内质网应激反应分子机理研究进展

内质网应激是导致心脑组织缺血梗塞、神经退行性疾病等发生的重要环节 .目前发现同型半胱氨酸、氧化应激、钙代谢紊乱等都能引起内质网应激级联反应 ,表现为蛋白质合成暂停、内质网应激蛋白表达和细胞凋亡等 .这些表现包括在未折叠蛋白反应 (UPR)、整合应激反应 (ISR)和内质网相关性死亡 (ERAD)三个相互关联的动态过程中 ,每一过程的分子机理现已逐步被揭示 .作为细胞保护性应对机制的内质网应激体系一旦遭到破坏 ,细胞将不能合成应有的蛋白质 ,亦不能发挥正常的生理功能 ,甚至会出现细胞凋亡 .掌握内质网应激过程对进一步理解多种疾病的发生机理有十分重要的理论意义     

内质网应激的细胞效应分子机制

内质网应激（endoplasmic reticulum stress,ERs）是内质网腔内错误折叠蛋白聚积的一种适应性反应,适度ERs通过激活未折叠蛋白反应起适应性的细胞保护作用,而过高和持久的ERs则通过诱导转录因子CHOP表达、激活caspase-12和c—Jun氨基末端激酶（JNK）等导致细胞凋亡。近年来,越来越多的研究提示内质网应激是神经退行性病变、2型糖尿病以及肥胖等疾病发生过程中的重要环节。对内质网应激的细胞效应分子机制进行综述。随着对ERs机制理解的深入,有可能会发现新的分子标志物或新的诊疗策略。     

疱疹病毒与内质网应激

内质网是分泌型蛋白和膜蛋白折叠及翻译后修饰的主要场所.病毒感染所引起的宿主细胞内环境的改变可使细胞或病毒的未折叠和/或错误折叠蛋白在内质网中大量聚集,使内质网处于生理功能紊乱的应激状态.为了缓解这种应激压力,细胞会启动未折叠蛋白反应(UPR),并通过一系列分子的信号转导维持内质网稳态;同时病毒也会通过对UPR的精密调控...     

Regulation of Enzyme Synthesis of the Glyoxylate,the Citric Acid,and the Methylcitric Acid Cycles in Candida lipolytica

Syntheses of the key enzymes of the glyoxylate cycle, in Candida lipolytica, were highly repressed by glucose. Syntheses of the key enzymes of the methylcitric acid cycle were also slightly repressed by glucose but the degrees of repression in the syntheses of these enzymes were nearly equal to those of repression in the syntheses of several enzymes of the citric acid cycle. All enzyme syntheses repressed by glucose were derepressed during incubation with succinate as well as with n-alkanes: enzyme syntheses of the methylcitric acid cycle did not necessitate the addition of propionate or odd-carbon n-alkanes. The enzymes of the methylcitric acid cycle seem to be constitutive, similarly as those of the citric acid cycle.

In the parent strain, the respective enzyme levels of the cells grown on an odd-numbered n-alkane were similar to those of the cells grown on an even-numbered n-alkane. But in the mutant strain lacking 2-methylisocitrate lyase, the cells grown on the odd-numbered alkane contained aconitate hydratase, NADP-Iinked isocitrate dehydrogenase, isocitrate lyase, 2- methylcitrate synthase and 2-methylaconitate hydratase all at higher levels than the cells grown on the even-numbered alkane. Both the parent cells and the mutant cells grown on the same carbon source contained at individually similar levels of the following six enzymes; citrate synthase, NAD-linked isocitrate dehydrogenase, succinate dehydrogenase, fumarate hydratase, malate dehydrogenase, and malate synthase. The pleiotropic changes of enzyme activities in the mutant cells grown on the odd-numbered alkane seem to be ascribable to direct or indirect stimulation caused by threo-d_s-2-methylisocitric acid accumulation.     

