Although acute lung injury (ALI) is an important problem in humans, its pathogenesis is poorly understood. Airway instillation of bacterial LPS, a known complement activator, represents a frequently used model of ALI. In the present study, pathways in the immunopathogenesis of ALI were evaluated. ALI was induced in wild-type, C3(-/-), and C5(-/-) mice by airway deposition of LPS. To assess the relevant inflammatory mediators, bronchoalveolar lavage fluids were evaluated by ELISA analyses and various neutralizing Abs and receptor antagonists were administered in vivo. LPS-induced ALI was neutrophil-dependent, but it was not associated with generation of C5a in the lung and was independent of C3, C5, or C5a. Instead, LPS injury was associated with robust generation of macrophage migration inhibitory factor (MIF), leukotriene B(4) (LTB4), and high mobility group box 1 protein (HMGB1) and required engagement of receptors for both MIF and LTB4. Neutralization of MIF or blockade of the MIF receptor and/or LTB4 receptor resulted in protection from LPS-induced ALI. These findings indicate that the MIF and LTB4 mediator pathways are involved in the immunopathogenesis of LPS-induced experimental ALI. Most strikingly, complement activation does not contribute to the development of ALI in the LPS model.

Pulmonary infection with Pseudomonas aeruginosa and neutrophilic lung inflammation significantly contribute to morbidity and mortality in cystic fibrosis (CF). High-mobility group box 1 protein (HMGB1), a ubiquitous DNA binding protein that promotes inflammatory tissue injury, is significantly elevated in CF sputum. However, its mechanistic and potential therapeutic implications in CF were previously unknown. We found that HMGB1 levels were significantly elevated in bronchoalveolar lavage fluids (BALs) of CF patients and cystic fibrosis transmembrane conductance regulator (CFTR )(-/-) mice. Neutralizing anti-HMGB1 monoclonal antibody (mAb) conferred significant protection against P. aeruginosa-induced neutrophil recruitment, lung injury and bacterial infection in both CFTR(-/-) and wild-type mice. Alveolar macrophages isolated from mice treated with anti-HMGB1 mAb had improved phagocytic activity, which was suppressed by direct exposure to HMGB1. In addition, BAL from CF patients significantly impaired macrophage phagocytotic function, and this impairment was attenuated by HMGB1-neutralizing antibodies. The HMGB1-mediated suppression of bacterial phagocytosis was attenuated in macrophages lacking toll-like receptor (TLR)-4, suggesting a critical role for TLR4 in signaling HMGB1-mediated macrophage dysfunction. These studies demonstrate that the elevated levels of HMGB1 in CF airways are critical for neutrophil recruitment and persistent presence of P. aeruginosa in the lung. Thus, HMGB1 may provide a therapeutic target for reducing bacterial infection and lung inflammation in CF.

Recent evidence in experimental models of seizures and in temporal lobe epilepsy support an important role of high-mobility group box 1 and toll-like receptor 4 signalling in the mechanisms of hyperexcitability leading to the development and perpetuation of seizures. In this study, we investigated the expression and cellular distribution of toll-like receptors 2 and 4, and of the receptor for advanced glycation end products, and their endogenous ligand high-mobility group box 1, in epilepsy associated with focal malformations of cortical development. Immunohistochemistry showed increased expression of toll-like receptors 2 and 4 and receptor for advanced glycation end products in reactive glial cells in focal cortical dysplasia, cortical tubers from patients with the tuberous sclerosis complex and in gangliogliomas. Toll-like receptor 2 was predominantly detected in cells of the microglia/macrophage lineage and in balloon cells in focal cortical dysplasia, and giant cells in tuberous sclerosis complex. The toll-like receptor 4 and receptor for advanced glycation end products were expressed in astrocytes, as well as in dysplastic neurons. Real-time quantitative polymerase chain reaction confirmed the increased receptors messenger RNA level in all pathological series. These receptors were not detected in control cortex specimens. In control cortex, high-mobility group box 1 was ubiquitously detected in nuclei of glial and neuronal cells. In pathological specimens, protein staining was instead detected in the cytoplasm of reactive astrocytes or in tumour astrocytes, as well as in activated microglia, predictive of its release from glial cells. In vitro experiments in human astrocyte cultures showed that nuclear to cytoplasmic translocation of high-mobility group box 1 was induced by interleukin-1β. Our findings provide novel evidence of intrinsic activation of these pro-inflammatory signalling pathways in focal malformations of cortical development, which could contribute to the high epileptogenicity of these developmental lesions.

