How is inflammation initiated? Individual influences of IL-1, IL-18 and HMGB1

Contribution of redox-dependent activation of endothelial Nlrp3 inflammasomes to hyperglycemia-induced endothelial dysfunction

Recent studies indicate that inflammasomes serve as intracellular machinery to initiate classical cytokine-mediated inflammatory responses and play a crucial role in the pathogenesis of cardiovascular diseases. However, whether or not the activation of endothelial inflammasomes directly causes cell dysfunction or tissue injury without recruitment of inflammatory cells is unknown. We explored the role of endothelial cell inflammasome activation in mediating tight junction disruption, a hallmark event of endothelial barrier dysfunction leading to endothelial hyperpermeability in diabetes. We used confocal microscopy to study the formation and activation of NOD-like receptor family pyrin domain containing-3 (Nlrp3) inflammasomes and expression of tight junction proteins in coronary arteries of streptozotocin-treated diabetic wild type and Nlrp3 gene-deleted mice. We found that Nlrp3 ablation prevented inflammasome activation and tight junction disassembly in the coronary arterial endothelium of diabetic mice. Similarly, Nlrp3 gene silencing prevented high glucose-induced down-regulation of tight junction proteins in cultured mouse vascular endothelial cells (MVECs). The high glucose-induced tight junction disruption and consequent endothelial permeability were attributed to increased release of the high mobility group box protein-1 (HMGB1), which is dependent on enhanced Nlrp3 inflammasome activity. Mechanistically, reducing reactive oxygen species (ROS) production abolished high glucose-induced inflammasome activation, tight junction disruption, and endothelial hyperpermeability in MVECs. Collectively, the ROS-dependent activation of endothelial Nlrp3 inflammasomes by hyperglycemia may be an important initiating mechanism to cause endothelial dysfunction. These effects could contribute to the early onset of endothelial injury in diabetes.

KEY MESSAGE

Endothelial tight junction disruption in diabetes requires Nlrp3 inflammasomes. High glucose activates Nlrp3 inflammasome in endothelial cells via ROS production. Activation of endothelial inflammasome by high glucose triggers release of HMGB1. Blockade of Nlrp3/HMGB1 axis inhibits high glucose-induced endothelial permeability.

Interleukin-1 β-targeted treatment strategies in inflammatory depression: toward personalized care

OBJECTIVES

It is unknown whether a cytokine signature may help the identification of subgroup of patient who would respond to personalized treatment. As interleukin-1 beta (Il-1β) seems to play a major role in mood disorder, a systematic review and meta-analysis of its potential role in major depressive disorder (MDD) was carried out.

METHODS

A systematic search was performed to identify appropriate MDD vs. control studies pertaining to Il-1β. Methodological quality and possible moderators were also assessed.

RESULTS

A total of 1922 studies were identified, and 53 articles were selected. Results showed an association between increased blood IL-1β and MDD in high-quality studies only. No association with age was found. No IL-1β gene-related polymorphisms has been associated with MDD. No effect of antidepressant on IL-1β level has been found, although the antidepressants investigated were various. Qualitative analyses indicate that MDD coupled to a history of childhood trauma may be a subgroup for IL-1β -targeted therapies. No difference in studies utilizing a stimulation method has been identified to date.

CONCLUSIONS

The present work has confirmed IL-1β as a biological marker of interest for innovative MDD treatments. However, further studies are needed to clarify the patients with MDD who may benefit from these therapies.

Molecular Mechanism Underlying Pathogenesis of Lewisite-Induced Cutaneous Blistering and Inflammation: Chemical Chaperones as Potential Novel Antidotes

Lewisite is a potent arsenic-based chemical warfare agent known to induce painful cutaneous inflammation and blistering. Only a few modestly effective antidotes have so far been described in the literature. However, the discovery of effective antidotes for lewisite was hampered by the paucity of the exact molecular mechanism underlying its cutaneous pathogenesis. We investigated the molecular mechanism underlying lewisite-induced cutaneous blistering and inflammation and describe its novel antidotes. On the basis of our initial screening, we used a highly sensitive murine model that recapitulates the known human pathogenesis of arsenicals-induced cutaneous inflammation and blistering. Topically administered lewisite induced potent acute inflammation and microvesication in the skin of Ptch1(+/-)/SKH-1 mice. Even at a very low dose, lewisite up-regulates unfolded protein response signaling, inflammatory response, and apoptosis. These cutaneous lesions were associated with production of reactive oxygen species and extensive apoptosis of the epidermal keratinocytes. We confirmed that activation of reactive oxygen species-dependent unfolded protein response signaling is the underlying molecular mechanism of skin damage. Similar alterations were noticed in lewisite-treated cultured human skin keratinocytes. We discovered that chemical chaperone 4-phenyl butyric acid and antioxidant N-acetylcysteine, which significantly attenuate lewisite-mediated skin injury, can serve as potent antidotes. These data reveal a novel molecular mechanism underlying the cutaneous pathogenesis of lewisite-induced lesions. We also identified novel potential therapeutic targets for lewisite-mediated cutaneous injury.

