Damage-associated molecular pattern molecules (DAMPs) are cellularly derived molecules that can initiate and perpetuate immune responses following trauma, ischemia and other types of tissue damage in the absence of pathogenic infection. High mobility group box 1 (HMGB1) is a prototypical DAMP and is associated with the hallmarks of cancer. Recently we found that HMGB1 release after chemotherapy treatment is a critical regulator of autophagy and a potential drug target for therapeutic interventions in leukemia. Overexpression of HMGB1 by gene transfection rendered leukemia cells resistant to cell death; whereas depletion or inhibition of HMGB1 and autophagy by RNA interference or pharmacological inhibitors increased the sensitivity of leukemia cells to chemotherapeutic drugs. HMGB1 release sustains autophagy as assessed by microtubule-associated protein 1 light chain 3 (LC3) lipidation, redistribution of LC3 into cytoplasmic puncta, degradation of p62 and accumulation of autophagosomes and autolysosomes. Moreover, these data suggest a role for HMGB1 in the regulation of autophagy through the PI3KC3-MEKERK pathway, supporting the notion that HMGB1-induced autophagy promotes tumor resistance to chemotherapy.
DAMP; autophagy; HMGB1; chemotherapy resistance; leukemia; PI3KC3; ERK
HMGB1 displaces Bcl-2 from Beclin1 to induce and sustain autophagy in response to cell stress.
Autophagy clears long-lived proteins and dysfunctional organelles and generates substrates for adenosine triphosphate production during periods of starvation and other types of cellular stress. Here we show that high mobility group box 1 (HMGB1), a chromatin-associated nuclear protein and extracellular damage-associated molecular pattern molecule, is a critical regulator of autophagy. Stimuli that enhance reactive oxygen species promote cytosolic translocation of HMGB1 and thereby enhance autophagic flux. HMGB1 directly interacts with the autophagy protein Beclin1 displacing Bcl-2. Mutation of cysteine 106 (C106), but not the vicinal C23 and C45, of HMGB1 promotes cytosolic localization and sustained autophagy. Pharmacological inhibition of HMGB1 cytoplasmic translocation by agents such as ethyl pyruvate limits starvation-induced autophagy. Moreover, the intramolecular disulfide bridge (C23/45) of HMGB1 is required for binding to Beclin1 and sustaining autophagy. Thus, endogenous HMGB1 is a critical pro-autophagic protein that enhances cell survival and limits programmed apoptotic cell death.
The functional relationship and cross-regulation between autophagy and apoptosis is complex. Here we show that high-mobility group box 1 protein (HMGB1) is a redox-sensitive regulator of the balance between autophagy and apoptosis. In cancer cells, anti-cancer agents enhanced autophagy and apoptosis as well as HMGB1 release. HMGB1 release may be a pro-survival signal for residual cells following various cytotoxic cancer treatments. Diminished HMGB1 by shRNA transfection or inhibition of HMGB1 release by ethyl pyruvate or other small molecules led to predominantly apoptosis and decreased autophagy in stressed cancer cells. In this setting, reducible HMGB1 binds to the receptor for advanced glycation end products (RAGE) but not Toll-like receptor 4 (TLR4), induces Beclin1-dependent autophagy, and promotes tumor resistance to alkylators (melphalan), tubulin disrupting agents (paclitaxel), DNA crosslinkers (ultraviolet light) and DNA-intercalators (oxaliplatin or adriamycin). Oxidized HMGB1 conversely increases the cytotoxicity of these agents and induces apoptosis mediated by the caspase-9/-3 intrinsic pathway. HMGB1 release as well as its redox state thus link autophagy and apoptosis, representing a suitable target when coupled with conventional tumor treatments.
High mobility group box 1 protein (HMGB1) is a major endogenous danger signal that triggers inflammation and immunity during septic and aseptic stresses. HMGB1 recently emerged as a key soluble factor in the pathogenesis of various infectious diseases, but nothing is known of its behaviour during herpesvirus infection. We therefore investigated the dynamics and biological effects of HMGB1 during HSV-2 infection of epithelial HEC-1 cells.
