Inflammasome-dependent release of the alarmin HMGB1 in endotoxemia

Role of inflammasomes in cancer immunity: mechanisms and therapeutic potential

Inflammasomes are multi-protein complexes that detect pathogenic and damage-associated molecular patterns, activating caspase-1, pyroptosis, and the maturation of pro-inflammatory cytokines such as IL-1β and IL-18Within the tumor microenvironment, inflammasomes like NLRP3 play critical roles in cancer initiation, promotion, and progression. Their activation influences the crosstalk between innate and adaptive immunity by modulating immune cell recruitment, cytokine secretion, and T-cell differentiation. While inflammasomes can contribute to tumor growth and metastasis through chronic inflammation, their components also present novel therapeutic targets. Several inhibitors targeting inflammasome components- such as sensor proteins (e.g., NLRP3, AIM2), adaptor proteins (e.g., ASC), caspase-1, and downstream cytokines- are being explored to modulate inflammasome activity. These therapeutic strategies aim to modulate inflammasome activity to enhance anti-tumor immune responses and improve clinical outcomes. Understanding the role of inflammasomes in cancer immunity is crucial for developing interventions that effectively bridge innate and adaptive immune responses for better therapeutic outcomes.

Physiological significance of antithrombin D-helix interaction with vascular GAGs

ABSTRACT

Antithrombin (AT) is an anticoagulant serpin involved in the regulation of proteolytic activities of coagulation proteases. AT also possesses a direct anti-inflammatory function. The anticoagulant function of AT is mediated through its reactive center loop-dependent inhibition of coagulation proteases, but anti-inflammatory function of AT is mediated via its D-helix-dependent interaction with vascular glycosaminoglycans (GAGs). In vitro assays have established that therapeutic heparins promote the anticoagulant function of AT by binding D-helix and activating the serpin, however, the contribution of vascular GAGs to D-helix-dependent anticoagulant function of AT has remained poorly understood in vivo. Here, we explored this question by using 2 AT mutants, (AT-4Mut), which exhibits neither affinity for heparin nor D-helix-dependent anti-inflammatory signaling but possesses normal protease-inhibitory function and an inactive signaling-selective AT mutant in which its P1-Arg425 is deleted (AT-R425del). In vivo properties of mutants were compared with wild-type AT (AT-WT) in a small interfering RNA (siRNA)-mediated AT-deficient mouse model. The siRNA knockdown efficiently reduced expression of AT and induced robust procoagulant and proinflammatory phenotypes in mice. Infusion of both AT-WT and AT-4Mut rescued the procoagulant phenotype of AT-deficient mice as evidenced by restoration of the plasma clotting time and inhibition of fibrin deposition. AT-WT also attenuated inflammation as evidenced by reduced VCAM-1 expression and leukocyte infiltration in the liver and lungs; however, AT-4Mut failed to attenuate inflammation. Interestingly, AT-R425del also effectively attenuated inflammation in AT-depleted mice. These results suggest that interaction of AT D-helix with vascular GAGs may primarily be responsible for anti-inflammatory signaling rather than protease-inhibitory function of the serpin.

Innate Immune Sensors and Cell Death-Frontiers Coordinating Homeostasis, Immunity, and Inflammation in Skin

The skin provides a life-sustaining interface between the body and the external environment. A dynamic communication among immune and non-immune cells in the skin is essential to ensure body homeostasis. Dysregulated cellular communication can lead to the manifestation of inflammatory skin conditions. In this review, we will focus on the following two key frontiers in the skin: innate immune sensors and cell death, as well as their cellular crosstalk in the context of skin homeostasis and inflammation. This review will highlight the recent advancements and mechanisms of how these pathways integrate signals and orchestrate skin immunity, focusing on inflammatory skin diseases and skin infections in mice and humans.

An adenoviral vector encoding an inflammation-inducible antagonist, HMGB1 Box A, as a novel therapeutic approach to inflammatory diseases

Influenza, as well as other respiratory viruses, can trigger local and systemic inflammation resulting in an overall "cytokine storm" that produces serious outcomes such as acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). We hypothesized that gene therapy platforms could be useful in these cases if the production of an anti-inflammatory protein reflects the intensity and duration of the inflammatory condition. The recombinant protein would be produced and released only in the presence of the inciting stimulus, avoiding immunosuppression or other unwanted side effects that may occur when treating infectious diseases with anti-inflammatory drugs. To test this hypothesis, we developed AdV.C3-Tat/HIV-Box A, an inflammation-inducible cassette that remains innocuous in the absence of inflammation but releases HMGB1 Box A, an antagonist of high mobility group box 1 (HMGB1), in response to inflammatory stimuli such as lipopolysaccharide (LPS) or influenza virus infection. We report here that this novel inflammation-inducible HMGB1 Box A construct in a non-replicative adenovirus (AdV) vector mitigates lung and systemic inflammation therapeutically in response to influenza infection. We anticipate that this strategy will apply to the treatment of multiple diseases in which HMGB1-mediated signaling is a central driver of inflammation.IMPORTANCEMany inflammatory diseases are mediated by the action of a host-derived protein, HMGB1, on Toll-like receptor 4 (TLR4) to elicit an inflammatory response. We have engineered a non-replicative AdV vector that produces HMGB1 Box A, an antagonist of HMGB1-induced inflammation, under the control of an endogenous complement component C3 (C3) promoter sequence, that is inducible by LPS and influenza in vitro and ex vivo in macrophages (Mϕ) and protects mice and cotton rats therapeutically against infection with mouse-adapted and human non-adapted influenza strains, respectively, in vivo. We anticipate that this novel strategy will apply to the treatment of multiple infectious and non-infectious diseases in which HMGB1-mediated TLR4 signaling is a central driver of inflammation.

Chicken GSDME, a major pore-forming molecule responsible for RNA virus-induced pyroptosis in chicken

Pyroptosis is an inflammatory type of programmed cell death that mainly depends on the formation of plasma membrane pores by Gasdermin D (GSDMD) in mammals. However, the genetic deficiency of GSDMD in chicken renders avian pyroptosis elusive. Here, we show that infection of DF-1 cells (a chicken cell line) with infectious bursal disease virus (IBDV) induced cell death associated with chicken GSDME (chGSDME) cleavage, and so did cells with other RNA virus (VSV, AIV, or NDV) infections, indicating a broad role of chGSDME in RNA virus-induced pyroptosis in chicken. Furthermore, infection of DF-1 cells by IBDV or treatment of cells with Poly(I:C) initiated MDA5-mediated signaling pathway, followed by the activation of chCaspase-3/7 cleaving chGSDME at a specific site 270DAVD273. Moreover, knockdown or knockout of chGSDME expression in cells markedly reduced IBDV-induced pyroptosis and viral release. These results unravel the mechanisms of pyroptosis in chickens with RNA virus infection, providing important clues to uncover the role of GSDM proteins of different species in host response against pathogenic infection.IMPORTANCEPyroptosis is an inflammatory type of programmed cell death that mainly depends on the function of GSDMD in mammals and plays a crucial role in the pathogenesis of viral infection, whereas the mechanism of pyroptosis in chicken remains elusive. Herein, we show that IBDV and other RNA virus induced pyroptosis through the chMDA5-CASP8/9-CASP3/7-chGSDME pathway. The finding advances our understanding of GSDM proteins of different species in host response against pathogenic infection.

Transplantation of gasdermin pores by extracellular vesicles propagates pyroptosis to bystander cells

Pyroptosis mediated by gasdermins (GSDMs) plays crucial roles in infection and inflammation. Pyroptosis triggers the release of inflammatory molecules, including damage-associated molecular patterns (DAMPs). However, the consequences of pyroptosis-especially beyond interleukin (IL)-1 cytokines and DAMPs-that govern inflammation are poorly defined. Here, we show intercellular propagation of pyroptosis from dying cells to bystander cells in vitro and in vivo. We identified extracellular vesicles (EVs) released by pyroptotic cells as the propagator of lytic death to naive cells, promoting inflammation. DNA-PAINT super-resolution and immunoelectron microscopy revealed GSDMD pore structures on EVs released by pyroptotic cells. Importantly, pyroptotic EVs transplant GSDMD pores on the plasma membrane of bystander cells and kill them. Overall, we demonstrate that cell-to-cell vesicular transplantation of GSDMD pores disseminates pyroptosis, revealing a domino-like effect governing disease-associated bystander cell death.

Preclinical development of the TLR4 antagonist FP12 as a drug lead targeting the HMGB1/MD-2/TLR4 axis in lethal influenza infection

BACKGROUND

Acute Lung Injuries (ALI) are a severe consequence of influenza-induced cytokine storm that can cause respiratory failure and death. It has been demonstrated that Toll-like Receptor 4 (TLR4) is involved in cytokine storm and that TLR4-/- mice are protected against ALI. Therefore, TLR4 is a prime target for protection against ALI. FP12 is a known TLR4 antagonist that reduces TLR4-dependent immune activation and it is a promising lead compound for the treatment of innate immunity related pathologies.

