scholarly journals Metabolism of cationized lipoproteins by human fibroblasts: biochemical and morphologic correlations

1977 ◽  
Vol 74 (1) ◽  
pp. 119-135 ◽  
Author(s):  
SK Basu ◽  
RGW Anderson ◽  
JL Goldstein ◽  
MS Brown
Keyword(s):  
Electron Microscopy ◽  
Cholesteryl Ester ◽  
Lipid Droplets ◽  
Human Fibroblasts ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Turnover Time ◽  
Cholesteryl Esters ◽  
Light Microscope Level ◽  
Cellular Content

Human plasma low density lipoprotein (LDL) that had been rendered polycationic by coupling with N, N-dimethyl-1, 3-propanediamine (DMPA) was shown by electron microscopy to bind in clusters to the surface of human fibroblasts. The clusters resembled those formed by polycationic ferritin (DMPA-feritin), a visual probe that binds to anionic site on the plasma membrane. Biochemical studies with (125)I-labeled DMPA-LDL showed that the membrane-bound lipoprotein was internalized and hydrolyzed in lysosomes. The turnover time for cell bound (125)I-DMPA-LDL, i.e., the time in which the amount of (125)I-DMPA-LDL degraded was equal to the steady-state cellular content of the lipoprotein, was about 50 h. Because the DMPA-LDL gained access to fibroblasts by binding nonspecifically to anionic sites on the cell surface rather than by binding to the physiologic LDL receptor, its uptake failed to be regulated under conditions in which the uptake of native LDL was reduced by feedback suppression of the LDL receptor. As a result, unlike the case with native LDL, the DMPA-LDL accumulated progressively within the cell, and this led to a massive increase in the cellular content of both free and esterified cholesterol. Studies with (14)C-oleate showed that at least 20 percent of the accumulated cholesteryl esters represented cholesterol that had been esterified within the cell. After 4 days of incubation with 10 μg/ml of DMPA-LDL, fibroblasts had accumulated so much cholesteryl ester that neutral lipid droplets were visible at the light microscope level with Oil Red O staining. By electron microscopy, these intracellular lipid droplets were observed to lack a tripartite limiting membrane. The ability to cause the overaccumulation of cholesteryl esters within cells by using DMPA-LDL provides a model system for study of the pathologic consequences at the cellular level of massive deposition of cholesteryl ester.

scholarly journals Morphological characterization of the cholesteryl ester cycle in cultured mouse macrophage foam cells.

1983 ◽  
Vol 97 (4) ◽  
pp. 1156-1168 ◽  
Author(s):  
D J McGookey ◽  
R G Anderson
Keyword(s):  
Cholesteryl Ester ◽  
Lipase Activity ◽  
Lipid Droplets ◽  
Free Cholesterol ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
The Body ◽  
Cyclic Process ◽  
Low Density ◽  
Cholesteryl Esters

Mouse peritoneal macrophages can be induced to accumulate cholesteryl esters by incubating them in the presence of acetylated low density lipoprotein. The cholesteryl esters are sequestered in neutral lipid droplets that remain in the cell even when the acetylated low density lipoprotein is removed from the culture media. Previous biochemical studies have determined that the cholesterol component of cholesteryl ester droplets constantly turns over with a half time of 24 h by a cyclic process of de-esterification and re-esterification. We have used morphologic techniques to determine the spatial relationship of cholesteryl ester, free cholesterol, and lipase activity during normal turnover and when turnover is disrupted. Lipid droplets were surrounded by numerous 7.5-10.0-nm filaments; moreover, at focal sites on the margin of each droplet there were whorles of concentrically arranged membrane that penetrated the matrix. Histochemically detectable lipase activity was associated with these stacks of membrane. Using filipin as a light and electron microscopic probe for free cholesterol, we determined that a pool of free cholesterol was associated with each lipid droplet. Following incubation in the presence of the exogenous cholesterol acceptor, high density lipoprotein, the cholesteryl ester droplets disappeared and were replaced with lipid droplets of a different lipid composition. Inhibition of cholesterol esterification caused cholesteryl ester droplets to disappear and free cholesterol to accumulate in numerous myelin-like structures in the body of the cell.

