Biomedical subjects

Oswald Quehenberger

Publications and source records attributed to Oswald Quehenberger.

12 recordsLinked to original sources

PubMed2006

Enhanced expression of the homeostatic chemokines CCL19 and CCL21 in clinical and experimental atherosclerosis: possible pathogenic role in plaque destabilization.

OBJECTIVE: Based on their role in T-cell homing into nonlymphoid tissue, we examined the role of the homeostatic chemokines CCL19 and CCL21 and their common receptor CCR7 in coronary artery disease (CAD). METHODS AND RESULTS: We performed studies in patients with stable (n=40) and unstable (n=40) angina and healthy controls (n=20), in vitro studies in T-cells and macrophages, and studies in apolipoprotein-E-deficient (ApoE-/-) mice and human atherosclerotic carotid plaques. We found increased levels of CCL19 and CCL21 within the atherosclerotic lesions of the ApoE-/- mice, in human atherosclerotic carotid plaques, and in plasma of CAD patients. Whereas strong CCR7 expression was seen in T-cells from murine and human atherosclerotic plaques, circulating T-cells from angina patients showed decreased CCR7 expression. CCL19 and CCL21 promoted an inflammatory phenotype in T-cells and macrophages and increased matrix metalloproteinase (MMP) and tissue factor levels in the latter cell type. Although aggressive statin therapy increased CCR7 and decreased CCL19/CCL21 levels in peripheral blood from CAD patients, conventional therapy did not. CONCLUSIONS: The abnormal regulation of CCL19 and CCL21 and their common receptor in atherosclerosis could contribute to disease progression by recruiting T-cells and macrophages to the atherosclerotic lesions and by promoting inflammatory responses in these cells.

Angioplasty, Balloon, Coronary↗

PubMed2006

The CC chemokine MCP-1 stimulates surface expression of CX3CR1 and enhances the adhesion of monocytes to fractalkine/CX3CL1 via p38 MAPK.

The membrane-anchored form of CX3CL1 has been proposed as a novel adhesion protein for leukocytes. This functional property of CX3CL1 is mediated through CX3CR1, a chemokine receptor expressed predominantly on circulating white blood cells. Thus far, it is still uncertain at what stage of the trafficking process CX3CR1 becomes importantly involved and how the CX3CR1-dependent adhesion of leukocytes is regulated during inflammation. The objective of this study was to examine the functional effects of chemokine stimulation on CX3CR1-mediated adhesion of human monocytes. Consistent with previous reports, our data indicate that the activity of CX3CR1 on resting monocytes is sufficient to mediate cell adhesion to CX3CL1. However, the basal, nonstimulated adhesion activity is low, and we hypothesized that like the integrins, CX3CR1 may require a preceding activation step to trigger firm leukocyte adhesion. Compatible with this hypothesis, stimulation of monocytes with MCP-1 significantly increased their adhesion to immobilized CX3CL1, under both static and physiological flow conditions. The increase of the adhesion activity was mediated through CCR2-dependent signaling and obligatory activation of the p38 MAPK pathway. Stimulation with MCP-1 also induced a rapid increase of CX3CR1 protein on the cell surface. Inhibition of the p38 MAPK pathway prevented this increase of CX3CR1 surface expression and blunted the effect of MCP-1 on cell adhesion, indicating a causal link between receptor surface density and adhesion activity. Together, our data suggest that a chemokine signal is required for firm CX3CR1-dependent adhesion and demonstrate that CCR2 is an important regulator of CX3CL1-dependent leukocyte adhesion.

Animals↗

PubMed2006

Minimally oxidized LDL offsets the apoptotic effects of extensively oxidized LDL and free cholesterol in macrophages.

