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V Terpstra

Publications and source records attributed to V Terpstra.

8 recordsLinked to original sources
PubMed2001

Scavenger receptors, oxidized LDL, and atherosclerosis.

Oxidized LDL (OxLDL) competes with oxidatively damaged and apoptotic cells for binding to mouse peritoneal macrophages, implying the presence of one or more common domains. However, the nature of the ligands involved has not been determined. Studies in this laboratory over the last several years provide evidence that oxidized phospholipids, present in OxLDL and also in the membrane of apoptotic cells, represent one such ligand. These oxidized phospholipids, either in the lipid phase of OxLDL or becoming attached covalently to apoprotein B during LDL oxidation, have been shown to play a major role in the binding of OxLDL to CD36 and to SR-B1 expressed in transfected cells. The lipid and protein moieties compete with each other to some extent, indicating that they are binding to at least one common site. A monoclonal antibody selected because of its reactivity with OxLDL proved to be an antibody against oxidized phospholipids (but not native phospholipids). This antibody (EO6) blocked the uptake of OxLDL by CD36 and by SR-B1 in transfected cells by as much as 80%; it also inhibited macrophage phagocytosis of apoptotic cells by about 40%. Thus, the persistence of receptors for OxLDL during evolution is probably accounted for by their role in recognition of ligands on the surfaces of oxidatively damaged or apoptotic cells. This has important implications in biology generally and specifically in atherogenesis, because apoptosis is a prominent feature of late lesions.

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PubMed2000

Scavenger receptors on liver Kupffer cells mediate the in vivo uptake of oxidatively damaged red blood cells in mice.

In vitro studies have shown that damaged red cells and apoptotic cells are efficiently phagocytosed by scavenger receptors from macrophages, even under non-opsonizing conditions. Damaged red blood cells are in vivo effectively removed from the blood circulation, but the responsible receptor systems are largely unknown. We used a murine model in which (51)Cr-labeled oxidized red blood cells were injected intravenously, and the cellular uptake sites and the potential involvement of scavenger receptors were analyzed. The decay of damaged red cells was rapid (more than 50% removed within 10 minutes after injection), whereas native red cells were not cleared. The main site of uptake of damaged red cells was the liver Kupffer cells, which contained 24% of the injected dose at 10 minutes after injection. The blood decay and liver uptake were inhibited by typical ligands for scavenger receptors, such as polyinosinic acid, liposomes containing phosphatidylserine, oxidized low-density lipoprotein, and fucoidan, but not by polyadenosinic acid or liposomes without phosphatidylserine. Mice lacking scavenger receptors class A type I and II showed no significant decrease in the ability to take up damaged red cells from the circulation. We conclude that Kupffer cells are mainly responsible for the removal of damaged red cells from the blood circulation, a process mediated by polyinosinic acid- and phosphatidylserine-sensitive scavenger receptors, different from scavenger receptor class A type I and II. Our data indicate that scavenger receptors, as pattern-recognizing receptors, play an important role in vivo in the removal of apoptotic, damaged, or other unwanted cells from the blood circulation. (Blood. 2000;95:2157-2163)

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PubMed1998

Evidence that the lipid moiety of oxidized low density lipoprotein plays a role in its interaction with macrophage receptors.

The binding of oxidatively damaged red blood cells (OxRBCs) to resident mouse peritoneal macrophages correlates with an increase in phosphatidylserine on the external leaflet of the plasma membrane. Liposomes rich in phosphatidylserine can inhibit this binding and also the binding of certain apoptotic cells. We have shown previously that oxidized low density lipoproteins (OxLDL) also can inhibit the binding of OxRBCs to resident mouse peritoneal macrophages. The present studies show that microemulsions prepared from the lipids extracted from OxLDL are very effective in inhibiting the binding of OxRBCs and also, to a lesser extent, of apoptotic thymocytes to macrophages. OxRBC binding was also inhibited by cholesterol phospholipid liposomes containing oxidized 1-stearoyl-2-linoleoyl-phosphatidylcholine. The binding and uptake of 125I-labeled OxLDL were also strongly inhibited by microemulsions of the lipids extracted from OxLDL and by cholesterol phospholipid liposomes containing oxidized 1-palmitoyl-2-arachidonoyl-phosphatidylcholine. Earlier studies have shown that the delipidated protein moiety of OxLDL can competitively inhibit macrophage binding of intact OxLDL, implicating the protein moiety as an effective receptor-binding domain of OxLDL with respect to some macrophage scavenger receptors. The present studies suggest that the lipid moiety of OxLDL may also play a role.

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PubMed1997

Macrophages lacking scavenger receptor A show a decrease in binding and uptake of acetylated low-density lipoprotein and of apoptotic thymocytes, but not of oxidatively damaged red blood cells.

Macrophage binding of oxidatively damaged red blood cells (OxRBC) and apoptotic thymocytes correlates in many instances with a loss of phospholipid bilayer asymmetry, i.e., with an increase in expression of phosphatidylserine on the outer leaflet of the plasma membrane. Oxidatively modified LDL (OxLDL) can compete for the binding of these ligands to macrophages. However, the receptor(s) responsible remains to be identified. The present studies show that mouse peritoneal macrophages totally lacking scavenger receptor A (SRA) bound OxRBC just as effectively as wild-type macrophages, whereas their binding and uptake of acetyl LDL was reduced by more than 80%. Binding of apoptotic thymocytes and binding of OxLDL were also reduced, but only by 20-30%. We conclude that SRA is not involved in the recognition of phosphatidylserine-rich membranes but contributes to the binding of OxLDL and apoptotic thymocytes. The binding of OxRBC was almost totally calcium-dependent, whereas the binding of apoptotic thymocytes was not, suggesting that the mechanisms involved in their uptake by macrophages under these conditions were different.

