Detection of Necroptosis in Ligand-Mediated and Hypoxia-Induced Injury of Hepatocytes Using a Novel Optic Probe-Detecting Receptor-Interacting Protein (RIP)1/RIP3 Binding

Immunogenic necroptosis in liver diseases: mechanisms and therapeutic potential

Necroptosis has received increasing attention and is extensively studied as a recently discovered mode of cell death distinct from necrosis and apoptosis. It is a programmed cell death with a necrotic morphology that occurs in various biological processes, including inflammation, immune response, embryonic development, and metabolic abnormalities. Necroptosis is indispensable in maintaining tissue homeostasis in vivo and closely correlates with the occurrence and development of various diseases. First, we outlined the etiology of necroptosis and how it affects the onset and development of prevalent liver diseases in this review. Additionally, we reviewed the therapeutic strategy by targeting the necroptosis pathway in related liver diseases. We conclude that the necroptosis signaling pathway is critical in the physiological control of liver diseases' onset, progression, and prognosis. It will likely be used as a therapeutic target in the future. Further research is required to determine the mechanisms governing the necroptosis signaling pathway and the effector molecules.

MLKL and other necroptosis-related genes promote the tumor immune cell infiltration, guiding for the administration of immunotherapy in bladder urothelial carcinoma

The involvement of necroptosis in the immunosuppressive tumor microenvironment has been established and has been shown to contribute to the growth of pancreatic ductal adenocarcinoma, indicating its role in promoting tumor development. However, the relationship between necroptosis and bladder urothelial carcinoma (BUC) has yet to be fully understood. To shed light on this issue, our study aimed to uncover the impact of necroptosis on immune cell infiltration and immunotherapy response in BUC patients. We conducted an analysis of 67 necroptosis genes to assess their expression and genomic changes across pan-cancer and identified 12 necroptosis genes that are prognostically relevant and associated with immune subtypes and tumor stemness in BUC. Using a public database of 1841 BUC samples, we then performed Unsupervised Cluster Analysis and discovered two distinct necroptotic phenotypes in BUC. These phenotypes showed significant differences in molecular subtypes, immune infiltration patterns, and gene mutation profiles. We confirmed this discovery in BUC through qPCR and WB experiments. To evaluate the impact of necroptosis on prognosis, chemotherapy sensitivity, and immunotherapy response (such as anti-PD-L1), we developed a principal component analysis model called NecroScore. Finally, we validated the effects of RIPK3 and MLKL through a nude mouse transplantation model for BUC. Our study has uncovered that necroptosis plays a role in shaping the tumor immune microenvironment in BUC. The high necroptosis phenotype (Cluster B) was characterized by a higher abundance of tumor immunosuppressive cells and more key biological processes driving tumor progression, while the low necroptosis group (Cluster A) had higher FGFR3 mutations. We found that the infiltration levels of immune cells, including CD8+ T cells, were significantly different between FGFR3 mutated and wild-type (WT) samples. Our results confirmed the reliability of NecroScore as a comprehensive assessment tool for evaluating the immunotherapeutic effect and prognosis of BUC patients, with high NecroScore values favoring basal-like differentiation and lower FGFR3 alterations. We also observed that high expression of MLKL had a significant inhibitory effect on tumor growth and increased neutrophil infiltration in vivo. In our study, we uncovered the regulation pattern of necroptosis in the tumor immune microenvironment of BUC. Additionally, we developed a scoring tool called NecroScore that can be utilized to predict the most suitable chemotherapy and immunotherapy strategy for bladder urothelial carcinoma patients. This tool can effectively guide the chemotherapy and immunotherapy regimens for patients with advanced BUC.