Despite a transcriptional shutdown of HMGB1 gene expression during infection, the intracellular pool of HMGB1 protein remained unaffected, indicating its remarkable stability. However, the dynamics of HMGB1 was deeply modified in infected cells. Whereas viral multiplication was concomitant with apoptosis and HMGB1 retention on chromatin, a subsequent release of HMGB1 was observed in response to HSV-2 mediated necrosis. Importantly, extracellular HMGB1 was biologically active. Indeed, HMGB1-containing supernatants from HSV-2 infected cells induced the migration of fibroblasts from murine or human origin, and reactivated HIV-1 from latently infected T lymphocytes. These effects were specifically linked to HMGB1 since they were blocked by glycyrrhizin or by a neutralizing anti-HMGB1 antibody, and were mediated through TLR2 and the receptor for Advanced Glycation End-products (RAGE). Finally, we show that genital HSV-2 active infections also promote HMGB1 release in vivo, strengthening the clinical relevance of our experimental data.
These observations target HMGB1 as an important actor during HSV-2 genital infection, notably in the setting of HSV-HIV co-infection.
High-mobility group box 1 protein (HMGB1), which mainly exists in the nucleus, has recently been shown to function as a sentinel molecule for viral nucleic acid sensing and an autophagy regulator in the cytoplasm. In this study, we studied the chaperone-like activity of HMGB1 and found that HMGB1 inhibited the chemically induced aggregation of insulin and lysozyme, as well as the heat-induced aggregation of citrate synthase. HMGB1 also restored the heat-induced suppression of cytoplasmic luciferase activity as a reporter protein in hamster lung fibroblast O23 cells with expression of HMGB1. Next, we demonstrated that HMGB1 inhibited the formation of aggregates and toxicity caused by expanded polyglutamine (polyQ), one of the main causes of Huntington disease. HMGB1 directly interacted with polyQ on immunofluorescence and coimmunoprecipitation assay, whereas the overexpression of HMGB1 or exogenous administration of recombinant HMGB1 protein remarkably reduced polyQ aggregates in SHSY5Y cells and hmgb1−/− mouse embryonic fibroblasts upon filter trap and immunofluorescence assay. Finally, overexpressed HMGB1 proteins in mouse embryonic primary striatal neurons also bound to polyQ and decreased the formation of polyQ aggregates. To this end, we have demonstrated that HMGB1 exhibits chaperone-like activity and a possible therapeutic candidate in polyQ disease.
Tumorigenesis and the efficacy of cancer therapeutics are both defined by the balance between autophagy and apoptosis. High-mobility group box 1 (HMGB1) is a DNA chaperone and extracellular damage-associated molecular pattern molecule (DAMP) with pro-autophagic activity. TP53/p53 plays a transcription-dependent and -independent role in the regulation of apoptosis, autophagy, metabolism, cell cycle progression, and many other processes. Both HMGB1 and TP53 are tightly linked with the development of cancer, associated with many of the hallmarks defining the altered biology of cancer. We have demonstrated that TP53-HMGB1 complexes regulate the balance between apoptosis and autophagy through regulation of the cytosolic localization of the reciprocal binding partner, whereby increased cytosolic HMGB1 enhances autophagy and increased cytosolic TP53 enhances apoptosis in colon cancer cells. We found that HMGB1-mediated autophagy promotes cell survival in TP53-dependent processes, and that TP53 inhibits autophagy through negative regulation of HMGB1-BECN1 complexes. Nuclear localization of TP53 and HMGB1 in tumors from patients with colon adenocarcinoma had a positive trend with survival time from diagnosis. Thus, HMGB1 and TP53 are critical in the crossregulation of apoptosis and autophagy and central to colon cancer biology.
Apoptosis; autophagy; colorectal cancer; HMGB1; TP53
Our recent study revealed a new role of nucleus accumbens-1 (NAC1), a transcription factor belonging to the BTB/POZ gene family, in regulating autophagy. Moreover, we found that the high-mobility group box 1 (HMGB1), a chromatin-associated nuclear protein acting as an extracellular damage associated molecular pattern molecule (DAMP), is the downstream executor of NAC1 in modulating autophagy. In response to stress such as therapeutic insults, NAC1 increases the expression, cytosolic translocation and release of HMGB1; elevated level of the cytoplasmic HMGB1 leads to activation of autophagy. The NAC1-HMGB1 partnership may represent a previously unrecognized pathway that regulates autophagy in response to various stresses such as chemotherapy.
