Successful treatment of collagen-induced arthritis in mice and rats by targeting extracellular high mobility group box chromosomal protein 1 activity

High-mobility group box proteins modulate tumor necrosis factor-alpha expression in osteoclastogenesis via a novel deoxyribonucleic acid sequence

We have previously shown that mice lacking the TSH receptor (TSHR) exhibit osteoporosis due to enhanced osteoclast formation. The fact that this enhancement is not observed in double-null mice of TSHR and TNFalpha suggests that TNFalpha overexpression in osteoclast progenitors (macrophages) may be involved. It is unknown how TNFalpha expression is regulated in osteoclastogenesis. Here, we describe a receptor activator for nuclear factor-kappaB ligand (RANKL)-responsive sequence (CCG AGA CAG AGG TGT AGG GCC), spanning from -157 to -137 bp of the 5'-flanking region of the TNFalpha gene, which functions as a cis-acting regulatory element. We further show how RANKL treatment stimulates the high-mobility group box proteins (HMGB) HMGB1 and HMGB2 to bind the RANKL-responsive sequence and up-regulates TNFalpha transcription. Exogenous HMGB elicits the expression of cytokines, including TNFalpha, as well as osteoclast formation. Conversely, TSH inhibits the expression of HMGB and TNFalpha and the formation of osteoclasts. These results suggest that HMGB play a pivotal role in osteoclastogenesis. We also show a direct correlation between the expression of HMGB and TNFalpha and osteoclast formation in TSHR-null mice and TNFalpha-null mice. Taken together, we conclude that HMGB and TNFalpha play critical roles in the regulation of osteoclastogenesis and the remodeling of bone.

Oxaliplatin retains HMGB1 intranuclearly and ameliorates collagen type II-induced arthritis

Introduction

High mobility group box chromosomal protein 1 (HMGB1) is a nuclear protein that acts as a pro-inflammatory mediator following extracellular release. The protein is aberrantly expressed extracellularly in the settings of clinical and experimental synovitis. Therapy based on HMGB1 antagonists has shown encouraging results in experimental arthritis and warrants further scientific exploration using independent methods. In the present study we asked whether nuclear sequestration of HMGB1 preventing HMGB1 release would be beneficial for synovitis treatment.

Methods

Oxaliplatin-based therapy was evaluated in collagen type II-induced arthritis in DBA/1 mice by clinical scoring and immunostaining of articular tissue. Oxaliplatin is an antineoplastic platinum-based compound that generates DNA adducts which tightly bind HMGB1. Secretion and intracellular location of HMGB1 were assessed by a novel HMGB1-specific ELISPOT assay and immunofluorescent staining.

Results

Intraperitoneal injections of oxaliplatin in early collagen type II-induced arthritis trapped HMGB1 with a distinct biphasic response pattern. Oxaliplatin therapy showed beneficial results for approximately 1 week. Microscopic evaluation of synovitis during this period showed strong nuclear HMGB1 staining in the oxaliplatin treated animals with much lower quantities of extracellular HMGB1 when compared to control treated animals. Furthermore, cellular infiltration, as well as cartilage and bone damage, were all reduced in the oxaliplatin treated group. A dramatic and as yet unexplained clinical relapse occurred later in the oxaliplatin exposed animals, which coincided with a massive synovial tissue expression of extracellular HMGB1 in all treated animals. This rebound-like reaction was also accompanied by a significantly increased incidence of arthritis in the oxaliplatin treated group. These results indicate a distinct temporal and spatial relationship between the clinical course of disease and the cellular localization of HMGB1. Beneficial effects were noted when extracellular HMGB1 expression was low, while severe inflammation coincided with substantial extracellular synovial HMGB1 expression.

Conclusion

Therapeutic compounds like oxaliplatin and gold salts share a capacity to inhibit nuclear HMGB1 release and to ameliorate the course of synovial inflammation. These observations support the hypothesis that HMGB1 plays an important functional role in the pathogenesis of arthritis and may represent a novel target molecule for therapy.

A direct inhibitor of HMGB1 cytokine

HMGB1 and the recently described interleukin-33 (IL-33) are abundant chromatin-associated nuclear factors with potent proinflammatory cytokine activities. In this issue of Chemistry & Biology, Mollica et al. [1] report the identification of the first direct small-molecule inhibitor of HMGB1.

The induction of HMGB1 release from RAW 264.7 cells by transfected DNA

High mobility group protein 1 (HMGB1) is a non-histone nuclear protein that can activate innate immunity when in an extracellular location. As shown in in vitro studies, while polyinosinic-polycytidylic acid [poly (I:C)] and LPS, TLR3 and TLR4 ligands, respectively, can induce HMGB1 release from macrophages, CpG DNA, a TLR 9 ligand, does not. Since DNA displays distinct immunostimulatory activity when transfected into cells, we investigated whether transfected DNA can induce HMGB1 release from macrophages. In these experiments, using RAW 264.7 cells as model, we show that DNA, either natural DNA or synthetic oligonucleotides, can induce HMGB1 release when used to stimulate cells with the transfection reagent Lipofectamine 2000; release occurred irrespective of the intrinsic activity of the DNA. The induction of HMGB1 release by transfected DNA was dependent on IFN-beta as shown by the inhibitory effects of an antibody. In addition, JNK activation mediated HMGB1 release induced by a transfected phosphorothioate oligonucleotide but not by transfected natural DNA. Together, these findings indicate that transfected DNA can stimulate macrophages to release HMGB1 under conditions in which free DNA is inactive and suggest a role of DNA in inducing inflammation when bound to molecules that influence its entry into cells.

Morphological characterization of intra-articular HMGB1 expression during the course of collagen-induced arthritis

High-mobility group chromosomal box protein 1 (HMGB1) is a structural nuclear protein that promotes inflammation when present extracellularly. Aberrant, extracellular HMGB1 expression has been demonstrated in human and experimental synovitis. The aim of the present study was to elucidate the temporal and spatial expression of HMGB1 compared to that of the central mediators tumor necrosis factor (TNF) and interleukin-1-beta (IL-1β) during the course of collagen-induced arthritis. Thus, Dark Agouti rats were immunized with homologous type II collagen and synovial tissue specimens were obtained at various time points prior to and during the course of clinical arthritis. Local cytokine responses were assessed by immunohistochemistry and by in situ hybridization. We demonstrate a distinct nuclear expression of HMGB1 at early disease-preceding time points. Preceding clinical onset by a few days, cytoplasmic HMGB1 expression was evident in synoviocytes within the non-proliferative lining layer. Pronounced cytoplasmic and additional extracellular HMGB1 expression coincided with the progression of clinical disease. In advanced arthritis, the number of cells with cytoplasmic HMGB1 expression was quantitatively comparable to that of cells expressing TNF and IL-1β. Interestingly, although HMGB1 was abundantly expressed throughout the inflamed synovium at a protein level, upregulation of HMGB1 mRNA was restricted mainly to areas of cartilage and bone destruction. In conclusion, these new findings implicate a role for HMGB1 in both inducing and perpetuating inflammatory events of significant importance in the destructive processes in chronic arthritis.

