IRE1

引言肝损伤是大多数肝病的核心病理过程，但导致肝损伤发生和发展的遗传因素仍不清楚。2024年3月8日，西北农林科技大学吴江维、空军军医大学陶开山及西安交通大学张晓刚共同通讯在Nature Communications发表题为“Deficiency of ASGR1 promotes liver injury by increasing GP73-mediated hepatic endoplasmic reticulum stress”的研究论文，本研究发现去唾液酸糖蛋白受体1 (ASGR1)是一种在肝脏中特异性表达的凝集素，在肝纤维化或肝硬化患者和肝损伤的雄性小鼠中表达下调。在雄性小鼠中，ASGR1缺乏加重了对乙酰氨基酚诱导的急性和CCL4诱导的慢性肝损伤，而其过表达减轻了肝损伤。机制上，ASGR1与内质网应激介质GP73结合并促进其溶酶体降解。ASGR1敲除增加循环GP73水平并促进GP73与BIP的相互作用激活内质网应激，导致肝损伤。在接受致死剂量对乙酰氨基酚的小鼠中，中和GP73不仅减轻了ASGR1缺陷引起的肝损伤，而且提高了生存率。综上所述，这些发现确定了ASGR1是肝损伤易感性的潜在遗传决定因素，并提出将其作为肝损伤治疗的一个治疗靶点。肝损伤以肝细胞损伤、肝脏炎症和纤维化为特征，被认为是全球肝病的最常见原因。肝损伤最终可能发展为严重的疾病，如肝硬化和肝细胞癌（HCC）。尽管人们普遍认为遗传因素在所有类型肝损伤的发病机制中起着至关重要的作用，肝损伤的确切遗传诱发因素仍未得到充分了解。去唾液酸糖蛋白受体1 (ASGR1)是ASGPR的主要亚单位，在哺乳动物中高度保守。它是一种在肝细胞中特异性表达的跨膜蛋白，在维持循环糖蛋白稳态中起着关键作用。通过与末端半乳糖/N-乙酰半乳糖胺结合，ASGR1 介导循环去唾液酸化糖蛋白的内吞作用和溶酶体降解，从而参与多种生物学功能。对冰岛人进行的大规模测序分析显示，ASGR1单倍剂量不足与冠心病(CAD)风险降低相关，这启动了对ASGR1在心血管疾病(CVD)发生中的探索。在之前的工作中，建立了一个ASGR1缺陷的猪模型，以研究ASGR1与CVD之间的潜在因果关系。该模型再现了人类CVD危险因素减少的情况，为了解ASGR1和CVD发病率之间的因果关系提供了重要见解。在本研究过程中，偶然观察到ASGR1缺陷猪在正常饲养条件下的肝损伤，提示肝脏ASGR1表达与肝损伤之间的潜在相关性。据报道，ASGR1缺乏症也会减轻LPS诱导的败血症小鼠的肝损伤。这些结果表明，除了其在心血管疾病中的既定作用外，ASGR1 还与肝损伤有关，需要进一步研究。越来越多的证据表明内质网（ER）应激在肝损伤的发生和发展中起着关键作用。持续的内质网应激会破坏内质网的结构和/或功能，导致细胞死亡和肝损伤。在非应激条件下，内质网应激标志物免疫球蛋白重链结合蛋白（BIP）与IRE-1、PERK和ATF-6三个传感器形成复合物，维持信号转导因子的非激活状态。当受到压力时，BIP 会与这些传感器解离，从而触发未折叠蛋白反应（UPR）。之前的研究表明，ASGR1缺陷猪的肝脏内质网应激升高，暗示 ASGR1缺乏诱导的肝损伤中的内质网应激。考虑ASGR1在循环糖蛋白的内吞作用和降解中的作用，以及特定糖蛋白对内质网应激的贡献，ASGR1缺乏可能会破坏某些循环糖蛋白的平衡，导致内质网应激和肝损伤。模式图（Credit: Nature Communications）为了探索ASGR1在肝损伤中的作用，该研究生成了一个ASGR1缺陷小鼠模型，并评估了这些小鼠在基础条件下的表型，APAP诱导的急性肝损伤和CCl4诱导的慢性肝损伤。结果表明，ASGR1缺乏在基础条件下诱导小鼠自发性肝损伤，并加重APAP诱导的急性和CCl4诱导的慢性肝损伤。相反，AAV8介导的肝脏Asgr1过表达可防止急性和慢性肝损伤。在机制上，研究发现ASGR1与内质网应激介质GP73相互作用并促进其溶酶体降解。因此，ASGR1 缺乏会导致 GP73 的循环水平升高。GP73的中和不仅减轻ASGR1缺陷小鼠的急性和慢性肝损伤，而且还提高了接受致死剂量APAP的小鼠的存活率。此外，研究发现，在肝硬化患者中，ASGR1表达降低的患者表现出血清 GP73 水平升高和肝内质网应激升高。研究结果表明，ASGR1缺乏会加剧肝损伤，并且 ASGR1-GP73 轴成为肝损伤的潜在治疗靶点。研究结果揭示了 ASGR1 是肝损伤的潜在遗传易感性的候选者，特别关注与 ASGR1 抑制作为预防和治疗 CAD 的治疗策略相关的潜在风险。原文链接https://doi-org.libproxy1.nus.edu.sg/10.1038/s41467-024-46135-9责编|探索君排版|探索君文章来源|“iNature”End往期精选围观一文读透细胞死亡(Cell Death) | 24年Cell重磅综述（长文收藏版）热文Nature | 破除传统：为何我们需要重新思考肿瘤的命名方式热文Nature | 2024年值得关注的七项技术热文Nature | 自身免疫性疾病能被治愈吗？科学家们终于看到了希望热文CRISPR技术进化史 | 24年Cell综述

An advanced human heart organoid system can be used to model embryonic heart development under pregestational diabetes-like conditions, researchers report. The organoids recapitulate hallmarks of pregestational diabetes-induced congenital heart disease found in mice and humans. The findings also showed that endoplasmic reticulum (ER) stress and lipid imbalance are critical factors contributing to these disorders, which could be ameliorated with exposure to omega-3s. An advanced human heart organoid system can be used to model embryonic heart development under pregestational diabetes-like conditions, researchers report February 8 in the journal Stem Cell Reports. The organoids recapitulate hallmarks of pregestational diabetes-induced congenital heart disease found in mice and humans. The findings also showed that endoplasmic reticulum (ER) stress and lipid imbalance are critical