SREBP-炎症小体在血液紊流促动脉粥样硬化中的机制

The focal nature of atherosclerosis in the arterial tree is correlated with athero-prone flow imposed on vascular endothelial cells (ECs). The flow patterns in these athero-prone regions are with low shear stress, oscillation, and reverse flow. In investigating the mechanotransduction mechanisms, we have previously reported that athero-prone flow activates sterol-regulatory element binding protein (SREBP) in ECs. Our recent data show that athero-prone flow induces inflammasome via SREBP. The induced inflammasome with ensuing pro-inflammatory responses can be mimicked by SREBP overexpression in ECs. With these pilot studies, the guiding hypothesis is that the prevalent distribution of atherosclerotic lesions is due, in part, to the flow-induced inflammasome via SREBP in ECs, resulting in an atherogenic milieu in the sub-endothelial space. Consequently, monocytes are recruited to the vessel wall and differentiated into M1 macrophage, leading to foam cell formation. To test our hypothesis, three Specific Aims are proposed: Aim 1 will study the molecular mechanism by which athero-prone flow induces SREBP, which in turn up-regulates inflammasome in ECs. Aim 2 will use an EC/monocyte co-culture system to examine the involvement of endothelial SREBP-inflammasome in the M1 transition of the macrophages. Aim 3 will use EC-specific SREBP transgenic mice to validate the role of SREBP-inflammasome in atherogenesis in vivo. Aiming at studying vascular impairment caused by the athero-prone flow, this project will establish a framework to further understand the mechano and molecular basis of vascular biology in health and disease regulated by flow.

动脉粥样硬化斑块的局灶性分布与局部血管内皮所承载的剪应力密切相关，在斑块高发区的紊流具有低剪应力及不稳定回流等特性。我们最早报道紊流可持续激活内皮细胞脂代谢关键调节因子-SREBP；最近我们发现紊流通过SREBP上调天然免疫重要蛋白复合体-炎症小体。因此，我们推断：动脉粥样硬化斑块的发生是由于紊流活化内皮细胞SREBP-炎症小体信号通路，形成促粥样硬化微环境，招募单核细胞并使之分化成M1型巨噬细胞，最终形成泡沫细胞。为验证这一假设，本课题：1）探讨紊流诱导内皮细胞SREBP进而上调炎症小体的分子机制；2）研究内皮SREBP-炎症小体在巨噬细胞分化中的作用；3）利用内皮特异性SREBP转基因小鼠验证SREBP-炎症小体信号通路在动脉粥样硬化中的作用。本课题将为阐明动脉粥样硬化机理及其防治策略提供新的思路。

核转录因子SREBP2转录调节几乎所有参与胆固醇合成的酶，在胆固醇合成中发挥着重要作用，最新研究表明SREBP2在天然免疫中也发挥着重要作用。本项目研究（1）首先证明了在紊流情况下，内皮细胞的SREBP2通过转录调节，直接结合到NLRP3和NOX2的启动子区域，调节其表达，从而促进NLRP3炎症小体形成，参与动脉粥样硬化的发生和发展。（2）其次在转录后调节方面，在氧化应激刺激下，SREBP2可以通过转录mir-92a，从而抑制维持内皮功能的重要分子，包括SRIT1、 KLF2 和 KLF4的表达，最终导致内皮细胞中的NLRP3炎症小体增高，eNOS的表达降低。（3）在信号转导方面，紊流引起的integrin β 5转移到脂筏可以激活NLRP3炎症小体，从而引起内皮功能障碍。动物实验表明，高脂喂养内皮特异性过表达SREBP2的小鼠，相比较WT小鼠生成更多的动脉粥样斑块。临床应用方面，通过85例冠心病病人病例的研究，我们发现血清中的mir-92a与血流介导的血管舒张负相关，与血清中的IL-1β正相关。综上所述，本项目的研究以内皮中的SREBP2及NLRP3炎症小体为核心，在细胞信号转导，转录水平，转录后水平等不同层次阐述其在内皮细胞及动脉粥样硬化中的重要作用，这些研究对氧化应激，天然免疫及内皮功能障碍相关疾病的诊断及治疗提供重要理论依据。