Neuron-specific deamidation of translational repressor 4E-BP2 in postnatal brain

大脑的发育、学习、记忆和感知依赖于一个错综复杂的蛋白质网络，这个网络协调着人类大脑的高级认知功能。调节这些分子功能的一个重要生物过程是蛋白质合成，也称为翻译。翻译控制着调节神经元之间连接强度的机制，这一过程被称为突触可塑性。抑制翻译会阻碍长时记忆的形成，而刺激翻译会促进记忆的形成。翻译是一个严格监管的过程。一个关键的翻译控制通路，通过mTORC1(雷帕霉素复合体1的机械性靶点)调节，与脑发育、突触可塑性、学习和记忆有关。MTORC1通过其主要下游靶点4E结合蛋白2(4E-BP2)调节大脑中的翻译。最近的研究表明，4E-BP2经历了自发的脑特异性天冬酰胺脱酰胺。然而，4E-BP2在大脑中脱酰胺的机制和这一过程的功能意义仍不清楚。我们的初步数据表明，去胺化形式的4E-BP2比野生型更不稳定，它的稳定性随着mTORC1的抑制而增加。鉴于mTORC1活性在出生后降低，这一机制可能解释了去酰胺化的4E-BP2在出生后大脑发育早期积累的原因。此外，我们还发现，去胺化的4E-BP2在神经元中过表达时，翻译版图会发生变化，这表明4E-BP2的翻译后修饰可能调节mTORC1/4E-BP2途径的输出，影响脑中mRNAs的翻译。在拟议的项目中，我们将进一步研究4E-BP2去酰胺化的机制，并研究其对脑功能的影响。具体地说，我们将产生表达去胺化但不是野生型4E-BP2的转基因小鼠，并研究神经元活动和行为是如何受到影响的。我们将使用生化、电生理、成像和行为学的方法来研究4E-BP2去酰胺化对大脑发育和成年期的影响。这项拟议的工作将为4E-BP2脱酰胺的作用和机制提供基本的见解，共同促进我们对翻译控制如何塑造大脑功能的理解。

Brain development, learning, memory, and perception rely on an intricate network of proteins that orchestrates higher cognitive functions of the human brain. An important biological process regulating the function of these molecules is protein synthesis, also termed translation. Translation controls the mechanisms regulating the strength of connection between neurons, a process called synaptic plasticity. Inhibition of translation blocks the formation of long-term memory and stimulation of translation promotes memory formation. Translation is a tightly regulated process. A key translational control pathway, regulated via the mTORC1 (mechanistic Target of Rapamycin Complex 1 (mTORC1)), is implicated in brain development, synaptic plasticity, learning, and memory. mTORC1 regulates translation in the brain via its major downstream target, 4E-binding protein 2 (4E-BP2). Recent studies have revealed that 4E-BP2 undergoes spontaneous brain-specific asparagine deamidation. However, the mechanisms underlying 4E-BP2 deamidation in the brain and the functional significance of this process remain unknown. Our preliminary data indicate that deamidated form of 4E-BP2 is less stable than wild-type form and its stability is increased in response to inhibition of mTORC1. Given that mTORC1 activity is reduced postnatally, this mechanism might explain the accumulation of deamidated 4E-BP2 during early postnatal brain development. Additionally, we found that translational landscape is altered when deamidated 4E-BP2 is overexpressed in neurons, suggesting that posttranslational modification of 4E-BP2 might regulate the output of mTORC1/4E-BP2 pathway and affect translation of mRNAs in the brain. In the proposed project, we will further investigate the mechanisms underlying 4E-BP2 deamidation and study its effect on brain functions. Specifically, we will generate genetically-modified mice expressing deamidated but not wild-type form of 4E-BP2, and study how neuronal activity and behaviours are affected. We will employ biochemical, electrophysiological, imaging and behavioral approaches to study the impact of 4E-BP2 deamidation on the brain during development and in adulthood. The proposed work will provide fundamental insights into the roles and mechanisms of 4E-BP2 deamidation, altogether advancing our understanding of how translational control shapes brain functions.