High-mobility group box1 protein promotes neuroinflammation after intracerebral hemorrhage in rats

HMGB1/RAGE axis in tumor development: unraveling its significance

High mobility group protein 1 (HMGB1) plays a complex role in tumor biology. When released into the extracellular space, it binds to the receptor for advanced glycation end products (RAGE) located on the cell membrane, playing an important role in tumor development by regulating a number of biological processes and signal pathways. In this review, we outline the multifaceted functions of the HMGB1/RAGE axis, which encompasses tumor cell proliferation, apoptosis, autophagy, metastasis, and angiogenesis. This axis is instrumental in tumor progression, promoting tumor cell proliferation, autophagy, metastasis, and angiogenesis while inhibiting apoptosis, through pivotal signaling pathways, including MAPK, NF-κB, PI3K/AKT, ERK, and STAT3. Notably, small molecules, such as miRNA-218, ethyl pyruvate (EP), and glycyrrhizin exhibit the ability to inhibit the HMGB1/RAGE axis, restraining tumor development. Therefore, a deeper understanding of the mechanisms of the HMGB1/RAGE axis in tumors is of great importance, and the development of inhibitors targeting this axis warrants further exploration.

Role of Inflammatory Processes in Hemorrhagic Stroke

Hemorrhagic stroke is the deadliest form of stroke and includes the subtypes of intracerebral hemorrhage and subarachnoid hemorrhage. A common cause of hemorrhagic stroke in older individuals is cerebral amyloid angiopathy. Intracerebral hemorrhage and subarachnoid hemorrhage both lead to the rapid collection of blood in the central nervous system and generate inflammatory immune responses that involve both brain resident and infiltrating immune cells. These responses are complex and can contribute to both tissue recovery and tissue injury. Despite the interconnectedness of these major subtypes of hemorrhagic stroke, few reviews have discussed them collectively. The present review provides an update on inflammatory processes that occur in response to intracerebral hemorrhage and subarachnoid hemorrhage, and the role of inflammation in the pathophysiology of cerebral amyloid angiopathy-related hemorrhage. The goal is to highlight inflammatory processes that underlie disease pathology and recovery. We aim to discuss recent advances in our understanding of these conditions and identify gaps in knowledge with the potential to develop effective therapeutic strategies.

The Role of Arginine-Vasopressin in Stroke and the Potential Use of Arginine-Vasopressin Type 1 Receptor Antagonists in Stroke Therapy: A Narrative Review

Stroke is a life-threatening condition in which accurate diagnoses and timely treatment are critical for successful neurological recovery. The current acute treatment strategies, particularly non-invasive interventions, are limited, thus urging the need for novel therapeutical targets. Arginine vasopressin (AVP) receptor antagonists are emerging as potential targets to treat edema formation and subsequent elevation in intracranial pressure, both significant causes of mortality in acute stroke. Here, we summarize the current knowledge on the mechanisms leading to AVP hyperexcretion in acute stroke and the subsequent secondary neuropathological responses. Furthermore, we discuss the work supporting the predictive value of measuring copeptin, a surrogate marker of AVP in stroke patients, followed by a review of the experimental evidence suggesting AVP receptor antagonists in stroke therapy. As we highlight throughout the narrative, critical gaps in the literature exist and indicate the need for further research to understand better AVP mechanisms in stroke. Likewise, there are advantages and limitations in using copeptin as a prognostic tool, and the translation of findings from experimental animal models to clinical settings has its challenges. Still, monitoring AVP levels and using AVP receptor antagonists as an add-on therapeutic intervention are potential promises in clinical applications to alleviate stroke neurological consequences.

HMGB1 in nervous system diseases: A common biomarker and potential therapeutic target

High-mobility group box-1 (HMGB1) is a nuclear protein associated with early inflammatory changes upon extracellular secretion expressed in various cells, including neurons and microglia. With the progress of research, neuroinflammation is believed to be involved in the pathogenesis of neurological diseases such as Parkinson's, epilepsy, and autism. As a key promoter of neuroinflammation, HMGB1 is thought to be involved in the pathogenesis of Parkinson's disease, stroke, traumatic brain injury, epilepsy, autism, depression, multiple sclerosis, and amyotrophic lateral sclerosis. However, in the clinic, HMGB1 has not been described as a biomarker for the above-mentioned diseases. However, the current preclinical research results show that HMGB1 antagonists have positive significance in the treatment of Parkinson's disease, stroke, traumatic brain injury, epilepsy, and other diseases. This review discusses the possible mechanisms by which HMGB1 mediates Parkinson's disease, stroke, traumatic brain injury, epilepsy, autism, depression, multiple sclerosis, amyotrophic lateral sclerosis, and the potential of HMGB1 as a biomarker for these diseases. Future research needs to further explore the underlying molecular mechanisms and clinical translation.

Treatment of Marmoset Intracerebral Hemorrhage with Humanized Anti-HMGB1 mAb

Intracerebral hemorrhage (ICH) is recognized as a severe clinical problem lacking effective treatment. High mobility group box-1 (HMGB1) exhibits inflammatory cytokine-like activity once released into the extracellular space from the nuclei. We previously demonstrated that intravenous injection of rat anti-HMGB1 monoclonal antibody (mAb) remarkably ameliorated brain injury in a rat ICH model. Therefore, we developed a humanized anti-HMGB1 mAb (OKY001) for clinical use. The present study examined whether and how the humanized anti-HMGB1 mAb ameliorates ICH injury in common marmosets. The results show that administration of humanized anti-HMGB1 mAb inhibited HMGB1 release from the brain into plasma, in association with a decrease of 4-hydroxynonenal (4-HNE) accumulation and a decrease in cerebral iron deposition. In addition, humanized anti-HMGB1 mAb treatment resulted in a reduction in brain injury volume at 12 d after ICH induction. Our in vitro experiment showed that recombinant HMGB1 inhibited hemoglobin uptake by macrophages through CD163 in the presence of haptoglobin, suggesting that the release of excess HMGB1 from the brain may induce a delay in hemoglobin scavenging, thereby allowing the toxic effects of hemoglobin, heme, and Fe2+ to persist. Finally, humanized anti-HMGB1 mAb reduced body weight loss and improved behavioral performance after ICH. Taken together, these results suggest that intravenous injection of humanized anti-HMGB1 mAb has potential as a novel therapeutic strategy for ICH.

HMGB1/TLR4 induces autophagy and promotes neuroinflammation after intracerebral hemorrhage

BACKGROUND AND PURPOSE

Intracerebral hemorrhage (ICH) causes autophagy as well as inflammation; the latter is known to involve the high-mobility group box 1 protein (HMGB1)/Toll-like receptor 4 (TLR4) axis. Here we investigated whether this axis may help mediate both the autophagy and inflammation associated with ICH.

METHODS

ICH was induced by injecting autologous blood into Sprague-Dawley rats, followed in some cases by intracerebroventricular injection of short interfering RNA (siRNA) against HMGB1 or TLR4 at 6 h after ICH induction or by intraperitoneal injection of the autophagy inhibitor 3-methyladenine (3-MA) or autophagy activator rapamycin at 6, 24, and 48 h after ICH induction. Western blotting, immunohistochemistry or immunofluorescence was used to assess levels of HMGB1/TLR4 signaling pathway proteins as well as markers of autophagy (LC3B, Beclin1, Atg5) or inflammation (IL-1 beta, TNF-α). Numbers of apoptotic cells were determined using TUNEL staining. Changes in levels of these proteins were correlated with neurological deficits measured using the modified Neurological Severity Score.