OBJECTIVE

Postoperative cognitive dysfunction (POCD) is a growing and largely underestimated problem without defined etiology. Herein, we sought to determine the relationship between cognitive decline, blood-brain barrier (BBB) permeability, and inflammation, namely high mobility group box-1 (HMGB1), after surgery in aged rats.

METHODS

Aged rats were randomly assigned as surgery group (n = 45, splenectomy under general anesthesia), anesthesia (n = 45, 2% isoflurane for 2 h), and naïve control (n = 15). Markers of inflammation were measured in plasma and brain. Blood-brain barrier ultrastructure and permeability were measured by transmission electron microscope (TEM) and IgG immunohistochemistry. Cognitive function was assessed in a reversal learning version of the Morris water maze (MWM).

RESULTS

Surgical trauma under general anesthesia caused distinct changes in systemic and central proinflammatory cytokines. Levels of HMGB1 and the receptor for advanced glycation end products (RAGE) were significantly upregulated in the hippocampus of operated animals. Immunohistochemistry and TEM showed BBB disruption induced by surgery and anesthesia. These molecular changes were associated with cognitive impairment in latency with the MWM up to postoperative day 3.

CONCLUSIONS

HMGB1 and RAGE signaling appear pivotal mediators of surgery-induced cognitive decline and may contribute to the changes in BBB permeability after peripheral surgical trauma.

High-mobility group box 1 (HMGB1) is a nuclear factor released extracellularly as a proinflammatory cytokine. We measured the HMGB1 concentration in the sera of mice with chemically induced colitis (DSS; dextran sulfate sodium salt) and found a marked increase. Inhibition of HMGB1 by neutralizing anti-HMGB1 antibody resulted in reduced inflammation in DSS-treated colons. In macrophages, HMGB1 induces several proinflammatory cytokines, such as IL-6, which are regulated by NF-kappaB activation. Two putative sources of HMGB1 were explored: in one, bacterial factors induce HMGB1 secretion from macrophages and in the other, necrotic epithelial cells directly release HMGB1. LPS induced a small amount of HMGB1 in macrophages, but macrophages incubated with supernatant prepared from necrotic cells and containing large amounts of HMGB1 activated NF-kappaB and induced IL-6. Using the colitis-associated cancer model, we demonstrated that neutralizing anti-HMGB1 antibody decreases tumor incidence and size. These observations suggest that HMGB1 is a potentially useful target for IBD treatment and the prevention of colitis-associated cancer.

The receptor for advanced glycation end-products (RAGE) is a pattern-recognition receptor involved in the host response to injury, infection and inflammation. It is a membrane receptor, but also has soluble forms (sRAGE). Deficiencies in sRAGE are linked to heightened inflammation in various chronic conditions. We determined whether airway and systemic levels of sRAGE and the RAGE ligands HMGB1 (high-mobility group box-1) and serum amyloid A (SAA) are related to neutrophilic inflammation in asthma and chronic obstructive pulmonary disease (COPD). Bronchial lavage fluid from subjects with moderate-to-severe persistent asthma (n = 16) or COPD (n = 37), or from healthy controls (n = 18), was analysed for neutrophils, total sRAGE, endogenous secretory RAGE (esRAGE), HMGB1 and SAA. We also determined systemic levels of sRAGE in a separate group of asthmatic (n = 101) and COPD (n = 34) subjects. Subjects with neutrophilic asthma or COPD had undetectable levels of lung sRAGE, while levels of sRAGE in asthma/COPD without neutrophilia were similar to those in controls. Systemic sRAGE was significantly decreased in subjects with neutrophilic asthma or COPD compared with those without airway neutrophilia. There was significant positive correlation between total sRAGE and esRAGE in the lung and systemically. HMGB1 levels were similar in all subject groups, while SAA was below detectable levels. Neutrophilic airway inflammation in asthma and COPD is associated with reduced sRAGE.