Endoplasmic reticulum proteostasis impairment in aging

Perturbed neuronal proteostasis is a salient feature shared by both aging and protein misfolding disorders. The proteostasis network controls the health of the proteome by integrating pathways involved in protein synthesis, folding, trafficking, secretion, and their degradation. A reduction in the buffering capacity of the proteostasis network during aging may increase the risk to undergo neurodegeneration by enhancing the accumulation of misfolded proteins. As almost one‐third of the proteome is synthetized at the endoplasmic reticulum (ER), maintenance of its proper function is fundamental to sustain neuronal function. In fact, ER stress is a common feature of most neurodegenerative diseases. The unfolded protein response (UPR) operates as central player to maintain ER homeostasis or the induction of cell death of chronically damaged cells. Here, we discuss recent evidence placing ER stress as a driver of brain aging, and the emerging impact of neuronal UPR in controlling global proteostasis at the whole organismal level. Finally, we discuss possible therapeutic interventions to improve proteostasis and prevent pathological brain aging.     

内质网应激及其在糖尿病肾病中的作用机制

糖尿病肾病（diabetic nephropathy,DN）是糖尿病最常见的微血管并发症,是导致终末期肾脏疾病（end-stage renal disease,ESRD）的继发性肾脏疾病的主要病因之一。多种因素如缺氧、氧化应激、病毒感染、遗传突变等,可导致内质网内稳态失衡,大量未折叠蛋白和错误折叠引起蛋白堆积,即形成内质网应激(endoplasmic reticulum stress, ERS),从而激活未折叠蛋白反应(unfolded protein response, UPR)介导的三条经典的细胞适应性应答通路以恢复内质网稳态和细胞活性。但如果刺激过强或持续存在,便会启动细胞凋亡信号通路。大量研究表明ERS与DN的发生发展相关,并参与不同类型肾细胞损伤的过程,因此ERS作为治疗DN的有效靶点具有很重要的研究前景,调控ERS可为DN的治疗提供新的理论支持。从ERS相关信号通路及其在DN中的作用和新进展领域作一综述,以期为DN的治疗研究提供参考。     

内质网应激介导的细胞凋亡

内质网是细胞内重要的细胞器,内质网功能的损伤引起ER应激(ERS).内质网通过激活未折叠蛋白质反应(UPR)以保护由内质网应激所引起的细胞损伤,恢复细胞功能,包括暂停早期蛋白质合成、内质网分子伴侣和折叠酶的转录激活、内质网相关性降解(ERAD)的诱导.长期过强的内质网应激诱导内质网相关性细胞凋亡,清除受损细胞,包括内质网应激诱导CHOP/GADD153表达、JNK的激活以及caspase-12蛋白水解酶的活化等一系列生物学效应.     

Glucose-6-phosphate Dehydrogenase and 6-Phosphogluconate Dehydrogenase of Candida tropicalis Partial Purification and Some Properties

Glucose-6-phosphate (G6P) dehydrogenase and 6-phosphogluconate (6PG) dehydrogenase were partially purified about 53-fold and 47-fold, respectively, from the cell-free extract of glucose-grown Candida tropicalis by means of ammonium sulfate fractionation and DEAE-cellulose column chromatography. AMP acted as the competitive inhibitor against G6P and NADP in the G6P dehydrogenase reaction. This inhibition was remarkable at low concentrations of NADP, increasing the sigmoidicity of the NADP-saturation curve. On the other hand, 6PG dehydrogenase was not affected by AMP. Fructose-1,6-bisphosphate (FDP) and phosphoenolpyruvate (PEP) inhibited slightly G6P dehydrogenase. 6PG dehydrogenase was also weakly inhibited by FDP. Apparent Km values of G6P dehydrogenase were calculated as 1.8 × 10^?4 m for G6P and 3.1 × 10^?5 m for NADP. Those of 6PG dehydrogenase were 9.4 × 10^?5 m for 6PG and 2.8 × 10^?5 m for NADP.     

