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Background: Excessive chondrocyte death is a critical player in the process of osteoarthritis (OA). The present study was aimed to study the role of receptor-interacting serine/threonine kinase (RIP) 1-mediated signaling for programmed cell death in OA. Methods: In the present study, RIP1 protein expression was evaluated in mouse OA cartilage and cultured primary murine chondrocytes exposed to tumor necrosis factor-alpha (TNF-α). Protein expression involved in necroptosis and apoptosis and chondrocyte-derived extracellular matrix were examined. Inhibition of RIP1 was conducted using the RNAi technique and pharmacological inhibition. Western blot, immunohistochemistry, and immunofluorescence examination were applied. Results: The protein presence of RIP1, but not RIP3, was increased in the mouse OA tissue and cultured chondrocytes exposed to TNF-α. Knockdown of RIP1 increased protein expression of collagen II and sex-determining region Y-box transcription factor 9, and reduced protein expression of matrix metallopeptidases 13 and a disintegrin and metalloproteinase with thrombospondin motifs 5. Inhibition of RIP1 reduced the phosphorylated NF-κB signals, decreased cell apoptosis, and restored extracellular matrix expression in cultured chondrocytes. Both RNAi and pharmacological inhibition of RIP1 decelerated the progress of OA in mice. Conclusion: RIP1 regulates chondrocyte apoptosis through NF-κB signaling. Inhibition of RIP1 provides a novel therapeutic approach for OA therapy. [ABSTRACT FROM AUTHOR]

[Display omitted] • ASIC1 facilitates atherosclerosis via impeding lipophagy. • ASIC1 promotes RIP1 phosphorylation. • ASIC1-RIP1 interaction contributes to defective autophagy flux. • ASIC1/RIP1 facilitates lipid accumulation via inhibiting lipophagy. • ASIC1/RIP1 may be a novel target for atherosclerotic treatment. Atherosclerosis, a major contributor to cardiovascular disease, remains a significant health concern worldwide. While previous research has shown that acid-sensing ion channel 1 (ASIC1) impedes macrophage cholesterol efflux, its precise role in atherogenesis and the underlying mechanisms have remained elusive. This study aimed to investigate the role of ASIC1 in atherosclerosis and its underlying mechanisms. First, data from a single-cell RNA sequencing (scRNA-seq) database were used to explore the relationships between ASIC1 differential expression and lipophagy in human atherosclerotic lesions. Finally, we validated the role of ASIC1/RIP1 signaling in lipophagy in vivo (human and mice) and in vitro (RAW264.7 and HTP-1 cells). Our results demonstrated a significant increase in ASIC1 protein levels within CD68+ macrophages in both human aortic lesions and AopE-/- mouse lesion areas compared to nonlesion regions. Concurrently, there was a notable decrease in lipophagy, a crucial process for lipid metabolism. In vitro assays further elucidated that ASIC1 interaction with RIP1 (receptor-interacting protein 1) promoted the phosphorylation of RIP1 at serine 166 and transcription factor EB (TFEB) at serine 142, leading to disrupted lipophagy and increased lipid accumulation. Intriguingly, all these events were reversed upon ASIC1 deficiency and RIP1 inhibition. Furthermore, in ApoE-/- mouse models of atherosclerosis, silencing ASIC1 expression or inhibiting RIP1 activation not only significantly attenuated atherogenesis but also restored TFEB-mediated lipophagy in aortic tissues. This was evidenced by reduced TFEB Ser-142 phosphorylation, decreased LC3II and LAMP1 protein expression, increased numbers of lipophagosomes, and a decrease in lipid droplets. Our findings unveil the critical role of macrophage ASIC1 in interacting with RIP1 to inhibit lipophagy, thereby promoting atherogenesis. Targeting ASIC1 represents a promising therapeutic avenue for the treatment of atherosclerosis. [ABSTRACT FROM AUTHOR]

Introduction: Atherosclerosis, a major contributor to cardiovascular disease, remains a significant health concern worldwide. While previous research has shown that acid-sensing ion channel 1 (ASIC1) impedes macrophage cholesterol efflux, its precise role in atherogenesis and the underlying mechanisms have remained elusive. Objectives: This study aimed to investigate the role of ASIC1 in atherosclerosis and its underlying mechanisms. Methods: First, data from a single-cell RNA sequencing (scRNA-seq) database were used to explore the relationships between ASIC1 differential expression and lipophagy in human atherosclerotic lesions. Finally, we validated the role of ASIC1/RIP1 signaling in lipophagy in vivo (human and mice) and in vitro (RAW264.7 and HTP-1 cells). Result: Our results demonstrated a significant increase in ASIC1 protein levels within CD68+ macrophages in both human aortic lesions and AopE-/- mouse lesion areas compared to nonlesion regions. Concurrently, there was a notable decrease in lipophagy, a crucial process for lipid metabolism. In vitro assays further elucidated that ASIC1 interaction with RIP1 (receptor-interacting protein 1) promoted the phosphorylation of RIP1 at serine 166 and transcription factor EB (TFEB) at serine 142, leading to disrupted lipophagy and increased lipid accumulation. Intriguingly, all these events were reversed upon ASIC1 deficiency and RIP1 inhibition. Furthermore, in ApoE-/- mouse models of atherosclerosis, silencing ASIC1 expression or inhibiting RIP1 activation not only significantly attenuated atherogenesis but also restored TFEB-mediated lipophagy in aortic tissues. This was evidenced by reduced TFEB Ser-142 phosphorylation, decreased LC3II and LAMP1 protein expression, increased numbers of lipophagosomes, and a decrease in lipid droplets. Conclusion: Our findings unveil the critical role of macrophage ASIC1 in interacting with RIP1 to inhibit lipophagy, thereby promoting atherogenesis. Targeting ASIC1 represents a promising therapeutic avenue for the treatment of atherosclerosis.

BackgroundAs important enzymes regulating acetylation, histone deacetylases (HDACs) participate in a series of cell physiological process. However, the mechanisms responsible for individual HDAC family members in regulating innate immunity remained to be elucidated. Here we sought to reveal the mechanism of HDAC3 in regulating the inflammatory response of macrophages.MethodsRNAseq was done to detect the transcriptional influence of HDAC3 on macrophages. Kyoto Encyclopedia of Genes and Genomes was used to reveal the change of signaling pathways after HDAC3 knockout. CHIPseq was done to detect the deacetylation modification of HDAC3 on chromosome. Western blot, immunofluorescence, and real-time quantitative PCR were used to measure the change of genes and proteins' levels. Mice were intratracheal instillation with lipopolysaccharide or Pseudomonas aeruginosa to determine the influence of HDAC3 on inflammatory response in vivo.ResultsHDAC3-deficient macrophages had increased expression of cathepsins resulting from elevated histone acetylation. Over-expressed cathepsins such as cathepsin B (CTSB) caused remarkable degradation of receptor (TNFRSF)-interacting serine-threonine kinase 1 (RIP1), which reduced TNFα mediated NF-κB activation and inflammatory response. Consistently, mice with macrophage specific knockout of HDAC3 were impaired in inflammatory response and thereby susceptible to Pseudomonas aeruginosa infection.ConclusionHDAC3 was required for protecting RIP1 from degrading by CTSB in macrophages. Decreased RIP1 in HDAC3 knockout macrophages impaired TNFα mediated NF-κB activation. Our studies uncovered important roles of HDAC3 in the regulation of cathepsin-mediated lysosomal degradation and RIP1-mediated inflammatory response in macrophages as well as in host defense against bacterial infection.

Necroptosis, a form of necrosis, and alterations in mitochondrial dynamics, a coordinated process of mitochondrial fission and fusion, have been implicated in the pathogenesis of cardiovascular diseases. This study aimed to determine the role of mitochondrial morphology in canonical necroptosis induced by a combination of TNFα and zVAD (TNF/zVAD) in H9c2 cells, rat cardiomyoblasts. Time-course analyses of mitochondrial morphology showed that mitochondria were initially shortened after the addition of TNF/zVAD and then their length was restored, and the proportion of cells with elongated mitochondria at 12 h was larger in TNF/zVAD-treated cells than in non-treated cells (16.3 ± 0.9% vs. 8.0 ± 1.2%). The knockdown of dynamin-related protein 1 (Drp1) and fission 1, fission promoters, and treatment with Mdivi-1, a Drp-1 inhibitor, had no effect on TNF/zVAD-induced necroptosis. In contrast, TNF/zVAD-induced necroptosis was attenuated by the knockdown of mitofusin 1/2 (Mfn1/2) and optic atrophy-1 (Opa1), proteins that are indispensable for mitochondrial fusion, and the attenuation of necroptosis was not canceled by treatment with Mdivi-1. The expression of TGFβ-activated kinase (TAK1), a negative regulator of RIP1 activity, was upregulated and the TNF/zVAD-induced RIP1-Ser166 phosphorylation, an index of RIP1 activity, was mitigated by the knockdown of Mfn1/2 or Opa1. Pharmacological TAK1 inhibition attenuated the protection afforded by Mfn1/2 and Opa1 knockdown. In conclusion, the inhibition of mitochondrial fusion increases TAK1 expression, leading to the attenuation of canonical necroptosis through the suppression of RIP1 activity. [ABSTRACT FROM AUTHOR]

