The Function of Prohibitin / Annexin 2 Interaction in White Adipose Tissue

描述(申请人提供)：肥胖是由于白色脂肪组织过度膨胀(WAT)所致。我们以前发现禁止素(PHB)是一种选择性地存在于WAT中内皮细胞(EC)表面的蛋白质，并使用与PHB结合并经历PHB介导的内吞作用的多肽CKGGRAKDC将一种细胞毒剂导向小鼠WAT，作为一种逆转肥胖的实验方法。为了更好地确立PHB作为一种预期的肥胖治疗靶点，我们已经开始在WAT中描述其目前未确定的功能。我们确定Annexin A2，也称为Annexin II(Anx2)，是一种由CKGGRAKDC多肽模拟的PHB结合蛋白。虽然Anx2已被证明具有促血管生成功能，提示PHB/Anx2相互作用在Wat内皮中发挥作用，但Anx2在脂肪生物学中的作用尚未被探索。我们的初步研究发现，PHB/Anx2复合体存在于细胞膜脂筏中，不仅在Wat内皮细胞中，而且在脂肪细胞中也存在。此外，我们还发现Anx2功能在脂肪形成过程中是必需的。基于这些观察，我们假设在EC和脂肪细胞中，PHB和Anx2形成一个受体复合体，在Wat的发育和动态平衡中发挥重要作用。为了验证我们的假设，我们将基于小鼠和细胞培养模型，以及我们确定PHB/Anx2相互作用区域的初步数据，在以下特定目的中剖析Anx2和PHB在WAT中的成脂和血管生成功能。(1)我们将研究Anx2在WAT发展中的作用。通过比较Anx2基因缺陷小鼠和野生型小鼠在不同发育阶段和饮食诱导肥胖时的Wat库，我们将通过评估Wat扩张和脂肪细胞特性，以及通过分析Wat血管形成和Wat细胞群的代表，来确定Anx2对脂肪形成和Wat血管生成的重要性。(2)探讨PHB/Anx2相互作用在脂肪生成和血管生成中的作用。在子目标2A中，我们将确定为什么Anx2功能的干扰会损害脂肪细胞中的脂滴堆积。通过使用完全缺乏Anx2或设计为缺乏PHB/Anx2结合的分化脂肪细胞，我们将评估标记脂肪生成的蛋白质的表达和定位的变化，并将测量葡萄糖和脂肪酸的摄取以及脂肪分解。在子目标2B中，我们将通过评估完全缺乏Anx2或设计为缺乏PHB/Anx2结合的EC的增殖、迁移和血管形成能力来测试PHB/Anx2相互作用在WAT血管系统中的作用。因此，我们将确定PHB和Anx2之间的细胞表面相互作用在WAT中的作用。这将有助于我们理解控制Wat组织扩张的机制，并提供关于这种蛋白质复合体生物学的有价值的信息，该蛋白质复合体可能成为抗肥胖治疗的靶点。

DESCRIPTION (provided by applicant): Obesity results from excessive expansion of white adipose tissue (WAT). We previously identified prohibitin (Phb) as a protein present on the endothelial cell (EC) surface selectively in WAT and have used a peptide CKGGRAKDC, which binds to Phb and undergoes Phb-mediated endocytosis, to direct a cytotoxic agent to mouse WAT as an experimental approach to obesity reversal. In order to better establish Phb as a prospective obesity therapy target, we have begun to characterize its currently undefined function in WAT. We identified annexin A2, also known as annexin II (Anx2), as a Phb-binding protein mimicked by the CKGGRAKDC peptide. While Anx2 has been previously shown to have a pro-angiogenic function, suggesting a role for Phb / Anx2 interaction in WAT endothelium, the role of Anx2 in adipose biology has not been explored. Our preliminary studies revealed Phb / Anx2 complex in cell membrane lipid rafts not only in WAT endothelium but also in adipocytes. Moreover, we discovered that Anx2 function is required during adipogenesis. Based on these observations, we hypothesize that in EC and in adipocytes Phb and Anx2 form a receptor complex that plays an important role in WAT development and homeostasis. To test our hypothesis, we will dissect the adipogenic and angiogenic functions of Anx2 and Phb in WAT based on mouse and cell culture models, as well as on our preliminary data identifying Phb / Anx2 interaction domains, in the following Specific Aims. (1) We will investigate the role of Anx2 in WAT development. By comparing individual WAT depots from Anx2-deficient and wild-type mice at different stages of development and upon diet-induced obesity induction, we will determine the importance of Anx2 for adipogenesis and WAT angiogenesis by assessing WAT expansion and adipocyte properties, as well as by analyzing WAT vascularization and the representation of WAT cell populations. (2) We will explore the function of Phb / Anx2 interaction in adipogenesis and WAT angiogenesis. In Sub-Aim 2A, we will determine why lipid droplet accumulation is impaired in adipocytes upon perturbation of Anx2 function. By using differentiating adipocytes either completely lacking Anx2 or designed to be deficient in Phb / Anx2 binding, we will assess changes in expression and localization of proteins marking adipogenesis and will measure glucose and fatty acid uptake, as well as lipolysis. In Sub-Aim 2B, we will test the role of Phb / Anx2 interaction in WAT vasculature by assessing proliferation, migration, and vasculature formation capacity of EC either completely lacking Anx2 or designed to be deficient in Phb / Anx2 binding. As a result, we will establish the role of the cell surface interaction between Phb and Anx2 in WAT. This will contribute to our understanding of the mechanisms governing WAT tissue expansion and provide valuable information on the biology of this protein complex potentially useful as a target of anti-obesity therapeutics.