HMGB1/RAGE Signaling and Pro-Inflammatory Cytokine Responses in Non-HIV Adults with Active Pulmonary Tuberculosis

BACKGROUND

We aimed to study the pathogenic roles of High-Mobility Group Box 1 (HMGB1) / Receptor-for-Advanced-Glycation-End-products (RAGE) signaling and pro-inflammatory cytokines in patients with active pulmonary tuberculosis (PTB).

METHODS

A prospective study was conducted among non-HIV adults newly-diagnosed with active PTB at two acute-care hospitals (n = 80); age-and-sex matched asymptomatic individuals (tested for latent TB) were used for comparison (n = 45). Plasma concentrations of 8 cytokines/chemokines, HMGB1, soluble-RAGE, and transmembrane-RAGE expressed on monocytes/dendritic cells, were measured. Gene expression (mRNA) of HMGB1, RAGE, and inflammasome-NALP3 was quantified. Patients' PBMCs were stimulated with recombinant-HMGB1 and MTB-antigen (lipoarabinomannan) for cytokine induction ex vivo.

RESULTS

In active PTB, plasma IL-8/CXCL8 [median(IQR), 6.0(3.6-15.1) vs 3.6(3.6-3.6) pg/ml, P<0.001] and IL-6 were elevated, which significantly correlated with mycobacterial load, extent of lung consolidation (rs +0.509, P<0.001), severity-score (rs +0.317, P = 0.004), and fever and hospitalization durations (rs +0.407, P<0.001). IL-18 and sTNFR1 also increased. Plasma IL-8/CXCL8 (adjusted OR 1.12, 95%CI 1.02-1.23 per unit increase, P = 0.021) and HMGB1 (adjusted OR 1.42 per unit increase, 95%CI 1.08-1.87, P = 0.012) concentrations were independent predictors for respiratory failure, as well as for ICU admission/death. Gene expression of HMGB1, RAGE, and inflammasome-NALP3 were upregulated (1.2-2.8 fold). Transmembrane-RAGE was increased, whereas the decoy soluble-RAGE was significantly depleted. RAGE and HMGB1 gene expressions positively correlated with cytokine levels (IL-8/CXCL8, IL-6, sTNFR1) and clinico-/radiographical severity (e.g. extent of consolidation rs +0.240, P = 0.034). Ex vivo, recombinant-HMGB1 potentiated cytokine release (e.g. TNF-α) when combined with lipoarabinomannan.

CONCLUSION

In patients with active PTB, HMGB1/RAGE signaling and pro-inflammatory cytokines may play important roles in pathogenesis and disease manifestations. Our clinico-immunological data can provide basis for the development of new strategies for disease monitoring, management and control.

Ethanol and Other Short-Chain Alcohols Inhibit NLRP3 Inflammasome Activation through Protein Tyrosine Phosphatase Stimulation

Immunosuppression is a major complication of alcoholism that contributes to increased rates of opportunistic infections and sepsis in alcoholics. The NLRP3 inflammasome, a multiprotein intracellular pattern recognition receptor complex that facilitates the cleavage and secretion of the proinflammatory cytokines IL-1β and IL-18, can be inhibited by ethanol, and we sought to better understand the mechanism through which this occurs and whether chemically similar molecules exert comparable effects. We show that ethanol can specifically inhibit activation of the NLRP3 inflammasome, resulting in attenuated IL-1β and caspase-1 cleavage and secretion, as well as diminished apoptosis-associated speck-like protein containing a CARD (ASC) speck formation, without affecting potassium efflux, in a mouse macrophage cell line (J774), mouse bone marrow-derived dendritic cells, mouse neutrophils, and human PBMCs. The inhibitory effects on the Nlrp3 inflammasome were independent of γ-aminobutyric acid A receptor activation or N-methyl-d-asparate receptor inhibition but were associated with decreased oxidant production. Ethanol treatment markedly decreased cellular tyrosine phosphorylation, whereas administration of the tyrosine phosphatase inhibitor sodium orthovanadate prior to ethanol restored tyrosine phosphorylation and IL-1β secretion subsequent to ATP stimulation. Furthermore, sodium orthovanadate-induced phosphorylation of ASC Y144, necessary and sufficient for Nlrp3 inflammasome activation, and secretion of phosphorylated ASC were inhibited by ethanol. Finally, multiple alcohol-containing organic compounds exerted inhibitory effects on the Nlrp3 inflammasome, whereas 2-methylbutane (isopentane), the analogous alkane of the potent inhibitor isoamyl alcohol (isopentanol), did not. Our results demonstrate that ethanol antagonizes the NLRP3 inflammasome at an apical event in its activation through the stimulation of protein tyrosine phosphatases, an effect shared by other short-chain alcohols.

