PMA and crystal‐induced neutrophil extracellular trap formation involves RIPK1‐RIPK3‐MLKL signaling

Neutrophil extracellular trap (NET) formation contributes to gout, autoimmune vasculitis, thrombosis, and atherosclerosis. The outside‐in signaling pathway triggering NET formation is unknown. Here, we show that the receptor‐interacting protein kinase (RIPK)‐1‐stabilizers necrostatin‐1 or necrostatin‐1s and the mixed lineage kinase domain‐like (MLKL)‐inhibitor necrosulfonamide prevent monosodium urate (MSU) crystal‐ or PMA‐induced NET formation in human and mouse neutrophils. These compounds do not affect PMA‐ or urate crystal‐induced production of ROS. Moreover, neutrophils of chronic granulomatous disease patients are shown to lack PMA‐induced MLKL phosphorylation. Genetic deficiency of RIPK3 in mice prevents MSU crystal‐induced NET formation in vitro and in vivo. Thus, neutrophil death and NET formation may involve the signaling pathway defining necroptosis downstream of ROS production. These data imply that RIPK1, RIPK3, and MLKL could represent molecular targets in gout or other crystallopathies.     

Protective action of ultrasound-guided intraparenchymal transplantation of BMSCs in adriamycin nephropathy rats through the RIPK3/MLKL and NLRP3 pathways

BackgroundBone marrow stromal cells (BMSCs) are an effective new strategy for the treatment of kidney diseases. At present, noninvasive and efficient transplantation approaches to homing BMSCs to the renal parenchyma is still a serious challenge. The aim of this study was to investigate the feasibility and potential mechanism of ultrasound-guided intraparenchymal transplantation of BMSCs for the treatment of adriamycin nephropathy (AN) in rats.Materials and methodsA rat AN model was induced by 2 injections of doxorubicin. The rats were randomly divided into 4 groups (n = 10 animals in each group) : normal group (N group, no treatment), control medium group (CM group, transplant medium 1.0 mL), adriamycin nephropathy group (ADR group, phosphate buffered saline 1.0 mL), or BMSCs group (BMSCs fluid 1.0 mL). Intraparenchymal injection was completed under ultrasound guidance. After 4 weeks of treatment, blood samples were collected for serum biochemical measurements and ELISAs. The kidneys were removed for histopathological examination, electron microscopy, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL), and western blot analysis.ResultsNo deaths occurred in any group after BMSCs transplantation through the renal parenchyma under ultrasound guidance. Compared with the N and CM groups, in the ADR group, blood serum creatinine (SCr), blood urea nitrogen (BUN) and urine albumin (ALb) were higher, glomerular and tubular dilatation was observed, the number of apoptotic cells was higher, and the protein levels of receptor-interacting protein kinase 3 (RIPK3)/mixed lineage kinase domain-like protein (MLKL) and nucleotide leukin-rich polypeptide 3 (NLRP3), key components of pathways in rat kidney, were significantly higher. Compared with those in the ADR group, the levels of SCr, BUN, ALb and serum proinflammatory cytokines in the BMSCs group were lower, the pathological structure of the kidney was improved, the number of apoptotic cells was lower, and the levels of RIPK3/MLKL and NLRP3 were significantly lower.ConclusionUltrasound-guided intraparenchymal transplantation of BMSCs regulated the RIPK3/MLKL and NLRP3 pathways in a minimally invasive and safe manner, thereby inhibiting renal necrosis and inflammation and playing a protective role in rat AN.     

Sublethal necroptosis signaling promotes inflammation and liver cancer

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Progress in studies of necroptosis and its relationship to disease processes

This review briefly introduces the mechanism and detection methods of necroptosis in recent years. The most significant points of this review focus on the involvement of necroptotic proteins in disease progression. The following aspects are summarized: 1) RIPs, MLKL, and the upstream and downstream molecules that mediate necroptosis; 2) The development of detection methods for necroptosis; 3) The involvement of related necroptotic proteins in diverse diseases etiology; and 4) The application of necroptotic proteins in disease diagnosis.     

RIPK3 in cell death and inflammation: the good,the bad,and the ugly

Necroptosis is a form of cell death that can be observed downstream of death receptor or pattern recognition receptor signaling under certain cellular contexts, or in response to some viral and bacterial infections. The receptor interacting protein kinases-1 (RIPK1) and RIPK3 are at the core of necroptotic signaling, among other proteins. Because this pathway is normally halted by the pro-apoptotic protease caspase-8 and the IAP ubiquitin ligases, how and when necroptosis is triggered in physiological settings are ongoing questions. Interestingly, accumulating evidence suggests that RIPK3 has functions beyond the induction of necroptotic cell death, especially in the areas of tissue injury and sterile inflammation. Here, we will discuss the role of RIPK3 in a variety of physiological conditions, including necroptotic and non-necroptotic cell death, in the context of viral and bacterial infections, tissue damage, and inflammation.     

