Cleavage of HMGB1 by Proteolytic Enzymes Associated with Inflammatory Conditions

Altered release of thrombomodulin and HMGB1 in the placenta complicated with preeclampsia

INTRODUCTION

Preeclampsia (PE) is a severe pregnancy complication due to placental dysfunction. Thrombomodulin (TM), a glycoprotein expressed on the trophoblast cell membrane, plays an organ-protective role in the placenta by regulating coagulation and inflammation. TM-mediated regulation of High Mobility Group Box1(HMGB1) is an essential mechanism that contributes to placental homeostasis and prevents pregnancy complications in mice. Here, we aimed to clarify the role of placental TM and HMGB1 in the pathophysiology of human PE.

METHODS AND RESULTS

In this study, maternal blood serum and placental tissue were obtained from 72 PE patients and 110 normal controls. Soluble TM(sTM) and HMGB1 levels in the maternal serum were assessed. The placental TM and HMGB1 expression levels were evaluated using immunohistochemistry and qPCR. Serum sTM and HMGB1 levels gradually increased with gestational age in normal pregnancies; however, both circulating sTM and HMGB1 levels were significantly higher in the PE group. Serum HMGB1/sTM ratio was elevated in PE patients compared to that in normal controls, which correlated positively with the clinical severity of PE. The immunohistochemistry analysis revealed the loss of TM and the increase in extranuclear HMGB1. TM mRNA expression was diminished in PE placentas, which negatively correlated with soluble fms-like tyrosine kinase-1 (sFlt-1) expression.

DISCUSSION

The increase in circulating sTM and HMGB1 could be attributed to the enhanced placental TM shedding in PE patients. The molecular events mediated by the imbalance in the placental TM and HMGB1 levels could be an underlying feature of PE; maternal serum HMGB1/sTM ratio could reflect this status.

HMGB1 cleavage by complement C1s and its potent anti-inflammatory product

Complement C1s association with the pathogenesis of several diseases cannot be simply explained only by considering its main role in activating the classical complement pathway. This suggests that non-canonical functions are to be deciphered for this protease. Here the focus is on C1s cleavage of HMGB1 as an auxiliary target. HMGB1 is a chromatin non-histone nuclear protein, which exerts in fact multiple functions depending on its location and its post-translational modifications. In the extracellular compartment, HMGB1 can amplify immune and inflammatory responses to danger associated molecular patterns, in health and disease. Among possible regulatory mechanisms, proteolytic processing could be highly relevant for HMGB1 functional modulation. The unique properties of HMGB1 cleavage by C1s are analyzed in details. For example, C1s cannot cleave the HMGB1 A-box fragment, which has been described in the literature as an inhibitor/antagonist of HMGB1. By mass spectrometry, C1s cleavage was experimentally identified to occur after lysine on position 65, 128 and 172 in HMGB1. Compared to previously identified C1s cleavage sites, the ones identified here are uncommon, and their analysis suggests that local conformational changes are required before cleavage at certain positions. This is in line with the observation that HMGB1 cleavage by C1s is far slower when compared to human neutrophil elastase. Recombinant expression of cleavage fragments and site-directed mutagenesis were used to confirm these results and to explore how the output of C1s cleavage on HMGB1 is finely modulated by the molecular environment. Furthermore, knowing the antagonist effect of the isolated recombinant A-box subdomain in several pathophysiological contexts, we wondered if C1s cleavage could generate natural antagonist fragments. As a functional readout, IL-6 secretion following moderate LPS activation of RAW264.7 macrophage was investigated, using LPS alone or in complex with HMGB1 or some recombinant fragments. This study revealed that a N-terminal fragment released by C1s cleavage bears stronger antagonist properties as compared to the A-box, which was not expected. We discuss how this fragment could provide a potent brake for the inflammatory process, opening the way to dampen inflammation.

