Distinct transcriptional profiles characterize oral epithelium-microbiota interactions

Transcriptional profiling, bioinformatics, statistical and ontology tools were used to uncover and dissect genes and pathways of human gingival epithelial cells that are modulated upon interaction with the periodontal pathogens Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis. Consistent with their biological and clinical differences, the common core transcriptional response of epithelial cells to both organisms was very limited, and organism-specific responses predominated. A large number of differentially regulated genes linked to the P53 apoptotic network were found with both organisms, which was consistent with the pro-apoptotic phenotype observed with A. actinomycetemcomitans and anti-apoptotic phenotype of P. gingivalis. Furthermore, with A. actinomycetemcomitans, the induction of apoptosis did not appear to be Fas- or TNF(alpha)-mediated. Linkage of specific bacterial components to host pathways and networks provided additional insight into the pathogenic process. Comparison of the transcriptional responses of epithelial cells challenged with parental P. gingivalis or with a mutant of P. gingivalis deficient in production of major fimbriae, which are required for optimal invasion, showed major expression differences that reverberated throughout the host cell transcriptome. In contrast, gene ORF859 in A. actinomycetemcomitans, which may play a role in intracellular homeostasis, had a more subtle effect on the transcriptome. These studies help unravel the complex and dynamic interactions between host epithelial cells and endogenous bacteria that can cause opportunistic infections.

Interactions of oral pathogens with toll-like receptors: possible role in atherosclerosis

Toll-like receptors (TLR) function as important signal transducers that mediate innate immune and inflammatory responses to pathogens through pattern recognition of virulence molecules. Although TLRs mediate protection against infection, it is also likely that they may have a pathophysiologic role in certain inflammatory diseases, such as atherosclerosis. In atherosclerotic lesions, endothelial cells and macrophages have been shown to upregulate TLR expression and may respond to TLR agonists of microbial origin, resulting in detrimental inflammatory reactions. Some of these potential TLR-activating virulence factors may be of oral origin. The detection in atherosclerotic plaques of DNA specific for Porphyromonas gingivalis and other periodontal pathogens suggests that these pathogens disseminate into the systemic circulation and localize in atheromas. The potential of periodontal and some other oral pathogens to activate TLRs in vivo is suggested by findings from cell culture experiments on interactions of selected virulence protein adhesins with TLRs and their coreceptors. Specifically, we have shown that proinflammatory cytokine induction by P. gingivalis fimbriae was inhibited by monoclonal antibodies to TLR2, TLR4, CD14, and beta2 integrins, but not by immunoglobulin isotype controls. Cytokine induction by Bacteroides forsythus protein A depended heavily on CD14 and TLR2. We also found that the ability of Streptococcus mutans protein AgI/II to stimulate cytokine release was partially dependent on CD14 and TLR4. Moreover, P. gingivalis fimbriae induced TLR-dependent activation of nuclear factor-kappaB and upregulation of costimulatory molecules in monocytic cells. These proinflammatory activities have been implicated in the pathogenesis of periodontitis, and similar inflammatory mechanisms could potentially operate in atherosclerosis. Studies by other groups have shown that P. gingivalis is capable of stimulating low-density lipoprotein oxidation, foam cell formation, and rupture of atherosclerotic plaque through induction of matrix metalloproteinases. Interestingly, at least some of these activities can be induced by TLR agonists (lipopolysaccharide and heat-shock protein-60) from Chlamydia pneumoniae, a major risk factor in atherosclerosis. Future research in animal models and in vitro cellular systems with defined mutations in TLRs may implicate TLR participation in oral pathogen-mediated atherosclerotic processes, thereby providing a mechanistic basis for the epidemiological findings linking oral pathogens to atherosclerotic disease.

Short fimbriae of Porphyromonas gingivalis and their role in coadhesion with Streptococcus gordonii

Porphyromonas gingivalis, one of the causative agents of adult periodontitis, attaches and forms biofilms on substrata of Streptococcus gordonii. Coadhesion and biofilm development between these organisms requires the interaction of the short fimbriae of P. gingivalis with the SspB streptococcal surface polypeptide. In this study we investigated the structure and binding activities of the short fimbriae of P. gingivalis. Electron microscopy showed that isolated short fimbriae have an average length of 103 nm and exhibit a helical structure with a pitch of ca. 27 nm. Mfa1, the major protein subunit of the short fimbriae, bound to SspB protein, and this reaction was inhibited by purified recombinant Mfa1 and monospecifc anti-Mfa1 serum in a dose-dependent manner. Complementation of a polar Mfa1 mutant with the mfa1 gene restored the coadhesion phenotype of P. gingivalis. Hence, the Mfa1 structural fimbrial subunit does not require accessory proteins for binding to SspB. Furthermore, the interaction of Mfa1 with SspB is necessary for optimal coadhesion between P. gingivalis and S. gordonii.

