Molecular Mechanisms of Lipase Maturation and Secretion

 描述（由申请人提供）：血浆甘油三酯（TG）和胆固醇水平长期以来被认为是心血管疾病风险的重要决定因素。在涉及的大量因素中，血管脂肪酶蛋白家族的三个成员在血浆脂质稳态中作为关键参与者脱颖而出。脂蛋白脂酶（LPL）是血浆TG浓度的主要决定因素，而肝脂酶（HL）和内皮脂酶（EL）主要参与HDL-胆固醇的代谢。而这些酶的细胞外因子的调节早已被赞赏，内质网（ER）内的翻译后加工最近出现作为一个重要的细胞内途径，影响活性脂肪酶的表达和血浆脂质稳态。在小鼠模型中使用遗传方法，我们确定了脂肪酶成熟因子1（LMF 1）和抑制/增强Lin-12样（SEL 1 L）基因作为翻译后成熟和活性脂肪酶分泌的关键参与者。LMF 1的突变导致小鼠和人类的脂肪酶缺乏和高脂血症，而SEL 1 L的遗传缺陷导致小鼠模型中脂肪组织LPL分泌受损和血浆TG水平升高。虽然这些研究暗示LMF 1和SEL 1 L在脂肪酶的生物合成和脂质稳态，潜在的分子机制仍然没有得到表征。在具体目标1中，我们将表征LMF 1在ER内活性脂肪酶的折叠和组装中的分子作用，并研究其与一般伴侣钙连接蛋白（CNX）的相互作用。在具体目标2中，我们将探索SEL 1 L在从ER释放脂肪酶中的作用，并研究CNX，LMF 1和SEL 1 L之间的分子复合物在脂肪酶成熟和分泌协调中的功能和结构方面。在具体目标3中，我们将通过最近在高脂血症人群中发现的编码变体的功能表征，研究LMF 1作为人类血脂异常的遗传决定因素。我们的研究将有助于更好地了解血管脂肪酶的翻译后加工，以及高脂血症的分子机制。

 DESCRIPTION (provided by applicant): Plasma levels of triglycerides (TG) and cholesterol have long been recognized as important determinants of cardiovascular disease risk. Among a large number of factors involved, three members of the vascular lipase protein family stand out as critical players in plasma lipid homeostasis. Lipoprotein lipase (LPL) is a principal determinant of plasma TG concentration, whereas hepatic lipase (HL) and endothelial lipase (EL) are primarily involved in the metabolism of HDL-cholesterol. Whereas the regulation of these enzymes by extracellular factors has long been appreciated, post-translational processing within the endoplasmic reticulum (ER) has recently emerged as an important intracellular pathway affecting the expression of active lipases and plasma lipid homeostasis. Using genetic approaches in mouse models, we identified the lipase maturation factor 1 (LMF1) and suppressor/enhancer of Lin-12-like (SEL1L) genes as critical players in the post-translational maturation and secretion of active lipases. Mutations in LMF1 cause combined lipase deficiency and hypertriglyceridemia in mice and humans, whereas a genetic defect in SEL1L leads to impaired LPL secretion from adipose tissue and elevated plasma TG levels in a mouse model. Although these studies implicate LMF1 and SEL1L in lipase biogenesis and lipid homeostasis, the underlying molecular mechanisms remain uncharacterized. In Specific Aim 1, we will characterize the molecular role of LMF1 in the folding and assembly of active lipases within the ER and investigate its interaction with the general chaperone, calnexin (CNX). In Specific Aim 2, we will explore the role of SEL1L in the release of lipases from the ER and investigate functional and structural aspects of a molecular complex between CNX, LMF1 and SEL1L in the coordination of lipase maturation and secretion. In Specific Aim 3, we will investigate LMF1 as a genetic determinant of dyslipidemia in humans through the functional characterization of coding variants recently discovered in hypertriglyceridemic populations. Our studies will contribute to a better understanding of the post-translational processing of vascular lipases, and the molecular mechanisms underlying hyperlipidemia.