Innate danger signals in acute injury: From bench to bedside

The description of the systemic inflammatory response syndrome (SIRS) as a reaction to numerous insults marked a turning point in the understanding of acute critical states, which are intensive care basic cases. This concept highlighted the final inflammatory response features whichever the injury mechanism is: infectious, or non-infectious such as extensive burns, traumas, major surgery or acute pancreatitis. In these cases of severe non-infectious insult, many endogenous mediators are released. Like infectious agents components, they can activate the immune system (via common signaling pathways) and initiate an inflammatory response. They are danger signals or alarmins. These molecules generally play an intracellular physiological role and acquire new functions when released in extracellular space. Many progresses brought new information on these molecules and on their function in infectious and non-infectious inflammation. These danger signals can be used as biomarkers and provide new pathophysiological and therapeutic approaches, particularly for immune dysfunctions occurring after an acute injury. We present herein the danger model, the main danger signals and the clinical consequences.

TRPV4-Mediated Detection of Hyposmotic Stress by Skin Keratinocytes Activates Developmental Immunity

As an organism is exposed to pathogens during very early development, specific defense mechanisms must take effect. In this study, we used a germ-free zebrafish embryo model to show that osmotic stress regulates the activation of immunity and host protection in newly hatched embryos. Mechanistically, skin keratinocytes were responsible for both sensing the hyposmolarity of the aquatic environment and mediating immune effector mechanisms. This occurred through a transient potential receptor vanilloid 4/Ca(2+)/TGF-β-activated kinase 1/NF-κB signaling pathway. Surprisingly, the genes encoding antimicrobial effectors, which do not have the potential to cause tissue damage, are constitutively expressed during development, independently of both commensal microbes and osmotic stress. Our results reveal that osmotic stress is associated with the induction of developmental immunity in the absence of tissue damage and point out to the embryo skin as the first organ with full capacities to mount an innate immune response.

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.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

Potential role of High mobility group box 1 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide and is characterized as a typical inflammation-related carcinoma. High mobility group box protein 1 (HMGB1), a non-histone DNA-binding protein, is identified as a potent proinflammatory mediator when presents extracellularly. Recently, a growing body of evidence indicates that HMGB1 plays a potential role in HCC, but many questions remain unanswered about the relationship between HMGB1 and HCC formation and development. This review focuses on the biological effect of HMGB1, and discusses the association of HMGB1 with HCC and potential use of strategies targeting HMGB1 in HCC treatment.

A physical/psychological and biological stress combine to enhance endoplasmic reticulum stress

The generation of an immune response against infectious and other foreign agents is substantially modified by allostatic load, which is increased with chemical, physical and/or psychological stressors. The physical/psychological stress from cold-restraint (CR) inhibits host defense against Listeria monocytogenes (LM), due to early effects of the catecholamine norepinephrine (NE) from sympathetic nerves on β1-adrenoceptors (β1AR) of immune cells. Although CR activates innate immunity within 2h, host defenses against bacterial growth are suppressed 2-3 days after infection (Cao and Lawrence 2002). CR enhances inducible nitric oxide synthase (iNOS) expression and NO production. The early innate activation leads to cellular reduction-oxidation (redox) changes of immune cells. Lymphocytes from CR-treated mice express fewer surface thiols. Splenic and hepatic immune cells also have fewer proteins with free thiols after CR and/or LM, and macrophages have less glutathione after the in vivo CR exposure or exposure to NE in vitro. The early induction of CR-induced oxidative stress elevates endoplasmic reticulum (ER) stress, which could interfere with keeping phagocytized LM within the phagosome or re-encapsuling LM by autophagy once they escape from the phagosome. ER stress-related proteins, such as glucose-regulated protein 78 (GRP78), have elevated expression with CR and LM. The results indicate that CR enhances the unfolded protein response (UPR), which interferes with host defenses against LM. Thus, it is postulated that increased stress, as exists with living conditions at low socioeconomic conditions, can lower host defenses against pathogens because of oxidative and ER stress processes.

