LDL Scavenger Receptor Research Articles

Role of LDL-Scavenger Receptor CD36-Positive Macrophages in Refractory Nephrotic Syndrome with Hyperlipidemia under High-Dosage Steroid Treatment

Role of LDL-Scavenger Receptor CD36-Positive Macrophages in Refractory Nephrotic Syndrome with Hyperlipidemia under High-Dosage Steroid Treatment

P46 Oxidisedoxidized LDL and LOX-1 scavenger receptor regulation of pro-atherogenic signal transduction

Atherosclerosis is a chronic inflammatory disease characterised by lipid-laden lesions within arterial blood vessel walls. Inflammation is a central driver in atherosclerosis and is regulated by different signal transduction pathways in vascular cells and tissues. A major risk factor that promotes atherosclerosis is elevated oxidised low-density lipoprotein (oxLDL) particles, which is recognised by lectin-like oxLDL scavenger receptor 1 (LOX-1). LOX-1 is implicated in promoting atherosclerosis but the mechanism of action is unclear. To assess how LOX-1 signal transduction promotes disease outcomes, we used genetically engineered cell and animal models. We made a tetracycline-inducible endothelial cell line that expresses tagged wild-type human LOX-1. Stimulation of LOX-1-expressing endothelial cells with oxLDL causes increased signal transduction consistent with a role for LOX-1 in promoting inflammation and apoptosis. OxLDL binding stimulates LOX-1 endocytosis; however, LOX-1 undergoes efficient recycling from endosome-to-plasma membrane under stimulated and non-stimulated conditions. Although LOX-1-null transgenic mice displayed no obvious defects, LOX-1/ApoE-double null transgenic mice showed ~30% increase in atherosclerosis incidence compared to controls. Tissue analysis indicates that the presence of LOX-1 suppresses ERK1/2, p38 MAPK and NF-κB signal transduction. LOX-1 is thus an important link between dietary fats, pro-inflammatory signal transduction and atherosclerosis.

Cytomegalovirus stimulated mRNA accumulation and cell surface expression of the oxidized LDL scavenger receptor, CD36

Objective : Cytomegalovirus (CMV) has been epidemiologically associated with multiple disease processes including coronary, carotid and cardiac graft atherosclerosis. An early initiating event in atherogenesis is the uptake by macrophages of oxidized low-density lipoproteins (OxLDL) via the scavenger receptor, CD36. Because CMV can activate host-cell gene transcription, we hypothesized that CMV may upregulate CD36 expression. Methods and results : THP-1 monocyte/macrophage cells were treated with Davis strain CMV and cell surface CD36 expression measured by flow cytometry. Virus challenge increased the percentage of cells expressing CD36 from 21.8 ± 1.7 to 48.2 ± 4.0% (mean ± S.D. for three experiments, P = 0.0005); CD36 mRNA accumulation was increased by CMV treatment as determined by reverse transcription-polymerase chain reaction. Viral challenge also upregulated the mitogen-activated protein kinase p38; further, the specific p38 inhibitor, SB203580, reversed the CMV-induced CD36 cell surface expression from 57.2% of cells to baseline levels (29.0 and 30.1% for SB203580 treated and control cells, respectively; P = 0.001). Treatment with virus also stimulated uptake of OxLDL: microscopically, virus-treated cells had a mean of 32 ± 4.0 lipid vacuoles compared with 20 ± 1.3 for control cells ( P = 0.01). Conclusions : These findings suggest that CMV-induced CD36 expression is one mechanism through which CMV may promote atherosclerosis. Other CMV-associated atherogenic mechanisms may exist; additional investigation is necessary.

Novel eicosanoid activators of PPAR gamma formed by RAW 264.7 macrophage cultures.

Prostaglandin D2 (PGD2) is a major arachidonic acid metabolite in mast cells, megakaryoblastic CMK cells and antigen presenting cells, for example various types of macrophages. It induces pulmonary vasoconstriction and bronchoconstriction. Increased formation of PGD2 may be responsible for the symptoms of mastocytosis, it may contribute to the development of allergic symptoms and there is evidence that PGD2 regulates sleep. In the presence of serum albumin, PGD2 is converted to several products (1,2) which exhibit antiproliferative properties. These prostaglandin J2 compounds have been proposed to bind to intracellular receptors and translocate to the cell nucleus (3-6). In 1995, one of the antiproliferative prostaglandins, 15-deoxy-Al2“4 —PGJ2 was suggested to be a natural ligand for peroxisome proliferator-activated receptor-y (PPAR y)and to play a role in the terminal differentiation of fat cells (7,8). Recent studies show that PGD2 inhibits the expression of the genes encoding inducible nitric oxide synthase, gelatinase B and LDL scavenger receptor RAW 264.7 macrophages (9). PGD2 itself is a poor PPARy ligand. Therefore, we assumed that the activity observed in (9) was mediated by PGD2 metabolites. The purpose of this investigation was to identify PGD2 metabolites which activate PPARy in macrophages.KeywordsMacrophage CultureMethoxyamine HydrochlorideUnlabeled Fatty AcidEicosanoid ActivatorCouple Reticulocyte Lysate SystemThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Evaluation of potential tracer ability of 99mTc-labeled acetylated LDL for scintigraphy of LDL-scavenger receptor sites of macrophageal origin

