Interleukin-6 Expression and Function in Adipose Cells

脂肪细胞中 IL-6 的表达和功能

• 批准号: 6468798
• 负责人: Joyce B. Harp
• 金额: $ 30.07万
• 依托单位: UNIV OF NORTH CAROLINA CHAPEL HILL
• 依托单位国家: 美国
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-04-01 至 2007-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6468798
• 关键词: 3T3 cells; adipocytes; affinity chromatography; athymic mouse; autocrine; biological signal transduction; cell cycle proteins; cell differentiation; colony stimulating factor; corticosterone; disease /disorder model; enzyme linked immunosorbent assay; gene expression; gene targeting; genetically modified animals; glucose metabolism; growth factor receptors; human tissue; interleukin 6; laboratory mouse; ligands; lipid metabolism; messenger RNA; obesity; protein structure function; transcription factor; western blottings

Elevated interleukin-6 (IL-6) is associated with fat wasting in systemic infection and cancer cachexia. However, important new data indicates that circulating IL-6 is also elevated in human obesity, and adipose tissue is the principal source of this elevation. Because obesity is among the most prevalent public health challenges in the United States, it is important to understand IL-6 expression and function in adipose tissue, and to determine whether dysregulated expression of adipose tissue IL-6 is involved in the development of obesity and obesity-related co-morbidities. IL-6 traditionally signals through STAT3 activation, but in differentiating preadipocytes, IL-6 inhibits and STAT3 appears to be necessary for adipocyte formation. In this proposal we propose the following Specific Aims.. Aim 1: To determine mechanisms involved in IL-6-induced inhibition of adipogenesis. We hypothesize that greater than or equal to 10 ng/ml IL-6 inhibits the preadipocyte to adipocyte conversion by altering normal cell cycle progression and subsequent adipogenic transcription factor expression. We will determine in 3T3-L1 preadipocytes the effect of IL-6 on cell cycle progression and differentiation. Using chimeric GM-CSF- gp130 receptor transfections, the signaling mechanisms involved to transduce IL-6 effects will be explored. To explore the physiological relevance of IL-6 in adipose tissue, we will determine whether IL-6 knockout mice have altered adipose tissue growth, glucose, and lipid metabolism on normal and high fat diets. Aim 2: To characterize adipose tissue IL-6 expression in animal models of obesity. We find IL-6 mRNA is expressed in adipose tissue of lean mice, but it has been reported that obese db/db mice do not express IL-6 mRNA in adipose tissue. Since glucocorticoids repress IL-6 expression, we hypothesize that IL-6 expression is depressed in adipose tissue of ob/ob and db/db mice by high systemic corticosterone levels that are characteristic of these models of obesity. We also predict that IL-6 expression is elevated in adipose tissue of diet-induced obese (DIO) mice, similarly to obese humans. DIO mice retain normal corticosterone levels with the development of obesity. We will characterize IL- 6 expression in adipose tissue of lean control, DIO, ob/ob, and db/db all on a C57BL/6J background at baseline and in response to glucocorticoid agonists and antagonists, and thiazolidinediones. Aim 3: To identify the differentiation-induced STAT3 activating ligand. Our new pilot data indicate that IL-6 is not the autocrine factor responsible for MDI-induced STAT3 activation, but that the heparin binding ligand midkine (MK) is. In this Aim, we will confirm our preliminary studies, and determine whether midkine is the sole STAT3 activating ligand released upon MDI stimulation of 3T3-LI cells. Aim 4: To determine the role of STAT3 activation in adipogenesis. We hypothesize that activation of STAT3 is necessary for adipogenesis. We will block MDI-induced STAT3 activation by overexpression of PIAS3. Alternately, we will mimic STAT3 activation by overexpression of a constitutively active STAT3 to determine whether STAT3 activation alone is necessary and sufficient to induce adipogenesis. The role of STAT3 in fat pad formation will be investigated by implantation into the subcutaneous space of nude mice human preadipocytes that express vector, PIAS3, or constitutively active STAT3.

白细胞介素 6 (IL-6) 升高与全身感染和癌症恶病质中的脂肪消耗有关。 然而，重要的新数据表明，循环中的 IL-6 在人类肥胖症中也会升高，而脂肪组织是这种升高的主要来源。 由于肥胖是美国最普遍的公共卫生挑战之一，因此了解脂肪组织中 IL-6 的表达和功能，并确定脂肪组织 IL-6 表达失调是否与肥胖和肥胖的发生有关非常重要。肥胖相关的并发症。 IL-6 传统上通过 STAT3 激活发出信号，但在分化前脂肪细胞时，IL-6 会抑制并且 STAT3 似乎是脂肪细胞形成所必需的。 在本提案中，我们提出以下具体目标。 目标 1：确定 IL-6 诱导的脂肪生成抑制所涉及的机制。 我们假设大于或等于 10 ng/ml IL-6 通过改变正常细胞周期进程和随后的脂肪形成转录因子表达来抑制前脂肪细胞向脂肪细胞的转化。 我们将确定 3T3-L1 前脂肪细胞中 IL-6 对细胞周期进展和分化的影响。 使用嵌合 GM-CSF-gp130 受体转染，将探索转导 IL-6 效应所涉及的信号传导机制。 为了探索 IL-6 在脂肪组织中的生理相关性，我们将确定 IL-6 敲除小鼠是否改变了正常和高脂肪饮食下的脂肪组织生长、葡萄糖和脂质代谢。 目标 2：表征肥胖动物模型中脂肪组织 IL-6 的表达。 我们发现瘦小鼠的脂肪组织中表达IL-6 mRNA，但有报道肥胖db/db小鼠的脂肪组织中不表达IL-6 mRNA。 由于糖皮质激素抑制 IL-6 表达，我们假设 ob/ob 和 db/db 小鼠的脂肪组织中 IL-6 表达因高全身皮质酮水平而受到抑制，这是这些肥胖模型的特征。 我们还预测饮食诱导肥胖 (DIO) 小鼠的脂肪组织中 IL-6 表达升高，与肥胖人类类似。 随着肥胖的发展，DIO 小鼠仍保持正常的皮质酮水平。 我们将表征瘦对照、DIO、ob/ob 和 db/db 的脂肪组织中 IL-6 表达的特征，所有这些都在基线时的 C57BL/6J 背景上以及对糖皮质激素激动剂和拮抗剂以及噻唑烷二酮的反应。目标 3：鉴定分化诱导的 STAT3 激活配体。 我们的新试验数据表明，IL-6 不是负责 MDI 诱导 STAT3 激活的自分泌因子，而是肝素结合配体中期因子 (MK)。 在这个目标中，我们将确认我们的初步研究，并确定中期因子是否是 MDI 刺激 3T3-LI 细胞时释放的唯一 STAT3 激活配体。 目标 4：确定 STAT3 激活在脂肪生成中的作用。 我们假设 STAT3 的激活对于脂肪生成是必要的。 我们将通过 PIAS3 的过表达来阻断 MDI 诱导的 STAT3 激活。或者，我们将通过组成型活性 STAT3 的过表达来模拟 STAT3 激活，以确定单独 STAT3 激活是否是诱导脂肪生成所必需和充分的。 将通过植入表达载体、PIAS3或组成型活性STAT3的裸鼠人前脂肪细胞的皮下空间来研究STAT3在脂肪垫形成中的作用。