A Janus tale of two active high mobility group box 1 (HMGB1) redox states

LncRNAs as nodes for the cross-talk between autophagy and Wnt signaling in pancreatic cancer drug resistance

Pancreatic cancer is a malignancy with high mortality. In addition to the few symptoms until the disease reaches an advanced stage, the high fatality rate is attributed to its rapid development, drug resistance and lack of appropriate treatment. In the selection and research of therapeutic drugs, gemcitabine is the first-line drug for pancreatic cancer. Solving the problem of gemcitabine resistance in pancreatic cancer will contribute to the progress of pancreatic cancer treatment. Long non coding RNAs (lncRNAs), which are RNA transcripts longer than 200 nucleotides, play vital roles in cellular physiological metabolic activities. Currently, our group and others have found that some lncRNAs are aberrantly expressed in pancreatic cancer cells, which can regulate the process of cancer through autophagy and Wnt/β-catenin pathways simultaneously and affect the sensitivity of cancer cells to therapeutic drugs. This review presents an overview of the recent evidence concerning the node of lncRNA for the cross-talk between autophagy and Wnt/β-catenin signaling in pancreatic cancer, together with the practicability of lncRNAs and the core regulatory factors as targets in therapeutic resistance.

Multiple functions of HMGB1 in cancer

High mobility group box 1 (HMGB1) is a nuclear DNA-binding protein with a dual role in cancer, acting as an oncogene and a tumor suppressor. This protein regulates nucleosomal structure, DNA damage repair, and genomic stability within the cell, while also playing a role in immune cell functions. This review comprehensively evaluates the biological and clinical significance of HMGB1 in cancer, including its involvement in cell death and survival, its potential as a therapeutic target and cancer biomarker, and as a prosurvival signal for the remaining cells after exposure to cytotoxic anticancer treatments. We highlight the need for a better understanding of the cellular markers and mechanisms involved in the involvement of HMGB1in cancer, and aim to provide a deeper understanding of its role in cancer progression.

Revealing the extracellular function of HMGB1 N-terminal region acetylation assisted by a protein semi-synthesis approach

HMGB1 (high-mobility group box 1) is a non-histone chromatin-associated protein that has been widely reported as a representative damage-associated molecular pattern (DAMP) and to play a pivotal role in the proinflammatory process once it is in an extracellular location. Accumulating evidence has shown that HMGB1 undergoes extensive post-translational modifications (PTMs) that actively regulate its conformation, localization, and intermolecular interactions. However, fully characterizing the functional implications of these PTMs has been challenging due to the difficulty in accessing homogeneous HMGB1 with site-specific PTMs of interest. In this study, we developed a streamlined protein semi-synthesis strategy via salicylaldehyde ester-mediated chemical ligations (Ser/Thr ligation and Cys/Pen ligation, STL/CPL). This methodology enabled us to generate a series of N-terminal region acetylated HMGB1 proteins. Further studies revealed that acetylation regulates HMGB1-heparin interaction and modulates HMGB1's stability against thrombin, representing a regulatory switch to control HMGB1's extracellular activity.

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.

HMGB1: a potential new target for tendinopathy treatment

Tendinopathy describes a complex pathology of the tendon characterized by abnormalities in the microstructure, composition, and cellularity of the tendon, leading to pain, limitation of activity and reduced function. Nevertheless, the mechanism of tendinopathy has not been fully elucidated, and the treatment of tendinopathy remains a challenge. High mobility group box 1 (HMGB1), a highly conserved and multifaceted nuclear protein, exerts multiple roles and high functional variability and is involved in many biological and pathological processes. In recent years, several studies have suggested that HMGB1 is associated with tendinopathy and may play a key role in the pathogenesis of tendinopathy. Therefore, this review summarizes the expression and distribution of HMGB1 in tendinopathy, focuses on the roles of HMGB1 and HMGB1-based potential mechanisms involved in tendinopathy, and finally summarizes the findings on HMGB1-based therapeutic approaches in tendinopathy, probably providing new insight into the mechanism and further potential therapeutic targets of tendinopathy.

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.

Inflachromene inhibits intimal hyperplasia through the HMGB1/2- regulated TLR4-NF-κB pathway

The contractile-syntheticphenotypicconversion of vascular smooth muscle cells (VSMCs) plays a key role in atherosclerosis, vascular restenosis, and hypertension. Our previous study explored the correlation between high mobility group box protein (HMGB) 1 and HMGB2 and neointimal hyperplasia after vascular injury. In the present study, we explore whether inflachromene (ICM), a novel inhibitor of the expression of both HMGB1 and HMGB2, modulates phenotypic changes in VSMCs and the mechanisms involved. Mice treated with ICM after carotid artery wire injury showed a decrease in excessive neointimal hyperplasia compared with that in the vehicle groups. In cultured VSMCs, pretreatment with ICM suppressed the angiotensin II (Ang II)-induced phenotypic conversion, proliferation, and migration. We discovered that ICM reduced the Ang II-induced upregulation of the expression of HMGB1 and HMGB2 and inhibited their shuttling between the nucleus and the cytosol. Mechanistically, Ang II-treated VSMCs exhibited higher levels of Toll-like receptor 4 (TLR4) and nuclear factor-κB (NF-κB) phosphorylation, which were attenuated by ICM. In addition, the NF-κB inhibitor Bay-117082 abolished the recombinant HMGB1-mediated VSMC phenotypic conversion, proliferation, and migration. Furthermore, ICM ameliorated the Ang II-induced increases in NAD[P]H oxidase expression, thereby attenuating the Ang II-induced proliferation and migration. These results reveal that ICM pretreatment attenuates Ang II-induced VSMC dedifferentiation, proliferation, and migration may by regulating the TLR4-NF-kB pathway. Thus, ICM is a potential therapy and preventive treatment for vascular proliferative diseases.

Upregulation of HMGB1 promotes vascular dysfunction in the soft palate of patients with obstructive sleep apnea via the TLR4/NF-κB/VEGF pathway

Obstructive sleep apnea (OSA) is characterized by the collapse of the soft palate in the upper airway, resulting in chronic intermittent hypoxia during sleep. Therefore, an understanding of the molecular mechanisms underlying pathophysiological dysfunction of the soft palate in OSA is necessary for the development of new therapeutic strategies. In the present study, we observed that high mobility group protein box 1 (HMGB1) was released by a large infiltration of macrophages in the soft palate of OSA patients. The toll-like receptor 4/nuclear factor kappa B pathway was observed to be activated by the release of HMGB1, and this was accompanied by an increased expression of pro-inflammatory factors, including tumor necrosis factor-α and interleukin-6. Importantly, increased expression of toll-like receptor 4 was observed in endothelial cells, contributing to upregulation of the angiogenesis-related factors vascular endothelial-derived growth factor and matrix metalloproteinase 9. Moreover, we confirmed the effect of the HMGB1-mediated toll-like receptor 4/nuclear factor kappa B pathway on cell proliferation and angiogenesis in an in vitro cell model of human umbilical vein endothelial cells. We conclude that HMGB1 may be a potential therapeutic target for preventing angiogenesis and pathology in OSA.

