Mechanism of atheroprotective function of Akt3 kinase

 描述（由申请人提供）：丝氨酸/苏氨酸激酶Akt（也称为PKB）是人类生理学和疾病核心中最重要和最通用的蛋白激酶之一。Akt调节许多细胞过程，包括细胞生长、葡萄糖和脂质代谢、分化、增殖和凋亡。三个高度同源的Akt亚型，由三个独立的基因编码，在哺乳动物中表达。小鼠中三种Akt同种型的组合缺失表明同种型的补偿和互补作用。然而，这三种异构体也有不同的功能，尽管特异性机制才刚刚开始出现。Akt，特别是Akt亚型在动脉粥样硬化形成中的作用的研究非常有限。最近的研究表明，基因消融Akt 1通过增强动脉壁中促炎基因的表达以巨噬细胞非依赖性方式促进冠状动脉粥样硬化。我们最近探索了Akt 3在动脉粥样硬化中的作用，使用Akt 3基因的基因消融小鼠。我们的研究已经证明了Akt 3在高脂血症ApoE-/-小鼠中的特异性、巨噬细胞依赖性、动脉粥样硬化保护作用。在一步一步的方式中，我们测试了各种潜在的机制，并证明了Akt 3的缺乏将巨噬细胞转化为通过两种机制积极积累胆固醇酯的细胞：通过胞饮增加脂蛋白摄取，以及平行增加胆固醇分解酶ACAT 1（也称为SOAT 1）的蛋白质稳定性。多条证据表明，Akt 3通过限制巨噬细胞中胆固醇酯积累和泡沫细胞形成来抑制动脉粥样硬化，这是动脉粥样硬化形成的早期和关键步骤。该机制是Akt亚型特异性的，我们的初步研究表明，特异性的一种机制是通过Akt 1（巨噬细胞中的主要亚型）和Akt 3在巨噬细胞中的差异亚细胞定位。该提案的长期目标是研究Akt 3调节巨噬细胞功能的分子机制。作为一个特定的假设，我们提出Akt 3通过抑制巨噬细胞胞饮作用和通过直接调节ACAT 1蛋白稳定性调节胆固醇代谢的特定分支-胆固醇酯化来特异性抑制巨噬细胞向脂质积累表型的转化。我们将研究AK 3在体内和体外动脉粥样硬化形成中的作用，特别关注Akt 3活性、ACAT 1表达和胞饮作用调节的分子机制。

 DESCRIPTION (provided by applicant): Serine/threonine kinases Akt (also known as PKB), are among the most important and versatile protein kinases at the core of human physiology and disease. Akt regulate numerous cellular processes, including cell growth, glucose and lipid metabolism, differentiation, proliferation, and apoptosis. Three highly homologous Akt isoforms, encoded by three separate genes, are expressed in mammals. Combined deletions of the three Akt isoforms in the mouse suggest compensatory and complementary roles of isoforms. However, the three isoforms also have distinct functions, even though the mechanisms of specificity are only starting to emerge. Studies of the role of Akt, and specifically of Akt isofors, in atherogenesis are very limited. It has been recently shown that genetic ablation of Akt1 promotes coronary atherosclerosis via the enhanced expression of proinflammatory genes in the artery wall in a macrophage independent manner. We have recently explored the role of Akt3 in atherosclerosis using mice with a genetic ablation of the Akt3 gene. Our studies have demonstrated a specific, macrophage dependent, atheroprotective role for Akt3 in hyperlipidemic ApoE-/- mice. In a step-by-step fashion, we tested various potential mechanisms and demonstrated that the absence of Akt3 transforms macrophage into cell which aggressively accumulates cholesterol esters via two mechanisms: increased lipoprotein uptake via pinocytosis, and parallel increased protein stability of cholesterol esterifying enzyme ACAT1 (also known as SOAT1). Multiple lines of evidence suggested that Akt3 suppresses atherosclerosis by restricting cholesteryl ester accumulation and foam cell formation in macrophages, an early and critical step in atherogenesis. The mechanism is Akt isoform specific, and our preliminary studies suggest that one mechanism for specificity is via differentia subcellular localization of Akt1 (a major isoform in macrophages) and Akt3 in macrophages. The long-term goal of this proposal is to investigate the molecular mechanism of Akt3 regulation of macrophage function. As a specific hypothesis, we propose that Akt3 specifically suppresses transformation of macrophage into lipid accumulating phenotype by inhibiting macrophage pinocytosis and by regulating a particular branch of cholesterol metabolism - cholesterol esterification via direct regulation of ACAT1 protein stability. We will investigate the role of AK3 in atherogenesis in vivo and in vitro with a particular focus on the molecular mechanisms of regulation of Akt3 activity, ACAT1 expression and pinocytosis.