USP9X promotes lipopolysaccharide-stimulated acute lung injury by deubiquitination of NLRP3

USP9X PROMOTES LPS-INDUCED FIBROBLAST CELL APOPTOSIS, INFLAMMATION, AND OXIDATIVE STRESS BY REGULATION OF TBL1XR1 DEUBIQUITINATION

ABSTRACT

Background: Ubiquitination and deubiquitination are involved in the progression of human diseases, including acute pneumonia. In this study, we aimed to explore the functions of ubiquitin-specific peptidase 9X-linked (USP9X) in lipopolysaccharide (LPS)-treated WI-38 cells. Methods: WI-38 cells were treated with LPS to induce the cellular damage and inflammation. 3-(4, 5-Dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) assay, and 5-ethynyl-2'-deoxyuridine (EdU) assay were performed to examine the proliferation of LPS-treated WI-38 cells. Flow cytometry analysis was conducted to detect LPS-treated WI-38 cell apoptosis. ELISA kits were utilized to determine the concentrations of inflammatory factors (IL-1β and TNF-α). Superoxide dismutase activity and reactive oxygen species level were examined with related kits. Ubibrowser (http://ubibrowser.bio-it.cn/ubibrowser/), ubiquitination assay, and co-immunoprecipitation assay demonstrated the interaction between USP9X and transducin β-like 1X related protein 1 (TBL1XR1). qRT-PCR assay and western blot assay were manipulated to determine the expression of USP9X and TBL1XR1. TBL1XR1 and USP9X knockdown experiments were conducted to explore their functions on LPS-induced WI-38 cell injury and inflammation. Results: TBL1XR1 expression was upregulated in LPS-treated WI-38 cells. TBL1XR1 knockdown promoted cell proliferation and repressed apoptosis, inflammation, and oxidative stress in LPS-treated WI-38 cells. Moreover, USP9X deubiquitinated TBL1XR1 to regulate TBL1XR1 expression. USP9X knockdown restored the effects of LPS on WI-38 cell proliferation, apoptosis, inflammation, and oxidative stress, but these effects of USP9X knockdown were further abolished by TBL1XR1 overexpression. In addition, USP9X promoted the NF-κB signaling pathway by the deubiquitination of TBL1XR1. Conclusion: USP9X promoted the apoptosis, inflammation, and oxidative stress of LPS-stimulated WI-38 cells through the deubiquitination of TBL1XR1.

Unraveling the priming phase of NLRP3 inflammasome activation: Molecular insights and clinical relevance

The NLRP3 inflammasome plays a pivotal role in the innate immune response. Its activation involves a two-step mechanism that consists of priming and activation. The priming of the NLRP3 inflammasome is a vital initial phase necessary for its activation and subsequent involvement in the immune response, though its understanding varies across studies. Recent research has identified key proteins that influence the priming process, revealing a sophisticated regulatory network. This review provides a comprehensive review of the priming phase of NLRP3 inflammasome activation, with a particular focus on the underlying molecular mechanisms, including transcriptional regulation, orchestration of the phosphorylation status, deubiquitination and the relationships with the inflammation-associated diseases. Understanding the intricacies of NLRP3 inflammasome priming not only elucidates fundamental aspects of immune regulation, but also provides potential avenues for therapeutic intervention in inflammatory diseases.

Inhibition of IRE1α/XBP1 axis alleviates LPS-induced acute lung injury by suppressing TXNIP/NLRP3 inflammasome activation and ERK/p65 signaling pathway

BACKGROUND

Acute lung injury or acute respiratory distress syndrome (ALI/ARDS) is a devastating clinical syndrome with high incidence and mortality rates. IRE1α-XBP1 pathway is one of the three major signaling axes of endoplasmic reticulum stress that is involved in inflammation, metabolism, and immunity. The role and potential mechanisms of IRE1α-XBP1 axis in ALI/ARDS has not well understood.