A Dual-Locked Tandem Fluorescent Probe for Imaging of Pyroptosis in Cancer Chemo-Immunotherapy

Real-time imaging of programmed cancer cell death (PCD) is imperative to monitor cancer therapeutic efficacy and tailor therapeutic regimens; however, specific in vivo detection of intratumoral pyroptosis remains challenging. Herein, a dual-locked and tandem activatable probe (DTAP) is reported for near-infrared fluorescence (NIRF) imaging of intratumoral pyroptosis during cancer chemo-immunotherapy in living mice. The probe comprises a hemicyanine dye dual-locked with an enzyme-responsive moiety that can be tandemly cleaved by pyroptosis-related biomarker (Caspase-1) and cancer biomarker (GGT) to turn on its NIRF signal. As pyroptosis plays a vital role in triggering anti-tumor immune responses, the activated signal of DTAP correlates well with the population of tumor-infiltrating cytotoxic T lymphocytes and tumor growth inhibition, consequently permitting the prediction of cancer therapeutic efficacy. This study also provides a non-invasive technique to study the regulatory mechanism of pyroptosis in cancer therapy and to optimize cancer chemo-immunotherapies for precision medicine.

Bioluminescent RIPoptosome Assay for FADD/RIPK1 Interaction Based on Split Luciferase Assay in a Human Neuroblastoma Cell Line SH-SY5Y

Different programed cell death (PCD) modalities involve protein-protein interactions in large complexes. Tumor necrosis factor α (TNFα) stimulated assembly of receptor-interacting protein kinase 1 (RIPK1)/Fas-associated death domain (FADD) interaction forms Ripoptosome complex that may cause either apoptosis or necroptosis. The present study addresses the interaction of RIPK1 and FADD in TNFα signaling by fusion of C-terminal (CLuc) and N-terminal (NLuc) luciferase fragments to RIPK1-CLuc (R1C) or FADD-NLuc (FN) in a caspase 8 negative neuroblastic SH-SY5Y cell line, respectively. In addition, based on our findings, an RIPK1 mutant (R1C K612R) had less interaction with FN, resulting in increasing cell viability. Moreover, presence of a caspase inhibitor (zVAD.fmk) increases luciferase activity compared to Smac mimetic BV6 (B), TNFα -induced (T) and non-induced cell. Furthermore, etoposide decreased luciferase activity, but dexamethasone was not effective in SH-SY5Y. This reporter assay might be used to evaluate basic aspects of this interaction as well as for screening of necroptosis and apoptosis targeting drugs with potential therapeutic application.

Poly(ADP-ribose) Polymerase (PARP) is Critically Involved in Liver Ischemia/reperfusion-injury

BACKGROUND

Poly(ADP-ribose) polymerase (PARP) is a DNA-repairing enzyme activated by extreme genomic stress, and therefore is potently activated in the remnant liver suffering from ischemia after surgical resection. However, the impact of PARP on post-ischemic liver injury has not been elucidated yet.

MATERIALS AND METHODS

We investigated the impact of PARP on murine hepatocyte/liver injury induced by hypoxia/ischemia, respectively.

RESULTS

PJ34, a specific inhibitor of PARP, markedly protected against hypoxia/reoxygenation (H/R)-induced cell death, though z-VAD-fmk, a pan-caspase inhibitor similarly showed the protective effect. PJ34 did not affect H/R-induced caspase activity or caspase-mediated cell death. z-VAD-fmk also did not affect the production of PAR (i.e., PARP activity). Therefore, PARP- and caspase-mediated cell death occurred in a mechanism independent of each other in H/R. H/R immediately induced activation of PARP and cell death afterwards, both of which were suppressed by PJ34 or Trolox, an antioxidant. This suggests that H/R-induced cell death occurred redox-dependently through PARP activation. H/R and OS induced nuclear translocation of apoptosis inducing factor (AIF, a marker of parthanatos) and RIP1-RIP3 interaction (a marker of necroptosis), both of which were suppressed by PJ34. H/R induced PARP-mediated parthanatos and necroptosis redox-dependently. In mouse experiments, PJ34 significantly reduced serum levels of AST, ALT & LDH and areas of hepatic necrosis after liver ischemia/reperfusion, similar to z-VAD-fmk or Trolox.

CONCLUSION

PARP, activated by ischemic damage and/or oxidative stress, may play a critical role in post-ischemic liver injury by inducing programmed necrosis (parthanatos and necroptosis). PARP inhibition may be one of the promising strategies against post-ischemic liver injury.

