Necroptosis-mediated HMGB1 secretion of keratinocytes as a key step for inflammation development in contact hypersensitivity

ZBP1-mediated PANoptosis is a crucial lethal form in diverse keratinocyte death modalities in UVB-induced skin injury

UVB irradiation induces diverse modalities of regulatory cell death in keratinocytes. Recently, the pattern of coexistence of pyroptosis, apoptosis, and necroptosis has been termed PANoptosis; however, whether PANoptosis occurs in keratinocytes in UVB-induced skin injury remains unclear. We observed that the key molecules of GSDMD-mediated pyroptosis, apoptosis, and necroptosis, which are N-terminal GSDMD, cleaved caspase-3/PARP, and phosphorylated MLKL, respectively, were elevated in keratinocytes of UVB-challenged mice and human skin tissue. Through keratinocyte-specific gene knockout or using corresponding inhibitors, we found that individual inhibition of GSDMD-mediated pyroptosis, caspase-3-mediated apoptosis, or MLKL-mediated necroptosis did not reduce the overall level of keratinocyte death after UVB exposure, and that the other two pathways maintained the activation. However, when the PANoptosome sensor ZBP1 was knocked out, keratinocyte death was reduced and epidermal thickening was alleviated in UVB-challenged mice. In conclusion, our study demonstrated that UVB irradiation induces ZBP1-mediated PANoptosis in keratinocytes, which is a crucial lethal form in diverse keratinocyte death modalities in UVB-induced skin injury. The above findings provide a new insight on the complexity of regulated cell death modalities in keratinocytes exposed to UV irradiation.

Necroptosis contributes to deoxynivalenol-induced activation of the hypothalamic-pituitary-adrenal axis in a piglet model

The mycotoxin deoxynivalenol (DON) is highly prevalent in cereals as an immune stressor. The hypothalamic-pituitary-adrenal (HPA) axis is activated during periods of stress, and the organism is accompanied by inflammation. Necroptosis is a newly identified type of cell death. However, the relationship between necroptosis and HPA axis activation induced by DON is rarely reported. Our study aimed to explore the role played by necroptosis in HPA activation in a stress of piglet model produced by DON. Our results indicated that both feeding with a contaminated-DON diet (4 ppm) and DON injection at 0.8 mg/kg BW increased the concentration of plasma corticotropin-releasing hormone (CRH) and adrenocorticotrophic hormone (ACTH) and the mRNA expression of adrenal steroidogenic acute regulatory protein (StAR). Furthermore, the mRNA expression of pro-inflammatory cytokines and factors related to necroptosis in the hypothalamus, pituitary gland, and adrenal gland were increased. As an inhibitor of necroptosis, necrostatin-1 (Nec-1) inhibited necroptosis through decreasing mRNA expression of necroptosis signal factors in the HPA axis. Nec-1 also reduced the mRNA levels of pro-inflammatory cytokines in the HPA axis. Meanwhile, the activation of the HPA axis was inhibited by Nec-1 as shown by the decrease of plasma CRH and ACTH concentrations and the mRNA expressions of hypothalamus CRH and pituitary POMC. These findings indicated that as a result of necroptosis, the HPA axis was activated by DON. In light of these findings, necroptosis could be considered as an intervention target that alleviates HPA axis activation and stress responses.

Necroptosis in alveolar epithelial cells drives lung inflammation and injury caused by SARS-CoV-2 infection

COVID-19, caused by SARS-CoV-2 infection, results in irreversible or fatal lung injury. We assumed that necroptosis of virus-infected alveolar epithelial cells (AEC) could promote local inflammation and further lung injury in COVID-19. Since CD8+ lymphocytes induced AEC cell death via cytotoxic molecules such as FAS ligands, we examined the involvement of FAS-mediated cell death in COVID-19 patients and murine COVID-19 model. We identified the occurrence of necroptosis and subsequent release of HMGB1 in the admitted patients with COVID-19. In the mouse model of COVID-19, lung inflammation and injury were attenuated in Fas-deficient mice compared to Fas-intact mice. The infection enhanced Type I interferon-inducible genes in both groups, while inflammasome-associated genes were specifically upregulated in Fas-intact mice. The treatment with necroptosis inhibitor, Nec1s, improved survival rate, lung injury, and systemic inflammation. SARS-CoV-2 induced necroptosis causes cytokine induction and lung damage, and its inhibition could be a novel therapeutic strategy for COVID-19.

