the pathophysiology of atherosclerosis ( 2 ). After LDL particles enter the intima of the artery wall, they can interact with proteoglycans, which are structural proteins residing in the extracellular matrix that consist of one or more glycosaminoglycan (GAG) side-chains attached to core proteins. The LDL-proteoglycan complex is generally regarded as an electrostatic interaction ( 3 ). The sulfation pattern of the acidic sugar groups that form the GAG chains on the proteoglycans results in an overall negative charge that can interact with clusters of positively charged amino acid residues on apoB-100, the primary apolipoprotein present on the LDL particle ( 4 ). A proteoglycan frequently deposited in atherosclerotic plaques of humans ( 5, 6 ) and mice is biglycan (BGN) ( 7 ).While plasma LDL cholesterol concentrations are predictive of the extent of atherosclerosis, LDL particles are heterogeneous in size and composition, and this heterogeneity may provide additional useful information about the role of LDL in atherosclerosis. For instance, studies have shown that diet-induced alterations in the FA composition of LDL core cholesteryl esters (CEs) can infl uence the atherogenic potential of LDL particles ( 8-11 ). In nonhuman primates, consumption of dietary MUFAs resulted in LDL particles containing a CE core enriched in cholesterol oleate (CO), which were positively associated with coronary artery atherosclerosis ( r = 0.8) ( 10, 11 ). Importantly, a similar diet-related shift in the CE FA composition of LDL has been observed in humans in which consumption of oleate-enriched diets resulted in elevations in the percentage of CO in the LDL CE ( 12 ). Additionally, the large Atherosclerosis Risk in Communities Study revealed a Abstract Several studies in humans and animals suggest that LDL particle core enrichment in cholesteryl oleate (CO) is associated with increased atherosclerosis. Diet enrichment with MUFAs enhances LDL CO content. Steroyl O -acyltransferase 2 (SOAT2) is the enzyme that catalyzes the synthesis of much of the CO found in LDL, and gene deletion of SOAT2 minimizes CO in LDL and protects against atherosclerosis. The purpose of this study was to test the hypothesis that the increased atherosclerosis associated with LDL core enrichment in CO results from an increased affi nity of the LDL particle for arterial proteoglycans. ApoB-100-only Ldlr − /− mice with and without Soat2 gene deletions were fed diets enriched in either cis -MUFA or n-3 PUFA, and LDL particles were isolated. LDL:proteogylcan binding was measured using surface plasmon resonance. Particles with higher CO content consistently bound with higher affi nity to human biglycan and the amount of binding was shown to be proportional to the extent of atherosclerosis of the LDL donor mice. The data strongly support the thesis that atherosclerosis was induced through enhanced proteoglycan binding of LDL resulting from LDL core CO