cultured with A. actinomycetemcomitans strain Y4 and key signaling pathways were analyzed using real-time PCR, Western blotting and cytokine production by ELISA. A. actinomycetemcomitans infection upregulated the transcription of TLR2, TLR4, NOD2 and NLRP3 in U937 macrophages, but not in HGECs. Transcription of IL-1β and IL-18 was upregulated in macrophages and HGECs after 1 h interaction with A. actinomycetemcomitans, but positive regulation persisted only in macrophages, resulting in the presence of IL-1β in macrophage supernatant. Immunoblot data revealed that A. actinomycetemcomitans induced the phosphorylation of AKT and ERK1/2, possibly leading to activation of the NF-κB pathway in macrophages. On the other hand, HGEC signaling induced by A. actinomycetemcomitans was distinct, since AKT and 4EBP1 were phosphorylated after stimulation with A. actinomycetemcomitans, whereas ERK1/2 was not. Furthermore, A. actinomycetemcomitans was able to induce the cleavage of caspase-1 in U937 macrophages in an NRLP3-dependent pathway. Differences in host cell responses, such as those seen between HGECs and macrophages, suggested that survival of A. actinomycetemcomitans in periodontal tissues may be favored by its ability to differentially activate host cells.

Tools of Aggregatibacter actinomycetemcomitans to Evade the Host Response

Periodontitis is an infection-induced inflammatory disease that affects the tooth supporting tissues, i.e., bone and connective tissues. The initiation and progression of this disease depend on dysbiotic ecological changes in the oral microbiome, thereby affecting the severity of disease through multiple immune-inflammatory responses. Aggregatibacter actinomycetemcomitans is a facultative anaerobic Gram-negative bacterium associated with such cellular and molecular mechanisms associated with the pathogenesis of periodontitis. In the present review, we outline virulence mechanisms that help the bacterium to escape the host response. These properties include invasiveness, secretion of exotoxins, serum resistance, and release of outer membrane vesicles. Virulence properties of A. actinomycetemcomitans that can contribute to treatment resistance in the infected individuals and upon translocation to the circulation, also induce pathogenic mechanisms associated with several systemic diseases.

Type I collagen deposition via osteoinduction ameliorates YAP/TAZ activity in 3D floating culture clumps of mesenchymal stem cell/extracellular matrix complexes

Background

Three-dimensional (3D) floating culture clumps of mesenchymal stem cell (MSC)/extracellular matrix (ECM) complexes (C-MSCs) consist of cells and self-produced ECM. Previous studies have demonstrated that C-MSCs can be transplanted into bony lesions without an artificial scaffold to induce bone regeneration. Moreover, osteoinductive medium (OIM)-treated C-MSCs (OIM-C-MSCs) have shown rapid and increased new bone formation in vivo. To apply OIM-C-MSCs for novel bone regenerative cell therapy, their cellular properties at the molecular level must be elucidated. The transcriptional co-activators yes-associated protein/transcriptional co-activator with PDZ-binding motif (YAP/TAZ) have been recognized as key players in the mechanotransduction cascade, controlling cell lineage commitment in MSCs. It is plausible that 3D C-MSCs/OIM-C-MSCs cultured in floating conditions could provide distinct microenvironments compared to conventional 2D culture systems and thereby induce unique mechanotransduction cascades. Therefore, this study investigated the YAP/TAZ activity in 3D-cultured C-MSCs/OIM-C-MSCs in floating conditions.

Methods

Human bone marrow-derived MSCs were cultured in growth medium supplemented with ascorbic acid. To obtain C-MSCs, confluent cells that had formed on the cellular sheet were scratched using a micropipette tip and were then torn off. The sheet was rolled to make round clumps of cells. Then, YAP/TAZ activity, filamentous actin (F-actin) integrity, collagen type I (COL1) production, and the differentiation potency in 3D floating culture C-MSCs/OIM-C-MSCs were analyzed.