Claudin‐6 (CLDN6) has been extensively studied in different tumors to date. However, in the case of nonsmall cell lung cancer (NSCLC), CLDN6 has a largely unknown role and molecular mechanism. We detected the expression of CLDN6 in NSCLC tissues and cells using reverse transcription‐quantitative polymerase chain reaction (PCR) and western blot assays. A gain‐of‐function experiment was performed to evaluate the biological effects of CLDN6 on NSCLC cell behaviors. Methylation‐specific PCR was utilized to detect the DNA methylation of CLDN6 gene promoter region. The interaction of CLDN6 and receptor interacting protein 1 (RIP1) was determined by coimmunoprecipitation assay. Furthermore, the modulation of CLDN6 on RIP1/apoptosis signal‐regulating kinase 1 (ASK1)/c‐Jun N‐terminal kinase (JNK) axis was confirmed. The results showed that in NSCLC tissues and cells, CLDN6 expression level was declined, and was associated with a high level of DNA methylation. CLDN6 overexpression suppressed the viability, invasion, migration, and promoted cell apoptosis. Besides, the enhanced expression of CLDN6 reduced the glycolysis and the dysfunction of mitochondrial respiration of NSCLC cells. Mechanistic investigation confirmed that CLDN6 interacted with RIP1 and inhibited cellular biological function of NSCLC cells via RIP1/ASK1/JNK axis. Besides, CLDN6 overexpression inhibited tumor growth in vivo. In conclusion, CLDN6 inhibited NSCLC cell proliferation through inactivating aerobic glycolysis via the RIP1/ASK1/JNK axis. Highlight: Low expression of CLDN6 and was associated with a high level of DNA methylation in NSCLC tissues and cell lines.CLDN6 interacted with RIP1 and inhibited promoted RIP1 expression.CLDN6 inhibited progression of NSCLC cells by inactivating aerobic glycolysis via the RIP1/ASK1/JNK axis. [ABSTRACT FROM AUTHOR]

The regulation of various types of cell death may help to restore the normal physiological function of cells and play a protective role in sepsis. In the current study, we explore the role of programmed cell necrosis in sepsis and the underlying mechanisms. The septic rat model is established by Cecal-ligation and perforation (CLP), and the in vitro model is established by LPS in IEC-6 cells. Our results demonstrate that receptor-interacting protein 1 (RIP1) is significantly upregulated in the ileum of septic rats and LPS-treated IEC-6 cells at both the mRNA and protein levels. Nec-1, an inhibitor of RIP1, reduces the protein levels of RIP1, p-RIP3, and phosphorylated mixed-lineage kinase domain-like (MLKL) (serine 358) and relieves intestinal injury in CLP-induced septic rats with decreased IL-6 and TNF-α levels. The in vitro experiments further reveal that LPS induces the colocalization of RIP1 and RIP3, resulting in the phosphorylation and translocation of MLKL to the plasma membrane in IEC-6 cells. LPS also facilitates ROS production in IEC-6 cells, but this effect is further reversed by Nec-1, si-RIP1 and si-RIP3. Furthermore, LPS-induced necrosis in IEC-6 cells is counteracted by NAC. Thus, we conclude that RIP1/RIP3-dependent programmed cell necrosis participates in intestinal injury in sepsis and may be associated with RIP1/RIP3-mediated ROS.

In mammals, the most remarkable T cell variations with aging are the shrinking of the naïve T cell pool and the enlargement of the memory T cell pool, which are partially caused by thymic involution. However, the mechanism underlying the relationship between T‐cell changes and aging remains unclear. In this study, we find that T‐cell‐specific Rip1 KO mice show similar age‐related T cell changes and exhibit signs of accelerated aging‐like phenotypes, including inflammation, multiple age‐related diseases, and a shorter lifespan. Mechanistically, Rip1‐deficient T cells undergo excessive apoptosis and promote chronic inflammation. Consistent with this, blocking apoptosis by co‐deletion of Fadd in Rip1‐deficient T cells significantly rescues lymphopenia, the imbalance between naïve and memory T cells, and aging‐like phenotypes, and prolongs life span in T‐cell‐specific Rip1 KO mice. These results suggest that the reduction and hyperactivation of T cells can have a significant impact on organismal health and lifespan, underscoring the importance of maintaining T cell homeostasis for healthy aging and prevention or treatment of age‐related diseases. Synopsis: T‐cell specific Rip1 KO mice show signs of accelerated aging‐like phenotypes, along with premature death. Blocking apoptosis by co‐deleting Fadd in Rip1tKO mice significantly rescues aging‐like phenotypes and prolongs shortened lifespan.Rip1tKO mice show similar age‐related T cell changes and exhibit signs of accelerated aging and a shorter lifespan.Rip1‐deficient T cells undergo excessive apoptosis, promoting chronic inflammation.Blocking necroptosis has little effect on the multimorbidity and premature aging seen in Rip1tKO mice.Blocking T cell apoptosis by co‐deleting Fadd rescues premature aging and multimorbidity in Rip1tKO mice. [ABSTRACT FROM AUTHOR]

Intracerebral hemorrhage (ICH) is a lethal stroke with high mortality or disability. However, effective therapy for ICH damage is generally lacking. Previous investigations have suggested that lysosomal protein transmembrane 5 (LAPTM5) is involved in various pathological processes, including autophagy, apoptosis, and inflammation. In this study, we aimed to identify the expression and functions of LAPTM5 in collagenase-induced ICH mouse models and hemoglobin-induced cell models. We found that LAPTM5 was highly expressed in brain tissues around the hematoma, and double immunostaining studies showed that LAPTM5 was co-expressed with microglia cells, neurons, and astrocytes. Following ICH, the mice presented increased brain edema, blood-brain barrier permeability, and neurological deficits, while pathological symptoms were alleviated after the LAPTM5 knockdown. Adeno-associated virus 9-mediated downregulation of LAPTM5 also improves ICH-induced secondary cerebral damage, including neuronal degeneration, the polarization of M1-like microglia, and inflammatory cascades. Furthermore, LAPTM5 promoted activation of the nuclear factor kappa-B (NF-κB) pathway in response to neuroinflammation. Further investigations indicated that brain injury improved by LAPTM5 knockdown was further exacerbated after the overexpression of receptor-interacting protein kinase 1 (RIP1), which is revealed to trigger the NF-κB pathway. In vitro experiments demonstrated that LAPTM5 silencing inhibited hemoglobin-induced cell function and confirmed regulation between RIP1 and LAPTM5. In conclusion, the present study indicates that LAPTM5 may act as a positive regulator in the context of ICH by modulating the RIP1/NF-κB pathway. Thus, it may be a candidate gene for further study of molecular or therapeutic targets. [ABSTRACT FROM AUTHOR]

Accumulating evidence suggests that necroptosis of cardiomyocytes contributes to cardiovascular diseases. Lethal disruption of the plasma membrane in necroptosis is induced by oligomers of mixed lineage kinase domain-like (MLKL) that is translocated to the membrane from the cytosol. However, the role played by cytoplasmic-nuclear shuttling of MLKL is unclear. Here, we tested the hypothesis that translocation of MLKL to the nucleus promotes the necroptosis of cardiomyocytes. Activation of the canonical necroptotic signaling pathway by a combination of TNF-α and zVAD (TNF/zVAD) increased nuclear MLKL levels in a RIP1-activity-dependent manner in H9c2 cells, a rat cardiomyoblast cell line. By use of site-directed mutagenesis, we found a nuclear export signal sequence in MLKL and prepared its mutant (MLKL-L280/283/284A), though a search for a nuclear import signal was unsuccessful. MLKL-L280/283/284A localized to both the cytosol and the nucleus. Expression of MLKL-L280/283/284A induced necroptotic cell death, which was attenuated by GppNHp, an inhibitor of Ran-mediated nuclear import, but not by inhibition of RIP1 activity or knockdown of RIP3 expression. GppNHp partly suppressed H9c2 cell death induced by TNF/zVAD treatment. These results suggest that MLKL that is translocated to the nucleus via RIP1-mediated necroptotic signaling enhances the necroptosis of cardiomyocytes through a RIP1-/RIP3-independent mechanism.

Smac mimetics are a group of compounds able to facilitate cell death in cancer cells. TNF-related apoptosis-inducing ligand (TRAIL) is a death receptor ligand currently explored in combination with Smac mimetics. The molecular mechanisms determining if the combination treatment results in apoptosis are however not fully understood. In this study, we aimed to shed light on these mechanisms in breast cancer cells. Three breast cancer cell lines, MDA-MB-468, CAMA-1 and MCF-7, were used to evaluate the effects of Smac mimetic LCL-161 and TRAIL using cell death assays and Western blot. The combination treatment induces apoptosis and caspase-8 cleavage in MDA-MB-468 and CAMA-1 but not in MCF-7 cells and downregulation of caspase-8 blocked apoptosis. Downregulation, but not kinase inhibition, of receptor-interacting protein 1 (RIP1) suppressed apoptosis in CAMA-1. Apoptosis is preceded by association of RIP1 with caspase-8. Downregulating cellular FLICE-like inhibitory protein (c-FLIP) resulted in increased caspase cleavage and some induction of apoptosis by TRAIL and LCL-161 in MCF-7. In CAMA-1, c-FLIP depletion potentiated TRAIL-induced caspase cleavage and LCL-161 did not increase it further. Our results lend further support to a model where LCL-161 enables the formation of a complex including RIP1 and caspase-8 and circumvents c-FLIP-mediated inhibition of caspase activation.

