HMGB1 in health and disease

HMGB1 Protein: A Therapeutic Target Inside and Outside the Cell

High-mobility group box 1 protein (HMGB1) is a nonhistone chromosomal protein discovered more than 30 years ago. It is an abundant nuclear protein that has a dual function-in the nucleus, it binds DNA and participates in practically all DNA-dependent processes serving as an architectural factor. Outside the cell, HMGB1 plays a different role-it acts as an alarmine that activates a large number of HMGB1-"competent" cells and mediates a broad range of physiological and pathological responses. This universality makes it an attractive target for innovative therapeutic strategies in the treatment of various diseases. Here we present an overview of the major nuclear and extracellular properties of HMGB1 and describe its interaction with different molecular partners as specific receptors or inhibitors, which are important for its role as a target in multiple diseases. We highlight its pivotal role as a target for cancer treatment at two aspects: first in terms of its substantial impact on the repair capacity of cancer cells, thus affecting the effectiveness of chemotherapy with the antitumor drug cis-platinum and, second, the possibility to be targeted by microRNAs influencing different pathways of human diseases, thus making it a promising candidate for a new strategy for therapeutic interventions against various pathological conditions but mainly cancer.

Fecal HMGB1 Reveals Microscopic Inflammation in Adult and Pediatric Patients with Inflammatory Bowel Disease in Clinical and Endoscopic Remission

BACKGROUND

Fecal high mobility group box 1 (HMGB1) has been suggested to be a novel noninvasive biomarker of gut inflammation. We aimed to assess the reliability of fecal HMGB1, compared with fecal calprotectin (FC), in detecting intestinal inflammation in pediatric and adult patients with inflammatory bowel disease (IBD) and to evaluate the accuracy of HMGB1 in identifying patients with IBD in clinical and endoscopic remission who still have histologic features of inflammation.

METHODS

Stool samples from 85 children with IBD (49 Crohn's disease [CD] and 36 ulcerative colitis [UC] and 119 adults [57 Crohn's disease and 62 ulcerative colitis]) were analyzed for the study. Age-matched healthy subjects were used as controls. Fecal HMGB1 and fecal calprotectin were detected through western blot and ELISA, respectively.

RESULTS

Fecal HMGB1 expression was significantly increased in pediatric and adult patients with Crohn's disease and ulcerative colitis and strongly correlated with the disease severity. Fecal calprotectin and HMGB1 significantly correlated in pediatric (r: 0.60, P < 0.001) and adult (r: 0.72, P < 0.001) IBD patients. Moreover, in patients with clinical and endoscopic remission only fecal HMGB1 showed a strong match with the degree of histological scores of inflammation (CGHAS/IGHAS for Crohn's disease and Geboes Score for ulcerative colitis).

CONCLUSIONS

Fecal HMGB1 is confirmed to be a reliable biomarker of intestinal inflammation; indeed, it significantly correlates with fecal calprotectin in pediatric and adult IBD patients. Moreover, only fecal HMGB1 identifies histologic inflammation in subjects with IBD in clinical and endoscopic remission.

Data-Driven Modeling for Precision Medicine in Pediatric Acute Liver Failure

Absence of early outcome biomarkers for Pediatric Acute Liver Failure (PALF) hinders medical and liver transplant decisions. We sought to define dynamic interactions among circulating inflammatory mediators to gain insights into PALF outcome sub-groups. Serum samples from 101 participants in the PALF study, collected over the first 7 days following enrollment, were assayed for 27 inflammatory mediators. Outcomes (Spontaneous survivors [S, n=61], Non-survivors [NS, n=12], and liver transplant patients [LTx, n=28]) were assessed at 21 days post-enrollment. Dynamic interrelations among mediators were defined using data-driven algorithms. Dynamic Bayesian Network inference identified a common network motif with HMGB1 as a central node in all patient sub-groups. The networks in S and LTx were similar, and differed from NS. Dynamic Network Analysis suggested similar dynamic connectivity in S and LTx, but a more highly-interconnected network in NS that increased with time. A Dynamic Robustness Index calculated to quantify how inflammatory network connectivity changes as a function of correlation stringency differentiated all three patient sub-groups. Our results suggest that increasing inflammatory network connectivity is associated with non-survival in PALF, and may ultimately lead to better patient outcome stratification.

TLR4-HMGB1 signaling pathway affects the inflammatory reaction of autoimmune myositis by regulating MHC-I

OBJECTIVES

To analyze the effects of TLR4 on the expression of the HMGB1, MHC-I and downstream cytokines IL-6 and TNF-α, and to investigate the biological role of the TLR4-HMGB1 signaling pathway in the development of the autoimmune myositis.

METHODS

We built mice models with experimental autoimmune myositis (EAM) and used the inverted screen experiment to measure their muscle endurance; we also examined inflammatory infiltration of muscle tissues after HE staining; and we assessed the expression of MHC-I using immunohistochemistry. In addition, peripheral blood mononuclear cells (PBMC) were extracted and flow cytometry was utilized to detect the effect of IFN-γ on the expression of MHC-I. Furthermore, PBMCs were treated with IFN-γ, anti-TLR4, anti-HMGB1 and anti-MHC-I. Real-time PCR and western blotting were employed to examine the expressions of TLR4, HMGB1 and MHC-I in different groups. The ELISA method was also utilized to detect the expression of the downstream cytokines TNF-α and IL-6.

RESULTS

The expressions of TLR4, HMGB1 and MHC-I in muscle tissues from mice with EAM were significantly higher than those in the control group (all P<0.05). After IFN-γ treatment, the expressions of TLR4, HMGB1, MHC-I, TNF-α and IL-6 in PBMCs significantly increased (all P<0.05). The treatment of anti-TLR4, anti-HMGB1 and anti-MHC-I could significantly downregulate the expression of MHC-I (all P<0.05). In addition, anti-TLR4 and anti-HMGB1 significantly reduced the expression of TNF-α and IL-6 (all P<0.05).

CONCLUSIONS

The TLR4-HMGB1 signaling pathway affects the process of autoimmune myositis inflammation by regulating the expression of MHC-I and other pro-inflammatory cytokines.

