In the classic form of α1-antitrypsin deficiency (ATD), the misfolded α1-antitrypsin Z (ATZ) variant accumulates in the endoplasmic reticulum (ER) of liver cells. A gain-of-function proteotoxic mechanism is responsible for chronic liver disease in a subgroup of homozygotes. Proteostatic response pathways, including conventional endoplasmic reticulum–associated degradation and autophagy, have been proposed as the mechanisms that allow cellular adaptation and presumably protection from the liver disease phenotype. Recent studies have concluded that a distinct lysosomal pathway called endoplasmic reticulum–to-lysosome completely supplants the role of the conventional macroautophagy pathway in degradation of ATZ. Here, we used several state-of-the-art approaches to characterize the proteostatic responses more fully in cellular systems that model ATD. We used clustered regularly interspaced short palindromic repeats (CRISPR)-mediated genome editing coupled to a cell selection step by fluorescence-activated cell sorter to perform screening for proteostasis genes that regulate ATZ accumulation and combined that with selective genome editing in 2 other model systems. Endoplasmic reticulum–associated degradation genes are key early regulators and multiple autophagy genes, from classic as well as from ER-to-lysosome and other newly described ER-phagy pathways, participate in degradation of ATZ in a manner that is temporally regulated and evolves as ATZ accumulation persists. Time-dependent changes in gene expression are accompanied by specific ultrastructural changes including dilation of the ER, formation of globular inclusions, budding of autophagic vesicles, and alterations in the overall shape and component parts of mitochondria. Macroautophagy is a critical component of the proteostasis response to cellular ATZ accumulation and it becomes more important over time as ATZ synthesis continues unabated. Multiple subtypes of macroautophagy and nonautophagic lysosomal degradative pathways are needed to respond to the high concentrations of misfolded protein that characterizes ATD and these pathways are attractive candidates for genetic variants that predispose to the hepatic phenotype.

中文翻译：

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ERAD、巨自噬和溶酶体降解途径的多基因核心参与 α1-抗胰蛋白酶缺乏症的蛋白质稳态反应

在 α1-抗胰蛋白酶缺乏症 (ATD) 的经典形式中，错误折叠的 α1-抗胰蛋白酶 Z (ATZ) 变体在肝细胞的内质网 (ER) 中积聚。功能获得性蛋白毒性机制是导致纯合子亚群慢性肝病的原因。蛋白质抑制反应途径，包括传统的内质网相关降解和自噬，已被认为是允许细胞适应并可能防止肝病表型的机制。最近的研究得出结论，一种称为内质网到溶酶体的独特溶酶体途径完全取代了传统的巨自噬途径在 ATZ 降解中的作用。在这里，我们使用了几种最先进的方法来更全面地描述模拟 ATD 的细胞系统中的蛋白质抑制反应。我们使用成簇规则间隔短回文重复序列 (CRISPR) 介导的基因组编辑与荧光激活细胞分选仪的细胞选择步骤相结合，以筛选调节 ATZ 积累的蛋白质稳态基因，并将其与其他 2 个模型系统中的选择性基因组编辑相结合。内质网相关降解基因是关键的早期调节因子，多种自噬基因，从经典的以及从 ER 到溶酶体和其他新描述的 ER 吞噬途径，以一种暂时调节的方式参与 ATZ 的降解，并演化为ATZ 积累持续存在。基因表达的时间依赖性变化伴随着特定的超微结构变化，包括内质网扩张、球状包涵体形成、自噬囊泡出芽以及线粒体整体形状和组成部分的改变。巨自噬是细胞 ATZ 积累的蛋白质稳态反应的关键组成部分，随着 ATZ 合成持续不减弱，它变得越来越重要。需要多种巨自噬和非自噬溶酶体降解途径亚型来响应高浓度的错误折叠蛋白（ATD 的特征），这些途径是易患肝表型的遗传变异的有吸引力的候选者。