Intracellular High Mobility Group Box 1 Research Articles

GLUT1 mediates the release of HMGB1 from airway epithelial cells in mixed granulocytic asthma

Asthma is quite heterogenous and can be categorized as eosinophilic, mixed granulocytic (presence of both eosinophils and neutrophils in the airways) and neutrophilic. Clinically, mixed granulocytic asthma (MGA) often tends to be severe and requires large doses of corticosteroids. High mobility group box 1 (HMGB1) is one of the epithelium-derived alarmins that contributes to type 2 inflammation and asthma. This study was aimed to investigate the role of glucose transporter 1 (GLUT1) in modulation of airway epithelial HMGB1 production in MGA. Induced sputum and bronchial biopsy specimens were obtained from healthy subjects and asthma patients. BALB/c mice, the airway epithelial cell line BEAS-2B, or primary human bronchial epithelial cells (HBECs) were immunized with allergens. Intracellular and extracellular HMGB1 were both detected. The role of GLUT1 was assessed by using a pharmacological antagonist BAY876. MGA patients have a significant higher sputum HMGB1 level than the health and subjects with other inflammatory phenotypes. Nuclear-to-cytoplasmic translocation of HMGB1 was also observed in the bronchial epithelia. Allergen exposure markedly induced GLUT1 expression in murine lungs and cultured epithelial cells. Pharmacological antagonism of GLUT1 with BAY876 dramatically decreased airway hyperresponsiveness, neutrophil and eosinophil accumulation, as well as type 2 inflammation in murine models of MGA. Besides, the allergen-induced up-regulation of HMGB1 was also partly recovered by BAY876, accompanied by inhibited secretion into the airway lumen. In vitro, treatment with BAY876 relieved the allergen-induced over-expression and secretion of HMGB1 in airway epithelia. Taken together, our data indicated that GLUT1 mediates bronchial epithelial HMGB1 release in MGA.

Deficiency of neutrophil high-mobility group box-1 in liver transplant recipients exacerbates early allograft injury in mice.

Early allograft dysfunction (EAD) is a severe event leading to graft failure after liver transplant (LT). Extracellular high-mobility group box-1 (HMGB1) is a damage-associated molecular pattern that contributes to hepatic ischemia-reperfusion injury (IRI). However, the contribution of intracellular HMGB1 to LT graft injury remains elusive. We hypothesized that intracellular neutrophil-derived HMGB1 from recipients protects from post-LT EAD. We generated mice with conditional ablation or overexpression of Hmgb1 in hepatocytes, myeloid cells, or both. We performed LTs and injected lipopolysaccharide (LPS) to evaluate the effect of intracellular HMGB1 in EAD. Ablation of Hmgb1 in hepatocytes and myeloid cells of donors and recipients exacerbated early allograft injury after LT. Ablation of Hmgb1 from liver grafts did not affect graft injury; however, lack of Hmgb1 from recipient myeloid cells increased reactive oxygen species (ROS) and inflammation in liver grafts and exacerbated injury. Neutrophils lacking HMGB1 were more activated, showed enhanced pro-oxidant and pro-inflammatory signatures, and reduced biosynthesis and metabolism of inositol polyphosphates (InsPs). On LT reperfusion or LPS treatment, there was significant neutrophil mobilization and infiltration into the liver and enhanced production of ROS and pro-inflammatory cytokines when intracellular Hmgb1 was absent. Depletion of neutrophils using anti-Ly6G antibody attenuated graft injury in recipients with myeloid cell Hmgb1 ablation. Neutrophil HMGB1 derived from recipients is central to regulate their activation, limits the production of ROS and pro-inflammatory cytokines, and protects from early liver allograft injury.