A novel high mobility group box 1 neutralizing chimeric antibody attenuates drug-induced liver injury and postinjury inflammation in mice

Acetaminophen (APAP) overdoses are of major clinical concern. Growing evidence underlines a pathogenic contribution of sterile postinjury inflammation in APAP-induced acute liver injury (APAP-ALI) and justifies development of anti-inflammatory therapies with therapeutic efficacy beyond the therapeutic window of the only current treatment option, N-acetylcysteine (NAC). The inflammatory mediator, high mobility group box 1 (HMGB1), is a key regulator of a range of liver injury conditions and is elevated in clinical and preclinical APAP-ALI. The anti-HMGB1 antibody (m2G7) is therapeutically beneficial in multiple inflammatory conditions, and anti-HMGB1 polyclonal antibody treatment improves survival in a model of APAP-ALI. Herein, we developed and investigated the therapeutic efficacy of a partly humanized anti-HMGB1 monoclonal antibody (mAb; h2G7) and identified its mechanism of action in preclinical APAP-ALI. The mouse anti-HMGB1 mAb (m2G7) was partly humanized (h2G7) by merging variable domains of m2G7 with human antibody-Fc backbones. Effector function-deficient variants of h2G7 were assessed in comparison with h2G7 in vitro and in preclinical APAP-ALI. h2G7 retained identical antigen specificity and comparable affinity as m2G7. 2G7 treatments significantly attenuated APAP-induced serum elevations of alanine aminotransferase and microRNA-122 and completely abrogated markers of APAP-induced inflammation (tumor necrosis factor, monocyte chemoattractant protein 1, and chemokine [C-X-C motif] ligand 1) with prolonged therapeutic efficacy as compared to NAC. Removal of complement and/or Fc receptor binding did not affect h2G7 efficacy.

CONCLUSION

This is the first report describing the generation of a partly humanized HMGB1-neutralizing antibody with validated therapeutic efficacy and with a prolonged therapeutic window, as compared to NAC, in APAP-ALI. The therapeutic effect was mediated by HMGB1 neutralization and attenuation of postinjury inflammation. These results represent important progress toward clinical implementation of HMGB1-specific therapy as a means to treat APAP-ALI and other inflammatory conditions. (Hepatology 2016;64:1699-1710).

HMGB1 exacerbates experimental mouse colitis by enhancing innate lymphoid cells 3 inflammatory responses via promoted IL-23 production

In inflammatory bowel diseases (IBD), high mobility group box 1 (HMGB1), as an endogenous inflammatory molecule, can promote inflammatory cytokines secretion by acting on TLR2/4 resulting in tissue damage. The underlying mechanisms remain unclear. Here we report a novel role of HMGB1 in controlling the maintenance and function of intestine-resident group-3 innate lymphoid cells (ILC3s) that are important innate effector cells implicated in mucosal homeostasis and IBD pathogenesis. We showed that mice treated with anti-HMGB1 Ab, or genetically deficient for TLR2-/- or TLR4-/- mice, displayed reduced intestinal inflammation. In these mice, the numbers of colonic ILC3s were significantly reduced, and the levels of IL-17 and IL-22 that can be secreted by ILC3s were also decreased in the colon tissues. Furthermore, HMGB1 promoted DCs via TLR2/4 signaling to produce IL-23, activating ILC3s to produce IL-17 and IL-22. Our data thus indicated that the HMGB1-TLR2/4-DCs-IL-23 cascade pathway enhances the functions of ILC3s to produce IL-17 and IL-22, and this signal way might play a vital role in the development of IBD.

High Mobility Group Box-1: A Missing Link between Diabetes and Its Complications

High mobility group box-1 (HMGB-1), a damage-associated molecular pattern, can be actively or passively released from various cells under different conditions and plays a pivotal role in the pathogenesis of inflammation and angiogenesis-dependent diseases. More and more evidence suggests that inflammation, in addition to its role in progression of diabetes, also promotes initiation and development of diabetic complications. In this review, we focus on the role of HMGB-1 in diabetes-related complications and the therapeutic strategies targeting HMGB-1 in diabetic complications.

PKM2-dependent glycolysis promotes NLRP3 and AIM2 inflammasome activation

Sepsis, severe sepsis and septic shock are the main cause of mortality in non-cardiac intensive care units. Immunometabolism has been linked to sepsis; however, the precise mechanism by which metabolic reprogramming regulates the inflammatory response is unclear. Here we show that aerobic glycolysis contributes to sepsis by modulating inflammasome activation in macrophages. PKM2-mediated glycolysis promotes inflammasome activation by modulating EIF2AK2 phosphorylation in macrophages. Pharmacological and genetic inhibition of PKM2 or EIF2AK2 attenuates NLRP3 and AIM2 inflammasomes activation, and consequently suppresses the release of IL-1β, IL-18 and HMGB1 by macrophages. Pharmacological inhibition of the PKM2-EIF2AK2 pathway protects mice from lethal endotoxemia and polymicrobial sepsis. Moreover, conditional knockout of PKM2 in myeloid cells protects mice from septic death induced by NLRP3 and AIM2 inflammasome activation. These findings define an important role of PKM2 in immunometabolism and guide future development of therapeutic strategies to treat sepsis.

Lipopolysaccharide Attenuates Induction of Proallergic Cytokines, Thymic Stromal Lymphopoietin, and Interleukin 33 in Respiratory Epithelial Cells Stimulated with PolyI:C and Human Parechovirus

Epidemiological studies based on the "hygiene hypothesis" declare that the level of childhood exposure to environmental microbial products is inversely related to the incidence of allergic diseases in later life. Multiple types of immune cell-mediated immune regulation networks support the hygiene hypothesis. Epithelial cells are the first line of response to microbial products in the environment and bridge the innate and adaptive immune systems; however, their role in the hygiene hypothesis is unknown. To demonstrate the hygiene hypothesis in airway epithelial cells, we examined the effect of lipopolysaccharide (LPS; toll-like receptor 4 ligand) on the expression of the proallergic cytokines thymic stromal lymphopoietin (TSLP) and interleukin 33 (IL33) in H292 cells (pulmonary mucoepidermoid carcinoma cells). Stimulation with the TLR ligand polyI:C and human parechovirus type 1 (HPeV1) but not LPS-induced TSLP and IL33 through interferon regulatory factor 3 (IRF3) and NF-κB activity, which was further validated by using inhibitors (dexamethasone and Bay 11-7082) and short hairpin RNA-mediated gene knockdown. Importantly, polyI:C and HPeV1-stimulated TSLP and IL33 induction was reduced by LPS treatment by attenuating TANK-binding kinase 1, IRF3, and NF-κB activation. Interestingly, the basal mRNA levels of TLR signaling proteins were downregulated with long-term LPS treatment of H292 cells, which suggests that such long-term exposure modulates the expression of innate immunity signaling molecules in airway epithelial cells to mitigate the allergic response. In contrast to the effects of LPS treatment, the alarmin high-mobility group protein B1 acts in synergy with polyI:C to promote TSLP and IL33 expression. Our data support part of the hygiene hypothesis in airway epithelia cells in vitro. In addition to therapeutic targeting of TSLP and IL33, local application of non-pathogenic LPS may be a rational strategy to prevent allergies.