Recent studies have identified molecular events characteristic of immunogenic cell death (ICD), including surface exposure of calreticulin (CRT), the heat shock proteins HSP70 and HSP90, the release of high-mobility group box protein 1 (HMGB1) and the release of ATP from dying cells. We investigated the potential of high hydrostatic pressure (HHP) to induce ICD in human tumor cells. HHP induced the rapid expression of HSP70, HSP90 and CRT on the cell surface. HHP also induced the release of HMGB1 and ATP. The interaction of dendritic cells (DCs) with HHP-treated tumor cells led to a more rapid rate of DC phagocytosis, upregulation of CD83, CD86 and HLA-DR and the release of interleukin IL-6, IL-12p70 and TNF-α. DCs pulsed with tumor cells killed by HHP induced high numbers of tumor-specific T cells. DCs pulsed with HHP-treated tumor cells also induced the lowest number of regulatory T cells. In addition, we found that the key features of the endoplasmic reticulum stress-mediated apoptotic pathway, such as reactive oxygen species production, phosphorylation of the translation initiation factor eIF2α and activation of caspase-8, were activated by HHP treatment. Therefore, HHP acts as a reliable and potent inducer of ICD in human tumor cells.

Receptor for advanced glycation end products (RAGE) is associated with invasion, metastasis, and poor prognosis in colorectal cancer. We studied the expression of RAGE in colorectal adenomas to elucidate the role of RAGE in cancer development. Expressions of RAGE and high-mobility group box-1 (HMGB1)/amphoterin RAGE ligand were examined in 96 colorectal adenomas using immunohistochemistry and in situ hybridization, respectively. Positivity and expression pattern of RAGE were compared with atypia, histological types, size, and HMGB1/amphoterin expression. Of 96 adenomas, 34 (35%) showed RAGE expression. RAGE positivity was significantly higher in adenomas with severe atypia (18/20, P<0.0001) and large-sized adenomas (-15 mm) (18/22, P<0.0001). RAGE expression showed three patterns: cytosolic (n=10), luminal (n=14), and membranous (n=10). Cytosolic pattern was associated with mild atypia and small size (-5 mm). Membranous pattern was associated with severe atypia, villous histological type, and co-expression with overexpressed HMGB1/amphoterin. These results suggest that RAGE expression, especially with membranous pattern, is associated with malignant potential of colorectal adenomas.

Pro-inflammatory cytokines are crucial for fighting infection and establishing immunity. Recently, other proteins, such as danger-associated molecular patterns (DAMPs), have also been appreciated for their role in inflammation and immunity. Following the formation and activation of multiprotein complexes, termed inflammasomes, two cytokines, IL-1β and IL-18, along with the DAMP High Mobility Group Box 1 (HMGB1), are released from cells. Although these proteins all lack classical secretion signals and are released by inflammasome activation, they each lead to different downstream consequences. This review examines how various inflammasomes promote the release of IL-1β, IL-18 and HMGB1 to combat pathogenic situations. Each of these effector molecules plays distinct roles during sterile inflammation, responding to viral, bacterial and parasite infection, and tailoring the innate immune response to specific threats.

Extracellular high-mobility group box 1 protein (HMGB1) triggers inflammatory events in the brain. We demonstrate that astrocytes, the main glial cells in the brain, acquire a specific reactive phenotype when exposed to HMGB1. This cell activation, which involves the receptor for advanced glycation end-products and the MAPK/ERK1/2 cascade, results in the transcriptional/translational induction of a restricted number of inflammatory mediators, including cyclooxygenase-2, matrix metalloproteinase-9, and several chemokines of the CC and CXC families. The mixture of factors released by HMGB1-reactive astrocytes displays a potent chemotactic activity on human monocytic cells. This study is the first to suggest that HMGB1/astrocyte interaction plays a specific functional role in the progression of inflammatory processes in the CNS by facilitating local leukocyte infiltration.

