Project 2: ANGPTL3-dependent mechanisms underlying adaptations in hepatic lipoprotein production and clearance

University Of Washington, Seattle WA

Investigators

Linked publications & trials

Abstract

PROJECT SUMMARY Inhibiting ANGPTL3 recently emerged as a novel therapeutic approach for reducing both LDL cholesterol and triglyceride-rich lipoproteins. Our recent studies found that HepG2 cells (an immortalized hepatoma cell line used to model hepatic lipoprotein assembly, secretion, and uptake) lacking ANGPTL3 secrete 50% less APOB100 and enhance the proteolysis of APOB that has left the endoplasmic reticulum but has not yet been secreted. Despite defective particle secretion, these ANGPTL3-deficient cells do not accumulate intracellular lipids, but instead decrease their secretion of newly synthesized triglycerides; they also increase fatty acid oxidation. Further, we found that uptake of LDL particles by HepG2 cells lacking both ANGPTL3 and the LDL receptor was equivalent to that of wild-type cells. However, the cellular mechanisms underlying these beneficial adaptations remain unclarified. Here, we propose to focus on the mechanisms of ANGPTL3- dependent adaptations in lipoprotein production and clearance, using a combination of mechanistic cell systems and mouse models to address two specific aims. In Aim 1, we will determine how ANGPTL3 deficiency lowers LDL through LDLR-independent mechanisms and how it also reduces hepatic VLDL production. To pursue this, we will test the hypotheses that hepatic ANGPTL3-deficiency promotes the LDLR- independent uptake of LDL by reducing the expression of a specific heparin sulfate proteoglycan while modulating lipoprotein secretion and intracellular lipid content by increasing intracellular hepatic lipase and/or PPAR-α activity. In Aim 2, we will exploit the ANGPTL3-dependent adaptations in VLDL production to modify hepatic steatosis and reduce circulating TRLs to mitigate atherosclerosis. To pursue this, we will examine mouse models of adaptive and maladaptive pathways affecting hepatic lipogenesis/lipid utilization, including models of type 2 diabetes. We will then determine the impact of those pathways on VLDL assembly/secretion, the effect of ANGPTL3 silencing, and explore the resulting functional changes in lipoprotein particle composition and their atherogenic potential. Our studies are poised to provide important insights into the mechanisms whereby ANGPTL3 impacts hepatic lipoprotein metabolism, with the potential to identify novel therapeutic targets and pathways.