Results

C-MSCs cultured in floating conditions lost their actin cytoskeleton to downregulate YAP/TAZ activity, which directed cells to undergo adipogenesis/chondrogenesis. OIM treatment induced abundant COL1 deposition, which facilitated Intβ1-dependent actin fiber formation and YAP/TAZ activity to elevate the expression levels of osteogenic master transcriptional factor runt-related transcription factor 2 (RUNX2) mRNA in C-MSCs. Importantly, elevation of YAP/TAZ activity via OIM was associated with COL1 deposition and F-actin integrity, suggesting a positive feedback loop in OIM-C-MSCs.

Conclusion

These findings suggest that OIM-C-MSCs, which form a unique microenvironment that maintains high YAP/TAZ activity, can serve as better candidates for bone regenerative cell therapy than C-MSCs.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1085-9) contains supplementary material, which is available to authorized users.

Role of OmpA1 and OmpA2 in Aggregatibacter actinomycetemcomitans and Aggregatibacter aphrophilus serum resistance

Aggregatibacter actinomycetemcomitans and Aggregatibacter aphrophilus belong to the HACEK group of fastidious Gram-negative organisms, a recognized cause of infective endocarditis. A. actinomycetemcomitans is also implicated in aggressive forms of periodontitis. We demonstrated that A. aphrophilus strains, as A. actinomycetemcomitans are ubiquitously serum resistant. Both species encode two Outer membrane protein A paralogues, here denoted OmpA1 and OmpA2. As their respective pangenomes contain several OmpA1 and OmpA2 alleles, they represent potential genotypic markers. A naturally competent strain of A. actinomycetemcomitans and A. aphrophilus, respectively were used to elucidate if OmpA1 and OmpA2 contribute to serum resistance. Whereas OmpA1 was critical for survival of A. actinomycetemcomitans D7SS in 50% normal human serum (NHS), serum resistant ompA1 mutants were fortuitously obtained, expressing enhanced levels of OmpA2. Similarly, OmpA1 rather than OmpA2 was a major contributor to serum resistance of A. aphrophilus HK83. Far-Western blot revealed that OmpA1^AA, OmpA2^AA, and OmpA1^AP can bind to C4-binding protein, an inhibitor of classical and mannose-binding lectin (MBL) complement activation. Indeed, ompA1 mutants were susceptible to these pathways, but also to alternative complement activation. This may at least partly reflect a compromised outer membrane integrity but is also consistent with alternative mechanisms involved in OmpA-mediated serum resistance.

Peptidoglycan-associated lipoprotein of Aggregatibacter actinomycetemcomitans induces apoptosis and production of proinflammatory cytokines via TLR2 in murine macrophages RAW 264.7 in vitro

Peptidoglycan-associated lipoprotein (PAL) is a conserved pro-inflammatory outer membrane lipoprotein in Gram-negative bacteria. Compared to systemic pathogens, little is known about the virulence properties of PAL in Aggregatibacter actinomycetemcomitans (AaPAL). The aims of this study were to investigate the cytolethality of AaPAL and its ability to induce pro-inflammatory cytokine production in macrophages. Mouse macrophages were stimulated with AaPAL, and the production of IL-1β, IL-6, TNF-α, and MCP-1 was measured after 6, 24, and 48 h. To investigate which receptor AaPAL employs for its interaction with macrophages, anti-toll-like receptor (TLR)2 and anti-TLR4 antibodies were used to block respective TLRs on macrophages. Metabolic activity and apoptosis of the macrophages were investigated after stimulation with AaPAL. AaPAL induced the production of MCP-1, TNF-α, IL-6, and IL-1β from mouse macrophages in order of decreasing abundance. The pre-treatment of macrophages with an anti-TLR2 antibody significantly diminished cytokine production. Under AaPAL stimulation, the metabolic activity of macrophages decreased in a dose- and time-dependent manner. Furthermore, AaPAL induced apoptosis in 56% of macrophages after 48 h of incubation. Our data suggest that AaPAL can kill macrophages by apoptosis. The results also emphasize the role of AaPAL as a potent pro-inflammatory agent in A. actinomycetemcomitans-associated infections.

