Loss of BMP receptor II, inflammation, and atherosclerosis

动脉粥样硬化是一种炎症性疾病，优先发生在与血流紊乱相关的动脉区域，而不发生在未扰动血流区域。我们已经证明，内皮细胞(EC)暴露在紊乱的血流条件下，刺激骨形态发生蛋白4(BMP4)的产生，从而诱导 内皮细胞的炎症反应与小鼠的高血压。最近，在研究BMP4的作用机制时，我们做了一个令人惊讶的矛盾的观察：siRNA介导的BMP受体II型(BMPRII)的敲除，而不是我们最初假设的阻断炎症反应，诱导了显著的 EC的炎症反应。我们还发现，随着人类冠状动脉粥样硬化病变的进展，BMPRII的表达减少。在一种新的血流诱导的动脉粥样硬化模型中也进行了类似的观察，该模型使用部分结扎Apo-E基因缺失的小鼠的颈动脉。我们的初步结果进一步表明，在使用BMPRir‘ApoE’‘小鼠的部分液化模型中，BMPRII缺乏显著地加速了动脉粥样硬化的发展，而在p47Phox缺陷的ApoE缺失小鼠(P47’‘APOE)中，BMPRII缺乏显著地钝化了动脉粥样硬化的发展，证明了BMPRII和NADPH氧化酶在血流诱导的动脉粥样硬化中的关键作用 动脉粥样硬化模型。我们还发现，在培养的内皮细胞中，促炎细胞因子TNFa降低BMPRII的表达，而降胆固醇的他汀类药物则增加BMPRII的表达。这些耐人寻味的发现让我们 提示BMPRII的缺失可能是血流紊乱部位病变发生和发展的中心事件。明确BMPRII参与血管炎症的潜在机制 动脉粥样硬化是这一应用的具体目标。BMPRII在血管炎症和动脉粥样硬化中的病理生理学重要性尚不清楚。然而，BMPRII基因突变是家族性原发性肺动脉高压的主要原因。BMPRII含有一条长长的细胞质尾巴，与包括p50b、NFKB、蛋白激酶CP和CSRC在内的34种蛋白结合。研究表明，BMPRII可能是一种支架蛋白，使结合的蛋白保持不活跃，直到被激动剂结合激活，就像如何 Caveolin-1功能。在这里，我们将检验一种假设，即BMPRII的表达被包括TNFa在内的促动脉粥样硬化因子下调，并被抗动脉粥样硬化条件和他汀类药物上调。BMPRII表达的减少释放了正常结合的信号蛋白 与受体结合并保持不活跃，导致血管炎症不受控制地激活，随后以NADPH氧化酶依赖的方式发展成动脉粥样硬化。我们将使用ECs和小鼠模型在四个目标上验证这一假设。目标1将定义BMPRII表达的变化 高脂饮食喂养的ApoE“”小鼠在颈动脉部分结扎或不部分结扎的情况下，血流紊乱的动脉粥样硬化病变。目的2将确定他汀类药物和TNFa调节内皮细胞和载脂蛋白E基因缺失小鼠BMPRII表达的机制。目标3将确定BMPRII基因敲除导致 内皮细胞中的炎症。目的4将利用高脂饮食喂养的BMPRir‘’_ApoE缺失小鼠，确定BMPRII表达减少对炎症和动脉粥样硬化的影响。这些研究的成功完成将为理解血管壁中BMPRII的缺失导致的动脉粥样硬化形成机制，以及动脉粥样硬化条件如何改变内皮细胞中的BMPRII水平提供新的见解。这一新的认识将为治疗和预防动脉粥样硬化提供新的治疗和诊断靶点。

Atherosclerosis is an inflammatory disease, occurring preferentially in arterial regions associated with disturbed flow while sparing the undisturbed flow regions. We have shown that exposure of endothelial cells (EC) to disturbed flow conditions stimulates production of bone morphogenic protein 4 {BMP4), which induces inflammatory responses in ECs and hypertension in mice. Recently, while studying the mechanism of BMP4 action, we made the surprising paradoxical observation that siRNA-mediated knockdown of the BMP receptor type II (BMPRII), instead of blocking the inflammatory response as we initially hypothesized, induces a striking inflammatory response in EC. We also found that BMPRII expression decreases as the atherosclerotic lesion advances in human coronary arteries. Similar observations were made in a novel model of flow-induced atherosclerosis using a partial ligation of the carotid artery in Apo-E null mice. Our preliminary results further show that BMPRII deficiency dramatically accelerates the development of atherosclerosis in the partially liqated model using BMPRir'ApoE'' mice, while it is significantly blunted in p47phox-deficient ApoE-null mice (P47'^APOE )¿ demonstrating the critical role of BMPRII and NADPH oxidases in the flow-induced atherosclerosis model. We also found that the pro-inflammatory cytokine TNFa decreases BMPRII expression, whereas the cholesterol lowering statins increase it in cultured endothelial cells. These intriguing findings led us to propose that loss of BMPRII may be a central event in lesion initiation and progression at sites of disturbed flow. Defining the underlying mechanisms through which BMPRII is involved in vascular inflammation and atherosclerosis is the specific goal of this application. The pathophysiological importance of BMPRII in vascular inflammation and atherosclerosis is not known. However, genetic mutations of BMPRII are a major cause of familial primary pulmonary hypertension. BMPRII contains a long cytoplasmic tail that binds more than 34 proteins including p50b NFKB, protein kinase Cp and cSrc. Studies suggest that the BMPRII may be a scaffolding protein that keeps the bound proteins inactive until activated by agonist binding, much like how caveolin-1 functions. Here, we will examine the hypothesis that BMPRII expression is downregulated by pro-atherogenic factors including TNFa and upregulated by anti-atherogenic conditions and drugs such as statins. The decrease in BMPRII expression unleashes the signaling proteins that are normally bound to the receptor and kept inactive, resulting in uncontrolled activation of vascular inflammation and subsequent atherosclerosis development in a NADPH oxidase-dependent manner. We will test the hypothesis using ECs and mouse models in four Aims. Aim 1 will define the changes in BMPRII expression in flow-disturbed atherosclerotic lesions in ApoE''' mice fed a high fat diet with or without a partial ligation of the carotid artery. Aim 2 will determine the mechanisms by which statins and TNFa regulate BMPRII expression in ECs and ApoE-null mice. Aim 3 will detennine the mechanisms by which BMPRII knockdown induces inflammation in ECs. Aim 4 will determine the effect of reduced BMPRII expression on inflammation and atherosclerosis using BMPRir''_ApoE-null mice fed a high fat diet. Successful completion of these studies will provide novel insight into understanding the atherogenic mechanisms caused by the loss of BMPRII in the vessel wall, and how atherogenic conditions alter BMPRII levels in endothelial cells. This new knowledge will provide a novel therapeutic and diagnostic target to treat and prevent atherosclerosis.