Ferroptosis: friend or foe in cancer immunotherapy?

Ferroptosis has gained interest due to it immunogenicity and the higher sensitivity of cancer cells to it. However, it was recently shown that ferroptosis in tumor-associated neutrophils leads to immunosuppression and negatively impacts therapy. Here, we discuss the potential implications of the two sides (friend versus foe) of ferroptosis in cancer immunotherapy.

Cytokine profiling in pulmonary arterial hypertension: the role of redox homeostasis and sex

Pulmonary arterial hypertension (PAH) is a fatal disease with a well-established sexual dimorphism. Activated inflammatory response and altered redox homeostasis, both known to manifest in a sex-specific manner, are implicated in the pathogenic mechanisms involved in PAH development. This study aimed to evaluate the impact of sex and plasma redox status on circulating cytokine profiles. Plasma oxidation-reduction potential (ORP), as a substitute measure of redox status, was analyzed in male and female Group 1 PAH and healthy subjects. The profiles of 27 circulating cytokines were compared in 2 PAH groups exhibiting the highest and lowest quartile for plasma ORP, correlated with clinical parameters, and used to predict patient survival. The analysis of the PAH groups with the highest and lowest ORP revealed a correlation between elevated cytokine levels and increased oxidative stress in females. In contrast, in males, cytokine expressions were increased in the lower oxidative environment (except for IL-1b). Correlations of the increased cytokine expressions with PAH severity were highly sex-dependent and corresponded to the increase in PAH severity in males and less severe PAH in females. Machine learning algorithms trained on the combined cytokine and redox profiles allowed the prediction of PAH mortality with 80% accuracy. We conclude that the profile of circulating cytokines in PAH patients is redox- and sex-dependent, suggesting the vital need to stratify the patient cohort subjected to anti-inflammatory therapies. Combined cytokine and/or redox profiling showed promising value for predicting the patients' survival.

Role of endoplasmic reticulum stress in impaired neonatal lung growth and bronchopulmonary dysplasia

Myeloperoxidase (MPO), oxidative stress (OS), and endoplasmic reticulum (ER) stress are increased in the lungs of rat pups raised in hyperoxia, an established model of bronchopulmonary dysplasia (BPD). However, the relationship between OS, MPO, and ER stress has not been examined in hyperoxia rat pups. We treated Sprague-Dawley rat pups with tunicamycin or hyperoxia to determine this relationship. ER stress was detected using immunofluorescence, transcriptomic, proteomic, and electron microscopic analyses. Immunofluorescence observed increased ER stress in the lungs of hyperoxic rat BPD and human BPD. Proteomic and morphometric studies showed that tunicamycin directly increased ER stress of rat lungs and decreased lung complexity with a BPD phenotype. Previously, we showed that hyperoxia initiates a cycle of destruction that we hypothesized starts from increasing OS through MPO accumulation and then increases ER stress to cause BPD. To inhibit ER stress, we used tauroursodeoxycholic acid (TUDCA), a molecular chaperone. To break the cycle of destruction and reduce OS and MPO, we used N-acetyl-lysyltyrosylcysteine amide (KYC). The fact that TUDCA improved lung complexity in tunicamycin- and hyperoxia-treated rat pups supports the idea that ER stress plays a causal role in BPD. Additional support comes from data showing TUDCA decreased lung myeloid cells and MPO levels in the lungs of tunicamycin- and hyperoxia-treated rat pups. These data link OS and MPO to ER stress in the mechanisms mediating BPD. KYC's inhibition of ER stress in the tunicamycin-treated rat pup's lung provides additional support for the idea that MPO-induced ER stress plays a causal role in the BPD phenotype. ER stress appears to expand our proposed cycle of destruction. Our results suggest ER stress evolves from OS and MPO to increase neonatal lung injury and impair growth and development. The encouraging effect of TUDCA indicates that this compound has the potential for treating BPD.

The C-Terminal Acidic Tail Modulates the Anticancer Properties of HMGB1

Energy metabolism reprogramming was recently listed as a hallmark of cancer. In this process, the switch from pyruvate kinase isoenzyme type M1 to pyruvate kinase isoenzyme type M2 (PKM2) is believed to play a crucial role. Interestingly, the activity of the active form of PKM2 can efficiently be inhibited by the high-mobility group box 1 (HMGB1) protein, leading to a rapid blockage of glucose-dependent aerobic respiration and cancer cell death. HMGB1 is a member of the HMG protein family. It contains two DNA-binding HMG-box domains and an acidic C-terminal tail capable of positively or negatively modulating its biological properties. In this work, we report that the deletion of the C-terminal tail of HMGB1 increases its activity towards a large panel of cancer cells without affecting the viability of normal immortalized fibroblasts. Moreover, in silico analysis suggests that the truncated form of HMGB1 retains the capacity of the full-length protein to interact with PKM2. However, based on the capacity of the cells to circumvent oxidative phosphorylation inhibition, we were able to identify either a cytotoxic or cytostatic effect of the proteins. Together, our study provides new insights in the characterization of the anticancer activity of HMGB1.

The Evolving Concept of Neuro-Thromboinflammation for Neurodegenerative Disorders and Neurotrauma: A Rationale for PAR1-Targeting Therapies

Interest in the role of coagulation and fibrinolysis in the nervous system was active in several laboratories dating back before cloning of the functional thrombin receptor in 1991. As one of those, our attention was initially on thrombin and plasminogen activators in synapse formation and elimination in the neuromuscular system, with orientation towards diseases such as amyotrophic lateral sclerosis (ALS) and how clotting and fibrinolytic pathways fit into its pathogenesis. This perspective is on neuro-thromboinflammation, emphasizing this emerging concept from studies and reports over more than three decades. It underscores how it may lead to novel therapeutic approaches to treat the ravages of neurotrauma and neurodegenerative diseases, with a focus on PAR1, ALS, and parmodulins.

Release of redox enzymes and micro-RNAs in extracellular vesicles, during infection and inflammation

Many studies reported that redox enzymes, particularly thioredoxin and peroxiredoxin, can be released by cells and act as soluble mediators in immunity. Recently, it became clear that peroxiredoxins can be secreted via the exosome-release route, yet it remains unclear how this exactly happens and why. This review will first introduce briefly the possible redox states of protein cysteines and the role of redox enzymes in their regulation. We will then discuss the studies on the extracellular forms of some of these enzymes, their association with exosomes/extracellular vesicles and with exosome micro-RNAs (miRNAs)/mRNAs involved in oxidative processes, relevant in infection and inflammation.

