Tissue specific production of RBP4 and mechanism of insulin resistance

RBP4 的组织特异性产生和胰岛素抵抗机制

• 批准号: 8253502
• 负责人: TIMOTHY E. GRAHAM
• 金额: --
• 依托单位: VA SALT LAKE CITY HEALTHCARE SYSTEM
• 依托单位国家: 美国
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-04-01 至 2014-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8253502
• 关键词: Adipocytes; Adverse effects; All-Trans-Retinol; Binding; Biochemical; Biological; Blood; Blood Vessels; Carrier Proteins; Cells; Cessation of life; Clinical; Data; Diet; Dose; Fatty acid glycerol esters; Fenretinide; Genetic Transcription; Glucose Intolerance; Hepatocyte; Human; Insulin; Insulin Resistance; Knock-out; Ligands; Liver; Mediating; Messenger RNA; Metabolic syndrome; Methods; Morbidity - disease rate; Mus; Non-Insulin-Dependent Diabetes Mellitus; Obese Mice; Obesity; Pathogenesis; Pathway interactions; Pharmaceutical Preparations; Physiological; Play; Prevention; Production; Proteins; Recombinants; Regulator Genes; Reporting; Retinol Binding Proteins; Rodent; Role; Serum; Source; Techniques; Technology; Testing; Thinness; Tissues; Tretinoin; Veterans; Vitamin A; base; blood glucose regulation; design; diabetic; human subject; in vivo; insulin sensitivity; interest; intraperitoneal; mouse model; novel; novel strategies; prevent; public health relevance; therapeutic target

DESCRIPTION (provided by applicant): Background: Serum retinol binding protein (RBP4) concentrations are elevated in insulin resistant states such as obesity, the metabolic syndrome, and type 2 diabetes, and RBP4 plays a causal role in insulin resistance and glucose intolerance. RBP4 is the sole specific transport protein for Vitamin A (retinol) in blood. While liver is the primary source of circulating RBP4, adipocytes may be an important secondary source in insulin resistant states. Despite significant clinical interest in RBP4 as a therapeutic target, tissue sources of circulating RBP4 and the basic mechanisms by which RBP4 interacts with cells to cause insulin resistance remain unclear. Based on tissue mRNA content, it has been inferred that up to 20% of circulating RBP4 is normally produced by adipocytes. In insulin resistant states, adipocyte mRNA content is dramatically increased and highly correlated with serum RBP4 concentrations, whereas hepatocyte RBP4 mRNA does not change. Based on these observations it has been suggested that increased expression of RBP4 in adipocytes is the sole source of increased circulating RBP4 in insulin resistant states, but this has never been formally tested. The tissue source of RBP4 in insulin resistant states is important because adipocytes do not store retinol efficiently and may secrete a distinct form of RBP4 that is not bound to retinol, conventionally referred to as "apo-RBP4". Hepatocytes, on the other hand, are known to primarily secrete retinol-bound RBP4, which typically comprises 80% of circulating RBP4 and is referred to as "holo-RBP4". It has recently been reported that concentrations of apo-RBP4 are increased 2- to 3-fold in insulin resistant human subjects, and our preliminary data demonstrate a similar increase of apo-RBP4 in insulin resistant obese mice. Because apo-RBP4 is defined simply as the fraction of RBP4 not bound to retinol, it remains possible that apo-RBP4 binds and transports one or more hydrophobic ligands (other than retinol) that mediate insulin resistance upon their delivery to tissues. Consistent with this, our preliminary data indicate that even very high amounts of dietary retinol do not cause insulin resistance in mice, and furthermore, treatment of mice with retinoic acid, a metabolite of retinol and broad regulator of gene transcription, causes leanness and enhances insulin sensitivity in mice. Together these data support the possibility that RBP4 and its potential non-retinol ligand(s) produced by adipocytes are materially distinct from the retinol-bound "holo-RBP4" produced by hepatocytes. Hypothesis: Insulin resistance associated with elevated serum RBP4 is principally caused by the fraction of RBP4 secreted from adipocytes. Specific aims: (i) To test whether "apo-RBP4" produced by adipocytes contributes to the elevation of RBP4 and insulin resistance associated with obesity; (ii) To test whether holo-RBP4 produced by hepatocytes plays a protective role in maintaining insulin- glucose homeostasis; (iii) To test whether circulating "apo-RBP4" and adipocyte-secreted RBP4 transport one or more non-retinol ligands that cause insulin resistance at the cellular level. Methods: We will employ mouse models of tissue specific-knockout of RBP4 expression in hepatocytes or adipocytes generated by means of Cre/loxP technology to study how RBP4 produced in each of these tissues contributes to systemic insulin resistance and glucose intolerance under normal conditions and in the setting of high fat diet. We will further employ a novel technique to produce recombinant RBP4 in vivo under insulin resistant conditions, in order to test its capacity for inducing insulin resistance at the cellular level. PUBLIC HEALTH RELEVANCE: A major cause of morbidity and death for our veterans is type 2 diabetes and its vascular complications. RBP4 is a circulating protein that contributes to the pathogenesis of type 2 diabetes. Drugs such as fenretinide which bind and lower serum RBP4 may be effective in treating or preventing pre-diabetic conditions of insulin resistance and glucose intolerance. A better understanding of the biochemical and physiologic mechanisms by which RBP4 causes insulin resistance will potentially: (i) enhance the ability to design novel RBP4-lowering agents with greater efficacy and fewer side effects; and (ii) elucidate new approaches for interfering with downstream pathways through which RBP4 causes insulin resistance in different tissues.

