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Rull A.,Research Institute Of The Hospital Of Sant Pau Iib Sant Pau | Jayaraman S.,Boston University | Gantz D.L.,Boston University | Rivas-Urbina A.,Research Institute Of The Hospital Of Sant Pau Iib Sant Pau | And 6 more authors.
Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids | Year: 2016

Low-density lipoprotein (LDL) aggregation is central in triggering atherogenesis. A minor fraction of electronegative plasma LDL, termed LDL(-), plays a special role in atherogenesis. To better understand this role, we analyzed the kinetics of aggregation, fusion and disintegration of human LDL and its fractions, LDL(+) and LDL(-). Thermal denaturation of LDL was monitored by spectroscopy and electron microscopy. Initially, LDL(-) aggregated and fused faster than LDL(+), but later the order reversed. Most LDL(+) disintegrated and precipitated upon prolonged heating. In contrast, LDL(-) partially retained lipoprotein morphology and formed soluble aggregates. Biochemical analysis of all fractions showed no significant degradation of major lipids, mild phospholipid oxidation, and an increase in non-esterified fatty acid (NEFA) upon thermal denaturation. The main baseline difference between LDL subfractions was higher content of NEFA in LDL(-). Since NEFA promote lipoprotein fusion, increased NEFA content can explain rapid initial aggregation and fusion of LDL(-) but not its resistance to extensive disintegration. Partial hydrolysis of apoB upon heating was similar in LDL subfractions, suggesting that minor proteins importantly modulate LDL disintegration. Unlike LDL(+), LDL(-) contains small amounts of apoA-I and apoJ. Addition of exogenous apoA-I to LDL(+) hampered lipoprotein aggregation, fusion and precipitation, while depletion of endogenous apoJ had an opposite effect. Therefore, the initial rapid aggregation of LDL(-) is apparently counterbalanced by the stabilizing effects of minor proteins such as apoA-I and apoJ. These results help identify key determinants for LDL aggregation, fusion and coalescence into lipid droplets in vivo. © 2016 Elsevier B.V. All rights reserved. Source

Martinez-Bujidos M.,Research Institute Of The Hospital Of Sant Pau Iib Sant Pau | Martinez-Bujidos M.,Autonomous University of Barcelona | Rull A.,Research Institute Of The Hospital Of Sant Pau Iib Sant Pau | Gonzalez-Cura B.,Research Institute Of The Hospital Of Sant Pau Iib Sant Pau | And 6 more authors.
FASEB Journal | Year: 2015

Clusterin/apolipoprotein J (apoJ) is an extracellular chaperone involved in the quality control system against protein aggregation. A minor part of apoJ is transported in blood bound to LDLs, but its function is unknown. Our aim was to determine the role of apoJ bound to LDLs. Total LDL from human plasma was fractionated into native LDL [LDL(+)] and electronegative LDL [LDL(-)]. The latter was separated into nonaggregated [nagLDL(-)] and aggregatedLDL(-)[agLDL (-)]. The content of apoJ was 6-fold higher in LDL(-) than in LDL(+) and 7-fold higher in agLDL(-) than in nagLDL(-). The proportion of LDL particles containing apoJ (LDL/J+) was 3-fold lower in LDL(+) than in LDL(-). LDL/J+ particles shared several characteristics with agLDL(-), including increased negative charge and aggregation. apoJ-depleted particles (LDL/J-) showed increased susceptibility to aggregation, whether spontaneous or induced by proteolysis or lipolysis, as was revealed by turbidimetric analysis, gel filtration chromatography, lipoprotein precipitation, native gradient gel electrophoresis, circular dichroism, and transmission electronic microscopy. The addition of purified apoJ to total LDL also prevented its aggregation induced by proteolysis or lipolysis. These findings point to apoJ as a key modulator of LDL aggregation and reveal a putative new therapeutic strategy against atherosclerosis. © FASEB. Source

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