Cadmium exposure induces necroptosis of porcine spleen via ROS-mediated activation of STAT1/RIPK3 signaling pathway.

Cadmium (Cd), a heavy metal, is used in a wide range of applications, such as plastics, electroplating process, electronics, and so forth. Due to its bioaccumulation ability, Cd can contaminate soil, water, air and food. To determine the effect of Cd exposure on the necroptosis in pig spleen and its mechanistic investigation, we constructed a model in pigs by feeding them food containing 20 mg/kg Cd. In this study, we analyzed the effects of Cd exposure on pig spleen through HE staining, Quantitative real-time PCR (qRT-PCR), Western blot (WB), and principal component analysis (PCA). Results show that Cd exposure can destroy the structure and function of pig spleen, which is closely related to necroptosis. Further results show that Cd exposure can induce necroptosis through ROS-mediated activation of Signal transducer and activator of transcription 1/Receptor-Interacting Serine/Threonine-Protein Kinase 3 (STAT1/RIPK3) signaling pathway in pig spleen. Additionally, Cd exposure also can affect the stability of mitochondrial-associated endoplasmic reticulum membrane (MAMs) structure, which also contributes to the process of necroptosis. Our study provides insights into the physiological toxicity caused by Cd exposure.

Neuroprotection for Age-Related Macular Degeneration.

Age-related macular degeneration (AMD) is a leading cause of blindness worldwide. Early to intermediate AMD is characterized by the accumulation of lipid- and protein-rich drusen. Late stages of the disease are characterized by the development of choroidal neovascularization, termed "exudative" or "neovascular AMD," or retinal pigment epithelium (RPE) cell and photoreceptor death, termed "geographic atrophy" (GA) in advanced nonexudative AMD. Although we have effective treatments for exudative AMD in the form of anti-VEGF agents, they have no role for patients with GA. Neuroprotection strategies have emerged as a possible way to slow photoreceptor degeneration and vision loss in patients with GA. These approaches include reduction of oxidative stress, modulation of the visual cycle, reduction of toxic molecules, inhibition of pathologic protein activity, prevention of cellular apoptosis or programmed necrosis (necroptosis), inhibition of inflammation, direct activation of neurotrophic factors, delivery of umbilical tissue-derived cells, and RPE replacement. Despite active investigation in this area and significant promise based on preclinical studies, many clinical studies have not yielded successful results. We discuss selected past and current neuroprotection trials for AMD, highlight the lessons learned from these past studies, and discuss our perspective regarding remaining questions that must be answered before neuroprotection can be successfully applied in the field of AMD research.

Novel role of macrophage TXNIP-mediated CYLD-NRF2-OASL1 axis in stress-induced liver inflammation and cell death.

