Regulation of Posttranslational Modifications of HMGB1 During Immune Responses

Psoralen alleviates acute lung injury by covalently targeting Cys106 of HMGB1 in macrophages to inhibit inflammatory responses

BACKGROUND

Acute lung injury (ALI) is a critical pathophysiological response in various respiratory diseases characterized by alveolar damage and excessive inflammation. It can progress to acute respiratory distress syndrome, with current treatments showing limited efficacy and considerable side effects. Psoralen (Pso), derived from Psoralea corylifolia l., has anti-inflammatory properties, but its role in ALI remains fully elucidated.

PURPOSE

This study aimed to investigate the therapeutic effects of Pso on ALI, and to explore its therapeutic targets and mechanisms.

METHODS

The therapeutic potential of Pso was assessed using a model of ALI induced by lipopolysaccharide (LPS). The direct target was investigated using alkynyl-Psoralen (A-Pso) for chemical proteomic analysis, and a series of molecular biology methods were used to explore the underlying mechanism.

RESULTS

Pso treatment significantly alleviated LPS-induced lung injury in mice, targeted macrophages, and inhibited the LPS-induced activation of macrophages. Target-fishing experiments identified high-mobility group box-1 (HMGB1) as a direct target of Pso in macrophages. FTS and CETSA confirmed Pso binding to HMGB1, and LC-MS/MS analysis indicated a covalent interaction between Pso and Cys106 of HMGB1. Furthermore, Pso covalently targeted Cys106, affecting HMGB1 binding to TLR4 and downregulating the phosphorylation of NF-κB, indicating the inhibition of the TLR4/NF-κB signaling pathway both in macrophages and in lung tissues of ALI mice. These findings suggest that Pso exerts its therapeutic effects by covalently targeting HMGB1 in macrophages and modulating the TLR4/NF-κB signaling pathway.

CONCLUSION

This study not only found that Pso improves LPS-induced ALI inflammation by targeting macrophages, but also verified that this mechanism of action is mainly caused by Pso covalently targeting Cys106 of HMGB1, inhibiting the HMGB1-TLR4 interaction, and thereby suppressing cytokine storm generation. As the first naturally derived HMGB1 covalent inhibitor with a clear binding site, Pso plays an important role in HMGB1 induced inflammatory diseases and is an active precursor for the development of new HMGB1 covalent inhibitors.

HMGB1: A New Target for Ischemic Stroke and Hemorrhagic Transformation

Stroke in China is distinguished by its high rates of morbidity, recurrence, disability, and mortality. The ultra-early administration of rtPA is essential for restoring perfusion in acute ischemic stroke, though it concurrently elevates the risk of hemorrhagic transformation. High-mobility group box 1 (HMGB1) emerges as a pivotal player in neuroinflammation after brain ischemia and ischemia-reperfusion. Released passively by necrotic cells and actively secreted, including direct secretion of HMGB1 into the extracellular space and packaging of HMGB1 into intracellular vesicles by immune cells, glial cells, platelets, and endothelial cells, HMGB1 represents a prototypical damage-associated molecular pattern (DAMP). It is intricately involved in the pathogenesis of atherosclerosis, thromboembolism, and detrimental inflammation during the early phases of ischemic stroke. Moreover, HMGB1 significantly contributes to neurovascular remodeling and functional recovery in later stages. Significantly, HMGB1 mediates hemorrhagic transformation by facilitating neuroinflammation, directly compromising the integrity of the blood-brain barrier, and enhancing MMP9 secretion through its interaction with rtPA. As a systemic inflammatory factor, HMGB1 is also implicated in post-stroke depression and an elevated risk of stroke-associated pneumonia. The role of HMGB1 extends to influencing the pathogenesis of ischemia by polarizing various subtypes of immune and glial cells. This includes mediating excitotoxicity due to excitatory amino acids, autophagy, MMP9 release, NET formation, and autocrine trophic pathways. Given its multifaceted role, HMGB1 is recognized as a crucial therapeutic target and prognostic marker for ischemic stroke and hemorrhagic transformation. In this review, we summarize the structure and redox properties, secretion and pathways, regulation of immune cell activity, the role of pathophysiological mechanisms in stroke, and hemorrhage transformation for HMGB1, which will pave the way for developing new neuroprotective drugs, reduction of post-stroke neuroinflammation, and expansion of thrombolysis time window.

Prolonged loss of nuclear HMGB1 in neurons following modeled TBI and implications for long-term genetic health

Under normal physiological conditions high mobility group box protein 1 (HMGB1) stabilizes chromatin, controls transcription, and contributes to DNA repair. Cellular stress or injury results in HMGB1 release from the nucleus acting as a proinflammatory cytokine. The objective of this study was to characterize the temporal progression of nuclear HMGB1 loss up to one week following modeled TBI in 250 g male rats and correlate these changes with the response of DNA damage proteins. HMGB1 was present in the cytoplasm and absent from the nucleus of neurons within 6 h of injury. Quantitative immunohistochemistry and Western blot analysis showed a significant decrease in nuclear HMGB1 expression at 6 and 24 h post-injury compared to controls. Approximately 20 % of neurons were lacking nuclear HMGB1 expression at 7 days post-injury. Cells which were negative for nuclear HMGB1 expression labelled positive for HIF1α, PARP, and γH2AX, indicators of oxidative stress and DNA damage. Nuclear HIF1α expression was detected at 6 h after injury. Nuclear expression of HIF1α, PARP, and γH2AX was observed at 7 days post-injury, suggesting activation of oxidative stress response mechanisms and DNA damage repair pathways. The temporal changes in HMGB1 translocation in conjunction with expression of DNA damage markers suggest a relationship between injury-induced HMGB1 loss in neurons and subsequent DNA damage. These results highlight a potential injury response mechanism with long-term implications in relation to genetic health of surviving neurons.

Lactate-induced macrophage HMGB1 lactylation promotes neutrophil extracellular trap formation in sepsis-associated acute kidney injury

BACKGROUND

Neutrophils play a key role in sepsis-associated acute kidney injury (SAKI), a common and life-threatening complication of organ failure. High mobility group box 1 (HMGB1) modulates inflammatory responses and the formation of neutrophil extracellular traps (NETs). The present work aimed to explore whether HMGB1 lactylation promotes NET formation and exacerbates SAKI.

METHODS

Venous blood samples were collected from healthy volunteers and SAKI patients. A SAKI mouse model was established using the cecal ligation and puncture method. A coculture system of macrophage-derived exosomes and neutrophils was established. Macrophage-derived exosomes were isolated and identified. ELISAs, immunofluorescence staining, coimmunoprecipitation, and Western blotting were utilized to determine protein levels.

RESULTS

Elevated blood lactate levels were associated with increased HMGB1 levels in patients with SAKI. In mouse models, lactate increased HMGB1 expression, promoted NET formation, and exacerbated SAKI. Lactate stimulated M1 macrophages to secrete exosomes, leading to the accumulation and release of HMGB1 in the cytoplasm. Additionally, lactate promoted HMGB1 lactylation in macrophages, triggering the release of mitochondrial DNA from neutrophils and activating the cyclic GMP‒AMP synthase/stimulator of interferon genes pathway.

CONCLUSION

This study revealed that lactate-induced HMGB1 lactylation in macrophages plays a role in promoting NET formation in SAKI through the cGAS/STING pathway. These findings suggest that HMGB1 could be a potential target for therapeutic intervention in SAKI.

Pain in rheumatoid arthritis: Emerging role of high mobility group box 1 protein-HMGB1

Rheumatoid arthritis (RA) is a chronic inflammatory disease where pain, driven by both inflammatory and non-inflammatory processes, is a major concern for patients. This pain can persist even after joint inflammation subsides. High mobility group box-1 (HMGB1) is a non-histone-DNA binding protein located in the nucleus that plays a key role in processes such as DNA transcription, recombination, and replication. HMGB1 can be released into the extracellular space through both passive and active mechanisms. Extracellular HMGB1 contributes to synovial inflammation, bone degradation, and the production of cytokines in RA by binding to toll-like receptors (TLRs) and receptors for advanced glycation end products (RAGE). It also forms complexes with molecules like lipopolysaccharide (LPS) and IL-1β, amplifying inflammatory responses. Due to its central role in these processes, HMGB1 is considered a promising therapeutic target in RA. It also acts as a nociceptive molecule in mediating pain in diseases such as diabetes and bone cancer. In this review, we explore how HMGB1 contributes to chronic pain in RA, supported by both in vitro and in vivo models. We begin by providing an overview of the mechanisms of pain in RA, the structure of HMGB1, its release mechanisms, and the therapeutic potential of targeting HMGB1 in RA. Following this, we highlight its role in peripheral and central pain sensitization through direct activation of the TLR4/MAPK/NF-κB pathway, as well as indirectly through downstream mediators, underscoring its potential as a target for managing RA pain.