Pivotal Advance: Inhibition of HMGB1 nuclear translocation as a mechanism for the anti-rheumatic effects of gold sodium thiomalate

Gold compounds such as gold sodium thiomalate (GST) can reduce the symptoms of rheumatoid arthritis (RA), although their mechanism of action is not well defined. As the proinflammatory mediator high mobility group box chromosomal protein 1 (HMGB1) may play a role in the pathogenesis of RA, we have performed in vitro studies to investigate whether GST inhibits HMGB1 release as the basis of its mode of action. Murine RAW 264.7 or human THP-1 macrophage cells were stimulated in culture with agents causing extracellular HMGB1 release, including LPS, IFN-gamma, polyinosinic:polycytidylic acid, IFN-beta, or NO in the presence of GST, ranging from 0 microM to 250 microM. Secretion and intracellular location of HMGB1 were assessed by Western blotting, HMGB1-specific ELISPOT assay, and immunofluorescent staining. In parallel, TNF and IFN-beta levels were analyzed by ELISPOT and/or ELISA. Supernatant NO production was analyzed by the Griess method. At pharmacologically relevant doses, GST inhibited the extracellular release of HMGB1 from activated macrophages and caused the nuclear retention of this protein; in contrast, no effects were observed on the secretion or production of TNF. Release of the key endogenous mediators of HMGB1 translocation, IFN-beta and NO, was inhibited by GST. This inhibition required gold, as sodium thiomalate did not affect the responses measured. Furthermore, gold chloride also inhibited release of HMGB1. Together, these results suggest a new mechanism for the anti-rheumatic effects of gold salts in RA and the potential of drugs, which interfere with intracellular HMGB1 transport mechanisms, as novel agents to treat RA.

Multiple effects of high mobility group box protein 1 in skeletal muscle regeneration

OBJECTIVE

High mobility group box 1 protein (HMGB1) is a cytokine released by necrotic and inflammatory cells in response to injury. We examined the role of HMGB1 in skeletal muscle regeneration after hindlimb ischemia.

METHODS AND RESULTS

Unilateral hindlimb ischemia was induced in mice by femoral artery dissection. HMGB1 levels increased in regenerating skeletal muscle and the blockade of endogenous HMGB1 by the administration of its truncated form, the BoxA, resulted in the reduction of vessel density. In contrast, intramuscular administration of HMGB1 enhanced perfusion and increased the number of regenerating fibers. To separately study the myogenic and the angiogenic effects of HMGB1, in vitro experiments were performed with isolated myoblasts and endothelial cells. Myoblasts were found to express the HMGB1 receptor RAGE and TLR4 which were downregulated during in vitro myogenic differentiation. HMGB1 was extracellularly released by differentiated myoblasts and exerted a chemotactic activity on myogenic cells. This effect was partially dependent on RAGE and was inhibited by BoxA treatment. Finally, HMGB1 stimulated tubular-like structure formation by endothelial cells through the activation of extracellular signal-regulated kinase (ERK) and JNK signal transduction pathways.

CONCLUSIONS

HMGB1 plays a role in skeletal muscle regeneration modulating, in an autocrine-paracrine manner, myoblast and endothelial cell functions.

The genetic variation of the human HMGB1 gene

High-mobility group box 1 protein (HMGB1) is a nuclear DNA-binding protein, which also functions as a pleiotropic cytokine, implicated in the pathology of several different immune-mediated diseases. The purpose of this study was to examine the HMGB1 gene for putative polymorphisms in 103 healthy Caucasian Danish blood donors. A total of six polymorphisms and four mutations were identified in the HMGB1 gene. Subsequent MatInspector estimation revealed that several polymorphisms might have a potential regulatory impact on HMGB1 transcription. This study has characterized genetic variations in the HMGB1 gene locus, which may have a regulating role in the expression of HMGB1, providing the basis for molecular investigations of the HMGB1 gene in different disease settings.

Cholinergic anti-inflammatory pathway activity and High Mobility Group Box-1 (HMGB1) serum levels in patients with rheumatoid arthritis

High Mobility Group Box-1 (HMGB1) is a cytokine implicated in the pathogenesis of rheumatoid arthritis (RA) and other inflammatory diseases. The cholinergic anti-inflammatory pathway, a vagus nerve-dependent mechanism, inhibits HMGB1 release in experimental disease models. Here, we examine the relationship between vagus nerve activity and HMGB1 in patients with RA. We compared RR interval variability, an index of cardiac vagal modulation, HMGB1 and hsCRP serum levels, and disease activity scores in thirteen RA patients and eleven age- and sex-matched controls. In RA patients, serum levels of HMGB1 and hsCRP were elevated as compared with controls (HMGB1=71 ng/mL [45-99] vs. 18 ng/mL [0-40], P<0.0001; hsCRP=14.5 mg/L [0.7-59] vs. 1 mg/L [0.4-2.9], P<0.001). RR interval variability in RA patients was significantly decreased as compared with controls (HF=38 msec2 [14-80] vs. 288 msec2 [38-364], P<0.0001; rMSSD=20.9+/-9.79 msec, 52.6+/-35.3 msec, P<0.01). HMGB1 levels and RR interval variability were significantly related (rho=-0.49, P<0.01). HMGB1 serum levels significantly correlated with disease activity scores (DAS-28) in patients with RA (P=0.004). The study design does not enable a determination of causality, but the results are consistent with the hypothesis that decreased cholinergic anti-inflammatory pathway activity is associated with increased HMGB1 levels in patients with RA.

Mechanisms of disease: a 'DAMP' view of inflammatory arthritis

Innate immunity achieves our primary host defense by recognizing invading microorganisms through pathogen-associated molecular patterns (PAMPs) and by reacting to tissue damage signals called damage-associated molecular patterns (DAMPs). DAMP molecules, including high mobility group box 1 protein (HMGB-1), heat-shock proteins (HSPs), uric acid, altered matrix proteins, and S100 proteins, represent important danger signals that mediate inflammatory responses through the receptor for advanced glycation end-products (RAGE, also known as AGER) and Toll-like receptors, after release from activated or necrotic cells. The terms 'alarmins' and 'endokines' have also been proposed for DAMP molecules. A prototypic DAMP molecule, the nuclear protein HMGB-1, is either passively released by necrotic cells or actively secreted with delay by activated cells. S100A8, S100A9, and S100A12 are calcium-binding proteins expressed in the cytoplasm of phagocytes. They are rapidly secreted by activated monocytes or neutrophils, which are abundant in inflamed synovial tissue. HSPs are involved in the crosstalk between innate and adaptive immune systems, and primarily mediate immune regulatory functions. Multiple positive feedback loops between DAMPs and PAMPs and their overlapping receptors temporally and spatially drive these processes and may represent the molecular basis for the observation that infections, as well as nonspecific stress factors, can trigger flares in rheumatic diseases.

Anti-high mobility group box 1 monoclonal antibody ameliorates brain infarction induced by transient ischemia in rats

The high mobility group box-1 (HMGB1), originally identified as an architectural nuclear protein, exhibits an inflammatory cytokine-like activity in the extracellular space. Here we show that treatment with neutralizing anti-HMGB1 monoclonal antibody (mAb; 200 microg, twice) remarkably ameliorated brain infarction induced by 2-h occlusion of the middle cerebral artery in rats, even when the mAb was administered after the start of reperfusion. Consistent with the 90% reduction in infarct size, the accompanying neurological deficits in locomotor function were significantly improved. Anti-HMGB1 mAb inhibited the increased permeability of the blood-brain barrier, the activation of microglia, the expression of TNF-alpha and iNOS, and suppressed the activity of MMP-9, whereas it had little effect on blood flow. Intracerebroventricular injection of HMGB1 increased the severity of infarction. Immunohistochemical study revealed that HMGB1 immunoreactivity in the cell nuclei decreased or disappeared in the affected areas, suggesting the release of HMGB1 into the extracellular space. These results indicate that HMGB1 plays a critical role in the development of brain infarction through the amplification of plural inflammatory responses in the ischemic region and could be an outstandingly suitable target for the treatment. Intravenous injection of neutralizing anti-HMGB1 mAb provides a novel therapeutic strategy for ischemic stroke.