Background & Aims: The stimulator of interferon genes (STING)/TANK-binding kinase 1 (TBK1) pathway is vital in mediating innate immune and inflammatory responses during oxidative/endoplasmic reticulum (ER) stress. However, it remains unknown whether macrophage thioredoxin-interacting protein (TXNIP) may regulate TBK1 function and cell death pathways during oxidative/ER stress. Methods: A mouse model of hepatic ischaemia/reperfusion injury (IRI), the primary hepatocytes, and bone marrow-derived macrophages were used in the myeloid-specific TXNIP knockout (TXNIPM-KO) and TXNIP-proficient (TXNIPFL/FL) mice. Results: The TXNIPM-KO mice were resistant to ischaemia/reperfusion (IR) stress-induced liver damage with reduced serum alanine aminotransferase (ALT)/aspartate aminotransferase (AST) levels, macrophage/neutrophil infiltration, and pro-inflammatory mediators compared with the TXNIPFL/FL controls. IR stress increased TXNIP, p-STING, and p-TBK1 expression in ischaemic livers. However, TXNIPM-KO inhibited STING, TBK1, interferon regulatory factor 3 (IRF3), and NF-κB activation with interferon-ß (IFN-ß) expression. Interestingly, TXNIPM-KO augmented nuclear factor (erythroid-derived 2)-like 2 (NRF2) activity, increased antioxidant gene expression, and reduced macrophage reactive oxygen species (ROS) production and hepatic apoptosis/necroptosis in IR-stressed livers. Mechanistically, macrophage TXNIP deficiency promoted cylindromatosis (CYLD), which colocalised and interacted with NADPH oxidase 4 (NOX4) to enhance NRF2 activity by deubiquitinating NOX4. Disruption of macrophage NRF2 or its target gene 2',5' oligoadenylate synthetase-like 1 (OASL1) enhanced Ras GTPase-activating protein-binding protein 1 (G3BP1) and TBK1-mediated inflammatory response. Notably, macrophage OASL1 deficiency induced hepatocyte apoptotic peptidase activating factor 1 (APAF1), cytochrome c, and caspase-9 activation, leading to increased caspase-3-initiated apoptosis and receptor-interacting serine/threonine-protein kinase 3 (RIPK3)-mediated necroptosis. Conclusions: Macrophage TXNIP deficiency enhances CYLD activity and activates the NRF2-OASL1 signalling, controlling IR stress-induced liver injury. The target gene OASL1 regulated by NRF2 is crucial for modulating STING-mediated TBK1 activation and Apaf1/cytochrome c/caspase-9-triggered apoptotic/necroptotic cell death pathway. Our findings underscore a novel role of macrophage TXNIP-mediated CYLD-NRF2-OASL1 axis in stress-induced liver inflammation and cell death, implying the potential therapeutic targets in liver inflammatory diseases. Lay summary: Liver inflammation and injury induced by ischaemia and reperfusion (the absence of blood flow to the liver tissue followed by the resupply of blood) is a significant cause of hepatic dysfunction and failure following liver transplantation, resection, and haemorrhagic shock. Herein, we uncover an underlying mechanism that contributes to liver inflammation and cell death in this setting and could be a therapeutic target in stress-induced liver inflammatory injury.

High Receptor-interacting Serine/Threonine-protein Kinase 3 (RIP3) Expression Serves as an Independent Poor Prognostic Factor for Triple-negative Breast Carcinoma.

BACKGROUND/AIM: Receptor-interacting serine/threonine-protein kinase 3 (RIP3) is a key component related to tumor necrosis factor-dependent necroptosis. RIP3 has been known to be a predictive biomarker in many types of carcinomas. We aimed to investigate whether RIP3 expression is correlated with clinicopathological characteristics and the outcomes of patients with breast carcinoma. PATIENTS AND METHODS: We performed immunostaining for RIP3 and analyzed the association of RIP3 expression status with the clinicopathological characteristics and survival of 203 patients with invasive ductal carcinoma of the breast. RESULTS: High RIP3 expression was significantly correlated with lymph node metastasis and human epidermal growth factor receptor 2 positivity. In patients with triple-negative breast carcinoma (TNBC), high RIP3 expression was an independent prognostic factor for disease-free survival (DFS). RIP3-high TNBC showed the lowest DFS rate. CONCLUSION: High RIP3 expression is associated with aggressive clinical behavior of breast carcinoma. Our data suggest that RIP3 serves as an independent prognostic factor in TNBC.

Correlation Between Plasma Levels of RIP3 and Acute Ischemic Stroke with Large-Artery Atherosclerosis.

BACKGROUND: Receptor-interacting serine-threonine protein kinase 3 (RIP3) was previously discovered to be an important medium in the occurrence and development of major atherosclerotic cerebral infarction. However, the role of RIP3 in acute ischemic stroke remains unclear. OBJECTIVE: This study aimed to explore the correlation between plasma levels of RIP3 and acute ischemic stroke with large-artery atherosclerosis (LAA). METHODS: This prospective study enrolled 116 patients with LAA, 40 healthy controls, and 30 acute ischemic stroke patients with small-artery occlusion. The patients with LAA were divided according to the quartile of plasma levels of RIP3. A logistic regression model was used for comparison. The ROC curve was performed to evaluate the predictive value. RESULTS: In patients with LAA, the RIP3 levels in patients with poor outcomes as well as neurological deterioration were significantly higher than those with good outcomes (P < 0.001) and without neurological deterioration (P = 0.014). Patients in the highest levels of plasma RIP3 quartile were more likely to have neurological deterioration (OR, 11.07; 95% CI, 1.990-61.582) and poor outcomes (OR, 35.970; 95% CI, 5.392-239.980) compared with the lowest. The optimal cut-off value for neurological deterioration was 1127.75 pg/mL (specificity, 66.7%; sensitivity, 69.2%) and that for poor prognosis was 1181.82 pg/mL (specificity, 89.7%; sensitivity, 62.1%). CONCLUSION: Elevated levels of plasma RIP3 were significantly associated with neurological deterioration and poor prognosis in patients with LAA. A significant increase in plasma RIP3 levels can predict neurological deterioration and the poor prognosis of these patients.