Targeting high-mobility-group-box-1-mediated inflammation: a promising therapeutic approach for myocardial infarction

Myocardial ischemia, resulting from coronary artery blockage, precipitates cardiac arrhythmias, myocardial structural changes, and heart failure. The pathophysiology of MI is mainly based on inflammation and cell death, which are essential in aggravating myocardial ischemia and reperfusion injury. Emerging research highlights the functionality of high mobility group box-1, a non-histone nucleoprotein functioning as a chromosomal stabilizer and inflammatory mediator. HMGB1's release into the extracellular compartment during ischemia acts as damage-associated molecular pattern, triggering immune reaction by pattern recognition receptors and exacerbating tissue inflammation. Its involvement in signaling pathways like PI3K/Akt, TLR4/NF-κB, and RAGE/HMGB1 underscores its significance in promoting angiogenesis, apoptosis, and reducing inflammation, which is crucial for MI treatment strategies. This review highlights the complex function of HMGB1 in the pathogenesis of myocardial infarction by summarizing novel findings on the protein in ischemic situations. Understanding the mechanisms underlying HMGB1 could widen the way to specific treatments that minimize the severity of MI and enhance patient outcomes.

Oxidative High Mobility Group Box-1 Accelerates Mitochondrial Transfer from Mesenchymal Stem Cells to Colorectal Cancer Cells Providing Cancer Cell Stemness

Mitochondria are important organelles for cell metabolism and tissue survival. Their cell-to-cell transfer is important for the fate of recipient cells. Recently, bone marrow mesenchymal stem cells (BM-MSCs) have been reported to provide mitochondria to cancer cells and rescue mitochondrial dysfunction in cancer cells. However, the details of the mechanism have not yet been fully elucidated. In this study, we investigated the humoral factors inducing mitochondrial transfer (MT) and the mechanisms. BM-MSCs produced MT in colorectal cancer (CRC) cells damaged by 5-fluorouracil (5-FU), but were suppressed by the anti-high mobility group box-1 (HMGB1) antibody. BM-MSCs treated with oxidized HMGB1 had increased expression of MT-associated genes, whereas reduced HMGB1 did not. Inhibition of nuclear factor-κB, a downstream factor of HMGB1 signaling, significantly decreased MT-associated gene expression. CRC cells showed increased stemness and decreased 5-FU sensitivity in correlation with MT levels. In a mouse subcutaneous tumor model of CRC, 5-FU sensitivity decreased and stemness increased by the MT from host mouse BM-MSCs. These results suggest that oxidized HMGB1 induces MTs from MSCs to CRC cells and promotes cancer cell stemness. Targeting of oxidized HMGB1 may attenuate stemness of CRCs.

Roles of the Receptor for Advanced Glycation End Products and Its Ligands in the Pathogenesis of Alzheimer's Disease

The Receptor for Advanced Glycation End Products (RAGE), part of the immunoglobulin superfamily, plays a significant role in various essential functions under both normal and pathological conditions, especially in the progression of Alzheimer's disease (AD). RAGE engages with several damage-associated molecular patterns (DAMPs), including advanced glycation end products (AGEs), beta-amyloid peptide (Aβ), high mobility group box 1 (HMGB1), and S100 calcium-binding proteins. This interaction impairs the brain's ability to clear Aβ, resulting in increased Aβ accumulation, neuronal injury, and mitochondrial dysfunction. This further promotes inflammatory responses and oxidative stress, ultimately leading to a range of age-related diseases. Given RAGE's significant role in AD, inhibitors that target RAGE and its ligands hold promise as new strategies for treating AD, offering new possibilities for alleviating and treating this serious neurodegenerative disease. This article reviews the various pathogenic mechanisms of AD and summarizes the literature on the interaction between RAGE and its ligands in various AD-related pathological processes, with a particular focus on the evidence and mechanisms by which RAGE interactions with AGEs, HMGB1, Aβ, and S100 proteins induce cognitive impairment in AD. Furthermore, the article discusses the principles of action of RAGE inhibitors and inhibitors targeting RAGE-ligand interactions, along with relevant clinical trials.

Sepsis-Induced Endothelial Dysfunction: Permeability and Regulated Cell Death

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Endothelial cells (ECs) are an important cell type typically affected in sepsis, resulting in compromised barrier function and various forms of regulated cell death (RCD). However, the precise mechanisms underlying sepsis-induced EC damage remain unclear. This review summarizes the recent research progress on factors and mechanisms that may affect the permeability and RCD of ECs under septic conditions, including glycocalyx, damage-associated molecular patterns, and various forms of RCD in ECs, such as apoptosis, pyroptosis, ferroptosis, and autophagy. This review offers important insights into the underlying mechanisms of endothelial dysfunction in sepsis, aiming to contribute to developing small-molecule targeted clinical therapies.

Glucocorticoids induce HMGB1 release in primary cultured rat cortical microglia

Stress, a risk factor for major depressive disorder and Alzheimer disease, leads to the release of high-mobility group box-1 (HMGB1) protein, which in turn causes neuroinflammation. The mechanism underlying stress-induced HMGB1 release is unknown, but stress-associated glucocorticoids could be involved. Primary cultured rat cortical microglia and neurons were treated with corticosterone, a stress-associated glucocorticoid, and HMGB1 release was measured by ELISA and western blotting to test this hypothesis. With corticosterone treatment, significant HMGB1 was released in microglia but not in neuronal cell cultures. HMGB1 mRNA expression and HMGB1 protein expression in microglia were not affected by corticosterone treatment. Thus, the source of extracellular HMGB1 released into the medium is likely to be existing nuclear HMGB1 rather than newly synthesized HMGB1. Corticosterone-induced HMGB1 release in microglia culture was significantly attenuated by blocking glucocorticoid receptors but not mineralocorticoid receptors. Dexamethasone, a selective glucocorticoid receptor agonist, and dexamethasone-bovine serum albumin (BSA), a membrane-impermeable glucocorticoid receptor agonist used to confirm the membrane receptor-mediated effects of glucocorticoids, increased the release of HMGB1. Immunocytochemistry showed that HMGB1 translocated from the nucleus to the cytoplasm following dexamethasone or dexamethasone-BSA treatment through glucocorticoid receptors. The present findings suggest that glucocorticoids stimulate microglial membrane glucocorticoid receptors and trigger cytoplasmic translocation and extracellular release of nuclear HMGB1. Thus, under stress conditions, glucocorticoids induce microglial HMGB1 release, leading to a neuroinflammatory state that could mediate neurological disorders.

High Mobility Group Box 1 and Cardiovascular Diseases: Study of Act and Connect

Cardiovascular disease is the deadly disease that can result in sudden death, and inflammation plays an important role in its onset and progression. High mobility group box 1 (HMGB1) is a nuclear protein that regulates transcription, DNA replication, repair, and nucleosome assembly. HMGB1 is released passively by necrotic tissues and actively secreted by stressed cells. Extracellular HMGB1 functions as a damage associated molecular patterns molecule, producing numerous redox forms that induce a range of cellular responses by binding to distinct receptors and interactors, including tissue inflammation and regeneration. Extracellular HMGB1 inhibition reduces inflammation and is protective in experimental models of myocardial ischemia/reperfusion damage, myocarditis, cardiomyopathies caused by mechanical stress, diabetes, bacterial infection, or chemotherapeutic drugs. HMGB1 administration following a myocardial infarction followed by permanent coronary artery ligation improves cardiac function by stimulating tissue regeneration. HMGB1 inhibits contractility and produces hypertrophy and death in cardiomyocytes, while also stimulating cardiac fibroblast activity and promoting cardiac stem cell proliferation and differentiation. Maintaining normal nuclear HMGB1 levels, interestingly, protects cardiomyocytes from apoptosis by limiting DNA oxidative stress, and mice with HMGB1cardiomyocyte-specific overexpression are partially protected from cardiac injury. Finally, elevated levels of circulating HMGB1 have been linked to human heart disease. As a result, following cardiac damage, HMGB1 elicits both detrimental and helpful responses, which may be due to the formation and stability of the various redox forms, the particular activities of which in this context are mostly unknown. This review covers recent findings in HMGB1 biology and cardiac dysfunction.

