Cell non-autonomous regulation of the unfolded protein response in aging

 描述(申请人提供)：生活压力很大。细胞反复暴露在破坏蛋白质稳态(蛋白质稳态)的各种应激源中，导致蛋白质错误折叠和聚集。为了维持蛋白稳定，细胞进化出特定的应激反应，目的是抑制翻译，诱导伴侣蛋白的表达，并清除受损的蛋白质。内质网负责折叠近三分之一的人类蛋白质组，包括几乎所有分泌的蛋白质。为了保护这个重要细胞器的功能，内质网可以启动未折叠的蛋白质反应 (UPRER)对错误折叠蛋白质的存在作出反应。我们的实验室检测了UPRER在线虫体内衰老过程中的作用，发现激活IRE-1/XBP-1途径响应ER胁迫的能力随着年龄的增长而被取消。UPRER的这种降低降低了对内质网应激诱导剂的保护。有趣的是，这种UPRER介导的对抗ER应激保护作用的年龄依赖性下降可以通过神经系统中结构性活性XBP-1的表达来防止。最引人注目的是，XBP-1在线虫中的神经元表达导致远端细胞类型的UPRER的细胞非自主激活，并延长寿命。最近有报道称，XBP-1s在下丘脑神经元中的过表达可以诱导XBP-1在肝脏中的剪接，从而保护小鼠免受饮食诱导的肥胖。因此，细胞非自主应激信号在线虫和啮齿动物之间是保守的，并调节关键的代谢功能。我们假设神经细胞的XBP-1s诱导了一种跨细胞的信号机制来协调整个生物体的应激反应，改善了代谢状态，并延长了寿命。然而，这种信号机制所需的遗传成分尚不清楚。在目标1中提出的新的CRISPR-Cas9遗传筛查中，我们将识别XBP1s跨细胞应激反应的基本介质，这将为衰老和代谢性疾病提供额外的、可能更特异的治疗靶点。此外，我们假设在哺乳动物中神经元XBP1s的过度表达将挽救UPRER的年龄损失并延长寿命。在目标2中，我们将使用在下丘脑神经元中过表达XBP1的转基因小鼠来验证我们的假设。由于我们的医疗体系面临的最大挑战之一是与年龄相关的代谢和神经疾病带来的日益增长的经济负担，因此阐明调控XBP1s诱导长寿的机制并确定XBP1s在哺乳动物中的作用具有至关重要的意义。回答这项提案中描述的问题不仅对正常衰老，而且对老年性疾病都有巨大的治疗意义。

 DESCRIPTION (provided by applicant): Life is stressful. Cells are repeatedly exposed to various stressors that disrupt protein homeostasis (proteostasis), resulting in protein misfolding and aggregation. To maintain proteostasis, cells have evolved compartment-specific stress responses aimed at repressing translation, inducing chaperone expression, and eliminating damaged proteins. The endoplasmic reticulum (ER) is responsible for the folding of nearly one third of the total human proteome, including almost all of the proteins that are secreted. To protect the function of this essential organelle, the ER can initiate the unfolded protein response (UPRER) in response to the presence of misfolded proteins. Our laboratory examined the role of the UPRER in aging within the nematode C. elegans and found that the ability to activate the IRE-1/XBP-1 pathway in response to ER stress is abrogated with age. This reduction in UPRER diminishes protection against ER stress-inducing agents. Interestingly, this age-dependent decline in UPRER-mediated protection against ER stress can be prevented by the expression of constitutively active XBP- 1s in the nervous system. Most striking, neuronal expression of XBP-1s in C. elegans leads to cell non- autonomous activation of the UPRER in distal cell types and increases lifespan. It was recently reported that overexpression of XBP-1s in neurons in the hypothalamus induces XBP-1 splicing in the liver and protected mice from diet-induced obesity. Therefore, cell non-autonomous stress signaling is conserved between C. elegans and rodents and regulates key metabolic functions. We hypothesize that neuronal XBP-1s induces a trans-cellular signaling mechanism to coordinate an organism-wide stress response, an improved metabolic state, and a longer lifespan. However, the genetic components required for this signaling mechanism are unknown. In the novel CRISPR-Cas9 genetic screen proposed in aim 1, we will identify essential mediators of the XBP1s transcellular stress response that will provide additional, potentially more specific, therapeutic targets for aging and metabolic disease. Furthermore, we hypothesize that neuronal XBP1s overexpression in mammals will rescue the age-onset loss of UPRER and increase longevity. In Aim 2 we will test our hypothesis using transgenic mice that overexpress XBP1s in hypothalamic neurons. Since one of the greatest challenges facing our healthcare system is the growing economic burden of age-related metabolic and neurologic diseases, elucidating the mechanisms that regulate XBP1s-induced longevity and determining the role of XBP1s in mammals are of paramount significance. Answering the questions described in this proposal will have enormous therapeutic implications not only for normal aging, but also age-onset diseases.