OBJECTIVES

We present here the preclinical development of FP12 as an anti-inflammatory lead compound acting on influenza-induced ALI.

METHODS

In vitro: We pre-treated THP-1 cells with FP12 (10 μM) for 0.5 h, then exposed to LPS (100 ng/ml) for 0 to 16 h. In some experiments, cells were simultaneously incubated with FP12 and LPS, or FP12 was added 30 min after LPS. Cytokine levels were measured by Western blot and ELISA assays. In vivo: WT C57BL/6J mice were infected with mouse-adapted influenza virus (PR8). Two days after infection, mice received either vehicle, FP7 (200 µg/mouse), or FP12 (200 µg/mouse) once daily (Day 2 to Day 6). Mice were monitored daily for survival for 14 days. Data were collected through histological staining, qRT-PCR, and ELISA assay.

RESULTS

FP12 treatment inhibited both LPS- and HMGB1-induced TLR4 intracellular pathways (MyD88 and TRIF) leading to significantly reduced levels of a variety of proinflammatory cytokines including Type I interferon (IFN-β), highlighting its effectiveness in controlling proinflammatory protein production and reducing inflammation. FP12 protected mice therapeutically from influenza virus-induced lethality and reduced both cytokine gene expression and High Mobility Group Box 1 (HMGB1) levels in the lungs as well as ALI.

CONCLUSION

FP12 can antagonize TLR4 activation in vitro and protects mice from severe influenza infection, most likely by reducing the TLR4-dependent cytokine storm mediated by danger-associated molecular patterns (DAMPs).

Connexin 43 and Pannexin 1 hemichannels as endogenous regulators of innate immunity in sepsis

Sepsis is a life-threatening organ dysfunction resulting from a dysregulated host response to infections that is initiated by the body's innate immune system. Nearly a decade ago, we discovered that bacterial lipopolysaccharide (LPS) and serum amyloid A (SAA) upregulated Connexin 43 (Cx43) and Pannexin 1 (Panx1) hemichannels in macrophages. When overexpressed, these hemichannels contribute to sepsis pathogenesis by promoting ATP efflux, which intensifies the double-stranded RNA-activated protein kinase R (PKR)-dependent inflammasome activation, pyroptosis, and the release of pathogenic damage-associated molecular pattern (DAMP) molecules, such as HMGB1. Mimetic peptides targeting specific regions of Cx43 and Panx1 can distinctly modulate hemichannel activity in vitro, and diversely impact sepsis-induced lethality in vivo. Along with extensive supporting evidence from others, we now propose that hemichannel molecules play critical roles as endogenous regulators of innate immunity in sepsis.

Role of the Receptor for Advanced Glycation End Products (RAGE) and Its Ligands in Inflammatory Responses

Since its discovery in 1992, the receptor for advanced glycation end products (RAGE) has emerged as a key receptor in many pathological conditions, especially in inflammatory conditions. RAGE is expressed by most, if not all, immune cells and can be activated by many ligands. One characteristic of RAGE is that its ligands are structurally very diverse and belong to different classes of molecules, making RAGE a promiscuous receptor. Many of RAGE ligands are damaged associated molecular patterns (DAMPs) that are released by cells under inflammatory conditions. Although RAGE has been at the center of a lot of research in the past three decades, a clear understanding of the mechanisms of RAGE activation by its ligands is still missing. In this review, we summarize the current knowledge of the role of RAGE and its ligands in inflammation.

Modification macrophage to foam cells in atherosclerosis disease: some factors stimulate or inhibit this process

Background

Atherosclerosis is an arterial blood vessel disease that begins and progresses by turning macrophages into foam cells. Uptake of oxidized low-density lipoprotein (ox-LDL), cholesterol esterification and cholesterol efflux are the most important factors in the formation of foam cells and play an important role in atherosclerosis.

Methods

The present study is based on the data obtained from the PubMed database (1961-2024) using the MeSH search terms "Atherosclerosis", "Macrophages" and "Foam cells". Reviews for writing the main text and non-English-language articles were excluded.

Result

The interaction between ox-LDL and macrophages plays an important role in plaque initiation and promotion processes. Macrophages abnormally digest ox-LDL, resulting in the accumulation of lipids and formation of foam cells. This is an important step in the development of atherosclerosis. Also, several other factors such as inflammatory factors, growth factors, hormones, etc. can play an important role in the development of atherosclerotic lesions or counteract it by affecting the formation of foam cells.

Conclusion

Several factors can affect the progression of atherosclerosis by affecting macrophage activity or its conversion to foam cells. Also, some of these factors play a protective role against the development and atherosclerosis progression. In this paper, we reviewed some of these factors and their effect on atherosclerosis.

Type-I interferon shapes peritoneal immunity in cirrhosis and drives caspase-5-mediated progranulin release upon infection

BACKGROUND & AIMS

Gut bacterial translocation contributes to immune dysfunction and spontaneous bacterial peritonitis (SBP) in cirrhosis. We hypothesized that exposure of peritoneal macrophages (PMs) to bacterial DNA results in type-I interferon (IFN) production, shaping subsequent immune responses, inflammasome activation, and the release of damage-associated molecular patterns (DAMPs).

METHODS

PMs from patients with cirrhosis were stimulated with E. coli single-stranded DNA (ssDNA), lipopolysaccharide and IFN, or infected with E. coli, S. aureus, and Group B streptococcus in vitro. Cytokine release, inflammasome activation, and DAMP release were quantified by quantitative-PCR, ELISA, western blots, and reporter cells employing primary PMs, monocytes, and caspase-deficient THP-1 macrophages. Serum progranulin concentration was correlated with transplant-free survival in 77 patients with SBP.

RESULTS

E. coli ssDNA induced strong type-I IFN activity in PMs and monocytes, priming them for enhanced lipopolysaccharide-mediated tumor necrosis factor production without inducing toll-like receptor 4 tolerance. During in vitro macrophage bacterial infection, type-I IFN release aligned with upregulated expression of IFN-regulatory factors (IRF)1/2 and guanylate binding proteins (GBP)2/5. PMs upregulated inflammasome-associated proteins and type-I IFN upon E. coli ssDNA exposure and released interleukin-1β upon bacterial infection. Proteomic screening in mouse macrophages revealed progranulin release as being caspase-11-dependent during E. coli infection. PMs and THP-1 macrophages released significant amounts of progranulin when infected with S. aureus or E. coli via gasdermin D in a type-I IFN- and caspase-5-dependent manner. During SBP, PMs upregulated IRF1, GBP2/5 and caspase-5 and higher serum progranulin concentrations were indicative of lower 90-day transplant-free survival after SBP.

CONCLUSIONS

Type-I IFN shapes peritoneal immune responses and regulates caspase-5-mediated progranulin release during SBP.

IMPACT AND IMPLICATIONS

Patients with cirrhosis exhibit impaired immune responses and increased susceptibility to bacterial infections. This study reveals that type-I interferon responses, triggered by pathogen-associated molecular patterns, are crucial in regulating macrophage activation and priming them for inflammatory responses. Additionally, we elucidate the mechanisms by which type-I interferons promote the release of progranulin from macrophages during spontaneous bacterial peritonitis. Our findings enhance understanding of how bacterial translocation affects immune responses, identify novel biomarkers for inflammasome activation during infections, and point to potential therapeutic targets.

Dual alarmin-receptor-specific targeting peptide systems for treatment of sepsis

The pathophysiology of sepsis is characterized by a systemic inflammatory response to infection; however, the cytokine blockade that targets a specific early inflammatory mediator, such as tumor necrosis factor, has shown disappointing results in clinical trials. During sepsis, excessive endotoxins are internalized into the cytoplasm of immune cells, resulting in dysregulated pyroptotic cell death, which induces the leakage of late mediator alarmins such as HMGB1 and PTX3. As late mediators of lethal sepsis, overwhelming amounts of alarmins bind to high-affinity TLR4/MD2 and low-affinity RAGE receptors, thereby amplifying inflammation during early-stage sepsis. In this study, we developed a novel alarmin/receptor-targeting system using a TLR4/MD2/RAGE-blocking peptide (TMR peptide) derived from the HMGB1/PTX3-receptors interacting motifs. The TMR peptide successfully attenuated HMGB1/PTX3- and LPS-mediated inflammatory cytokine production by impairing its interactions with TLR4 and RAGE. Moreover, we developed TMR peptide-conjugated liposomes (TMR-Lipo) to improve the peptide pharmacokinetics. In combination therapy, moderately antibiotic-loaded TMR-Lipo demonstrated a significant therapeutic effect in a mouse model of cecal ligation- and puncture-induced sepsis. The identification of these peptides will pave the way for the development of novel pharmacological tools for sepsis therapy.