Apoptosis and necroptosis overlap in their initial signaling but diverge to produce non-inflammatory and pro-inflammatory outcomes, respectively. High glucose pushes signaling in favor of necroptosis producing a hyperglycemic shift from apoptosis to necroptosis. This shift depends on receptor-interacting protein 1 (RIP1) and mitochondrial reactive oxygen species (ROS). Here, we show that RIP1, mixed lineage kinase domain-like (MLKL) protein, Bcl-2 agonist/killer (Bak), Bcl-2 associated x (Bax) protein, and dynamin-related protein 1 (Drp1) traffic to the mitochondria in high glucose. RIP1 and MLKL appear in the mitochondria in their activated, phosphorylated states while Drp1 appears in its activated, dephosphorylated state in high glucose. Mitochondrial trafficking is prevented in rip1 KO cells and upon treatment with N-acetylcysteine. Induction of ROS replicated the mitochondrial trafficking seen in high glucose. MLKL forms high MW oligomers in the outer and inner mitochondrial membranes while Bak and Bax form high MW oligomers in the outer mitochondrial membrane in high glucose, suggesting pore formation. MLKL, Bax, and Drp1 promoted cytochrome c release from the mitochondria as well as a decrease in mitochondrial membrane potential in high glucose. These results indicate that mitochondrial trafficking of RIP1, MLKL, Bak, Bax, and Drp1 are key events in the hyperglycemic shift from apoptosis to necroptosis. This is also the first report to show oligomerization of MLKL in the inner and outer mitochondrial membranes and dependence of mitochondrial permeability on MLKL. [ABSTRACT FROM AUTHOR]

Cancer-derived small extracellular vesicles (sEVs) serve as critical mediators of cell-to-cell communication. Manzamine A (MA), a unique marine-derived alkaloid with various bioactivities, exerts anticancer effects against several kinds of tumors, but it remains unclear whether it has the same activity against breast cancer. Here, we proved that MA inhibits MDA-MB-231 and MCF-7 cell proliferation, migration, and invasion in a time- and dose-dependent manner. In addition, MA promotes autophagosome formation but suppresses autophagosome degradation in breast cancer cells. Importantly, we also found that MA stimulates sEVs secretion and increases autophagy-related protein accumulation in secreted sEVs, further potentiated by autophagy inhibitor chloroquine (CQ). Mechanistically, MA decreases the expression level of RIP1, the key upstream regulator of the autophagic pathway, and reduces the acidity of lysosome. Overexpression of RIP1 activated AKT/mTOR signaling, thus attenuating MA-induced autophagy and the corresponding secretion of autophagy-associated sEVs. Collectively, these data suggested that MA is a potential inhibitor of autophagy by preventing autophagosome turnover, and RIP1 mediates MA-induced secretory autophagy, which may be efficacious for breast cancer treatment. [ABSTRACT FROM AUTHOR]

Abstract Background As important enzymes regulating acetylation, histone deacetylases (HDACs) participate in a series of cell physiological process. However, the mechanisms responsible for individual HDAC family members in regulating innate immunity remained to be elucidated. Here we sought to reveal the mechanism of HDAC3 in regulating the inflammatory response of macrophages. Methods RNAseq was done to detect the transcriptional influence of HDAC3 on macrophages. Kyoto Encyclopedia of Genes and Genomes was used to reveal the change of signaling pathways after HDAC3 knockout. CHIPseq was done to detect the deacetylation modification of HDAC3 on chromosome. Western blot, immunofluorescence, and real-time quantitative PCR were used to measure the change of genes and proteins’ levels. Mice were intratracheal instillation with lipopolysaccharide or Pseudomonas aeruginosa to determine the influence of HDAC3 on inflammatory response in vivo. Results HDAC3-deficient macrophages had increased expression of cathepsins resulting from elevated histone acetylation. Over-expressed cathepsins such as cathepsin B (CTSB) caused remarkable degradation of receptor (TNFRSF)-interacting serine-threonine kinase 1 (RIP1), which reduced TNFα mediated NF-κB activation and inflammatory response. Consistently, mice with macrophage specific knockout of HDAC3 were impaired in inflammatory response and thereby susceptible to Pseudomonas aeruginosa infection. Conclusion HDAC3 was required for protecting RIP1 from degrading by CTSB in macrophages. Decreased RIP1 in HDAC3 knockout macrophages impaired TNFα mediated NF-κB activation. Our studies uncovered important roles of HDAC3 in the regulation of cathepsin-mediated lysosomal degradation and RIP1-mediated inflammatory response in macrophages as well as in host defense against bacterial infection.

Amyloid aggregates play a major role in diseases as well as in normal physiological function. Receptor-interacting protein kinases 1 and 3 (RIP1/RIP3) aggregates complexes in cellular necroptosis is one example of protein aggregation in normal cellular function. Although recently there have been several studies on full kinase proteins aggregation, the aggregation potential of small peptide sequences of RIP1/RIP3, the physicochemical properties, and the potential in biomedical applications have not been explored. Hence, in this paper, we study the aggregation propensity of peptides consisting of four and twelve amino acid sequences in the RHIM region of RIP1/RIP3 proteins that are known to drive the beta-sheet formation and the subsequent aggregation. The aggregation kinetics, physicochemical characterization, mechanosensitive properties, cellular effects, and potential as a cancer drug depot have been investigated. The results show that the number and concentration of amino acids play a role in amyloid-like aggregates' properties. Further, the aggregates when formulated with cisplatin-induced significant lung cancer cell toxicity compared to an equal amount of cisplatin with and without ultrasound. The study would serve as a platform for further investigation on RIP1/RIP3 peptide and protein aggregates, their role in multiple cellular functions and diseases, and their potential as drug depots. [ABSTRACT FROM AUTHOR]

Introduction: Retinoic acid-inducible gene 1 (RIG-1) and melanoma differentiation-associated protein 5 (MDA5) are the well-known cytoplasmic sensors that recognize microbial DNA or RNA and active down-stream molecules, including IFN-β promoter stimulator-1 (IPS-1) and receptor interacting protein 1 (RIP1). The roles played by the networked molecules on the infection with SARS-CoV-2 needs more investigations. Material and method: In this project MDA5, RIG-1, IPS-1 and RIP1 mRNA levels were evaluated in 45 hospitalized patients suffering from coronavirus disease of 2019 (COVID-19) and 45 healthy subjects using Real Time-qPCR technique. Result: The results showed significant decreased RIG-1 and IPS-1 in the SARS-CoV-2 infected patients when compared to healthy cases. MDA5 and RIP1 did not change when compared two groups. Male patients had similar expression of MDA5, RIG-1, IPS-1 and RIP1 when compared to female patients. Conclusion: Based on the results, it seems that RIG-1 and its signaling molecule, IPS-1, play key roles in the peripheral blood immune cells against SARS-CoV-2 and, their down-regulation may be induced by the virus to escape from immune responses. [ABSTRACT FROM AUTHOR]

• Necroptosis is involved in the regulation of apoptosis and autophagy. • Necroptosis plays a crucial role in the pathogenesis of intervertebral disc degeneration. • Necroptosis pathway is a potential therapeutic target in intervertebral disc degeneration. Intervertebral disc degeneration (IDD) is the leading cause of low back pain, which is one of the major factors leading to disability and severe economic burden. Necroptosis is an important form of programmed cell death (PCD), a highly regulated caspase-independent type of cell death that is regulated by receptor-interacting protein kinase 1 (RIPK1), RIPK3 and mixed lineage kinase domain-like protein (MLKL)-mediated, play a key role in the pathophysiology of various inflammatory, infectious and degenerative diseases. Recent studies have shown that necroptosis plays an important role in the occurrence and development of IDD. In this review, we provide an overview of the initiation and execution of necroptosis and explore in depth its potential mechanisms of action in IDD. The analysis focuses on the connection between NP cell necroptosis and mitochondrial dysfunction-oxidative stress pathway, inflammation, endoplasmic reticulum stress, apoptosis, and autophagy. Finally, we evaluated the possibility of treating IDD by inhibiting necroptosis, and believed that targeting necroptosis may be a new strategy to alleviate the symptoms of IDD. [ABSTRACT FROM AUTHOR]

Coumarin has a variety of biological activities and widely exists in plants. Biscoumarin, derived from coumarin, their synthetic methods and bioactivities of biscoumarins is the hotspot of the current research. In this study, we evaluated for the first time the anticancer of a synthetic biscoumarin (3,3'-(4-chlorophenyl)methylene)bis(4-hydroxy-2H-chromen-2-one, C3) on lung cancer cells and explored the related mechanism. C3 was simply prepared by 4-hydroxycoumarin and 4-chlorobenzaldehyde under ethanol. The structure of C3 was elucidated by various spectroscopic analyses. The antiproliferation effect of C3 was evaluated by the cell counting kit-8 assay. Cell cycle and apoptosis analysis were detected by flow cytometry. The expression of correlated proteins was determined using Western blotting. The result showed that C3 displayed a strong cytostatic effect on Lewis lung cancer (LLC) cells. C3 inhibited the proliferation of LLC cells, and induced G2/M phase cell cycle arrest. In addition, C3 possessed a significant reduction on cell apoptosis by increasing of RIP1 expression. Our data showed that C3 suppresses lung cancer cell proliferation and induces cell apoptosis, which is possibly involved with the RIP1.

