Postprandial Vitamin A

该更新申请是针对一个项目，其总体目标是了解视黄醇结合蛋白4（RBP 4）诱导的代谢疾病的分子基础。我们从新产生的转基因小鼠模型（adi-hRBP 4小鼠）的研究中发现，脂肪细胞（白色和棕色脂肪细胞）中RBP 4表达的适度增加导致脂肪组织内炎症的显著增加。这导致未酯化脂肪酸从脂肪细胞重新分配到肝脏，在肝脏中以甘油三酯形式积累。我们还鉴定了RBP 4在棕色脂肪细胞中的作用，我们认为这有助于在adi-RBP 4小鼠中观察到的响应于高脂肪饮食喂养的过度体重增加。我们在前一阶段的发现使我们得出结论，脂肪细胞RBP 4是一种重要的自分泌/旁分泌因子，其在代谢疾病病因中的不良作用主要限于脂肪组织区室。我们现在提出新的研究，这些研究直接来源于前一时期发表的初步研究结果。本研究将涉及动物模型、成熟棕色脂肪细胞和棕色脂肪细胞前体细胞的培养以及体外研究。我们的初步数据表明，RBP 4的行为，以调节BAT产热能力和能量消耗，这涉及到全反式维甲酸（ATRA）的BAT信号转导的影响。在具体目标1和2中，我们建议探索这些观察结果的分子基础。具体目标1将研究棕色脂肪细胞中RBP 4表达对肥胖发展的作用。在《特定目标2》的补充研究中，我们将确定棕色脂肪细胞中的ATRA信号传导如何影响肥胖的发展。我们已经表明，RBP 4的脂肪细胞合成导致肝脏中过量的脂肪积累。我们现在希望进一步研究RBP 4诱导的肝病的进展。具体地，我们希望确定，在对肝脏的进一步损伤（第二次“撞击”）的情况下，由RBP 4诱导的脂肪炎症使肝脏对伴随纤维化的非酒精性脂肪性肝炎敏感。这个问题将是具体目标3的重点。在最近的文献中已经提出，RBP 4可能携带视黄醇以外的配体，这可能解释了脂肪细胞RBP 4表达和RBP 4诱导的代谢表型之间观察到的关系。我们在具体目标4中建议进行系统研究，以确定以高亲和力（相当于或优于视黄醇）结合RBP 4的新型生物活性配体。在这里，我们将采用一种新的高通量的方法，我们最近开发和使用，以确定新的高亲和力配体的其他两个视黄醇结合蛋白，RBP 1和RBP 2。我们认为具体目标4是一个高风险，但潜在的非常大的收益了解RBP 4在代谢疾病中的作用。

This renewal application is for a project that had as its overall goal to gain understanding of the molecular bases for retinol-binding protein 4 (RBP4)-induced metabolic disease. We found from investigations of a newly generated transgenic mouse model (adi-hRBP4 mice) that modest increases in RBP4 expression in adipocytes (in both white and brown adipocytes) results in significantly increased inflammation within adipose tissue. This gives rise to a redistribution of unesterified fatty acids from adipocytes to the liver where they accumulated as triglyceride. We also identified effects of RBP4 in brown adipocytes that we propose contribute to the excessive body weight gain observed in adi-RBP4 mice in response to high fat diet feeding. Our findings from the previous period led us to conclude that adipocyte RBP4 is an important autocrine/paracrine factor whose adverse actions in metabolic disease causation are largely confined to the adipose tissue compartment. We are now proposing new research that grows directly out of published and preliminary findings obtained during the previous period. This research will involve animal models, mature brown adipocytes and brown adipocyte precursor cells in culture, and in vitro studies. Our preliminary data indicate that RBP4 acts to modulate BAT thermogenic capacity and energy expenditure and that this involves effects on all-trans-retinoic acid (ATRA)- signaling in BAT. In Specific Aims 1 and 2, we propose to explore the molecular bases for these observations. Specific Aim 1 will investigate the role that RBP4 expression in brown adipocytes has on obesity development. In complementary studies in Specific Aim 2, we will identify how ATRA signaling in brown adipocytes influences obesity development. We have shown that adipocyte-synthesis of RBP4 leads to excessive fat accumulation in the liver. We now wish to study further the progression of RBP4-induced hepatic disease. Specifically, we wish to establish that adipose inflammation induced by RBP4, in the setting of further insults to the liver (second “hits”), sensitizes the liver to non-alcoholic steatohepatitis with accompanying fibrosis. This question will be the focus of Specific Aim 3. It has been suggested in the recent literature that RBP4 may carry ligands other than retinol and that this may account for the observed relationships between adipocyte RBP4 expression and the RBP4-induced metabolic phenotypes. We are proposing in Specific Aim 4 to undertake a systematic investigation to identify novel bioactive ligands that bind RBP4 with high affinity (equivalent to or better than retinol). Here, we will employ a new high throughput method that we recently developed and used to identify novel high affinity ligands for two other retinol-binding proteins, RBP1 and RBP2. We consider Specific Aim 4 to be one with high risks but potentially very great gains for understanding RBP4 actions in metabolic disease.