HMGB1 as a drug target in staphylococcal pneumonia

RAGE participates in the intracellular transport of Campylobacter jejuni cytolethal distending toxin

BACKGROUND

Cytolethal distending toxin (CDT) belongs to the genotoxin family and is closely related to Campylobacter jejuni-associated gastroenteritis. We recently reported that CDT triggers the danger-associated molecular pattern (DAMP) signaling to exert deleterious effects on host cells. However, how CDT traffics in cells and the mechanism of CDT intoxication remain to be elucidated.

METHODS

Recombinant CDT subunits (CdtA, CdtB, and CdtC) were purified, and their activity was characterized in gastrointestinal cells. Molecular approaches and image tracking were employed to analyze the delivery of CDT in host cells.

RESULTS

In this study, we found that CDT interacts with the receptor of advanced glycation end products (RAGE) and high mobility group box 1 (HMGB1) to enter the cells. Our results further showed that CdtB transport in cells through the dynamin-dependent endocytic pathway and lysosome is involved in this process. Conversely, blockage of RAGE signaling resulted in a reduction in CDT-arrested cell cycles, indicating that RAGE is involved in CDT intracellular transport and its subsequent pathogenesis.

CONCLUSION

Our results demonstrate that RAGE is important for CDT trafficking in the cells. These findings expand our understanding of important issues related to host cell intoxication by C. jejuni CDT.

High Mobility Group Box 1 and Interleukin 6 at Intensive Care Unit Admission as Biomarkers in Critically Ill COVID-19 Patients

Exuberant inflammation manifesting as a "cytokine storm" has been suggested as a central feature in the pathogenesis of severe coronavirus disease 2019 (COVID-19). This study investigated two prognostic biomarkers, the high mobility group box 1 (HMGB1) and interleukin-6 (IL-6), in patients with severe COVID-19 at the time of admission in the intensive care unit (ICU). Of 60 ICU patients with COVID-19 enrolled and analyzed in this prospective cohort study, 48 patients (80%) were alive at ICU discharge. HMGB1 and IL-6 plasma levels at ICU admission were elevated compared with a healthy control, both in ICU nonsurvivors and ICU survivors. HMGB1 and IL-6 plasma levels were higher in patients with a higher Sequential Organ Failure Assessment (SOFA) score (> 10), and the presence of septic shock or acute kidney injury. HMGB1 and IL-6 plasma levels were also higher in patients with a poor oxygenation status (PaO2/FiO2 < 150 mm Hg) and a longer duration of ventilation (> 7 days). Plasma HMGB1 and IL-6 levels at ICU admission also correlated with other prognostic markers, including the maximum neutrophil/lymphocyte ratio, D-dimer levels, and C-reactive protein levels. Plasma HMGB1 and IL-6 levels at ICU admission predicted ICU mortality with comparable accuracy to the SOFA score and the COVID-GRAM risk score. Higher HMGB1 and IL-6 were not independently associated with ICU mortality after adjustment for age, gender, and comorbidities in multivariate analysis models. In conclusion, plasma HMGB1 and IL6 at ICU admission may serve as prognostic biomarkers in critically ill COVID-19 patients.

HMGB1-Neutralizing IgM Antibody Is a Normal Component of Blood Plasma

Extracellular high-mobility group box 1 (HMGB1) is a prototypic damage-associated molecular pattern. Although a homeostatic level of extracellular HMGB1 may be beneficial for immune defense, tissue repair, and tissue regeneration, excessive HMGB1 is linked to inflammatory diseases. This prompts an intriguing question: how does a healthy body control the level of extracellular HMGB1? In this study, in the plasma of both healthy humans and healthy mice, we have identified an anti-HMGB1 IgM autoantibody that neutralizes extracellular HMGB1 via binding specifically to a 100% conserved epitope, namely HMW4 (HMGB1_98-112). In mice, this anti-HMW4 IgM is produced by peritoneal B-1 cells, and concomitant triggering of their BCR and TLR4 by extracellular HMGB1 stimulates the production of anti-HMW4 IgM. The ability of extracellular HMGB1 to induce its own neutralizing Ab suggests a feedback loop limiting the level of this damage-associated molecular pattern in a healthy body.

