SumlnaryCD14 is a 55-kD protein found as a glycosylphosphatidylinositol (GPI)-anchored protein on the surface of monocytes, macrophages, and polymorphonuclear leukocytes, and as a soluble protein in the blood. Both forms of CD14 participate in the serum-dependent responses of cells to bacterial lipopolysaccharide (LPS). While CD14 has been described as a receptor for complexes of LPS with LPS-binding protein (LBP), there has been no direct evidence showing whether a ternary complex of LPS, LBP, and CD14 is formed, or whether CD14 binds LPS directly. Using nondenaturing polyacrylamide gel electrophoresis (native PAGE), we show that recombinant soluble CD14 (rsCD14) binds LPS in the absence of LBP or other proteins. Binding of LPS to CD14 is stable and of low stoichiometry (one or two molecules of LPS per rsCD14). Recombinant LBP (rLBP) does not form detectable ternary complexes with rsCD14 and LPS, but it does accelerate the binding of LPS to rsCD14, rLBP facilitates the interaction of LPS with rsCD14 at substoichiometric concentrations, suggesting that LBP functions catalytically, as a lipid transfer protein. Complexes of LPS and rsCD14 formed in the absence of LBP or other serum proteins strongly stimulate integrin function on PMN and expression of E-selectin on endothelial cells, demonstrating that LBP is not necessary for CD14-dependent stimulation of cells. These results suggest that CD14 acts as a soluble and cell surface receptor for LPS, and that LBP may function primarily to accelerate the binding of LPS to CD14. R cent work has described several serum and cell surface proteins that are necessary for responses of leukocytes to low concentrations of bacterial LPS (endotoxin) (1). LPSbinding protein (LBP),I an acute phase reactant, binds LPS (2) and greatly enhances the sensitivity of cells to LPS (3). Normal serum and plasma also enhance responses to LPS, and a multicomponent factor termed septin has been proposed to serve this function (4). LBP (5) and septin (4) each bind to LPS-coated particles and promote the interaction of these particles with CD14 (6, 7), a glycosylphosphatidylinositol (GPI)-anchored protein of monocytes, macrophages, and PMN (8, 9, 10). CD14 is necessary for serum-or LBPmediated responses of cells to LPS, such as the production 1 Abbreviations used in this paper: CHO, Chinese hamster ovary; ELPS, sheep erythrocytes coated with LPS; ELPS-LBP, ELPS opsonized with LBP; GPI, glycosylphosphatidylinositol; HAP, Dulbecco's PBS with 0.5 U/ml aprotinin, 0.05% human serum albumin, 3 mM D-glucose; HUVEC, human umbilical vein endothelial cells; LBP, LPS-binding protein; NHP, normal human plasma; PD-EDTA, Dulbecco's PBS lacking Ca 2+ and Mg 2+ with 1 mM EDTA; Ra, strain R60; Re, strain R595; rLBP, recombinant LBP; rsCD14, recombinant soluble CD14. of TNF by monocytes (6) and an increase in the adhesive properties of 132-integrins on PMN (7).Cells that do not express CD14, such as endothelial cells, also respond to low concentrations of LPS in the presence of serum. We have shown that these resp...
Background The molecular basis for the focal nature of atherosclerotic lesions is poorly understood. Here, we explored whether disturbed flow patterns activate an innate immune response to form the NLRP3 inflammasome scaffold in vascular endothelial cells (ECs) via sterol regulatory element binding protein 2 (SREBP2). Methods and Results Oscillatory flow activates SREBP2 and induces NLRP3 inflammasome in ECs. The underlying mechanisms involve SREBP2 transactivating NADPH oxidase 2 (NOX2) and NLRP3. Consistently, SREBP2, NOX2, and NLRP3 levels were elevated in atheroprone areas of mouse aortas, suggesting that the SREBP2-activated NLRP3 inflammasome causes functionally disturbed endothelium with increased inflammation. Mimicking the effect of atheroprone flow, EC-specific overexpression of the activated form of SREBP2 synergized with hyperlipidemia to increase atherosclerosis in the atheroresistant areas of mouse aortas. Conclusions Atheroprone flow induces NLRP3 inflammasome in endothelium through SREBP2 activation. This increased innate immunity in endothelium synergizes with hyperlipidemia to cause topographic distribution of atherosclerotic lesions.
Toll-like receptor (TLR) agonists are being developed for use as vaccine adjuvants and as stand-alone immunomodulators because of their ability to stimulate innate and adaptive immune responses. Among the most thoroughly studied TLR agonists are the lipid A molecules that target the TLR4 complex. One promising candidate, monophosphoryl lipid A, which is a derivative of lipid A from Salmonella minnesota, has proven to be safe and effective as a vaccine adjuvant in > 120,000 human doses. A new class of synthetic lipid A mimetics, the aminoalkyl glucosaminide 4-phosphates (AGPs), have been engineered specifically to target human TLR4 and are showing promise as vaccine adjuvants and as monotherapeutic agents capable of eliciting nonspecific protection against a wide range of infectious pathogens. In this review, the authors provide an update of the preclinical and clinical experiences with the TLR4 agonists, MPL (Corixa Corporation) adjuvant and the AGPs.
Current evidence indicates that the chronic inflammation observed in the intestines of patients with inflammatory bowel disease is due to an aberrant immune response to enteric flora. We have developed a lipid A-mimetic, CRX-526, which has antagonistic activity for TLR4 and can block the interaction of LPS with the immune system. CRX-526 can prevent the expression of proinflammatory genes stimulated by LPS in vitro. This antagonist activity of CRX-526 is directly related to its structure, particularly secondary fatty acyl chain length. In vivo, CRX-526 treatment blocks the ability of LPS to induce TNF-α release. Importantly, treatment with CRX-526 inhibits the development of moderate-to-severe disease in two mouse models of colonic inflammation: the dextran sodium sulfate model and multidrug resistance gene 1a-deficient mice. By blocking the interaction between enteric bacteria and the innate immune system, CRX-526 may be an effective therapeutic molecule for inflammatory bowel disease.
Background Oxidative stress activates endothelial innate immunity and disrupts endothelial functions, including eNOS-derived NO bioavailability. Here, we postulated that oxidative stress induces sterol regulatory element binding protein 2 (SREBP2) and microRNA-92a (miR-92a), which in turn activate endothelial innate immune response, leading to dysfunctional endothelium. Methods and Results Using cultured endothelial cells (ECs) challenged by diverse oxidative stresses, hypercholesterolemic zebrafish, and Ang II-infused or aged mice, we demonstrated that SREBP2 transactivation of microRNA-92a (miR-92a) is oxidative stress-inducible. The SREBP2-induced miR-92a targets key molecules in endothelial homeostasis, including Sirtuin 1, Krüppel-like factor 2 (KLF2), and KLF4, leading to NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome activation and eNOS inhibition. In EC-specific SREBP2 transgenic mice, locked nucleic acid (LNA)-modified antisense miR-92a (LNA-92a) attenuates inflammasome, improves vasodilation, and ameliorates Ang II-induced and aging-related atherogenesis. In patients with coronary artery disease, the level of circulating miR-92a is inversely correlated with EC-dependent, flow-mediated vasodilation and is positively correlated with serum level of IL-1β. Conclusions Our findings suggest that SREBP2-miR-92a-inflammasome exacerbates endothelial dysfunction during oxidative stress. Identification of this mechanism may help in diagnosis and/or treatment of disorders associated with oxidative stress, innate immune activation, and endothelial dysfunction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
334 Leonard St
Brooklyn, NY 11211
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.