Necrostatin-1, an inhibitor of necroptosis, can effectively inhibit necrotic apoptosis in neurological diseases, which results in the inhibition of inflammation, endoplasmic reticulum stress, and reactive oxygen species production and substantial improvement of neurological function. However, the effects of necrostatin-1 on intraventricular hemorrhage (IVH) remain unknown. In this study, we established a mouse model of IVH by injecting autologous blood into the lateral ventricle of the brain. We also injected necrostatin-1 into the lateral ventricle one hour prior to IVH induction. We found that necrostatin-1 effectively reduced the expression levels of the necroptosis markers receptor-interacting protein kinase (RIP)1, RIP3, mixed lineage kinase domain-like protein (MLKL), phosphorylated (p)-RIP3, and p-MLKL and the levels of interleukin-1β , interleukin-6, and tumor necrosis factor-α in the surrounding areas of the lateral ventricle. However, necrostatin-1 did not reduce ependymal ciliary injury or brain water content. These findings suggest that necrostatin-1 can prevent local inflammation and microglial activation induced by IVH but does not greatly improve prognosis.

Receptor-interacting protein (RIP) kinase 1 is involved in immune-mediated inflammatory diseases including ulcerative colitis (UC) by regulating necroptosis and inflammation. Our group previously identified TAK-632 (5) as an effective necroptosis inhibitor by dual-targeting RIP1 and RIP3. In this study, using ligand-based substituent-anchoring design strategy, we focused on the benzothiazole ring to obtain a series of TAK-632 analogues showing significantly improving on the anti-necroptosis activity and RIP1 selectivity over RIP3. Among them, a conformational constrained fluorine-substituted derivative (25) exhibited 333-fold selectivity for RIP1 (Kd = 15 nmol/L) than RIP3 (Kd > 5000 nmol/L). This compound showed highly potent activity against cell necroptosis (EC50 = 8 nmol/L) and systemic inflammatory response syndrome (SIRS) induced by TNF-α in vivo. Especially, it was able to exhibit remarkable anti-inflammatory treatment efficacy in a DSS-induced mouse model of UC. Taken together, the highly potent, selective, orally active anti-necroptosis inhibitor represents promising candidate for clinical treatment of UC.

Objective: Salidroside (SAL) is a marker glycoside of Rhodiola rosea with significant antioxidant, anti-inflammatory, and other health benefits. In this study, we determined its neuroprotective effects against Cd-induced toxicity in cultured cells and mice. Materials and methods: GL261 cell and Cd-intoxicated mouse model were used. ICP-MS and MWM were performed to measure Cd content and Cd-induced cognitive impairment in mice, respectively. Results: SAL attenuated Cd toxicity in GL261 cells as well as protected mice from substantial organic damage and cognitive deficits. SAL treatment alleviated Cd-induced oxidative stress, glial cell activation, and elevation of pro-inflammatory factors including TNF-α, IL-1β, and IL-6. Cd-induced cognitive deficits observed in the Morris water maze in mice were rescued by SAL. At the mechanistic level, SAL maintained the activity of antioxidant enzymes such as SOD and GSH-Px in the serum and brain, and scavenged the peroxidation product MDA, thereby restoring redox homeostasis in vivo, attenuating neuronal damage, and ultimately antagonized Cd-induced toxicity. Furthermore, Cd activated the RIP1-driven inflammatory signaling pathway and Notch/HES-1 signaling axis in the brain, leading to inflammation and neuronal loss, which could be attenuated by SAL. Conclusion: SAL is a natural product with good anti-Cd effects, indicating that Rhodiola rosea is promising plant that is worthy of cultivation for health and economic benefits. [ABSTRACT FROM AUTHOR]

The tuber of Coeloglossum viride var. bracteatum is a Tibetan medicine that has been used for generations as a tonic for Yang and Qi, tranquilizing, to enhance intelligence and to promote longevity. We have previously characterized the constituents of Coeloglossum viride var. bracteatum extract (CE) and investigated its anti-Alzheimer's disease (AD) effect in mice models. However, the exact role of CE in Parkinson's disease (PD), especially the neurotrophic and inflammatory pathways regulated by CE, remains unknown. In this study, we investigated the anti-PD effects of CE in an MPTP-induced acute mouse model and its underlying mechanisms, focusing on BDNF, FGF2 and their mediated signaling pathways and RIP1-driven inflammatory signaling axis. Pole test and traction test were performed for behavioral analysis. RT-PCR, IHC and Western blotting were performed to assay the mRNA, tissues, and protein, respectively. We found that CE improved dyskinesia in MPTP-intoxicated mice, which was confirmed by the pole test and traction test. Also, oxidative stress and astrocyte activation and inflammation were alleviated. MPTP-intoxication disrupted the levels of BDNF, FGF2 and their mediated signaling pathways, triggered elevation of pro-inflammatory factors such as TNF-α, IL-1β, and IL-6, and activated RIP1-driven inflammatory axis. However, CE restored the levels of BDNF, FGF2 and TrkB/Akt signaling pathways while inhibiting the RIP1-driven inflammatory signaling axis, thereby inhibiting apoptosis, preventing loss of nigrostriatal neurons, and maintaining cellular homeostasis. Thus, CE is a promising agent for the treatment of PD. [ABSTRACT FROM AUTHOR]

Receptor interacting protein 1 (RIP1) plays important roles not only in cell-death pathways but also in host innate immune responses. In the present study, a RIP1 ortholog named Lc-RIP1 was cloned and characterized in large yellow croaker (Larimichthys crocea). The open reading frame (ORF) of Lc-RIP1 is 2,046 bp, encoding a protein of 681 amino acids (aa), with an N-terminal kinase domain, an RHIM domain, and a C-terminal death domain. Subcellular localization analysis revealed that Lc -RIP1 was a cytosolic protein, which was broadly expressed in examined tissues/organs, and could be up-regulated under poly I:C, LPS, PGN, and Pseudomonas plecoglossicida stimulation in vivo based on qRT-PCR analysis. Notably, Lc -RIP1 could induce NF-κB, but not IRF3, IRF7 or type I IFN promoter activation. In addition, Lc -RIP1 overexpression could enhance Lc -MAVS, Lc -TRAF3, and Lc -TRAF6 mediated NF-κB promoter activation, and also Lc -TRIF and Lc -MAVS mediated IRF3 promoter activation, whereas suppress Lc -TRIF mediated NF-κB and type I IFN promoter activation, as well as Lc -TRAF3 and Lc -IRF3 mediated IRF3 promoter activation, Lc -IRF3 mediated type I IFN promoter activation and Lc -IRF7 mediated IRF7 promoter activation. These results collectively indicated that Lc -RIP1 function importantly in regulation of host innate immune signaling. • Lc-RIP1 can be induced by both viral and bacterial PAMPs stimulation. • Lc -RIP1 induces NF-κB, but not IRF3, IRF7 or type I IFN promoter activation. • Lc -RIP1 enhances MAVS, TRAF3, and TRAF6 mediated NF-κB activation, and also TRIF and MAVS mediated IRF3 activation. • Lc -RIP1 suppresses TRIF mediated NF-κB activation, and also TRAF3 and IRF3 mediated IRF3 activation. [ABSTRACT FROM AUTHOR]

The tuber of Coeloglossum viride var. bracteatum is a Tibetan medicine that has been used for generations as a tonic for Yang and Qi, tranquilizing, to enhance intelligence and to promote longevity. We have previously characterized the constituents of Coeloglossum viride var. bracteatum extract (CE) and investigated its anti-Alzheimer’s disease (AD) effect in mice models. However, the exact role of CE in Parkinson’s disease (PD), especially the neurotrophic and inflammatory pathways regulated by CE, remains unknown. In this study, we investigated the anti-PD effects of CE in an MPTP-induced acute mouse model and its underlying mechanisms, focusing on BDNF, FGF2 and their mediated signaling pathways and RIP1-driven inflammatory signaling axis. Pole test and traction test were performed for behavioral analysis. RT-PCR, IHC and Western blotting were performed to assay the mRNA, tissues, and protein, respectively. We found that CE improved dyskinesia in MPTP-intoxicated mice, which was confirmed by the pole test and traction test. Also, oxidative stress and astrocyte activation and inflammation were alleviated. MPTP-intoxication disrupted the levels of BDNF, FGF2 and their mediated signaling pathways, triggered elevation of pro-inflammatory factors such as TNF-α, IL-1β, and IL-6, and activated RIP1-driven inflammatory axis. However, CE restored the levels of BDNF, FGF2 and TrkB/Akt signaling pathways while inhibiting the RIP1-driven inflammatory signaling axis, thereby inhibiting apoptosis, preventing loss of nigrostriatal neurons, and maintaining cellular homeostasis. Thus, CE is a promising agent for the treatment of PD.

