Plasma levels of high density lipoprotein (HDL) cholesterol are inversely associated with risk of atherosclerotic cardiovascular disease in humans, and preclinical studies have consistently demonstrated that intervention to raise HDL inhibits progression or induces regression of atherosclerosis (1). HDL is believed to protect against atherosclerosis by promoting """"""""reverse cholesterol transport"""""""" (2), as well as potentially through a variety of other protective properties. However, despite advances over the last decade, the molecular regulation of HDL metabolism and reverse cholesterol transport (RCT) remain incompletely understood, the relevance of other HDL properties remains uncertain, and the concept of directly targeting HDL therapeutically in humans remains unproven (3). There are relatively few validated targets for developing novel therapeutic approaches targeted toward HDL (4). The most advanced, CETP inhibition, has come into question as a therapeutic strategy (5). Recent genome-wide association studies (GWAS) have begun to identify previously unsuspected genes involved in regulating HDL-C levels, and have also established that all three members of the subfamily of extracellular lipases that act on lipoproteins, lipoprotein lipase (LPL), hepatic lipase (HL), and endothelial lipase (EL), are significantly associated with variation in HDL-C levels. Clearly this subfamily plays a key role in modulating HDL metabolism, as well as risk of atherosclerosis. However, the detailed mechanisms by which these lipases influence HDL metabolism, the environmental and genetic factors that regulate their expression, and the other gene products they interact with to regulate HDL metabolism and function remain incompletely understood. We propose to address the interactions of EL with HL in modulating HDL metabolism and atherogenesis, the interactions of EL and HL with the lipid transfer proteins cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP), the implications and mechanisms of upregulation of EL activity in the obese insulin resistant state, and the regulation of HDL metabolism through naturally-occurring genetic polymorphisms in the coding region and promoter of the EL gene. These studies span biochemical, cell biology, mouse, and human translational studies in an effort to address the questions. This subfamily of lipases is a potential target for novel therapeutic development, and these studies will provide greater understanding of their effects on HDL metabolism and function, enabling future treatments to prevent atherosclerosis.

Public Health Relevance

The goal of this project is to provide important new insight into the role of lipid-degrading enzymes (lipases) and their interactions with lipid transfer proteins in modulating HDL (good cholesterol) metabolism and atherosclerosis, as well as their role in mediating the low HDL associated with the obese insulin resistant state;and their human genetics as it relates to effects on HDL and coronary artery disease.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Method to Extend Research in Time (MERIT) Award (R37)
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Integrative Nutrition and Metabolic Processes Study Section (INMP)
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Liu, Lijuan
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University of Pennsylvania
Internal Medicine/Medicine
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United States
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Khetarpal, Sumeet A; Babb, Paul L; Zhao, Wei et al. (2018) Multiplexed Targeted Resequencing Identifies Coding and Regulatory Variation Underlying Phenotypic Extremes of High-Density Lipoprotein Cholesterol in Humans. Circ Genom Precis Med 11:e002070
Xu, Yu-Xin; Redon, Valeska; Yu, Haojie et al. (2018) Role of angiopoietin-like 3 (ANGPTL3) in regulating plasma level of low-density lipoprotein cholesterol. Atherosclerosis 268:196-206
Kuwano, Takashi; Bi, Xin; Cipollari, Eleonora et al. (2017) Overexpression and deletion of phospholipid transfer protein reduce HDL mass and cholesterol efflux capacity but not macrophage reverse cholesterol transport. J Lipid Res 58:731-741
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
Qamar, Arman; Khetarpal, Sumeet A; Khera, Amit V et al. (2015) Plasma apolipoprotein C-III levels, triglycerides, and coronary artery calcification in type 2 diabetics. Arterioscler Thromb Vasc Biol 35:1880-8
Khetarpal, Sumeet A; Rader, Daniel J (2015) Triglyceride-rich lipoproteins and coronary artery disease risk: new insights from human genetics. Arterioscler Thromb Vasc Biol 35:e3-9
Mehta, Nidhi; Qamar, Arman; Qu, Liming et al. (2014) Differential association of plasma angiopoietin-like proteins 3 and 4 with lipid and metabolic traits. Arterioscler Thromb Vasc Biol 34:1057-63
Yang, Yanbo; Kuwano, Takashi; Lagor, William R et al. (2014) Lipidomic analyses of female mice lacking hepatic lipase and endothelial lipase indicate selective modulation of plasma lipid species. Lipids 49:505-15
Miksztowicz, VerĂ³nica; Schreier, Laura; McCoy, Mary et al. (2014) Role of SN1 lipases on plasma lipids in metabolic syndrome and obesity. Arterioscler Thromb Vasc Biol 34:669-75
Miksztowicz, Veronica; McCoy, Mary G; Schreier, Laura et al. (2012) Endothelial lipase activity predicts high-density lipoprotein catabolism in hemodialysis: novel phospholipase assay in postheparin human plasma. Arterioscler Thromb Vasc Biol 32:3033-40

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