Stimulation of excitatory amino acid release from adult mouse brain glia subcellular particles by high mobility group box 1 protein

Neuroinflammation microenvironment sharpens seizure circuit

A large set of inflammatory molecules and their receptors are induced in epileptogenic foci of patients with pharmacoresistant epilepsies of structural etiologies or with refractory status epilepticus. Studies in animal models mimicking these clinical conditions have shown that the activation of specific inflammatory signallings in forebrain neurons or glial cells may modify seizure thresholds, thus contributing to both ictogenesis and epileptogenesis. The search for mechanisms underlying these effects has highlighted that inflammatory mediators have CNS-specific neuromodulatory functions, in addition to their canonical activation of immune responses for pathogen recognition and clearance. This review reports the neuromodulatory effects of inflammatory mediators and how they contribute to alter the inhibitory/excitatory balance in neural networks that underlie seizures. In particular, we describe key findings related to the ictogenic role of prototypical inflammatory cytokines (IL-1β and TNF) and danger signals (HMGB1), their modulatory effects of neuronal excitability, and the mechanisms underlying these effects. It will be discussed how harnessing these neuromodulatory properties of immune mediators may lead to novel therapies to control drug-resistant seizures.

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.

Microglia Susceptibility to Free Bilirubin Is Age-Dependent

Increased concentrations of unconjugated bilirubin (UCB), namely its free fraction (Bf), in neonatal life may cause transient or definitive injury to neurons and glial cells. We demonstrated that UCB damages neurons and glial cells by compromising oligodendrocyte maturation and myelination, and by activating astrocytes and microglia. Immature neurons and astrocytes showed to be especially vulnerable. However, whether microglia susceptibility to UCB is also age-related was never investigated. We developed a microglia culture model in which cells at 2 days in vitro (2DIV) revealed to behave as the neonatal microglia (amoeboid/reactive cells), in contrast with those at 16DIV microglia that performed as aged cells (irresponsive/dormant cells). Here, we aimed to unveil whether UCB-induced toxicity diverged from the young to the long-cultured microglia. Cells were isolated from the cortical brain of 1- to 2-day-old CD1 mice and incubated for 24 h with 50/100 nM Bf levels, which were associated to moderate and severe neonatal hyperbilirubinemia, respectively. These concentrations of Bf induced early apoptosis and amoeboid shape in 2DIV microglia, while caused late apoptosis in 16DIV cells, without altering their morphology. CD11b staining increased in both, but more markedly in 2DIV cells. Likewise, the gene expression of HMGB1, a well-known alarmin, as well as HMGB1 and GLT-1–positive cells, were enhanced as compared to long-maturated microglia. The CX3CR1 reduction in 2DIV microglia was opposed to the 16DIV cells and suggests a preferential Bf-induced sickness response in younger cells. In conformity, increased mitochondrial mass and NO were enhanced in 2DIV cells, but unchanged or reduced, respectively, in the 16DIV microglia. However, 100 nM Bf caused iNOS gene overexpression in 2DIV and 16DIV cells. While only arginase 1/IL-1β gene expression levels increased upon 50/100 nM Bf treatment in long-maturated microglia, MHCII/arginase 1/TNF-α/IL-1β/IL-6 (>10-fold) were upregulated in the 2DIV microglia. Remarkably, enhanced inflammatory-associated microRNAs (miR-155/miR-125b/miR-21/miR-146a) and reduced anti-inflammatory miR-124 were found in young microglia by both Bf concentrations, while remained unchanged (miR/21/miR-125b) or decreased (miR-155/miR-146a/miR-124) in aged cells. Altogether, these findings support the neurodevelopmental susceptibilities to UCB-induced neurotoxicity, the most severe disabilities in premature babies, and the involvement of immune-inflammation neonatal microglia processes in poorer outcomes.

Neuronal HMGB1 in nucleus accumbens regulates cocaine reward memory

Cocaine is a common abused drug that can induce abnormal synaptic and immune responses in the central nervous system (CNS). High mobility group box 1 (HMGB1) is one kind of inflammatory molecules that is expressed both on neurons and immune cells. Previous studies of HMGB1 in the CNS have largely focused on immune function, and the role of HMGB1 in neurons and cocaine addiction remains unknown. Here, we show that cocaine exposure induced the translocation and release of HMGB1 in the nucleus accumbens (NAc) neurons. Gain and loss of HMGB1 in the NAc bidirectionally regulate cocaine-induced conditioned place preference. From the nucleus to the cytosol, HMGB1 binds to glutamate receptor subunits (GluA2/GluN2B) on the membrane, which regulates cocaine-induced synaptic adaptation and the formation of cocaine-related memory. These data unveil the role of HMGB1 in neurons and provide the evidence for the HMGB1 involvement in drug addiction.

HMGB1 involved in stress-induced depression and its neuroinflammatory priming role: a systematic review

Background

Evidence from clinical and preclinical studies has demonstrated that stress can cause depressive-like symptoms including anhedonia and psychomotor retardation, namely, the manifestation of motivational deficits in depression. The proximate mediator of linking social-environmental stress with internal motivational deficits remains elusive, although substantial studies proposed neural endocrine mechanisms. As an endogenous danger-associated molecule, high mobility group box-1 (HMGB1) is necessary and sufficient for stress-induced sensitization of innate immune cells and subsequent (neuro)inflammation.

Aim

This review aims to provide evidence to unveil the potential mechanism of the relationship between motivational deficits and stress in depression.

Methods

We reviewed original case-control studies investigating the association between HMGB1-mediated inflammation and stress-induced depression. The literature search of Pubmed and Web of Science electronic database from inception up to March 28th, 2019 were conducted by two independent authors. We performed a qualitative systematic review approach to explore the correlation between HMGB1-mediated inflammation and anhedonia/psychomotor retardation in depression.

Results

A total of 69 studies based on search strategy were retrieved and seven eligible studies met the inclusion criteria. Studies showed that HMGB1 was implicated with depressive-like behaviors, which are similar with motivational deficits. Furthermore, HMGB1-mediated inflammation in depressive-like behaviors may be involved in Nod-like receptor family pyrin domain containing three (NLRP3) inflammasome and proinflammatory cytokines, abnormal kynurenine pathway and imbalance between neuroprotective and neurotoxic factors.

Conclusions

We found that stress-induced inflammation mediated by HMGB1 may affect motivational deficits through regulating dopamine pathway in corticostriatal neurocircuitry. The systematic review may shed light on the novel neurobiological underpinning for treatment of motivation deficits in depression.