Immune Homeostasis in Epithelial Cells: Evidence and Role of Inflammasome Signaling Reviewed

The epithelium regulates the interaction between the noxious xenogenous, as well as the microbial environment and the immune system, not only by providing a barrier but also by expressing a number of immunoregulatory membrane receptors, and intracellular danger sensors and their downstream effectors. Amongst these are a number of inflammasome sensor subtypes, which have been initially characterized in myeloid cells and described to be activated upon assembly into multiprotein complexes by microbial and environmental triggers. This review compiles a vast amount of literature that supports a pivotal role for inflammasomes in the various epithelial barriers of the human body as essential factors maintaining immune signaling and homeostasis.

Anti-inflammatory effect of Impatiens textori Miq. extract via inhibition of NLRP3 inflammasome activation in in vitro and in vivo experimental models

ETHNOPHARMACOLOGICAL RELEVANCE

Impatiens textori Miq. (I. textori, Balsaminaceae) is a traditional medicinal herb used for centuries to treat several inflammatory related skin infections and allergic disorders in Asian countries.

AIM OF THE STUDY

In this study, we elucidated the effects of whole plant extracts of I. textori on inflammasome activation using in vitro and in vivo models.

MATERIALS AND METHODS

LPS-stimulated murine bone marrow macrophages were used to study the regulatory effect of I. textori extract (IT) on inflammasome activation. ATP, nigericin and MSU were used as danger-associated molecules to activate the NLRP3 inflammasome. An LPS-induced acute lung injury (ALI) mouse model was used to study the in vivo effect of IT on inflammasome activation.

RESULTS

IT treated at 25, 50, and 100μg/mL concentrations suppressed interleukin-1β secretion through the attenuation of NLRP3 inflammasome activation (p<0.001 at 100μg/mL) leading to the decreased amount of ASC oligomerization and caspase-1 maturation. For the in vivo model, IT inhibited the NLRP3 expression and cell recruitment at the lung tissue in the ALI mouse model.

CONCLUSION

IT exhibited potent anti-inflammatory effects via the attenuation of NLRP3 inflammasome activation supporting the traditional claims and may provide a valuable therapeutic strategy in treating various inflammation-related disorders.

Evidence for the involvement of gamma delta T cells in the immune response in Rasmussen encephalitis

Background

Rasmussen encephalitis (RE) is a rare neuroinflammatory disease characterized by intractable seizures and progressive atrophy on one side of the cerebrum. Perivascular cuffing and clusters of T cells in the affected cortical hemisphere are indicative of an active cellular immune response.

Methods

Peripheral blood mononuclear cells (PBMCs) and brain-infiltrating lymphocytes (BILs) were isolated from 20 RE surgery specimens by standard methods, and CD3⁺ T cell populations were analyzed by flow cytometry. Gamma delta T cell receptor spectratyping was carried out by nested PCR of reversed transcribed RNA extracted from RE brain tissue, followed by high resolution capillary electrophoresis. A MiSeq DNA sequencing platform was used to sequence the third complementarity determining region (CDR3) of δ1 chains.

Results

CD3⁺ BILs from all of the RE brain specimens comprised both αβ and γδ T cells. The median αβ:γδ ratio was 1.9 (range 0.58–5.2) compared with a median ratio of 7.7 (range 2.7–40.8) in peripheral blood from the same patients. The αβ T cells isolated from brain tissue were predominantly CD8⁺, and the majority of γδ T cells were CD4⁻ CD8⁻. Staining for the early activation marker CD69 showed that a fraction of the αβ and γδ T cells in the BILs were activated (median 42 %; range 13–91 %, and median 47 %; range 14–99 %, respectively). Spectratyping T cell receptor (TCR) Vδ1-3 chains from 14 of the RE brain tissue specimens indicated that the γδ T cell repertoire was relatively restricted. Sequencing δ1 chain PCR fragments revealed that the same prevalent CDR3 sequences were found in all of the brain specimens. These CDR3 sequences were also detected in brain tissue from 15 focal cortical dysplasia (FCD) cases.

Conclusion

Neuroinflammation in RE involves both activated αβ and γδ T cells. The presence of γδ T cells with identical TCR δ1 chain CDR3 sequences in all of the brain specimens examined suggests that a non-major histocompatibility complex (MHC)-restricted immune response to the same antigen(s) is involved in the etiology of RE. The presence of the same δ1 clones in CD brain implies the involvement of a common inflammatory pathway in both diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0352-2) contains supplementary material, which is available to authorized users.