Identification of glyceraldehyde-3-phosphate dehydrogenase of epithelial cells as a second molecule that binds toPorphyromonas gingivalisfimbriae

Binding of Porphyromonas gingivalis to the host cells is an essential step in the pathogenesis of periodontal disease. P. gingivalis binds to and invades epithelial cells, and fimbriae are thought to be involved in this process. In our earlier studies, two major epithelial cell components of 40 and 50 kDa were identified as potential fimbrial receptors. Sequencing of a cyanogen bromide digestion fragment of the 50-kDa component resulted in an internal sequence identical to keratin I molecules, and hence this cytokeratin represents one of the epithelial cell receptors for P. gingivalis fimbriae. In this study, the 40-kDa component of KB cells was isolated and its amino-terminal sequence determined. The N-terminal amino sequence was found to be GKVKVGVNGF and showed perfect homology with human glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Furthermore, purified P. gingivalis fimbriae were found to bind to rabbit muscle GAPDH. Antibodies directed against internal peptide 49-68 and 69-90 of fimbrillin were shown to inhibit the binding of P. gingivalis and of fimbriae to epithelial cells. Antibodies against these peptides also inhibited the binding of fimbriae to GAPDH. Our results confirmed that the amino-terminal domain corresponding to amino residues 49-68 of the fimbrillin protein is the major GAPDH binding domain. These studies point to GAPDH as a major receptor for P. gingivalis major fimbriae and, as such, GAPDH likely plays a role in P. gingivalis adherence and colonization of the oral cavity, as well as triggering host cell processes involved in the pathogenesis of P. gingivalis infections.

Neuropeptide release from dental pulp cells by RgpB via proteinase-activated receptor-2 signaling

Dental pulp inflammation often results from dissemination of periodontitis caused mostly by Porphyromonas gingivalis infection. Calcitonin gene-related peptide and substance P are proinflammatory neuropeptides that increase in inflamed pulp tissue. To study an involvement of the periodontitis pathogen and neuropeptides in pulp inflammation, we investigated human dental pulp cell neuropeptide release by arginine-specific cysteine protease (RgpB), a cysteine proteinase of P. gingivalis, and participating signaling pathways. RgpB induced neuropeptide release from cultured human pulp cells (HPCs) in a proteolytic activity-dependent manner at a range of 12.5-200 nM. HPCs expressed both mRNA and the products of calcitonin gene-related peptide, substance P, and proteinase-activated receptor-2 (PAR-2) that were also found in dental pulp fibroblast-like cells. The PAR-2 agonists, SLIGKV and trypsin, also induced neuropeptide release from HPCs, and HPC PAR-2 gene knockout by transfection of PAR-2 antisense oligonucleotides inhibited significantly the RgpB-elicited neuropeptide release. These results indicated that RgpB-induced neuropeptide release was dependent on PAR-2 activation. The kinase inhibitor profile on the RgpB-neuropeptide release from HPC revealed a new PAR-2 signaling pathway that was mediated by p38 MAPK and activated transcription factor-2 activation, in addition to the PAR-2-p44/42 p38MAPK and -AP-1 pathway. This new RgpB activity suggests a possible link between periodontitis and pulp inflammation, which may be modulated by neuropeptides released in the lesion.

Molecular mechanism for connective tissue destruction by dipeptidyl aminopeptidase IV produced by the periodontal pathogen Porphyromonas gingivalis

Porphyromonas gingivalis is a pathogen associated with adult periodontitis. It produces dipeptidyl aminopeptidase IV (DPPIV), which may act as a virulence factor by contributing to the degradation of connective tissue. We investigated the molecular mechanism by which DPPIV contributes to the destruction of connective tissue. DPPIV itself did not show gelatinase or collagenase activity toward human type I collagen, but it promoted the activity of the host-derived matrix metalloproteinase 2 (MMP-2) (gelatinase) and MMP-1 (collagenase). DPPIV bound to fibronectin and mediated the adhesion of P. gingivalis to fibronectin. Mutant DPPIV with catalytic Ser mutagenized to Ala (DPPSA) did not accelerate the degradation of collagen and gelatin by MMPs but retained fibronectin-binding activity. The adhesion of human gingival fibroblasts and NIH 3T3 cells to fibronectin was inhibited by DPPIV. Strain 4351ADPPSA exhibited an intermediate level of virulence in mice, between that of the strain expressing wild-type DPPIV (4351ADPP) and that of the strain harboring only the plasmid vector (4351AVEC). It is suggested that both activity promoting the degradation of collagen and gelatin and binding to fibronectin are required for full virulence. These results reveal novel biological functions of DPPIV and suggest a pathological role in the progression of periodontitis.

