Novel Role of ??-Adrenergic Receptors to Activate the mTOR-S6K1 Signaling Pathway

描述(由申请人提供)：E/NE激活脂肪细胞中的肾上腺素能受体(ARs)可增加cAMP水平和cAMP依赖的蛋白激酶(PKA)活性。PKA使几个促进脂肪分解的关键靶点磷酸化，释放游离脂肪酸和甘油。与这种分解代谢反应相反的是胰岛素，它刺激脂肪细胞中的脂肪生成和燃料储存。胰岛素通过激活mTOR-S6K1途径也是重要的生长促进剂。MTOR是一种保守的Ser/Thr激酶，它调节细胞的生长和代谢，以响应环境信号，如生长因子，以及营养物质，如葡萄糖和氨基酸。与它们在脂肪中相反的功能一致，胰岛素和儿茶酚胺系统也在不同水平上对抗彼此的信号通路，从而提供对能量需求的动态和敏感控制。除了传统上ARs在刺激脂解和抑制胰岛素作用方面的作用外，我们的新研究意外地表明，Ars以cAMP和PKA依赖的方式激活mTOR-S6K1途径。这种活性可以在人类和啮齿动物的脂肪细胞、白色和棕色脂肪细胞中观察到。这一途径主要参与特定mRNAs组的调控翻译。脂肪细胞越来越被认为是多肽脂肪因子、血管生成因子甚至其他多肽神经递质的重要来源，但对这些因子是如何合成、调节或分泌的了解有限。在这个R21试点和可行性项目中提出的研究将检验以下两个特定的假设：(1)AR和cAMP刺激的脂肪细胞S6K1活性的作用是选择性地刺激一组不同于胰岛素调控的mRNAs的翻译，我们建议鉴定这些转录本。所采取的方法包括多聚体分级，然后对差异重新分配的转录本进行微阵列分析。(2)AR和cAMP激活的S6K1在脂肪细胞中的作用是使胰岛素信号通路脱敏，这是通过S6K1对IRS-1的丝氨酸磷酸化实现的。鉴于脂肪组织在代谢综合征病因学中的综合作用，这一探索性研究项目既提供了一个机会，扩大了可能确定干预代谢性疾病的新靶点的领域，又促进了我们对脂肪细胞细胞生物学的基本了解。 公共卫生相关性：美国(以及世界各地)II型糖尿病发病率的持续上升正在给医疗保健系统、工人生产力和患者的生活质量带来巨大负担。我们知道大量关于胰岛素细胞内作用的级联步骤的信息，以及它们在II型糖尿病发展的早期阶段如何受到干扰。我们知道，脂肪细胞储存能量并调节其释放的能力是体内适当营养分配的重要组成部分。然而，脂肪细胞不仅是储存多余代谢能量的银行，在卡路里不足的时候作为货币使用，而且它也是蛋白质荷尔蒙的重要来源。这些包括控制食欲的激素，在肌肉等其他组织中适当的胰岛素作用，脂肪甚至是调节血管生长和免疫反应的因素的来源。越来越多的人意识到，脂肪细胞也可以是能量的净消费者，因此甚至有可能与肥胖作斗争。然而，与我们所知道的脂肪储存和释放相比，我们对脂肪细胞衍生的激素和信号分子的控制知之甚少，这些激素和信号分子本身受到胰岛素和肾上腺素等循环激素的控制。这项提议的目的是测试从我们实验室出人意料的新发现中发展出来的新想法，在这些发现中，我们提议证明在脂肪细胞中存在控制不重叠的蛋白质生产的独特过程，并且我们假设这些差异调节的蛋白质中的一些将编码这些脂肪细胞衍生的激素。

DESCRIPTION (provided by applicant): Activation of ¿-adrenergic receptors (¿ARs) in adipocytes by E/NE increases cAMP levels and cAMP- dependent protein kinase (PKA) activity. PKA phosphorylates several key targets that promote lipolysis to release free fatty acids and glycerol. Opposing this catabolic response is insulin, which stimulates lipogenesis and fuel conservation in adipocytes. Insulin is also an important growth promoter though its ability to activate the mTOR-S6K1 pathway. mTOR is a conserved Ser/Thr kinase that regulates cell growth and metabolism in response to environmental cues such as growth factors, and nutrients such as glucose and amino acids. Consistent with their opposing functions in fat, the insulin and catecholamine systems also antagonize eachother's signaling pathways at several levels, thus providing dynamic and sensitive control of energy needs. In addition to the traditional role of ¿ARs in the stimulation of lipolysis and suppression of insulin- action, our new studies unexpectedly show that ¿ARs activate the mTOR-S6K1 pathway in a cAMP and PKA dependent manner. This activity can be observed in human and rodent fat cells, white and brown adipocytes. This pathway is principally involved in the regulated translation of specific sets of mRNAs. The fat cell is increasingly recognized as an important source of peptide adipokines, angiogenic factors, and perhaps even other peptide neurotransmitters, but there is limited understanding of how these factors are synthesized, regulated or secreted. The studies proposed here in this R21 Pilot and Feasiblility project will test the following two specific hypotheses: (1) The role of ¿AR and cAMP-stimulated S6K1 activity in adipocytes is to selectively stimulate the translation of a set of mRNAs that are distinct from those regulated by insulin, and we propose to identify these transcripts. The approach taken involves polysome fractionation followed by microarray profiling of differentially redistributed transcripts. (2) The role of ¿AR and cAMP-stimulated S6K1 activity in adipocytes is to desensitize the insulin-signaling pathway, and this is achieved through Ser phosphorylation of IRS-1 by S6K1. Given the integrative role of adipose tissue in the etiology of metabolic syndrome, this exploratory research project provides both an opportunity to expand the terrain from which new targets for intervention in metabolic disease might be identified, as well as promote our basic understanding of the cell biology of the adipocyte. PUBLIC HEALTH RELEVANCE: The continuing escalation in the incidence of Type II diabetes in the US (and around the world) is placing an enormous burden on the health care system, on worker productivity and on quality of life for those afflicted. We know a great deal of information about the steps in the cascade of intracellular actions of insulin and how they tend to be perturbed in the early phases of the development of Type II diabetes. We know that the ability of fat cells to store energy and to regulate its release is an important component of proper nutrient partitioning in the body. However the fat cell is not only a bank in which excess metabolic energy is stored as currency for use during times of caloric deficit, but it is also an important source of protein hormones. These include hormones to control appetite, proper insulin action in other tissue such as muscle, and fat is even a source of factors to regulate blood vessel growth and immune responses. There is also increasing appreciation that fat cells can also be net consumers of energy and thus have the potential to even fight obesity. However, compared to what we know about fat storage and release, we know comparatively very little about the control of fat cell-derived hormones and signaling molecules, which are themselves controlled by circulating hormones such as insulin and adrenaline. The purpose of this proposal is to test new ideas that developed from unexpected new findings in our laboratory, in which we propose to demonstrate that there are unique processes in fat cells that control non-overlapping sets of protein production, and we postulate that some of these differentially regulated proteins will code for these fat cell-derived hormones.