Apoptosis; autophagy; cisplatin; HMGB1; NAC1
Autophagy, the process by which cells break down spent biochemical and damaged components, plays an important role in cell survival following stress. High mobility group box 1 (HMGB1) regulates autophagy in response to oxidative stress.
Exogenous hydrogen peroxide (H2O2) treatment or knockdown of the major superoxide scavenger enzyme, superoxide dismutase 1 (SOD1), by small interfering RNA (siRNA) increases autophagy in mouse and human cell lines. Addition of either SOD1 siRNA or H2O2 promotes cytosolic HMGB1 expression and extracellular release. Importantly, inhibition of HMGB1 release or loss of HMGB1 decreases the number of autophagolysosomes and autophagic flux under oxidative stress in vivo and in vitro.
HMGB1 release may be a common mediator of response to oxidative stress.
HMGB1 is important for oxidative stress-mediated autophagy and serves as a new target for the treatment of stress-associated disorders. Antioxid. Redox Signal. 15, 2185–2195.
High-mobility group box 1 protein (HMGB1), a chromatin associated nuclear protein and extracellular damage associated molecular pattern molecule (DAMP), is an evolutionarily ancient and critical regulator of cell death and survival. Overexpression of HMGB1 is associated with each of the hallmarks of cancer including unlimited replicative potential, ability to develop blood vessels (angiogenesis), evasion of programmed cell death (apoptosis), self-sufficiency in growth signals, insensitivity to inhibitors of growth, inflammation, tissue invasion and metastasis. Our studies and those of our colleagues suggest that HMGB1 is central to cancer (abnormal wound healing) and many of the findings in normal wound healing as well. Here, we focus on the role of HMGB1 in cancer, the mechanisms by which it contributes to carcinogenesis, and therapeutic strategies based on targeting HMGB1.
High mobility group box 1 (HMGB1), an evolutionarily highly conserved and abundant nuclear protein also has roles within the cytoplasm and as an extracellular damage-associated molecular pattern (DAMP) molecule. Extracellular HMGB1 is the prototypic endogenous ‘danger signal’ that triggers inflammation and immunity. Recent findings suggest that posttranslational modifications dictate the cellular localization and secretion of HMGB1. HMGB1 is actively secreted from immune cells and stressed cancer cells, or passively released from necrotic cells. During cancer development or administration of therapeutic agents including chemotherapy, radiation, epigenetic drugs, oncolytic viruses, or immunotherapy, the released HMGB1 may either promote or limit cancer growth, depending on the state of progression and vascularization of the tumor. Extracellular HMGB1 enhances autophagy and promotes persistence of surviving cancer cells following initial activation. When oxidized, it chronically suppresses the immune system to promote cancer growth and progression, thereby enhancing resistance to cancer therapeutics. In its reduced form, it can facilitate and elicit innate and adaptive anti-tumor immunity, recruiting and activating immune cells, in conjunction with cytotoxic agents, particularly in early transplantable tumor models. We hypothesize that HMGB1 also functions as an epigenetic modifier, mainly through regulation of NF-kB-dependent signaling pathways, to modulate the behavior of surviving cancer cells as well as the immune cells found within the tumor microenvironment. This has significant implications for developing novel cancer therapeutics.
Cancer; HMGB1; NF-kB signaling; activation; innate immunity; dendritic cells; CD8+ T cells; epigenetic pathways
High mobility group box 1 (HMGB1), the prototypic damage–associated molecular pattern molecule, is released at sites of inflammation and/or tissue damage. There, it promotes cytokine production and chemokine production/cell migration. New work shows that the redox status of HMGB1 distinguishes its cytokine-inducing and chemokine activity. Reduced all-thiol-HMGB1 has sole chemokine activity, whereas disulfide-HMGB1 has only cytokine activity, and oxidized, denatured HMGB1 has neither. Autophagy (programmed cell survival) and apoptosis (programmed cell death) have been implicated in controlling both innate and adaptive immune functions. Reduced HMGB1 protein promotes autophagy, whereas oxidized HMGB1 promotes apoptosis. Thus, the differential activity of HMGB1 in immunity, inflammation and cell death depends on the cellular redox status within tissues.
