Metabolic Characterization of the Novel Adipokine CTRP3

描述(由申请人提供)： 肥胖及其相关的II型糖尿病在美国已经成为一个巨大的医疗负担， 导致每年花费数十亿美元来治疗这些代谢紊乱。需要大量研究来了解肥胖相关的胰岛素抵抗和糖尿病的根本原因，以便有效地治疗这些疾病。Acrp30/脂联素是一种由脂肪组织产生的胰岛素增敏多聚体蛋白，在调节全身糖和脂代谢方面发挥着重要作用。等位基因多态和血清脂联素水平降低与糖尿病和代谢综合征密切相关。本实验室最近发现了一个与脂联素同源的新的分泌蛋白家族，命名为Clq/肿瘤坏死因子相关蛋白1-10(CTRP1-10)。我们已经证明了该家族的一些成员，CTRP1和CTRP9，能够在体内降低血糖水平，并在培养的肌管中激活AMPK和Akt信号通路。自从我加入王博士的实验室以来，我的研究重点是使用分子、生化和活体方法来表征CTRP3的功能和调控。在我的研究过程中，我鉴定了CTRP3的两种特殊亚型(CTRP3A和CTRP3B)，它们是基因选择性剪接的结果。当同时表达时，CTRP3A和CTRP3B形成杂三聚体和杂低聚物；这种物理复合体显著阻止CTRP3B的蛋白水解性切割。研究表明，瘦素和炎性细胞因子对CTRP3.1的转录和蛋白水平有调节作用。 肥胖(ob/ob)小鼠与瘦对照组比较。利用纯化的重组蛋白，我发现CTRP3增强了胰岛素激活小鼠成肌细胞Akt信号通路的作用，并进一步将重组CTRP3注射到小鼠体内，显著降低了小鼠的血糖水平。这些结果以及CTRP3与脂联素的结构同源性表明CTRP3具有重要的代谢功能。本提案的总体目标是确定CTRP3的代谢功能和作用机制。我们的总体假设是CTRP3增加了胰岛素敏感性，从而增强了葡萄糖代谢，促进了骨骼肌的增殖。我将使用体外(基于细胞培养)和体内(转基因过表达和重组蛋白注射)两种方法来研究CTRP3的代谢功能。预计这项研究将促进我们对脂肪组织分泌因子(统称为脂肪因子)如何协调全身能量平衡的了解，从而为治疗代谢紊乱提供新的见解。

DESCRIPTION (provided by applicant): Obesity and its associated type II diabetes have become a huge medical burden in the United States, resulting in billions of dollars being spent yearly to treat these metabolic disorders. Much research is needed to understand the underlying cause of obesity-linked insulin resistance and diabetes in order to effectively treat these disorders. Acrp30/Adiponectin is an insulin-sensitizing, multimeric protein produced by adipose tissue that plays a major role in regulating whole body glucose and lipid metabolism. Allelic polymorphism and reduced serum adiponectin levels are tightly linked to diabetes and metabolic syndrome. Our laboratory has recently discovered a family of ten novel secreted proteins homologous to adiponectin, designated as Clq/TNF-related proteins 1-10 (CTRP1-10). We have shown that some members of this family, CTRP1 and CTRP9, are able to reduce blood glucose levels in vivo and activate AMPK and Akt signaling pathways in culture myotubes. Since I joined Dr. Wong's laboratory, my research focuses on characterizing the function and regulation of CTRP3 using molecular, biochemical, and in vivo approaches. In the course of my study, I identified two specific isoforms of CTRP3 (CTRP3A and CTRP3B) that resulted from alternative splicing of the gene. When expressed concurrently, CTRP3A and CTRP3B form heterotrimers and heterooligomers; this physical complex markedly prevents CTRP3B from proteolytic cleavage. I showed that leptin and inflammatory cytokines modulate the transcript and protein levels of CTRP3.1 demonstrated that the circulating levels of CTRP3 protein are higher in female mice and its levels are also significantly higher in obese (ob/ob) mice compared to lean controls. Using purified recombinant protein, I showed that CTRP3 potentiates the action of insulin in activating the Akt signaling pathway in mouse myoblasts, and furthermore injection of recombinant CTRP3 into mice significantly lowered their blood glucose levels. These results along with the structural homology of CTRP3 to adiponectin suggest important metabolic function for CTRP3. The overall goal of this proposal is to detemnine the metabolic function and mechanisms of action of CTRP3. Our overall hypothesis is that CTRP3 increases insulin sensitivity and thus enhances glucose metabolism and promote skeletal muscle proliferation. I will use both in vitro (cell culture-based) and in vivo (transgenic over-expression and recombinant protein injection) approaches to investigate the metabolic function of CTRP3. It is anticipated that this study will advance our knowledge on how adipose tissuesecreted factors (collectively termed adipokine) coordinate systemic energy balance and thus provide novel insights to treat metabolic disorders.