Angiopoietin-like protein 3 (ANGPTL3) is a hepatically secreted protein and therapeutic target for reducing plasma triglyceride-rich lipoproteins (TRL) and low-density lipoprotein cholesterol (LDL). Although ANGPTL3 modulates the metabolism of circulating lipoproteins, its role in TRL assembly and secretion remains unknown. CRISPR-associated protein 9 (CRISPR/Cas9) was used to target ANGPTL3 in HepG2 cells (ANGPTL3^-/-) whereupon we observed ∼50% reduction of ApoB100 secretion, accompanied by an increase in ApoB100 early presecretory degradation by a predominantly lysosomal mechanism. Despite defective particle secretion in ANGPTL3^-/- cells, targeted lipidomic analysis did not reveal neutral lipid accumulation in ANGPTL3^-/- cells, but rather ANGPTL3^-/- cells demonstrated decreased secretion of newly synthesized triglycerides and increased fatty acid oxidation. Furthermore, RNA sequencing demonstrated significantly altered expression of key lipid metabolism genes, including targets of PPARα, consistent with decreased lipid anabolism and increased lipid catabolism. In contrast, CRISPR/Cas9 LDLR deletion in ANGPTL3^-/- cells did not result in a secretion defect at baseline, but proteasomal inhibition strongly induced compensatory late presecretory degradation of ApoB100 and impaired its secretion. Additionally, these ANGPTL3^-/-;LDLR^-/- cells rescued the deficient LDL clearance of LDLR^-/- cells. Our findings suggest an unanticipated intrahepatic role for ANGPTL3, whose function varies with LDLR status. ANGPTL3 deficiency alone leads to the production of fewer lipoprotein particles due to early presecretory defects in particle assembly that are associated with adaptive changes in intrahepatic lipid metabolism. When LDLR is absent, ANGPTL3 deficiency is associated with late presecretory regulation of ApoB100 degradation.

中文翻译：

---

ANGPTL3 缺乏会损害脂蛋白的产生并导致肝脏脂质代谢发生适应性变化。

血管生成素样蛋白 3 (ANGPTL3) 是一种肝脏分泌蛋白，也是降低血浆富含甘油三酯脂蛋白 (TRL) 和低密度脂蛋白胆固醇 (LDL) 的治疗靶点。尽管 ANGPTL3 调节循环脂蛋白的代谢，但其在 TRL 组装和分泌中的作用仍不清楚。CRISPR 相关蛋白 9 (CRISPR/Cas9) 用于靶向 HepG2 细胞 (ANGPTL3 ^-/- ) 中的 ANGPTL3，随后我们观察到 ApoB100 分泌减少约 50%，同时主要通过溶酶体机制导致 ApoB100 早期分泌前降解增加。尽管ANGPTL3 ^-/-细胞中的颗粒分泌有缺陷，但靶向脂质组学分析并未揭示ANGPTL3 ^-/-细胞中的中性脂质积累，而是ANGPTL3 ^-/-细胞表现出新合成的甘油三酯的分泌减少和脂肪酸氧化增加。此外，RNA 测序表明关键脂质代谢基因（包括 PPARα 靶标）的表达显着改变，这与脂质合成代谢减少和脂质分解代谢增加一致。相比之下，ANGPTL3 ^-/-细胞中的 CRISPR/Cas9 LDLR 缺失不会导致基线分泌缺陷，但蛋白酶体抑制强烈诱导 ApoB100 的补偿性晚期分泌前降解并损害其分泌。此外，这些ANGPTL3 ^-/- ;LDLR ^{-/-细胞挽救了LDLR -/-}细胞的低密度脂蛋白清除缺陷。我们的研究结果表明 ANGPTL3 具有意想不到的肝内作用，其功能随 LDLR 状态而变化。由于颗粒组装的早期分泌前缺陷，单独的ANGPTL3缺陷会导致脂蛋白颗粒的产生减少，而颗粒组装与肝内脂质代谢的适应性变化相关。当 LDLR 缺失时，ANGPTL3 缺乏与 ApoB100 降解的晚期分泌前调节相关。