A family harboring an MLKL loss of function variant implicates impaired necroptosis in diabetes

Maturity-onset diabetes of the young, MODY, is an autosomal dominant disease with incomplete penetrance. In a family with multiple generations of diabetes and several early onset diabetic siblings, we found the previously reported P33T PDX1 damaging mutation. Interestingly, this substitution was also present in a healthy sibling. In contrast, a second very rare heterozygous damaging mutation in the necroptosis terminal effector, MLKL, was found exclusively in the diabetic family members. Aberrant cell death by necroptosis is a cause of inflammatory diseases and has been widely implicated in human pathologies, but has not yet been attributed functions in diabetes. Here, we report that the MLKL substitution observed in diabetic patients, G316D, results in diminished phosphorylation by its upstream activator, the RIPK3 kinase, and no capacity to reconstitute necroptosis in two distinct MLKL-/- human cell lines. This MLKL mutation may act as a modifier to the P33T PDX1 mutation, and points to a potential role of impairment of necroptosis in diabetes. Our findings highlight the importance of family studies in unraveling MODY's incomplete penetrance, and provide further support for the involvement of dysregulated necroptosis in human disease.

Resveratrol inhibits necroptosis by mediating the TNF-α/RIP1/RIP3/MLKL pathway in myocardial hypoxia/reoxygenation injury

Resveratrol (RES) protects myocardial cells from hypoxia/reoxygenation (H/R)-caused injury. However, the mechanism of this effect has not been clarified. Thus, in this study, we aimed to determine whether RES attenuates H/R-induced cell necroptosis by inhibiting the tumor necrosis factor-alpha (TNF-α)/receptor-interacting protein kinase 1 (RIP1)/RIP3/mixed-lineage kinase domain-like (MLKL) signaling pathway. Rat myocardial ischemia/reperfusion (I/R) models and H/R-injured cell models were constructed. Our study showed that myocardial H/R injury significantly increased the levels of TNF-α, RIP1, RIP3, and p-MLKL/MLKL by western blot analysis. Cell viability assay and 4,6-dianmidino-2-phenylindole (DAPI)-propidium iodide staining showed that the cell viability was decreased, and necroptosis was increased after myocardial H/R injury. The expressions of TNF-α, RIP1, RIP3, and p-MLKL/MLKL in H/R myocardial cells treated with different concentrations of RES were significantly downregulated. In addition, we also found that the cell viability was increased and necroptosis was decreased in dose-dependent manners when H/R-injured cells were treated with RES. In addition, the enhanced effect of TNF-α on necroptosis in myocardial H/R-injured cells was improved by RES, and the effect of RES was confirmed in vivo in I/R rats. This study also showed that RES suppresses necroptosis in H9c2 cells, which may occur through the inhibition of the TNF-α/RIP1/RIP3/MLKL signaling pathway. Our data suggest that necroptosis is a promising therapeutic target and may be a promising therapeutic target for the treatment of myocardial I/R injury.

The PKR/P38/RIPK1 Signaling Pathway as a Therapeutic Target in Alzheimer's Disease

Neuropathological lesions in Alzheimer’s disease (AD) include amyloid plaques formed by the accumulation of amyloid peptides, neurofibrillary tangles made of hyperphosphorylated tau protein, synaptic and neuronal degenerations, and neuroinflammation. The cause of AD is unknown, but according to the amyloid hypothesis, amyloid oligomers could lead to the activation of kinases such as eukaryotic translation initiation factor 2-alpha kinase 2 (PKR), p38, and receptor-interacting serine/threonine-protein kinase 1 (RIPK1), which all belong to the same stress-activated pathway. Many toxic kinase activations have been described in AD patients and in experimental models. A p38 mitogen-activated protein kinase inhibitor was recently tested in clinical trials but with unsuccessful results. The complex PKR/P38/RIPK1 (PKR/dual specificity mitogen-activated protein kinase kinase 6 (MKK6)/P38/MAP kinase-activated protein kinase 2 (MK2)/RIPK1) is highly activated in AD brains and in the brains of AD transgenic animals. To delineate the implication of this pathway in AD, we carried out a search on PubMed including PKR/MKK6/p38/MK2/RIPK1, Alzheimer, and therapeutics. The involvement of this signaling pathway in the genesis of AD lesions, including Aβ accumulations and tau phosphorylation as well as cognitive decline, is demonstrated by the reports described in this review. A future combination strategy with kinase inhibitors should be envisaged to modulate the consequences for neurons and other brain cells linked to the abnormal activation of this pathway.

