慢性内质网应激诱导的凋亡在动脉粥样硬化斑块形成中的作用

内质网应激(ERS)与促进动脉粥样硬化(As)的非动脉壁系统和动脉壁系统因素均密切相关。未折叠蛋白反应(UPR)作为ERS长期激活的标志,可导致细胞的病理状态及组织功能受损。已有大量研究表明As斑块内的细胞,尤其是易损斑块区域的内皮细胞和巨噬细胞均表现有UPR被慢性激活。病理性的慢性ERS通过诱导细胞(内皮细胞、巨噬细胞及平滑肌细胞)凋亡而促进坏死核形成,激活炎症信号通路,影响易损斑块的形成与稳定性,有重要的促As效应。造成慢性ERS的应激源:氧化应激、氧化型胆固醇、细胞内高水平胆固醇及饱和脂肪酸等在As病程中表现明显,且在肥胖、胰岛素抵抗及糖尿病等促进As临床病程的因素中更为突出。近年研究已经部分揭示了ERS促As易损斑块形成的机制及体内的相关性,为ERS药物靶向性治疗途径提供了思路,但仍需大量深入的研究才能转化为具有临床意义的防治方法。     

Consequences and therapeutic implications of macrophage apoptosis in atherosclerosis: the importance of lesion stage and phagocytic efficiency

Macrophage apoptosis occurs throughout all stages of atherosclerosis, yet new findings in vivo suggest that the consequences of this event may be very different in early versus late atherosclerotic lesions. In early lesions, where phagocytic clearance of apoptotic cells appears to be efficient, macrophage apoptosis is associated with diminished lesion cellularity and decreased lesion progression. In late lesions, however, a number of factors may contribute to defective phagocytic clearance of apoptotic macrophages, leading to secondary necrosis of these cells and a proinflammatory response. The cumulative effect of these late lesional events is generation of the necrotic core, which, in concert with proatherogenic effects of residual surviving macrophages, promotes further inflammation, plaque instability, and thrombosis. Thus, the ability or lack thereof of lesional phagocytes to safely clear apoptotic macrophages may be an important determinant of acute atherothrombotic clinical events. Further understanding of the mechanisms involved in macrophage apoptosis and phagocytic clearance might lead to novel therapeutic strategies directed against the progression of advanced plaques.     

Melatonin and endoplasmic reticulum stress: relation to autophagy and apoptosis

Endoplasmic reticulum (ER) is a dynamic organelle that participates in a number of cellular functions by controlling lipid metabolism, calcium stores, and proteostasis. Under stressful situations, the ER environment is compromised, and protein maturation is impaired; this causes misfolded proteins to accumulate and a characteristic stress response named unfolded protein response (UPR). UPR protects cells from stress and contributes to cellular homeostasis re‐establishment; however, during prolonged ER stress, UPR activation promotes cell death. ER stressors can modulate autophagy which in turn, depending of the situation, induces cell survival or death. Interactions of different autophagy‐ and apoptosis‐related proteins and also common signaling pathways have been found, suggesting an interplay between these cellular processes, although their dynamic features are still unknown. A number of pathologies including metabolic, neurodegenerative and cardiovascular diseases, cancer, inflammation, and viral infections are associated with ER stress, leading to a growing interest in targeting components of the UPR as a therapeutic strategy. Melatonin has a variety of antioxidant, anti‐inflammatory, and antitumor effects. As such, it modulates apoptosis and autophagy in cancer cells, neurodegeneration and the development of liver diseases as well as other pathologies. Here, we review the effects of melatonin on the main ER stress mechanisms, focusing on its ability to regulate the autophagic and apoptotic processes. As the number of studies that have analyzed ER stress modulation by this indole remains limited, further research is necessary for a better understanding of the crosstalk between ER stress, autophagy, and apoptosis and to clearly delineate the mechanisms by which melatonin modulates these responses.     

Combinatorial pattern recognition receptor signaling alters the balance of life and death in macrophages

