title: Regulation of macrophage apoE secretion and sterol efflux by the LDL receptor.
abstract: Factors that regulate apolipoprotein E (apoE) secretion by macrophages will have important effects on vessel wall lipid flux and atherosclerosis. Macrophages express the LDL receptor, which binds apoE with high affinity and could thereby affect the net secretion of apoE from macrophages. In these studies, we demonstrate that treatment of J774 macrophages transfected to constitutively express a human apoE3 cDNA with simvastatin, to increase LDL receptor activity, reduces the secretion of apoE. To further examine the relationship between LDL receptor expression and apoE secretion from macrophages, mouse peritoneal macrophages (MPMs) were isolated from mice with constitutively high expression of human LDL receptor to increase overall LDL receptor expression by 2- to 3-fold. Cells with increased LDL receptor expression also showed reduced apoE secretion compared with MPMs with basal LDL receptor expression. The effect of changes in LDL receptor expression on apoE secretion was isoform-specific, with greater reduction of apoE4 compared with apoE3 secretion and no reduction of apoE2 secretion, paralleling the known affinity of each isoform for LDL receptor binding. The effect of the LDL receptor on apoE secretion for each isoform was further reflected in LDL receptor-dependent changes in apoE-mediated cholesterol efflux. These results establish a regulatory interaction between two branches of macrophage sterol homeostatic pathways that could facilitate a rapid response to changes in macrophage sterol content relative to need.
authors.affiliation: Department of Medicine, University of Illinois at Chicago, Chicago, IL, USA.
authors.forename: Danijela
authors.initials: D
authors.lastname: Lucic
authors.forename: Zhi Hua
authors.initials: ZH
authors.lastname: Huang
authors.forename: De Sheng
authors.initials: de S
authors.lastname: Gu
authors.forename: Michael K
authors.initials: MK
authors.lastname: Altenburg
authors.forename: Nobuyo
authors.initials: N
authors.lastname: Maeda
authors.forename: Theodore
authors.initials: T
authors.lastname: Mazzone
mesh_terms: D000818:Animals; D053329:Apolipoprotein E2 / Q000378:metabolism; D053318:Apolipoprotein E3 / Q000378:metabolism; D053327:Apolipoprotein E4 / Q000378:metabolism; D001057:Apolipoproteins E / Q000378:metabolism*; D005786:Gene Expression Regulation; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D020033:Protein Isoforms; D011973:Receptors, LDL / Q000378:metabolism*; D019821:Simvastatin / Q000494:pharmacology; D013261:Sterols / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D053329:Apolipoprotein E2; D053318:Apolipoprotein E3; D053327:Apolipoprotein E4; D001057:Apolipoproteins E; D020033:Protein Isoforms; D011973:Receptors, LDL; D013261:Sterols; D019821:Simvastatin