RESULTS

ICH caused HMGB1 to translocate from the nucleus into the cytoplasm, and it up-regulated expression of TLR4 and myeloid differentiation factor 88 (MyD88), and induced neurological deficits. Administering siRNA against HMGB1 or TLR4 reversed this up-regulation. Levels of markers of autophagy (LC3B, Beclin1, Atg5) or inflammation (IL-1 beta, TNF-α) were significantly higher 72 h after ICH than at baseline, as were the numbers of TUNEL-positive cells. Administering siRNA against HMGB1 or TLR4 markedly alleviated inflammation, and autophagy, apoptosis, and neurological deficits. Similarly, administering autophagy inhibitor 3-MA alleviated inflammation, apoptosis, and neurological deficits. Conversely, autophagy activator rapamycin exacerbated these effects of ICH.

CONCLUSIONS

During the acute phase of ICH, the HMGB1/TLR4/MyD88 axis acts via autophagy to promote inflammation.

Diet-Induced High Serum Levels of Trimethylamine-N-oxide Enhance the Cellular Inflammatory Response without Exacerbating Acute Intracerebral Hemorrhage Injury in Mice

Trimethylamine-N-oxide (TMAO), an intestinal flora metabolite of choline, may aggravate atherosclerosis by inducing a chronic inflammatory response and thereby promoting the occurrence of cerebrovascular diseases. Knowledge about the influence of TMAO-related inflammatory response on the pathological process of acute stroke is limited. This study was designed to explore the effects of TMAO on neuroinflammation, brain injury severity, and long-term neurologic function in mice with acute intracerebral hemorrhage (ICH). We fed mice with either a regular chow diet or a chow diet supplemented with 1.2% choline pre- and post-ICH. In this study, we measured serum levels of TMAO with ultrahigh-performance liquid chromatography-tandem mass spectrometry at 24 h and 72 h post-ICH. The expression level of P38-mitogen-protein kinase (P38-MAPK), myeloid differentiation factor 88 (MyD88), high-mobility group box1 protein (HMGB1), and interleukin-1β (IL-1β) around hematoma was examined by western blotting at 24 h. Microglial and astrocyte activation and neutrophil infiltration were examined at 72 h. The lesion was examined on days 3 and 28. Neurologic deficits were examined for 28 days. A long-term choline diet significantly increased serum levels of TMAO compared with a regular diet at 24 h and 72 h after sham operation or ICH. Choline diet-induced high serum levels of TMAO did not enhance the expression of P38-MAPK, MyD88, HMGB1, or IL-1β at 24 h. However, it did increase the number of activated microglia and astrocytes around the hematoma at 72 h. Contrary to our expectations, it did not aggravate acute or long-term histologic damage or neurologic deficits after ICH. In summary, choline diet-induced high serum levels of TMAO increased the cellular inflammatory response probably by activating microglia and astrocytes. However, it did not aggravate brain injury or worsen long-term neurologic deficits. Although TMAO might be a potential risk factor for cerebrovascular diseases, this exploratory study did not support that TMAO is a promising target for ICH therapy.

Dysregulation of microRNA and Intracerebral Hemorrhage: Roles in Neuroinflammation

Intracerebral hemorrhage (ICH) is a major public health problem and devastating subtype of stroke with high morbidity and mortality. Notably, there is no effective treatment for ICH. Neuroinflammation, a pathological hallmark of ICH, contributes to both brain injury and repair and hence, it is regarded as a potential target for therapeutic intervention. Recent studies document that microRNAs, small non-coding RNA molecules, can regulate inflammatory brain response after ICH and are viable molecular targets to alter brain function. Therefore, there is an escalating interest in studying the role of microRNAs in the pathophysiology of ICH. Herein, we provide, for the first time, an overview of the microRNAs that play roles in ICH-induced neuroinflammation and identify the critical knowledge gap in the field, as it would help design future studies.

Intracerebral Hemorrhage and Diabetes Mellitus: Blood-Brain Barrier Disruption, Pathophysiology, and Cognitive Impairments

There is a surge in diabetes incidence with an estimated 463 million individuals been diagnosed worldwide. Diabetes Mellitus (DM) is a major stroke-related comorbid condition that increases the susceptibility of disabling post-stroke outcomes. Although less common, intracerebral hemorrhage (ICH) is the most dramatic subtype of stroke that is associated with higher mortality, particularly in DM population. Previous studies have focused mainly on the impact of DM on ischemic stroke. Few studies have focused on impact of DM on ICH and discussed the blood-brain barrier disruption, brain edema, and hematoma formation. However, more recently, investigating the role of oxidative damage and reactive oxygen species (ROS) production in preclinical studies involving DM-ICH animal models has gained attention. But, little is known about the correlation between neuroinflammatory processes, glial cells activation, and peripheral immune cell invasion with DM-ICH injury. DM and ICH patients experience impaired abilities in multiple cognitive domains by relatively comparable mechanisms, which could get exacerbated in the setting of comorbidities. In this review, we discuss both the pathology of DM as a comorbid condition for ICH and the potential molecular therapeutic targets for the clinical management of the ICH and its recovery.

High Mobility Group Box-1 and Blood-Brain Barrier Disruption

Increasing evidence suggests that inflammatory responses are involved in the progression of brain injuries induced by a diverse range of insults, including ischemia, hemorrhage, trauma, epilepsy, and degenerative diseases. During the processes of inflammation, disruption of the blood–brain barrier (BBB) may play a critical role in the enhancement of inflammatory responses and may initiate brain damage because the BBB constitutes an interface between the brain parenchyma and the bloodstream containing blood cells and plasma. The BBB has a distinct structure compared with those in peripheral tissues: it is composed of vascular endothelial cells with tight junctions, numerous pericytes surrounding endothelial cells, astrocytic endfeet, and a basement membrane structure. Under physiological conditions, the BBB should function as an important element in the neurovascular unit (NVU). High mobility group box-1 (HMGB1), a nonhistone nuclear protein, is ubiquitously expressed in almost all kinds of cells. HMGB1 plays important roles in the maintenance of chromatin structure, the regulation of transcription activity, and DNA repair in nuclei. On the other hand, HMGB1 is considered to be a representative damage-associated molecular pattern (DAMP) because it is translocated and released extracellularly from different types of brain cells, including neurons and glia, contributing to the pathophysiology of many diseases in the central nervous system (CNS). The regulation of HMGB1 release or the neutralization of extracellular HMGB1 produces beneficial effects on brain injuries induced by ischemia, hemorrhage, trauma, epilepsy, and Alzheimer’s amyloidpathy in animal models and is associated with improvement of the neurological symptoms. In the present review, we focus on the dynamics of HMGB1 translocation in different disease conditions in the CNS and discuss the functional roles of extracellular HMGB1 in BBB disruption and brain inflammation. There might be common as well as distinct inflammatory processes for each CNS disease. This review will provide novel insights toward an improved understanding of a common pathophysiological process of CNS diseases, namely, BBB disruption mediated by HMGB1. It is proposed that HMGB1 might be an excellent target for the treatment of CNS diseases with BBB disruption.

