Endogenous Danger Signal Molecule Research Articles

Alarmin HMGB1 induces systemic and brain inflammatory exacerbation in post-stroke infection rat model

Post-stroke infection (PSI) is known to worsen functional outcomes of stroke patients and accounts to one-third of stroke-related deaths in hospital. In our previous reports, we demonstrated that massive release of high-mobility group box protein 1 (HMGB1), an endogenous danger signal molecule, is promoted by N-methyl-d-aspartic acid-induced acute damage in the postischemic brain, exacerbating neuronal damage by triggering delayed inflammatory processes. Moreover, augmentation of proinflammatory function of lipopolysaccharides (LPS) by HMGB1 via direct interaction has been reported. The aim of this study was to investigate the role of HMGB1 in aggravating inflammation in the PSI by exacerbating the function of LPS. PSI animal model was produced by administrating a low-dose LPS at 24 h post-middle cerebral artery occlusion (MCAO). Profound aggravations of inflammation, deterioration of behavioral outcomes, and infarct expansion were observed in LPS-injected MCAO animals, in which serum HMGB1 surge, especially disulfide type, occurred immediately after LPS administration and aggravated brain and systemic inflammations probably by acting in synergy with LPS. Importantly, blockage of HMGB1 function by delayed administrations of therapeutic peptides known to inhibit HMGB1 (HMGB1 A box, HPep1) or by treatment with LPS after preincubation with HMGB1 A box significantly ameliorated damages observed in the rat PSI model, demonstrating that HMGB1 plays a crucial role. Furthermore, administration of Rhodobacter sphaeroides LPS, a selective toll-like receptor 4 antagonist not only failed to exert these effects but blocked the effects of LPS, indicating its TLR4 dependence. Together, these results indicated that alarmin HMGB1 mediates potentiation of LPS function, exacerbating TLR4-dependent systemic and brain inflammation in a rat PSI model and there is a positive-feedback loop between augmentation of LPS function by HMGB1 and subsequent HMGB1 release/serum. Therefore, HMGB1 might be a valuable therapeutic target for preventing post-stroke infection.

Local production of tenascin-C acts as a trigger for monocyte/macrophage recruitment that provokes cardiac dysfunction.

Tenascin-C (TNC) is an endogenous danger signal molecule strongly associated with inflammatory diseases and with poor outcome in patients with cardiomyopathies. Its function within pathological cardiac tissue during pressure overload remains poorly understood. We showed that TNC accumulates after 1 week of transverse aortic constriction (TAC) in the heart of 12-week-old male mice. By cross bone marrow transplantation experiments, we determined that TNC deposition relied on cardiac cells and not on haematopoietic cells. The expression of TNC induced by TAC, or by administration of a recombinant lentivector coding for TNC, triggered a pro-inflammatory cardiac microenvironment, monocyte/macrophage (MO/MΦ) accumulation, and systolic dysfunction. TNC modified macrophage polarization towards the pro-inflammatory phenotype and stimulated RhoA/Rho-associated protein kinase (ROCK) pathways to promote mesenchymal to amoeboid transition that enhanced macrophage migration into fibrillar collagen matrices. The amplification of inflammation and MO/MΦ recruitment by TNC was abrogated by genetic invalidation of TNC in knockout mice. These mice showed less ventricular remodelling and an improved cardiac function after TAC as compared with wild-type mice. By promoting a pro-inflammatory microenvironment and macrophage migration, TNC appears to be a key factor to enable the MO/MΦ accumulation within fibrotic hearts leading to cardiac dysfunction. As TNC is highly expressed during inflammation and sparsely during the steady state, its inhibition could be a promising therapeutic strategy to control inflammation and immune cell infiltration in heart disease.

Differential Regulation of IL-1β and IL-6 Release in Murine Macrophages.

