Enhanced binding of low and high density lipoproteins to human adipocyte plasma membranes: effects of temperature and proteases

1986 ◽  
Vol 64 (12) ◽  
pp. 1378-1382
Author(s):  
Bessie S. Fong ◽  
Pedro O. Rodrigues ◽  
Aubie Angel
Keyword(s):  
Plasma Membranes ◽  
Specific Binding ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
High Density ◽  
High Density Lipoproteins ◽  
Dependent Manner ◽  
Human Adipocyte ◽  
Ldl Binding ◽  
Adipocyte Plasma Membranes

The specific binding of 125I-labelled low density lipoprotein ([125I]LDL to human adipocyte plasma membranes was higher at 37 than at 0 °C. Prior treatment of membranes with pronase had no effect on LDL binding measured at 0 °C but consistently stimulated binding at 37 °C. Plasmin was similar to pronase in enhancing LDL-specific binding, but thrombin was not as effective. 125I-labelled high density lipoprotein ([125I]HDL2) specific binding to human adipocyte plasma membranes was similarly sensitive to temperature and pronase treatment. Addition of the protease inhibitor aprotinin in the adipocyte membrane binding assay significantly reduced [125I]LDL binding at 37 °C (p < 0.05), suggesting the involvement of a protease activity intrinsic to the lipoproteins and (or) membranes. These data demonstrate that both LDL and HDL binding in human adipocyte plasma membranes can be "up-regulated" by specific proteolytic perturbations in a temperature-dependent manner.

Characterization of high-density lipoprotein binding to rat adipocytes and adipocyte plasma membranes

1988 ◽  
Vol 66 (9) ◽  
pp. 986-997 ◽  
Author(s):  
Eva Zsigmond ◽  
Bessie Fong ◽  
Aubie Angel
Keyword(s):  
Adipose Tissue ◽  
Plasma Membranes ◽  
Density Lipoprotein ◽  
Membrane System ◽  
Rat Plasma ◽  
High Density ◽  
High Density Lipoproteins ◽  
Binding Characteristics ◽  
Isolated Adipocytes ◽  
Adipocyte Plasma Membranes

The interaction of high-density lipoproteins (HDL) with adipocytes is important in the regulation of cellular cholesterol flux. To study the mechanisms of HDL binding and cellular processing, we incubated adipocytes isolated from epididymal and perirenal adipose tissue of male Wistar rats (300 g) with HDL1 (1.07–1.10 g/mL) and HDL2 (1.10–1.14 g/mL) fractions separated from rat plasma by gradient ultracentrifugation. Freshly isolated adipocytes were incubated with 125I-labeled HDL for 2 h at 37 °C to determine cell-associated uptake and degradation. Adipocytes from both fat regions showed significant cell-associated HDL1 and HDL2 uptake and very high medium degradation (2- to 6-fold higher than uptake). To assess 125I-labeled HDL binding independent of cellular metabolism, we purified adipocyte plasma membranes from isolated adipocytes and used them in binding assays. Binding of HDL1 and HDL2 in the membrane system was 85–95% specific, sensitive to high NaCl concentrations, and abolished by pronase treatment. In contrast to HDL2 binding, the maximum HDL1 binding to perirenal plasma membranes was significantly higher than its binding to epididymal membranes (7.2 ± 1.3 vs. 4.4 ± 0.2 μg/mg, n = 6, p < 0.05). This increment in HDL1 binding to perirenal membranes represented an EDTA- sensitive, calcium-dependent component. These results indicate that HDL binding to adipocyte plasma membranes depends on both adipose tissue region and HDL subtype. The membrane binding characteristics, taken together with the cellular uptake results, suggest that adipocytes bind and metabolize HDL and that this interaction may involve a protein receptor.

scholarly journals Characterization of high density lipoprotein binding to human adipocyte plasma membranes.

1985 ◽  
Vol 75 (6) ◽  
pp. 1804-1812 ◽  
Author(s):  
B S Fong ◽  
P O Rodrigues ◽  
A M Salter ◽  
B P Yip ◽  
J P Despres ◽  
...  
Keyword(s):  
High Density Lipoprotein ◽  
Plasma Membranes ◽  
Density Lipoprotein ◽  
High Density ◽  
Human Adipocyte ◽  
Lipoprotein Binding ◽  
Adipocyte Plasma Membranes

The interaction of lipolysis products of very low density lipoprotein with plasma high density lipoprotein (HDL): perfusate HDL with plasma HDL subfractions

1987 ◽  
Vol 65 (3) ◽  
pp. 252-260 ◽  
Author(s):  
S. P. Tam ◽  
W. C. Breckenridge
Keyword(s):  
Particle Size ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
High Density ◽  
Molar Ratio ◽  
High Density Lipoproteins ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Hdl Subfractions ◽  
Apo E

