Emerging Functions of Mitochondrial Fission in Postischemic Endothelial Cells

描述（由申请人提供）：缺血(I)后内皮细胞（EC）早期再灌注（RP）功能障碍被认为是由于内源性氧化应激，特别是由于线粒体超氧化物(O27-)/活性氧（ROS）的产生而发生的。生物可利用性一氧化氮（NO）的下降损害了ec依赖性冠状血管扩张。众所周知，一氧化氮本身和通过过氧亚硝酸盐的形成，可以促进线粒体O27-的产生。暴露于剪切应力下的培养EC也显示导致no介导的线粒体O27-产生。氧化应激被认为可以诱导线粒体通透性过渡孔（mtPTP）的打开，从而激活线粒体凋亡途径。然而，最近的文献表明，线粒体凋亡的诱导与线粒体分裂有关，由此产生的去极化线粒体通过自噬降解，可导致细胞存活、凋亡或自噬性细胞死亡。我们发现，静态或剪切ec维持其线粒体网络。缺氧(H)/再氧化（RO）暴露的ECs线粒体形态发生变化，但与体外I/RP暴露的ECs相比，裂变明显减少（I模拟为H， RP模拟为RO，并添加流量）。抗氧化剂或NO合成酶抑制剂抑制了I/ rp暴露的内皮细胞的裂变，并伴有裂变蛋白动力蛋白相关蛋白1 （Drp1）的磷酸化和自噬增加。为了了解I/RP诱导的EC线粒体形态变化及其是否决定细胞命运，我们建议：(a)评估H/RO和I/RP对培养EC线粒体动力学的差异影响，并描述导致线粒体裂变增加的细胞内信号通路。转染在线粒体中表达绿色荧光蛋白的慢病毒将用于分析它们在静态、剪切、H/RO或I/RP过程中的动态行为。我们将研究异常的线粒体动力学是否伴随着融合/裂变蛋白的变化，重点关注Drp1水平/活性对裂变的调节，并将描述ROS， NO和mtPTP在Drp1激活和线粒体裂变中的作用。(b)检查阻断I/RP引起的广泛裂变是否会保护内皮线粒体功能并抑制细胞凋亡，以及裂变对细胞功能的影响是否至少部分由自噬介导。在药理学Drp1抑制剂存在或Drp1显性阴性形式或融合蛋白mitofusin 2过表达的情况下，ECs将暴露于I/RP，并测量线粒体功能、自噬和凋亡。后者也将在自噬抑制剂存在的情况下进行测量。本研究基于线粒体网络动力学变化可能导致RP后EC功能障碍的新假设。我们的目标是，通过更好地了解EC功能障碍（心脏I/RP损伤的第一个关键步骤），开发针对线粒体裂变的新治疗策略。

DESCRIPTION (provided by applicant): Emerging Functions of Mitochondrial Fission in Postischemic Endothelial Cells Endothelial cell (EC) dysfunction upon early reperfusion (RP) following ischemia (I) is thought to occur due to endogenous oxidative stress, and, specifically, due to mitochondrial superoxide (O27-)/reactive oxygen species (ROS) generation. The decline in bioavailable nitric oxide (NO) impairs the EC-dependent dilation in coronary vessels. NO, both by itself and via peroxynitrite formation, is known to promote mitochondrial O27- production. Cultured EC exposure to shear stress was also shown to result in NO-mediated mitochondrial O27- production. Oxidative stress is thought to induce the opening of the mitochondrial permeability transition pore (mtPTP) leading to activation of the mitochondrial pathway of apoptosis. However, recent literature suggests that induction of mitochondrial apoptosis correlates with mitochondrial fission, and the resultant depolarized mitochondria are degraded via autophagy, which can lead to cell survival, apoptosis or autophagic cell death. We found that static or sheared ECs maintain their mitochondrial network. Hypoxia (H)/reoxygenation (RO)- exposed ECs undergo mitochondrial morphology changes, but fission is significantly less compared to that in ECs exposed to in vitro I/RP (I is simulated as H; RP is simulated as RO with the addition of flow). Fission in I/RP-exposed ECs is inhibited by antioxidants or NO synthase inhibitors, and is accompanied by phosphorylation of the fission protein dynamin-related protein 1 (Drp1) and increased autophagy. In order to understand the I/RP-induced EC mitochondrial morphology changes and whether these dictate the cell fate, we propose to: (a) Assess the differential effects of H/RO and I/RP on cultured EC mitochondrial dynamics, and delineate the intracellular signaling pathways that lead to increased mitochondrial fission. Transfection with a lentivirus that expresses green fluorescent protein in mitochondria will be used to analyze their dynamic behavior during static, shear, H/RO or I/RP. We will examine if abnormal mitochondrial dynamics are accompanied by fusion/fission protein changes, with a focus on fission regulation by Drp1 levels/activity, and will also delineate the roles of ROS, NO, and mtPTP in Drp1 activation and mitochondrial fission. (b) Examine if blocking the extensive fission due to I/RP will preserve the endothelial mitochondrial function and suppress apoptosis, and if the effect of fission on cell function is, at least in part, mediated by autophagy. ECs, in the presence of a pharmacological Drp1 inhibitor or following overexpression of either a dominant negative Drp1 form or the fusion protein mitofusin 2, will be exposed to I/RP, and mitochondrial function, autophagy and apoptosis will be measured. The latter will also be measured in the presence of autophagy inhibitors. This study is based on the novel hypothesis that changes in mitochondrial network dynamics may be responsible for the EC dysfunction upon RP. Our goal is, via better understanding of the EC dysfunction (the first critical step in cardiac I/RP injury), to develop new therapeutic strategies that will target mitochondrial fission. PUBLIC HEALTH RELEVANCE: Although early coronary reperfusion following acute myocardial infarction is the primary clinical intervention for improving patient outcome, reperfusion itself, primarily via generation of free radicals, may cause further tissue damage. The endothelium in coronary arteries is an early critical target of ischemia/reperfusion injury. This proposal aims to better understand the role of mitochondrial fragmentation/fission and its repercussions on postischemic endothelial cell survival, and to propose new therapeutic strategies that target the endothelial mitochondrial dynamics.