Asbestos and silica (exogenous danger) and adenosine triphosphate (ATP, endogenous danger-signaling molecule) synergistically increase IL-1β release from endotoxin-primed macrophage, which is mediated by NOD-like receptor protein 3 (NLRP3) inflammasome. However, the conversion of pro-IL-1β to its active form seems to depend on the macrophage cell types. In the present study, bone marrow-derived macrophages (BMM) and three murine macrophage cell lines, J774.1, J774A.1, and RAW264.7 were exposed to ATP or fibrous titanium dioxide (FTiO2) in the presence or absence of lipopolysaccharide (LPS), and the concentrations of IL-1β and IL-6 in both cell lysates and in the culture media were measured by immunoblotting to differentiate active form of IL-1β from pro-IL-1β. IL-1β release was synergistically increased when the cells were exposed to both LPS and ATP or FTiO2, while IL-6 was readily released by LPS alone. IL-1β released into the culture medium was pro-IL-1β in J774.1 and RAW264.7, and most of the pro-IL-1β remained inside the cells. In contrast, the active form of IL-1β was released together with pro-IL-1β from J774A.1 and BMM after the co-stimulation. J774A.1 and BMM express apoptosis-associated speck-like protein contains a carboxyl-terminal CARD (ASC) while J774.1 and RAW264.7 do not or only faintly express ASC, and accordingly, caspase-1, which converts pro-IL-1β to its active form, is activated only in J774A.1 and BMM. Collectively, the canonical inflammasome pathway is not activated in J774.1 and RAW264.7, and the apparent synergistical increase of IL-1β in the culture medium mostly reflects the leakage of pro-IL-1β from these cells.

Effect of inflammatory mediators on cardiovascular function.

Inflammatory mediators can interfere with cardiovascular system. This article describes some recent findings in this field. In septic cardiomyopathy, direct and indirect interactions of endotoxin with the pacemaker current contribute to cardiac autonomic dysfunction and inadequately high heart rate, worsening prognosis. In myocardial infarction, inflammatory blood cells correlate with impaired coronary microvascular reperfusion. In cardiogenic shock, systemic inflammation and development of multiorgan dysfunction syndrome have a major impact on mortality. Shock patients have low levels of activated protein C and high levels of the endogenous danger signal molecule peroxiredoxin 1; both conditions might represent further therapeutic targets. As major cause of cytopathic hypoxia, mitochondrial dysfunction has also been identified in mitochondria from peripheral blood mononuclear cells in paediatric septic shock. Transcatheter aortic valve endocarditis, a new endocarditis entity after transcatheter aortic valve implantation in old and very old patients, needs our special attention, because immunosenescence may modify the clinical course in a negative sense. Systemic spreading of endocarditis to septic shock adds to the local valve infection the problem of septic shock. Not only in septic shock, but also in classic heart diseases like cardiogenic shock and endocarditis, the detrimental role of inflammatory mediators becomes more and more evident, whereas effective anti-inflammatory treatment concepts are still missing.

From Genesis to Revelation: The Role of Inflammatory Mediators in Chronic Respiratory Diseases and their Control by Nucleic Acid-based Drugs.

Asthma, chronic obstructive pulmonary disease, cystic fibrosis, and idiopathic pulmonary fibrosis, are among the most common chronic diseases and their prevalence is increasing. Each of these diseases is characterized by the secretion of cytokines and pro-inflammatory molecules which are thought to play a critical role in their pathogenesis. Moreover, immune cells, particularly neutrophils, macrophages and dendritic cells as well structural cells such as epithelial and airway smooth muscle cells are also involved in the pathogenic cycle of these diseases. There is a pressing need for the development of new therapies for these pulmonary diseases, particularly as no existing treatment has been shown to reduce disease progression. HMGB1 (high-mobility group box 1), originally identified as a nuclear non histone protein with DNA-binding domains can be secreted by living and dying cells and it is now regarded as an important endogenous danger signaling molecule. Besides as a signal of tissue injury, HMGB1 is considered a powerful mediator of inflammation and high levels of HMGB1 are found in chronic lung diseases. The role of HMGB1 in respiratory diseases is still elusive nevertheless these studies suggest an involvement of this cytokine in their pathogenesis. Nucleic acid-based drugs (NABDs) are a novel class of pharmaceuticals including antisense oligonucleotides, DNA-zymes, and RNA interference as mediated by small interfering RNA (siRNA), which are used to dampen the expression of disease-causing genes having therapeutic potential for controlling chronic airway diseases. Due to their inherent difficulties, such as for example sensitivity to endonucleases, their delivery in vivo should be assured by vectors. Non-viral lipid- and polymer-based nanosystems have acquired much importance in this context. In this review, we will discuss these emerging tools in gene therapy of chronic lung diseases, particularly the use of siRNA in the down-regulation of critical molecules in the pathogenesis of chronic lung diseases, with particular emphasis on HMGB1 as therapeutic target.