Abstract Titanium dioxide nanomaterials are applied in numerous fields due to their splendid physicochemical characteristics, which in turn poses a potential threat to human health. Recently, numerous in vivo studies have revealed that titanium dioxide nanoparticles (TNPs) can be transported into animal brains after exposure through various routes. Absorbed TNPs can accumulate in the brain and may disturb neuronal cells, leading to brain dysfunction. In vitro studies verified the neurotoxicity of TNPs. The mechanisms underlying the neurotoxicity of TNPs remains unclear. Whether necroptosis is involved in the neurotoxicity of TNPs is unknown. Therefore, we performed an in vitro study and found that TNPs induced inflammatory injury in SH-SY5Y cells in a dose-dependent way, which was mitigated by necrostatin-1 (Nec-1) pretreatment. Since receptor-interacting protein kinase 1 (RIP1) is reported to be the target of Nec-1, we silenced it by siRNA. We exposed mutant and wild-type cells to TNPs and assessed inflammatory injury. Silencing RIP1 expression inhibited inflammatory injury induced by TNPs exposure. Taken together, Nec-1 ameliorates the neurotoxicity of TNPs through RIP1. However, more studies should be performed to comprehensively assess the correlation between the neurotoxicity of TNPs and RIP1.

Hippocampal neurons undergo various forms of cell death after status epilepticus. Necrostatin-1 specifically inhibits necroptosis mediated by receptor interacting protein kinase 1 (RIP1) and RIP3 receptors. However, there are no reports of necroptosis in mouse models of status epilepticus. Therefore, in this study, we investigated the effects of necrostatin-1 on hippocampal neurons in mice with status epilepticus, and, furthermore, we tested different amounts of the compound to identify the optimal concentration for inhibiting necroptosis and apoptosis. A mouse model of status epilepticus was produced by intraperitoneal injection of kainic acid, 12 mg/kg. Different concentrations of necrostatin-1 (10, 20, 40, and 80 μM) were administered into the lateral ventricle 15 minutes before kainic acid injection. Hippocampal damage was assessed by hematoxylin-eosin staining 24 hours after the model was successfully produced. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining, western blot assay and immunohistochemistry were used to evaluate the expression of apoptosis-related and necroptosis-related proteins. Necrostatin-1 alleviated damage to hippocampal tissue in the mouse model of epilepsy. The 40 μM concentration of necrostatin-1 significantly decreased the number of apoptotic cells in the hippocampal CA1 region. Furthermore, necrostatin-1 significantly downregulated necroptosis-related proteins (MLKL, RIP1, and RIP3) and apoptosis-related proteins (cleaved-Caspase-3, Bax), and it upregulated the expression of anti-apoptotic protein Bcl-2. Taken together, our findings show that necrostatin-1 effectively inhibits necroptosis and apoptosis in mice with status epilepticus, with the 40 μM concentration of the compound having an optimal effect. The experiments were approved by the Animal Ethics Committee of Fujian Medical University, China (approval No. 2016-032) on November 9, 2016.

Cancer-derived small extracellular vesicles (sEVs) serve as critical mediators of cell-to-cell communication. Manzamine A (MA), a unique marine-derived alkaloid with various bioactivities, exerts anticancer effects against several kinds of tumors, but it remains unclear whether it has the same activity against breast cancer. Here, we proved that MA inhibits MDA-MB-231 and MCF-7 cell proliferation, migration, and invasion in a time- and dose-dependent manner. In addition, MA promotes autophagosome formation but suppresses autophagosome degradation in breast cancer cells. Importantly, we also found that MA stimulates sEVs secretion and increases autophagy-related protein accumulation in secreted sEVs, further potentiated by autophagy inhibitor chloroquine (CQ). Mechanistically, MA decreases the expression level of RIP1, the key upstream regulator of the autophagic pathway, and reduces the acidity of lysosome. Overexpression of RIP1 activated AKT/mTOR signaling, thus attenuating MA-induced autophagy and the corresponding secretion of autophagy-associated sEVs. Collectively, these data suggested that MA is a potential inhibitor of autophagy by preventing autophagosome turnover, and RIP1 mediates MA-induced secretory autophagy, which may be efficacious for breast cancer treatment.

Amyloid aggregates play a major role in diseases as well as in normal physiological function. Receptor-interacting protein kinases 1 and 3 (RIP1/RIP3) aggregates complexes in cellular necroptosis is one example of protein aggregation in normal cellular function. Although recently there have been several studies on full kinase proteins aggregation, the aggregation potential of small peptide sequences of RIP1/RIP3, the physicochemical properties, and the potential in biomedical applications have not been explored. Hence, in this paper, we study the aggregation propensity of peptides consisting of four and twelve amino acid sequences in the RHIM region of RIP1/RIP3 proteins that are known to drive the beta-sheet formation and the subsequent aggregation. The aggregation kinetics, physicochemical characterization, mechanosensitive properties, cellular effects, and potential as a cancer drug depot have been investigated. The results show that the number and concentration of amino acids play a role in amyloid-like aggregates’ properties. Further, the aggregates when formulated with cisplatin-induced significant lung cancer cell toxicity compared to an equal amount of cisplatin with and without ultrasound. The study would serve as a platform for further investigation on RIP1/RIP3 peptide and protein aggregates, their role in multiple cellular functions and diseases, and their potential as drug depots.

Hepatitis B virus X protein (HBx), encoded by the hepatitis B virus (HBV) genome, plays a pivotal in mediating pathogenicity in liver diseases. However, the underlying mechanisms are still needed to be elucidated. Receptor-interacting protein 1 (RIP1) has been identified as a serine/threonine kinase with various biological functions in cell fate, proliferation, and death. In the current study, we found that overexpression of HBx in LO2 human normal hepatocytes increased the expression of RIP1. Importantly, our results indicate that blockage of RIP1 using its specific antagonist necrostatin-1 (Nec-1) ameliorated HBx-induced oxidative stress by mitigating the production of ROS and Nox-4 expression. Also, the presence of Nec-1 improved HBx-induced mitochondrial dysfunction by increasing MMP. Importantly, we found that Nec-1 could inhibit the production of pro-inflammatory cytokines IL-6, IL-8, and CXCL2 as well as the secretion of HMGB1. Mechanistically, we found that Nec-1 treatment suppressed the activation of the JNK/AP-1 and NF-κB signalling pathways. Our findings implicated a novel biological function of RIP1 in HBx-induced cytotoxicity and inflammation in human normal hepatocytes. Antagonism of RIP1 might be a potential therapeutic approach for the treatment of HBV-associated liver diseases.

There remains a significant gap in our quantitative understanding of crosstalk between apoptosis and necroptosis pathways. By employing the SWATH-MS technique, we quantified absolute amounts of up to thousands of proteins in dynamic assembling/de-assembling of TNF signaling complexes. Combining SWATH-MS-based network modeling and experimental validation, we found that when RIP1 level is below ~1000 molecules/cell (mpc), the cell solely undergoes TRADD-dependent apoptosis. When RIP1 is above ~1000 mpc, pro-caspase-8 and RIP3 are recruited to necrosome respectively with linear and nonlinear dependence on RIP1 amount, which well explains the co-occurrence of apoptosis and necroptosis and the paradoxical observations that RIP1 is required for necroptosis but its increase down-regulates necroptosis. Higher amount of RIP1 (>~46,000 mpc) suppresses apoptosis, leading to necroptosis alone. The relation between RIP1 level and occurrence of necroptosis or total cell death is biphasic. Our study provides a resource for encoding the complexity of TNF signaling and a quantitative picture how distinct dynamic interplay among proteins function as basis sets in signaling complexes, enabling RIP1 to play diverse roles in governing cell fate decisions. [ABSTRACT FROM AUTHOR]

Many studies have investigated the role of receptor-interacting protein 1 (RIP1) kinase in acetaminophen (APAP) overdose-induced acute liver injury. However, the results were not consistent and there still remain controversies. Importantly, in these previous studies, the usage of DMSO to dissolve the RIP1 kinase inhibitor Nec-1, resulted in misleading conclusion. Our study aimed to determine the role of RIP1 kinase in APAP-induced liver injury, via genetically or pharmaceutically inhibition of RIP1 kinase activity. Our results indicated that APAP-induced liver injury was significantly attenuated in RIP1 kinase-dead (Rip1 K45A/K45A ) mice compared to WT control. High dosage of APAP-induced mortality was also rescued by RIP1 kinase inactivation. In agreement, RIP1 kinase inhibitor, Nec-1 which was formulated with PEG400, could efficiently alleviate APAP-induced hepatotoxicity. For the underlying mechanism, our results suggested that RIP1 kinase inactivation did not influence the hepatic GSH depletion, but significantly reduced the hepatic cell death and inflammation induced by APAP treatment. Using bone marrow transplantation model, we also demonstrated that it was RIP1 kinase activity in tissue-resident hepatic cells other than hematopoietic-derived cells mainly responsible for APAP-induced liver injury. Our study confirmed the important role of RIP1 kinase activity in APAP-induced acute liver failure. [Display omitted] • APAP-induced liver injury is significantly attenuated in RIP1 kinase-dead (Rip1 K45A/K45A ) mice. • APAP-induced liver injury is significantly attenuated by RIP1 kinase inhibitor Nec-1 dissolved in PEG400. • RIP1 kinase inactivation reduced the hepatic cell death and inflammation induced by APAP. [ABSTRACT FROM AUTHOR]

