Enhancing Energy Expending Adipocytes in White Adipose Tissue

描述(由申请人提供)： 肥胖已经达到了大流行的程度，导致2型糖尿病和心血管疾病的发病率急剧增加。肥胖个体脂肪组织的膨胀是这些疾病的直接原因，原因是甘油三酯(TGS)在白色脂肪(WAT)脂肪细胞中过度积累。有两种主要的脂肪，白色储存TGS，棕色(BAT)氧化它们产生热量。直到最近，人们还认为蝙蝠只存在于新生儿的肩关节间区，但最近的几项研究发现蝙蝠存在于颈部、锁骨上、腋窝。 以及成年人类的椎旁区域。BAT对动物静息代谢率和健康体重动态平衡的贡献现已得到证实。蝙蝠是一种灵活的组织，在没有刺激的情况下，可以通过刺激和萎缩来招募。事实上，研究表明棕色脂肪细胞聚集到WAT来解释不同效应器引起的能量平衡的变化。我们最近发现，小鼠缺乏MRTF-A(血清反应因子的转录共激活因子，SRF)，会导致棕色(米色)脂肪细胞向WAT募集。在一系列体外研究中，我们已经证明了转化生长因子超家族的两个成员，转化生长因子β和骨形态发生蛋白7对MRTF-A活性和这些效应物将间充质干细胞转化为棕色/米色成脂与血管系的能力具有相反的影响。具体地说，BMP7通过抑制Rho激酶(ROCK)活性，导致F-肌动蛋白解聚和细胞质G-肌动蛋白积聚，诱导棕色脂肪生成。这通过阻止MRTF-A移位到细胞核中来减弱SRF靶基因的表达。使用小分子抑制剂CCG1423抑制SRF活性，促进MSCs对不依赖BMP7的脂肪细胞系的承诺。另一方面，转化生长因子通过促进MRTF-A进入细胞核来激活SRF的活性，从而导致脂肪细胞基因的抑制和血管基因的激活，包括平滑肌(SM)肌动蛋白(SM)、SM重链肌球蛋白(SM-MHC)和SM22。基于这些令人兴奋的数据，我们假设WAT的褐化是通过抑制SRF靶基因表达的机制招募祖细胞来调节的。我们提出了三个目的来检验这一假设。在目标1中，我们将确定BMP7和转化生长因子β对岩石活性和间充质干细胞形态的相反影响的调节机制。在目标2中，我们将确定MRTF-A/SRF调节造脂祖细胞与血管祖细胞命运的机制。在目标3中，我们将确定MRTF-A缺乏对小鼠白色脂肪组织褐化和能量平衡的影响。了解生理效应器调节Wat褐变的分子机制并确定促进这一过程的化合物将对肥胖症相关疾病的治疗方法的发展做出重大贡献。

DESCRIPTION (provided by applicant): Obesity has reached pandemic proportions contributing to the dramatic increases in the incidence of type 2- diabetes and cardiovascular disease. The expansion of adipose tissue in obese individuals is a direct cause of these diseases due to an excessive accumulation of triglycerides (TGs) within white adipose (WAT) adipocytes. There are two major types of adipose, white that stores TGs and brown (BAT) that oxidizes them to produce heat. Until recently, it was thought that BAT only existed within the interscapular regions of newborns, but several recent investigations have identified BAT depots in the cervical, supraclavicular, axillary and paravertebral regions of adult humans. The contribution of BAT to resting metabolic rate and healthy body weight homeostasis in animals is now well established. BAT is a flexible tissue that can be recruited by stimuli and atrophies in the absence of a stimulus. In fact, studies have implicated the recruitment of brown adipocytes to WAT to explain changes in energy balance in response to different effectors. We have recently shown that lack of MRTF-A (the transcriptional coactivator of serum response factor, SRF), in mice leads to recruitment of brown-like (beige) adipocytes to WAT. In a series of in vitro studies, we have demonstrated that two members of the TGF¿ superfamily, TGF¿ and BMP7 have opposing effects on MRTF-A activity and the ability of these effectors to commit mesenchymal stem cells to an brown/beige adipogenic versus vascular lineage. Specifically, BMP7 induces brown adipogenesis by suppressing Rho kinase (ROCK) activity leading to depolymerization of F-actin and accumulation of cytoplasmic G-actin. This attenuates expression of SRF target genes by preventing translocation of MRTF- A into the nucleus. Inhibition of SRF activity with a small molecule inhibitor, CCG1423 promotes commitment of MSCs to the adipocyte lineage independent of BMP7. TGF¿ on the other hand activates SRF activity by promoting MRTF-A movement into the nucleus, which leads to suppression of adipocyte genes and activation of vascular genes including smooth muscle (SM) actin, SM heavy chain myosin (SM- MHC) and SM22. Based on these exciting data, we hypothesize that the browning of WAT is regulated by recruitment of progenitors through mechanisms involving suppression of SRF target gene expression. We propose three aims to test this hypothesis. In Aim 1, we will identify the mechanisms regulating the opposing effects of BMP7 and TGF¿ on ROCK activity and the morphology of mesenchymal stem cells. In Aim 2, we will identify the mechanisms by which MRTF-A/SRF regulates the fate of progenitors to an adipogenic versus vascular lineage. In Aim 3, we will determine the effect of MRTF-A deficiency on browning of white adipose tissue and energy balance in mice. Understanding the molecular mechanisms by which physiological effectors regulate the "browning" of WAT and identifying compounds that promote this process will significantly contribute to the development of therapeutics for obesity-associated disorders.