HMGB1 Promotes the Release of Sonic Hedgehog From Astrocytes

High mobility group box 1 protein (HMGB1) is known to be a trigger of inflammation in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). However, it may play a different role in some way. Here we investigated the effect of HMGB1 on promoting sonic hedgehog (shh) release from astrocytes as well as the possible signal pathway involved in it. Firstly, shh increased in astrocytes after administration of recombinant HMGB1 or decreased after HMGB1 was blocked when stimulated by homogenate of the onset stage of EAE. Moreover, the expression of HMGB1 receptors, toll-like receptor (TLR) 2 and receptor for advanced glycation end products (RAGE) increased after HMGB1 administration in primary astrocytes. However, the enhancing effect of HMGB1 on shh release from astrocytes was suppressed only after RAGE was knocked out or blocked. Mechanistically, HMGB1 functioned by activating RAGE-mediated JNK, p38, stat3 phosphorylation. Moreover, HMGB1 could induce shh release in EAE. Additionally, intracerebroventricular injection of recombinant shh protein on the onset stage of EAE alleviated the progress of disease and decreased demylination, compared to the mice with normal saline treatment. Overall, HMGB1 promoted the release of shh from astrocytes through signal pathway JNK, p38 and stat3 mediated by receptor RAGE, which may provide new insights of HMGB1 function in EAE.

Expatiating the molecular approaches of HMGB1 in diabetes mellitus: Highlighting signalling pathways via RAGE and TLRs

Diabetes mellitus (DM) has become one of the major healthcare challenges worldwide in the recent times and inflammation being one of its key pathogenic process/mechanism affect several body parts including the peripheral and central nervous system. High-mobility group box 1 (HMGB1) is one of the major non-histone proteins that plays a key role in triggering the inflammatory response. Upon its release into the extracellular milieu, HMGB1 acts as an "alarmin" for the immune system to initiate tissue repair as a component of the host defense system. Furthermore, HMGB1 along with its downstream receptors like Toll-like receptors (TLRs) and receptors for advanced glycation end products (RAGE) serve as the suitable target for DM. The forthcoming research in the field of diabetes would potentially focus on the development of alternative approaches to target the centre of inflammation that is primarily mediated by HMGB1 to improve diabetic-related complications. This review covers the therapeutic actions of HMGB1 protein, which acts by activating the RAGE and TLR molecules to constitute a functional tripod system, in turn activating NF-κB pathway that contributes to the production of mediators for pro-inflammatory cytokines associated with DM. The interaction between TLR2 and TLR4 with ligands present in the host and the activation of RAGE stimulates various immune and metabolic responses that contribute to diabetes. This review emphasizes to elucidate the role of HMGB1 in the initiation and progression of DM and control over the inflammatory tripod as a promising therapeutic approach in the management of DM.

Endothelial TLR2 promotes proangiogenic immune cell recruitment and tumor angiogenesis

Toll-like receptor 2 (TLR2) is implicated in various pathologies, mainly in terms of its function within innate immune cells. However, TLR2 is also present in endothelial cells. Here, we explored the physiological and pathophysiological roles of endothelial TLR2 signaling. We found that TLR2 was highly abundant in the endothelium within various tissues using TLR2-IRES-EGFP reporter mice and was required for proinflammatory endothelial cell function. Endothelial cells lacking TLR2 exhibited reduced proinflammatory potential at the protein, cell, and tissue levels. Loss of endothelial TLR2 blunted the inflammatory response to both exogenous and endogenous danger signals in endothelial cells in culture and in vivo. Endothelial TLR2 promoted tumor growth, angiogenesis, and protumorigenic immune cell recruitment in a mouse model of prostate cancer. Furthermore, the cell surface localization of P-selectin and the subsequent production of other critical cell adhesion molecules (such as E-selectin, ICAM-1 and VCAM-1) that recruit immune cells required endothelial TLR2. Our findings demonstrate that endothelial cells actively contribute to innate immune pathways and propose that endothelial TLR2 has a pathological role in proinflammatory conditions.

Moonlighting Proteins Are Important Players in Cancer Immunology

Plasticity and adaptation to environmental stress are the main features that tumor and immune system share. Except for intrinsic and high-defined properties, cancer and immune cells need to overcome the opponent's defenses by activating more effective signaling networks, based on common elements such as transcriptional factors, protein-based complexes and receptors. Interestingly, growing evidence point to an increasing number of proteins capable of performing diverse and unpredictable functions. These multifunctional proteins are defined as moonlighting proteins. During cancer progression, several moonlighting proteins are involved in promoting an immunosuppressive microenvironment by reprogramming immune cells to support tumor growth and metastatic spread. Conversely, other moonlighting proteins support tumor antigen presentation and lymphocytes activation, leading to several anti-cancer immunological responses. In this light, moonlighting proteins could be used as promising new potential targets for improving current cancer therapies. In this review, we describe in details 12 unprecedented moonlighting proteins that during cancer progression play a decisive role in guiding cancer-associated immunomodulation by shaping innate or adaptive immune response.

Serum high-mobility group box 1 protein level correlates with the lowest SaO2 in patients with sleep apnea: a preliminary study

Introduction

Serum level of high-mobility group box 1 protein is reportedly correlated with the severity of obstructive sleep apnea.

Objective

We tried to evaluate the possibility of using the serum high-mobility group box 1 protein level as a biologic marker in obstructive sleep apnea patients.

Methods

We generated a chronic intermittent hypoxia murine model that reflected human obstructive sleep apnea. Obstructive sleep apnea patients who underwent polysomnography were prospectively enrolled. Serum samples were obtained from mice and obstructive sleep apnea patients, and the serum high-mobility group box1 protein level was measured by enzyme-linked immunosorbent assay.

Results

Serum high-mobility group box 1 protein level was 56.16 ± 30.33 ng/mL in chronic intermittent hypoxia and 18.63 ± 6.20 ng/mL in control mice (p < 0.05). The mean apnea-hypopnea index and respiratory disturbance index values of enrolled obstructive sleep apnea patients were 50.35 ± 27.96 and 51.56 ± 28.53, respectively, and the mean serum high-mobility group box 1 protein level was 30.13 ± 19.97 ng/mL. The apnea–hypopnea index and respiratory disturbance index were not significantly correlated with the serum high-mobility group box 1 protein level (p > 0.05). Instead, this protein level was significantly correlated with lowest arterial oxygen concentration (SaO₂) (p < 0.05).

Conclusion

High-mobility group box 1 protein may be involved in the pathogenesis of obstructive sleep apnea, and the possibility of this protein being a useful biologic marker in obstructive sleep apnea should be further evaluated.