Receptor-interacting protein (RIP) kinase 1 is involved in immune-mediated inflammatory diseases including ulcerative colitis (UC) by regulating necroptosis and inflammation. Our group previously identified TAK-632 (5) as an effective necroptosis inhibitor by dual-targeting RIP1 and RIP3. In this study, using ligand-based substituent-anchoring design strategy, we focused on the benzothiazole ring to obtain a series of TAK-632 analogues showing significantly improving on the anti-necroptosis activity and RIP1 selectivity over RIP3. Among them, a conformational constrained fluorine-substituted derivative (25) exhibited 333-fold selectivity for RIP1 (K d = 15 nmol/L) than RIP3 (K d > 5000 nmol/L). This compound showed highly potent activity against cell necroptosis (EC 50 = 8 nmol/L) and systemic inflammatory response syndrome (SIRS) induced by TNF- α in vivo. Especially, it was able to exhibit remarkable anti-inflammatory treatment efficacy in a DSS-induced mouse model of UC. Taken together, the highly potent, selective, orally active anti-necroptosis inhibitor represents promising candidate for clinical treatment of UC. Ligand-based substituent-anchoring design led to a C-5-F-substituted benzothiazole 25 with different conformation of TAK-632 showed high RIP1 selectivity (K d = 15 nmol/L) over RIP3 (K d > 5000 nmol/L). It exhibited significant anti-necroptosis activity and anti-inflammatory therapeutic efficacy in a DSS-induced mouse model of ulcerative colitis. [Display omitted] [ABSTRACT FROM AUTHOR]

Inhibition of receptor-interacting protein kinase 1 (RIP1) has been recognized as a compelling tool for limiting necroptosis. Recent findings have indicated that RIP1 inhibitor, necrostatin-1 (Nec-1), is also able to modify heart function under non-cell death conditions. In this study, we investigated its underlying molecular mechanisms and compared with those of novel pharmacologically improved agents (Nec-1s and GSK'772) and its inactive analog (Nec-1i). Heart function was examined in Langendorff-perfused rat hearts. Certain proteins regulating myocardial contraction–relaxation cycle and oxidative stress (OS) were evaluated by immunoblotting and as the extent of lipid peroxidation, protein carbonylation and nitration, respectively. In spite of the increase of left ventricular developed pressure (LVDP) due to treatment by both Nec-1 and Nec-1i, only the former agent increased the phosphorylation of Ca2+/calmodulin-dependent protein kinase II delta (CaMKIIδ) at threonine 287 and cardiac myosin-binding protein-C (cMyBPc) at serine 282. In contrast, Nec-1s did not elicit such changes, while it also increased LVDP. GSK'772 activated CaMKIIδ-phospholamban (PLN) axis. Neither protein kinase A (PKA) nor its selected molecular targets, such as serine 16 phosphorylated PLN and sarco/endoplasmic reticulum Ca2+-ATPase 2a (SERCA2a), were affected by either RIP1 inhibitor. Nec-1, like other necrostatins (Nec-1i, Nec-1s), but not GSK'772, elevated protein tyrosine nitration without affecting other markers of OS. In conclusion, this study indicated for the first time that Nec-1 may affect basal heart function by the modulation of OS and activation of some proteins of contraction–relaxation cycle. [ABSTRACT FROM AUTHOR]

Background: The risk of contrast-induced nephropathy (CIN) is high in patients with chronic kidney disease (CKD). However, the mechanism of CIN in CKD is not fully understood. Here, we prepared a clinically relevant model of CIN and examined the role of necroptosis, which potentially cross-talks with autophagy, in CIN. Methods: In Sprague–Dawley rats, CKD was induced by subtotal nephrectomy (SNx, 5/6 nephrectomy) 4 weeks before induction of CIN. CIN was induced by administration of a contrast medium (CM), iohexol, following administration of indomethacin and N-omega-Nitro-l-arginine methyl ester. Renal function and tissue injuries were assessed 48 h after CM injection. Results: Serum creatinine (s-Cre) and BUN were increased from 0.28 ± 0.01 to 0.52 ± 0.02 mg/dl and from 15.1 ± 0.7 to 29.2 ± 1.2 mg/dl, respectively, after SNx alone. CM further increased s-Cre and BUN to 0.69 ± 0.03 and 37.2 ± 2.1, respectively. In the renal tissue after CM injection, protein levels of receptor-interacting serine/threonine-protein kinase (RIP) 1, RIP3, cleaved caspase 3, and caspase 8 were increased by 64 ~ 212%, while there was reduction in LC3-II and accumulation of p62. Necrostatin-1, an RIP1 inhibitor, administered before and 24 h after CM injection significantly suppressed elevation of s-Cre, BUN and urinary albumin levels, kidney injury molecule-1 expression and infiltration of CD68-positive macrophages in renal tissues after CM injection. Conclusion: The results suggest that necroptosis of proximal tubular cells contributes to CIN in CKD and that suppression of protective autophagy by pro-necroptotic signaling may also be involved. [ABSTRACT FROM AUTHOR]

Necroptosis is a programmed form of necrosis characterized by mitochondrial alterations and plasma membrane permeabilization resulting in the release of cytoplasmic content into extracellular space, and leading to inflammatory reactions. Besides its critical role in viral defense mechanisms and inflammatory diseases, necroptosis plays pivotal functions in the drug response of tumors, including prostate cancer. Necroptosis is mainly governed by kinase enzymes, including RIP1, RIP3, and MLKL, and conversely to apoptosis, is a caspase-independent mechanism of cell death. Numerous compounds induce necroptosis in prostate cancer models, including (i) compounds of natural origin, (ii) synthetic and semisynthetic small molecules, and (iii) selenium and selenium-based nanoparticles. Here, we overview the molecular mechanisms underlying necroptosis and discuss the possible implications of drugs inducing necroptosis for prostate cancer therapy.

Objective(s): Carbon tetrachloride (CCL4) toxicity triggers fibrosis, activating various mechanisms within the cell. We aimed to create damage with CCL4 and investigate the effectiveness of L-carnitine on the mechanisms we identified. Materials and Methods: Forty rats were divided into 5 groups with equal number of rats in each group. Group I: Control group, Group II: L-carnitine group, 200 mg/kg L-carnitine twice a week, Group III: CCL4 group, 0.2 ml/100 gr CCL4, IP, dissolved in olive oil 2 times a week during 6 weeks; Group IV: L-carnitine + CCL4 group, 200 mg/kg L-carnitine 24 hr before 0.2 ml/100 g CCL4 application twice a week; Group V: CCL4 + L-carnitine, 200 mg/kg L-carnitine half an hour after 0.2 ml/100 g CCL4 application. The liver was evaluated histologically. Immunohistochemically stained with a-SMA, iNOS, HSP90, HIF-1α, and RIP1. TNF-α, TGF-p, AST, ALT, ALP, and GGT measurements were evaluated. Results: In the classical lobule periphery, an increase in lipid accumulation and a decrease in glycogen accumulation were observed. After immunohistochemical measurements and biochemical analyzes, an increase in the expression density of all proteins was observed in group III. In group IV and V, an improvement in tissue and a decrease in protein expression densities were observed. Conclusion: iNOS serves as a free radical scavenger in response to damage caused by increased toxicity of a-SMA, HSP90, and HIF-1aα Especially, increased RIP1 level in the tissue indicates the presence of necrosis in the tissue after CCL4-toxicity. Supplementing the amount of endogenous L-carnitine with supplementation provides a significant improvement in the tissue. [ABSTRACT FROM AUTHOR]

Here, we demonstrate that interleukin-1β (IL-1β) contributes to the γ-ionizing radiation (IR)-induced increase of migration/invasion in A549 lung cancer cells, and that this occurs via RIP1 upregulation. We initially observed that the protein expression and secreted concentration of IL-1β were increased upon exposure of A549 cells to IR. We then demonstrated that IR-induced IL-1β is located downstream of the NF-κB–RIP1 signaling pathway. Treatments with siRNA and specific pharmaceutical inhibitors of RIP1 and NF-κB suppressed the IR-induced increases in the protein expression and secreted concentration of IL-1β. IL-1Ra, an antagonist of IL-1β, treatment suppressed the IR-induced epithelial-mesenchymal transition (EMT) and IR-induced invasion/migration in vitro. These results suggest that IL-1β could regulate IR-induced EMT. We also found that IR could induce the expression of IL-1β expression in vivo and that of IL-1 receptor (R) I/II in vitro and in vivo. The IR-induced increases in the protein levels of IL-1 RI/II and IL-1β suggest that an autocrine loop between IL-1β and IL-1 RI/II might play important roles in IR-induced EMT and migration/invasion. Based on these collective results, we propose that IR concomitantly activates NF-κB and RIP1 to trigger the NF-κB–RIP1–IL-1β–IL-1RI/II–EMT pathway, ultimately promoting metastasis. • We found γ-ionizing radiation (IR) induces IL-1β expression and secretion. • NF-κB and RIP1 regulate the IR-induced upregulation and secretion of IL-1β. • IR-induced IL-1β promotes cancer cell migration and invasion via EMT induction. • IR induces expressions of IL-1β and its receptors, IL-1RI/II, in vitro and in vivo. • We validated new signaling pathway: IR–RIP1–NF-κB–IL-1β–IL-1β receptor I/II–EMT signaling. [ABSTRACT FROM AUTHOR]

Necroptosis is a type of programmed necrosis which depends on the activation of receptor-interacting protein kinase 3 (RIP3). Herpes simplex virus type 1 (HSV-1) is known to block necroptosis by the viral protein ICP6 in human cells, but its specific inhibitory mechanism is not fully understood. Here we reported that ICP6 could promote rather than suppress the formation of necrosome, the necroptosis signaling complex containing RIP3 and upstream regulator receptor-interacting protein kinase 1 (RIP1), but blocked RIP3 activation. Moreover, ICP6 could reduce the necroptosis-specific auto-phosphorylation of RIP1 regardless of the presence of RIP3. These results indicate that ICP6 block necroptosis through preventing RIP1 activation dependent signal transduction in necrosome.

