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: 8398931
• 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/8398931
• 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.

描述（由申请人提供）： 背景资料：血清视黄醇结合蛋白（RBP 4）浓度在胰岛素抵抗状态如肥胖、代谢综合征和2型糖尿病中升高，并且RBP 4在胰岛素抵抗和葡萄糖耐受不良中起因果作用。RBP 4是血液中维生素A（视黄醇）的唯一特异性转运蛋白。虽然肝脏是循环RBP 4的主要来源，但脂肪细胞可能是胰岛素抵抗状态中重要的次要来源。尽管RBP 4作为治疗靶点具有显著的临床意义，但循环RBP 4的组织来源以及RBP 4与细胞相互作用引起胰岛素抵抗的基本机制仍不清楚。基于组织mRNA含量，已经推断高达20%的循环RBP 4通常由脂肪细胞产生。在胰岛素抵抗状态下，脂肪细胞mRNA含量显著增加，并与血清RBP 4浓度高度相关，而肝细胞RBP 4 mRNA不发生变化。基于这些观察，已经表明脂肪细胞中RBP 4表达的增加是胰岛素抵抗状态中循环RBP 4增加的唯一来源，但这从未被正式测试。胰岛素抵抗状态下的RBP 4的组织来源是重要的，因为脂肪细胞不能有效地储存视黄醇，并且可以分泌不与视黄醇结合的不同形式的RBP 4，通常称为“apo-RBP 4”。另一方面，已知肝细胞主要分泌视黄醇结合的RBP 4，其通常占循环RBP 4的80%，并被称为“全RBP 4”。最近有报道，apo-RBP 4的浓度在胰岛素抵抗的人类受试者中增加了2至3倍，并且我们的初步数据证明了在胰岛素抵抗的肥胖小鼠中apo-RBP 4的类似增加。因为apo-RBP 4被简单地定义为未结合至视黄醇的RBP 4的部分，所以apo-RBP 4仍然可能结合并转运一种或多种疏水性配体（除视黄醇之外），所述疏水性配体在递送至组织时介导胰岛素抗性。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不会导致小鼠的胰岛素抵抗，而且，用视黄酸（视黄醇的代谢产物和基因转录的广泛调节剂）治疗小鼠，会导致小鼠消瘦并增强胰岛素敏感性。这些数据一起支持了这样的可能性，即由脂肪细胞产生的RBP 4及其潜在的非视黄醇配体与由肝细胞产生的视黄醇结合的“全RBP 4”实质上不同。假设：与血清RBP 4升高相关的胰岛素抵抗主要由脂肪细胞分泌的RBP 4部分引起。具体目标：（i）测试由脂肪细胞产生的“apo-RBP 4”是否有助于RBP 4的升高和与肥胖相关的胰岛素抗性;（iii）为了测试循环“apo-RBP 4”和脂肪细胞分泌的RBP 4是否转运一种或多种非脂蛋白，在细胞水平引起胰岛素抵抗的视黄醇配体。研究方法：我们将使用通过Cre/loxP技术产生的肝细胞或脂肪细胞中RBP 4表达的组织特异性敲除的小鼠模型来研究这些组织中的每一种中产生的RBP 4如何在正常条件下和在高脂肪饮食的设置下促成全身性胰岛素抵抗和葡萄糖耐受不良。我们将进一步采用一种新的技术在胰岛素抵抗条件下体内产生重组RBP 4，以测试其在细胞水平诱导胰岛素抵抗的能力。