Roles of Arg- and Lys-gingipains in coaggregation of Porphyromonas gingivalis: identification of its responsible molecules in translation products of rgpA, kgp, and hagA genes

Arg- (Rgp) and Lys-gingipains (Kgp) are two individual cysteine proteinases produced by Porphyromonas gingivalis , an oral anaerobic bacterium, and are implicated as major virulence factors in a wide range of pathologies of adult periodontitis. Coaggregation of this bacterium with other oral bacteria is an initial and critical step in infectious processes, yet the factors and mechanisms responsible for this process remain elusive. Here we show that the initial translation products of the rgpA , kgp and hemagglutinin hagA genes are responsible for coaggregation of P. gingivalis and that the proteolytic activity of Rgp and Kgp is indispensable in this process. The rgpA rgpB kgp- and rgpA kgp hagA -deficient triple mutants exhibited no coaggregation activity with Actinomyces viscosus , whereas the kgp -null and rgpA rgpB -deficient double mutants significantly retained this activity. Consistently, the combined action of Rgp- and Kgp-specific inhibitors strongly inhibited the coaggregation activity of the bacterium, although single use of Rgp- or Kgp-specific inhibitor significantly retained this activity. We also demonstrate that the 47- and 43-kDa proteins produced from the translation products of the rgpA , kgp , and hagA genes by proteolytic activity of both Rgp and Kgp are responsible for the coaggregation of P. gingivalis.

Parotid secretory protein is expressed and inducible in human gingival keratinocytes

BACKGROUND

Parotid secretory protein (PSP) is a major salivary protein that is thought to possess both antibacterial and anti-inflammatory activity. A major question is whether PSP expression can be regulated by humoral factors and bacteria. Periodontitis is an inflammatory lesion initiated by interaction between gingival keratinocytes and periodontopathogenic microorganisms such as the Gram-negative anaerobe Porphyromonas gingivalis. Cytokines and sex hormones have been implicated in the progression of various forms of periodontal diseases.

MATERIALS AND METHODS

We investigated the expression of PSP and its regulation in primary cultures of human gingival keratinocytes (HGK). HGK at the third or fourth passage were exposed to heat-killed P. gingivalis, tumor necrosis factor-alpha (TNF-alpha) and 17beta-estradiol. The PSP mRNA levels were examined by real-time polymerase chain reaction (PCR). The protein expression of PSP was confirmed by immunofluorescence.

RESULTS

Heat-killed P. gingivalis, TNF-alpha and 17beta-estradiol all resulted in increased HGK levels of mRNA for PSP as determined by real-time PCR analysis. Immunofluorescence demonstrated increased PSP localized within the cytoplasm of HGK following exposure to killed P. gingivalis.

CONCLUSION

The present study has demonstrated for the first time that PSP is expressed in keratinocytes and that it can be up-regulated by bacteria and humoral factors. Thus PSP may have a role in the innate defense system at the gingival epithelial surface.

Oral streptococcal glyceraldehyde-3-phosphate dehydrogenase mediates interaction with Porphyromonas gingivalis fimbriae

Interaction of Porphyromonas gingivalis with plaque-forming bacteria is necessary for its colonization in periodontal pockets. Participation of Streptococcus oralis glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and P. gingivalis fimbriae in this interaction has been reported. In this investigation, the contribution of various oral streptococcal GAPDHs to interaction with P. gingivalis fimbriae was examined. Streptococcal cell surface GAPDH activity was measured by incubation of a constant number of streptococci with glyceraldehyde-3-phosphate and analysis for the conversion of NAD+ to NADH based on the absorbance at 340 nm. Coaggregation activity was measured by a turbidimetric assay. Cell surface GAPDH activity was correlated with coaggregation activity (r = 0.854, P < 0.01) with Spearman's rank correlation coefficient. S. oralis ATCC 9811 and ATCC 10557, Streptococcus gordonii G9B, Streptococcus sanguinis ATCC 10556, and Streptococcus parasanguinis ATCC 15909 exhibited high cell surface GAPDH activity and coaggregation activity; consequently, their cell surface GAPDHs were extracted with mutanolysin and purified on a Cibacron Blue Sepharose column. Subsequently, their DNA sequences were elucidated. Purified GAPDHs bound P. gingivalis recombinant fimbrillin by Western blot assay, furthermore, their DNA sequences displayed a high degree of homology with one another. Moreover, S. oralis recombinant GAPDH inhibited coaggregation between P. gingivalis and the aforementioned five streptococcal strains in a dose-dependent manner. These results suggest that GAPDHs of various plaque-forming streptococci may be involved in their attachment to P. gingivalis fimbriae and that they may contribute to P. gingivalis colonization.

Porphyromonas gingivalis induces its uptake by human macrophages and promotes foam cell formation in vitro

Porphyromonas gingivalis is an etiologic agent of periodontal disease in humans, which has been linked to an increased risk for atherosclerosis-related events. In this study, we examined the effect of P. gingivalis infection on human macrophages with respect to foam cell formation, the hallmark of early atherogenesis, and the potential of P. gingivalis to induce its uptake by these cells. Human monocyte-derived macrophages were incubated with low density lipoprotein and infected with P. gingivalis FDC381 or its fimbriae deficient mutant, DPG3. Consistent with a role for fimbriae in this process, strain 381 significantly increased foam cell formation as compared to DPG3. Recovery of viable P. gingivalis in antibiotic protection experiments was significantly higher for strain 381 than for DPG3. By transmission electron microscopy, the wild-type strain was shown to adhere to and enter THP-1 cells. These results suggest that properties of P. gingivalis which render it capable of adhering to/invading other cell types may also be operative in macrophages and play an important role in its atherogenic potential.