Receptor interacting protein 1 (RIP1) is an essential sensor of cellular stress, which may respond to apoptosis or cell survival and participate in antiviral pathways. To investigate the roles of fish RIP1 in Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV) infection, a RIP1 homolog from orange-spotted grouper (Epinephelus coioides) (EcRIP1) was cloned and characterized. EcRIP1 encoded a 679 amino acid protein that shares 83.28% identity with that of Perca flavescens and contained a homologous N-terminal kinase (S-TKc) domain, a RIP isotype interaction motif (RHIM), and a C-terminal domain (DD). EcRIP1 was predominantly detected in immune tissues, and its expression was induced by RGNNV or SGIV infection in vitro. Subcellular localization showed that EcRIP1 was distributed in the cytoplasm with point-like uniform and dot-like aggregation forms. Overexpression of EcRIP1 inhibited SGIV and RGNNV replication and positively regulated the expression levels of interferon (IFN) and IFN-stimulated genes and pro-inflammatory factors. EcRIP1 may interact with grouper tumor necrosis factor receptor type 1-associated DEATH domain protein (EcTRADD) to promote SGIV-induced apoptosis, and interact with grouper Toll/interleukin-1 receptor (TIR) domain containing adapter inducing interferon-β (EcTRIF) and participate in Myeloid Differentiation Factor 88 (MyD88)-independent toll-like receptor (TLR) signaling. EcRIP1 may also interact with grouper tumor necrosis factor receptor-associated factors (TRAFs) as intracellular linker proteins and mediate the signaling of various downstream signaling pathways, including NF-κB and IFN. These results suggest that EcRIP1 may inhibit SGIV and RGNNV infection by regulating apoptosis and various signaling molecules. Our study offers new insights into the regulatory mechanism of RIP1-related signaling, and provides a novel perspective on fish diseases mediated by RIP1.

Xingfen Su,1 Handong Wang,2 Yuanxiang Lin,1 Fuxiang Chen1 1Department of Neurosurgery, The First Affiliated Hospital of Fujian Medical University, Fuzhou 350005, Fujian, People’s Republic of China; 2Department of Neurosurgery, Jinling Hospital, School of Medicine, Nanjing University, Nanjing 210002, Jiangsu, People’s Republic of China Background: Intracerebral hemorrhage (ICH) is a devastating neurological injury associated with significant mortality. Necroptosis is a newly identified type of programmed necrosis initiated by the activation of tumor necrosis factor alpha. Evidences had demonstrated the importance of necroptosis in neuronal cell death. Necrostatin-1 is a specific inhibitor of necroptosis. The present study was carried out to explore whether RIP1/RIP3 pathways participate in hemin induced cell death in HT-22 hippocampal neuronal cells and investigate the potential neuroprotection of necrostatin-1 in hemin induced cell death in HT-22. Methods: First, different concentrations of hemin (0, 25, 50, 100 µmol/L) were added to HT-22 cells. Propidium iodide (PI) positive cells and cell viability were measured at 24 hours after hemin treatment. Then, necrostatin-1, pan-caspase inhibitor Benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone (z-VAD-fmk) and reactive oxygen species (ROS) scavenger butylated hydroxyanisole (BHA) were applied to hemin-treated HT-22 cells. PI positive cells and cell viability were measured at 24 hours after hemin treatment. MitoSox Red was used to indicate ROS level. Last, the effect of RIP3 in hemin induced HT-22 cell death was explored through RIP3 knockdown using siRNA. PI positive cells, cell viability and ROS lever were measured at 24 h after hemin treatment. Results: Hemin could induce a dose dependent cell death in HT22 neural cells. RIP1 specific inhibitor necrostatin-1 significantly inhibited cell death induced by hemin in HT-22 cells, greatly reducing PI positive cells, dramatically improving cell viability and decreasing ROS accumulation. BHA could significantly inhibit PI positive cells induced by hemin in HT-22 cells. Furthermore, silencing of RIP3 using siRNA attenuated hemin induced cell death in HT-22 cells, greatly reducing PI positive cells, dramatically improving cell viability and decreasing ROS accumulation. Conclusion: These data revealed that RIP1/RIP3 might mediate hemin induced cell death in HT-22 cells, and necrostatin-1 played a neuroprotection role in hemin induced cell death in HT-22. RIP1 and RIP3 might represent novel therapeutic targets for ICH. Keywords: intracerebral hemorrhage, necroptosis, HT22, RIP1, RIP3, necrostatin-1

Receptor interacting protein 1 (RIP1) is an essential sensor of cellular stress, which may respond to apoptosis or cell survival and participate in antiviral pathways. To investigate the roles of fish RIP1 in Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV) infection, a RIP1 homolog from orange-spotted grouper (Epinephelus coioides) (EcRIP1) was cloned and characterized. EcRIP1 encoded a 679 amino acid protein that shares 83.28% identity with that of Perca flavescens and contained a homologous N-terminal kinase (S-TKc) domain, a RIP isotype interaction motif (RHIM), and a C-terminal domain (DD). EcRIP1 was predominantly detected in immune tissues, and its expression was induced by RGNNV or SGIV infection in vitro. Subcellular localization showed that EcRIP1 was distributed in the cytoplasm with point-like uniform and dot-like aggregation forms. Overexpression of EcRIP1 inhibited SGIV and RGNNV replication and positively regulated the expression levels of interferon (IFN) and IFN-stimulated genes and pro-inflammatory factors. EcRIP1 may interact with grouper tumor necrosis factor receptor type 1-associated DEATH domain protein (EcTRADD) to promote SGIV-induced apoptosis, and interact with grouper Toll/interleukin-1 receptor (TIR) domain containing adapter inducing interferon-β (EcTRIF) and participate in Myeloid Differentiation Factor 88 (MyD88)-independent toll-like receptor (TLR) signaling. EcRIP1 may also interact with grouper tumor necrosis factor receptor-associated factors (TRAFs) as intracellular linker proteins and mediate the signaling of various downstream signaling pathways, including NF-κB and IFN. These results suggest that EcRIP1 may inhibit SGIV and RGNNV infection by regulating apoptosis and various signaling molecules. Our study offers new insights into the regulatory mechanism of RIP1-related signaling, and provides a novel perspective on fish diseases mediated by RIP1. [ABSTRACT FROM AUTHOR]

Receptor interacting protein kinase 1 (RIP1) is a critical effector of inflammatory responses and cell death activation. Cell death pathways regulated by RIP1 include caspase‐dependent apoptosis and caspase‐independent necroptosis. The kinase activity of RIP1 has been associated with a number of inflammatory, neurodegenerative, and oncogenic diseases. In this study, we use the RIP1 kinase inhibitor GNE684 to demonstrate that RIP1 inhibition can effectively block skin inflammation and immune cell infiltrates in livers of Sharpin mutant (Cpdm; chronic proliferative dermatitis) mice in an interventional setting, after disease onset. On the other hand, genetic inactivation of RIP1 (RIP1 KD) or ablation of RIP3 (RIP3 KO) or MLKL (MLKL KO) did not affect testicular pathology of aging male mice. Likewise, infection with vaccinia virus or with mouse gammaherpesvirus MHV68 resulted in similar viral clearance in wild‐type, RIP1 KD, and RIP3 KO mice. In summary, this study highlights the benefits of inhibiting RIP1 in skin inflammation, as opposed to its lack of relevance for testicular longevity and the response to certain viral infections. [ABSTRACT FROM AUTHOR]