Cytosolic Hmgb1 accumulation in mesangial cells aggravates diabetic kidney disease progression via NFκB signaling pathway

Diabetic kidney disease (DKD) is the predominant type of end-stage renal disease. Increasing evidence suggests thatglomerular mesangial cell (MC) inflammation is pivotal for cell proliferation and DKD progression. However, the exactmechanism of MC inflammation remains largely unknown. This study aims to elucidate the role of inflammatoryfactor high-mobility group box 1 (Hmgb1) in DKD. Inflammatory factors related to DKD progression are screened viaRNA sequencing (RNA-seq). In vivo and in vitro experiments, including db/db diabetic mice model, CCK-8 assay, EdUassay, flow cytometric analysis, Co-IP, FISH, qRT-PCR, western blot, single cell nuclear RNA sequencing (snRNA-seq),are performed to investigate the effects of Hmgb1 on the inflammatory behavior of MCs in DKD. Here, wedemonstrate that Hmgb1 is significantly upregulated in renal tissues of DKD mice and mesangial cells cultured withhigh glucose, and Hmgb1 cytopasmic accumulation promotes MC inflammation and proliferation. Mechanistically,Hmgb1 cytopasmic accumulation is two-way regulated by MC-specific cyto-lncRNA E130307A14Rik interaction andlactate-mediated acetylated and lactylated Hmgb1 nucleocytoplasmic translocation, and accelerates NFκB signalingpathway activation via directly binding to IκBα. Together, this work reveals the promoting role of Hmgb1 on MCinflammation and proliferation in DKD and helps expound the regulation of Hmgb1 cytopasmic accumulation in twoways. In particular, Hmgb1 may be a promising therapeutic target for DKD.

Role of Histiocyte-Derived frHMGB1 as a Facilitator in Noncanonical Pyroptosis of Monocytes/Macrophages in Lethal Sepsis

In this study, we investigated the role of the noncanonical pyroptosis pathway in the progression of lethal sepsis. Our findings emphasize the significance of noncanonical pyroptosis in monocytes/macrophages for the survival of septic mice. We observed that inhibiting pyroptosis alone significantly improved the survival rate of septic mice and that the HMGB1 A box effectively suppressed this noncanonical pyroptosis, thereby enhancing the survival of septic mice. Additionally, our cell in vitro experiments unveiled that frHMGB1, originating from lipopolysaccharide-carrying histiocytes, entered macrophages via RAGE, resulting in the direct activation of caspase 11 and the induction of noncanonical pyroptosis. Notably, A box's competitive binding with lipopolysaccharide impeded its entry into the cell cytosol. These findings reveal potential therapeutic strategies for slowing the progression of lethal sepsis by modulating the noncanonical pyroptosis pathway.

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.

Musashi-2 potentiates colorectal cancer immune infiltration by regulating the post-translational modifications of HMGB1 to promote DCs maturation and migration

Post-translational modifications (PTMs) of the non-histone protein high-mobility group protein B1 (HMGB1) are involved in modulating inflammation and immune responses. Recent studies have implicated that the RNA-binding protein (RBP) Musashi-2 (MSI2) regulates multiple critical biological metabolic and immunoregulatory functions. However, the precise role of MSI2 in regulating PTMs and tumor immunity in colorectal cancer (CRC) remains unclear. Here, we present data indicating that MSI2 potentiates CRC immunopathology in colitis-associated colon cancer (CAC) mouse models, cell lines and clinical specimens, specifically via HMGB1-mediated dendritic cell (DC) maturation and migration, further contributes to the infiltration of CD4+ and CD8+ T cells and inflammatory responses. Under stress conditions, MSI2 can exacerbate the production, nucleocytoplasmic transport and extracellular release of damage-associated molecular patterns (DAMPs)-HMGB1 in CRC cells. Mechanistically, MSI2 mainly enhances the disulfide HMGB1 production and protein translation via direct binding to nucleotides 1403-1409 in the HMGB1 3' UTR, and interacts with the cytoplasmic acetyltransferase P300 to upregulate its expression, further promoting the acetylation of K29 residue in HMGB1, thus leading to K29-HMGB1 nucleocytoplasmic translocation and extracellular release. Furthermore, blocking HMGB1 activity with glycyrrhizic acid (Gly) attenuates MSI2-mediated immunopathology and immune infiltration in CRC in vitro and in vivo. Collectively, this study suggests that MSI2 may improve the prognosis of CRC patients by reprogramming the tumor immune microenvironment (TIME) through HMGB1-mediated PTMs, which might be a novel therapeutic option for CRC immunotherapy.

Flavonoids Regulate Redox-Responsive Transcription Factors in Glioblastoma and Microglia

The tumor microenvironment (TME) has emerged as a valuable therapeutic target in glioblastoma (GBM), as it promotes tumorigenesis via an increased production of reactive oxygen species (ROS). Immune cells such as microglia accumulate near the tumor and its hypoxic core, fostering tumor proliferation and angiogenesis. In this study, we explored the therapeutic potential of natural polyphenols with antioxidant and anti-inflammatory properties. Notably, flavonoids, including fisetin and quercetin, can protect non-cancerous cells while eliminating transformed cells (2D cultures and 3D tumoroids). We tested the hypothesis that fisetin and quercetin are modulators of redox-responsive transcription factors, for which subcellular location plays a critical role. To investigate the sites of interaction between natural compounds and stress-responsive transcription factors, we combined molecular docking with experimental methods employing proximity ligation assays. Our findings reveal that fisetin decreased cytosolic acetylated high mobility group box 1 (acHMGB1) and increased transcription factor EB (TFEB) abundance in microglia but not in GBM. Moreover, our results suggest that the most powerful modulator of the Nrf2-KEAP1 complex is fisetin. This finding is in line with molecular modeling and calculated binding properties between fisetin and Nrf2-KEAP1, which indicated more sites of interactions and stronger binding affinities than quercetin.

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.

Contributing Role of High Mobility Group Box 1 Signaling in Oral Cancer Development and Therapy

Oral squamous cell carcinoma (OSCC) is the most frequent type of oral cancer of multifactorial origin, characterized by histological and clinical manifestations. To date, there are no specific biomarkers or treatment modalities available to efficiently manage this neoplasia, demanding further research on the molecular background of OSCC pathology. Elucidation of signal transduction pathways and associated molecules with differential expression and function in OSCC are expected to enhance the future development of molecular targeted therapies. Among signaling proteins with a potential functional role in OSCC, the High Mobility Group Box 1 (HMGB1) protein has stimulated scientific interest due to frequent upregulation, and implication in the progression of many types of head and neck cancer types. HMGB1 is a nuclear nonhistone protein and an extracellularly secreted cytokine that can interact with several signaling molecules implicated in the pathogenic pathways of OSCC. Binding of HMGB1 to specific receptors on OSCC cells such as the receptor of AGE (RAGE) and the toll-like receptor (TLR) has been shown to initiate several intercellular signaling cascades that can promote OSCC growth, invasion, and metastasis, indicating a potential target for patient prognosis and therapeutic approaches. The purpose of this review is to explore the functional role and associated signaling of HMGB1 in OSCC in order to reveal potential therapeutic targeting options.

HMGB1 in depression: An overview of microglial HMBG1 in the pathogenesis of depression

Depression is a prevalent psychiatric disorder with elusive pathogenesis. Studies have proposed that enhancement and persistence of aseptic inflammation in the central nervous system (CNS) may be closely associated with the development of depressive disorder. High mobility group box 1 (HMGB1) has obtained significant attention as an evoking and regulating factor in various inflammation-related diseases. It is a non-histone DNA-binding protein that can be released as a pro-inflammatory cytokine by glial cells and neurons in the CNS. Microglia, as the immune cell of the brain, interacts with HMGB1 and induces neuroinflammation and neurodegeneration in the CNS. Therefore, in the current review, we aim to investigate the role of microglial HMGB1 in the pathogenetic process of depression.

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.