METHODS

The ALI murine model was established by intratracheal administration of lipopolysaccharide (LPS). Hematoxylin and eosin (H&E) staining and analysis of bronchoalveolar lavage fluid (BALF) were used to evaluate degree of lung injury. Inflammatory responses were assessed by ELISA and RT-PCR. Apoptosis was evaluated using TUNEL staining and western blot. Moreover, western blot, immunohistochemistry, and immunofluorescence were applied to test expression of IRE1α, XBP1, NLRP3, TXNIP, IL-1β, ERK1/2 and NF-κB p65.

RESULTS

The expression of IRE1α significantly increased after 24 h of LPS treatment. Inhibition of the IRE1α-XBP1 axis with 4µ8C notably improved LPS-induced lung injury and inflammatory infiltration, reduced the levels of IL-6, IL-1β, and TNF-α, and decreased cell apoptosis as well as the activation of the NLRP3 inflammasome. Besides, in LPS-stimulated Beas-2B cells, both 4µ8C and knockdown of XBP1 diminished the mRNA levels of IL-6 and IL-1B, inhibited cell apoptosis and reduced the protein levels of TXNIP, NLRP3 and secreted IL-1β. Mechanically, the phosphorylation and nuclear translocation of ERK1/2 and p65 were significantly suppressed by 4µ8C and XBP1 knockdown.

CONCLUSIONS

In summary, our findings suggest that IRE1α-XBP1 axis is crucial in the pathogenesis of ALI/ARDS, whose suppression could mitigate the pulmonary inflammatory response and cell apoptosis in ALI through the TXNIP/NLRP3 inflammasome and ERK/p65 signaling pathway. Our study may provide new evidence that IRE1α-XBP1 may be a promising therapeutic target for ALI/ARDS.

The regulation of pyroptosis by post-translational modifications: molecular mechanisms and therapeutic targets

Pyroptosis, a type of programmed cell death mediated by gasdermin family proteins, releases a large amount of immune stimulatory substances, which further contribute to inflammation and elicit an adaptive immune response against tumours and pathogens. And it occurs through multiple pathways that involve the activation of specific caspases and the cleavage of gasdermins. Post-translational modifications (PTMs) could influence the chemical properties of the modified residues and neighbouring regions, ultimately affecting the activity, stability, and functions of proteins to regulate pyroptosis. Many studies have been conducted to explore the influence of PTMs on the regulation of pyroptosis. In this review, we provide a comprehensive summary of different types of PTMs that influence pyroptosis, along with their corresponding modifying enzymes. Moreover, it elaborates on the specific contributions of different PTMs to pyroptosis and delves into how the regulation of these modifications can be leveraged for therapeutic interventions in cancer and inflammatory diseases.

Phillyrin prevents sepsis-induced acute lung injury through inhibiting the NLRP3/caspase-1/GSDMD-dependent pyroptosis signaling pathway

Acute lung injury (ALI) is a severe pulmonary disorder of sepsis with high clinical incidence and mortality. Nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3)-cysteinyl aspartate specific proteinase 1-gasdermin D (GSDMD)-dependent pyroptosis of alveolar epithelial cells (AECs) has emerged as a crucial contributor to ALI during sepsis. Phillyrin (PHI), a natural lignan isolated from the traditional Chinese herbal medicine Forsythia suspensa, has been shown to have anti-inflammatory, antioxidant and antiviral properties. However, little is known about the protective role and potential mechanism of PHI in sepsis-induced ALI, and it is uncertain whether the protective effect of PHI in sepsis-induced ALI is connected to pyroptosis. This study aims to examine the preventive effects of PHI on sepsis-induced ALI via the inhibition of NLRP3/caspase-1/GSDMD-mediated pyroptosis in AECs. Our findings demonstrate that preadministration of PHI successfully reduces sepsis-induced pulmonary edema, systemic/pulmonary inflammation, and pulmonary histological damage in lung tissues, bronchoalveolar lavage fluid, and the serum of septic mice. Intriguingly, PHI preadministration suppresses sepsis-induced protein expressions of pyroptosis-specific markers, especially their active forms. In vitro assays show that PHI pretreatment also protects type II AECs (MLE-12) from lipopolysaccharide-induced pyroptosis by preventing the activation of the pyroptosis signaling pathway. The results from molecular docking and surface plasmon resonance reveal that PHI has a significant affinity for direct binding to the GSDMD protein, suggesting that GSDMD is a potential pharmacological target for PHI. In conclusion, PHI can prevent sepsis-triggered ALI by effectively suppressing the activation of the canonical pyroptosis signaling pathway and pyroptosis of AECs.