Inflammation and reactive oxygen species as disease modifiers in epilepsy

Neuroinflammation and reactive oxygen and nitrogen species are rapidly induced in the brain after acute cerebral injuries that are associated with an enhanced risk for epilepsy in humans and related animal models. These phenomena reinforce each others and persist during epileptogenesis as well as during chronic spontaneous seizures. Anti-inflammatory and anti-oxidant drugs transiently administered either before, or shortly after the clinical onset of symptomatic epilepsy, similarly block the progression of spontaneous seizures, and may delay their onset. Moreover, neuroprotection and rescue of cognitive deficits are also observed in the treated animals. Therefore, although these treatments do not prevent epilepsy development, they offer clinically relevant disease-modification effects. These therapeutic effects are mediated by targeting molecular signaling pathways such as the IL-1β-IL-1 receptor type 1 and TLR4, P2X7 receptors, the transcriptional anti-oxidant factor Nrf2, while the therapeutic impact of COX-2 inhibition for reducing spontaneous seizures remains controversial. Some anti-inflammatory and anti-oxidant drugs that are endowed of disease modification effects in preclinical models are already in medical use and have a safety profile, therefore, they provide potential re-purposed treatments for improving the disease course and for reducing seizure burden. Markers of neuroinflammation and oxidative stress can be measured in blood or by neuroimaging, therefore they represent testable prognostic and predictive biomarkers for selecting the patient's population at high risk for developing epilepsy therefore eligible for novel treatments. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

High-mobility group box 1-mediated microglial activation induces anxiodepressive-like behaviors in mice with neuropathic pain

Clinical evidence indicates that major depression is a common comorbidity of chronic pain, including neuropathic pain. However, the cellular basis for chronic pain-mediated major depression remains unclear. High-mobility group box 1 protein (HMGB1) has a key role in innate immune responses and appears to be have a role in mediating diverse disorders, including neuropathic pain and depression. The current study aimed to characterize neuropathic pain-induced changes in affect over time and to determine whether HMGB1 has a role in neuropathic pain-induced changes in affect. Neuropathic pain was induced by partial sciatic nerve ligation (PSNL) in mice. Anxiodepressive-like behaviors in mice were evaluated over 10 weeks, in the social interaction, forced swim, and novelty suppressed feeding tests. Mice developed anxiodepressive-like behavior 6 to 8 weeks after induction of neuropathy. Accompanying anxiodepressive-like behavior, increased HMGB1 protein and microglia activation were observed in frontal cortex at 8 weeks after PSNL. Intracerebroventricular administration of rHMGB1 in naïve mice induced anxiodepressive-like behavior and microglia activation. Blockage of HMGB1 in PSNL mice with glycyrrhizic acid (GZA) or anti-HMGB1 antibody reduced microglia activation and anxiodepressive-like behavior. These results indicate that PSNL-induced anxiodepressive-like behavior is likely mediated by HMGB1. Furthermore, the data indicate that inhibition of HMGB1-dependent microglia activation could be a strategy for the treatment of depression associated with neuropathic pain.

High expression of the HMGB1-TLR4 axis and its downstream signaling factors in patients with Parkinson's disease and the relationship of pathological staging

Objective

To detect the expression of high-mobility group box protein 1 (HMGB1) and toll-like receptor 4 (TLR4) and their downstream signaling factors-myeloid differentiation factor 88 (MyD88), nuclear factor kappa B (NF-κB), and tumor necrosis factor alpha (TNF-α)-in the sera of patients with Parkinson's disease (PD) in order to evaluate the relationship of the HMGB1-TLR4 axis with PD development and progression.

Methods

The serum HMGB1 and TLR4 protein levels of 120 patients with PD and 100 healthy volunteers were measured using double-antibody sandwich ELISA, and their correlations with PD staging, disease duration, drug treatment effectiveness, and clinical classification were analyzed. In addition, their correlations with the key downstream factors of the HMGB1-TLR4 axis (MyD88, NF-κB, and TNF-α) were analyzed.

Results

HMGB1 and TLR4 expressions were higher in the peripheral blood of patients with PD than in healthy volunteers. PD patients with poor drug treatment outcomes had significantly higher HMGB1 and TLR4 expressions than PD patients with stable drug treatment outcomes. Higher HMGB1 and TLR4 expressions were found in patients at higher PD stages, and patients with >4-year disease duration had significantly higher HMGB1 and TLR4 expressions than patients with <4-year disease duration. No significant difference in HMGB1 and TLR4 expressions was found among patients with tremor-dominant, akinetic-rigid, and mixed subtypes of PD. NF-κB and TNF-α expressions were positively correlated with high expression of the HMGB1-TLR4 axis.

Conclusion

High expression of the HMGB1-TLR4 axis is closely associated with PD development, progression, drug treatment effectiveness, staging, and disease duration and has great significance for PD diagnosis and treatment.

Systemic impact on secondary brain aggravation due to ischemia/reperfusion injury in post-cardiac arrest syndrome: a prospective observational study using high-mobility group box 1 protein

BACKGROUND

Ischemia/reperfusion injury (I/R) is an important pathophysiology of post-cardiac arrest syndrome (PCAS) against multiple organ dysfunction and mortality. The inflammatory response in PCAS causes systemic I/R. The purpose of this study was to demonstrate the pathophysiology of systemic I/R for secondary brain damage using the biomarkers high-mobility group box 1 (HMGB1), neuron-specific enolase (NSE), and interleukin-6 (IL-6).

METHODS

This study was designed as a single-institution prospective observational study. Subjects were observed for 90 days, and neurological outcome was classified according to the Glasgow-Pittsburgh Cerebral Performance Categories Scale (CPC). Serum HMGB1, NSE, and IL-6 were evaluated for variability, correlation with each biomarker, or the Sequential Organ Function Assessment (SOFA) score and CPC at return of spontaneous circulation at 0, 24, 48, and 168 h.

RESULTS

A total of 128 patients were enrolled in this study. Initial HMGB1 correlated with CPC (ρ = 0.27, p = 0.036) and SOFA score (ρ = 0.33, p < 0.001). The early phase of HMGB1 (0-24 h), all phases of IL-6, and the delayed phase of NSE (24-168 h) manifested poor neurological outcome. HMGB1 showed a significant correlation with NSE (ρ = 0.29, p = 0.002 at 0 h; ρ = 0.42, p < 0.001 at 24 h) and IL-6 (ρ = 0.36, p < 0.001 at 24 h).

CONCLUSIONS

Serum HMGB1 for first 24 h after cardiac arrest was significantly correlated with SOFA score, NSE, and IL-6. This result suggests that systemic I/R may contribute to secondary brain aggravation. It is expected that research on HMGB1 focused on systemic I/R will help prevent aggravating neurological outcomes.