High Mobility Group Box 1 in Human Cancer

High mobility group box 1 (HMGB1) is an extremely versatile protein that is located predominantly in the nucleus of quiescent eukaryotic cells, where it is critically involved in maintaining genomic structure and function. During cellular stress, however, this multifaceted, cytokine-like protein undergoes posttranslational modifications that promote its translocation to the cytosol, from where it is released extracellularly, either actively or passively, according to cell type and stressor. In the extracellular milieu, HMGB1 triggers innate inflammatory responses that may be beneficial or harmful, depending on the magnitude and duration of release of this pro-inflammatory protein at sites of tissue injury. Heightened awareness of the potentially harmful activities of HMGB1, together with a considerable body of innovative, recent research, have revealed that excessive production of HMGB1, resulting from misdirected, chronic inflammatory responses, appears to contribute to all the stages of tumorigenesis. In the setting of established cancers, the production of HMGB1 by tumor cells per se may also exacerbate inflammation-related immunosuppression. These pro-inflammatory mechanisms of HMGB1-orchestrated tumorigenesis, as well as the prognostic potential of detection of elevated expression of this protein in the tumor microenvironment, represent the major thrusts of this review.

HMGB1-Mediated Neuroinflammatory Responses in Brain Injuries: Potential Mechanisms and Therapeutic Opportunities

Brain injuries are devastating conditions, representing a global cause of mortality and morbidity, with no effective treatment to date. Increased evidence supports the role of neuroinflammation in driving several forms of brain injuries. High mobility group box 1 (HMGB1) protein is a pro-inflammatory-like cytokine with an initiator role in neuroinflammation that has been implicated in Traumatic brain injury (TBI) as well as in early brain injury (EBI) after subarachnoid hemorrhage (SAH). Herein, we discuss the implication of HMGB1-induced neuroinflammatory responses in these brain injuries, mediated through binding to the receptor for advanced glycation end products (RAGE), toll-like receptor4 (TLR4) and other inflammatory mediators. Moreover, we provide evidence on the biomarker potential of HMGB1 and the significance of its nucleocytoplasmic translocation during brain injuries along with the promising neuroprotective effects observed upon HMGB1 inhibition/neutralization in TBI and EBI induced by SAH. Overall, this review addresses the current advances on neuroinflammation driven by HMGB1 in brain injuries indicating a future treatment opportunity that may overcome current therapeutic gaps.

Interplay between RAGE and TLR4 Regulates HMGB1-Induced Inflammation by Promoting Cell Surface Expression of RAGE and TLR4

Receptor for advanced glycation end-products (RAGE) and TLR4 play an important role in the inflammatory response against High-mobility group box 1 protein (HMGB1), a late proinflammatory cytokine and a damage-associated molecular pattern. As cell surface receptors, both RAGE and TLR4 are constantly trafficking between the cytoplasm and plasma membrane. However, whether TLR4 is related to the intracellular transport of RAGE in HMGB1-induced inflammation remains unknown. In this study, we demonstrated that HMGB1 not only increased RAGE expression in both the cytoplasm and plasma membrane but also upregulated the expression of TLR4 in the plasma membrane. Knocking out of RAGE led to decreased MAPK activation, TLR4 cellular membrane expression, and corresponding inflammatory cytokine generation. Meanwhile, inhibiting MAPK activation also decreased TLR4 surface expression. These results indicated that HMGB1 may bind to cell surface RAGE receptors on the cell surface, leading to MAPK activation, thus promoting TLR4 translocation on the cell surface, but does not regulate its transcription and translation. In contrast, TLR4 can increase the transcription and translation of RAGE, which translocates to the cell surface and is able to bind to more HMGB1. The cell surface receptors TLR4 and RAGE bind to HMGB1, leading to the transcription and secretion of inflammatory cytokines. Finally, we also observed these results in the mice pseudofracture model, which is closely related to HMGB1-induced inflammatory response. All these results demonstrated that the interplay between RAGE and TLR4 are critical for HMGB1-induced inflammatory response.

Immunological Significance of HMGB1 Post-Translational Modification and Redox Biology

Most extracellular proteins are secreted via the classical endoplasmic reticulum (ER)/Golgi-dependent secretion pathway; however, some proteins, including a few danger-associated molecular patterns (DAMPs), are secreted via non-classical ER/Golgi-independent secretion pathways. The evolutionarily conserved high mobility group box1 (HMGB1) is a ubiquitous nuclear protein that can be released by almost all cell types. HMGB1 lacks signal peptide and utilizes diverse non-canonical secretion mechanisms for its extracellular export. Although the post-translational modifications of HMGB1 were demonstrated, the oxidation of HMGB1 and secretion mechanisms are not highlighted yet. We currently investigated that peroxiredoxins I and II (PrxI/II) induce the intramolecular disulfide bond formation of HMGB1 in the nucleus. Disulfide HMGB1 is preferentially transported out of the nucleus by binding to the nuclear exportin chromosome-region maintenance 1 (CRM1). We determined the kinetics of HMGB1 oxidation in bone marrow-derived macrophage as early as a few minutes after lipopolysaccharide treatment, peaking at 4 h while disulfide HMGB1 accumulation was observed within the cells, starting to secrete in the late time point. We have shown that HMGB1 oxidation status, which is known to determine the biological activity in extracellular HMGB1, is crucial for the secretion of HMGB1 from the nucleus. This review summarizes selected aspects of HMGB1 redox biology relevant to the induction and propagation of inflammatory diseases. We implicate the immunological significance and the need for novel HMGB1 inhibitors through mechanism-based studies.

High Mobility Group Box-1 and Diabetes Mellitus Complications: State of the Art and Future Perspectives

Diabetes mellitus (DM) is an endemic disease, with growing health and social costs. The complications of diabetes can affect potentially all parts of the human body, from the heart to the kidneys, peripheral and central nervous system, and the vascular bed. Although many mechanisms have been studied, not all players responsible for these complications have been defined yet. High Mobility Group Box-1 (HMGB1) is a non-histone nuclear protein that has been implicated in many pathological processes, from sepsis to ischemia. The purpose of this review is to take stock of all the most recent data available on the role of HMGB1 in the complications of DM.

Gender Difference in Damage-Mediated Signaling Contributes to Pulmonary Arterial Hypertension

Aims: Pulmonary arterial hypertension (PAH) is a progressive lethal disease with a known gender dimorphism. Female patients are more susceptible to PAH, whereas male patients have a lower survival rate. Initial pulmonary vascular damage plays an important role in PAH pathogenesis. Therefore, this study aimed at investigating the role of gender in activation of apoptosis/necrosis-mediated signaling pathways in PAH. Results: The media collected from pulmonary artery endothelial cells (PAECs) that died by necrosis or apoptosis were used to treat naive PAECs. Necrotic cell death stimulated phosphorylation of toll-like receptor 4, accumulation of interleukin 1 beta, and expression of E-selectin in a redox-dependent manner; apoptosis did not induce any of these effects. In the animal model of severe PAH, the necrotic marker, high mobility group box 1 (HMGB1), was visualized in the pulmonary vascular wall of male but not female rats. This vascular necrosis was associated with male-specific redox changes in plasma, activation of the same inflammatory signaling pathway seen in response to necrosis in vitro, and an increased endothelial-leukocyte adhesion in small pulmonary arteries. In PAH patients, gender-specific changes in redox homeostasis correlated with the prognostic marker, B-type natriuretic peptide. Males had also shown elevated circulating levels of HMGB1 and pro-inflammatory changes. Innovation: This study discovered the role of gender in the initiation of damage-associated signaling in PAH and highlights the importance of the gender-specific approach in PAH therapy. Conclusion: In PAH, the necrotic cell death is augmented in male patients compared with female patients. Factors released from necrotic cells could alter redox homeostasis and stimulate inflammatory signaling pathways.