Regulation of Autophagy-Related Protein and Cell Differentiation by High Mobility Group Box 1 Protein in Adipocytes

High mobility group box 1 protein (HMGB1) is a molecule related to the development of inflammation. Autophagy is vital to maintain cellular homeostasis and protect against inflammation of adipocyte injury. Our recent work focused on the relationship of HMGB1 and autophagy in 3T3-L1 cells. In vivo experimental results showed that, compared with the normal-diet group, the high-fat diet mice displayed an increase in adipocyte size in the epididymal adipose tissues. The expression levels of HMGB1 and LC3II also increased in epididymal adipose tissues in high-fat diet group compared to the normal-diet mice. The in vitro results indicated that HMGB1 protein treatment increased LC3II formation in 3T3-L1 preadipocytes in contrast to that in the control group. Furthermore, LC3II formation was inhibited through HMGB1 knockdown by siRNA. Treatment with the HMGB1 protein enhanced LC3II expression after 2 and 4 days but decreased the expression after 8 and 10 days among various differentiation stages of adipocytes. By contrast, FABP4 expression decreased on the fourth day and increased on the eighth day. Hence, the HMGB1 protein modulated autophagy-related proteins and lipid-metabolism-related genes in adipocytes and could be a new target for treatment of obesity and related metabolic diseases.

Reduced HMGB 1-Mediated Pathway and Oxidative Stress in Resveratrol-Treated Diabetic Mice: A Possible Mechanism of Cardioprotection of Resveratrol in Diabetes Mellitus

Myocardial fibrosis and inflammation are intricately linked in diabetic cardiomyopathy (DCM), and resveratrol has been shown to attenuate oxidative stress, inflammation, and fibrosis in several cell types or animal models. High mobility group box 1 (HMGB 1), a proinflammatory cytokine, has been reported to regulate fibrosis and inflammation in various organs. Then the present study aimed to reveal the expression of HMGB 1-mediated signaling pathway and oxidative stress in resveratrol-treated diabetic mice. The significant increase in serum HMGB 1 concentration in diabetic mice was attenuated by treatment with resveratrol. Similarly, western blot analysis revealed a significant increase of HMGB 1 protein in monocytes and heart tissues of diabetic mice, and resveratrol partly normalized the changes. In addition, resveratrol abrogated the increased expression of HMGB 1-mediated signaling pathway, oxidative stress, fibrosis, and inflammation in diabetic hearts. In conclusion, inhibition of HMGB 1-mediated signaling pathway and oxidative stress may contribute to resveratrol-induced anti-inflammatory and antifibrotic effects in DCM.

A novel PINK1- and PARK2-dependent protective neuroimmune pathway in lethal sepsis

Although the PINK1-PARK2 pathway contributes to the pathogenesis of Parkinson disease, its roles in sepsis (a major challenge for critical care) were previously unknown. Here, we show that pink1^-/- and park2^-/- mice are more sensitive to polymicrobial sepsis-induced multiple organ failure and death. The decrease in the circulating level of the neurotransmitter dopamine in pink1^-/- and park2^-/- mice accelerates the release of a late sepsis mediator, HMGB1, via HIF1A-dependent anaerobic glycolysis and subsequent NLRP3-dependent inflammasome activation. Genetic depletion of Nlrp3 or Hif1a in pink1^-/- and park2^-/- mice confers protection against lethal polymicrobial sepsis. Moreover, pharmacological administration of dopamine agonist (e.g., pramipexole), HMGB1-inhibitor (e.g., neutralizing antibody or glycyrrhizin), or NLRP3-inhibitor (e.g., MCC950) reduces septic death in pink1^-/- and park2^-/- mice. The mRNA expression of HIF1A and NLRP3 is upregulated, whereas the mRNA expression of PINK1 and PARK2 is downregulated in peripheral blood mononuclear cells of patients with sepsis. Thus, an impaired PINK1-PARK2-mediated neuroimmunology pathway contributes to septic death and may represent a novel therapeutic target in critical care medicine.

HMGB1 overexpression as a prognostic factor for survival in cancer: a meta-analysis and systematic review

As there are millions of cancer deaths every year, it is of great value to identify applicable prognostic biomarkers. As an important alarm, the prognostic role of high mobility group box 1 (HMGB1) in cancer remains controversial. We aim to assess the association of HMGB1 expression with prognosis in cancer patients. Systematic literature searches of PubMed, Embase and Web of Science databases were performed for eligible studies of HMGB1 as prognostic factor in cancer. Pooled hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated to evaluate the influence of HMGB1 expression on overall survival (OS) and progression-free survival (PFS) in cancer patients. 18 studies involving 11 different tumor types were included in meta-analysis. HMGB1 overexpression was significantly associated with poorer OS (HR: 1.99; 95% CI, 1.71-2.31) and PFS (HR: 2.26; 95% CI, 1.65-3.10) irrespective of cancer types including gastric cancer, colorectal cancer, hepatocellular carcinoma, pancreatic cancer, nasopharyngeal carcinoma, head and neck squamous-cell carcinoma, esophageal cancer, malignant pleural mesothelioma, bladder cancer, prostate cancer, and cervical carcinoma. Subgroup analyses indicated geographical area and size of studies did not affect the prognostic effects of HMGB1 for OS. Morever, HMGB1 overexpression had a consistent correlation with poorer OS when detected by immunohistochemistry in tissues and enzyme-linked immunosorbent assay in serum, whereas the correlation did not exist by quantitative real-time reverse-transcription polymerase chain reaction in tissues. HMGB1 overexpression is associated with poorer prognosis in patients with various types of cancer, suggesting that it is a prognostic factor and potential biomarker for survival in cancer.

A core viral protein binds host nucleosomes to sequester immune danger signals

Viral proteins mimic host protein structure and function to redirect cellular processes and subvert innate defenses. Small basic proteins compact and regulate both viral and cellular DNA genomes. Nucleosomes are the repeating units of cellular chromatin and play an important part in innate immune responses. Viral-encoded core basic proteins compact viral genomes, but their impact on host chromatin structure and function remains unexplored. Adenoviruses encode a highly basic protein called protein VII that resembles cellular histones. Although protein VII binds viral DNA and is incorporated with viral genomes into virus particles, it is unknown whether protein VII affects cellular chromatin. Here we show that protein VII alters cellular chromatin, leading us to hypothesize that this has an impact on antiviral responses during adenovirus infection in human cells. We find that protein VII forms complexes with nucleosomes and limits DNA accessibility. We identified post-translational modifications on protein VII that are responsible for chromatin localization. Furthermore, proteomic analysis demonstrated that protein VII is sufficient to alter the protein composition of host chromatin. We found that protein VII is necessary and sufficient for retention in the chromatin of members of the high-mobility-group protein B family (HMGB1, HMGB2 and HMGB3). HMGB1 is actively released in response to inflammatory stimuli and functions as a danger signal to activate immune responses. We showed that protein VII can directly bind HMGB1 in vitro and further demonstrated that protein VII expression in mouse lungs is sufficient to decrease inflammation-induced HMGB1 content and neutrophil recruitment in the bronchoalveolar lavage fluid. Together, our in vitro and in vivo results show that protein VII sequesters HMGB1 and can prevent its release. This study uncovers a viral strategy in which nucleosome binding is exploited to control extracellular immune signaling.

