Greco Giulia, Balogh Gabor, Brunelli Roberto, Costa Graziella, De Spirito Marco, Lenzi Laura, Mei Giampiero, Ursini Fulvio, Parasassi Tiziana
Istituto di Neurobiologia e Medicina Molecolare, CNR, Rome, Italy.
Biophys J. 2009 Jul 22;97(2):628-35. doi: 10.1016/j.bpj.2009.05.005.
Human plasma contains small amounts of a low density lipoprotein in which apoprotein is misfolded. Originally identified and isolated by means of anion-exchange chromatography, this component was subsequently described as electronegative low density lipoprotein (LDL)(-), with increased concentrations associated with elevated cardiovascular disease risk. It has been recognized recently as the trigger of LDL amyloidogenesis, which produces aggregates similar to subendothelial droplets observed in vivo in early atherogenesis. Although LDL(-) has been produced in vitro through various manipulations, the mechanisms involved in its generation in vivo remain obscure. By using a more physiological model, we demonstrate spontaneous, sustained and noticeable production of LDL(-) during incubation of unprocessed human plasma at 37 degrees C. In addition to a higher fraction of amyloidogenic LDL(-), LDL purified from incubated plasma contains an increased level of lysophospholipids and free fatty acids; analysis of LDL lipids packing shows their loosening. As a result, during plasma incubation, lipid destabilization and protein misfolding take place, and aggregation-prone particles are generated. All these phenomena can be prevented by inhibiting calcium-dependent secretory phospholipases A2. Our plasma incubation model, without removal of reaction products, effectively shows a lipid-protein interplay in LDL, where lipid destabilization after lipolysis threatens the apoprotein's structure, which misfolds and becomes aggregation-prone.
人血浆中含有少量载脂蛋白发生错误折叠的低密度脂蛋白。该成分最初通过阴离子交换色谱法鉴定和分离，随后被描述为带负电的低密度脂蛋白（LDL）（-），其浓度升高与心血管疾病风险增加相关。最近它被认为是LDL淀粉样变性的触发因素，这种淀粉样变性会产生与早期动脉粥样硬化体内观察到的内皮下液滴相似的聚集体。尽管LDL（-）已通过各种体外操作产生，但其在体内产生的机制仍不清楚。通过使用更符合生理的模型，我们证明了在37℃孵育未处理的人血浆期间会自发、持续且显著地产生LDL（-）。除了更高比例的可形成淀粉样蛋白的LDL（-）外，从孵育血浆中纯化的LDL含有更高水平的溶血磷脂和游离脂肪酸；对LDL脂质堆积的分析表明其变得疏松。因此，在血浆孵育过程中，会发生脂质不稳定和蛋白质错误折叠，并产生易于聚集的颗粒。通过抑制钙依赖性分泌型磷脂酶A2可以防止所有这些现象。我们的血浆孵育模型在不去除反应产物的情况下，有效地展示了LDL中脂质与蛋白质的相互作用，其中脂解后脂质的不稳定会威胁到载脂蛋白的结构，使其错误折叠并易于聚集。