Background: Breast cancer remains a great threat to females worldwide. As a recently defined programmed cell death pathway that associates with immune activation, RIP1/RIP3/MLKL necroptosis signaling has been implicated in a variety of diseases. The present study aimed to investigate the role of RIP1/RIP3/MLKL signaling in breast cancer cell proliferation and metastasis in vivo and in vitro. Methods: Western blot and quantitative real-time PCR were performed to evaluate the activation of necroptosis signaling in clinical human breast cancer tissues. Correlation of necroptosis signaling markers with clinicopathological parameters was statistically assessed. Cell viability assay, colony formation assay, wound healing assay, and transwell migration and invasion assays were performed to investigate the effects of necroptosis inhibition on breast cancer cell proliferation and metastasis. Results: Clinical breast cancer tissues showed significantly higher levels of tumor necrosis factor alpha (TNFα), RIP1, RIP3 and MLKL at both mRNA and protein levels as compared with their paired non-cancerous tissues. Phosphorylation of RIP3 and MLKL was also remarkably provoked. Statistics showed that both RIP1 and MLKL positively correlated with cancer parameters such as N-cadherin (p=0.002 for RIP1 and p=0.021 for MLKL) and Ki67 (p=0.031 for RIP1 and p=0.05 for MLKL). The MLKL expression level significantly correlated with tumor size (p=0.001) and the proliferation indicator Ki67 (p=0.018). In addition, pharmacological inhibition of the necroptosis signaling using necrostatin-1 promoted breast cancer cell proliferation and colony formation by approximately 50%. Blockade of necroptosis signaling also accelerated wound healing process and cell transmigration in breast cancer cells. Conclusion: Our results suggested that pharmacological inhibition of necroptosis promoted breast cancer cell proliferation and metastasis. Modulation of tumor cell necroptosis might represent a novel strategy as to breast cancer treatment. [ABSTRACT FROM AUTHOR]

Titanium dioxide nanomaterials are applied in numerous fields due to their splendid physicochemical characteristics, which in turn poses a potential threat to human health. Recently, numerous in vivo studies have revealed that titanium dioxide nanoparticles (TNPs) can be transported into animal brains after exposure through various routes. Absorbed TNPs can accumulate in the brain and may disturb neuronal cells, leading to brain dysfunction. In vitro studies verified the neurotoxicity of TNPs. The mechanisms underlying the neurotoxicity of TNPs remains unclear. Whether necroptosis is involved in the neurotoxicity of TNPs is unknown. Therefore, we performed an in vitro study and found that TNPs induced inflammatory injury in SH-SY5Y cells in a dose-dependent way, which was mitigated by necrostatin-1 (Nec-1) pretreatment. Since receptor-interacting protein kinase 1 (RIP1) is reported to be the target of Nec-1, we silenced it by siRNA. We exposed mutant and wild-type cells to TNPs and assessed inflammatory injury. Silencing RIP1 expression inhibited inflammatory injury induced by TNPs exposure. Taken together, Nec-1 ameliorates the neurotoxicity of TNPs through RIP1. However, more studies should be performed to comprehensively assess the correlation between the neurotoxicity of TNPs and RIP1. [ABSTRACT FROM AUTHOR]

Objective and design: Sepsis, a systemic inflammatory response syndrome, is still a common cause of death even the patients who are in the intensive care unit. Alleviating septic liver damage may be effective in improving sepsis. Necroptosis and miRNAs have been regarded as a potential target in sepsis. Material or subjects: The aim of this work is to explain the potential role of miR-425-5p in septic liver damage. LPS was intraperitoneal-injection to C57BL/6 mice for sepsis, and hepatocytes treated with septic serum in vitro. H&E staining for histological evaluation, luciferase reporter assay for target validation, and qRT-PCR, WB, and ELISA analysis for assessment of miR-425-5p, RIP1, inflammatory factors, and LDH levels. Results: Down-regulated miR-425-5p and up-regulated RIP1/RIP3 were in LPS-induced sepsis mice. Liver damage, RIP1-mediated necroptosis, IL-1β, and TNF-α were suppressed by miR-425-5p agomiR, but further aggravated by miR-425-5p antagomiR. Furthermore, we demonstrated miR-425-5p targeted the 3′UTR of RIP1 mRNA to inhibit RIP1 expression and activated RIP1 reversed miR-425-5p-induced suppression of necroptosis and inflammation in septic hepatocytes. Conclusions: The data suggest miR-425-5p negatively controls the RIP1-mediated necroptotic signaling cascades and inflammation, and sepsis-related liver damage. miR-425-5p/RIP1 axis is a potential therapeutic strategy for sepsis-related liver damage through necroptosis and inflammation. [ABSTRACT FROM AUTHOR]

Background: Programmed cell death is critical to maintain tissue homeostasis. Necroptosis, as well as apoptosis, has been considered as another form of regulated cell death which can be used as an effective way to overcome apoptosis-resistant tumor tissue growth. The aim of present study was to test whether or not ripk1, ripk3, or mlkl expression levels, as the key necroptotic modulators in different stages of prostate tumor growth. Methods: Sixty-seven prostate tissues representing histologically confirmed cancer were selected. The cancer samples were categorized into 4 different stages based on cellular differentiation, tumor growth rate, and extra tissue expansion to regional lymph nodes, average PSA levels, and tumor volume. RNA extraction, cDNA synthesis and quantitative real time PCR were done based on standard guidelines. Results: No statistically significant changes in ripk1 expression showed in all three stages (stage II to IV). The expression pattern of ripk3 represented a remarkable elevation in early stage, while, predominantly repressed in final cancer stage (IV). Also, there has been a significant negative correlation between ripk3 gene expression and tumor size and PSA levels. Conclusions: We cannot exclude the importance of the key regulator proteins in development and progression of prevalent lethal disease like prostate cancer. The ripk1/ripk3 mediated necroptosis pathway is more activated in early stages of prostate cancer via induced ripk3 expression, while repressed during prostate cancer final stages. Also, the repression of ripk3 is related to elevation of both PSA levels and tumor volume which represented the tumor progression in final stages. [ABSTRACT FROM AUTHOR]

Summary: Emodin, an anthraquinone compound extracted from rhubarb and other traditional Chinese medicines, has been proven to have a wide range of pharmacological effects, such as anti-inflammatory, antiviral, and antitumor activities. Previous studies have confirmed that emodin has inhibitory effects on various solid tumors, such as osteosarcoma, liver cancer, prostate cancer and glioma. This study aimed to investigate the effects and mechanisms of emodin-induced necroptosis in the glioma cell line U251 by targeting the TNF-α/RIP1/RIP3 signaling pathway. We found that emodin could significantly inhibit U251 cell proliferation, and the viability of U251 cells treated with emodin was reduced in a dose- and time-dependent manner. Flow cytometry assays and Hoechst-PI staining assays showed that emodin induced apoptosis and necroptosis. Real-time PCR and western blot analysis showed that emodin upregulated the levels of TNF-α, RIP1, RIP3 and MLKL. Furthermore, the RIP1 inhibitor Nec-1 and the RIP3 inhibitor GSK872 attenuated the killing effect of emodin on U251 cells. In addition, emodin could increase the levels of TNF-α, RIP1, RIP3 and MLKL in vivo. The results demonstrate that emodin could induce necroptosis in glioma possibly through the activation of the TNF-α/RIP1/RIP3 axis. These studies provide novel insight into the induction of necroptosis by emodin and indicate that emodin might be a potential candidate for treating glioma through the necroptosis pathway. [ABSTRACT FROM AUTHOR]

• Activating cIAP1 and subsequently blocking the phosphorylation pathway of RIP1 ameliorates the pathogenesis of OA. • TNF-α exacerbated the inflammatory response resulting in an imbalance in the metabolism and decomposition process of chondrocytes. • AZD8330 may inhibit chondrocyte necrosis and ECM degradation through cIAP1. • AZD8330′s strong effectiveness in preventing the development of OA in DMM mice. Osteoarthritis (OA) is a prevalent degenerative joint disease [1]. It has come to light that AZD8330 can suppress the generation of proinflammatory factors and deter the inflammatory response [2]. Given that inflammation is a primary causative factor in OA, it is posited that AZD8330 might exhibit superior efficacy in OA management. In this study, we investigated the potential of intraperitoneal injection of AZD8330 to retard the progression of osteoarthritis in a murine model with surgically induced medial meniscus destruction (DMM). Concurrently, we employed ATDC5 cartilage cells to dissect the mechanism through which AZD8330 inhibits the TNF-α-induced NF-κB signaling pathway via modulation of RIP1. The findings revealed that AZD8330 mitigated cartilage degradation and the inflammatory response, leading to a substantial reduction in OARSI scores among DMM mice treated with AZD8330. Mechanistically, AZD8330 functioned as a suppressor of the TNF-α-induced NF-κB/p65 signaling pathway by facilitating the phosphorylation activation of cIAP1-mediated RIP1. The combination of data from both in vivo and in vitro experiments supports the conclusion that AZD8330 can attenuate chondrocyte degradation, thereby alleviating OA, by regulating the NF-κB/P65 signaling pathway through modulation of RIP1 activity. Consequently, the utilization of AZD8330 may hold potential in the prophylaxis of osteoarthritis. Our investigation delineates the role of AZD8330 in the regulation of inflammation in the context of OA treatment. Furthermore, we have unveiled that the inhibitory impact of AZD8330 on OA may hinge upon the activation of cIAP1, which in turn downregulates RIP1, thereby restraining the NF-κB/P65 signaling pathway. This study lends credence to the notion that AZD8330 may be a promising contender for osteoarthritis therapy. Our study provides compelling evidence attesting to the capacity of AZD8330 in managing inflammation within the realm of OA treatment. Likewise, our study has elucidated that the attenuation of OA by AZD8330 relies on the activation of cIAP1 to inhibit RIP1, consequently suppressing the NF-κB signaling pathway. On the strength of our present study, we may have identified a viable drug candidate for OA treatment. [ABSTRACT FROM AUTHOR]