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1.  Induction of inflammatory and immune responses by HMGB1–nucleosome complexes: implications for the pathogenesis of SLE 
The Journal of Experimental Medicine  2008;205(13):3007-3018.
Autoantibodies against double-stranded DNA (dsDNA) and nucleosomes represent a hallmark of systemic lupus erythematosus (SLE). However, the mechanisms involved in breaking the immunological tolerance against these poorly immunogenic nuclear components are not fully understood. Impaired phagocytosis of apoptotic cells with consecutive release of nuclear antigens may contribute to the immune pathogenesis. The architectural chromosomal protein and proinflammatory mediator high mobility group box protein 1 (HMGB1) is tightly attached to the chromatin of apoptotic cells. We demonstrate that HMGB1 remains bound to nucleosomes released from late apoptotic cells in vitro. HMGB1–nucleosome complexes were also detected in plasma from SLE patients. HMGB1-containing nucleosomes from apoptotic cells induced secretion of interleukin (IL) 1β, IL-6, IL-10, and tumor necrosis factor (TNF) α and expression of costimulatory molecules in macrophages and dendritic cells (DC), respectively. Neither HMGB1-free nucleosomes from viable cells nor nucleosomes from apoptotic cells lacking HMGB1 induced cytokine production or DC activation. HMGB1-containing nucleosomes from apoptotic cells induced anti-dsDNA and antihistone IgG responses in a Toll-like receptor (TLR) 2–dependent manner, whereas nucleosomes from living cells did not. In conclusion, HMGB1–nucleosome complexes activate antigen presenting cells and, thereby, may crucially contribute to the pathogenesis of SLE via breaking the immunological tolerance against nucleosomes/dsDNA.
PMCID: PMC2605236  PMID: 19064698
2.  High Mobility Group Box Protein 1 (HMGB1)-Partner Molecule Complexes Enhance Cytokine Production by Signaling Through the Partner Molecule Receptor 
Molecular Medicine  2011;18(1):224-230.
The nuclear protein high mobility group box protein 1 (HMGB1) promotes inflammation upon extracellular release. HMGB1 induces proinflammatory cytokine production in macrophages via Toll-like receptor (TLR)-4 signaling in a redox-dependent fashion. Independent of its redox state and endogenous cytokine-inducing ability, HMGB1 can form highly immunostimulatory complexes by interaction with certain proinflammatory mediators. Such complexes have the ability to enhance the induced immune response up to 100-fold, compared with induction by the ligand alone. To clarify the mechanisms for these strong synergistic effects, we studied receptor requirements. Interleukin (IL)-6 production was assessed in supernatants from cultured peritoneal macrophages from mice each deficient in one of the HMGB1 receptors (receptor for advanced glycation end products [RAGE], TLR2 or TLR4) or from wild-type controls. The cultures were stimulated with the TLR4 ligand lipopolysaccaride (LPS), the TLR2 ligand Pam3CysSerLys4 (Pam3CSK4), noninflammatory HMGB1 or each TLR ligand in complex with noninflammatory HMGB1. The activity of the HMGB1-TLR ligand complexes relied on engagement of the same receptor as for the noncomplexed TLR ligand, since HMGB1-LPS complexes used TLR4 and HMGB1-Pam3CSK4 complexes used TLR2. Deletion of any of the intracellular adaptor molecules used by TLR2 (myeloid differentiation factor-88 [MyD88], TIR domain–containing adaptor protein [TIRAP]) or TLR4 (MyD88, TIRAP, TIR domain–containing adaptor-inducing interferon-β [TRIF], TRIF-related adaptor molecule [TRAM]) had similar effects on HMGB1 complex activation compared with noncomplexed LPS or Pam3CSK4. This result implies that the enhancing effects of HMGB1-partner molecule complexes are not regulated by the induction of additional signaling cascades. Elucidating HMGB1 receptor usage in processes where HMGB1 acts alone or in complex with other molecules is essential for the understanding of basic HMGB1 biology and for designing HMGB1-targeted therapies.
PMCID: PMC3320135  PMID: 22076468
3.  High-Mobility Group Box 1 Inhibits Gastric Ulcer Healing through Toll-Like Receptor 4 and Receptor for Advanced Glycation End Products 
PLoS ONE  2013;8(11):e80130.
High-mobility group box 1 (HMGB1) was initially discovered as a nuclear protein that interacts with DNA as a chromatin-associated non-histone protein to stabilize nucleosomes and to regulate the transcription of many genes in the nucleus. Once leaked or actively secreted into the extracellular environment, HMGB1 activates inflammatory pathways by stimulating multiple receptors, including Toll-like receptor (TLR) 2, TLR4, and receptor for advanced glycation end products (RAGE), leading to tissue injury. Although HMGB1’s ability to induce inflammation has been well documented, no studies have examined the role of HMGB1 in wound healing in the gastrointestinal field. The aim of this study was to evaluate the role of HMGB1 and its receptors in the healing of gastric ulcers. We also investigated which receptor among TLR2, TLR4, or RAGE mediates HMGB1’s effects on ulcer healing. Gastric ulcers were induced by serosal application of acetic acid in mice, and gastric tissues were processed for further evaluation. The induction of ulcer increased the immunohistochemical staining of cytoplasmic HMGB1 and elevated serum HMGB1 levels. Ulcer size, myeloperoxidase (MPO) activity, and the expression of tumor necrosis factor α (TNFα) mRNA peaked on day 4. Intraperitoneal administration of HMGB1 delayed ulcer healing and elevated MPO activity and TNFα expression. In contrast, administration of anti-HMGB1 antibody promoted ulcer healing and reduced MPO activity and TNFα expression. TLR4 and RAGE deficiency enhanced ulcer healing and reduced the level of TNFα, whereas ulcer healing in TLR2 knockout (KO) mice was similar to that in wild-type mice. In TLR4 KO and RAGE KO mice, exogenous HMGB1 did not affect ulcer healing and TNFα expression. Thus, we showed that HMGB1 is a complicating factor in the gastric ulcer healing process, which acts through TLR4 and RAGE to induce excessive inflammatory responses.
PMCID: PMC3823709  PMID: 24244627
4.  Stepwise Release of Biologically Active HMGB1 during HSV-2 Infection 
PLoS ONE  2011;6(1):e16145.
High mobility group box 1 protein (HMGB1) is a major endogenous danger signal that triggers inflammation and immunity during septic and aseptic stresses. HMGB1 recently emerged as a key soluble factor in the pathogenesis of various infectious diseases, but nothing is known of its behaviour during herpesvirus infection. We therefore investigated the dynamics and biological effects of HMGB1 during HSV-2 infection of epithelial HEC-1 cells.
