The physiological role of the unfolded protein response in the nervous system

The unfolded protein response(UPR)is a cellular stress response pathway activated when the endoplasmic reticulum,a crucial organelle for protein folding and modification,encounters an accumulation of unfolded or misfolded proteins.The UPR aims to restore endoplasmic reticulum homeostasis by enhancing protein folding capacity,reducing protein biosynthesis,and promoting protein degradation.It also plays a pivotal role in coordinating signaling cascades to determine cell fate and function in response to endoplasmic reticulum stress.Recent research has highlighted the significance of the UPR not only in maintaining endoplasmic reticulum homeostasis but also in influencing various physiological processes in the nervous system.Here,we provide an overview of recent findings that underscore the UPR’s involvement in preserving the function and viability of neuronal and myelinating cells under physiological conditions,and highlight the critical role of the UPR in brain development,memory storage,retinal cone development,myelination,and maintenance of myelin thickness.

Mesenchymal stromal cells modulate unfolded protein response and preserve β-cell mass in type 1 diabetes

Introduction:Transplantation of mesenchymal stromal cells(MSCs)is a promising therapy for type 1 diabetes(T1D).However,whether the infused MSCs affect the endoplasmic reticulum stress or subsequent unfolded protein response inβcells remains unclear.Methods:To investigate this,we induced early-onset T1D in non-obese diabetic mice using streptozotocin.Subsequently,T1D mice were randomly assigned to receive either MSCs or phosphate-buffered saline.We observed the in vivo homing of MSCs and assessed their effectiveness by analyzing blood glucose levels,body weight,histopathology,pancreatic protein expression,and serum levels of cytokines,proinsulin,and C-peptide.Results:Infused MSCs were found in the lungs,liver,spleen,and pancreas of T1D mice.They exhibited various effects,including reducing blood glucose levels,regulating immunity,inhibiting inflammation,increasingβ-cell areas,and reducing the expression of key proteins in the unfolded protein response pathway.Fasting serum proinsulin and C-peptide levels were significantly higher in the MSCs treatment group than in the T1D model group.However,there was no significant difference in the biomarker ofβ-cell endoplasmic reticulum stress,the ratio of fasting serum proinsulin to C-peptide,between the two groups.Conclusion:Ourfindings reveal that MSCs infusion does not alleviate endoplasmic reticulum stress inβcells directly but modulates the unfolded protein response pathway to preserveβ-cell mass and function in T1D mice.

Hypoxia Affects Autophagy in Human Umbilical Vein Endothelial Cells via the IRE1 Unfolded Protein Response

Objective:The purpose of this study was to investigate the role of the unfolded protein response,specifically the inositol-requiring enzyme 1(IRE1)signaling pathway,in hypoxia-induced autophagy in human umbilical venous endothelial cells(HUVECs).Methods:The expression of IRE1 and autophagy relative protein in HUVECs with hypoxia was explored by Western blotting,qRT-PCR and confocal microscopy.Further,we evaluated the biological effects of HUVECs by tube formation assay and wound healing assay in vitro.Finally,we examined the function of IRE1 in local blood vessels through animal models,Results:Hypoxia activated the IRE1 signaling pathway and induced autophagy in a time-dependent manner in HUVECs and further influenced the biological effects of HUVECs.Intraperitoneal injection of IRE1 inhibitors inhibited local vascular autophagy levels and lipid accumulation in model animals.Conclusion:Hypoxia can induce autophagy and activate the IRE1 signaling pathway in HUVECs and the IRE1 signaling pathway is involved in autophagy in hypoxic conditions.

