scholarly journals Receptor activities for low-density lipoprotein and acetylated low-density lipoprotein in a mouse macrophage cell line (IC21) and in human monocyte-derived macrophages.

1981 ◽  
Vol 154 (6) ◽  
pp. 1852-1867 ◽  
Author(s):  
M G Traber ◽  
V Defendi ◽  
H J Kayden
Keyword(s):  
Cholesteryl Ester ◽  
Cholesterol Synthesis ◽  
Low Density Lipoprotein ◽  
Primary Cultures ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Simian Virus 40 ◽  
Human Monocyte ◽  
Peritoneal Macrophages ◽  
Low Density

IC21 macrophages, a permanent culture of a line of cells derived from a single colony of mouse peritoneal macrophages transformed with simian virus 40, demonstrate most of the characteristics of lipoprotein metabolism that have been described for primary cultures of rodent or canine peritoneal macrophages. IC21 macrophages have low but demonstrable low-density lipoprotein (LDL) receptor activity. They actively degrade acetylated LDL (AcLDL), which has a negative charge and is not recognized by the LDL receptor. Incubation of IC21 macrophages with human lipoprotein-depleted serum leads to a marked increase in cholesterol synthesis, as measured by incorporation of labeled acetate into sterols. Sterol synthesis is inhibited by further incubation with AcLDL; incubation with LDL also decreases cholesterol synthesis with an accumulation of radioactivity from acetate in sterol intermediates, which indicates that some uptake of LDL occurs. Incubation with AcLDL but not LDL leads to a marked stimulation of cholesterol esterification, as measured by labeled oleic acid incorporation into cholesteryl esters, and a concomitant increase in cellular cholesteryl ester content. IC21 macrophages as compared with human monocyte-derived macrophages are shown to have marked difference in their abilities to degrade native LDL and AcLDL. Human monocyte-derived macrophages degrade LDL at low concentrations at a rate sevenfold greater than do IC21 macrophages. The rate of cholesteryl ester synthesis after LDL receptor induction and incubation with LDL increases linearly with LDL concentration in HMD macrophages, but no increase was found in similarly incubated IC21 macrophages. IC21 macrophages degrade AcLDL at a rate two- to fourfold greater than do human monocyte-derived macrophages.

scholarly journals Degradation of lipoproteins by human monocyte-derived macrophages. Evidence for two distinct processes for the degradation of abnormal very-low-density lipoprotein from subjects with type III hyperlipidaemia

1984 ◽  
Vol 218 (1) ◽  
pp. 101-111 ◽  
Author(s):  
A K Soutar ◽  
B L Knight
Keyword(s):  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Human Monocyte ◽  
Normal Subjects ◽  
Peritoneal Macrophages ◽  
Low Density Lipoproteins ◽  
Low Density ◽  
Free Medium ◽  
Very Low Density Lipoproteins ◽  
Type Iii

Human blood monocyte-derived macrophages that had been cultured in medium containing human serum for 7 days degraded the abnormal very-low-density lipoproteins (VLDL) from the plasma of subjects with type III hyperlipoproteinaemia by two distinct saturable processes. One process was stimulated when cells from normal subjects were preincubated with lipoprotein-free medium, was inhibited by excess unlabelled low-density lipoproteins (LDL) and was absent from cells from subjects with homozygous familial hypercholesterolaemia; on these criteria it was identified as an LDL-receptor-dependent process. Degradation by the second process was of equal magnitude in both cell types and was unaffected by excess unlabelled LDL or acetylated LDL. The activity of this process was reduced when the cells were preincubated in lipoprotein-free medium. The abnormal VLDL from the plasma of cholesterol-fed rabbits were also degraded by this process, which was similar to that in mouse peritoneal macrophages mediated by the receptor for VLDL of beta-electrophoretic mobility [Goldstein, Ho, Brown, Innerarity & Mahley (1980) J. Biol. Chem. 255, 1839-1848].

scholarly journals Immunoprecipitation of the low-density-lipoprotein (LDL) receptor and its precursor from human monocyte-derived macrophages

1986 ◽  
Vol 233 (3) ◽  
pp. 683-690 ◽  
Author(s):  
A K Soutar ◽  
B L Knight
Keyword(s):  
Mononuclear Cells ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Human Monocyte ◽  
Skin Fibroblasts ◽  
Receptor Protein ◽  
Low Density ◽  
Human Mononuclear Cells ◽  
Cell Extracts

Synthesis of the low-density-lipoprotein (LDL) receptor protein by cultured human monocyte-derived macrophages was demonstrated by immunoprecipitation of [35S]methionine-labelled cell extracts with a monoclonal antibody to the bovine adrenal LDL receptor. Although the antibody does not bind to or inhibit binding of 125I-LDL to the LDL receptor on intact fibroblasts, it specifically binds to a protein in extracts of human skin fibroblasts, of Mr approx. 130,000 under non-reducing conditions, that is able to bind LDL. In monocyte-derived macrophages, as in fibroblasts, the receptor is synthesized as a low-Mr precursor that is converted into the mature protein. The half-life of the precursor in human macrophages is approx. 44 min. In cells from two homozygous familial-hypercholesterolaemic subjects, only the precursor form of the receptor is synthesized. Detection of abnormalities of LDL-receptor synthesis in human mononuclear cells may be a useful aid in diagnosis of familial hypercholesterolaemia that is simpler and quicker than methods requiring growth of cultured skin fibroblasts.

scholarly journals Human monocyte-derived macrophages bind low-density-lipoprotein-proteoglycan complexes by a receptor different from the low-density-lipoprotein receptor

