High binding affinity of electronegative LDL to human aortic proteoglycans depends on its aggregation level

Abstract

Electronegative LDL [LDL (2)] is an atherogenic subfraction of plasma LDL that has increased apolipoprotein E (apoE) and apoC-III content, high density, and increased susceptibility to aggregation. These characteristics suggest that LDL(2) could bind to proteoglycans (PGs); therefore, our aim was to evaluate its affinity to PGs. Binding of LDL(2) and native LDL [LDL(1)] to human aortic PGs was determined by precipitation of LDL-glycosaminoglycan complexes, LDL incubation in PG-coated microtiter wells, and affinity chromatography on PG column. All methods showed that LDL(2) had higher binding affinity to PGs than did LDL(1). PG capacity to bind LDL(2) was increased approximately 4-fold compared with LDL(1) in precipitation and microtiter assays. Chromatography on PG column showed LDL(2) to consist of two subpopulations, one with higher and one with lower PG binding affinity than LDL(1). Unexpectedly, the lower PG affinity subpopulation had increased apoE and apoC-III content. In contrast, the high PG affinity subpopulation presented phospholipase C (PLC)-like activity and increased aggregation. These results suggest that PLC-like activity could alter LDL lipid composition, thereby promoting particle aggregation and binding to PGs. This propensity of a subpopulation of LDL(2) to bind to PGs could facilitate its retention in the extracellular matrix of arterial intima and contribute to atherosclerosis progression.-Bancells, C., S. Benítez, M. Jauhiainen, J. Ordóñez-Llanos, P. T. Kovanen, S. Villegas, J. L. Sánchez-Quesada, and K. Öörni. High binding affinity of electronegative LDL to human aortic proteoglycans depends on its aggregation level. J. Lipid Res. 2009. 50: 446-455.

Immunochemical Analysis of the Electronegative LDL Subfraction Shows That Abnormal N-terminal Apolipoprotein B Conformation Is Involved in Increased Binding to Proteoglycans

“…ApoB-100 in LDL(Ϫ) possesses impaired affinity to the LDL receptor (15,16). Moreover, LDL(Ϫ) has higher affinity to arterial PG than native LDL (17). Some of these atherogenic characteristics of LDL(Ϫ) are likely related to an altered structure of the LDL particle and specifically to changes of the apoB-100 conformation.…”

Modified Forms of LDL in Plasma

“…It has been reported that the capacity to induce aggregation could be mediated by the PLC-like activity (Bancells, 2010b), although other authors have suggested that plasma sPLA 2 could be involved in apoB misfolding (Greco, 2009). Regarding secondary structure of apoB, some authors have reported loss of secondary -helix structures whereas others did not find differences with native LDL (Asatryan, 2005;Bancells, 2009;Benitez, 2004b;Parasassi, 2001). …”

“…Aggregation of lipoproteins favors PG binding, and LDL(-) has a high tendency to aggregate (Bancells, 2010b). In fact, a subfraction of aggregated LDL(-) is responsible for the binding to PG (Bancells, 2009). This subfraction has an abnormal conformation that exposes an epitope in apoB, known as site Ib, that is an alternative binding site to PGs (Bancells, 2011).…”

“…A subpopulation of aggregated LDL(-) has recently been isolated and characterized. This subpopulation, which accounts for only 0.1-0.5 of total LDL in blood, has high affinity to arterial PG (Bancells, 2009). This increased binding seems to be mediated by abnormal conformation of the aminoterminal extreme of apoB (Bancells, 2011).…”

“…LDL(-) and PG present a high affinity for binding (Bancells, 2009). This could favor the subendothelial retention of LDL(-) and trigger the inflammatory response.…”