Lipocalin 2 in Inflammation and Metabolic Control

描述（由申请人提供）：肥胖是发生胰岛素抵抗和代谢疾病的主要风险。脂肪组织作为内分泌器官和慢性低度炎症的主要来源，在调节胰岛素作用和能量代谢中起着至关重要的作用。功能失调的脂肪组织以脂肪因子/细胞因子的异常产生为特征，与肥胖及其相关的炎症、胰岛素抵抗和代谢失调有关。然而，哪些脂肪因子/细胞因子介导了这种联系，以及肥胖过程中涉及的机制在很大程度上仍然未知。缺乏这些知识是一个关键问题，因为它是解决肥胖及其相关代谢综合征的分子谜题的关键。我们的长期目标是阐明脂肪衍生因子在炎症和代谢稳态调节中的作用和机制。通过蛋白质组学和微阵列筛选，我们最近发现脂钙蛋白2 （LCN2）是一种新的脂肪因子，可能与肥胖和胰岛素抵抗有关。LCN2属于脂钙蛋白亚家族成员，脂钙蛋白是一种小分泌蛋白，其结构与脂肪酸结合蛋白（FABPs）相似，能够结合FFA和维甲酸（RA）等疏水小分子。LCN2启动子具有NF-(B)和C/EBP结合位点和糖皮质激素反应元件，LCN2的分泌受LPS和TNF（）的高度调控。在我们之前的研究中，LCN2在遗传性肥胖动物的脂肪组织和肝脏中表达水平上调。这种增加在服用TZD后明显逆转。LCN2似乎增强胰岛素作用并拮抗TNF(对3T3- L1脂肪细胞葡萄糖代谢、PPAR（基因表达）和胰岛素抵抗的影响。此外，LCN2抑制TNF -和lps诱导的脂肪细胞和巨噬细胞中细胞因子/趋化因子的产生。最引人注目的是，LCN2调节脂肪细胞产生瘦素和脂联素。我们的研究结果导致LCN2通过负反馈调节机制稳态调节脂肪细胞中的炎症反应和胰岛素作用，LCN2缺乏导致促炎状态，脂肪分泌失调，最终导致全身性胰岛素抵抗。我们进一步假设LCN2通过配体结合和受体介导的转运机制在脂肪细胞中发挥其生物学功能。本研究使用LCN2缺失小鼠、LCN2敲低3T3-L1脂肪细胞和缺乏配体结合能力的LCN2突变体来测试三个特定目标。目的1研究LCN2在炎症、胰岛素作用、脂肪细胞代谢和脂肪因子/细胞因子产生中的调节作用。目的2定义LCN2的配体结合和功能特性。目的3评估LCN2缺乏对小鼠炎症反应、胰岛素作用和代谢稳态的影响。公共卫生相关性：

DESCRIPTION (provided by applicant): Obesity is a major risk for developing insulin resistance and metabolic diseases. Adipose tissue plays a critical role as an endocrine organ and a major source of chronic low-grade inflammation in the regulation of insulin action and energy metabolism. Dysfunctional adipose tissue characterized by abnormal production of adipokines/cytokines has been linked to obesity and its associated inflammation, insulin resistance, and metabolic dysregulation. However, which adipokines/cytokines mediate this linkage and the mechanisms involved during obesity remain largely unknown. Lack of such knowledge is a critical problem as it is the key to solve the molecular puzzle of obesity and its related metabolic syndrome. Our long-term goal is to elucidate the role and mechanisms of adipose-derived factors in the regulation of inflammation and metabolic homeostasis. Through the proteomics and microarray screening, we recently identified lipocalin 2 (LCN2) as a new adipokine that potentially connects obesity and insulin resistance. LCN2 belongs to the lipocalin subfamily members that are small secreted proteins with a structural similarity to fatty acid binding proteins (FABPs) and the ability to bind small hydrophobic molecules such as FFA and retinoic acid (RA). LCN2 promoter possesses NF-(B and C/EBP binding sites and glucocorticoid response element; and LCN2 secretion is highly regulated by LPS and TNF(. In our previous studies, the level of LCN2 expression is up-regulated in adipose tissue and liver of genetically obese animals. This increase is significantly reversed by TZD administration. LCN2 appears to potentiate insulin action and antagonize TNF( effects on glucose metabolism, PPAR( gene expression and insulin resistance in 3T3- L1 adipocytes. Moreover, LCN2 suppresses TNF(- and LPS-induced cytokine/chemokine production in adipocytes as well as macrophages. Most strikingly, LCN2 regulates the adipocyte production of leptin and adiponectin. Our results lead to the hypothesis that LCN2 homeostatically regulates inflammatory response and insulin action in adipocytes by a negative feedback regulatory mechanism, and that LCN2 deficiency causes a proinflammatory state, dysregulation of adipose secretion, and ultimately systemic insulin resistance. We further hypothesize that LCN2 exerts its biological functions in adipocytes via the ligand binding and receptor-mediated transport mechanism. This proposal uses LCN2 null mice, LCN2 knockdown 3T3-L1 adipocytes, and mutants of LCN2 that lack ligand binding ability to test three specific aims. Aim 1 investigates the regulation of LCN2 in inflammation, insulin action, adipocyte metabolism, and adipokine/cytokine production. Aim 2 defines the ligand binding and functional properties of LCN2. Aim 3 assesses the impact of LCN2 deficiency on inflammatory response, insulin action, and metabolic homeostasis in mice. PUBLIC HEALTH RELEVANCE: Increasing evidence supports the role of adipose tissue inflammation, lipid metabolic defects, and endocrine dysfunction in obesity and insulin resistance. This proposal aims at identifying and characterizing the role and mechanism of lipocalin 2, a new adipose-derived factor, in the regulation of inflammation, insulin action, and adipocyte lipid/glucose metabolism in cell-based as well as animal studies. The knowledge obtained will provide the key to solve the molecular puzzle of obesity and lead to the identification of novel strategies for preventive and therapeutic interventions.