Cytoplasmic HMGB1 induces renal tubular ferroptosis after ischemia/reperfusion

As a damage-associated molecular pattern molecule, high-mobility group box 1 (HMGB1) is well-studied and is released from injured tubular epithelial cells to trigger cell death. However, the role of intracellular HMGB1 induced cell death during acute kidney injury (AKI) is poorly understood. We showed that cytosolic HMGB1 induced ferroptosis by binding to acyl-CoA synthetase long-chain family member 4 (ACSL4), the driver of ferroptosis, following renal ischemia/reperfusion (I/R). Both mouse and human kidneys with acute tubular injury were characterized by nucleocytoplasmic translocation of HMGB1in tubular cells. Pharmacological inhibition of HMGB1 nucleocytoplasmic translocation and deletion of HMGB1 in tubular epithelial cells in mice inhibited I/R-induced AKI, tubular ferroptosis, and inflammation compared to those in controls. Co-immunoprecipitation and serial section staining confirmed the interaction between HMGB1 and ACSL4. Taken together, our results demonstrated that cytoplasmic HMGB1 is essential for exacerbating inflammation-associated cellular injury by activating renal tubular ferroptosis via ACSL4 after I/R injury. These findings indicate that cytoplasmic HMGB1 is a regulator of ferroptosis and a promising therapeutic target for AKI.

Tubular Epithelial Cell HMGB1 Promotes AKI-CKD Transition by Sensitizing Cycling Tubular Cells to Oxidative Stress: A Rationale for Targeting HMGB1 during AKI Recovery.

Cells undergoing necrosis release extracellular high mobility group box (HMGB)-1, which triggers sterile inflammation upon AKI in mice. Neither deletion of HMGB1 from tubular epithelial cells, nor HMGB1 antagonism with small molecules, affects initial ischemic tubular necrosis and immediate GFR loss upon unilateral ischemia/reperfusion injury (IRI). On the contrary, tubular cell-specific HMGB1 deficiency, and even late-onset pharmacological HMGB1 inhibition, increased functional and structural recovery from AKI, indicating that intracellular HMGB1 partially counters the effects of extracellular HMGB1. In vitro studies indicate that intracellular HMGB1 decreases resilience of tubular cells from prolonged ischemic stress, as in unilateral IRI. Intracellular HMGB1 is a potential target to enhance kidney regeneration and to improve long-term prognosis in AKI. Late diagnosis is a hurdle for treatment of AKI, but targeting AKI-CKD transition may improve outcomes. High mobility group box-1 (HMGB1) is a nuclear regulator of transcription and a driver of necroinflammation in AKI. We hypothesized that HMGB1 would also modulate AKI-CKD transition in other ways. We conducted single-cell transcriptome analysis of human and mouse AKI and mouse in vivo and in vitro studies with tubular cell-specific depletion of Hmgb1 and HMGB1 antagonists. HMGB1 was ubiquitously expressed in kidney cells. Preemptive HMGB1 antagonism with glycyrrhizic acid (Gly) and ethyl pyruvate (EP) did not affect postischemic AKI but attenuated AKI-CKD transition in a model of persistent kidney hypoxia. Consistently, tubular Hmgb1 depletion in Pax8 rtTA, TetO Cre, Hmgb1fl/fl mice did not protect from AKI, but from AKI-CKD transition. In vitro studies confirmed that absence of HMGB1 or HMGB1 inhibition with Gly and EP does not affect ischemic necrosis of growth-arrested differentiated tubular cells but increased the resilience of cycling tubular cells that survived the acute injury to oxidative stress. This effect persisted when neutralizing extracellular HMGB1 with 2G7. Consistently, late-onset HMGB1 blockade with EP started after the peak of ischemic AKI in mice prevented AKI-CKD transition, even when 2G7 blocked extracellular HMGB1. Treatment of AKI could become feasible when ( 1 ) focusing on long-term outcomes of AKI; ( 2 ) targeting AKI-CKD transition with drugs initiated after the AKI peak; and ( 3 ) targeting with drugs that block HMGB1 in intracellular and extracellular compartments.