Transplantation of olfactory ensheathing cells promotes the therapeutic effect of neural stem cells on spinal cord injury by inhibiting necrioptosis

Transplantation of neural stem cells (NSCs) is one of the most promising treatments for spinal cord injury (SCI). However, the limited survival of transplanted NSCs reduces their therapeutic effects. The aim of the present study was to examine whether a co-transplantation of olfactory ensheathing cells (OECs) may enhance the survival of NSCs and improve the beneficial effects of NSCs in rats with SCI, as well as to investigate potential mechanisms underlying such efficacies. Co-transplantation of OECs and NSCs was used to treat rats with SCI. Sympathetic nerve function was determined by measuring sympathetic skin responses. The results showed that OEC/NSC co-transplantation improved motor function and autonomic nerve function in rats with SCI. Co-transplantation of OECs promoted NSC-induced neuroprotection and inhibited programmed necrosis of NSCs, which was mediated by receptor-interacting protein kinase 3 (RIP3) and mixed lineage kinase domain-like protein (MLKL). Furthermore, OECs increased the proliferation and differentiation of NSCs in vitro, and improved the survival rate of NSCs in vivo. Taken together, we conclude that transplantation of OECs inhibited programmed necrosis of co-transplanted NSCs to promote therapeutic effects on SCI. Therefore, co-transplantation of OECs and NSCs may represent a promising strategy for treating patients with SCI.

Impaired RIPK1 ubiquitination sensitizes mice to TNF toxicity and inflammatory cell death

Receptor-interacting protein 1 (RIP1; RIPK1) is a key regulator of multiple signaling pathways that mediate inflammatory responses and cell death. TNF-TNFR1 triggered signaling complex formation, subsequent NF-κB and MAPK activation and induction of cell death involve RIPK1 ubiquitination at several lysine residues including Lys376 and Lys115. Here we show that mutating the ubiquitination site K376 of RIPK1 (K376R) in mice activates cell death resulting in embryonic lethality. In contrast to Ripk1K376R/K376R mice, Ripk1K115R/K115R mice reached adulthood and showed slightly higher responsiveness to TNF-induced death. Cell death observed in Ripk1K376R/K376R embryos relied on RIPK1 kinase activity as administration of RIPK1 inhibitor GNE684 to pregnant heterozygous mice effectively blocked cell death and prolonged survival. Embryonic lethality of Ripk1K376R/K376R mice was prevented by the loss of TNFR1, or by simultaneous deletion of caspase-8 and RIPK3. Interestingly, elimination of the wild-type allele from adult Ripk1K376R/cko mice was tolerated. However, adult Ripk1K376R/cko mice were exquisitely sensitive to TNF-induced hypothermia and associated lethality. Absence of the K376 ubiquitination site diminished K11-linked, K63-linked, and linear ubiquitination of RIPK1, and promoted the assembly of death-inducing cellular complexes, suggesting that multiple ubiquitin linkages contribute to the stability of the RIPK1 signaling complex that stimulates NF-κB and MAPK activation. In contrast, mutating K115 did not affect RIPK1 ubiquitination or TNF stimulated NF-κB and MAPK signaling. Overall, our data indicate that selective impairment of RIPK1 ubiquitination can lower the threshold for RIPK1 activation by TNF resulting in cell death and embryonic lethality.

Necroptosis and RhoA/ROCK pathways: molecular targets of Nesfatin-1 in cardioprotection against myocardial ischemia/reperfusion injury in a rat model

Nesfatin-1 as a new energy-regulating peptide has been known to display a pivotal role in modulation of cardiovascular functions and protection against ischemia/reperfusion injury. However, the detailed knowledge about molecular mechanisms underlying this protection has not been completely investigated yet. This study was designed to clarify the molecular mechanisms by which nesfatin-1 exert cardioprotection effects against myocardial ischemia-reperfusion (MI/R). Left anterior descending coronary artery (LAD) was ligated for 30 min to create a MI/R model in rats. MI/R rats were treated with three concentrations of nesfatin-1 (10, 15 and 20 µg/kg) then expression of necroptosis and necrosis mediators were measured by western blotting assay. Fibrosis, morphological damages, cardiac function, myocardial injury indictors and oxidative stress factors were evaluated as well. Induction of MI/R model resulted in cardiac dysfunction, oxidative stress, increased activity of RIPK1-RIPK3-MLKL axis and RhoA/ROCK pathway, extension of fibrosis and heart tissue damage. Highest tested concentration of nesfatin-1 markedly improved cardiac function. Moreover, it reduced oxidative stress, collagen deposition, and morphological damages, through inhibiting the expression of necroptosis mediators and also, necrosis including RIPK1, RIPK3, MLKL, ROCK1, and ROCK2 proteins. The lowest and middle tested concentrations of nesfatin-1 failed to exert protective effects against MI/R. These findings have shown that nesfatin-1 can exert cardioprotection against MI/R in a dose dependent manner by suppressing necroptosis via modulation of RIPK1-RIPK3-MLKL axis and RhoA/ROCK/RIP3 signaling pathway.

