Binding site on macrophages that mediates uptake and degradation of acetylated low density lipoprotein, producing massive cholesterol deposition

Abstract

ABSTRACIResident mouse peritoneal macro hages were shown to take up and degrade acetylated 1251 abeled low density lipoprotein (15I-acetyl-LDL) in vitro at rates that were 20fold greater than those for the uptake and degradation of 125I-LDL. The uptake of 1251-acetyl-LDL and its subsequent degradation in lysosomes were attributable to a high-affinity, trypsin-sensitive, surface binding site that recognized acetyl-LDL but not native LDL. When 25I-acetyl-LDL was bound to this site at 4VC and the macrophages were subsequently warmed to 370C, 75% of the cell-bound radioactivity was Studies in cultured human fibroblasts and blood lymphocytes have defined a receptor-mediated pathway by which cells take up and degrade low density lipoprotein (LDL), the major cholesterol-transport protein in human plasma (1, 2). This LDL uptake pathway is believed to function primarily in extrahepatic parenchymal cells where it serves a dual function: it provides the major physiologic route of LDL degradation in the human body and, at the same time, it supplies cholesterol to cells for the synthesis of membranes and steroid hormones.Patients with familial hypercholesterolemia (FH) have a mutation in the gene specifying the LDL receptor (1, 2). In these patients, LDL degradation through the physiologic pathway is blocked, and each LDL particle survives in the circulation 2-3 times longer than it does in normal subjects (3-5). As a result, the lipoprotein accumulates to abnormally high levels in plasma. Eventually the LDL is degraded through an alternate pathway. Inasmuch as the excess LDL-cholesterol becomes deposited in nonparenchymal cells throughout the body, including hepatic Kupffer cells and macrophages of the spleen, kidney, bone marrow, skin, tendons, and other organs (2, 6, 7), we have postulated that the alternate pathway for LDL degradation is expressed primarily in such scavenger cells (2, 5). Because this scavenger mechanism acts on plasma LDL that has circulated for an abnormally long time in vio, it may recognize some form of LDL that has become denatured or chemically modified. The clearance of denatured proteins in vivo by macrophages is well known (8, 9).As a first step in a search for the postulated macrophage system mediating the uptake and degradation of modified or denatured LDL, we have used as a probe 125I-labeled LDL (125I-LDL) that has been extensively acetylated in vitro (125I-acetyl-LDL). The rationale for this choice was based on previous studies showing that acetylation of LDL altered the lipoprotein to the extent that it was no longer recognized by the LDL receptor in fibroblasts (10). As a model cell system for studying the metabolism of '25I-acetyl-LDL, we have used resident mouse peritoneal macrophages isolated by the techniques developed by Cohn and coworkers (11, 12). We demonstrate that these cells possess a high-affinity binding site that recognizes acetyl-LDL but not native LDL. This binding site, which so far appears to occur only on macrophages, mediates the rapid uptake and degradation of acety...

MICA/B expression in macrophage foam cells infiltrating atherosclerotic plaques

“…When the MDMs obtained with the 11 protocol described above were cultured for 1 h in the presence of Alexa 488-conjugated AcLDL, they internalized AcLDL and transformed into foam cells. SR-A is a major macrophage receptor responsible for the uptake of modified LDL (Goldstein et al, 1979;Kunjathoor et al, 2002). We confirmed that SR-A expression was frequently detected in AcLDL-loaded MDMs generated by our new method (Figure 2D We showed that MDMs can be induced by coculture with autologous non-adherent PBMCs without adding any growth factors (Figure 2).…”

“…Infiltrating macrophages accumulate in fatty streak lesions and transform into foam cells, which then undergo necrotic or apoptotic cell death in loco, leading to the formation of atherosclerotic plaques (Sakakura et al, 2013). The class A scavenger receptor (SR-A) is a major macrophage receptor responsible for the uptake of modified low-density lipoprotein (LDL) such as oxidized LDL and acetylated LDL (AcLDL) (Goldstein et al, 1979;Kunjathoor et al, 2002) that converts macrophages into foam cells. Thus, SR-A expression is frequently observed in atherosclerotic lesions (Naito et al, 1992).…”

Selective and organotypic culture of intrahepatic bile duct cells from adult pig liver

“…Macrophages were shown to take up acetylated LDL by specific receptor-mediated processes (Goldstein et al, 1979). BDE cultures were exposed to 1,1'-dioctadecyl-3,3,3',3'-tetramethylindo-carbocyanine perchlorate-acetylated lowdensity lipoprotein (DiI-Ac-LDL) at 10 gg per ml of 10% DMEM for 4 h at 370 C according to the manufacturer's instructions (Biomedical Technologies Inc., Stoughton, MA).…”

Blood vessel formation in the avian limb bud involves angioblastic and angiotrophic growth

“…In order to test the two alternatives-sprouting or angioblastic recruitment-we used specific markers for the angiogenic cell lineage. By in vivo application of acetylated low density lipoprotein coupled to the fluorescent probe 1,l 'dioctadecyl-l-3,3,3',3'-tetra-methyIindo-carbocyanine perchlorate (DiI-Ac-LDL), it is possible to label endothelial cells and macrophages (Goldstein et al, 1979;Stein and Stein, 1980;Voyta et al, 1984), while the QH-1 antibody (Pardanaud et al, 1987) is specific for haemangioblasts of the quail. Using a double-labelling procedure, we expected to discriminate between isolated angioblasts originating from patent vessels by sprouting and angioblasts recruited from limb bud mesoderm.…”