The Dual Role of HMGB1 in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of exocrine pancreatic cancer with a 9% five-year survival rate. High mobility group box 1 (HMGB1) is a nuclear protein that can act as a DNA chaperone in the sustainment of chromosome structure and function. When released into the extracellular space, HMGB1 becomes the most well-characterized damage-associated molecular pattern (DAMP) to trigger immune responses. Recent evidence indicates that intracellular HMGB1 is a novel tumor suppressor in PDAC, which is connected to its role in the prevention of oxidative stress, genomic instability, and histone release. However, since extracellular HMGB1 is a DAMP and pro-inflammatory cytokine, cancer cells can also exploit it to survive through the receptor for advanced glycation endproducts (RAGE) in the pancreatic tumor microenvironment. Interestingly, targeting the HMGB1-RAGE pathway has become a new anticancer therapy strategy for PDAC.

Danger-Associated Molecular Patterns (DAMPs): Molecular Triggers for Sterile Inflammation in the Liver

Inflammatory liver diseases in the absence of pathogens such as intoxication by xenobiotics, cholestatic liver injury, hepatic ischemia-reperfusion injury (I/R), non-alcoholic steatohepatitis (NASH), or alcoholic liver disease (ALD) remain threatening conditions demanding specific therapeutic options. Caused by various different noxae, all these conditions have been recognized to be triggered by danger- or death-associated molecular patterns (DAMPs), discompartmentalized self-structures released by dying cells. These endogenous, ectopic molecules comprise proteins, nucleic acids, adenosine triphosphate (ATP), or mitochondrial compounds, among others. This review resumes the respective modes of their release—passively by necrotic hepatocytes or actively by viable or apoptotic parenchymal cells—and their particular roles in sterile liver pathology. It addresses their sensors and the initial inflammatory responses they provoke. It further addresses a resulting second wave of parenchymal death that might be of different mode, boosting the release of additional, second-line DAMPs. Thus, triggering a more complex and pronounced response. Initial and secondary inflammatory responses comprise the activation of Kupffer cells (KCs), the attraction and activation of monocytes and neutrophil granulocytes, and the induction of type I interferons (IFNs) and their effectors. A thorough understanding of pathophysiology is a prerequisite for identifying rational therapeutic targets.

AMPK regulates immunometabolism in sepsis

Sepsis and septic shock remain challenging for intensive care units worldwide and have limited treatment options; therefore, identification of targetable key players in systemic inflammation and multiple organ failure is urgently needed. Here, we show that AMP-activated protein kinase (AMPK) is a negative regulator of bioenergetic reprogramming in immune cells and suppresses sepsis development in vivo. Mechanistically, AMPK deficiency increases pyruvate kinase isozyme M2 (PKM2)-dependent aerobic glycolysis, which leads to the release of high mobility group box 1 (HMGB1, a late mediator of lethal systemic inflammation) in macrophages and monocytes. Consequently, activation of AMPK by A-769662 protects whereas depletion of AMPKα in myeloid cells promotes endotoxic shock and polymicrobial sepsis in mice. Additionally, administration of the PKM2 inhibitor shikonin reduces lactate production, HMGB1 release, and septic death in AMPKα-deficient mice. These findings suggest that disruption of the AMPK-dependent immunometabolism pathway may contribute to sepsis development and hence constitute a target for therapeutic intervention.

Approaches in Immunotherapy, Regenerative Medicine, and Bioengineering for Type 1 Diabetes

Recent advances on using immune and stem cells as two-pronged approaches for type 1 diabetes mellitus (T1DM) treatment show promise for advancement into clinical practice. As T1DM is thought to arise from autoimmune attack destroying pancreatic β-cells, increasing treatments that use biologics and cells to manipulate the immune system are achieving better results in pre-clinical and clinical studies. Increasingly, focus has shifted from small molecule drugs that suppress the immune system nonspecifically to more complex biologics that show enhanced efficacy due to their selectivity for specific types of immune cells. Approaches that seek to inhibit only autoreactive effector T cells or enhance the suppressive regulatory T cell subset are showing remarkable promise. These modern immune interventions are also enabling the transplantation of pancreatic islets or β-like cells derived from stem cells. While complete immune tolerance and body acceptance of grafted islets and cells is still challenging, bioengineering approaches that shield the implanted cells are also advancing. Integrating immunotherapy, stem cell-mediated β-cell or islet production and bioengineering to interface with the patient is expected to lead to a durable cure or pave the way for a clinical solution for T1DM.

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

Adiponectin suppression of late inflammatory mediator, HMGB1-induced cytokine expression in RAW264 macrophage cells

High-mobility group protein B1 (HMGB1) is a late inflammatory mediator released from inflammatory cells when stimulated, resulting in exaggerating septic symptoms. We recently demonstrated that full-length adiponectin, a potent anti-inflammatory adipokine, inhibits lipopolysaccharide-induced HMGB1 release. However, the effects of adiponectin on HMGB1-induced exaggerating signals currently remain unknown. This study aimed to investigate the effects of adiponectin on the pro-inflammatory function of HMGB1 in RAW264 macrophage cells. The treatment of RAW264 cells with HMGB1 significantly up-regulated the mRNA expression of tumour necrosis factor-α, interleukin-1β and C-X-C motif chemokine 10. HMGB1-induced cytokine expression was markedly suppressed by a toll-like receptor 4 (TLR4) antagonist and slightly suppressed by an antagonist of the receptor for advanced glycation end products. A prior treatment with full-length or globular adiponectin dose-dependently suppressed all types of HMGB1-induced cytokine expression, and this suppression was abolished by compound C, an AMPK inhibitor, but not by the haem oxygenase (HO)-1 inhibitor, zinc protoporphyrin IX. Both forms of adiponectin also reduced the mRNA expression of TLR4. These results suggest that full-length and globular adiponectin suppress HMGB1-induced cytokine expression through an AMPK-mediated HO-1-independent pathway.

High Mobility Group Box-1 (HMGb1): Current Wisdom and Advancement as a Potential Drug Target

High mobility group box-1 (HMGb1) protein, a nuclear non-histone protein that is released or secreted from the cell in response to damage or stress, is a sentinel for the immune system that plays a critical role in cell survival/death pathways. This review highlights key features of the endogenous danger-associated molecular pattern (DAMP) protein, HMGb1 in the innate inflammatory response along with various cofactors and receptors that regulate its downstream effects. The evidence demonstrating increased levels of HMGb1 in human inflammatory diseases and conditions is presented, along with a summary of current small molecule or peptide-like antagonists proven to specifically target HMGb1. Additionally, we delineate the measures needed toward validating this protein as a clinically relevant biomarker or bioindicator and as a relevant drug target.