未折叠蛋白质应答

内质网是真核细胞中蛋白质合成、折叠与分泌的重要细胞器.细胞进化出一套完整的机制来监督和帮助内质网内蛋白质的折叠与修饰.而当错误折叠的蛋白质累积时,细胞通过一系列信号转导途径,对其进行应答,包括增强蛋白质折叠能力、停滞大多数蛋白质的翻译、加速蛋白质的降解等.如果内质网功能素乱持续,细胞将最终启动凋亡程序.这些反应被统称为未折叠蛋白质应答(unfolded protein response,UPR).UPR是多个信号转导通路的总称,包括IRE1-XBP1、PERK-ATF4以及ATF6等信号途径.除了应激条件外,UPR还被用于正常生理条件下的调节,例如胆固醇合成代谢的负反馈调控.     

Conversion of the Extracellular Dextransucrase Isoenzymes from Leuconostoc mesenteroides NRRL B-1299

Effect of oxygen tension on l-lysine, l-threonine and l-isoleucine accumulation was investigated. Sufficient supply of oxygen to satisfy the cell’s oxygen demand was essential for the maximum production in each fermentation. The dissolved oxygen level must be controlled at greater than 0.01 atm in every fermentation, and the optimum redox potentials of culture media were above ?170 mV in l-lysine and l-threonine and above ?180 mV in l-isoleucine fermentations. The maximum concentrations of the products were 45.5 mg/ml for l-lysine, 10.3 mg/ml for l-threonine and 15.1 mg/ml for l-isoleucine. The degree of the inhibition due to oxygen limitation was slight in the fermentative production of l-lysine, l-threonine and l-isoleucine, whose biosynthesis is initiated with l-aspartic acid, in contrast to the accumulation of l-proline, l-glutamine and l-arginine, which is biosynthesized by way of l-glutamic acid.     

Suppressive effects of 4-phenylbutyrate on the aggregation of Pael receptors and endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress is defined as an accumulation of unfolded proteins in the endoplasmic reticulum. 4-phenylbutyrate (4-PBA) has been demonstrated to promote the normal trafficking of the DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) mutant from the ER to the plasma membrane and to restore activity. We have reported that 4-PBA protected against cerebral ischemic injury and ER stress-induced neuronal cell death. In this study, we revealed that 4-PBA possesses chemical chaperone activity in vitro, which prevents the aggregation of denatured alpha-lactalbumin and bovine serum albumin (BSA). Furthermore, we investigated the effects of 4-PBA on the accumulation of Parkin-associated endothelin receptor-like receptor (Pael-R) pathologically relevant to the loss of dopaminergic neurons in autosomal recessive juvenile parkinsonism (AR-JP). Interestingly, 4-PBA restored the normal expression of Pael-R protein and suppressed ER stress induced by the overexpression of Pael-R. In addition, we showed that 4-PBA attenuated the activation of ER stress-induced signal transduction pathways and subsequent neuronal cell death. Moreover, 4-PBA restored the viability of yeasts that fail to induce an ER stress response under ER stress conditions. These results suggest that 4-PBA suppresses ER stress by directly reducing the amount of misfolded protein, including Pael-R accumulated in the ER.     

Redox-based endoplasmic reticulum dysfunction in neurological diseases

The redox homeostasis of the endoplasmic reticulum lumen is characteristically different from that of the other subcellular compartments. The concerted action of membrane transport processes and oxidoreductase enzymes maintain the oxidized state of the thiol-disulfide and the reducing state of the pyridine nucleotide redox systems, which are prerequisites for the normal functions of the organelle. The powerful thiol-oxidizing machinery allows oxidative protein folding but continuously challenges the local antioxidant defense. Alterations of the cellular redox environment either in oxidizing or reducing direction affect protein processing and may induce endoplasmic reticulum stress and unfolded protein response. The activated signaling pathways attempt to restore the balance between protein loading and processing and induce apoptosis if the attempt fails. Recent findings strongly support the involvement of this mechanism in brain ischemia, neuronal degenerative diseases and traumatic injury. The redox changes in the endoplasmic reticulum are integral parts of the pathomechanism of neurological diseases, either as causative agents, or as complications.     