High Mobility Group Box 1 (HMGB1): Molecular Signaling and Potential Therapeutic Strategies

High Mobility Group Box 1 (HMGB1) is a highly conserved non-histone chromatin-associated protein across species, primarily recognized for its regulatory impact on vital cellular processes, like autophagy, cell survival, and apoptosis. HMGB1 exhibits dual functionality based on its localization: both as a non-histone protein in the nucleus and as an inducer of inflammatory cytokines upon extracellular release. Pathophysiological insights reveal that HMGB1 plays a significant role in the onset and progression of a vast array of diseases, viz., atherosclerosis, kidney damage, cancer, and neurodegeneration. However, a clear mechanistic understanding of HMGB1 release, translocation, and associated signaling cascades in mediating such physiological dysfunctions remains obscure. This review presents a detailed outline of HMGB1 structure-function relationship and its regulatory role in disease onset and progression from a signaling perspective. This review also presents an insight into the status of HMGB1 druggability, potential limitations in understanding HMGB1 pathophysiology, and future perspective of studies that can be undertaken to address the existing scientific gap. Based on existing paradigm of various studies, HMGB1 is a critical regulator of inflammatory cascades and drives the onset and progression of a broad spectrum of dysfunctions. Studies focusing on HMGB1 druggability have enabled the development of biologics with potential clinical benefits. However, deeper understanding of post-translational modifications, redox states, translocation mechanisms, and mitochondrial interactions can potentially enable the development of better courses of therapy against HMGB1-mediated physiological dysfunctions.

Mitochondrial dysfunction and NLRP3 inflammasome: key players in kidney stone formation

The mitochondrion serves as a critical intracellular organelle, engaging in essential roles in the regulation of energy production, oxidative stress management, calcium homeostasis, and apoptosis. One such disease that has been particularly associated with these functions is kidney stone disease (KSD), specifically calcium oxalate (CaOx). It is underpinned by oxidative stress and tissue inflammation. Recent studies have shed light on the vital involvement of mitochondrial dysfunction, the nucleotide-binding domain and leucine-rich repeat containing protein 3 (NLRP3) inflammasome, endoplasmic reticulum stress and subsequent cell death in CaOx crystal retention and aggregation. These processes are pivotal in the pathogenesis of kidney stone formation. This review focuses on the pivotal roles of mitochondria in renal cell functions and provides an overview of the intricate interconnectedness between mitochondrial dysfunction and NLRP3 inflammasome activation in the context of KSD. It is essential to recognise the utmost significance of gaining a comprehensive understanding of the mechanisms that safeguard mitochondrial function and regulate the NLRP3 inflammasome. Such knowledge carries significant scientific implications and opens up promising avenues for the development of innovative strategies to prevent the formation of kidney stones.

Elevated levels of damage-associated molecular patterns HMGB1 and S100A8/A9 coupled with toll-like receptor-triggered monocyte activation are associated with inflammation in patients with myelofibrosis

Inflammation plays a pivotal role in the pathogenesis of primary and post-essential thrombocythemia or post-polycythemia vera myelofibrosis (MF) in close cooperation with the underlying molecular drivers. This inflammatory state is induced by a dynamic spectrum of inflammatory cytokines, although recent evidence points to the participation of additional soluble inflammatory mediators. Damage-associated molecular patterns (DAMPs) represent endogenous signals released upon cell death or damage which trigger a potent innate immune response. We assessed the contribution of two prototypical DAMPs, HMGB1 and S100A8/A9, to MF inflammation. Circulating HMGB1 and S100A8/A9 were elevated in MF patients in parallel to the degree of systemic inflammation and levels increased progressively during advanced disease stages. Patients with elevated DAMPs had higher frequency of adverse clinical features, such as anemia, and inferior survival, suggesting their contribution to disease progression. Monocytes, which are key players in MF inflammation, were identified as a source of S100A8/A9 but not HMGB1 release, while both DAMPs correlated with cell death parameters, such as serum LDH and cell-free DNA, indicating that passive release is an additional mechanism leading to increased DAMPs. HMGB1 and S100A8/A9 promote inflammation through binding to Toll-like receptor (TLR) 4, whereas the former also binds TLR2. Monocytes from MF patients were shown to be hyperactivated at baseline, as reflected by higher CD11b and tissue factor exposure and increased expression levels of proinflammatory cytokines IL-1β and IL-6. Patient monocytes showed preserved TLR4 and TLR2 expression and were able to mount normal or even exacerbated functional responses and cytokine upregulation following stimulation of TLR4 and TLR2. Elevated levels of endogenous TLR ligands HMGB1 and S100A8/A9 coupled to the finding of preserved or hyperreactive TLR-triggered responses indicate that DAMPs may promote monocyte activation and cytokine production in MF, fueling inflammation. Plasma IL-1β and IL-6 were elevated in MF and correlated with DAMPs levels, raising the possibility that DAMPs could contribute to cytokine generation in vivo. In conclusion, this study highlights that, in cooperation with classic proinflammatory cytokines, DAMPs represent additional inflammatory mediators that may participate in the generation of MF inflammatory state, potentially providing novel biomarkers of disease progression and new therapeutic targets.

Genetic and epigenetic regulation of inflammasomes: Role in atherosclerosis

The cardiovascular complications of atherosclerosis are thought to arise from an inflammatory response to the accumulation of cholesterol-rich lipoproteins in the arterial wall. The positive outcome of CANTOS (Canakinumab Anti-inflammatory Thrombosis Outcome Study) provided key evidence to support this concept and suggested that inflammasomes and IL-1β are important inflammatory mediators in human atherosclerotic cardiovascular diseases (ACVD). In specific settings NLRP3 or AIM2 inflammasomes can induce inflammatory responses in the arterial wall and promote the formation of unstable atherosclerotic plaques. Clonal hematopoiesis (CH) has recently emerged as a major independent risk factor for ACVD. CH mutations arise during ageing and commonly involves variants in genes mediating epigenetic modifications (TET2, DNMT3A, ASXL1) or cytokine signaling (JAK2). Accumulating evidence points to the role of inflammasomes in the progression of CH-induced ACVD events and has shed light on the regulatory pathways and possible therapeutic approaches that specifically target inflammasomes in atherosclerosis. Epigenetic dynamics play a vital role in regulating the generation and activation of inflammasome components by causing changes in DNA methylation patterns and chromatin assembly. This review examines the genetic and epigenetic regulation of inflammasomes, the intersection of macrophage cholesterol accumulation with inflammasome activation and their roles in atherosclerosis. Understanding the involvement of inflammasomes in atherosclerosis pathogenesis may lead to customized treatments that reduce the burden of ACVD.

Pyroptosis, gasdermins and allergic diseases

Pyroptosis is an inflammatory form of programmed cell death that is distinct from necrosis and apoptosis. Pyroptosis is primarily mediated by the gasdermin family of proteins (GSDMA-E and PVJK), which, when activated by proteolytic cleavage, form pores in the plasma membrane, leading to cell death. While much of the past research on pyroptosis has focused on its role in cancer, metabolic disorders, and infectious diseases, recent experimental and observational studies have begun to implicate pyroptosis in allergic diseases. These studies suggest that gasdermin-mediated pyroptosis contributes to the development of allergic conditions and could offer novel targets for therapy. Here, we review our current understanding of pyroptosis with an emphasis on the role of gasdermins as executioners of pyroptosis and potential mediators to allergic disease. We highlight new discoveries that establish a mechanistic link between the biochemical actions of gasdermins and the onset of allergic diseases. Additionally, we discuss how pyroptosis and gasdermins might contribute to the dysfunction of epithelial barrier, a key factor believed to initiate the progression of various allergic diseases.

No Time to Die: How Cytomegaloviruses Suppress Apoptosis, Necroptosis, and Pyroptosis

Viruses are obligate intracellular pathogens as their replication depends on the metabolism of the host cell. The induction of cellular suicide, known as programmed cell death (PCD), has the potential to hinder viral replication and act as a first line of defense against viral pathogens. Apoptosis, necroptosis, and pyroptosis are three important PCD modalities. Different signaling pathways are involved in their execution, and they also differ in their ability to cause inflammation. Cytomegaloviruses (CMV), beta-herpesviruses with large double-stranded DNA genomes, encode a great variety of immune evasion genes, including several cell death suppressors. While CMV inhibitors of apoptosis and necroptosis have been known and studied for years, the first pyroptosis inhibitor has been identified and characterized only recently. Here, we describe how human and murine CMV interfere with apoptosis, necroptosis, and pyroptosis signaling pathways. We also discuss the importance of the different PCD forms and their viral inhibitors for the containment of viral replication and spread in vivo.

