A novel role of interleukin-1-converting enzyme in cytokine-mediated inducible nitric oxide synthase gene expression: Implications for neuroinflammatory diseases

Cytokine profile in Leishmania-positive blood donors

Serum levels of interleukin 2 (IL-2), interleukin 4 (IL-4), interleukin 6 (IL-6), interleukin 10 (IL-10), interleukin 17 (IL-17), interferon gamma (IFN-γ), tumor necrosis factor α (TNF-α), and interleukin 1β (IL-1β), cytokines involved in the immune response, were investigated in 75 Leishmania-positive blood donors living in endemic areas. Based on their status in 2011 and 2015, the subjects were clustered into three groups: positive for at least one diagnostic method in both years, but lacking clinical progression to disease (G1); positive on at least one method in 2011 but negative in 2015 (G2); negative on all methods in both years (G3). Donors were interviewed for sociodemographic data collection and underwent clinical evaluation and laboratory tests. Serum cytokines were quantified using a CBA Flex set (BD Biosciences). Significant differences were found for all the cytokines evaluated, with lower concentrations in consistently Leishmania-negative individuals. The exception was IFN-γ, with similar levels among all donors. No changes consistent with active disease were observed in the laboratory results for Leishmania-positive donors who underwent clinical evaluation, none of whom progressed to disease. This suggests that infection control is associated with serum IL-17 levels. Resolution of Leishmania infection in positive donors may be related to high levels of IL-17 and low levels of IL-10, highlighting the role played by IL-17 in asymptomatic Leishmania-infected individuals.

Effect of Lead (Pb) on Inflammatory Processes in the Brain

That the nervous system is the main target of lead (Pb) has long been considered an established fact until recent evidence has linked the Pb effect on the immune system to the toxic effects of Pb on the nervous system. In this paper, we present recent literature reports on the effect of Pb on the inflammatory processes in the brain, particularly the expression of selected cytokines in the brain (interleukin 6, TGF-β1, interleukin 16, interleukin 18, and interleukin 10); expression and activity of enzymes participating in the inflammatory processes, such as cyclooxygenase 2, caspase 1, nitrogen oxide synthase (NOS 2) and proteases (carboxypeptidases, metalloproteinases and chymotrypsin); and the expression of purine receptors P2X4 and P2X7. A significant role in the development of inflammatory processes in the brain is also played by microglia (residual macrophages in the brain and the spinal cord), which act as the first line of defense in the central nervous system, and astrocytes—Whose most important function is to maintain homeostasis for the proper functioning of neurons. In this paper, we also present evidence that exposure to Pb may result in micro and astrogliosis by triggering TLR4-MyD88-NF-κB signaling cascade and the production of pro-inflammatory cytokines.

Shedding of the tumor necrosis factor (TNF) receptor from the surface of hepatocytes during sepsis limits inflammation through cGMP signaling

Proteolytic cleavage of the tumor necrosis factor (TNF) receptor (TNFR) from the cell surface contributes to anti-inflammatory responses and may be beneficial in reducing the excessive inflammation associated with multiple organ failure and mortality during sepsis. Using a clinically relevant mouse model of polymicrobial abdominal sepsis, we found that the production of inducible nitric oxide synthase (iNOS) in hepatocytes led to the cyclic guanosine monophosphate (cGMP)-dependent activation of the protease TACE (TNF-converting enzyme) and the shedding of TNFR. Furthermore, treating mice with a cGMP analog after the induction of sepsis increased TNFR shedding and decreased systemic inflammation. Similarly, increasing the abundance of cGMP with a clinically approved phosphodiesterase 5 inhibitor (sildenafil) also decreased markers of systemic inflammation, protected against organ injury, and increased circulating amounts of TNFR1 in mice with sepsis. We further confirmed that a similar iNOS-cGMP-TACE pathway was required for TNFR1 shedding by human hepatocytes in response to the bacterial product lipopolysaccharide. Our data suggest that increasing the bioavailability of cGMP might be beneficial in ameliorating the inflammation associated with sepsis.

microRNA control of interferons and interferon induced anti-viral activity

Interferons (IFNs) are cytokines that are spontaneously produced in response to virus infection. They act by binding to IFN-receptors (IFN-R), which trigger JAK/STAT cell signalling and the subsequent induction of hundreds of IFN-inducible genes, including both protein-coding and microRNA genes. IFN-induced genes then act synergistically to prevent virus replication and create an anti-viral state. miRNA are therefore integral to the innate response to virus infection and are important components of IFN-mediated biology. On the other hand viruses also encode miRNAs that in some cases interfere directly with the IFN response to infection. This review summarizes the important roles of miRNAs in virus infection acting both as IFN-stimulated anti-viral molecules and as critical regulators of IFNs and IFN-stimulated genes. It also highlights how recent knowledge in RNA editing influence miRNA control of virus infection.

