Sensitization of human aortic endothelial cells to lipopolysaccharide via regulation of Toll-like receptor 4 by bacterial fimbria-dependent invasion

Toll-like receptors (TLRs) are differentially up-regulated in response to microbial infection and chronic inflammatory diseases such as atherosclerosis. Epidemiological data support the idea that periodontal disease may be a risk factor for acceleration of atherosclerosis. Porphyromonas gingivalis, the etiological agent of periodontal disease, invades endothelium, has been detected in human atheromatous tissue, and accelerates atheroma formation in apolipoprotein E-/- mice with concurrent induction of TLRs in the aorta. As endothelial cells can present antigen via TLRs and play an important role in the development of atherosclerosis, we examined TLR expression in human aortic endothelial cells (HAEC) cultured with wild-type P. gingivalis, a fimbria-deficient mutant, and purified antigens. We observed increased TLR expression in HAEC infected with wild-type P. gingivalis by fluorescence-activated cell sorter, but not with noninvasive, fimbria-deficient mutant or purified P. gingivalis antigens. Following a wild-type P. gingivalis challenge, functional TLR2 and TLR4 activation was assessed by subsequent stimulation with TLR agonists Staphylococcus aureus lipoteichoic acid (SLTA; TLR2 ligand) and Escherichia coli lipopolysaccharide (LPS; TLR4 ligand). Unchallenged HAEC failed to elicit monocyte chemoattractant protein 1 (MCP-1) in response to LPS or SLTA but did so when cultured with wild-type P. gingivalis. P. gingivalis-induced TLR2 and -4 expression on HAEC functionally reacted to SLTA and E. coli LPS as measured by a further increase in MCP-1 production. Furthermore, MCP-1 expression elicited by E. coli LPS was inhibitable with TLR4-specific antibody and polymyxin B. These results indicate that invasive P. gingivalis stimulates TLR expression on the surface of endothelium and these primed cells respond to defined TLR-specific ligands.     

Fimbria-Dependent Activation of Cell Adhesion Molecule Expression in Porphyromonas gingivalis-Infected Endothelial Cells

Porphyromonas gingivalis is an oral pathogen that has recently been associated with chronic inflammatory diseases such as atherosclerosis. The strength of the epidemiological associations of P. gingivalis with atherosclerosis can be increased by the demonstration that P. gingivalis can initiate and sustain growth in human vascular cells. We previously established that P. gingivalis can invade aortic, heart, and human umbilical vein endothelial cells (HUVEC), that fimbriae are required for invasion of endothelial cells, and that fimbrillin peptides can induce the expression of the chemokines interleukin 8 and monocyte chemotactic protein. In this study, we examined the expression of surface-associated cell adhesion molecules on endothelial cells in response to P. gingivalis infection by fluorescence-activated cell sorting FACS analysis and confocal microscopy. Coculture of HUVEC with P. gingivalis strain 381 or A7436 resulted in the induction in the expression of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and P- and E-selectins, which was maximal at 48 h postinfection. In contrast, we did not observe induction of ICAM-1, VCAM-1, or P- or E-selectin expression in HUVEC cultured with the noninvasive P. gingivalis fimA mutant DPG3 or when P. gingivalis was incubated with fimbrillin peptide-specific anti-sera prior to the addition to HUVEC. Furthermore, the addition of a peptide corresponding to the N-terminal domain of fimbrillin to HUVEC resulted in an increase in ICAM-1, VCAM-1, and P- and E-selectins, which was maximal at 48 h and similar to that observed for live P. gingivalis. Treatment of P. gingivalis-infected HUVEC with cytochalsin D, which prevented P. gingivalis invasion, also resulted in the inhibition of ICAM-1, VCAM-1, or P- and E-selectin expression. Taken together, these results indicate that active P. gingivalis invasion of HUVEC mediated via the major fimbriae stimulates surface-associated cell adhesion molecule expression. Stimulation of adhesion molecules involved in the recruitment of leukocytes to sites of inflammation by P. gingivalis may play a role in the pathogenesis of systemic inflammatory diseases associated with this microorganism, including atherosclerosis.     