BACKGROUND

Toll-Like Receptor 4 (TLR4) signaling mediates early inflammation after cold ischemia-reperfusion (I/R). We hypothesized that the TLR4 coreceptor CD14, the intracellular adaptor proteins myeloid differentiation factor 88 (MyD88) and TIR domain-containing-adaptor inducing IFNbeta (TRIF) would be required for cold I/R induced inflammation. High mobility group box 1 (HMGB1) is a putative endogenous activator of TLR4. Therefore, we also assessed the contribution of HMGB1 in cold I/R induced inflammation.

METHODS

Syngeneic heart transplants were performed in mice deficient in CD14, MyD88, TRIF, or wild-type mice. In other experiments, anti-HMGB1 neutralizing antibody or control IgG was administered at reperfusion. Donor hearts were subjected to 2 hr of cold ischemia and retrieved after 3 hr of reperfusion.

RESULTS

After cold I/R, grafts revealed striking translocation of HMGB1 out of the nucleus in cardiac myocytes. Administration of an anti-HMGB1 neutralizing antibody resulted in reduced systemic interleukin (IL)-6, tumor necrosis factor alpha (TNFalpha), and intercellular adhesion molecule-1 (ICAM-1) messenger RNA (mRNA) levels (P< or =0.05). Compared with controls, CD14 knock-out (KO) mice exhibited significantly lower (P< or =0.05) systemic IL-6 and JE/monocyte chemotractant protein-1 levels after cold I/R. Intragraft TNFalpha and IL-1beta mRNA levels were also significantly lower (P< or =0.05) in CD14 KO grafts. MyD88 KO mice exhibited significantly lower (P< or=0.05) systemic IL-6 levels compared with control mice after cold I/R. Intragraft TNFalpha, IL-6, and ICAM-1 mRNA levels were also significantly lower (P< or =0.05) in MyD88 KO grafts. Significantly lower levels (P< or =0.05) of serum IL-6, monocyte chemotractant protein-1 as well as intragraft TNFalpha, IL-6, IL-1beta, and ICAM-1 were observed after cold I/R in TRIF deficient animals compared with controls.

CONCLUSIONS

CD14, MyD88, TRIF, and HMGB1 contribute to the inflammatory response that occurs after cold I/R. These results provide insight into the mechanisms of TLR4-mediated inflammation after cold I/R.

Neuroimmune gene induction is involved in many brain pathologies including addiction. Although increased expression of proinflammatory cytokines has been found in ethanol-treated mouse brain and rat brain slice cultures as well as in post-mortem human alcoholic brain, the mechanisms remain elusive. High-mobility group box 1 (HMGB1) protein is a nuclear protein that has endogenous cytokine-like activity. We previously found increased HMGB1 in post-mortem alcoholic human brain as well as in ethanol treated mice and rat brain slice cultures. The present study investigated the mechanisms for ethanol-induced release of HMGB1 and neuroimmune activation in a model of rat hippocampal-entorhinal cortex (HEC) brain slice cultures. Ethanol exposure triggered dose-dependent HMGB1 release, predominantly from neuronal cells. Inhibitors of histone deacetylases (HDACs) promoted nucleocytoplasmic mobilization of HDAC1/4 and HMGB1 resulting in increased total HMGB1 and acetylated HMGB1 release. Similarly, ethanol treatment was found to induce the translocation of HDAC1/4 and HMGB1 proteins from nuclear to cytosolic fractions. Furthermore, ethanol treatment reduced HDAC1/4 mRNA and increased acetylated HMGB1 release into the media. These results suggest decreased HDAC activity may be critical in regulating acetylated HMGB1 release from neurons in response to ethanol. Ethanol and HMGB1 treatment increased mRNA expression of proinflammatory cytokines TNFα and IL-1β as well as toll-like receptor 4 (TLR4). Targeting HMGB1 or microglial TLR4 by using siRNAs to HMGB1 and TLR4, HMGB1 neutralizing antibody, HMGB1 inhibitor glycyrrhizin and TLR4 antagonist as well as inhibitor of microglial activation all blocked ethanol-induced expression of proinflammatory cytokines TNFα and IL-1β. These results support the hypothesis that ethanol alters HDACs that regulate HMGB1 release and that danger signal HMGB1 as endogenous ligand for TLR4 mediates ethanol-induced brain neuroimmune signaling through activation of microglial TLR4. These findings provide new therapeutic targets for brain neuroimmune activation and alcoholism.

