Regulation of Extracellular Chaperone Capacity by the Unfolded Protein Response

描述（由申请人提供）：细胞外蛋白聚集与人类神经退行性疾病，如阿尔茨海默病、克雅氏病和转甲状腺素淀粉样病变有着密不可分的联系。蛋白质聚集在这些疾病中的重要性导致了大量的实验努力，重点是表征调节细胞外蛋白质稳态（或蛋白质稳态）的细胞途径。通过这些努力确定细胞外蛋白质静止的两个主要决定因素是内质网（ER）质量控制途径的效率和细胞外伴侣的光谱和活性。内质网的一个主要功能是促进蛋白质的适当折叠，以便运输到分泌途径的下游环境，如细胞外环境，同时防止分泌不稳定的、容易错误折叠的蛋白质。通过这种所谓的质量控制机制，内质网通过减少可用于浓度依赖性聚集的易发生错误折叠的细胞外蛋白群，间接影响细胞外的蛋白质静止。另外，细胞外伴侣如clusterin通过结合易发生错误折叠的蛋白质直接影响细胞外蛋白质稳态，阻止其聚集。正常情况下，内质网质量控制通路和细胞外伴侣蛋白的联合活性有效地调节细胞外蛋白质稳态，但环境、遗传或衰老相关损伤引起的内质网质量控制效率失衡可导致易聚集蛋白的分泌增加，从而挑战细胞外伴侣蛋白的能力。为了应对这一挑战，细胞激活未折叠蛋白反应（UPR），这是一种应激反应信号通路，通过翻译和转录重塑内质网质量控制途径。因此，UPR激活恢复内质网功能，并减弱易聚集蛋白的分泌。尽管UPR在调节内质网和分泌途径下游环境中的蛋白质稳态方面具有重要作用，但目前尚未建立UPR激活与细胞外陪伴能力之间的联系。我们假设UPR的激活，在应激反应中，增加了细胞外伴侣的分泌，以防止异常的，细胞外聚集的错误折叠倾向的蛋白质。在此，我们确定ERdj3 （DNAJB11）是一种以前未被表征的、受uprr调控的细胞外伴侣。我们建议评估ERdj3在细胞外环境中减弱病理性蛋白聚集的能力，表征应激诱导ERdj3分泌的生物学途径，并确定在正常生理和应激反应中与ERdj3相互作用的分泌蛋白亚群。本文的实验成功将为UPR在调节细胞外蛋白质平衡能力方面的直接功能作用提供原理证明，催化研究确定其他UPR调节的细胞外蛋白质平衡因子，并探索诱导UPR依赖的细胞外伴侣能力增加的潜力，以治疗聚集相关的退行性疾病。

DESCRIPTION (provided by applicant): Extracellular protein aggregation is inextricably linked to human neurodegenerative diseases such as Alzheimer's disease, Creutzfeldt-Jakob disease and the transthyretin amyloidoses. The importance of protein aggregation in these disorders has led to significant experimental effort focused on characterizing the cellular pathways that regulate extracellular protein homeostasis (or proteostasis). Two primary determinants in defining extracellular proteostasis identified through these efforts are the efficiency of endoplasmic reticulum (ER) quality control pathways and the spectrum and activity of extracellular chaperones. A primary function of the ER is to facilitate the proper folding of proteins for trafficking to downstream environments of the secretory pathway such as the extracellular environment, while preventing the secretion of destabilized, misfolding-prone proteins. Through this so-called quality control mechanism, the ER indirectly influences extracellular proteostasis by reducing the extracellular population of misfolding prone proteins available for concentration- dependent aggregation. Alternatively, extracellular chaperones such as clusterin directly influence extracellular proteostasis by binding misfolding prone proteins, preventing their aggregation. While the combined activity of ER quality control pathways and extracellular chaperones efficiently regulate extracellular proteostasis under normal conditions, imbalances in ER quality control efficiency induced by environmental, genetic or aging- related insults can lead to increased secretion of aggregation-prone proteins that challenge extracellular chaperoning capacity. To confront this challenge, cells activate the unfolded protein response (UPR) - a stress-responsive signaling pathway that translationally and transcriptionally remodels ER quality control pathways. Thus, UPR activation restores ER function and attenuates the secretion of aggregation-prone proteins. Despite the importance of the UPR in regulating proteostasis in the ER and downstream environments of the secretory pathway, no link between UPR activation and extracellular chaperoning capacity has been established. We hypothesize that UPR activation, in response to stress, increases secretion of extracellular chaperones to prevent the aberrant, extracellular aggregation of misfolding prone proteins. Herein, we identify ERdj3 (DNAJB11) as a previously uncharacterized, UPR-regulated extracellular chaperone. We propose to evaluate the capacity for ERdj3 to attenuate pathologic protein aggregation in the extracellular environment, characterize the biological pathways responsible for stress-induced ERdj3 secretion, and identify the subset of secreted proteins that interacts with ERdj3 during normal physiology and in response to stress. Experimental success herein will provide proof-of-principle of a direct, functional role for the UPR in regulating extracellular proteostasis capacit, catalyzing research to both identify other UPR-regulated extracellular proteostasis factors and explore the potential for inducing the UPR-dependent increase in extracellular chaperone capacity to treat aggregation-associated degenerative disorders.