Macrophage pattern recognition receptors (PRRs) play key roles in innate immunity, but they also may contribute to disease processes under certain pathological conditions. We recently showed that engagement of the type A scavenger receptor (SRA), a PRR, triggers JNK-dependent apoptosis in endoplasmic reticulum (ER)-stressed macrophages. In advanced atherosclerotic lesions, the SRA, activated JNK, and ER stress are observed in macrophages, and macrophage death in advanced atheromata leads to plaque necrosis. Herein, we show that SRA ligands trigger apoptosis in ER-stressed macrophages by cooperating with another PRR, Toll-like receptor 4 (TLR4), to redirect TLR4 signaling from prosurvival to proapoptotic. Common SRA ligands activate both TLR4 signaling and engage the SRA. The TLR4 effect results in activation of the proapoptotic MyD88-JNK branch of TLR4, whereas the SRA effect silences the prosurvival IRF-3-IFN-beta branch of TLR4. The normal cell-survival effect of LPS-induced TLR4 activation is converted into an apoptosis response by immunoneutralization of IFN-beta, and the apoptosis effect of SRA ligands is converted into a cell-survival response by reconstitution with IFN-beta. Thus, combinatorial signaling between two distinct PRRs results in a functional outcome-macrophage apoptosis that does not occur with either PRR alone. PRR-induced macrophage death may play important roles in advanced atherosclerosis and in other innate immunity-related processes in which the balance between macrophage survival and death is critical.     

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。     

Stress hypERactivation in the β-cell

In pancreatic β-cells, the endoplasmic reticulum (ER) is the crucial site for insulin biosynthesis, as this is where the protein-folding machinery for secretory proteins is localized. Perturbations to ER function of the β-cell, such as a high demand for insulin secretion, can lead to an imbalance in protein homeostasis and lead to ER stress. This stress can be mitigated by an adaptive, cellular response, the unfolded protein response (UPR). UPR activation is vital to the survival of β-cells, as these cells represent one of the most susceptible tissues for ER stress, due to their highly secretory function. However, in some cases, this response is not sufficient to relieve stress, leading to apoptosis and contributing to the pathogenesis of diabetes. Recent evidence shows that ER stress plays a significant role in both type 1 and type 2 diabetes. In this review, we outline the mechanisms of ER stress-mediated β-cell death and focus on the role of ER stress in various forms of diabetes, particularly a genetic form of diabetes called Wolfram syndrome.     

Pathobiology of atherosclerosis--a brief review

Considerable progress has been made recently in understanding the pathobiology of atherosclerosis. To a significant degree it is an inflammatory disease of the vessel wall. Progression of atherosclerosis or its stabilization reflects the tension between cytokines and effectors that play both an inhibiting and a facilitating role in the progression of atherosclerosis, including platelet-derived growth factor (PDGF), interleukin-1, tumor necrosis factor (TNF) -alpha, and MCP-1. The response to injury model remains central to our understanding of atherogenesis. Numerous factors may initiate endothelial injury, including mechanical factors (hypertension and high shear stress in the artery), homocysteine, oxidized low-density lipoprotein (LDL), possibly infectious agents such as Chlamydia, viruses, and toxins such as nicotine. These factors lead to endothelial cells' increasing expression of receptors for LDL and increased adherence of monocytes and macrophages and T cells. Progression of atherosclerosis can lead to the development of a plaque that is vulnerable to rupture and that would then produce an acute coronary syndrome. In addition to standard biomarkers and angiographic approaches for detecting plaque rupture, novel diagnostic approaches are under development, including near infrared spectroscopy, catheter-based thermography, and optical coherence tomography. Our better understanding of the atherosclerotic plaque provides multiple opportunities for interdicting arterial injury, and the response to it.     

神经导向因子Netrin-1调节单核巨噬细胞迁移与动脉粥样斑块关系的研究进展

动脉粥样硬化是动脉壁的一种慢性炎症性疾病,单核巨噬细胞在其发生发展中起着关键作用。动脉粥样斑块中单核巨噬细胞迁移能力受损,滞留于斑块内,增加了斑块不稳定性,加速动脉粥样硬化病变的进展。目前研究表明动脉粥样斑块中巨噬细胞分泌的神经导向因子Netrin-1通过与巨噬细胞表面相应受体结合,可以抑制巨噬细胞迁出斑块,促进动脉粥样硬化的进展。但在动脉粥样硬化形成初期,血管内皮细胞表达的Netrin-1却被发现对动脉粥样硬化起到保护作用。     