Tumor-derived factors modulating dendritic cell function

Dendritic cells (DC) play unique and diverse roles in the tumor occurrence, development, progression and response to therapy. First of all, DC can actively uptake tumor-associated antigens, process them and present antigenic peptides to T cells inducing and maintaining tumor-specific T cell responses. DC interaction with different immune effector cells may also support innate antitumor immunity, as well as humoral responses also known to inhibit tumor development in certain cases. On the other hand, DC are recruited to the tumor site by specific tumor-derived and stroma-derived factors, which may also impair DC maturation, differentiation and function, thus resulting in the deficient formation of antitumor immune response or development of DC-mediated tolerance and immune suppression. Identification of DC-stimulating and DC-suppressing/polarizing factors in the tumor environment and the mechanism of DC modulation are important for designing effective DC-based vaccines and for recovery of immunodeficient resident DC responsible for maintenance of clinically relevant antitumor immunity in patients with cancer. DC-targeting tumor-derived factors and their effects on resident and administered DC in the tumor milieu are described and discussed in this review.

HMGB1 as biomarker and drug target

High Mobility Group Box 1 protein was discovered as a nuclear protein, but it has a "second life" outside the cell where it acts as a damage-associated molecular pattern. HMGB1 is passively released or actively secreted in a number of diseases, including trauma, chronic inflammatory disorders, autoimmune diseases and cancer. Extracellular HMGB1 triggers and sustains the inflammatory response by inducing cytokine release and by recruiting leucocytes. These characteristics make extracellular HMGB1 a key molecular target in multiple diseases. A number of strategies have been used to prevent HMGB1 release or to inhibit its activities. Current pharmacological strategies include antibodies, peptides, decoy receptors and small molecules. Noteworthy, salicylic acid, a metabolite of aspirin, has been recently found to inhibit HMGB1. HMGB1 undergoes extensive post-translational modifications, in particular acetylation and oxidation, which modulate its functions. Notably, high levels of serum HMGB1, in particular of the hyper-acetylated and disulfide isoforms, are sensitive disease biomarkers and are associated with different disease stages. In the future, the development of isoform-specific HMGB1 inhibitors may potentiate and fine-tune the pharmacological control of inflammation. We review here the current therapeutic strategies targeting HMGB1, in particular the emerging and relatively unexplored small molecules-based approach.

HMGB1-RAGE Axis Makes No Contribution to Cardiac Remodeling Induced by Pressure-Overload

High-mobility group box1 (HMGB1) exerts effects on inflammation by binding to receptor for advanced glycation end products (RAGE) or Toll-like receptor 4. Considering that inflammation is involved in pressure overload-induced cardiac hypertrophy, we herein attempted to investigate whether HMGB1 plays a role in myocardial hypertrophy in RAGE knockout mice as well as in the growth and apoptosis of cardiomyocytes. The myocardial expression of RAGE was not significantly changed while TLR4 mRNA was upregulated in response to transverse aortic constriction (TAC) for 1 week. The myocardial expression of HMGB1 protein was markedly increased in TAC group when compared to the sham group. Heart weight to body weight ratio (HW/BW) and lung weight to body weight ratio (LW/BW) were evaluated in RAGE knockout (KO) and wild-type (WT) mice 1 week after TAC. Significant larger HW/BW and LW/BW ratios were found in TAC groups than the corresponding sham groups, but no significant difference was found between KO and WT TAC mice. Similar results were also found when TAC duration was extended to 4 weeks. Cultured neonatal rat cardiomyocytes were treated with different concentrations of recombinant HMGB1, then cell viability was determined using MTT and CCK8 assays and cell apoptosis was determined by Hoechst staining and TUNEL assay. The results came out that HMGB1 exerted no influence on viability or apoptosis of cardiomyocytes. Besides, the protein expression levels of Bax and Bcl2 in response to different concentrations of HMGB1 were similar. These findings indicate that HMGB1 neither exerts influence on cardiac remodeling by binding to RAGE nor induces apoptosis of cardiomyocytes under physiological condition.

HMGB1Modulates the Treg/Th17 Ratio in Atherosclerotic Patients

AIM

Atherosclerosis (AS) characterized as a chronic inflammatory disease. Multiple immune cells and inflammatory cytokines, such as high mobility group protein (HMGB1), regulatory T (Treg) cells, T helper (Th17) cells, and inflammation-related cytokines, play a key role in its pathophysiology. A large number of studies report that HMGB1 and Th17 cells may promote atherosclerosis progression, whereas Treg cells may play a protective role in atherosclerosis; thus, alterations in the Treg/Th17 ratio may exist in atherosclerosis diseases. Up till now, the relationships between HMGB1 levels and the Treg/Th17 ratio remain incompletely understood. The major purpose of this study was to investigate the relationship between HMGB1 levels and the Treg/Th17 ratio in patients with coronary artery atherosclerotic plaques.

METHODS

We enrolled patients with coronary atherosclerosis and normal coronary artery as the research subjects. Flow cytometry was used to analyze the Treg cells, the Th17 cells frequency, and the Treg/Th17 ratio. Otherwise, real-time polymerase chain reaction was used for assays the mRNA expressions of HMGB1, retinoic acid-related orphan nuclear receptor C (RORC), and forkhead-winged helix transcription factor (Foxp3). Moreover, enzyme-linked immunosorbent assays were used to detect the level of protein and cytokines, such as HMGB1, IL-10, TGF-β1, IL-17A, and IL-23.

RESULTS

Using flow cytometry, we observed a significantly increased of Th17 cell frequency, whereas Treg cell frequency significantly decreased in atherosclerotic patients. Consistently, the levels of RORC mRNA were significantly increased in coronary atherosclerosis (AS) group compared to normal coronary artery (NCA) group (P＜0.01). In contrast, the expression of Foxp3 mRNA was markedly lower in the AS group than in the NCA group (P＜0.01). Furthermore, we observed the serum concentrations of HMGB1, IL-17A, and IL-23 were significantly higher in the AS group than in the NCA group (P＜0.01, respectively), whereas the concentrations of serum IL-10 and TGF-β1 were significantly lower in the AS group than in the NCA group (P＜0.01, respectively). In addition, we also found that HMGB1 levels showed negative correlation with the Treg/Th17 ratio in the two groups (r=－0.6984, P＜0.01).

CONCLUSIONS

The data in our study indicated that HMGB1 may promote atherosclerosis progression via modulating the imbalance in the Treg/Th17 ratio.