Hepatocyte high-mobility group box 1 protects against steatosis and cellular stress during high fat diet feeding

BackgroundCirculating high-mobility group box 1 (HMGB1) plays important roles in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Intracellular HMGB1 is critical for the biology of hepatocytes. However, the intracellular role of HMGB1 in hepatocellular steatosis is unknown. Therefore, we aimed to investigate the role of hepatocyte-specific HMGB1 (HC-HMGB1) in development of hepatic steatosis.MethodsWild type (WT) C57BL/6 and HC-HMGB1−/− mice were fed high-fat diet (HFD) or low-fat diet (LFD) for up to 16 weeks.ResultsAs expected, HMGB1 translocated from nuclear into cytoplasm and released into circulation after HFD treatment. HC-HMGB1 deficiency significantly reduced circulating HMGB1, suggesting that hepatocyte is a major source of circulating HMGB1 during NAFLD. Unexpectedly, HC-HMGB1 deficiency promoted rapid weight gain with enhanced hepatic fat deposition compared with WT at as early as 4 weeks after HFD treatment. Furthermore, there was no difference between WT and HC-HMGB1−/− mice in glucose tolerance, energy expenditure, liver damage or systemic inflammation. Interestingly, hepatic gene expression related to free fatty acid (FFA) β-oxidation was significantly down-regulated in HC-HMGB1−/− mice compared with WT, and endoplasmic reticulum (ER) stress markers were significantly higher in livers of HC-HMGB1−/− mice. In vitro experiments using primary mouse hepatocytes showed absence of HMGB1 increased FFA-induced intracellular lipid accumulation, accompanied by increased ER-stress, significant downregulation of FFA β-oxidation, and reduced oxidative phosphorylation.ConclusionsOur findings suggest that hepatocyte HMGB1 protects against dysregulated lipid metabolism via maintenance of β-oxidation and prevention of ER stress. This represents a novel mechanism for HMGB1-regulation of hepatocellular steatosis, and suggests that stabilizing HMGB1 in hepatocytes may be effective strategies for prevention and treatment of NAFLD.

Cardiomyocyte-Restricted High-mobility group box 1 (HMGB1) deletion leads to small heart and inflammation through GR/PGC-1a signaling

Abstract Cardiomyocyte-Restricted High-mobility group box 1 (HMGB1) Deletion Leads to small heart and inflammation Through GR/PGC-1a signaling Background Cardiac growth and remodeling are key biological process influencing the physiological performance of the heart. Previous study showed critical role of intracellular HMGB1 in vitro. However, the in vivo study using conditional Hmgb1 ablation did not significantly affect the cellular and organic function. Purpose Previously we have demonstrated the extracellular effect of HMGB1 as a proinflammatory molecule on cardiac remodeling. Here, to elucidate the intracellular effect of HMGB1 on cardiac function in vivo, we perform the study. Methods Conditional genetic deletion of HMGB1 mouse was constructed using cTnT-Cre Hmgb1fl/fl. And then we detected body weight, and analyzed cardiac function of 12-week old mice using echocardiography. The subcelluar morphology was detected using the transmission electron microscopy (TEM) examination, and the changes of glycolipid metabolism was detected by the positron emission tomography (PET)/computed tomography (CT) imaging and GC-FID/MS analysis in heart tissue. And Then we used RNA-seq to find transcriptomic changes. And co-immunoprecipitation experiments, chromatin immunoprecipiptation (ChIP) were used to validate the binding of HMGB1 and glucocorticoid receptor (GR). The downstream signal changes were detected using western blot analysis. To validate the result, we further constructed the cardiac HMGB1 deficient mouse using Ckmm-Cre Hmgb1fl/fl, and measured body weight and cardiac function. Results We found HMGB1 deletion by cTnT-Cre in mouse hearts altered GR function, glycolipid metabolism, and eventually led to growth retardation, small heart, and heart failure. The subcelluar morphology didn't show significant change caused by HMGB1 knockout. The heart showed significantly elevation of glycolysis and free fatty acid deposition, and related enzyme changes. Transcriptomic analysis revealed a list of differential expressed genes, which coincide with the glucocorticoid receptor function in neonatal mice, and significant increase inflammatory genes of the adult ones. The cardiac HMGB1 knockout lead to a series changes of PGC-1a, UCP3, and glycerol kinase, which were the cause of metabolic change and further impact the cardiac function. And the Ckmm-Cre Hmgb1fl/fl mouse didn't show significant phenotype, which was consistent with the reported negative result of Cardiomyocyte-specific Hmgb1 deletion via MHC-Cre. Conclusions Therefore, our results demonstrated that HMGB1 plays an essential role in maintaining normal cardiac growth and function by regulating GR function and glycolipid metabolism. And the strikingly different phenotype from the cardiac-specific HMGB1-deficient mice may be caused by the cross with different Cre mouse. Main results and graphic summary Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): National Natural Science Foundation of China

