Macrophage Akt and IKKalpha signaling in apoptosis and atherosclerosis

描述（由申请人提供）：动脉粥样硬化是一种进行性炎症性疾病，是心脏病发作和中风的潜在原因。巨噬细胞在动脉粥样硬化病变的形成和发展中起着至关重要的作用。巨噬细胞凋亡发生在动脉粥样硬化的所有阶段，对早期和晚期动脉粥样硬化病变形态的影响不同。早期病变中巨噬细胞的损失被认为可以减小病变大小，而晚期病变中的细胞死亡有助于核心坏死和斑块不稳定。Tabas及其同事的研究表明，有缺陷的吞噬清除导致动脉粥样硬化斑块中凋亡细胞的积累。在这里，我们提出巨噬细胞抵抗促凋亡刺激的内在能力可能是动脉粥样硬化病变中巨噬细胞存活和凋亡细胞数量的另一个重要决定因素。有两种主要的促生存通路，PI3K/Akt和NF-kB，它们在动脉粥样硬化病变的巨噬细胞和巨噬细胞源性泡沫细胞中都具有组成性活性。我们实验室最近的研究表明，造血细胞中前列腺素E2受体EP4的遗传缺陷通过调节PI3K/Akt和NF-kB信号通路促进动脉粥样硬化病变中的巨噬细胞凋亡。两种Akt亚型在巨噬细胞中表达，Akt1和Akt2，但它们在巨噬细胞凋亡和动脉粥样硬化中的相对作用尚未确定。有趣的是，Akt已被报道通过IKKa介导信号通路，其抗凋亡活性可能激活NF-kB通路。我们假设Akt和NF-kB信号通路之间的串扰是巨噬细胞存活和动脉粥样硬化形成的关键决定因素。在本提案中，我们打算确定Akt NF-kB信号通路的不同成员，包括Akt1， Akt2和IKKa，对巨噬细胞存活和动脉粥样硬化病变形成的贡献。我们假设Akt-1和Akt-2都有助于巨噬细胞的存活，但这两种亚型的缺乏会比单独缺乏任何一种亚型更大程度地促进巨噬细胞凋亡。Specific Aim 1的目的是研究造血细胞缺乏Akt1、Akt2或两者对LDLR-/-小鼠体内巨噬细胞存活和动脉粥样硬化的影响。特异性目的2的目的是确定巨噬细胞缺乏Akt1和/或Akt2对细胞凋亡以及Akt和NF-:B信号通路的影响。Akt和IKKa是信号转导过程中TORC1形成所必需的。因此，我们将检验巨噬细胞缺乏Akt1和/或Akt2会抑制mTOR活性的假设。在Specific Aim 3中，我们将研究造血细胞中IKKa缺乏会通过改变Akt和NF-:B信号通路降低巨噬细胞存活并影响动脉粥样硬化的假设。更好地了解巨噬细胞存活的分子机制可能为预防动脉粥样硬化和心血管事件提供新的靶点。

DESCRIPTION (provided by applicant): Atherosclerosis is a progressive inflammatory disease and the underlying cause of heart attack and stroke. Macrophages play a crucial role in the formation and progression of atherosclerotic lesions. Macrophage apoptosis occurs throughout all stages of atherosclerosis with a differential impact on lesion morphology in early versus late atherosclerosis. Loss of macrophages in early lesions is thought to reduce lesion size, whereas cell death in advanced lesions contributes to the necrotic core and plaque destabilization. Studies by Tabas and coworkers have demonstrated that defective phagocytic clearance results in apoptotic cell accumulation in atherosclerotic plaques. Here we propose that the intrinsic ability of macrophages to resist pro- apoptotic stimuli may be another important determinant of macrophage survival and apoptotic cell numbers in atherosclerotic lesions. There are two major pro-survival pathways, PI3K/Akt and NF-kB, and both are constitutively active in macrophages and macrophage-derived foam cells of atherosclerotic lesions. Recent studies in our laboratory have shown that genetic deficiency of the prostaglandin E2 receptor, EP4, in hematopoietic cells promotes macrophage apoptosis in atherosclerotic lesions by modulating the PI3K/Akt and NF-kB signaling pathways. Two Akt isoforms are expressed in macrophages, Akt1 and Akt2, yet their relative contributions to macrophage apoptosis and atherogenesis have not been determined. Interestingly, Akt has been reported to mediate signaling through IKKa that may activate the NF-kB pathways with its anti-apoptotic activity. We hypothesize that cross-talk between the Akt and NF-kB signaling pathways is a critical determinant of macrophage survival and atherogenesis. In this proposal we intend to define the contribution of distinct members of the Akt NF-kB signaling pathways, including Akt1, Akt2, and IKKa, to macrophage survival and atherosclerotic lesion formation. We hypothesize that both Akt-1 and Akt-2 contribute to macrophage survival but that deficiency of both isoforms will promote macrophage apoptosis to a greater extent than deficiency of either isoform alone. The goal of Specific Aim 1 is to examine the impact of hematopoietic cell deficiency of Akt1, Akt2, or both on macrophage survival and atherogenesis in LDLR-/- mice in vivo. The goal of Specific Aim 2 is to define the impact of macrophage deficiency of Akt1 and/or Akt2 on apoptosis and the Akt and NF- :B signaling pathways in vitro. Akt and IKKa are necessary for TORC1 formation in signal transduction. Therefore, we will examine the hypothesis that macrophage deficiency of Akt1 and/or Akt2 will suppress mTOR activity. In Specific Aim 3, we will examine the hypothesis that IKKa deficiency in hematopoietic cells will reduce macrophage survival and impact atherogenesis through alterations in the Akt and NF-:B signaling pathways. A better understanding of the molecular mechanisms of macrophage survival may provide new targets for the prevention of atherosclerosis and cardiovascular events.