Modulation of microenvironment for controlling the fate of periodontal ligament cells: the role of Rho/ROCK signaling and cytoskeletal dynamics

Cells behave in a variety of ways when they perceive changes in their microenvironment; the behavior of cells is guided by their coordinated interactions with growth factors, niche cells, and extracellular matrix (ECM). Modulation of the microenvironment affects the cell morphology and multiple gene expressions. Rho/Rho-associated coiled-coil-containing protein kinase (ROCK) signaling is one of the key regulators of cytoskeletal dynamics and actively and/or passively determines the cell fate, such as proliferation, migration, differentiation, and apoptosis, by reciprocal communication with the microenvironment. During periodontal wound healing, it is important to recruit the residential stem cells into the defect site for regeneration and homeostasis of the periodontal tissue. Periodontal ligament (PDL) cells contain a heterogeneous fibroblast population, including mesenchymal stem cells, and contribute to the reconstruction of tooth-supporting tissues. Therefore, bio-regeneration of PDL cells has been the ultimate goal of periodontal therapy for decades. Recent stem cell researches have shed light on intrinsic ECM properties, providing paradigm shifts in cell fate determination. This review focuses on the role of ROCK activity and the effects of Y-27632, a specific inhibitor of ROCK, in the modulation of ECM-microenvironment. Further, it presents the current understanding of how Rho/ROCK signaling affects the fate determination of stem cells, especially PDL cells. In addition, we have also discussed in detail the underlying mechanisms behind the reciprocal response to the microenvironment.

Xenotransplantation of interferon-gamma-pretreated clumps of a human mesenchymal stem cell/extracellular matrix complex induces mouse calvarial bone regeneration

Background

Three-dimensional cultured clumps of a mesenchymal stem cell (MSC)/extracellular matrix (ECM) complex (C-MSC) consists of cells and self-produced ECM. C-MSC can regulate the cellular function in vitro and induce successful bone regeneration using ECM as a cell scaffold. Potentiating the immunomodulatory capacity of C-MSCs, which can ameliorate the allo-specific immune response, may be helpful in developing beneficial “off-the-shelf” cell therapy for tissue regeneration. It is well reported that interferon (IFN)-γ stimulates the immunosuppressive properties of MSC via upregulation of the immunomodulatory enzyme IDO. Therefore, the aim of this study was to investigate the effect of IFN-γ on the immunomodulatory capacity of C-MSC in vitro and to test the bone regenerative activity of C-MSC or IFN-γ-pretreated C-MSC (C-MSCγ) xenografts in a mice calvarial defect model.

Methods

Human bone marrow-derived MSCs were seeded at a density of 2.0 × 10⁵ cells/well into 24-well plates and cultured with growth medium supplemented with 50 μg/mL L-ascorbic acid for 4 days. To obtain C-MSC, confluent cells that had formed on the cellular sheet were scratched using a micropipette tip and were then torn off. The cellular sheet was rolled to make a round clump of cells. C-MSC was stimulated with IFN-γ and IDO expression, immunosuppressive capacity, and immunophenotype were evaluated in vitro. Moreover, C-MSC or C-MSCγ was xenotransplanted into immunocompetent or immunodeficient mice calvarial defect models without artificial scaffold, respectively.

Results

IFN-γ stimulated IDO expression in C-MSC. C-MSCγ, but not C-MSC, attenuated CD3/CD28-induced T cell proliferation and its suppressive effect was reversed by an IDO inhibitor. C-MSCγ showed upregulation of HLA-DR expression, but its co-stimulatory molecule, CD86, was not detected. Xenotransplantation of C-MSCγ into immunocompetent mice calvarial defect induced bone regeneration, whereas C-MSC xenograft failed and induced T cell infiltration in the grafted area. On the other hand, both C-MSC and C-MSCγ xenotransplantation into immunodeficient mice caused bone regeneration.