Cholinergic anti-inflammatory pathway activity and High Mobility Group Box-1 (HMGB1) serum levels in patients with rheumatoid arthritis

High Mobility Group Box-1 (HMGB1) is a cytokine implicated in the pathogenesis of rheumatoid arthritis (RA) and other inflammatory diseases. The cholinergic anti-inflammatory pathway, a vagus nerve-dependent mechanism, inhibits HMGB1 release in experimental disease models. Here, we examine the relationship between vagus nerve activity and HMGB1 in patients with RA. We compared RR interval variability, an index of cardiac vagal modulation, HMGB1 and hsCRP serum levels, and disease activity scores in thirteen RA patients and eleven age- and sex-matched controls. In RA patients, serum levels of HMGB1 and hsCRP were elevated as compared with controls (HMGB1=71 ng/mL [45-99] vs. 18 ng/mL [0-40], P<0.0001; hsCRP=14.5 mg/L [0.7-59] vs. 1 mg/L [0.4-2.9], P<0.001). RR interval variability in RA patients was significantly decreased as compared with controls (HF=38 msec2 [14-80] vs. 288 msec2 [38-364], P<0.0001; rMSSD=20.9+/-9.79 msec, 52.6+/-35.3 msec, P<0.01). HMGB1 levels and RR interval variability were significantly related (rho=-0.49, P<0.01). HMGB1 serum levels significantly correlated with disease activity scores (DAS-28) in patients with RA (P=0.004). The study design does not enable a determination of causality, but the results are consistent with the hypothesis that decreased cholinergic anti-inflammatory pathway activity is associated with increased HMGB1 levels in patients with RA.

The relationship between apoptosis and high-mobility group protein 1 release from murine macrophages stimulated with lipopolysaccharide or polyinosinic-polycytidylic acid

High-mobility group protein 1 (HMGB1) is a nonhistone nuclear protein whose function depends on cellular location. Inside the cell, HMGB1 modulates a variety of important cellular processes, including transcription, whereas outside the cell, HMGB1 acts as a cytokine that can promote inflammation and mediate sepsis and arthritis in animal models. In in vitro studies, proinflammatory molecules such as LPS, lipoteichoic acid, polyinosinic-polycytidylic acid (poly(I:C)), TNF-alpha, and type I and II IFNs can induce HMGB1 release from macrophages. Although these agents can activate cells, they can also induce apoptosis under certain circumstances. Therefore, because of evidence that apoptotic as well as necrotic cells can contribute to HMGB1-mediated events in sepsis, we have investigated the relationship between apoptosis and HMGB1 release in macrophages and other cells. In these experiments, using RAW 264.7 cells as a model, LPS and poly(I:C) caused HMGB1 release into the medium whereas CpG ODN failed to induce this response. With both LPS and poly(I:C), the extent of HMGB1 release correlated with the occurrence of apoptosis as measured by caspase 3 activation, lactate dehydrogenase release, and TUNEL staining. Similar results were obtained with primary murine macrophages as well as human Jurkat T cells. For Jurkat cells, poly(I:C) and NO donors induced apoptosis as well as HMGB1 release. Together, these results indicate that HMGB1 release from macrophages is correlated with the occurrence of apoptosis and suggest that these processes reflect common mechanisms and can occur concomitantly.

Masquerader: High Mobility Group Box-1 and Cancer

Since its identification a third of a century ago, the high-mobility group box-1 (HMGB1) protein has been linked to varied diverse cellular processes, including release from necrotic cells and secretion by activated macrophages engulfing apoptotic cells. Initially described as solely chromatin-associated, HMGB1 was additionally discovered in the cytoplasm of several types of cultured mammalian cells 6 years later. In addition to its intracellular role, HMGB1 has been identified extracellularly as a putative leaderless cytokine and differentiation factor. In the years since its discovery, HMGB1 has also been implicated in disease states, including Alzheimer's, sepsis, ischemia-reperfusion, arthritis, and cancer. In cancer, overexpression of HMGB1, particularly in conjunction with its receptor for advanced glycation end products, has been associated with the proliferation and metastasis of many tumor types, including breast, colon, melanoma, and others. This review focuses on current knowledge and speculation on the role of HMGB1 in the development of cancer, metastasis, and potential targets for therapy.

Mechanisms of Disease: the role of high-mobility group protein 1 in the pathogenesis of inflammatory arthritis

High-mobility group protein 1 (HMG1) is a nonhistone nuclear protein that is a prototype of a dual-function alarmin whose immune activity is dependent upon its cellular location. Inside the cell, HMG1 binds to DNA and has a role in transcriptional regulation. Outside the cell, HMG1 acts as a cytokine and has activities that resemble those of tumor necrosis factor. The cytokine activities of HMG1 become manifest when this protein translocates from the nucleus to the cytoplasm and, eventually, into the external milieu; this translocation occurs during cell activation and cell death. Given its cytokine activity, HMG1 has been implicated in the pathogenesis of a broad range of immune-mediated diseases including arthritis. The role for this protein in arthritis was established by observations of the expression of HMG1 in synovial tissue of patients with rheumatoid arthritis as well as in the joints of animals used to model arthritis. Furthermore, in the mouse model of collagen-induced arthritis, treatment with antibodies to HMG1 or to an inhibitory domain of HMG1 can attenuate joint inflammation and damage. These studies identify a novel pathway in the pathogenesis of inflammatory arthritis, as well as a new target for biologic therapy.

HMGB1 is a bone-active cytokine

High mobility group box 1 (HMGB1) is a chromatin protein that acts as an immunomodulatory cytokine upon active release from myeloid cells. HMGB1 is also an alarmin, an endogenous molecule released by dying cells that acts to initiate tissue repair. We have previously reported that osteoclasts and osteoblasts release HMGB1 and release by the latter is regulated by parathyroid hormone (PTH), an agent of bone remodeling. A recent study suggests that HMGB1 acts as a chemotactic agent to osteoclasts and osteoblasts during endochondral ossification. To explore the potential impact of HMGB1 in the bone microenvironment and its mechanism of release by osseous cells, we characterized the effects of recombinant protein (rHMGB1) on multiple murine bone cell preparations that together exhibit the various cell phenotypes present in bone. We also inquired whether apoptotic bone cells release HMGB1. rHMGB1 enhanced the RANKL/OPG steady state mRNA ratio and dramatically augmented the release of tumor necrosis factor-alpha (TNFalpha) and interleukin-6 (IL6) in osteoblastogenic bone marrow stromal cell (BMSC) cultures but not in the calvarial-derived MC3T3-E1 cells. Interestingly, rHMGB1 promoted GSK-3beta phosphorylation in MC3T3-E1 cells but not in BMSCs. Apoptotic bone cells released HMGB1, including MLO-Y4 osteocyte-like cells. MLO-Y4 release of HMGB1 was coincident with caspase-3 cleavage. Furthermore, the anti-apoptotic action of PTH on MC3T3-E1 cells correlated with the observed decrease in HMGB1 release. Our data suggest that apoptotic bone cells release HMGB1, that within the marrow HMGB1 is a bone resorption signal, and that intramembraneous and endochondral osteoblasts exhibit differential responses to this cytokine.