Mechanisms and treatment of post-traumatic liver injury

Multiple organ failure is the leading cause of death in patients with severe multiple trauma in the early stage after injury. Hepatic insufficiency is common in intensive care unit (ICU), and about 27% of the patients with severe trauma suffer hepatic failure. However, the pathogenesis of traumatic liver damage is complicated due to the following main reasons: liver trauma, ischemia-reperfusion injury, severe sepsis, danger associated molecular patterns and so on. Clinically, trauma-induced liver injury can be managed conservatively or surgically, therefore, clarifying the mechanisms of traumatic liver damage, finding a new therapeutic target and improving its diagnosis and treatment are very important. This paper reviews the mechanism of post-traumatic liver injury and its diagnosis and treatment.

Porphyromonas gingivalis attenuates ATP-mediated inflammasome activation and HMGB1 release through expression of a nucleoside-diphosphate kinase

Many intracellular pathogens evade the innate immune response in order to survive and proliferate within infected cells. We show that Porphyromonas gingivalis, an intracellular opportunistic pathogen, uses a nucleoside-diphosphate kinase (NDK) homolog to inhibit innate immune responses due to stimulation by extracellular ATP, which acts as a danger signal that binds to P2X7 receptors and induces activation of an inflammasome and caspase-1. Thus, infection of gingival epithelial cells (GECs) with wild-type P. gingivalis results in inhibition of ATP-induced caspase-1 activation. However, ndk-deficient P. gingivalis is less effective than wild-type P. gingivalis in reducing ATP-mediated caspase-1 activation and secretion of the pro-inflammatory cytokine, IL-1β, from infected GECs. Furthermore, P. gingivalis NDK modulates release of high-mobility group protein B1 (HMGB1), a pro-inflammatory danger signal, which remains associated with chromatin in healthy cells. Unexpectedly, infection with either wild-type or ndk-deficient P. gingivalis causes release of HMGB1 from the nucleus to the cytosol. But HMGB1 is released to the extracellular space when uninfected GECs are further stimulated with ATP, and there is more HMGB1 released from the cells when ATP-treated cells are infected with ndk-deficient mutant than wild-type P. gingivalis. Our results reveal that NDK plays a significant role in inhibiting P2X7-dependent inflammasome activation and HMGB1 release from infected GECs.

Phosphatidylinositol 3-kinases pathway mediates lung caspase-1 activation and high mobility group box 1 production in a toluene-diisocyanate induced murine asthma model

We have previously demonstrated that downregulating HMGB1 decreases airway neutrophil inflammation in a toluene-diisocyanate (TDI)-induced murine asthma model, yet how HMGB1 is regulated in the lung remains uncertain. In this study, we intended to explore whether PI3K signaling pathway mediates pulmonary HMGB1 production in TDI-induced asthma model and the possible roles of NLRP3 inflammasome and caspase-1 in this process. BALB/c mice were sensitized and challenged with TDI to establish a TDI-induced asthma model. LY294002, a specific inhibitor of PI3K, was given intratracheally 1h before each challenge. Here we showed that airway hypersensitivity, airway infiltration of neutrophils and eosinophils, serum IgE and IL-4 in supernatant of cervical lymphocytes in TDI induced asthmatic mice were all markedly decreased by LY294002, accompanied by suppressed pulmonary expression of HMGB1. At the same time, we observed elevated protein levels of cleaved caspase-1 and IL-1β after TDI challenge, as well as increased immunoreactivity in lung, all of which were significantly recovered by LY294002. While both the protein expression and immunodistribution of NLRP3 in the lung stayed unchanged. These data suggest that PI3K mediates lung caspase-1 activation and HMGB1 production in TDI-induced murine asthma model.

Inflammasomes in pancreatic physiology and disease

In this review we summarize the role of inflammasomes in pancreatic physiology and disease with a focus on acute pancreatitis where much recent progress has been made. New findings have identified inducers of and cell specificity of inflammasome component expression in the pancreas, the contribution of inflammasome-regulated effectors to pancreatitis, and metabolic regulation of inflammasome activation, which are strong determinants of injury in pancreatitis. New areas of pancreatic biology will be highlighted in the context of our evolving understanding of gut microbiome- and injury-induced inflammasome priming, pyroptosis, and innate immune-mediated regulation of cell metabolism.