The Role and Mechanism of Unfolded Protein Response Pathway in Tumor Drug Resistance

In the process of tumor proliferation and metastasis,tumor cells encounter hypoxia,low glucose,acidosis,and other stressful environments.These conditions prompt tumor cells to generate endoplasmic reticulum stress(ERS).As a signal mechanism that mitigates ERS in eukaryotic cells,the unfolded protein response(UPR)pathway can activate cells and tissues,regulating pathological activities in various cells,and maintaining ER homeostasis.It forms the most crucial adaptive and defensive mechanism for cells.However,under the continuous influence of chemotherapy drugs,the quantity of unfolded proteins and erroneous proteins produced by tumor cells significantly increases,surpassing the normal regulatory range of UPR.Consequently,ERS fails to function properly,fostering tumor cell proliferation and the development of drug resistance.This review delves into the study of three UPR pathways(PERK,IRE1,and ATF6),elucidating the mechanisms of drug resistance and research progress in the signal transduction pathway of UPR related to cancers.It provides a profound understanding of the role and relationship between UPR and anti-tumor drugs,offering a new direction for effective clinical treatment.

Acinar cell injury induced by inadequate unfolded protein response in acute pancreatitis

Acute pancreatitis (AP) is an inflammatory disorder of pancreatic tissue initiated in injured acinar cells. Severe AP remains a significant challenge due to the lack of effective treatment. The widely-accepted autodigestion theory of AP is now facing challenges, since inhibiting protease activation has negligible effectiveness for AP treatment despite numerous efforts. Furthermore, accumulating evidence supports a new concept that malfunction of a self-protective mechanism, the unfolded protein response(UPR), is the driving force behind the pathogenesis of AP. The UPR is induced by endoplasmic reticulum(ER) stress, a disturbance frequently found in acinar cells, to prevent the aggravation of ER stress that can otherwise lead to cell injury. In addition, the UPR's signaling pathways control NFκB activation and autophagy flux, and these dysregulations cause acinar cell inflammatory injury in AP, but with poorly understood mechanisms. We therefore summarize the protective role of the UPR in AP, propose mechanistic models of how inadequate UPR could promote NFκB's pro-inflammatory activity and impair autophagy's protective function in acinar cells, and discuss its relevance to current AP treatment. We hope that insight provided in this review will help facilitate the research and management of AP.

The unfolded protein response signaling and retinal Müller cell metabolism

The retina is one of the most energy demanding tissues in the body. Like most neurons in the central nervous system, retinal neurons consume high amounts of adenosine-5′-triphosphate（ATP） to generate visual signal and transmit the information to the brain. Disruptions in retinal metabolism can cause neuronal dysfunction and degeneration resulting in severe visual impairment and even blindness. The homeostasis of retinal metabolism is tightly controlled by multiple signaling pathways, such as the unfolded protein response（UPR）, and the close interactions between retinal neurons and other retinal cell types including vascular cells and Müller glia. The UPR is a highly conserved adaptive cellular response and can be triggered by many physiological stressors and pathophysiological conditions. Activation of the UPR leads to changes in glycolytic rate, ATP production, de novo serine synthesis, and the hexosamine biosynthetic pathway, which are considered critical components of Müller glia metabolism and provide metabolic support to surrounding neurons. When these pathways are disrupted, neurodegeneration occurs rapidly. In this review, we summarize recent advance in studies of the UPR in Müller glia and highlight the potential role of the UPR in retinal degeneration through regulation of Müller glia metabolism.

Roles of mitochondrial unfolded protein response in mammalian stem cells

The mitochondrial unfolded protein response(UPRmt)is an evolutionarily conserved adaptive mechanism for improving cell survival under mitochondrial stress.Under physiological and pathological conditions,the UPRmt is the key to maintaining intracellular homeostasis and proteostasis.Important roles of the UPRmt have been demonstrated in a variety of cell types and in cell development,metabolism,and immune processes.UPRmt dysfunction leads to a variety of pathologies,including cancer,inflammation,neurodegenerative disease,metabolic disease,and immune disease.Stem cells have a special ability to selfrenew and differentiate into a variety of somatic cells and have been shown to exist in a variety of tissues.These cells are involved in development,tissue renewal,and some disease processes.Although the roles and regulatory mechanisms of the UPRmt in somatic cells have been widely reported,the roles of the UPRmt in stem cells are not fully understood.The roles and functions of the UPRmt depend on stem cell type.Therefore,this paper summarizes the potential significance of the UPRmt in embryonic stem cells,tissue stem cells,tumor stem cells,and induced pluripotent stem cells.The purpose of this review is to provide new insights into stem cell differentiation and tumor pathogenesis.

