PorphyromonasgingivalisLipopolysaccharide AntagonizesEscherichiacoliLipopolysaccharide at Toll-Like Receptor 4 in HumanEndothelialCells

Abstract

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 g/ml inhibited both E. coli LPS (10 ng/ml) and Mycobacterium tuberculosis heat shock protein (HSP) 60.1 (10 g/ml) stimulation of E-selectin mRNA expression in human umbilical vein endothelial cells (HUVEC) without inhibiting interleukin-1 beta (IL-1␤) stimulation. P. gingivalis LPS (1 g/ml) also blocked both E. coli LPS-dependent and M. tuberculosis HSP60.1-dependent but not IL-1␤-dependent activation of NF-B 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-B 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.The role that Porphyromonas gingivalis plays in the development of periodontal disease likely involves its ability to invade the gingiva and modulate innate host inflammatory responses via proteinases and lipopolysaccharide (LPS) (28,32,46,47). Previous studies have demonstrated that P. gingivalis disrupts the ability of gingival epithelial cells to produce interleukin-8 (IL-8) (8). These data suggest that such "chemokine paralysis" suppresses the host's ability to recruit and localize neutrophils to gingival sites of the infection via an IL-8 gradient (48). Gingival fibroblasts are likely to figure prominently in inflammatory responses to P. gingivalis. For example, P. gingivalis LPS has been shown to stimulate the production of a variety of cytokines, including IL-1, IL-6, and IL-8, in gingival fibroblasts, and it is chronic and excessive cytokine production that is believed to participate in tissue destruction during the course of periodontal disease (49). On the other hand, monocytes and human endothelial cells exhibit a low responsiveness to P. gingivalis LPS compared to E. coli LPS (7, 9, 30). In addition, in vivo studies demonstrated the low biological activity of P. gingivalis LPS in stimulating cytokine and adhesion molecule expression in mice (38).Another key property of P. gingivalis LPS is that it not only fails to stimulate E-selectin expression or p38 mitogen-activated protein kinase activation in human umbilical endothelial cells (HUVEC), but can potently antagonize the ability of E. coli LPS...

Toll-Like Receptor 4 on Nonhematopoietic Cells Sustains CNS Inflammation during Endotoxemia, Independent of Systemic Cytokines

“…1). The exact identity of TLR4-bearing cells at these locations is unresolved and, similar to peripheral tissues, may include myeloid (Rehli et al, 2000;Oshikawa and Sugiyama, 2003), endothelial (Faure et al, 2001;Coats et al, 2003), or epithelial (Cario and Podolsky, 2000;Song et al, 2001) lineages. One novel finding from the highresolution analysis of TLR4 distribution was its presence in parenchymal microglial cells but not astrocytes in the brain parenchyma.…”

Critical Role of Apoptotic Speck Protein Containing a Caspase Recruitment Domain (ASC) and NLRP3 in Causing Necrosis and ASC Speck Formation Induced by Porphyromonas gingivalis in Human Cells

“…Where indicated, cells were treated for 24 -72 h with P. gingivalis strain A7436, Escherichia coli or Salmonella typhi at the indicated multiplicity of infection (MOI), with 0.1-1 M staurosporine (Sigma-Aldrich), or with 0.01 or 0.1 g/ml Ultrapure P. gingivalis LPS (InvivoGen). P. gingivalis LPS was purified from strain ATCC33277 (12) according to the manufacturer's instructions and would be expected to function as either a TLR2 or a TLR4 agonist (InvivoGen). ApoAlert VAD-fmk (pan-caspase inhibitor; 10 M) or YVAD-cmk (caspase-1 inhibitor; both from BD Clontech) or 10 g/ml IL-1 receptor antagonist Anakinra (Kineret; Amgen) was added 2 h before P. gingivalis where indicated.…”

“…3A). The P. gingivalis LPS is purified from strain ATCC33277 according to the method of Coats et al (12) and should be composed of lipid A species that are both agonists of TLR2 and TLR4. THP1 cells treated with P. gingivalis LPS appeared to clump together, a phenomenon not observed in bacteria exposed cells.…”

Human Schistosomiasis Is Associated with Endotoxemia and Toll-Like Receptor 2- and 4-Bearing B Cells

“…The number of acyl chains on lipid A, the inflammatory moiety of LPS, can dictate whether LPS is agonistic or antagonistic. 23 For example, lipid A from Escherichia coli is hyperacylated with six acyl chains that mediate inflammatory pathways through TLR4. In contrast, lipid A from various species of commensal bacteria may be hypoacylated and act in an antiinflammatory manner.…”

“…In contrast, lipid A from various species of commensal bacteria may be hypoacylated and act in an antiinflammatory manner. 23 In fact, in Crohn's disease (CD), systemic LPS may be immunosuppressive for B cells through a reduced systemic LPS lipid A acylation burden. 22 We sought to determine if B cells were modified in human schistosomiasis and the potential effect of this disease on measurable TLR ligands in the bloodstream.…”