Ferrostatin-1 alleviates skin inflammation and inhibits ferroptosis of neutrophils and CD8+ T cells in allergic contact dermatitis

BACKGROUND

Ferroptosis is considered as an immunogenic type of regulated cell death and associated with the pathogenesis of inflammatory skin diseases. However, the involvement and function of ferroptosis in allergic contact dermatitis (ACD) remains unknown.

OBJECTIVE

To explore the role of ferroptosis in ACD. To reveal which type of cells develops ferroptosis in ACD.

METHODS

We detected the key markers of ferroptosis in 1-Chloro-2,4-dinitrochlorobenzene (DNCB)-induced ACD mice model. We applicated ferrostatin-1 (Fer-1) to restrain ferroptosis in ACD mice and then compared the severity of dermatitis and the level of inflammation and ferroptosis in dermis and epidermis, respectively. Keratinocyte-specific Gpx4 conditional knockout (cKO) mice were used to investigate the function of keratinocyte ferroptosis in the development of ACD. Single-cell RNA sequencing was conducted to analyze the affection of Fer-1 on different type of cells in ACD.

RESULTS

Ferroptosis was involved in DNCB-induced ACD mice. Ferroptosis activation was more remarkable in dermis rather than in epidermis. Gpx4 cKO mice showed similar severity of skin dermatitis as control mice. Fer-1 alleviated skin inflammation in mice and reduced ferroptosis in neutrophils and CD8+ T cells both of which contribute to development of ACD.

CONCLUSION

Ferroptosis was activated in immune cells, especially neutrophils and CD8+ T cells in DNCB-induced ACD mice. Fer-1 treatment inhibited ferroptosis of neutrophils and CD8+ T cells and relieved skin damage in ACD mice.

Necrostatin-1 protects corneal epithelial cells by inhibiting the RIPK1/RIPK3/MLKL cascade in a benzalkonium chloride-induced model of necroptosis

PURPOSE

Benzalkonium chloride (BAC) is commonly used as a preservative in ophthalmic medications, despite its potential to induce chemical injury. Extensive research has demonstrated that BAC can lead to adverse effects, including injuries to the ocular surface. Our study aimed to elucidate the underlying mechanism of necroptosis induced by BAC.

METHODS

Human corneal epithelial (HCE) cells and mouse corneas were subjected to chemical injury, and the necrostatin-1 (Nec1) group was compared to the dimethylsulfoxide (DMSO) group. The extent of damage to HCE cells was assessed using CCK-8 and flow cytometry. Hematoxylin and eosin staining, as well as fluorescein sodium staining, were used to detect and characterize corneal injury. The activation of inflammatory cytokines and necroptosis-related proteins and genes was evaluated using Western blotting, immunofluorescence staining, and quantitative RT‒PCR.

RESULTS

In our study, the induction of necroptosis by a hypertonic solution was not observed. However, necroptosis was observed in HCE cells exposed to NaOH and BAC, which activated the receptor-interacting protein kinase 1 (RIPK1) - receptor-interacting protein kinase 3 (RIPK3) - mixed lineage kinase domain-like protein (MLKL) signaling pathway. In mouse corneal tissues, BAC could induce necroptosis and inflammation. The administration of Nec1 mitigated the inflammatory response and ocular surface damage caused by BAC-induced necroptosis in our experimental models. Furthermore, our in vivo experiments revealed that the severity of necroptosis was greater in the 3-day group than in the 7-day group.

CONCLUSIONS

Necroptosis plays a role in the pathological development of ocular surface injury caused by exposure to BAC. Furthermore, our study demonstrated that the administration of Nec1 could mitigate the pathological effects of necroptosis induced by BAC in clinical settings.

Necrosulfonamide promotes hair growth and ameliorates DHT-induced hair growth inhibition

BACKGROUND

Alopecia affects patients' appearance and psychology. Mixed-lineage kinase domain-like pseudokinase (MLKL)-mediated necroptosis plays a role in various skin diseases, but its effect on hair growth is unclear.

OBJECTIVE

To investigate the effects of MLKL on hair growth and its regulatory mechanisms and to determine the potential clinical value of Necrosulfonamide (NSA, a MLKL-targeting inhibitor) in promoting hair growth and counteracting dihydrotestosterone (DHT) inhibition of hair growth.