Amino Acids in Cerebrospinal Fluid of Patients with Aneurysmal Subarachnoid Haemorrhage: An Observational Study

Background

The authors are aware of only one article investigating amino acid concentrations in cerebrospinal fluid (CSF) in patients with ruptured intracranial aneurysms, and this was published 31 years ago. Since then, both management of subarachnoid haemorrhage (SAH) and amino acid assay techniques have seen radical alterations, yet the pathophysiology of SAH remains unclear.

Objective

To analyse the pattern of concentrations of amino acids and related compounds in patients with different outcomes following aneurysmal SAH.

Methods

49 CSF samples were collected from 23 patients on days 0–3, 5, and 10 post-SAH. Concentrations of 33 amino acids and related compounds were assayed by liquid chromatography tandem mass spectrometry in patients with good [Glasgow Outcome Scale (GOS) 1–3] and poor (GOS 4–5) outcome.

Results

Of the 33 compounds assayed, only hydroxyproline and 3-aminoisobutyric acid appeared not to increase significantly following SAH. In poor outcome patients, we found significantly higher concentrations of aspartic acid (p = 0.038), glutamic acid (p = 0.038), and seven other compounds on days 0–3 post-SAH; glutamic acid (p = 0.041) on day 5 post-SAH, and 2-aminoadipic acid (p = 0.033) on day 10 post-SAH. The most significant correlation with GOS at 3 months was found for aminoadipic acid on day 10 post-SAH (cc = −0.81).

Conclusion

Aneurysmal rupture leads to a generalised increase of amino acids and related compounds in CSF. The patterns differ between good and poor outcome cases. Increased excitatory amino acids are strongly indicative of poor outcome.

Effect of pregabalin administration upon reperfusion in a rat model of hyperglycemic stroke: Mechanistic insights associated with high-mobility group box 1

Hyperglycemia, which reduces the efficacy of treatments and worsens clinical outcomes, is common in stroke. Ability of pregabalin to reduce neuroexcitotoxicity may provide protection against stroke, even under hyperglycemia. We investigated its protective effect against hyperglycemic stroke and its possible molecular mechanisms. Male Wistar rats administered dextrose to cause hyperglycemia, underwent middle cerebral artery occlusion for 1 h and subsequent reperfusion. Rats were treated with an intraperitoneal injection of 30 mg/kg pregabalin or an equal amount of normal saline at the onset of reperfusion (n = 16 per group). At 24 h after reperfusion, neurological deficit, infarct volume, and apoptotic cell count were assessed. Western blot analysis was performed to determine protein expression of high-mobility group box 1 (HMGB1), toll-like receptor-4 (TLR-4), phosphorylated nuclear factor-kappa B (p-NF-κB), interleukin-1beta (IL-1β), tumor necrosis factor-alpha (TNF-α), phosphorylated inducible and endothelial nitric oxide synthase (p-iNOS, p-eNOS), Bcl-2, Bax, Cytochrome C, and caspase-3 in the brain. Pregabalin-treated rats showed significantly improved neurological function (31% decrease in score), reduced infarct size (by 33%), fewer apoptotic cells (by 63%), and lower expression levels of HMGB1, TLR4, p-NF-κB, IL-1β, and TNF- α, compared with control rats. Decreased p-iNOS and increased p-eNOS expressions were also observed. Expression of Bax, Cytochrome C, and cleaved caspase-3/caspase3 was significantly downregulated, while Bcl-2 expression was increased by pregabalin treatment. Pregabalin administration upon reperfusion decreased neuronal death and improved neurological function in hyperglycemic stroke rats. Cogent mechanisms would include attenuation of HMGB1/TLR-4-mediated inflammation and favorable modulation of the NOS.

Adolescent Alcohol Exposure Persistently Impacts Adult Neurobiology and Behavior

Adolescence is a developmental period when physical and cognitive abilities are optimized, when social skills are consolidated, and when sexuality, adolescent behaviors, and frontal cortical functions mature to adult levels. Adolescents also have unique responses to alcohol compared with adults, being less sensitive to ethanol sedative-motor responses that most likely contribute to binge drinking and blackouts. Population studies find that an early age of drinking onset correlates with increased lifetime risks for the development of alcohol dependence, violence, and injuries. Brain synapses, myelination, and neural circuits mature in adolescence to adult levels in parallel with increased reflection on the consequence of actions and reduced impulsivity and thrill seeking. Alcohol binge drinking could alter human development, but variations in genetics, peer groups, family structure, early life experiences, and the emergence of psychopathology in humans confound studies. As adolescence is common to mammalian species, preclinical models of binge drinking provide insight into the direct impact of alcohol on adolescent development. This review relates human findings to basic science studies, particularly the preclinical studies of the Neurobiology of Adolescent Drinking in Adulthood (NADIA) Consortium. These studies focus on persistent adult changes in neurobiology and behavior following adolescent intermittent ethanol (AIE), a model of underage drinking. NADIA studies and others find that AIE results in the following: increases in adult alcohol drinking, disinhibition, and social anxiety; altered adult synapses, cognition, and sleep; reduced adult neurogenesis, cholinergic, and serotonergic neurons; and increased neuroimmune gene expression and epigenetic modifiers of gene expression. Many of these effects are specific to adolescents and not found in parallel adult studies. AIE can cause a persistence of adolescent-like synaptic physiology, behavior, and sensitivity to alcohol into adulthood. Together, these findings support the hypothesis that adolescent binge drinking leads to long-lasting changes in the adult brain that increase risks of adult psychopathology, particularly for alcohol dependence.

Pattern recognition receptors in chronic pain: Mechanisms and therapeutic implications

For the individual, it is vital to promptly detect and recognize a danger that threatens the integrity of the body. Pattern recognition receptors (PRRs) are several classes of protein families originally classified as receptors detecting exogenous pathogens. PRRs are also capable of recognizing molecules released from damaged tissues (damage-associated molecular pattern molecules; DAMPs) and thereby contribute to danger recognition. Importantly, it is now evident that PRRs, such as toll-like receptors (TLRs) and receptors for advanced glycation end products (RAGE), are not only expressed in peripheral immune cells but also present in neurons and glial cells in the nervous system. These PRR-expressing cells work in concert, enabling highly sensitive danger recognition. However, this sensitiveness can act as a double-edged sword. Accumulated evidence has led to the hypothesis that aberrant activation of PRRs may play a crucial role in the pathogenesis of pathological pain. Indeed, numerous studies employing gene deletion or pharmacological inhibition of PRRs successfully reversed or prevented pathological pain in experimental animal models. Furthermore, a number of preclinical studies have shown the therapeutic potential of targeting PRRs for chronic pain. Here, we review the current knowledge regarding the role of PRRs in chronic pain and discuss the promise and challenges of targeting PRRs as a novel therapeutic approach for chronic pain.