Bisphenol AF elevates procoagulant platelets by inducing necroptosis via RIPK1-inflammasome axis

Bisphenol AF, an analogue of Bisphenol A, is an important raw material used in the production of plastic and rubber substances like plastic bottles and containers, toys, and medical supplies. Increased contamination of air, water, dust, and food with BPA/BPAF, poses an enormous threat to humans, globally. BPAF/BPA are endocrine-disrupting chemicals that mimic estrogen hormone, thus increasing the risks of various metabolic and chronic disorders. Exposure of human blood cells to BPA/BPAF induces oxidative stress and genotoxicity. However, its effects on platelets, which play central roles in hemostasis and thrombosis, are not well-documented. In this study, we demonstrate that BPAF induces RIPK1-inflammasome axis-mediated necroptosis in platelets, increasing procoagulant platelet levels in vivo and in vitro. We also show that BPAF-induced rise in procoagulant platelets worsens pulmonary thromboembolism in vivo. The elevated procoagulant platelets are shown to increase platelet-neutrophil/monocyte aggregates that mediate pathogenesis of CVD, thrombosis, and chronic inflammatory diseases. Our results demonstrate the toxic effects of BPAF on platelets and how it propagates the clinical complications by elevating procoagulant platelet numbers. Altogether, our study sends a cautionary message against extensive use of BPAF in the plastic and rubber industries, resulting in frequent human exposure to it, thus endangering platelet functions.

Necrostatin-1 Analog DIMO Exerts Cardioprotective Effect against Ischemia Reperfusion Injury by Suppressing Necroptosis via Autophagic Pathway in Rats

AIM

It has been reported that necrostatin-1 (Nec-1) is a specific necroptosis inhibitor that could attenuate programmed cell death induced by myocardial ischemia/reperfusion (I/R) injury. This study aimed to observe the effect and mechanism of novel Nec-1 analog (Z)-5-(3,5-dimethoxybenzyl)-2-imine-1-methylimidazolin-4-1 (DIMO) on myocardial I/R injury.

METHODS

Male SD rats underwent I/R injury with or without different doses of DIMO (1, 2, or 4 mg/kg) treatment. Isolated neonatal rat cardiomyocytes were subjected to oxygen-glucose deprivation/reoxygenation (OGD/R) treatment with or without DIMO (0.1, 1, 10, or 100 μM). Myocardial infarction was measured by TTC staining. Cardiomyocyte injury was assessed by lactate dehydrogenase assay (LDH) and flow cytometry. Receptor-interacting protein 1 kinase (RIP1K) and autophagic markers were detected by co-immunoprecipitation and Western blotting analysis. Molecular docking of DIMO into the ATP binding site of RIP1K was performed using GLIDE.

RESULTS

DIMO at doses of 1 or 2 mg/kg improved myocardial infarct size. However, the DIMO 4 mg/kg dose was ineffective. DIMO at the dose of 0.1 μM decreased LDH leakage and the ratio of PI-positive cells followed by OGD/R treatment. I/R or OGD/R increased RIP1K expression and in its interaction with RIP3K, as well as impaired myocardial autophagic flux evidenced by an increase in LC3-II/I ratio, upregulated P62 and Beclin-1, and activated cathepsin B and L. In contrast, DIMO treatment reduced myocardial cell death and reversed the above mentioned changes in RIP1K and autophagic flux caused by I/R and OGD/R. DIMO binds to RIP1K and inhibits RIP1K expression in a homology modeling and ligand docking.

CONCLUSION

DIMO exerts cardioprotection against I/R- or OGD/R-induced injury, and its mechanisms may be associated with the reduction in RIP1K activation and restoration impaired autophagic flux.

Differential role of MLKL in alcohol-associated and non-alcohol-associated fatty liver diseases in mice and humans

Hepatocellular death contributes to progression of alcohol-associated (ALD-associated) and non-alcohol-associated (NAFL/NASH) liver diseases. However, receptor-interaction protein kinase 3 (RIP3), an intermediate in necroptotic cell death, contributes to injury in murine models of ALD but not NAFL/NASH. We show here that a differential role for mixed-lineage kinase domain-like protein (MLKL), the downstream effector of RIP3, in murine models of ALD versus NAFL/NASH and that RIP1-RIP3-MLKL can be used as biomarkers to distinguish alcohol-associated hepatitis (AH) from NASH. Phospho-MLKL was higher in livers of patients with NASH compared with AH or healthy controls (HCs). MLKL expression, phosphorylation, oligomerization, and translocation to plasma membrane were induced in WT mice fed diets high in fat, fructose, and cholesterol but not in response to Gao-binge (acute on chronic) ethanol exposure. Mlkl-/- mice were not protected from ethanol-induced hepatocellular injury, which was associated with increased expression of chemokines and neutrophil recruitment. Circulating concentrations of RIP1 and RIP3, but not MLKL, distinguished patients with AH from HCs or patients with NASH. Taken together, these data indicate that MLKL is differentially activated in ALD/AH compared with NAFL/NASH in both murine models and patients. Furthermore, plasma RIP1 and RIP3 may be promising biomarkers for distinguishing AH and NASH.