Corrigendum: RIPK3: A New Player in Renal Fibrosis.

[This corrects the article DOI: 10.3389/fcell.2020.00502.].

RIPK3: A New Player in Renal Fibrosis.

Chronic kidney disease (CKD) is the end result of a plethora of renal insults, including repeated episodes of acute or toxic kidney injury, glomerular, or diabetic kidney disease. It affects a large number of the population worldwide, resulting in significant personal morbidity and mortality and economic cost to the community. Hence it is appropriate to focus on treatment strategies that interrupt the development of kidney fibrosis, the end result of all forms of CKD, in addition to upstream factors that may be specific to certain diseases. However, the current clinical approach to prevent or manage renal fibrosis remains unsatisfactory. The rising importance of receptor-interacting serine/threonine-protein kinase (RIPK) 3 in the inflammatory response and TGF-ß1 signaling is increasingly recognized. We discuss here the biological functions of RIPK3 and its role in the development of renal fibrosis.

RIPK3 Promotes JEV Replication in Neurons via Downregulation of IFI44L.

Japanese encephalitis virus (JEV), the leading cause of viral encephalitis in Asia, is neurovirulent and neuroinvasive. Neurons are the main target of JEV infection and propagation. Receptor interacting serine/threonine-protein kinase 3 (RIPK3) has been reported to contribute to neuroinflammation and neuronal death in many central nervous system diseases. In this study, we found that the progression of JE was alleviated in RIPK3-knockout (RIPK3-/-) mice in both peripheral and intracerebral infection. RIPK3-knockdown (RIPK3-RNAi) neuro2a cells showed higher cell viability during JEV infection. Moreover, the JEV load was significantly decreased in RIPK3-/- mouse-derived primary neurons and RIPK3-RNAi neuro2a cells compared with wild-type neurons, but this was not observed in microglia. Furthermore, RNA sequencing of brain tissues showed that the level of the interferon (IFN)-induced protein 44-like gene (IFI44L) was significantly increased in JEV-infected RIPK3-/- mouse brains, RIPK3-/- neurons, and RIPK3-RNAi-neuro2a cells. Then, it was demonstrated that the propagation of JEV was inhibited in IFI44L-overexpressing neuro2a cells and enhanced in IFI44L and RIPK3 double knockdown neuro2a cells. Taken together, our results showed that the increased expression of RIPK3 following JEV infection played complicated roles. On the one hand, RIPK3 participated in neuroinflammation and neuronal death during JEV infection. On the other hand, RIPK3 inhibited the expression of IFI44L to some extent, leading to the propagation of JEV in neurons, which might be a strategy for JEV to evade the cellular innate immune response.

FKBP12 mediates necroptosis by initiating RIPK1-RIPK3-MLKL signal transduction in response to TNF receptor 1 ligation.

Necroptosis is a regulated form of necrotic cell death that is mediated by receptor-interacting serine/threonine-protein kinase 1 (RIPK1), RIPK3 and mixed-lineage kinase domain-like protein (MLKL), which mediates necroptotic signal transduction induced by tumor necrosis factor (TNF). Although many target proteins for necroptosis have been identified, no report had indicated that FK506-binding protein 12 (FKBP12, also known as FKBP1A), an endogenous protein that regulates protein folding and conformation alteration, is involved in mediating necroptosis. In this study, we found that FKBP12 acts as a novel target protein in mediating necroptosis and the related systemic inflammatory response syndrome triggered by TNF. The mechanistic study discovered that FKBP12 is essential for initiating necrosome formation and RIPK1-RIPK3-MLKL signaling pathway activation in response to TNF receptor 1 ligation. In addition, FKBP12 is indispensable for RIPK1 and RIPK3 expression and subsequent spontaneous phosphorylation, which are essential processes for initial necrosome formation and necroptotic signal transduction; therefore, FKBP12 may target RIPK1 and RIPK3 to mediate necroptosis in vitro and in vivo Collectively, our data demonstrate that FKBP12 could be a potential therapeutic target for the clinical treatment of necroptosis-associated diseases.

