ANGPTL3 deficiency impairs lipoprotein production and produces adaptive changes in hepatic lipid metabolism

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.