LC3-associated phagocytosis in microbial pathogenesis

Phagocytosis is essential for uptake and elimination of pathogenic microorganisms. Autophagy is a highly conserved mechanism for incorporation of cellular constituents to replenish nutrients by degradation. Recently, parts of the autophagy machinery - above all microtubule-associated protein 1 light chain 3 (LC3) - were found to be specifically recruited to phagosomal membranes resulting in phagosome-lysosome fusion and efficient degradation of internalized cargo in a process termed LC3-associated phagocytosis (LAP). Many pathogenic bacterial, fungal and parasitic microorganisms reside within LAP-targeted single-membrane phagosomes or vacuoles after infection of host cells. In this minireview we describe the state of knowledge on the interaction of pathogens with LAP or LAP-like pathways and report on various pathogens that have evolved strategies to circumvent degradation in LAP compartments.

Association between HMGB1 and asthma: a literature review

Background

Recently, some studies demonstrated that HMGB1, as proinflammatory mediator belonging to the alarmin family, has a key role in different acute and chronic immune disorders. Asthma is a complex disease characterised by recurrent and reversible airflow obstruction associated to airway hyper-responsiveness and airway inflammation.

Objective

This literature review aims to analyse advances on HMGB1 role, employment and potential diagnostic application in asthma.

Methods

We reviewed experimental studies that investigated the pathogenetic role of HMGB in bronchial airway hyper-responsiveness, inflammation and the correlation between HMGB1 level and asthma.

Results

A total of 19 studies assessing the association between HMGB1 and asthma were identified.

Conclusions

What emerged from this literature review was the confirmation of HMGB-1 involvement in diseases characterised by chronic inflammation, especially in pulmonary pathologies. Findings reported suggest a potential role of the alarmin in being a stadiation method and a marker of therapeutic efficacy; finally, inhibiting HMGB1 in humans in order to contrast inflammation should be the aim for future further studies.

Innate Immune Regulations and Liver Ischemia-Reperfusion Injury

Liver ischemia reperfusion activates innate immune system to drive the full development of inflammatory hepatocellular injury. Damage-associated molecular patterns (DAMPs) stimulate myeloid and dendritic cells via pattern recognition receptors (PRRs) to initiate the immune response. Complex intracellular signaling network transduces inflammatory signaling to regulate both innate immune cell activation and parenchymal cell death. Recent studies have revealed that DAMPs may trigger not only proinflammatory but also immune regulatory responses by activating different PRRs or distinctive intracellular signaling pathways or in special cell populations. Additionally, tissue injury milieu activates PRR-independent receptors which also regulate inflammatory disease processes. Thus, the innate immune mechanism of liver ischemia-reperfusion injury involves diverse molecular and cellular interactions, subjected to both endogenous and exogenous regulation in different cells. A better understanding of these complicated regulatory pathways/network is imperative for us in designing safe and effective therapeutic strategy to ameliorate liver ischemia-reperfusion injury in patients.

White matter damage after traumatic brain injury: A role for damage associated molecular patterns

Traumatic brain injury (TBI) is a leading cause of mortality and long-term morbidity worldwide. Despite decades of pre-clinical investigation, therapeutic strategies focused on acute neuroprotection failed to improve TBI outcomes. This lack of translational success has necessitated a reassessment of the optimal targets for intervention, including a heightened focus on secondary injury mechanisms. Chronic immune activation correlates with progressive neurodegeneration for decades after TBI; however, significant challenges remain in functionally and mechanistically defining immune activation after TBI. In this review, we explore the burgeoning evidence implicating the acute release of damage associated molecular patterns (DAMPs), such as adenosine 5'-triphosphate (ATP), high mobility group box protein 1 (HMGB1), S100 proteins, and hyaluronic acid in the initiation of progressive neurological injury, including white matter loss after TBI. The role that pattern recognition receptors, including toll-like receptor and purinergic receptors, play in progressive neurological injury after TBI is detailed. Finally, we provide support for the notion that resident and infiltrating macrophages are critical cellular targets linking acute DAMP release with adaptive immune responses and chronic injury after TBI. The therapeutic potential of targeting DAMPs and barriers to clinical translational, in the context of TBI patient management, are discussed.

Alarmins and central nervous system inflammation in HIV-associated neurological disorders

In the era of highly active antiretroviral therapy (HAART), HIV-1-associated neurocognitive disorders (HAND) persist in infected individuals with adequate immunological and virological status. Risk factors for cognitive impairment include hepatitis C virus co-infection, host genetic factors predisposing to HAND, the early establishment of the virus in the CNS and its persistence under HAART; thus, the CNS is an important reservoir for HIV. Microglial cells are permissive to HIV-1, and NLRP3 inflammasome-associated genes were found expressed in brains of HIV-1-infected persons, contributing to brain disease. Inflammasomes can be triggered by alarmins or danger-associated molecular patterns (DAMPs), which directly stimulate the production of proinflammatory mediators by glial cells, contribute to blood-brain barrier injury through induction of release of various proteases and allow the passage of infected macrophages, and trigger IL-1β release from primed cells. Amongst alarmins involved in HIV-1-induced neuropathogenesis, IL-33 and high-mobility group box 1 (HMGB1) are of particular interest. Neurocognitive alterations were recently associated with dysregulation of the IL-33/ST2 axis in the CNS, leading to the induction of neuronal apoptosis, decrease in synaptic function and neuroinflammation. Specific biomarkers, including HMGB1 and anti-HMGB1 antibodies, have been identified in cerebrospinal fluid from patients with HAND, correlated with immune activation and identifying a very early stage of neurocognitive impairment that precedes changes in metabolites detected by magnetic resonance spectroscopy. Moreover, HMGB1 plays a crucial role in HIV-1 persistence in dendritic cells and in the constitution of viral reservoirs. In this review, the mechanisms whereby alarmins contribute to HIV-1-induced CNS inflammation and neuropathogenesis will be discussed.

The self-association of HMGB1 and its possible role in the binding to DNA and cell membrane receptors

High mobility group box 1 (HMGB1), a chromatin protein, interacts with DNA and controls gene expression. However, when HMGB1 is released from apoptotic or damaged cells, it triggers proinflammatory reactions by interacting with various receptors, mainly receptor for advanced glycation end-products (RAGE) and toll-like receptors (TLRs). The self-association of HMGB1 has been found to be crucial for its DNA-related biological functions. It is influenced by several factors, such as ionic strength, pH, specific divalent metal cations, redox environment and acetylation. This self-association may also play a role in the interaction with RAGE and TLRs and the concomitant inflammatory responses. Future studies should address the potential role of HMGB1 self-association on its interactions with DNA, RAGE and TLRs, as well as the influence of physicochemical factors in different cellular environments on these interactions.