Recent advances in physiological lipoprotein metabolism

2014 ◽  
Vol 52 (12) ◽  
Author(s):  
Indra Ramasamy
Keyword(s):  
High Density Lipoprotein ◽  
Cholesteryl Ester ◽  
Ldl Receptor ◽  
Lipoprotein Metabolism ◽  
Density Lipoprotein ◽  
High Density ◽  
Low Density ◽  
Transfer Protein ◽  
Recent Advances ◽  
The Right

AbstractResearch into lipoprotein metabolism has developed because understanding lipoprotein metabolism has important clinical indications. Lipoproteins are risk factors for cardiovascular disease. Recent advances include the identification of factors in the synthesis and secretion of triglyceride rich lipoproteins, chylomicrons (CM) and very low density lipoproteins (VLDL). These included the identification of microsomal transfer protein, the cotranslational targeting of apoproteinB (apoB) for degradation regulated by the availability of lipids, and the characterization of transport vesicles transporting primordial apoB containing particles to the Golgi. The lipase maturation factor 1, glycosylphosphatidylinositol-anchored high density lipoprotein binding protein 1 and an angiopoietin-like protein play a role in lipoprotein lipase (LPL)-mediated hydrolysis of secreted CMs and VLDL so that the right amount of fatty acid is delivered to the right tissue at the right time. Expression of the low density lipoprotein (LDL) receptor is regulated at both transcriptional and post-transcriptional level. Proprotein convertase subtilisin/kexin type 9 (PCSK9) has a pivotal role in the degradation of LDL receptor. Plasma remnant lipoproteins bind to specific receptors in the liver, the LDL receptor, VLDL receptor and LDL receptor-like proteins prior to removal from the plasma. Reverse cholesterol transport occurs when lipid free apoAI recruits cholesterol and phospholipid to assemble high density lipoprotein (HDL) particles. The discovery of ABC transporters (ABCA1 and ABCG1) and scavenger receptor class B type I (SR-BI) provided further information on the biogenesis of HDL. In humans HDL-cholesterol can be returned to the liver either by direct uptake by SR-BI or through cholesteryl ester transfer protein exchange of cholesteryl ester for triglycerides in apoB lipoproteins, followed by hepatic uptake of apoB containing particles. Cholesterol content in cells is regulated by several transcription factors, including the liver X receptor and sterol regulatory element binding protein. This review summarizes recent advances in knowledge of the molecular mechanisms regulating lipoprotein metabolism.

scholarly journals Fluorescent low density lipoprotein for observation of dynamics of individual receptor complexes on cultured human fibroblasts.

1981 ◽  
Vol 90 (3) ◽  
pp. 595-604 ◽  
Author(s):  
L S Barak ◽  
W W Webb
Keyword(s):  
Low Density Lipoprotein ◽  
Human Fibroblasts ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Receptor Internalization ◽  
Low Density ◽  
Receptor Complexes ◽  
Heparin Sulfate ◽  
Cultured Human Fibroblasts ◽  
Coa Reductase

The visible wavelength excited fluorophore 3,3'-dioctadecylindocarbocyanine iodide (Dil[3]) was incorporated into human low density lipoprotein (LDL) to form the highly fluorescent LDL derivative dil(3)-LDL. Dil(3)-LDL binds to normal human fibroblasts and to human fibroblasts defective in LDL receptor internalization but does not bind to LDL receptor-negative human fibroblasts at 4 degrees C or 37 degrees C. It is internalized rapidly at 37 degrees C by normal fibroblasts and depresses the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) in a manner similar to that of LDL. It is prevented from binding to the LDL receptor by an excess of unlabeled LDL or by heparin sulfate. Identical distributions of dil(3)-LDL are observed on cells by either indirect immunofluorescence with fluorescein-labeled antibody or directly by dil(3) fluorescence. Upwards of 45 molecules of dil(3) are incorporated per molecule of LDL without affecting binding to the receptor. This labeling renders individual molecules visible by their fluorescence and enables the derivative to be used in dynamic studies of LDL-receptor motion on living fibroblasts by standard fluorescence techniques at low LDL receptor density. Observations with this derivative indicate that the LDL-receptor complex is immobilized on the surface of human fibroblasts but, when free of this linkage, undergoes a Brownian motion consistent with theory.

scholarly journals Tissue-specific sorting of the human LDL receptor in polarized epithelia of transgenic mice.

1990 ◽  
Vol 111 (2) ◽  
pp. 347-359 ◽  
Author(s):  
R K Pathak ◽  
M Yokode ◽  
R E Hammer ◽  
S L Hofmann ◽  
M S Brown ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Transgenic Mice ◽  
Intestinal Epithelial Cells ◽  
Low Density Lipoprotein ◽  
Human Fibroblasts ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Intestinal Epithelial ◽  
Coated Pits ◽  
Ldl Receptors

The distribution of human low density lipoprotein (LDL) receptors was studied by immunofluorescence and immunoelectron microscopy in epithelial cells of transgenic mice that express high levels of receptors under control of the metallothionein-I promoter. In hepatocytes and intestinal epithelial cells, the receptors were confined to the basal and basolateral surfaces, respectively. Very few LDL receptors were present in coated pits or intracellular vesicles. In striking contrast, in the epithelium of the renal tubule the receptors were present on the apical (lumenal) surface where they appeared to be concentrated at the base of microvilli and were abundant in vesicles of the endocytic recycling pathway. Intravenously administered LDL colloidal gold conjugates bound to the receptors on hepatocyte microvilli and were slowly internalized, apparently through slow migration into coated pits. We conclude that (a) sorting of LDL receptors to the surface of different epithelial cells varies with each tissue; and (b) in addition to a signal for clustering in coated pits, the LDL receptor may contain a signal for retention in noncoated membrane that is manifest in hepatocytes and intestinal epithelial cells, but not in renal epithelial cells or cultured human fibroblasts.

