Role of heparan sulfate proteoglycans in the binding and uptake of apolipoprotein E-enriched remnant lipoproteins by cultured cells

Several characteristics of the rabbit make it an excellent model for the study of lipoprotein metabolism and atherosclerosis. New Zealand White (NZW) rabbits have low plasma total cholesterol concentrations, high cholesteryl ester transfer protein activity, low hepatic lipase (HL) activity, and lack an analogue of human apolipoprotein (apo) A-II, providing a unique system in which to assess the effects of human transgenes on plasma lipoproteins and atherosclerosis susceptibility. Additionally, rabbit models of human lipoprotein disorders, such as the Watanabe Heritable Hyperlipidemic (WHHL) and St. Thomas' Hospital strains, models of familial hypercholesterolemia and familial combined hyperlipidemia, respectively, allow for the assessment of candidate genes for potential use in the treatment of dyslipoproteinemic patients. To date, transgenes for human apo(a), apoA-I, apoB, apoE 2 , apoE 3 , HL, and lecithin:cholesterol acyltransferase (LCAT), as well as for rabbit apolipoprotein B mRNA-editing enzyme catalytic polypeptide 1 (APOBEC-1), have been expressed in NZW rabbits, whereas only those for human apoA-I and LCAT have been introduced into the WHHL background. All of these transgenes have been shown to have significant effects on plasma lipoprotein concentrations. In both NZW and WHHL rabbits, human apoA-I expression was associated with a significant reduction in the extent of aortic atherosclerosis, which was similarly the case for LCAT in rabbits having at least one functional LDL receptor allele. Conversely, expression of apoE 2 in NZW rabbits caused increased susceptibility to atherosclerosis. These studies provide new insights into the mechanisms responsible for the development of atherosclerosis, emphasizing the strength of the rabbit model in cardiovascular disease research. -Brousseau, M. E., and J. M. Hoeg. Transgenic rabbits as models for atherosclerosis research.

Section: Apolipoprotein Esupporting

confidence: 60%

Transgenic rabbits as models for atherosclerosis research

Brousseau¹,

Hoeg²

1999

“…Several other identified apoE variants with defective receptor-binding ability have been shown to have associations with impaired catabolism of remnant particles which leads to the dominant expression of type III hyperlipoproteinemia (9). In addition to its interaction with lipoprotein receptors, apoE also mediates the cellular uptake of remnant lipoproteins through its interaction with proteoglycans on the cell surface (10,11).…”

mentioning

confidence: 99%

Characterization of apolipoprotein E7 (Glu244→Lys, Glu245→Lys), a mutant apolipoprotein E associated with hyperlipidemia and atherosclerosis

Yamamura

Li²,

Yamamoto

1999

Previously, a mutant apolipoprotein (apo) E, apolipoprotein E7 (Glu 244 ¨ Lys, Glu 245 ¨ Lys), has been identified in association with hyperlipidemia and atherosclerosis. To investigate the effects of its structural changes on lipoprotein metabolisms and its correlation with atherosclerosis, we characterized this mutant apoE with respect to its receptor-binding, heparin-binding, and lipoprotein association. In a competitive binding assay, apoE7 и dimyristoylphosphatidylcholine displayed a defective binding to the low density lipoprotein (LDL) receptor. The concentration of apoE7 required for 50% displacement of 125 I-labeled LDL was 0.223 g/ml, while that for apoE3 was 0.048 g/ml. ApoE7 possesses only 23% of normal binding activity. To investigate the lipoprotein preference of apoE7, we determined the relative amounts of apoE7 in plasma lipoprotein fractions obtained by ultracentrifugation or gel filtration. Like human apoE4, apoE7 was preferentially associated with the very low density lipoproteins (VLDL). For determination of heparin-binding activity, apoVLDL was applied to a heparin-Sepharose affinity column and the bound materials were eluted with a salt gradient. The apoE7 was eluted at a higher NaCl concentration (157 m m ) than apoE3 (126 m m ), indicating that this mutant has a higher affinity for heparin than does apoE3. While the reduced receptor-binding activity indicates delayed clearance of the triglyceride-rich lipoproteins, the preferential association of apoE7 with larger-size lipoproteins and the stronger interaction with heparin may compensate, to some extent, for the delayed clearance of triglyceride-rich lipoproteins. The strong interaction with proteoglycans in the arterial wall seems to be one of the possible explanations for the association of apoE7 with atherosclerosis.-Yamamura, T., L-M. Dong, and A. Yamamoto. Characterization of apolipoprotein E7 (Glu 244 ¨ Lys, Glu 245 ¨ Lys), a mutant apolipoprotein E associated with hyperlipidemia and atherosclerosis. J.

“…Heparinase, sodium chlorate, and EGTA were purchased from Sigma (St. Louis, MO). To test the role of cell surface glycans in the binding of LDL to MEF4 cells in the presence of peptides, cells were treated with 2.5 U/ml heparinase for 45 min at 37 Њ C and washed prior to the start of the experiment as described by Ji et al (16). In addition, cells were grown for 48 h in the presence of 25 m m NaClO 3 , an inhibitor of enzymatic sulfation (17).…”

Section: Effects Of Pretreating Cells With Heparinase Naclo 3 Lpds and Egta On Ldl Binding To The Cell Surfacementioning

confidence: 99%

Peptide model of a highly conserved, N-terminal domain of apolipoprotein E is able to modulate lipoprotein binding to a member of the class A scavenger receptor family

Dominguez

Miller-Auer

Reardon

et al. 1999

Apolipoprotein E plays a critical role in plasma lipoprotein clearance. Peptide models of a highly conserved, N-terminal domain of this protein have been shown to increase the binding of low density lipoprotein (LDL) to fibroblast cell surfaces independently of the low density lipoprotein receptor. Here we provide data to show that these peptides not only increase the binding of LDL, but also of high density lipoprotein, though not acetylated LDL. We also have data suggesting that this novel activity is mediated, at least in part, by a member of the scavenger receptor family, SR-AI. Furthermore, we show that this activity is also prominent in macrophages, a cell relevant to atherogenesis. In addition, this current paper provides evidence suggesting that this complex binding activity is initiated by a peptide-receptor interaction, and that our peptides are able to induce activity at physiologically relevant concentrations. This study provides evidence for a possible novel receptor interaction and further anti-atherogenic properties of apolipoprotein E and raises the possibility of a therapeutic potential of our peptide models.-Dominguez, S. R., H. Miller-Auer, C. A. Reardon, and S. C. Meredith. Peptide model of a highly conserved, N-terminal domain of apolipoprotein E is able to modulate lipoprotein binding to a member of the class A scavenger receptor family.