Mitochondria are organelles centrally important for bioenergetics as well as regulation of apoptotic death in eukaryotic cells. High mobility group box 1 (HMGB1), an evolutionarily conserved chromatin-associated protein which maintains nuclear homeostasis, is also a critical regulator of mitochondrial function and morphology. We show that heat shock protein beta-1 (HSPB1/ HSP27) is the downstream mediator of this effect. Disruption of the HSPB1 gene in embryonic fibroblasts with wild-type HMGB1 recapitulates the mitochondrial fragmentation, deficits in mitochondrial respiration, and adenosine triphosphate (ATP) synthesis observed with targeted deletion of HMGB1. Forced expression of HSPB1 reverses this phenotype in HMGB1 knockout cells. Mitochondrial effects mediated by HMGB1 regulation of HSPB1 expression, serves as a defense against mitochondrial abnormality, enabling clearance and autophagy in the setting of cellular stress. Our findings reveal a novel role for HMGB1 in autophagic surveillance with important effects on mitochondrial quality control.
A human homologue of high mobility group box 1 (HMGB1) protein was cloned and characterized from the human filarial parasites Wuchereria bancrofti and Brugia malayi. Sequence analysis showed that W. bancrofti HMGB1 (WbHMGB1) and B. malayi HMGB1 (BmHMGB1) proteins share 99 % sequence identity. Filarial HMGB1 showed typical architectural sequence characteristics of HMGB family of proteins and consisted of only a single HMG box domain that had significant sequence similarity to the pro-inflammatory B box domain of human HMGB1. When incubated with mouse peritoneal macrophages and human promyelocytic leukemia cells, rBmHMGB1 induced secretion of significant levels of pro-inflammatory cytokines such as TNF-α, GM-CSF, and IL-6. Functional analysis also showed that the filarial HMGB1 proteins can bind to supercoiled DNA similar to other HMG family of proteins. BmHMGB1 protein is expressed in the adult and microfilarial stages of the parasite and is found in the excretory secretions of the live parasites. These findings suggest that filarial HMGB1 may have a significant role in lymphatic pathology associated with lymphatic filariasis.
High mobility group box 1 (HMGB1) was originally discovered as a chromatin-binding protein several decades ago. It is now increasingly evident that HMGB1 plays a major role in several disease conditions such as atherosclerosis, diabetes, arthritis, sepsis, and cancer. It is intriguing how deregulation of HMGB1 can result in a myriad of disease conditions. Interestingly, HMGB1 is involved in cell proliferation, angiogenesis, and metastasis during cancer progression. Furthermore, HMGB1 has been demonstrated to exert intracellular and extracellular functions, activating key oncogenic signaling pathways. This paper focuses on the role of HMGB1 in prostate cancer development and highlights the potential of HMGB1 to serve as a key target for prostate cancer treatment.
The balance between apoptosis (“programmed cell death”) and autophagy (“programmed cell survival”) is important in tumor development and response to therapy. Here we show that HMGB1 and p53 form a complex which regulates the balance between tumor cell death and survival. We demonstrate that knockout of p53 inHCT116 cells increases expression of cytosolic HMGB1 and induces autophagy. Conversely, knockout of HMGB1 in mouse embryonic fibroblasts increases p53 cytosolic localization and decreases autophagy. p53 is thus a negative regulator of the HMGB1/Beclin 1 complex, and HMGB1 promotes autophagy in the setting of diminished p53. HMGB1-mediated autophagy promotes tumor cell survival in the setting of p53-dependent processes. The HMGB1/p53 complex affects the cytoplasmic localization of the reciprocal binding partner thereby regulating subsequent levels of autophagy and apoptosis. These insights provide a novel link between HMGB1 and p53 in the crossregulation of apoptosis and autophagy in the setting of cell stress, providing insights into their reciprocal roles in carcinogenesis.
