Lipase maturation factor 1 is required for endothelial lipase activity

Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
The Journal of Lipid Research (Impact Factor: 4.42). 03/2011; 52(6):1162-9. DOI: 10.1194/jlr.M011155
Source: PubMed


Lipase maturation factor 1 (Lmf1) is an endoplasmic reticulum (ER) membrane protein involved in the posttranslational folding and/or assembly of lipoprotein lipase (LPL) and hepatic lipase (HL) into active enzymes. Mutations in Lmf1 are associated with diminished LPL and HL activities ("combined lipase deficiency") and result in severe hypertriglyceridemia in mice as well as in human subjects. Here, we investigate whether endothelial lipase (EL) also requires Lmf1 to attain enzymatic activity. We demonstrate that cells harboring a (cld) loss-of-function mutation in the Lmf1 gene are unable to generate active EL, but they regain this capacity after reconstitution with the Lmf1 wild type. Furthermore, we show that cellular EL copurifies with Lmf1, indicating their physical interaction in the ER. Finally, we determined that post-heparin phospholipase activity in a patient with the LMF1(W464X) mutation is reduced by more than 95% compared with that in controls. Thus, our study indicates that EL is critically dependent on Lmf1 for its maturation in the ER and demonstrates that Lmf1 is a required factor for all three vascular lipases, LPL, HL, and EL.

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    • "At first glance, this is a surprising observation considering the critical role of LPL in the maturation of HDL particles [18] and severely reduced HDL-cholesterol in LPL-deficient mice [17,19,20]. However, in addition to LPL, LMF1-/- animals are also deficient in active HL and EL [7], lipases that promote HDL catabolism [21-23]. Thus, we propose that unaltered HDL-cholesterol level in LMF1-/- mice is a result of combined lipase deficiency involving lipases with opposite effects on HDL metabolism. "
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    ABSTRACT: Background Lipase Maturation Factor 1 (LMF1) is an ER-chaperone involved in the post-translational maturation and catalytic activation of vascular lipases including lipoprotein lipase (LPL), hepatic lipase (HL) and endothelial lipase (EL). Mutations in LMF1 are associated with lipase deficiency and severe hypertriglyceridemia indicating the critical role of LMF1 in plasma lipid homeostasis. The currently available mouse model of LMF1 deficiency is based on a naturally occurring truncating mutation, combined lipase deficiency (cld), which may represent a hypomorphic allele. Thus, development of LMF1-null mice is needed to explore the phenotypic consequences of complete LMF1 deficiency. Findings In situ hybridization and qPCR analysis in the normal mouse embryo revealed ubiquitous and high-level LMF1 expression. To investigate if LMF1 was required for embryonic viability, a novel mouse model based on a null-allele of LMF1 was generated and characterized. LMF1-/- progeny were born at Mendelian ratios and exhibited combined lipase deficiency, hypertriglyceridemia and neonatal lethality. Conclusion Our results raise the possibility of a previously unrecognized role for LMF1 in embryonic development, but indicate that LMF1 is dispensable for the viability of mouse embryo. The novel mouse model developed in this study will be useful to investigate the full phenotypic spectrum of LMF1 deficiency.
    Full-text · Article · Aug 2014 · Nutrition & Metabolism
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    • "EL is regulated at the transcriptional level by cytokine stimuli [6] mostly via NF-kB [7] [8] as well as by transcriptional regulators of the lipid metabolism such as liver X receptor and peroxisome proliferator-activated receptor a [9]. In addition, similar to LPL, the activity of EL is regulated at the post-transcriptional level via a direct interaction with angiopoietin-like protein 3 and lipase maturation factor 1 [10] [11] suggesting that also other regulators of LPL could affect EL. SREBPs are well known regulators of genes involved in lipid metabolism and they have been shown to regulate LPL [12] [13]. "
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    ABSTRACT: Objective: Endothelial lipase (EL) regulates HDL cholesterol levels and in inflammatory states, like atherosclerosis, EL expression is increased contributing to low HDL cholesterol. The regulation of EL expression is poorly understood and has mainly been attributed to inflammatory stimuli. As sterol regulatory element binding proteins (SREBPs) are regulators of genes involved in lipid metabolism, we hypothesized that EL is regulated by SREBPs and that EL expression is modified by the SREBP activator vascular endothelial growth factor A (VEGF-A). Methods: and results: Quantitative PCR and Western blot results demonstrated that starvation increased EL expression in human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAECs). Also, 25-hydroxycholesterol (25HC), an inhibitor of SREBP activation inhibited EL expression. With siRNA-mediated inhibition of SREBPs the effect of starvation was shown to be SREBP-2 dependent. VEGF-A decreased EL expression in both endothelial cell lines used, most likely via inhibition of SREBP-2 binding determined by chromatin immunoprecipitation (ChIP). Furthermore, in atherosclerosis prone LDLR(-/-)ApoB(100/100) mice, systemic adenoviral gene transfer with human VEGF-A decreased EL mRNA in peripheral tissues and increased plasma HDL cholesterol. Conclusions: These results identify SREBPs as novel regulators of EL expression. VEGF-A as an endogenous EL inhibitor could be therapeutically relevant in atherosclerosis by increasing systemic HDL cholesterol levels.
    Full-text · Article · Oct 2012 · Atherosclerosis
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    • ") LMF1 is a membrane-bound endoplasmic reticulum (ER) protein that is the causative locus for the spontaneous mouse combined lipase deficiency (cld) mutant [33], a neonatal lethal mutation in Lmf1 (formerly Tmem112) [34]. LMF1 is required for post-translational folding and assembly of monomeric lipases [35], including lipoprotein lipase (LPL), hepatic lipase, and endothelial lipase [34] [36]. Mutations in LMF1 impair proper assembly of lipases in vitro [37], with >95% of LPL and HL retained in the ER [38], although seemingly without direct interaction or changes in sub-cellular localization. "
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    ABSTRACT: The genetic underpinnings of both normal and pathological variation in plasma triglyceride (TG) concentration are relatively well understood compared to many other complex metabolic traits. For instance, genome-wide association studies (GWAS) have revealed 32 common variants that are associated with plasma TG concentrations in healthy epidemiologic populations. Furthermore, GWAS in clinically ascertained hypertriglyceridemia (HTG) patients have shown that almost all of the same TG-raising alleles from epidemiologic samples are also associated with HTG disease status, and that greater accumulation of these alleles reflects the severity of the HTG phenotype. Finally, comprehensive resequencing studies show a burden of rare variants in some of these same genes - namely in LPL, GCKR, APOB and APOA5 - in HTG patients compared to normolipidemic controls. A more complete understanding of the genes and genetic variants associated with plasma TG concentration will enrich our understanding of the molecular pathways that modulate plasma TG metabolism, which may translate into clinical benefit. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.
    Full-text · Article · Oct 2011 · Biochimica et Biophysica Acta
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