scholarly journals Selective uptake of cholesteryl esters from apolipoprotein-E-free high-density lipoproteins by rat parenchymal cells in vivo is efficiently coupled to bile acid synthesis

1991 ◽  
Vol 280 (2) ◽  
pp. 359-365 ◽  
Author(s):  
M N Pieters ◽  
D Schouten ◽  
H F Bakkeren ◽  
B Esbach ◽  
A Brouwer ◽  
...  
Keyword(s):  
Bile Acid ◽  
Cholesteryl Ester ◽  
Bile Acids ◽  
Density Lipoprotein ◽  
Cholesteryl Oleate ◽  
Cholesteryl Esters ◽  
Liver Uptake ◽  
Selective Uptake ◽  
Parenchymal Cells ◽  
Kinetics Of

[3H]Cholesteryl ester-labelled human high-density lipoprotein (HDL) was injected into rats and its decay, intrahepatic cellular distribution and the kinetics of biliary secretion were determined. At 10 min after injection the hepatic uptake of cholesteryl esters from HDL was 3-fold higher as compared with the apolipoprotein. Selective uptake was exerted only by parenchymal cells (5.6-fold more cholesteryl esters than apolipoprotein) and not by liver endothelial or Kupffer cells. The kinetics of biliary secretion of processed cholesteryl esters initially associated with HDL or low-density lipoprotein (LDL) were compared in unrestrained rats, equipped with permanent catheters in bile duct, duodenum and heart. At 72 h after injection of [3H]cholesteryl oleate-labelled HDL, 51.0 +/- 2.5% of the injected dose was recovered as bile acids, which is about twice as high as the secretion of biliary radioactivity after injection of [3H]cholesteryl oleate-labelled LDL. Oestradiol treatment stimulated only liver uptake of LDL cholesteryl esters, and resulted in a 2-fold higher liver uptake than with HDL. However, the rate of radioactive bile acid formation from [3H]cholesteryl oleate-labelled HDL was still more rapid than for LDL. It is concluded that the selective uptake pathway for cholesteryl esters from HDL in parenchymal cells is more efficiently coupled to the formation of bile acids than is the cholesteryl ester uptake from LDL. This efficient coupling may facilitate the role of HDL in reverse cholesterol transport.

The LDL receptor is not necessary for acute adrenal steroidogenesis in mouse adrenocortical cells

2007 ◽  
Vol 292 (2) ◽  
pp. E408-E412 ◽  
Author(s):  
Fredric B. Kraemer ◽  
Wen-Jun Shen ◽  
Shailja Patel ◽  
Jun-ichi Osuga ◽  
Shun Ishibashi ◽  
...  
Keyword(s):  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Vital Role ◽  
Hormone Sensitive Lipase ◽  
Cholesteryl Esters ◽  
Selective Uptake ◽  
Adrenal Cells ◽  
Adrenal Steroidogenesis ◽  
Hormone Sensitive

Steroid hormones are synthesized using cholesterol as precursor. To determine the functional importance of the low density lipoprotein (LDL) receptor and hormone-sensitive lipase (HSL) in adrenal steroidogenesis, adrenal cells were isolated from control, HSL−/−, LDLR−/−, and double LDLR/HSL−/− mice. The endocytic and selective uptake of apolipoprotein E-free human high density lipoprotein (HDL)-derived cholesteryl esters did not differ among the mice, with selective uptake accounting for >97% of uptake. In contrast, endocytic uptake of either human LDL- or rat HDL-derived cholesteryl esters was reduced 80–85% in LDLR−/− and double- LDLR/HSL−/− mice. There were no differences in the selective uptake of either human LDL- or rat HDL-derived cholesteryl esters among the mice. Maximum corticosterone production induced by ACTH or dibutyryl cyclic AMP and lipoproteins was not altered in LDLR−/− mice but was reduced 80–90% in HSL−/− mice. Maximum corticosterone production was identical in HSL−/− and double- LDLR/HSL−/− mice. These findings suggest that, although the LDL receptor is responsible for endocytic delivery of cholesteryl esters from LDL and rat HDL to mouse adrenal cells, it appears to play a negligible role in the delivery of cholesterol for acute adrenal steroidogenesis in the mouse. In contrast, HSL occupies a vital role in adrenal steroidogenesis because of its link to utilization of selectively delivered cholesteryl esters from lipoproteins.

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