HMGB1 signals through toll-like receptor (TLR) 4 and TLR2

In response to bacterial endotoxin (e.g., LPS) or endogenous proinflammatory cytokines (e.g., TNF and IL-1beta), innate immune cells release HMGB1, a late cytokine mediator of lethal endotoxemia and sepsis. The delayed kinetics of HMGB1 release makes it an attractive therapeutic target with a wider window of opportunity for the treatment of lethal systemic inflammation. However, the receptor(s) responsible for HMGB1-mediated production of proinflammatory cytokines has not been well characterized. Here we demonstrate that in human whole blood, neutralizing antibodies against Toll-like receptor 4 (TLR4, but not TLR2 or receptor for advanced glycation end product) dose-dependently attenuate HMGB1-induced IL-8 release. Similarly, in primary human macrophages, HMGB1-induced TNF release is dose-dependently inhibited by anti-TLR4 antibodies. In primary macrophages from knockout mice, HMGB1 activates significantly less TNF release in cells obtained from MyD88 and TLR4 knockout mice as compared with cells from TLR2 knockout and wild-type controls. However, in human embryonic kidney 293 cells transfected with TLR2 or TLR4, HMGB1 effectively induces IL-8 release only from TLR2 overexpressing cells. Consistently, anti-TLR2 antibodies dose-dependently attenuate HMGB1-induced IL-8 release in human embryonic kidney/TLR2-expressing cells and markedly reduce HMGB1 cell surface binding on murine macrophage-like RAW 264.7 cells. Taken together, our data suggest that there is a differential usage of TLR2 and TLR4 in HMGB1 signaling in primary cells and in established cell lines, adding complexity to studies of HMGB1 signaling which was not previously expected.

DAMPs, PAMPs and alarmins: all we need to know about danger

Multicellular animals detect pathogens via a set of receptors that recognize pathogen-associated molecular patterns (PAMPs). However, pathogens are not the only causative agents of tissue and cell damage: trauma is another one. Evidence is accumulating that trauma and its associated tissue damage are recognized at the cell level via receptor-mediated detection of intracellular proteins released by the dead cells. The term "alarmin" is proposed to categorize such endogenous molecules that signal tissue and cell damage. Intriguingly, effector cells of innate and adaptive immunity can secrete alarmins via nonclassical pathways and often do so when they are activated by PAMPs or other alarmins. Endogenous alarmins and exogenous PAMPs therefore convey a similar message and elicit similar responses; they can be considered subgroups of a larger set, the damage-associated molecular patterns (DAMPs).

Human malarial disease: a consequence of inflammatory cytokine release

Malaria causes an acute systemic human disease that bears many similarities, both clinically and mechanistically, to those caused by bacteria, rickettsia, and viruses. Over the past few decades, a literature has emerged that argues for most of the pathology seen in all of these infectious diseases being explained by activation of the inflammatory system, with the balance between the pro and anti-inflammatory cytokines being tipped towards the onset of systemic inflammation. Although not often expressed in energy terms, there is, when reduced to biochemical essentials, wide agreement that infection with falciparum malaria is often fatal because mitochondria are unable to generate enough ATP to maintain normal cellular function. Most, however, would contend that this largely occurs because sequestered parasitized red cells prevent sufficient oxygen getting to where it is needed. This review considers the evidence that an equally or more important way ATP deficiency arises in malaria, as well as these other infectious diseases, is an inability of mitochondria, through the effects of inflammatory cytokines on their function, to utilise available oxygen. This activity of these cytokines, plus their capacity to control the pathways through which oxygen supply to mitochondria are restricted (particularly through directing sequestration and driving anaemia), combine to make falciparum malaria primarily an inflammatory cytokine-driven disease.

The role of IFN-alpha and nitric oxide in the release of HMGB1 by RAW 264.7 cells stimulated with polyinosinic-polycytidylic acid or lipopolysaccharide

High mobility group protein 1 (HMGB1) is a nonhistone nuclear protein with a dual function. Inside the cell, HMGB1 binds to DNA and modulates a variety of processes, including transcription. Outside the cell, HMGB1 displays cytokine activity and can promote inflammation, serving as a mediator in models of shock and arthritis. In in vitro studies, proinflammatory molecules such as LPS, lipoteichoic acid, dsRNA, TNF-alpha, and IFN-gamma can induce HMGB1 release from macrophages. To define further the release process, we investigated the role of the downstream mediators, NO and IFN-alpha, in the release of HMGB1 from RAW 264.7 macrophage cells stimulated with LPS or polyinosinic-polycytidylic acid (poly(I:C)). In these experiments, 1400W, an inhibitor of NO production by the inducible NO synthase, reduced HMGB1 release stimulated by LPS, but not poly(I:C), whereas neutralizing IFN-alpha prevented HMGB1 release induced by poly(I:C), but not LPS. The addition of an NO donor and rIFN-alpha to RAW 264.7 cells caused HMGB1 release. Furthermore, inhibition of JNK activation attenuated HMGB1 release induced by either LPS or poly(I:C). Analysis of bone marrow-derived macrophages stimulated by LPS or poly(I:C) showed patterns of HMGB1 release similar to those of RAW 264.7 cells. Together, these experiments indicate that, although both LPS and poly(I:C) induce HMGB1 release from RAW 264.7 cells and murine macrophages, the response is differentially dependent on NO and IFN-alpha.

HMGB1-secreting capacity of multiple cell lineages revealed by a novel HMGB1 ELISPOT assay

High mobility group box protein 1 (HMGB1) exerts different biological functions dependent on its cellular localization. Nuclear HMGB1 maintains chromatin architecture and is required for undisturbed transcription activity, and extracellularly released HMGB1 mediates inflammation and tissue regeneration. A present paucity of readily accessible methods to quantify released HMGB1 represents a problem concerning the exploration of HMGB1 biology. We have now developed a HMGB1-specific ELISPOT assay enabling enumeration of individual HMGB1-releasing cells. The method also allows automated, semiquantitative assessment of released HMGB1 by evaluating areas of single HMGB1 spots. Actively secreted HMGB1 as well as cells passively releasing the protein following necrotic cell death are visualized distinctly using this ELISPOT assay. Kinetics of HMGB1 secretion after different stimuli was studied using cell lines of various lineages. IFN-gamma already induced substantial HMGB1 secretion from the monocytic cell line RAW 264.7 within 24 h and even more so after 48 h. LPS only stimulated a modest HMGB1 release within 24 h, but this increased considerably by 48 h. TNF-induced HMGB1 release was unexpectedly low. Mast cells, which share the secretory, lysosomal pathway with macrophages/monocytes, did not secrete HMGB1 in response to any studied mode of activation. Most transformed cells overexpress HMGB1, but the ELISPOT assay revealed that all transformed cell lines will not actively secrete the protein. We believe the ELISPOT method provides a novel tool to study pathways promoting or inhibiting HMGB1 secretion.

The lectin-like domain of thrombomodulin interferes with complement activation and protects against arthritis

BACKGROUND

Thrombomodulin (TM) is predominantly a vascular endothelial cell plasma membrane glycoprotein that, via distinct structural domains, interacts with multiple ligands, thereby modulating coagulation, fibrinolysis, complement activation, inflammation and cell proliferation. We previously reported that by mediating signals that interfere with mitogen-activated protein kinase and nuclear factor kappaB pathways, the amino-terminal C-type lectin-like domain of TM has direct anti-inflammatory properties.