Association between high-mobility group box 1 levels and febrile seizures in children: a systematic review and meta-analysis

The relationship between High-mobility group box 1 (HMGB1) and febrile seizures (FS) in children remains unclear. This study aimed to apply meta-analysis to reveal the correlation between HMGB1 levels and FS in children. Databases including PubMed, EMBASE, Web of science, Cochrane library, CNKI, SinoMed and WanFangData were searched for relevant studies. Pooled standard mean deviation and 95% confidence interval were calculated as effect size since the random-effects model was used when I² > 50%. Meanwhile, between-study heterogeneity was determined by performing subgroup and sensitivity analyses. A total of 9 studies were finally included. Meta-analysis showed that the children with FS had significantly higher HMGB1 levels compared with healthy children and children with fever but no seizures (P<0.05). Additionally, subgroup analysis showed that the HMGB1 level in children with complex FS was higher than those with simple FS (P<0.05), and children with duration >15 min were higher than those with duration ≤15min (P<0.05). There were no statistical differences between children with or without a family history of FS (P>0.05). Finally, children with FS who converted to epilepsy exhibited higher HMGB1 levels than those who did not convert to epilepsy (P<0.05). The level of HMGB1 may be implicated in the prolongation, recurrence and development of FS in children. Thus, it was necessary to evaluate the precise concentrations of HMGB1 in FS patients and to further determine the various activities of HMGB1 during FS by well-designed, large-scale, and case-controlled trials.

Anti-depressant effects of acupuncture: The insights from NLRP3 mediated pyroptosis and inflammation

The NLRP3-mediated pyroptosis, which could affect inflammation response, plays a key role in the development of depression. Acupuncture has been shown to be an effective treatment for depression. In this study, we aimed to determine whether acupuncture could confer antidepressant activity via decreasing NLRP3-mediated pyroptosis by reducing inflammation. Here, depression model of rats was induced by chronic unpredictable mild stress (CUMS) for 4 weeks. Acupuncture group was subjected to acupuncture at the Shangxing (GV23) and Fengfu (GV16) acupoints for 20 min every other day (a total of 14 times). Fluoxetine group was administered with fluoxetine (2.1 mg/kg with the concentration of 0.21 mg/mL) by oral gavage (1 mL/100 g) once a day for 28 days. Rats' depression-like phenotypes were reflected with behavioral tests and biological detection methods. Results showed that acupuncture significantly improved the depression-like behavior of CUMS rat, suppressed the expressions of NLRP3, ASC, caspase-1, GSDMD, IL-1β, IL-18, HMGB1, IFN-γ, IL-6 and TNF-α in the serum and hippocampus, restored the %area of microglia, astrocytes and neuronal cells in the hippocampus. These indicate that acupuncture can prevent CUMS-induced depression-like behaviors by reducing NLRP3-mediated pyroptosis and inflammation.

The role of HMGB1 in inflammatory skin diseases

High-mobility group box 1 protein (HMGB1) is a highly abundant, non-histone nuclear protein that can serve as an alarmin to promote the pathogenesis of inflammatory diseases. In response to various stimuli, HMGB1 can translocate from the nucleus to the cytoplasm as well as the extracellular space through passive or active release, accompanied with different post-translational modifications. Depending on the redox state of three cysteine residues, HMGB1 determines its activity to induce cytokine production or tissue repair through binding with several different receptors. In addition, HMGB1 can form immunostimulatory complexes with cytokines and other endogenous/exogenous molecules and synergistically enhance their biological effect. Cell death is an important source of HMGB1 and major cell death forms such as apoptosis, necrosis and pyroptosis can modulate the redox state of HMGB1. In various human skin diseases as well as animal models, HMGB1 levels in cytoplasm, tissue and blood are increased and blockade of HMGB1 attenuates disease severity in animal models. These findings indicate that HMGB1 can serve as a unique biomarker as well as a target of new therapy in many inflammatory skin diseases.

The Role of HMGB1 in Rheumatic Diseases

HMGB1, a highly conserved non-histone nuclear protein, is widely expressed in mammalian cells. HMGB1 in the nucleus binds to the deoxyribonucleic acid (DNA) to regulate the structure of chromosomes and maintain the transcription, replication, DNA repair, and nucleosome assembly. HMGB1 is actively or passively released into the extracellular region during cells activation or necrosis. Extracellular HMGB1 as an alarmin can initiate immune response alone or combined with other substances such as nucleic acid to participate in multiple biological processes. It has been reported that HMGB1 is involved in various inflammatory responses and autoimmunity. This review article summarizes the physiological function of HMGB1, the post-translational modification of HMGB1, its interaction with different receptors, and its recent advances in rheumatic diseases and strategies for targeted therapy.