The pro-inflammatory role of high-mobility group box 1 protein (HMGB-1) in photoreceptors and retinal explants exposed to elevated pressure

To determine the role of high-mobility group box 1 protein (HMGB-1) in cellular and tissue models of elevated pressure-induced neurodegeneration, regeneration, and inflammation. Mouse retinal photoreceptor-derived cells (661W) and retinal explants were incubated either under elevated pressure or in the presence of recombinant HMGB-1 (rHMGB-1) to investigate the mechanisms of response of photoreceptors. Immunohistochemistry, western blotting, and the quantitative real-time PCR were used to examine the expression levels of immunological factors (eg, HMGB-1, receptor for advanced glycation end products (RAGE)), Toll-like receptors 2 and 4 (TLR-2, TLR-4), apoptosis-related factors (eg, B-cell lymphoma 2 (Bcl-2), Bcl-2-associated death promoter (Bad)) as well as cytokine expression (eg, tumor necrosis factor alpha (TNF-α), interleukin (IL)-4, IL-6, and vascular endothelial growth factor (VEGF)). The data revealed increased the expression of HMGB-1 and its receptors RAGE, TLR-2, and TLR-4, and TNF-α as well as pro-apoptotic factors (eg, Bad) as well as apoptosis in 661W cells exposed to elevated pressure. Co-cultivation of 661W cells with rHMGB-1 increased the expression levels of pro-apoptotic Bad and cleaved Caspase-3 resulting in apoptosis. Cytokine array studies revealed an increased release of TNF-α, IL-4, IL-6, and VEGF after incubation of 661W cells with rHMGB-1. Upregulation of HMGB-1, TLR-2, and RAGE as well as anti-apoptotic Bcl-2 expression levels was found in the retinal explants exposed to rHMGB-1 or elevated pressure. The results suggest that HMGB-1 promotes an inflammatory response and mediates apoptosis in the pathology of photoreceptors and retinal homeostasis. HMGB-1 may have a key role in ongoing damage of retinal cells under conditions of elevated intraocular pressure.

Inhibiting HMGB1 with Glycyrrhizic Acid Protects Brain Injury after DAI via Its Anti-Inflammatory Effect

High-mobility group box 1 (HMGB1), a nuclear protein that has endogenous cytokine-like activity, is involved in several neurological diseases by mediating inflammatory response. In this study, a lateral head rotation device was used to establish a rat diffuse axonal injury (DAI) model. The dynamic expression of HMGB1, apoptosis-associated proteins, and proinflammatory cytokines were detected by Western blot, and neuronal apoptosis was observed by TUNEL staining. The extracellular release of HMGB1 and the accumulation of β-APP were observed by immunofluorescence and immunohistochemistry, respectively. The brain injury was indicated by modified neurological severity score (mNSS), brain water content (BWC), and the extravasation of Evans blue. We showed that HMGB1 level obviously decreased within 48 h after DAI, accompanied by neuronal apoptosis, the activation of caspases 3 and 9, and the phosphorylation of BCL-2. Inhibiting HMGB1 with glycyrrhizic acid (GL) can suppress the activation of apoptosis-associated proteins and inhibit the expression of proinflammatory cytokines, which ameliorated motor and cognitive deficits, reduced neuronal apoptosis, and protected the integrity of blood brain barrier (BBB) and axonal injury after experimental DAI in rats. Thus, HMGB1 may be involved in the inflammatory response after DAI, and inhibition of HMGB1 release with GL can notably alleviate the brain injury after DAI.

Modulation of neuronal excitability by immune mediators in epilepsy

A complex set of inflammatory molecules and their receptors has been described in epileptogenic foci in different forms of pharmacoresistant epilepsies. By activating receptor-mediated pathways in neurons, these molecules have profound neuromodulatory effects that are distinct from their canonical activation of immune functions. Importantly, the neuromodulatory actions of some inflammatory molecules contribute to hyperexcitability in neural networks that underlie seizures. This review summarizes recent findings related to the role of cytokines (IL-1beta and TNF-alpha) and danger signals (HMGB1) in decreasing seizure threshold, thereby contributing to seizure generation and the associated neuropathology. We will discuss preclinical studies suggesting that pharmacological inhibition of specific inflammatory signals may be useful to treat drug-resistant seizures in human epilepsy, and possibly arrest epileptogenesis in individuals at risk of developing the disease.

Physiological Roles of Calpain 1 Associated to Multiprotein NMDA Receptor Complex

We have recently demonstrated that in resting conditions calpain 1, but not calpain 2, is specifically associated to the N-Methyl-D-Aspartate receptor (NMDAR) multiprotein complex. We are here reporting that in SKNBE neuroblastoma cells or in freshly isolated nerve terminals from adult rat hippocampus, the proteolytic activity of calpain 1 resident at the NMDAR is very low under basal conditions and greatly increases following NMDAR stimulation. Since the protease resides at the NMDAR in saturating amounts, variations in Ca2+ influx promote an increase in calpain 1 activity without affecting the amount of the protease originally associated to NMDAR. In all the conditions examined, resident calpain 1 specifically cleaves NR2B at the C-terminal region, leading to its internalization together with NR1 subunit. While in basal conditions intracellular membranes include small amounts of NMDAR containing the calpain-digested NR2B, upon NMDAR stimulation nearly all the receptor molecules are internalized. We here propose that resident calpain 1 is involved in NMDAR turnover, and following an increase in Ca2+ influx, the activated protease, by promoting the removal of NMDAR from the plasma membranes, can decrease Ca2+ entrance through this channel. Due to the absence of calpastatin in such cluster, the activity of resident calpain 1 may be under the control of HSP90, whose levels are directly related to the activation of this protease. Observations of different HSP90/calpain 1 ratios in different ultrasynaptic compartments support this conclusion.

High-mobility group Box-1 is involved in NMDA-induced retinal injury the in rat retina

High-mobility group Box-1 (HMGB1) is known to be released from injured cells and to induce an inflammatory response. Although HMGB1 was reported to mediate ischemia-reperfusion injury of the brain, its role in glutamate excitotoxicity of the retina remains controversial. Here, the authors demonstrated the evidence that HMGB1 is involved in the retinal damage induced by NMDA. Under ketamine/xylazine anesthesia, male Sprague-Dawley rats were subjected to intravitreal injection of NMDA (200 nmol/eye) or HMGB1 protein derived from bovines (5-15 μg/eye). Intravitreal anti-HMGB1 IgY (5 μg/eye) was simultaneously administered with NMDA or HMGB1. Seven days later, animals were killed and 5-μm retinal sections through the optic nerve head were obtained. These specimens were subjected to morphometry. Intravitreal NMDA and HMGB1 protein evoked cell loss in the ganglion cell layer 7 days later. Intravitreal anti-HMGB1 IgY reduced these damages. Anti-HMGB1 IgY reduced the number of 8-hydroxy-deoxyguanosine (8-OHdG)-positive cells induced by intravitreal NMDA. Toll-like receptor 2/4 antagonist peptide, receptor for advanced glycation end-products (RAGE) antagonist peptide, and FPS-ZM1 significantly reduced the retinal damage induced by HMGB1 protein. The results in the present study suggest that HMGB1 is at least in part involved in NMDA-induced retinal injury, and probably induces cell death of retinal ganglion cells with increase of oxidative stress, via activation of toll-like receptor 2/4 and RAGE in the rat retina.