Brain injury and repair after intracerebral hemorrhage: The role of microglia and brain-infiltrating macrophages

Intracerebral hemorrhage (ICH) is a major public health problem characterized by cerebral bleeding. Despite recent advances in preclinical studies, there is no effective treatment for ICH making it the deadliest subtype of stroke. The lack of effective treatment options partly attributes to the complexity as well as poorly defined pathophysiology of ICH. The emerging evidence indicates the potential of targeting secondary brain damage and hematoma resolution for improving neurological outcomes after ICH. Herein, we provide an overview of our understanding of the functional roles of activated microglia and brain-infiltrating monocyte-derived macrophages in brain injury and repair after ICH. The clinical and preclinical aspects that we discuss in this manuscript are related to ICH that occurs in adults, but not in infants. Also, we attempt to identify the knowledge gap in the field for future functional studies given the potential of targeting microglia and brain-infiltrating macrophages for therapeutic intervention after ICH.

Interaction of Microglia and Astrocytes in the Neurovascular Unit

The interaction between microglia and astrocytes significantly influences neuroinflammation. Microglia/astrocytes, part of the neurovascular unit (NVU), are activated by various brain insults. The local extracellular and intracellular signals determine their characteristics and switch of phenotypes. Microglia and astrocytes are activated into two polarization states: the pro-inflammatory phenotype (M1 and A1) and the anti-inflammatory phenotype (M2 and A2). During neuroinflammation, induced by stroke or lipopolysaccharides, microglia are more sensitive to pathogens, or damage; they are thus initially activated into the M1 phenotype and produce common inflammatory signals such as IL-1 and TNF-α to trigger reactive astrocytes into the A1 phenotype. These inflammatory signals can be amplified not only by the self-feedback loop of microglial activation but also by the unique anatomy structure of astrocytes. As the pathology further progresses, resulting in local environmental changes, M1-like microglia switch to the M2 phenotype, and M2 crosstalk with A2. While astrocytes communicate simultaneously with neurons and blood vessels to maintain the function of neurons and the blood-brain barrier (BBB), their subtle changes may be identified and responded by astrocytes, and possibly transferred to microglia. Although both microglia and astrocytes have different functional characteristics, they can achieve immune "optimization" through their mutual communication and cooperation in the NVU and build a cascaded immune network of amplification.

High-mobility group box 1 protein (HMGB1) from Cherry Valley duck mediates signaling pathways and antiviral activity

High-mobility group box 1 protein (HMGB1) shows endogenous damage-associated molecular patterns (DAMPs) and is also an early warning protein that activates the body's innate immune system. Here, the full-length coding sequence of HMGB1 was cloned from the spleen of Cherry Valley duck and analyzed. We find that duck HMGB1(duHMGB1) is mostly located in the nucleus of duck embryo fibroblast (DEF) cells under normal conditions but released into the cytoplasm after lipopolysaccharide (LPS) stimulation. Knocking-down or overexpressing duHMGB1 had no effect on the baseline apoptosis rate of DEF cells. However, overexpression increased weakly apoptosis after LPS activation. In addition, overexpression strongly activated the IFN-I/IRF7 signaling pathway in DEF cells and significantly increased the transcriptional level of numerous pattern recognition receptors (PRRs), pro-inflammatory cytokines (IL-6, TNF-α), IFNs and antiviral molecules (OAS, PKR, Mx) starting from 48 h post-transfection. Overexpression of duHMGB1 strongly impacted duck virus replication, either by inhibiting it from the first stage of infection for novel duck reovirus (NDRV) and at late stage for duck Tembusu virus (DTMUV) or duck plague virus (DPV), or promoting replication at early stage for DTMUV and DPV infection. Importantly, data from duHMGB1 overexpression and knockdown experiments, time-dependent DEF cells transcriptional immune responses suggest that duHMGB1 and RIG-I receptor might cooperate to promote the expression of antiviral proteins after NDRV infection, as a potential mechanism of duHMGB1-mediated antiviral activity.

Nrdp1 increases neuron apoptosis via downregulation of Bruce following intracerebral haemorrhage

Background

Neuregulin receptor degradation protein-1 (Nrdp1) is an E3 ubiquitin ligase that plays an important role in regulating cell growth, apoptosis and oxidative stress. However, the data regarding its expression and exact mechanism in neuronal injury following ICH has not been well identified.

Methods

In this study, primary cortical neurons from C57BL/6 mice were subjected to erythrocyte lysates. Nrdp1 expression, cell apoptosis, caspase-3 and BRUCE levels were detected. In addition, inflammatory response, brain edema, and neurological injury in ICH mice were also assessed.

Results

We found that the expression of Nrdp1 was significantly increased in neuron cells accompanied by up-regulation of active caspase-3 and decreased expression of BRUCE (an inhibitor of apoptosis protein). However, inhibiting Nrdp1 levels of neurons reduced caspase-3 activity but induced up-regulation of BRUCE. In vivo, inhibiting Nrdp1 levels increased pro-inflammatory cytokines, brain edema, and neurological injury following ICH.

Conclusions

Taken together, the data suggested that Nrdp1 might play a crucial role in neuronal apoptosis via inhibiting BRUCE following ICH.

Anti-HMGB1 monoclonal antibody therapy for a wide range of CNS and PNS diseases

High mobility group box-1 (HMGB1), a representative damage associated-molecular pattern (DAMP), has been reported to be involved in many inflammatory diseases. Several drugs are thought to have potential to control the translocation and secretion of HMGB1, or to neutralize extracellular HMGB1 by binding to it. One of these drugs, anti-HMGB1 monoclonal antibody (mAb), is highly specific for HMGB1 and has been shown to be effective for the treatment of a wide range of CNS diseases when modeled in animals, including stroke, traumatic brain injury, Parkinson's disease, epilepsy and Alzheimer's disease. Thus, anti-HMGB1 mAb not only is useful for target validation but also has extensive potential for the treatment of the above-mentioned diseases. In this review, we summarize existing knowledge on the effects of anti-HMGB1 mAb on CNS and PNS diseases, the common features of translocation and secretion of HMGB1 and the functional roles of HMGB1 in these diseases. The existing literature suggests that anti-HMGB1 mAb therapy would be effective for a wide range of CNS and PNS diseases.

Phenotypic Effects of Wild-Type and Mutant SOD1 Expression in N9 Murine Microglia at Steady State, Inflammatory and Immunomodulatory Conditions

Accumulation of mutated superoxide dismutase 1 (mSOD1) in amyotrophic lateral sclerosis (ALS) involves injury to motor neurons (MNs), activation of glial cells and immune unbalance. However, neuroinflammation, besides its detrimental effects, also plays beneficial roles in ALS pathophysiology. Therefore, the targeting of microglia to modulate the release of inflammatory neurotoxic mediators and their exosomal dissemination, while strengthening cell neuroprotective properties, has gained growing interest. We used the N9 microglia cell line to identify phenotype diversity upon the overexpression of wild-type (WT; hSOD1WT) and mutated G93A (hSOD1G93A) protein. To investigate how each transduced cell respond to an inflammatory stimulus, N9 microglia were treated with lipopolysaccharide (LPS). Glycoursodeoxycholic acid (GUDCA) and dipeptidyl vinyl sulfone (VS), known to exert neuroprotective properties, were tested for their immunoregulatory properties. Reduced Fizz1, IL-10 and TLR4 mRNAs were observed in both transduced cells. However, in contrast with hSOD1WT-induced decreased of inflammatory markers, microglia transduced with hSOD1G93A showed upregulation of pro-inflammatory (TNF-α/IL-1β/HMGB1/S100B/iNOS) and membrane receptors (MFG-E8/RAGE). Importantly, their derived exosomes were enriched in HMGB1 and SOD1. When inflammatory-associated miRNAs were evaluated, increased miR-146a in cells with overexpressed hSOD1WT was not recapitulated in their exosomes, whereas hSOD1G93A triggered elevated exosomal miR-155/miR-146a, but no changes in cells. LPS stimulus increased M1/M2 associated markers in the naïve microglia, including MFG-E8, miR-155 and miR-146a, whose expression was decreased in both hSOD1WT and hSOD1G93A cells treated with LPS. Treatment with GUDCA or VS led to a decrease of TNF-α, IL-1β, HMGB1, S100B and miR-155 in hSOD1G93A microglia. Only GUDCA was able to increase cellular IL-10, RAGE and TLR4, together with miR-21, while decreased exosomal miR-155 cargo. Conversely, VS reduced MMP-2/MMP-9 activation, as well as upregulated MFG-E8 and miR-146a, while producing miR-21 shuttling into exosomes. The current study supports the powerful role of overexpressed hSOD1WT in attenuating M1/M2 activation, and that of hSOD1G93A in switching microglia from the steady state into a reactive phenotype with low responsiveness to stimuli. This work further reveals GUDCA and VS as promising modulators of microglia immune response by eliciting common and compound-specific molecular mechanisms that may promote neuroregeneration.

