ELUCIDATION OF THE MAINTENANCE MECHANISM OF SYNAPTIC STRUCTURE AND FUNCTION BY THE PROTEIN QUALTY CONTROL SYSTEM AND ITS APPLICATION TO NEUROREGENERATION

我们之前发现泛素c端水解酶L1 （UCH-L1）在细轴索营养不良（gad）小鼠中不表达。gad小鼠的病理特征是轴突变性的死退型，因此该突变体似乎是研究泛素系统与突触之间关系的合适模型。在本研究中，我们旨在阐明UCH-L1在维持突触结构和功能中的生理和病理生理作用。我们首先发现UCH-L1意外地结合并稳定了神经元中的单泛素。在稳定过程中，不需要UCH-L1的水解酶活性。在小鼠中，单泛素水平降低。这些结果表明UCH-L1可能以多种方式发挥作用：在体内作为水解酶和泛素结合蛋白。其次，通过蛋白质组分析，我们观察到四种蛋白质在小鼠体内被高度氧化。我们还证明UCH-L1本身被氧化，并随着氧化的增加而降低其水解酶活性。第三，我们观察到UCH-L1在突触可塑性中起一定作用。由于UCH-L1在神经元中选择性表达，我们的研究结果表明UCH-L1可能在突触传递中发挥重要作用。

We previously identified that ubiquitin C-terminal hydrolase L1 (UCH-L1) was not expressed in the gracile axonal dystrophy (gad) mouse. The gad mouse is pathologically characterized by dying-back type of axonal degeneration, and thus the mutant appears to be a suitable model for investigating the relationship between the ubiquitin system and synapes. In this study, we aimed to elucidate the physiological and pathophysiological roles of UCH-L1 in the maintenance of synaptic structure and function. We first identified that UCH-L1 unexpectedly bound to and stabilized monoubiquitin in neurons. In the stablization, hydrolase activity of UCH-L1 was not required. In the gad mouse, monoubiquitin level was decreased. These results suggest that UCH-L1 may function in multiple ways : as a hydrolase and as a ubiquitin-binding protein in vivo. Second, by proteaome analysis, we observed that four proteins were highly oxidized in the gad mouse. We also demonstrated that UCH-L1 itself was oxidized and decreased its hydrolase activity as the oxidation increased. Third, we observed that UCH-L1 played some role in synaptic plasticity. Since UCH-L1 is selectively expressed in neurons, our results suggest that UCH-L1 may play an essential role in synaptic transmission.