PARP1 Activation Induces HMGB1 Secretion Promoting Intestinal Inflammation in Mice and Human Intestinal Organoids

Extracellular High-mobility group box 1 (HMGB1) contributes to the pathogenesis of inflammatory disorders, including inflammatory bowel diseases (IBD). Poly (ADP-ribose) polymerase 1 (PARP1) has been recently reported to promote HMGB1 acetylation and its secretion outside cells. In this study, the relationship between HMGB1 and PARP1 in controlling intestinal inflammation was explored. C57BL6/J wild type (WT) and PARP1^-/- mice were treated with DSS to induce acute colitis, or with the DSS and PARP1 inhibitor, PJ34. Human intestinal organoids, which are originated from ulcerative colitis (UC) patients, were exposed to pro-inflammatory cytokines (INFγ + TNFα) to induce intestinal inflammation, or coexposed to cytokines and PJ34. Results show that PARP1^-/- mice develop less severe colitis than WT mice, evidenced by a significant decrease in fecal and serum HMGB1, and, similarly, treating WT mice with PJ34 reduces the secreted HMGB1. The exposure of intestinal organoids to pro-inflammatory cytokines results in PARP1 activation and HMGB1 secretion; nevertheless, the co-exposure to PJ34, significantly reduces the release of HMGB1, improving inflammation and oxidative stress. Finally, HMGB1 release during inflammation is associated with its PARP1-induced PARylation in RAW264.7 cells. These findings offer novel evidence that PARP1 favors HMGB1 secretion in intestinal inflammation and suggest that impairing PARP1 might be a novel approach to manage IBD.

Selective activation of cholinergic neurotransmission from the medial septal nucleus to hippocampal pyramidal neurones improves sepsis-induced cognitive deficits in mice

BACKGROUND

Sepsis-associated encephalopathy is characterised by cognitive dysfunction, and might be mediated by deficits in neurotransmission. Reduced cholinergic neurotransmission in the hippocampus impairs memory function. We assessed real-time alterations of acetylcholine neurotransmission from the medial septal nucleus to the hippocampus, and explored whether sepsis-induced cognitive deficits can be relieved by activating upstream cholinergic projections.

METHOD

Lipopolysaccharide (LPS) injection or caecal ligation and puncture (CLP) was used to induce sepsis and associated neuroinflammation in wild-type and mutant mice. Adeno-associated viruses for calcium and acetylcholine imaging, and for optogenetic and chemogenetic modulation of cholinergic neurones were injected into the hippocampus or medial septum, and a 200-μm-diameter optical fibre was implanted to collect acetylcholine and calcium signals. Cholinergic activity of the medial septum was manipulated and combined with cognitive assessment after LPS injection or CLP.

RESULTS

Intracerebroventricular LPS injection reduced postsynaptic acetylcholine (from 0.146 [0.001] to 0.0047 [0.0005]; p=0.004) and calcium (from 0.0236 [0.0075] to 0.0054 [0.0026]; p=0.0388) signals in hippocampal Vglut2-positive glutamatergic neurones, whereas optogenetic activation of cholinergic neurones in the medial septum reversed LPS-induced reductions in these two signals. Intraperitoneal LPS injection decreased acetylcholine concentration in the hippocampus (476 [20] pg ml^-1 to 382 [14] pg ml^-1; p=0.0001). Reduction in long-term potentiation (238 [23] % to 150 [12] %; p=0.0082) and enhancement of hippocampal pyramidal neurone action potential frequency (5.8 [1.5] Hz to 8.2 [1.8] Hz; p=0.0343) were relieved, and neurocognitive performance was improved by chemogenetic activation of cholinergic innervation of the hippocampus 3 days after LPS injection in septic mice.

CONCLUSIONS

Systemic or local LPS reduced cholinergic neurotransmission from the medial septum to hippocampal pyramidal neurones, and their selective activation alleviated defects in hippocampal neuronal function and synaptic plasticity and ameliorated memory deficits in sepsis model mice through enhanced cholinergic neurotransmission. This provides a basis for targeting cholinergic signalling to the hippocampus in sepsis-induced encephalopathy.

The redox protein HMGB1 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 non-histone nuclear protein that acts as a DNA 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 depends 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 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.

Danger signals in traumatic hemorrhagic shock and new lines for clinical applications

Hemorrhage is the leading cause of death in severe trauma injuries. When organs or tissues are subjected to prolonged hypoxia, danger signals-known as damage-associated molecular patterns (DAMPs)-are released into the intercellular environment. The endothelium is both the target and a major provider of damage-associated molecular patterns, which are directly involved in immuno-inflammatory dysregulation and the associated tissue suffering. Although damage-associated molecular patterns release begins very early after trauma, this release and its consequences continue beyond the initial treatment. Here we review a few examples of damage-associated molecular patterns to illustrate their pathophysiological roles, with emphasis on emerging therapeutic interventions in the context of severe trauma. Therapeutic intervention administered at precise points during damage-associated molecular patterns release may have beneficial effects by calming the inflammatory storm triggered by traumatic hemorrhagic shock.

Review: The role of HMGB1 in spinal cord injury

High mobility group box 1 (HMGB1) has dual functions as a nonhistone nucleoprotein and an extracellular inflammatory cytokine. In the resting state, HMGB1 is mainly located in the nucleus and regulates key nuclear activities. After spinal cord injury, HMGB1 is rapidly expressed by neurons, microglia and ependymal cells, and it is either actively or passively released into the extracellular matrix and blood circulation; furthermore, it also participates in the pathophysiological process of spinal cord injury. HMGB1 can regulate the activation of M1 microglia, exacerbate the inflammatory response, and regulate the expression of inflammatory factors through Rage and TLR2/4, resulting in neuronal death. However, some studies have shown that HMGB1 is beneficial for the survival, regeneration and differentiation of neurons and that it promotes the recovery of motor function. This article reviews the specific timing of secretion and translocation, the release mechanism and the role of HMGB1 in spinal cord injury. Furthermore, the role and mechanism of HMGB1 in spinal cord injury and, the challenges that still need to be addressed are identified, and this work will provide a basis for future studies.

HMGB1 accumulation in cytoplasm mediates noise-induced cochlear damage

Damage-associated molecular pattern molecules (DAMPs) play a critical role in mediating cochlear cell death, which leads to noise-induced hearing loss (NIHL). High-mobility group box 1 (HMGB1), a prototypical DAMP released from cells, has been extensively studied in the context of various diseases. However, whether extracellular HMGB1 contributes to cochlear pathogenesis in NIHL and the potential signals initiating HMGB1 release from cochlear cells are not well understood. Here, through the transfection of the adeno-associated virus with HMGB1-HA-tag, we first investigated early cytoplasmic accumulation of HMGB1 in cochlear hair cells after noise exposure. We found that the cochlear administration of HMGB1-neutralizing antibody immediately after noise exposure significantly alleviated hearing loss and outer hair cells (OHCs) death induced by noise exposure. In addition, activation of signal transducer and activators of transcription 1 (STAT1) and cellular hyperacetylation were verified as potential canonical initiators of HMGB1 cytoplasmic accumulation. These findings reveal the adverse effects of extracellular HMGB1 on the cochlea and the potential signaling events mediating HMGB1 release in hair cells, indicating multiple potential pharmacotherapeutic targets for NIHL.

Oxidative Stress-Induced HMGB1 Translocation in Myenteric Neurons Contributes to Neuropathy in Colitis

High-mobility group box 1 (HMGB1) is a damage-associated molecular pattern released by dying cells to stimulate the immune response. During cell death, HMGB1 is translocated from the nucleus to the cytoplasm and passively released. High levels of secreted HMGB1 are observed in the faeces of inflammatory bowel disease (IBD) patients, indicating its role in IBD pathophysiology and potential as a non-invasive IBD biomarker. HMGB1 is important in regulating neuronal damage in the central nervous system; its pathological activity is intertwined with oxidative stress and inflammation. In this study, HMGB1 expression in the enteric nervous system and its relevance to intestinal neuroinflammation is explored in organotypic cultures of the myenteric plexus exposed to oxidative stimuli and in Winnie mice with spontaneous chronic colitis. Oxidative stimuli induced cytoplasmic translocation of HMGB1 in myenteric neurons in organotypic preparations. HMGB1 translocation correlated with enteric neuronal loss and oxidative stress in the myenteric ganglia of Winnie mice. Inhibition of HMGB1 by glycyrrhizic acid ameliorated HMGB1 translocation and myenteric neuronal loss in Winnie mice. These data highlight modulation of HMGB1 signalling as a therapeutic strategy to reduce the consequences of enteric neuroinflammation in colitis, warranting the exploration of therapeutics acting on the HMGB1 pathway as an adjunct treatment with current anti-inflammatory agents.