Murine Gammaherpesvirus 68 Pathogenesis Is Independent of Caspase-1 and Caspase-11 in Mice and Impairs Interleukin-1β Production upon Extrinsic Stimulation in Culture

Gammaherpesviruses establish lifelong infections that are associated with the development of cancer. These viruses subvert many aspects of the innate and adaptive immune response of the host. The inflammasome, a macromolecular protein complex that controls inflammatory responses to intracellular danger signals generated by pathogens, is both activated and subverted during human gammaherpesvirus infection in culture. The impact of the inflammasome response on gammaherpesvirus replication and latency in vivo is not known. Caspase-1 is the inflammasome effector protease that cleaves the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18. We infected caspase-1-deficient mice with murine gammaherpesvirus 68 (MHV68) and observed no impact on acute replication in the lung or latency and reactivation from latency in the spleen. This led us to examine the effect of viral infection on inflammasome responses in bone marrow-derived macrophages. We determined that infection of macrophages with MHV68 led to a robust interferon response but failed to activate caspase-1 or induce the secretion of IL-1β. In addition, MHV68 infection led to a reduction in IL-1β production after extrinsic lipopolysaccharide stimulation or upon coinfection with Salmonella enterica serovar Typhimurium. Interestingly, this impairment occurred at the proIL-1β transcript level and was independent of the RTA, the viral lytic replication and transcription activator. Taken together, MHV68 impairs the inflammasome response by inhibiting IL-1β production during the initial stages of infection.

IMPORTANCE

Gammaherpesviruses persist for the lifetime of the host. To accomplish this, they must evade recognition and clearance by the immune system. The inflammasome consists of proteins that detect foreign molecules in the cell and respond by secreting proinflammatory signaling proteins that recruit immune cells to clear the infection. Unexpectedly, we found that murine gammaherpesvirus pathogenesis was not enhanced in mice lacking caspase-1, a critical inflammasome component. This led us to investigate whether the virus actively impairs the inflammasome response. We found that the inflammasome was not activated upon macrophage cell infection with murine gammaherpesvirus 68. Infection also prevented the host cell inflammasome response to other pathogen-associated molecular patterns, indicated by reduced production of the proinflammatory cytokine IL-1β upon bacterial coinfection. Taken together, murine gammaherpesvirus impairment of the inflammatory cytokine IL-1β in macrophages identifies one mechanism by which the virus may inhibit caspase-1-dependent immune responses in the infected animal.

Physiologic concentrations of HMGB1 have no impact on cytokine-mediated eosinophil survival or chemotaxis in response to Eotaxin-2 (CCL24)

HMGB1 is an alarmin that can stimulate the innate immune system alone or in a complex with other inflammatory mediators. Given the recent interest in HMGB1 with respect to the pathogenesis of eosinophil-associated disorders, including asthmatic inflammation and chronic rhinosinusitis, we have explored the role of this mediator and in promoting eosinophil activation. HMGB1 receptors RAGE and TLR4 but not TLR2 were detected on freshly isolated human eosinophils from healthy donors. Physiologic and relevant pathophysiologic levels of biologically-active HMGB1 had no effect on survival of human eosinophils alone or in combination with pro-survival cytokines IL-5, IL-3, or GM-CSF, and increasing concentrations of HMGB1 had no impact on surface expression of RAGE, TLR2 or TLR4. Similarly, HMGB1 did not elicit chemotaxis of human eosinophils alone and had no effect in combination with the eosinophil chemotactic agent, eotaxin-2 (CCL24). However, surface expression of TLR2 and TLR4 increased in response to cell stress, notably on eosinophils that remain viable after 48 hours without IL-5. As such, HMGB1 signaling on eosinophils may be substantially more detailed, and may involve complex immunostimulatory pathways other than or in addition to those evaluated here.

Thymic stromal lymphopoietin induction by skin irritation is independent of tumour necrosis factor-α, but supported by interleukin-1

BACKGROUND

Thymic stromal lymphopoietin (TSLP) is an extensively studied cytokine linked to the pathogenesis of allergic diseases, but the inherent activities behind TSLP expression are not well defined.

OBJECTIVES

To explore the conditions favourable to TSLP induction outside of a typically allergic set-up and determine the associated mechanisms, and to assess whether TSLP is similarly controlled in murine and human skin.

METHODS

A combination of primary keratinocytes, skin explants/epidermal sheets and in vivo strategies was employed. The skin of wild-type and tumour necrosis factor knockout (TNF-/-) mice was subjected to acute irritation. Cells and specimens were stimulated with a range of TSLP inducers in the presence or absence of neutralizing antibodies. TSLP was quantitated by quantitative reverse-transcriptase polymerase chain reaction, enzyme-linked immunosorbent assay and immunohistochemistry.