MicroRNA-205‑5b inhibits HMGB1 expression in LPS-induced sepsis

Inflammatory cytokines belonging to high mobility group box (HMGB)1 play a key role in sepsis through yet unknown mechanisms. The inflammatory response is modulated by microRNAs (miRNAs or miRs) at multiple levels and is poorly understood. In this study, the regulation of HMGB1 by miRNAs was evaluated using 3-(2,4-dimethoxybenzylidene)anabaseine (GTS-21) to activate the cholinergic anti-inflammatory pathway (CAP) and decrease HMGB1 expression in RAW264.7 cells. Microarray-based miRNA expression profiling of RAW264.7 cells was used to screen target miRNAs through genetic screening, GO analysis and hierarchical clustering. The expression of miRNA targets in the serum, colon, spleen, livers and lungs of BALB/c mice was quantified by RT-qPCR. Serum protein levels were quantified by ELISA. Western blot analysis and RT-qPCR were used for verification in vitro. Using miRNA array analysis, we screened 3 miRNAs (miR‑205‑5b, miR‑196a and miR‑193b). Animal experiments with miR‑205‑5b indicated its high degree of expression in the serum, colon, spleen, liver and lungs following the downregulation of HMGB1 in the tissues. RAW264.7 cells transfected with miR‑205‑5b mimics downregulated HMGB1 protein expression, suggesting translational regulation. HMGB1 expression negatively correlated with miR‑205‑5b expression in LPS-induced sepsis. By contrast, HMGB1 expression in LPS-stimulated RAW264.7 cells was increased following transfection with miR‑205‑5b inhibitor. miR‑205‑5b is a critical mediator of cholinergic anti-inflammatory activity in late sepsis. The upregulation of miR‑205‑5b as a potential therapeutic target for the treatment of inflammatory diseases is a possible novel therapeutic strategy against late sepsis. The mechanisms involved include the by post-transcriptional suppression of HMGB1 in cells and tissues.

The Emerging Role of HMGB1 in Neuropathic Pain: A Potential Therapeutic Target for Neuroinflammation

Neuropathic pain (NPP) is intolerable, persistent, and specific type of long-term pain. It is considered to be a direct consequence of pathological changes affecting the somatosensory system and can be debilitating for affected patients. Despite recent progress and growing interest in understanding the pathogenesis of the disease, NPP still presents a major diagnostic and therapeutic challenge. High mobility group box 1 (HMGB1) mediates inflammatory and immune reactions in nervous system and emerging evidence reveals that HMGB1 plays an essential role in neuroinflammation through receptors such as Toll-like receptors (TLR), receptor for advanced glycation end products (RAGE), C-X-X motif chemokines receptor 4 (CXCR4), and N-methyl-D-aspartate (NMDA) receptor. In this review, we present evidence from studies that address the role of HMGB1 in NPP. First, we review studies aimed at determining the role of HMGB1 in NPP and discuss the possible mechanisms underlying HMGB1-mediated NPP progression where receptors for HMGB1 are involved. Then we review studies that address HMGB1 as a potential therapeutic target for NPP.

Inhibition of the translocation and extracellular release of high-mobility group box 1 alleviates liver damage in fibrotic mice in response to D-galactosamine/lipopolysaccharide challenge

Acute liver injury in the setting of fibrosis is an area of interest in investigations, and remains to be fully elucidated. Previous studies have suggested the beneficial effects of liver fibrosis induced by thioacetamide and partial bile duct ligation against Fas‑mediated acute liver injury. The activation of AKT and extracellular signal-regulated kinase signaling is considered to be crucial in this hepatoprotection. To demonstrate the protection of CCl4‑induced liver fibrosis against lethal challenge, the present study compared the reactivity to lethal doses of D‑galactosamine (D-GalN)/lipopolysaccharide (LPS) between fibrotic mice and control mice groups. The extent of hepatic damage was assessed by survival rate and histopathological analysis. The molecular basis of the fibrosis‑based hepatoprotection was examined, with a particular focus on the translocation and release of high‑mobility group box (HMGB)1 and the inflammatory response triggered by HMGB1. Hepatoprotection induced by fibrosis was demonstrated by improved survival rates (100%, vs. 20%) and improved preservation of liver architecture in fibrotic mice subjected to D‑GalN/LPS, compared with control mice treated in the same way. D‑GalN/LPS evoked the translocation and release of HMGB1, detected by immunohistochemistry, in the control mice, which was significantly inhibited in the fibrotic mice. The gene expression levels of HMGB1‑associated proinflammatory cytokines, including interleukin (IL)‑1β, IL‑6, tumor necrosis factor‑α and IL‑12p40, were markedly inhibited in the fibrotic mice when exposed to D‑GalN/LPS. These findings confirmed that CCl4‑based fibrosis induced hepatoprotection, and provided evidence that fibrosis inhibited the translocation and release of HMGB1, and the proinflammatory response triggered by HMGB1. This alleviated liver damage following exposure to D‑GalN/LPS challenge.

Regnase-1 in microglia negatively regulates high mobility group box 1-mediated inflammation and neuronal injury

Extracellular high mobility group box 1 (HMGB1) has been demonstrated to function as a proinflammatory cytokine and induces neuronal injury in response to various pathological stimuli in central nervous system (CNS). However, the regulatory factor involved in HMGB1-mediated inflammatory signaling is largely unclear. Regulatory RNase 1 (Regnase-1) is a potent anti-inflammation enzyme that can degrade a set of mRNAs encoding proinflammatory cytokines. The present study aims to determine the role of Regnase-1 in the regulation of HMGB1-mediated inflammatory injury in CNS. Cultured microglia and rat brain were treated with recombinant HMGB1 to examine the induction of Regnase-1 expression. Moreover, the role of Regnase-1 in modulating the expression of inflammatory cytokines and neuronal injury was then investigated in microglia by specific siRNA knockdown upon HMGB1 treatment. Results showed that HMGB1 could significantly induce the de novo synthesis of Regnase-1 in cultured microglia. Consistently, Regnase-1 was elevated and found to be co-localized with microglia marker in the brain of rat treated with HMGB1. Silencing Regnase-1 in microglia enhanced HMGB1-induced expression of proinflammatory cytokines and exacerbated neuronal toxicity. Collectively, these results suggest that Regnase-1 can be induced by HMGB1 in microglia and negatively regulates HMGB1-mediated neuroinflammation and neuronal toxicity.

Plumbagin Protects Mice from Lethal Sepsis by Modulating Immunometabolism Upstream of PKM2

Sepsis is characterized by dysregulated systemic inflammation with release of early (for example, interleukin (IL)-1β) and late (for example, HMGB1) proinflammatory mediators from macrophages. Plumbagin, a medicinal plant-derived naphthoquinone, has been reported to exhibit antiinflammatory activity, but the underling mechanisms remain unclear. Here, we have demonstrated that plumbagin inhibits the inflammatory response through interfering with the immunometabolism pathway in activated macrophages. Remarkably, plumbagin inhibited lipopolysaccharide (LPS)-induced aerobic glycolysis by downregulating the expression of pyruvate kinase M2 (PKM2), a protein kinase responsible for the final and rate-limiting reaction step of the glycolytic pathway. Moreover, the NADPH oxidase 4 (NOX4)-mediated oxidative stress was required for LPS-induced PKM2 expression, because pharmacologic or genetic inhibition of NOX4 by plumbagin or RNA interference limited LPS-induced PKM2 expression, lactate production and subsequent proinflammatory cytokine (IL-1β and HMGB1) release in macrophages. Finally, plumbagin protected mice from lethal endotoxemia and polymicrobial sepsis induced by cecal ligation and puncture. These findings identify a new approach for inhibiting the NOX4/PKM2-dependent immunometabolism pathway in the treatment of sepsis and inflammatory diseases.

