Dissertation
The regulation of endothelial lipase and lipoprotein lipase by ANGPTL3 and ANGPTL8
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2021
DOI: 10.17077/etd.006244
Abstract
Low levels of circulating high density lipoproteins (HDL) and high levels of plasma triglycerides (TG) are risk factors for cardiac disease and atherosclerosis. The liver-expressed protein angiopoietin-like 3 (ANGPTL3) regulates both plasma TG and HDL levels through inhibition of lipoprotein lipase (LPL), which hydrolyzes the triglycerides of TG-rich lipoproteins, and endothelial lipase (EL), which hydrolyzes the phospholipids of HDL. Recently ANGPTL8 has been shown to be essential for the ANGPTL3-mediated inhibition of LPL. However, the role of ANGPTL8 in modulating the inhibition of EL by ANGPTL3 (and thus modulating HDL levels) is not clear, nor has the mechanism by which ANGPTL3 inhibits LPL and EL been elucidated. In this thesis, I characterize the inhibition of EL by ANGPTL3 as most likely catalytic and show evidence that the ANGPTL proteins do not use cleavage as a mechanism to inhibit EL and LPL. I show that the presence of heparin partially blocks ANGPTL3 inhibition of EL and that EL bound to cells are protected from ANGPTL3 inhibition. I test ANGPTL3 mutants to provide information on how the protein structure alters its binding and inhibitory functions towards EL. Importantly, this thesis identifies that ANGPTL8 has no role in EL inhibition by ANGPTL3 and tests a common ANGPTL8 variant, R59W, to elucidate how LPL inhibition is altered. Finally, I characterize the activity of the T111I EL variant and found no differences in activity or ANGPTL3 inhibition of this mutant compared to wild-type. The contributions of this thesis increase our understanding of how ANGPTL3 and ANGTPL3+8 complexes regulate EL and LPL and modulate plasma lipoprotein levels and HDL. Understanding the mechanisms of ANGPTL3 inhibition of lipases and the role of ANGPTL8 in this inhibition, may advance efforts to pharmacologically target ANGPTL3 and ANGPTL8 to treat metabolic disorders caused by improper regulation and delivery of plasma lipids.
Details
- Title: Subtitle
- The regulation of endothelial lipase and lipoprotein lipase by ANGPTL3 and ANGPTL8
- Creators
- Kelli Larissa Davie
- Contributors
- Brandon Davies (Advisor)Eric Taylor (Committee Member)Brian O'Neill (Committee Member)Miles Pufall (Committee Member)Madeline Shea (Committee Member)Marc Wold (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Biochemistry
- Date degree season
- Autumn 2021
- DOI
- 10.17077/etd.006244
- Publisher
- University of Iowa
- Number of pages
- xiv, 125 pages
- Copyright
- Copyright 2021 Kelli Larissa Davie
- Comment
- This thesis has been optimized for improved web viewing. If you require the original version, contact the University Archives at the University of Iowa: https://www.lib.uiowa.edu/sc/contact/
- Language
- English
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (pages 106-125)
- Public Abstract (ETD)
High levels of fat (triglycerides) and low levels of “good” cholesterol (high-density lipoprotein, HDL) in the blood put individuals at risk to develop cardiovascular diseases, including heart attacks, or strokes. Clearance of fat and cholesterol from the blood depends on the activity of proteins called lipases. Lipoprotein lipase (LPL) clears triglycerides, and endothelial lipase (EL) indirectly clears HDL cholesterol. The action of these enzymes is controlled by a protein called angiopoietin-like 3 (ANGPTL3). ANGPTL3 is made in the liver and blocks EL from acting, which increases cholesterol levels in the blood. When ANGPTL3 works together with another protein, angiopoietin-like 8 (ANGPTL8), the complex of the two proteins blocks the action of LPL. Preventing LPL from working increases fat levels in the blood. There is still much to be learned about how these proteins interact and work together, as well as how the ANGPTL proteins block the action of EL and LPL. This thesis characterized the inhibition of EL by ANGPTL3 to be catalytic, identified binding and inhibition of EL are separable events, and found that ANGPTL8 does not contribute to ANGPTL3 blocking EL action. As part of these goals, I tested ANGPTL8 and EL mutations which are found in humans to understand how the mutations affected the function and interaction with other proteins. Since these proteins can alter the levels of triglycerides and cholesterol, understanding how to control their function and activity could help treat or prevent cardiovascular diseases.
- Academic Unit
- Biochemistry and Molecular Biology
- Record Identifier
- 9984210442602771
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