Key Mediator Of Neuroinflammation Research Articles

Modulation of hippocampal protein expression by a brain penetrant biologic TNF‐α inhibitor in the 3xTg Alzheimer’s disease mice

AbstractBackgroundAlzheimer’s disease (AD) is a chronic neuroinflammatory condition and the proinflammatory cytokine, tumor necrosis factor alpha (TNF‐α), is a key mediator of neuroinflammation in AD. Biologic TNF‐α inhibitors (bTNFIs) can block cerebral TNF‐α if these large molecules cross the blood‐brain barrier (BBB). Thus, a model bTNFI, the extracellular domain of type II TNF‐α receptor (TNFR) which can bind to and sequester TNF‐α, has been reengineered to enable brain delivery by fusion with a mouse transferrin receptor antibody (TfRMAb). TfRMAb binds to the BBB TfR to deliver the TNFR into the brain via receptor‐mediated transcytosis. Previously, we found the TfRMAb‐TNFR to be protective in a mouse model of amyloidosis (APP/PS1) and tauopathy (PS19), and the aim of the current study was to investigate its effects in a mouse model that combines both amyloidosis and tauopathy (3xTg‐AD mice).MethodEight‐month‐old female triple transgenic 3xTg‐AD mice were injected intraperitoneally with saline (n = 11) or TfRMAb‐TNFR (3 mg/kg; n = 11) three days per week for 12 weeks. At the end of treatment, brains were processed for hippocampal immunohistochemistry and high‐resolution multiplex NanoString spatial proteomics using the GeoMx protein assays for neuroscience.ResultTfRMAb‐TNFR treatment significantly reduced mature β‐sheet rich Aβ plaques and increased plaque‐associated microglial localization around larger plaques in the 3xTg mice. Further, TfRMAb‐TNFR increased plaque‐associated microglial TREM2 compared with saline‐treated 3xTg mice. From a total of 64 target proteins studied using spatial proteomics (comparing protein expression in the Aβ‐plaque bearing vs. plaque‐free regions), 39 (61%) differentially expressed proteins (DEP) were identified in the 11‐month‐old 3xTg mice, comprising of proteins related to neurodegeneration (10% of DEP), neuroinflammation (41% of DEP), amyloid (21% of DEP) and tau (10% of DEP) pathology, autophagy (10% of DEP) and other pathways (8% of DEP). TfRMAb‐TNFR treatment modulated proteins involved in Aβ clearance and processing, microglial function, RNA processing, and neurodegeneration. Majority of these proteins were relevant to microglial function (∼ 40%).ConclusionThe study highlights that TfRMAb‐TNFR modulates several proteins involved in AD pathology and progression and largely suggests a microglia‐centric mechanism of action of this treatment in the 3xTg mice.

Inhibiting NLRP3 inflammasome signaling pathway promotes neurological recovery following hypoxic-ischemic brain damage by increasing p97-mediated surface GluA1-containing AMPA receptors