OBJECTIVE: Lipid-loaded macrophage-derived foam cells populate atherosclerotic lesions and produce many pro-inflammatory and plaque-destabilizing factors. An excessive accumulation of extensively oxidized low-density lipoprotein (OxLDL) or free cholesterol (FC), both of which are believed to be major lipid components of macrophages in advanced lesions, rapidly induces apoptosis in macrophages. Indeed, there is evidence of macrophage death in lesions, but how the surviving macrophages avoid death induced by OxLDL, FC, and other factors is not known. METHODS AND RESULTS: Minimally oxidized LDL (mmLDL), which is an early product of progressive LDL oxidation in atherosclerotic lesions, countered OxLDL-induced or FC-induced apoptosis and stimulated macrophage survival both in cell culture and in vivo. DNA fragmentation and caspase-3 activity in OxLDL-treated peritoneal macrophages were significantly reduced by coincubation with mmLDL. In a separate set of experiments, mmLDL significantly reduced annexin V binding to macrophages in which apoptosis was induced by FC loading. In both cellular models, mmLDL activated a pro-survival PI3K/Akt signaling pathway, and PI3K inhibitors, wortmannin and LY294002, eliminated the pro-survival effect of mmLDL. Immunohistochemical examination demonstrated phospho-Akt in murine atherosclerotic lesions. CONCLUSIONS: Minimally oxidized LDL, an early form of oxidized LDL in atherosclerotic lesions, may contribute to prolonged survival of macrophage foam cells in lesions via a PI3K/Akt-dependent mechanism.

Animals↗

PubMed2006

Oxidized low-density lipoprotein inhibits hepatitis C virus cell entry in human hepatoma cells.

Cell entry of hepatitis C virus, pseudoparticles (HCVpp) and cell culture grown virus (HCVcc), requires the interaction of viral glycoproteins with CD81 and other as yet unknown cellular factors. One of these is likely to be the scavenger receptor class B type I (SR-BI). To further understand the role of SR-BI, we examined the effect of SR-BI ligands on HCVpp and HCVcc infectivity. Oxidized low-density lipoprotein (oxLDL), but not native LDL, potently inhibited HCVpp and HCVcc cell entry. Pseudoparticles bearing unrelated viral glycoproteins or bovine viral diarrhea virus were not affected. A dose-dependent inhibition was observed for HCVpp bearing diverse viral glycoproteins with an approximate IC50 of 1.5 microg/mL apolipoprotein content, which is within the range of oxLDL reported to be present in human plasma. The ability of lipoprotein components to bind to target cells associated with their antiviral activity, suggesting a mechanism of action which targets a cell surface receptor critical for HCV infection of the host cell. However, binding of soluble E2 to SR-BI or CD81 was not affected by oxLDL, suggesting that oxLDL does not act as a simple receptor blocker. At the same time, oxLDL incubation altered the biophysical properties of HCVpp, suggesting a ternary interaction of oxLDL with both virus and target cells. In conclusion, the SR-BI ligand oxLDL is a potent cell entry inhibitor for a broad range of HCV strains in vitro. These findings suggest that SR-BI is an essential component of the cellular HCV receptor complex.

CD36 Antigens↗

PubMed2005

The amino terminus and the third extracellular loop of CX3CR1 contain determinants critical for distinct receptor functions.

The G protein-coupled receptor CX3CR1 is a specific receptor for the CX3C chemokine fractalkine (CX3CL1 according to the new chemokine nomenclature). The aim of this study was to identify receptor elements that contribute independently to agonist binding and receptor activation. Targeted mutation of selected acidic amino acid residues demonstrated that the binding activity of CX3CR1 was critically dependent on the two negatively charged residues Asp25 and Glu254 located on the N-terminal domain and third extracellular loop, respectively. In addition, mutation of the uncharged polar residue Tyr14 in the amino terminus caused a reduction in the ligand binding affinity. In contrast, the three acidic residues Glu13, Asp16, and Asp266 did not contribute to ligand binding but were crucial for receptor activation. The mutant receptors E13A, D16A, and D266A bound fractalkine with high affinity but were unable to induce signaling events necessary to support chemotaxis. These acidic residues may engage in electrostatic interactions with basic residues on fractalkine that are necessary for receptor function but not for binding. Our data are consistent with a model of chemokine receptor activation consisting of a multi-step mechanism. Step one mediates the high-affinity fractalkine binding involving Tyr14, Asp25, and Glu254. The initial interaction then triggers the engagement of Glu13, Asp16, and Asp266, which are necessary for CX3CR1 activation.

Amino Acid Sequence↗

PubMed2005

Expression of fractalkine (CX3CL1) and its receptor, CX3CR1, is elevated in coronary artery disease and is reduced during statin therapy.