Developmental lead effects on behavior and brain gene expression in male and female BALB/cAnNTac mice

Lead (Pb) was one of the first poisons identified, and the developing nervous system is particularly vulnerable to its toxic effects. Relatively low, subclinical doses, of Pb that produce no overt signs of encephalopathy can affect cognitive, emotional, and motor functions. In the present study, the effects of developmental Pb-exposure on behavioral performance and gene expression in BALB/cAnNTac mice were evaluated. Pups were exposed to Pb from gestational-day (gd) 8 to postnatal-day (pnd) 21 and later evaluated in exploratory behavior, rotarod, Morris water maze, and resident-intruder assays as adults. Pb-exposure caused significant alterations in exploratory behavior and water maze performance during the probe trial, but rotarod performance was not affected. Pb-exposed males displayed violent behavior towards their cage mates, but not to a stranger in the resident-intruder assay. Gene expression analysis at pnd21 by microarray and qRT-PCR was performed to provide a molecular link to the behavior changes that were observed. Pb strongly up-regulated gene expression within the signaling pathways of mitogen activated protein kinases (MAPKs), extra-cellular matrix (ECM) receptor, focal adhesion, and vascular endothelial growth-factor (VEGF), but Pb down-regulated gene expression within the pathways for glycan structures-biosynthesis 1, purine metabolism, and N-glycan biosynthesis. Pb increased transcription of genes for major histocompatibility (MHC) proteins, the chemokine Ccl28, chemokine receptors, IL-7, IL7R, and proteases. The qRT-PCR analysis indicated an increase of gene expression in the whole brain for caspase 1 and NOS2. Analysis of IL-1β, caspase 1, NOS2, Trail, IL-18 and IL-33 gene expression of brain regions indicated that Pb perturbed the inter-regional expression pattern of pro-inflammatory genes. Brain region protein concentrations for IL-10, an anti-inflammatory cytokine, showed a significant decrease only within the cortex region. Results indicate that Pb differentially affects the behavior of male and female mice in that females did less exploration and the males were selectively more aggressive. Gene expression data pointed to evidence of neuroinflammation in the brain of both female and male mice. Pb had more of an effect in the males on expression of vomeronasal receptor genes associated with odor detection and social behavior.

Astrocytes support hippocampal-dependent memory and long-term potentiation via interleukin-1 signaling

Recent studies indicate that astrocytes play an integral role in neural and synaptic functioning. To examine the implications of these findings for neurobehavioral plasticity we investigated the involvement of astrocytes in memory and long-term potentiation (LTP), using a mouse model of impaired learning and synaptic plasticity caused by genetic deletion of the interleukin-1 receptor type I (IL-1RI). Neural precursor cells (NPCs), derived from either wild type (WT) or IL-1 receptor knockout (IL-1rKO) neonatal mice, were labeled with bromodeoxyuridine (BrdU) and transplanted into the hippocampus of either IL-1rKO or WT adult host mice. Transplanted NPCs survived and differentiated into astrocytes (expressing GFAP and S100β), but not to neurons or oligodendrocytes. The NPCs-derived astrocytes from WT but not IL-1rKO mice displayed co-localization of GFAP with the IL-1RI. Four to twelve weeks post-transplantation, memory functioning was examined in the fear-conditioning and the water maze paradigms and LTP of perforant path-dentate gyrus synapses was assessed in anesthetized mice. As expected, IL-1rKO mice transplanted with IL-1rKO cells or sham operated displayed severe memory disturbances in both paradigms as well as a marked impairment in LTP. In contrast, IL-1rKO mice transplanted with WT NPCs displayed a complete rescue of the impaired memory functioning as well as partial restoration of LTP. These findings indicate that astrocytes play a critical role in memory functioning and LTP, and specifically implicate astrocytic IL-1 signaling in these processes. The results suggest novel conceptualization and therapeutic targets for neuropsychiatric disorders characterized by impaired astrocytic functioning concomitantly with disturbed memory and synaptic plasticity.

