Cationic domain 141-150 of apoE covalently linked to a class A amphipathic helix enhances atherogenic lipoprotein metabolism in vitro and in vivo

Abstract

We previously showed (1) that a peptide, Ac-hE18A-NH 2 , in which the arginine-rich heparin-binding domain of apolipoprotein E (apoE) [residues 141-150] (LRKLRKRLLR), covalently linked to 18A (DWLKAFYDKVAEKLKEAF; a class A amphipathic helix with high lipid affinity), enhanced LDL uptake and clearance. Because VLDL and remnants contain more cholesterol per particle than LDL, enhanced hepatic clearance of VLDL could lead to an effective lowering of plasma cholesterol. Therefore, in the present article we compared the ability of this peptide to mediate/facilitate the uptake and degradation of LDL and VLDL in HepG2 cells. The peptide Ac-hE18A-NH 2 , but not Ac-18A-NH 2 , enhanced the uptake of LDL by HepG2 cells 5-fold and its degradation 2-fold. The association of the peptides with VLDL resulted in the displacement of native apoE; however, only Ac-hE18A-NH 2 but not Ac-18A-NH 2 caused markedly enhanced uptake (6-fold) and degradation (3-fold) of VLDL. Ac-hE18A-NH 2 also enhanced the uptake (15-fold) and degradation (2-fold)of trypsinized VLDL Sf 100-400 (containing no immunodetectable apoE), indicating that the peptide restored the cellular interaction of VLDL in the absence of its essential native ligand (apoE). Pretreatment of HepG2s with heparinase and heparitinase abrogated all peptide-mediated enhanced cellular activity, implicating a role for cell-surface heparan sulfate proteoglycans (HSPG). Intravenous administration of Ac-hE18A-NH 2 into apoE gene knockout mice reduced plasma cholesterol by 88% at 6 h and 30% at 24 h after injection. We conclude that this dual-domain peptide associates with LDL and VLDL and results in rapid hepatic uptake via a HSPG-facilitated pathway.

An Apolipoprotein E-Derived Peptide Mediates Uptake of Sterically Stabilized Liposomes into Brain Capillary Endothelial Cells

“…HSPG is also involved in the apoE-related clearance of remnant lipoproteins (67), and an apoE-peptide consisting of residues (141-150) and a model class A amphipathic helix has been shown to enhance internalization of LDL into cells via an HSPG-mediated pathway (33). The dependence of uptake upon charge distribution of the peptide led to the suggestion that also specific components might be involved (35). Most likely, specific interactions with the LDLr-related protein play a role (20).…”

“…The role of cell-surface HSPG in liposome binding and uptake was investigated by removal of HSPG with heparinase I (heparin lyase I from Flavobacterium heparinum ) as previously reported ( , ). A stock solution was prepared by dissolving heparinase I in sterile 0.15 M NaCl.…”

“…Whereas the sequence (141-155) is not recognized, its tandem dimer competes with LDL for receptor binding (30), and also the tandem dimer (141-150) 2 induces an endocytotic process in cultivated cortical neurons (34). For a peptide composed of the monomer (141-150) and a high-affinity lipid-associating domain, it was found that the enhanced internalization and degradation of LDL in fibroblasts was caused by an LDLr-independent but heparan sulfate proteoglycan (HSPG)-associated pathway (35).…”

Are apolipoprotein E fragments a promising new therapeutic target for Alzheimer’s disease?

“…ApoE3 includes a domain for lipid association between aa 203-266 and a globular domain between aa 1-191 encompassing the LDL-R-binding region. 83 , 84 ApoE3 promotes clearance of triglyceride-rich lipoprotein particles, producing normal plasma lipid levels. Residues 1-167 of the N-terminal domain form an antiparallel 4 α-helix bundle 85 and present the nonpolar aspect of the amphipathic helices.…”

“…The ApoE N-terminal 22 kDa fragment originating from the ApoE4 isoform shows greater neurotoxicity compared to that originating from ApoE3. 71 , 84 …”