Role of high-mobility group box-1 protein in disruption of vascular barriers and regulation of leukocyte-endothelial interactions

High-mobility group box-1 protein (HMGB1) is a highly conserved non-histone DNA-binding protein present in the nuclei and cytoplasm of nearly all cell types. The results from recent research provide evidence that HMGB1 is secreted into the extracellular milieu and acts as a pro-inflammatory cytokine and exhibits angiogenic effects to fire the immunological response against the pathological effects. Recently, a great deal of evidence has indicated the critical importance of HMGB1 in mediating vascular barriers dysfunction by modulating the expression of adhesion molecules, such as intercellular adhesion molecule-1, vascular cell adhesion protein 1 and E-selectin on the surface of endothelial cells. Such process promotes the adhesion and migration of leukocytes across the endothelium, leading to breakdown of vascular barriers (blood-brain barrier and blood-retinal barrier) via modulating the expression, content, phosphorylation, and distribution of tight junction proteins. Therefore, here we give an abridged review to understand the mechanistic link between HMGB1 and vascular barriers dysfunction, including interaction with cell-surface receptors and intracellular signaling pathways.

Does brain inflammation mediate pathological outcomes in epilepsy?

Inflammation in the central nervous system (CNS) is associated with epilepsy and is characterized by the increased levels of a complex set of soluble molecules and their receptors in epileptogenic foci with profound neuromodulatory effects. These molecules activate receptor-mediated pathways in glia and neurons that contribute to hyperexcitability in neural networks that underlie seizure generation. As a consequence, exciting new opportunities now exist for novel therapies targeting the various components of the immune system and the associated inflammatory mediators, especially the IL-1β system. This review summarizes recent findings that increased our understanding of the role of inflammation in reducing seizure threshold, contributing to seizure generation, and participating in epileptogenesis. We will discuss preclinical studies supporting the hypothesis that pharmacological inhibition of specific proinflammatory signalings may be useful to treat drug-resistant seizures in human epilepsy, and possibly delay or arrest epileptogenesis.

Proteomic analysis of gliosomes from mouse brain: identification and investigation of glial membrane proteins

Astrocytes are being increasingly recognized as crucial contributors to neuronal function at synapses, axons, and somas. Reliable methods that can provide insight into astrocyte proteins at the neuron-astrocyte functional interface are highly desirable. Here, we conducted a mass spectrometry analysis of Percoll gradient-isolated gliosomes, a viable preparation of glial subcellular particles often used to study mechanisms of astrocytic transmitter uptake and release and their regulation. Gliosomes were compared with synaptosomes, a preparation containing the neurotransmitter release machinery, and, accordingly, synaptosomes were enriched for proteins involved in synaptic vesicle-mediated transport. Interestingly, gliosome preparations were found to be enriched for different classes of known astrocyte proteins, such as VAMP3 (involved in astrocyte exocytosis), Ezrin (perisynaptic astrocyte cytoskeletal protein), and Basigin (astrocyte membrane glycoprotein), as well as for G-protein-mediated signaling proteins. Mass spectrometry data are available via ProteomeXchange with the identifier PXD001375. Together, these data provide the first detailed description of the gliosome proteome and show that gliosomes can be a useful preparation to study glial membrane proteins and associated processes.

High-mobility group box-1 in sterile inflammation

High-mobility group box 1 (HMGB1) was originally defined as a ubiquitous nuclear protein, but it was later determined that the protein has different roles both inside and outside of cells. Nuclear HMGB1 regulates chromatin structure and gene transcription, whereas cytosolic HMGB1 is involved in inflammasome activation and autophagy. Extracellular HMGB1 has drawn attention because it can bind to related cell signalling transduction receptors, such as the receptor for advanced glycation end products, Toll-like receptor (TLR)2, TLR4 and TLR9. It also participates in the development and progression of a variety of diseases. HMGB1 is actively secreted by stimulation of the innate immune system, and it is passively released by ischaemia or cell injury. This review focuses on the important role of HMGB1 in the pathogenesis of acute and chronic sterile inflammatory conditions. Strategies that target HMGB1 have been shown to significantly decrease inflammation in several disease models of sterile inflammation, and this may represent a promising clinical approach for treatment of certain conditions associated with sterile inflammation.

The proinflammatory cytokine high-mobility group box-1 mediates retinal neuropathy induced by diabetes

To test the hypothesis that increased expression of proinflammatory cytokine high-mobility group box-1 (HMGB1) in epiretinal membranes and vitreous fluid from patients with proliferative diabetic retinopathy and in retinas of diabetic rats plays a pathogenetic role in mediating diabetes-induced retinal neuropathy. Retinas of 1-month diabetic rats and HMGB1 intravitreally injected normal rats were studied using Western blot analysis, RT-PCR and glutamate assay. In addition, we studied the effect of the HMGB1 inhibitor glycyrrhizin on diabetes-induced biochemical changes in the retina. Diabetes and intravitreal injection of HMGB1 in normal rats induced significant upregulation of HMGB1 protein and mRNA, activated extracellular signal-regulated kinase 1 and 2 (ERK1/2), cleaved caspase-3 and glutamate; and significant downregulation of synaptophysin, tyrosine hydroxylase, glutamine synthetase, and glyoxalase 1. Constant glycyrrhizin intake from the onset of diabetes did not affect the metabolic status of the diabetic rats, but it significantly attenuated diabetes-induced upregulation of HMGB1 protein and mRNA, activated ERK1/2, cleaved caspase-3, and glutamate. In the glycyrrhizin-fed diabetic rats, the decrease in synaptophysin, tyrosine hydroxylase, and glyoxalase 1 caused by diabetes was significantly attenuated. These findings suggest that early retinal neuropathy of diabetes involves upregulated expression of HMGB1 and can be ameliorated by inhibition of HMGB1.