Methodology/Principal Findings
Despite a transcriptional shutdown of HMGB1 gene expression during infection, the intracellular pool of HMGB1 protein remained unaffected, indicating its remarkable stability. However, the dynamics of HMGB1 was deeply modified in infected cells. Whereas viral multiplication was concomitant with apoptosis and HMGB1 retention on chromatin, a subsequent release of HMGB1 was observed in response to HSV-2 mediated necrosis. Importantly, extracellular HMGB1 was biologically active. Indeed, HMGB1-containing supernatants from HSV-2 infected cells induced the migration of fibroblasts from murine or human origin, and reactivated HIV-1 from latently infected T lymphocytes. These effects were specifically linked to HMGB1 since they were blocked by glycyrrhizin or by a neutralizing anti-HMGB1 antibody, and were mediated through TLR2 and the receptor for Advanced Glycation End-products (RAGE). Finally, we show that genital HSV-2 active infections also promote HMGB1 release in vivo, strengthening the clinical relevance of our experimental data.
These observations target HMGB1 as an important actor during HSV-2 genital infection, notably in the setting of HSV-HIV co-infection.
PMCID: PMC3023802  PMID: 21283827
5.  Inhibitor of NF-κB Kinases α and β Are Both Essential for High Mobility Group Box 1-Mediated Chemotaxis 
Inhibitor of NF-κB kinases β (IKKβ) and α (IKKα) activate distinct NF-κB signaling modules. The IKKβ/canonical NF-κB pathway rapidly responds to stress-like conditions, whereas the IKKα/noncanonical pathway controls adaptive immunity. Moreover, IKKα can attenuate IKKβ-initiated inflammatory responses. High mobility group box 1 (HMGB1), a chromatin protein, is an extracellular signal of tissue damage-attracting cells in inflammation, tissue regeneration, and scar formation. We show that IKKα and IKKβ are each critically important for HMGB1-elicited chemotaxis of fibroblasts, macrophages, and neutrophils in vitro and neutrophils in vivo. By time-lapse microscopy we dissected different parameters of the HMGB1 migration response and found that IKKα and IKKβ are each essential to polarize cells toward HMGB1 and that each kinase also differentially affects cellular velocity in a time-dependent manner. In addition, HMGB1 modestly induces noncanonical IKKα-dependent p52 nuclear translocation and p52/RelB target gene expression. Akin to IKKα and IKKβ, p52 and RelB are also required for HMGB1 chemotaxis, and p52 is essential for cellular orientation toward an HMGB1 gradient. RAGE, a ubiquitously expressed HMGB1 receptor, is required for HMGB1 chemotaxis. Moreover, IKKβ, but not IKKα, is required for HMGB1 to induce RAGE mRNA, suggesting that RAGE is at least one IKKβ target involved in HMGB1 migration responses, and in accord with these results enforced RAGE expression rescues the HMGB1 migration defect of IKKβ, but not IKKα, null cells. Thus, proinflammatory HMGB1 chemotactic responses mechanistically require the differential collaboration of both IKK-dependent NF-κB signaling pathways.
PMCID: PMC2915896  PMID: 20231695
6.  Overexpression of Receptor for Advanced Glycation End Products and High-Mobility Group Box 1 in Human Dental Pulp Inflammation 
Mediators of Inflammation  2014;2014:754069.
High mobility group box 1 (HMGB1), a nonhistone DNA-binding protein, is released into the extracellular space and promotes inflammation. HMGB1 binds to related cell signaling transduction receptors, including receptor for advanced glycation end products (RAGE), which actively participate in vascular and inflammatory diseases. The aim of this study was to examine whether RAGE and HMGB1 are involved in the pathogenesis of pulpitis and investigate the effect of Prevotella intermedia (P. intermedia) lipopolysaccharide (LPS) on RAGE and HMGB1 expression in odontoblast-like cells (OLC-1). RAGE and HMGB1 expression levels in clinically inflamed dental pulp were higher than those in healthy dental pulp. Upregulated expression of RAGE was observed in odontoblasts, stromal pulp fibroblasts-like cells, and endothelial-like cell lining human pulpitis tissue. Strong cytoplasmic HMGB1 immunoreactivity was noted in odontoblasts, whereas nuclear HMGB1 immunoreactivity was seen in stromal pulp fibroblasts-like cells in human pulpitis tissue. LPS stimulated OLC-1 cells produced HMGB1 in a dose-dependent manner through RAGE. HMGB1 translocation towards the cytoplasm and secretion from OLC-1 in response to LPS was inhibited by TPCA-1, an inhibitor of NF-κB activation. These findings suggest that RAGE and HMGB1 play an important role in the pulpal immune response to oral bacterial infection.
PMCID: PMC4121219  PMID: 25114379
7.  High mobility group B1 protein interacts with its receptor RAGE in tumor cells but not in normal tissues 
Oncology Letters  2011;3(1):214-218.
The high mobility group box 1 (HMGB1) protein is an abundant non-histone component of chromatin well known for its two DNA binding domains, HMG box A and HMG box B. The main characteristics of the HMGB1 protein as an ‘architectural’ factor are its ability to recognize and bind with high affinity to distorted DNA and its ability to induce kinks in linear DNA fragments. The HMGB1 protein has been correlated to cancer progression. An elevated expression of HMGB1 occurred in certain types of primary tumor, including melanoma and colon, prostate, pancreatic and breast cancers, and in the majority of cases HMGB1 is associated with invasion and metastasis. The main signaling pathway is activated through the interaction of HMGB1 with its Receptor for Advanced Glycation End products (RAGE). Certain data indicate that an elevated expression of RAGE and HMGB1 is not always a prerequisite of poor prognosis of tumor development. The cellular localization of the ligand/receptor pair also requires consideration. The data concerning the expression of HMGB1 protein and its receptor RAGE in various tissues and tumor cells reflect the overall production of the proteins. However, they do not refer to their cellular localization and there is no direct evidence for the formation of a stable complex between them. In the present study, we investigated the subcellular distribution of HMGB1 and its receptor RAGE in various rat organs compared to Guerin ascites tumor cells. In the normal tissues the proteins exist in their soluble form, whereas in the tumor cells they are insoluble and membrane-bound. HMGB1 forms a stable complex with RAGE only in the protein extract derived from the cancer cells predominantly in the membrane fraction.
PMCID: PMC3362388  PMID: 22740883
HMGB1 protein; RAGE; tumorigenesis; subcellular localization
8.  High mobility group box 1 (HMGB1) and anti-HMGB1 antibodies and their relation to disease characteristics in systemic lupus erythematosus 
High Mobility Group Box 1 (HMGB1) is a nuclear non-histone protein. HMGB1, which is secreted by inflammatory cells and passively released from apoptotic and necrotic cells, may act as a pro-inflammatory mediator. As apoptotic cells accumulate in systemic lupus erythematosus (SLE), HMGB1 levels might be increased in SLE. HMGB1 may also serve as an autoantigen, leading to the production of anti-HMGB1 antibodies. In this study we determined levels of HMGB1 and anti-HMGB1 in SLE patients in comparison to healthy controls (HC) and analysed their relation with disease activity.