Budesonide and N-acetylcysteine inhibit activation of the NLRP3 inflammasome by regulating miR-381 to alleviate acute lung injury caused by the pyroptosis-mediated inflammatory response

Background

The anti-inflammatory effects of budesonide (BUN) and N-acetylcysteine (NAC) attenuate acute lung injury (ALI). The aim of this study was to investigate the effects of combination therapy consisting of BUN and NAC on ALI and the underlying mechanisms.

Methods

In vitro and in vivo models of ALI were generated by LPS induction. Western blotting was used to detect the expression levels of pyroptosis-related proteins and inflammation-related factors, and RT-qPCR was used to detect the expression of miR-381. Cell proliferation and apoptosis were detected by CCK-8 and flow cytometry, respectively. ELISA was used to detect the levels of inflammation-related factors. HE staining was used to detect lung injury.

Results

The results showed that LPS effectively induced pyroptosis in cells and promoted the expression of pyroptosis-related proteins (Caspase1, Gasdermin D and NLRP3) and inflammatory cytokines (TNF-α, IL-6 and IL-1β). The combination of BUN and NAC significantly alleviated LPS-induced pyroptosis and inflammation. In addition, the combination of BUN and NAC effectively promoted miR-381 expression. Transfection of miR-381 mimics effectively alleviated LPS-induced pyroptosis and inflammation, while transfection of miR-381 inhibitors had the opposite effect. miR-381 negatively regulates NLRP3 expression. Treatment with a miR-381 inhibitor or pc-NLRP3 reversed the effects of the combination of BUN and NAC. In a mouse model of ALI, the combination of BUN and NAC effectively improved lung injury, while treatment with a miR-381 inhibitor or pc-NLRP3 effectively reversed this effect.

Conclusion

Overall, this study revealed that BUN + NAC inhibits the activation of NLRP3 by regulating miR-381, thereby alleviating ALI caused by pyroptosis-mediated inflammation.

NLRP3 inflammasome in atherosclerosis: Mechanisms and targeted therapies

Atherosclerosis (AS) is the primary pathology behind various cardiovascular diseases and the leading cause of death and disability globally. Recent evidence suggests that AS is a chronic vascular inflammatory disease caused by multiple factors. In this context, the NLRP3 inflammasome, acting as a signal transducer of the immune system, plays a critical role in the onset and progression of AS. The NLRP3 inflammasome is involved in endothelial injury, foam cell formation, and pyroptosis in AS. Therefore, targeting the NLRP3 inflammasome offers a new treatment strategy for AS. This review highlights the latest insights into AS pathogenesis and the pharmacological therapies targeting the NLRP3 inflammasome, focusing on optimal targets for small molecule inhibitors. These insights are valuable for rational drug design and the pharmacological assessment of new targeted NLRP3 inflammasome inhibitors in treating AS.

HMGB1 as an extracellular pro-inflammatory cytokine: Implications for drug-induced organic damage

Drug-induced organic damage encompasses various intricate mechanisms, wherein HMGB1, a non-histone chromosome-binding protein, assumes a significant role as a pivotal hub gene. The regulatory functions of HMGB1 within the nucleus and extracellular milieu are interlinked. HMGB1 exerts a crucial regulatory influence on key biological processes including cell survival, inflammatory regulation, and immune response. HMGB1 can be released extracellularly from the cell during these processes, where it functions as a pro-inflammation cytokine. HMGB1 interacts with multiple cell membrane receptors, primarily Toll-like receptors (TLRs) and receptor for advanced glycation end products (RAGE), to stimulate immune cells and trigger inflammatory response. The excessive or uncontrolled HMGB1 release leads to heightened inflammatory responses and cellular demise, instigating inflammatory damage or exacerbating inflammation and cellular demise in different diseases. Therefore, a thorough review on the significance of HMGB1 in drug-induced organic damage is highly important for the advancement of pharmaceuticals, ensuring their effectiveness and safety in treating inflammation as well as immune-related diseases. In this review, we initially outline the characteristics and functions of HMGB1, emphasizing their relevance in disease pathology. Then, we comprehensively summarize the prospect of HMGB1 as a promising therapeutic target for treating drug-induced toxicity. Lastly, we discuss major challenges and propose potential avenues for advancing the development of HMGB1-based therapeutics.

Oxylipins and metabolites from pyroptotic cells act as promoters of tissue repair

Pyroptosis is a lytic cell death mode that helps limit the spread of infections and is also linked to pathology in sterile inflammatory diseases and autoimmune diseases1-4. During pyroptosis, inflammasome activation and the engagement of caspase-1 lead to cell death, along with the maturation and secretion of the inflammatory cytokine interleukin-1β (IL-1β). The dominant effect of IL-1β in promoting tissue inflammation has clouded the potential influence of other factors released from pyroptotic cells. Here, using a system in which macrophages are induced to undergo pyroptosis without IL-1β or IL-1α release (denoted Pyro-1), we identify unexpected beneficial effects of the Pyro-1 secretome. First, we noted that the Pyro-1 supernatants upregulated gene signatures linked to migration, cellular proliferation and wound healing. Consistent with this gene signature, Pyro-1 supernatants boosted migration of primary fibroblasts and macrophages, and promoted faster wound closure in vitro and improved tissue repair in vivo. In mechanistic studies, lipidomics and metabolomics of the Pyro-1 supernatants identified the presence of both oxylipins and metabolites, linking them to pro-wound-healing effects. Focusing specifically on the oxylipin prostaglandin E2 (PGE2), we find that its synthesis is induced de novo during pyroptosis, downstream of caspase-1 activation and cyclooxygenase-2 activity; further, PGE2 synthesis occurs late in pyroptosis, with its release dependent on gasdermin D pores opened during pyroptosis. As for the pyroptotic metabolites, they link to immune cell infiltration into the wounds, and polarization to CD301+ macrophages. Collectively, these data advance the concept that the pyroptotic secretome possesses oxylipins and metabolites with tissue repair properties that may be harnessed therapeutically.

Pyroptosis-related crosstalk in osteoarthritis: Macrophages, fibroblast-like synoviocytes and chondrocytes

The pathogenesis of osteoarthritis (OA) involves a multifaceted interplay of inflammatory processes. The initiation of pyroptosis involves the secretion of pro-inflammatory cytokines and has been identified as a critical factor in regulating the development of OA. Upon initiation of pyroptosis, a multitude of inflammatory mediators are released and can be disseminated throughout the synovial fluid within the joint cavity, thereby facilitating intercellular communication across the entire joint. The main cellular components of joints include chondrocytes (CC), fibroblast-like synoviocytes (FLS) and macrophages (MC). Investigating their interplay can enhance our understanding of OA pathogenesis. Therefore, we comprehensively examine the mechanisms underlying pyroptosis and specifically investigate the intercellular interactions associated with pyroptosis among these three cell types, thereby elucidating their collective contribution to the progression of OA. We propose the concept of ' CC-FLS-MC pyroptosis-related crosstalk', describe the various pathways of pyroptotic interactions among these three cell types, and focus on recent advances in intervening pyroptosis in these three cell types for treating OA. We hope this will provide a possible direction for diversification of treatment for OA. The Translational potential of this article. The present study introduces the concept of 'MC-FLS-CC pyroptosis-related crosstalk' and provides an overview of the mechanisms underlying pyroptosis, as well as the pathways through which it affects MC, FLS, and CC. In addition, the role of regulation of these three types of cellular pyroptosis in OA has also been concerned. This review offers novel insights into the interplay between these cell types, with the aim of providing a promising avenue for diversified management of OA.

Spotlight on macrophage pyroptosis: A bibliometric and visual analysis from 2001 to 2023

Macrophage pyroptosis plays a significant role in the pathogenesis of various diseases, especially acute lung injury, atherosclerosis, and sepsis. Despite its importance, analysis of the existing literature has been limited. Therefore, we conducted a bibliometric analysis to provide a comprehensive overview of research on macrophage pyroptosis and identify the current research foci and trends in this field. We collected articles related to macrophage pyroptosis published between 2001 and 2022 from the Web of Science Core Collection and PubMed. Citespace, VOSviewer, bibliometrix R package, and Microsoft Excel 2019 were used to analyze co-occurrence relationships and the contribution of countries/regions, institutions, journals, authors, references, and keywords. In total, 1321 papers were included. China and the United States of America published the most articles in this field. TD Kanneganti had the most publications; BT Cookson was the most cited. Although China contributed the most publications, it had a relatively low ratio of multiple-country collaborations (0.132). Among journals, Frontiers in Immunology and Cell Death Disease published the most papers; Nature and the Journal of Immunology were frequently co-cited. Frequently occurring keywords included "inflammation," "NLRP3 inflammasome," "apoptosis," "caspase-1," and "cell death." Moreover, with the advancement of gene editing technology and the integration of clinical applications, novel molecules ("caspases," "GSDMD," "ASC"), programmed cell death topics ("pyroptosis," "ferroptosis," "necrosis"), and clinical applications ("alveolar macrophage," "atherosclerosis," "prognosis") emerged as frontiers. The macrophage pyroptosis field is rapidly evolving and holds promise as a potential target for treating macrophage pyroptosis-related diseases.