Until Death Do Us Part: Necrosis and Oxidation Promote the Tumor Microenvironment

Tumor proliferation is concomitant with autophagy, limited apoptosis, and resultant necrosis. Necrosis is associated with the release of damage-associated molecular pattern molecules (DAMPs), which act as 'danger signals', recruiting inflammatory cells, inducing immune responses, and promoting wound healing. Most of the current treatment strategies for cancer (chemotherapy, radiation therapy, hormonal therapy) promote DAMP release following therapy-induced tumor death by necroptosis and necrosis. Myeloid cells (monocytes, dendritic cells (DCs), and granulocytes), as well as mesenchymal stromal cells (MSCs) belong to the early immigrants in response to unscheduled cell death, initiating and modulating the subsequent inflammatory response. Responding to DAMPs, MSCs, and DCs promote an immunosuppressive milieu, while eosinophils induce oxidative conditions limiting the biologic activity of DAMPs over time and distance. Regulatory T cells are strongly affected by pattern recognition receptor signaling in the tumor microenvironment and limit immune reactivity coordinately with myeloid-derived suppressor cells. Means to 'aerobically' oxidize DAMPs provide a novel strategy for limiting tumor progression. The present article summarizes our current understanding of the impact of necrosis on the tumor microenvironment and the influence of oxidative conditions found within this setting.

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.

CCL2-CCR2 signaling promotes hepatic ischemia/reperfusion injury

BACKGROUND

Liver ischemia/reperfusion (I/R) injury is a type of uncontrolled inflammatory cascade in which neutrophils, an early infiltrating immune cell population, elicit significant tissue damage. However, the precise mechanism for neutrophil recruitment and infiltration remains to be fully characterized.

METHODS

A hepatic partial I/R model was reproduced in wild-type, CCL2(-/-) and CCR2(-/-) mice. Tissue damage was evaluated by serum enzyme analysis, hematoxylin-eosin staining, and cytokine production measurement. Mobilization of neutrophils from the bone marrow and subsequent infiltration into the liver were measured by flow cytometry. C-C motif chemokine receptor 2 (CCR2) expression on neutrophils and C-C motif chemokine ligand 2 (CCL2) chemotaxis were measured using flow cytometry. The cellular source of CCL2 in the liver was determined by deleting specific cell groups and performing intracellular staining.

RESULTS

Liver damage was ameliorated, and neutrophil recruitment and accumulation were decreased in both CCL2(-/-) and CCR2(-/-) mice compared with wild-type mice. Neutrophils displayed upregulated expression of CCR2 during I/R, and these cells were required for CCL2-induced chemotaxis. Depletion of Kupffer cells protected the liver from I/R injury. Furthermore, genetic ablation of CCL2 reduced liver injury, as demonstrated by decreases in the levels of alanine aminotransferase and aspartate aminotransferase and subsequent reductions in neutrophil recruitment and accumulation.

CONCLUSIONS

Kupffer cells secrete CCL2 to promote CCR2-expressing neutrophil recruitment from the bone marrow and subsequent infiltration into the liver during I/R. These findings reveal a novel pro-inflammatory role of cell-mediated CCL2-CCR2 interactions during this sterile insult.

Ionizing Radiation Induces HMGB1 Cytoplasmic Translocation and Extracellular Release

OBJECTIVE

A nucleosomal protein, HMGB1, can be secreted by activated immune cells or passively released by dying cells, thereby amplifying rigorous inflammatory responses. In this study we aimed to test the possibility that ionizing radiation similarly induces cytoplasmic HMGB1 translocation and extracellular release.

METHOD

Human skin fibroblast (GM0639) and bronchial epithelial (16HBE) cells and animals (rats) were exposed to X-ray radiation, and HMGB1 translocation and release were assessed by immunocytochemistry and immunoassay, respectively.

RESULTS

At a wide dose range (4.0 - 12.0 Gy), X-ray radiation induced a dramatic cytoplasmic HMGB1 translocation, and triggered a time- and dose-dependent HMGB1 release both in vitro and in vivo. The radiation-mediated HMGB1 release was associated with noticeable chromosomal DNA damage and loss of cell viability.

CONCLUSION

radiation induces HMGB1 cytoplasmic translocation and extracellular release through active secretion and passive leakage processes.

Ethyl pyruvate attenuated coxsackievirus B3-induced acute viral myocarditis by suppression of HMGB1/RAGE/NF-ΚB pathway

Inflammation plays important roles in the pathogenesis of coxsackievirus B3 (CVB3)-induced acute viral myocarditis (AVMC). Ethyl pyruvate (EP) has been shown to be an anti-inflammatory agent. High mobility group box 1 (HMGB1)/receptor for advanced glycation end product (RAGE)/nuclear factor (NF)-ΚB pathway has close relation with inflammatory responses. Here, we investigated the effects of EP on CVB3-induced AVMC and potential mechanisms. The mice with AVMC were treated with EP (40 or 80 mg/kg/day) from day 5 to day 7 post-infection. EP significantly decreased the mortality of mice with AVMC. H&E staining and immunohistochemistry for HMGB1 demonstrated less inflammatory lesions and fewer abnormal location of HMGB1 in the hearts of AVMC mice receiving EP. Immuoblot showed that EP significantly inhibited the levels of HMGB1, RAGE, phospho(p)-NF-ΚB and p-I-ΚBα, and raised I-ΚBα expression in the hearts of AVMC mice. Furthermore, real-time PCR and Elisa displayed decreased levels of HMGB1, TNF-α, IL-1β, IL-17 and increased levels of IL-10 in the hearts and serum of AVMC mice treated with EP. Our findings suggest that EP protects against CVB3-induced AVMC that is associated with inhibition of HMGB1/RAGE/NF-ΚB pathway.

The repair capacity of lung cancer cell lines A549 and H1299 depends on HMGB1 expression level and the p53 status

Elucidation of the cellular components responsive to chemotherapeutic agents as cisplatin rationalizes the strategy for anticancer chemotherapy. The removal of the cisplatin/DNA lesions gives the chance to the cancer cells to survive and compromises the chemotherapeutical treatment. Therefore, the cell repair efficiency is substantial for the clinical outcome. High mobility group box 1 (HMGB1) protein is considered to be involved in the removal of the lesions as it binds with high affinity to cisplatin/DNA adducts. We demonstrated that overexpression of HMGB1 protein inhibited cis-platinated DNA repair in vivo and the effect strongly depended on its C-terminus. We registered increased levels of DNA repair after HMGB1 silencing only in p53 defective H1299 lung cancer cells. Next, introduction of functional p53 resulted in DNA repair inhibition. H1299 cells overexpressing HMGB1 were significantly sensitized to treatment with cisplatin demonstrating the close relation between the role of HMGB1 in repair of cis-platinated DNA and the efficiency of the anticancer drug, the process being modulated by the C-terminus. In A549 cells with functional p53, the repair of cisplatin/DNA adducts is determined by а complex action of HMGB1 and p53 as an increase of DNA repair capacity was registered only after silencing of both proteins.

