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Scavenger receptors, which include various classes, play an important role in atherogenesis by mediating the unrestricted uptake of modified lipoproteins, resulting in the massive accumulation of cholesteryl esters. Because macrophage-derived foam cells are considered to be an important feature in early atherogenesis, we investigated the role of scavenger receptor class A (SR-A) overexpression, especially on macrophages in lipoprotein metabolism and atherosclerosis. Bone marrow from human SR-A (MSR1)-overexpressing mice was transplanted into irradiated low density lipoprotein receptor knockout [LDLR(-/-)] mice. The transplantation resulted in an increase in total serum cholesterol (approximately 15 to 25%), especially in the VLDL fraction, when compared with LDLR(-/-) mice that were transplanted with bone marrow of wild-type littermates. Quantification of atherosclerotic lesions in the mice that were fed a 'Western-type' diet for 3 months revealed that there were no differences in mean lesion area between LDLR(-/-) mice transplanted with MSR1 overexpressing and wild-type littermate bone marrow, despite increased scavenger receptor activity in vitro. The presence or absence of the LDLR in the transplanted bone marrow did not influence these results. In conclusion, introduction of MSR1-overexpressing bone marrow in LDLR(-/-) mice via bone marrow transplantation resulted in a slight increase in lipoprotein levels, but had no effect on the atherosclerotic lesion area, despite increased scavenger receptor activity in vitro. - Herijgers, N., M. P. J. de Winther, M. Van Eck, L. M. Havekes, M. H. Hofker, P. M. Hoogerbrugge, and T. J. C. Van Berkel. Effect of human scavenger receptor class A overexpression in bone marrow-derived cells on lipoprotein metabolism and atherosclerosis in low density lipoprotein receptor knockout mice. Chemicals/CAS: acetyl-LDL; Cell Adhesion Molecules; Lipoproteins; Lipoproteins, LDL; MSR1 protein, human; Msr1 protein, mouse; Receptors, Immunologic; Receptors, LDL; Receptors, Scavenger; Scavenger Receptors, Class A

In the arterial wall, scavenger receptor class A (SRA) is implicated in pathological lipid deposition. In contrast, in the liver, SRA is suggested to remove modified lipoproteins from the circulation, thereby protecting the body from their pathological action. The role of SRA on bone marrow-derived cells in lipid metabolism and atherogenesis was assessed in vivo by transplantation of bone marrow cells overexpressing human SRA (MSR1) to apoE-deficient mice. In vitro studies with peritoneal macrophages from the transplanted mice showed that macrophage scavenger receptor function, as measured by cell association and degradation studies with acetylated LDL, was ≃3-fold increased on overexpression of MSR1 in bone marrow-derived cells as compared with control mice. Despite the increased macrophage scavenger receptor function in vitro, no significant effect of MSR1 overexpression in bone marrow-derived cells on the in vivo atherosclerotic lesion development was found. In addition to arterial wall macrophages, liver sinusoidal Kupffer cells also overexpress MSR1 after bone marrow transplantation, which may scavenge atherogenic particles more efficiently from the blood compartment. Introduction of bone marrow cells overexpressing human MSR1 in apoE-deficient mice induced a significant reduction in serum cholesterol levels of ≃20% (P < 0.001, 2-way ANOVA) as the result of a decrease in VLDL cholesterol. It is suggested that the reduction in VLDL cholesterol levels is due to increased clearance of modified lipoproteins by the overexpressed MSR 1 in Kupffer cells of the liver, thereby protecting the arterial wall against the proatherogenic action of modified lipoproteins. Chemicals/CAS: acetyl-LDL; Apolipoproteins E; Cholesterol, VLDL; Lipoproteins, LDL; Membrane Proteins; oxidized low density lipoprotein; Receptors, Immunologic; Receptors, Lipoprotein; Receptors, Scavenger; Scarb1 protein, mouse; Scavenger Receptors, Class A; Scavenger Receptors, Class B; Triglycerides

The effect of monocyte/macrophage-derived wild-type mouse apolipoprotein E (apoE), human apoE3-Leiden, and human apoE2 on serum cholesterol levels and the development of atherosclerosis in apoE-deficient (apoe-/-) mice was investigated by using bone marrow transplantation (BMT). At 4 weeks after BMT, murine apoe+/+ bone marrow reduced serum cholesterol levels by 87% in apoe-/- mice, whereas macrophage-derived human apoE3-Leiden and human apoE2 induced a maximal, transient reduction of 35% and 48%, respectively. At 4 months after BMT, atherosclerosis was 23-fold (P<0.001) reduced in apoe+/+→apoe-/- mice, whereas no significant reduction in apoE3-Leiden.apoe- /-→apoe-/- and apoE2.apoe-/-→apoe-/- mice could be demonstrated. A highly significant decrease in serum cholesterol levels (78% reduction) and atherosclerosis (21-fold, P<0.001) was found in apoE3-Leiden.apoe-/- animals expressing high levels of apoE in multiple tissues, whereas apoE2 was ineffective even at high concentrations. Furthermore, in contrast to apoE- deficient macrophages, cholesterol efflux from apoE2 or apoE3-Leiden macrophages was not impaired. In conclusion, apoE3-Leiden as well as apoE2 are less effective in reducing cholesterol levels and atherosclerosis in apoe-/- animals, compared with apoe+/+, with apoE2<apoE3-Leiden<apoe+/+, irrespective of the observed adequate efflux of cholesterol from macrophages expressing apoE2 and apoE3-Leiden, indicating that normalization of cholesterol efflux by macrophages is not accompanied by measurable effects on lesion growth. Chemicals/CAS: Apolipoprotein E2; apolipoprotein E3 (Leidein); Apolipoprotein E3; Apolipoproteins E; Cholesterol, 57-88-5