Induction of {beta}-defensin resistance in the oral anaerobe Porphyromonas gingivalis

Induction of resistance of oral anaerobes to the effects of human beta-defensin 1 (hbetaD-1) to hbetaD-4 was investigated by pretreating cells with either sublethal levels of defensins or environmental factors, followed by a challenge with lethal levels of defensins. Cultures of Porphyromonas gingivalis were (i) pretreated with defensins at 1 ng/ml, (ii) heated to 42 degrees C (heat stress), (iii) exposed to normal atmosphere (oxidative stress), or (iv) exposed to 1 mM hydrogen peroxide (peroxide stress). Samples (10 microl) were distributed among the wells of sterile 384-well plates containing hbetaD-1 to -4 (100 microg/ml). Plates were incubated at 37 degrees C for 36 h in an anaerobe chamber. Growth inhibition was determined by a system that measures the total nucleic acid of a sample with a DNA binding dye. The MICs of the four defensins for P. gingivalis were 3 to 12 microg/ml. We found that sublethal levels of the defensins and heat and peroxide stress, but not oxidative stress, induced resistance to 100 microg of defensin per ml in P. gingivalis. Resistance induced by sublethal levels of hbetaD-2 lasted 90 min, and the resistance induced by each defensin was effective against the other three. Multiple strains exposed to hbetaD-2 all evidenced resistance induction. Defensin resistance is vital to the pathogenic potential of several human pathogens. This is the first report describing the induction of defensin resistance in the oral periodontal pathogen P. gingivalis. Such resistance may have an effect on the ability of oral pathogens to persist in the mouth and to withstand innate human immunity.

Inhibitory effects of Porphyromonas gingivalis fimbriae on interactions between extracellular matrix proteins and cellular integrins

Porphyromonas gingivalis is a predominant periodontal pathogen, whose fimbriae are considered to be a major virulence factor, especially for bacterial adherence and invasion of host cells. In the present study, we investigated the influence of fimbriae on the interactions between alphavbeta3- and alpha5beta1-integrins and their ligand extracellular matrix (ECM) proteins (vitronectin and fibronectin), using human alphavbeta3- and alpha5beta1-integrin-overexpressing CHO cell lines (CHOalphavbeta3 and CHOalpha5beta1, respectively). P. gingivalis was found to have significantly greater binding to CHOalphavbeta3 and CHOalpha5beta1 than to control cells, whereas a fimbria-deficient mutant showed negligible binding to any of the tested cell lines. CHOalphavbeta3 and CHOalpha5beta1 cells attached to the polystyrene culture dishes in the presence of their ligand ECM proteins, while fimbriae markedly inhibited those attachments in a dose-dependent manner, with the highest dose of fimbriae achieving complete inhibition. In addition, the binding of vitronectin and fibronectin to CHOalphavbeta3 and CHOalpha5beta1 was inhibited by P. gingivalis cells. These results suggest that P. gingivalis fimbriae compete with ECM proteins for alphavbeta3- and alpha5beta1-integrins, and inhibit integrin/ECM protein-related cellular functions.

Single species biofilm-forming ability of root canal isolates on gutta-percha points

The participation of bacterial biofilms in the over-filled gutta-percha points associated with refractory periapical periodontitis has recently been reported. This study investigated the initial biofilm-forming ability of root canal isolates (Enterococcus faecalis, Streptococcus sanguis, Strep. intermedius, Strep. pyogenes, Staphylococcus aureus, Fusobacterium nucleatum, Propionibacterium acnes, Porphyromonas gingivalis and Prevotella intermedia) on gutta-percha points in vitro. Each bacterial strain was suspended in 100% cell culture medium or in culture medium containing 4.5, 45 or 90% (vol/vol) serum. The bacterial suspensions were then co-incubated anaerobically with gutta-percha points for 7 d. The gutta-percha points were processed for scanning electron microscopic observation and examined for biofilm presence and thickness. E. faecalis, Strep. sanguis, Strep. intermedius, Strep. pyogenes and Staph. aureus biofilms were generated on the surfaces of the specimens incubated in culture medium supplemented with 45 or 90% (vol/vol) serum. The E. faecalis and Strep. sanguis biofilms were significantly thicker than those of Strep. intermedius, Strep. pyogenes and Staph. aureus. No biofilms were detected on the specimens incubated with F. nucleatum, Prop. acnes, Porph. gingivalis and Prev. intermedia. These findings suggest that Gram-positive facultative anaerobes have the ability to colonize and form extracellular matrices on gutta-percha points, while serum plays a crucial role in biofilm formation.

