Coronary artery disease (CAD) remains among the highest disease burdens in the modern world. Despite effective treatments focused on specific risk factors such as LDL cholesterol (LDL-C), prevalence and mortality from this disease remains very high. This necessitates investigating additional risk factors and identifying novel targets for treatment. Apolipoproteins C-III and A-V are reciprocal regulators of TG in plasma and were recently implicated through human genetics as being significantly related to risk of developing CAD. Genetic studies suggested that inactivating ApoC-III or enhancing ApoA-V, may protect against CAD. However, we currently have very little understanding of the structure and mechanisms of these two proteins and how the disease-associated mutations exert their effects to regulate TG levels and CAD risk. In this proposal, we seek to elucidate the helical and structural dynamics of the wild-type (WT) forms of these two apolipoproteins in the lipid-free and lipid-bound states through hydrogen-deuterium exchange and mass spectrometry to amino acid- level resolution. We will also study the effects the identified coding mutations on protein folding, dynamics, and lipid binding. We posit that the identified mutations influence lipid binding and cause altered TG metabolism through impacting lipoprotein association, LPL activity, TG-rich lipoprotein clearance and hepatic TG metabolism. We will test hypotheses for how each variant is acting through biochemical approaches and complementary in vivo studies comparing expression of WT and mutant ApoC-III/A-V in humanized mouse models. Finally, we will assess the impact of the CAD-associated ApoC-III/A-V mutations on atherogenesis in vivo. The proposed experiments will decipher the specific mechanisms of action of ApoC-III and ApoA-V in regulating TG metabolism and risk of CAD, and determine the structural features most crucial to these functions.
High triglycerides are a risk factor for cardiovascular disease. ApoC-III and ApoA-V are proteins found in the blood that play major roles in regulating the amount of circulating triglycerides. This study aims to understand how ApoC-III and ApoA-V function in regulating the metabolism of blood triglycerides. Specifically, we want to understand how ApoC-III and ApoA-V, which have been shown to regulate the breakdown of triglycerides, interact with triglycerides to regulate their turnover. In addition, we want to know how mutations in ApoC-III that result in lower triglyceride levels and mutations in ApoA-V that cause higher triglycerides affect the structure and function of these proteins, triglyceride metabolism, and how they lead to increased risk of cardiovascular disease and heart attacks.
| Khetarpal, Sumeet A; Zeng, Xuemei; Millar, John S et al. (2017) A human APOC3 missense variant and monoclonal antibody accelerate apoC-III clearance and lower triglyceride-rich lipoprotein levels. Nat Med 23:1086-1094 |
