Postprandial Vitamin A

这个更新申请是为了一个项目，其总体目标是了解视黄醇结合蛋白4 （RBP4）诱导代谢疾病的分子基础。我们通过对新生成的转基因小鼠模型（adi-hRBP4小鼠）的研究发现，脂肪细胞（白色和棕色脂肪细胞）中RBP4表达的适度增加导致脂肪组织内炎症显著增加。这导致未酯化脂肪酸从脂肪细胞重新分配到肝脏，在那里它们以甘油三酯的形式积累。我们还发现了RBP4在棕色脂肪细胞中的作用，我们认为这有助于adi-RBP4小鼠对高脂肪饮食喂养的过度体重增加。我们前期的研究结果使我们得出结论，脂肪细胞RBP4是一种重要的自分泌/旁分泌因子，其在代谢性疾病引起中的不良作用主要局限于脂肪组织腔室。我们现在提出的新研究直接来自于前一时期发表的和初步的研究结果。这项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和体外研究。我们的初步数据表明，RBP4调节BAT的产热能力和能量消耗，这涉及到BAT中全反式维甲酸（ATRA）信号的影响。在具体目标1和2中，我们建议探索这些观察的分子基础。特异性目的1将研究RBP4在棕色脂肪细胞中的表达在肥胖发展中的作用。在Specific Aim 2的补充研究中，我们将确定棕色脂肪细胞中的ATRA信号如何影响肥胖的发展。我们已经证明，脂肪细胞合成RBP4会导致肝脏中过多的脂肪堆积。我们现在希望进一步研究rbp4诱导的肝脏疾病的进展。具体来说，我们希望确定由RBP4诱导的脂肪炎症，在进一步损伤肝脏的情况下（第二次“攻击”），使肝脏对伴有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。最近的文献表明，RBP4可能携带视黄醇以外的配体，这可能解释了脂肪细胞RBP4表达与RBP4诱导的代谢表型之间的关系。我们在Specific Aim 4中提议进行一项系统的研究，以鉴定具有高亲和力（相当于或优于视黄醇）结合RBP4的新型生物活性配体。在这里，我们将采用一种新的高通量方法，我们最近开发并用于鉴定另外两种视黄醇结合蛋白RBP1和RBP2的新型高亲和力配体。我们认为Specific Aim 4具有高风险，但对于了解RBP4在代谢性疾病中的作用具有潜在的巨大益处。

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.