Porphyromonas gingivalis lipopolysaccharide antagonizes Escherichia coli lipopolysaccharide at toll-like receptor 4 in human endothelial cells

E. coli lipopolysaccharide (LPS) induces cytokine and adhesion molecule expression via the toll-like receptor 4 (TLR4) signaling complex in human endothelial cells. In the present study, we investigated the mechanism by which Porphyromonas gingivalis LPS antagonizes E. coli LPS-dependent activation of human endothelial cells. P. gingivalis LPS at 1 micro g/ml inhibited both E. coli LPS (10 ng/ml) and Mycobacterium tuberculosis heat shock protein (HSP) 60.1 (10 micro g/ml) stimulation of E-selectin mRNA expression in human umbilical vein endothelial cells (HUVEC) without inhibiting interleukin-1 beta (IL-1beta) stimulation. P. gingivalis LPS (1 micro g/ml) also blocked both E. coli LPS-dependent and M. tuberculosis HSP60.1-dependent but not IL-1beta-dependent activation of NF-kappaB in human microvascular endothelial (HMEC-1) cells, consistent with antagonism occurring upstream from the TLR/IL-1 receptor adaptor protein, MyD88. Surprisingly, P. gingivalis LPS weakly but significantly activated NF-kappaB in HMEC-1 cells in the absence of E. coli LPS, and the P. gingivalis LPS-dependent agonism was blocked by transient expression of a dominant negative murine TLR4. Pretreatment of HUVECs with P. gingivalis LPS did not influence the ability of E. coli LPS to stimulate E-selectin mRNA expression. Taken together, these data provide the first evidence that P. gingivalis LPS-dependent antagonism of E. coli LPS in human endothelial cells likely involves the ability of P. gingivalis LPS to directly compete with E. coli LPS at the TLR4 signaling complex.     

Modulation of an interleukin-12 and gamma interferon synergistic feedback regulatory cycle of T-cell and monocyte cocultures by Porphyromonas gingivalis lipopolysaccharide in the absence or presence of cysteine proteinases

Interleukin 12 (IL-12) is an efficient inducer and enhancer of gamma interferon (IFN-gamma) production by both resting and activated T cells. There is evidence that human monocytes exposed to IFN-gamma have enhanced ability to produce IL-12 when stimulated with lipopolysaccharide (LPS). In this study, it was demonstrated that LPS from the oral periodontal pathogen Porphyromonas gingivalis stimulated monocytes primed with IFN-gamma to release IL-12, thereby enhancing IFN-gamma accumulation in T-cell populations. P. gingivalis LPS was shown to enhance IL-12 induction of IFN-gamma in T cells in a manner independent from TNF-alpha contribution. The levels of T-cell IL-12 receptors were not affected by P. gingivalis LPS and played only a minor role in the magnitude of the IFN-gamma response. These data suggest that LPS from P. gingivalis establishes an activation loop with IL-12 and IFN-gamma with potential to augment the production of inflammatory cytokines in relation to the immunopathology of periodontitis. We previously reported that the major cysteine proteinases (gingipains) copurifying with LPS in this organism were responsible for reduced IFN-gamma accumulation in the presence of IL-12. However, the addition of the gingipains in the presence of LPS resulted in partial restoration of the IFN-gamma levels. In the destructive periodontitis lesion, release of gingipains from the outer membrane (OM) of P. gingivalis could lead to the downregulation of Th1 responses, while gingipain associated with LPS in the OM or in OM vesicles released from the organism could have net stimulatory effects.     