RIP1/RIP3/MLKL-mediated necroptosis contributes to vinblastine-induced myocardial damage

Vinblastine (VBL) has been considered as a first-line anti-tumor drug for many years. However, vinblastine-caused myocardial damage has been continually reported. The underlying molecular mechanism of the myocardial damage remains unknown. Here, we show that vinblastine induces myocardial damage and necroptosis is involved in the vinblastine-induced myocardial damage both in vitro and in vivo. The results of WST-8 and flow cytometry analysis show that vinblastine causes damage to H9c2 cells, and the results of animal experiments show that vinblastine causes myocardial cell damage. The necrosome components, receptor-interacting protein 1 (RIP1) receptor-interacting protein 3 (RIP3), are significantly increased in vinblastine-treated H9c2 cells, primary neonatal rat ventricular myocytes and rat heart tissues. And the downstream substrate of RIP3, mixed lineage kinase domain like protein (MLKL) was also increased. Pre-treatment with necroptosis inhibitors partially inhibits the necrosome components and MLKL levels and alleviates vinblastine-induced myocardial injury both in vitro and in vivo. This study indicates that necroptosis participated in vinblastine-evoked myocardial cell death partially, which would be a potential target for relieving the chemotherapy-related myocardial damage.

RIPK3 Contributes to Lyso-Gb3-Induced Podocyte Death

Fabry disease is a lysosomal storage disease with an X-linked heritage caused by absent or decreased activity of lysosomal enzymes named alpha-galactosidase A (α-gal A). Among the various manifestations of Fabry disease, Fabry nephropathy significantly affects patients' morbidity and mortality. The cellular mechanisms of kidney damage have not been elusively described. Necroptosis is one of the programmed necrotic cell death pathways and is known to play many important roles in kidney injury. We investigated whether RIPK3, a protein phosphokinase with an important role in necroptosis, played a crucial role in the pathogenesis of Fabry nephropathy both in vitro and in vivo. The cell viability of podocytes decreased after lyso-Gb3 treatment in a dose-dependent manner, with increasing RIPK3 expression. Increased reactive oxygen species (ROS) generation after lyso-Gb3 treatment, which was alleviated by GSK'872 (a RIPK3 inhibitor), suggested a role of oxidative stress via a RIPK3-dependent pathway. Cytoskeleton rearrangement induced by lyso-Gb3 was normalized by the RIPK3 inhibitor. When mice were injected with lyso-Gb3, increased urine albuminuria, decreased podocyte counts in the glomeruli, and effaced foot processes were observed. Our results showed that lyso-Gb3 initiated albuminuria, a clinical manifestation of Fabry nephropathy, by podocyte loss and subsequent foot process effacement. These findings suggest a novel pathway in Fabry nephropathy.

Reconstitution of Human Necrosome Interactions in Saccharomyces cerevisiae

The necrosome is a large-molecular-weight complex in which the terminal effector of the necroptotic pathway, Mixed Lineage Kinase Domain-Like protein (MLKL), is activated to induce necroptotic cell death. The precise mechanism of MLKL activation by the upstream kinase, Receptor Interacting Serine/Threonine Protein Kinase 3 (RIPK3) and the role of Receptor Interacting Serine/Threonine Protein Kinase 1 (RIPK1) in mediating MLKL activation remain incompletely understood. Here, we reconstituted human necrosome interactions in yeast by inducible expression of these necrosome effectors. Functional interactions were reflected by the detection of phosphorylated MLKL, plasma membrane permeabilization, and reduced proliferative potential. Following overexpression of human necrosome effectors in yeast, MLKL aggregated in the periphery of the cell, permeabilized the plasma membrane and compromised clonogenic potential. RIPK1 had little impact on RIPK3/MLKL-mediated yeast lethality; however, it exacerbated the toxicity provoked by co-expression of MLKL with a RIPK3 variant bearing a mutated RHIM-domain. Small molecule necroptotic inhibitors necrostatin-1 and TC13172, and viral inhibitors M45 (residues 1–90) and BAV_Rmil, abated the yeast toxicity triggered by the reconstituted necrosome. This yeast model provides a convenient tool to study necrosome protein interactions and to screen for and characterize potential necroptotic inhibitors.

ABIN3 Negatively Regulates Necroptosis-induced Intestinal Inflammation Through Recruiting A20 and Restricting the Ubiquitination of RIPK3 in Inflammatory Bowel Disease

BACKGROUND AND AIMS

There is evidence for a disturbed necroptosis function in many inflammatory diseases, but its role in inflammatory bowel diseases [IBD] and the underlying mechanisms are unclear. Here, we studied the functional significance and molecular mechanisms of ABIN3, a ubiquitin-binding protein, in regulating the ubiquitination and activation of necroptosis in IBD.