factors contributing to these disorders, which could be ameliorated with exposure to omega-3s. "The new stem cell-based organoid technology employed will enable physiologically relevant studies in humans, allowing us to bypass animal models and obtain more information about relevant disease mechanisms, accelerating drug discovery and medical translation," says senior study author Aitor Aguirre of Michigan State University. Congenital heart disease is the most common type of congenital defect in humans. Pregestational diabetes -- diabetes affecting the mother before and during the first trimester of pregnancy -- is an important factor contributing to congenital heart disease and is present in a significant, growing population of diabetic female patients of reproductive age. Newborns from mothers with pregestational diabetes can have up to a 12-fold increased risk of congenital heart disease. Unfortunately, pregestational diabetes is hard to manage clinically due to the sensitivity of the developing embryo to glucose oscillations, and it represents a critical health problem for the mother and the fetus. The limited access to human tissues for research of early-stage disease has resulted in an overreliance on animal models. But it remains unclear to what extent rodent models recapitulate abnormalities present in humans, given critical species differences in heart size, cardiac physiology, electrophysiology, and bioenergetics. In addition, rodent models and many in vitro cell models rely on aggressive diabetic conditions, leading to exaggerated features that may not be clinically relevant. "Advances in biotechnology and bioengineering are enabling the creation of human mini-organs in vitro," Aguirre says. "These mini-organs can currently be used to understand human disease much better without the drawbacks of animal models." In the new study, Aguirre and his team used an advanced heart organoid model derived from human pluripotent stem cells. This model recapitulates human heart development during the first trimester, including critical steps such as chamber formation, vascularization, cardiac tissue organization, and relevant cardiac cell types. To specifically model the effects of pregestational diabetes, the researchers modified culture conditions to accurately reflect reported physiological levels of glucose and insulin in patients. The resulting pregestational diabetes heart organoids (PGDHOs) developed features observed in previous mouse and human studies. For example, the diabetic human heart organoids were larger, suggesting signs of cardiac hypertrophy -- a first hallmark of maternal pregestational diabetes. This observation was confirmed by studying cardiomyocyte size. The PGDHOs also displayed arrythmias and a reduction in beat frequency, which has been observed in neonatal rats from diabetic mothers. In addition, single-cell transcriptomic analysis of PGDHOs revealed a reduction in cardiomyocyte numbers, a significant expansion of tissue on the outer surface of the heart, and the absence of a well-developed vasculature