| Summary: | Electronegative LDL [LDL(−)] 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(−) could bind to proteoglycans (PGs); therefore, our aim was to evaluate its affinity to PGs. Binding of LDL(−) and native LDL [LDL(+)] 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(−) had higher binding affinity to PGs than did LDL(+). PG capacity to bind LDL(−) was increased approximately 4-fold compared with LDL(+) in precipitation and microtiter assays. Chromatography on PG column showed LDL(−) to consist of two subpopulations, one with higher and one with lower PG binding affinity than LDL(+). 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(−) to bind to PGs could facilitate its retention in the extracellular matrix of arterial intima and contribute to atherosclerosis progression.
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