High-mobility group box 1 (HMGB1), a nonhistone nuclear protein, is released by macrophages into the extracellular milieu consequent to cellular activation. Extracellular HMGB1 has properties of a pro-inflammatory cytokine through its interaction with receptor for advanced glycation endproducts (RAGE) and/or toll-like receptors (TLR2 and TLR4). Although HMGB1 is highly expressed in macrophages and differentiating osteoclasts, its role in osteoclastogenesis remains largely unknown. In this report, we present evidence for a function of HMGB1 in this event. HMGB1 is released from macrophages in response to RANKL stimulation and is required for RANKL-induced osteoclastogenesis in vitro and in vivo. In addition, HMGB1, like other osteoclastogenic cytokines (e.g., TNFalpha), enhances RANKL-induced osteoclastogenesis in vivo and in vitro at subthreshold concentrations of RANKL, which alone would be insufficient. The role of HMGB1 in osteoclastogenesis is mediated, in large part, by its interaction with RAGE, an immunoglobin domain containing family receptor that plays an important role in osteoclast terminal differentiation and activation. HMGB1-RAGE signaling seems to be important in regulating actin cytoskeleton reorganization, thereby participating in RANKL-induced and integrin-dependent osteoclastogenesis. Taken together, these observations show a novel function of HMGB1 in osteoclastogenesis and provide a new link between inflammatory mechanisms and bone resorption.

The contribution of different DC subsets to effector and memory CD8(+) T cell generation during infection and the mechanism by which DCs controls these fate decisions is unclear. Here we demonstrated that the CD103(+) and CD11b(hi) migratory respiratory DC (RDC) subsets after influenza virus infection activated naive virus-specific CD8(+) T cells differentially. CD103(+) RDCs supported the generation of CD8(+) T effector (Teff) cells, which migrate from lymph nodes to the infected lungs. In contrast, migrant CD11b(hi) RDCs activated CD8(+) T cells characteristic of central memory CD8(+) T (CD8(+) Tcm) cells including retention within the draining lymph nodes. CD103(+) RDCs expressed CD24 at an elevated level, contributing to the propensity of this DC subpopulation to support CD8(+) Teff cell differentiation. Mechanistically, CD24 was shown to regulate CD8(+) T cell activation through HMGB1-mediated engagement of T cell RAGE. Thus, there is distribution of labor among DC subsets in regulating CD8(+) T cell differentiation.

The mobilization of dendritic cells (DCs) from peripheral tissues is critical for the establishment of T cell-dependent immune responses or tolerance, because the physical interaction of DCs with naive T cells takes place in the T cell areas of lymph nodes. The autocrine/paracrine release of the high mobility group box 1 (HMGB1) nuclear protein by DCs controls the outcome of the DC-T cell interaction, influencing the priming/Th1 polarization of naive T cells. We herein present evidence that the receptor for advanced glycation end products (RAGE), a multiligand member of the Ig superfamily of cell-surface molecules that acts as a receptor for HMGB1, plays a nonredundant role in DC homing to lymph nodes. We used noninvasive imaging by magnetic resonance and immunohistochemistry to track DCs after s.c. injection in the footpad of wild-type(+/+) or RAGE(-/-) mice. Maturing DCs expressing RAGE effectively migrated in both conditions. In contrast, RAGE(-/-) DCs failed to reach the draining popliteal lymph nodes of +/+ and -/- mice, indicating that the integrity of RAGE is required for DC mobilization. Thus the HMGB1-RAGE pathway is a checkpoint in DC maturation and function and a candidate for targeted therapies.