The Role of HMGB1 in the Pathogenesis of Type 2 Diabetes

Significance. With an alarming increase in recent years, diabetes mellitus has become a global challenge. Despite advances in treatment of diabetes mellitus, currently, medications available are unable to control the progression of diabetes and its complications. Growing evidence suggests that inflammation is an important pathogenic mediator in the development of diabetes mellitus. The perspectives including suggestions for new therapies involving the shift from metabolic stress to inflammation should be taken into account. Critical Issues. High-mobility group box 1 (HMGB1), a nonhistone nuclear protein regulating gene expression, was rediscovered as an endogenous danger signal molecule to trigger inflammatory responses when released into extracellular milieu in the late 1990s. Given the similarities of inflammatory response in the development of T2D, we will discuss the potential implication of HMGB1 in the pathogenesis of T2D. Importantly, we will summarize and renovate the role of HMGB1 and HMGB1-mediated inflammatory pathways in adipose tissue inflammation, insulin resistance, and islet dysfunction. Future Directions. HMGB1 and its downstream receptors RAGE and TLRs may serve as potential antidiabetic targets. Current and forthcoming projects in this territory will pave the way for prospective approaches targeting the center of HMGB1-mediated inflammation to improve T2D and its complications.

HMGB1-binding heptamer suppresses the synergistic effect of HMGB1 and LPS by interacting directly with HMGB1

High mobility group box 1 (HMGB1) is an endogenous danger signal molecule. In the postischemic brain, HMGB1 is massively released during acute damaging process and triggers inflammatory processes. Moreover, it has been reported HMGB1 augments the proinflammatory effect of LPS by direct interaction. In previous studies, the authors showed intranasally delivered a HMGB1 binding heptamer peptide (HBHP; HMSKPVQ) has robust neuroprotective effects in the ischemic brain after middle cerebral artery occlusion and that it exerts an anti-inflammatory effect. In the present study, the authors investigated whether HBHP suppresses the augmentation of the proinflammatory effect of LPS by HMGB1. In primary microglial cultures, low doses of LPS (5ng/ml) and recombinant HMGB1 (rHMGB1, 20ng/ml) synergistically activated microglial cells, and HMGB1–LPS binding was detected. In addition, synergistic NO accumulation along with direct HMGB1–LPS binding was also observed when primary microglial cultures were treated with LPS (5ng/ml) and HMGB1 accumulated in NMDA-conditioned medium (NCM). Co-treatment of microglial cells with HBHP and LPS or rHMGB1 (NCM), or treatment with rHMGB1 or NCM and LPS after pre-incubating rHMGB1 (or NCM) with HBHP markedly suppressed their synergistic activation. Furthermore, interactions between rHMGB1 and LPS or between HMGB1 in NCM and LPS were suppressed dose-dependently by HBHP, indicating that HBHP suppressed the synergism between HMGB1 and LPS and the underlying mechanism involved inhibition of HMGB1–LPS binding. Together these results show HBHP has anti-inflammatory effects, and that it inhibits synergism caused by the binding of HMGB1 and LPS.

HMGB1-Binding Heptamer Confers Anti-Inflammatory Effects in Primary Microglia Culture