The study population consisted of 70 SLE patients and 35 age- and sex-matched HC. Thirty-three SLE patients had quiescent disease, the other 37 patients were selected for having active disease. Nineteen of these had lupus nephritis. HMGB1 levels were measured with both Western blot and ELISA. Anti-HMGB1 levels were measured by ELISA. Clinical and serological parameters were assessed according to routine procedures.
HMGB1 levels in SLE patients could be measured reliably by Western blotting only, and were significantly increased compared to HC. During active disease HMGB1 levels increased, in particular in patients with renal involvement. Serum HMGB1 levels correlated with SLEDAI, proteinuria, and anti-dsDNA levels, and showed a negative correlation with complement C3. Anti-HMGB1 levels were significantly increased in SLE patients compared to HC, and positively correlated with HMGB1 levels.
Levels of HMGB1 in the sera of SLE patients, in particular in those with active renal disease, are increased. Serum HMGB1 levels are related to SLEDAI scores and proteinuria, as well as to levels of anti-HMGB1 antibodies. These findings suggest that besides HMGB1, HMGB1-anti-HMGB1 immune complexes play a role in the pathogenesis of SLE, in particular in patients with renal involvement.
PMCID: PMC3218880  PMID: 21548924
9.  The High-Mobility Group Box-1 Nuclear Factor Mediates Retinal Injury after Ischemia Reperfusion 
Hmgb1 binds with high affinity to Rage that triggers inflammation and damage. Our results suggest that an increased level of Hmgb1 and signaling via Rage contribute to neurotoxicity following retinal ischemia.
High-mobility group protein B1 (Hmgb1) is released from necrotic cells and induces an inflammatory response. Although Hmgb1 has been implicated in ischemia/reperfusion (IR) injury of the brain, its role in IR injury of the retina remains unclear. Here, the authors provide evidence that Hmgb1 contributes to retinal damage after IR.
Retinal IR injury was induced by unilateral elevation of intraocular pressure and the level of Hmgb1 in vitreous humor was analyzed 24 hours after reperfusion. To test the functional significance of Hmgb1 release, ischemic or normal retinas were treated with the neutralizing anti-Hmgb1 antibody or recombinant Hmgb1 protein respectively. To elucidate in which cell type Hmgb1 exerts its effect, primary retinal ganglion cell (RGC) cultures and glia RGC cocultures were treated with Hmgb1. To clarify the downstream signaling pathways involved in Hmgb1-induced effects in the ischemic retina, receptor for advanced glycation end products (Rage)-deficient mice (RageKO) were used.
Hmgb1 is accumulated in the vitreous humor 24 hours after IR. Inhibition of Hmgb1 activity with neutralizing antibody significantly decreased retinal damage after IR, whereas treatment of retinas or retinal cells with Hmgb1 induced a loss of RGCs. The analysis of RageKO versus wild-type mice showed significantly reduced expression of proinflammatory genes 24 hours after reperfusion and significantly increased survival of ganglion cell layer neurons 7 days after IR injury.
These results suggest that an increased level of Hmgb1 and signaling via the Rage contribute to neurotoxicity after retinal IR injury.
PMCID: PMC3207720  PMID: 21828158
10.  Pathogenic Anti-DNA Antibodies Modulate Gene Expression in Mesangial Cells: 
Immunology letters  2008;121(1):61-73.
1. Summary
Although anti-DNA antibodies have been decisively linked to the pathogenesis of lupus nephritis, the mechanisms have not been conclusively determined. Recently, we reported that anti-DNA antibodies may contribute to kidney damage by upregulation of proinflammatory genes in mesangial cells (MC), a process involving both Fc receptor dependent and independent pathways. In investigating the mechanism by which pathogenic anti-DNA antibodies modulate gene expression in MC, we found that the pathogenic anti-DNA antibody 1A3F bound to high mobility group binding protein 1 (HMGB1), an endogenous ligand for TLR2/4 and RAGE (receptor for advanced glycation end-products). Interestingly, HMGB1 treatment of MC induced a similar pattern of genes as stimulation with 1A3F. Furthermore, HMGB1 and 1A3F exhibited a synergistic proinflammatory effect in the kidney, where increased expression of HMGB1 was found in lupus patients but not in patients with other types of renal disease. TLR2/Fc and RAGE/Fc inhibited the proinflammatory effects of 1A3F on MC. Finally, we found enhanced susceptibility of lupus prone MRL-lpr/lpr (MRL/lpr) as compared to normal BALB/c derived MC to pathogenic anti-DNA antibody and LPS stimulation (in particular enhanced chemokine synthesis), in addition to significantly increased expression of TLR4. Our results suggest that gene upregulation in MC induced by nephritogenic anti-DNA antibodies is TLR2/4 and RAGE dependent. Finally, HMGB1 may act as a proinflammatory mediator in antibody induced kidney damage in systemic lupus erythematosus (SLE).
PMCID: PMC2677706  PMID: 18822317
Systemic Lupus Erythematosus; Autoantibodies; Inflammation
11.  HMGB1 and TLR4 mediate skeletal muscle recovery in a murine model of hindlimb ischemia 
Journal of vascular surgery  2013;58(2):460-469.
We have previously shown that the danger signal High Mobility Group Box 1 (HMGB1) promotes angiogenesis when administered to ischemic muscle. HMGB1 signals through Toll-like receptor 4 (TLR4) as well as the receptor for advanced glycation end-products (RAGE). However, the actions of these receptors in ischemic injury and muscle recovery are not known. We hypothesize that TLR4 mediates tissue recovery and angiogenesis in response to ischemia.
Femoral artery ligation was performed in control, TLR4 competent (C3H/HeOuJ), and incompetent (C3H/HeJ) mice, as well as RAGE knockout mice and their C57B6 control counterparts. In other experiments, control mice were pretreated with anti-HMGBI neutralizing antibody before femoral artery ligation. After two weeks, limb perfusion was evaluated using laser Doppler perfusion imaging (LDPI) and reported as the ratio of blood flow in the ischemic to nonischemic limb. Muscle necrosis, fat replacement, and vascular density in the anterior tibialis muscle were quantified histologically. In vitro, TLR4 and RAGE expression was evaluated in human dermal microvascular endothelial cells (HDMVECs) in response to hypoxia. HDMVECs treated with HMGB1 alone and in the presence of anti-TLR4 antibody were probed for phosphorylated ERK (p-ERK), a signaling molecule critical to EC angiogenic behavior.