Hyperglycemia induces apoptosis of pancreatic islet endothelial cells via reactive nitrogen species-mediated Jun N-terminal kinase activation

Hyperglycemia significantly stimulates pancreatic islet endothelial cell apoptosis; however, the precise mechanisms are not fully understood. In the present study, treating pancreatic islet endothelial (MS-1) cells with high glucose (30mmol/l) but not mannitol significantly increased the number of apoptotic cells as compared with a physiological glucose concentration (5.5mmol/l). Hyperglycemia significantly stimulated the expression of inducible nitric oxide synthase (iNOS) and production of NO and peroxynitrite (ONOO(-)), relevant to MS-1 cell apoptosis. Moreover, induced reactive nitrogen species (RNS) significantly increased the expression of bax, cleaved caspase-3 and poly adenosine diphosphate (ADP)-ribose polymerase (PARP) via JNK activation, but the expression of bcl-2 was not altered. Furthermore, SP600125 (a specific inhibitor of JNK) and 1400W (a specific inhibitor of iNOS) significantly attenuated cell apoptosis induced by high glucose. Therefore, hyperglycemia triggers MS-1 cell apoptosis by activating an intrinsic-dependent apoptotic pathway via RNS-mediated JNK activation.

A novel pathway for inducible nitric-oxide synthase activation through inflammasomes

Innate immune recognition of flagellin is shared by transmembrane TLR5 and cytosolic Nlrc4 (NOD-like receptor family CARD (caspase activation recruitment domain) domain containing 4)/Naip5 (neuronal apoptosis inhibitory protein 5). TLR5 activates inflammatory genes through MYD88 pathway, whereas Nlrc4 and Naip5 assemble multiprotein complexes called inflammasomes, culminating in caspase-1 activation, IL-1β/IL-18 secretion, and pyroptosis. Although both TLR5 and Naip5/Nlrc4 pathways cooperate to clear infections, little is known about the relative anti-pathogen effector mechanisms operating through each of them. Here we show that the cytosolic flagellin (FLA-BSDot) was able to activate iNOS, an enzyme previously associated with TLR5 pathway. Using Nlrc4- or Naip5-deficient macrophages, we found that both receptors are involved in iNOS activation by FLA-BSDot. Moreover, distinct from extracellular flagellin (FLA-BS), iNOS activation by intracellular flagellin is completely abrogated in the absence of caspase-1. Interestingly, IL-1β and IL-18 do not seem to be important for FLA-BSDot-mediated iNOS production. Together, our data defined an additional anti-pathogen effector mechanism operated through Naip5 and Nlrc4 inflammasomes and illustrated a novel signaling transduction pathway that activates iNOS.

Dexamethasone inhibits the induction of iNOS gene expression through destabilization of its mRNA in proinflammatory cytokine-stimulated hepatocytes

In the inflamed liver, proinflammatory cytokines including TNF-alpha, IL-1beta, and IFN-gamma stimulate the induction of iNOS gene expression, leading to excess production of NO and resulting in liver injury. The induction of iNOS is regulated by transactivation of the iNOS promoter with transcription factors such as nuclear factor kappaB and by posttranscriptional modifications such as mRNA stabilization. The synthetic glucocorticoid dexamethasone has been reported to inhibit iNOS induction, which may contribute to its inflammation-reducing effects. The objective was to investigate the mechanisms involved in the down-regulation of iNOS gene expression by dexamethasone. Primary cultured rat hepatocytes were treated with IL-1beta (1 nM) in the presence or absence of dexamethasone. The induction of iNOS and its signal were analyzed. Dexamethasone (10-250 nM) inhibited the expression of iNOS mRNA and protein dose and time dependently, resulting in decreases in NO production. However, dexamethasone did not inhibit the up-regulation of type I IL-1 receptor stimulated by IL-1beta. Dexamethasone also had no effect on the degradation of IkappaB proteins and on the activation of nuclear factor kappaB. Transfection experiments with iNOS promoter-luciferase constructs revealed that dexamethasone had no effect on the transactivation of the iNOS promoter but decreased the stabilization of iNOS mRNA. In support of the latter observation, dexamethasone inhibited the expression of an iNOS gene antisense transcript, which stabilizes iNOS mRNA by interacting with its 3'-untranslated region and 3'-untranslated region-binding proteins. Dexamethasone may inhibit the induction of iNOS gene expression at the step of mRNA stabilization rather than promoter activation and may provide useful therapeutic effects in iNOS induction involved in liver injuries.