METHODS

The expression level of MLKL was detected in the scalp of androgenetic alopecia (AGA) patients and the skin tissues of mice. Knock down MLKL expression or use NSA to observe hair growth in vivo and in vitro.

RESULTS

In AGA patients, MLKL expression is elevated in the alopecia areas. In mice, MLKL is significantly expressed in the outer root sheath (ORS) cells of hair follicles, peaking during the catagen phase. Knockdown expression of MLKL in mice skin promoted hair growth. NSA enhanced hair growth and prevented hair follicle regression via the Wnt signaling. Reduced MLKL boosts ORS cell proliferation without directly impacting DPCs' growth. Interestingly, NSA boosts DPCs' proliferation and induction when co-cultured with ORS cells. Besides, NSA alleviated the inhibition of DHT on hair growth in vivo and vitro.

CONCLUSION

NSA inhibited the activation of MLKL in ORS cells, promoted the activation of Wnt signal in DPC cells, and improved the inhibition of hair growth by DHT, illuminating a new alopecia mechanism and aiding anti-alopecia drug development.

The evaluation of skin sensitization potential of the UVCB substance diisopentyl phthalate by in silico and in vitro methods

Diisopentyl phthalate (DiPeP) is primarily used as a plasticizer or additive within the production of polyvinyl chloride (PVC), and has many additional industrial applications. Its metabolites were recently found in urinary samples of pregnant women; thus, this substance is of concern as relates to human exposure. Depending upon the nature of the alcohol used in its synthesis, DiPeP may exist either as a mixture consisting of several branched positional isomers, or as a single defined structure. This article investigates the skin sensitization potential and immunomodulatory effects of DiPeP CAS No. 84777-06-0, which is currently marketed and classified as a UVCB substance, by in silico and in vitro methods. Our findings showed an immunomodulatory effect for DiPeP in LPS-induced THP-1 activation assay (increased CD54 expression). In silico predictions using QSAR TOOLBOX 4.5, ToxTree, and VEGA did not identify DiPeP, in the form of a discrete compound, as a skin sensitizer. The keratinocyte activation (Key Event 2 (KE2) of the adverse outcome pathway (AOP) for skin sensitization) was evaluated by two different test methods (HaCaT assay and RHE assay), and results were discordant. While the HaCaT assay showed that DiPeP can activate keratinocytes (increased levels of IL-6, IL-8, IL-1α, and ILA gene expression), in the RHE assay, DiPeP slightly increased IL-6 release. Although inconclusive for KE2, the role of DiPeP in KE3 (dendritic cell activation) was demonstrated by the increased levels of CD54 and IL-8 and TNF-α in THP-1 cells (THP-1 activation assay). Altogether, findings were inconclusive regarding the skin sensitization potential of the UVCB DiPeP-disagreeing with the results of DiPeP in the form of discrete compound (skin sensitizer by the LLNA assay). Additional studies are needed to elucidate the differences between DiPeP isomer forms, and to better understand the applicability domains of non-animal methods in identifying skin sensitization hazards of UVCB substances.

Identification of necroptosis-related genes in ankylosing spondylitis by bioinformatics and experimental validation

The pathogenesis of ankylosing spondylitis (AS) remains unclear, and while recent studies have implicated necroptosis in various autoimmune diseases, an investigation of its relationship with AS has not been reported. In this study, we utilized the Gene Expression Omnibus database to compare gene expressions between AS patients and healthy controls, identifying 18 differentially expressed necroptosis-related genes (DENRGs), with 8 upregulated and 10 downregulated. Through the application of three machine learning algorithms-least absolute shrinkage and selection operation, support vector machine-recursive feature elimination and random forest-two hub genes, FASLG and TARDBP, were pinpointed. These genes demonstrated high specificity and sensitivity for AS diagnosis, as evidenced by receiver operating characteristic curve analysis. These findings were further supported by external datasets and cellular experiments, which confirmed the downregulation of FASLG and upregulation of TARDBP in AS patients. Immune cell infiltration analysis suggested that CD4+ T cells, CD8+ T cells, NK cells and neutrophils may be associated with the development of AS. Notably, in the group with high FASLG expression, there was a significant infiltration of CD8+ T cells, memory-activated CD4+ T cells and resting NK cells, with relatively less infiltration of memory-resting CD4+ T cells and neutrophils. Conversely, in the group with high TARDBP expression, there was enhanced infiltration of naïve CD4+ T cells and M0 macrophages, with a reduced presence of memory-resting CD4+ T cells. In summary, FASLG and TARDBP may contribute to AS pathogenesis by regulating the immune microenvironment and immune-related signalling pathways. These findings offer new insights into the molecular mechanisms of AS and suggest potential new targets for therapeutic strategies.