Cardiomyocyte-restricted high-mobility group box 1 (HMGB1) deletion leads to small heart and glycolipid metabolic disorder through GR/PGC-1\u03b1 signalling

Cardiac growth and remodelling are key biological processes influencing the physiological performance of the heart, and a previous study showed a critical role for intracellular HMGB1 in vitro. However, the in vivo study, which used conditional Hmgb1 ablation, did not show a significant effect on cellular or organic function. We have demonstrated the extracellular effect of HMGB1 as a pro-inflammatory molecule on cardiac remodelling. In this study, we found that HMGB1 deletion by cTnT-Cre in mouse hearts altered glucocorticoid receptor (GR) function and glycolipid metabolism, eventually leading to growth retardation, small heart and heart failure. The subcellular morphology did not show a significant change caused by HMGB1 knockout. The heart showed significant elevation of glycolysis, free fatty acid deposition and related enzyme changes. Transcriptomic analysis revealed a list of differentially expressed genes that coincide with glucocorticoid receptor function in neonatal mice and a significant increase in inflammatory genes in adult mice. Cardiac HMGB1 knockout led to a series of changes in PGC-1α, UCP3 and GyK, which were the cause of metabolic changes and further impacted cardiac function. Ckmm-Cre Hmgb1fl/fl mice did not show a specific phenotype, which was consistent with the reported negative result of cardiomyocyte-specific Hmgb1 deletion via MHC-Cre. We concluded that HMGB1 plays essential roles in maintaining normal cardiac growth, and different phenotype from cardiac-specific HMGB1-deficient mice may be caused by the cross with mice of different Cre strains.

Endothelial HMGB1 Is a Critical Regulator of LDL Transcytosis via an SREBP2-SR-BI Axis.

LDL (low-density lipoprotein) transcytosis across the endothelium is performed by the SR-BI (scavenger receptor class B type 1) receptor and contributes to atherosclerosis. HMGB1 (high mobility group box 1) is a structural protein in the nucleus that is released by cells during inflammation; extracellular HMGB1 has been implicated in advanced disease. Whether intracellular HMGB1 regulates LDL transcytosis through its nuclear functions is unknown. Approach and Results: HMGB1 was depleted by siRNA in human coronary artery endothelial cells, and transcytosis of LDL was measured by total internal reflection fluorescence microscopy. Knockdown of HMGB1 attenuated LDL transcytosis without affecting albumin transcytosis. Loss of HMGB1 resulted in reduction in SR-BI levels and depletion of SREBP2 (sterol regulatory element-binding protein 2)-a transcription factor upstream of SR-BI. The effect of HMGB1 depletion on LDL transcytosis required SR-BI and SREBP2. Overexpression of HMGB1 caused an increase in LDL transcytosis that was unaffected by inhibition of extracellular HMGB1 or depletion of RAGE (receptor for advanced glycation endproducts)-a cell surface receptor for HMGB1. The effect of HMGB1 overexpression on LDL transcytosis was prevented by knockdown of SREBP2. Loss of HMGB1 caused a reduction in the half-life of SREBP2; incubation with LDL caused a significant increase in nuclear localization of HMGB1 that was dependent on SR-BI. Animals lacking endothelial HMGB1 exhibited less acute accumulation of LDL in the aorta 30 minutes after injection and when fed a high-fat diet developed fewer fatty streaks and less atherosclerosis. Endothelial HMGB1 regulates LDL transcytosis by prolonging the half-life of SREBP2, enhancing SR-BI expression. Translocation of HMGB1 to the nucleus in response to LDL requires SR-BI.