Cell-specific and concentration-dependent actions of interleukin-1 in acute brain inflammation

Interleukin (IL)-1 is a pivotal pro-inflammatory cytokine and an important mediator of both acute and chronic central nervous system (CNS) injuries. Despite intense research in CNS IL-1 biology over the past two decades, its precise mechanism of action in inflammatory responses to acute brain disorders remains largely unknown. In particular, much effort has been focussed on using in vitro approaches to better understand the cellular and signalling mechanisms of actions of IL-1, yet some discrepancies in the literature regarding the effects produced by IL-1beta in in vitro paradigms of injury still exist, particularly as to whether IL-1 exerts neurotoxic or neuroprotective effects. Here we aim to review the cell-specific and concentration-dependent actions of IL-1 in brain cells, to depict the mechanism by which this cytokine induces neurotoxicity or neuroprotection in acute brain injury.

Role of CX3CR1 (fractalkine receptor) in brain damage and inflammation induced by focal cerebral ischemia in mouse

CX3CR1 (fractalkine receptor) is important for sustaining normal microglial activity in the brain. Lack of CX3CR1 reportedly results in neurotoxic microglial phenotype in disease models. The objective of this study was to test the hypothesis that the absence of CX3CR1 worsens the outcome in cerebral ischemia. We observed significantly smaller (56%) infarcts and blood-brain barrier damage in CX3CR1-deficient (CX3CR1-/-) animals compared with CX3CR1+/- and wild-type mice after transient occlusion of the middle cerebral artery (MCAo). Functional recovery of CX3CR1-/- animals was enhanced, while less number of apoptotic cells and infiltrating leukocytes were found in the ipsilateral hemisphere. Expression of IL-1beta mRNA, protein, and interleukin (IL)-1Ra and tumor necrosis factor (TNF)-alpha mRNAs was lower in CX3CR1-/- mice, whereas no difference was observed in the number of IL-1beta-expressing microglia or plasma IL-1beta concentration. We observed early IL-1beta expression in astrocytes in vivo after MCAo and after oxygen-glucose deprivation in vitro, which might contribute to the ischemic damage. Our findings indicate that lack of CX3CR1 does not result in microglial neurotoxicity after MCAo, but rather significantly reduces ischemic damage and inflammation. Reduced IL-1beta and TNFalpha expression as well as decreased leukocyte infiltration might be involved in the development of smaller infarcts in CX3CR1-/- animals.

Rebamipide, anti-gastric ulcer drug, up-regulates the induction of iNOS in proinflammatory cytokine-stimulated hepatocytes

Nitric oxide (NO) generated from inducible NO synthase (iNOS) during hepatic injury has been reported to contribute to cytoprotection or cellular damage. Rebamipide, anti-gastric ulcer drug, has protective effects in a variety of tissue and organ injury. However, it remains unknown whether rebamipide is involved in the regulation of iNOS gene expression under pathological conditions. We examined whether rebamipide influences the induction of iNOS in hepatocytes exposed to pro-inflammatory cytokine. Primary cultured rat hepatocytes were treated with interleukin (IL)-1beta in the presence or absence of rebamipide. Pretreatment of cells with rebamipide resulted in up-regulation of iNOS induction by IL-1beta, followed by increased NO production. Rebamipide enhanced the degradation of IkappaBalpha and the activation of NF-kappaB. Further, rebamipide super-induced the up-regulation of type I IL-1 receptor (IL-1RI), which is essential for iNOS induction in addition to the IkappaB/NF-kappaB pathway. Transfection experiments revealed that rebamipide increased the transactivation of iNOS promoter and the stability of iNOS mRNA. In the latter, rebamipide increased the antisense-transcript corresponding to the 3'-UTR of iNOS mRNA, which stabilizes iNOS mRNA by interacting with the 3'-UTR and RNA-binding proteins. These findings demonstrate that rebamipide up-regulates iNOS by iNOS promoter activation through NF-kappaB, and by its mRNA stabilization presumably through the super-induction of IL-1RI and antisense-transcript. Rebamipide may contribute to a novel potentiated treatment in liver injuries.