Low-density lipoprotein (LDL) receptors are ubiquitously present in a variety of human tissues. Scavenger receptors, which are the activated macrophages bearing receptors for modified LDL, have been shown to be densely located at the atherosclerotic lesions. Acetylated LDL competes with oxidized LDL for access to these receptors. The present study was undertaken to optimize 99mTc labeling of two different forms of LDLs [i.e., native (Na) and acetylated (Ac)] and to explore their utility for the scintigraphy of densely localized scavenger LDL-receptor activity in vivo. Native and acetyl-LDL were labeled with 99mTc using sodium dithionite as a reducing agent. Significant hepatic and muscular uptake precluded optimal availability of 99mTc-Ac-LDL in blood, which favors macrophageal binding in sterile abscess models in rabbits. 99mTc-Ac-LDL behave as a novel tracer for imaging densely localized scavenger receptor sites constituted by activated macrophages at the site of independent inflammatory lesions and appears promising for the scintigraphy of atherosclerotic lesions.

Atherogenic properties of human monocytes induced by the carboxyl terminal proteolytic fragment of alpha-1-antitrypsin

Atherosclerotic plaques contain a significant number of macrophage foam cells and are associated with an inflammatory state. Inflammation induces the secretion from monocytes and other cells of cytokines, reactive oxygen species, proteinases and proteinase inhibitors among many other molecular species. AAT is prominent among the serine proteinase inhibitors and is an important regulator of leukocyte elastase and proteinase-3. It has been shown that the stable AAT-proteinase complex can upregulate AAT biosynthesis, and we have shown that the shorter, carboxyl terminal peptide (C-36) resulting from proteinase cleavage of AAT polymerizes, and in its fibrillar form alters cellular metabolism. To test for a possible link between the inflammation-generated C-36 peptide and cellular processes associated with atherogenesis, we have studied the effects of the fibrillar form of this peptide at varying concentrations on human monocytes in culture. We have found that fibrillar C-36 at concentrations of greater than or equal to 5 μmol/l in monocyte cultures for 24 h significantly increases LDL binding and uptake, upregulates LDL receptors, induces cytokine production and glutathione reductase activity, and upregulates AAT synthesis. The expression of CD36 protein, LDL Scavenger receptor, is also upregulated by fibrillar C-36 and native LDL in the presence of C-36-activated monocytes is more oxidized than with unactivated control monocytes. The majority of monocytes cultured for 24 h in the presence of C-36 fibrils were transformed morphologically into macrophages. These data establish a direct molecular link, mediated by C-36 peptide of AAT, between inflammation and the oxidation and accumulation of lipid in monocyte-derived macrophages. This may be important for an understanding of the events conducing to atherogenesis.

Suppression of interleukin-1 beta and LDL scavenger receptor expression in macrophages by a selective protein kinase C inhibitor.

A human monocytic cell line, THP-1, stimulated with 40 nM phorbol myristate acetate (PMA), differentiated to macrophage-like cells, and exhibited increased expression and release of interleukin-1 beta and expression of acetylated low density lipoprotein (ac-LDL) receptors. A selective inhibitor, MDL 29,152 (4-propyl-5-(4-quinolinyl)-2(3H)-oxazolone) was used to show that this induction required activation of protein kinase C. MDL 29,152 acts in the catalytic domain of protein kinase C and is at least 200-fold selective for protein kinase C over cAMP-dependent protein kinase in THP-1 cells. MDL 29,152 (50 microM) reduced levels of interleukin-1 beta mRNA in PMA-stimulated cells by 76% and eliminated detectable interleukin-1 beta in the media. Flow cytometric analysis showed that 48 h after THP-1 activation, approximately 50% of the cells expressed ac-LDL receptors, while in the presence of 100 microM MDL 29,152, less than 5% of the cells expressed receptors. The relationship between THP-1 differentiation and protein kinase C activation was determined by following the expression of the cell surface antigen MO-1. Expression of MO-1 antigen increases as monocytes differentiate to macrophages. After 48 h of phorbol activation, 90% of the THP-1 population was MO-1-positive; less than 16% of the population was MO-1-positive when 100 microM MDL 29,152 was present. By dual analysis, it was found that within the differentiated, MO-1-positive population, only approximately 50% of the cells also expressed ac-LDL receptors. Based on these findings, we conclude that protein kinase C promotes processes important in THP-1 activation and differentiation to macrophage-like cells including interleukin-1 beta expression and secretion, ac-LDL receptor and MO-1 expression.