Proximity proteomics reveals UCH-L1 as an essential regulator of NLRP3-mediated IL-1β production in human macrophages and microglia

Activation of the NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome complex is an essential innate immune signaling mechanism. To reveal how human NLRP3 inflammasome assembly and activation are controlled, in particular by components of the ubiquitin system, proximity labeling, affinity purification, and RNAi screening approaches were performed. Our study provides an intricate time-resolved molecular map of different phases of NLRP3 inflammasome activation. Also, we show that ubiquitin C-terminal hydrolase 1 (UCH-L1) interacts with the NACHT domain of NLRP3. Downregulation of UCH-L1 decreases pro-interleukin-1β (IL-1β) levels. UCH-L1 chemical inhibition with small molecules interfered with NLRP3 puncta formation and ASC oligomerization, leading to altered IL-1β cleavage and secretion, particularly in microglia cells, which exhibited elevated UCH-L1 expression as compared to monocytes/macrophages. Altogether, we profiled NLRP3 inflammasome activation dynamics and highlight UCH-L1 as an important modulator of NLRP3-mediated IL-1β production, suggesting that a pharmacological inhibitor of UCH-L1 may decrease inflammation-associated pathologies.

Cellular functions, molecular signalings and therapeutic applications: Translational potential of deubiquitylating enzyme USP9X as a drug target in cancer treatment

Protein ubiquitination, one of the most significant post-translational modifications, plays an important role in controlling the proteins activity in diverse cellular processes. The reversible process of protein ubiquitination, known as deubiquitination, has emerged as a critical mechanism for maintaining cellular homeostasis. The deubiquitinases (DUBs), which participate in deubiquitination process are increasingly recognized as potential candidates for drug discovery. Among these DUBs, ubiquitin-specific protease 9× (USP9X), a highly conserved member of the USP family, exhibits versatile functions in various cellular processes, including the regulation of cell cycle, protein endocytosis, apoptosis, cell polarity, immunological microenvironment, and stem cell characteristics. The dysregulation and abnormal activities of USP9X are influenced by intricate cellular signaling pathway crosstalk and upstream non-coding RNAs. The complex expression patterns and controversial clinical significance of USP9X in cancers suggest its potential as a prognostic biomarker. Furthermore, USP9X inhibitors has shown promising antitumor activity and holds the potential to overcome therapeutic resistance in preclinical models. However, a comprehensive summary of the role and molecular functions of USP9X in cancer progression is currently lacking. In this review, we provide a comprehensive delineation of USP9X participation in numerous critical cellular processes, complicated signaling pathways within the tumor microenvironment, and its potential translational applications to combat therapeutic resistance. By systematically summarizing the updated molecular mechanisms of USP9X in cancer biology, this review aims to contribute to the advancement of cancer therapeutics and provide essential insights for specialists and clinicians in the development of improved cancer treatment strategies.

LL-37 improves sepsis-induced acute lung injury by suppressing pyroptosis in alveolar epithelial cells

BACKGROUND

LL-37 (also known as murine CRAMP) is a human antimicrobial peptide that plays a crucial role in innate immune defence against sepsis through various mechanisms. However, its involvement in sepsis-induced lung injury remains unclear.

OBJECTIVES

This work investigates the impact of LL-37 on pyroptosis generated by LPS in alveolar epithelial cells. The research utilizes both in vivo and in vitro sepsis-associated acute lung injury (ALI) models to understand the underlying molecular pathways.