Necrosome Formation and Necroptosis in Experimental Cholestasis.

Necroptosis is emerging as a critical pathogenic mechanism in several liver diseases, including cholestatic disorders. Necroptosis was recently described as a novel cell death subroutine, activated downstream of death receptor stimulation and dependent on receptor-interacting serine/threonine-protein kinase 3 activity and mixed lineage kinase domain-like oligomerization and translocation to cell membrane. Here, we describe a combination of methods to evaluate necroptosis triggering in in vitro and in vivo models of cholestasis. Particularly, we detail alternative protocols to isolate total and soluble/insoluble protein extracts from tissues and cell cultures, as well as in vitro receptor-interacting serine/threonine-protein kinase 3 kinase activity assays, and subsequent Western blot analysis.

TRADD Mediates RIPK1-Independent Necroptosis Induced by Tumor Necrosis Factor.

As a programmed necrotic cell death, necroptosis has the intrinsic initiators, including receptor-interacting serine/threonine-protein kinase 1 (RIPK1), RIPK3 and mixed-lineage kinase domain-like protein (MLKL), which combine to form necroptotic signaling pathway and mediate necroptosis induced by various necroptotic stimuli, such as tumor necrosis factor (TNF). Although chemical inhibition of RIPK1 blocks TNF-induced necroptosis, genetic elimination of RIPK1 does not suppress but facilitate necroptosis triggered by TNF. Moreover, RIPK3 has been reported to mediate the RIPK1-independent necroptosis, but the involved mechanism is unclear. In this study, we found that TRADD was essential for TNF-induced necroptosis in RIPK1-knockdown L929 and HT-22 cells. Mechanistic study demonstrated that TRADD bound RIPK3 to form new protein complex, which then promoted RIPK3 phosphorylation via facilitating RIPK3 oligomerization, leading to RIPK3-MLKL signaling pathway activation. Therefore, TRADD acted as a partner of RIPK3 to initiate necroptosis in RIPK1-knockdown L929 and HT-22 cells in response to TNF stimulation. In addition, TRADD was critical for the accumulation of reactive oxygen species (ROS), which contributed to RIPK1-independent necroptosis triggered by TNF. Collectively, our data demonstrate that TRADD acts as the new target protein for TNF-induced RIPK3 activation and the subsequent necroptosis in a RIPK1-independent manner.

NR6A1 promotes vascular smooth muscle cell apoptosis by up-regulating RIPK3 gene expression / 中国病理生理杂志

AIM:To determine the role of nuclear receptor subfamily 6,group A,member 1 (NR6A1) in vascular smooth muscle cell (VSMC) apoptosis.METHODS:NR6A1 protein was over-expressed in the VSMCs by infection of adenovirus.The effect of NR6A1 on the viability of VSMCs was measured by MTT assay.DAPI staining,TUNEL staining and caspase activity assay were conducted.DNA microarray was used to quickly screen the target genes of NR6A1.The effect of receptor-interacting serine/threonine-protein kinase 3 (RIPK3) silencing on NR6A1-induced apoptosis of the VSMCs was further analyzed.RESULTS:Adenovirus-mediated over-expression of NR6A1 induced the apoptosis of VSMCs.The RIPK3 gene expression was up-regulated by NR6A1 over-expression in the VSMCs.NR6A1-induced VSMC apoptosis was inhibited by RIPK3 silencing.CONCLUSION:NR6A1 promotes VSMC apoptosis by up-regulating the RIPK3 gene expression.