8-oxo-7,8-dihydroguanine is removed by a nucleotide excision repair-like mechanism in Porphyromonas gingivalis W83

A consequence of oxidative stress is DNA damage. The survival of Porphyromonas gingivalis in the inflammatory microenvironment of the periodontal pocket requires an ability to overcome oxidative stress caused by reactive oxygen species (ROS). 8-oxo-7,8-dihydroguanine (8-oxoG) is typical of oxidative damage induced by ROS. There is no information on the presence of 8-oxoG in P. gingivalis under oxidative stress conditions or on a putative mechanism for its repair. High-pressure liquid chromatography with electrochemical detection analysis of chromosomal DNA revealed higher levels of 8-oxoG in P. gingivalis FLL92, a nonpigmented isogenic mutant, than in the wild-type strain. 8-oxoG repair activity was also increased in cell extracts from P. gingivalis FLL92 compared to those from the parent strain. Enzymatic removal of 8-oxoG was catalyzed by a nucleotide excision repair (NER)-like mechanism rather than the base excision repair (BER) observed in Escherichia coli. In addition, in comparison with other anaerobic periodontal pathogens, the removal of 8-oxoG was unique to P. gingivalis. Taken together, the increased 8-oxoG levels in P. gingivalis FLL92 could further support a role for the hemin layer as a unique mechanism in oxidative stress resistance in this organism. In addition, this is the first observation of an NER-like mechanism as the major mechanism for removal of 8-oxoG in P. gingivalis.

Inhibition ofPorphyromonas gingivalisHemagglutinating Activity by Synthetic Peptides Derived from Phage Display Selection Using MAb Against the Recombinant Outer Membrane Protein

Porphyromonas gingivalis has been implicated as an pathogen in the development of periodontitis, and hemagglutinins have been identified as an important adhesion onto the gingival tissue cells, and to attach and lyse erythrocytes to uptake Fe ion as an essential nutriant. The 40-kDa outer membrane protein (OMP) has been moleculary cloned from P. gingivalis 381. Since the antibody against recombinant (r) 40-kDa OMP inhibited the hemagglutinating activity, and the polymeric form of r40-kDa OMP itself expressed hemagglutinating activity, the 40-kDa OMP is thought to be one of the hemagglutinins. Moreover, we established MAbs against r40-kDa OMP which were capable of inhibiting hemagglutinating activity of P. gingivalis vesicles. In the present study, a phage-displayed epitope mapping system was used to identify the functional domain expressing hemagglutinating activity by biopanning using the neutralizing mAb, Pg-ompA1. The minimal epitope requirements of the MAb and the predicted amino acid sequences were identified in the region of (96)IALDQTLGIP(105) in 40-kDa OMP. Synthetic peptide, (87)WPRVGQLFIALDQTLGIPTFSVCRME(116), mapped the relevant molecule within a short stretch and is corresponding to residues of 40-kDa OMP. Chemically synthesized peptide was used to determine its inhibitory activity against hemagglutinating activity. The synthetic peptide significantly abolished hemagglutinating activity in a dose-dependent manner. These findings suggest that the synthetic peptide is an effective antagonist of erythrocyte binding, and this peptide may be a potent inhibitor of hemagglutination of P. gingivalis cells. The use of synthetic peptide neutralizing hemagglutinating activity of P. gingivalis represents a possible new therapeutic approach to P. gingivalis infected periodontitis.

Attachment of oral gram-negative anaerobic rods to a smooth titanium surface: an electron microscopy study

PURPOSE

Attachment of bacteria to titanium may differ not only between bacterial species but also between strains within a species. The aim of the present in vitro study was to examine differences in bacterial attachment using 4 gram-negative anaerobic species of bacteria that are considered potential periodontal pathogens.

MATERIALS AND METHODS

The attachment of clinical and laboratory strains (n = 23) representing 2 Fusobacterium nucleatum subspecies, Porphyromonas gingivalis, and Prevotella intermedia to smooth, commercially pure titanium was examined using scanning electron microscopy.

RESULTS

All bacterial strains were attached to the smooth titanium surface by their outer membrane. F nucleatum cells were poorly attached to the titanium, unlike P gingivalis or P intermedia cells, but only slight differences were observed in the quantity of attached cells between the strains within each bacterial group.

DISCUSSION

In favorable conditions, some anaerobes can attach directly to an inert titanium surface. Microbial adhesion and subsequent colonization on the dental implant surface can lead to infection of the peri-implant tissue.

CONCLUSION

The results indicated that the avidity of bacterial attachment to a smooth titanium surface varies between species of oral gram-negative anaerobes but not between strains.