BackgroundThe nucleotide-binding oligomeric domain (NOD)-like receptor protein 3 (NLRP3) inflammasome is believed to be a key mediator of neuroinflammation and subsequent secondary brain injury induced by ischemic stroke. However, the role and underlying mechanism of the NLRP3 inflammasome in neonates with hypoxic-ischemic encephalopathy (HIE) are still unclear.MethodsThe protein expressions of the NLRP3 inflammasome including NLRP3, cysteinyl aspartate specific proteinase-1 (caspase-1) and interleukin-1β (IL-1β), the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionicacid receptor (AMPAR) subunit, and the ATPase valosin-containing protein (VCP/p97), were determined by Western blotting. The interaction between p97 and AMPA glutamate receptor 1 (GluA1) was determined by co-immunoprecipitation. The histopathological level of hypoxic-ischemic brain damage (HIBD) was determined by triphenyltetrazolium chloride (TTC) staining. Polymerase chain reaction (PCR) and Western blotting were used to confirm the genotype of the knockout mice. Motor functions, including myodynamia and coordination, were evaluated by using grasping and rotarod tests. Hippocampus-dependent spatial cognitive function was measured by using the Morris-water maze (MWM).ResultsWe reported that the NLRP3 inflammasome signaling pathway, such as NLRP3, caspase-1 and IL-1β, was activated in rats with HIBD and oxygen-glucose deprivation (OGD)-treated cultured primary neurons. Further studies showed that the protein level of the AMPAR GluA1 subunit on the hippocampal postsynaptic membrane was significantly decreased in rats with HIBD, and it could be restored to control levels after treatment with the specific caspase-1 inhibitor AC-YVAD-CMK. Similarly, in vitro studies showed that OGD reduced GluA1 protein levels on the plasma membrane in cultured primary neurons, whereas AC-YVAD-CMK treatment restored this reduction. Importantly, we showed that OGD treatment obviously enhanced the interaction between p97 and GluA1, while AC-YVAD-CMK treatment promoted the dissociation of p97 from the GluA1 complex and consequently facilitated the localization of GluA1 on the plasma membrane of cultured primary neurons. Finally, we reported that the deficits in motor function, learning and memory in animals with HIBD, were ameliorated by pharmacological intervention or genetic ablation of caspase-1.ConclusionInhibiting the NLRP3 inflammasome signaling pathway promotes neurological recovery in animals with HIBD by increasing p97-mediated surface GluA1 expression, thereby providing new insight into HIE therapy.

LRRK2 Kinase Inhibition Attenuates Neuroinflammation and Cytotoxicity in Animal Models of Alzheimer's and Parkinson's Disease-Related Neuroinflammation.

Chronic neuroinflammation plays a crucial role in the progression of several neurodegenerative diseases (NDDs), including Parkinson's disease (PD) and Alzheimer's disease (AD). Intriguingly, in the last decade, leucine-rich repeat kinase-2 (LRRK2), a gene mutated in familial and sporadic PD, was revealed as a key mediator of neuroinflammation. Therefore, the anti-inflammatory properties of LRRK2 inhibitors have started to be considered as a disease-modifying treatment for PD; however, to date, there is little evidence on the beneficial effects of targeting LRRK2-related neuroinflammation in preclinical models. In this study, we further validated LRRK2 kinase modulation as a pharmacological intervention in preclinical models of AD- and PD-related neuroinflammation. Specifically, we reported that LRRK2 kinase inhibition with MLi2 and PF-06447475 (PF) molecules attenuated neuroinflammation, gliosis and cytotoxicity in mice with intracerebral injection of Aβ1-42 fibrils or α-syn preformed fibrils (pffs). Moreover, for the first time in vivo, we showed that LRRK2 kinase activity participates in AD-related neuroinflammation and therefore might contribute to AD pathogenesis. Overall, our findings added evidence on the anti-inflammatory effects of LRRK2 kinase inhibition in preclinical models and indicate that targeting LRRK2 activity could be a disease-modifying treatment for NDDs with an inflammatory component.

Naturally Occurring HMGB1 Inhibitor, Glycyrrhizin, Modulates Chronic Seizures-Induced Memory Dysfunction in Zebrafish Model.

Glycyrrhizin (GL) is a well-known pharmacological inhibitor of high mobility group box 1 (HMGB1) and is abundantly present in the licorice root (Glycyrrhiza radix). HMGB1 protein, a key mediator of neuroinflammation, has been implicated in several neurological disorders, including epilepsy. Epilepsy is a devastating neurological disorder with no effective disease-modifying treatment strategies yet, suggesting a pressing need for exploring novel therapeutic options. In the current investigation, using a second hit pentylenetetrazol (PTZ) induced chronic seizure model in adult zebrafish, regulated mRNA expression of HMGB1 was inhibited by pretreatment with GL (25, 50, and 100 mg/kg, ip). A molecular docking study suggests that GL establishes different binding interactions with the various amino acid chains of HMGB1 and Toll-like receptor-4 (TLR4). Our finding suggests that GL pretreatment reduces/suppresses second hit PTZ induced seizure, as shown by the reduction in the seizure score. GL also regulates the second hit PTZ induced behavioral impairment and rescued second hit PTZ related memory impairment as demonstrated by an increase in the inflection ratio (IR) at the 3 h and 24 h T-maze trial. GL inhibited seizure-induced neuronal activity as demonstrated by reduced C-fos mRNA expression. GL also modulated mRNA expression of BDNF, CREB-1, and NPY. The possible mechanism underlying the anticonvulsive effect of GL could be attributed to its anti-inflammatory activity, as demonstrated by the downregulated mRNA expression level of HMGB1, TLR4, NF-kB, and TNF-α. Overall, our finding suggests that GL exerts an anticonvulsive effect and ameliorates seizure-related memory disruption plausibly through regulating of the HMGB1-TLR4-NF-kB axis.