Dynamic protein changes in the perihaemorrhagic zone of Surgically Treated Intracerebral Haemorrhage Patients

The secondary injury cascades exacerbating the initial brain injury following intracerebral haemorrhage (ICH) are incompletely understood. We used dual microdialysis (MD) catheters placed in the perihaemorrhagic zone (PHZ) and in seemingly normal cortex (SNX) at time of surgical ICH evacuation in ten patients (range 26–70 years). Routine interstitial MD markers (including glucose and the lactate/pyruvate ratio) were analysed and remaining microdialysate was analysed by two-dimensional gel electrophoresis (2-DE) and nano-liquid chromatography tandem mass spectrometry (nLC-MS/MS). Two time intervals were analysed; median 2–10 hours post-surgery (time A) and median 68–76 hours post-ICH onset (time B). Using 2-DE, we quantified 232 ± 31 different protein spots. Two proteins differed between the MD catheters at time A, and 12 proteins at time B (p < 0.05). Thirteen proteins were significantly altered between time A and time B in the SNX and seven proteins in the PHZ, respectively. Using nLC-MS/MS ca 800 proteins were identified out of which 76 were present in all samples. At time A one protein was upregulated and two downregulated, and at time B, seven proteins were upregulated, and four downregulated in the PHZ compared to the SNX. Microdialysis-based proteomics is feasible for study of secondary injury mechanisms and discovery of biomarkers after ICH.

Glycyrrhizin, an HMGB1 inhibitor, exhibits neuroprotective effects in rats after lithium-pilocarpine-induced status epilepticus

Objectives

It has been proven that extracellular HMGB1 is involved in progression of neurologic disorders, such as stroke, traumatic brain injury, meningitis and epilepsy. Glycyrrhizin (GL) is a direct inhibitor of HMGB1, and blocks HMGB1 release into the extracellular. We aim in this study to investigate the neuroprotective effects of GL in a rat model after lithium-pilocarpine-induced status epilepticus (SE).

Methods

Adult male SD rats were divided into three groups: Sham group, SE-group and (SE + GL)-treated group. The HMGB1 expression in serum and hippocampus, the damage extent of blood brain barrier (BBB) and hippocampal neuronal damage were evaluated by enzyme-linked immunosorbent assay, immunohistochemistry, western blot and nissl's staining.

Key findings

Glycyrrhizin markedly reduced HMGB1 expression in serum and hippocampus, prevented HMGB1 translocation from nucleus to cytoplasm in hippocampal CA1, CA3 and hilus areas of SE rats. Meanwhile, GL significantly ameliorated neuronal damage in the CA1, CA3 and hilus areas of hippocampus, and protected BBB disruption after SE. The administration of GL significantly decreased the mortality from 25 to 8.9% in rats.

Conclusions

Glycyrrhizin may exert neuroprotective effects via inhibiting HMGB1 and protect BBB permeability in lithium-pilocarpine-induced rats with SE.

HMGB1: A Common Biomarker and Potential Target for TBI, Neuroinflammation, Epilepsy, and Cognitive Dysfunction

High mobility group box protein 1 (HMGB1) is a ubiquitous nuclear protein released by glia and neurons upon inflammasome activation and activates receptor for advanced glycation end products (RAGE) and toll-like receptor (TLR) 4 on the target cells. HMGB1/TLR4 axis is a key initiator of neuroinflammation. In recent days, more attention has been paid to HMGB1 due to its contribution in traumatic brain injury (TBI), neuroinflammatory conditions, epileptogenesis, and cognitive impairments and has emerged as a novel target for those conditions. Nevertheless, HMGB1 has not been portrayed as a common prognostic biomarker for these HMGB1 mediated pathologies. The current review discusses the contribution of HMGB1/TLR4/RAGE signaling in several brain injury, neuroinflammation mediated disorders, epileptogenesis and cognitive dysfunctions and in the light of available evidence, argued the possibilities of HMGB1 as a common viable biomarker of the above mentioned neurological dysfunctions. Furthermore, the review also addresses the result of preclinical studies focused on HMGB1 targeted therapy by the HMGB1 antagonist in several ranges of HMGB1 mediated conditions and noted an encouraging result. These findings suggest HMGB1 as a potential candidate to be a common biomarker of TBI, neuroinflammation, epileptogenesis, and cognitive dysfunctions which can be used for early prediction and progression of those neurological diseases. Future study should explore toward the translational implication of HMGB1 which can open the windows of opportunities for the development of innovative therapeutics that could prevent several associated HMGB1 mediated pathologies discussed herein.

The role of HMGB1 in neuroinflammation and tissue repair: A potential therapeutic target for depression?

High mobility group protein box 1 (HMGB1), a sophisticated danger signal with pleiotropic functions, has been proved to function as a pro-inflammatory cytokine. In the central neural system (CNS), HMGB1 can stimulate microglia, the immune cell in the CNS, to release inflammatory factors and to cause chronic neurodegeneration. The evidence showed that HMGB1 can act as a pro-inflammatory cytokine mainly through its receptors like advanced glycation end product (RAGE), Toll-like 4 (TLR4), and so on. Moreover, HMGB1 contributed to the priming effects of stress-pretreatment and played a key role in neurodegeneration diseases via mediating neuroinflammation. However, the evidence also showed that HMGB1 played a role in tissue repair, with the ability to promote cell migration and proliferation, to induce the differentiation of mesenchymal stem cells (MSCs), and to regenerate spinal cord. These pleiotropic functions of HMGB1 make it possible to play a role from cell death to new life. Depression is a chronic, severe, and often life-threatening disease accompanied with impaired neurogenesis. The evidence showed that neuroinflammation played a key role in the process of depression. Depressive patients often showed a high expression of inflammatory cytokines in the blood and an activation of microglia in the brain. Meanwhile, they also showed a neuron deficit in the brain. Though they lack direct evidence linking HMGB1 with depression, the ability of HMGB1 that can function from neuroinflammation to tissue repair makes HMGB1 a promising therapeutic target of depression.