METHODS

In the current study, we use murine models of acute inflammatory arthritis and biochemical approaches to assess the mechanism by which the lectin-like domain of TM modifies disease progression.

RESULTS

Mice lacking the lectin-like domain of TM (TM(LeD/LeD)mice) develop inflammatory arthritis that is more rapid in onset and more severe than that developed in their wildtype counterparts. In two models of arthritis, treatment of mice with recombinant soluble lectin-like domain of TM significantly suppresses clinical evidence of disease and diminishes monocyte/macrophage infiltration into the synovium, with weaker expression of the pro-inflammatory high mobility group box chromosomal protein 1. While thrombin-TM mediated activation of thrombin activatable fibrinolysis inhibitor inactivates complement factors C3a and C5a, we show that TM has a second independent mechanism to regulate complement: the lectin-like domain of TM directly interferes with complement activation via the classical and lectin pathways.

CONCLUSIONS

These data extend previous insights into the mechanisms by which TM modulates innate immunity, and highlight its potential as a therapeutic target for inflammatory diseases.

Recombinant HMGB1 with cytokine-stimulating activity

We describe methods for the isolation, purification, and characterization of full-length high-mobility group box 1 (HMGB1) and truncated mutants expressed in bacteria and in mammalian Chinese Hamster Ovary (CHO) cells. HMGB1 is an abundant nuclear and cytoplasmic protein, highly conserved across species and widely distributed in eukaryotic cells from yeast to man. As a ubiquitous nuclear DNA binding protein, HMGB1 binds DNA, facilitates gene transcription, and stabilizes nucleosome structure. In addition to these intracellular roles, HMGB1 can be released into the extracellular milieu by activated innate immune cells (i.e., macrophages, monocytes) and functions as a mediator of lethal endotoxemia and sepsis. The proinflammatory cytokine activity of HMGB1 has become an intense area of research and recombinant protein can be a useful tool to probe HMGB1 functions. Due to its dipolar charged properties, HMGB1 isolated by some methods can be contaminated with bacterial products (such as CpG DNA or lipopolysaccharide [LPS]) that may interfere with immunological analyses. Here we report our newly developed methods for the isolation and purification of biologically active HMGB1 from bacteria or mammalian CHO cells that is essentially free of contaminants. This strategy provides an important advance in methodology to facilitate future HMGB1 studies.

Rapamycin-induced inhibition of Janus kinase/signal transducer and activator of transcription pathway affects expression of high-mobility group box 1 in rats with acute liver injury

AIM: To investigate the effect of rapamycin (RPM) on the expression of high-mobility group box 1 (HMGB1) in rats with acute liver injury (ALI) by inhibiting Janus kinase/signal transducer and activator of transcription pathway.

METHODS: Wistar rats were randomly divided into normal control group (n = 30), ALI group (n = 30) and RPM treatment group (n = 30). ALI was induced by intraperitoneal administration of D-Galactosamine/lipopolysaccharide (D-Galn/LPS). The animals in each group were sacrificed at different time points to collect the blood and hepatic tissue samples for the detection of alanine aminotransferase (ALT) level and HMGB1 expression, respectively.

RESULTS: In comparison with that in the normal controls (1.00 ± 0.02), HMGB1 expression was significantly increased in liver tissues 24, 48 and 72 h after ALI (3.12 ± 0.06, 3.9 ± 0.08, 2.83 ± 0.04, respectively, t = 16.01, 3.86, 10.46, all P < 0.01), and serum ALT levels were markedly elevated. The expression of HMGB1 in liver tissues was dramatically inhibited 24, 48 and 72 h after RPM treatment as compared with that in ALI group (1.67 ± 0.05 vs 3.12 ± 0.06; 1.93 ± 0.06 vs 3.9 ± 0.08; 1.47 ± 0.04 vs 2.83 ± 0.04; t = 20.11, 41.90, 26.02, all P < 0.01). In addition, serum ALT levels were also markedly reduced during 24-72 h after RPM treatment (P < 0.01). HMGB1 expression was positively correlated with ALT level (r = 0.741, P < 0.01).

CONCLUSION: The activation of JAK/STAT pathway may be involved in the up-regulation of HMGB1 expression in ALI. RPM treatment can markedly down-regulates HMGB1 expression and attenuates ALI.

The role of high mobility group box-1 protein in severe sepsis

PURPOSE OF REVIEW

Despite medical advances, mortality in severe sepsis remains high. As our understanding of the innate immune system has expanded, clinical trials have focused on inhibiting cytokines present early in the infectious process such as interleukin-1 and tumor necrosis factor-alpha, although with disappointing results. There is evidence that the nuclear protein high mobility group box-1 protein, when released extracellularly, acts as a persistent mediator of sepsis and is therefore a promising candidate for therapeutic intervention. This review summarizes current knowledge of the protein and highlights recent relevant findings.

RECENT FINDINGS

High mobility group box-1 protein may be released into the circulation either due to necrosis of cells or by active release from macrophages and endothelial cells. Models of experimental sepsis in mice have shown a strong association between extracellular high mobility group box-1 protein and lethality. Treatments against the biological activities of high mobility group box-1 protein reduce lethality in these models. Other studies have shown high mobility group box-1 protein as a key regulator in acute and chronic inflammation. Recent findings confirm that high mobility group box-1 protein is persistently elevated in human patients with severe sepsis.

SUMMARY

Despite all efforts, mortality in severe sepsis remains high. A massive amount of evidence indicates high mobility group box-1 protein as a delayed and important propagator of inflammation. Recent studies confirm persisting high levels of high mobility group box-1 protein in serum up to 1 week after hospitalization. Reducing levels of the protein by anti-high mobility group box-1 protein treatment may be one way to moderate uncontrolled inflammation seen in sepsis.

Inflammation-induced chondrocyte hypertrophy is driven by receptor for advanced glycation end products

The multiligand receptor for advanced glycation end products (RAGE) mediates certain chronic vascular and neurologic degenerative diseases accompanied by low-grade inflammation. RAGE ligands include S100/calgranulins, a class of low-molecular-mass, calcium-binding polypeptides, several of which are chondrocyte expressed. Here, we tested the hypothesis that S100A11 and RAGE signaling modulate osteoarthritis (OA) pathogenesis by regulating a shift in chondrocyte differentiation to hypertrophy. We analyzed human cartilages and cultured human articular chondrocytes, and used recombinant human S100A11, soluble RAGE, and previously characterized RAGE-specific blocking Abs. Normal human knee cartilages demonstrated constitutive RAGE and S100A11 expression, and RAGE and S100A11 expression were up-regulated in OA cartilages studied by immunohistochemistry. CXCL8 and TNF-alpha induced S100A11 expression and release in cultured chondrocytes. Moreover, S100A11 induced cell size increase and expression of type X collagen consistent with chondrocyte hypertrophy in vitro. CXCL8-induced, IL-8-induced, and TNF-alpha-induced but not retinoic acid-induced chondrocyte hypertrophy were suppressed by treatment with soluble RAGE or RAGE-specific blocking Abs. Last, via transfection of dominant-negative RAGE and dominant-negative MAPK kinase 3, we demonstrated that S100A11-induced chondrocyte type X collagen expression was dependent on RAGE-mediated p38 MAPK pathway activation. We conclude that up-regulated chondrocyte expression of the RAGE ligand S100A11 in OA cartilage, and RAGE signaling through the p38 MAPK pathway, promote inflammation-associated chondrocyte hypertrophy. RAGE signaling thereby has the potential to contribute to the progression of OA.