Advanced research on the regulated necrosis mechanism in myocardial ischemia-reperfusion injury

Myocardial ischemia-reperfusion injury is an important factor that seriously affects the prognosis of patients with myocardial infarction. It can cause myocardial stun, no-reflow phenomenon, reperfusion arrhythmia, and even irreversible cardiomyocyte death. Regulated necrosis is a newly discovered type of regulatory cell death that is different from apoptosis, including necroptosis, pyrolysis, iron death and other forms. Regulated necrosis plays an important role in myocardial infarction, heart failure and other cardiovascular diseases, as well as myocardial ischemia-reperfusion injury and other pathophysiological processes, and is expected to become a new target for intervention in this type of disease.

Phosphorylation of eIF2α mitigates endoplasmic reticulum stress and hepatocyte necroptosis in acute liver injury

INTRODUCTION AND OBJECTIVES

Necroptosis and endoplasmic reticulum (ER) stress has been implicated in acute and chronic liver injury. Activated eukaryotic initiation factor 2 alpha (eIF2α) attenuates protein synthesis and relieves the load of protein folding in the ER. In this study, we aimed to analyze the impact of eIF2α phosphorylation on hepatocyte necroptosis in acute liver injury.

MATERIALS AND METHODS

Male BALB/c mice were injected with tunicamycin or d-galactosamine, and LO2 cells were incubated with tunicamycin to induce acute liver injury. 4-Phenylbutyric acid (PBA) and salubrinal were used to inhibit ER stress and eIF2α dephosphorylation, respectively. We analyzed the eIF2α phosphorylation, ER stress, and hepatocyte necroptosis in mice and cells model.

RESULTS

Tunicamycin or d-galactosamine significantly induced ER stress and necroptosis, as well as eIF2α phosphorylation, in mice and LO2 cells (p<0.05). ER stress aggravated tunicamycin-induced hepatocyte necroptosis in mice and LO2 cells (p<0.05). Elevated eIF2α phosphorylation significantly mitigated hepatocyte ER stress (p<0.05) and hepatocyte necroptosis in mice (34.37±3.39% vs 22.53±2.18%; p<0.05) and LO2 cells (1±0.11 vs 0.33±0.05; p<0.05). Interestingly, tumor necrosis factor receptor (TNFR) 1 protein levels were not completely synchronized with necroptosis. TNFR1 expression was reduced in d-galactosamine-treated mice (p<0.05) and cells incubated with tunicamycin for 12 and 24h (p<0.05). ER stress partially restored TNFR1 expression and increased necroptosis in tunicamycin-incubated cells (p<0.05).

CONCLUSIONS

These results imply that ER stress can mediate hepatocyte necroptosis independent of TNFR1 signaling and elevated eIF2α phosphorylation can mitigate ER stress during acute liver injury.

Remifentanil preconditioning protects against hypoxia-induced senescence and necroptosis in human cardiac myocytes in vitro

Remifentanil and other opioids are suggested to be protective against ischemia-reperfusion injury in animal models and coronary artery bypass surgery patients, however the molecular basis of such protection is far from being understood. In the present study, we have used a model of human cardiomyocytes treated with the hypoxia-mimetic agent cobalt chloride to investigate remifentanil preconditioning-based adaptive responses and underlying mechanisms. Hypoxic conditions promoted oxidative and nitrosative stress, p21-mediated cellular senescence and the activation of necroptotic pathway that was accompanied by a 2.2-, 9.6- and 8.2-fold increase in phosphorylation status of mixed lineage kinase domain-like pseudokinase (MLKL) and release of pro-inflammatory cytokine IL-8 and cardiac troponin I, a marker of myocardial damage, respectively. Remifentanil preconditioning was able to lower hypoxia-mediated protein carbonylation and limit MLKL-based signaling and pro-inflammatory response to almost normoxic control levels, and decrease hypoxia-induced pro-senescent activity of about 21% compared to control hypoxic conditions. In summary, we have shown for the first time that remifentanil can protect human cardiomyocytes against hypoxia-induced cellular senescence and necroptosis that may have importance with respect to the use of remifentanil to diminish myocardial ischemia and reperfusion injury in patients undergoing cardiac surgery.