Conclusions

Xenotransplantation of C-MSCγ, which exerts immunomodulatory properties via the upregulation of IDO activity in vitro, may attenuate xenoreactive host immune response, and thereby induce bone regeneration in mice. Accordingly, C-MSCγ may constitute a promising novel allograft cell therapy for bone regeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0550-1) contains supplementary material, which is available to authorized users.

TRAP-positive osteoclast precursors mediate ROS/NO-dependent bactericidal activity via TLR4

Osteoclastogenesis was induced by RANKL stimulation in mouse monocytes to examine the possible bactericidal function of osteoclast precursors (OCp) and mature osteoclasts (OCm) relative to their production of NO and ROS. Tartrate-resistant acid phosphatase (TRAP)-positive OCp, but few or no OCm, phagocytized and killed Escherichia coli in association with the production of reactive oxygen species (ROS) and nitric oxide (NO). Phagocytosis of E. coli and production of ROS and NO were significantly lower in TRAP+ OCp derived from Toll-like receptor (TLR)-4 KO mice than that derived from wild-type (WT) or TLR2-KO mice. Interestingly, after phagocytosis, TRAP+ OCp derived from wild-type and TLR2-KO mice did not differentiate into OCm, even with continuous exposure to RANKL. In contrast, E. coli-phagocytized TRAP+ OCp from TLR4-KO mice could differentiate into OCm. Importantly, neither NO nor ROS produced by TRAP+ OCp appeared to be engaged in phagocytosis-induced suppression of osteoclastogenesis. These results suggested that TLR4 signaling not only induces ROS and NO production to kill phagocytized bacteria, but also interrupts OCm differentiation. Thus, it can be concluded that TRAP+ OCp, but not OCm, can mediate bactericidal activity via phagocytosis accompanied by the production of ROS and NO via TLR4-associated reprograming toward phagocytic cell type.

Aggregatibacter actinomycetemcomitans outer membrane protein 29 (Omp29) induces TGF-β-regulated apoptosis signal in human gingival epithelial cells via fibronectin/integrinβ1/FAK cascade

Gingival junctional epithelial cell apoptosis caused by periodontopathic bacteria exacerbates periodontitis. This pathological apoptosis is involved in the activation of transforming growth factor β (TGF-β). However, the molecular mechanisms by which microbes induce the activation of TGF-β remain unclear. We previously reported that Aggregatibacter actinomycetemcomitans (Aa) activated TGF-β receptor (TGF-βR)/smad2 signalling to induce epithelial cell apoptosis, even though Aa cannot bind to TGF-βR. Additionally, outer membrane protein 29 kDa (Omp29), a member of the Aa Omps family, can induce actin rearrangements via focal adhesion kinase (FAK) signalling, which also plays a role in the activation of TGF-β by cooperating with integrin. Accordingly, we hypothesized that Omp29-induced actin rearrangements via FAK activity would enhance the activation of TGF-β, leading to gingival epithelial cell apoptosis in vitro. By using human gingival epithelial cell line OBA9, we found that Omp29 activated TGF-βR/smad2 signalling and decreased active TGF-β protein levels in the extracellular matrix (ECM) of cell culture, suggesting the transactivation of TGF-βR. Inhibition of actin rearrangements by cytochalasin D or blebbistatin and knockdown of FAK or integrinβ1 expression by siRNA transfection attenuated TGF-βR/smad2 signalling activity and reduction of TGF-β levels in the ECM caused by Omp29. Furthermore, Omp29 bound to fibronectin (Fn) to induce its aggregation on integrinβ1, which is associated with TGF-β signalling activity. All the chemical inhibitors and siRNAs tested blocked Omp29-induced OBA9 cells apoptosis. These results suggest that Omp29 binds to Fn in order to facilitate Fn/integrinβ1/FAK signalling-dependent TGF-β release from the ECM, thereby inducing gingival epithelial cell apoptosis via TGF-βR/smad2 pathway.