HMGB1; p53; Autophagy; Apoptosis; Colorectal cancer
AIM: To examine how high-mobility group box 1 (HMGB1) regulates hepatocyte apoptosis and, furthermore, to determine whether glycyrrhizin (GL), a known HMGB1 inhibitor, prevents HMGB1-induced hepatocyte apoptosis.
METHODS: A human hepatocellular carcinoma cell line stably transfected with a bile acid transporter (Huh-BAT cells), were used in this study. Apoptosis was quantified using 4’,6-diamidino-2-phenylindole dihydrochloride staining and the APO Percentage apoptosis assay, and its signaling cascades were explored by immunoblot analysis. Kinase signaling was evaluated by immunoblotting and by using selective inhibitors. It is also tried to identify hepatocyte apoptosis affected by the HMGB1 inhibitor, GL.
RESULTS: HMGB1 increased cellular apoptosis in Huh-BAT cells. HMGB1 led to increased cytochrome c release from mitochondria into the cytosol, and induced the cleavage of procaspase 3. However, it did not affect the activation of caspase 8. HMGB1-induced caspase 3 activation was significantly attenuated by the p38 inhibitor SB203580. GL significantly attenuated HMGB1-induced hepatocyte apoptosis. GL also prevented HMGB1-induced cytochrome c release and p38 activation in Huh-BAT cells.
CONCLUSION: The present study demonstrated that HMGB1 promoted hepatocyte apoptosis through a p38-dependent mitochondrial pathway. In addition, GL had an anti-apoptotic effect on HMGB1-treated hepatocytes.
High-mobility group box 1; Hepatocyte; Apoptosis; Glycyrrhizin; p38; Mitochondria
High mobility group box 1 (HMGB1) is a highly conserved protein with multiple intracellular and extracellular functions, including transcriptional regulation as well as modulation of inflammation, cell migration, and ingestion of apoptotic cells. In the present experiments, we examined a potential role for intracellular HMGB1 in modulating phagocytosis. We found that phagocytosis of apoptotic cells resulted in translocation of HMGB1 into the cytoplasm and extracellular space. Transient or stable inhibition of HMGB1 expression in bone marrow derived macrophages resulted in increased phagocytosis of apoptotic thymocytes and apoptotic neutrophils. Knockdown of HMGB1 was associated with enhanced activation of Rac-1 as well as cytoskeletal rearrangement. Intracellular events involved in phagocytosis and upstream of Rac-1 activation, such as phosphorylation of ERK and FAK, were increased after knockdown of HMGB1. Inhibition of Src kinase activity prevented the increase in phosphorylation of FAK and ERK present during phagocytosis in HMGB1 knockdown cells, and also abrogated the enhancement in phagocytosis associated with HMGB1 knockdown. Interaction between Src and FAK in the cytoplasm of HMGB1 knockdown fibroblasts was enhanced compared with that present in control fibroblasts. Under in vitro conditions, the presence of HMGB1 diminished interactions between purified FAK and Src. The present studies demonstrate a novel role for HMGB1 in the regulation of phagocytosis. In particular, these experiments show that intracellular HMGB1, through associating with Src kinase and inhibiting interactions between Src and FAK, diminishes the phagocytic ability of macrophages and other cell populations.
Necrotic cells release inflammatory mediators that activate cytokine production from innate immune cells. One mediator of this activation is high mobility group box 1 protein (HMGB1). HMGB1 is normally a chromatin-associated protein and is sequestered at condensed chromatin during apoptosis. How it is released from chromatin during necrotic cell death is not known. Here we show that after DNA-alkylating damage, the activation of poly(ADP)-ribose polymerase (PARP) regulates the translocation of HMGB1 from the nucleus to the cytosol. This displaced HMGB1 is subject to release if the cell then loses plasma membrane integrity as a result of necrosis. Both full-length HMGB1 and a truncated form of HMGB1 lacking the highly conserved glutamate-rich C-terminal tail can induce macrophage activation and tumor necrosis factor-α production. However, displacement of HMGB1 from the nucleus following PARP activation requires the presence of the glutamate-rich C-terminal tail. Although the C-terminal tail is not the sole substrate for PARP modification of HMGB1, it appears to be required to destabilize HMGB1 association with chromatin following PARP-dependent chromatin modifications. These data suggest that PARP-dependent nuclear-to-cytosolic translocation of HMGB1 serves to establish the ability of cells to release this potent inflammatory mediator upon subsequent necrotic death.
