Regulation of Extracellular Chaperone Capacity by the Unfolded Protein Response

描述（由申请人提供）：细胞外蛋白质聚集与人类神经退行性疾病如阿尔茨海默病、克雅氏病和甲状腺素运载蛋白淀粉样变性有着千丝万缕的联系。蛋白质聚集在这些疾病中的重要性已经导致了显著的实验努力，其集中于表征调节细胞外蛋白质稳态（或蛋白质稳态）的细胞途径。通过这些努力确定的定义细胞外蛋白质稳态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谱和活性。ER的主要功能是促进蛋白质的正确折叠以运输到分泌途径的下游环境，例如细胞外环境，同时防止不稳定的、易错误折叠的蛋白质的分泌。通过这种所谓的质量控制机制，ER通过减少可用于浓度依赖性聚集的易错误折叠蛋白质的细胞外群体来间接影响细胞外蛋白质稳态。或者，细胞外伴侣蛋白如丛生蛋白通过结合易错误折叠的蛋白质，防止其聚集，直接影响细胞外蛋白质稳定。虽然ER质量控制途径和细胞外伴侣的组合活性在正常条件下有效地调节细胞外蛋白质稳态，但由环境、遗传或老化相关损伤诱导的ER质量控制效率的不平衡可导致挑战细胞外伴侣能力的易聚集蛋白质的分泌增加。为了应对这一挑战，细胞激活未折叠蛋白反应（UPR）-一种应激反应信号通路，其在转录和转录上重塑ER质量控制通路。因此，UPR激活恢复ER功能并减弱易聚集蛋白的分泌。尽管UPR在调节ER和分泌途径的下游环境中的蛋白质稳态中的重要性，但UPR活化和细胞外伴侣能力之间没有联系。我们假设，UPR激活，在应激反应，增加分泌的细胞外伴侣，以防止异常，细胞外聚集的错误折叠倾向的蛋白质。在此，我们确定ERdj 3（DNAJB 11）作为一个以前未表征的，UPR调节的细胞外伴侣。我们建议评估ERdj 3在细胞外环境中减弱病理性蛋白质聚集的能力，表征负责应激诱导的ERdj 3分泌的生物学途径，并确定在正常生理过程中和应激反应中与ERdj 3相互作用的分泌蛋白的子集。本文的实验成功将提供UPR在调节细胞外蛋白质稳定能力中的直接功能作用的原理证明，催化研究以鉴定其他UPR调节的细胞外蛋白质稳定因子并探索诱导细胞外伴侣蛋白能力的UPR依赖性增加以治疗聚集相关退行性疾病的潜力。

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.