Both anti-HMGB1 antibody as well as defective TLR4 signaling in HeJ mice resulted in prominent muscle necrosis two weeks after femoral artery ligation. Control HeOuJ mice had less necrosis than TLR4 incompetent HeJ mice, but a greater amount of fat replacement. In contrast to control C3H mice, control C57B6 mice demonstrated prominent muscle regeneration with very little necrosis. Muscle regeneration was not dependent on RAGE. While vascular density did not differ between strains, mice with intact RAGE and TLR4 signaling had less blood flow in ischemic limbs compared to mutant strains. In vitro, EC TLR4 expression increased in response to hypoxia while TLR4 antagonism decreased HMGB1-induced activation of ERK.
Both HMGB1 and TLR4 protect against muscle necrosis after hindlimb ischemia. However, muscle regeneration does not appear to be tied to vascular density. HMGB1 likely activates angiogenic behavior in EC in vitro, and this activation may be modulated by TLR4. The improvement in blood flow seen in mice with absent TLR4 and RAGE signaling may suggest anti-angiogenic roles for both receptors, or vasoconstriction induced by TLR4 and RAGE mediated inflammatory pathways.
PMCID: PMC3657591  PMID: 23414695
12.  HMGB1 promotes MMP-9 upregulation through TLR4 after cerebral ischemia 
Background and Purpose
HMGB1 is a nuclear protein and an alarmin that signals cell damage in response to injury. It is believed that following release from injured cells, HMGB1 binds to its receptors to stimulate cross-talk among cells and to drive components of the inflammatory cascade. This study was intended to investigate the role of extracellular HMGB1 in ischemic stroke by examining the response of the zymogen, matrix metalloproteinase-9 (MMP-9) to HMGB1, in vivo and in vitro.
TLR2, TLR4, RAGE and MMP-9 expression was examined using quantitative RT-PCR in primary cultured neurons, astrocytes as well as in mouse brain following HMGB1 addition. MMP-9 expression/activity was examined using zymography. Middle cerebral artery occlusion was induced for 60 minutes using a filament model.
MMP-9 and TLR4 are highly expressed in neurons, astrocytes and mouse brain. HMGB1 addition to neuronal and glial cell cultures caused MMP-9 upregulation in a dose- and time-dependent manner. Lack of TLR4 function attenuated MMP-9 expression induced by HMGB1 in vitro. Following striatal microinjection of HMGB1, MMP-9 was upregulated, and the response was independent of TNFα. Interestingly, MMP-9 upregulation was reduced in TLR4 missense mutant mice after ischemia compared to wild-type controls as was infarct volume.
Our results suggest that HMGB1 triggers MMP-9 upregulation in neurons and astrocytes predominantly via TLR4 after cerebral ischemia. Hence, targeting HMGB1/TLRs signaling pathway may reduce the acute inflammatory response and reduce tissue damage in cerebral ischemia.
PMCID: PMC3066477  PMID: 20671243
cerebral ischemia; matrix metalloproteinase; high-mobility group box 1
13.  HMGB1 Mediates Endogenous TLR2 Activation and Brain Tumor Regression 
PLoS Medicine  2009;6(1):e1000010.
Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor that carries a 5-y survival rate of 5%. Attempts at eliciting a clinically relevant anti-GBM immune response in brain tumor patients have met with limited success, which is due to brain immune privilege, tumor immune evasion, and a paucity of dendritic cells (DCs) within the central nervous system. Herein we uncovered a novel pathway for the activation of an effective anti-GBM immune response mediated by high-mobility-group box 1 (HMGB1), an alarmin protein released from dying tumor cells, which acts as an endogenous ligand for Toll-like receptor 2 (TLR2) signaling on bone marrow-derived GBM-infiltrating DCs.
Methods and Findings
Using a combined immunotherapy/conditional cytotoxic approach that utilizes adenoviral vectors (Ad) expressing Fms-like tyrosine kinase 3 ligand (Flt3L) and thymidine kinase (TK) delivered into the tumor mass, we demonstrated that CD4+ and CD8+ T cells were required for tumor regression and immunological memory. Increased numbers of bone marrow-derived, tumor-infiltrating myeloid DCs (mDCs) were observed in response to the therapy. Infiltration of mDCs into the GBM, clonal expansion of antitumor T cells, and induction of an effective anti-GBM immune response were TLR2 dependent. We then proceeded to identify the endogenous ligand responsible for TLR2 signaling on tumor-infiltrating mDCs. We demonstrated that HMGB1 was released from dying tumor cells, in response to Ad-TK (+ gancyclovir [GCV]) treatment. Increased levels of HMGB1 were also detected in the serum of tumor-bearing Ad-Flt3L/Ad-TK (+GCV)-treated mice. Specific activation of TLR2 signaling was induced by supernatants from Ad-TK (+GCV)-treated GBM cells; this activation was blocked by glycyrrhizin (a specific HMGB1 inhibitor) or with antibodies to HMGB1. HMGB1 was also released from melanoma, small cell lung carcinoma, and glioma cells treated with radiation or temozolomide. Administration of either glycyrrhizin or anti-HMGB1 immunoglobulins to tumor-bearing Ad-Flt3L and Ad-TK treated mice, abolished therapeutic efficacy, highlighting the critical role played by HMGB1-mediated TLR2 signaling to elicit tumor regression. Therapeutic efficacy of Ad-Flt3L and Ad-TK (+GCV) treatment was demonstrated in a second glioma model and in an intracranial melanoma model with concomitant increases in the levels of circulating HMGB1.
Our data provide evidence for the molecular and cellular mechanisms that support the rationale for the clinical implementation of antibrain cancer immunotherapies in combination with tumor killing approaches in order to elicit effective antitumor immune responses, and thus, will impact clinical neuro-oncology practice.
Maria Castro and colleagues use cell line and transgenic mouse approaches to study the mechanisms underlying the immune response to glioblastoma multiforme.
Editors' Summary
Every year, more than 175,000 people develop a primary brain tumor (a cancer that starts in the brain rather than spreading in from elsewhere). Like all cancers, brain tumors develop when a cell acquires genetic changes that allow it to grow uncontrollably and that change other aspects of its behavior, including the proteins it makes. There are many different types of cells in the brain and, as a result, there are many different types of brain tumors. However, one in five primary brain tumors is glioblastoma multiforme (GBM; also known as grade 4 astrocytoma), a particularly aggressive cancer. With GBM, the average time from diagnosis to death is one year and only one person in 20 survives for five years after a diagnosis of GBM. Symptoms of GBM include headaches, seizures, and changes in memory, mood, or mental capacity. Treatments for GBM, which include surgery, radiotherapy, and chemotherapy, do not “cure” the tumor but they can ease these symptoms.
Why Was This Study Done?