Cloning and characterization of a high mobility group box 1 (HMGB1) homologue protein from Schistosoma mansoni

Mammalian homologue of high mobility group box chromatin protein (HMGB) 1 was identified and cloned from human parasites, Schistosoma mansoni and S. haematobium. Sequence analyses showed that the parasite HMGB1s has 35-40% identity to human and rodent HMGB1s, and 33% identity to Caenorhabditis elegans HMGB1. Parasite HMGB1s also contains an A box and B box domain similar to mammalian HMGB1, however, it lacks the C-terminal tail that is present in mammalian HMGB1s. Analysis of the expression of HMGB1 in various life cycle stages of S. mansoni reveal S. mansoni HMGB1 (SmHMGB1) as a stage-specific protein, expressed abundantly in egg and adult female stages and at moderate levels in skin-stage schistosomula. Significant levels of SmHMGB1 were also present in excretory secretions of egg stages. Subsequent characterization studies showed that SmHMGB1 is a potent inducer of pro-inflammatory cytokines such as TNFalpha, IL-1Ralpha, IL-2Ralpha, IL-6, IL-13, IL-13Ralpha1, IL-15 and MIP-1alpha from mouse peritoneal macrophages. Pro-inflammatory activity, especially production of TNFalpha-inducing activity, appears to be a function of the B box domain protein. This was confirmed by both real-time reverse transcription PCR and by cytokine ELISA. Thus, results presented in this study suggest that SmHMGB1 may be a key molecule in the development of host inflammatory immune responses associated with schistosomiasis.

The phase 2 enzyme inducers ethacrynic acid, DL-sulforaphane, and oltipraz inhibit lipopolysaccharide-induced high-mobility group box 1 secretion by RAW 264.7 cells

The diuretic ethacrynic acid (EA) has been shown to inhibit signaling by the proinflammatory transcription factor nuclear factor-kappaB (NF-kappaB). Accordingly, we sought to determine whether this compound is capable of inhibiting the release of cytokines [interleukin (IL)-6 and IL-10] and NO from RAW 264.7 murine macrophage-like cells stimulated with lipopolysaccharide (LPS). Additionally, we sought to determine whether EA can inhibit secretion of high-mobility group box 1 (HMGB1), a nuclear protein that is secreted by immunostimulated macrophages and functions in the extracellular milieu as a proinflammatory mediator. In a concentration-dependent manner, EA inhibited secretion of IL-6, IL-10, nitric oxide, and HMGB1. As expected, EA inhibited NF-kappaB DNA binding in LPS-stimulated RAW 264.7 cells. Treating these cells with pyrrolidine dithiocarbamate, SN50 (amino acid sequence AAVALLPAVLLALLAPVQRKRQKLMP) or 5-(thien-3-yl)-3-aminothiophene-2-carboxamide (SC-514) also inhibited LPS-induced NF-kappaB DNA binding, but these compounds failed to inhibit LPS-induced HMGB1 secretion. These findings suggested that inhibition of HMGB1 secretion by EA might occur via a mechanism unrelated to the NF-kappaB signaling pathway. Because EA is an electrophilic compound that is known to be capable of inducing expression of so-called phase 2 proteins, we sought to determine whether two other phase 2 enzyme inducers, oltipraz and DL-sulforaphane, also are capable of inhibiting HMGB1 release from immunostimulated macrophages. Incubating RAW 264.7 cells with either oltipraz or DL-sulforaphane inhibited LPS-induced HMGB1 secretion. Moreover, both EA and DL-sulforaphane inhibited relocalization of nuclear HMGB1 into the cytoplasm of LPS-stimulated RAW 264.7 cells. These data suggest that phase 2 inducers may exert anti-inflammatory effects by inhibiting secretion of the cytokine-like nuclear protein HMGB1.

Cytokine networks—towards new therapies for rheumatoid arthritis

Success achieved so far in the blockade of tumor necrosis factor and interleukin (IL)-1 in rheumatoid arthritis exemplifies the feasibility and potential therapeutic application of antagonizing cytokine signaling. Despite these advances, there remains a considerable unmet clinical need in this field. A number of preclinical development programs are ongoing to target a variety of cytokines that are central to immune regulation and tissue-matrix destruction in rheumatoid arthritis. Evidence indicates that IL-6 antagonists might represents a useful approach and preliminary data similarly identify IL-15 as an intriguing target. Numerous additional cytokines are under investigation at the preclinical stage, including IL-12-IL-23, IL-17 and IL-18. As therapeutic goals move from disease control towards remission induction, development of the capacity for cytokine targeting to modify the underlying immune dysregulation remains a major priority.

HMGB1: guiding immunity from within

Two of the main challenges that eukaryotic multicellular organisms faced during evolution were to eliminate and replace dying cells and to cope with invading microorganisms. The innate immune system evolved to handle both tasks: to scavenge cellular debris and to form the first line of defence against microbes. In this review, we focus on high mobility group box 1 (HMGB1) protein as a common signal that alerts the innate immune system to excessive or deregulated cell death and to microbial invasion. HMGB1, which is well known nuclear protein, has revealed unexpected facets as an extracellular mediator. The role of HMGB1 as an endogenous molecule that facilitates immune responses and has an important role in tissue homeostasis and disease will be highlighted here.

Soluble RAGE: a hot new biomarker for the hot joint?

The receptor for advanced glycation endproducts (RAGE) interacts with distinct ligand families linked to the inflammatory response. Studies in animal models suggest that RAGE is upregulated in the inflamed joint and that blockade of the receptor, using a ligand decoy soluble form of RAGE (sRAGE), attenuates joint inflammation and expression of inflammatory and tissue-destructive mediators. In this issue of Arthritis Research & Therapy, Rille Pullerits and colleagues reported that plasma levels of sRAGE were reduced in subjects with rheumatoid arthritis compared with healthy controls or subjects with non-inflammatory joint disease. These findings suggest the possibility that levels of sRAGE might be a biomarker of inflammation. Not resolved by these studies, however, is the intriguing possibility that endogenously higher levels of sRAGE might be linked to a lower incidence of arthritis or to the extent of inflammation. Nevertheless, although 'cause or effect' relationships may not be established in this report, fascinating insights into RAGE, inflammation and human arthritis emerge from these studies.

Do We Need New Treatment That Goes beyond Tumor Necrosis Factor Blockers for Rheumatoid Arthritis?

