Abstract 116: Angptl3 Regulates Hepatic Lipoprotein Production: A New Model For Lipid Lowering?

Abstract

Background: Angiopoietin-like protein 3 (ANGPTL3 ) is a hepatically secreted protein and therapeutic target for reducing plasma triglyceride-rich lipoproteins and low-density lipoprotein cholesterol (LDL). Although ANGPTL3 modulates lipolytic pathways in lipoprotein metabolism, its potential intra-hepatocyte role in very low-density lipoprotein (VLDL) assembly and secretion remains unknown. Furthermore, although ANGPTL3 inhibition reduces low-density lipoprotein cholesterol (LDL), humans with complete LDL receptor (LDLR) deficiency exhibit LDLR-independent LDL lowering. Methods: We established hepatocyte cell culture systems, including CRISPR/Cas9-edited HepG2 cells with ANGPTL3 “knocked out” (KO). We also generated hepatocyte-like cells from patient-derived isogenic pluripotent stem cells (iPSCs) with and without ANGPTL3 KO. Radiolabeling was used to quantify apolipoprotein and triglyceride synthesis. Negative stain electron microscopy (NS-EM) was used to quantify the size of secreted lipoproteins. Results: We observed reduction of both apolipoprotein B100 and triglyceride synthesis and secretion in ANGPTL3 KO HepG2 cells. NS-EM demonstrated ANGPTL3-deficient HepG2 cells secrete significantly smaller lipoprotein particles compared to WT control cells. Together, these three findings suggest ANGPTL3 deficiency in hepatocytes results in the production of fewer, smaller, underlipidated lipoprotein particles. Conclusion: Our results point to an important intracellular role for ANGPTL3 within hepatocytes, suggesting that ANGPTL3 modifies the assembly and remodeling, as well as clearance, of hepatically secreted lipoproteins. Further experiments are planned to identify and characterize mechanistic mediators of this process. These studies have potential to identify additional targets for reducing plasma lipids via LDLR-independent pathways.