Porphyromonas gingivalis lipopolysaccharides induce maturation of dendritic cells with CD14+CD16+ phenotype

Primary immune responses are initiated by dendritic cells (DC) that inform naive T helper cells about invading pathogens. DC undergo sequential events leading to irreversible maturation upon bacterial stimulation. To investigate the responses of DC during periodontal infection, we studied the effects of LPS from Porphyromonas gingivalis on DC. DC generated from human peripheral monocytes by culture with IL-4 and GM-CSF were incubated with P. gingivalis LPS (Pg LPS) or Escherichia coli LPS (Ec LPS). Flow cytometry and real-time quantitative RT-PCR analysis revealed that Pg LPS, but not Ec LPS, preferentially up-regulated CD14 and CD16 expression at protein and mRNA levels. Furthermore, Pg LPS preferentially induced the secretion of soluble CD14. CD1a, HLA-DR and CD54 were highly expressed on DC stimulated with both kinds of LPS; however, CD40, CD80, CD83 and CD86 expression on Pg LPS-stimulated DC was lower than on Ec LPS-stimulated DC. With regard to IL-6, IL-8, IL-10, IL-12 and RANTES production from DC and allogeneic T cell proliferation, Pg LPS was a weaker stimulator than Ec LPS. These results suggested that Pg LPS triggers maturation of DC with unique characteristics, which exhibited weak immunostimulatory activity and may contribute to induction of chronic inflammation at the site of periodontal infection.     

牙龈卟啉单胞菌在单核细胞对内皮细胞黏附作用中的影响

目的 观察牙龈卟啉单胞菌(P.gingivalis)W83和ATCC33277株侵入在单核细胞对内皮细胞黏附作用中的影响,及在内皮细胞细胞间黏附分子l(ICAM-1)转录和翻译中的作用. 方法 建立体外P.gingivalis侵入内皮细胞模型,孟加拉玫瑰红活细胞染色法测定P.gingivalis侵入前后单核细胞对内皮细胞黏附的变化;RT-PCR和mRNA比色定量法检测内皮细胞ICAM-1基因表达;West-ern blot检测ICAM-1蛋白水平的变化. 结果 P.gingivalis W83和ATCC33277株侵入可增加单核细胞对内皮细胞的黏附,抗ICAM-1抗体部分抑制P.gingivalis侵入介导的单核细胞对内皮细胞黏附增加;P.gingivalis侵入上调内皮细胞ICAM-l基因和蛋白的表达,W83诱导单核细胞对内皮细胞黏附增强及内皮细胞ICAM-1表达的能力强于ATCC33277. 结论 ICAM-1在P.gingivalis介导的单核细胞对内皮细胞黏附增强过程中起部分作用,P.gingivalis侵入内皮细胞诱导ICAM-1表达可能是其诱发动脉粥样硬化疾病的机制之一.     

Translocation of Porphyromonas gingivalis infected monocytes and associated cellular responses

Porphyromonas gingivalis (P. gingivalis), an important periodontal pathogen in adult chronic periodontitis, has been reported to colocalize in human atheromatous lesions. We have studied the phagocytosis and survival of P. gingivalis in human monocytes, together with the cellular responses of infected human monocytes. Human monocytes were cocultured with P. gingivalis and the external bacteria were killed with metronidazole and gentamycin. Localization of P. gingivalis in cells was studied by transmission electron microscopy (TEM). The survival of P. gingivalis was determined by lysing the monocytes and plating on blood agar under anaerobic conditions. Interleukin-1 beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) were determined using specific enzyme-linked immunosorbent assays (ELISAs) kits. The transwell chamber system was used to investigate the chemotactic response of the infected cells. TEM showed that P. gingivalis organisms were localized within the autophagosome-like structure of monocytes. No significant difference on the survival of P. gingivalis at 0, 4 and 8 h after infection was found. IL-1beta and TNF-alpha were present in the cell culture media in response to bacterial challenge. The infected monocytes showed a normal chemotactic response to monocyte chemotactic protein-1 (MCP-1). The number of monocyte cells migrating through membrane in the presence and absence of P. gingivalis were 18.64 +/- 2.33 x 10(4) cells and 19.11 +/- 1.76 x 10(4) cells respectively. The number of viable P. gingivalis per monocyte following translocation in response to the chemotactic gradient was 5.83 +/- 1.45 x 10(-3) CFU/cell. The results indicate that P. gingivalis can stimulate cytokine production and survive in monocytes without affecting cell migration.     