Rheumatoid arthritis (RA) has a prevalence of approximately 1%, making it the most common inflammatory rheumatic disease. The outcome for RA patients has significantly improved during recent years. Factors include the introduction of new therapies such as tumor necrosis factor (TNF)-blocking agents and new treatment strategies, especially early and aggressive therapy, including combinations of several disease-modifying antirheumatic drugs (DMARDs). However, only 60-70% of RA patients respond to treatment with a TNF-blocking agent. In addition, most of these patients show only a partial response according to ACR20 criteria. Therefore, to ameliorate painful joint inflammation and prevent disability in RA patients, new treatment principles and more intelligent combination therapies are urgently needed. Interestingly, the strategy of switching patients who no longer respond to one of the TNF blockers to another has often turned out to be effective. Areas of ongoing research include combining TNF-blocking agents with DMARDs other than methotrexate. Also, several new biologics are being tested in clinical trials that promise to soon enhance the therapeutic armamentarium to fight RA. These biologics' mechanisms of action feature blockade of T cell costimulation by a CTLA4Ig fusion protein (abatacept); blockade of interleukin (IL)-6 signaling with an antibody to the IL-6 receptor (MRA); neutralizing IL-15 by a monoclonal antibody; and targeting B cells with an anti-CD20 antibody (rituximab). Other therapeutic approaches, such as blockade of chemokine receptors, adhesion molecules, complement components, and transcription factors regulating the inflammatory response, appear promising; however, they still need careful evaluation in placebo-controlled clinical studies.

High-mobility group box 1 protein (HMGB1): nuclear weapon in the immune arsenal

High-mobility group box 1 protein (HMGB1), which previously was thought to function only as a nuclear factor that enhances transcription, was recently discovered to be a crucial cytokine that mediates the response to infection, injury and inflammation. These observations have led to the emergence of a new field in immunology that is focused on understanding the mechanisms of HMGB1 release, its biological activities and its pathological effects in sepsis, arthritis, cancer and other diseases. Here, we discuss these features of HMGB1 and summarize recent advances that have led to the preclinical development of therapeutics that modulate HMGB1 release and activity.

Monocytes promote natural killer cell interferon gamma production in response to the endogenous danger signal HMGB1

Substantial attention has been paid to the role of the toll-like receptor (TLR) ligands of late and their role in regulating the innate immune response. They serve as exogenous danger signals important in informing and driving the distal adaptive immune response to pathogens. Less clear has been the role of the nominal endogenous danger signals released and recognized in stressed cells following genotoxic or metabolic stress as occurs in progressively growing tumors. HMGB1 (high-mobility group B1) is a nuclear protein well characterized for its ability to modify DNA access to transcriptional proteins that is released from necrotic cells as well as secreted through the endosomal route from hematopoietic cells, serving as a late mediator of sepsis. It interacts with high-affinity RAGE (receptor for advanced glycation end products) and TLR2 receptors. Here we show that HMGB1 enhances interferon gamma release from macrophage (but not dendritic cell)-stimulated NK cells. This is effective only when coupled with other pro-inflammatory cytokines particularly with IL-2 in combination with IL-1 or IL-12. We have used this information to suggest that HMGB1, which also promotes epithelial migration and proliferation, drives repair in the absence or inhibition of other factors but enhances inflammation in their presence. The implications for tumorigenesis and tumor progression are quite important as they may be for other states of chronic inflammation.

Extracellular HMGB1 as a proinflammatory cytokine

High mobility group box-1 protein (HMGB1, formerly known as HMG-1), a highly conserved ubiquitous protein, has been for a long time described as a nuclear DNA-binding protein involved in nucleosome stabilization and gene transcription. Recent discoveries indicate that HMGB1 is released from activated innate immune cells or necrotic cells and functions as an important mediator of endotoxemia, sepsis, arthritis, and local inflammation. Therapeutic agents that inhibit HMGB1 release or action confer significant protection against endotoxemia, sepsis, and arthritis in animal models and thus hold potential for the clinical management of various inflammatory diseases.

High mobility group box 1 (HMGB1) protein: possible amplification signal in the pathogenesis of falciparum malaria

High mobility group box 1 (HMGB1) protein, a DNA-binding protein that can also act as a pro-inflammatory cytokine if released from cells, is an important amplification signal in various forms of inflammation. The concentration of HMGB1 in serum taken at admission was increased in falciparum malaria in sixteen African children, more so in fatal cases than in those who subsequently recovered (P<0.001). Serum from both non-fatal (P=0.0048) and fatal (P<0.001) cases contained significantly more circulating HMGB1 than did serum from healthy Caucasian adults. These data provide an additional argument that malaria is fundamentally a systemic inflammatory state. In keeping with its developing role in sepsis, HMGB1 may enhance and prolong the inflammatory processes, and thus illness, in malaria.

Pathogenic role of HMGB1 in SARS?

High mobility group box 1 protein (HMGB1) is released by necrotic cells or activated macrophages/monocytes, and functions as a late mediator of lethal systemic and local pulmonary inflammation. Passive immunization with anti-HMGB1 antibodies confers significant protection against lethal endotoxemia, sepsis, and acute lung injury, even when antibodies are administered after the onset of these diseases. In light of observations that three Chinese herbal formulations recommended for treatment of severe acute respiratory syndrome (SARS) specifically inhibited the release of HMGB1 from innate immune cells, we hypothesize that HMGB1 might occupy a pathogenic role in SARS by mediating an injurious pulmonary inflammatory response.

Activation of human umbilical vein endothelial cells leads to relocation and release of high-mobility group box chromosomal protein 1

The nuclear protein high-mobility group box chromosomal protein 1 (HMGB1) was recently described to act as a pro-inflammatory cytokine and as a late mediator of severe sepsis and septic shock. The protein is released from monocytes in response to endotoxin and activates monocytes and endothelial cells through nuclear factor kappa B. We have previously demonstrated that the B-box of HMGB1 mediates a pro-inflammatory effect on endothelial cells including the upregulation of cell-adhesion molecules and release of interleukin (IL)-8 and granulocyte colony-stimulating factor. Here, we report that HMGB1 is released from human umbilical vein endothelial cells (HUVEC) in response to lipopolysaccharide (LPS) and tumour necrosis factor (TNF)-alpha. A nuclear relocation of HMGB1 to the cytoplasm was seen at 4 h. Subsequently, high amounts of HMGB1 could be seen in the supernatants from stimulated cells after 16 h. It was also observed that the pro-inflammatory activity of HMGB1 is sensitive to dexamethasone. Interestingly, the HMGB1-induced TNF-alpha release from monocytes could be inhibited by either the A-box of the protein or the p38 inhibitor CNI-1493, but neither had any inhibitory effects on the HMGB1-dependent upregulation of cell-adhesion molecules on HUVEC. Altogether, these results suggest that HUVEC may be an important source of HMGB1 secretion in response to systemic infection and that endothelial cells and monocytes may use different signalling pathways.

Differential macrophage expression of IL-12 and IL-23 upon innate immune activation defines rat autoimmune susceptibility

Rodents typically demonstrate strain-specific susceptibilities to induced autoimmune models such as experimental arthritis and encephalomyelitis. A common feature of the local pathology of these diseases is an extensive infiltration of activated macrophages (MPhi). Different functional activation states can be induced in MPhi during innate immune activation, and it is this differential activation that might be important in susceptibility/resistance to induction or perpetuation of autoimmunity. In this study, we present an extensive, comparative analysis of the activation phenotypes of MPhi derived from autoimmune-susceptible and autoimmune-resistant rat strains to describe a cellular phenotype that defines the disease phenotype. We included investigation of receptor function, intracellular signaling pathways, cytokines, and other soluble mediators released after activation of cells using a panel of stimuli embracing many activation routes. We report that activation of MPhi from the autoimmune-susceptible strain was associated with alternative activation indicated by induction of arginase activity, a lower production of classical proinflammatory mediators, and a high production of interleukin (IL)-23, and MPhi from the autoimmune-resistant strains were associated with a higher production of proinflammatory mediators, a classical activation phenotype, and preferential induction of IL-12. These MPhi phenotypes thus reflect disparate, genetic cellular programs that define autoimmune susceptibility.