Distinction Between Cell Proliferation and Apoptosis Signals Regulated by Brain-Derived Neurotrophic Factor in Human Periodontal Ligament Cells and Gingival Epithelial Cells

Previously, we reported that brain-derived neurotrophic factor (BDNF) enhances periodontal tissue regeneration by inducing periodontal ligament cell proliferation in vivo. In addition, the down growth of gingival epithelial cells, which comprises a major obstacle to the regeneration, was not observed. However, the underlying molecular mechanism is still unclear. Therefore, this study aimed to investigate the effect of BDNF on cell proliferation and apoptosis in human periodontal ligament (HPL) cells and human gingival epithelial cells (OBA9 cells) and to explore the molecular mechanism in vitro. HPL cells dominantly expressed a BDNF receptor, TrkB, and BDNF increased cell proliferation and ERK phosphorylation. However, its proliferative effect was diminished by a MEK1/2 inhibitor (U0126) and TrkB siRNA transfection. Otherwise, OBA9 cells showed a higher expression level of p75, which is a pan-neurotrophin receptor, than that of HPL cells. BDNF facilitated not cell proliferation but cell apoptosis and JNK phosphorylation in OBA9 cells. A JNK inhibitor (SP600125) and p75 siRNA transfection attenuated the BDNF-induced cell apoptosis. Moreover, OBA9 cells pretreated with SP600125 or p75 siRNA showed cell proliferation by BDNF stimulation, though it was reduced by U0126 and TrkB siRNA. Interestingly, overexpression of p75 in HPL cells upregulated cell apoptosis and JNK phosphorylation by BDNF treatment. These results indicated that TrkB-ERK signaling regulates BDNF-induced cell proliferation, whereas p75-JNK signaling plays roles in cell apoptotic and cytostatic effect of BDNF. Overall, BDNF activates periodontal ligament cells proliferation and inhibits the gingival epithelial cells growth via the distinct pathway. J. Cell. Biochem. 117: 1543-1555, 2016. © 2015 Wiley Periodicals, Inc.

Transcriptional regulation of the Aggregatibacter actinomycetemcomitans ygiW-qseBC operon by QseB and integration host factor proteins

The QseBC two-component system plays a pivotal role in regulating virulence and biofilm growth of the oral pathogen Aggregatibacter actinomycetemcomitans. We previously showed that QseBC autoregulates the ygiW-qseBC operon. In this study, we characterized the promoter that drives ygiW-qseBC expression. Using lacZ transcriptional fusion constructs and 5'-rapid amplification of cDNA ends, we showed that ygiW-qseBC expression is driven by a promoter that initiates transcription 53 bases upstream of ygiW and identified putative cis-acting promoter elements, whose function was confirmed using site-specific mutagenesis. Using electrophoretic mobility shift assays, two trans-acting proteins were shown to interact with the ygiW-qseBC promoter. The QseB response regulator bound to probes containing the direct repeat sequence CTTAA-N6-CTTAA, where the CTTAA repeats flank the -35 element of the promoter. The ygiW-qseBC expression could not be detected in A. actinomycetemcomitans ΔqseB or ΔqseBC strains, but was restored to WT levels in the ΔqseBC mutant when complemented by single copy chromosomal insertion of qseBC. Interestingly, qseB partially complemented the ΔqseBC strain, suggesting that QseB could be activated in the absence of QseC. QseB activation required its phosphorylation since complementation did not occur using qseB(pho-), encoding a protein with the active site aspartate substituted with alanine. These results suggest that QseB is a strong positive regulator of ygiW-qseBC expression. In addition, integration host factor (IHF) bound to two sites in the promoter region and an additional site near the 5' end of the ygiW ORF. The expression of ygiW-qseBC was increased by twofold in ΔihfA and ΔihfB strains of A. actinomycetemcomitans, suggesting that IHF is a negative regulator of the ygiW-qseBC operon.