1993 ◽  
Vol 289 (3) ◽  
pp. 837-844 ◽  
Author(s):  
P Vijayagopal ◽  
S R Srinivasan ◽  
B Radhakrishnamurthy ◽  
G S Berenson
Keyword(s):  
Cholesteryl Ester ◽  
Proteolytic Enzymes ◽  
Chondroitin Sulphate ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Human Monocyte ◽  
Human Aorta ◽  
Minor Role ◽  
Low Density ◽  
Ester Synthesis

We have shown recently that lipoprotein-proteoglycan complexes isolated from human atherosclerotic lesions stimulated cholesteryl ester synthesis in human monocyte-derived macrophages [Vijayagopal, Srinivasan, Radhakrishnamurthy and Berenson (1992) Arterioscler. Thromb. 12, 237-249]. The present study was conducted to determine the mechanism of cellular uptake of the complexes. A chondroitin sulphate-dermatan sulphate proteoglycan was isolated from normal human aorta and complexed to 125I-labelled human low-density lipoprotein (LDL). The binding and degradation of 125I-LDL-proteoglycan complex were then studied in human monocyte-derived macrophages. The specific binding and degradation of the complex showed saturability and concentration-dependency. The Kd for binding was 1.5 x 10(-8) M, which was greater than that reported for LDL in monocyte-derived macrophages. Binding of the complex was not subject to down-regulation. Chloroquine inhibited degradation of the complex and the resultant stimulation of cholesteryl ester synthesis. Limited treatment of macrophages with proteolytic enzymes abolished binding and degradation of the complex significantly. Macrophages bound 125I-methyl-LDL-proteoglycan complex to the same extent as 125I-LDL-proteoglycan complex. Excess LDL and proteoglycan did not compete against the binding of the complex; however, excess acetyl-LDL competed for 61% of the binding. Likewise, excess LDL-proteoglycan complex inhibited the binding of 125I-acetyl-LDL by 64%. Polyinosinic acid and cytochalasin D inhibited the binding of 125I-LDL-proteoglycan complex by 60% and 36% respectively. Compared with that of acetyl-LDL, the degradation of LDL-proteoglycan complex was retarded in human macrophages. The results indicate that the uptake of LDL-proteoglycan complex in human monocyte-derived macrophages is not mediated through binding to the LDL receptor; but occurs predominantly via the scavenger receptor, with phagocytosis playing a minor role in the process.

scholarly journals The influence of particle size and multiple apoprotein E-receptor interactions on the endocytic targeting of beta-VLDL in mouse peritoneal macrophages.

1991 ◽  
Vol 115 (6) ◽  
pp. 1547-1560 ◽  
Author(s):  
I Tabas ◽  
J N Myers ◽  
T L Innerarity ◽  
X X Xu ◽  
K Arnold ◽  
...  
Keyword(s):  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Peritoneal Macrophages ◽  
Low Density ◽  
Cholesterol Acyl Transferase ◽  
Ldl Receptors ◽  
Apo E ◽  
Partial Neutralization ◽  
Mouse Peritoneal Macrophages

Low density lipoprotein (LDL) and beta-very low density lipoprotein (beta-VLDL) are internalized by the same receptor in mouse peritoneal macrophages and yet their endocytic patterns differ; beta-VLDL is targeted to both widely distributed and perinuclear vesicles, whereas LDL is targeted almost entirely to perinuclear lysosomes. This endocytic divergence may have important metabolic consequences since beta-VLDL is catabolized slower than LDL and is a more potent stimulator of acyl-CoA/cholesterol acyl transferase (ACAT) than LDL. The goal of this study was to explore the determinants of beta-VLDL responsible for its pattern of endocytic targeting. Fluorescence microscopy experiments revealed that large, intestinally derived, apoprotein (Apo) E-rich beta-VLDL was targeted mostly to widely distributed vesicles, whereas small, hepatically derived beta-VLDL was targeted more centrally (like LDL). Furthermore, the large beta-VLDL had a higher ACAT-stimulatory potential than the smaller beta-VLDL. The basis for these differences was not due to fundamental differences in the means of uptake; both large and small beta-VLDL were internalized by receptor-mediated endocytosis (i.e., not phagocytosis) involving the interaction of Apo E of the beta-VLDL with the macrophage LDL receptor. However, large beta-VLDL was much more resistant to acid-mediated release from LDL receptors than small beta-VLDL. Furthermore, partial neutralization of the multiple Apo Es on these particles by immunotitration resulted in a more perinuclear endocytic pattern, a lower ACAT-stimulatory potential, and an increased sensitivity to acid-mediated receptor release. These data are consistent with the hypothesis that the interaction of the multivalent Apo Es of large beta-VLDL with multiple macrophage LDL receptors leads to a diminished or retarded release of the beta-VLDL from its receptor in the acidic sorting endosome which, in turn, may lead to the widely distributed endocytic pattern of large beta-VLDL. These findings may represent a physiologically relevant example of a previously described laboratory phenomenon whereby receptor cross-linking by multivalent ligands leads to a change in receptor targeting.

Glycosylation of Low-Density Lipoprotein Enhances Cholesteryl Ester Synthesis in Human Monocyte-Derived Macrophages

Diabetes ◽  
1988 ◽  
Vol 37 (5) ◽  
pp. 550-557 ◽  
Author(s):  
M. F. Lopes-Virella ◽  
R. L. Klein ◽  
T. J. Lyons ◽  
H. C. Stevenson ◽  
J. L. Witztum
Keyword(s):  
Cholesteryl Ester ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Human Monocyte ◽  
Low Density ◽  
Ester Synthesis
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