Better treatments for GBM are badly needed, and one avenue that is being explored is immunotherapy—a treatment in which the immune system is used to fight the cancer. Because many tumors make unusual proteins, the immune system can sometimes be encouraged to recognize tumor cells as foreign invaders and kill them. Unfortunately, attempts to induce a clinically useful anti-GBM immune response have been unsuccessful, partly because the brain contains very few dendritic cells, a type of immune system cell that kick-starts effective immune responses by presenting foreign proteins to other immune system cells. Another barrier to immunotherapy for GBM is immune evasion by the tumor. Many tumors develop ways to avoid the immune response as they grow. For example, they sometimes reduce the expression of proteins that the immune system might recognize as foreign. In this study, the researchers test a new combined treatment strategy for GBM in which dendritic cells are encouraged to enter the brain and tumor cells are killed to release proteins capable of stimulating an effective antitumor immune response.
What Did the Researchers Do and Find?
The researchers first established brain tumors in mice. Then, they injected harmless viruses carrying the genes for Fms-like tyrosine kinase 3 ligand (Ftl3L; a protein that attracts dendritic cells) and for thymidine kinase (TK; cells expressing TK are killed by a drug called gancyclovir) into the tumor. Expression of both Flt3L and TK (but not of either protein alone) plus gancyclovir treatment shrank the tumors and greatly improved the survival of the mice. The researchers show that their strategy increased the migration of dendritic cells into the tumor provided they expressed an immune system protein called Toll-like receptor 2 (TLR2). TLR2 expression on the dendritic cells was also needed for an effective anti-tumor immune response and for tumor regression. TLR2 normally activates dendritic cells by binding to specific proteins on invading pathogens, so what was TLR2 binding to in the mouse tumors? The researchers reveal that TLR2 was responding to high-mobility-group box 1 (HMGB1), a protein released by the dying tumor cells by showing that treatment of the tumor-bearing mice with the HMGB1 inhibitor glycyrrhizin blocked the therapeutic effect of Flt3L/TK expression. Finally, the researchers report that other tumor cell types release HMGB1 when they are killed and that the Flt3L/TK expression strategy can also kill other tumors growing in mouse brains.
What Do These Findings Mean?
Results obtained in mouse models of human diseases do not always lead to effective treatments for human patients. Nevertheless, the findings of this study provide new insights into how an effective immune response against brain tumors might be brought about. Most importantly, they show that an effective strategy might need to both attract dendritic cells into the brain tumor and to kill tumor cells, so they release proteins that can activate the dendritic cells. That is, the authors suggest it's important to combine immunotherapies with tumor-killing strategies to provide effective treatments for primary and metastatic brain tumors
Additional Information.
Please access these Web sites via the online version of this summary at
The US National Cancer Institute provides information about brain tumors for patients and health professionals and about the the immune system and how it can be harnessed to fight cancer (in English and Spanish)
Cancer Research UK provides information on all aspects of brain tumors for patients and their caregivers
MedlinePlus provides links to further information about brain cancer, (including some links to information in Spanish)
The American Brain Tumor Association provides brain tumor resources and information
The National Brain Tumor Society provides educational and support services regarding brain tumors
PMCID: PMC2621261  PMID: 19143470
14.  Release of Neuronal HMGB1 by Ethanol through Decreased HDAC Activity Activates Brain Neuroimmune Signaling 
PLoS ONE  2014;9(2):e87915.
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.
PMCID: PMC3925099  PMID: 24551070
15.  Mammalian DNA Is an Endogenous Danger Signal That Stimulates Local Synthesis and Release of Complement Factor B 
Molecular Medicine  2012;18(1):851-860.
Complement factor B plays a critical role in ischemic tissue injury and autoimmunity. Factor B is dynamically synthesized and released by cells outside of the liver, but the molecules that trigger local factor B synthesis and release during endogenous tissue injury have not been identified. We determined that factor B is upregulated early after cold ischemia–reperfusion in mice, using a heterotopic heart transplant model. These data suggested upregulation of factor B by damage-associated molecular patterns (DAMPs), but multiple common DAMPs did not induce factor B in RAW264.7 mouse macrophages. However, exogenous DNA induced factor B mRNA and protein expression in RAW cells in vitro, as well as in peritoneal and alveolar macrophages in vivo. To determine the cellular mechanisms involved in DNA-induced factor B upregulation we then investigated the role of multiple known DNA receptors or binding partners. We stimulated peritoneal macrophages from wild-type (WT), toll-like receptor 9 (TLR9)-deficient, receptor for advanced glycation end products (RAGE)−/− and myeloid differentiation factor 88 (MyD88)−/− mice, or mouse macrophages deficient in high-mobility group box proteins (HMGBs), DNA-dependent activator of interferon-regulatory factors (DAI) or absent in melanoma 2 (AIM2), with DNA in the presence or absence of lipofection reagent. Reverse transcription–polymerase chain reaction, Western blotting and immunocytochemical analysis were employed for analysis. Synthesis of factor B was independent of TLR9, RAGE, DAI and AIM2, but was dependent on HMGBs, MyD88, p38 and NF-κB. Our data therefore show that mammalian DNA is an endogenous molecule that stimulates factor B synthesis and release from macrophages via HMGBs, MyD88, p38 and NF-κB signaling. This activation of the immune system likely contributes to damage following sterile injury such as hemorrhagic shock and ischemia-reperfusion.
PMCID: PMC3409274  PMID: 22526919
16.  Identification and Characterization of the Lamprey High-Mobility Group Box 1 Gene 
PLoS ONE  2012;7(4):e35755.
High-mobility group box 1 (HMGB1), a highly conserved DNA-binding protein, plays an important role in maintaining nucleosome structures, transcription, and inflammation. We identified a homolog of HMGB1 in the Japanese lamprey (Lampetra japonica). The Lampetra japonica HMGB1 gene (Lj-HMGB1) has over 70% sequence identity with its homologs in jawed vertebrates. Despite the reasonably high sequence identity with other HMGB1 proteins, Lj-HMGB1 did not group together with these proteins in a phylogenetic analysis. We examined Lj-HMGB1 expression in lymphocyte-like cells, and the kidneys, heart, gills, and intestines of lampreys before and after the animals were challenged with lipopolysaccharide (LPS) and concanavalin A (ConA). Lj-HMGB1 was initially expressed at a higher level in the heart, but after treatment with LPS and ConA only the gills demonstrated a significant up-regulation of expression. The recombinant Lj-HMGB1 (rLj-HMGB1) protein bound double-stranded DNA and induced the proliferation of human adenocarcinoma cells to a similar extent as human HMGB1. We further revealed that Lj-HMGB1 was able to induce the production of tumor necrosis factor-α (TNF-α), a pro-inflammatory mediator, in activated human acute monocytic leukemia cells. These results suggest that lampreys use HMGB1 to activate their innate immunity for the purpose of pathogen defense.