Intermittent selective clamping improves rat liver regeneration by attenuating oxidative and endoplasmic reticulum stress

Intermittent clamping of the portal trial is an effective method to avoid excessive blood loss during hepatic resection, but this procedure may cause ischemic damage to liver. Intermittent selective clamping of the lobes to be resected may represent a good alternative as it exposes the remnant liver only to the reperfusion stress. We compared the effect of intermittent total or selective clamping on hepatocellular injury and liver regeneration. Entire hepatic lobes or only lobes to be resected were subjected twice to 10 min of ischemia followed by 5 min of reperfusion before hepatectomy. We provided evidence that the effect of intermittent clamping can be damaging or beneficial depending to its mode of application. Although transaminase levels were similar in all groups, intermittent total clamping impaired liver regeneration and increased apoptosis. In contrast, intermittent selective clamping improved liver protein secretion and hepatocyte proliferation when compared with standard hepatectomy. This beneficial effect was linked to better adenosine-5′-triphosphate (ATP) recovery, nitric oxide production, antioxidant activities and endoplasmic reticulum adaptation leading to limit mitochondrial damage and apoptosis. Interestingly, transient and early chaperone inductions resulted in a controlled activation of the unfolded protein response concomitantly to endothelial nitric oxide synthase, extracellular signal-regulated kinase-1/2 (ERK1/2) and p38 MAPK activation that favors liver regeneration. Endoplasmic reticulum stress is a central target through which intermittent selective clamping exerts its cytoprotective effect and improves liver regeneration. This procedure could be applied as a powerful protective modality in the field of living donor liver transplantation and liver surgery.     

酵母PMT1基因参与内质网应激的调控机制

【目的】内质网应激(Endoplasmic reticulum stress,ERS)可激活细胞保护性信号级联反应——未折叠蛋白质反应(Unfolded protein response,UPR)。研究表明,酵母细胞中的UPR信号通路由转录因子Hac1p和ERS感应因子Ire1p共同介导。前期研究发现:蛋白质-O-甘露糖转移酶1(Protein-O-mannosyltransferase 1,PMT1)基因缺失能延长酵母细胞的复制性寿命,其机制与上调UPR通路活性相关。本文进一步探讨PMT1基因缺失在酵母ERS反应中的作用。【方法】观察PMT1基因与IRE1或HAC1基因双缺失酵母菌株(pmt1?hac1?和pmt1?ire1?)在ERS反应条件下的克隆形成能力;通过比色法检测各菌株的细胞增殖活性;RT-PCR检测各菌株UPR通路下游部分靶基因的转录水平。【结果】与对照菌株比较,PMT1基因缺失菌株(pmt1?)在ERS反应条件下生长较慢,而HAC1和IRE1单基因缺失菌株(hac1?和ire1?)在ERS反应条件下无法存活;在hac1?或ire1?菌株的基础上进一步缺失PMT1基因,可以改善hac1?菌株在ERS反应条件下的生长状态;但缺失PMT1基因没有上调hac1?菌株UPR通路靶基因的转录水平。【结论】缺失PMT1基因可增强hac1?菌株对ERS诱导剂衣霉素的抗性,机制与已知的UPR通路不相关,提示可能存在其它途径参与ERS反应的调控。     

利用人工锌指文库选育高乙醇耐受性工业酵母菌株

选育高乙醇耐性的酿酒酵母菌株对提高燃料乙醇的发酵效率具有重要意义.锌指蛋白广泛存在于多种生物中,对基因的转录和翻译起重要的调节作用.利用人工设计的锌指蛋白可定向设计锌指序列及其排列顺序,实现对细胞内多个基因的全局调控.由于与环境胁迫反应相关的基因很多,因此可利用人工锌指蛋白技术获得耐受性提高的微生物重组菌.文中将人工锌指文库转入到酿酒酵母模式菌株S288c,选育了具有高乙醇耐受性的重组菌株M01,并分离了与乙醇耐受性提高相关的人工锌指蛋白表达载体pRS316ZFP-M01,转入工业酿酒酵母Sc4126,在含有不同浓度乙醇的平板上,工业酵母Sc4126的重组菌株表现出显著的耐受性提高.在高糖培养基(250 g/L)条件下进行乙醇发酵,发现重组菌的乙醇发酵效率明显快于野生型,发酵时间提前24 h,且发酵终点乙醇浓度提高6.3％.结果表明人工锌指文库能够提高酵母的乙醇耐受性,为构建发酵性能优良的酵母菌种奠定了基础.     