描述(由申请人提供)： 背景：在肥胖、代谢综合征和2型糖尿病等胰岛素抵抗状态下，血清视黄醇结合蛋白(RBP4)浓度升高，RBP4在胰岛素抵抗和糖耐量减低中起因果作用。RBP4是血液中维生素A(视黄醇)的唯一特异性运输蛋白。虽然肝脏是循环RBP4的主要来源，但脂肪细胞可能是胰岛素抵抗状态的重要次要来源。尽管RBP4作为一种治疗靶点具有重要的临床意义，但循环RBP4的组织来源以及RBP4与细胞相互作用导致胰岛素抵抗的基本机制仍不清楚。根据组织中的信使核糖核酸含量推测，正常情况下高达20%的循环RBP4是由脂肪细胞产生的。在胰岛素抵抗状态下，脂肪细胞的mRNA含量显著增加，并与血清RBP4浓度高度相关，而肝细胞RBP4的mRNA水平无明显变化。基于这些观察，有人认为脂肪细胞中RBP4的表达增加是胰岛素抵抗状态下循环RBP4增加的唯一来源，但这一点从未得到正式测试。处于胰岛素抵抗状态的RBP4的组织来源很重要，因为脂肪细胞不能有效地储存视黄醇，可能会分泌一种不与视黄醇结合的独特形式的RBP4，通常被称为“apo-RBP4”。另一方面，肝细胞主要分泌视黄醇结合的RBP4，它通常占循环RBP4的80%，被称为全息RBP4。最近有报道称，在胰岛素抵抗的人类受试者中，apo-RBP4的浓度增加了2-3倍，我们的初步数据表明，在胰岛素抵抗的肥胖小鼠中，apo-RBP4的浓度也有类似的增加。因为apo-RBP4被简单地定义为RBP4不与视黄醇结合的部分，所以apo-RBP4仍然有可能结合并运输一个或多个疏水配体(视黄醇除外)，这些配体在传递到组织时介导胰岛素抵抗。与此一致，我们的初步数据表明，即使是非常高的饮食视黄醇也不会导致小鼠的胰岛素抵抗，此外，用视黄醇的代谢物和广泛的基因转录调节因子维甲酸治疗小鼠，会导致小鼠消瘦并增强胰岛素敏感性。总之，这些数据支持这样一种可能性，即脂肪细胞产生的RBP4及其潜在的非视黄醇配体(S)与肝细胞产生的视黄醇结合的全息RBP4在本质上是不同的。假设：与血清RBP4升高相关的胰岛素抵抗主要是由脂肪细胞分泌的RBP4部分引起的。具体目的：(I)检测脂肪细胞产生的“apo-RBP4”是否导致RBP4升高和与肥胖相关的胰岛素抵抗；(Ii)检测肝细胞产生的holo-RBP4是否在维持胰岛素-葡萄糖稳态方面起到保护作用；(Iii)检测循环中的“apo-RBP4”和脂肪细胞分泌的RBP4是否在细胞水平转运一个或多个导致胰岛素抵抗的非视黄醇配体。方法：我们将利用Cre/loxP技术产生的肝细胞或脂肪细胞中RBP4表达的小鼠组织特异性敲除模型，研究正常条件下和高脂饮食环境下，这些组织中产生的RBP4在全身胰岛素抵抗和葡萄糖耐量异常中的作用。我们将进一步利用一种新的技术在胰岛素抵抗条件下在体内生产重组RBP4，以测试其在细胞水平上诱导胰岛素抵抗的能力。 公共卫生相关性： 导致退伍军人发病和死亡的一个主要原因是2型糖尿病及其血管并发症。RBP4是一种循环蛋白，参与了2型糖尿病的发病机制。结合和降低血清RBP4的药物，如非维甲酸，可能在治疗或预防糖尿病前期的胰岛素抵抗和葡萄糖耐量异常方面有效。更好地了解RBP4引起胰岛素抵抗的生化和生理机制可能会：(I)提高设计更有效、副作用更少的新型RBP4降压剂的能力；以及(Ii)阐明干扰RBP4在不同组织中引起胰岛素抵抗的下游途径的新方法。