Porphyromonas gingivalis strain-dependent activation of human endothelial cells

Porphyromonas gingivalis is an important bacterium involved in periodontal diseases. Colonization by periodontopathogens has been associated with severe local inflammatory reactions in the connective tissue. In this study we characterized P. gingivalis-mediated infection and activation of human umbilical vein endothelial cells by using two strains of different virulence capacities, strains ATCC 53977 and DSMZ 20709. Both strains were able to adhere to and infect endothelial cells with an infection rate of 0.48% for ATCC 53977 and 0.007% for DSMZ 20709. The triggering of two signal transduction pathways in P. gingivalis-infected endothelial cells was demonstrated for both strains, with a rapid increase of p38 mitogen-activated protein kinase phosphorylation and a more delayed degradation of IkappaBalpha, followed by nuclear translocation of NF-kappaB. In addition, both strains induced enhanced expression of endothelial adhesion molecules E-selectin and intracellular adhesion molecule 1 (ICAM-1). Target cell activation was independent of bacterial fimbriae expression since the fimA knockout strain A7436 DeltafimA induced the same level of ICAM-1 as the corresponding wild type (A7436-WT). Thus, two P. gingivalis strains, ATCC 53799 and DSMZ 20709, infect endothelial cells and trigger signaling cascades leading to endothelial activation, which in turn may result in or promote severe local and systemic inflammation.

Reduced expression of gamma interferon in serum and marked lymphoid depletion induced by Porphyromonas gingivalis increase murine morbidity and mortality due to cytomegalovirus infection

Porphyromonas gingivalis, a gram-negative anaerobe, is a major etiological agent of severe forms of periodontal disease. Although periodontal disease is considered a localized disease, accumulating evidence indicates that it may lead to a predisposition to a decline in immunocompetence. Human cytomegalovirus (CMV) commonly infects all human populations without producing significant clinical symptoms. Immunocompromised patients usually develop a primary or reactivated CMV infection, which is associated with high rates of morbidity and mortality. The aim of this study was to determine whether P. gingivalis increases animal susceptibility to CMV infection. Mice were inoculated with CMV and infected locally with P. gingivalis 3 days after the virus inoculation. Mortality rates were monitored, and traces of viral DNA and bacterial infection were detected systemically by using real-time PCR. Local and systemic cytokine secretion was measured, and histological sections were used to assess the pathological state of infected organs. P. gingivalis- and CMV-coinfected mice showed dramatically higher mortality rates than mice infected with P. gingivalis or CMV only. Although the organs of coinfected mice exhibited decreased viral titers, distinct necrosis and tissue damage were more evident in the livers and spleens of these mice than in those of mice infected with CMV only. Furthermore, systemic gamma interferon levels were decreased in coinfected mice, and marked lymphoid depletion was observed in their necrotic organs. In parallel control Escherichia coli-CMV coinfection experiments, the mortality and pathological results were the same as those found in mice infected with CMV only. Our results suggest a specific influence of P. gingivalis on the mouse immune response, causing increased susceptibility to CMV infection.

Inhibitory effects of green tea polyphenol (-)-epigallocatechin gallate on the expression of matrix metalloproteinase-9 and on the formation of osteoclasts

BACKGROUND

Alveolar bone resorption is a characteristic feature of periodontal diseases and involves the removal of both the mineral and organic constituents of the bone matrix, which is caused by either multinucleated osteoclast cells or matrix metalloproteinases (MMPs). The gram-negative bacterium, Porphyromonas gingivalis has been reported to stimulate the activity and expression of several groups of MMPs, whereas (-)-epigallocatechin gallate (EGCG), the main constituent of green tea polyphenols, has been reported to have inhibitory effects on the activity and expression of MMPs.

OBJECTIVES

In the present study, we investigated the effects of the green tea polyphenol, EGCG, on the gene expression of osteoblast-derived MMP-2, -9 and -13, stimulated by P. gingivalis, and on the formation of osteoclasts.

METHODS

The effect of EGCG on the gene expression of MMPs was examined by treating mouse calvarial primary osteoblastic cells with EGCG (20 microM) in the presence of sonicated P. gingivalis extracts. The transcription levels of MMP-2, -9 and -13 were assessed by reverse transcription-polymerase chain reaction (RT-PCR). The effect of EGCG on osteoclast formation was confirmed by tartrate-resistant acid phosphatase (TRAP) staining in a co-culture system of mouse bone marrow cells and calvarial primary osteoblastic cells.

RESULTS

Treatment with the sonicated P. gingivalis extracts stimulated the expression of MMP-9 mRNA and this effect was significantly reduced by EGCG, whereas the transcription levels of MMP-2 and MMP-13 were not affected by either the sonicated P. gingivalis extracts or EGCG. In addition, EGCG significantly inhibited osteoclast formation in the co-culture system at a concentration of 20 microM.

CONCLUSIONS

These findings suggest that EGCG may prevent the alveolar bone resorption that occurs in periodontal diseases by inhibiting the expression of MMP-9 in osteoblasts and the formation of osteoclasts.