Three branches to rule them all? UPR signalling in response to chemically versus misfolded proteins‐induced ER stress

Study of the unfolded protein responses (UPR) is mainly addressed by challenging eukaryotic cells with chemical compounds that impair calcium, redox or glycan homeostasis. These dramatically alter the endoplasmic reticulum (ER) environment and function, but also trigger pleiotropic effects that may result in multi‐organellar failure and cell death. Recent works showed that UPR induced by the accumulation of unfolded polypeptides in the ER lumen drastically differs from chemically induced UPR. Unfolded proteins are tolerated by cells, which activate a finely tuned UPR without entering apoptotic programs. How cells adapt the UPR to the burden of misfolded proteins, what structural features of the accumulating proteins determine UPR intensity and how these mechanisms translate into disease are crucial questions to be address in the future.     

植物内质网胁迫研究进展

内质网是蛋白质折叠和蛋白质糖基化修饰的重要场所。在内质网中存在多种调控机制来确保其中的蛋白质被正确地折叠、修饰和组装,以维持内质网稳态,这对于细胞正常的生理活动十分重要。然而,多种物理、化学因素均可使内质网稳态失衡,即在应激条件下,错误折叠和未折叠蛋白质的大量积累将导致内质网胁迫(endoplasmic reticulum stress, ERS),进而会引起未折叠蛋白质响应(unfolded protein response, UPR),极端情况下还会启动细胞程序性死亡(program cell death, PCD)。目前,植物内质网胁迫方面的研究较酵母和动物滞后,因此,从内质网质量控制系统和未折叠蛋白质响应2个方面对植物内质网胁迫现有研究进行了综述,以期为进一步理解内质网胁迫与植物逆境胁迫的关系提供参考。     

4-苯基丁酸钠通过抑制内质网应激减轻皮层神经元氧糖剥夺/再灌注损伤

4-苯基丁酸钠（4-phenylbutyric acid,4-PBA）是协助内质网中蛋白质转录后修饰和折叠的分子伴侣,故可减轻非折叠蛋白反应（unfolded protein response,UPR）及其介导的细胞凋亡。既往研究表明,4-PBA可以减轻脑组织的缺血性损伤,但采用原代皮层神经元构建氧糖剥夺/再灌注（oxygen glucose deprivation/reoxygenation, OGD/R）损伤模型,来研究4-PBA对神经元损伤的保护作用及其机制尚未见报道。本文采用原代培养的皮层神经元OGD/R损伤模型,同时给予4-PBA处理,探讨4-PBA对OGD/R诱导的神经元内质网应激（endoplasmic reticulum stress,ERS）的作用及其机制。分别采用MTT、LDH和Hoechst 33342染色法检测神经元存活率、细胞膜完整性和细胞凋亡情况。Western印迹检测ERS标志物葡萄糖调节蛋白78 (glucose regulated protein 78,GRP78),以及肌醇必需酶1（inositol requiring enzyme 1, IRE1）通路相关蛋白质的表达。Western印迹结果显示,在OGD/R后0～48 h,GRP78的表达较对照组明显升高。MTT、LDH漏出率和Hoechst 33342染色法检测显示,4-PBA显著改善OGD/R所导致的神经元存活率下降、LDH漏出率升高和细胞凋亡增加,且具有明显的剂量依赖性。通过Western印迹检测发现,4-PBA显著逆转OGD/R所致GRP78蛋白表达水平的上调。此外,对肌醇必需酶1通路相关蛋白质的检测显示,4-PBA下调氧糖剥夺/再灌注组神经元p IRE1和p JNK的表达,增加抗凋亡蛋白Bcl 2表达。上述研究结果表明,4-PBA在氧糖剥夺/再灌注情况下对神经元具有保护作用,该保护作用可能是通过抑制肌醇必需酶1信号通路介导的非折叠蛋白反应和内质网应激实现的。