HMGB1 in Radiotherapy: A Two Headed Signal Regulating Tumor Radiosensitivity and Immunity.

Radiotherapy (RT) is a mainstay of cancer treatment. Recent studies have shown that RT not only directly induces cell death but also has late and sustained immune effects. High mobility group box 1 (HMGB1) is a nuclear protein released during RT, with location-dependent functions. It is essential for normal cellular function but also regulates the proliferation and migration of tumor cells by binding to high-affinity receptors. In this review, we summarize recent evidence on the functions of HMGB1 in RT according to the position, intracellular HMGB1 and extracellular HMGB1. Intracellular HMGB1 induces radiation tolerance in tumor cells by promoting DNA damage repair and autophagy. Extracellular HMGB1 plays a more intricate role in radiation-related immune responses, wherein it not only stimulates the anti-tumor immune response by facilitating the recognition of dying tumor cells but is also involved in maintaining immunosuppression. Factors that potentially affect the role of HMGB1 in RT-induced cytotoxicity have also been discussed in the context of possible therapeutic applications, which helps to develop effective and targeted radio-sensitization therapies.

Involvement of Intracellular and Extracellular High-Mobility Group Box-1 in the Progression of Esophageal Squamous Cell Carcinoma.

High-mobility group box-1 (HMGB1) is involved in a broad range of inflammatory responses and the progression of various types of malignancy. However, the roles of HMGB1 in the progression of esophageal squamous cell carcinoma (ESCC) are unclear. The aim of this study was to investigate the significance of intracellular and extracellular HMGB1 in ESCC. HMGB1 levels were measured in the tissue and plasma of patients with ESCC, or in ESCC cell lines and their conditioned medium. The effects of downregulation of intracellular HMGB1 or upregulation of extracellular HMGB1 on proliferation, cell migration, and invasion were evaluated using proliferation, transwell, and wound healing assays. Downregulation of HMGB1 expression inhibited cell proliferation, migration, and invasion. On the other hand, upregulation of extracellular HMGB1 level by addition of recombinant HMGB1 promoted the migratory and invasive abilities of ESCC cells through increases of phosphorylation of the signal-regulated kinase 1/2 and NF-κBp65 proteins. These effects of extracellular HMGB1 were attenuated by treatment with recombinant soluble thrombomodulin, which adsorbs HMGB1. The expression of HMGB1 was significantly higher in tumor tissue (p = 0.008), and the concentration of HMGB1 in the plasma was significantly higher in patients with ESCC than in healthy volunteers (p = 0.04). Cancer-specific survival was worse in patients with high concentration of plasma HMGB1 (p = 0.01). Increase of HMGB1 levels in tumor cells or plasma plays a crucial role in the malignant potential of ESCC. Intracellular and extracellular HMGB1 may be a therapeutic target in ESCC.

Analysis of Circulating HMGB1 in Human Serum.

As a ubiquitous nuclear protein, high-mobility group box 1 (HMGB1) is constitutively expressed and can be actively secreted by macrophages/monocytes, as well as passively released from damaged cells following pathological injuries. Studies indicate that HMGB1 functions as a mediator of infection- and injury-elicited inflammatory diseases. Although intracellular HMGB1 functions as a regulator of tumorigenesis, epigenetic anticancer agents or therapeutic γ-ray irradiation could also cause active secretion or passive release of HMGB1, enabling serum HMGB1 to serve as a biomarker for the diagnosis and therapy of various cancers. Here we describe a semiquantitative immune blotting method to measure HMGB1 in human serum, in comparison with a commercially available HMGB1 enzyme-linked immunosorbent assay (ELISA) technique.