The Relationship BetweenPorphyromonas gingivalisInfection and Local and Systemic Factors in Children

BACKGROUND

Porphyromonas gingivalis (P. gingivalis) is a major pathogen related to periodontitis. There are few reports on the prevalence and effect of P. gingivalis in children. The purpose of the present study was to describe in children the level of DNA-P gingivalis in subgingival plaque and the IgG serum reactivity to P. gingivalis (IgG-Pg), and examine their relationship to demographic, systemic, and oral variables.

METHODS

Thirty-four children, aged 1.83 to 13.42 years, were included in the study; 16 with no systemic disease and 18 with systemic conditions. The demographic data for caries incidence, plaque and gingival indices, probing depth, and alveolar bone height were recorded. The IgG-Pg and DNA-Pg levels were determined by enzyme-linked immunosorbent assay and DNA-DNA hybridization, respectively. The relationships between the IgG-Pg and DNA-Pg values to the demographics, oral parameters, and systemic conditions were examined.

RESULTS

IgG-Pg was evident in 53% of the children and DNA-Pg in 47%. IgG-Pg values significantly correlated positively with age, plaque index, and bone height. DNA-Pg values had statistically significant positive correlations with age. IgG-Pg and DNA-Pg values correlated with probing depth among children with systemic diseases. Neither the IgG-Pg nor the DNA-Pg values had a significant correlation to systemic conditions. Multiple regression analyses indicated that only age remained significantly related to IgG-Pg and DNA-Pg values.

CONCLUSIONS

P. gingivalis can be found in significant levels in the plaque of young children and elicits an immune reaction that increases with age and may be related to incipient signs of periodontal disease. Plaque DNA-Pg and serum IgG-Pg levels correlate significantly.

Herpesviral-bacterial interrelationships in aggressive periodontitis

BACKGROUND

Recent findings have begun to provide a basis for a causal link between herpesviruses and aggressive periodontitis. One theory is that herpesviruses cooperate with specific bacteria in the etiopathogenesis of the disease. This study examined whether the presence of herpesviruses [human cytomegalovirus (HCMV), Epstein-Barr virus (EBV) type 1, herpes simplex virus (HSV) type 1 and 2] is associated with the presence of putative pathogenic bacteria (Porphyromonas gingivalis, Prevotella intermedia, Tannerella forsythia, Campylobacter rectus, Actinobacillus actinomycetemcomitans) in aggressive periodontitis lesions.

METHODS

The study included 18 young adults with advanced periodontitis and 16 periodontally healthy subjects from Ankara, Turkey. Subgingival specimens pooled from two sites in each subject were collected by a periodontal curette. Qualitative polymerase chain reaction methodology was used to identify herpesviruses and bacteria. Chi-square tests were employed to determine statistical associations among herpesviruses, bacteria and periodontal disease.

RESULTS

HCMV, EBV-1 and HSV-1 were each detected in 72-78% of the aggressive periodontitis patients. HSV-2 occurred in 17% of the periodontitis patients. EBV-1 was detected in one periodontally healthy subject. The study bacteria occurred in 78-83% (P. gingivalis, T. forsythia, C. rectus) and in 44% (P. intermedia, A. actinomycetemcomitans) of the periodontitis samples, and in 0-19% of the samples from healthy periodontal sites. HCMV, EBV-1 and HSV-1 were positively associated with P. gingivalis, P. intermedia, T. forsythia and C. rectus, but not with A. actinomycetemcomitans. HSV-2 was not associated with any test bacteria.

CONCLUSIONS

These results support the notion that the clinical outcome of some types of severe periodontal infection depends on the presence of specific herpesviruses and bacterial pathogens. Our findings open the door to testing a variety of hypotheses regarding the deleterious aspects of combined herpesviral-bacterial infections in periodontal sites.

Essential role for the gtfA gene encoding a putative glycosyltransferase in the adherence of Porphyromonas gingivalis

Porphyromonas gingivalis, an oral bacterium, might play a role in the pathogenesis or progression of adult periodontitis. In this study, we isolated from P. gingivalis a putative glycosyltransferase gene, designated gtfA, which had a consensus domain for glycosyltransferase in its N terminus. GtfA consisted of 248 amino acids and its predicted molecular mass was 28 kDa; however, as the molecular mass of endogenous GtfA protein was around 40 kDa, this suggested that GtfA had undergone some posttranslational modifications. To reveal the role of the gtfA gene in P. gingivalis, we established gtfA-deficient strains by allelic replacement. Morphologically, gtfA-deficient P. gingivalis lacked mature fimbriae. gtfA-deficient P. gingivalis also showed a very low ability for autoaggregation, and its ability to attach to epithelial cells was severely impaired. Thus, the results indicate that the gtfA gene is required for P. gingivalis autoaggregation as well as attachment to epithelial cells. These results suggest that GtfA might have an important role in the pathogenicity of P. gingivalis by regulating adhesion.