High mobility group box 1 (HMGB1) is widely expressed in cells of vertebrates in two forms: a nuclear "architectural" factor and a secreted inflammatory factor. During early brain development, HMGB1 displays a complex temporal and spatial distribution pattern in the central nervous system. It facilitates neurite outgrowth and cell migration critical for processes, such as forebrain development. During adulthood, HMGB1 serves to induce neuroinflammation after injury, such as lesions in the spinal cord and brain. Receptor for advanced glycation end products and Toll-like receptors signal transduction pathways mediate HMGB1-induced neuroinflammation and necrosis. Increased levels of endogenous HMGB1 have also been detected in neurodegenerative diseases. However, in Huntington's disease, HMGB1 has been reported to protect neurons through activation of apurinic/apyrimidinic endonuclease and 5'-flap endonuclease-1, whereas in other neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis, HMGB1 serves as a risk factor for memory impairment, chronic neurodegeneration, and progression of neuroinflammation. Thus, HMGB1 plays important and double-edged roles during neural development and neurodegeneration. The HMGB1-mediated pathological mechanisms have remained largely elusive. Knowledge of these mechanisms is likely to lead to therapeutic targets for neurological diseases.

Tissue fibrosis and chronic inflammation are common causes of progressive organ damage, including progressive renal disease, leading to loss of physiological functions. Recently, it was shown that Toll-like receptor 2 (TLR2) is expressed in the kidney and activated by endogenous danger signals. The expression and function of TLR2 during renal fibrosis and chronic inflammation has however not yet been elucidated. Therefore, we studied TLR2 expression in human and murine progressive renal diseases and explored its role by inducing obstructive nephropathy in TLR2(-/-) or TLR2(+/+) mice. We found that TLR2 is markedly upregulated on tubular and tubulointerstitial cells in patients with chronic renal injury. In mice with obstructive nephropathy, renal injury was associated with a marked upregulation and change in distribution of TLR2 and upregulation of murine TLR2 danger ligands Gp96, biglycan, and HMGB1. Notably, TLR2 enhanced inflammation as reflected by a significantly reduced influx of neutrophils and production of chemokines and TGF-beta in kidneys of TLR2(-/-) mice compared with TLR2(+/+) animals. Although, the obstructed kidneys of TLR2(-/-) mice had less interstitial myofibroblasts in the later phase of obstructive nephropathy, tubular injury and renal matrix accumulation was similar in both mouse strains. Together, these data demonstrate that TLR2 can initiate renal inflammation during progressive renal injury and that the absence of TLR2 does not affect the development of chronic renal injury and fibrosis.

Dendritic cells (DCs) initiate and control immune responses, participate in the maintenance of immunological tolerance and are pivotal players in the pathogenesis of autoimmunity. In patients with autoimmune disease and in experimental animal models of autoimmunity, DCs show abnormalities in both numbers and activation state, expressing immunogenic levels of costimulatory molecules and pro-inflammatory cytokines. Exogenous and endogenous danger signals activate DCs to stimulate the immune response. Classic endogenous danger signals are released, activated, or secreted by host cells and tissues experiencing stress, damage, and non-physiologic cell death; and are therefore referred to as damage-associated molecular patterns (DAMPs). Some DAMPs are released from cells, where they are normally sequestered, during necrosis (e.g., heat shock proteins, uric acid, ATP, HMGB1, mitochondria-derived molecules). Others are actively secreted, like Type I Interferons. Here we discuss important DAMPs in the context of autoimmunity. For some, there is a clear pathogenic link (e.g., nucleic acids and lupus). For others, there is less evidence. Additionally, we explore emerging danger signals. These include inorganic materials and man-made technologies (e.g., nanomaterials) developed as novel therapeutic approaches. Some nanomaterials can activate DCs and may trigger unintended inflammatory responses. Finally, we will review "homeostatic danger signals," danger signals that do not derive directly from pathogens or dying cells but are associated with perturbations of tissue/cell homeostasis and may signal pathological stress. These signals, like acidosis, hypoxia, and changes in osmolarity, also play a role in inflammation and autoimmunity.