Expression profiling and inflammatory activation analysis of high-mobility group box 1 in Schizothorax prenanti

OBJECTIVE

High-mobility group box 1 (HMGB1) is a highly conserved nuclear protein and participates in the immune response to pathogens in bony fish. In this study, the structure and function of HMGB1 in the cyprinid fish Schizothorax prenanti (SpHMGB1) were investigated.

METHODS

The spatial structure of SpHMGB1 was predicted by CPHmodels. Quantitative reverse transcription PCR was used to detect the mRNA of SpHMGB1 in different tissues and Streptococcus agalactiae infection. The macrophage was treated with synthetic SpHMGB1-B box peptide to analyze the inflammatory activity.

RESULT

Structurally, SpHMGB1 had the conserved A box, B box, and acid tail compared with Zebrafish Danio rerio and mice Mus musculus. SpHMGB1 was universally expressed in various tissues, with the highest expression in the middle kidney. In vivo, SpHMGB1 was significantly induced in response to Streptococcus agalactiae infection in the blood and spleen. Synthetic SpHMGB1-B box peptide activated respiratory burst and up-regulated the messenger RNA expression of interleukin-1β, tumor necrosis factor α, interleukin-10, interferon regulatory factor 1, interferon regulatory factor 7, C-X-C motif chemokine ligand 11-1, C-X-C motif chemokine ligand 11-2, and toll-like receptor 4 in macrophages.

CONCLUSION

This study suggested that SpHMGB1 participated in the response to bacterial pathogens and that SpHMGB1-B box peptide played an important role in mediating the immune response of S. prenanti.

HMGB1 from Astrocytes Promotes EAE by Influencing the Immune Cell Infiltration-Associated Functions of BMECs in Mice

High mobility group box 1 (HMGB1) has been reported to play an important role in experimental autoimmune encephalomyelitis (EAE). Astrocytes are important components of neurovascular units and tightly appose the endothelial cells of microvessels by their perivascular endfeet and directly regulate the functions of the blood-brain barrier. Astrocytes express more HMGB1 during EAE while the exact roles of astrocytic HMGB1 in EAE have not been well elucidated. Here, using conditional-knockout mice, we found that astrocytic HMGB1 depletion decreased morbidity, delayed the onset time, and reduced the disease score and demyelination of EAE. Meanwhile, there were fewer immune cells, especially pathogenic T cells infiltration in the central nervous system of astrocytic HMGB1 conditional-knockout EAE mice, accompanied by up-regulated expression of the tight-junction protein Claudin5 and down-regulated expression of the cell adhesion molecules ICAM1 and VCAM1 in vivo. In vitro, HMGB1 released from astrocytes decreased Claudin5 while increased ICAM1 and VCAM1 expressed by brain microvascular endothelial cells (BMECs) through TLR4 or RAGE. Taken together, our results demonstrate that HMGB1 derived from astrocytes aggravates EAE by directly influencing the immune cell infiltration-associated functions of BMECs.

Identification and characterization of high mobility group box 1 and high mobility group box 2 in Siberian sturgeon (Acipenser baerii)

High mobility group box 1 (HMGB1) and high mobility group box 2 (HMGB2) were highly conserved nonhistone chromosomal proteins involved in DNA damage repair, innate immune and inflammatory response. In this study, Acipenser baerii HMGB1 (AbHMGB1) and HMGB 2 (HMGB2) were identified. The open reading frame (ORF) of AbHMGB1 was 621 bp which encoded 206 amino acids, and the ORF of AbHMGB2 was 630 bp encoded 209 amino acids. AbHMGB1 and AbHMGB2 were conserved compared with bony fish by phylogenetic analyzing. qRT-PCR showed that AbHMGB1 and AbHMGB2 were expressed in all examined tissues, AbHMGB1 was expressed abundantly in muscle, followed by head kidney and brain, and AbHMGB2 was highest expressed in gill, followed by brain and muscle. After Streptococcus iniae infection and PAMPs treatment, AbHMGB1 and AbHMGB2 were induced significantly. This study indicated that AbHMGB1 and AbHMGB2 are involved in the process of pathogenic infection and provided a basis for exploring the mechanism of Acipenser baerii enteritis induced by Streptococcus iniae.

Endothelial Dysfunction, HMGB1, and Dengue: An Enigma to Solve

Dengue is a viral infection caused by dengue virus (DENV), which has a significant impact on public health worldwide. Although most infections are asymptomatic, a series of severe clinical manifestations such as hemorrhage and plasma leakage can occur during the severe presentation of the disease. This suggests that the virus or host immune response may affect the protective function of endothelial barriers, ultimately being considered the most relevant event in severe and fatal dengue pathogenesis. The mechanisms that induce these alterations are diverse. It has been suggested that the high mobility group box 1 protein (HMGB1) may be involved in endothelial dysfunction. This non-histone nuclear protein has different immunomodulatory activities and belongs to the alarmin group. High concentrations of HMGB1 have been detected in patients with several infectious diseases, including dengue, and it could be considered as a biomarker for the early diagnosis of dengue and a predictor of complications of the disease. This review summarizes the main features of dengue infection and describes the known causes associated with endothelial dysfunction, highlighting the involvement and possible relationship between HMGB1 and DENV.

α-Iso-cubebene attenuates neointima formation by inhibiting HMGB1-induced monocyte to macrophage differentiation via suppressing ROS production

α-Iso-cubebene (ICB) is a dibenzocyclooctadiene lignin contained in Schisandra chinensis, a medicinal herb used to improve cardiovascular symptoms. To investigate the mechanisms involved, the effects of ICB on cellular production of reactive oxygen species (ROS) was determined using cultured human THP-1 cells. When THP-1 cells were stimulated with HMGB1, cellular concentration of ROS was increased in dose- and time-dependent manners. These increases were significantly attenuated in cells pretreated with NADPH oxidase inhibitors, diphenyleneiodonium chloride and apocynin, but not by other inhibitors related to ROS generation in monocytes. The expression of constitutively expressed NADPH oxidase (NOX) subunits including NOX1, NOX2, NOX4 and NOX5 was not affected by HMGB1, but HMGB1-induced ROS production was exclusively attenuated in NOX2-deficient cells using siRNA, suggesting an enhanced NOX2 complex assembly. When cells were stimulated with HMGB1, p47phox phosphorylation at ser345, ser359 and ser370 was increased in dose- and time-dependent manners, which were significantly attenuated in ICB (3-10 μg/mL)-pretreated cells. In addition, HMGB1-induced monocyte-macrophage differentiation (MMD) in bone marrow-derived cells isolated from mice were significantly attenuated in cells treated with apocynin and ICB. Also, macrophage infiltration and intimal hyperplasia in the wire-injured femoral artery were significantly attenuated in ICB-treated mice compared to wild-type control mice. The results of this study show that ICB inhibits HMGB1-induced MMD by suppressing ROS production in monocytes, thus suggest that ICB has therapeutic potential for vascular inflammation with subsequent intimal hyperplasia related to vascular injury.

RAGE management: ETS1- EGR1 mediated transcriptional networks regulate angiogenic factors in wood frogs

Freeze-tolerant species, such as wood frogs (Rana sylvatica), are susceptible to multiple co-occurring stresses that they must overcome to survive. Freezing is accompanied by mechanical stress and dehydration due to ice crystal formation in the extracellular space, ischemia/anoxia due to interruption in blood flood, and hyperglycemia due to cryoprotective measures. Wood frogs can survive dehydration, anoxia, and high glucose stress independently of freezing, thereby creating a multifactorial model for studying freeze-tolerance. Oxidative stress and high glucose levels favors the production of pro-oxidant molecules and advanced glycation end product (AGE) adducts that could cause substantial cellular damage. In this study, the involvement of the high mobility group box 1 (HMGB1)-AGE/RAGE (receptor for AGE) axis and the regulation of ETS1 and EGR1-mediated angiogenic responses were investigated in liver of wood frogs expose to freeze/thaw, anoxia/reoxygenation and dehydration/rehydration treatments. HMGB1 and not AGE-adducts are likely to induce the activation of ETS1 and EGR1 via the RAGE pathway. The increase in nuclear localization of both ETS1 and EGR1, but not DNA binding activity in response to stress hints to a potential spatial and temporal regulation in inducing angiogenic factors. Freeze/thaw and dehydration/rehydration treatments increase the levels of both pro- and anti-angiogenic factors, perhaps to prepare for the distribution of cryoprotectants or enable the repair of damaged capillaries and wounds when needed. Overall, wood frogs appear to anticipate the need for angiogenesis in response to freezing and dehydration but not anoxic treatments, probably due to mechanical stress associated with the two former conditions.

