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相关，并影响美国和其他发达国家相当大且快速增长的人口。为了确定治疗目标以预防或治疗肥胖症和相关病症，已经做出了相当大的努力来了解伴随肥胖的脂肪组织的变化。尽管在这一领域取得了进展，但制定的有效战略很少。因此，我们研究的一个中心目标是确定新的因素和过程，可能作为新的干预策略的目标。本申请中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和脂肪组织炎症中的作用。我们预计这些研究将确定CREB对动物模型中脂肪组织形成和功能的影响，并强调CREB及其相关因子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：肥胖症的特征在于由于现有脂肪细胞肥大和通过产生新的脂肪细胞（增生）而导致的脂肪组织质量增加。新的脂肪细胞来源于前脂肪细胞和间质干细胞。这些前体细胞向成熟脂肪细胞的转化需要转录因子包括C/EBP 1和2以及PPAR 3的时间协调表达，这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的激活也需要诱导3 T3-L1前脂肪细胞的成脂转化。CREB激活还可以在体外保护成熟脂肪细胞免受凋亡。虽然从这些体外研究中已经学到了很多，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，CREB水平在肥胖小鼠和大鼠的脂肪组织中减少。这可能部分解释了在肥胖个体中观察到的脂肪细胞凋亡增加和脂肪生成抑制。它也可以解释来自肥胖受试者的脂肪组织与巨噬细胞的浸润，因为3 T3-L1脂肪细胞中CREB活性的抑制不仅诱导它们的凋亡，而且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）。我们的初步研究使我们提出了两个假设相关的CREB功能在脂肪生物学。首先，我们假设CREB是脂肪生成、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、CXCL 13、SDF-1和/或MCP-3促进脂肪组织中巨噬细胞的募集或保留。四个特定目的将使用体内和体外模型来检验这些假设。目的1将测试前脂肪细胞中CREB的强制性缺失是否抑制体内脂肪形成，以及脂肪细胞中CREB的强制性缺失是否诱导其体内凋亡性死亡。目的2将研究脂肪细胞特异性CREB耗竭对肥胖和整个动物生理的影响。目的3将确定CREB在单独的脂肪细胞或脂肪细胞和巨噬细胞中的强制损失是否促进巨噬细胞向脂肪组织的募集。第四个目标将探索脂肪细胞中CREB的强制消耗在体外促进巨噬细胞募集和/或粘附至脂肪细胞的能力。我们预计这些研究将确定CREB对动物模型中脂肪组织形成和功能的影响，并强调CREB及其相关因子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.