Novel chemotype NLRP3 inhibitors that target the CRID3-binding pocket with high potency

The NLRP3 inflammasome plays a central role in various human diseases. Despite significant interest, most clinical-grade NLRP3 inhibitors are derived from sulfonylurea inhibitor CRID3 (also called MCC950). Here, we describe a novel chemical class of NLRP3-inhibiting compounds (NIC) that exhibit potent and selective NLRP3 inflammasome inhibition in human monocytes and mouse macrophages. BRET assays demonstrate that they physically interact with NLRP3. Structural modeling further reveals they occupy the same binding site of CRID3 but in a critically different conformation. Furthermore, we show that NIC-11 and NIC-12 lack the off-target activity of CRID3 against the enzymatic activity of carbonic anhydrases I and II. NIC-12 selectively reduces circulating IL-1ß levels in the LPS-endotoxemia model in mice and inhibits NLRP3 inflammasome activation in CAPS patient monocytes and mouse macrophages with about tenfold increased potency compared with CRID3. Altogether, this study unveils a new chemical class of highly potent and selective NLRP3-targeted inhibitors with a well-defined molecular mechanism to complement existing CRID3-based NLRP3 inhibitors in pharmacological studies and serve as novel chemical leads for the development of NLRP3-targeted therapies.

Inflammasomes in epithelial innate immunity: front line warriors

Our epithelium represents a battle ground against a variety of insults including pathogens and danger signals. It encodes multiple sensors that detect and respond to such insults, playing an essential role in maintaining and defending tissue homeostasis. One key set of defense mechanisms is our inflammasomes which drive innate immune responses including, sensing and responding to pathogen attack, through the secretion of pro-inflammatory cytokines and cell death. Identification of physiologically relevant triggers for inflammasomes has greatly influenced our ability to decipher the mechanisms behind inflammasome activation. Furthermore, identification of patient mutations within inflammasome components implicates their involvement in a range of epithelial diseases. This review will focus on exploring the roles of inflammasomes in epithelial immunity and cover: the diversity and differential expression of inflammasome sensors amongst our epithelial barriers, their ability to sense local infection and damage and the contribution of the inflammasomes to epithelial homeostasis and disease.

Metabolism-inflammasome crosstalk shapes innate and adaptive immunity

Inflammasomes are a central component of innate immunity and play a vital role in regulating innate immune response. Activation of inflammasomes is also indispensable for adaptive immunity, modulating the development and response of adaptive immunity. Recently, increasing studies have shown that metabolic alterations and adaptations strongly influence and regulate the differentiation and function of the immune system. In this review, we will take a holistic view of how inflammasomes bridge innate and adaptive (especially T cell) immunity and how inflammasomes crosstalk with metabolic signals during the immune responses. And, special attention will be paid to the metabolic control of inflammasome-mediated interactions between innate and adaptive immunity in disease. Understanding the metabolic regulatory functions of inflammasomes would provide new insights into future research directions in this area and may help to identify potential targets for inflammasome-associated diseases and broaden therapeutic avenues.

DAMPs and radiation injury

The heightened risk of ionizing radiation exposure, stemming from radiation accidents and potential acts of terrorism, has spurred growing interests in devising effective countermeasures against radiation injury. High-dose ionizing radiation exposure triggers acute radiation syndrome (ARS), manifesting as hematopoietic, gastrointestinal, and neurovascular ARS. Hematopoietic ARS typically presents with neutropenia and thrombocytopenia, while gastrointestinal ARS results in intestinal mucosal injury, often culminating in lethal sepsis and gastrointestinal bleeding. This deleterious impact can be attributed to radiation-induced DNA damage and oxidative stress, leading to various forms of cell death, such as apoptosis, necrosis and ferroptosis. Damage-associated molecular patterns (DAMPs) are intrinsic molecules released by cells undergoing injury or in the process of dying, either through passive or active pathways. These molecules then interact with pattern recognition receptors, triggering inflammatory responses. Such a cascade of events ultimately results in further tissue and organ damage, contributing to the elevated mortality rate. Notably, infection and sepsis often develop in ARS cases, further increasing the release of DAMPs. Given that lethal sepsis stands as a major contributor to the mortality in ARS, DAMPs hold the potential to function as mediators, exacerbating radiation-induced organ injury and consequently worsening overall survival. This review describes the intricate mechanisms underlying radiation-induced release of DAMPs. Furthermore, it discusses the detrimental effects of DAMPs on the immune system and explores potential DAMP-targeting therapeutic strategies to alleviate radiation-induced injury.

Pathological and Therapeutical Implications of Pyroptosis in Psoriasis and Hidradenitis Suppurativa: A Narrative Review

This manuscript explores the role of pyroptosis, an inflammatory programmed cell death, in the pathogenesis of two chronic dermatoses, psoriasis and hidradenitis suppurativa (HS). The diseases, though clinically diverse, share common pathogenetic pathways involving the unbalanced interaction between the adaptive and innate immune systems. This review focuses on the molecular changes in psoriatic and HS skin, emphasizing the activation of dendritic cells, secretion of interleukins (IL-17, IL-22, and TNF-α), and the involvement of inflammasomes, particularly NLRP3. This manuscript discusses the role of caspases, especially caspase-1, in driving pyroptosis and highlights the family of gasdermins (GSDMs) as key players in the formation of pores leading to cell rupture and the release of proinflammatory signals. This study delves into the potential therapeutic implications of targeting pyroptosis in psoriasis and HS, examining existing medications like biologics and Janus kinase inhibitors. It also reviews the current limitations and challenges in developing therapies that selectively target pyroptosis. Additionally, the manuscript explores the role of pyroptosis in various inflammatory disorders associated with psoriasis and HS, such as inflammatory bowel disease, diabetes mellitus, and cardiovascular disorders. The review concludes by emphasizing the need for further research to fully elucidate the pathomechanisms of these dermatoses and develop effective, targeted therapies.

Drugging the NLRP3 inflammasome: from signalling mechanisms to therapeutic targets

Diseases associated with chronic inflammation constitute a major health burden across the world. As central instigators of the inflammatory response to infection and tissue damage, inflammasomes - and the NACHT, LRR and PYD domain-containing protein 3 (NLRP3) inflammasome in particular - have emerged as key regulators in diverse rheumatic, metabolic and neurodegenerative diseases. Similarly to other inflammasome sensors, NLRP3 assembles a cytosolic innate immune complex that activates the cysteine protease caspase-1, which in turn cleaves gasdermin D (GSDMD) to induce pyroptosis, a regulated mode of lytic cell death. Pyroptosis is highly inflammatory, partly because of the concomitant extracellular release of the inflammasome-dependent cytokines IL-1β and IL-18 along with a myriad of additional danger signals and intracellular antigens. Here, we discuss how NLRP3 and downstream inflammasome effectors such as GSDMD, apoptosis-associated speck-like protein containing a CARD (ASC) and nerve injury-induced protein 1 (NINJ1) have gained significant traction as therapeutic targets. We highlight the recent progress in developing small-molecule and biologic inhibitors that are advancing into the clinic and serving to harness the broad therapeutic potential of modulating the NLRP3 inflammasome.

Ferroptosis and tumor immunity: In perspective of the major cell components in the tumor microenvironment

Ferroptosis is an iron-dependent form of cell death driven by lipid peroxidation, which is morphologically, biochemically, and genetically distinct from apoptosis, necrosis, and autophagy. Mounting studies on the essential role of ferroptosis have been published in the progression of solid tumors, metastasis, therapy, and therapy resistance. Studies showed that ferroptosis is a "double-edged sword" in tumor immunity, which means it may have both tumor-antagonizing and tumor-promoting functions. The tumor microenvironment (TME) comprises not only tumor cells but also surrounding immune cells, stromal cells, as well as noncellular components such as the extracellular matrix (ECM), cytokines, growth factors, and extracellular vesicles (EVs). In the complex and diverse condition in TME where tumor cells grow, changes in each constituent may impact tumor destiny differently. Recently, several studies have revealed the interaction between ferroptosis and different constituents in TME. Both tumor cells and nontumor cells have a dual role in tumor immunity and influence tumor progression through ferroptosis. Herein, this review aims at summarizing the role of ferroptosis in tumor immunity based on TME, focusing on the mechanisms of the interaction between the ferroptosis and the different constituents in TME, illuminating how ferroptosis plays its role in promoting or antagonizing tumors by acting with varying components in TME and proposing several questions in immunomodulatory effects of ferroptosis and ferroptosis-associated immunotherapy.