Evaluation of serum high-mobility group box 1 concentration in dogs with epilepsy: A case-control study.

BackgroundHigh‐mobility group box 1 (HMGB1) is a key mediator of neuroinflammation and there are increased HMGB1 levels in laboratory animal models of epilepsy and human patients with epilepsy.ObjectivesTo determine serum HMGB1 levels in dogs with epilepsy.AnimalsTwenty‐eight epileptic dogs, 12 dogs with nonepileptic brain diseases, and 26 healthy dogs.MethodsIn this case‐control study, serum HMGB1 concentrations were estimated using the canine‐specific enzyme‐linked immunosorbent assay kit. Diagnosis of dogs with epilepsy was based on medical history, physical and neurological examination findings, laboratory test results, magnetic resonance image, and cerebrospinal fluid analysis.ResultsSerum HMGB1 levels were significantly higher in epileptic dogs (median = 0.41 ng/mL; range, 0.03‐5.28) than in healthy dogs (median = 0.12 ng/mL; range, 0.02‐1.45; P = .002). In contrast, serum HMGB1 levels of dogs with non‐epileptic brain diseases (median = 0.19 ng/mL; range, 0.03‐1.04) were not significantly increased compared to those of healthy dogs (P = .12). Regarding idiopathic epilepsy, dogs with an epilepsy course of >3 months showed a higher serum HMGB1 concentration (median = 0.87 ng/mL; range, 0.42‐2.88) than those with that of ≤3 months (median = 0.26 ng/mL; range, 0.03‐0.88; P = .02).Conclusions and Clinical ImportanceSerum HMGB1 could be a biomarker of epilepsy.

Targeting high-mobility group box protein 1 (HMGB1) in pediatric traumatic brain injury: Chronic neuroinflammatory, behavioral, and epileptogenic consequences

High mobility group box protein-1 (HMGB1) has been implicated as a key mediator of neuroinflammation and neurodegeneration in a range of neurological conditions including traumatic brain injury (TBI) and epilepsy. To date, however, most studies have examined only acute outcomes, and the adult brain. We have recently demonstrated HMGB1 release after experimental TBI in the pediatric mouse. This study therefore examined the chronic consequences of acute HMGB1 inhibition in the same model, to test the hypothesis that HMGB1 is a pivotal mediator of neuropathological, neurobehavioral, and epilepsy outcomes in pediatric TBI. HMGB1 was inhibited by treatment with 50 mg/kg i.p. Glycyrrhizin (Gly), compared to vehicle controls, commencing 1 h prior to moderate TBI or sham surgery in post-natal day 21 mice. We first demonstrated that Gly reduced brain HMGB1 levels and brain edema at an acute time point of 3 days post-injury. Subsequent analysis over a chronic time course found that pediatric TBI resulted in short-term spatial memory and motor learning deficits alongside an apparent increase in hippocampal microglial reactivity, which was prevented in Gly-treated TBI mice. In contrast, Gly treatment did not reduce the severity of evoked seizures, the proportion of animals exhibiting chronic spontaneous seizure activity, or cortical tissue loss. Together, our findings contribute to a growing appreciation for HMGB1's role in neuropathology and associated behavioral outcomes after TBI. However, further work is needed to fully elucidate the contribution of HMGB1 to epileptogenesis in this context.