The Fatal Circle of NETs and NET-Associated DAMPs Contributing to Organ Dysfunction

The innate immune system is the first line of defense against invading pathogens or sterile injuries. Pattern recognition receptors (PRR) sense molecules released from inflamed or damaged cells, or foreign molecules resulting from invading pathogens. PRRs can in turn induce inflammatory responses, comprising the generation of cytokines or chemokines, which further induce immune cell recruitment. Neutrophils represent an essential factor in the early immune response and fulfill numerous tasks to fight infection or heal injuries. The release of neutrophil extracellular traps (NETs) is part of it and was originally attributed to the capture and elimination of pathogens. In the last decade studies revealed a detrimental role of NETs during several diseases, often correlated with an exaggerated immune response. Overwhelming inflammation in single organs can induce remote organ damage, thereby further perpetuating release of inflammatory molecules. Here, we review recent findings regarding damage-associated molecular patterns (DAMPs) which are able to induce NET formation, as well as NET components known to act as DAMPs, generating a putative fatal circle of inflammation contributing to organ damage and sequentially occurring remote organ injury.

Treadmill training improves respiratory function in rats after spinal cord injury by inhibiting the HMGB1/TLR-4/NF-κB signaling pathway

OBJECTIVE

To investigate the effects of treadmill training on lung injury and HMGB1/TLR4/NF-κB after spinal cord injury (SCI) in rats.

METHODS

A total of 108 female SD rats were randomly divided into three groups: sham operation group, SCI brake group, and SCI exercise group. The rats in the SCI exercise group began treadmill running training on the 3rd day after the operation. The rats in the SCI brake group underwent braking treatment. The lung tissues were obtained on the 3rd, 7th, and 14th days after exercise. Locomotor functional recovery was determined using the BBB scores and inclined plane test. Respiratory function was determined via abdominal aortic blood gas analysis. HE staining was used to detect pathological changes in rat lung tissue. RNA sequencing was used to identify differentially expressed genes at different phases in each group of lung tissues. HMGB1, TLR4, and NF-κB in lung tissue were detected using immunohistochemistry and immunofluorescence. Detection of HMGB1 levels in serum, spinal cord tissues and lung tissues by ELISA. HMGB1, TLR4, NF-κB, IL-1β, IL-6, TNF-α mRNA, and protein expression levels were detected via qRT PCR and western blot.

RESULTS

Motor and respiratory functions significantly decreased after SCI (P<0.05). However, locomotion and respiratory functions were significantly improved after treadmill training intervention (P < 0.05). HE staining showed that interstitial thickening, inflammatory cells, and erythrocyte infiltration occurred in lung tissue of rats after SCI (P<0.05). Moreover, inflammatory reaction in lung tissue was significantly reduced after treadmill training intervention (P<0.05). A total of 428 differentially expressed mRNAs [(|log2(FC)| > 2, P < 0.05)] were identified in the intersection of the three groups. KEGG analysis identified five enriched signal pathways, including NF-kappa B. ELISA results showed that treadmill training could significantly reduce the levels of HMGB1 in serum, spinal cord tissue and lung tissue that were elevated after SCI (P < 0.05). Immunohistochemistry, immunofluorescence, qRT PCR, and Western blot showed that HMGB1, TLR4, IL-1β, IL-6, TNF-α, and NF-κB expressions were significantly up-regulated at the 3rd, 7th and 14th days after SCI, compared with the sham operation group. Besides, inflammatory cytokines were significantly lower in the SCI exercise group than in the SCI brake group at all time points after intervention (P < 0.05).

CONCLUSION

Treadmill training alleviates lung tissue inflammation and promotes recovery of motor and respiratory functions by inhibiting the HMGB1/TLR4/NF-κB signaling pathway after SCI in rats.

PRRSV Induces HMGB1 Phosphorylation at Threonine-51 Residue to Enhance Its Secretion

Porcine reproductive and respiratory syndrome virus (PRRSV) induces secretion of high mobility group box 1 (HMGB1) to mediate inflammatory response that is involved in the pulmonary injury of infected pigs. Our previous study indicates that protein kinase C-delta (PKC-delta) is essential for HMGB1 secretion in PRRSV-infected cells. However, the underlying mechanism in HMGB1 secretion induced by PRRSV infection is still unclear. Here, we discovered that the phosphorylation level of HMGB1 in threonine residues increased in PRRSV-infected cells. A site-directed mutagenesis study showed that HMGB1 phosphorylation at threonine-51 was associated with HMGB1 secretion induced by PRRSV infection. Co-immunoprecipitation (co-IP) of HMGB1 failed to precipitate PKC-delta, but interestingly, mass spectrometry analysis of the HMGB1 co-IP product showed that PRRSV infection enhanced HMGB1 binding to ribosomal protein S3 (RPS3), which has various extra-ribosomal functions. The silencing of RPS3 by siRNA blocked HMGB1 secretion induced by PRRSV infection. Moreover, the phosphorylation of HMGB1 at threonine-51 was correlated with the interaction between HMGB1 and RPS3. In vivo, PRRSV infection also increased RPS3 levels and nuclear accumulation in pulmonary alveolar macrophages. These results demonstrate that PRRSV may induce HMGB1 phosphorylation at threonine-51 and increase its interaction with RPS3 to enhance HMGB1 secretion. This finding provides insights into the pathogenesis of PRRSV infection.

Nonoxid-HMGB1 Attenuates Cognitive Impairment After Traumatic Brain Injury in Rats

Traumatic brain injury (TBI) is a major global burden of health. As an accepted inflammatory mediator, high mobility group box 1 (HMGB1) is found to be effective in facilitating neurogenesis and axonal regeneration. SH3RF2 (also known as POSHER), an E3 ligase SH3 domain-containing ring finger 2, belongs to the SH3RF family of proteins. Here, we aimed to investigate the role of redox states of HMGB1 on neurite outgrowth and regeneration both in vitro and in vivo. In this study, distinct recombinant HMGB1 redox isoforms were used. Sequencing for RNA-seq and data analysis were performed to find the potential downstream target of nonoxid-HMGB1 (3S-HMGB1). Protein changes and distribution of SH3RF2 were evaluated by western blot assays and immunofluorescence. Lentivirus and adeno-associated virus were used to regulate the expression of genes. Nonoxid-HMGB1-enriched exosomes were constructed and used to treat TBI rats. Neurological function was evaluated by OF test and NOR test. Results demonstrated that nonoxid-HMGB1 and fr-HMGB1, but not ds-HMGB1, promoted neurite outgrowth and axon elongation. RNA-seq and western blot assay indicated a significant increase of SH3RF2 in neurons after treated with nonoxid-HMGB1 or fr-HMGB1. Notably, the beneficial effects of nonoxid-HMGB1 were attenuated by downregulation of SH3RF2. Furthermore, nonoxid-HMGB1 ameliorated cognitive impairment in rats post-TBI via SH3RF2. Altogether, our experimental results suggest that one of the promoting neurite outgrowth and regeneration mechanisms of nonoxid-HMGB1 is mediated through the upregulated expression of SH3RF2. Nonoxid-HMGB1 is an attractive therapeutic candidate for the treatment of TBI.

Targeting HMGB1 for the treatment of sepsis and sepsis-induced organ injury

High mobility group box 1 (HMGB1) is a ubiquitous nuclear protein that is present in almost all cells and regulates the activity of innate immune responses in both intracellular and extracellular settings. Current evidence suggests that HMGB1 plays a pivotal role in human pathological and pathophysiological processes such as the inflammatory response, immune reactions, cell migration, aging, and cell death. Sepsis is a systemic inflammatory response syndrome (SIRS) that occurs in hosts in response to microbial infections with a proven or suspected infectious etiology and is the leading cause of death in intensive care units worldwide, particularly in the aging population. Dysregulated systemic inflammation is a classic characteristic of sepsis, and suppression of HMGB1 may ameliorate inflammation and improve patient outcomes. Here, we focus on the latest breakthroughs regarding the roles of HMGB1 in sepsis and sepsis-related organ injury, the ways by which HMGB1 are released, and the signaling pathways and therapeutics associated with HMGB1. This review highlights recent advances related to HMGB1: the regulation of HMBG1 might be helpful for both basic research and drug development for the treatment of sepsis and sepsis-related organ injury.