Cannabinoid receptor 2 promotes the intracellular degradation of HMGB1 via the autophagy-lysosome pathway in macrophage

High mobility group box 1 (HMGB1) is a late phase inflammatory mediator in many inflammatory diseases. Extracellular HMGB1 could bind to many membrane receptors to activate downstream signaling molecules and promote inflammation resulting in cell and tissue damage. In our previous work, we found cannabinoid receptor Ⅱ(CB2R) inhibited the expression of HMGB1 in lipopolysaccharide (LPS)-induced septic models in vivo and in vitro, but the underlying mechanism is still unclear. The present study was aimed to explore the possible pathway through which CB2R suppressed HMGB1. Here, we found that the specific agonist of CB2R, GW405833 (GW) could induce intracellular HMGB1 degradation without influencing HMGB1 mRNA in peritoneal macrophages. Then we observed that autophagy inhibitor 3-methyladenine (3-MA) but not proteasome inhibitor MG-132 (MG) could block GW-induced HMGB1 degradation, which indicated that the autophagy-lysosome but not the ubiquitination pathway was involved in this process. Further study showed that GW could promote the integrity of autophagy flux in macrophages in terms of increased level of LC3Ⅱand decreased expression of p62 protein. It also observed that inhibition of autophagy blocked GW-induced nuclear translocation of HMGB1 in macrophages. GW could up-regulate expression of Cathepsin B (CTSB), and inhibition of CTSB blocked GW-induced HMGB1 degradation. In summary, all the data showed that activation of CB2R could promote the intracellular degradation of HMGB1 via the autophagy-lysosome pathway in macrophage.

Role of High-Mobility Group Box-1 in Liver Pathogenesis.

High-mobility group box 1 (HMGB1) is a highly abundant DNA-binding protein that can relocate to the cytosol or undergo extracellular release during cellular stress or death. HMGB1 has a functional versatility depending on its cellular location. While intracellular HMGB1 is important for DNA structure maintenance, gene expression, and autophagy induction, extracellular HMGB1 acts as a damage-associated molecular pattern (DAMP) molecule to alert the host of damage by triggering immune responses. The biological function of HMGB1 is mediated by multiple receptors, including the receptor for advanced glycation end products (RAGE) and Toll-like receptors (TLRs), which are expressed in different hepatic cells. Activation of HMGB1 and downstream signaling pathways are contributing factors in the pathogenesis of non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease (ALD), and drug-induced liver injury (DILI), each of which involves sterile inflammation, liver fibrosis, ductular reaction, and hepatic tumorigenesis. In this review, we will discuss the critical role of HMGB1 in these pathogenic contexts and propose HMGB1 as a bona fide and targetable DAMP in the setting of common liver diseases.

High Mobility Group Box 1: An Immune-regulatory Protein.

High mobility group box 1 (HMGB1) presents in almost all somatic cells as a component of the cell nucleus. It is necessary for transcription regulation during cell development. Recent studies indicate that extracellular HMGB1, coming from necrotic cells or activated immune cells, triggers inflammatory response whereas intracellular HMGB1 controls the balance between autophagy and apoptosis. In addition, reduced HMGB1 can effectively mediate tissue regeneration. HMGB1, therefore, is regarded as a therapeutic target for inflammatory diseases. In this review, we summarized and discussed the immunomodulatory effect of HMGB1.

HMGB1 mediated autophagy protects glioblastoma cells from carbon-ion beam irradiation injury