The Role of HMGB1, a Nuclear Damage-Associated Molecular Pattern Molecule, in the Pathogenesis of Lung Diseases

Significance: High-mobility group protein box 1 (HMGB1), a ubiquitous nuclear protein, regulates chromatin structure and modulates the expression of many genes involved in the pathogenesis of lung cancer and many other lung diseases, including those that regulate cell cycle control, cell death, and DNA replication and repair. Extracellular HMGB1, whether passively released or actively secreted, is a danger signal that elicits proinflammatory responses, impairs macrophage phagocytosis and efferocytosis, and alters vascular remodeling. This can result in excessive pulmonary inflammation and compromised host defense against lung infections, causing a deleterious feedback cycle. Recent Advances: HMGB1 has been identified as a biomarker and mediator of the pathogenesis of numerous lung disorders. In addition, post-translational modifications of HMGB1, including acetylation, phosphorylation, and oxidation, have been postulated to affect its localization and physiological and pathophysiological effects, such as the initiation and progression of lung diseases. Critical Issues: The molecular mechanisms underlying how HMGB1 drives the pathogenesis of different lung diseases and novel therapeutic approaches targeting HMGB1 remain to be elucidated. Future Directions: Additional research is needed to identify the roles and functions of modified HMGB1 produced by different post-translational modifications and their significance in the pathogenesis of lung diseases. Such studies will provide information for novel approaches targeting HMGB1 as a treatment for lung diseases.

HMGB1 signaling blocking protects against carbapenem-resistant klebsiella pneumoniae in a murine model of infection

PURPOSE OF THE STUDY

Pulmonary infection with Klebsiella pneumoniae (KP) and carbapenem-resistant Klebsiella pneumoniae (CRKP) significantly contribute to morbidity and mortality in pneumonia. Recent studies have indicated that High-Mobility Group Box 1 Protein (HMGB1) plays an important role in the prevention and treatment of pneumonia. However the role of HMGB1 in CRKP-induced pneumonia has not been addressed. Materials andMethods: In vivo, we successfully established the KP and CRKP-induced pneumonia mouse model. We then tested the anti-HMGB1 IgG prevents CRKP-induced pneumonia.

RESULTS

The mice treated with the anti-HMGB1 IgG ameliorated CRKP-induced pulmonary infiltration of inflammatory cells, dissemination of bacteria and the cytokine storm by suppressing the HMGB1 signaling pathways.

CONCLUSION

These results indicate that HMGB1 may be an important contributor in these changes of CRKP-induced pneumonia. Thus, HMGB1 may provide a therapeutic target for reducing bacterial infection and lung inflammation in CRKP pneumonia.

Glycyrrhizin, an HMGB1 inhibitor, exhibits neuroprotective effects in rats after lithium-pilocarpine-induced status epilepticus

Objectives

It has been proven that extracellular HMGB1 is involved in progression of neurologic disorders, such as stroke, traumatic brain injury, meningitis and epilepsy. Glycyrrhizin (GL) is a direct inhibitor of HMGB1, and blocks HMGB1 release into the extracellular. We aim in this study to investigate the neuroprotective effects of GL in a rat model after lithium-pilocarpine-induced status epilepticus (SE).

Methods

Adult male SD rats were divided into three groups: Sham group, SE-group and (SE + GL)-treated group. The HMGB1 expression in serum and hippocampus, the damage extent of blood brain barrier (BBB) and hippocampal neuronal damage were evaluated by enzyme-linked immunosorbent assay, immunohistochemistry, western blot and nissl's staining.

Key findings

Glycyrrhizin markedly reduced HMGB1 expression in serum and hippocampus, prevented HMGB1 translocation from nucleus to cytoplasm in hippocampal CA1, CA3 and hilus areas of SE rats. Meanwhile, GL significantly ameliorated neuronal damage in the CA1, CA3 and hilus areas of hippocampus, and protected BBB disruption after SE. The administration of GL significantly decreased the mortality from 25 to 8.9% in rats.

Conclusions

Glycyrrhizin may exert neuroprotective effects via inhibiting HMGB1 and protect BBB permeability in lithium-pilocarpine-induced rats with SE.

Vitamin D reduces inflammatory response in asthmatic mice through HMGB1/TLR4/NF‑κB signaling pathway

The present study aimed to investigate the effects of vitamin D (VD) on inflammatory responses in asthmatic mice and the underlying mechanism, providing a theoretical basis for clinical application of targeted drug therapy, and the development of novel drugs against asthma. Mouse models of asthma were established. Hematoxylin‑eosin staining was performed to observe the pathological changes of the lung tissue. Pulmonary function tests were conducted to determine airway resistance in asthmatic mice. ELISA was performed to measure the serum levels of inflammatory factors. Western blot analysis and reverse transcription‑quantitative polymerase chain reaction were performed to determine the changes in apoptosis‑inducing factors, and high mobility group box 1 protein (HMGB1)/Toll‑like receptor‑4 (TLR4)/nuclear factor (NF)‑κB signaling pathway‑related proteins. VD reduced infiltrated inflammatory factors, attenuated the airway resistance of asthmatic mice, decreased serum levels of interleukin (IL)‑1β, IL‑6, tumor necrosis factor (TNF)‑α, increased serum levels of IL‑10, decreased apoptotic factor Bcl‑2‑associated X and caspase‑3 expression, downregulated HMGB1 and TLR4, NF‑κB and phosphorylated‑NF‑κB p65 expression. When TLR4 expression was inhibited, the anti‑inflammatory effects of VD were attenuated, and HMGB1, TLR4, NF‑κB and p‑NF‑κB p65 expression was increased. VD was able reduce the inflammatory response of asthmatic mice and apoptosis in lung tissue through the HMGB1/TLR4/NF‑κB signaling pathway.

