Regulation of Triglyceride Metabolism by the transcription factor CREB-H

描述（由申请人提供）：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选择性表达。CREB-H的激活需要高尔基蛋白酶对其前体蛋白进行序列切割，从而释放该蛋白的成熟n端部分，该部分定位于细胞核，作为转录反激活子。CREB-H是由脂肪酸、脂肪酸氧化调节剂PPAR1和肝脏禁食诱导产生的，提示其可能参与营养和能量代谢。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通过禁食在肝脏中诱导，并控制对TG和脂蛋白代谢至关重要的基因子集。CREB-H缺陷小鼠表现出严重的高甘油三酯血症，继发于由脂蛋白脂肪酶（LPL）催化的TG清除效率低下。遗传分析显示，CREB-H缺陷与LPL共激活因子Apoc2、Apoa4和Apoa5载脂蛋白的表达减少以及LPL抑制剂Apoc3的同时增加有关。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，这些突变产生了低形态或无功能的CREB-H蛋白。我们确定CREB-H是一种新的转录因子，控制啮齿动物和人类的TG代谢。本课题旨在进一步探讨CREB-H在脂质代谢中的功能和作用机制。我们建议解决以下问题：目标1。CREB-H在肝脏和小肠中的器官特异性功能是什么，通过在这些器官中选择性缺乏CREB-H的条件CREB-H敲除小鼠进行评估？目标2和3。CREB-H和PPAR1具有参与脂肪酸氧化的共同靶基因。CREB-H与PPAR1之间的功能关系是什么？CREB-H在肝脂肪变性中起作用吗？考虑到CREB-H对PCPCK的诱导作用，葡萄糖稳态是否需要CREB-H ？肝脏和肠道中CREB-H靶基因的范围是什么？哪些营养和激素信号调节CREB-H，以及CREB-H如何在多个水平上激活，包括转录激活、高尔基易位和其他翻译后修饰。CREB-H的激活模式在肝脏和小肠中似乎是不同的，我们将进一步研究解释这一现象的确切机制。考虑到CREB-H缺乏导致高脂血症，增加CREB-H活性是否对治疗血脂异常有益？我们将通过诱导过表达组成活性CREB-H来解决这个问题。目标4。最后，由CREB3L3突变引起的患者高甘油三酯血症的分子机制是什么？我们设想，这些研究将揭示新的信号通路，可能导致发现潜在的靶点，开发新的治疗二血脂症。

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. PUBLIC HEALTH RELEVANCE: We have much left to learn about the genes that regulate lipid metabolism and contribute to human dyslipidemias. We have recently demonstrated that CREB-H is a novel key transcription factor controlling triglyceride metabolism both in mouse and human by investigating CREB-H deficient mice and identifying CREB-H (CREB3L3) mutations in patients with hypertriglyceridemia. The current proposal aims to define the precise molecular mechanisms that explain the function of CREB-H in lipid metabolism.