Endotoxins and Disease Mechanisms

231

208

Genetic evidence indicating that TOLL-like receptor 4 (Tlr4) is the lipopolysaccharide (LPS) receptor in mice was reported. However, biochemical evidence that murine Tlr4 confers LPS responsiveness has not been convincingly demonstrated. Inducible cyclooxygenase (COX-2) is selectively expressed in LPS-stimulated macrophages in part mediated through the activation of NFB. Thus, we determined whether murine Tlr4 confers LPS responsiveness as evaluated by the activation of NFB and COX-2 expression. Transfection of a murine macrophage-like cell line (RAW264.7) with the constitutively active form (⌬Tlr4) of Tlr4 is sufficient to activate NFB and COX-2 expression. However, the truncated form (⌬Tlr4(P712H)) of the missense mutant Tlr4(P712H) found in LPS-hyporesponsive mouse strain (C3H/HeJ) inhibits LPS-induced NFB activation and COX-2 expression. The inability of ⌬Tlr4(P712H) to activate NFB and induce COX-2 expression is rescued by a constitutively active adapter protein myeloid differentiation factor 88 (MyD88), which interacts directly with the cytoplasmic domain of Tlr proteins. Furthermore, MyD88 is co-immunoprecipitated with the wild-type ⌬Tlr4 but not with the ⌬Tlr4(P712H) mutant. Together, these results indicate that Tlr4 confers LPS responsiveness in RAW264.7 cells and suggest that hyporesponsiveness of C3H/HeJ mice to LPS is attributed to the disruption of Tlr4-mediated signaling pathways that results from the inability of the mutant Tlr4(P712H) to interact with MyD88.

mentioning

confidence: 99%

Murine TOLL-like Receptor 4 Confers Lipopolysaccharide Responsiveness as Determined by Activation of NFκB and Expression of the Inducible Cyclooxygenase

Rhee

Hwang

2000

231

208

“…LPS mediates a number of biologic manifestations of sepsis, including fever, hypotension, multiple organ failure, shock, and death (3). These effects of endotoxin are believed to result from an uncontrolled production of proinflammatory cytokines produced by cells of the reticuloendothelial system, particularly macrophages.…”

mentioning

confidence: 99%

Genetic Deletion of the Tumor Necrosis Factor Receptor p60 or p80 Sensitizes Macrophages to Lipopolysaccharide-induced Nuclear Factor-κB, Mitogen-activated Protein Kinases, and Apoptosis

Takada

Aggarwal

2003

Whether deletion of tumor necrosis factor (TNF) receptor 1 or 2 affects lipopolysaccharide (LPS)-mediated signaling is not understood. In this report, we used macrophages derived from wild type (wt) mice and from mice null for the type 1 receptor (p60 ؊/؊ ), the type 2 receptor (p80 ؊/؊ ), or both (p60 ؊/؊ p80 ؊/؊ ) to investigate the effect of these receptors on LPS-mediated activation of NF-B, mitogen-activated protein kinases, and apoptosis. LPS activated NF-B by 3-4-fold in wt cells but by 9 -10-fold in p60 ؊/؊ , p80 ؊/؊ , and p60 ؊/؊ p80 ؊/؊ macrophages. These results correlated with the I B␣ kinase activation, which is needed for NF-B activation. LPSinduced cyclooxygenase-2 and inducible NO synthase proteins and NO production were maximum in p60 ؊/؊ p80 ؊/؊ macrophages and minimum in wt cells. LPS activated C-Jun N-terminal kinase, p38 MAPK , and extracellular signal-regulated kinase in wt cells, but the levels were much higher in p60 ؊/؊ , p80 ؊/؊ , and p60 ؊/؊ p80 ؊/؊ cells. LPS-induced cytotoxicity, poly(ADP-ribose) polymerase cleavage, and annexin V staining were also highest in p60 ؊/؊ p80 ؊/؊ cells and lowest in wt cells. The difference in LPS signaling was unrelated to the expression of LPS receptors, CD14, or toll-like receptor 4. Overall, our studies indicate that deletion of either of the TNF receptors sensitizes the macrophages to LPS and provide evidence for cross-talk between TNF and LPS signaling.It has been known for decades that Gram-negative bacteria and their component lipopolysaccharides (LPS) 1 have antitumor properties in vivo and that these properties are mediated primarily through production of tumor necrosis factor (TNF) (1, 2). LPS or endotoxin is a glycolipid and is an integral component of the outer membrane of Gram-negative bacteria.LPS mediates a number of biologic manifestations of sepsis, including fever, hypotension, multiple organ failure, shock, and death (3). These effects of endotoxin are believed to result from an uncontrolled production of proinflammatory cytokines produced by cells of the reticuloendothelial system, particularly macrophages. LPS-dependent macrophage activation results in the release of TNF, IL-1, IL-6, IL-8, IL-10, and IL-12.LPS interacts with most cells through CD14, a 55-kDa glycosylphosphatidylinositol-anchored protein expressed on the surface of monocytes and neutrophils (4, 5). The binding of LPS to CD14 is enhanced by the LPS-binding protein present in the serum (5, 6). Mice that lack the CD14 gene show resistance to LPS-induced shock (7). LPS is then transferred to the transmembrane signaling receptor toll-like receptor 4 (TLR4) and its accessory protein MD2 (8 -10). LPS stimulation of human monocytes activates several intracellular signaling pathways that include the I B kinase (IKK)-NF-B pathway (11-15) and three mitogen-activated protein kinase (MAPK) pathways: p42/p44 MAPK /extracellular signal-regulated kinases 1 and 2 (ERK1/2) (16 -21), stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) (22), and p38 MAPK (23,24).Both LPS ...

“…Lipopolysaccharide (LPS) 1 is one of the toxic principles of Gram-negative bacteria (1), and is a classic example of an initiator of septic shock. Shock triggered by LPS administration is often called endotoxin shock.…”

mentioning

confidence: 99%

Syndecan-4 Deficiency Leads to High Mortality of Lipopolysaccharide-injected Mice

Ishiguro¹,

Kadomatsu²,

Kojima³

et al. 2001

118

Syndecan-4 is a transmembrane heparan sulfate proteoglycan belonging to the syndecan family. Following intraperitoneal injection of lipopolysaccharide (LPS), syndecan-4-deficient mice exhibited high mortality compared with wild-type controls. Severe endotoxin shock was observed in the deficient mice: systolic blood pressure and left ventricular fractional shortening were lower in the deficient mice than in the wild-type controls 9 h after LPS injection. Although histological examinations revealed no apparent differences between two groups, the plasma level of interleukin (IL)-1␤ was higher in the deficient mice than in the wild-type controls 9 h after LPS injection. Consistent with the regulatory roles of syndecan-4, its expression in monocytes and endothelial cells of microvasculature increased in the wild-type mice after LPS administration. Although IL-1␤ was produced to the same extent by macrophages from syndecan-4-deficient and wild-type mice after LPS stimulation, inhibition of its production by transforming growth factor-␤1 was impaired in the syndecan-4-deficient macrophages. These results indicate that syndecan-4 could be involved in prevention of endotoxin shock, at least partly through the inhibitory action of transforming growth factor-␤1 on IL-1␤ production.