METHODS

The expression of necroptosis hallmarks and ABIN3 were assessed in inflamed samples of IBD patients, dextran sodium sulphate [DSS]-induced colitis models, and azoxymethane [AOM]/DSS models in mice. ABIN3 was overexpressed and silenced to explore its function in regulating necroptosis, inflammation, and intestinal barrier function. Immuoprecipitiation [IP] and co-IP assays were performed to investigate the cross-talk between ABIN3 and deubiquitinating enzyme A20, and the mechanisms of coordinating ubiquitination modification to regulate necroptosis.

RESULTS

Excessive necroptosis is an important contributory factor towards the uncontrolled inflammation and intestinal barrier defects in IBD and experimental colitis. Blocking necroptosis by Nec-1s or GSK'872 significantly prevented cell death and alleviated DSS-induced colitis in vivo, whereas in the AOM/DSS model, necroptosis inhibitors aggravated the severity of colitis-associated colon carcinogenesis [CAC]. Mechanistically, ABIN3 is rapidly recruited to the TNF-RSC complex, which interacts and coordinates with deubiquitinating enzyme A20 to control the K63 deubiquitination modification and subsequent activation of the critical necroptosis kinase, RIPK3, to suppress necroptosis.

CONCLUSIONS

ABIN3 regulates inflammatory response and intestinal barrier function by interacting with A20 and coordinating the K63 deubiquitination modification of necroptosis in IBD.

ZBP1 promotes LPS-induced cell death and IL-1β release via RHIM-mediated interactions with RIPK1

Inflammation and cell death are closely linked arms of the host immune response to infection, which when carefully balanced ensure host survival. One example of this balance is the tightly regulated transition from TNFR1-associated pro-inflammatory complex I to pro-death complex II. By contrast, here we show that a TRIF-dependent complex containing FADD, RIPK1 and caspase-8 (that we have termed the TRIFosome) mediates cell death in response to Yersinia pseudotuberculosis and LPS. Furthermore, we show that constitutive binding between ZBP1 and RIPK1 is essential for the initiation of TRIFosome interactions, caspase-8-mediated cell death and inflammasome activation, thus positioning ZBP1 as an effector of cell death in the context of bacterial blockade of pro-inflammatory signaling. Additionally, our findings offer an alternative to the TNFR1-dependent model of complex II assembly, by demonstrating pro-death complex formation reliant on TRIF signaling.

Targeting the pathways of regulated necrosis: a potential strategy for alleviation of cardio-cerebrovascular injury

Apoptosis, necrosis and autophagy-dependent cell death are the three major types of cell death. Traditionally, necrosis is thought as a passive and unregulated form of cell death. However, certain necrosis can also occur in a highly regulated manner, referring to regulated necrosis. Depending on the signaling pathways, regulated necrosis can be further classified as necroptosis, pyroptosis, ferroptosis, parthanatos and CypD-mediated necrosis. Numerous studies have reported that regulated necrosis contributes to the progression of multiple injury-relevant diseases. For example, necroptosis contributes to the development of myocardial infarction, atherosclerosis, heart failure and stroke; pyroptosis is involved in the progression of myocardial or cerebral infarction, atherosclerosis and diabetic cardiomyopathy; while ferroptosis, parthanatos and CypD-mediated necrosis participate in the pathological process of myocardial and/or cerebral ischemia/reperfusion injury. Thereby, targeting the pathways of regulated necrosis pharmacologically or genetically could be an efficient strategy for reducing cardio-cerebrovascular injury. Further study needs to focus on the crosstalk and interplay among different types of regulated necrosis. Pharmacological intervention of two or more types of regulated necrosis simultaneously may have advantages in clinic to treat injury-relevant diseases.

Exogenous sodium hydrosulfide protects against high glucose‑induced injury and inflammation in human umbilical vein endothelial cells by inhibiting necroptosis via the p38 MAPK signaling pathway

In recent years hydrogen sulfide (H2S) has demonstrated vasculoprotective effects against cell death, which suggests its promising therapeutic potential for numerous types of disease. Additionally, a protective effect of exogenous H2S in HG‑induced injuries in HUVECs was demonstrated, suggesting a potential protective effect for diabetic vascular complications. The present study aimed to investigate the mechanism accounting for the cytoprotective role of exogenous H2S against high glucose [HG (40 mM glucose)]‑induced injury and inflammation in human umbilical vein endothelial cells (HUVECs). HUVECs were exposed to HG for 24 h to establish an in vitro model of HG‑induced cytotoxicity. The cells were pretreated with sodium hydrosulfide (NaHS), a donor of H2S, or inhibitors of necroptosis and p38 MAPK prior to the exposure to HG. Cell viability, intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), IL‑1β, IL‑6, IL‑8, TNF‑α, phosphorylated‑(p)38 and receptor‑interacting protein 3 (RIP3) expression levels were detected using the indicated methods, including Cell Counting Kit 8, fluorescence detection, western blotting, immunofluorescence assay and ELISAs. The results demonstrated that necroptosis and the p38 MAPK signaling pathway mediated HG‑induced injury and inflammation. Notably, NaHS was discovered to significantly ameliorate p38 MAPK/necroptosis‑mediated injury and inflammation in response to HG, as evidenced by an increase in cell viability, a decrease in ROS generation and loss of MMP, as well as the reduction in the secretion of proinflammatory cytokines. In addition, the upregulated expression of RIP3 induced by HG was repressed by treatment with SB203580, while the HG‑induced upregulation of p‑p38 expression levels were significantly downregulated following the treatment of Nec‑1 and RIP3‑siRNA. In conclusion, the findings of the present study indicated that NaHS may protect HUVECs against HG‑induced injury and inflammation by inhibiting necroptosis via the p38 MAPK signaling pathway, which may represent a promising drug for the therapy of diabetic vascular complications.