Insights into the Impact of Gold Nanoclusters Au10SG10 on Human Microglia

The purpose of the current study is to uncover the impact of small liganded gold nanoclusters with 10 gold atoms and 10 glutathione ligands (Au₁₀SG₁₀) on several biomarkers in human microglia. We established the links connecting the atomically precise structure of Au₁₀SG₁₀ with their properties and changes in several biomolecules under oxidative stress. Au₁₀SG₁₀ caused the loss of mitochondrial metabolic activity, increased lipid peroxidation and translocation of an alarmin molecule, high mobility group box 1 (HMGB1), from the nucleus to the cytosol. Molecular modeling provided an insight into the location of amino acid interaction sites with Au₁₀SG₁₀ and the nature of bonds participating in these interactions. We show that Au₁₀SG₁₀ can bind directly to the defined sites of reduced, oxidized, and acetylated HMGB1. Further studies with similar complementary approaches merging live-cell analyses, determination of biomarkers, and cell functions could lead to optimized gold nanoclusters best suited for diagnostic and bioimaging purposes in neuroscience.

Potential of Polyphenols to Restore SIRT1 and NAD+ Metabolism in Renal Disease

SIRT1 is an NAD⁺-dependent class III histone deacetylase that is abundantly expressed in the kidney, where it modulates gene expression, apoptosis, energy homeostasis, autophagy, acute stress responses, and mitochondrial biogenesis. Alterations in SIRT1 activity and NAD⁺ metabolism are frequently observed in acute and chronic kidney diseases of diverse origins, including obesity and diabetes. Nevertheless, in vitro and in vivo studies and clinical trials with humans show that the SIRT1-activating compounds derived from natural sources, such as polyphenols found in fruits, vegetables, and plants, including resveratrol, quercetin, and isoflavones, can prevent disease and be part of treatments for a wide variety of diseases. Here, we summarize the roles of SIRT1 and NAD⁺ metabolism in renal pathophysiology and provide an overview of polyphenols that have the potential to restore SIRT1 and NAD⁺ metabolism in renal diseases.

The mechanism of HMGB1 secretion and release

High mobility group box 1 (HMGB1) is a nonhistone nuclear protein that has multiple functions according to its subcellular location. In the nucleus, HMGB1 is a DNA chaperone that maintains the structure and function of chromosomes. In the cytoplasm, HMGB1 can promote autophagy by binding to BECN1 protein. After its active secretion or passive release, extracellular HMGB1 usually acts as a damage-associated molecular pattern (DAMP) molecule, regulating inflammation and immune responses through different receptors or direct uptake. The secretion and release of HMGB1 is fine-tuned by a variety of factors, including its posttranslational modification (e.g., acetylation, ADP-ribosylation, phosphorylation, and methylation) and the molecular machinery of cell death (e.g., apoptosis, pyroptosis, necroptosis, alkaliptosis, and ferroptosis). In this minireview, we introduce the basic structure and function of HMGB1 and focus on the regulatory mechanism of HMGB1 secretion and release. Understanding these topics may help us develop new HMGB1-targeted drugs for various conditions, especially inflammatory diseases and tissue damage.

A nuclear protein that gets released after cell death or is actively secreted by immune cells offers a promising therapeutic target for treating diseases linked to excessive inflammation. Daolin Tang from the University of Texas Southwestern Medical Center in Dallas, USA, and colleagues review how cellular stresses can trigger the accumulation of HMGB1, a type of alarm signal protein that promotes the recruitment and activation of inflammation-promoting immune cells. The researchers discuss various mechanisms that drive both passive and active release of HMGB1 into the space around cells. These processes, which include enzymatic modifications of the HMGB1 protein, cell–cell interactions and molecular pathways of cell death, could be targeted by drugs to lessen tissue damage and inflammatory disease caused by HMGB1-induced immune responses

Heme oxygenase-1 gene delivery for altering high mobility group box-1 protein in pancreatic islet

Pancreatic islet transplantation is a promising strategy for the treatment of type I diabetes. High-mobility group box-1 (HMGB1), highly expressed in islet cells, is a potent immune stimulator in immune rejection. Heme oxygenase-1 (HO1) gene therapy can modulate the release of HMGB1 by altering intracellular molecules for successful cell transplantation. After delivery of the heme oxygenase-1 (HO1) gene to islet cells using an adeno-associated viral vector (AAV), it was evaluated the changes in cytoplasmic Ca²⁺ ions and calcineurin activity as well as histone acetyltransferase (HAT) and Poly(ADP) ribose polymerase-1 (PARP-1). Inhibition of HMGB1 release was evaluated through altering these intracellular molecules. Then, after transplantation of HO1-transduced islets, the therapeutic effect of them was evaluated through measuring blood glucose level to diabetic mice and through immunohistochemical analysis. The transduced HO1 gene significantly inhibited HMGB1 release in islets that was under the cell damage by hypoxia exposure. It was confirmed that this result was initially due to the decrease in cytoplasmic Ca²⁺ ion concentration and calcineurin activity. In addition, the delivered HO1 gene simultaneously reduced the activity of HAT and PARP-1, which are involved in the translocation of HMGB1 from the nucleus to the cytoplasm. As a result, when the HO1 gene-transduced islets were transplanted into diabetic mice, the treatment efficiency of diabetes was effectively improved by increasing the survival rate of the islets. Collectively, these results suggest that HO1 gene transfer can be used for successful islet transplantation by altering the activity of intracellular signal molecules and reducing HMGB1 release.

Increased expression of HMGB1 in the implantation phase endometrium is related to recurrent implantation failure

BACKGROUND

Impaired endometrial receptivity was the main cause of recurrent implantation failure (RIF); however, its underlying mechanisms had not been elucidated. This study aimed to determine the expression level of high-mobility group box protein 1 (HMGB1) in the endometrium with RIF and its effect on endometrial receptivity.

METHODS AND RESULTS

Genome-wide expression profiling, real-time reverse transcription PCR, immunohistochemical staining, western blot, and in vitro assays were performed in this study. We found that HMGB1 expression was significantly decreased in the implantation phase endometrium in the control group (patients with tubal infertility and successfully achieve conception after the first embryo transfer) (P = 0.006). However, the expression levels of HMGB1 mRNA and protein were significantly upregulated during the implantation phase in endometrial tissues obtained from patients with RIF compared to that in the control group (P = 0.001), consistent with the results of the genome-wide expression profiling. Moreover, in vitro assays showed that increased expression of HMGB1 in human endometrial epithelial cells dramatically displayed a marked deficiency in supporting blastocysts and human embryonic JAR cells adhesion, which mimic the process of embryo adhesion.

CONCLUSION

These findings strongly indicated that increased HMGB1 levels suppressed the epithelial cell adhesion capability, therefore contributing to impaired endometrial receptivity in patients with recurrent implantation failure, which can be used as a target for the recognition and treatment of recurrent implantation failure in clinical practice.

HMGB1-Induced Hepatocyte Pyroptosis Expanding Inflammatory Responses Contributes to the Pathogenesis of Acute-on-Chronic Liver Failure (ACLF)

Background

Acute-on-chronic liver failure (ACLF) is a critical disease with a high fatality rate. Immune dysfunction and inflammatory responses are key risk factors in ACLF. Pyroptosis is a form of programmed cell death characterized by the release of inflammatory cytokines, which causes the strong inflammatory responses. High mobility group box-1 (HMGB1) could induce pyroptosis and is closely related to ACLF. However, the role of HMGB1-induced hepatocyte pyroptosis in ACLF has never been proposed; whether HMGB1-induced hepatocyte pyroptosis participates in the development of ACLF and the mechanisms involved are barely understood.

Purpose

This study aimed to clarify the roles of HMGB1-induced hepatocyte pyroptosis in ACLF and the molecular mechanisms involved.