Features of pancreatitis associated with ulcerative colitis: a case series analysis

Trimethyltin (TMT), a neurotoxic organotin compound, is selectively localized within the limbic system. The mechanisms of TMT-induced hippocampal neurodegeneration include inflammatory responses, oxidative stress, and neuronal death. Increasing evidence shows that the inflammatory response, mediated by activated inflammasomes, is involved in apoptosis and cellular dysfunction during brain injury. This study aimed to assess the role of the nucleotide-binding oligomerization domain-like receptor pyrin-domain-containing protein 3 (NLRP3) inflammasome in TMT-induced central nervous system (CNS) injury. In addition, the mechanisms underlying TMT neurotoxicity are similar to those involved in the pathogenesis of multiple neurodegenerative diseases; hence, a study on TMT cytotoxicity may be informative for the understanding of human CNS diseases. Microglia were significantly activated in the rat hippocampal dentate gyrus after TMT treatment. The mRNA expression of pro-inflammatory cytokines, interleukin-1β and interleukin-18, was induced both in vitro and in vivo. TMT treatment activated the NLRP3 inflammasome in the microglial cell line BV2. NLRP3 RNA interference significantly protected these cells from TMT-induced neuroinflammation. Our results demonstrate that the NLRP3 inflammasome is a key mediator of neuroinflammation and plays an important role in TMT-induced neuroinflammation.

NLRP3 inflammasome activation is involved in trimethyltin-induced neuroinflammation

Trimethyltin (TMT), a neurotoxic organotin compound, is selectively localized within the limbic system. The mechanisms of TMT-induced hippocampal neurodegeneration include inflammatory responses, oxidative stress, and neuronal death. Increasing evidence shows that the inflammatory response, mediated by activated inflammasomes, is involved in apoptosis and cellular dysfunction during brain injury. This study aimed to assess the role of the nucleotide-binding oligomerization domain-like receptor pyrin-domain-containing protein 3 (NLRP3) inflammasome in TMT-induced central nervous system (CNS) injury. In addition, the mechanisms underlying TMT neurotoxicity are similar to those involved in the pathogenesis of multiple neurodegenerative diseases; hence, a study on TMT cytotoxicity may be informative for the understanding of human CNS diseases. Microglia were significantly activated in the rat hippocampal dentate gyrus after TMT treatment. The mRNA expression of pro-inflammatory cytokines, interleukin-1β and interleukin-18, was induced both in vitro and in vivo. TMT treatment activated the NLRP3 inflammasome in the microglial cell line BV2. NLRP3 RNA interference significantly protected these cells from TMT-induced neuroinflammation. Our results demonstrate that the NLRP3 inflammasome is a key mediator of neuroinflammation and plays an important role in TMT-induced neuroinflammation.

STING-mediated type-I interferons contribute to the neuroinflammatory process and detrimental effects following traumatic brain injury

BackgroundTraumatic brain injury (TBI) represents a major cause of disability and death worldwide with sustained neuroinflammation and autophagy dysfunction contributing to the cellular damage. Stimulator of interferon genes (STING)-induced type-I interferon (IFN) signalling is known to be essential in mounting the innate immune response against infections and cell injury in the periphery, but its role in the CNS remains unclear. We previously identified the type-I IFN pathway as a key mediator of neuroinflammation and neuronal cell death in TBI. However, the modulation of the type-I IFN and neuroinflammatory responses by STING and its contribution to autophagy and neuronal cell death after TBI has not been explored.MethodsC57BL/6J wild-type (WT) and STING−/− mice (8–10-week-old males) were subjected to controlled cortical impact (CCI) surgery and brains analysed by QPCR, Western blot and immunohistochemical analyses at 2 h or 24 h. STING expression was also analysed by QPCR in post-mortem human brain samples.ResultsA significant upregulation in STING expression was identified in late trauma human brain samples that was confirmed in wild-type mice at 2 h and 24 h after CCI. This correlated with an elevated pro-inflammatory cytokine profile with increased TNF-α, IL-6, IL-1β and type-I IFN (IFN-α and IFN-β) levels. This expression was suppressed in the STING−/− mice with a smaller lesion volume in the knockout animals at 24 h post CCI. Wild-type mice also displayed increased levels of autophagy markers, LC3-II, p62 and LAMP2 after TBI; however, STING−/− mice showed reduced LAMP2 expression suggesting a role for STING in driving dysfunctional autophagy after TBI.ConclusionOur data implicates a detrimental role for STING in mediating the TBI-induced neuroinflammatory response and autophagy dysfunction, potentially identifying a new therapeutic target for reducing cellular damage in TBI.