Differential transcription of virulence genes in Aggregatibacter actinomycetemcomitans serotypes

Background

Aggregatibacter actinomycetemcomitans serotypes are clearly associated with periodontitis or health, which suggests distinct strategies for survival within the host.

Objective

We investigated the transcription profile of virulence-associated genes in A. actinomycetemcomitans serotype b (JP2 and SUNY 465) strains associated with disease and serotype a (ATCC 29523) strain associated with health.

Design

Bacteria were co-cultured with immortalized gingival epithelial cells (OBA-9). The adhesion efficiency after 2 hours and the relative transcription of 13 genes were evaluated after 2 and 24 hours of interaction.

Results

All strains were able to adhere to OBA-9, and this contact induced transcription of pgA for polysaccharide biosynthesis in all tested strains. Genes encoding virulence factors as Omp29, Omp100, leukotoxin, and CagE (apoptotic protein) were more transcribed by serotype b strains than by serotype a. ltxA and omp29, encoding the leukotoxin and the highly antigenic Omp29, were induced in serotype b by interaction with epithelial cells. Factors related to colonization (aae, flp, apaH, and pgA) and cdtB were upregulated in serotype a strain after prolonged interaction with OBA-9.

Conclusion

Genes relevant for surface colonization and interaction with the immune system are regulated differently among the strains, which may help explaining their differences in association with disease.

Multispecies biofilms and host responses: "discriminating the trees from the forest"

Periodontal diseases reflect a tissue destructive process of the hard and soft tissues of the periodontium that are initiated by the accumulation of multispecies bacterial biofilms in the subgingival sulcus. This accumulation, in both quantity and quality of bacteria, results in a chronic immunoinflammatory response of the host to control this noxious challenge, leading to collateral damage of the tissues. As knowledge of the characteristics of the host-bacterial interactions in the oral cavity has expanded, new knowledge has become available on the complexity of the microbial challenge and the repertoire of host responses to this challenge. Recent results from the Human Microbiome Project continue to extend the array of taxa, genera, and species of bacteria that inhabit the multiple niches in the oral cavity; however, there is rather sparse information regarding variations in how host cells discriminate commensal from pathogenic species, as well as how the host response is affected by the three-dimensional architecture and interbacterial interactions that occur in the oral biofilms. This review provides some insights into these processes by including existing literature on the biology of nonoral bacterial biofilms, and the more recent literature just beginning to document how the oral cavity responds to multispecies biofilms.

Proteomics of protein secretion by Aggregatibacter actinomycetemcomitans

The extracellular proteome (secretome) of periodontitis-associated bacteria may constitute a major link between periodontitis and systemic diseases. To obtain an overview of the virulence potential of Aggregatibacter actinomycetemcomitans, an oral and systemic human pathogen implicated in aggressive periodontitis, we used a combined LC-MS/MS and bioinformatics approach to characterize the secretome and protein secretion pathways of the rough-colony serotype a strain D7S. LC-MS/MS revealed 179 proteins secreted during biofilm growth. Further to confirming the release of established virulence factors (e.g. cytolethal distending toxin [CDT], and leukotoxin [LtxA]), we identified additional putative virulence determinants in the secretome. These included DegQ, fHbp, LppC, Macrophage infectivity protein (MIP), NlpB, Pcp, PotD, TolB, and TolC. This finding indicates that the number of extracellular virulence-related proteins is much larger than previously demonstrated, which was also supported by in silico analysis of the strain D7S genome. Moreover, our LC-MS/MS and in silico data revealed that at least Type I, II, and V secretion are actively used to excrete proteins directly into the extracellular space, or via two-step pathways involving the Sec/Tat systems for transport across the inner membrane, and outer membrane factors, secretins and auto-transporters, respectively for delivery across the outer membrane. Taken together, our results provide a molecular basis for further elucidating the role of A. actinomycetemcomitans in periodontal and systemic diseases.