Methods

Wistar rats were randomly divided into five groups, viz.: Normal, ACLF model, HMGB1 inhibitor, Caspase-1 inhibitor, and HMGB1 inhibitor+Caspase-1 inhibitor groups. The ACLF rat model was established using 40% carbon tetrachloride-induced liver fibrosis, followed by D-galactosamine and lipopolysaccharide joint acute attacks. The liver function, coagulation function and pathological damage of rats in each group were evaluated. The biological mechanisms of HMGB1-induced pyroptosis and the release of inflammatory cytokines were investigated using Western blot, quantitative real-time PCR (RT-qPCR), immunofluorescence, enzyme-linked immunosorbent assay (ELISA), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay.

Results

The liver function and coagulation function of ACLF rats were seriously impaired; liver tissue showed massive or submassive necrosis, accompanied by inflammatory cell infiltration; the percentage of pyroptotic hepatocytes significantly increased, and a large number of inflammatory cytokines were released. The expression levels of pyroptosis-related genes and proteins in liver tissues and serum significantly increased. But these phenomenons were improved by the inhibition of HMGB1, and the dual inhibition of HMGB1 and Caspase-1 showed a stronger effect.

Conclusion

The findings indicate, for the first time, that pyroptosis is a crucial pathophysiological event of ACLF involved in its pathogenesis, and HMGB1-induced hepatocyte pyroptosis expands inflammatory responses to aggravate ACLF, suggesting that it may be a potential therapeutic target for ACLF treatment.

Serum Sirtuin-1, HMGB1-TLR4, NF-KB and IL-6 Levels in Alzheimer's: The Relation Between Neuroinflammatory Pathway and Severity of Dementia

Alzheimer's disease (AD), which affects the world's aging population, is a progressive neurodegenerative disease requiring markers or tools to accurately and easily diagnose and monitor the process.

OBJECTIVE

In this study, serum Sirtuin-1(SIRT-1), High Mobility Group Box 1 (HMGB1), Toll-Like Receptor-4 (TLR4), Nuclear Factor Kappa B (NF-kB), Interleukin-6 (IL-6), Amyloid βeta-42 (Aβ- 42), and p-tau181 levels in patients diagnosed with AD according to NINCS-ADRA criteria were studied. We investigated the inflammatory pathways that lead to progressive neuronal loss and highlight their possible relationship with dementia severity in the systemic circulation.

METHODS

Patients over 60 years of age were grouped according to their Standard Mini Mental Test results, MRI, and/or Fludeoxyglucose positron emission tomography or according to their CT findings as Control n:20; AD n:32; Vascular Dementia (VD) n:17; AD + VD; n = 21. Complete blood count, Glucose, Vitamin B12, Folic Acid, Enzymes, Urea, Creatinine, Electrolytes, Bilirubin, and Thyroid Function tests were evaluated. ELISA was used for the analysis of serum SIRT1, HMGB1, TLR4, NF-kB, IL-6, Aβ-42, and p-tau181 levels.

RESULTS

Levels of serum Aβ-42, SIRT1, HMGB1, and IL-6 were significantly higher (p< 0.001, p< 0.01, p< 0.001, and p< 0.001, respectively), and TLR4 levels were significantly lower (p< 0.001) in the dementia group than in the control group. No significant difference was observed between dementia and control groups for serum NF-kB and p-tau181 levels.

CONCLUSION

Our results show that the levels of the Aβ42, SIRT 1, HMGB1, and TLR4 pathways are altered in AD and VD. SIRT 1 activity plays an important role in the inflammatory pathway of dementia development, particularly in AD.

Damage-Associated Molecular Patterns As Double-Edged Swords in Sepsis

Significance: Sepsis is defined as a life-threatening organ dysfunction caused by dysregulated host response to infection. This leads to an uncontrolled inflammatory response at the onset of infection, followed by immunosuppression. The development of a specific treatment modality for sepsis is still challenging, reflecting our inadequate understanding of its pathophysiology. Understanding the mechanism and transition of the early hyperinflammation to late stage of immunosuppression in sepsis is critical for developing sepsis therapeutics. Recent Advances: Damage-associated molecular patterns (DAMPs) are intracellular molecules and released upon tissue injury and cell death in sepsis. DAMPs are recognized by pattern recognition receptors to initiate inflammatory cascades. DAMPs not only elicit an inflammatory response but also they subsequently induce immunosuppression, both are equally important for exacerbating sepsis. Recent advances on a new DAMP, extracellular cold-inducible RNA-binding protein for fueling inflammation and immunosuppression in sepsis, have added a new avenue into the dual functions of DAMPs in sepsis. Critical Issues: The molecular modification of DAMPs and their binding to pattern recognition receptors transit dynamically by the cellular environment in pathophysiologic conditions. Correlation between the dynamic changes of the impacts of DAMPs and the clinical outcomes in sepsis still lacks adequate understanding. Here, we focus on the impacts of DAMPs that cause inflammation as well as induce immunosuppression in sepsis. We further discuss the therapeutic potential by targeting DAMPs to attenuate inflammation and immunosuppression for mitigating sepsis. Future Directions: Uncovering pathways of the transition from inflammation to immunosuppression of DAMPs is a potential therapeutic avenue for mitigating sepsis.

LPS-induced macrophage HMGB1-loaded extracellular vesicles trigger hepatocyte pyroptosis by activating the NLRP3 inflammasome

Extracellular vesicles (EVs) have emerged as important vectors of intercellular dialogue. High mobility group box protein 1 (HMGB1) is a typical damage-associated molecular pattern (DAMP) molecule, which is cytotoxic and leads to cell death and tissue injury. Whether EVs are involved in the release of HMGB1 in lipopolysaccharide (LPS)-induced acute liver injuries need more investigation. EVs were identified by transmission electron microscopy, nanoparticle tracking analysis (NTA), and western blotting. The co-localization of HMGB1, RAGE (receptor for advanced glycation end-products), EEA1, Rab5, Rab7, Lamp1 and transferrin were detected by confocal microscopy. The interaction of HMGB1 and RAGE were investigated by co-immunoprecipitation. EVs were labeled with the PKH67 and used for uptake experiments. The pyroptotic cell death was determined by FLICA 660-YVAD-FMK. The expression of NLRP3 (NOD-like receptor family pyrin domain containing 3) inflammasomes were analyzed by western-blot or immunohistochemistry. Serum HMGB1, ALT (alanine aminotransferase), AST (aspartate aminotransferase), LDH (lactate dehydrogenase) and MPO (myeloperoxidase) were measured using a commercial kit. The extracellular vesicle HMGB1 was detected in the serums of sepsis patients. Macrophages were found to contribute to HMGB1 release through the EVs. HMGB1-RAGE interactions participated in the loading of HMGB1 into the EVs. These EVs shuttled HMGB1 to target cells by transferrin-mediated endocytosis leading to hepatocyte pyroptosis by the activation of NLRP3 inflammasomes. Moreover, a positive correlation was verified between the sepsis serum EVs-HMGB1 level and clinical liver damage. This finding provides insights for the development of novel diagnostic and therapeutic strategies for acute liver injuries.

HMGB1 could restrict 1,3-β-glucan induced mice lung inflammation by affecting Beclin1 and Bcl2 interaction and promoting the autophagy of epithelial cells

Fungi were microorganisms that are ubiquitous in a variety of environments. Inhalation of fungi-contaminated organic dust led to hypersensitivity pneumonitis and might eventually cause irreversible pulmonary fibrosis. Studies showed that maintaining the homeostasis of epithelial cells was vital for defending the exogenous fungi invasion. HMGB1-dependent autophagy played a critical role in maintaining cell homeostasis in multiple inflammatory diseases. However, the actual role of HMGB1-dependent autophagy in hypersensitivity pneumonitis was unclear. In our study, mice were exposed to 0.3 mg/50 μL 1,3-β-glucan solution by intratracheal instillation to set up the lung inflammation model. To investigate the role of HMGB1-dependent autophagy in 1,3-β-glucan induced lung inflammation, AAV-sh-HMGB1 was intratracheally injected to silence HMGB1 in the lung. Our finding suggested that silencing HMGB1 could aggravate the 1,3-β-glucan induced lung inflammation by inhibiting the autophagy of epithelial cells. And ubiquitination of Beclin1 contributed to decreasing the interaction of Beclin1 and Bcl2, which might be a key regulatory mechanism of HMGB1 on 1,3-β-glucan induced autophagy.