Role of unfolded protein response in lipogenesis

The signal transduction network in regulating lipid metabolism is a hot topic of biomedical research. Recent research endeavors reveal that intracellular stress signaling from a cellular organelle called endoplasmic reticulum (ER) is critically involved in lipid homeostasis and the development of metabolic disease. The ER is a site where newly-synthesized proteins are folded and assembled into their three-dimensional structures, modified and transported to their precise cellular destinations. A wide range of biochemical, physiological and pathological stimuli can interrupt the protein folding process in the ER and cause accumulation of unfolded or misfolded proteins in the ER lumen, a condition referred to as ER stress. To cope with this stress condition, the ER has evolved highly-specifi c signaling pathways collectively termed Unfolded Protein Response (UPR) or ER stress response. The UPR regulates transcriptionaland translational programs, affecting broad aspects of cellular metabolism and cell fate. Lipogenesis, the metabolic process of de novo lipid biosynthesis, occurs primarily in the liver where metabolic signals regulate expression of key enzymes in glycolytic and lipogenic pathways. Recent studies suggest that the UPR plays crucial roles in modulating lipogenesis under metabolic conditions. Here we address some of recent representative evidence regarding the role of the UPR in lipogenesis.

Mannogalactoglucan from mushrooms protects pancreatic islets via restoring UPR and promotes insulin secretion in TIDM mice

Type 1 diabetes mellitus(T1DM) lacks insulin secretion due to autoimmune deficiency of pancreaticβ-cells.Protecting pancreatic islets and enhancing insulin secretion has been therapeutic approaches.Mannogalactoglucan is the main type of polysaccharide from natural mushroom,which has potential medicinal prospects.Nevertheless,the antidiabetic property of mannogalactoglucan in T1DM has not been fully elucidated.In this study,we obtained the neutral fraction of alkali-soluble Armillaria mellea polysaccharide(AAMP-N) with the structure of mannogalactoglucan from the fruiting body of A.mellea and investigated the potential therapeutic value of AAMP-N in T1DM.We demonstrated that AAMP-N lowered blood glucose and improved diabetes symptoms in T1DM mice.AAMP-N activated unfolded protein response(UPR) signaling pathway to maintain ER protein folding homeostasis and promote insulin secretion in vivo.Besides that,AAMP-N promoted insulin synthesis via upregulating the expression of transcription factors,increased Ca^(2+) signals to stimulate intracellular insulin secretory vesicle transport via activating calcium/calmodulin-dependent kinase Ⅱ(CamkⅡ) and cAMP/PKA signals,and enhanced insulin secretory vesicle fusion with the plasma membrane via vesicle-associated membrane protein 2(VAMP2).Collectively,these studies demonstrated that the therapeutic potential of AAMP-N on pancreatic islets function,indicating that mannogalactoglucan could be natural nutraceutical used for the treatment of T1DM.

3-52 Unfolded Protein Response Induced by X-rays in Breast Cancer Cells

Expand ER stress is triggered due to the loss of homeostasis in the ER which causes the accumulation ofmisfolded proteins within the ER lumen. Severe or prolonged ER stress may induce the unfolded protein response(UPR), which is an adaptive mechanism aimed at reducing levels of unfolded proteins and keeping balance in theER. CHOP, Bip, JNK, EIF2 are major elements in these pathways.In this study, we investigated the activation of CHOP, Bip, total JNK and phosphorylated JNK (P-JNK), totalEIF2 and phosphorylated EIF2 (P- EIF2) in response to X-rays in breast cancer MCF-7 and MDA-MB-231 cellsusing western blot analysis.

