Necroptosis, a recently discovered form of cell-programmed death that is distinct from apoptosis, has been confirmed to play a significant role in the pathogenesis of bacterial infections in various animal models. Necroptosis is advantageous to the host, but in some cases, it can be detrimental. To understand the impact of necroptosis on the pathogenesis of bacterial infections, we described the roles and molecular mechanisms of necroptosis caused by different bacterial infections in this review.

Targeting receptor-interacting protein kinase 1 (RIPK1) has emerged as a promising therapeutic stratagem for neurodegenerative disorders, particularly Alzheimer\'s disease (AD). A positron emission tomography (PET) probe enabling brain RIPK1 imaging can provide a powerful tool to unveil the neuropathology associated with RIPK1. Herein, the development of a new PET radioligand, [11C]CNY-10 is reported, which may enable brain RIPK1 imaging. [11C]CNY-10 is radiosynthesized with a high radiochemical yield (41.8%) and molar activity (305 GBq/µmol). [11C]CNY-10 is characterized by PET imaging in rodents and a non-human primate, demonstrating good brain penetration, binding specificity, and a suitable clearance kinetic profile. It is performed autoradiography of [11C]CNY-10 in human AD and healthy control postmortem brain tissues, which shows strong radiosignal in AD brains higher than healthy controls. Subsequently, it is conducted further characterization of RIPK1 in AD using [11C]CNY-10-based PET studies in combination with immunohistochemistry leveraging the 5xFAD mouse model. It is found that AD mice revealed RIPK1 brain signal significantly higher than WT control mice and that RIPK1 is closely related to amyloid plaques in the brain. The studies enable further translational studies of [11C]CNY-10 for AD and potentially other RIPK1-related human studies.

Necroptosis is implicated in the pathogenesis of ischemic stroke. However, the mechanism underlying the sequential recruitment of receptor-interacting protein kinase 1 (RIPK1) and N-ethylmaleimide-sensitive fusion ATPase (NSF) in initiating necroptosis remains poorly understood, and the role of NSF in ischemic stroke is a subject of controversy. Here, we utilized a recently emerging RNA-targeting CRISPR system known as CasRx, delivered by AAVs, to knockdown Ripk1 mRNA and Nsf mRNA around the ischemic brain tissue. This approach resulted in a reduction in infarct and edema volume, as well as an improvement in neurological deficits assessed by Bederson score, RotaRod test, and Adhesive removal test, which were achieved by RIPK1/receptor-interacting protein kinase 3/mixed lineage kinase domain-like protein signaling pathway involved in neuronal necroptosis. In conclusion, the downregulation of Ripk1 mRNA and Nsf mRNA mediated by CRISPR-CasRx holds promise for future therapeutic applications aimed at ameliorating cerebral lesions and neurological deficits following the ischemic stroke.

The effects of lycopene (LP) on macrophage immune responses were evaluated in this study. Compared with the control treatment, LP treatment significantly increased cell vitality, phagocytic activity, and chemokine production in RAW264.7 cells. Additionally, compared with the control treatment, 4 μM LP treatment significantly activated autophagy, enhanced mitochondrial membrane potential, and upregulated receptor-interacting protein kinase 1 (RIPK1), while necrostatin-1 significantly reversed these effects of LP. Furthermore, compared with that in the control group, RIPK1 was significantly upregulated in the 4 μM LP and 4 μM LP + spautin-1 groups, whereas p-mTOR levels were reduced. More importantly, compared with that in the control group, p62 was significantly downregulated, and Beclin1, LC3-II, and Atg7 were upregulated in the 4 μM LP group, while spautin-1 significantly reversed these effects of LP. These results confirm that LP activates the mTOR/Beclin1/LC3/p62 autophagy signaling pathway through RIPK1, thereby enhancing the immune response of macrophages.