Potential of the angiotensin receptor blockers (ARBs) telmisartan, irbesartan, and candesartan for inhibiting the HMGB1/RAGE axis in prevention and acute treatment of stroke

Stroke is a major cause of mortality and disability worldwide. The main cause of stroke is atherosclerosis, and the most common risk factor for atherosclerosis is hypertension. Therefore, antihypertensive treatments are recommended for the prevention of stroke. Three angiotensin receptor blockers (ARBs), telmisartan, irbesartan and candesartan, inhibit the expression of the receptor for advanced glycation end-products (RAGE), which is one of the pleiotropic effects of these drugs. High mobility group box 1 (HMGB1) is the ligand of RAGE, and has been recently identified as a lethal mediator of severe sepsis. HMGB1 is an intracellular protein, which acts as an inflammatory cytokine when released into the extracellular milieu. Extracellular HMGB1 causes multiple organ failure and contributes to the pathogenesis of hypertension, hyperlipidemia, diabetes mellitus, atherosclerosis, thrombosis, and stroke. This is the first review of the literature evaluating the potential of three ARBs for the HMGB1-RAGE axis on stroke therapy, including prevention and acute treatment. This review covers clinical and experimental studies conducted between 1976 and 2013. We propose that ARBs, which inhibit the HMGB1/RAGE axis, may offer a novel option for prevention and acute treatment of stroke. However, additional clinical studies are necessary to verify the efficacy of ARBs.

Potentiation of NMDA receptor-dependent cell responses by extracellular high mobility group box 1 protein

Background

Extracellular high mobility group box 1 (HMGB1) protein can operate in a synergistic fashion with different signal molecules promoting an increase of cell Ca²⁺ influx. However, the mechanisms responsible for this effect of HMGB1 are still unknown.

Principal Findings

Here we demonstrate that, at concentrations of agonist per se ineffective, HMGB1 potentiates the activation of the ionotropic glutamate N-methyl-D-aspartate receptor (NMDAR) in isolated hippocampal nerve terminals and in a neuroblastoma cell line. This effect was abolished by the NMDA channel blocker MK-801. The HMGB1-facilitated NMDAR opening was followed by activation of the Ca²⁺-dependent enzymes calpain and nitric oxide synthase in neuroblastoma cells, resulting in an increased production of NO, a consequent enhanced cell motility, and onset of morphological differentiation. We have also identified NMDAR as the mediator of HMGB1-stimulated murine erythroleukemia cell differentiation, induced by hexamethylenebisacetamide. The potentiation of NMDAR activation involved a peptide of HMGB1 located in the B box at the amino acids 130–139. This HMGB1 fragment did not overlap with binding sites for other cell surface receptors of HMGB1, such as the advanced glycation end products or the Toll-like receptor 4. Moreover, in a competition assay, the HMGB1_(130–139) peptide displaced the NMDAR/HMGB1 interaction, suggesting that it comprised the molecular and functional site of HMGB1 regulating the NMDA receptor complex.

Conclusion

We propose that the multifunctional cytokine-like molecule HMGB1 released by activated, stressed, and damaged or necrotic cells can facilitate NMDAR-mediated cell responses, both in the central nervous system and in peripheral tissues, independently of other known cell surface receptors for HMGB1.

Regulation of retinal proteome by topical antiglaucomatous eye drops in an inherited glaucoma rat model

Examination of the response of the retinal proteome to elevated intraocular pressure (IOP) and to the pharmacological normalization of IOP is crucial, in order to develop drugs with neuroptorective potential. We used a hereditary rat model of ocular hypertension to lower IOP with travaprost and dorzolamide applied topically on the eye surface, and examine changes of the retinal proteome. Our data demonstrate that elevated IOP causes alterations in the retinal protein profile, in particular in high-mobility-group-protein B1 (HMGB1), calmodulin, heat-shock-protein (HSP) 70 and carbonic anhydrase II expression. The changes of the retinal proteome by dorzolamide or travoprost are different and independent of the IOP lowering effect. This fact suggests that the eye drops exert a direct IOP-independent effect on retinal metabolism. Further investigations are required to elucidate the potential neuroprotective mechanisms signaled through changes of HMGB1, calmodulin, HSP70 and carbonic anhydrase II expression in glaucoma. The data may facilitate development of eye drops that exert neuroprotection through direct pharmacological effect.

Group I metabotropic glutamate autoreceptors induce abnormal glutamate exocytosis in a mouse model of amyotrophic lateral sclerosis

Glutamate-mediated excitotoxicity plays a major role in ALS and reduced astrocytic glutamate transport was suggested as a cause. Based on previous work we have proposed that abnormal release may represent another source of excessive glutamate. In this line, here we studied the modulation of glutamate release in ALS by Group I metabotropic glutamate (mGlu) receptors, that comprise mGlu1 and mGlu5 members. Synaptosomes from the lumbar spinal cord of SOD1/G93A mice, a widely used murine model for human ALS, and controls were used in release, confocal or electron microscopy and Western blot experiments. Concentrations of the mGlu1/5 receptor agonist 3,5-DHPG >0.3 μM stimulated the release of [(3)H]d- aspartate, used to label the releasing pools of glutamate, both in control and SOD1/G93A mice. At variance, ≤0.3 μM 3,5-DHPG increased [(3)H]d-aspartate release in SOD1/G93A mice only. Experiments with selective antagonists indicated the involvement of both mGlu1 and mGlu5 receptors, mGlu5 being preferentially involved in the high potency effects of 3,5-DHPG. High 3,5-DHPG concentrations increased IP3 formation in both mouse strains, whereas low 3,5-DHPG did it in SOD1/G93A mice only. Release experiments confirmed that 3,5-DHPG elicited [(3)H]d-aspartate exocytosis involving intra-terminal Ca(2+) release through IP3-sensitive channels. Confocal microscopy indicated the co-existence of both receptors presynaptically in the same glutamatergic nerve terminal in SOD1/G93A mice. To conclude, activation of mGlu1/5 receptors produced abnormal glutamate release in SOD1/G93A mice, suggesting that these receptors are implicated in ALS and that selective antagonists may be predicted for new therapeutic approaches. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Deleterious role of anti-high mobility group box 1 monoclonal antibody in retinal ischemia-reperfusion injury

PURPOSE

To investigate the effect of anti-high mobility group box 1 (HMGB1) monoclonal antibody (mAb) against ischemia-reperfusion injury in the rat retina.

MATERIALS AND METHODS

Retinal ischemia was induced by increasing and then maintaining intraocular pressure at 130 mmHg for 45 min. An intraperitoneal injection of anti-HMGB1 mAb was administered 30 min before ischemia. Retinal damage was evaluated at 7 days after the ischemia. Immunohistochemistry and image analysis were used to measure changes in the levels of reactive oxygen species (ROS) and the localization of anti-HMGB1 mAb. Dark-adapted full-field electroretinography (ERG) was also performed.

RESULTS

Pretreatment with anti-HMGB1 mAb significantly enhanced the ischemic injury of the retina. HMGB1 expression increased at 6-12 h after ischemia in the retina. After the ischemia, production of ROS was detected in retinal cells. However, pretreatment with anti-HMGB1 mAb increased the production of ROS. On the seventh postoperative day, the amplitudes of both the ERG a- and b-waves were significantly higher in the vehicle group than in the groups pretreated with anti-HMGB1 mAb.