A vicinal oxygen chelate protein facilitates viral infection by triggering the unfolded protein response in Nicotiana benthamiana

Vicinal oxygen chelate(VOC)proteins are members of an enzyme superfamily with dioxygenase or non-dioxygenase activities.However,the biological functions of VOC proteins in plants are poorly understood.Here,we show that a VOC in Nicotiana benthamiana(NbVOC1)facilitates viral infection.NbVOC1 was significantly induced by infection by beet necrotic yellow vein virus(BNYVV).Transient overexpression of NbVOC1 or its homolog from Beta vulgaris(BvVOC1)enhanced BNYVV infection in N.benthamiana,which required the nuclear localization of VOC1.Consistent with this result,overexpressing NbVOC1 facilitated BNYVV infection,whereas,knockdown and knockout of NbVOC1 inhibited BNYVV infection in transgenic N.benthamiana plants.NbVOC1 interacts with the basic leucine zipper transcription factors bZIP17/28,which enhances their self-interaction and DNA binding to the promoters of unfolded protein response(UPR)-related genes.We propose that bZIP17/28 directly binds to the NbVOC1 promoter and induces its transcription,forming a positive feedback loop to induce the UPR and facilitating BNYVV infection.Collectively,our results demonstrate that NbVOC1 positively regulates the UPR that enhances viral infection in plants.

UPRmt改善乙醇诱导的肝细胞坏死性凋亡的分子机制研究

背景坏死性凋亡作为一种新型程序性细胞死亡方式参与酒精性肝病的发生发展。线粒体未折叠的蛋白质反应(mitochondrial unfolded protein response,UPR^(mt))能够促进应激反应中细胞修复并改善线粒体网络的调控,探究乙醇诱导下肝细胞内UPR^(mt)调控机制可能为酒精性肝病的临床治疗提供新的潜在靶点。目的探讨UPR^(mt)对乙醇诱导下肝细胞线粒体功能和坏死性凋亡的影响,及其在肝细胞线粒体网络中的作用机制。方法利用正常小鼠肝细胞AML12构建正常对照组、乙醇组、UPR^(mt)激活对照组、UPR^(mt)激活乙醇组模型。经浓度250 mmol/L无水乙醇培养细胞构建乙醇组模型,通过造模前6 h给予10μmol/L寡霉素A激活正常小鼠肝细胞UPR^(mt)构建干预组。利用RT-PCR检测UPR^(mt)、线粒体分裂和坏死性凋亡相关基因转录水平,荧光探针观察线粒体功能,蛋白质印迹法检测自噬相关蛋白表达水平。结果乙醇诱导下UPR^(mt)相关基因mtDNAj、CHOP、ATF5和炎症因子TNF-α、IL-6、Timp1转录水平升高,坏死性凋亡关键基因RIPK3、PGAM5表达增加(P<0.05)。荧光探针观察到乙醇诱导下线粒体膜电位显著下降,线粒体ROS产生量增多(P<0.05),蛋白免疫印迹结果显示乙醇诱导下肝细胞内线粒体自噬被抑制,线粒体分裂增加。寡霉素A干预增强细胞内UPR^(mt),从而改善乙醇诱导下炎症产生和氧化应激,维持线粒体正常功能,抑制肝细胞坏死性凋亡。结论UPR^(mt)通过减少细胞氧化应激、维持线粒体正常功能,从而缓解乙醇诱导的肝细胞坏死性凋亡和炎症损伤。

New insights into the unfolded protein response(UPR)-anterior gradient 2(AGR2)pathway in the regulation of intestinal barrier function in weaned piglets

Sustained dysfunction of the intestinal barrier caused by early weaning is a major factor that induces postweaning diarrhea in weaned piglets.In both healthy and diseased states,the intestinal barrier is regulated by goblet cells.Alterations in the characteristics of goblet cells are linked to intestinal barrier dysfunction and inflammatory conditions during pathogenic infections.In this review,we summarize the current understanding of the mechanisms of the unfolded protein response(UPR)and anterior gradient2(AGR2)in maintaining intestinal barrier function and how modifications to these systems affect mucus barrier characteristics and goblet cell dysregulation.We highlight a novel mechanism underlying the UPR-AGR2 pathway,which affects goblet cell differentiation and maturation and the synthesis and secretion of mucin by regulating epidermal growth factor receptor and mucin 2.This study provides a theoretical basis and new insights into the regulation of intestinal health in weaned piglets.