In vitro and in vivo macrophage function can occur independently of SLP-76

Expression of SH2 domain-containing leukocyte-specific phosphoprotein of 76 kDa (SLP-76), a hematopoietic cell-specific adapter protein, is required to couple Syk family tyrosine kinase activation to downstream mediators such as phospholipase C (PLC)-gamma following TCR, platelet collagen receptor and mast cell Fc epsilon R stimulation. In addition to T cells, mast cells and platelets, SLP-76 is expressed in monocytes and macrophages. To determine the role of SLP-76 in Fc gamma R-stimulated signaling pathways in macrophages, we examined cultured bone marrow-derived macrophages (BMM) from SLP-76(-/-) and wild-type mice. In this study, we show that Fc gamma R cross-linking rapidly induces tyrosine phosphorylation of SLP-76 in wild-type BMM. Surprisingly, however, BMM from SLP-76(-/-) mice activate ERK2 and phosphorylate PLC-gamma 2 following Fc gamma R ligation. Furthermore, SLP-76(-/-) BMM display normal Fc gamma R-dependent phagocytic function and reactive oxygen intermediate production. SLP-76(-/-) and SLP-76(+/+) BMM secrete comparable levels of IL-12 in response to lipopolysaccharide and IFN-gamma. To examine macrophage function in vivo, SLP-76(-/-) mice were challenged i.v. with Listeria monocytogenes. SLP-76(-/-) mice survive and efficiently contain the acute phase of infection similar to wild-type mice but exhibit a stable chronic infection attributed to the lack of mature T cells. These data show that, although SLP-76 is required to couple Syk family PTK activity to downstream mediators and effector functions in Fc gamma R-induced pathways in some cell types, activation of Fc gamma R-dependent pathways occurs independently of SLP-76 in BM     

程序性细胞坏死及细胞焦亡信号通路研究进展概述

细胞死亡是生命活动中一个非常重要的事件,真核生物可因物理损伤刺激导致细胞死亡,因特异信号通路介导的程序性细胞死亡近年来得到越来越多的关注。目前程序性细胞死亡主要存在以下3种方式:凋亡(apoptosis)、程序性坏死(necroptosis)、细胞焦亡(pyroptosis)。程序性坏死和细胞焦亡是近年来才发现的新的细胞程序性死亡方式,在细菌或病毒感染宿主细胞过程中起着关键作用。这两种细胞死亡都是细胞裂解型死亡,但其信号通路存在明显差异。本文就这两种程序性细胞死亡的形态学特征、信号转导通路及其在病原体感染过程中的作用等方面的研究进展作一综述。     

A class of viral inducer of degradation of the necroptosis adaptor RIPK3 regulates virus-induced inflammation

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溶酶体膜蛋白-2抗体诱导中性粒细胞胞外捕网形成的实验研究

目的研究溶酶体膜蛋白-2抗体(LAMP-2-antibody)诱导中性粒细胞胞外捕网形成(NETosis)的作用,为进一步探讨这种新型细胞死亡模式在系统性小血管炎中的作用及机制奠定基础。方法采用PolymorphprepTM进行密度梯度离心法分离健康志愿者外周静脉血中性粒细胞,抗LAMP-2抗体刺激中性粒细胞,以及通过NADPH氧化酶抑制剂二甲苯基碘(DPI)阻断活性氧簇的产生,电镜、免疫荧光观测胞外捕网的形成,激光共聚焦检测自身抗原LAMP-2、PR3、MPO的表达。结果 LAMP-2抗体促进中性粒细胞胞外捕网NETs形成,自身抗原MPO、PR3及LAMP-2包含在NETs内,抑制NADPH氧化酶的活性可以阻断NETs形成。结论 LAMP-2抗体可能通过诱导中性粒细胞异常死亡,释放内源性危险信号,激活自身免疫反应等来维持血管炎的恶性持续状态。     

Accumulation of RIPK1 into mitochondria is requisite for oxidative stress-mediated necroptosis and proliferation in Rat Schwann cells