A review focusing on the role of pyroptosis in prostate cancer

As one of the types of programmed cell death, pyroptosis has become a focus of research in recent years. Numerous studies have shown that pyroptosis plays a regulatory role in tumor cell invasiveness, differentiation, proliferation, and metastasis. It has been demonstrated that pyroptosis is involved in the regulation of signaling pathways implicated in the pathogenesis of prostate cancer (PCa). Furthermore, the loss of expression of pyroptosis-related genes in PCa has been reported, and pyroptosis-related genes have demonstrated a considerable ability in predicting the prognosis of PCa. Therefore, the potential role of pyroptosis in regulating the development of PCa warrants further investigation and attention. In this review, we summarize the basics of the role of pyroptosis and also discuss research into the mechanisms of action associated with pyroptosis in PCa. It is hoped that by exploring the potential of the pyroptosis pathway in intervening in PCa, it will provide a viable direction for the diversification of PCa treatment.

Host extracellular vesicles confer cytosolic access to systemic LPS licensing non-canonical inflammasome sensing and pyroptosis

Intracellular surveillance for systemic microbial components during homeostasis and infections governs host physiology and immunity. However, a long-standing question is how circulating microbial ligands become accessible to intracellular receptors. Here we show a role for host-derived extracellular vesicles (EVs) in this process; human and murine plasma-derived and cell culture-derived EVs have an intrinsic capacity to bind bacterial lipopolysaccharide (LPS). Remarkably, circulating host EVs capture blood-borne LPS in vivo, and the LPS-laden EVs confer cytosolic access for LPS, triggering non-canonical inflammasome activation of gasdermin D and pyroptosis. Mechanistically, the interaction between the lipid bilayer of EVs and the lipid A of LPS underlies EV capture of LPS, and the intracellular transfer of LPS by EVs is mediated by CD14. Overall, this study demonstrates that EVs capture and escort systemic LPS to the cytosol licensing inflammasome responses, uncovering EVs as a previously unrecognized link between systemic microbial ligands and intracellular surveillance.

The multifunctional protein HMGB1: 50 years of discovery

Fifty years since the initial discovery of HMGB1 in 1973 as a structural protein of chromatin, HMGB1 is now known to regulate diverse biological processes depending on its subcellular or extracellular localization. These functions include promoting DNA damage repair in the nucleus, sensing nucleic acids and inducing innate immune responses and autophagy in the cytosol and binding protein partners in the extracellular environment and stimulating immunoreceptors. In addition, HMGB1 is a broad sensor of cellular stress that balances cell death and survival responses essential for cellular homeostasis and tissue maintenance. HMGB1 is also an important mediator secreted by immune cells that is involved in a range of pathological conditions, including infectious diseases, ischaemia-reperfusion injury, autoimmunity, cardiovascular and neurodegenerative diseases, metabolic disorders and cancer. In this Review, we discuss the signalling mechanisms, cellular functions and clinical relevance of HMGB1 and describe strategies to modify its release and biological activities in the setting of various diseases.

Regulated cell death in neutrophils: From apoptosis to NETosis and pyroptosis

Neutrophils are among the most abundant immune cells, representing about 50%- 70% of all circulating leukocytes in humans. Neutrophils rapidly infiltrate inflamed tissues and play an essential role in host defense against infections. They exert microbicidal activity through a variety of specialized effector mechanisms, including phagocytosis, production of reactive oxygen species, degranulation and release of secretory vesicles containing broad-spectrum antimicrobial factors. In addition to their homeostatic turnover by apoptosis, recent studies have revealed the mechanisms by which neutrophils undergo various forms of regulated cell death. In this review, we will discuss the different modes of regulated cell death that have been described in neutrophils, with a particular emphasis on the current understanding of neutrophil pyroptosis and its role in infections and autoinflammation.

The mechanisms of minocycline in alleviating ischemic stroke damage and cerebral ischemia-reperfusion injury

Stroke is a group of diseases resulting from cerebral vascular rupture or obstruction and subsequent brain blood circulation disorder, leading to rapid neurological deficits. Ischemic stroke accounts for the majority of all stroke cases. The current treatments for ischemic stroke mainly include t-PA thrombolytic therapy and surgical thrombectomy. However, these interventions aimed at recanalizing cerebral vessels can paradoxically lead to ischemia-reperfusion injury, which exacerbates the severity of brain damage. Minocycline, a semi-synthetic tetracycline antibiotic, has been shown to possess a wide range of neuroprotective effects independent of its antibacterial activity. Here we summarize the mechanisms underlying the protective effects of minocycline against cerebral ischemia-reperfusion injury based on the pathogenesis of cerebral ischemia-reperfusion injury, including its modulation of oxidative stress, inflammatory response, excitotoxicity, programmed cell death and blood-brain barrier injury, and also introduce the role of minocycline in alleviating stroke-related complications, in order to provide a theoretical basis for the clinical application of minocycline in cerebral ischemia-reperfusion injury.

Pyroptosis-induced inflammation and tissue damage

Pyroptosis is a programmed necrotic cell death executed by gasdermins, a family of pore-forming proteins. The cleavage of gasdermins by specific proteases enables their pore-forming activity. The activation of the prototype member of the gasdermin family, gasdermin D (GSDMD), is linked to innate immune monitoring by inflammasomes. Additional gasdermins such as GSDMA, GSDMB, GSDMC, and GSDME are activated by inflammasome-independent mechanisms. Pyroptosis is emerging as a key host defense strategy against pathogens. However, excessive pyroptosis causes cytokine storm and detrimental inflammation leading to tissue damage and organ dysfunction. Consequently, dysregulated pyroptotic responses contribute to the pathogenesis of various diseases, including sepsis, atherosclerosis, acute respiratory distress syndrome, and neurodegenerative disorders. This review will discuss the inflammatory consequences of pyroptosis and the mechanisms of pyroptosis-induced tissue damage and disease pathogenesis.

The Redox Protein High-Mobility Group Box 1 in Cell Death and Cancer

Significance: As a redox-sensitive protein, high-mobility group box 1 (HMGB1) is implicated in regulating stress responses to oxidative damage and cell death, which are closely related to the pathology of inflammatory diseases, including cancer. Recent Advances: HMGB1 is a nonhistone nuclear protein that acts as a deoxyribonucleic acid chaperone to control chromosomal structure and function. HMGB1 can also be released into the extracellular space and function as a damage-associated molecular pattern protein during cell death, including during apoptosis, necrosis, necroptosis, pyroptosis, ferroptosis, alkaliptosis, and cuproptosis. Once released, HMGB1 binds to membrane receptors to shape immune and metabolic responses. In addition to subcellular localization, the function and activity of HMGB1 also depend on its redox state and protein posttranslational modifications. Abnormal HMGB1 plays a dual role in tumorigenesis and anticancer therapy (e.g., chemotherapy, radiation therapy, and immunotherapy) depending on the tumor types and stages. Critical Issues: A comprehensive understanding of the role of HMGB1 in cellular redox homeostasis is important for deciphering normal cellular functions and pathological manifestations. In this review, we discuss compartmental-defined roles of HMGB1 in regulating cell death and cancer. Understanding these advances may help us develop potential HMGB1-targeting drugs or approaches to treat oxidative stress-related diseases or pathological conditions. Future Directions: Further studies are required to dissect the mechanism by which HMGB1 maintains redox homeostasis under different stress conditions. A multidisciplinary effort is also required to evaluate the potential applications of precisely targeting the HMGB1 pathway in human health and disease. Antioxid. Redox Signal. 39, 569-590.

Neuronal Death Caused by HMGB1-Evoked via Inflammasomes from Thrombin-Activated Microglia Cells

Microglial cells are a macrophage-like cell type residing within the CNS. These cells evoke pro-inflammatory responses following thrombin-induced brain damage. Inflammasomes, which are large caspase-1-activating protein complexes, play a critical role in mediating the extracellular release of HMGB1 in activated immune cells. The exact role of inflammasomes in microglia activated by thrombin remains unclear, particularly as it relates to the downstream functions of HMGB1. After receiving microinjections of thrombin, Sprague Dawley rats of 200 to 250 gm were studied in terms of behaviors and immunohistochemical staining. Primary culture of microglia cells and BV-2 cells were used for the assessment of signal pathways. In a water maze test and novel object recognition analysis, microinjections of thrombin impaired rats' short-term and long-term memory, and such detrimental effects were alleviated by injecting anti-HMGB-1 antibodies. After thrombin microinjections, the increased oxidative stress of neurons was aggravated by HMGB1 injections but attenuated by anti-HMGB-1 antibodies. Such responses occurred in parallel with the volume of activated microglia cells, as well as their expressions of HMGB-1, IL-1β, IL-18, and caspase-I. In primary microglia cells and BV-2 cell lines, thrombin also induced NO release and mRNA expressions of iNOS, IL-1β, IL-18, and activated caspase-I. HMGB-1 aggravated these responses, which were abolished by anti-HMGB-1 antibodies. In conclusion, thrombin induced microglia activation through triggering inflammasomes to release HMGB1, contributing to neuronal death. Such an action was counteracted by the anti-HMGB-1 antibodies. The refinement of HMGB-1 modulated the neuro-inflammatory response, which was attenuated in thrombin-associated neurodegenerative disorder.