Minocycline protects developing brain against ethanol-induced damage

Fetal alcohol spectrum disorders (FASD) are caused by ethanol exposure during the pregnancy and is the leading cause of mental retardation. Ethanol exposure during the development results in the loss of neurons in the developing brain, which may underlie many neurobehavioral deficits associated with FASD. It is important to understand the mechanisms underlying ethanol-induced neuronal loss and develop appropriate therapeutic strategies. One of the potential mechanisms involves neuroimmune activation. Using a third trimester equivalent mouse model of ethanol exposure, we demonstrated that ethanol induced a wide-spread neuroapoptosis, microglial activation, and neuroinflammation in C57BL/6 mice. Minocycline is an antibiotic that inhibits microglial activation and alleviates neuroinflammation. We tested the hypothesis that minocycline may protect neurons ethanol-induced neuron death by inhibiting microglial activation and neuroinflammation. We showed that minocycline significantly inhibited ethanol-induced caspase-3 activation, microglial activation, and the expression of pro-inflammatory cytokines. In contrast, minocycline reversed ethanol inhibition of anti-inflammatory cytokines. Minocycline blocked ethanol-induced activation of GSK3β, a key mediator of neuroinflammation and microglial activation in the developing brain. Consistent with the in vivo observations, minocycline inhibited ethanol-induced the expression of pro-inflammatory cytokines and activation of GSK3β in a microglia cell line (SIM-9). GSK3β inhibitor eliminated ethanol activation of pro-inflammatory cytokines in SIM-9 cells. Co-cultures of cortical neurons and SIM-9 microglia cells sensitized neurons to alcohol-induced neuronal death. Minocycline protected neurons against ethanol-induced neuronal death in neurons/microglia co-cultures. Together, these results suggest that minocycline may ameliorate ethanol neurotoxicity in the developing by alleviating GSK3β-mediated neuroinflammation.

Attenuation of mechanical pain hypersensitivity by treatment with Peptide5, a connexin-43 mimetic peptide, involves inhibition of NLRP3 inflammasome in nerve-injured mice

Connexin43 (Cx43) hemichannels in spinal cord astrocytes are implicated in the maintenance of neuropathic pain following peripheral nerve injury. Peptide5 is a Cx43 mimetic peptide that blocks hemichannels. In this study, we investigated the effects of spinal delivery of Peptide5 on mechanical pain hypersensitivity in two mouse models of neuropathic pain, peripheral nerve injury and chemotherapy-induced peripheral neuropathy (CIPN). We demonstrated that 10days following a chronic constriction injury (CCI) of the sciatic nerve, Cx43 expression, co-localised predominantly with astrocytes, was increased in the ipsilateral L3–L5 lumbar spinal cord. An intrathecal injection of Peptide5 into nerve-injured mice, on day 10 when pain was well-established, caused significant improvement in mechanical pain hypersensitivity 8h after injection. Peptide5 treatment resulted in significantly reduced Cx43, and microglial and astrocyte activity in the dorsal horn of the spinal cord, as compared to control saline-treated CCI mice. Further in vitro investigations on primary astrocyte cultures showed that 1h pre-treatment with Peptide5 significantly reduced adenosine triphosphate (ATP) release in response to extracellular calcium depletion. Since ATP is a known activator of the NOD-like receptor protein 3 (NLRP3) inflammasome complex, a key mediator of neuroinflammation, we examined the effects of Peptide5 treatment on NLRP3 inflammasome expression. We found that NLRP3, its adaptor apoptosis-associated spec-like protein (ASC) and caspase-1 protein were increased in the ipsilateral spinal cord of CCI mice and reduced to naïve levels following Peptide5 treatment. In the models of oxaliplatin- and paclitaxel-induced peripheral neuropathy, treatment with Peptide5 had no effect on mechanical pain hypersensitivity. Interestingly, in these CIPN models, although spinal Cx43 expression was significantly increased at day 13 following chemotherapy, NLRP3 expression was not altered. These results suggest that the analgesic effect of Peptide5 is specifically achieved by reducing NLRP3 expression. Together, our findings demonstrate that blocking Cx43 hemichannels with Peptide5 after nerve injury attenuates mechanical pain hypersensitivity by specifically targeting the NLRP3 inflammasome in the spinal cord.

