Retention of Low-Density Lipoprotein in Atherosclerotic Lesions of the Mouse

Abstract

Abstract-Direct binding of apolipoprotein (apo)B-containing lipoproteins to proteoglycans is the initiating event inatherosclerosis, but the processes involved at later stages of development are unclear. Here, we investigated the importance of the apoB-proteoglycan interaction in the development of atherosclerosis over time and investigated the role of lipoprotein lipase (LPL) to facilitate low-density lipoprotein (LDL) retention at later stages of development. Atherosclerosis was analyzed in apoB transgenic mice expressing LDL with normal (control LDL) or reduced proteoglycan-binding (RK3359-3369SA LDL) activity after an atherogenic diet for 0 to 40 weeks. The initiation of atherosclerosis was delayed in mice expressing RK3359-3369SA LDL, but they eventually developed the same level of atherosclerosis as mice expressing control LDL. Retention studies in vivo showed that although higher levels of 131 I-tyramine cellobiose-labeled control LDL ( 131 I-TC-LDL) were retained in nonatherosclerotic aortae compared with RK3359-3369SA 131 I-TC-LDL, the retention was significantly higher and there was no difference between the groups in atherosclerotic aortae. Lower levels of control 125 I-TC-LDL and RK3359-3369SA 125 I-TC-LDL were retained in atherosclerotic aortae from ldlr Ϫ/Ϫ mice transplanted with lpl Ϫ/Ϫ compared with lpl ϩ/ϩ bone marrow. Uptake of control LDL or RK3359-3369SA LDL into macrophages with specific expression of human catalytically active or inactive LPL was increased compared with control macrophages. 1 We tested the response-toretention hypothesis 2 in an earlier study using genetically modified mice that expressed human recombinant lowdensity lipoproteins (LDLs) with reduced proteoglycanbinding activity and provided direct evidence showing that subendothelial retention of apolipoprotein (apo)B100-containing lipoproteins is the initiating event in atherogenesis. 3 Furthermore, we demonstrated that the atherogenicity of LDL is linked to their proteoglycan-binding activity. 3 Lipoproteins associate with artery wall proteoglycans via both direct and indirect interactions. Direct binding between LDL and proteoglycans involves an ionic interaction between basic amino acids in apoB100 (Site B; residues 3359 to 3369) and negatively charged sulfate groups on the glycosaminoglycan (GAG) chains of proteoglycans. 4,5 Indirect binding between LDL and proteoglycans is facilitated by apoE, 3 which is found in human atherosclerotic plaques together with apoB. 6 ApoE binds vascular proteoglycans, and apoEenrichment of proteoglycan-binding-defective LDL (in which Site B has been inactivated by mutagenesis) partly restores proteoglycan binding. 3 Mouse LDL contains significant amounts of apoE, and consequently proteoglycan-bindingdefective LDL isolated from mouse plasma displays Ϸ30% of normal proteoglycan binding. 3 Subendothelial retention of LDL via indirect binding to GAGs can also be facilitated by lipoprotein lipase (LPL). 7 We have shown previously that the binding between LPL and LDL is mediated throug...

Serum Amyloid A, but Not C-Reactive Protein, Stimulates Vascular Proteoglycan Synthesis in a Pro-Atherogenic Manner

“…55 The role of proteoglycans in atherosclerosis is complex because they play many roles in addition to lipoprotein binding, and the relative importance of proteoglycanmediated lipoprotein retention may alter with progression of the atherosclerotic lesion development. 10 However, given the co-localization observed between apoB and biglycan in both mouse and human atherosclerosis, we propose that biglycan is a key proteoglycan of interest. There are no data on the effect of biglycan deficiency or overexpression on atherosclerosis development, but overexpression of biglycan in vitro led to increased retention of LDL on complex extracellular matrices.…”

Conformational changes of apoB-100 in SMase-modified LDL mediate formation of large aggregates at acidic pH

“…In this work, lipoprotein lipase was found to play a purely structural role in linking aggregated LDL to the matrix. Interestingly, arterial-wall matrix, lipoprotein lipase, and SMase have each been shown to contribute to retention of apoB-100-containing lipoproteins and atherogenesis in vivo ( 6,(42)(43)(44).…”

Antisense oligonucleotide reduction of apoB-ameliorated atherosclerosis in LDL receptor-deficient mice

“…Interestingly, there was a 53% reduction of aortic sinus atherosclerosis in mice given 75 mg/kg/wk relative to the 50 mg/kg/wk treatment. Strong evidence exists that apoB is atherogenic due to its ability to bind and retain lipoproteins on the vascular wall and thereby facilitate oxidative modifi cations of LDL (28)(29)(30).…”