OBJECTIVE: Recent data derived primarily from studies in animal models suggest that fractalkine (CX3CL1) and its cognate receptor, CX3CR1, play a role in atherogenesis. We, therefore, hypothesized that enhanced CX3CL1/CX3CR1 expression may promote atherogenesis in patients with coronary artery disease (CAD). METHODS AND RESULTS: We examined the plasma levels of CX3CL1 and CX3CR1 expression in peripheral blood mononuclear cells (PBMC) in various CAD populations (30 patients with previous myocardial infarction, 40 patients with stable angina, 40 patients with unstable angina, and a total of 35 controls) and used various experimental approaches to characterize CX3CL1-mediated leukocyte responses. We found that the plasma levels of CX3CL1 are greatly increased in CAD, particularly in unstable disease. The parallel increase of CX3CR1 expression in PBMC was predominantly attributable to an expansion of the (CX3CR1+)(CD3+)(CD8+) T cell subset and was associated with enhanced chemotactic, adhesive, and inflammatory responses to CX3CL1. Statin therapy for 6 months reduced the expression of CX3CL1 and CX3CR1, reaching statistical significance for both parameters only during aggressive (atorvastatin, 80 mg qd) but not conventional (simvastatin, 20 mg qd) therapy. Consequently, the functional responses of the PBMC to CX3CL1 including migration, adhesion, and secretion of interleukin-8 were attenuated by the treatments. CONCLUSIONS: Our results suggest that the CX3CL1/CX3CR1 dyad may contribute to atherogenesis and plaque destabilization in human CAD.

Angina, Unstable↗

PubMed2005

The mouse CCR2 gene is regulated by two promoters that are responsive to plasma cholesterol and peroxisome proliferator-activated receptor gamma ligands.

We have previously shown that the expression of monocyte CCR2, the receptor for monocyte chemoattractant protein-1, is induced by plasma cholesterol. The present study examines the mechanisms that regulate monocyte CCR2 expression in hypercholesterolemia using a mouse model. Our data demonstrate that in the mouse, CCR2 expression in circulating monocytes is controlled by two promoters P1 and P2. The two distinct transcripts, which encode the same protein, are produced by alternative splicing in the 5'-untranslated region. Both promoters are constitutively active, but only P2 is stimulated by cholesterol. However, both promoters are repressed by peroxisome proliferator-activated receptor gamma.

Animals↗

PubMed2005

Thematic review series: the immune system and atherogenesis. Molecular mechanisms regulating monocyte recruitment in atherosclerosis.

Cardiovascular disease, a progressive disorder characterized by the accumulation of lipids in the artery wall, is a leading cause of death in Western societies. One of the initial events in atherogenesis involves the recruitment of inflammatory cells from the circulation into the developing lesion. Studies during the past decade have underscored the role of inflammatory mediators in disease initiation and progression. Critical progress has been made in our understanding of the complex mechanisms by which monocytes, macrophages, and T-cells accumulate in atherosclerotic plaques. Experimental research has identified several candidate adhesion proteins and chemokines that are critically involved in the recruitment process, and encouraging data provide a mechanistic framework for new therapeutic targets. This review provides an overview of our current understanding of the mechanisms that direct the recruitment of monocytes to, and their retention in, atherosclerotic lesions.

Atherosclerosis↗

PubMed2005

Phosphocholine as a pattern recognition ligand for CD36.

We have previously shown that CD36 recognizes oxidation products of phospholipids on oxidized LDL (OxLDL) such as 1-palmitoyl-2-(5'-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC). The current study was designed to examine whether the phosphocholine (PC) headgroup in POVPC constitutes an obligatory binding target for CD36. To examine the contribution of PC in the binding of POVPC to CD36, we used well-defined synthetic oxidized phospholipids (OxPLs) cross-linked to BSA or to a hexapeptide. The OxPL adducts were then tested for their ability to bind to CD36-transfected cells and for their ability to inhibit OxLDL binding to CD36. Both POVPC-BSA and POVPC-peptide adducts were high-affinity ligands for CD36 and potent inhibitors of OxLDL binding. Enzymatic removal of the entire PC moiety of the POVPC-peptide, or of the choline headgroup alone, as well as substitution of the choline headgroup by ethanolamine abrogated the inhibitory activity of POVPC. Interestingly, PC by itself or cross-linked to BSA did not show any intrinsic competition activity. In conclusion, our data demonstrate that the PC headgroup of OxPL alone is sufficient for binding to CD36, but only if presented in the correct conformation as in OxPL of OxLDL or as in POVPC-peptide adducts.

