载脂蛋白AV(APOA5)通过与血管生成素样蛋白3/8复合物(ANGPTL3/8)结合并抑制其抑制脂蛋白脂酶(LPL)催化活性的能力以及将LPL从结合位点分离的能力,从而降低血浆甘油三酯(TG)水平。毛细血管。然而,APOA5中抑制ANGPTL3/8活性所需的序列从未被定义。这些序列的同一性的线索是,两名患有APOA5突变的患者中存在严重的高甘油三酯血症,该突变将APOA5截短了35个残基(“APOA5Δ35”)。我们发现野生型(WT)人APOA5而不是APOA5Δ35抑制ANGPTL3/8抑制LPL催化活性的能力。为了追求这一发现,我们制备了缺乏40个C端氨基酸的突变小鼠APOA5蛋白(“APOA5Δ40”)。小鼠WT-APOA5,而不是APOA5Δ40,抑制了ANGPTL3/8抑制LPL催化活性的能力,并急剧降低了小鼠的血浆TG水平。WT-APOA5,而不是APOA5Δ40,在Apoa5-/-小鼠(其中TG水平高,血管内LPL水平低)中增加了毛细血管内LPL水平,并降低了血浆TG水平。此外,WT-APOA5,而不是APOA5Δ40,阻断了ANGPTL3/8从培养细胞中分离LPL的能力。最后,在WT小鼠中,针对与小鼠APOA5的最后26个氨基酸相对应的合成肽的抗体降低了毛细管内LPL水平并增加了血浆TG水平.我们得出的结论是,APOA5中的C端序列对于在体外抑制ANGPTL3/8活性以及在体内调节毛细管内LPL水平和血浆TG水平至关重要。
Apolipoprotein AV (APOA5) lowers plasma triglyceride (TG) levels by binding to the angiopoietin-like protein 3/8 complex (ANGPTL3/8) and suppressing its capacity to inhibit lipoprotein lipase (LPL) catalytic activity and its ability to detach LPL from binding sites within capillaries. However, the sequences in APOA5 that are required for suppressing ANGPTL3/8 activity have never been defined. A clue to the identity of those sequences was the presence of severe hypertriglyceridemia in two patients harboring an APOA5 mutation that truncates APOA5 by 35 residues (\"APOA5Δ35\"). We found that wild-type (WT) human APOA5, but not APOA5Δ35, suppressed ANGPTL3/8\'s ability to inhibit LPL catalytic activity. To pursue that finding, we prepared a mutant mouse APOA5 protein lacking 40 C-terminal amino acids (\"APOA5Δ40\"). Mouse WT-APOA5, but not APOA5Δ40, suppressed ANGPTL3/8\'s capacity to inhibit LPL catalytic activity and sharply reduced plasma TG levels in mice. WT-APOA5, but not APOA5Δ40, increased intracapillary LPL levels and reduced plasma TG levels in Apoa5-/- mice (where TG levels are high and intravascular LPL levels are low). Also, WT-APOA5, but not APOA5Δ40, blocked the ability of ANGPTL3/8 to detach LPL from cultured cells. Finally, an antibody against a synthetic peptide corresponding to the last 26 amino acids of mouse APOA5 reduced intracapillary LPL levels and increased plasma TG levels in WT mice. We conclude that C-terminal sequences in APOA5 are crucial for suppressing ANGPTL3/8 activity in vitro and for regulating intracapillary LPL levels and plasma TG levels in vivo.