PMCID: PMC3338530  PMID: 22563397
17.  Poly(ADP-Ribosyl)ation of High Mobility Group Box 1 (HMGB1) Protein Enhances Inhibition of Efferocytosis 
Molecular Medicine  2011;18(1):359-369.
Phagocytosis of apoptotic cells by macrophages, known as efferocytosis, is a critical process in the resolution of inflammation. High mobility group box 1 (HMGB1) protein was first described as a nuclear nonhistone DNA-binding protein, but is now known to be secreted by activated cells during inflammatory processes, where it participates in diminishing efferocytosis. Although HMGB1 is known to undergo modification when secreted, the effect of such modifications on the inhibitory actions of HMGB1 during efferocytosis have not been reported. In the present studies, we found that HMGB1 secreted by Toll-like receptor 4 (TLR4) stimulated cells is highly poly(ADP-ribosyl)ated (PARylated). Gene deletion of poly(ADP)-ribose polymerase (PARP)-1 or pharmacological inhibition of PARP-1 decreased the release of HMGB1 from the nucleus to the extracellular milieu after TLR4 engagement. Preincubation of macrophages or apoptotic cells with HMGB1 diminished efferocytosis through mechanisms involving binding of HMGB1 to phosphatidylserine on apoptotic cells and to the receptor for advanced glycation end products (RAGE) on macrophages. Preincubation of either macrophages or apoptotic cells with PARylated HMGB1 inhibited efferocytosis to a greater degree than exposure to unmodified HMGB1, and PARylated HMGB1 demonstrated higher affinity for phosphatidylserine and RAGE than unmodified HMGB1. PARylated HMGB1 had a greater inhibitory effect on Ras-related C3 botulinum toxin substrate 1 (Rac-1) activation in macrophages during the uptake of apoptotic cells than unmodified HMGB1. The present results, showing that PARylation of HMGB1 enhances its ability to inhibit efferocytosis, provide a novel mechanism by which PARP-1 may promote inflammation.
PMCID: PMC3356430  PMID: 22204001
18.  DAMP Signaling is a Key Pathway Inducing Immune Modulation after Brain Injury 
The Journal of Neuroscience  2015;35(2):583-598.
Acute brain lesions induce profound alterations of the peripheral immune response comprising the opposing phenomena of early immune activation and subsequent immunosuppression. The mechanisms underlying this brain-immune signaling are largely unknown. We used animal models for experimental brain ischemia as a paradigm of acute brain lesions and additionally investigated a large cohort of stroke patients. We analyzed release of HMGB1 isoforms by mass spectrometry and investigated its inflammatory potency and signaling pathways by immunological in vivo and in vitro techniques. Features of the complex behavioral sickness behavior syndrome were characterized by homecage behavior analysis. HMGB1 downstream signaling, particularly with RAGE, was studied in various transgenic animal models and by pharmacological blockade. Our results indicate that the cytokine-inducing, fully reduced isoform of HMGB1 was released from the ischemic brain in the hyperacute phase of stroke in mice and patients. Cytokines secreted in the periphery in response to brain injury induced sickness behavior, which could be abrogated by inhibition of the HMGB1-RAGE pathway or direct cytokine neutralization. Subsequently, HMGB1-release induced bone marrow egress and splenic proliferation of bone marrow-derived suppressor cells, inhibiting the adaptive immune responses in vivo and vitro. Furthermore, HMGB1-RAGE signaling resulted in functional exhaustion of mature monocytes and lymphopenia, the hallmarks of immune suppression after extensive ischemia. This study introduces the HMGB1-RAGE-mediated pathway as a key mechanism explaining the complex postischemic brain-immune interactions.
PMCID: PMC4293412  PMID: 25589753
alarmins; HMGB1; immunomodulation; myeloid-derived suppressor cell; RAGE; stroke
19.  Hyperglycemia-Induced Reactive Oxygen Species Increase Expression of the Receptor for Advanced Glycation End Products (RAGE) and RAGE Ligands 
Diabetes  2009;59(1):249-255.
RAGE interacts with the endogenous ligands S100 calgranulins and high mobility group box 1 (HMGB1) to induce inflammation. Since hyperglycemia-induced reactive oxygen species (ROS) activate many pathways of diabetic tissue damage, the effect of these ROS on RAGE and RAGE ligand expression was evaluated.
Expression of RAGE, S100A8, S100A12, and HMGB1 was evaluated in human aortic endothelial cells (HAECs) incubated in normal glucose, high glucose, and high glucose after overexpression of either uncoupling protein 1 (UCP1), superoxide dismutase 2 (SOD2), or glyoxalase 1 (GLO1). Expression was also evaluated in normal glucose after knockdown of GLO1. Expression was next evaluated in high glucose after knockdown of nuclear factor (NF)-κB p65 (RAGE) and after knockdown of activated protein-1 (AP-1) (S100A8, S100A12, and HMGB1), and chromatin immunoprecipitation (ChIP) was performed ± GLO1 overexpression for NFκB p65 (RAGE promoter) and AP-1 (S100A8, S100A12, and HMGB1 promoters). Finally, endothelial cells from nondiabetic mice, STZ diabetic mice, and STZ diabetic mice treated with the superoxide dismutase mimetic Mn(III)tetrakis(4-benzoic acid)porphyrin chloride (MnTBAP) were evaluated.
High glucose increased RAGE, S100A8, S100A12, and HMGB1 expression, which was normalized by overexpression of UCP1, SOD2, or GLO1. GLO1 knockdown mimicked the effect of high glucose, and in high glucose, overexpression of GLO1 normalized increased binding of NFκB p65 and AP-1. Diabetes increased RAGE, S100A8, and HMGB1 expression, and MnTBAP treatment normalized this.
These results show that hyperglycemia-induced ROS production increases expression of RAGE and RAGE ligands. This effect is mediated by ROS-induced methylglyoxal, the major substrate of glyoxalase 1.
PMCID: PMC2797929  PMID: 19833897
20.  Clinical chorioamnionitis is characterized by increased expression of the alarmin HMGB1 and One of Its Receptors, sRAGE 
High-mobility group box-1 (HMGB1) protein is an alarmin, a normal cell constituent, which is released into the extracellular environment upon cellular stress/damage, and is capable of activating inflammation and tissue repair. The receptor for advanced glycation end products (RAGE) can bind HMGB1. RAGE, in turn, can induce the production of pro-inflammatory cytokines; this may be modulated the soluble truncated forms of RAGE, including soluble RAGE (sRAGE) and endogenous secretory RAGE (esRAGE). The objective of this study was to determine: 1) if clinical chorioamnionitis at term is associated with changes in amniotic fluid concentrations of HMGB1, sRAGE and esRAGE; and 2) if the amniotic fluid concentration of HMGB1 changes with labor or as a function of gestational age.