The present study investigated autophagy changes and the expression of HMGB1 in human glioblastoma cells, responding to carbon-ion beam irradiation (35 keV/μm, 80.55 MeV/u). U251 cells were irradiated with carbon-ion beams and cell proliferation was measured by counting the number of living cells. The expression of Light Chain 3 beta (LC3B), Beclin 1, high-mobility-group box 1 (HMGB1), pro-form caspase-3 and Cellular FLICE-like inhibitory protein (c-FLIP) was analyzed by western blotting. Caspase enzyme activity was determined via a caspase cleavage based florescent substrate commercial Kit. Living cell counting demonstrated a time- and dose-dependent cell death in U251 cells. The expression of LC3B and Beclin 1 revealed that, a high level of autophagy was induced 24 h after irradiation with 1 Gy carbon ions and then decreased in a time- and dose-dependent manner. The expression of the whole HMGB1 showed a well correlation with the dynamic autophagic level. Cytoplasmic HMGB1 maintained autophagy was concluded. Enzyme-Linked Immuno Sorbent Assay (ELISA) measurement found that, HMGB1 was released into the extracellular space in a time- and dose-dependent manner. Lower intracellular HMGB1 levels correlated with decreased autophagy as measured by the expression of LC3B. Decreased expression of pro-form caspase-3 and c-FLIP as well as the increased caspase enzyme activity indicated that apoptosis was induced by carbon-ion beam irradiation. Inhibition of HMGB1 release from the area of intracellular to that of extracellular significantly increased cell survival. In summary, carbon-ion beam irradiation could elevate autophagy and HMGB1 expression efficiently, which would protect the cells from programmed cell death via inducing autophagy. Apoptosis as measured by expression of caspase activities increased as the dose increased, which was accompanied with decreased levels of LC3B and HMGB1.

Cytosolic HMGB1 Mediates Autophagy Activation in an Emulsified Isoflurane Anesthesia Cell Model.

Inhalation anesthetic isoflurane may cause an increased risk of cognitive impairment. Previous studies have indicated that this cognitive decline is associated with neuroinflammation mediated by high mobility group box 1 (HMGB1). HMGB1 is released from cells and acts as a damage-associated molecule in neurodegenerative diseases. However, the effect of intracellular HMGB1 during emulsified isoflurane (EI) exposure is poorly understood. The purpose of this study was to investigate the effect of autophagy on neuroprotection, evaluate variation of HMGB1, and determine its role in autophagic flux after EI exposure in vitro. We observed that EI decreased cell viability in a concentration-dependent manner, accompanied by an increase in autophagic flux. EI exposure also elevates the HMGB1 level in cytoplasm. Further, cytosolic HMGB1 was necessary for autophagy by perturbing the beclin1-Bcl-2 interaction. Most importantly, autophagy induction by rapamycin alleviated EI-provoked cell injury, and HMGB1 knockdown induced autophagy inhibition, which exacerbated cell damage. Based on these findings, we propose that autophagic flux is sustained and upregulated in response to EI exposure by increased cytosolic HMGB1, and that autophagy activation serves as a protective mechanism against EI-induced cytotoxicity. Thus, the complex roles of HMGB1 make it pivotal in reducing EI-induced neuronal damage.

High Mobility Group Box 1 (HMGB1) Predicts Invasion and Poor Prognosis of Glioblastoma Multiforme via Activating AKT Signaling in an Autocrine Pathway.

BackgroundAs a nuclear protein and a secreted protein, HMGB1 is involved in many cellular processes such as proliferation, transcription, and inflammation. The overexpression of HMGB1 in various types of cancers is reported, but its clinical significance and prognostic value in glioblastoma multiforme (GBM) has not been well defined.Material/MethodsThe expression of HMGB1 in 116 patients with GBM was investigated with immunohistochemistry, and was detected with qRT-PCR in 12 pairs of tumor tissues and adjacent tissues. The correlations between HMGB1 and clinicopathological factors were analyzed with the chi-square test. Prognostic value of HMGB1 was evaluated with univariate analysis and multivariate analysis. By knocking down HMGB1 by siRNA, the functions of HMGB1 in progression of GBM cell lines were investigated by experiments in vitro.ResultsIn our study, patients with high HMGB1 expression accounted for 42.2% of all the patients. High HMGB1 was correlated with low survival rates and was identified as an independent prognostic factor of GBM. Knockdown of intracellular HMGB1 remarkably decreased GBM cells proliferation and invasion. In hypoxia, intracellular HMGB1 of GBM cells was released out and activated AKT and ERK signaling pathways, thus promoting GBM cell invasion in this autocrine pathway.ConclusionsHMGB1 is an independent prognostic biomarker for unfavorable prognosis of patients with GBM. Released HMGB1 of GBM cells can activate AKT and ERK signaling pathways and promote GBM cells invasion in this autocrine pathway, indicating that anti-HMGB1 therapy may be a promising treatment for GBM.