内质网应激PERK-eIF2α-AFT4-CHOP信号通路在血液肿瘤中的研究进展

在生理状态下,内质网主要负责蛋白质的生物合成和成熟。然而,当机体稳态受到内外因素干扰破坏后,引发内质网中未折叠和错误折叠蛋白的累积,进而诱导产生内质网应激和未折叠蛋白反应(UPR)。在内质网应激条件下,未折叠蛋白反应可通过不同途径来维持细胞内稳态,其中活化蛋白激酶R样内质网激酶(PERK)是其重要途径之一。活化的PERK使真核翻译起始因子2亚基α(eIF2α)磷酸化,引发活性转录因子4(ATF4)选择性翻译,并与促凋亡转录因子C/EBP同源蛋白(CHOP)的启动子直接结合诱导细胞凋亡。该信号通路也是UPR参与血液肿瘤细胞和免疫细胞调节的重要机制之一。本文阐述了PERK-eIF2α-ATF4-CHOP信号通路在血液肿瘤中的研究进展,以及靶向该信号通路在血液肿瘤治疗中的潜在价值。

内质网应激在肝脏疾病中的作用及机制研究进展

肝脏疾病病种繁多且病因不明,严重影响人类健康。内质网是维持细胞内稳态的关键细胞器,然而其长期暴露于危险因素会引发内质网应激(ERS),并伴随下游信号通路的异常活化。ERS可导致肝细胞脂质积累,并诱发炎症、氧化损伤和凋亡,引起肝损伤,促进多种肝脏疾病的发生发展。然而,ERS也可通过若干机制保护肝细胞,如通过启动内质网相关降解和自噬降低细胞内压力,恢复细胞功能并维持胞内稳态;诱发受感染细胞、癌细胞的凋亡以阻断疾病进展等。因此,靶向ERS或其通路中的关键蛋白有望成为治疗肝脏疾病的有效方法。

未折叠蛋白反应在非酒精性脂肪性肝病中的作用研究进展

内质网应激(endoplasmic reticulum stress,ERS)下的未折叠蛋白反应(unfolded protein response,UPR)可调节脂质代谢,与非酒精性脂肪性肝病(non-alcoholic fatty liver disease,NAFLD)的进展有极大的相关性。当肝细胞在受到某些刺激,如缺氧或氧化应激时,会发生ERS,启动UPR以恢复细胞稳态。ERS又有急性ERS和慢性持续性ERS两种形式,急性ERS所触发的UPR是维持细胞稳态的重要反应机制,而慢性持续性ERS会启动细胞的凋亡程序,诱导细胞凋亡,与NAFLD的发生发展密切相关,其可能是NAFLD进程中的关键因素。本文回顾了NAFLD进展与UPR的联系,从脂质代谢、自噬角度讨论了UPR与NAFLD的关系,以期进一步深入了解NAFLD的发病机制,为NAFLD的预防和治疗提供指导。