Role of Extracellular High-Mobility Group Box-1 as a Therapeutic Target of Gastric Cancer

Background: High-mobility group box-1 (HMGB1) is involved in the tumorigenesis and metastasis of various cancers. The present study investigated the roles of extracellular HMGB1 in the progression of gastric cancer (GC) and the therapeutic effects of recombinant human soluble thrombomodulin (rTM) targeting HMGB1. Methods: The effects of extracellular HMGB1 and rTM on GC cells were assessed using proliferation and Transwell assays. Their effects on local tumor growth and metastasis were evaluated using subcutaneous tumor and liver metastasis mouse models, respectively. Plasma HMGB1 concentrations in GC patients were measured using ELISA. The relationships between plasma HMGB1 concentrations and the prognosis and clinicopathological factors of patients were also investigated. Results: GC proliferation, migration, and invasion abilities were promoted by increases in extracellular HMGB1 concentrations and alleviated by rTM. In the subcutaneous tumor model, local tumor growth was promoted by the addition of rhHMGB1 and alleviated by rTM. Similar changes occurred in the liver metastasis model. Recurrence-free survival (p < 0.01) and overall survival (p = 0.01) were significantly worse in patients with high plasma HMGB1 concentrations. Conclusion: Plasma HMGB1 concentrations are a prognostic marker in GC patients. Extracellular HMGB1 promotes cancer progression and has potential as a novel treatment target in GC cells for rTM.

Antileukemic Natural Product Induced Both Apoptotic and Pyroptotic Programmed Cell Death and Differentiation Effect

Acute myeloid leukemia (AML) is one of the most common forms of leukemia. Despite advances in the management of such malignancies and the progress of novel therapies, unmet medical needs still exist in AML because of several factors, including poor response to chemotherapy and high relapse rates. Ardisianone, a plant-derived natural component with an alkyl benzoquinone structure, induced apoptosis in leukemic HL-60 cells. The determination of dozens of apoptosis-related proteins showed that ardisianone upregulated death receptors and downregulated the inhibitor of apoptosis protein (IAPs). Western blotting showed that ardisianone induced a dramatic increase in tumor necrosis factor receptor 2 (TNFR2) protein expression. Ardisianone also induced downstream signaling by activating caspase-8 and -3 and degradation in Bid, a caspase-8 substrate. Furthermore, ardisianone induced degradation in DNA fragmentation factor 45 kDa (DFF45), a subunit of inhibitors of caspase-activated DNase (ICAD). Q-VD-OPh (a broad-spectrum caspase inhibitor) significantly diminished ardisianone-induced apoptosis, confirming the involvement of caspase-dependent apoptosis. Moreover, ardisianone induced pyroptosis. Using transmission electron microscopic examination and Western blot analysis, key markers including gasdermin D, high mobility group box1 (HMGB1), and caspase-1 and -5 were detected. Notably, ardisianone induced the differentiation of the remaining survival cells, which were characterized by an increase in the expression of CD11b and CD68, two markers of macrophages and monocytes. Wright–Giemsa staining also showed the differentiation of cells into monocyte and macrophage morphology. In conclusion, the data suggested that ardisianone induced the apoptosis and pyroptosis of leukemic cells through downregulation of IAPs and activation of caspase pathways that caused gasdermin D cleavage and DNA double-stranded breaks and ultimately led to programmed cell death. Ardisianone also induced the differentiation of leukemic cells into monocyte-like and macrophage-like cells. The data suggested the potential of ardisianone for further antileukemic development.

The Effect and Regulatory Mechanism of High Mobility Group Box-1 Protein on Immune Cells in Inflammatory Diseases

High mobility group box-1 protein (HMGB1), a member of the high mobility group protein superfamily, is an abundant and ubiquitously expressed nuclear protein. Intracellular HMGB1 is released by immune and necrotic cells and secreted HMGB1 activates a range of immune cells, contributing to the excessive release of inflammatory cytokines and promoting processes such as cell migration and adhesion. Moreover, HMGB1 is a typical damage-associated molecular pattern molecule that participates in various inflammatory and immune responses. In these ways, it plays a critical role in the pathophysiology of inflammatory diseases. Herein, we review the effects of HMGB1 on various immune cell types and describe the molecular mechanisms by which it contributes to the development of inflammatory disorders. Finally, we address the therapeutic potential of targeting HMGB1.