MiR-193b promotes autophagy and non-apoptotic cell death in oesophageal cancer cells

BACKGROUND

Successful treatment of oesophageal cancer is hampered by recurrent drug resistant disease. We have previously demonstrated the importance of apoptosis and autophagy for the recovery of oesophageal cancer cells following drug treatment. When apoptosis (with autophagy) is induced, these cells are chemosensitive and will not recover following chemotherapy treatment. In contrast, when cancer cells exhibit only autophagy and limited Type II cell death, they are chemoresistant and recover following drug withdrawal.

METHODS

MicroRNA (miRNA) expression profiling of an oesophageal cancer cell line panel was used to identify miRNAs that were important in the regulation of apoptosis and autophagy. The effects of miRNA overexpression on cell death mechanisms and recovery were assessed in the chemoresistant (autophagy inducing) KYSE450 oesophageal cancer cells.

RESULTS

MiR-193b was the most differentially expressed miRNA between the chemosensitive and chemoresistant cell lines with higher expression in chemosensitive apoptosis inducing cell lines. Colony formation assays showed that overexpression of miR-193b significantly impedes the ability of KYSE450 cells to recover following 5-fluorouracil (5-FU) treatment. The critical mRNA targets of miR-193b are unknown but target prediction and siRNA data analysis suggest that it may mediate some of its effects through stathmin 1 regulation. Apoptosis was not involved in the enhanced cytotoxicity. Overexpression of miR-193b in these cells induced autophagic flux and non-apoptotic cell death.

CONCLUSION

These results highlight the importance of miR-193b in determining oesophageal cancer cell viability and demonstrate an enhancement of chemotoxicity that is independent of apoptosis induction.

Poly-ADP-ribosylation of HMGB1 regulates TNFSF10/TRAIL resistance through autophagy

Both apoptosis ("self-killing") and autophagy ("self-eating") are evolutionarily conserved processes, and their crosstalk influences anticancer drug sensitivity and cell death. However, the underlying mechanism remains unclear. Here, we demonstrated that HMGB1 (high mobility group box 1), normally a nuclear protein, is a crucial regulator of TNFSF10/TRAIL (tumor necrosis factor [ligand] superfamily, member 10)-induced cancer cell death. Activation of PARP1 (poly [ADP-ribose] polymerase 1) was required for TNFSF10-induced ADP-ribosylation of HMGB1 in cancer cells. Moreover, pharmacological inhibition of PARP1 activity or knockdown of PARP1 gene expression significantly inhibited TNFSF10-induced HMGB1 cytoplasmic translocation and subsequent HMGB1-BECN1 complex formation. Furthermore, suppression of the PARP1-HMGB1 pathway diminished autophagy, increased apoptosis, and enhanced the anticancer activity of TNFSF10 in vitro and in a subcutaneous tumor model. These results indicate that PARP1 acts as a prominent upstream regulator of HMGB1-mediated autophagy and maintains a homeostatic balance between apoptosis and autophagy, which provides new insight into the mechanism of TNFSF10 resistance.

Relationship between HMGB1 and PAI-1 after allogeneic hematopoietic stem cell transplantation

Background

Conditioning regimens including total body irradiation (TBI) or cyclophosphamide can mobilize high-mobility group box 1 (HMGB1) to peripheral blood. Additionally, increased plasminogen activator inhibitor (PAI)-1 levels are associated with post-allogeneic hematopoietic stem cell transplantation (aHSCT). However, changes to circulating levels of HMGB1 after aHSCT are poorly understood.

Materials and methods

The study cohort included 289 patients who underwent aHSCT at one of 25 institutions in Japan. We have investigated the relationship between HMGB1 and PAI-1 following aHSCT. A significant increase in HMGB1 levels occurred after conditioning treatment. Additionally, levels of HMGB1 at day 0 were significantly increased in TBI+ patients and cyclophosphamide/TBI patients.

Conclusion

Our data revealed that an increased level of HMGB1 at day 0 following aHSCT correlates with increased PAI-1 after aHSCT, which is consistent with previous reports. Increased HMGB1 at day 0 after a conditioning regimen may play a role in transplantation-associated coagulopathy following aHSCT, because PAI-1 can accelerate procoagulant activity.

Prognostic potential of an immune score based on the density of CD8+ T cells, CD20+ B cells, and CD33+/p-STAT1+ double-positive cells and HMGB1 expression within cancer nests in stage IIIA gastric cancer patients

OBJECTIVE

There is heterogeneity in the prognosis of gastric cancers staged according to the tumornodes- metastasis (TNM) system. This study evaluated the prognostic potential of an immune score system to supplement the TNM staging system.

METHODS

An immunohistochemical analysis was conducted to assess the density of T cells, B cells, and myeloid-derived suppressor cells (MDSCs) in cancer tissues from 100 stage IIIA gastric cancer patients; the expression of the high-mobility group protein B1 (HMGB1) was also evaluated in cancer cells. The relationship between the overall survival (OS), disease-free survival (DFS), and immunological parameters was analyzed.

RESULTS

An immune score system was compiled based on the prognostic role of the density of T cells, B cells, MDSCs, and the expression of HMGB1 in cancer tissues. The median 5-year survival of this group of patient was 32%. However, the 5-year survival rates of 80.0%, 51.7%, 0%, 5.8%, and 0% varied among the patients with an immune score of 4 to those with an immune score of 0 based on the immune score system, respectively. Similarly, differences in DFS rates were observed among the immune score subgroups.

CONCLUSIONS

An immune score system could effectively identify the prognostic heterogeneity within stage IIIA gastric cancer patients, implying that this immune score system may potentially supplement the TNM staging system, and help in identifying a more homogeneous group of patients who on the basis of prognosis can undergo adjuvant therapy.