Inhibition of GSDMD activation by Z-LLSD-FMK or Z-YVAD-FMK reduces vascular inflammation and atherosclerotic lesion development in ApoE-/- mice

Pyroptosis is a form of pro-inflammatory cell death that can be mediated by gasdermin D (GSDMD) activation induced by inflammatory caspases such as caspase-1. Emerging evidence suggests that targeting GSDMD activation or pyroptosis may facilitate the reduction of vascular inflammation and atherosclerotic lesion development. The current study investigated the therapeutic effects of inhibition of GSDMD activation by the novel GSDMD inhibitor N-Benzyloxycarbonyl-Leu-Leu-Ser-Asp(OMe)-fluoromethylketone (Z-LLSD-FMK), the specific caspase-1 inhibitor N-Benzyloxycarbonyl-Tyr-Val-Ala-Asp(OMe)-fluoromethylketone (Z-YVAD-FMK), and a combination of both on atherosclerosis in ApoE-/- mice fed a western diet at 5 weeks of age, and further determined the efficacy of these polypeptide inhibitors in bone marrow-derived macrophages (BMDMs). In vivo studies there was plaque formation, GSDMD activation, and caspase-1 activation in aortas, which increased gradually from 6 to 18 weeks of age, and increased markedly at 14 and 18 weeks of age. ApoE-/- mice were administered Z-LLSD-FMK (200 µg/day), Z-YVAD-FMK (200 µg/day), a combination of both, or vehicle control intraperitoneally from 14 to 18 weeks of age. Treatment significantly reduced lesion formation, macrophage infiltration in lesions, protein levels of vascular cell adhesion molecule-1 and monocyte chemoattractant protein-1, and pyroptosis-related proteins such as activated caspase-1, activated GSDMD, cleaved interleukin(IL)-1β, and high mobility group box 1 in aortas. No overt differences in plasma lipid contents were detected. In vitro treatment with these polypeptide inhibitors dramatically decreased the percentage of propidium iodide-positive BMDMs, the release of lactate dehydrogenase and IL-1β, and protein levels of pyroptosis-related proteins both in supernatants and cell lysates elevated by lipopolysaccharide + nigericin. Notably however, there were no significant differences in the above-mentioned results between the Z-LLSD-FMK group and the Z-YVAD-FMK group, and the combination of both did not yield enhanced effects. These findings indicate that suppression of GSDMD activation by Z-LLSD-FMK or Z-YVAD-FMK reduces vascular inflammation and lesion development in ApoE-/- mice.

NRF2 transcriptionally regulates Caspase-11 expression to activate HMGB1 release by Autophagy-deficient hepatocytes

Injury or stress can induce intracellular translocation and release of nuclear HMGB1, a DAMP molecule known to participate in inflammation and other pathological processes. Active release of HMGB1 from stimulated macrophages can be mediated by inflammasomes, which cleave Gasdermin D to form pores on cytoplasmic membranes. We previously had shown that active release of HMGB1 from autophagy deficient hepatocytes also depended on the inflammasome but how the inflammasome was activated was not known. Here we report that persistent activation of transcription factor NRF2 under the autophagy deficient condition led to transcriptional upregulation of Caspase-11 expression, which could then activate the CASPASE-1inflammasome. Using chromatin immunoprecipitation (CHIP) and luciferase-based reporter assays, we show that NRF2 directly binds to the Caspase-11 promoter and transcriptionally increase the expression of Caspase-11. Genetic deletion of Caspase-11 in autophagy-deficient livers represses the release of HMGB1 and its pathological consequence, ductular cell proliferation. Consistently, deletion of NLRP3, which can activate CASPASE-1 mediated inflammasomes under other types of signals, did not prevent HMGB1 release and ductular cell proliferation in autophagy deficient livers. Surprisingly, while cleavage of GASDEMIN D occurred in autophagy-deficient livers its deletion did not prevent the HMGB1 release, suggesting that CASPASE-11-mediated inflammasome activation may also engage in a different mechanism for HMGB1 release by the autophagy deficient hepatocytes. Collectively, this work reveals the novel role of NRF2 in transcriptional upregulation of Caspase-11 and in inflammasome activation to promote active release of HMGB via a non-Gasdermin D mediated avenue.

A two-decade journey in identifying high mobility group box 1 (HMGB1) and procathepsin L (pCTS-L) as potential therapeutic targets for sepsis

INTRODUCTION

Microbial infections and resultant sepsis are leading causes of death in hospitals, representing approximately 20% of total deaths worldwide. Despite the difficulties in translating experimental insights into effective therapies for often heterogenous patient populations, an improved understanding of the pathogenic mechanisms underlying experimental sepsis is still urgently needed. Sepsis is partly attributable to dysregulated innate immune responses manifested by hyperinflammation and immunosuppression at different stages of microbial infections.

AREAS COVERED

Here we review our recent progress in searching for late-acting mediators of experimental sepsis and propose high mobility group box 1 (HMGB1) and procathepsin-L (pCTS-L) as potential therapeutic targets for improving outcomes of lethal sepsis and other infectious diseases.

EXPERT OPINION

It will be important to evaluate the efficacy of HMGB1- or pCTS-L-targeting agents for the clinical management of human sepsis and other infectious diseases in future studies.

The role of HMGB1 in COVID-19-induced cytokine storm and its potential therapeutic targets: A review

Hyperinflammation characterized by elevated proinflammatory cytokines known as 'cytokine storms' is the major cause of high severity and mortality seen in COVID-19 patients. The pathology behind the cytokine storms is currently unknown. Increased HMGB1 levels in serum/plasma of COVID-19 patients were reported by many studies, which positively correlated with the level of proinflammatory cytokines. Dead cells following SARS-CoV-2 infection might release a large amount of HMGB1 and RNA of SARS-CoV-2 into extracellular space. HMGB1 is a well-known inflammatory mediator. Additionally, extracellular HMGB1 might interact with SARS-CoV-2 RNA because of its high capability to bind with a wide variety of molecules including nucleic acids and could trigger massive proinflammatory immune responses. This review aimed to critically explore the many possible pathways by which HMGB1-SARS-CoV-2 RNA complexes mediate proinflammatory responses in COVID-19. The contribution of these pathways to impair host immune responses against SARS-CoV-2 infection leading to a cytokine storm was also evaluated. Moreover, since blocking the HMGB1-SARS-CoV-2 RNA interaction might have therapeutic value, some of the HMGB1 antagonists have been reviewed. The HMGB1- SARS-CoV-2 RNA complexes might trigger endocytosis via RAGE which is linked to lysosomal rupture, PRRs activation, and pyroptotic death. High levels of the proinflammatory cytokines produced might suppress many immune cells leading to uncontrolled viral infection and cell damage with more HMGB1 released. Altogether these mechanisms might initiate a proinflammatory cycle leading to a cytokine storm. HMGB1 antagonists could be considered to give benefit in alleviating cytokine storms and serve as a potential candidate for COVID-19 therapy.

HMGB1, angel or devil, in ischemic stroke

INTRODUCTION

High-mobility group box 1 protein (HMGB1) is extensively involved in causing ischemic stroke, pathological damage of ischemic brain injury, and neural tissue repair after ischemic brain injury. However, the precise role of HMGB1 in ischemic stroke remains to be elucidated.

METHODS

Comprehensive literature search and narrative review to summarize the current field of HMGB1 in cerebral ischemic based on the basic structure, structural modification, and functional roles of HMGB1 described in the literature.

RESULTS

Studies have exhibited the crucial roles of HMGB1 in cell death, immunity and inflammation, thrombosis, and remodeling and repair. HMGB1 released after cerebral infarction is extensively involved in the pathological injury process in the early stage of cerebral infarction, whereas it is involved in the promotion of brain tissue repair and remodeling in the late stage of cerebral infarction. HMGB1 plays a neurotrophic role in acute white matter stroke, whereas it causes sustained activation of inflammation and plays a damaging role in chronic white matter ischemia.

CONCLUSIONS

HMGB1 plays a complex role in cerebral infarction, which is related to not only the modification of HMGB1 and bound receptors but also different stages and subtypes of cerebral infarction. future studies on HMGB1 should investigate the spatial and temporal dynamics of HMGB1 after cerebral infarction. Moreover, future studies on HMGB1 should attempt to integrate different stages and infarct subtypes of cerebral infarction.