Porphyromonas gingivalis lipopolysaccharide is both agonist and antagonist for p38 mitogen-activated protein kinase activation

Lipopolysaccharide (LPS) is a key inflammatory mediator. It has been proposed to function as an important molecule that alerts the host of potential bacterial infection. Although highly conserved, LPS contains important structural differences among different bacterial species that can significantly alter host responses. For example, LPS obtained from Porphyromonas gingivalis, an etiologic agent for periodontitis, evokes a highly unusual host cell response. Human monocytes respond to this LPS by the secretion of a variety of different inflammatory mediators, while endothelial cells do not. In addition, P. gingivalis LPS inhibits endothelial cell expression of E-selectin and interleukin 8 (IL-8) induced by other bacteria. In this report the ability of P. gingivalis LPS to activate p38 mitogen-activated protein (MAP) kinase was investigated. It was found that p38 MAP kinase activation occurred in response to P. gingivalis LPS in human monocytes. In contrast, no p38 MAP kinase activation was observed in response to P. gingivalis LPS in human endothelial cells or CHO cells transfected with human Toll-like receptor 4 (TLR-4). In addition, P. gingivalis LPS was an effective inhibitor of Escherichia coli-induced p38 MAP kinase phosphorylation in both endothelial cells and CHO cells transfected with human TLR-4. These data demonstrate that P. gingivalis LPS activates the LPS-associated p38 MAP kinase in monocytes and that it can be an antagonist for E. coli LPS activation of p38 MAP kinase in endothelial and CHO cells. These data also suggest that although LPS is generally considered a bacterial component that alerts the host to infection, LPS from P. gingivalis may selectively modify the host response as a means to facilitate colonization.     

Interleukin-8 and intercellular adhesion molecule 1 regulation in oral epithelial cells by selected periodontal bacteria: multiple effects of Porphyromonas gingivalis via antagonistic mechanisms

Interaction of bacteria with mucosal surfaces can modulate the production of proinflammatory cytokines and adhesion molecules produced by epithelial cells. Previously, we showed that expression of interleukin-8 (IL-8) and intercellular adhesion molecule 1 (ICAM-1) by gingival epithelial cells increases following interaction with several putative periodontal pathogens. In contrast, expression of IL-8 and ICAM-1 is reduced after Porphyromonas gingivalis ATCC 33277 challenge. In the present study, we investigated the mechanisms that govern the regulation of these two molecules in bacterially infected gingival epithelial cells. Experimental approaches included bacterial stimulation of gingival epithelial cells by either a brief challenge (1.5 to 2 h) or a continuous coculture throughout the incubation period. The kinetics of IL-8 and ICAM-1 expression following brief challenge were such that (i) secretion of IL-8 by gingival epithelial cells reached its peak 2 h following Fusobacterium nucleatum infection whereas it rapidly decreased within 2 h after P. gingivalis infection and remained decreased up to 30 h and (ii) IL-8 and ICAM-1 mRNA levels were up-regulated rapidly 2 to 4 h postinfection and then decreased to basal levels 8 to 20 h after infection with either Actinobacillus actinomycetemcomitans, F. nucleatum, or P. gingivalis. Attenuation of IL-8 secretion was facilitated by adherent P. gingivalis strains. The IL-8 secreted from epithelial cells after F. nucleatum stimulation could be down-regulated by subsequent infection with P. gingivalis or its culture supernatant. Although these results suggested that IL-8 attenuation at the protein level might be associated with P. gingivalis proteases, the Arg- and Lys-gingipain proteases did not appear to be solely responsible for IL-8 attenuation. In addition, while P. gingivalis up-regulated IL-8 mRNA expression, this effect was overridden when the bacteria were continuously cocultured with the epithelial cells. The IL-8 mRNA levels in epithelial cells following sequential challenge with P. gingivalis and F. nucleatum and vice versa were approximately identical and were lower than those following F. nucleatum challenge alone and higher than control levels or those following P. gingivalis challenge alone. Thus, together with the protease effect, P. gingivalis possesses a powerful strategy to ensure the down-regulation of IL-8 and ICAM-1.     