基于内质网应激反应探究针刺治疗卒中后抑郁的机制

卒中后抑郁(Post Stroke Depression,PSD)发生在脑卒中后,以情感低落、兴趣丧失、自我价值感下降、睡眠障碍等症状为主要临床表现。为探究针刺治疗PSD的具体分子机制,作者通过查阅近年来PubMed、CNKI、万方、维普等国内外数据库的资料和文献,将PSD与内质网应激反应(endoplasmic reticulum stress,ERS)的关系及针刺通过干预ERS来治疗PSD的临床研究和动物实验研究进行总结分析,厘清ERS的发生机制以及针刺干预ERS的可能靶点。该文章得出推论,针刺可能通过调节ERS相关通路蛋白,抑制炎症反应及超负荷ERS介导的细胞凋亡来改善PSD患者的临床症状。因此,该研究将针刺治疗手段调控PSD后发生ERS的相关靶点机制进行归纳,以期日后为针刺治疗PSD的可探索靶点方向提供新的思路及一定的科学依据。

线粒体未折叠蛋白反应在棕榈酸诱导肾小管上皮细胞脂质聚集中的作用

目的探讨线粒体未折叠蛋白反应(mitochondrial unfolded protein reaction,UPR^(mt))对肾小管上皮细胞(human kidney 2,HK-2)脂代谢的影响。方法采用棕榈酸(palmitic acid,PA)诱导HK-2细胞内脂质聚集,分别予siRNA抑制UPR^(mt)或巴多索隆(the 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid,CDDO)增强UPR^(mt)。油红染色观察细胞内脂质聚集情况,线粒体膜电位检测试剂盒(JC-1)测定线粒体膜电位(mitochondrial membrane potential,MMP),Mito-SOX测定线粒体内活性氧(reactive oxygen species,ROS)含量,Western blotting检测HSP60、LONP1、CLPP、ACOX1、PPARα、PGC1α、CPT1α蛋白表达。结果PA诱导HK-2细胞脂质聚集、MMP降低、ROS产生增多及UPR^(mt)关键蛋白HSP60、LONP1表达降低;抑制UPR^(mt)可加剧PA导致的脂质聚集、MMP降低、ROS产生增多,HSP60、LONP1表达进一步降低;增强UPR^(mt)可缓解PA导致的脂质聚集、MMP降低、ROS产生增多以及HSP60、LONP1表达降低。结论PA诱导的HK-2细胞脂质聚集可能与线粒体功能障碍有关,UPR^(mt)在该过程中对HK-2细胞具有保护作用。

内质网应激与心血管疾病的研究进展

内质网(ER)是真核细胞最主要的膜性结构,是细胞内重要生理过程发生的关键细胞器。在多种内外因素的作用下,ER的稳态受到破坏,导致蛋白质加工运输受阻,未折叠蛋白或错误折叠蛋白在ER腔内聚集,形成内质网应激(ERS),并触发未折叠蛋白反应(UPR)。适度的ERS通过UPR信号通路减少蛋白质合成、促进蛋白质降解、增加协助蛋白质折叠的分子伴侣,最终缓解ER压力。但是,如果ERS过强或持续时间过长,超过细胞的自身调节能力时,UPR可启动细胞凋亡,亦可导致疾病。大量研究表明,ERS与多种心血管疾病(CVD)的发生发展密切相关。该综述主要阐述UPR在几种常见CVD中的研究进展和靶向UPR作为CVD的潜在治疗方法。

内质网质量控制系统调控及其与帕金森病关系的研究进展

帕金森病是常见的神经系统退行性疾病,发病率逐年升高,其病理特征主要表现为中脑黑质致密部多巴胺能神经元退行性变及α-突触核蛋白的异常聚集。内质网对于蛋白质折叠修饰、加工、运输发挥重要作用。内质网稳态被破坏则会导致未折叠蛋白质、错误折叠蛋白质的积累,诱导内质网应激,导致细胞凋亡。为维持内质网功能和稳态,内质网质量控制系统即未折叠蛋白反应、内质网相关蛋白质降解途径和内质网自噬发挥了作用。研究提示内质网应激与帕金森病的发病有着紧密的联系,但内质网质量控制系统在帕金森病进展中的作用尚不清晰。本文对内质网质量控制系统异常与帕金森病发生发展的关系进行综述,为探索帕金森病的发病机制提供新的思路。