Elimination of Mitochondrial Anchoring is Neuroprotective in Demyelination

描述（由申请人提供）：线粒体是一种动态细胞器，通过代谢匹配维持髓鞘轴突的健康，其中线粒体移动并停留在高能量需求区域。在诸如多发性硬化症（MS）之类的脱髓鞘疾病中，由于髓磷脂的丢失，大面积的被剥落的轴突暴露在外，因此能量需求会大幅增加。因此，更多的线粒体移动并固定在病变部位，导致轴突线粒体含量大量增加。普遍的假设是，轴突线粒体含量的增加是维持适当代谢以保护轴突的适应性变化。然而，这种线粒体的增加也可能是不适应的，并通过过量的自由基产生来破坏轴突。天平到底向哪个方向倾斜从未被测试过。随着线粒体在多发性硬化症发病机制中扮演关键角色，确定轴突线粒体含量的增加是好是坏变得至关重要。最近，我们开始解决这个问题，通过遗传减少增加轴突线粒体含量在一个动物模型的髓鞘发育异常（Shiverer）。我们将Shiverer杂交到一个缺乏线粒体固定蛋白（syntaphilin）的背景中，该蛋白通常有助于增加轴突线粒体含量。令人惊讶的是，突触蛋白的缺失极大地延长了Shiverer突变体的预期寿命。基于这些存活数据，本R21探讨了线粒体锚定是否有助于脱髓鞘中的轴突杀伤，以及通过消除固定来增加线粒体流动性是否能对脱髓鞘轴突提供神经保护。在Aim #1中，我们将使用免疫组织化学和形态学分析来观察缺乏突触蛋白的Shiverer小鼠的轴突是否受到保护。在Shiverer中（含有合成酶）有

DESCRIPTION (provided by applicant): Mitochondria are dynamic organelles that maintain the health of myelinated axons by metabolic matching, in which mitochondria move to and pause at regions of high energy demands. In demyelinating diseases such as multiple sclerosis (MS), there is a huge increase in energy demand as large areas of denuded axons are exposed by the loss of myelin. In response, more mitochondria move to and become immobilized at lesion sites, contributing to a large increase in axonal mitochondrial content. The prevailing hypothesis is that this increase in axonal mitochondria content is an adaptive change to maintain proper metabolism to protect axons. However, this mitochondrial increase could also be maladaptive and tip the scale to damage axons by excess free radical production. Which way the scale actually tips has never been tested. With mitochondria emerging as a key player in the pathogenesis of MS, it becomes critical to determine whether this well-known increase in axonal mitochondrial content is friend or foe. Recently we started to address this issue by genetically reducing the increase in axonal mitochondrial content in an animal model of dysmyelination (Shiverer). We interbred the Shiverer into a background lacking a mitochondrial immobilization protein (syntaphilin) that normally contributes to the increase in axonal mitochondrial content. Surprisingly, deletion of syntaphilin dramatically extends the life expectancy of the Shiverer mutant. Based on this survival data, this R21 explores whether mitochondrial anchoring contributes to axon killing in demyelination, and whether increasing mitochondrial mobility by elimination of immobilization confers neuroprotection on demyelinated axons. In Aim #1, we will use immunohistochemistry and morphologic analysis to see if axons are protected in Shiverer mice lacking syntaphilin. In Shiverer (with syntaphilin present) there is an age-dependent axonal degeneration in various regions in the CNS. We will examine if elimination of mitochondrial anchoring delays or reduces this age-dependent axonal degeneration. We will also transfect syntaphilin in the DRG to directly test if excessive mitochondrial anchoring kills axons in the spinal cord. In Aim #2, we will examine if elimination of mitochondrial anchoring similarly protects mice in EAE, an inflammatory demyelination model for MS. We will induce EAE in mice with or without syntaphilin to see if the clinical scores are improved in the syntaphilin-null background. Conclusion: This R21 proposal explores a potentially ground-breaking paradigm in mitochondrial research in MS. In contrast to existing research focusing on mitochondria as a down-stream target of upstream degenerating changes, we might have pinpointed an upstream event involving mitochondrial dynamics (excessive anchoring) that leads to downstream degeneration. It further suggests an exciting therapeutic possibility that altering the ratio of mobile to immobile mitochondria could profoundly alter disease progression. The proposed experiments will determine whether there is firm footing for a future R01 application.