Necroptosis in Cholangiocarcinoma

Necroptosis is a type of regulated cell death that is increasingly being recognized as a relevant pathway in different pathological conditions. Necroptosis can occur in response to multiple stimuli, is triggered by the activation of death receptors, and is regulated by receptor-interacting protein kinases 1 and 3 and mixed-lineage kinase domain-like, which form a regulatory complex called the necrosome. Accumulating evidence suggests that necroptosis plays a complex role in cancer, which is likely context-dependent and can vary among different types of neoplasms. Necroptosis serves as an alternative mode of programmed cell death overcoming apoptosis and, as a pro-inflammatory death type, it may inhibit tumor progression by releasing damage-associated molecular patterns to elicit robust cross-priming of anti-tumor CD8+ T cells. The development of therapeutic strategies triggering necroptosis shows great potential for anti-cancer therapy. In this review, we summarize the current knowledge on necroptosis and its role in liver biliary neoplasms, underlying the potential of targeting necroptosis components for cancer treatment.

Cellular and molecular mechanisms of liver regeneration: Proliferation, growth, death and protection of hepatocytes

Liver regeneration is an important and necessary process that the liver depends on for recovery from injury. The regeneration process consists of a complex network of cells and organs, including liver cells (parenchymal and non-parenchymal cells) and extrahepatic organs (thyroid, adrenal glands, pancreas, duodenum, spleen, and autonomic nervous system). The regeneration process of a normal, healthy liver depends mainly on hepatocyte proliferation, growth, and programmed cell death. Cell proliferation and growth are regulated in a cooperative manner by interleukin (IL)-6/janus kinase (Jak)/signal transducers and activators of transcription-3 (STAT3), and phosphoinositide 3-kinase (PI3-K)/phosphoinositide-dependent protein kinase 1 (PDK1)/Akt pathways. The IL-6/Jak/STAT3 pathway regulates hepatocyte proliferation and protects against cell death and oxidative stress. The PI3-K/PDK1/Akt pathway is primarily responsible for the regulation of cell size, sending mitotic signals in addition to pro-survival, antiapoptotic and antioxidative signals. Though programmed cell death may interfere with liver regeneration in a pathological situation, it seems to play an important role during the termination phase, even in a normal, healthy liver regeneration. However, further study is needed to fully elucidate the mechanisms regulating the processes of liver regeneration with regard to cell-to-cell and organ-to-organ networks at the molecular and cellular levels.

Evidence of necroptosis in osteoarthritic disease: investigation of blunt mechanical impact as possible trigger in regulated necrosis

Joint injuries are highly associated with cell death and development of posttraumatic osteoarthritis (PTOA). The present study focused on necroptosis as a possible modality of chondrocyte death after cartilage trauma and its relevance in OA disease in general. For this purpose, apoptosis- and necroptosis-associated markers were determined in highly degenerated (ICRS ≥ 3) as well as macroscopically intact cartilage tissue (ICRS ≤ 1) by means of real-time PCR and immunohistochemistry (IHC). Moreover, influence of blunt trauma and/or stimulation with cycloheximide (CHX), TNF-a, and caspase-inhibitor zVAD were investigated in cartilage explants (ICRS ≤ 1). Further characterization of necroptosis was performed in isolated chondrocytes. We found that gene expression levels of RIPK3 (4.2-fold, P < 0.0001) and MLKL (2.7-fold, P < 0.0001) were elevated in highly degenerated cartilage tissue, which was confirmed by IHC staining. After ex vivo trauma and/or CHX/TNF stimulation, addition of zVAD further enhanced expression of necroptosis-related markers as well as release of PGE2 and nitric oxide, which was in line with increased cell death and subsequent release of intracellular HMGB1 and dsDNA in CHX/TNF stimulated chondrocytes. However, trauma and/or chemically induced cell death and subsequent release of pro-inflammatory mediators could be largely attenuated by RIPK1-inhibitor necrostatin 1 or antioxidant N-acetylcysteine. Overall, the study provided clear evidence of necroptotic cell death in OA disease. Moreover, a possible link between cartilage injury and necroptotic processes was found, depending on oxidative stress and cytokine release. These results contribute to further understanding of cell death in PTOA and development of novel therapeutic approaches.

