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依赖性蛋白激酶（PKA）活性。PKA磷酸化几个促进脂肪分解释放游离脂肪酸和甘油的关键靶点。与这种分解代谢反应相反的是胰岛素，它刺激脂肪细胞的脂肪生成和燃料保存。胰岛素通过其激活mTOR-S6K1通路的能力也是一个重要的生长促进剂。mTOR是一种保守的丝氨酸/苏氨酸激酶，根据生长因子等环境因素和葡萄糖、氨基酸等营养物质调节细胞生长和代谢。胰岛素和儿茶酚胺系统与它们在脂肪中的相反功能一致，它们也在多个水平上相互拮抗信号通路，从而提供动态和敏感的能量需求控制。除了在刺激脂肪分解和抑制胰岛素作用方面的传统作用外，我们的新研究出人意料地表明，¿ARs以cAMP和PKA依赖的方式激活mTOR-S6K1途径。这种活性可以在人和啮齿类动物的脂肪细胞、白色和棕色脂肪细胞中观察到。该途径主要参与特定mrna组的调控翻译。脂肪细胞越来越被认为是肽脂肪因子、血管生成因子，甚至可能是其他肽神经递质的重要来源，但对这些因子如何合成、调节或分泌的理解有限。在这个R21试点和可行性项目中提出的研究将测试以下两个特定的假设：(1)¿AR和camp刺激的S6K1活性在脂肪细胞中的作用是选择性地刺激一组mrna的翻译，这些mrna与胰岛素调节的mrna不同，我们建议鉴定这些转录本。所采取的方法包括多聚体分馏，然后是差异再分布转录本的微阵列分析。(2)在脂肪细胞中，AR和camp刺激的S6K1活性的作用是使胰岛素信号通路脱敏，这是通过S6K1对IRS-1的Ser磷酸化来实现的。鉴于脂肪组织在代谢综合征病因学中的综合作用，本探索性研究项目既提供了扩大代谢疾病干预新靶点的机会，也促进了我们对脂肪细胞细胞生物学的基本认识。

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.