Gasdermin E promotes translocation of p65 and c-jun into nucleus in keratinocytes for progression of psoriatic skin inflammation

Gasdermin E (GSDME) has recently been identified as a critical executioner to mediate pyroptosis. While epidermal keratinocytes can initiate GSDME-mediated pyroptosis, the role of keratinocyte GSDME in psoriatic dermatitis remains poorly characterized. Through analysis of GEO datasets, we found elevated GSDME levels in psoriatic lesional skin. Additionally, GSDME levels correlated with both psoriasis severity and response to biologics treatments. Single-cell RNA sequencing (scRNA-seq) from a GEO dataset revealed GSDME upregulation in keratinocytes of psoriasis patients. In the imiquimod (IMQ)-induced psoriasis-like dermatitis mouse model, both full-length and cleaved forms of caspase-3 and GSDME were elevated in the epidermis. Abnormal proliferation and differentiation of keratinocytes and dermatitis were attenuated in Gsdme-/- mice and keratinocyte-specific Gsdme conditional knockout mice after IMQ stimulation. Exposure of keratinocytes to mixed cytokines (M5), mimicking psoriatic conditions, led to GSDME cleavage. Moreover, the interaction between GSDME-FL and p65 or c-jun was significantly increased after M5 stimulation. GSDME knockdown inhibited nuclear translocation of p65 and c-jun and decreased upregulation of psoriatic inflammatory mediators such as IL1β, CCL20, CXCL1, CXCL8, S100A8, and S100A9 in M5-challenged keratinocytes. In conclusion, GSDME in keratinocytes contributes to the pathogenesis and progression of psoriasis, potentially in a pyroptosis-independent manner by interacting and promoting translocation of p65 and c-jun. These findings suggest that keratinocyte GSDME could serve as a potential therapeutic target for psoriasis treatment.

Intranasal Exendin-4 modifies necroptosis-mediated innate immune response to combat septic encephalopathy in rats: Role of mTORC1 in immunogenic and tolerogenic cell demise

Septic encephalopathy (SE) is a critical mental status associated with potential long-term cognitive deficits and higher mortality rates in ICU patients. The shortfall in comprehending its pathophysiology limits effective treatment options, however, GLP-1 agonists opened an entry point for future neurodegenerative disease management. This work aims to explore the mTORC1 prospective role in the pathogenesis of SE using rapamycin (RAPA) and investigate the involvement of this complex in exendin-4 (EX4) neurotherapeutic potential using cecal ligation and puncturing (CLP)-induced SE model, focusing on necroptosis as a novel intervention besides necrosis and apoptosis. EX4 was administered intranasally alone or preceded by RAPA, which was also solely given to male Sprague-Dawley rats subjected to CLP. First, opposite to the SE effect, RAPA inhibited mTORC1 and blunted TNF-α-induced necroptosis and Drp1, a mitochondrial fission marker. However, RAPA worsened the SE effect on endotoxemia, functional/cortical structures, and apoptotic/necrotic cell deaths. Second, EX4 increased mTORC1 assembly in the cerebral cortex and reduced sepsis-induced endotoxemia and behavioral/cerebral histopathology deficits in an mTOR-dependent manner. EX4 also reduced the inflammatory marker TNF-α and necroptosis as indicated by RIPK-1/RIPK-3/MLKL dephosphorylation and deactivated PGAM/Drp1 axis. Besides, EX4 turned off the apoptotic cue, caspase-3&8/cytochrome-C. However, RAPA pre-administration nullified the EX4 effect on apoptosis and HMGB1-induced necrosis. In conclusion, our research declares that targeting mTORC1 could be a promising approach for managing SE. Additionally, we highlight that the novel neuroprotective effect of EX4 in ameliorating SE is achieved by reducing necroptosis and utilizing the anti-apoptotic and anti-necrotic properties of mTORC1.