Necroptotic Cell Death in Liver Transplantation and Underlying Diseases: Mechanisms and Clinical Perspective

Cell death is a natural process for the turnover of aged cells, but it can also arise as a result of pathological conditions. Cell death is recognized as a key feature in both acute and chronic hepatobiliary diseases caused by drug, alcohol, and fat uptake; by viral infection; or after surgical intervention. In the case of chronic disease, cell death can lead to (chronic) secondary inflammation, cirrhosis, and the progression to liver cancer. In liver transplantation, graft preservation and ischemia/reperfusion injury are associated with acute cell death. In both cases, so-called programmed cell death modalities are involved. Several distinct types of programmed cell death have been described of which apoptosis and necroptosis are the most well known. Parenchymal liver cells, including hepatocytes and cholangiocytes, are susceptible to both apoptosis and necroptosis, which are triggered by distinct signal transduction pathways. Apoptosis is dependent on a proteolytic cascade of caspase enzymes, whereas necroptosis induction is caspase-independent. Moreover, different from the "silent" apoptotic cell death, necroptosis can cause a secondary inflammatory cascade, so-called necroinflammation, triggered by the release of various damage-associated molecular patterns (DAMPs). These DAMPs activate the innate immune system, leading to both local and systemic inflammatory responses, which can even cause remote organ failure. Therapeutic targeting of necroptosis by pharmacological inhibitors, such as necrostatin-1, shows variable effects in different disease models.

A toll-like receptor 9 agonist sensitizes mice to mitochondrial dysfunction-induced hepatic apoptosis via the Fas/FasL pathway

Early hepatocyte death occurs in most liver injury cases and triggers liver inflammation, which in combination with other risk factors leads to the development of liver disease. However, the pathogenesis of early phase hepatocyte death remains poorly understood. Here, C57BL/6J mice were treated with the hepatotoxic drug flucloxacillin (FLUX) and the toll-like receptor 9 agonist CpG oligodeoxynucleotide (ODN) to reproduce the early phase of drug-induced hepatotoxicity and investigate its pathogenesis. C57BL/6J mice were treated with FLUX (100 mg/kg, gavage) alone or in combination with ODN (40 μg/mouse, intraperitoneally). Plasma alanine aminotransferase (ALT) level was measured as a marker of hepatotoxicity. FLUX or ODN alone was insufficient to induce ALT elevation, whereas combination treatment with FLUX and ODN increased ALT levels 24 h after FLUX treatment and upregulated Fas ligand in natural killer T (NKT) cells and Fas in hepatocytes. FLUX induced mitochondrial permeability transition (MPT), and pretreatment with ODN sensitized mitochondria to FLUX-induced MPT. The increase in ALT levels induced by ODN and FLUX co-treatment was suppressed in Fas ligand (gld/gld)-deficient mice and in mice deficient in a component of MPT pore opening (cyclophilin D-knockout mice). These results suggested that ODN activated the Fas/Fas ligand-mediated pathway in NKT cells and hepatocytes, which may predispose to FLUX-induced mitochondrial dysfunction and lead to early phase hepatocyte apoptosis. Taken together, these findings elucidate a potentially novel mechanism underlying drug-induced early phase hepatocyte death related to the Fas/Fas ligand death receptor pathway and mitochondrial dysfunction.

Progress in studies of necroptosis and its relationship to disease processes

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

Induction of Signal Transduction by Using Non-Channelrhodopsin-Type Optogenetic Tools

Signal transductions are the basis for all cellular functions. Previous studies investigating signal transductions mainly relied on pharmacological inhibition, RNA interference, and constitutive active/dominant negative protein expression systems. However, such studies do not allow the modulation of protein activity with high spatial and temporal precision in cells, tissues, and organs in animals. Recently, non-channelrhodopsin-type optogenetic tools for regulating signal transduction have emerged. These photoswitches address several disadvantages of previous techniques, and allow us to control a variety of signal transductions such as cell membrane dynamics, calcium signaling, lipid signaling, and apoptosis. In this review we summarize recent advances in the development of such photoswitches and in how these optotools are applied to signaling processes.