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...     

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。     

Advanced glycation end products suppress osteoblastic differentiation of stromal cells by activating endoplasmic reticulum stress

Advanced glycation end products (AGEs) are involved in bone quality deterioration in diabetes mellitus. We previously showed that AGE2 or AGE3 inhibited osteoblastic differentiation and mineralization of mouse stromal ST2 cells, and also induced apoptosis and decreased cell growth. Although quality management for synthesized proteins in endoplasmic reticulum (ER) is crucial for the maturation of osteoblasts, the effects of AGEs on ER stress in osteoblast lineage are unknown. We thus examined roles of ER stress in AGE2- or AGE3-induced suppression of osteoblastogenesis of ST2 cells. An ER stress inducer, thapsigargin (TG), induced osteoblastic differentiation of ST2 cells by increasing the levels of Osterix, type 1 collagen (Col1), alkaline phosphatase (ALP) and osteocalcin (OCN) mRNA. AGE2 or AGE3 suppressed the levels of ER stress sensors such as IRE1α, ATF6 and OASIS, while they increased the levels of PERK and its downstream molecules, ATF4. A reduction in PERK level by siRNA did not affect the AGEs-induced suppression of the levels of Osterix, Col1 and OCN mRNA. In conclusion, AGEs inhibited the osteoblastic differentiation of stromal cells by suppressing ER stress sensors and accumulating abnormal proteins in the cells. This process might accelerate AGEs-induced suppression of bone formation found in diabetes mellitus.     

内质网应激响应在脂肪组织中的代谢调节作用

在真核细胞中,内质网是蛋白合成、加工及质量监控的关键细胞器,也是Ca2+储存及脂质合成的重要场所.细胞通过未折叠蛋白响应(unfolded protein response,UPR)感应外界不同刺激引发的内质网应激,在维持细胞功能稳态中发挥至关重要的作用.在哺乳动物中,三个位于内质网的跨膜蛋白——肌醇依赖酶la(ino...     

Peroxidative stress selectively down-regulates the neuronal stress response activated under conditions of endoplasmic reticulum dysfunction

Oxidative stress has been implicated in mechanisms leading to neuronal cell injury in various pathological states of the brain. Here, we investigated the effect of peroxide exposure on the expression of genes coding for cytoplasmic and endoplasmic reticulum (ER) stress proteins. Primary neuronal cell cultures were exposed to H(2)O(2) for 6 h and mRNA levels of hsp70, grp78, grp94, gadd153 were evaluated by quantitative PCR. In addition, peroxide-induced changes in protein synthesis and cell viability were investigated. Peroxide treatment of cells triggered an almost 12-fold increase in hsp70 mRNA levels, but a significant decrease in grp78, grp94 and gadd153 mRNA levels. To establish whether peroxide exposure blocks the ER-resident stress response, cells were also exposed to thapsigargin (Tg, a specific inhibitor of ER Ca(2+)-ATPase) which has been shown to elicit the ER stress response. Tg exposure induced 7.2-fold, 3.6-fold and 8.8-fold increase in grp78, grp94 and gadd153 mRNA levels, respectively. However, after peroxide pre-exposure, the Tg-induced effect on grp78, grp94 and gadd153 mRNA levels was completely blocked. The results indicate that oxidative damage causes a selective down-regulation of the neuronal stress response activated under conditions of ER dysfunction. This down-regulation was only observed in cultures exposed to peroxide levels which induced severe suppression of protein synthesis and cell injury, implying a causative link between peroxide-induced down-regulation of ER stress response system and development of neuronal cell injury. These observations could have implications for our understanding of the mechanisms underlying neuronal cell injury in pathological states of the brain associated with oxidative damage, including Alzheimer's disease where the neuronal stress response activated under conditions of ER dysfunction has been shown to be down-regulated. Down-regulation of ER stress response may increase the sensitivity of neurones to an otherwise nonlethal form of stress.     

Inhibition of endoplasmic reticulum associated degradation reduces endoplasmic reticulum stress and alters lysosomal morphology and distribution

Disturbances in proteostasis are observed in many neurodegenerative diseases. This leads to activation of protein quality control to restore proteostasis, with a key role for the removal of aberrant proteins by proteolysis. The unfolded protein response (UPR) is a protein quality control mechanism of the endoplasmic reticulum (ER) that is activated in several neurodegenerative diseases. Recently we showed that the major proteolytic pathway during UPR activation is via the autophagy/lysosomal system. Here we investigate UPR induction if the other major proteolytic pathway of the ER -ER associated degradation (ERAD)-is inhibited. Surprisingly, impairment of ERAD results in decreased UPR activation and protects against ER stress toxicity. Autophagy induction is not affected under these conditions, however, a striking relocalization of the lysosomes is observed. Our data suggest that a protective UPR-modulating mechanism is activated if ERAD is inhibited, which involves lysosomes. Our data provide insight in the cross-talk between proteolytic pathways involved in ER proteostasis. This has implications for neurodegenerative diseases like Alzheimer’s disease where disturbed ER proteostasis and proteolytic impairment are early phenomena in the pathology.     