The formation of advanced glycation end products (AGEs) is a result of the non-enzymatic reaction between sugars and free amino groups of proteins. AGEs, through interacting with their specific receptor for AGEs (RAGE), result in activation of pro-inflammatory states and are involved in numerous pathologic situations. The soluble form of RAGE (sRAGE) is able to act as a decoy to avoid interaction of RAGE with its pro-inflammatory ligands (AGEs, HMGB1, S100 proteins). sRAGE levels have been found to be decreased in chronic inflammatory diseases including atherosclerosis, diabetes, renal failure and the aging process. The use of measuring circulating sRAGEs may prove to be a valuable vascular biomarker and in this review, we describe the implications of sRAGE in inflammation and propose that this molecule may represent a future therapeutic target in chronic inflammatory diseases.

OBJECTIVE

HMGB1 (high-mobility group box-1) is a nuclear protein containing a consensus RB (retinoblastoma)-binding LXCXE motif. In this study, we studied the potential association of HMGB1 and RB and the in vitro and in vivo activities of HMGB1 in human breast cancer cells.

METHODS

The protein-protein interaction was determined by immunoprecipitation-Western blotting and glutathione-S-transferase capture assays; cell growth and radiosensitivity were examined by cell counts, MTT assay, and clonogenic assay; cell cycle progression and apoptosis were evaluated using flow cytometry; and the antitumor activity of HMGB1 was examined with tumor xenografts in nude mice.

RESULTS

HMGB1 was associated with RB via a LXCXE motif-dependent mechanism. HMGB1 enhanced the ability of RB for E2F and cyclin A transcription repression. The increased expression of HMGB1 conferred an altered phenotypes characterized by the suppression of cell growth; G1 arrest and apoptosis was induced in MCF-7 cells containing the wild-type retinoblastoma (Rb) gene, but showed no activities in BT-549 cells containing the Rb gene deletion. The HMGB1-induced apoptosis accompanied by caspase 3 activation and PARP (poly(ADP-ribose)polymerase) cleavage. HMGB1 elevated the radiosensitivity of breast cancer cells in both the MCF-7 and BT-549 cell lines. The enhanced expression of HMGB1 caused a suppression of growth of MCF-7 tumor xenografts in nude mice, while LXCXE-defective HMGB1 completely lost antitumor growth activity.

CONCLUSIONS

HMGB1 functions as a tumor suppressor and radiosensitizer in breast cancer. A HMGB1-RB interaction is critical for the HMGB1-mediated transcriptional repression, cell growth inhibition, G1 cell cycle arrest, apoptosis induction, and tumor growth suppression, but is not required for radiosensitization. Therefore, it may be possible to design new therapies for the treatment of breast cancer that exert their effects by modulating the HMGB1 and RB regulatory pathway and HMGB1-related gene therapy.

BACKGROUND

Chronic inflammation plays a key role in atherogenesis, which is followed by atheromatous plaque instability. High-mobility group box 1 is released by activated macrophages as a late-phase mediator during prolonged inflammation. However, the expression of high-mobility group box 1 and its effect on the production of C-reactive protein and matrix metalloproteinases, particularly on human vascular smooth muscle cells, still remain unknown.

RESULTS

Immunohistochemical studies revealed that high-mobility group box 1 was abundantly expressed in vascular smooth muscle cells of carotid and coronary atheromatous plaques, but not in atrophic vascular smooth muscle cells of fibrous plaques and normal medial vascular smooth muscle cells. Receptor for advanced glycation end products was also detected in vascular smooth muscle cells positive for high-mobility group box 1. Moreover, vascular smooth muscle cells positive for high-mobility group box 1 were found to express both C-reactive protein and matrix metalloproteinases (2, 3, and 9). Administration of exogenous high-mobility group box 1 to cultured vascular smooth muscle cells caused a marked elevation of C-reactive protein mRNA by reverse transcriptase-polymerase chain reaction and of C-reactive protein levels by enzyme-linked immunosorbent assay. Conversely, C-reactive protein also triggered a significant release of high-mobility group box 1 in vascular smooth muscle cell culture medium as determined by immunoblot.

