Necroptosis

Extensive loss of alveolar epithelial cells (AECs) undergoing necroptosis is a crucial mechanism of acute lung injury (ALI), but its triggering mechanism needs to be thoroughly investigated. Neutrophil extracellular traps (NETs) play a significant role in ALI. However, the effect of NETs on AECs' death has not been clarified. Our study found that intratracheal instillation of NETs disrupted lung tissue structure, suggesting that NETs could induce ALI in mice. Moreover, we observed that NETs could trigger necroptosis of AECs in vivo and in vitro. The phosphorylation levels of RIPK3 and MLKL were increased in MLE12 cells after NETs treatment (P P via endocytosis can activate the cGAS-STING pathway and trigger AECs necroptosis to promote ALI in mice. Our findings indicate that targeting the NETs/cGAS-STING/necroptosis pathway in AECs is an effective strategy for treating ALI.

Conditional deletion of caspase-8 in mouse epidermal keratinocytes (Casp8E-KO) causes necroptosis-driven lethal dermatitis1-7. Here we find that the loss of Casp8 leads to an accumulation of cytosolic DNA that is responsible for the activation of a cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING)-mediated transcriptional program. Genetic and biochemical evidence indicate that STING upregulates both Z-DNA-binding protein 1 (ZBP1) and mixed lineage kinase domain-like pseudokinase. Combined caspase-8-deficiency- and STING-activation-driven accumulation of Z-nucleic acids activates ZBP1 and triggers the formation of a ZBP1-RIPK1-RIPK3 complex independently of the FADD-RIPK1-RIPK3 complex, enabling execution of necroptosis. Genetically, we reveal a functional overlap between STING and ZBP1 as drivers of lethal dermatitis independently of tumour necrosis factor receptor 1 (TNFR1), identifying an aetiology of necroptotic inflammation. As gain-of-function mutations in human STING cause STING-associated vasculopathy with onset in infancy (SAVI), we assessed the role of STING-induced necroptosis in SAVI's aetiology. Chronic activation of STING in patients orchestrates a necroptotic transcriptional program that is confirmed in the Sting1N153S SAVI preclinical mouse model in which immune-cell-driven pathology and lethality are rescued by receptor-interacting serine/threonine-protein kinase 3 (Ripk3) co-deletion. These findings establish STING-driven ZBP1-mediated necroptosis as a central pathogenic mechanism in both caspase-8-deficient inflammation and SAVI and suggest that targeting the ZBP1-RIPK3-MLKL axis holds therapeutic potential for interferonopathies characterized by excessive necroptosis.

Rationale: Macrophage polarization plays an important role in the inflammatory regulation of ulcerative colitis (UC). In this context, necroptosis is a type of cell death that regulates intestinal inflammation, and selenoprotein S (SelS) is a selenoprotein expressed in intestinal epithelial cells and macrophages that prevents intestinal inflammation. However, the underlying mechanisms of SelS in both cell types in regulating UC inflammatory responses remain unclear. Therefore, the direct effect of SelS deficiency on necroptosis in colonic epithelial cells (CECs) was investigated. In addition, whether SelS knockdown exacerbated intestinal inflammation by modulating macrophage polarization to promote necroptosis in CECs was assessed. Methods: The UC model of SelS knockdown mice was established with 3.5% sodium dextran sulfate, and clinical indicators and colon injury were evaluated in the mice. Moreover, SelS knockdown macrophages and CECs cultured alone/cocultured were treated with IL-1β. The M1/M2 polarization, NF-κB/NLRP3 signaling pathway, oxidative stress, necroptosis, inflammatory cytokine, and tight junction indicators were analyzed. In addition, co-immunoprecipitation, liquid chromatography-mass spectrometry, laser confocal analysis, and molecular docking were performed to identify the interacting proteins of SelS. The GEO database was used to assess the correlation of SelS and its target proteins with macrophage polarization. The intervention effect of four selenium supplements on UC was also explored. Results: Ubiquitin A-52 residue ribosomal protein fusion product 1 (Uba52) was identified as a potential interacting protein of SelS and SelS, Uba52, and yes-associated protein (YAP) was associated with macrophage polarization in the colon tissue of patients with UC. SelS deficiency in CECs directly induced reactive oxygen species (ROS) production, necroptosis, cytokine release, and tight junction disruption. SelS deficiency in macrophages inhibited YAP ubiquitination degradation by targeting Uba52, promoted M1 polarization, and activated the NF-κB/NLRP3 signaling pathway, thereby exacerbating ROS-triggered cascade damage in CECs. Finally, exogenous selenium supplementation could effectively alleviate colon injury in UC. Conclusion: SelS is required for maintaining intestinal homeostasis and that its deletion enhances necroptosis in CECs, which is further exacerbated by promoting M1 macrophage polarization, and triggers more severe barrier dysfunction and inflammatory responses in UC.

Necroptosis is a form of lytic cell death that is overactivated during infections and in inflammatory pathologies1. NINJ1 was recently found to be a mediator of plasma membrane rupture (PMR) during pyroptosis, toxin-induced necrosis, apoptosis, and ferroptosis2,3, but the mediator of PMR during necroptotic cell death remained unknown. Here, using a CRISPR-Cas9-based genome-wide knockout approach, we identify SIGLEC12 as a key mediator of necroptosis downstream of MLKL at the PMR step. Cells with knockdown or knockout of SIGLEC12 are defective in necroptosis-induced PMR and demonstrate ballooning morphology. During necroptosis, SIGLEC12 undergoes dephosphorylation, interacts with MLKL, forms cytosolic puncta and assembles into fibrils. Notably, SIGLEC12 is cleaved by TMPRSS4 during necroptosis to produce a 20-kDa fragment highly homologous to NINJ1, and this cleavage event is required and sufficient to induce PMR during necroptosis. A SIGLEC12 variant associated with cancer (Ser458Phe) and a variant found in the general human population (Arg528Trp) attenuate SIGLEC12 cleavage by TMPRSS4. Knockout of Siglec12 in mouse cells does not affect PMR, suggesting a species-specific role. Our identification of SIGLEC12 as a mediator of PMR expands our understanding of how programmed necrosis is executed and offers new approaches for targeting this proinflammatory form of cell death in human diseases.