BACKGROUND: There is growing evidence indicating that deubiquitinating enzymes may contribute to tumor progression and can serve as promising therapeutic targets.
METHODS: The overexpression of deubiquitinase OTUD6B in lung adenocarcinoma (LUAD) and its adjacent tissues was analyzed by immunohistochemistry and TCGA/GO database. Survival analysis further supported OTUD6B as a potential target for LUAD treatment. We assessed the effect of OTUD6B on LUAD cell growth using cell viability assays and conducted TUNEL staining, migration, and invasion experiments to investigate the impact of OTUD6B on the apoptosis and metastasis of LUAD cells. Additionally, we established a transplanted tumor model in nude mice to validate our findings in vivo. Finally, using IP mass spectrometry and co-IP experiments, we screened and confirmed the influence of RIPK1 as a substrate of OTUD6B in LUAD.
RESULTS: OTUD6B is highly overexpressed in human LUAD and predicts poor prognosis in LUAD patients. OTUD6B knockdown inhibited the proliferation of LUAD cells and enhanced apoptosis and inhibited metastasis in LUAD cells suppressed. A549 xenografts revealed that OTUD6B deletion can slow down tumour growth. Additionally, OTUD6B can bind to RIPK1, reduce its ubiquitination level and increase its protein stability.
CONCLUSIONS: Our results suggest that OTUD6B is a promising clinical target for LUAD treatment and that targeting OTUD6B may constitute an effective anti-LUAD strategy.

Perturbation of the apoptosis and necroptosis pathways critically influences embryogenesis. Receptor-associated protein kinase-1 (RIPK1) interacts with Fas-associated via death domain (FADD)-caspase-8-cellular Flice-like inhibitory protein long (cFLIPL) to regulate both extrinsic apoptosis and necroptosis. Here, we describe Ripk1-mutant animals (Ripk1R588E [RE]) in which the interaction between FADD and RIPK1 is disrupted, leading to embryonic lethality. This lethality is not prevented by further removal of the kinase activity of Ripk1 (Ripk1R588E K45A [REKA]). Both Ripk1RE and Ripk1REKA animals survive to adulthood upon ablation of Ripk3. While embryonic lethality of Ripk1RE mice is prevented by ablation of the necroptosis effector mixed lineage kinase-like (MLKL), animals succumb to inflammation after birth. In contrast, Mlkl ablation does not prevent the death of Ripk1REKA embryos, but animals reach adulthood when both MLKL and caspase-8 are removed. Ablation of the nucleic acid sensor Zbp1 largely prevents lethality in both Ripk1RE and Ripk1REKA embryos. Thus, the RIPK1-FADD interaction prevents Z-DNA binding protein-1 (ZBP1)-induced, RIPK3-caspase-8-mediated embryonic lethality, affected by the kinase activity of RIPK1.

BACKGROUND: The innate immune system serves as the first line of host defense. Transforming growth factor-β-activated kinase 1 (TAK1) is a key regulator of innate immunity, cell survival, and cellular homeostasis. Because of its importance in immunity, several pathogens have evolved to carry TAK1 inhibitors. In response, hosts have evolved to sense TAK1 inhibition and induce robust lytic cell death, PANoptosis, mediated by the RIPK1-PANoptosome. PANoptosis is a unique innate immune inflammatory lytic cell death pathway initiated by an innate immune sensor and driven by caspases and RIPKs. While PANoptosis can be beneficial to clear pathogens, excess activation is linked to pathology. Therefore, understanding the molecular mechanisms regulating TAK1 inhibitor (TAK1i)-induced PANoptosis is central to our understanding of RIPK1 in health and disease.
RESULTS: In this study, by analyzing results from a cell death-based CRISPR screen, we identified protein phosphatase 6 (PP6) holoenzyme components as regulators of TAK1i-induced PANoptosis. Loss of the PP6 enzymatic component, PPP6C, significantly reduced TAK1i-induced PANoptosis. Additionally, the PP6 regulatory subunits PPP6R1, PPP6R2, and PPP6R3 had redundant roles in regulating TAK1i-induced PANoptosis, and their combined depletion was required to block TAK1i-induced cell death. Mechanistically, PPP6C and its regulatory subunits promoted the pro-death S166 auto-phosphorylation of RIPK1 and led to a reduction in the pro-survival S321 phosphorylation.
CONCLUSIONS: Overall, our findings demonstrate a key requirement for the phosphatase PP6 complex in the activation of TAK1i-induced, RIPK1-dependent PANoptosis, suggesting this complex could be therapeutically targeted in inflammatory conditions.