Early antagonism of cerebral high mobility group box-1 protein is benefit for sepsis induced brain injury

Sepsis induced brain injury acts as an acute complication and accounts for deterioration and high mortality rate of septic condition. HMGB1 is a late inflammatory mediator that plays a critical role in brain dysfunction and diseases. However, the role of HMGB1 in sepsis induced brain dysfunction remains intricate. The current study investigated the effect of HMGB1 on brain injury in septic mice model with intracerebroventricular injection of BoxA (a specific antagonist of HMGB1). The expression of HMGB1, morphological changes of brain tissues, apoptosis of brain cells, and alteration of behavior were determined. The expressions of HMGB1 in cortex, hippocampus, and striatum were significantly enhanced in the sepsis group when compared with the sham group. In septic conditions, brain tissues showed significant abnormalities in tissue structure, and increased apoptosis of brain cells which was caspase-3 dependent. Septic mice showed suppression of locomotor activity and impairment of memory and learning. Neutralizing brain HMGB1 significantly improved brain injury and apoptosis of brain cells, and further ameliorated disturbed locomotor activities and damaged memory and learning. However, no significant improvement of survival rate was seen after inhibiting central HMGB1. These results reveal that HMGB1 is a potential target for ameliorating sepsis induced brain injury with early antagonizing.

RETRACTED: Effect of microRNA-129-5p targeting HMGB1-RAGE signaling pathway on revascularization in a collagenase-induced intracerebral hemorrhage rat model

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. An Expression of Concern for this article was previously published while an investigation was conducted (see related editorial: https://doi.org/10.1016/j.biopha.2022.113812). This retraction notice supersedes the Expression of Concern published earlier. Concern was raised about the reliability of the Western blot data in Figure 2A, which contain suspected image duplications within the β-actin blot, and appear to represent a distinct phenotype as found in many other publications, as detailed here: https://pubpeer.com/publications/83FD53A8F4C5B60E2187CBF9F29B01; and here: https://docs.google.com/spreadsheets/d/1r0MyIYpagBc58BRF9c3luWNlCX8VUvUuPyYYXzxWvgY/edit#gid=262337249. Independent analysis confirmed these findings and also identified additional suspected image duplications within Figures 3 and 4A. The journal requested the corresponding author comment on these concerns and provide the associated raw data. The authors did not respond to this request and therefore the Editor-in-Chief decided to retract the article.

Modulators of microglial activation and polarization after intracerebral haemorrhage

Intracerebral haemorrhage (ICH) is the most lethal subtype of stroke but currently lacks effective treatment. Microglia are among the first non-neuronal cells on the scene during the innate immune response to ICH. Microglia respond to acute brain injury by becoming activated and developing classic M1-like (proinflammatory) or alternative M2-like (anti-inflammatory) phenotypes. This polarization implies as yet unrecognized actions of microglia in ICH pathology and recovery, perhaps involving microglial production of proinflammatory or anti-inflammatory cytokines and chemokines. Furthermore, alternatively activated M2-like microglia might promote phagocytosis of red blood cells and tissue debris, a major contribution to haematoma clearance. Interactions between microglia and other cells modulate microglial activation and function, and are also important in ICH pathology. This Review summarizes key studies on modulators of microglial activation and polarization after ICH, including M1-like and M2-like microglial phenotype markers, transcription factors and key signalling pathways. Microglial phagocytosis, haematoma resolution, and the potential crosstalk between microglia and T lymphocytes, neurons, astrocytes, and oligodendrocytes in the ICH brain are described. Finally, the clinical and translational implications of microglial polarization in ICH are presented, including the evidence that therapeutic approaches aimed at modulating microglial function might mitigate ICH injury and improve brain repair.

HMGB1 promotes neurovascular remodeling via Rage in the late phase of subarachnoid hemorrhage

High-mobility group box1 (HMGB1) is a nuclear protein widely expressed in the central nervous system. Extracellular HMGB1 serves as a proinflammatory cytokine and contributes to brain injury during the acute stage post-stroke. Recently, increasing evidence has demonstrated beneficial effects of HMGB1 in some types of brain injury, but little is known about its effects during the late phase of subarachnoid hemorrhage (SAH). This study was designed to explore the potential roles and mechanisms of HMGB1 and its receptor, receptor for advanced glycation end-products (Rage), on brain recovery in the late stage of experimental SAH. Two inhibitors of HMGB1, ethyl pyruvate and glycyrrhizin (EP and GA), and Rage antagonist FPS-ZM1 were used to determine whether HMGB1 promotes brain recovery after SAH. The administration of EP, GA, and FPS-ZM1 effectively reduced HMGB1 and Rage expression. Correspondingly, protein levels of beneficial growth factors (NGF, BDNF, and VEGF) and numbers of BrdU and DCX positive neurons in the cortex were also decreased. The biphasic roles of HMGB1 may be based on the different redox modifications of cysteine residues. In this research, rats injected with two different redox status HMGB1 showed different prognosises at 7-14day after SAH. Recombinant HMGB1 can promote cytokine stimulating activity and aggravate brain injury. However, oxidized HMGB1 was unable to stimulate TNF production but can promote brain recovery by promoting neurotrophin expression. In conclusion, our investigation identified that HMGB1 promotes neurovascular recovery via Rage and may act in the oxidized state in the late stage of SAH.

Anti-high mobility group box-1 (HMGB1) antibody inhibits hemorrhage-induced brain injury and improved neurological deficits in rats

As one of the most lethal stroke subtypes, intracerebral hemorrhage (ICH) is acknowledged as a serious clinical problem lacking effective treatment. Available evidence from preclinical and clinical studies suggests that inflammatory mechanisms are involved in the progression of ICH-induced secondary brain injury. High mobility group box-1 (HMGB1) is a ubiquitous and abundant nonhistone DNA-binding protein, and is also an important proinflammatory molecule once released into the extracellular space from the nuclei. Here, we show that treatment with neutralizing anti-HMGB1 mAb (1 mg/kg, i.v. twice) remarkably ameliorated ICH-injury induced by local injection of collagenase IV in the striatum of rats. Administration of anti-HMGB1 mAb inhibited the release of HMGB1 into the extracellular space in the peri-hematomal region, reduced serum HMGB1 levels and decreased brain edema by protecting blood-brain barrier integrity, in association with decreased activated microglia and the expression of inflammation-related factors at 24 h after ICH. Consequently, anti-HMGB1 mAb reduced the oxidative stress and improved the behavioral performance of rats. These results strongly indicate that HMGB1 plays a critical role in the development of ICH-induced secondary injury through the amplification of plural inflammatory responses. Intravenous injection of neutralizing anti-HMGB1 mAb has potential as a novel therapeutic strategy for ICH.

Stages of the Inflammatory Response in Pathology and Tissue Repair after Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a major health concern, with high rates of mortality and morbidity and no highly effective clinical interventions. Basic research in animal models of ICH has provided insight into its complex pathology, in particular revealing the role of inflammation in driving neuronal death and neurologic deficits after hemorrhage. The response to ICH occurs in four distinct phases: (1) initial tissue damage and local activation of inflammatory factors, (2) inflammation-driven breakdown of the blood-brain barrier, (3) recruitment of circulating inflammatory cells and subsequent secondary immunopathology, and (4) engagement of tissue repair responses that promote tissue repair and restoration of neurologic function. The development of CNS inflammation occurs over many days after initial hemorrhage and thus may represent an ideal target for treatment of the disease, but further research is required to identify the mechanisms that promote engagement of inflammatory versus anti-inflammatory pathways. In this review, the authors examine how experimental models of ICH have uncovered critical mediators of pathology in each of the four stages of the inflammatory response, and focus on the role of the immune system in these processes.