METHODS

In vivo, an acute lung injury model induced by sepsis was established by intratracheal administration of LPS in C57BL/6J mice, which were subsequently treated with low-dose CRAMP (recombinant murine cathelicidin, 2.5 mg.kg-1) and high-dose CRAMP (5.0 mg.kg-1). In vitro, pyroptosis was induced in a human alveolar epithelial cell line (A549) by stimulation with LPS and ATP. Treatment was carried out with recombinant human LL-37, or LL-37 was knocked out in A549 cells using small interfering RNA (siRNA). Subsequently, haematoxylin and eosin staining was performed to observe the histopathological changes in lung tissues in the control group and sepsis-induced lung injury group. TUNEL and PI staining were used to observe DNA fragmentation and pyroptosis in mouse lung tissues and cells in the different groups. An lactate dehydrogenase (LDH) assay was performed to measure the cell death rate. The expression levels of NLRP3, caspase1, caspase 1 p20, GSDMD, NT-GSDMD, and CRAMP were detected in mice and cells using Western blotting, qPCR, and immunohistochemistry. ELISA was used to assess the levels of interleukin (IL)-1β and IL-18 in mouse serum, bronchoalveolar lavage fluid (BALF) and lung tissue and cell culture supernatants.

RESULTS

The expression of NLRP3, caspase1 p20, NT-GSDMD, IL 18 and IL1β in the lung tissue of mice with septic lung injury was increased, which indicated activation of the canonical pyroptosis pathway and coincided with an increase in CRAMP expression. Treatment with recombinant CRAMP improved pyroptosis in mice with lung injury. In vitro, treatment with LPS and ATP upregulated these classic pyroptosis molecules, LL-37 knockdown exacerbated pyroptosis, and recombinant human LL-37 treatment alleviated pyroptosis in alveolar epithelial cells.

CONCLUSION

These findings indicate that LL-37 protects against septic lung injury by modulating the expression of classic pyroptotic pathway components, including NLRP3, caspase1, and GSDMD and downstream inflammatory factors in alveolar epithelial cells.

Posttranslational modifications of NLRP3 and their regulatory roles in inflammasome activation

The NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome is a multimolecular complex that plays a fundamental role in inflammation. Optimal activation of NLRP3 inflammasome is crucial for host defense against pathogens and the maintenance of immune homeostasis. Aberrant NLRP3 inflammasome activity has been implicated in various inflammatory diseases. Posttranslational modifications (PTMs) of NLRP3, a key inflammasome sensor, play critical roles in directing inflammasome activation and controlling the severity of inflammation and inflammatory diseases, such as arthritis, peritonitis, inflammatory bowel disease, atherosclerosis, and Parkinson's disease. Various NLRP3 PTMs, including phosphorylation, ubiquitination, and SUMOylation, could direct inflammasome activation and control inflammation severity by affecting the protein stability, ATPase activity, subcellular localization, and oligomerization of NLRP3 as well as the association between NLRP3 and other inflammasome components. Here, we provide an overview of the PTMs of NLRP3 and their roles in controlling inflammation and summarize potential anti-inflammatory drugs targeting NLRP3 PTMs.

Targeting immunometabolism against acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are life-threatening conditions triggered by multiple intra- and extra-pulmonary injury factors, characterized by complicated molecular mechanisms and high mortality. Great strides have been made in the field of immunometabolism to clarify the interplay between intracellular metabolism and immune function in the past few years. Emerging evidence unveils the crucial roles of immunometabolism in inflammatory response and ALI. During ALI, both macrophages and lymphocytes undergo robust metabolic reprogramming and discrete epigenetic changes after activated. Apart from providing ATP and biosynthetic precursors, these metabolic cellular reactions and processes in lung also regulate inflammation and immunity.In fact, metabolic reprogramming involving glucose metabolism and fatty acidoxidation (FAO) acts as a double-edged sword in inflammatory response, which not only drives inflammasome activation but also elicits anti-inflammatory response. Additionally, the features and roles of metabolic reprogramming in different immune cells are not exactly the same. Here, we outline the evidence implicating how adverse factors shape immunometabolism in differentiation types of immune cells during ALI and summarize key proteins associated with energy expenditure and metabolic reprogramming. Finally, novel therapeutic targets in metabolic intermediates and enzymes together with current challenges in immunometabolism against ALI were discussed.