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。氨基酸不足（AAI）会降低生长，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恢复力之间关系的分子事件将推进当前的饮食和药物方法，以促进健康和治疗代谢障碍疾病。综合应激反应（integrated stress response， ISR）是维持蛋白质稳态的重要前哨信号网络。ISR的一个中心特征是激活转录因子4 （ATF4）优先翻译真核起始因子2磷酸化（eIF2-P），由AAI传感器，一般控制非抑制2 （GCN2）。GCN2通过与另一个营养应答靶标——哺乳动物雷帕霉素复合物1 （mTORC1）——合作来改变蛋白质合成。在AAI期间，Gcn2的缺失会释放mTORC1活性，造成代谢状态和需求之间的不匹配，并导致蛋白质毒性应激。本提案的目的1旨在定义GCN2在AAI响应中抑制mTORC1信号传导的机制。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，并促进肝脏脂肪变性的发展。目的2关注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对ATF4翻译的独立控制。然后，我们将研究两个转录因子，像ATF4一样，优先翻译响应eIF2-P。首先是CCAAT/增强子结合蛋白同源蛋白（CHOP），一种促凋亡转录因子和ATF4结合伙伴。第二种是ATF5，一种ATF4的类似物，在肝脏中非常丰富。我们将使用固定的小鼠模型来诱导这些转录因子单独或相互联合的肝脏特异性或全身缺失，并在AAI期间监测蛋白质平衡以及肝脏健康和代谢的测量。上述目标的成功完成将显著改变ISR对AAI的激活在生物医学上的理解和应用。这是很重要的，因为规范通路的局限性目前阻碍了针对蛋白质平衡网络和/或干预时机的治疗方法的发展，无论是促进恢复力还是治疗疾病。

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.