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PubMed1997

Characterization of CLA-1, a human homologue of rodent scavenger receptor BI, as a receptor for high density lipoprotein and apoptotic thymocytes.

Recently, a murine scavenger receptor type B class I (SR-BI) was identified that binds high density lipoprotein (HDL) and mediates the selective uptake of cholesterol esters. The human CD36 and LIMPII analogous-1 (CLA-1) receptor shows high sequence homology with SR-BI, but their functional relationship has not been determined. Transfected cells expressing CLA-1 bound HDL with a Kd of about 35 microg/ml, similar to the Kd for HDL binding to rodent SR-BI. This binding resulted in an intracellular accumulation of HDL-derived [3H]cholesterol esters without internalization or degradation of 125I-apolipoprotein. CLA-1 was strongly expressed in the adrenal gland and was also abundant in liver and testis, suggesting that CLA-1, like SR-BI, could play a role in the metabolism of HDL. However, CLA-1 was also expressed in monocytes and, like SR-BI, recognized modified forms of low density lipoproteins as well as native LDL and anionic phospholipids. These findings suggest that CLA-1 might have additional physiological functions. We found that CLA-1 recognizes apoptotic thymocytes. Our results demonstrate that CLA-1, a close structural homologue of SR-BI, is also functionally related to SR-BI and may play an important role as a "docking receptor" for HDL in connection with selective uptake of cholesterol esters. An additional role in recognition of damaged cells is suggested by these studies.

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PubMed1997

Independent mechanisms for macrophage binding and macrophage phagocytosis of damaged erythrocytes. Evidence of receptor cooperativity.

The binding and phagocytosis of oxidatively damaged red blood cells (OxRBCs) by mouse peritoneal macrophages can be inhibited by oxidatively modified LDL (OxLDL), implying some commonality at their receptor-binding domains. Studies from many different laboratories support the view that OxRBC binding is due to the disruption of plasma membrane phospholipid asymmetry and the subsequent exposure of phosphatidylserine (PS) on the outer membrane leaflet. Presumably, oxidation of LDL creates a surface structure on it in some way homologous to the PS-rich domain on OxRBCs. Apoptotic cells in some instances are also recognized because of PS exposure on the outer leaflet of the membrane, and apoptotic cells are a common feature of atherosclerotic lesions. In the present studies, the mechanisms of binding and internalization of cells recognized by virtue of their membrane PS were studied using OxRBCs or vanadate-treated erythrocytes (VaRBCs) as models. Disruption of phospholipid asymmetry with vanadate produced cells that were bound by macrophages in the same divalent cation-dependent manner as OxRBCs. However, whereas OxRBCs were rapidly phagocytosed, VaRBCs were not. Stimulation of mouse macrophages with phorbol myristate acetate resulted in a concentration-dependent induction of phagocytosis of bound VaRBCs, an effect that could be prevented by the protein kinase C inhibitor staurosporine. Because phagocytosis of OxRBCs occurred unassisted, we speculated that there must be additional membrane changes induced by oxidation (over and above the disruption of phospholipid asymmetry) that contribute to phagocytosis of OxRBCs, possibly resulting in the ligation of a distinct receptor that does not necessarily contribute to adherence. This proposal is supported by the finding that ligation of macrophage Fc gamma receptors by the anti-Fc gamma RII/RIII antibody 2.4G2 triggers the phagocytosis of bound VaRBCs. Phagocytosis is also triggered by subthreshold opsonization of VaRBC, i.e., by antibody concentrations that do not by themselves cause binding and phagocytosis of native RBCs. Finally, treatment with low concentrations of glutaraldehyde, which causes membrane protein cross-linking, promotes the phagocytosis of VaRBCs, but, at the low concentration used, has little or no effect on binding and phagocytosis of native RBCs. We suggest that the internalization of damaged cells, bound because of PS exposure, requires the cooperation of a PS-binding receptor with at least one additional receptor to trigger an intracellular signaling pathway to initiate phagocytosis.

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PubMed1996

Cell surface expression of mouse macrosialin and human CD68 and their role as macrophage receptors for oxidized low density lipoprotein.

We have previously identified a 94- to 97-kDa oxidized low density lipoprotein (LDL)-binding protein in mouse macrophages as macrosialin (MS), a member of the lamp family. Earlier immunostaining studies have shown that MS and its human homolog, CD68, are predominantly intracellular proteins. However, using sensitive techniques such as flow cytometry (FACS) and cell-surface-specific biotinylation, we now show that there is significant surface expression of these proteins. FACS analysis of intact cells using mAb FA/11 showed small but definite surface expression of MS in resident mouse peritoneal macrophages but this was greatly enhanced with thioglycollate elicitation. Biotinylation of intact cells and detergent-solubilized cell preparations followed by immunoprecipitation revealed 10-15% of the total MS content of elicited macrophages on the plasma membrane. Similar results were obtained with untreated RAW 264.7 cells. FACS analysis of intact THP-1 monocytic cells showed minimal surface expression of CD68 on unactivated cells (4% of total cell content). Stimulation with phorbol 12-myristate 13-acetate increased both surface and total CD68 expression considerably. Furthermore, the specific binding at 4 degrees C and uptake at 37 degrees C of 125I-labeled oxidized LDL by activated THP-1 cells was inhibited by 30-50% by CD68 mAbs KP-1 and EBM-11. Thus, although the surface expression of MS/CD68 at steady-state represents only a small percentage of their total cellular content, these proteins can play a significant role in oxidized LDL uptake by activated macrophages in vitro and could contribute to foam cell formation in atherosclerotic lesions.

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