Redox-dependent regulation of hepatocyte absent in melanoma 2 inflammasome activation in sterile liver injury in mice

Sterile liver inflammation, such as liver ischemia-reperfusion, hemorrhagic shock after trauma, and drug-induced liver injury, is initiated and regulated by endogenous mediators including DNA and reactive oxygen species. Here, we identify a mechanism for redox-mediated regulation of absent in melanoma 2 (AIM2) inflammasome activation in hepatocytes after redox stress in mice, which occurs through interaction with cytosolic high mobility group box 1 (HMGB1). We show that in liver during hemorrhagic shock in mice and in hepatocytes after hypoxia with reoxygenation, cytosolic HMGB1 associates with AIM2 and is required for activation of caspase-1 in response to cytosolic DNA. Activation of caspase-1 through AIM2 leads to subsequent hepatoprotective responses such as autophagy. HMGB1 binds to AIM2 at a non-DNA-binding site on the hematopoietic interferon-inducible nuclear antigen domain of AIM2 to facilitate inflammasome and caspase-1 activation in hepatocytes. Furthermore, binding of HMGB1 to AIM2 is stronger with fully reduced all-thiol HMGB1 than with partially oxidized disulfide-HMGB1, and binding strength corresponds to caspase-1 activation. These data suggest that HMGB1 redox status regulates AIM2 inflammasome activation.

CONCLUSION

These findings suggest a novel and important mechanism for regulation of AIM2 inflammasome activation in hepatocytes during redox stress and may suggest broader implications for how this and other inflammasomes are activated and how their activation is regulated during cell stress, as well as the mechanisms of inflammasome regulation in nonimmune cell types. (Hepatology 2017;65:253-268).

Secreted HMGB1 from Wnt activated intestinal cells is required to maintain a crypt progenitor phenotype

BACKGROUND AND AIMS

Colorectal cancer (CRC) arises via multiple genetic changes. Mutation of the tumour suppressor gene APC, a key regulator of Wnt signalling, is recognised as a frequent early driving mutation in CRC. We have previously shown that conditional loss of Apc within the murine small intestine (Apcfloxmice) results in acute Wnt signalling activation, altered crypt-villus architecture and many hallmarks of neoplasia. Our transctipomic profiling (Affymetrix Microarrays) and proteomic profiling (iTRAQ-QSTAR) of Apc-deficient intestine inferred the involvement of High Mobility Group Box 1 (Hmgb1) in CRC pathogenesis. Here we assess the contribution of HMGB1 to the crypt progenitor phenotype seen following Apc loss.

RESULTS

Elevated HMGB1 was confirmed in intestinal epithelia and serum following conditional loss of Apc. Treatment of Apcflox mice with anti-HMGB1 neutralising antibody significantly reduced many of the crypt progenitor phenotypes associated with Apc loss; proliferation and apoptosis levels were reduced, cell differentiation was restored and the expansion of stem cell marker expression was eradicated.

METHODS

Hmgb1 levels in intestinal epithelia and serum in Apcflox and ApcMin mice were assessed using qRT-PCR, Western blot and ELISA assays. The functional importance of elevated extracellular Hmgb1 was assessed using an anti-HMGB1 neutralising antibody in Apcflox mice.

CONCLUSIONS

HMGB1 is expressed and secreted from intestinal epithelial cells in response to Wnt signalling activation. This secreted HMGB1 is required to maintain nearly all aspects of the crypt progenitor phenotype observed following Apc loss and add to the body of accumulating evidence indicating that targeting HMGB1 may be a viable novel therapeutic approach.

Prognostic value of HMGB1 in early breast cancer patients under neoadjuvant chemotherapy

The response to neoadjuvant chemotherapy in breast cancer patients is usually assessed by pCR and RCB score. However, the prognostic value of these parameters is still in discussion. We showed recently that an epirubicin/docetaxel therapy is associated with an increase in the cell death marker high‐mobility group box 1 protein (HMGB1) in the circulation. Here, we investigate whether this increase correlates with the long‐term outcome. Thirty‐six early breast cancer patients under neoadjuvant epirubicin/docetaxel combination chemotherapy were included in this study. To determine the immediate effect of this treatment on HMGB1, we collected blood samples before and 24–96 h after the initial dose. This time course was then compared to the 5‐year follow‐up of the patients. HMGB1 levels varied before chemotherapy between 4.1 and 11.3 ng/mL and reacted differently in response to therapy. Some patients showed an increase while others did not show any changes. Therefore, we subdivided the patient collective into two groups: patients with an at least 1.1 ng/mL increase in HMGB1 and patients with smaller changes. The disease‐free survival was longer in the HMGB1 increase group (56.2 months vs. 46.6 months), but this difference did not reach significance. The overall survival (OS) was significantly better in patients with an increase in HMGB1 (log rank P = 0.021). These data suggest that an immediate increase in HMGB1 levels correlates with improved outcome in early breast cancer patients receiving neoadjuvant chemotherapy, and may be a valuable complementary biomarker for early estimation of prognosis.

Identification of CD163 as an antiinflammatory receptor for HMGB1-haptoglobin complexes

Secreted by activated cells or passively released by damaged cells, extracellular HMGB1 is a prototypical damage-associated molecular pattern (DAMP) inflammatory mediator. During the course of developing extracorporeal approaches to treating injury and infection, we inadvertently discovered that haptoglobin, the acute phase protein that binds extracellular hemoglobin and targets cellular uptake through CD163, also binds HMGB1. Haptoglobin-HMGB1 complexes elicit the production of antiinflammatory enzymes (heme oxygenase-1) and cytokines (e.g., IL-10) in WT but not in CD163-deficient macrophages. Genetic disruption of haptoglobin or CD163 expression significantly enhances mortality rates in standardized models of intra-abdominal sepsis in mice. Administration of haptoglobin to WT and to haptoglobin gene-deficient animals confers significant protection. These findings reveal a mechanism for haptoglobin modulation of the inflammatory action of HMGB1, with significant implications for developing experimental strategies targeting HMGB1-dependent inflammatory diseases.

Mechanisms of neuroimmune gene induction in alcoholism

RATIONALE

Alcoholism is a primary, chronic relapsing disease of brain reward, motivation, memory, and related circuitry. It is characterized by an individual's continued drinking despite negative consequences related to alcohol use, which is exemplified by alcohol use leading to clinically significant impairment or distress. Chronic alcohol consumption increases the expression of innate immune signaling molecules (ISMs) in the brain that alter cognitive processes and promote alcohol drinking.

OBJECTIVES

Unraveling the mechanisms of alcohol-induced neuroimmune gene induction is complicated by positive loops of multiple cytokines and other signaling molecules that converge on nuclear factor kappa-light-chain-enhancer of activated B cells and activator protein-1 leading to induction of additional neuroimmune signaling molecules that amplify and expand the expression of ISMs.