The Pro-inflammatory Effects of Glucocorticoids in the Brain

Glucocorticoids are a class of steroid hormones derived from cholesterol. Their actions are mediated by the glucocorticoid and mineralocorticoid receptors, members of the superfamily of nuclear receptors, which, once bound to their ligands, act as transcription factors that can directly modulate gene expression. Through protein-protein interactions with other transcription factors, they can also regulate the activity of many genes in a composite or tethering way. Rapid non-genomic signaling was also demonstrated since glucocorticoids can act through membrane receptors and activate signal transduction pathways, such as protein kinases cascades, to modulate other transcriptions factors and activate or repress various target genes. By all these different mechanisms, glucocorticoids regulate numerous important functions in a large variety of cells, not only in the peripheral organs but also in the central nervous system during development and adulthood. In general, glucocorticoids are considered anti-inflammatory and protective agents due to their ability to inhibit gene expression of pro-inflammatory mediators and other possible damaging molecules. Nonetheless, recent studies have uncovered situations in which these hormones can act as pro-inflammatory agents depending on the dose, chronicity of exposure, and the structure/organ analyzed. In this review, we will provide an overview of the conditions under which these phenomena occur, a discussion that will serve as a basis for exploring the mechanistic foundation of glucocorticoids pro-inflammatory gene regulation in the brain.

Ti–O based nanomaterials ameliorate experimental autoimmune encephalomyelitis and collagen-induced arthritis

Administration of Ti–O based nanomaterials ameliorated the clinical severity of experimental autoimmune encephalomyelitis and collagen induced arthritis, thus provide novel therapeutic approach for multiple sclerosis and rheumatoid arthritis.

Cysteine redox state plays a key role in the inter-domain movements of HMGB1: a molecular dynamics simulation study

We have modelled and simulated different states of HMGB1, suggesting that the fully reduced HMGB1 maintains the inter-domain movements during the activity.

Stress-induced neuroinflammatory priming: A liability factor in the etiology of psychiatric disorders

Stress and glucocorticoids (GCs) have universally been considered to be anti-inflammatory, however in recent years, stress and GCs have been found to exert permissive effects (immunological priming) on neuroinflammatory processes. This phenomenon of priming is characterized by prior stress or GC exposure potentiating the neuroinflammatory response to a subsequent immune challenge. A considerable body of evidence is discussed here that supports this permissive effect of stress and GCs.

In light of this evidence, a mechanism of neuroinflammatory priming is proposed involving a signal cascade in the brain involving danger-associated molecular patterns (HMGB-1) and inflammasomes (NLRP3), which results in an exaggerated or amplified neuroinflammatory response and subsequently, the amplification of the physiological and behavioral sequelae of this response (i.e. sickness). Finally, we explore the notion that stressor-induced sensitization of the neuroimmune microenvironment may predispose individuals to psychiatric disorders, in which exaggerated innate immune/inflammatory responses in the brain are now thought to play a key role.

PPARγ inhibits HMGB1 expression through upregulation of miR-142-3p in vitro and in vivo

Peroxisome proliferator-activated receptor gamma (PPARγ) belongs to the nuclear receptor superfamily and it has received much attention because of its anti-inflammatory activity. However, the underlying molecular mechanism is not completely understood. In the present study, we demonstrated that the level of PPARγ is inversely correlated with that of high mobility group box 1 (HMGB1, a late proinflammatory mediator) in patients with sepsis. Activation of PPARγ inhibits the basal and LPS-induced expression of HMGB1. The PPARγ-mediated inhibition of HMGB1 is associated with the upregulation of miR-142-3p, which can target the 3'-UTR of HMGB1, by directly binding to the PPRE in the miR-142-3p promoter region. Functional experiments reveal that the PPARγ-induced miR-142-3p suppresses inflammatory response in vivo. These results suggest that PPARγ-mediated upregulation of miR-142-3p inhibits the HMGB1 expression, which, in turn, is a novel anti-inflammatory mechanism of PPARγ and has an important role in the treatment of inflammatory diseases.

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.

Perineural expression of high-mobility group box-1 contributes to long-lasting mechanical hypersensitivity via matrix metalloprotease-9 up-regulation in mice with painful peripheral neuropathy

High-mobility group box-1 (HMGB1) has been shown to be critical in the modulation of nociceptive transduction following a peripheral neuropathy. However, the precise role of peripherally expressed HMGB1 in neuropathic pain has yet to be fully elaborated. Following a partial sciatic nerve ligation (PSNL) in mice, a persistent ipsilateral up-regulation of HMGB1 was observed from 3 to 21 days after PSNL, in paralleled with a robust ipsilateral hind paw mechanical hypersensitivity. Increased HMGB1 was detected in both infiltrating macrophages and proliferating Schwann cells in the ipsilateral nerve 14 days following PSNL. Repeated perineural treatment with anti-HMGB1 antibody significantly ameliorated PSNL-induced mechanical hypersensitivity. Several pronociceptive molecules, including matrix metalloprotease-9 (MMP-9), tumor necrosis factor-α, interleukin-1β (IL-1β), and cyclooxygenase-2, were up-regulated in injured sciatic nerve 14 days following PSNL. Repeated perineural treatment with an anti-HMGB1 antibody significantly suppressed expression of MMP-9, but not other pronociceptive molecules. Perineural treatment with a selective MMP-9 inhibitor ameliorated PSNL-induced mechanical hypersensitivity. The current findings demonstrate that the maintenance of the neuropathic state following an injured nerve is dependent on the up-regulation of HMGB1 and MMP-9. Thus, blocking HMGB1 function in sciatic nerve could be a potent therapeutic strategy for the treatment of neuropathic pain. Increased peripheral high-mobility group box-1 (HMGB1) is involved in the modulation of nociceptive transduction following a peripheral neuropathy. Following nerve injury in mice, increased HMGB1 is detected in both infiltrating macrophages and proliferating Schwann cells in the ipsilateral nerve. Repeated perineural treatment with anti-HMGB1 antibody significantly ameliorates nerve injury-induced mechanical hypersensitivity, and suppresses expression of matrix metalloprotease-9 (MMP-9). The findings demonstrate that the maintenance of the neuropathic state following an injury nerve is dependent on the up-regulation of HMGB1 and MMP-9.

The Role of HMGB1 in Cardiovascular Biology: Danger Signals

SIGNIFICANCE

Cardiovascular disease (CVD) is the leading cause of mortality worldwide. Accumulating evidence shows that dysregulated immune response contributes to several types of CVDs such as atherosclerosis and pulmonary hypertension (PH). Vascular intimal impairment and low-density lipoprotein oxidation trigger a complex network of innate immune responses and sterile inflammation.

RECENT ADVANCES

High-mobility group box 1 (HMGB1), a nuclear DNA-binding protein, was recently discovered to function as a damage-associated molecular pattern molecule (DAMP) that initiates the innate immune responses. These findings lead to the understanding that HMGB1 plays a critical role in the inflammatory response in the pathogenesis of CVD.

CRITICAL ISSUES

In this review, we highlight the role of extracellular HMGB1 as a proinflammatory mediator as well as a DAMP in coronary artery disease, cerebral artery disease, peripheral artery disease, and PH.

FUTURE DIRECTIONS

A key focus for future researches on HMGB1 location, structure, modification, and signaling will reveal HMGB1's multiple functions and discover a targeted therapy that can eliminate HMGB1-mediated inflammation without interfering with adaptive immune responses.