Monocyte chemoattractant protein 1 and interleukin-8 production in mononuclear cells stimulated by oral microorganisms.

Chemokines are a family of low-molecular-weight proinflammatory cytokines that stimulate recruitment of leukocytes. The chemokines interleukin-8 (IL-8) and monocyte chemoattractant protein 1 (MCP-1) are relatively specific chemoattractants for neutrophils and monocytes, respectively. Chemokine expression contributes to the presence of different leukocyte populations observed in normal and pathologic states. In the present studies, peripheral blood mononuclear cells (PBMC) were stimulated by microbes (Candida albicans, Streptococcus mutans, Porphyromonas gingivalis, and Actinobacillus actinomycetemcomitans) selected based upon their importance as oral pathogens. IL-8 and MCP-1 gene expression and protein release were determined by Northern blot (RNA blot) analysis and enzyme-linked immunosorbent assay. C. albicans, P. gingivalis, and A. actinomycetemcomitans induced high levels of production of both MCP-1 and IL-8. S. mutans was a strong inducer of MCP-1, but it did not stimulate significant production of IL-8. C. albicans, S. mutans, and A. actinomycetemcomitans were 500 to 5,000 times more potent than P. gingivalis in terms of MCP-1 production. In general, the microbe-to-PBMC ratios required for maximum gene expression of MCP-1 were lower than those for IL-8. However, for actual protein release of MCP-1 versus IL-8, differences in the effects of various microbe concentrations were observed only for A. actinomycetemcomitans. These results demonstrate that different oral pathogens induce specific dose-dependent patterns of chemokine gene expression and release. Such patterns may help explain the immunopathology of oral infections, particularly with regard to inflammatory leukocyte recruitment.     

Porphyromonas gingivalis-induced inflammatory mediator profile in an ex vivo human whole blood model

Periodontitis is characterized by an accumulation of inflammatory cells in periodontal tissue and subgingival sites. Leukocytes play a major role in the host response to Porphyromonas gingivalis, a major aetiological agent of chronic periodontitis. Secretion of high levels of inflammatory mediators, including cytokines and prostaglandins, by leucocytes is believed to contribute to periodontal tissue destruction. The aim of this study was to investigate the inflammatory response of an ex vivo whole blood model to P. gingivalis stimulation. The production of interleukin-1 beta (IL-1beta), IL-4, IL-5, IL-6, IL-8, IL-10, IL-12p70, IL-13, tumour necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma), IFN-gamma-inducible protein 10 (IP-10), monocyte chemoattractant protein-1 (MCP-1), Regulated on Activation Normal T cell Expressed and Secreted (RANTES) and prostaglandin E2 (PGE2) were quantified by enzyme-linked immunosorbent assays. P. gingivalis induced the secretion of the pro-inflammatory cytokines IL-1beta, TNF-alpha, IL-6 and IFN-gamma, the chemokines IL-8, RANTES and MCP-1 and the inflammatory mediator PGE2 in an ex vivo human whole blood model. The secretion levels were dependent on the strain and the infectious dose used. While the mediator profiles were comparable between six healthy subjects, a high interindividual variability in the levels of secreted mediators was observed. This study supports the view that P. gingivalis, by inducing high levels of inflammatory mediators from a mixed leucocyte population, can contribute to the progression of periodontitis.     

LPS、TNF-α、IL-1β对人脐静脉内皮细胞COX-2表达的影响

目的:探讨LPS、TNF-α、IL-1β对人脐静脉内皮细胞(HUVEC)环氧合酶2(COX-2)表达及前列腺素(PGs)的影响。方法:在分离培养的HUVEC细胞给予LPS、TNF-α、IL-1β刺激24h后,采用原位杂交、逆转录-聚合酶链反应(RT-PCR)、免疫组化检测HUVECCOX-2mRNA及蛋白的表达并观察了培养液前列腺素(PGs)的变化。结果:静息状态的HUVEC表达极少量的COX-2;受炎性刺激后,HUVEC大量表达COX-2mRNA及蛋白,同时伴有PGs的升高。结论:结果提示,静息状态下HUVEC表达极少量的COX-2,炎性刺激可诱发COX-2高表达和PGs升高,因此内皮细胞可通过COX-2的调节参与炎症反应。     

