Mapping the sites of the lipoprotein lipase (LPL)–angiopoietin-like protein 4 (ANGPTL4) interaction provides mechanistic insight into LPL inhibition

Aspen R Gutgsell,Swapnil V Ghodge,Albert A Bowers,Saskia B Neher

doi:10.1074/jbc.ra118.005932

Aspen R Gutgsell, Swapnil V Ghodge + Show 2 more

Open Access

https://doi.org/10.1074/jbc.ra118.005932

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Abstract

Cardiovascular disease has been the leading cause of death throughout the world for nearly 2 decades. Hypertriglyceridemia affects more than one-third of the population in the United States and is an independent risk factor for cardiovascular disease. Despite the frequency of hypertriglyceridemia, treatment options are primarily limited to diet and exercise. Lipoprotein lipase (LPL) is an enzyme responsible for clearing triglycerides from circulation, and its activity alone can directly control plasma triglyceride concentrations. Therefore, LPL is a good target for triglyceride-lowering therapeutics. One approach for treating hypertriglyceridemia may be to increase the amount of enzymatically active LPL by preventing its inhibition by angiopoietin-like protein 4 (ANGPTL4). However, little is known about how these two proteins interact. Therefore, we used hydrogen-deuterium exchange MS to identify potential binding sites between LPL and ANGPTL4. We validated sites predicted to be located at the protein-protein interface by using chimeric variants of LPL and an LPL peptide mimetic. We found that ANGPTL4 binds LPL near the active site at the lid domain and a nearby α-helix. Lipase lid domains cover the active site to control both enzyme activation and substrate specificity. Our findings suggest that ANGPTL4 specifically inhibits LPL by binding the lid domain, which could prevent substrate catalysis at the active site. The structural details of the LPL-ANGPTL4 interaction uncovered here may inform the development of therapeutics targeted to disrupt this interaction for the management of hypertriglyceridemia.

Highlights

Cardiovascular disease has been the leading cause of death throughout the world for nearly 2 decades
The difference in deuterium uptake for bovine LPL (bLPL) was measured under ϪnANGPTL4 and ϩnANGPTL4 conditions and is represented using a heat map to highlight areas with decreased exchange and increased exchange (Fig. 1A)
Peptide sequences that were statistically significantly different (p value Ͻ 0.05) between the ϪnANGPTL4 and ϩnANGPTL4 conditions are represented with percent deuterium uptake curves (Fig. 1A) and colored based on differential deuterium exchange on a computational model of Lipoprotein lipase (LPL) generated by Hayne et al (Fig. 1B)

Summary

Introduction

Cardiovascular disease has been the leading cause of death throughout the world for nearly 2 decades. Our findings suggest that ANGPTL4 inhibits LPL by binding the lid domain, which could prevent substrate catalysis at the active site. Inhibition of LPL in adipose tissue, while simultaneously leaving LPL active in oxidative tissue, directs free fatty acids to these tissues for catabolism [15]. Site-specific interactions between LPL and ANGPTL4 decreases their risk for developing cardiovascular disease (19 –21). Previous studies using either antibody to silence ANGPTL4 in monkeys or the genetic loss of ANGPTL4 in mice recapitulate low levels of plasma triglycerides seen in humans with loss-of-function ANGPTL4 mutations [25, 27] Both ANGPTL4 knockdown monkeys and knockout mice inexplicably developed severe mesenteric lymphadenitis, or inflammation in the abdominal lymph nodes, when placed on a high-fat diet [25, 27, 28]. Individuals with loss-of-function mutations in ANGPTL4 do not have increased rates of lymphadenopathy, and the animals do not develop this phenotype on standard chow or low-fat diets [25, 26]

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