High-mobility group box 1 protein (HMGB1), an abundant nuclear protein, was recently established as a proinflammatory mediator of experimental sepsis. Although extracellular HMGB1 has been found in atherosclerotic plaques, its potential role in the pathogenesis of atherothrombosis remains elusive. In the present study, we determined whether HMGB1 induces tissue factor (TF) expression in vascular endothelial cells (ECs) and macrophages. Our data showed that HMGB1 stimulated ECs to express TF (but not TF pathway inhibitor) mRNA and protein in a concentration- and time-dependent manner. Blockade of cell surface receptors (including TLR4, TLR2, and RAGE) with specific neutralizing antibodies partially reduced HMGB1-induced TF expression. Moreover, HMGB1 increased expression of Egr-1 and nuclear translocation of NF-κB (c-Rel/p65) in ECs. Taken together, our data suggest that HMGB1 induces TF expression in vascular endothelial cells via cell surface receptors (TLR4, TLR2, and RAGE), and through activation of transcription factors (NF-κB and Egr-1).
tissue factor; HMGB1; thrombosis; atherosclerosis
High mobility group box-1 (HMGB-1) is a DNA-binding protein secreted by
activated monocytes and has been identified as a key late mediator of endotoxic shock. We investigated the regulation of HMGB-1 in human peripheral blood mononuclear cells (PBMCs) following stimulation with the staphylococcal superantigen, toxic shock syndrome toxin-1 (TSST-1), and found that TSST-1, like LPS, induced the secretion of HMGB-1 from human PBMC. However, unlike monocyte-driven sepsis caused by endotoxin, translocation and secretion of HMGB-1 mediated by TSST-1 was dependent on the presence of both activated T cells and monocytes. Furthermore, we show that nuclear HMGB-1 is released from TSST-1 stimulated T cells. This finding presents a basis for investigating the potential of targeting HMGB-1 for the treatment of toxic shock syndrome, and provides further insight on the role of HMGB-1 in the cross-talk between activated monocytes and T cells.
High mobility group box chromosomal protein 1 (HMGB1) is a DNA-binding nuclear protein that can be released from dying cells and activated myeloid cells. Extracellularly, HMGB1 promotes inflammation. Experimental studies demonstrate HMGB1 to be a pathogenic factor in many inflammatory conditions including arthritis. HMGB1-blocking therapies in arthritis models alleviate disease and confer significant protection against cartilage and bone destruction. So far, the most successful HMGB1-targeted therapies have been demonstrated with HMGB1-specific polyclonal antibodies and with recombinant A box protein, a fragment of HMGB1. The present study is the first to evaluate the potential of a monoclonal anti-HMGB1 antibody (2G7, mouse IgG2b) to ameliorate arthritis. Effects of repeated injections of this antibody have now been studied in two conceptually different models of arthritis: collagen type II–induced arthritis (CIA) in DBA/1 mice and in a spontaneous arthritis disease in mice with combined deficiencies for genes encoding for the enzyme DNase type II and interferon type I receptors. These mice are unable to degrade phagocytozed DNA in macrophages and develop chronic, destructive polyarthritis. Therapeutic intervention in CIA and prophylactic administration of anti-HMGB1 monoclonal antibody (mAb) in the spontaneous arthritis model significantly ameliorated the clinical courses. Anti-HMGB1 mAb therapy also partially prevented joint destruction, as demonstrated by histological examination. The beneficial antiarthritic effects by the anti-HMGB1 mAb in two diverse models of arthritis represent additional proof-of-concept, indicating that HMGB1 may be a valid target molecule to consider for development of future clinical therapy.