Endoplasmic reticulum stress as a therapeutic target in cardiovascular disease

Cardiovascular disease constitutes a major and increasing health burden in developed countries. Although treatments have progressed, the development of novel treatments for patients with cardiovascular diseases remains a major research goal. The endoplasmic reticulum (ER) is the cellular organelle in which protein folding, calcium homeostasis, and lipid biosynthesis occur. Stimuli such as oxidative stress, ischemic insult, disturbances in calcium homeostasis, and enhanced expression of normal and/or folding-defective proteins lead to the accumulation of unfolded proteins, a condition referred to as ER stress. ER stress triggers the unfolded protein response (UPR) to maintain ER homeostasis. The UPR involves a group of signal transduction pathways that ameliorate the accumulation of unfolded protein by increasing ER-resident chaperones, inhibiting protein translation and accelerating the degradation of unfolded proteins. The UPR is initially an adaptive response but, if unresolved, can lead to apoptotic cell death. Thus, the ER is now recognized as an important organelle in deciding cell life and death. There is compelling evidence that the adaptive and proapoptotic pathways of UPR play fundamental roles in the development and progression of cardiovascular diseases, including heart failure, ischemic heart diseases, and atherosclerosis. Thus, therapeutic interventions that target molecules of the UPR component and reduce ER stress will be promising strategies to treat cardiovascular diseases. In this review, we summarize the recent progress in understanding UPR signaling in cardiovascular disease and its related therapeutic potential. Future studies may clarify the most promising molecules to be investigated as targets for cardiovascular diseases.     

Mammalian endoplasmic reticulum stress sensor IRE1 signals by dynamic clustering

Accumulation of misfolded proteins in the endoplasmic reticulum (ER) triggers the unfolded protein response (UPR), an intracellular signaling pathway that adjusts the protein folding capacity of the ER according to need. If homeostasis in the ER protein folding environment cannot be reestablished, cells commit to apoptosis. The ER-resident transmembrane kinase-endoribonuclease inositol-requiring enzyme 1 (IRE1) is the best characterized UPR signal transduction molecule. In yeast, Ire1 oligomerizes upon activation in response to an accumulation of misfolded proteins in the ER. Here we show that the salient mechanistic features of IRE1 activation are conserved: mammalian IRE1 oligomerizes in the ER membrane and oligomerization correlates with the onset of IRE1 phosphorylation and RNase activity. Moreover, the kinase/RNase module of human IRE1 activates cooperatively in vitro, indicating that formation of oligomers larger than four IRE1 molecules takes place upon activation. High-order IRE1 oligomerization thus emerges as a conserved mechanism of IRE1 signaling. IRE1 signaling attenuates after prolonged ER stress. IRE1 then enters a refractive state even if ER stress remains unmitigated. Attenuation includes dissolution of IRE1 clusters, IRE1 dephosphorylation, and decline in endoribonuclease activity. Thus IRE1 activity is governed by a timer that may be important in switching the UPR from the initially cytoprotective phase to the apoptotic mode.     

未折叠蛋白反应与2型糖尿病胰岛β细胞凋亡

内质网(ER)是细胞内蛋白质合成、折叠的重要场所,对应激极为敏感.多种因素均可导致ER功能发生改变,统称为内质网应激(ERS).ERS可以启动细胞内一系列适应性反应,即未折叠蛋白反应(UPR),以恢复细胞内环境的稳态.但持久和(或)剧烈的ERS将启动细胞凋亡程序.胰岛β细胞具有高度发达的ER,使其对2型糖尿病长期高血糖和游离脂肪酸所致的应激更为敏感.大量的研究表明,作为ERS组成部分之一的UPR在β细胞凋亡中起重要作用.现综述UPR导致2型糖尿病胰岛β细胞凋亡的具体机制.     

Apoptosis in atherosclerosis: beneficial or detrimental?

Several groups have demonstrated apoptotic cell death in atherosclerotic plaques. The significance of apoptosis in atherosclerosis depends on the stage of the plaque, localization and the cell types involved. Both macrophages and smooth muscle cells undergo apoptosis in atherosclerotic plaques. Apoptosis of macrophages is mainly present in regions showing signs of DNA synthesis/repair. Smooth muscle cell apoptosis is mainly present in less cellular regions and is not associated with DNA synthesis/repair. Even in early stages of atherosclerosis smooth muscle cells become susceptible to undergoing apoptosis since they increase different pro-apoptotic factors. Moreover, recent data indicate that smooth muscle cells may be killed by activated macrophages. The loss of the smooth muscle cells can be detrimental for plaque stability since most of the interstitial collagen fibers, which are important for the tensile strength of the fibrous cap, are produced by SMC. Apoptosis of macrophages could be beneficial for plaque stability if apoptotic bodies are removed. Apoptotic cells that are not scavenged in the plaque activate thrombin which could further induce intraplaque thrombosis. It can be concluded that apoptosis in the primary atherosclerosis is detrimental since it could lead to plaque rupture and thrombosis. Recent data of our group indicate that apoptosis decreases after lipid lowering which could be important in our understanding of the cell biology of plaque stabilization.     