Live-Cell Imaging Technique to Visualize DAMPs Release During Regulated Cell Death

The present protocol introduces a live-cell imaging of secretion activity (LCI-S) that is useful to visualize the real-time release of molecules from individual cells using an immunoassay coupled with total internal reflection fluorescence (FL) microscopy. This novel "live"-cell imaging technique has helped uncover the dynamics of regulated cell "death" by using this new approach. This protocol can observe the final stages of the regulated cell death process via single-cell imaging by targeting the extracellular release of damage-associated molecular patterns (DAMPs) from the cells expressing fluorescence resonance energy transfer (FRET) biosensors, such as a sensor for MLKL activation by RIPK3 based on FRET (SMART) and a sensor for caspase-1 activation based on FRET (SCAT1), which specifically identify the occurrence of regulated cell death processes.

Effects of vitamin B12 on methotrexate hepatotoxicity: evaluation of receptor-interacting protein (RIP) kinase

In the study, we aimed to show the effects of vitamin B12 on the necrosis caused by methotrexate (MTX), a folic acid antagonist. Thirty-two rats were randomly assigned to four groups of eight rats per group. Control (n = 8), Vit B12 (n = 8) 3 μg/kg/ip B12 (15 days) per day throughout the experiment, MTX (n = 8) injected with a single dose of 20 mg/kg/ip MTX on 8th day of experiment, MTX + Vit B12 (n = 8) injected with a single dose of 20 mg/kg ip methotrexate on 8th day of experiment + 3 μg/kg/ip Vit B12 (15 days) per day throughout the experiment. Oxidant (TOS)/antioxidant (TAS) system, TNF-α and TGF-β levels, AST and ALT, serum vitamin B12 levels were determined in the tissue. Cyclooxygenase-2 (Cox-2), receptor-interacting protein kinase 1 (RIP1) and 3 (RIP3) immunohistochemistry were applied to the liver tissue. TOS increased; TAS decreased; TNF-α and TGF-β levels increased; AST and ALT levels changed after MTX hepatotoxicity. Vit B12 decreased significantly. COX-2, RIP1, and RIP3 immunoreactivity increased. Vit B12 showed improvement in all of the negative results. Vit B12 is an important supplement to be used against necrosis in tissue after MTX hepatotoxicity.

An incoherent feedforward loop interprets NFκB/RelA dynamics to determine TNF-induced necroptosis decisions

Balancing cell death is essential to maintain healthy tissue homeostasis and prevent disease. Tumor necrosis factor (TNF) not only activates nuclear factor κB (NFκB), which coordinates the cellular response to inflammation, but may also trigger necroptosis, a pro-inflammatory form of cell death. Whether TNF-induced NFκB affects the fate decision to undergo TNF-induced necroptosis is unclear. Live-cell microscopy and model-aided analysis of death kinetics identified a molecular circuit that interprets TNF-induced NFκB/RelA dynamics to control necroptosis decisions. Inducible expression of TNFAIP3/A20 forms an incoherent feedforward loop to interfere with the RIPK3-containing necrosome complex and protect a fraction of cells from transient, but not long-term TNF exposure. Furthermore, dysregulated NFκB dynamics often associated with disease diminish TNF-induced necroptosis. Our results suggest that TNF's dual roles in either coordinating cellular responses to inflammation, or further amplifying inflammation are determined by a dynamic NFκB-A20-RIPK3 circuit, that could be targeted to treat inflammation and cancer.

Antiviral mechanism of carvacrol on HSV-2 infectivity through inhibition of RIP3-mediated programmed cell necrosis pathway and ubiquitin-proteasome system in BSC-1 cells

BACKGROUND

Carvacrol, as the major components of aromatic plants used for treating human skin diseases including origanum, Satureja, thymus, and coridothymus species, presented a kind of antiviral activity. To explore the mechanisms of carvacrol against herpes simplex virus (HSV) in vitro.

METHOD

The BSC-1 cells model of HSV infection was established, and from the two aspects of viral replication level and cell death pathway, the antiviral effects of carvacrol on HSV infected cells were also evaluated by plaque assay under the three modes including prevention, treatment, and direct inactivation.