High-mobility group box 1 (HMGB1), a highly conserved DNA-binding protein, plays an important role in maintaining nucleosome structures, transcription, and inflammation. We identified a homolog of HMGB1 in the Japanese lamprey (Lampetra japonica). The Lampetra japonica HMGB1 gene (Lj-HMGB1) has over 70% sequence identity with its homologs in jawed vertebrates. Despite the reasonably high sequence identity with other HMGB1 proteins, Lj-HMGB1 did not group together with these proteins in a phylogenetic analysis. We examined Lj-HMGB1 expression in lymphocyte-like cells, and the kidneys, heart, gills, and intestines of lampreys before and after the animals were challenged with lipopolysaccharide (LPS) and concanavalin A (ConA). Lj-HMGB1 was initially expressed at a higher level in the heart, but after treatment with LPS and ConA only the gills demonstrated a significant up-regulation of expression. The recombinant Lj-HMGB1 (rLj-HMGB1) protein bound double-stranded DNA and induced the proliferation of human adenocarcinoma cells to a similar extent as human HMGB1. We further revealed that Lj-HMGB1 was able to induce the production of tumor necrosis factor-α (TNF-α), a pro-inflammatory mediator, in activated human acute monocytic leukemia cells. These results suggest that lampreys use HMGB1 to activate their innate immunity for the purpose of pathogen defense.
Severe sepsis, a lethal syndrome after infection or injury, is the third leading cause of mortality in the United States. The pathogenesis of severe sepsis is characterized by organ damage and accumulation of apoptotic lymphocytes in the spleen, thymus, and other organs. To examine the potential causal relationships of apoptosis to organ damage, we administered Z-VAD-FMK, a broad-spectrum caspase inhibitor, to mice with sepsis. We found that Z-VAD-FMK–treated septic mice had decreased levels of high mobility group box 1 (HMGB1), a critical cytokine mediator of organ damage in severe sepsis, and suppressed apoptosis in the spleen and thymus. In vitro, apoptotic cells activate macrophages to release HMGB1. Monoclonal antibodies against HMGB1 conferred protection against organ damage but did not prevent the accumulation of apoptotic cells in the spleen. Thus, our data indicate that HMGB1 production is downstream of apoptosis on the final common pathway to organ damage in severe sepsis.
High-mobility group box 1 (HMGB1) was originally identified as a highly conserved nuclear DN A-binding protein that participates in DN A replication, repair and transcriptional regulation of gene expression. Although the nuclear role of HMGB1 is not quite understood, recent studies characterized the emerging role of extracellular HMGB1 as a prototypical danger signal that regulates inflammatory and repair responses. Under conditions of infection, injury and sterile inflammation, HMGB1 can be passively released from damaged cells or actively secreted from activated immune cells. Inflammasomes, large caspase-1-activating protein complexes, were recently shown to play a critical role in mediating the extracellular release of HMGB1 from activated and infected immune cells.
HMGB1; inflammasome; caspase-1; NLR; danger signal; alarmin; infection; inflammation; NLRP3; NLRC4
High-mobility group box-1 protein (HMGB1) is a nuclear protein that regulates gene expression throughout the body. It can also become cytoplasmic and function as a neuromodulatory cytokine after tissue damage or injury. The manner in which HMGB1 influences the peripheral nervous system following nerve injury is unclear. The present study investigated the degree to which HMGB1 signaling contributes to the maintenance of neuropathic pain behavior in the rodent.
Redistribution of HMGB1 from the nucleus to the cytoplasm occurred in both sensory neurons derived from a tibial nerve injured (TNI) rat and in a sensory neuron-like cell line following exposure to a depolarizing stimulus. We also observe that exogenous administration of HMGB1 to acutely dissociated sensory neurons derived from naïve or TNI rodents elicit increased excitability. Furthermore systemic injection of glycyrrhizin (50 mg/kg; i.p.), a known inhibitor of HMGB1, reversed TNI-induced mechanical hyperalgesia at fourteen days and three months following nerve injury.
We have identified that a persistent endogenous release of HMGB1 by sensory neurons may be a potent, physiologically relevant modulator of neuronal excitability. More importantly, the use of the anti-inflammatory compound and known inhibitor of HMGB1, glycyrrhizin, has the ability to diminish persistent pain behavior in a model of peripheral neuropathy, presumably through its ability to neutralize the cyotkine. The identification of HMGB1 as a potential therapeutic target may contribute to a better understanding of mechanisms associated with chronic pain syndromes.