Hemophilia A, an X-linked bleeding disorder caused by deficiency of factor VIII (FVIII), is treated by protein replacement. Unfortunately, this regimen is costly due to the expense of producing recombinant FVIII as a consequence of its low-level secretion from mammalian host cells. FVIII expression activates the endoplasmic reticulum (ER) stress response, causes oxidative stress and induces apoptosis. Importantly, little is known about the factors that cause protein misfolding and aggregation in metazoans. Here we identified intrinsic and extrinsic factors that cause FVIII to form aggregates. We show that FVIII forms amyloid-like fibrils within the ER lumen upon increased FVIII synthesis or inhibition of glucose metabolism. Significantly, FVIII amyloids can be dissolved upon restoration of glucose metabolism to produce functional secreted FVIII. Two ER chaperone families and their co-chaperones, BiP and CANX/CRT, promote FVIII solubility in the ER, where the former is also required for disaggregation. A short aggregation motif in the FVIII A1 domain (termed Aggron) is necessary and sufficient to seed b-sheet polymerization and BiP binding to this Aggron prevents amyloidogenesis. Our findings provide novel insight into mechanisms that limit FVIII secretion and ER protein aggregation in general and have implication for ongoing hemophilia A gene therapy clinical trials.

中文翻译：

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因子 VIII 在内质网中表现出伴侣依赖性和葡萄糖调节的可逆淀粉样蛋白形成


A 型血友病是一种由因子 VIII (FVIII) 缺乏引起的 X 连锁出血性疾病，可通过蛋白质替代治疗。不幸的是，由于哺乳动物宿主细胞分泌的重组 FVIII 水平较低，因此该方案的成本很高。 FVIII 表达激活内质网 (ER) 应激反应，引起氧化应激并诱导细胞凋亡。重要的是，我们对导致后生动物中蛋白质错误折叠和聚集的因素知之甚少。在这里，我们确定了导致 FVIII 形成聚集体的内在和外在因素。我们发现，当 FVIII 合成增加或葡萄糖代谢受到抑制时，FVIII 会在 ER 腔内形成淀粉样蛋白样原纤维。值得注意的是，FVIII 淀粉样蛋白可以在葡萄糖代谢恢复后溶解，产生功能性分泌型 FVIII。两个 ER 伴侣家族及其共伴侣 BiP 和 CANX/CRT 可促进 FVIII 在 ER 中的溶解度，其中前者也是解聚所必需的。 FVIII A1 结构域中的短聚集基序（称为 Aggron）对于种子 b-片层聚合是必要且充分的，BiP 与该 Aggron 的结合可防止淀粉样蛋白生成。我们的研究结果为限制 FVIII 分泌和 ER 蛋白聚集的机制提供了新的见解，并对正在进行的血友病 A 基因治疗临床试验具有意义。