RESULTS

Studies from our laboratory employing reverse transcription polymerase chain reaction (RT-PCR) to assess mRNA, immunohistochemistry and Western blot analysis to assess protein expression, and others suggest that ethanol increases brain neuroimmune gene and protein expression through two distinct mechanisms involving (1) systemic induction of innate immune molecules that are transported from blood to the brain and (2) the direct release of high-mobility group box 1 (HMGB1) from neurons in the brain. Released HMGB1 signals through multiple receptors, particularly Toll-like receptor (TLR) 4, that potentiate cytokine receptor responses leading to a hyperexcitable state that disrupts neuronal networks and increases excitotoxic neuronal death. Innate immune gene activation in brain is persistent, consistent with the chronic relapsing disease that is alcoholism. Expression of HMGB1, TLRs, and other ISMs is increased several-fold in the human orbital frontal cortex, and expression of these molecules is highly correlated with each other as well as lifetime alcohol consumption and age of drinking onset.

CONCLUSIONS

The persistent and cumulative nature of alcohol on HMGB1 and TLR gene induction support their involvement in alcohol-induced long-term changes in brain function and neurodegeneration.

Redox-Dependent HMGB1 Isoforms as Pivotal Co-Ordinators of Drug-Induced Liver Injury: Mechanistic Biomarkers and Therapeutic Targets

SIGNIFICANCE

High-mobility group box 1 (HMGB1) is a critical protein in the coordination of the inflammatory response in drug-induced liver injury (DILI). HMGB1 is released from necrotic hepatocytes and activated immune cells. The extracellular function of HMGB1 is dependent upon redox modification of cysteine residues that control chemoattractant and cytokine-inducing properties. Existing biomarkers of DILI such as alanine aminotransferase (ALT) have limitations such as lack of sensitivity and tissue specificity that can adversely affect clinical intervention.

RECENT ADVANCES

HMGB1 isoforms have been shown to be more sensitive biomarkers than ALT for predicting DILI development and the requirement for liver transplant following acetaminophen (APAP) overdose. Hepatocyte-specific conditional knockout of HMGB1 has demonstrated the pivotal role of HMGB1 in DILI and liver disease. Tandem mass spectrometry (MS/MS) enables the characterization and quantification of different mechanism-dependent post-translationally modified isoforms of HMGB1.

CRITICAL ISSUES

HMGB1 shows great promise as a biomarker of DILI. However, current diagnostic assays are either too time-consuming to be clinically applicable (MS/MS) or are unable to distinguish between different redox and acetyl isoforms of HMGB1 (ELISA). Additionally, HMGB1 is not liver specific, so while it outperforms ALT (also not liver specific) as a biomarker for the prediction of DILI development, it should be used in a biomarker panel along with liver-specific markers such as miR-122.

FUTURE DIRECTIONS

A point-of-care test for HMGB1 and the development of redox and acetyl isoform-targeting antibodies will advance clinical utility. Work is ongoing to validate baseline levels of circulating HMGB1 in healthy volunteers.

High Mobility Group-Box 1 (HMGB1) levels are increased in amniotic fluid of women with intra-amniotic inflammation-determined preterm birth, and the source may be the damaged fetal membranes

BACKGROUND

High Mobility Group Box-1 (HMGB1) is considered a prototype alarmin molecule. Upon its extracellular release, HMGB1 engages pattern recognition receptors and the Receptor for Advanced Glycation End-products (RAGE) followed by an outpouring of inflammatory cytokines, including interleukin (IL)-6.

METHODS

We assayed the amniotic fluid (AF) levels of HMGB1 and IL-6 in 255 women that either had a normal pregnancy outcome or delivered preterm. Immunohistochemistry on fetal membranes was used for cellular localization and validation of immunoassay findings. HMGB1 also was analyzed in amniochorion tissue explants subjected to endotoxin.

RESULTS

AF HMGB1 levels are not gestational age regulated but are increased in women with intra-amniotic inflammation and preterm birth. The likely source is the damaged amniochorion, as demonstrated by immunohistochemistry and explant experiments.

CONCLUSIONS

Our research supports a role for HMGB1 in the inflammatory response leading to preterm birth. As a delayed phase cytokine, in utero exposure to elevated AF HMGB1 levels may have an impact on the newborn beyond the time of birth.

Association between HMGB1 and COPD: A Systematic Review

HMGB1 is an alarmin, a protein that warns and activates inflammation. Chronic obstructive pulmonary disease (COPD) is characterised by a progressive airflow obstruction and airway inflammation. Current anti-inflammatory therapies are poorly effective in maintaining lung function and symptoms of COPD. This underlines the need for finding new molecular targets involved in disease pathogenesis in order to block pathology progression. This review aims to analyse latest advances on HMGB1 role, utilisation, and potential application in COPD. To this purpose we reviewed experimental studies that investigated this alarmin as marker as well as a potential treatment in chronic obstructive pulmonary disease. This systematic review was conducted according to PRISMA guidelines. In almost all the studies, it emerged that HMGB1 levels are augmented in smokers and in patients affected by COPD. It emerged that cigarette smoking, the most well-known causative factor of COPD, induces neutrophils death and necrosis. The necrosis of neutrophil cells leads to HMGB1 release, which recruits other neutrophils in a self-maintaining process. According to the results reported in the paper both inhibiting HMGB1 and its receptor (RAGE) and blocking neutrophils necrosis (inducted by cigarette smoking) could be the aim for further studies.

The HMGB1-RAGE Inflammatory Pathway: Implications for Brain Injury-Induced Pulmonary Dysfunction

SIGNIFICANCE

Deceased patients who have suffered severe traumatic brain injury (TBI) are the largest source of organs for lung transplantation. However, due to severely compromised pulmonary lung function, only one-third of these patients are eligible organ donors, with far fewer capable of donating lungs (∼ 20%). As a result of this organ scarcity, understanding and controlling the pulmonary pathophysiology of potential donors are key to improving the health and long-term success of transplanted lungs.

RECENT ADVANCES

Although the exact mechanism by which TBI produces pulmonary pathophysiology remains unclear, it may be related to the release of damage-associated molecular patterns (DAMPs) from the injured tissue. These heterogeneous, endogenous host molecules can be rapidly released from damaged or dying cells and mediate sterile inflammation following trauma. In this review, we highlight the interaction of the DAMP, high-mobility group box protein 1 (HMGB1) with the receptor for advanced glycation end-products (RAGE), and toll-like receptor 4 (TLR4).

CRITICAL ISSUES

Recently published studies are reviewed, implicating the release of HMGB1 as producing marked changes in pulmonary inflammation and physiology following trauma, followed by an overview of the experimental evidence demonstrating the benefits of blocking the HMGB1-RAGE axis.

FUTURE DIRECTIONS

Targeting the HMGB1 signaling axis may increase the number of lungs available for transplantation and improve long-term benefits for organ recipient patient outcomes.