High mobility group box 1 (HMGB1) is an endogenous danger signal molecule. In the postischemic brain, HMGB1 is massively released during NMDA-induced acute damage and triggers inflammatory processes. In a previous study, we demonstrated that intranasally delivered HMGB1 binding heptamer peptide (HBHP; HMSKPVQ) affords robust neuroprotective effects in the ischemic brain after middle cerebral artery occlusion (MCAO, 60 minutes). In the present study, we investigated HBHP-induced anti-inflammatory effects on microglia activation. In LPS-treated primary microglia culture, HMGB1 was rapidly released and accumulated in culture media. Furthermore, LPS-conditioned media collected from primary microglia cultures (LCM) activated naïve microglia and markedly induced NO and proinflammatory cytokines. However, the suppression of HMGB1 by siRNA-HMGB1, HMGB1 A box, or anti-HMGB1 antibody significantly attenuated LCM-induced microglial activation, suggesting that HMGB1 plays a critical role in this process. A pull-down assay using biotin-labeled HBHP showed that HBHP binds directly to HMGB1 (more specifically to HMGB1 A box) in LCM. In addition, HBHP consistently inhibited LCM-induced microglial activation and suppressed the inductions of iNOS and proinflammatory cytokines. Together these results suggest that HBHP confers anti-inflammatory effects in activated microglia cultures by forming a complex with HMGB1.

Current study of Toll-like receptor and fundus disease

Toll-like receptors (TLRs) can recognize pathogens associated molecular of micro-organisms,leading to activation of the downstream signal transduction pathway and participate in innate and adaptive immune response.TLRs can also recognize endogenous danger signaling molecule and therefore be involved in pathogenesis of many low-grade chronic inflammatory and autoimmune diseases.TLRs are always expressed on immune cells,and recent studies confirmed that retinal pigment epithelial (RPE) cells also express TLRs.This review focuses on the research progress of fundus diseases and TLRs,such as the recognition of exogenous pathogenic microorganisms and endogenous danger signals in fundus,induction of inflammatory response,phagocytosis of photoreceptor outer segment by RPE and angiogenesis of fundus diseases. Key words: Toll-like receptors; Fundus disease; Angiogenesis; Inflammation

Intranasal delivery of HMGB1-binding heptamer peptide confers a robust neuroprotection in the postischemic brain

High mobility group box 1 (HMGB1) is an endogenous danger signal molecule. In a previous report, we showed that HMGB1 is massively released during NMDA-induced acute damaging process in the postischemic brain and triggers inflammatory processes and induces neuronal apoptosis. We have also reported a robust neuroprotection of intranasally delivered HMGB1 siRNA in the postischemic rat brain (middle cerebral artery occlusion (MCAO), 60min). In the present study, we investigated the therapeutic efficacy of intranasally delivered HMGB1 binding heptamer peptide (HBHP; HMSKPVQ), which was selected using a phage display approach, in the same stroke animal model. A pull-down assay using biotin-labeled HBHP showed that HBHP binds directly to HMGB1, specifically to HMGB1 A box, confirming HMGB1/HBHP interaction. HBHP significantly suppressed HMGB1-mediated neuronal cell death in primary cortical cultures and HMGB1/HBHP binding was detected in NMDA-conditioned culture media. However, a heptamer peptide composed of a scrambled sequence of the seven amino acids in HBHP failed to bind HMGB1 and had no protective effect. Furthermore, HBHP (300ng) delivered intranasally at 30min before MCAO significantly suppressed infarct volume in the postischemic rat brain (maximal reduction by 41.8±5.4%) and ameliorated neurological and behavioral deficits. In contrast, scrambled heptamer peptide had no protective effect at the same dose. Together these results suggest that intranasal HBHP ameliorates neuronal damage in the ischemic brain by binding HMGB1, which might inhibit the function of HMGB1 as an endogenous danger signal molecule.

Mechanical Skin Injury Induces TLR4/MyD88 Dependent IL-23 Expression In Epidermal Keratinocytes