The injury of Schwann cells is an important pathological feature of peripheral neuropathy. However, the explicit molecular mechanism and blocking method remains to be explored. In this study, we identified an pivotal executor of necroptosis—RIPK1, performed an unique function in response to oxidative stress-induced injury in Rat Schwann cells. We found that after oxidative stress-simulation by H₂O₂, RIPK1 was activated independent of genetic up-regulation, but through the post-translational modification, including its protein levels, phosphorylation of Serine 166 and Serine 321 sites and its general ubiquitination levels. Under a confocal microscopy, we found that RIPK1 was significantly accumulated into the mitochondria. And the phosphorylation, ubiquitination levels were also elevated in mitochondrial RIPK1, as indicated by immunoprecipitation. Through the administration of N-Acetyl-L-cysteine (NAC), a ROS inhibitor, we found that the phosphorylation, ubiquitination and mitochondrial location of RIPK1 was significantly suppressed. While administration of Necrostatin-1 (Nec-1) failed to influence the levels of ROS and mitochondrial membrane potential, revealing that RIPK1 served as the down-stream regulators of ROS. Lastly, pharmacological inhibition of RIPK1 by Nec-1 attenuated the levels of necroptosis, increased proliferation, as indicated by Annexin V/PI evaluation, CCK-8 detection, TEM scanning and EdU staining. Our results indicate a previous un-recognized post-translational change of RIPK1 in response to oxidative stress in Schwann cells.     

Challenges in the characterization of neutrophil extracellular traps: The truth is in the details

Neutrophil extracellular traps play a key role in defense against extracellular pathogens. The release of these chromatin structures, that contain a combination of cytoplasmic and granule proteins, is known as NETosis, a regulated cell death modality typical of neutrophils. NETosis is induced by pathogens as well as other stimuli such as activated platelets. Our understanding of the molecular events underlying this phenomenon remains incomplete. The currently used experimental approaches to study NETs are semi‐quantitative, subjective in nature, and low throughput, rendering it difficult to compare results between laboratories. This is highlighted in two articles published in this issue of the European Journal of Immunology which present what appear to be contradicting results on NET formation. Considering the extensive research on NETosis and the importance of this phenomenon in the immune response, we find it timely to briefly review the lacunae in the most commonly used methods to investigate NETosis. The impact these technical difficulties have on the advancement of our knowledge in this field as well as potential solutions are also discussed.     

Pyroptosis in neutrophils: Multimodal integration of inflammasome and regulated cell death signaling pathways

Pyroptosis is a proinflammatory mode of lytic cell death mediated by accumulation of plasma membrane (PM) macropores composed of gasdermin-family (GSDM) proteins. It facilitates two major functions in innate immunity: (i) elimination of intracellular replicative niches for pathogenic bacteria; and (ii) non-classical secretion of IL-1 family cytokines that amplify host-beneficial inflammatory responses to microbial infection or tissue damage. Physiological roles for gasdermin D (GSDMD) in pyroptosis and IL-1β release during inflammasome signaling have been extensively characterized in macrophages. This involves cleavage of GSDMD by caspase-1 to generate GSDMD macropores that mediate IL-1β efflux and progression to pyroptotic lysis. Neutrophils, which rapidly accumulate in large numbers at sites of tissue infection or damage, become the predominant local source of IL-1β in coordination with their potent microbiocidal capacity. Similar to macrophages, neutrophils express GSDMD and utilize the same spectrum of diverse inflammasome platforms for caspase-1-mediated cleavage of GSDMD. Distinct from macrophages, neutrophils possess a remarkable capacity to resist progression to GSDMD-dependent pyroptotic lysis to preserve their viability for efficient microbial killing while maintaining GSDMD-dependent mechanisms for export of bioactive IL-1β. Rather, neutrophils employ cell-specific mechanisms to conditionally engage GSDMD-mediated pyroptosis in response to bacterial pathogens that use neutrophils as replicative niches. GSDMD and pyroptosis have also been mechanistically linked to induction of NETosis, a signature neutrophil pathway that expels decondensed nuclear DNA into extracellular compartments for immobilization and killing of microbial pathogens. This review summarizes a rapidly growing number of recent studies that have produced new insights, unexpected mechanistic nuances, and some controversies regarding the regulation of, and roles for, neutrophil inflammasomes, pyroptosis, and GSDMs in diverse innate immune responses.     

