Macrophage Akt and IKKalpha signaling in apoptosis and atherosclerosis

描述(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根本原因。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。巨噬细胞凋亡存在于动脉粥样硬化的所有阶段，在动脉粥样硬化早期和晚期对病变形态的影响不同。早期病变中巨噬细胞的丢失被认为可以缩小病变大小，而晚期病变中的细胞死亡有助于坏死核心和斑块的不稳定。Tabas及其同事的研究表明，吞噬细胞清除缺陷会导致动脉粥样硬化斑块中凋亡细胞的聚集。在此，我们认为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。PI3K/Akt和NF-kB是两条主要的促生存通路，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是结构性活跃的。我们实验室最近的研究表明，造血细胞前列腺素E_2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巨噬细胞的凋亡。在巨噬细胞中表达两种Akt亚型Akt1和Akt2，但它们在巨噬细胞凋亡和动脉粥样硬化形成中的相对作用尚未确定。有趣的是，Akt被报道通过Ikka介导信号转导，从而激活具有抗凋亡活性的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。在这个提案中，我们打算定义Akt NF-kB信号通路的不同成员，包括Akt1、Akt2和Ikka，在巨噬细胞存活和动脉粥样硬化病变形成中的作用。我们假设Akt-1和Akt-2都有助于巨噬细胞的存活，但这两种亚型的缺失将比单独缺乏任何一种亚型更大程度地促进巨噬细胞的凋亡。特异性目标1的目的是在体内检测Akt1或Akt2的造血细胞缺陷对LDLR-/-小鼠巨噬细胞存活和动脉粥样硬化形成的影响。特异性目标2的目的是明确巨噬细胞Akt1和/或Akt2的缺失对体外细胞凋亡和Akt和NF-：B信号通路的影响。AKT和Ikka是TORC1形成所必需的信号转导途径。因此，我们将检验巨噬细胞缺乏Akt1和/或Akt2会抑制mTOR活性的假说。在特定的目标3中，我们将检验这一假说，即造血细胞中的Ikka缺乏将通过Akt和NF-：B信号通路的改变而降低巨噬细胞的存活率并影响动脉粥样硬化的形成。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.