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

Abstract

Edited by George M. CarmanCardiovascular 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 ␣-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.

Unfolding of monomeric lipoprotein lipase by ANGPTL4: Insight into the regulation of plasma triglyceride metabolism

“…Second, the concentration of ANGPTL4 used in those studies would have, at least in our hands, resulted in irreversible inhibition of LPL before the first time point. Third, there was no time dependence in deuterium uptake within the putative ANGPTL4 interaction sites, which is surprising given the high K i that was reported (49). Similar caveats also confound the findings in a second HDX-MS-based study (54), which concludes that ANGPTL4 binds to another region in LPL that harbors the catalytic site (i.e., residues 130 to 162).…”

“…The biological importance of ANGPTLs in regulating plasma triglyceride homeostasis by inhibiting LPL activity has been firmly established by human and mouse genetics (15)(16)(17)(18)(19) and by pharmacological studies (7,(45)(46)(47), but the molecular mechanism for LPL inactivation has remained controversial. One view holds that ANGTPL4 is a reversible and noncompetitive LPL inhibitor with an inhibition constant (K i ) of 0.9 to 1.7 μM (48,49), but that view relies on studies performed in the presence of deoxycholate (a detergent that stabilizes LPL) (4,50). Moreover, the low inhibitory efficacy of ANGPTL4 in those studies is difficult to reconcile with the fact that low nanomolar concentrations of ANGPTL4 readily inhibit triglyceride hydrolysis by low nanomolar concentrations of LPL (4-6, 29, 30, 43, 51).…”

“…Should HDX-MS experiments be used to map the binding site for ANGPTL4 on LPL it will be essential to differentiate between correlated and uncorrelated exchange mechanisms (4,20,44,53). A recent HDX-MS-based study proposed that ANGPTL4 interacts with the lid (226 to 238) and a nearby α-helix (89 to 102) in LPL (49), but that finding is subject to important caveats. Primarily, the study provided no information on the presence of bimodal isotopic envelopes appearing as a consequence of ANGPTL-induced unfolding of LPL (i.e., coexisting LPL conformations).…”

Hepatic DNA Methylation in Response to Early Stimulation of Microbiota with Lactobacillus Synbiotics in Broiler Chickens

“…It was shown that Lactobacillus probiotic bacteria have an effect to lower body fat levels with higher ANGTPL4 expression levels [19]. The ANPTL4 gene is responsible for the inhibition of LPL, which leads to a decrease in fat storage [20]. Studies in mice have shown that the ANGPTL4 gene and the intestinal microbiota control body weight [19].…”

Liver-specific suppression of ANGPTL4 improves obesity-associated diabetes and mitigates atherosclerosis in mice

“…However, conflicting reports exist on the regulation of HL activity by ANGPTL4. Koster et al, using global ANGPTL4 KO mice and liver-specific overexpression of ANGPTL4, and Gutsell et al, using an in vitro system, have shown that ANGPTL4 does not affect HL activity(28,43). In contrast, Lichtenstein et al observed that adenovirus-mediated overexpression of ANGPTL4 inhibits postheparin HL activity(12).…”