Apolipoprotein AV accelerates plasma hydrolysis of triglyceride-rich lipoproteins by interaction with proteoglycan-bound lipoprotein lipase
Apolipoprotein AV accelerates plasma hydrolysis of triglyceride-rich lipoproteins by interaction with proteoglycan-bound lipoprotein lipase
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DOI：
10.1074/jbc.m411412200
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发表时间：
2005-06-03
影响因子：
4.8
通讯作者：
Heeren, J
中科院分区：
文献类型：
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作者：
Merkel, M;Loeffler, B;Heeren, J
载脂蛋白A5(APOA5)与甘油三酯水平的差异和家族性混合性高脂血症有关。在基因工程小鼠中，载脂蛋白病毒血浆水平与血浆甘油三酯呈负相关。为了阐明载脂蛋白AV影响血浆甘油三酯的机制，进行了代谢研究和类似生理条件的体外测定。在人APOA5转基因小鼠(HAPOA5tr)中，由于脂蛋白脂肪酶(LPL)加速了甘油三酯的血浆水解率，乳糜粒和极低密度脂蛋白(VLDL)的分解代谢加快。肝脏极低密度脂蛋白和肠道乳糜粒的产生不受影响。通过将apoA5基因敲除的人LPL转基因与hAPOA5tR杂交到LPL缺失的背景中，进一步研究了apoAV和LPL之间的功能相互作用。脂蛋白脂酶活性的增加完全使载脂蛋白5缺陷小鼠的高甘油三酯血症正常化；然而，当脂蛋白脂蛋白降低时，人载脂蛋白AV的过表达仅轻微地调节甘油三酯水平。为了反映LPL与细胞表面蛋白多糖结合的生理状况，我们研究了在蛋白多糖存在或不存在的情况下的水解性。在没有蛋白多糖的情况下，来自富含甘油三酯的脂蛋白、hAPOA5tR高密度脂蛋白或重组来源的apoAV都不会改变LPL的水解率。然而，在蛋白多糖存在的情况下，apoAV导致LPL介导的极低密度脂蛋白甘油三酯水解率显著增加，且呈剂量依赖关系。这些结果在使用蛋白多糖缺陷细胞系的细胞培养中得到了证实。通过配体印迹实验发现LPL与apoAV之间存在直接相互作用。有人提出，载脂蛋白通过引导极低密度脂蛋白和乳糜粒结合到蛋白多糖结合的LPL进行脂解来降低甘油三酯水平。
Apolipoprotein A5 (APOA5) is associated with differences in triglyceride levels and familial combined hyperlipidemia. In genetically engineered mice, apoAV plasma levels are inversely correlated with plasma triglycerides. To elucidate the mechanism by which apoAV influences plasma triglycerides, metabolic studies and in vitro assays resembling physiological conditions were performed. In human APOA5 transgenic mice (hAPOA5tr), catabolism of chylomicrons and very low density lipoprotein (VLDL) was accelerated due to a faster plasma hydrolysis of triglycerides by lipoprotein lipase (LPL). Hepatic VLDL and intestinal chylomicron production were not affected. The functional interplay between apoAV and LPL was further investigated by cross-breeding a human LPL transgene with the apoa5 knock-out and the hAPOA5tr to an lpl-deficient background. Increased LPL activity completely normalized hypertriglyceridemia of apoa5-deficient mice; however, overexpression of human apoAV modulated triglyceride levels only slightly when LPL was reduced. To reflect the physiological situation in which LPL is bound to cell surface proteoglycans, we examined hydrolysis in the presence or absence of proteoglycans. Without proteoglycans, apoAV derived either from triglyceride-rich lipoproteins, hAPOA5tr high density lipoprotein, or a recombinant source did not alter the LPL hydrolysis rate. In the presence of proteoglycans, however, apoAV led to a significant and dose-dependent increase in LPL-mediated hydrolysis of VLDL triglycerides. These results were confirmed in cell culture using a proteoglycan-deficient cell line. A direct interaction between LPL and apoAV was found by ligand blotting. It is proposed, that apoAV reduces triglyceride levels by guiding VLDL and chylomicrons to proteoglycan-bound LPL for lipolysis.