RationaleScratching and epidermal hyperplasia are hallmarks of atopic dermatitis. IL-23 is a cytokine that induces epidermal hyperplasia. We examined the hypothesis that mechanical skin injury by tape stripping, a surrogate of scratching, induces IL-23 expression in the skin.MethodsEar skin of mice was tape stripped then examined 6 hrs later for IL-23 expression by quantitative RT-PCR and immunohistochemistry. Low molecular weight hyaluronic acid (HA) was injected intradermally, and 3 hrs later, skin was harvested. Langerhans cells were depleted by i.p. injection of 1 μg diphtheria toxin (DT) into langerin-eGFP-DTR mice, and 24 hrs later ear skin was tape stripped then harvested. The keratinocyte cell line, PAM212 cells was treated with HA (50 μg/ml) for 3hResultsTape stripping induced epidermal IL-23 expression of WT, but not TLR4 and MyD88 deficient mice. IL-23 induction by tape stripping in germ free mice was comparable to that in specific pathogen free mice. Skin of LC-depleted mice showed the same level of IL-23 induction compared to intact mice. Intradermal injection of the endogenous danger signal molecule, HA induced IL-23 expression in the skin of WT, but not TLR4 deficient mice. HA treatment induced IL-23 expression by PAM212 cells in vitro.ConclusionScratching may contribute to epidermal hyperplasia in AD through the release of the endogenous danger signal molecule HA, which directly induces IL-23 expression from keratinocytes through TLR4/MyD88 signaling. RationaleScratching and epidermal hyperplasia are hallmarks of atopic dermatitis. IL-23 is a cytokine that induces epidermal hyperplasia. We examined the hypothesis that mechanical skin injury by tape stripping, a surrogate of scratching, induces IL-23 expression in the skin. Scratching and epidermal hyperplasia are hallmarks of atopic dermatitis. IL-23 is a cytokine that induces epidermal hyperplasia. We examined the hypothesis that mechanical skin injury by tape stripping, a surrogate of scratching, induces IL-23 expression in the skin. MethodsEar skin of mice was tape stripped then examined 6 hrs later for IL-23 expression by quantitative RT-PCR and immunohistochemistry. Low molecular weight hyaluronic acid (HA) was injected intradermally, and 3 hrs later, skin was harvested. Langerhans cells were depleted by i.p. injection of 1 μg diphtheria toxin (DT) into langerin-eGFP-DTR mice, and 24 hrs later ear skin was tape stripped then harvested. The keratinocyte cell line, PAM212 cells was treated with HA (50 μg/ml) for 3h Ear skin of mice was tape stripped then examined 6 hrs later for IL-23 expression by quantitative RT-PCR and immunohistochemistry. Low molecular weight hyaluronic acid (HA) was injected intradermally, and 3 hrs later, skin was harvested. Langerhans cells were depleted by i.p. injection of 1 μg diphtheria toxin (DT) into langerin-eGFP-DTR mice, and 24 hrs later ear skin was tape stripped then harvested. The keratinocyte cell line, PAM212 cells was treated with HA (50 μg/ml) for 3h ResultsTape stripping induced epidermal IL-23 expression of WT, but not TLR4 and MyD88 deficient mice. IL-23 induction by tape stripping in germ free mice was comparable to that in specific pathogen free mice. Skin of LC-depleted mice showed the same level of IL-23 induction compared to intact mice. Intradermal injection of the endogenous danger signal molecule, HA induced IL-23 expression in the skin of WT, but not TLR4 deficient mice. HA treatment induced IL-23 expression by PAM212 cells in vitro. Tape stripping induced epidermal IL-23 expression of WT, but not TLR4 and MyD88 deficient mice. IL-23 induction by tape stripping in germ free mice was comparable to that in specific pathogen free mice. Skin of LC-depleted mice showed the same level of IL-23 induction compared to intact mice. Intradermal injection of the endogenous danger signal molecule, HA induced IL-23 expression in the skin of WT, but not TLR4 deficient mice. HA treatment induced IL-23 expression by PAM212 cells in vitro. ConclusionScratching may contribute to epidermal hyperplasia in AD through the release of the endogenous danger signal molecule HA, which directly induces IL-23 expression from keratinocytes through TLR4/MyD88 signaling. Scratching may contribute to epidermal hyperplasia in AD through the release of the endogenous danger signal molecule HA, which directly induces IL-23 expression from keratinocytes through TLR4/MyD88 signaling.

