apoE, arterial biomechanics, and cardiovascular disease

描述（由申请人提供）：动脉硬化是心血管疾病的危险因素，但动脉如何保持柔软以及动脉硬化如何导致疾病尚不清楚。我们的初步研究表明，载脂蛋白E (apoE) 和含有apoE 的HDL 通过抑制细胞外基质基因的表达来维持动脉弹性。 ApoE 中断机械驱动的前馈回路，该回路会增加 I 型胶原蛋白、纤连蛋白和赖氨酰氧化酶的表达，以响应基质硬化。这些作用与 apoE 脂质结合结构域无关。 apoE 缺失小鼠的动脉僵硬度增加，这种僵硬可以通过施用赖氨酰氧化酶抑制剂 BAPN 来减轻，尽管胆固醇高度升高，但 BAPN 治疗可以减轻动脉粥样硬化。在体内，BAPN 会减少病变中巨噬细胞的丰度，在体外，单核细胞/巨噬细胞的粘附会因基质软化而减少。从机制上讲，我们发现 apoE 和含有 apoE 的 HDL 抑制 Rho-GTP 活性并降低 VSMC 中的细胞内力。 VSMC 力学的这些变化会影响 ECM 基因表达。最后，我们发现，除了调节（纤维状）I 型胶原蛋白外，apoE 和 apoE-HDL 还能抑制 VIII 型胶原蛋白的表达，VIII 型胶原蛋白是一种非纤维状胶原蛋白，对 VSMC 功能和动脉粥样硬化具有深远影响，但其机械特性和机制效应在很大程度上尚未被探索。总体而言，我们的数据描述了 apoE 和 apoE-HDL 的全新作用，其独立于血浆胆固醇水平，与细胞和组织力学生物学密切相关，并与预防动脉粥样硬化有因果关系。我们现在提出三个具体目标来表征 apoE、细胞内力、基质重塑和动脉粥样硬化保护之间的关系。在目标 1 中，我们将使用新的 VSMC 微组织微制造平台来研究胶原蛋白 VIII 对 Rho 活性、收缩性、 ECM 基因表达和 3D 组织硬度。我们还将使用该系统来确定胶原蛋白 VIII 如何控制对 apoE 的机械反应。这些体外研究将与从 WT 和胶原蛋白 VIII 缺陷小鼠分离的 apoE / 和 apoE-/- 动脉的离体分析相补充。在目标 2 中，我们研究了硬度控制动脉粥样硬化病变发展的机制，具体目标是识别机械敏感的粘附受体，这些受体解释了单核细胞和巨噬细胞与内皮下 ECM 蛋白的硬度依赖性附着。与目标 1 一样，现有小鼠模型的补充体内实验将测试动脉僵硬度对体内单核细胞丰度的影响。目标 3 将通过开发一种新的小鼠模型将前两个目标的结果联系起来，该模型可以从 VSMC 中删除 RhoA，并确定细胞内力减少对 ECM 基因表达、动脉僵硬度和体内动脉粥样硬化的影响。这项工作汇集了由三位 PI（Assoian、Chen 和 Bendeck）组成的团队，他们具有互补的专业知识和良好的合作发表记录，他们将共同确定这种通过 apoE 对 ECM 和 VSMC 机制的新颖调节如何提供不依赖于胆固醇的心血管疾病保护。

DESCRIPTION (provided by applicant): Arterial stiffening is a risk factor for cardiovascular disease, but how arteries stay supple and how arterial stiffness contributes to disease are unknown. Our preliminary studies show that arterial elasticity is maintained by Apo lipoprotein E (apoE) and apoE-containing HDL through a suppressive effect on the expression of extracellular matrix genes. ApoE interrupts a mechanically driven feed-forward loop that increases the expression of collagen-I, fibronectin, and lysyl oxidase in response to substratum stiffening. These effects are independent of the apoE lipid-binding domain. Arterial stiffness is increased in apoE-null mice, this stiffening can be reduced by administration of the lysyl oxidase inhibitor, BAPN, and BAPN treatment attenuates atherosclerosis despite highly elevated cholesterol. Macrophage abundance in lesions is reduced by BAPN in vivo, and monocyte/macrophage adhesion is reduced by substratum softening in vitro. Mechanistically, we show that apoE and apoE-containing HDL inhibit Rho-GTP activity and reduce intracellular force in VSMCs. These changes in VSMC mechanics then affect ECM gene expression. Finally, we show that in addition to regulating (fibrillar) collagen-I, apoE and apoE-HDL inhibit the expression of collagen-VIII, a non-fibrillar collagen that has profound effects on VSMC function and atherosclerosis, yet is largely unexplored in terms of its mechanical properties and mechanistic effects. Overall, our data describe a completely new role for apoE and apoE-HDL that is independent of plasma cholesterol levels, intimately connected to cell and tissue mechanobiology, and causally linked to protection from atherosclerosis. We now propose three specific aims to characterize the relationships between apoE, intracellular force, matrix remodeling, and protection from atherosclerosis. In Aim 1, we will use a new micro fabrication platform of VSMC micro-tissues to study the effect of collagen-VIII on Rho-activity, contractility, ECM gene expression, and tissues stiffness in 3D. We will also use this system to determine how collagen-VIII controls the mechanical response to apoE. These in vitro studies will be complemented with an ex vivo analysis of arterial stiffness in apoE+/+ and apoE-/- arteries isolated from WT and collagen-VIII deficient mice. In Aim 2, we examine the mechanism by which stiffness controls atherosclerotic lesion development, with the particular goal of identifyin mechano-sensitive adhesion receptors that account for stiffness-dependent attachment of monocytes and macrophages to sub endothelial ECM protein. As in Aim 1, complementary in vivo experiments with existing mouse models will test the effect of arterial stiffness on monocyte abundance in vivo. Aim 3 will link the results in the first two aims by developing a new mouse model that can delete RhoA from VSMCs and establish the effect of reduced intracellular force on ECM gene expression, arterial stiffness, and atherosclerosis in vivo. This work brings together a team of three PI's (Assoian, Chen and Bendeck) with complementary expertise and an established track record of co- publication who, jointly, will establish how this novel regulatin of the ECM and VSMC mechanics by apoE provides cholesterol-independent protection against cardiovascular disease.