CONCLUSIONS

Activated vascular smooth muscle cells are the source of high-mobility group box 1 in human advanced atherosclerotic lesions. High-mobility group box 1 directly stimulates the production of both C-reactive protein and matrix metalloproteinase through receptor for advanced glycation end product. These findings provide new evidence that high-mobility group box 1 produced by activated vascular smooth muscle cells may contribute to the progression and vulnerability of human atherosclerotic lesions toward rupture.

OBJECTIVE

The implication of innate immunity in type 1 diabetes development has long been proposed. High-mobility group box 1 (HMGB1), an evolutionarily conserved chromosomal protein, was recently recognized to be a potent innate inflammatory mediator when released extracellularly. We sought to test the hypothesis that HMGB1 acts as an innate immune mediator implicated in type 1 diabetes pathogenesis.

METHODS

Eight- and 12-week-old NOD mice were treated with an HMGB1 neutralizing antibody once a week until 25 weeks of age and monitored for insulitis progression and diabetes onset. The underlying mechanisms of HMGB1 regulation of autoimmune response were further explored.

RESULTS

During autoimmunity, HMGB1 can be passively released from damaged pancreatic beta-cells and actively secreted by islet infiltrated immune cells. Extracellular HMGB1 is potent in inducing NOD dendritic cell maturation and stimulating macrophage activation. Blockade of HMGB1 significantly inhibited insulitis progression and diabetes development in both 8- and 12-week-old NOD mice. HMGB1 antibody treatment decreased the number and maturation of pancreatic lymph node (PLN) CD11c(++)CD11b(+) dendritic cells, a subset of dendritic cells probably associated with autoantigen presentation to naïve T-cells, but increased the number for PLN CD4(+)Foxp3(+) regulatory T-cells. Blockade of HMGB1 also decreased splenic dendritic cell allo-stimulatory capability associated with increased tolergenic CD11c(+)CD8a(+) dendritic cells. Interestingly, the number of CD8(+)interferon-gamma(+) (Tc1) T-cells was increased in the PLNs and spleen after blockade of HMGB1, which could be associated with retarded migration of activated autoreactive T-cells into the pancreatic islets.

CONCLUSIONS

Extracellular HMGB1 functions as a potent innate immune mediator contributing to insulitis progression and diabetes onset.

Despite recent advances in antibiotic therapy and intensive care, sepsis remains a widespread problem in critically ill patients. The high mortality from sepsis is in part mediated by bacterial endotoxin, which stimulates macrophages/monocytes to sequentially release early (e.g., tumor necrosis factor, interleukin-1, and interferon-gamma) and late [e.g., high mobility group box 1 protein (HMGB1)] proinflammatory cytokines. Our discovery of HMGB1 as a late mediator of lethal systemic inflammation has initiated a new field of investigation for the development of experimental therapeutics. A popular Chinese herb, Angelica sinensis (also known as Dang Gui or Dong Quai) has been used traditionally for treating women with gynecological disorders (such as dysmenorrheal and hot flashes). Here we examined the effect of Angelica sinensis extract on endotoxin-induced HMGB1 release in vitro, and explored its therapeutic potential in animal models of lethal endotoxemia and sepsis [induced by cecal ligation and puncture (CLP)] in vivo. We demonstrated that a low-molecular-weight (<10 kDa) fraction of A. sinensis extract significantly attenuated endotoxin-induced HMGB1 release in part through interfering with its cytoplasmic translocation in macrophage cultures. Prophylactic administration of an aqueous extract of A. sinensis significantly attenuated systemic HMGB1 accumulation in vivo, and conferred a dose-dependent protection against lethal endotoxemia. Furthermore, delayed administration of A. sinensis extract beginning 24 h after CLP attenuated systemic HMGB1 accumulation, and significantly rescued mice from lethal sepsis. Taken together, these data suggest that A. sinensis contains water-soluble components that exert protective effects against lethal endotoxemia and experimental sepsis in part by attenuating systemic accumulation of a late proinflammatory cytokine, HMGB1.