RESULTS

In the three ways, the half-maximal effective concentration (EC50) of 2% true carvacrol solution on HSV-2 infected cells were severally 0.43, 0.19 and 0.51 mmol/L, and the corresponding therapeutic index (TI) were 4.02, 9.11 and 3.39, respectively. It's the opposite of the increased levels caused by HSV-2 infection, that both the expressions at the transcription genes and protein levels of virus own replication key factors (including ICP4, ICP27, VP16, gB, and UL30) and cytokines (including RIP3, TNF-α, and MLKL) of infected cells treated with carvacrol were dose-dependently inhibited. Besides, HSV-2 infection can cause the decrease of intracellular protein ubiquitination level, and carvacrol can reverse the ubiquitination decrease level caused by HSV-2 infection.

CONCLUSION

Carvacrol exhibits significant antiviral activity by inhibiting the HSV-2 proliferation process and HSV-2-induced TNF-α increasing levels, decreasing RIP3 and MLKL protein expressions through the intracellular RIP3-mediated programmed cell necrosis pathway. In addition, carvacrol also may exhibit anti-HSV-2 activity by reversing the ubiquitination decrease level caused by HSV-2 infection on the ubiquitin-proteasome system, which provides insights into the molecular mechanism.

NLRC3-like 1 inhibits NOD1-RIPK2 pathway via targeting RIPK2

Both NLRC3 and NOD1 belong to regulatory NLR subfamily based on their best-characterized function. In mammals, NLRC3 was reported to function by attenuating signaling cascades initiated by other families of PRRs. In teleosts, multiple NLRC3-like genes were identified through transcriptome sequencing. However, the functions of many NLRC3-like genes, especially the fish-specific NLRC3-like genes, remain unclear. In the present study, we report the functional characterization of a novel category of NLRC3-like proteins (named as NLRC3-like 1) from the zebrafish, which consists of a fish-specific FISNA, a conserved NACHT and five C-terminal LRRs domains. The expression of zebrafish NLRC3-like 1 was inducible in response to Edwardsiella piscicida infection. During bacterial infection, the in vitro and in vivo studies revealed that zebrafish NLRC3-like 1 overexpression facilitated bacterial growth and dissemination, together with the decreased survival rate of zebrafish larvae infected with E. piscicida. The attenuated response by zebrafish NLRC3-like 1 in response to bacterial infection were characterized by the impaired expression of antibacterial genes, proinflammatory cytokines and Nox genes. Furthermore, zebrafish NLRC3-like 1 interacted with the adaptor protein RIPK2 of NODs signaling via the FISNA (Fish-specific NACHT associated domain) and NACHT domains. However, the interaction between zebrafish NLRC3-like 1 and RIPK2 inhibited the assembly of the NOD1-RIPK2 complex. Importantly, zebrafish NLRC3-like 1 inhibited NOD1-mediated antibacterial activity, NF-κB and MAPK pathways and proinflammatory cytokine production. All together, these results firstly demonstrate that zebrafish NLRC3-like 1 inhibits NOD1-RIPK2 antibacterial pathway via targeting the adaptor protein RIPK2.

The Role of RIPK1 and RIPK3 in Cardiovascular Disease

Cardiovascular diseases, including peripheral arterial and venous disease, myocardial infarction, and stroke, are the number one cause of death worldwide annually. In the last 20 years, the role of necroptosis, a newly identified form of regulated necrotic cell death, in cardiovascular disease has come to light. Specifically, the damaging role of two kinase proteins pivotal in the necroptosis pathway, Receptor Interacting Protein Kinase 1 (RIPK1) and Receptor Interacting Protein Kinase 3 (RIPK3), in cardiovascular disease has become a subject of great interest and importance. In this review, we provide an overview of the current evidence supporting a pathologic role of RIPK1 and RIPK3 in cardiovascular disease. Moreover, we highlight the evidence behind the efficacy of targeted RIPK1 and RIPK3 inhibitors in the prevention and treatment of cardiovascular disease.

miR-325-3p Protects Neurons from Oxygen-Glucose Deprivation and Reoxygenation Injury via Inhibition of RIP3

OBJECTIVE

Recent reports have corroborated that micro-RNAs (miRs) are related to the pathological changes of cerebral ischemia-reperfusion (CIR) induced injury. This work aimed to unearth the role and potential mechanism of miR-325-3p in regulating neuronal survival in CIR injury.

METHODS

To conduct this investigation, we established an in vitro model of CIR injury by subjecting neurons to oxygen-glucose deprivation and reoxygenation (OGD/R). Gain and loss of function of miR-325-3p and receptor-interacting serine-threonine kinase 3 (RIP3) in neurons were performed to observe its effect on cell apoptosis and the release of lactate dehydrogenase. The levels of miR-325-3p and RIP3 in neurons were detected by qRT-PCR. Western blot was employed to inspect the levels of caspase3, Bax, and Bcl-2, as well as p38 and JNK phosphorylation. The relationship between miR-325-3p and RIP3 was detected by TargetScan and validated by dual-luciferase reporter assay.

