Homeostatic Responses to Amino Acid Insufficiency

氨基酸营养是代谢障碍和慢性疾病发展的关键决定因素。氨基酸缺乏(AAI)会减少生长，但也会增加细胞对压力的抵抗力，改善心脏代谢健康，减缓代谢衰老。更清楚地了解改变氨基酸营养和蛋白质组弹性之间关系的分子事件，将推动目前的饮食和药物方法，以促进健康，跨度和治疗代谢障碍的情况。整合应激反应(ISR)是蛋白质平衡维持过程中一个重要的前哨信号网络。ISR的一个中心特征是激活转录因子4(ATF4)在真核细胞起始因子2磷酸化(eIF2-P)时被AAI传感器通用控制不可降压2(GCN2)优先翻译。GCN2与另一个营养反应靶点雷帕霉素复合体1(MTORC1)的哺乳动物靶点协同作用改变蛋白质的合成。GCN2的缺失会在AAI过程中释放mTORC1活性，在代谢状态和需求之间造成不匹配，导致蛋白毒性应激。本提案的目的1旨在定义GCN2抑制mTORC1信号以响应AAI的机制。我们将描述这些信号网络如何影响肝脏蛋白质平衡和代谢的昼夜节律，并有助于肝脏脂肪变性的发展。目标2集中于组合转录调控如何影响AAI的生理结果。为了解决这个问题，我们将首先确定eIF2-P独立控制ATF4翻译。然后我们将研究两个转录因子，如ATF4，它们优先被翻译为对eIF2-P的反应。第一个是CCAAT/增强子结合蛋白同源蛋白(CHOP)，它是一种促凋亡转录因子和ATF4结合伙伴。其次是ATF5，这是一种ATF4类似物，在肝脏中含量唯一丰富。我们将使用小鼠模型来单独或联合诱导肝脏特异性或全身缺失这些转录因子，并在AAI期间监测蛋白平衡以及肝脏健康和新陈代谢的测量。上述目标的成功实现将显著改变人们对ISR激活AAI的理解和生物医学上的应用。这一点意义重大，因为目前规范途径的局限性阻碍了适当针对蛋白平衡网络的治疗方法的发展和/或干预的时机，无论是为了提高复原力还是治疗疾病。

PAmino acid nutrition is a key determinant in the development of dysmetabolism and chronic disease. Amino acid insufficiency (AAI) reduces growth, but also acts to increase cellular resistance to stress, improve cardiometabolic fitness and slow metabolic aging. A clearer understanding of the molecular events altering the relationship between amino acid nutrition and resilience of the proteome will advance current dietary and pharmaceutical approaches to promote health span and treat dysmetabolic conditions. The integrated stress response (ISR) is a vital sentinel signaling network in proteostasis maintenance. A central feature of the ISR is the preferential translation of Activating Transcription Factor 4 (ATF4) upon eukaryotic initiation factor 2 phosphorylation (eIF2-P) by the AAI sensor, General Control Nonderepressible 2 (GCN2). GCN2 alters protein synthesis in cooperation with another nutrient-responsive target, the mammalian target of rapamycin complex 1 (mTORC1). Loss of Gcn2 unleashes mTORC1 activity during AAI, creating a mismatch between metabolic state and need and resulting in proteotoxic stress. Aim 1 of this proposal seeks to define the mechanism by which GCN2 suppresses mTORC1 signaling in response to AAI. We will delineate how these signaling networks influence diurnal rhythms in liver proteostasis and metabolism and contribute to the development of liver steatosis. Aim 2 is focused on how combinatorial transcriptional regulation influences physiological outcomes to AAI. To address this, we will first ascertain eIF2-P independent control of ATF4 translation. We will then study two transcription factors that, like ATF4, are preferentially translated in response to eIF2-P. First is CCAAT/enhancer-binding protein Homologous Protein (CHOP) a pro-apoptotic transcription factor and ATF4 binding partner. Second is ATF5, an ATF4 paralog that is uniquely abundant in liver. We will use floxed mouse models to induce liver-specific or whole body deletion of these transcription factors alone or in combination with each other and monitor proteostasis alongside measurements of liver health and metabolism during AAI. Successful completion of the above aims will significantly change how activation of the ISR to AAI is understood and applied biomedically. This is significant because limitations in the canonical pathways currently prevent development of therapeutics properly targeting the proteostasis network and/or the timing of intervention, either to promote resilience or treat disease.