Ubiquitination as an acute regulator of synaptic transmission

描述（由申请人提供）：突触传递是神经系统的一个重要特征，并且在许多不同的时间尺度上受到严格调节。泛素-蛋白酶体系统（UPS）通过维持适当的蛋白稳态在突触传递中起重要作用。UPS通过塑造长期可塑性、改变活跃突触的数量和改变囊泡池的大小来调节发育过程中的突触形成。所有这些调节功能发生在数小时到数天的时间尺度上，并且与UPS在蛋白质降解中的核心作用一致：泛素标签蛋白的共价附着被蛋白酶体降解。我们最近发现UPS还能在几分钟或更短的时间内调节神经递质的释放。这使我们提出这样的假设：突触的泛素化通过改变靶蛋白的活性水平而不是改变它们的半衰期来快速调节释放。因此，蛋白质泛素化可以作为突触功能的急性动态调节剂。鉴于突触传递在神经系统功能中的核心作用，这代表了一种新的调控途径，具有明确的基础科学兴趣。然而，该途径也具有明确的临床意义，因为它可能为与神经退行性疾病相关的功能障碍的早期步骤提供见解。在许多神经退行性疾病中，突触功能障碍的体征先于临床症状。神经退行性疾病还以UPS为特征，该UPS因通路突变、错误折叠的蛋白质或环境毒素而受损。认识到UPS在形成突触传递中的快速调节作用可能提供UPS损伤和突触功能障碍之间的早期因果联系。在这项拨款申请中，我们将测试通过泛素化介导突触前释放快速调节的生理机制（目的1）。与突触泛素（Aim2）的鉴定一起，这些实验将使发现具有基础科学兴趣的途径和过程，并可能为神经系统疾病提供新的药物靶点。

DESCRIPTION (provided by applicant): Synaptic transmission is a critical feature of the nervous system and is as such tightly regulated on many different time-scales. The ubiquitin-proteasome system (UPS) plays an important role in synaptic transmission by maintaining appropriate protein homeostasis. The UPS regulates synapse formation during development, by shaping long-term plasticity, by altering the number of active synapses and by changing the size of vesicle pools. All of these regulatory functions occur on a time scale of hours to days and are consistent with the central role of the UPS in protein degradation: covalent attachment of ubiquitin tags proteins for degradation by the proteasome. We have recently discovered that the UPS also regulates neurotransmitter release on a time-scale of a few minutes or less. This led us to the hypothesis that ubiquitination at the synapse rapidly regulates release by changing the activity level of target proteins rather than changing their half-life. Thus, protein ubiquitination can serve as an acute dynamic regulator of synaptic function. This represents a novel regulatory pathway that is of clear basic science interest given the central role of synaptic transmission in nervous system function. However, the pathway is also of clear clinical interest as it might offer insight into the earliest steps of dysfunction associated with neurodegenerative diseases. In many neurodegenerative diseases signs of synaptic dysfunction precede clinical symptoms. Neurodegenerative diseases are also characterized by a UPS that is impaired either through mutations in the pathway, by misfolded proteins or via environmental toxins. The recognition of the rapid regulatory role of the UPS in shaping synaptic transmission might offer an early causal link between UPS impairment and synaptic dysfunction. In this grant application we will test the physiological mechanisms that mediate the rapid regulation of presynaptic release by ubiquitination (Aim 1). Together with the identification of the synaptic ubiquitome (Aim2) these experiments will enable discovery of pathways and processes that are of basic science interest and that might provide novel druggable targets for neurological diseases. PUBLIC HEALTH RELEVANCE: In this grant application we propose to test the hypothesis that protein ubiquitination at the synapse can serve as a rapid, posttranslational modification that regulates synaptic transmission, rather than simply representing a signal for protein degradation by the proteasome. Early stages of many neurodegenerative diseases, such as Parkinson's, Alzheimer's and Huntington's Disease, are characterized by changes in synaptic function and protein ubiquitination is compromised either by mutations in the pathway or by accumulation of misfolded proteins. Our experiments on the role of rapid protein ubiquitination in the regulation of synaptic transmission suggest a causal link between these observations and thus indicate novel druggable targets and pathways.