RESULTS

Firstly, miR-325-3p expression was obviously downregulated while RIP3 expression was upregulated in neurons following OGD/R treatment. Overexpressed miR-325-3p or downexpressed RIP3 ameliorated OGD/R-induced neuronal injury. Besides, RIP3 was a direct target mRNA of miR-325-3p. Additionally, Western blot revealed the mitogen-activated protein kinase (MAPK) pathway was involved in the regulation of miR-325-3p on OGD/R-induced neuronal injury. Furthermore, miR-325-3p was verified to hinder OGD/R-induced neuronal injury through downregulating RIP3.

CONCLUSION

This study demonstrated that miR-325-3p targets RIP3 to inactivate the MAPK pathway, thereby protecting neurons against OGD/R-induced injury.

Necrostatin-1 Synergizes the Pan Caspase Inhibitor to Attenuate Lung Injury Induced by Ischemia Reperfusion in Rats

BACKGROUND

Both apoptosis and necroptosis have been recognized to be involved in ischemia reperfusion-induced lung injury. We aimed to compare the efficacies of therapies targeting necroptosis and apoptosis and to determine if there is a synergistic effect between the two therapies in reducing lung ischemia reperfusion injury.

METHODS

Forty Sprague-Dawley rats were randomized into 5 groups: sham (SM) group, ischemia reperfusion (IR) group, necrostatin-1+ischemia reperfusion (NI) group, carbobenzoxy-Val-Ala-Asp-fluoromethylketone+ischemia reperfusion (ZI) group, and necrostatin-1+carbobenzoxy-Val-Ala-Asp-fluoromethylketone+ischemia reperfusion (NZ) group. The left lung hilum was exposed without being clamped in rats from the SM group, whereas the rats were subjected to lung ischemia reperfusion by clamping the left lung hilum for 1 hour, followed by reperfusion for 3 hours in the IR group. 1 mg/kg necrostatin-1 (Nec-1: a specific necroptosis inhibitor) and 3 mg/kg carbobenzoxy-Val-Ala-Asp-fluoromethylketone (z-VAD-fmk: a pan caspase inhibitor) were intraperitoneally administrated prior to ischemia in NI and ZI groups, respectively, and the rats received combined administration of Nec-1 and z-VAD-fmk in the NZ group. Upon reperfusion, expressions of receptor-interacting protein 1 (RIP1), receptor-interacting protein 3 (RIP3), and caspase-8 were measured, and the flow cytometry analysis was used to assess the cell death patterns in the lung tissue. Moreover, inflammatory marker levels in the bronchoalveolar lavage fluid and pulmonary edema were evaluated.

RESULTS

Both Nec-1 and z-VAD-fmk, either alone or in combination, significantly reduced morphological damage, inflammatory markers, and edema in lung tissues following reperfusion, and cotreatment of z-VAD-fmk with Nec-1 produced the optimal effect. The rats treated with Nec-1 had lower levels of inflammatory markers in the bronchoalveolar lavage fluid than those receiving z-VAD-fmk alone (P < 0.05). Interestingly, the z-VAD-fmk administration upregulated RIP1 and RIP3 expressions in the lung tissue from the ZI group compared to those in the IR group (P < 0.05). Reperfusion significantly increased the percentages of necrotic and apoptotic cells in lung tissue single-cell suspension, which could be decreased by Nec-1 and z-VAD-fmk, respectively (P < 0.05).

CONCLUSIONS

Nec-1 synergizes the pan caspase inhibitor to attenuate lung ischemia reperfusion injury in rats. Our data support the potential use of Nec-1 in lung transplantation-related disorders.

Programmed Cell Death in the Left and Right Ventricle of the Late Phase of Post-Infarction Heart Failure

While necroptosis has been shown to contribute to the pathogenesis of post-infarction heart failure (HF), the role of autophagy remains unclear. Likewise, linkage between these two cell death modalities has not been sufficiently investigated. HF was induced by 60-min left coronary occlusion in adult Wistar rats and heart function was assessed 6 weeks later followed by immunoblotting analysis of necroptotic and autophagic proteins in both the left (LV) and right ventricle (RV). HF had no effect on RIP1 and RIP3 expression. PhosphoSer229-RIP3, acting as a pro-necroptotic signal, was increased in LV while deceased in RV of failing hearts. Total MLKL was elevated in RV only. Decrease in pSer555-ULK1, increase in pSer473-Akt and no significant elevation in beclin-1 and LC3-II/I ratio indicated rather a lowered rate of autophagy in LV. No beclin-1 upregulation and decreased LC3 processing also suggested the inhibition of both autophagosome formation and maturation in RV of failing hearts. In contrast, p89 PARP1 fragment, a marker of executed apoptosis, was increased in RV only. This is the first study showing a different signaling in ventricles of the late phase of post-infarction HF, highlighting necroptosis itself rather than its linkage with autophagy in LV, and apoptosis in RV.