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的增加有关，并影响到美国和其他发达国家相当大且迅速增长的人口。为了确定预防或治疗肥胖及相关疾病的治疗靶点，人们已经做出了相当大的努力来了解伴随肥胖而来的脂肪组织的变化。尽管在这一领域取得了进展，但制定的有效战略却很少。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成为新的干预策略的靶点。本申请中提出的研究旨在评估CREB对脂肪组织发育的影响，它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在动物模型中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是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：肥胖的特征是由于现有脂肪细胞肥大和新脂肪细胞(增殖)的产生而导致脂肪组织质量增加。新的脂肪细胞来源于常驻的前脂肪细胞和间质间充质干细胞。这些前体细胞向成熟脂肪细胞的转化需要转录因子C/EBPS 1和2以及PPAR3的临时协调表达，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所必需的。CREB的激活在体外也能保护成熟脂肪细胞免于凋亡。虽然从这些体外研究中已经学到了很多东西，但CREB在脂肪生物学中的作用还没有在动物模型中得到探索。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。这可能在一定程度上解释了肥胖者脂肪细胞凋亡增加和脂肪生成抑制的原因。抑制3T3-L1脂肪细胞CREB活性不仅可诱导其凋亡，还可增加细胞间黏附分子-1(ICAM-1)、巨噬细胞移动抑制因子-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两个与脂肪生物学中CREB功能相关的假说。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)。第二，我们假设在凋亡的脂肪细胞中CREB的缺失通过上调ICAM-1、MCSF-1、MIF-1、CXCL13、SDF-1和/或MCP-3来促进巨噬细胞在脂肪组织中的募集或滞留。四个特定的目标将使用体内和体外模型来验证这些假设。目的1检测强迫耗竭前体脂肪细胞CREB是否在体内抑制脂肪的生成，以及强迫缺失CREB是否在体内诱导脂肪细胞的凋亡死亡。目的2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在脂肪细胞中强制丢失，还是同时在脂肪细胞和巨噬细胞中促进巨噬细胞向脂肪组织募集。第四个目的是探索强制去除脂肪细胞中CREB的能力，以促进体外培养的巨噬细胞募集和/或与脂肪细胞的黏附。我们预计这些研究将确定CREB在动物模型中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是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.