HMGB1 as a mediator of necrosis-induced inflammation and a therapeutic target in arthritis

For the second time in recent history, studies directed at the pathogenesis of infectious disease have led to the identification of an endogenous mediator of arthritis. HMGB1, a 30-kD nuclear and cytoplasmic protein widely studied as a DNA-binding protein, is a newly described cytokine and a necessary and sufficient mediator of lethal sepsis. HMGB1 is passively released during cell necrosis, but not apoptosis; it activates an inflammatory response to necrosis,but not apoptosis. Furthermore, HMGB1 can also be actively secreted by stimulated macrophages or monocytes in a process that requires acetylation of the molecule, enabling a translocation from the nucleus to secretory lysosomes. Recent evidence indicates that HMGB1 is a mediator of arthritis because of the following: (1) it is produced at the site of joint inflammation, (2) it causes the development of arthritis when applied to normal joints, and (3) therapies that inhibit HMGB1 prevent the progression of collagen-induced arthritis in rodents. Anti-HMGB1 may be studied in future clinical trials of diseases of excessive production of HMGB1, such as severe sepsis and arthritis.

Pathogenesis of malaria and clinically similar conditions

There is now wide acceptance of the concept that the similarity between many acute infectious diseases, be they viral, bacterial, or parasitic in origin, is caused by the overproduction of inflammatory cytokines initiated when the organism interacts with the innate immune system. This is also true of certain noninfectious states, such as the tissue injury syndromes. This review discusses the historical origins of these ideas, which began with tumor necrosis factor (TNF) and spread from their origins in malaria research to other fields. As well the more established proinflammatory mediators, such as TNF, interleukin-1, and lymphotoxin, the roles of nitric oxide and carbon monoxide, which are chiefly inhibitory, are discussed. The established and potential roles of two more recently recognized contributors, overactivity of the enzyme poly(ADP-ribose) polymerase 1 (PARP-1) and the escape of high-mobility-group box 1 (HMGB1) protein from its normal location into the circulation, are also put in context. The pathogenesis of the disease caused by falciparum malaria is then considered in the light of what has been learned about the roles of these mediators in these other diseases, as well as in malaria itself.

Down-regulation of the aberrant expression of the inflammation mediator high mobility group box chromosomal protein 1 in muscle tissue of patients with polymyositis and dermatomyositis treated with corticosteroids

OBJECTIVE

High mobility group box chromosomal protein 1 (HMGB-1) is an endogenous nuclear protein that can be translocated to the cytoplasm and then released extracellularly. It can induce tumor necrosis factor and interleukin-1 production in myeloid cells. Increased expression of these 2 cytokines has been observed in muscle tissue of patients with polymyositis (PM) and dermatomyositis (DM). The present study was therefore undertaken to investigate how HMGB-1 is expressed in muscle tissue of patients with myositis and, if so, whether such expression is modulated by prednisolone therapy.

METHODS

Muscle biopsy specimens from 5 patients with PM and 4 patients with DM, obtained before and 3-6 months after initiation of prednisolone therapy, were assessed by conventional microscopic evaluation and computerized image analysis, and HMGB-1 expression was investigated by immunohistochemical staining. Muscle biopsy specimens from 7 healthy controls were also studied.

RESULTS

Cytoplasmic HMGB-1 expression was detected in infiltrating rounded mononuclear cells, vascular endothelial cells, and muscle fibers of PM and DM patients. Extracellular staining surrounding the inflammatory cells was also observed. After treatment with high-dose prednisolone, cytoplasmic and extracellular HMGB-1 expression was significantly reduced, coinciding mainly with a decreased number of infiltrating inflammatory cells. Cytoplasmic HMGB-1 expression was still evident in endothelial cells and muscle fibers. No HMGB-1 expression was observed in muscle tissue from healthy controls.

CONCLUSION

The cytoplasmic and extracellular distribution of HMGB-1 in muscle tissue may indicate an important role of this proinflammatory molecule in the pathogenesis of PM and DM. Furthermore, our findings indicate that systemically administered high-dose corticosteroids selectively down-regulate aberrant expression of HMGB-1 in mononuclear inflammatory cells in vivo.

Chromatin and cell death

HMGB1, a very mobile chromatin protein, leaks out from necrotic cells and signals to neighbouring cells that tissue damage has occurred. At least one receptor for extracellular HMGB1 exists, and signals to different cells to divide, migrate, activate inflammation or start an immune response. Remarkably, apoptotic chromatin binds HMGB1 irreversibly, thereby ensuring that it will not diffuse away to activate responses from neighbouring cells. Thus, dying cells use their own chromatin to signal how they have died. We argue that the nuclear events in apoptosis serve to control the molecular signals that dying cells send out.

HMGB1 is a potent trigger of arthritis

Rheumatoid arthritis is a chronic inflammatory disease characterized by synovial inflammation and structural damage of joints. Although the cause of rheumatoid arthritis (RA) remains unknown, the excessive production of proinflammatory cytokines such as tumour necrosis factor (TNF) and interleukin-1 (IL-1) by intra-articular macrophages occupies a critical pathogenic role in the development and progression of the disease. High mobility group box chromosomal protein 1 (HMGB1) is a recently identified mediator of interest in human and experimental arthritides. HMGB1 can either be actively secreted from macrophages or passively released from necrotic cells of all kinds. Activated macrophages and unprogrammed cell death caused by ischaemia or activated complement are all prominent features of chronic arthritis, contributing to the persistent synovial inflammation. HMGB1 is cytoplasmically and extracellularly overexpressed in inflammatory synovial tissue in human RA as well as experimental collagen-induced arthritis. Elevated levels of HMGB1 are also present in synovial fluid samples from RA patients. Synovial tissue from rats with experimental arthritis exhibits aberrant deposition of HMGB1 preceding the onset of clinical signs of arthritis, and the expression becomes prominent after the onset of clinical disease. The synovial levels of HMGB1 are comparable with those of TNF and IL-1beta at the peak of manifest disease. HMGB1-targeted intervention with either neutralizing antibodies or the antagonistic A box domain of HMGB1 ameliorates collagen-induced arthritis both in mice and rats, and inhibits the local overexpression of IL-1beta in the joints. It is thus conceivable that therapeutic HMGB1 blockade may contribute to future treatment of human chronic arthritis.

Extracellular role of HMGB1 in inflammation and sepsis

High mobility group box 1 (HMGB1), a 30 kDa nuclear and cytosolic protein widely studied as a transcription factor and growth factor, has recently been identified as a cytokine mediator of lethal systemic inflammation (e.g. endotoxaemia and sepsis), arthritis and local inflammation. It is released by activated macrophages, and serum levels increase significantly during endotoxaemia, sepsis and arthritis with significant delayed kinetics in comparison with tumour necrosis factor (TNF) and interleukin-1beta. Recently identified biological activities of HMGB1 include activation of macrophages/monocytes to release proinflammatory cytokines, upregulation of endothelial adhesion molecules, stimulation of epithelial cell barrier failure, and mediation of fever and anorexia. Passive immunization with anti-HMGB1 antibodies confers significant protection against lethal endotoxaemia, sepsis, arthritis and lipopolysaccharide-induced acute lung injury, even when antibody administration is delayed until after the early TNF responses have resolved. Strategies to inhibit HMGB1 activity and release are being investigated in these and other preclinical models of acute and chronic inflammation.