The nature of the interaction of high density lipoproteins (HDL), formed during lipolysis of human very low density lipoprotein (VLDL) by perfused rat heart, with subfractions of human plasma HDL was investigated. Perfusate HDL, containing apoliproproteins (apo) E, C-II, and C-III but no apo A-I or A-II, was incubated with a subfraction of HDL (HDL-A) containing apo A-I and A-II, but devoid of apo C-II, C-III, and E. The products of the incubation were resolved by heparin-Sepharose or hydroxylapatite chromatography under conditions which allowed the resolution of the initial HDL-A and perfusate HDL. The fractions were analyzed for apolipoprotein content and lipid composition and assessed for particle size by electron microscopy. Following the incubation, the apo-E-containing lipoproteins were distinct from perfusate HDL since they contained apo A-I as a major component and apo C-II and C-III in reduced proportions. However, the HDL-A fraction contained apo C-II and C-III as major constituents. Associated with these changes in apolipoprotein composition, the apo-E-rich lipoproteins acquired cholesteryl ester from the HDL-A fraction and lost phospholipid to the HDL-A fraction. The HDL-A fraction maintained a low unesterified cholesterol/phospholipid molar ratio (0.23), while the apo-E-containing lipoproteins possessed a high ratio (0.75) characteristic of the perfusate HDL. The particle size of apo-E-containing lipoproteins (138.9 ± 22.5 Å; 1 Å = 0.1 nm) was larger than the initial HDL-A (126.5 ± 17.6 Å) or the new HDL-A-like fraction (120.9 ± 17.4 Å) obtained following incubation with perfusate HDL. It is concluded that incubation of perfusate HDL containing apo E, C-II, and C-III with plasma HDL subfractions results in the acquisition of apo A-I and cholesteryl esters by the apo-E-containing perfusate HDL and the loss of apo C-II, C-III, and phospholipid to the plasma HDL-A fraction. The process does not appear to be due to fusion of the particles, since the apo-E-containing lipoproteins maintain a cholesterol/phospholipid ratio distinct from the HDL-A fraction. The data provide evidence for a potential mechanism for the formation of HDL-E, an apo-E-containing lipoprotein of HDL size and density, through lipolysis of VLDL.

Selective uptake of cholesteryl ester from high density lipoproteins by plasma membranes of adipose tissue

1990 ◽  
Vol 68 (5) ◽  
pp. 870-879 ◽  
Author(s):  
Joel G. Parkes ◽  
Aubie Angel
Keyword(s):  
Adipose Tissue ◽  
Cholesteryl Ester ◽  
Plasma Membranes ◽  
Divalent Cations ◽  
High Density ◽  
Metabolic Energy ◽  
High Density Lipoproteins ◽  
High Affinity ◽  
Lipoprotein Binding ◽  
Adipocyte Plasma Membranes

The interaction between high density lipoproteins (HDL) and adipose tissue is an important pathway for cholesterol and cholesteryl ester flux. In intact fat cells, a disproportionately greater net uptake of cholesteryl ester occurs subsequent to lipoprotein binding than would have been predicted from a consideration of holoparticle uptake alone. To characterize the early events in this process, cholesteryl hexadecyl ether, a nonmetabolizable, accumulative marker of cholesteryl ester, was incorporated into canine HDL2, and its uptake by omental adipocyte plasma membranes was measured in relation to the binding of HDL2, which in this animal species is enriched in apolipoprotein A-I and free of apolipoprotein E. The dose–response profile for HDL2 binding was consistent with a single lipoprotein binding site at all concentrations of HDL2, whereas uptake of cholesteryl ester from HDL2 was biphasic, suggesting a high affinity site at low HDL2 concentrations and a low affinity site at high lipoprotein concentrations. Pronase treatment stimulated binding twofold and this was accompanied by a parallel twofold stimulation of cholesteryl ester uptake. EDTA, on the other hand, reduced binding and uptake of cholesteryl ester by 20%, indicating partial dependence upon divalent cations. The proportion of HDL2 cholesteryl ester accumulated by plasma membranes relative to HDL2 protein bound was not altered by either pronase or EDTA, despite the fact that these agents had opposite effects upon binding. In dissociation studies, a portion of membrane-associated HDL2 did not equilibrate with exogenous HDL2 and a greater proportion of the cholesteryl ester failed to dissociate. A stepwise mechanism for cholesteryl ester uptake, involving (i) saturable, high affinity HDL2 binding to cell surface sites, (ii) vectoral, HDL2 concentration-dependent delivery of cholesteryl ester to the membrane, and (iii) cholesteryl ester sequestration into a nonexchangeable membrane compartment, appears to be independent of metabolic energy or cell processing.Key words: cholesteryl ester transport, high density lipoprotein receptor, cholesterol storage.

scholarly journals The sites of degradation of rat high-density-lipoprotein apolipoprotein E specifically labelled with O-(4-diazo-3-[125I]iodobenzoyl)sucrose

1985 ◽  
Vol 226 (3) ◽  
pp. 715-721 ◽  
Author(s):  
F M Van't Hooft ◽  
A Van Tol
Keyword(s):  
Serum Proteins ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
High Density ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Serum Lipoproteins ◽  
Rat Serum ◽  
Apo E ◽  
Fasted Rats

O-(4-Diazo-3-[125I]iodobenzoyl)sucrose ([125I]DIBS), a novel labelling compound specifically designed to study the catabolic sites of serum proteins [De Jong, Bouma, & Gruber (1981) Biochem. J. 198, 45-51], was applied to study the tissue sites of degradation of serum lipoproteins. [125I]DIBS-labelled apolipoproteins (apo) E and A-I, added in tracer amounts to rat serum, associate with high-density lipoproteins (HDL) just like conventionally iodinated apo E and A-I. No difference is observed between the serum decays of chromatographically isolated [125I]DIBS-labelled and conventionally iodinated HDL labelled specifically in either apo E or apo A-I. When these specifically labelled HDLs are injected into fasted rats, a substantial [125I]DIBS-dependent 125I accumulation occurs in the kidneys and in the liver. No [125I]DIBS-dependent accumulation is observed in the kidneys after injection of labelled asialofetuin or human low-density lipoprotein. It is concluded that the kidneys and the liver are important sites of catabolism of rat HDL apo E and A-I.

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