Molecular insights into the pathogenic impact of vitamin D deficiency in neurological disorders

Neurological disorders are the major cause of disability, leading to a decrease in quality of life by impairing cognitive, sensorimotor, and motor functioning. Several factors have been proposed in the pathogenesis of neurobehavioral changes, including nutritional, environmental, and genetic predisposition. Vitamin D (VD) is an environmental and nutritional factor that is widely distributed in the central nervous system's subcortical grey matter, neurons of the substantia nigra, hippocampus, thalamus, and hypothalamus. It is implicated in the regulation of several brain functions by preserving neuronal structures. It is a hormone rather than a nutritional vitamin that exerts a regulatory role in the pathophysiology of several neurological disorders, including Alzheimer's disease, Parkinson's disease, epilepsy, and multiple sclerosis. A growing body of epidemiological evidence suggests that VD is critical in neuronal development and shows neuroprotective effects by influencing the production and release of neurotrophins, antioxidants, immunomodulatory, regulation of intracellular calcium balance, and direct effect on the growth and differentiation of nerve cells. This review provides up-to-date and comprehensive information on vitamin D deficiency, risk factors, and clinical and preclinical evidence on its relationship with neurological disorders. Furthermore, this review provides mechanistic insight into the implications of vitamin D and its deficiency on the pathogenesis of neurological disorders. Thus, an understanding of the crucial role of vitamin D in the neurobiology of neurodegenerative disorders can assist in the better management of vitamin D-deficient individuals.

Protective effects of an anti-4-HNE monoclonal antibody against liver injury and lethality of endotoxemia in mice

4-hydroxy-2-nonenal (4-HNE) is a lipid peroxidation product that is known to be elevated during oxidative stress. During systemic inflammation and endotoxemia, plasma levels of 4-HNE are elevated in response to lipopolysaccharide (LPS) stimulation. 4-HNE is a highly reactive molecule due to its generation of both Schiff bases and Michael adducts with proteins, which may result in modulation of inflammatory signaling pathways. In this study, we report the production of a 4-HNE adduct-specific monoclonal antibody (mAb) and the effectiveness of the intravenous injection of this mAb (1 mg/kg) in ameliorating LPS (10 mg/kg, i.v.)-induced endotoxemia and liver injury in mice. Endotoxic lethality in control mAb-treated group was suppressed by the administration of anti-4-HNE mAb (75 vs. 27%). After LPS injection, we observed a significant increase in the plasma levels of AST, ALT, IL-6, TNF-α and MCP-1, and elevated expressions of IL-6, IL-10 and TNF-α in the liver. All these elevations were inhibited by anti-4-HNE mAb treatment. As to the underlining mechanism, anti-4-HNE mAb inhibited the elevation of plasma high mobility group box-1 (HMGB1) levels, the translocation and release of HMGB1 in the liver and the formation of 4-HNE adducts themselves, suggesting a functional role of extracellular 4-HNE adducts in hypercytokinemia and liver injury associated with HMGB1 mobilization. In summary, this study reveals a novel therapeutic application of anti-4-HNE mAb for endotoxemia.

High Mobility Group Box 1 (HMGB1): Potential Target in Sepsis-Associated Encephalopathy

Sepsis-associated encephalopathy (SAE) remains a challenge for intensivists that is exacerbated by lack of an effective diagnostic tool and an unambiguous definition to properly identify SAE patients. Risk factors for SAE development include age, genetic factors as well as pre-existing neuropsychiatric conditions. Sepsis due to certain infection sites/origins might be more prone to encephalopathy development than other cases. Currently, ICU management of SAE is mainly based on non-pharmacological support. Pre-clinical studies have described the role of the alarmin high mobility group box 1 (HMGB1) in the complex pathogenesis of SAE. Although there are limited data available about the role of HMGB1 in neuroinflammation following sepsis, it has been implicated in other neurologic disorders, where its translocation from the nucleus to the extracellular space has been found to trigger neuroinflammatory reactions and disrupt the blood–brain barrier. Negating the inflammatory cascade, by targeting HMGB1, may be a strategy to complement non-pharmacologic interventions directed against encephalopathy. This review describes inflammatory cascades implicating HMGB1 and strategies for its use to mitigate sepsis-induced encephalopathy.

Myeloid autophagy genes protect mice against fatal TNF- and LPS-induced cytokine storm syndromes

ABBREVIATIONS

ATG5: autophagy related 5; ATG7: autophagy related 7; ATG14: autophagy related 14; ATG16L1: autophagy related 16-like 1 (S. cerevisiae); BECN1: beclin 1, autophagy related; CASP1: caspase 1; CASP4/CASP11: caspase 4, apoptosis-related cysteine peptidase; CIM: conditionally immortalized macrophage; CLP: cecal ligation and puncture; CSS: cytokine storm syndrome; DC: dendritic cell; IFNG/IFNγ: interferon gamma; IFNGR1: interferon gamma receptor 1; ip: intraperitoneal; iv: intravenous; IL12/p70: interleukin 12, p70 heterodimer; IL18: Interleukin 18; ITGAX/CD11c: integrin alpha X; LAP: LC3-associated phagocytosis; LPS: lipopolysaccharide; LYZ2/LYSM: lysozyme 2; MAP1LC3A/LC3: microtubule-associated protein 1 light chain 3 alpha; RB1CC1/FIP200: RB1-inducible coiled-coil 1; S100A8/MRP8: S100 calcium binding protein A8 (calgranulin A); TICAM1/TRIF: TIR domain containing adaptor molecule 1; TLR4: toll-like receptor 4; TNF: tumor necrosis factor.

Human Resistin Induces Cardiac Dysfunction in Pulmonary Hypertension

Background Cardiac failure is the primary cause of death in most patients with pulmonary arterial hypertension (PH). As pleiotropic cytokines, human resistin (Hresistin) and its rodent homolog, resistin-like molecule α, are mechanistically critical to pulmonary vascular remodeling in PH. However, it is still unclear whether activation of these resistin-like molecules can directly cause PH-associated cardiac dysfunction and remodeling. Methods and Results In this study, we detected Hresistin protein in right ventricular (RV) tissue of patients with PH and elevated resistin-like molecule expression in RV tissues of rodents with RV hypertrophy and failure. In a humanized mouse model, cardiac-specific Hresistin overexpression was sufficient to cause cardiac dysfunction and remodeling. Dilated hearts exhibited reduced force development and decreased intracellular Ca2+ transients. In the RV tissues overexpressing Hresistin, the impaired contractility was associated with the suppression of protein kinase A and AMP-activated protein kinase. Mechanistically, Hresistin activation triggered the inflammation mediated by signaling of the key damage-associated molecular pattern molecule high-mobility group box 1, and subsequently induced pro-proliferative Ki67 in RV tissues of the transgenic mice. Intriguingly, an anti-Hresistin human antibody that we generated protected the myocardium from hypertrophy and failure in the rodent PH models. Conclusions Our data indicate that Hresistin is expressed in heart tissues and plays a role in the development of RV dysfunction and maladaptive remodeling through its immunoregulatory activities. Targeting this signaling to modulate cardiac inflammation may offer a promising strategy to treat PH-associated RV hypertrophy and failure in humans.

Isopropyl 3-(3, 4-dihydroxyphenyl)-2-hydroxypropanoate protects lipopolysaccharide-induced acute lung injury in mice by attenuating pyroptosis

Isopropyl 3-(3,4-dihydroxyphenyl)-2-hydroxypropanoate (IDHP) is one of the main bioactive metabolites of the Chinese medicinal herb Danshen, which can be absorbed into blood compounds by oral administration of Compound Danshen dripping pills (CDDPs). Previous study showed that IDHP exerted anti-inflammatory effects by abolishing the secretion of proinflammatory factors stimulated by lipopolysaccharide (LPS). However, the effects of IDHP on LPS-induced acute lung injury (ALI) are not fully understood. In the present study, we observed the effects of IDHP on mortality and lung injury in LPS-treated mice and on LPS-induced THP-1 macrophages. Pretreatment with high dose of IDHP was found to reduce the mortality of ALI mice, significantly improve LPS-induced pathological changes, and reduce protein leakage and inhibited myeloperoxidase (MPO) activity in lung tissue. IDHP also inhibited the release of inflammatory factors in bronchoalveolar lavage fluid (BALF) and lung tissue. Meanwhile, IDHP treatment significantly reduced the expression of active-caspase1, Nlrp3, Asc speck formation, Gsdmd (part of the canonical pyroptosis pathway), caspase4 (part of the non-canonical pyroptosis pathway), therefore decreasing IL-1β, IL-18, and ROS secretion in LPS-stimulated THP-1 macrophages. Moreover, after co-culturing endothelial/epithelial cells with conditioned medium (CM) from LPS-stimulated THP-1 macrophages, we found that the protein levels of occludin and Zonula occludens-1 (Zo-1) were increased in IDHP CM-treated endothelial cells compared to those that were LPS CM-treated. Lactic dehydrogenase (LDH) assay shows that IDHP also alleviated LPS-induced endothelial/epithelial cell injury. These findings indicate that the protective effect of IDHP on LPS-induced lung injury may be partly due to the inhibition of pyroptosis pathways.