Animals↗

PubMed2004

Uptake and transport of high-density lipoprotein (HDL) and HDL-associated alpha-tocopherol by an in vitro blood-brain barrier model.

The present study aimed to investigate pathways that contribute to uptake and transcytosis of high-density lipoproteins (HDLs) and HDL-associated alpha-tocopherol (alpha TocH) across an in vitro model of the blood-brain barrier (BBB). In primary porcine brain capillary endothelial cells HDL-associated alpha TocH was taken up in 10-fold excess of HDL holoparticles, indicating efficient selective uptake, a pathway mediated by scavenger receptor class B, type I (SR-BI). SR-BI was present in caveolae of brain capillary endothelial cells and expressed almost exclusively at the apical membrane. Disruption of caveolae with methyl-beta-cyclodextrin (CDX) resulted in (mis)sorting of SR-BI to the basolateral membrane. Immunohistochemistry of porcine brain cryosections revealed SR-BI expression on brain capillary endothelial cells and presumably astrocytic endfeet. HDL-associated [(14)C]alpha TocH taken up by brain capillary endothelial cells was recovered in sucrose gradient fractions containing the majority of cellular caveolin-1, the major caveolae-associated protein. During mass transfer studies using alpha TocH-enriched HDL, approximately 50% of cellular alpha TocH was recovered with the bulk of cellular caveolin-1 and SR-BI. Efflux experiments revealed that a substantial amount of cell-associated [(14)C]alpha TocH could be mobilized into the culture medium. In addition, apical-to-basolateral transport of HDL holoparticles and HDL-associated alpha TocH was saturable. Results from the present study suggest that part of cerebral apolipoprotein A-I and alpha TocH originates from plasma HDL transcytosed across the BBB and that caveolae-located SR-BI facilitates selective uptake of HDL-associated alpha TocH at the BBB.

Animals↗

PubMed2003

LDL activates signaling pathways leading to an increase in cytosolic free calcium and stimulation of CD11b expression in monocytes.

In the present study, we investigated the mechanisms by which plasma lipoproteins modulate the integrin-dependent adhesion properties of monocytes. LDL induced the expression of the monocyte CD11b in vitro as well as in vivo via intracellular signaling mechanisms involving calcium transients. The effect on CD11b transcription was specific for native LDL and was blocked by a neutralizing anti-LDL receptor antibody. Neither oxidized LDL nor HDL had any effect on CD11b expression. Although LDL stimulated CD11b surface expression, the integrins were not activated. To initiate the CD11b-specific adhesion to the endothelium, the engagement of chemokine receptor CCR2 and intact chemokine-to-integrin signaling was necessary. However, the activation of CCR2 with monocyte chemoattractant protein-1 not only stimulated the integrins preexisting on the cell surface, but also increased the number of CD11b molecules on the cell surface. This was particularly pronounced in THP-1 cells after treatment with LDL. In a previous study, we showed that LDL induces the expression of CCR2 in monocytes. We conclude that this may be the underlying cause of the enhanced chemokine effect on CD11b expression and activation observed with these cells.

Animals↗

PubMed2002

Differential expression of the isoforms for the monocyte chemoattractant protein-1 receptor, CCR2, in monocytes.

Two isoforms of human CCR2, the receptor for monocyte chemoattractant protein-1 (MCP-1), have been identified but their relative expression in monocytes and contribution to inflammatory responses mediated by MCP-1 remain uncertain. All available information on CCR2 expression is based on mRNA data because isoform-specific antibodies were not available until now. To analyze the relative expression of each isoform, we made two antibodies that specifically recognized CCR2A and CCR2B. Examination of receptor protein with these isoform-specific antibodies showed that the total expression of CCR2B in monocytes was about 10-fold higher than that of CCR2A with an equal distribution between the cell surface and intracellular pools. A detailed analysis using purified plasma membranes demonstrated that about 90% of all CCR2 on the cell surface were composed of CCR2B. The relatively abundant expression of CCR2B on the cell surface suggests a principal role of this isoform as a mediator of monocyte responses to MCP-1 in inflammation.

Animals↗