Functions and mechanisms of microglia/macrophages in neuroinflammation and neurogenesis after stroke

Microglia/macrophages are the major immune cells involved in the defence against brain damage. Their morphology and functional changes are correlated with the release of danger signals induced by stroke. These cells are normally responsible for clearing away dead neural cells and restoring neuronal functions. However, when excessively activated by the damage-associated molecular patterns following stroke, they can produce a large number of proinflammatory cytokines that can disrupt neural cells and the blood-brain barrier and influence neurogenesis. These effects indicate the important roles of microglia/macrophages in the pathophysiological processes of stroke. However, the modifiable and adaptable nature of microglia/macrophages may also be beneficial for brain repair and not just result in damage. These distinct roles may be attributed to the different microglia/macrophage phenotypes because the M1 population is mainly destructive, while the M2 population is neuroprotective. Additionally, different gene expression signature changes in microglia/macrophages have been found in diverse inflammatory milieus. These biofunctional features enable dual roles for microglia/macrophages in brain damage and repair. Currently, it is thought that the proper inflammatory milieu may provide a suitable microenvironment for neurogenesis; however, detailed mechanisms underlying the inflammatory responses that initiate or inhibit neurogenesis remain unknown. This review summarizes recent progress concerning the mechanisms involved in brain damage, repair and regeneration related to microglia/macrophage activation and phenotype transition after stroke. We also argue that future translational studies should be targeting multiple key regulating molecules to improve brain repair, which should be accompanied by the concept of a "therapeutic time window" for sequential therapies.

Different effects of arginine vasopressin on high-mobility group box 1 expression in astrocytes isolated from stroke-prone spontaneously hypertensive rats and congenic SHRpch1_18 rats

Stroke-prone spontaneously hypertensive rats (SHRSP/Izm) develop severe hypertension and astrocytic oedema following ischaemic stimulation. During ischaemic stress high-mobility group box 1 (Hmgb1) expression in astrocytes is induced, and subsequently potentiates deterioration of the brain due to ischaemic injury, which manifests as both cerebral inflammation and astrocytic oedema. Arginine vasopressin (AVP) induces brain injury and increases astrocytic swelling. After stroke, Hmgb1 and peroxiredoxin (Prx) are released at different times and activate macrophages in the brain via Toll-like receptors (Tlr2s). The purpose of this study was to examine whether AVP and/or hypoxia and reoxygenation (H/R) contribute to Hmgb1 regulation following ischaemic stroke. Thus, Hmgb1, Prx2 and Tlr2 expression levels in astrocytes isolated from Wistar Kyoto rats (WKY/Izm), spontaneously hypertensive rats (SHR/Izm), SHRSP/Izm and congenic rat strain SHRpch1_18 treated with AVP and/or H/R were compared. Gene and protein expression levels were determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and real-time quantitative PCR, and Western blot. mRNA expression of Hmgb1, Prx2 and Tlr2 induced by AVP was dose-dependent, and Hmgb1 and Prx2 expression was higher in SHR/Izm, SHRSP/Izm and SHRch1_18 than in WKY/Izm. Tlr2 expression with AVP was reduced in SHR/Izm compared to WKY/Izm. In SHRpch1_18, Hmgb1 expression increased after AVP plus H/R. AVP-modulated expression of Hmgb1 protein was reduced by the addition of the antioxidant N-acetylcysteine (NAC). These results suggest that oxidative stress by AVP enhanced expression of Hmgb1, Prx2 and Tlr2 in astrocytes. We hypothesize that regulation of Hmgb1 by AVP during H/R might be related to induction of inflammation and stroke in SHRSP/Izm and SHRpch1_18 rats.

Microglial Polarization and Inflammatory Mediators After Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of stroke with high mortality and morbidity. When a diseased artery within the brain bursts, expansion and absorption of the resulting hematoma trigger a series of reactions that cause primary and secondary brain injury. Microglia are extremely important for removing the hematoma and clearing debris, but they are also a source of ongoing inflammation. This article discusses the role of microglial activation/polarization and related inflammatory mediators, such as Toll-like receptor 4, matrix metalloproteinases, high-mobility group protein box-1, nuclear factor erythroid 2-related factor 2, heme oxygenase, and iron, in secondary injury after ICH and highlights the potential targets for ICH treatment.

The Role of HMGB1 in Cardiovascular Biology: Danger Signals

SIGNIFICANCE

Cardiovascular disease (CVD) is the leading cause of mortality worldwide. Accumulating evidence shows that dysregulated immune response contributes to several types of CVDs such as atherosclerosis and pulmonary hypertension (PH). Vascular intimal impairment and low-density lipoprotein oxidation trigger a complex network of innate immune responses and sterile inflammation.

RECENT ADVANCES

High-mobility group box 1 (HMGB1), a nuclear DNA-binding protein, was recently discovered to function as a damage-associated molecular pattern molecule (DAMP) that initiates the innate immune responses. These findings lead to the understanding that HMGB1 plays a critical role in the inflammatory response in the pathogenesis of CVD.

CRITICAL ISSUES

In this review, we highlight the role of extracellular HMGB1 as a proinflammatory mediator as well as a DAMP in coronary artery disease, cerebral artery disease, peripheral artery disease, and PH.

FUTURE DIRECTIONS

A key focus for future researches on HMGB1 location, structure, modification, and signaling will reveal HMGB1's multiple functions and discover a targeted therapy that can eliminate HMGB1-mediated inflammation without interfering with adaptive immune responses.

Brain recovery mediated by toll-like receptor 4 in rats after intracerebral hemorrhage

Activation of the immune system via toll-like receptor 4 (TLR4) is implicated in both negative and positive processes in the central nervous system, including inflammation and angiogenesis. Whether TLR4 also participates in brain recovery following intracerebral hemorrhage (ICH) has not been investigated. We used the rat model of collagenase-induced ICH to determine whether TLR4 acts as a key regulator of brain recovery in the late phase of injury. After ICH, TLR4 levels in the ipsilateral striatum were significantly higher in the ICH group than in the Sham group on days 1, 3, 7 and 14 after ICH induction. By 14 d, the ICH group showed significantly higher levels of vascular endothelial growth factor, brain-derived neurotrophic factor, and MMP-9 than the Sham group, as well as greater numbers of vessels and BrdU- and DCX-positive cells. All these ICH-induced increases were significantly smaller in the TAK-242 group. The TLR4 antagonist also inhibited the recovery of neurological function after ICH. A TLR4 antagonist reduced ICH-induced neurogenesis and angiogenesis in a rat. These findings suggest that TLR4 may promote brain repair in the late phase of ICH.

Blockade of high mobility group box-1 signaling via the receptor for advanced glycation end-products ameliorates inflammatory damage after acute intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating disease with no specific treatment. Increasing evidence indicates that inflammatory response plays a critical role in ICH-induced damage. High mobility group box-1 protein (HMGB1) may trigger inflammatory response via three putative receptors: receptor for advanced glycation end-products (RAGE), toll-like receptor-2 (TLR2) and toll-like receptor-4 (TLR4). Which receptor participates in HMGB1-induced inflammation during acute ICH is unknown. Using a rat model to examine the early phase of injury in collagenase-induced ICH, we found that treating animals with HMGB1 antagonist significantly reduced the expression of all three receptors. Treating animals with the HMGB1 antagonist EP or RAGE antagonist FPS-ZM1 significantly reduced inflammatory cell infiltration and expression of IL-1β, matrix metalloproteinase-9 in the perihematoma after ICH. Treatment with EP or FPS-ZM1 also led to greater neurobehavioral function and less brain edema, hemorrhage volume and brain damage after ICH. In contrast, treatment with TLR2/4 antagonists did not significantly affect these post-ICH outcomes. Our results suggest that RAGE may play a specific role in the acute phase of ICH, so targeting the HMGB1-RAGE signaling pathway may be a promising therapeutic strategy.