CONCLUSIONS

The current in vivo model of retinal injury demonstrated that anti-HMGB1 mAb plays a large deleterious role in ischemia-reperfusion injury. In order to develop neuroprotective therapeutic strategies for acute retinal ischemic disorders, further studies on anti-HMGB1 mAb function are needed.

HMGB1 is a therapeutic target for sterile inflammation and infection

A key question in immunology concerns how sterile injury activates innate immunity to mediate damaging inflammation in the absence of foreign invaders. The discovery that HMGB1, a ubiquitous nuclear protein, mediates the activation of innate immune responses led directly to the understanding that HMGB1 plays a critical role at the intersection of the host inflammatory response to sterile and infectious threat. HMGB1 is actively released by stimulation of the innate immune system with exogenous pathogen-derived molecules and is passively released by ischemia or cell injury in the absence of invasion. Established molecular mechanisms of HMGB1 binding and signaling through TLR4 reveal signaling pathways that mediate cytokine release and tissue damage. Experimental strategies that selectively target HMGB1 and TLR4 effectively reverse and prevent activation of innate immunity and significantly attenuate damage in diverse models of sterile and infection-induced threat.

Characterization of GABA(A) receptors expressed in glial cell membranes of adult mouse neocortex using a Xenopus oocyte microtransplantation expression system

Cell membranes isolated from nervous tissue can be easily injected into Xenopus oocytes, thereby effectively "microtransplanting" functional neurotransmitter receptors. This technique therefore allows a direct functional characterization of the original membrane receptor/ion channel proteins and the associated molecules while still embedded in their natural lipid environment. Cell membranes will contain components from different types of cells, i.e. neurons and glial cells, expressing their own receptors, with possibly different properties. To study the receptor properties of a single cell type, we injected oocytes with membranes isolated only from glia (gliosomes) of adult mouse neocortex and we focused our work on GABA(A) receptors incorporated in the oocyte cell membrane. We found that GABA(A)-activated currents allowed a good biophysical and pharmacological characterization of glial GABA(A) receptors. Therefore, the microtransplantation of gliosomes into oocytes can represent a good model to study the electrical and pharmacological properties of adult glial cells under different physiological and pathological conditions. Moreover, since gliosomes can be isolated from frozen tissues, this approach can be extended to post-mortem human tissues.

High mobility group box 1 protein as a potential drug target for infection- and injury-elicited inflammation

In response to infection or injury, a ubiquitous nucleosomal protein, HMGB1 is secreted actively by innate immune cells, and / or released passively by injured/damaged cells. Subsequently, extracellular HMGB1 alerts, recruits, and activates various innate immune cells to sustain a rigorous inflammatory response. A growing number of HMGB1 inhibitors ranging from neutralizing antibodies, endogenous hormones, to medicinal herb-derived small molecule HMGB1 inhibitors (such as nicotine, glycyrrhizin, tanshinones, and EGCG) are proven protective against lethal infection and ischemic injury. Here we review emerging evidence that support extracellular HMGB1 as a proinflammatory alarmin(g) danger signal, and discuss a wide array of HMGB1 inhibitors as potential therapeutic agents for sepsis and ischemic injury.

High-mobility group protein box-1 and its relevance to cerebral ischemia

High-mobility group box-1 (HMGB1) was originally identified as a ubiquitously expressed, abundant, nonhistone DNA-binding protein. It has well-established functions in the maintenance of nuclear homeostasis. The HMGB1 can either be passively released into the extracellular milieu in response to necrotic signals or actively secreted in response to inflammatory signals. Extracellular HMGB1 interacts with receptors, including those for advanced glycation endproducts (RAGEs) as well as Toll-like receptor 2 (TLR2) and TLR4. The HMGB1 functions in a synergistic manner with other proinflammatory mediators and acts as a potent proinflammatory cytokine-like factor that contributes to the pathogenesis of diverse inflammatory and infectious disorders. Numerous reports point to HMGB1 as a novel player in the ischemic brain. This review provides an appraisal of the emerging roles of HMGB1 in cerebral ischemia injury, highlighting the relevance of HMGB1-blocking agents as potent therapeutic tools for neuroprotection.

Novel HMGB1-inhibiting therapeutic agents for experimental sepsis. Shock. 2009;32:348-357. [PMID: 19333143 DOI: 10.1097/SHK.0b013e3181a551bd]

Sepsis refers to a systemic inflammatory response syndrome resulting from a microbial infection. The inflammatory response is partly mediated by innate immune cells (such as macrophages, monocytes, and neutrophils), which not only ingest and eliminate invading pathogens but also initiate an inflammatory response by producing early (e.g., TNF and IFN-gamma) and late (e.g., high-mobility group box [HMGB1]) proinflammatory cytokines. Here, we briefly review emerging evidence that support extracellular HMGB1 as a late mediator of experimental sepsis and discuss therapeutic potential of several HMGB1-inhibiting agents (including neutralizing antibodies and steroid-like tanshinones) in experimental sepsis.

Targeting HMGB1 in inflammation

High mobility group box 1 (HMGB1), a highly conserved, ubiquitous protein present in the nuclei and cytoplasm of nearly all cell types, is a necessary and sufficient mediator of inflammation during sterile and infection-associated responses. Elevated levels of HMGB1 in serum and tissues occur during sterile tissue injury and during infection, and targeting HMGB1 with antibodies or specific antagonists is protective in established preclinical inflammatory disease models including lethal endotoxemia or sepsis, collagen-induced arthritis, and ischemia-reperfusion induced tissue injury. Future advances in this field will stem from understanding the biological basis for the success of targeting HMGB1 to therapeutic improvement in the treatment of inflammation, infection and ischemia-reperfusion induced injury.

Glycyrrhizin and its metabolite 18 beta-glycyrrhetinic acid in glycyrrhiza, a constituent herb of yokukansan, ameliorate thiamine deficiency-induced dysfunction of glutamate transport in cultured rat cortical astrocytes

Effects of yokukansan, a traditional Japanese medicine, on thiamine deficiency (TD)-induced decrease of glutamate uptake were examined in cultured rat cortical astrocytes. Yokukansan (100-500 microg/ml) ameliorated the TD-induced decrease in glutamate uptake by astrocytes, implying that yokukansan may contain active herbs and compounds possessing this effect. Among the seven constituent herbs of yokukansan, significant effects were found for glycyrrhiza. Furthermore, glycyrrhizin and its metabolite 18 beta-glycyrrhetinic acid (10(-7)-10(-4)M), among the eight components of glycyrrhiza, ameliorated the TD-induced decrease of glutamate uptake in astrocytes in a concentration-dependent manner. These substances inhibited protein kinase C (PKC) activity under the in vitro conditions. These lines of evidence suggest that glycyrrhizin, a main component of glycyrrhiza, and its metabolite 18 beta-glycyrrhetinic acid are likely responsible for amelioration of dysfunction of glutamate transport in astrocytes. The inhibition of the PKC activity might be related to the pharmacological efficacy of these substances.