RESULTS

In addition to cytokines, skin irritation brought about by various causes (e.g. shaving, scratching and chemical perturbation) elicited uniformly high-level production of TSLP, which entered the circulatory system. Despite the potency of TNF-α as an in vitro TSLP inducer, the use of TNF-/- mice revealed that this mechanism was completely independent of endogenous TNF-α. Conversely, irritation-elicited TSLP depended on interleukin (IL)-1, which had a more pronounced influence in human skin than in murine skin. Murine and human skin differed considerably regarding TSLP regulation.

CONCLUSIONS

Thymic stromal lymphopoietin is a general responder to disrupted skin homeostasis and may have a role in triggering the alarm system of the skin. TSLP induction is rapid, transient and driven by a mechanism that does not involve TNF-α, but partially relies on the evolutionarily ancient IL-1 system. The irritated skin secretes TSLP into the circulatory system. TSLP regulation varies between species.

HMGB1 genetic polymorphisms in oral squamous cell carcinoma and oral lichen planus patients

OBJECTIVES

This study examined the single nucleotide polymorphisms (SNPs) in high-mobility group box 1 (HMGB1) gene in patients with oral squamous cell carcinoma (OSCC) and oral lichen planus (OLP).

MATERIALS AND METHODS

The study was conducted on 93 patients with OSCC, 53 patients with OLP, and 100 controls, all Caucasians of the same ethnicity, matched by age. HMGB1 genotypes for 4 SNPs, 2262G/A (rs1045411), 1177G/C (rs3742305), 3814C/G (rs2249825), and rs4540927, were assessed using TaqMan SNP Genotyping Assays, Applied Biosystems.

RESULTS

The HMGB1 1177GG genotype was associated with lymph-node metastasis and tumor stage in OSCCs (P = 0.016 and P = 0.030, respectively). Genotype 1177GG resulted in poorer recurrence-free survival (RFS), P = 0.000. The 1177G/C polymorphism was an independent predictor of RFS compared to GG genotype, P = 0.001. The three polymorphisms were in linkage disequilibrium (LD). The AGC and GGC haplotypes were associated with an increased oral cancer risk, determined over the haplotype odds ratios (HOR = 13.316, P = 0.015, and HOR = 5.769, P = 0.029, respectively). The AGC haplotype was related to erosive OLP progression to OSCC (HOR = 12.179, P = 0.001).

CONCLUSIONS

HMGB1 polymorphism 1177G/C could be associated with tumor progression and recurrence-free survival in patients with OSCC. The haplotypes of HMGB1 gene might be associated with susceptibility to OSCC and OLP progression to OSCC.

Sirt1 restrains lung inflammasome activation in a murine model of sepsis

Excessive inflammation is a major cause of organ damage during sepsis. The elderly are highly susceptible to sepsis-induced organ injury. Sirt1 expression is reduced during aging. In the present study, we investigated the role of Sirt1, a histone deacetylase, in controlling inflammatory responses in a murine sepsis model induced by cecal ligation and puncture (CLP). We examined lung inflammatory signaling in inducible Sirt1 knockout (Sirt1(-/-)) mice and wild-type littermates (Sirt1(+/+)) after CLP. Our results demonstrated that Sirt1 deficiency led to severe lung inflammatory injury. To further investigate molecular mechanisms of Sirt1 regulation of lung inflammatory responses in sepsis, we conducted a series of experiments to assess lung inflammasome activation after CLP. We detected increased lung inflammatory signaling including NF-κB, signal transducer and activator of transcription 3, and ERK1/2 activation in Sirt1(-/-) mice after CLP. Furthermore, inflammasome activity was increased in Sirt1(-/-) mice after CLP, as demonstrated by increased IL-1β and caspase-7 cleavage and activation. Aggravated inflammasome activation in Sirt1(-/-) mice was associated with the increased production of lung proinflammatory mediators, including ICAM-1 and high-mobility group box 1, and further disruption of tight junctions and adherens junctions, as demonstrated by dramatic reduction of lung claudin-1 and vascular endothelial-cadherin expression, which was associated with the upregulation of matrix metallopeptidase 9 expression. In summary, our results suggest that Sirt1 suppresses acute lung inflammation during sepsis by controlling inflammasome activation pathway.