Intercellular cross-talk in intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating cerebrovascular disorder with high mortality and morbidity. Currently, there are few treatment strategies for ICH-induced brain injury. A recent increase in interest in the pathophysiology of ICH has led to elucidation of the pathways underlying ICH-induced brain injury, pathways where intercellular and hematoma to cell signaling play important roles. In this review, we summarize recent advances in ICH research focusing on intercellular and hematoma:cell cross-talk related to brain injury and recovery after ICH. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

HMGB1 may act via RAGE to promote angiogenesis in the later phase after intracerebral hemorrhage

Following intracerebral hemorrhage (ICH), high-mobility group box 1 protein (HMGB1) may promote vascular remodeling. Whether HMGB1 supports angiogenesis after ICH is unclear, as are the receptors and downstream signaling pathway(s) involved. We used the rat model of collagenase-induced ICH to determine whether HMGB1 acts via the receptor for advanced glycation end-products (RAGE) to upregulate vascular endothelial growth factor (VEGF), a potent mitogen of endothelial cells and key regulator of normal and abnormal angiogenesis in the late phase of injury. At 3d after ICH induction, rats were treated with saline, ethyl pyruvate (EP) or N-benzyl-4-chloro-N-cyclohexylbenzamide (FPS-ZM1). ICH induced the movement of HMGB1 from the nucleus into the cytoplasm. Levels of HMGB1 and RAGE in the ipsilateral striatum increased within a few days of induction and continued to rise for 7-14d afterward. By 14d after induction, levels of VEGF and vessel density were higher than in the Sham group. Administering EP 3 days after ICH induction prevented much of the stroke-induced increases in vessel density and in expression of HMGB1, RAGE, and VEGF. Administering FPS-ZM1 after ICH blocked much of the stroke-induced increases in vessel density and VEGF expression. Our results suggest that after ICH, HMGB1 may upregulate VEGF in the ipsilateral striatum predominantly via RAGE. Hence, targeting the HMGB1/RAGE signaling pathway may help reduce inappropriate angiogenesis after ICH.

Activation of the High-Mobility Group Box 1 Protein-Receptor for Advanced Glycation End-Products Signaling Pathway in Rats During Neurogenesis After Intracerebral Hemorrhage

Background and Purpose—

Following intracerebral hemorrhage (ICH), high-mobility group box 1 protein (HMGB1) may promote neurogenesis that supports functional recovery. How HMGB1 regulates or participates in this process is unclear, as are the pattern recognition receptors and signaling pathways involved.

Methods—

ICH was induced by injection of collagenase in Sprague–Dawley rats, which were treated 3 days later with saline, with the HMGB1 inhibitor ethyl pyruvate or with FPS-ZM1, an antagonist of the receptor for advanced glycation end-products. A Sham group was treated with saline solution instead of collagenase and then treated 3 days later with saline again or with ethyl pyruvate or N-benzyl-4-chloro-N-cyclohexylbenzamide (FPS-ZM1). Expression of the following proteins was measured by Western blot, immunohistochemistry, or immunofluorescence: HMGB1, receptor for advanced glycation end-products, toll-like receptor (TLR)-2, TLR4, brain-derived neurotrophic factor, and matrix metalloproteinase-9. The number of cells positive for 5-bromo-2-deoxyuridine or doublecortin was determined by immunohistochemistry and immunofluorescence.

Results—

Levels of HMGB1, receptor for advanced glycation end-products, TLR4, TLR2, brain-derived neurotrophic factor, and matrix metalloproteinase-9 were significantly higher 14 days after ICH than at baseline, as were the numbers of 5-bromo-2-deoxyuridine- or doublecortin-positive cells. At the same time, HMGB1 moved from the nucleus into the cytoplasm. Administering ethyl pyruvate significantly reduced all these ICH-induced increases, except the increase in TLR4 and TLR2. Administering FPS-ZM1 reduced the ICH-induced increases in the expression of brain-derived neurotrophic factor and matrix metalloproteinase-9 and in the numbers of 5-bromo-2-deoxyuridine- or doublecortin-positive cells.

Conclusions—

These findings suggest that HMGB1 acts via the receptor for advanced glycation end-products signaling pathway to promote neurogenesis in later phases of ICH.

High-mobility group box 1 released from astrocytes promotes the proliferation of cultured neural stem/progenitor cells

Astrocytes are major components of the adult neurogenic niche and play a crucial role in regulating neural stem cell proliferation and differentiation. Following brain injury, astrocytes become reactive and release high-mobility group box 1 (HMGB1), which plays a crucial role in the inflammatory process. However, although it has been reported that HMGB1 promotes neural stem/progenitor cell (NS/PC) proliferation in the developing brain, whether HMGB1 released by reactive astrocytes regulates NS/PC proliferation remains unknown. In this study, we aimed to investigate whether HMGB1 released from reactive astrocytes enhances NS/PC proliferation and to elucidate the possible mechanisms involved in this process. To evaluate the effects of HMGB1 on NS/PC proliferation, NS/PCs were cultured in HMGB1 culture medium and astrocyte-conditioned medium with or without reactive astrocyte-derived HMGB1 by RNA interference (RNAi). To explore the possible mechanisms, the HMGB1 receptor for advanced glycation endproducts (RAGE) in the NS/PCs was blocked with anti-RAGE antibody, and c-Jun N-terminal protein kinase (JNK) in the NS/PCs was inhibited using the potent JNK inhibitor, SP600125. Our results suggested that HMGB1 released from reactive astrocytes promoted NS/PC proliferation in vitro, and the blockade of RAGE or the inhibition of the JNK signaling pathway in the NS/PCs prevented the HMGB1-induced NS/PC proliferation. Our findings demonstrated that HMGB1 released by reactive astrocytes promoted NS/PC proliferation by binding RAGE and enhancing the phosphorylation of the JNK signaling pathway. These findings support a previously described mechanism of a crosstalk between astrocytes and NS/PCs, and suggest that reactive astrocyte-derived HMGB1 plays an important role in the repair of the central nervous system following brain injury.

CCR2+ Ly6C(hi) inflammatory monocyte recruitment exacerbates acute disability following intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating type of stroke that lacks a specific treatment. An intense immune response develops after ICH, which contributes to neuronal injury, disability, and death. However, the specific mediators of inflammation-induced injury remain unclear. The objective of the present study was to determine whether blood-derived CCR2+ Ly6C(hi) inflammatory monocytes contribute to disability. ICH was induced in mice and the resulting inflammatory response was quantified using flow cytometry, confocal microscopy, and neurobehavioral testing. Importantly, blood-derived monocytes were distinguished from resident microglia by differential CD45 staining and by using bone marrow chimeras with fluorescent leukocytes. After ICH, blood-derived CCR2+ Ly6C(hi) inflammatory monocytes trafficked into the brain, outnumbered other leukocytes, and produced tumor necrosis factor. Ccr2(-/-) mice, which have few circulating inflammatory monocytes, exhibited better motor function following ICH than control mice. Chimeric mice with wild-type CNS cells and Ccr2(-/-) hematopoietic cells also exhibited early improvement in motor function, as did wild-type mice after inflammatory monocyte depletion. These findings suggest that blood-derived inflammatory monocytes contribute to acute neurological disability. To determine the translational relevance of our experimental findings, we examined CCL2, the principle ligand for the CCR2 receptor, in ICH patients. Serum samples from 85 patients were collected prospectively at two hospitals. In patients, higher CCL2 levels at 24 h were independently associated with poor functional outcome at day 7 after adjusting for potential confounding variables. Together, these findings suggest that inflammatory monocytes worsen early disability after murine ICH and may represent a therapeutic target for patients.