BACKGROUND: Prion diseases are transmissible and fatal neurodegenerative diseases characterized by accumulation of misfolded prion protein isoform (PrPSc), astrocytosis, microgliosis, spongiosis, and neurodegeneration. Elevated levels of cell membrane associated PrPSc protein and inflammatory cytokines hint towards the activation of death receptor (DR) pathway/s in prion diseases. Activation of DRs regulate, either cell survival or apoptosis, autophagy and necroptosis based on the adaptors they interact. Very little is known about the DR pathways activation in prion disease. DR3 and DR5 that are expressed in normal mouse brain were never studied in prion disease, so also their ligands and any DR adaptors. This research gap is notable and investigated in the present study.
METHODS: C57BL/6J mice were infected with Rocky Mountain Laboratory scrapie mouse prion strain. The progression of prion disease was examined by observing morphological and behavioural abnormalities. The levels of PrP isoforms and GFAP were measured as the marker of PrPSc accumulation and astrocytosis respectively using antibody-based techniques that detect proteins on blot and brain section. The levels of DRs, their glycosylation and ectodomain shedding, and associated factors warrant their examination at protein level, hence western blot analysis was employed in this study.
RESULTS: Prion-infected mice developed motor deficits and neuropathology like PrPSc accumulation and astrocytosis similar to other prion diseases. Results from this research show higher expression of all DR ligands, TNFR1, Fas and p75NTR but decreased levels DR3 and DR5. The levels of DR adaptor proteins like TRADD and TRAF2 (primarily regulate pro-survival pathways) are reduced. FADD, which primarily regulate cell death, its level remains unchanged. RIPK1, which regulate pro-survival, apoptosis and necroptosis, its expression and proteolysis (inhibits necroptosis but activates apoptosis) are increased.
CONCLUSIONS: The findings from the present study provide evidence towards the involvement of DR3, DR5, DR6, TL1A, TRAIL, TRADD, TRAF2, FADD and RIPK1 for the first time in prion diseases. The knowledge obtained from this research discuss the possible impacts of these 16 differentially expressed DR factors on our understanding towards the multifaceted neuropathology of prion diseases and towards future explorations into potential targeted therapeutic interventions for prion disease specific neuropathology.

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) functions as a critical stress sentinel that coordinates cell survival, inflammation, and immunogenic cell death (ICD). Although the catalytic function of RIPK1 is required to trigger cell death, its non-catalytic scaffold function mediates strong pro-survival signaling. Accordingly, cancer cells can hijack RIPK1 to block necroptosis and evade immune detection. We generated a small-molecule proteolysis-targeting chimera (PROTAC) that selectively degraded human and murine RIPK1. PROTAC-mediated depletion of RIPK1 deregulated TNFR1 and TLR3/4 signaling hubs, accentuating the output of NF-κB, MAPK, and IFN signaling. Additionally, RIPK1 degradation simultaneously promoted RIPK3 activation and necroptosis induction. We further demonstrated that RIPK1 degradation enhanced the immunostimulatory effects of radio- and immunotherapy by sensitizing cancer cells to treatment-induced TNF and interferons. This promoted ICD, antitumor immunity, and durable treatment responses. Consequently, targeting RIPK1 by PROTACs emerges as a promising approach to overcome radio- or immunotherapy resistance and enhance anticancer therapies.

Acute respiratory distress syndrome (ARDS)/acute lung injury (ALI) is a severe complication of sepsis characterized by acute respiratory distress, hypoxemia, and diffuse bilateral pulmonary infiltrates. The regulation of RIPK1 is an important part of the inflammatory response, and cIAP1/2 serves as the E3 ubiquitin ligase for RIPK1. In this study, we investigated the effect and mechanism of cIAP1/2 inhibition on sepsis-induced lung injury. Our results showed that cIAP1/2 inhibition can alleviate sepsis-induced lung injury and reduce the inflammatory response, which is accompanied by downregulation of RIPK1 phosphorylation and ubiquitination. Additionally, cIAP1/2 inhibition led to the up-regulation of programmed cell death, including apoptosis, necroptosis, and pyroptosis, and inhibiting these three cell death pathways can further reduce the inflammatory response, which is similar to the recently discovered programmed cell death pathway PANoptosis. Our findings suggest that cIAP1/2 and PANoptosis inhibition may be a new strategy for treating sepsis-induced lung injury and provide important references for further exploring the mechanism of sepsis-induced lung injury and identifying new therapeutic targets.