PDGFbeta Receptor Activation Promotes Atheroprotective Changes in SMC Phenotype

动脉粥样硬化是一种进行性疾病，是西方世界死亡的主要原因。值得注意的是， 尽管经过了几十年的研究，关于平滑肌细胞（SMC）的作用仍然存在很大的模糊性 以及控制斑块稳定性和斑块破裂概率的机制 可能有心肌梗死或中风。一般的教条是，SMC主要涉及晚期 而不是早期病变，它们的主要作用是通过促进纤维化的形成来保护动脉粥样硬化。 章然而，我们实验室最近的自然医学研究涉及同时SMC特异性谱系追踪， 干细胞多能性基因Oct 4或Klf 4的敲除（KO）提供了令人信服的证据，表明SMC 在病变发病机制中发挥的作用比人们普遍认识到的要大得多。主要发现包括我们的 显示：1）ApoE-/-小鼠的晚期病变内>80%的SMC衍生细胞缺乏可检测的表达 2）晚期小鼠和人类病变中30-40%的SMC衍生细胞缺乏 可检测的SMC标志物，并具有活化的M β标志物;和3）SMC可以具有主要的有益或 对病变发病机制的有害影响取决于其表型转变的性质。因此， 迫切需要确定促进SMC表型有益变化的因素和机制。研究的 该提案将检验总体假设，即SMC表型中PDGFβ R依赖性变化具有动脉粥样硬化保护作用， PDGFβR信号通路的增强应该是治疗糖尿病的主要治疗靶点之一。 晚期动脉粥样硬化这一假设将在两个具体目标中得到检验。目的1将检验PDGFβR- SMC表型的依赖性转变在动脉粥样硬化的发生和发展中起关键作用。目的 1a将扩展我们的初步研究，表明SMC特异性条件性PDGFβR KO在6-8周龄时，随后在18周龄时， 西方饮食（WD）周导致BCA病变较大，但实际上缺乏SMC，以纳入严格的分析 斑块稳定性的指标和病变内SMC数量减少的机制。目标1b将检验假设 SMC特异性PDGFβR的条件性KO导致SMC表型的有害转变，包括增加 SMC来源的Lgals 3+泡沫细胞（SMC-FC）数量和SMC来源的肌成纤维细胞（SMC-MF）数量减少 在纤维帽内。目的2验证PDGFβ R信号通路具有抗动脉粥样硬化作用的假说 在晚期动脉粥样硬化病变中至少部分通过诱导SMC表型的有利变化。研究 将测试SMC特异性或整体遗传或药理学抑制（目的2a-2c）或增强（输注rPDGF-1） DD，Aim 2d）在喂食西方饮食的晚期动脉粥样硬化病变ApoE-/-小鼠中，PDGFβR信号传导的总体影响 病变发病机制、斑块稳定性指数、SMC表型转变和斑块破裂发生率。结果 可能导致新的治疗方法的发展，以减少动脉粥样硬化的晚期临床并发症 通过诱导SMC经历表型-功能的有益变化，促进形成更厚的 机械上更稳定的纤维帽，从而降低斑块破裂和可能的MI或中风的可能性。

Atherosclerosis is a progressive disease that is a leading cause of death in the Western world. Remarkably, despite decades of research, there remain major ambiguities regarding the role of smooth muscle cells (SMC) in lesion pathogenesis, as well as mechanisms that control plaque stability and the probability of plaque rupture with possible myocardial infarction (MI) or stroke. The general dogma is that SMC are primarily involved in late not early stage lesions, and that their primary role is atheroprotective by contributing to formation of a fibrous cap. However, recent Nature Medicine studies by our lab involving simultaneous SMC-specific lineage tracing and knockout (KO) of the stem cell pluripotency genes, Oct4 or Klf4 provided compelling evidence that SMC play a much greater role in lesion pathogenesis than has been generally appreciated. Key findings include our showing that: 1) >80% of SMC-derived cells within advanced lesions of ApoE-/- mice lack detectable expression of typical SMC markers; 2) 30-40% of SMC-derived cells within both advanced mouse and human lesions lack detectable SMC markers and have activated markers of MФs; and 3) SMC can have major beneficial or detrimental effects on lesion pathogenesis depending on the nature of their phenotypic transitions. Thus, there is a critical need to identify factors and mechanisms that promote beneficial changes in SMC phenotype. Studies in this proposal will test the overall hypothesis that PDGFβR-dependent changes in SMC phenotype are atheroprotective and that augmentation of the PDGFβR signaling pathway should be one of the primary therapeutic targets for treating advanced atherosclerosis. This hypothesis will be tested in two specific aims. Aim 1 will test the hypothesis that PDGFβR- dependent transitions in SMC phenotypic play a critical role in the development and progression of atherosclerosis. Aim 1a will extend our initial studies showing that SMC specific conditional PDGFβR KO at 6-8 weeks of age followed by 18 weeks of Western diet (WD) resulted in BCA lesions that were larger but virtually lacking SMC to include rigorous analysis of indices of plaque stability and mechanisms for reductions in SMC number within lesions. Aim 1b will test the hypothesis that SMC-specific conditional KO of PDGFβR results in detrimental transitions in SMC phenotype including increased numbers of SMC-derived Lgals3+ foam cells (SMC-FC) and reduced numbers of SMC derived myofibroblasts (SMC-MF) within the fibrous cap. Aim 2 will test the hypothesis that PDGFβR-signaling pathways confer atheroprotective effects within advanced atherosclerotic lesions at least in part through inducing favorable changes in SMC phenotype. Studies will test how SMC-specific or global genetic or pharmacologic inhibition (Aims 2a-2c) or augmentation (infusion of rPDGF- DD, Aim 2d) of PDGFβR signaling in Western diet fed ApoE-/- mice with advanced atherosclerotic lesions impacts overall lesion pathogenesis, indices of plaque stability, SMC phenotypic transitions, and the incidence of plaque rupture. Results may lead to development of novel therapeutic approaches for reducing late stage clinical complications of atherosclerosis by inducing SMC to undergo beneficial changes in phenotype-function that promote formation of a thicker and mechanically more stable fibrous cap, thus reducing the probability of plaque rupture and a possible MI or stroke.