Glycyrrhizic acid affords robust neuroprotection in the postischemic brain via anti-inflammatory effect by inhibiting HMGB1 phosphorylation and secretion

High mobility group box 1 (HMGB1) is an endogenous danger signal molecule. In a previous report, we showed that HMGB1 is massively released during NMDA-induced acute damaging process in the postischemic brain and triggers inflammatory processes, like microglial activation. siRNA-mediated HMGB1 knockdown markedly reduced infarct volumes, confirming the crucial role played by HMGB1 in the postischemic brain. In the present study, we showed neuroprotective effects of glycyrrhizin (GL) in the postischemic rat brain after middle cerebral artery occlusion (MCAO). GL, a triterpene present in the roots and rhizomes of licorice, Glycyrrhiza glabra, has been shown to have anti-inflammatory and anti-viral effects. It has been reported that GL binds directly to HMGB1, and inhibits its chemoattractant and mitogenic activities. The administration of GL (10mg/kg) intravenously at 3 or 6h after MCAO reduced infarct volumes to 12.9±4.2% and 46.2±9.9%, respectively, of untreated control. This neuroprotective effect was accompanied by improvements in motor impairment and neurological deficits and suppressions of microglia activation and proinflammatory cytokine induction. Interestingly, GL almost completely blocked HMGB1 secretion in the postischemic brain and in lipopolysaccharide (LPS)-treated microglia cells. Furthermore, HMGB1 phosphorylation, which is the initial step for HMGB1 secretion, and the interaction between HMGB1 and protein kinase C (PKC) or calcium/calmodulin-dependent protein kinase IV (CaMKIV) were suppressed dose-dependently by GL. Here, we hypothesized that the blockage for the putative phosphorylation sites in HMGB1 by GL might be attributed to this suppression. In addition to the anti-inflammatory effects, we found that GL has anti-excitotoxic and anti-oxidative effects in neurons. Together these results indicate that GL has neuroprotective efficacy in the postischemic brain via its anti-inflammatory, anti-excitotoxic, and anti-oxidative effects and in particular, it exerts anti-inflammatory effect, at least in part, by inhibiting HMGB1 secretion.

Galectin-3 Exerts Cytokine-Like Regulatory Actions through the JAK–STAT Pathway

Galectin-3, a β-galactoside-binding lectin, has been proposed to have multifaceted functions in various pathophysiological conditions. However, the characteristics of galectin-3 and its molecular mechanisms of action are still largely unknown. In this study, we show that galectin-3 exerts cytokine-like regulatory actions in rat and mouse brain-resident immune cells. Both the expression of galectin-3 and its secretion into the extracellular compartment were significantly enhanced in glia under IFN-γ-stimulated, inflamed conditions. After exposure to galectin-3, glial cells produced high levels of proinflammatory mediators and exhibited activated properties. Notably, within minutes after exposure to galectin-3, JAK2 and STAT1, STAT3, and STAT5 showed considerable enhancement of tyrosine phosphorylation; thereafter, downstream events of STAT signaling were also significantly enhanced. Treatment of the cells with pharmacological inhibitors of JAK2 reduced the galectin-3-stimulated increases of inflammatory mediators. Using IFN-γ receptor 1-deficient mice, we further found that IFN-γR 1 might be required for galectin-3-dependent activation of the JAK-STAT cascade. However, galectin-3 significantly induced phosphorylation of STATs in glial cells from IFN-γ-deficient mice, suggesting that IFN-γ does not mediate activation of STATs. Collectively, our findings suggest that galectin-3 acts as an endogenous danger signaling molecule under pathological conditions in the brain, providing a potential explanation for the molecular basis of galectin-3-associated pathological events.

Virus-mediated oncolysis induces danger signal and stimulates cytotoxic T-lymphocyte activity via proteasome activator upregulation

Dendritic cells (DCs) are the most potent antigen-presenting cells and acquire cellular antigens and danger signals from dying cells to initiate antitumor immune responses via direct cell-to-cell interaction and cytokine production. The optimal forms of tumor cell death for priming DCs for the release of danger signals are not fully understood. OBP-301 (Telomelysin) is a telomerase-specific replication-competent adenovirus that induces selective E1 expression and exclusively kills human cancer cells. Here, we show that OBP-301 replication produced the endogenous danger signaling molecule, uric acid, in infected human tumor cells, which in turn stimulated DCs to produce interferon-gamma (IFN-gamma) and interleukin 12 (IL-12). Subsequently, IFN-gamma release upregulated the endogenous expression of the proteasome activator PA28 in tumor cells and resulted in the induction of cytotoxic T-lymphocytes. Our data suggest that virus-mediated oncolysis might be the effective stimulus for immature DCs to induce specific activity against human cancer cells.