TRAF3抑制NF-κB引起的肾囊腔形成作用

目的:研究肿瘤坏死因子受体相关因子3(TRAF3)对多囊肾集合管上皮细胞中核因子κB(NF-κB)信号通路及其下游产物表达的影响;观察TRAF3基因过表达的多囊肾集合管上皮细胞形成管状分支结构的变化,探讨TRAF3在多囊肾囊腔形成的发生发展中可能产生的作用。方法:Western blot检测多囊肾集合管上皮细胞和TRAF3基因过表达多囊肾集合管上皮细胞中NF-κB信号通路的变化,同时检测下游凋亡因子Bax及Bid的表达及caspase-3活性变化;通过Annexin V-FITC/PI双染法检测各组细胞的凋亡情况;应用三维(3D)培养法观察多囊肾集合管上皮细胞形成管状分支结构变化的差异。结果:TRAF3的过表达能显著抑制多囊肾集合管上皮细胞中NF-κB信号通路的活性,使下游的Bax及Bid表达显著下调,细胞凋亡明显减少;TRAF3基因过表达多囊肾集合管上皮细胞管状分支结构较多囊肾集合管上皮细胞组明显增多。结论:TRAF3可能通过调节NF-κB信号通路降低Bax及Bid活性,抑制细胞凋亡,从而抑制多囊肾囊腔形成。     

CD95 death-inducing signaling complex formation and internalization occur in lipid rafts of type I and type II cells

We investigated the membrane localization of CD95 in type I and type II cells, which differ in their ability to recruit and activate caspase-8. We found that CD95 was preferentially located in lipid rafts of type I cells, while it was present both in raft and non-raft plasma membrane sub-domains of type II cells. After stimulation, CD95 located in phospholipid-rich plasma membrane was recruited to lipid rafts in both types of cells. Similarly, CD95 cross-linking resulted in caspase-independent translocation of FADD/MORT1 and caspase-8 to the lipid rafts, which was prevented by a death domain-defective receptor. CD95 internalization was then rapid in type I and delayed in type II cells and showed a substantial correlation with the kinetics of Fas-associated death domain (FADD)and caspase-8 recruitment to lipid rafts. Finally, electron microscopy analysis showed that after CD95 stimulation lipid rafts aggregated in large clusters that were internalized in endosomal vesicles, where caspase-8 underwent massive processing. Taken together, our data demonstrate that CD95 death-inducing signaling complex formation and internalization in type I and type II cells occur in lipid rafts, which are a major site of caspase-8 activation.     

Role of platelets in neutrophil extracellular trap (NET) production and tissue injury

In addition to their well-known role as the cellular mediator of thrombosis, numerous studies have identified key roles for platelets during various disease processes. Importantly, platelets play a critical role in the host immune response, directly interacting with, and eliminating pathogens, from the blood stream. In addition to pathogen clearance, platelets also contribute to leukocyte recruitment at sites of infection and inflammation, and modulate leukocyte activity. Platelet interaction with activated neutrophils is a potent inducer of neutrophil extracellular trap (NET). NETs consist of a diffuse, sticky web of extracellular DNA, nuclear and granular proteins, and serve to ensnare and kill pathogens. In addition to catching pathogens, the cytotoxic molecules and proteases on NETs have the potential to inflict significant tissue damage. Additionally, NET components have been suggested to be key activators of infection-induced coagulopathy. These critical roles, at the interface between hemostasis and immunity, highlight the need for balance in the platelet response; too little platelet activity results in bleeding and immune deficit, too much leads to tissue pathogenesis. In this review, we highlight recent advances in our understanding of the role platelets play in inflammation, the link between platelets and NETs and the role platelets play in disease pathogenesis.     

Nucleosome-induced neutrophil activation occurs independently of TLR9 and endosomal acidification: implications for systemic lupus erythematosus

The nucleosome is a major autoantigen known to activate PMN in systemic lupus erythematosus (SLE). TLR9 recognizes bacterial and even mammalian DNA under certain circumstances. Nevertheless, the role of TLR9 in SLE development is still unclear. Since nucleosomes are composed of DNA, we investigated whether TLR9 is required for nucleosome-induced PMN activation. Isolated neutrophils were cultured with nucleosomes, plasma from lupus patients and other stimuli in the presence/absence of various inhibitors. Cells were analyzed by flow cytometry, ELISA and confocal microscopy. We found that nucleosomes circulating in lupus plasma induce the secretion of pro-inflammatory cytokines by PMN. Nucleosomes activate human PMN independently of unmethylated CpG sequences in nucleosomal DNA, leading to IL-8/IL-6/TNF secretion and CD11b up-regulation. Nucleosomes accumulate in the cytoplasm of PMN upon endocytosis, induce TLR9 up-regulation and act synergistically with TLR9 ligands. Nucleosome-induced activation was not inhibited by polymyxin B (PB), chloroquine (CQ), ammonium chloride (AC) or a TLR9 antagonist. Moreover, both PMN isolated from WT and TLR9-KO mice were activated by nucleosomes, as detected by MIP-2 secretion and CD11b up-regulation. Activation occurred therefore independently of endotoxins, endosomal acidification, TLR9 and CpG motifs. TLR9 may thus be differently required in the triggering of nucleosome-induced innate immunity and anti-nucleosome B-cell autoimmunity.