Regulation of Triglyceride Metabolism by the transcription factor CREB-H

描述(申请人提供)：CREB-H是一种内质网(ER)结合的转录因子，仅在肝脏和小肠中高度和选择性地表达。CREB-H的激活需要高尔基蛋白酶对其前体蛋白的顺序切割，从而释放蛋白的成熟N端部分，该部分定位于细胞核，起到转录反式激活因子的作用。CREB-H是由脂肪酸、脂肪酸氧化调节剂PPAR1和肝脏中的禁食诱导的，提示它可能参与了营养和能量代谢。我们证明CREB-H是维持体内正常甘油三酯(TG)水平所必需的。CREB-H是通过禁食在肝脏中诱导的，并控制着对甘油三酯和脂蛋白代谢至关重要的一组基因。CREB-H基因缺陷小鼠表现出严重的高甘油三酯血症，继发于脂蛋白脂酶(LPL)催化的甘油三酯清除效率低下。遗传图谱显示，CREB-H缺乏与LPL共激活因子Apo2、Apoa4和Apoa5载脂蛋白表达降低以及LPL抑制物ApoC3同时增强有关。在极端高甘油三酯血症患者中发现了CREB3L3的多个非同义突变，这些突变产生低形态或无功能的CREB-H蛋白。我们建立了CREB-H作为一种新的转录因子，它调控啮齿动物和人类的甘油三酯代谢。本研究旨在进一步研究CREB-H在脂质代谢中的作用和作用机制。我们建议解决以下问题：目的1.用选择性缺乏CREB-H的条件性CREB-H基因敲除小鼠来评估CREB-H在肝脏和小肠中的器官特异性功能？目的2和3.CREB-H和PPAR1具有共同的参与脂肪酸氧化的靶基因。CREB-H和PPAR1之间的功能关系是什么？CREB-H在肝脏脂肪变性中起作用吗？在CREB-H诱导PCPCK的情况下，CREB-H是否是维持血糖稳态所必需的？CREB-H针对肝脏和肠道中的基因的宇宙是什么？什么营养和激素信号调节CREB-H，以及如何在多个水平上实现CREB-H的激活，包括转录激活、高尔基体易位和其他翻译后修饰。CREB-H在肝脏和小肠的激活模式似乎不同，我们将进一步研究其确切机制。既然CREB-H缺乏会导致高脂血症，那么CREB-H活性的增强对治疗血脂异常有好处吗？我们将通过诱导活性CREB-H的诱导过表达来解决这个问题。目的4.最后，CREB3L3基因突变导致患者高甘油三酯血症的分子机制是什么？我们预计，这些研究将发现新的信号通路，可能导致发现潜在的靶点，开发新的治疗血脂的方法。

DESCRIPTION (provided by applicant): CREB-H is an endoplasmic reticulum (ER)-bound transcription factor that is highly and selectively expressed only in the liver and the small intestine. CREB-H activation requires a sequential cleavage of its precursor protein by Golgi proteases that liberate the mature N-terminal portion of the protein, which localizes to the nucleus to act as a transcriptional transactivator. CREB-H is induced by fatty acids, the fatty acid oxidation regulator PPAR1, and fasting in the liver, suggesting that it might participate in nutrient and energy metabolism. We demonstrated that CREB-H is required for the maintenance of normal trigylceride (TG) levels in vivo. CREB-H is induced in the liver by fasting and controls a subset of genes that are critical for TG and lipoprotein metabolism. CREB-H deficient mice displayed severe hypertriglyceridemia secondary to inefficient TG clearance catalyzed by lipoprotein lipase (LPL). Genetic profiling revealed that CREB-H deficiency was associated with decreased expression of the LPL coactivators, Apoc2, Apoa4, and Apoa5 apolipoproteins and concurrent augmentation of the LPL inhibitor, Apoc3. Multiple nonsynonymous mutations in CREB3L3 that produced hypomorphic or nonfunctional CREB-H protein were identified in patients with extreme hypertriglyceridemia. We establish CREB-H as a novel transcription factor that governs TG metabolism in rodents and humans. The current proposal aims to further investigate the function and mechanism of action of CREB-H in lipid metabolism. We propose to address the following questions: Aim 1. What is the organ specific function of CREB-H in liver and small intestine, as assessed using conditional CREB-H knock-out mice that selectively lack CREB-H in these organs? Aim 2 and 3. CREB-H and PPAR1 share common target genes that are involved in fatty acid oxidation. What is the functional relationship between CREB-H and PPAR1? Does CREB-H play a role in hepatic steatosis? Given the induction of PCPCK by CREB-H, is CREB-H required for glucose homeostasis? What is the universe of CREB-H targets genes in the liver and intestine? What nutritional and hormonal signals regulate CREB-H, and how CREB-H activation can be achieved at multiple levels, which include transcriptional activation, Golgi translocation, and other post-translational modifications. The mode of CREB-H activation appears be distinct in liver and small intestine, and we will further investigate the precise mechanisms that account for this. Given that CREB-H deficiency resulted in hyperlipidemia, would the augmentation of CREB-H activity be beneficial in the treatment of dyslipidemia? We will address this question by inducible overexpression of constitutively active CREB-H. Aim 4. Finally, what is the molecular mechanism for hypertriglyceridemia caused by mutations in CREB3L3 in patients? We envision that these studies will uncover novel signaling pathways that may lead to the discovery of potential targets for developing novel therapeutics for dislipidemia.