Emerging role of HMGB1 in lung diseases: friend or foe

Lung diseases remain a serious problem for public health. The immune status of the body is considered to be the main influencing factor for the progression of lung diseases. HMGB1 (high‐mobility group box 1) emerges as an important molecule of the body immune network. Accumulating data have demonstrated that HMGB1 is crucially implicated in lung diseases and acts as independent biomarker and therapeutic target for related lung diseases. This review provides an overview of updated understanding of HMGB1 structure, release styles, receptors and function. Furthermore, we discuss the potential role of HMGB1 in a variety of lung diseases. Further exploration of molecular mechanisms underlying the function of HMGB1 in lung diseases will provide novel preventive and therapeutic strategies for lung diseases.

High mobility group box 1 gene polymorphism is associated with the risk of postoperative atrial fibrillation after coronary artery bypass surgery

Background

The inflammatory response triggered by cardiac surgery with cardiopulmonary bypass (CPB) is a primary cause of postoperative atrial fibrillation (POAF). The objective of this study was to determine the relationships between rs2249825 (C/G) polymorphism in high-mobility group box protein 1 (HMGB1) and POAF in patients who underwent coronary artery bypass grafting (CABG) under CPB.

Methods

A prospective cohort study was carried out between February 2011 and January 2014. Patients who had no history of atrial fibrillation undergoing CABG with CPB were recruited in this study, and were matched based on preoperative characteristics. Blood samples were obtained before, and at 4, and 24 h after CPB. HMGB1 level was measured by enzyme immunoassay. Patients were genotyped for single nucleotide polymorphisms of HMGB1 (rs2249825). Patients were genotyped for single nucleotide polymorphisms of HMGB1 (rs2249825) using pyrosequencing method. The primary clinical end point was the incidence of POAF after surgery.

Results

After matching, a total of 128 patients undergoing elective CABG with CPB were eligible for analysis. Plasma HMGB1 concentrations were increased 4 h after CPB (p <0.0001) and were still increased at 24 h (p <0.0001). The frequencies of CC, CG, GG genotypes were 21 (56.8 %), 29 (37.8 %), and 2 (5.4 %) in patients with POAF and 81.3, 16.5, and 2.2 % in patients without POAF (p = 0.016). CG + GG genotype was associated with high HMGB1 levels compared with the genotype CC at 4 h (p = 0.023), and 24 h (p = 0.015) after CPB. Multivariate analysis showed that age older than 60 years (OR = 1.40; 95 % CI: 1.03 to 1.89; p = 0.021) and allele G of polymorphisms (OR = 1.61; 95 % CI: 1.08 to 2.04; p = 0.034) were independent risk factors for POAF.

Conclusions

The HMGB1 rs2249825 was associated with the susceptibility to POAF after CABG with CPB in a Chinese Han population.

Alarmin function of galectin-9 in murine respiratory tularemia

Sepsis is a complex immune disorder that is characterized by systemic hyperinflammation. Alarmins, which are multifunctional endogenous factors, have been implicated in exacerbation of inflammation in many immune disorders including sepsis. Here we show that Galectin-9, a host endogenous β-galactoside binding lectin, functions as an alarmin capable of mediating inflammatory response during sepsis resulting from pulmonary infection with Francisella novicida, a Gram negative bacterial pathogen. Our results show that this galectin is upregulated and is likely released during tissue damage in the lungs of F. novicida infected septic mice. In vitro, purified recombinant galectin-9 exacerbated F. novicida-induced production of the inflammatory mediators by macrophages and neutrophils. Concomitantly, Galectin-9 deficient (Gal-9^-/-) mice exhibited improved lung pathology, reduced cell death and reduced leukocyte infiltration, particularly neutrophils, in their lungs. This positively correlated with overall improved survival of F. novicida infected Gal-9^-/- mice as compared to their wild-type counterparts. Collectively, these findings suggest that galectin-9 functions as a novel alarmin by augmenting the inflammatory response in sepsis development during pulmonary F. novicida infection.