at early developmental stages. The PGDHOs also exhibited increased accumulation of reactive oxygen species (ROS), revealing increased oxidative stress and mitochondrial swelling -- also hallmarks of diabetic embryonic heart conditions. A significant portion of ROS was localized to the ER and could be impairing its function, leading to a condition known as ER stress. Moreover, the PGDHOs revealed a clear imbalance in very long chain fatty acids, particularly affecting omega-3 polyunsaturated fatty acids, which are mostly synthesized in the ER. Taken together, these results point to a major ER-induced lipid imbalance in PGDHOs. This imbalance is linked to the degradation of fatty acid desaturase 2 (FADS2) -- a key lipid biosynthesis enzyme presents in the ER -- by the IRE1-dependent mRNA decay (RIDD) pathway, which has been implicated in several other cardiac conditions. In an attempt to remedy the effects of ER stress, the researchers tested several potentially therapeutic compounds on PGDHOs. A mixture of omega-3 fatty acids ameliorated diabetic features, while targeting inositol-requiring enzyme 1 (IRE1) reduced cardiomyocyte hypertrophy. All the compounds also restored FADS2 levels. "The organoids still lack some features that could be important, such as external vascularization and outflow tract, and better chamber formation, so we might still be missing important aspects of congenital heart disease and diabetic cardiomyopathy," Aguirre says. "On one hand, we want to partner with clinicians to establish the efficacy and safety of our findings in pregnant women. On the other hand, we want to apply our organoid model to other conditions affecting congenital heart disease so we can improve the lives of these children in the future." This research was supported by the National Institutes of Health, the National Science Foundation, the Michigan Diabetes Research Center, the University of Michigan, the American Heart Association and the Spectrum-MSU Alliance Foundation.

山东师范大学何洪彬教授和中国农业科学院长春兽医研究所高玉伟研究员在“Journal of Virology”上发表了题目为“SARS-CoV-2 ORF8 Protein InducesEndoplasmic Reticulum Stress-like Responses and Facilitates Virus Replicationby Triggering Calnexin: an Unbiased Study”的研究论文，该研究发现ORF8是SARS-CoV-2的关键独特毒力基因，可能有助于COVID-19特异性和/或人类特异性发病机制.严重急性呼吸系统综合症冠状病毒 2（SARS-CoV-2）是导致全球 2019年冠状病毒病（COVID-19）大流行的病毒病原体。新型 SARS-CoV-2 ORF8 蛋白与已知蛋白质（包括其他冠状病毒的辅助蛋白）同源性较低。尽管SARS-CoV-2ORF8 结构在SARS-CoV-2流行开始后不久就已确定，但其特性和功能的机制细节尚未完全确定。在哺乳动物细胞中，未折叠蛋白反应 （UPR）的三个分支被激活以缓解内质网应激。具体来说，（i）内质网应激的细胞感应导致激活转录因子 6 （ATF6）切割，然后其N末端片段ATF6（N）进入细胞核以激活 UPR靶基因;（ii）当被内质网应激激活时，双链RNA活化蛋白激酶样内质网激酶（PERK）直接磷酸化真核起始因子2（eIF2α）的α亚基，导致整体mRNA翻译衰减，从而减轻内质网应激;（iii）应激激活的肌醇蛋白 1（IRE1）剪接X-box结合蛋白1（XBP1）mRNA并编码一种名为剪接XBP1（sXBP1）的碱性亮氨酸转录因子，激活 UPR 靶基因。在这里，作者研究发现SARS-CoV-2ORF8 可以通过IRE1分支激活内质网应激，并通过与钙联接蛋白的相互作用促进病毒复制。本研究结果证明SARS-CoV-2ORF8蛋白的无偏倚分子特征，并证明它诱导快速产生但高度可控的内质网应激样反应，并通过触发人细胞而非小鼠细胞中的钙联蛋白来促进病毒复制，为SARS-CoV-2感染患者和小鼠之间ORF8的体内毒力差异提供了解释。识别微信二维码，添加生物制品圈小编，符合条件者即可加入生物制品微信群！请注明：姓名+研究方向！版权声明本公众号所有转载文章系出于传递更多信息之目的，且明确注明来源和作者，不希望被转载的媒体或个人可与我们联系(cbplib@163.com)，我们将立即进行删除处理。所有文章仅代表作者观点，不代表本站立场。