The dual role of HMGB1 in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of exocrine pancreatic cancer with a 9% five-year survival rate. High mobility group box 1 (HMGB1) is a nuclear protein that can act as a DNA chaperone in the sustainment of chromosome structure and function. When released into the extracellular space, HMGB1 becomes the most well-characterized damage-associated molecular pattern (DAMP) to trigger immune responses. Recent evidence indicates that intracellular HMGB1 is a novel tumor suppressor in PDAC, which is connected to its role in the prevention of oxidative stress, genomic instability, and histone release. However, since extracellular HMGB1 is a DAMP and pro-inflammatory cytokine, cancer cells can also exploit it to survive through the receptor for advanced glycation endproducts (RAGE) in the pancreatic tumor microenvironment. Interestingly, targeting the HMGB1-RAGE pathway has become a new anticancer therapy strategy for PDAC.

Effects of remote ischaemic preconditioning on intraportal islet transplantation in a rat model.

Remote ischaemic preconditioning (RIPC), which is the intermittent interruption of blood flow to a site distant from the target organ, is known to improve solid organ resistance to ischaemia-reperfusion injury. This procedure could be of interest in islet transplantation to mitigate hypoxia-related loss of islet mass after isolation and transplantation. Islets isolated from control or RIPC donors were analyzed for yield, metabolic activity, gene expression and high mobility group box-1 (HMGB1) content. Syngeneic marginal mass transplantation was performed in four streptozotocin-induced diabetic groups: control, RIPC in donor only, RIPC in recipient only, and RIPC in donor and recipient. Islets isolated from RIPC donors had an increased yield of 20% after 24h of culture compared to control donors (P=0.007), linked to less cell death (P=0.08), decreased expression of hypoxia-related genes (Hif1a P=0.04; IRP94 P=0.008), and increased intra-cellular (P=0.04) and nuclear HMGB1. The use of RIPC in recipients only did not allow for reversal of diabetes, with increased serum HMGB1 at day 1; the three other groups demonstrated significantly better outcomes. Performing RIPC in the donors increases islet yield and resistance to hypoxia. Validation is needed, but this strategy could help to decrease the number of donors per islet recipient.

Lack of Benefit on Brain Edema, Blood-Brain Barrier Permeability, or Cognitive Outcome in Global Inducible High Mobility Group Box 1 Knockout Mice Despite Tissue Sparing after Experimental Traumatic Brain Injury.

High mobility group box 1 (HMGB1) is a prototypical danger-associated molecular pattern molecule that is considered a late mediator of neuro-inflammation after traumatic brain injury (TBI). Prior studies have suggested that targeting HMGB1 may lead to neuroprotective effects, but none of these studies have reported cognitive outcomes. We hypothesized that loss of HMGB1 before and after TBI would markedly attenuate post-traumatic brain edema, blood-brain barrier (BBB) permeability, improve functional deficits and long-term neuropathology versus control mice. Using the controlled cortical impact model and conditional global HMGB1 knockout (HMGB1 KO) mice, we demonstrate that there was a neuroprotective effect seen in the HMGB1 KO versus wild-type control evidenced by a significant reduction in contusion volume. However, two surprising findings were 1) the lack of benefit on either post-traumatic brain edema or BBB permeability, and 2) that spatial memory performance was impaired in HMGB1 KO naïve mice such that the behavioral effects of HMGB1 deletion in uninjured naïve mice were similar to those observed after TBI. Our data suggest the possibility that the role of HMGB1 in TBI is a "double-edged sword"; that is, despite the benefits on selected aspects of secondary injury, the sustained absence of HMGB1 may impair cognitive function, even in naïve mice. Given the pleiotropic actions of extracellular and intracellular HMGB1, when evaluating the potential use of therapies targeting HMGB1, effects on long-term cognitive outcome should be carefully evaluated. It also may be prudent in future studies to examine cell-specific effects of manipulating the HMGB1 pathway.