Inhibition of presynaptic release-facilitatory kainate autoreceptors by extracellular cyclic GMP

We found that both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate autoreceptors were present on the glutamate-releasing terminals of cerebellar parallel/climbing fibers and that they functioned as facilitatory autoreceptors. Extracellular cGMP inhibited the neurotransmitter release evoked by presynaptic kainate receptor activation; the inhibitory effect of extracellular cGMP was selective for the kainate autoreceptor-mediated response and did not affect the AMPA autoreceptor-mediated response. Endogenously synthesized cGMP might be the physiological source for the extracellular cGMP modulating the response to kainate autoreceptor activation.

Glutamate release from astrocytic gliosomes under physiological and pathological conditions

Glial subcellular particles (gliosomes) have been purified from rat cerebral cortex or mouse spinal cord and investigated for their ability to release glutamate. Confocal microscopy showed that gliosomes are enriched with glia-specific proteins, such as GFAP and S-100 but not neuronal proteins, such as PSD-95, MAP-2, and beta-tubulin III. Furthermore, gliosomes exhibit labeling neither for integrin-alphaM nor for myelin basic protein, specific for microglia and oligodendrocytes, respectively. The gliosomal fraction contains proteins of the exocytotic machinery coexisting with GFAP. Consistent with ultrastructural analysis, several nonclustered vesicles are present in the gliosome cytoplasm. Finally, gliosomes represent functional organelles that actively export glutamate when subjected to releasing stimuli, such as ionomycin, high KCl, veratrine, 4-aminopyridine, AMPA, or ATP by mechanisms involving extracellular Ca2+, Ca2+ release from intracellular stores as well as reversal of glutamate transporters. In addition, gliosomes can release glutamate also by a mechanism involving heterologous transporter activation (heterotransporters) located on glutamate-releasing and glutamate transporter-expressing (homotransporters) gliosomes. This glutamate release involves reversal of glutamate transporters and anion channel opening, but not exocytosis. Both the exocytotic and the heterotransporter-mediated glutamate release were more abundant in gliosomes prepared from the spinal cord of transgenic mice, model of amyotrophic lateral sclerosis, than in controls; suggesting the involvement of astrocytic glutamate release in the excitotoxicity proposed as a cause of motor neuron degeneration. The results support the view that gliosomes may represent a viable preparation that allows to study mechanisms of astrocytic transmitter release and its regulation in healthy animals and in animal models of brain diseases.

Intraocular expression and release of high-mobility group box 1 protein in retinal detachment

High-mobility group box 1 (HMGB1) protein is a multifunctional protein, which is mainly present in the nucleus and is released extracellularly by dying cells and/or activated immune cells. Although extracellular HMGB1 is thought to be a typical danger signal of tissue damage and is implicated in diverse diseases, its relevance to ocular diseases is mostly unknown. To determine whether HMGB1 contributes to the pathogenesis of retinal detachment (RD), which involves photoreceptor degeneration, we investigated the expression and release of HMGB1 both in a retinal cell death induced by excessive oxidative stress in vitro and in a rat model of RD-induced photoreceptor degeneration in vivo. In addition, we assessed the vitreous concentrations of HMGB1 and monocyte chemoattractant protein 1 (MCP-1) in human eyes with RD. We also explored the chemotactic activity of recombinant HMGB1 in a human retinal pigment epithelial (RPE) cell line. The results show that the nuclear HMGB1 in the retinal cell is augmented by death stress and upregulation appears to be required for cell survival, whereas extracellular release of HMGB1 is evident not only in retinal cell death in vitro but also in the rat model of RD in vivo. Furthermore, the vitreous level of HMGB1 is significantly increased and is correlated with that of MCP-1 in human eyes with RD. Recombinant HMGB1 induced RPE cell migration through an extracellular signal-regulated kinase-dependent mechanism in vitro. Our findings suggest that HMGB1 is a crucial nuclear protein and is released as a danger signal of retinal tissue damage. Extracellular HMGB1 might be an important mediator in RD, potentially acting as a chemotactic factor for RPE cell migration that would lead to an ocular pathological wound-healing response.

Neural-activity-dependent release of S100B from astrocytes enhances kainate-induced gamma oscillations in vivo

S100B is the principal calcium-binding protein of astrocytes and known to be secreted to extracellular space. Although secreted S100B has been reported to promote neurite extension and cell survival via its receptor [receptor for advanced glycation end products (RAGE)], effects of extracellular S100B on neural activity have been mostly unexplored. Here, we demonstrate that secreted S100B enhances kainate-induced gamma oscillations. Local infusion of S100B in S100B(-/-) mice enhanced hippocampal kainate-induced gamma oscillations in vivo. In a complementary set of experiments, local application of anti-S100B antibody in wild-type mice attenuated the gamma oscillations. Both results indicate that the presence of extracellular S100B enhances the kainate-induced gamma oscillations. In acutely isolated hippocampal slices, kainate application increased S100B secretion in a neural-activity-dependent manner. Further pharmacological experiments revealed that S100B secretion was critically dependent on presynaptic release of neurotransmitter and activation of metabotropic glutamate receptor 3. Moreover, the kainate-induced gamma oscillations were attenuated by the genetic deletion or antibody blockade of RAGE in vivo. These results suggest RAGE activation by S100B enhances the gamma oscillations. Together, we propose a novel pathway of neuron-glia communications--astrocytic release of S100B modulates neural network activity through RAGE activation.

Therapeutic potential of HMGB1-targeting agents in sepsis

Sepsis refers to a systemic inflammatory response syndrome resulting from a microbial infection. The inflammatory response is partly mediated by innate immune cells (such as macrophages, monocytes and neutrophils), which not only ingest and eliminate invading pathogens but also initiate an inflammatory response upon recognition of pathogen-associated molecular patterns (PAMPs). The prevailing theories of sepsis as a dysregulated inflammatory response, as manifested by excessive release of inflammatory mediators such as tumour necrosis factor and high-mobility group box 1 protein (HMGB1), are supported by extensive studies employing animal models of sepsis. Here we review emerging evidence that support extracellular HMGB1 as a late mediator of experimental sepsis, and discuss the therapeutic potential of several HMGB1-targeting agents (including neutralising antibodies and steroid-like tanshinones) in experimental sepsis.