CREB Regulates Adipogenesis and Adipocyte Survival

描述（由申请人提供）：肥胖和体重增加与发病率和死亡率增加有关，并影响到美国和其他发达国家大量快速增长的人口。为了找到预防和治疗肥胖及相关疾病的治疗靶点，人们已经付出了相当大的努力来了解伴随肥胖的脂肪组织的变化。尽管在这方面取得了进展，但尚未制定多少有效的战略。因此，我们研究的中心目标是确定新的因素和过程，这些因素和过程可能作为新的干预策略的目标。本申请提出的研究旨在评估CREB对脂肪组织发育的影响，其在成熟脂肪细胞存活中的作用，以及脂肪组织炎症。我们预计这些研究将在动物模型中确定CREB对脂肪组织形成和功能的影响，并强调CREB及其相关因素和过程作为治疗或预防肥胖和其他脂肪疾病的潜在靶点。公共卫生相关性：肥胖的特点是由于现有脂肪细胞肥大和新脂肪细胞的产生（增生）而导致脂肪组织质量增加。新的脂肪细胞由原脂肪细胞和间质间充质干细胞产生。这些前体细胞向成熟脂肪细胞的转化需要包括C/ ebp 1和2以及PPAR3在内的转录因子在时间上的协调表达，从而导致与成熟脂肪细胞表型相关的因子的表达。我们的研究表明，转录因子CREB的激活也是诱导3T3-L1前脂肪细胞成脂转化的必要条件。在体外，CREB激活还可以保护成熟脂肪细胞免于凋亡。虽然从这些体外研究中学到了很多，但CREB在脂肪生物学中的作用尚未在动物模型中探索。最近的初步研究表明，肥胖小鼠和大鼠的脂肪组织中CREB水平降低。这可能部分解释了肥胖个体中脂肪细胞凋亡增加和脂肪生成抑制的原因。这也可能解释了巨噬细胞浸润肥胖患者脂肪组织的原因，因为抑制3T3-L1脂肪细胞中的CREB活性不仅会诱导其凋亡，还会增加细胞间粘附分子-1 （ICAM-1）、巨噬细胞迁移抑制因子-1 （MIF-1）、巨噬细胞集落刺激因子-1 （MCSF-1）、CXC配体13、基质细胞衍生因子-1 （SDF-1）和单核细胞趋化蛋白-3 （MCP-3）的表达。我们的初步研究使我们提出了与CREB在脂肪生物学中的功能有关的两个假设。首先，我们假设CREB是脂肪形成、脂肪组织发育和脂肪细胞存活所必需的（图1）。其次，我们假设凋亡脂肪细胞中CREB的缺失通过上调ICAM-1、MCSF-1、MIF-1、CXCL13、SDF-1和/或MCP-3来促进脂肪组织中巨噬细胞的募集或保留。Four Specific Aims将使用体内和体外模型验证这些假设。目的1将测试体内强迫消耗脂肪前细胞中的CREB是否会抑制脂肪形成，以及脂肪细胞中强迫失去CREB是否会诱导其在体内的凋亡死亡。目的2将研究脂肪细胞特异性CREB消耗对肥胖和整个动物生理的影响。目的3将确定是否强迫脂肪细胞或脂肪细胞和巨噬细胞的CREB损失促进巨噬细胞募集到脂肪组织。第四个目标将探索体外脂肪细胞中强制CREB消耗促进巨噬细胞募集和/或与脂肪细胞粘附的能力。我们预计这些研究将在动物模型中确定CREB对脂肪组织形成和功能的影响，并强调CREB及其相关因素和过程作为治疗或预防肥胖和其他脂肪疾病的潜在靶点。

DESCRIPTION (provided by applicant): Obesity and weight gain are associated with increased morbidity and mortality, and affect a sizable and rapidly increasing population in the U.S. and other developed countries. Considerable effort has gone into understanding the changes in adipose tissue that accompany obesity in order to identify therapeutic targets to prevent of treat obesity and related conditions. In spite of progress in this area, few effective strategies have been developed. A central goal of our research, therefore, is to identify new factors and processes that may serve as targets for novel interventional strategies. The research proposed in this application is designed to assess the impact of CREB on the development of fat tissue, its role in mature adipocyte survival, and adipose tissue inflammation. We anticipate that these studies will define the impact of CREB on adipose tissue formation and function in animal models, and highlight CREB and associated factors and processes as potential targets for therapies designed to treat or prevent obesity and other adipose disorders. PUBLIC HEALTH RELEVANCE: Obesity is characterized by an increase in adipose tissue mass due to hypertrophy of existing fat cells and through the generation of new adipocytes (hyperplasia). New adipocytes arise from resident preadipocytes and interstitial mesenchymal stem cells. Conversion of these precursor cells to mature adipocytes requires the temporally orchestrated expression of transcription factors including C/EBPs 1 and 2, and PPAR3, which leads to the expression of factors associated with the mature adipocyte phenotype. Our studies have shown that activation of the transcription factor CREB is also required to induce adipogenic conversion of 3T3-L1 preadipocytes. CREB activation also protects mature adipocytes from apoptosis in vitro. While much has been learned from these in vitro studies, the role of CREB in adipose biology has not been explored in animal models. Recent preliminary studies show that CREB levels are diminished in adipose tissue from obese mice and rats. This may account, in part, for the increased adipocyte apoptosis and suppression of adipogenesis observed in obese individuals. It may also account for the infiltration of fat tissue from obese subjects with macrophages, since inhibition of CREB activity in 3T3-L1 adipocytes not only induces their apoptosis, but also increases expression of intercellular adhesion molecule-1 (ICAM-1), macrophage migration inhibitory factor-1 (MIF-1), macrophage colony stimulating factor-1 (MCSF-1), CXC ligand 13, stromal cell-derived factors -1 (SDF-1) and monocyte chemotactic protein-3 (MCP-3). Our preliminary studies have led us to propose two hypotheses related to CREB function in adipose biology. First, we hypothesize that CREB is required for adipogenesis, adipose tissue development, and adipocyte survival (Fig.1). Second, we hypothesize that loss of CREB in apoptotic adipocytes promotes the recruitment or retention of macrophages in adipose tissue via the upregulation of ICAM-1, MCSF-1, MIF-1, CXCL13, SDF-1 and/or MCP-3. Four Specific Aims will test these hypotheses using in vivo and in vitro models. Aim 1 will test whether forced depletion of CREB in preadipocytes inhibits adipogenesis in vivo, and whether forced loss of CREB in adipocytes induces their apoptotic death in vivo. Aim 2 will investigate the impact of adipocyte- specific CREB depletion on adiposity and whole animal physiology. Aim 3 will determine whether forced loss of CREB in adipocytes alone or both adipocytes and macrophages promotes macrophage recruitment to adipose tissue. The fourth Aim will explore the ability of forced CREB depletion in adipocytes to promote macrophage recruitment and/or adhesion to adipocytes in vitro. We anticipate that these studies will define the impact of CREB on adipose tissue formation and function in animal models, and highlight CREB and associated factors and processes as potential targets for therapies designed to treat or prevent obesity and other adipose disorders.