NR6A1 promotes vascular smooth muscle cell apoptosis by up-regulating RIPK3 gene expression / 中国病理生理杂志

AIM:To determine the role of nuclear receptor subfamily 6,group A,member 1 (NR6A1) in vascular smooth muscle cell (VSMC) apoptosis.METHODS:NR6A1 protein was over-expressed in the VSMCs by infection of adenovirus.The effect of NR6A1 on the viability of VSMCs was measured by MTT assay.DAPI staining,TUNEL staining and caspase activity assay were conducted.DNA microarray was used to quickly screen the target genes of NR6A1.The effect of receptor-interacting serine/threonine-protein kinase 3 (RIPK3) silencing on NR6A1-induced apoptosis of the VSMCs was further analyzed.RESULTS:Adenovirus-mediated over-expression of NR6A1 induced the apoptosis of VSMCs.The RIPK3 gene expression was up-regulated by NR6A1 over-expression in the VSMCs.NR6A1-induced VSMC apoptosis was inhibited by RIPK3 silencing.CONCLUSION:NR6A1 promotes VSMC apoptosis by up-regulating the RIPK3 gene expression.

Programmed necrosis and necroptosis signalling.

In recent years, the paradigm of cell death regulation has changed. Nowadays, not only apoptosis but also several forms of necrosis (e.g. necroptosis) are considered to be regulated. The central roles of receptor-interacting serine/threonine protein kinase1 (RIPK1), RIPK3, and mixed-lineage kinase domain-like protein, and the molecular signalling platforms in which these molecules participate, are being intensively studied. In particular, the role of RIPK1, being both a kinase and a scaffold molecule, in different cell death regulatory complexes is of great relevance for the field. This minireview aims to introduce the emerging and dynamic field of necroptosis to the reader, with a specific focus on intracellular signalling pathways involved in this process.

Reprint of Neutrophil cell surface receptors and their intracellular signal transduction pathways.

Neutrophils play a critical role in the host defense against bacterial and fungal infections, but their inappropriate activation also contributes to tissue damage during autoimmune and inflammatory diseases. Neutrophils express a large number of cell surface receptors for the recognition of pathogen invasion and the inflammatory environment. Those include G-protein-coupled chemokine and chemoattractant receptors, Fc-receptors, adhesion receptors such as selectins/selectin ligands and integrins, various cytokine receptors, as well as innate immune receptors such as Toll-like receptors and C-type lectins. The various cell surface receptors trigger very diverse signal transduction pathways including activation of heterotrimeric and monomeric G-proteins, receptor-induced and store-operated Ca(2+) signals, protein and lipid kinases, adapter proteins and cytoskeletal rearrangement. Here we provide an overview of the receptors involved in neutrophil activation and the intracellular signal transduction processes they trigger. This knowledge is crucial for understanding how neutrophils participate in antimicrobial host defense and inflammatory tissue damage and may also point to possible future targets of the pharmacological therapy of neutrophil-mediated autoimmune or inflammatory diseases.

Neutrophil cell surface receptors and their intracellular signal transduction pathways.

Neutrophils play a critical role in the host defense against bacterial and fungal infections, but their inappropriate activation also contributes to tissue damage during autoimmune and inflammatory diseases. Neutrophils express a large number of cell surface receptors for the recognition of pathogen invasion and the inflammatory environment. Those include G-protein-coupled chemokine and chemoattractant receptors, Fc-receptors, adhesion receptors such as selectins/selectin ligands and integrins, various cytokine receptors, as well as innate immune receptors such as Toll-like receptors and C-type lectins. The various cell surface receptors trigger very diverse signal transduction pathways including activation of heterotrimeric and monomeric G-proteins, receptor-induced and store-operated Ca(2+) signals, protein and lipid kinases, adapter proteins and cytoskeletal rearrangement. Here we provide an overview of the receptors involved in neutrophil activation and the intracellular signal transduction processes they trigger. This knowledge is crucial for understanding how neutrophils participate in antimicrobial host defense and inflammatory tissue damage and may also point to possible future targets of the pharmacological therapy of neutrophil-mediated autoimmune or inflammatory diseases.