Fimbriated Porphyromonas gingivalis is more efficient than fimbria-deficient P. gingivalis in entering human dendritic cells in vitro and induces an inflammatory Th1 effector response

Porphyromonas gingivalis is a fimbriated mucosal pathogen implicated in chronic periodontitis (CP). The fimbriae are required for invasion of the gingival mucosa and for induction of CP in animal models of periodontitis. CP is associated with infection of immature dendritic cells (DCs) by P. gingivalis in situ and with increased numbers of dermal DCs (DDCs) and mature DCs in the lamina propria. The role of fimbriae in gaining entry into human DCs and how this modulates the inflammatory and effector immune responses, however, have not been explored. To address this, we generated monocyte-derived DCs (MDDCs) in vitro which phenotypically and functionally resemble DDCs. We show here that virulent fimbriated P. gingivalis 381, in contrast to its fimbria-deficient mutant, P. gingivalis DPG3, efficiently gains entry to MDDCs in a manner dependent on active cell metabolism and cytoskeletal rearrangement. In addition, uptake of 381, unlike DPG3, induces DCs to undergo maturation, upregulate costimulatory molecules, and secrete inflammation cytokines interleukin-1beta (IL-1beta), IL-6, tumor necrosis factor alpha, IL-10, and IL-12. Moreover, MDDCs pulsed with 381 also stimulated a higher autologous mixed lymphocyte reaction and induced a Th1-type response, with gamma interferon (IFN-gamma) being the main cytokine. Monocytes used as controls demonstrated fimbria-dependent uptake of 381 as well but produced low levels of inflammatory cytokines compared to MDDCs. When MDDCs were pulsed with recombinant fimbrillin of P. gingivalis (10 micro g/ml), maturation of MDDCs was also induced; moreover, matured MDDCs induced proliferation of autologous CD4(+) T cells and release of IFN-gamma. Thus, these results establish the significance of P. gingivalis fimbriae in the uptake of P. gingivalis by MDDCs and in induction of immunostimulatory Th1 responses.

Glyceraldehyde-3-phosphate dehydrogenase of Streptococcus oralis functions as a coadhesin for Porphyromonas gingivalis major fimbriae

Cohesive interactions between Porphyromonas gingivalis and plaque-forming bacteria, such as Streptococcus oralis, are considered to play an important role in the colonization of P. gingivalis in periodontal sites. Although P. gingivalis fimbriae have been reported to mediate coaggregation with S. oralis, the S. oralis molecule involved has not been identified. We identified the coadhesin of S. oralis ATCC 9811 and purified it by affinity column chromatography. We found that the molecular mass of the purified protein was approximately 40 kDa. Dot blot and Western blot assays showed binding of the 40-kDa protein to P. gingivalis fimbriae. Further, turbidimetric assays showed that the coadhesin inhibited coaggregation between P. gingivalis and S. oralis in a dose-dependent manner. Analyses of the amino-terminal sequences of the protein and its lysyl endopeptidase-cleaved fragments revealed that the coadhesin was identical to glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Next, we cloned the gene that encodes S. oralis GAPDH and found that the sequence had a high degree of homology with the sequences of GAPDHs of various bacteria, including Streptococcus gordonii and Fusobacterium nucleatum. To confirm the contribution of S. oralis GAPDH to the interaction with P. gingivalis, a recombinant GAPDH protein was generated in Escherichia coli; this protein bound to P. gingivalis fimbriae and had an inhibitory effect on coaggregation. These results suggest that S. oralis GAPDH functions as a coadhesin for P. gingivalis fimbriae. In addition, considering the high degree of homology of the GAPDHs of various bacteria, those of other plaque-forming bacteria also may contribute to the colonization of P. gingivalis.

The effect of oxygen on the growth and physiology of Porphyromonas gingivalis

Oxygen constitutes a constant challenge for the survival of strict anaerobes in the oral environment. The aim of this study was to investigate the effect of oxygen on the physiology and growth of Porphyromonas gingivalis in a continuous culture system when grown under conditions of hemin limitation and excess. Results showed that, when grown in the presence of hemin at 0.5 mg/l, P. gingivalis could tolerate low levels of oxygen, being able to reach steady-state when 6% oxygen was present in the incoming gas mixture. When the hemin concentration was increased to 5 mg/l, the culture tolerated 10% oxygen. Anaerobically-grown cells were coccoid in shape, whereas those grown in the presence of oxygen were bacillary. Acetate was the predominant end-product in cultures grown in the presence of oxygen or in cultures hemin-limited. Despite some changes in the activity of Arg- and Lys-gingipain, most of the proteolytic activity was retained in the presence of oxygen. Activity of each of the three anti-oxidant enzymes tested (NADH oxidase, NADH peroxidase and SOD) was detected under all conditions and usually increased under oxygenated environments. Higher activities were also seen in the hemin-limited cultures. These results show some of the changes that occur in the physiology of P. gingivalis as a result of oxidative stress and confirm that hemin has a protective effect on the growth of the microorganism in the presence of oxygen.