Amniotic fluid samples were collected from the following groups: 1) mid-trimester (MT) (n=45); 2) term with (n=48) and without labor (n=22) without intra-amniotic infection; and 3) term with clinical chorioamnionitis (n=46). Amniotic fluid concentrations of HMGB1, sRAGE and esRAGE concentrations were determined by ELISA.
1) the median amniotic fluid HMGB1 concentration was higher in patients at term with clinical chorioamnionitis than that of those without this condition (clinical chorioamnionitis: median 3.8 ng/mL vs. term in labor: median 1.8 ng/mL, p=0.007; and vs. term not in labor median 1.1 ng/mL, p=0.003); 2) in contrast, patients with clinical chorioamnionitis had a lower median sRAGE concentration than those without this condition (clinical chorioamnionitis: median 9.3 ng/mL vs. term in labor: median 18.6 ng/mL, p=0.001; and vs. term not in labor median 28.4 ng/mL, p<0.001); 3) amniotic fluid concentrations of esRAGE did not significantly change in patients with clinical chorioamnionitis at term (clinical chorioamnionitis: median 5.4 ng/mL vs. term in labor: median 6.1 ng/mL, p=0.9; and vs. term not in labor median 9.5 ng/mL, p=0.06); and 4) there was no significant difference in the median AF HMGB1 concentration between women at term in labor and those not in labor (p=0.4) and between women in the mid-trimester and those at term not in labor (mid-trimester: median 1.5 ng/mL; p=0.2).
An increase in the amniotic fluid HMGB1 concentration and a decrease in sRAGE were observed in clinical chorioamnionitis at term. This finding provides evidence that an alarmin, HMGB1, and one of its receptors, sRAGE, are engaged in the process of clinical chorioamnionitis at term. These changes are quite different from those observed in cases of intra-amniotic infection/inflammation in preterm gestations.
PMCID: PMC3914307  PMID: 22578261
danger signal; intra-amniotic inflammation; sterile inflammation; pregnancy; neuroinflammation; neuro-immune reflects; amniotic fluid; DAMPs; damage-associated molecular patterns; intra-amniotic infection; term labor
21.  Receptor for Advanced Glycation End Products (RAGE) on iNKT Cells Mediates Lung Ischemia-Reperfusion Injury 
Activation of invariant natural killer T (iNKT) cells and signaling through receptor for advanced glycation end products (RAGE) are known to independently mediate lung ischemia-reperfusion injury. This study tests the hypothesis that activation of RAGE specifically on iNKT cells via alveolar macrophage-produced high mobility group box 1 (HMGB1) is critical for the initiation of lung ischemia-reperfusion injury. A murine in vivo hilar clamp model was utilized, which demonstrated that RAGE−/− mice were significantly protected from ischemia-reperfusion injury. Treatment of WT mice with soluble RAGE (a decoy receptor), or anti-HMGB1 antibody, attenuated lung ischemia-reperfusion injury and inflammation, whereas treatment with recombinant HMGB1 enhanced ischemia-reperfusion injury in WT mice but not RAGE−/− mice. Importantly, lung dysfunction, cytokine production and neutrophil infiltration were significantly attenuated after ischemia-reperfusion in Jα18−/− mice reconstituted with RAGE−/− iNKT cells (versus WT iNKT cells). In vitro studies demonstrated that, after hypoxia-reoxygenation, alveolar macrophage-derived HMGB1 augmented IL-17 production from iNKT cells in a RAGE-dependent manner. These results suggest that HMGB1-mediated RAGE activation on iNKT cells is critical for initiation of lung ischemia-reperfusion injury and that a crosstalk between macrophages and iNKT cells via the HMGB1/RAGE axis mediates IL-17 production by iNKT cells causing neutrophil infiltration and lung ischemia-reperfusion injury.
PMCID: PMC3776006  PMID: 23865790
HMGB1; alveolar macrophages; iNKT cells; RAGE; IL-17; lung transplantation
22.  sRAGE in diabetic and non-diabetic critically ill patients: effects of intensive insulin therapy 
Critical Care  2011;15(4):R203.
Hyperglycemia represents an independent prognostic factor in critically ill non-diabetic patients but not in those with diabetes. In this context, there is an ongoing debate on the benefit of an intensive insulin therapy, particularly in diabetic patients. We tested the hypothesis that expression of the receptor for advanced glycation end-products (RAGE), an important signal transduction receptor that elicits long-lasting nuclear factor kappa B (NF-κB) activation, may underlie this difference. RAGE expression is regulated by multiple ligands, including high mobility group box-1 (HMGB-1), and is reflected by its released soluble form (sRAGE).
A predesigned analysis was conducted of prospectively collected samples from 76 hyperglycemic critically ill patients (33 type-2 diabetes, 43 non-diabetes) aged ≥18 years with blood glucose of > 6.1 mmol/L enrolled in a randomized controlled trial comparing intensive insulin therapy with conventional insulin therapy. sRAGE and its ligand HMGB-1 together with IL-6, and soluble thrombomodulin (as markers of inflammation and endothelial cell injury, respectively) were evaluated in ICU, at Days 1, 3, 5 and 7. Plasma samples from 18 healthy subjects were used as controls.
Both diabetic and non-diabetic hyperglycemic patients showed increased plasma sRAGE, HMGB-1 and soluble thrombomodulin levels at the time of admission to ICU. Plasma IL-6 concentration was only increased in non-diabetic patients. Plasma levels of sRAGE were higher in diabetic compared with non-diabetic patients. Intensive insulin therapy resulted in a significant decrease of sRAGE and thrombomodulin at Day 7, in diabetic but not in non-diabetic patients. Circulating sRAGE levels correlated positively with IL-6 and soluble thrombomodulin levels and inversely with HMGB-1. Multivariate regression analysis demonstrated that sRAGE remains independently correlated with HMGB-1 only in diabetic patients. Neither sRAGE nor any inflammatory markers are associated with mortality.
These findings support the hypothesis that sRAGE release, time-course and response to intensive insulin therapy differ between hyperglycemic diabetic and non-diabetic critically ill patients. Whether this difference underlies the dissimilarity in clinical outcome of hyperglycemia in these two conditions warrants further studies.
PMCID: PMC3387645  PMID: 21871056
23.  Urine levels of HMGB1 in Systemic Lupus Erythematosus patients with and without renal manifestations 
Arthritis Research & Therapy  2012;14(4):R184.