Endoplasmic Reticulum Stress in Cardiometabolic Disorders

When endoplasmic reticulum (ER) homeostasis is disrupted, an adaptive signaling pathway, called the unfolded protein response (UPR) is activated to help ER cope with the stress. The UPR is an important signal transduction pathway, crucial for the survival and function of all cells. Recently, there has been a substantial progress made in understanding the molecular mechanisms of physiological UPR regulation and its role in the pathogenesis of many diseases including metabolic diseases. Studies using mouse models lacking or overexpressing the factors involved in ER stress signaling as well as work performed on humans have revealed the contribution of UPR to disease progression. This review focuses on the regulation of UPR signaling and its relevance in pathogenesis of metabolic diseases.     

Niemann-Pick C heterozygosity confers resistance to lesional necrosis and macrophage apoptosis in murine atherosclerosis

Macrophage death in advanced atherosclerotic lesions leads to lesional necrosis and likely promotes plaque instability, a precursor of acute vascular events. Macrophages in advanced lesions accumulate large amounts of unesterified cholesterol, which is a potent inducer of macrophage apoptosis. We have shown recently that induction of apoptosis in cultured macrophages requires cholesterol trafficking to the endoplasmic reticulum (ER). Moreover, macrophages from mice with a heterozygous mutation in the cholesterol-trafficking protein Npc1 have a selective defect in cholesterol trafficking to the ER and are protected from cholesterol-induced apoptosis. The goal of the present study was to test the importance of intracellular cholesterol trafficking in atherosclerotic lesional macrophage death by comparing lesion morphology in Npc1+/+;Apoe-/- and Npc1+/-;Apoe-/- mice. Although advanced lesions in Npc1+/+;Apoe-/- mice had extensive acellular areas that were rich in unesterified cholesterol and macrophage debris, the lesions of Npc1+/-;Apoe-/- mice were substantially more cellular and less necrotic. Moreover, compared with Npc1+/-;Apoe-/- lesions, Npc1+/+;Apoe-/- lesions had a greater number of large, TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling)-positive areas surrounding necrotic areas, indicative of macrophage apoptosis. These differences were observed despite similar total lesion area and similar plasma lipid levels in the two groups of mice. These data provide in vivo evidence that intact intracellular cholesterol trafficking is important for macrophage apoptosis in advanced atherosclerotic lesions and that the ER-based model of cholesterol-induced cytotoxicity is physiologically relevant. Moreover, by showing that lesional necrosis can be diminished by a subtle defect in intracellular trafficking, these findings suggest therapeutic strategies to stabilize atherosclerotic plaques.     

Implications of ER Stress,the Unfolded Protein Response,and Pro‐ and Anti‐Apoptotic Protein Fingerprints in Human Monocyte‐Derived Dendritic Cells Treated With Alcohol

Background: Dendritic cells (DCs) are responsible for the activation of T cells and B cells. There is accumulating evidence that psychoactive substances such as alcohol can affect immune responses. We hypothesize that this occurs by modulating changes in proteins triggering a process known as unfolded protein response (UPR). This process protects cells from the toxic effects of misfolded proteins responsible for causing endoplasmic reticulum (ER) stress. Although much is known about ER stress, little is understood about the consequences of ethanol use on DC’s protein expression. Methods: In this study, we investigated alterations in the proteins of human monocyte‐derived dendritic cells (MDDC) treated with 0.1% of alcohol by two‐dimensional (2D) gel electrophoresis followed by liquid chromatography–tandem mass spectrometry, protein identification, and confirmation at the gene expression level by qRT‐PCR. Results: Proteomes of related samples demonstrated 32 differentially expressed proteins that had a 2‐fold or greater change in expression (18 spots were up‐regulated and 14 were down‐regulated), compared to the control cultures (untreated cells). Alcohol significantly changed the expression of several components of the UPR stress‐induced pathways that include chaperones, ER stress, antioxidant enzymes, proteases, alcohol dehydrogenase, cytoskeletal and apoptosis‐regulating proteins. qRT‐PCR analyses highlighted the enhanced expression of UPR and antioxidant genes that increased (18 hours) with alcohol treatment. Conclusion: Results of these analyses provide insights into alcohol mechanisms of regulating DC and suggest that alcohol induced specifically the UPR in DC. We speculate that activation of a UPR by alcohol may protect the DC from oxidant injury but may lead to the development of alcohol‐related diseases.     

内质网应激与缺血性脑损伤

内质网应激是内质网内未折叠或错误折叠蛋白积聚所致。作为对内质网应激的响应,细胞形成了一条称为未折叠蛋白反应(UPR)的自我保护信号转导通路。然而,如果脑缺血诱导的内质网应激严重且持续时间长,UPR最终会启动细胞凋亡通路,导致神经元死亡。文章对脑缺血再灌注诱导内质网应激和UPR的研究进展做了综述。