Role for Porphyromonas gingivalis in the progression of atherosclerosis

An association between atherosclerosis and Porphyromonas gingivalis (P. gingivalis), a major periodontopathogen, has been shown. However, the question of whether this relationship is causal or coincidental still exist. Many individuals with evidence of atherosclerosis demonstrate seropositivity to this pathogen. Both in vitro studies and in animal models document that P. gingivalis can accelerate atheroma deposition. Recently, evidence from diverse sources has suggested P. gingivalis can activate host innate immune responses associated with atherosclerosis. These studies confirm that the inflammatory response to P. gingivalis could exacerbate vascular inflammation via secreted cytokines and/or chemokines that ultimately modulate early atherogenesis that spontaneously develop atherosclerosis. Meanwhile, the cytokine and chemokines interact in the progression of atherosclerosis. Moreover, the reaction of endothelial cells in response to P. gingivalis and its various virulence factors are diverse, the expression of chemokine differ through different signal transduction pathways accordingly. Results from these studies reinforce the connection between P. gingivalis and atherosclerosis. Given the role of P. gingivalis in the initiation and progression of atherosclerosis, attaching importance to periodontal disease may offer new therapeutic options for the management of patients with atherosclerosis.     

Assessment of internalization and viability of Porphyromonas gingivalis in KB epithelial cells by confocal microscopy

Porphyromonas gingivalis (P. gingivalis) is considered to be one of the main periodontal pathogens. The goal of this work was to confirm the ability of P. gingivalis to invade host cells. We detected P. gingivalis inside KB cells by confocal microscopy and analyzed the various aspects of the adherence and internalization process. Lysates of P. gingivalis-infected KB cells were also examined using anaerobic growth techniques. The results showed the viability and ability to replicate, inside the host cells, of the internalized pathogen. The production of vesicles was also tracked for the first time. Confocal microscopy revealed P. gingivalis in a perinuclear position.     

Cytokine profiling of macrophages exposed to Porphyromonas gingivalis, its lipopolysaccharide, or its FimA protein

To characterize the roles of Porphyromonas gingivalis and its components in the disease processes, we investigated the cytokine profile induced by live P. gingivalis, its lipopolysaccharides (LPS), and its major fimbrial protein, fimbrillin (FimA). Using cytokine antibody arrays, we found that P. gingivalis LPS and FimA induced a similar profile of cytokine expression when exposed to mouse peritoneal macrophages but that this profile differed significantly in response to live P. gingivalis. In vitro, mouse peritoneal macrophages were stimulated to produce interleukin-6 (IL-6), granulocyte colony-stimulating factor, and lymphotactin by live P. gingivalis, but not by P. gingivalis LPS or FimA, while RANTES, gamma interferon, IL-17, vascular cell adhesion molecule 1 (VCAM-1), and vascular endothelial growth factor were induced by P. gingivalis LPS or FimA, but not by live P. gingivalis. In vivo, IL-6 mRNA was strongly induced only by live P. gingivalis while monocyte chemoattractant protein 1 mRNA was strongly induced only by P. gingivalis LPS and FimA in mouse calvarial scalp, further confirming the differences of cytokine profile induced in vitro. Cytokine antibody arrays using toll-like receptor 2 (TLR2)- and TLR4-deficient macrophages revealed that most of the cytokines induced by P. gingivalis LPS or FimA signal through TLR2, while most of cytokines induced by live P. gingivalis signal through both TLR2 and TLR4. Interestingly, the activation of TLR2 by live P. gingivalis inhibited the release of RANTES, VCAM-1, and IL-1alpha from mouse peritoneal macrophages. A tumor necrosis factor alpha enzyme-linked immunosorbent assay further confirmed that P. gingivalis LPS and FimA activate mouse peritoneal macrophages via TLR2. These results indicate that host immune cells sense live P. gingivalis and its components differently, which translates into the expression of different inflammatory cytokine profiles.