Lupus nephritis (LN) is a severe and frequent manifestation of systemic lupus erythematosus (SLE). Its pathogenesis has not been fully elucidated but immune complexes are considered to contribute to the inflammatory pathology in LN. High Mobility Group Box 1 (HMGB1) is a nuclear non-histone protein which is secreted from different types of cells during activation and/or cell death and may act as a pro-inflammatory mediator, alone or as part of DNA-containing immune complexes in SLE. Urinary excretion of HMGB1 might reflect renal inflammatory injury. To assess whether urinary HMGB1 reflects renal inflammation we determined serum levels of HMGB1 simultaneously with its urinary levels in SLE patients with and without LN in comparison to healthy controls (HC). We also analyzed urinary HMGB1 levels in relation with clinical and serological disease activity.
The study population consisted of 69 SLE patients and 17 HC. Twenty-one patients had biopsy proven active LN, 15 patients had a history of LN without current activity, and 33 patients had non-renal SLE. Serum and urine levels of HMGB1 were both measured by western blotting. Clinical and serological parameters were assessed according to routine procedures. In 17 patients with active LN a parallel analysis was performed on the expression of HMGB1 in renal biopsies.
Serum and urinary levels of HMGB1 were significantly increased in patients with active LN compared to patients without active LN and HC. Similarly, renal tissue of active LN patients showed strong expression of HMGB1 at cytoplasmic and extracellular sites suggesting active release of HMGB1. Serum and urinary levels in patients without active LN were also significantly higher compared to HC. Urinary HMGB1 levels correlated with SLEDAI, and showed a negative correlation with complement C3 and C4.
Levels of HMGB1 in urine of SLE patients, in particular in those with active LN, are increased and correlate with SLEDAI scores. Renal tissue of LN patients shows increased release of nuclear HMGB1 compared to control renal tissue. HMGB1, although at lower levels, is, however, also present in the urine of patients without active LN. These data suggest that urinary HMGB1 might reflect both local renal inflammation as well as systemic inflammation.
PMCID: PMC3580580  PMID: 22892043
24.  Attenuation of Myocardial Injury by HMGB1 Blockade during Ischemia/Reperfusion Is Toll-Like Receptor 2-Dependent 
Mediators of Inflammation  2013;2013:174168.
Genetic or pharmacological ablation of toll-like receptor 2 (TLR2) protects against myocardial ischemia/reperfusion injury (MI/R). However, the endogenous ligand responsible for TLR2 activation has not yet been detected. The objective of this study was to identify HMGB1 as an activator of TLR2 signalling during MI/R. C57BL/6 wild-type (WT) or TLR2−/−-mice were injected with vehicle, HMGB1, or HMGB1 BoxA one hour before myocardial ischemia (30 min) and reperfusion (24 hrs). Infarct size, cardiac troponin T, leukocyte infiltration, HMGB1 release, TLR4-, TLR9-, and RAGE-expression were quantified. HMGB1 plasma levels were measured in patients undergoing coronary artery bypass graft (CABG) surgery. HMGB1 antagonist BoxA reduced cardiomyocyte necrosis during MI/R in WT mice, accompanied by reduced leukocyte infiltration. Injection of HMGB1 did, however, not increase infarct size in WT animals. In TLR2−/−-hearts, neither BoxA nor HMGB1 affected infarct size. No differences in RAGE and TLR9 expression could be detected, while TLR2−/−-mice display increased TLR4 and HMGB1 expression. Plasma levels of HMGB1 were increased MI/R in TLR2−/−-mice after CABG surgery in patients carrying a TLR2 polymorphism (Arg753Gln). We here provide evidence that absence of TLR2 signalling abrogates infarct-sparing effects of HMGB1 blockade.
PMCID: PMC3859028  PMID: 24371373
25.  Damage-associated molecular patterns (DAMPs) in preterm labor with intact membranes and preterm PROM: a study of the alarmin HMGB1 
Preterm parturition is a syndrome caused by multiple etiologies. Although intra-amniotic infection is causally linked with intrauterine inflammation and the onset of preterm labor, other patients have preterm labor in the absence of demonstrable infection. It is now clear that inflammation may be elicited by activation of the Damage-Associated Molecular Patterns (DAMPs), which include pathogen-associated molecular patterns (PAMPs) as well as “alarmins” (endogenous molecules that signal tissue and cellular damage). A prototypic alarmin is high-mobility group box-1 (HMGB1) protein, capable of inducing inflammation and tissue repair when it reaches the extracellular environment. HMGB1 is a late-mediator of sepsis, and blockade of HMGB1 activity reduces mortality in an animal model of endotoxemia, even if administered late during the course of the disorder. The objectives of this study were to: 1) determine whether intra-amniotic infection/inflammation (IAI) is associated with changes in amniotic fluid concentrations of HMGB1; and 2) localize immunoreactivity of HMGB1 in the fetal membranes and umbilical cord of patients with chorioamnionitis.
Amniotic fluid samples were collected from the following groups: 1) preterm labor with intact membranes (PTL) with (n=42) and without IAI (n=84); and 2) preterm prelabor rupture of membranes (PROM) with (n=38) and without IAI (n=35). IAI was defined as either a positive amniotic fluid culture or amniotic fluid concentration of interleukin-6 (IL-6) ≥2.6 ng/mL. HMGB1 concentrations in amniotic fluid were determined by ELISA. Immunofluorescence staining for HMGB1 was performed in the fetal membranes and umbilical cord of pregnancies with acute chorioamnionitis.
Amniotic fluid HMGB1 concentrations were higher in patients with IAI than in those without IAI in both the PTL and preterm PROM groups (PTL IAI: median 3.1 ng/mL vs. without IAI; median 0.98 ng/mL; p<0.001; and preterm PROM with IAI median 7.3 ng/mL vs. without IAI median 2.6 ng/mL; p=0.002);
patients with preterm PROM without IAI had a higher median amniotic fluid HMGB1 concentration than those with PTL and intact membranes without IAI (p<0.001); and
HMGB1 was immunolocalized to amnion epithelial cells and stromal cells in the Wharton’s jelly (prominent in the nuclei and cytoplasm). Myofibroblasts and macrophages of the chorioamniotic connective tissue layer and infiltrating neutrophils showed diffuse cytoplasmic HMGB1 immunoreactivity.
Intra-amniotic infection/inflammation is associated with elevated amniotic fluid HMGB1 concentrations regardless of membrane status;
preterm PROM was associated with a higher amniotic fluid HMGB1 concentration than PTL with intact membranes, suggesting that rupture of membranes is associated with an elevation of alarmins;
immunoreactive HMGB1 was localized to amnion epithelial cells, Wharton’s jelly and cells involved in the innate immune response; and
we propose that HMGB1 released from stress or injured cells into amniotic fluid may be responsible, in part, for intra-amniotic inflammation due to non-microbial insults.
PMCID: PMC3419589  PMID: 21958433
preterm prelabor rupture of membranes; intra-amniotic infection; intra-amniotic inflammation; chorioamnionitis; alarmin; RAGE; amniotic fluid; danger signal

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