Catestatin improves glucose homeostasis and insulin sensitivity in diet-induced obese mice

项目摘要。 肥胖代表一种慢性、低级别的组织炎症状态，导致胰岛素抵抗(IR) 脂肪变性和2型糖尿病(T2 DM)。对有效治疗的需求需要改进 对疾病的了解。在我们对内生因素的理解上存在着显著的差距 调节炎症反应和胰岛素敏感性。在这个应用中，我们展示了一种多肽， 儿茶素(CST)，源于基因产物，嗜铬粒素A(CGA)，直接改善脂肪代谢和 炎症导致肥胖小鼠胰岛素抵抗(IR)的逆转。CST提高了 饮食诱导肥胖(DIO)小鼠，体重不减。我们培育了CST缺陷基因敲除(CST-KO)小鼠， 在正常的饮食中是肥胖和胰岛素抵抗的。作为一种可能的机制，我们的数据表明 CST通过抑制AMP-脱氨酶(AMPD)、刺激AMP依赖性激酶(AMPK)升高AMP水平 DIO肝脏和肝细胞培养中的信号和AKT磷酸化，意味着直接的CST效应。 这种由CST激活的AMPK和AKT信号通过磷酸化抑制糖异生 CRTC2和FoxO1，并通过激活磷酸葡萄糖变位酶(PGM)增加糖原的产生。另一个 CST作用的结果是减轻由巨噬细胞介导的AMPK依赖的炎症 举止。这是通过抑制细胞因子的产生和促炎信号来实现的，在 反过来，可以增强AKT信号转导。肝组织切片的透射电子显微镜分析 而CST治疗后DIO小鼠的脂肪组织显示渗透或聚集减少 促炎巨噬细胞。我们假设CST抑制AMPD2的活性，使其升高 AMP水平和AMPK的激活，进而减少脂肪变性和巨噬细胞介导的 炎症导致DIO和DIO的胰岛素信号增强和糖异生抑制 CST-KO小鼠。我们将通过两个具体的目标来验证我们的假设：目标I.测试CST 通过抑制AMP-脱氨酶2激活AMPK来抑制肝脏葡萄糖的产生 (AMPD2)，提高AMPK激活所需的AMP水平。为了达到这个目的，我们将研究 CST在肝脏和肝细胞中的作用机制集中在AMPK和PGM的激活上。目标二.测试 CST介导的AMPK激活导致抑制炎症和血糖的假说 在DIO和CST-KO小鼠中通过增强AKT信号产生。在这个目标中，我们将分析 CST介导的AMPK激活所激活的抑制炎症和葡萄糖的通路 制作。我们将通过摧毁AMPD2和AMPKα的活动来执行这些具体目标 分析它们对CST介导的信号转导、AMP/ATP比值、PGM活性、细胞因子和血糖的影响 制作。我们相信，通过对这一建议的研究，我们将发现一条新的监管路径 胰岛素敏感性和葡萄糖动态平衡。

Project Summary. Obesity represents a state of chronic, low-grade tissue inflammation that contributes to insulin resistance (IR) steatosis and type 2 diabetes mellitus (T2DM). The demands for effective therapy call for improved understanding of the disease. There is a significant gap in our understanding of the endogenous factors that regulate both inflammatory responses and insulin sensitivity. In this application, we showed that a peptide, catestatin (CST), derived from a gene product, chromogranin A (CgA), directly improves lipid disposal and inflammation leading to reversal of insulin resistance (IR) in a mouse model of obesity. CST improved IR in diet-induced obese (DIO) mice without weight loss. We generated CST-deficient knockout (CST-KO) mice, which are obese and insulin resistant in normal chow diet. As a possible mechanism, our data suggested that CST raised AMP levels by inhibiting AMP-deaminase (AMPD), stimulated AMP-dependent Kinase (AMPK) signaling and AKT phosphorylation in DIO liver as well as in hepatocyte cultures, signifying a direct CST effect. This activation of AMPK and AKT signaling by CST suppresses gluconeogenesis via phosphorylation of CRTC2 and FoxO1 and elevates glycogen production via activation of phosphoglucomutase (PGM). Another consequence of CST action is to attenuate inflammation, mediated by macrophages, in an AMPK-dependent manner. This is accomplished by suppressing cytokine production and proinflammatory signaling, which in turn, could enhance AKT signaling. Analysis by transmission electron microscopy (TEM) of the sections of liver and adipose tissue of DIO mice after CST treatment indicated diminished infiltration or recruitment of proinflammatory macrophages. We hypothesize that CST inhibits activity of AMPD2 giving rise to elevated level of AMP, and activation of AMPK, which in turn, reduces steatosis and macrophage-mediated inflammation leading to enhancement of insulin signaling and suppression of gluconeogenesis in DIO and CST-KO mice. We will verify our hypothesis by working with two specific aims: Aim I. To test whether CST suppresses hepatic glucose production through activation of AMPK via inhibition of AMP-deaminase 2 (AMPD2) which elevates AMP levels necessary for AMPK activation. In this aim, we will examine the mechanism of CST action in liver and hepatocyte focusing on AMPK and PGM activation. Aim II. To test the hypothesis that CST-mediated activation of AMPK leads to suppression of inflammation and glucose production via enhancement of AKT signaling in DIO and CST-KO mice. In this aim, we will analyze the pathways invoked by CST-mediated AMPK activation that lead to suppression of inflammation and glucose production. We will execute these specific aims by knocking down activities of AMPD2 and AMPKα and analyzing their impacts on CST mediated signaling, AMP/ATP ratio, PGM activity, cytokine and glucose production. Through investigation with this proposal, we believe we will discover a novel pathway for regulation of insulin sensitivity and glucose homeostasis.