Muscarinic type 3 receptor induces cytoprotective signaling in salivary gland cells through epidermal growth factor receptor transactivation

Muscarinic type 3 receptor (M3R) plays a pivotal role in the induction of glandular fluid secretions. Although M3R is often the target of autoantibodies in Sjögren's syndrome (SjS), chemical agonists for M3R are clinically used to stimulate saliva secretion in patients with SjS. Aside from its activity in promoting glandular fluid secretion, however, it is unclear whether activation of M3R is related to other biological events in SjS. This study aimed to investigate the cytoprotective effect of chemical agonist-mediated M3R activation on apoptosis induced in human salivary gland (HSG) cells. Carbachol (CCh), a muscarinic receptor-specific agonist, abrogated tumor necrosis factor α/interferon γ-induced apoptosis through pathways involving caspase 3/7, but its cytoprotective effect was decreased by a M3R antagonist, a mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (ERK) inhibitor, a phosphatidylinositol 3-kinase/Akt inhibitor, or an epidermal growth factor receptor (EGFR) inhibitor. Ligation of M3R with CCh transactivated EGFR and phosphorylated ERK and Akt, the downstream targets of EGFR. Inhibition of intracellular calcium release or protein kinase C δ, both of which are involved in the cell signaling of M3R-mediated fluid secretion, did not affect CCh-induced ERK or Akt phosphorylation. CCh stimulated Src phosphorylation and binding to EGFR. A Src inhibitor attenuated the CCh/M3R-induced cytoprotective effect and EGFR transactivation cascades. Overall, these results indicated that CCh/M3R induced transactivation of EGFR through Src activation leading to ERK and Akt phosphorylation, which in turn suppressed caspase 3/7-mediated apoptotic signals in HSG cells. This study, for the first time, proposes that CCh-mediated M3R activation can promote not only fluid secretion but also survival of salivary gland cells in the inflammatory context of SjS.

Signaling transduction analysis in gingival epithelial cells after infection with Aggregatibacter actinomycetemcomitans

Periodontal diseases result from the interaction of bacterial pathogens with the host's gingival tissue. Gingival epithelial cells are constantly challenged by microbial cells and respond by altering their transcription profiles, inducing the production of inflammatory mediators. Different transcription profiles are induced by oral bacteria and little is known about how the gingival epithelium responds after interaction with the periodontopathogenic organism Aggregatibacter actinomycetemcomitans. In the present study, we examined the transcription of genes involved in signaling transduction pathways in gingival epithelial cells exposed to viable A. actinomycetemcomitans. Immortalized gingival epithelial cells (OBA-9) were infected with A. actinomycetemcomitans JP2 for 24 h and the transcription profile of genes encoding human signal transduction pathways was determined. Functional analysis of inflammatory mediators positively transcribed was performed by ELISA in culture supernatant and in gingival tissues. Fifteen of 84 genes on the array were over-expressed (P < 0.01) after 24 h of infection with viable A. actinomycetemcomitans. Over-expressed genes included those implicated in tissue remodeling and bone resorption, such as CSF2, genes encoding components of the LDL pathway, nuclear factor-κB-dependent genes and other cytokines. The ELISA data confirmed that granulocyte-macrophage colony-stimulating factor/colony-stimulating factor 2, tumor necrosis factor-α and intercellular adhesion molecule-1 were highly expressed by infected gingival cells when compared with control non-infected cells, and presented higher concentrations in tissues from patients with aggressive and chronic periodontitis than in tissues from healthy controls. The induction in epithelial cells of factors such as the pro-inflammatory cytokine CSF2, which is involved in osteoclastogenesis, may help to explain the outcomes of A. actinomycetemcomitans infection.