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.     

IGL-1 solution reduces endoplasmic reticulum stress and apoptosis in rat liver transplantation

Injury due to cold ischemia reperfusion (I/R) is a major cause of primary graft non-function following liver transplantation. We postulated that I/R-induced cellular damage during liver transplantation might affect the secretory pathway, particularly at the endoplasmic reticulum (ER). We examined the involvement of ER stress in organ preservation, and compared cold storage in University of Wisconsin (UW) solution and in Institute Georges Lopez-1 (IGL-1) solution. In one group of rats, livers were preserved in UW solution for 8 h at 4 °C, and then orthotopic liver transplantation was performed according to Kamada''s cuff technique. In another group, livers were preserved in IGL-1 solution. The effect of each preservation solution on the induction of ER stress, hepatic injury, mitochondrial damage and cell death was evaluated. As expected, we found increased ER stress after liver transplantation. IGL-1 solution significantly attenuated ER damage by reducing the activation of three pathways of unfolded protein response and their effector molecules caspase-12, C/EBP homologous protein-10, X-box-binding protein 1, tumor necrosis factor-associated factor 2 and eukaryotic translation initiation factor 2. This attenuation of ER stress was associated with a reduction in hepatic injury and cell death. Our results show that IGL-1 solution may be a useful means to circumvent excessive ER stress reactions associated with liver transplantation, and may optimize graft quality.     

Evaluating endoplasmic reticulum stress and unfolded protein response through the lens of ecology and evolution

Considerable progress has been made in understanding the physiological basis for variation in the life-history patterns of animals, particularly with regard to the roles of oxidative stress and hormonal regulation. However, an underappreciated and understudied area that could play a role in mediating inter- and intraspecific variation of life history is endoplasmic reticulum (ER) stress, and the resulting unfolded protein response (UPR^ER). ER stress response and the UPR^ER maintain proteostasis in cells by reducing the intracellular load of secretory proteins and enhancing protein folding capacity or initiating apoptosis in cells that cannot recover. Proper modulation of the ER stress response and execution of the UPR^ER allow animals to respond to intracellular and extracellular stressors and adapt to constantly changing environments. ER stress responses are heritable and there is considerable individual variation in UPR^ER phenotype in animals, suggesting that ER stress and UPR^ER phenotype can be subjected to natural selection. The variation in UPR^ER phenotype presumably reflects the way animals respond to ER stress and environmental challenges. Most of what we know about ER stress and the UPR^ER in animals has either come from biomedical studies using cell culture or from experiments involving conventional laboratory or agriculturally important models that exhibit limited genetic diversity. Furthermore, these studies involve the assessment of experimentally induced qualitative changes in gene expression as opposed to the quantitative variations that occur in naturally existing populations. Almost all of these studies were conducted in controlled settings that are often quite different from the conditions animals experience in nature. Herein, we review studies that investigated ER stress and the UPR^ER in relation to key life-history traits including growth and development, reproduction, bioenergetics and physical performance, and ageing and senescence. We then ask if these studies can inform us about the role of ER stress and the UPR^ER in mediating the aforementioned life-history traits in free-living animals. We propose that there is a need to conduct experiments pertaining to ER stress and the UPR^ER in ecologically relevant settings, to characterize variation in ER stress and the UPR^ER in free-living animals, and to relate the observed variation to key life-history traits. We urge others to integrate multiple physiological systems and investigate how interactions between ER stress and oxidative stress shape life-history trade-offs in free-living animals.     

内质网应激偶联炎症反应与慢性病发病机制

内质网是合成细胞内分泌蛋白和膜蛋白并进行蛋白折叠的主要细胞器。新近研究证明,当内质网蛋白质合成与折叠的负担增加、非折叠或错误折叠蛋白质堆积,可激活内质网的几组特定信号转导通路,将这些应激信号传递到细胞浆和细胞核,引起未/错误折叠蛋白反应。这对维持细胞动态平衡和生物体的发育具有重要意义。更为重要的是,未/错误折叠蛋白反应能够与细胞内炎症反应信号转导通路偶联,是非感染性致病原引发炎症反应的主要原因。因此,内质网应激-未/错误折叠蛋白反应-炎症反应在特定的细胞发生偶联是许多炎症疾病的发病机制。本文综述该领域的研究进展,并介绍了内质网应激信号和炎症反应偶联参与一些慢性病发病的分子细胞机制。这些研究不仅加深人们对这些慢性病发病机制的了解,也有助于对调节内质网应激-炎症反应的药物的研发。     

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.     

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.