High-mobility group box 1: a novel target for treatment of Pseudomonas aeruginosa keratitis

High-mobility group box 1 (HMGB1), a prototypic alarmin, mediates the systemic inflammatory response syndrome. Treatment with vasoactive intestinal peptide, an anti-inflammatory neuropeptide, downregulates proinflammatory cytokines and promotes healing in a susceptible (cornea perforates) model of Pseudomonas aeruginosa keratitis, and also significantly downregulates HMGB1 expression. Therefore, we examined targeting HMGB1 for the treatment of P. aeruginosa keratitis to avoid delivery and other issues associated with vasoactive intestinal peptide. For this, HMGB1 was silenced using small interfering RNA, whereas controls were treated with a nonspecific scrambled sequence small interfering RNA. Less disease was seen postinfection in siHMGB1 compared with control mice and was documented by clinical score and photographs with a slit lamp. Real-time RT-PCR and ELISA confirmed HMGB1 knockdown. RT-PCR analysis also revealed reduced mRNA levels of IL-1β, MIP-2, TNF-α, TLR4, and receptor for advanced glycation end products, whereas mRNA levels of anti-inflammatory TLRs single Ig IL-1-related receptor and ST2 were increased significantly. HMGB1 knockdown also decreased IL-1β and MIP-2 proteins, reducing polymorphonuclear cell number in the infected cornea. mRNA and protein levels of CXCL12 and CXCR4, as well as mononuclear cells, were reduced significantly after HMGB1 knockdown. Ab neutralization of HMGB1, infection with a clinical isolate, and recombinant HMGB1 treatment of resistant mice supported the silencing studies. These data provide evidence that silencing HMGB1 promotes better resolution of P. aeruginosa keratitis by decreasing levels of proinflammatory mediators (decreasing polymorphonuclear cell infiltration), increasing anti-inflammatory TLRs, reducing CXCL12 (preventing HMGB1/CXCL12 heterodimer formation), and signaling through CXCR4, reducing monocyte/macrophage infiltration.

Involvement of major components from Sporothrix schenckii cell wall in the caspase-1 activation, nitric oxide and cytokines production during experimental sporotrichosis

Sporotrichosis is a chronic infection caused by the dimorphic fungus Sporothrix schenckii, involving all layers of skin and the subcutaneous tissue. The role of innate immune toll-like receptors 2 and 4 in the defense against this fungus has been reported, but so far, there were no studies on the effect of cell wall major components over the cytosolic oligo-merization domain (NOD)-like receptors, important regulators of inflammation and responsible for the maturation of IL-1β and IL-18, whose functions are dependents of the caspase-1 activation, that can participate of inflammasome. It was evaluated the percentage of activation of caspase-1, the production of IL-1β, IL-18, IL-17, IFN-γ and nitric oxide in a Balb/c model of S. schenckii infection. It was observed a decreased activity of caspase-1 during the fourth and sixth weeks of infection accompanied by reduced secretion of the cytokines IL-1β, IL-18 and IL-17 and high production of nitric oxide. IFN-γ levels were elevated during the entire time course of infection. This temporal reduction in caspase-1 activity coincides exactly with the reported period of fungal burden associated with a transitory immunosuppression induced by this fungus and detected in similar infection models. These results indicate the importance of interaction between caspase-1, cytokines IL-1β and IL-18 in the host defense against S. schenckii infection, suggesting a participation the inflammasome in this response.

The role of toll-like receptor 4 in corneal epithelial wound healing

PURPOSE

We evaluated the role of Toll-like receptor 4 (TLR4) in corneal epithelial wound healing.

METHODS

The expression of TLR4 during in vivo corneal epithelial wound healing was examined by immunostaining in mice. The expression and activation of TLR4 was studied in primary or telomerase-immortalized human corneal epithelial cells (HCEC). Scratch assay was performed to evaluate in vitro wound closure using live time-lapse microscopy. Transwell migration assay and Ki67 immunostaining were done to evaluate migration and proliferation, respectively. Lipopolysaccharide (LPS) was used to activate TLR4, whereas CLI-095 was used for its inhibition. The expression of inflammatory cytokines was determined by RT-PCR and ELISA. The activation of p42/44 and p38 was determined by immunoblotting.

RESULTS

In the murine model, TLR4 immunostaining was noted prominently in the epithelium 8 hours after wounding. There was a 4-fold increase in the expression of TLR4 6 hours after in vitro scratch wounding (P < 0.001). Confocal microscopy confirmed the membrane localization of TLR4/MD2 complex. There was a significant increase in migration, proliferation, and wound closure in HCEC treated with LPS (P < 0.05), while there was significant decrease with TLR4 inhibition (P < 0.05). Addition of LPS to wounded HCEC resulted in a significant increase in the expression of IL-6, TNF-α, CXCL8/IL8, and CCL5/RANTES at the mRNA and protein levels. Likewise, LPS increased the activation of p42/44 and p38 in wounded HCEC.

CONCLUSIONS

These results suggest that epithelial wounding induces the expression of functional TLR4. Toll-like receptor 4 signaling appears to contribute to early corneal epithelial wound repair by enhancing migration and proliferation.