Ethyl pyruvate decreases airway neutrophil infiltration partly through a high mobility group box 1-dependent mechanism in a chemical-induced murine asthma model

BACKGROUND

Diisocyanates are one of the leading causes of occupational asthma, which is dominated by granulocytic inflammation in the airway. In this study, we intended to explore the role of ethyl pyruvate (EP) on neutrophil infiltration in a toluene-2,4-diisocyanate (TDI)-induced murine asthma model.

METHODS

The experimental mice were first dermally sensitized and then challenged with TDI via oropharyngeal aspiration. The mice were treated intraperitoneally with 100, 50 or 10mg/kg EP 1h before each challenge. One day after the last challenge, airway reactivity to methacholine was measured by a barometric plethysmographic chamber. Total and differential cell counts, along with levels of macrophage inflammatory protein-2 (MIP-2), TNF-α in bronchoalveolar lavage (BAL) fluid and mRNA expression of CXCR2 in the lung were assessed. To depict neutrophils, a naphthol AS-D chloroacetate esterase kit was used. High mobility group box 1 (HMGB1) was determined by western blot and immunohistochemistry.

RESULTS

Treatment with EP dramatically decreased airway hyperresponsiveness in TDI-challenged mice, as well as numbers of neutrophils in BAL fluid and peribronchovascular regions. Both the TDI-induced raised protein level and abnormal distribution of HMGB1 were significantly recovered by EP in a dose-dependent manner. The concentration of MIP-2 in TDI-induced asthma mice was significantly higher than that of the control ones, while EP had few effects on MIP-2. The mRNA expression of CXCR2 didn't change significantly, and TNF-α was not detected in BAL fluids.

CONCLUSION

EP reduces airway neutrophil infiltration partly through downregulating HMGB1 in a chemical-induced murine asthma model.

Ethyl pyruvate inhibits proliferation and induces apoptosis of hepatocellular carcinoma via regulation of the HMGB1-RAGE and AKT pathways

Ethyl pyruvate (EP) was recently identified as a stable lipophilic derivative of pyruvic acid with significant antineoplastic activities. The high mobility group box-B1 (HMGB1)-receptor for advanced glycation end-products (RAGE) and the protein kinase B (Akt) pathways play a crucial role in tumorigenesis and development of many malignant tumors. We tried to observe the effects of ethyl pyruvate on liver cancer growth and explored its effects in hepatocellular carcinoma model. In this study, three hepatocellular carcinoma cell lines were treated with ethyl pyruvate. An MTT colorimetric assay was used to assess the effects of EP on cell proliferation. Flow cytometry and TUNEL assays were used to analyze apoptosis. Real-time PCR, Western blotting and immunofluorescence demonstrated ethyl pyruvate reduced the HMGB1-RAGE and AKT pathways. The results of hepatoma orthotopic tumor model verified the antitumor effects of ethyl pyruvate in vivo. EP could induce apoptosis and slow the growth of liver cancer. Moreover, EP decreased the expression of HMGB1, RAGE, p-AKT and matrix metallopeptidase-9 (MMP9) and increased the Bax/Bcl-2 ratio. In conclusion, this study demonstrates that ethyl pyruvate induces apoptosis and cell-cycle arrest in G phase in hepatocellular carcinoma cells, plays a critical role in the treatment of cancer.

Inflammation in intracerebral hemorrhage: from mechanisms to clinical translation

Intracerebral hemorrhage (ICH) accounts for 10-15% of all strokes and is associated with high mortality and morbidity. Currently, no effective medical treatment is available to improve functional outcomes in patients with ICH. Potential therapies targeting secondary brain injury are arousing a great deal of interest in translational studies. Increasing evidence has shown that inflammation is the key contributor of ICH-induced secondary brain injury. Inflammation progresses in response to various stimuli produced after ICH. Hematoma components initiate inflammatory signaling via activation of microglia, subsequently releasing proinflammatory cytokines and chemokines to attract peripheral inflammatory infiltration. Hemoglobin (Hb), heme, and iron released after red blood cell lysis aggravate ICH-induced inflammatory injury. Danger associated molecular patterns such as high mobility group box 1 protein, released from damaged or dead cells, trigger inflammation in the late stage of ICH. Preclinical studies have identified inflammatory signaling pathways that are involved in microglial activation, leukocyte infiltration, toll-like receptor (TLR) activation, and danger associated molecular pattern regulation in ICH. Recent advances in understanding the pathogenesis of ICH-induced inflammatory injury have facilitated the identification of several novel therapeutic targets for the treatment of ICH. This review summarizes recent progress concerning the mechanisms underlying ICH-induced inflammation. We focus on the inflammatory signaling pathways involved in microglial activation and TLR signaling, and explore potential therapeutic interventions by targeting the removal of hematoma components and inhibition of TLR signaling.

Microglial responses after ischemic stroke and intracerebral hemorrhage

Stroke is a leading cause of death worldwide. Ischemic stroke is caused by blockage of blood vessels in the brain leading to tissue death, while intracerebral hemorrhage (ICH) occurs when a blood vessel ruptures, exposing the brain to blood components. Both are associated with glial toxicity and neuroinflammation. Microglia, as the resident immune cells of the central nervous system (CNS), continually sample the environment for signs of injury and infection. Under homeostatic conditions, they have a ramified morphology and phagocytose debris. After stroke, microglia become activated, obtain an amoeboid morphology, and release inflammatory cytokines (the M1 phenotype). However, microglia can also be alternatively activated, performing crucial roles in limiting inflammation and phagocytosing tissue debris (the M2 phenotype). In rodent models, microglial activation occurs very early after stroke and ICH; however, their specific roles in injury and repair remain unclear. This review summarizes the literature on microglial responses after ischemic stroke and ICH, highlighting the mediators of microglial activation and potential therapeutic targets for each condition.

Innate immunity activation involved in unprotected porcine auto-transplant kidneys preserved by naked caspase-3 siRNA

Background

The naked caspase-3 small interfering RNA (siRNA) infused into the renal artery during cold preservation was effective, but did not protect auto-transplant porcine kidneys with increased inflammation and apoptosis in our previous study. The mechanisms involved, in particular, whether siRNA or complementary systemic feedback eliciting innate immune responses are worthy to be further investigated.

Methods

The protein and mRNA expression of innate immunity-related molecules were detected by western blotting and quantitative PCR in the tissues previously collected from 48 h auto-transplant kidneys. The donor kidneys were retrieved from mini pigs and cold preserved by University of Wisconsin solution with/without 0.3 mg caspase-3 siRNA for 24 h.

Results

The protein level of Toll like receptor (TLR) 3, TLR7, and their main adapters, TRIF and MyD88, was up-regulated in the siRNA preserved auto-transplant kidneys. The mRNA level of NF-κB and c-Jun was increased, as well as pro-inflammatory cytokines, including IL-1β, IL-6, TNF-α and interferon (IFN)-α, β and γ. In addition, the non-TLR RNA sensor PKR protein, but not RIG1, was also increased in the siRNA preserved auto-transplant kidneys.

Conclusions

The activation of innate immunity with amplified inflammatory responses in the caspase-3 siRNA preserved auto-transplant kidneys are associated with increased TLR3, TLR7 and PKR, which might be due to complementary systemic feedback, although persistent actions initiated by short-acting caspase-3 siRNA cannot be completely ruled out. These results provided valuable evidence to guide future siRNA design and pre-clinic studies.