Modulation of cerebral RAGE expression following nitric oxide synthase inhibition in rats subjected to focal cerebral ischemia

The receptor for advanced glycation endproducts (RAGE) is a key mediator of neuroinflammation following cerebral ischemia. Nitric oxide (NO) plays a dualistic role in cerebral ischemia, depending on whether it originates from neuronal, inducible or endothelial synthase. Although a dynamic interplay between RAGE and NO pathways exists, its relevance in ischemic stroke has not been investigated. The aim of this study is to evaluate the effect of the NO synthase (NOS) inhibition on RAGE expression in rats subjected to transient middle cerebral artery occlusion (tMCAo). Full-length (fl-RAGE) gene expression was elevated in the striatum and, to a lesser extent, in the cortex of rats undergone tMCAo. The exacerbation of cortical damage caused by systemic administration of L-N-(1-iminoethyl)ornithine (L-NIO), a relatively selective inhibitor of endothelial NOS (eNOS), was associated with elevated mRNA levels of interleukin (IL)−6, tumor necrosis factor (TNF)-α and fl-RAGE in both the cortex and the striatum. Conversely, NG-nitro-l-arginine methyl ester (L-NAME), a non-selective NOS inhibitor, decreased cortical damage, did not affect cerebral cytokine mRNA levels, while it increased fl-RAGE mRNA expression only in the striatum. Fl-RAGE striatal protein levels varied accordingly with observed mRNA changes in the striatum, while in the cortex, RAGE protein levels were reduced by tMCAo and further decreased following L-NIO treatment. Modulation of RAGE expression by different inhibitors of NOS may have opposite effects on transient cortical ischemia: the non selective inhibition of NOS activity is protective, while the selective inhibition of eNOS is harmful, probably via the activation of inflammatory pathways.

Abstract # 1834 IL-[formula omitted] negatively impacts upon expression of both inflammatory and neurogenesis-associated signalling molecules in hippocampal neural stem cells in vitro

Hippocampal neurogenesis, the process by which new neurons are produced, is involved in some forms of memory and emotion regulation. IL- 1 β , a key mediator of neuroinflammation within the brain, suppresses proliferation of neural stem cells (NSCs). TLX is an orphan nuclear receptor known to regulate the proliferation of NSCs and IL- 1 β reduces TLX expression in proliferating NSCs. We aim to elucidate the mechanisms of how IL- 1 β signalling interacts with TLX. Using embryonic day 18 hippocampal neurosphere cultures from rats, we examined the effects of IL- 1 β on gene and protein expression of p65, a downstream effector of IL- 1 β , TLX, and associated co-signalling molecules. IL- 1 β impaired neurosphere growth after 3 days in vitro. p65 signalling is activated within 10 min of IL- 1 β exposure. We also show that a negative feedback mechanism appears after 30 min of IL- 1 β exposure to NSCs as shown by increased I κ B α expression, a negative inhibitor of p65 signalling. IL- 1 β did not affect expression the p65 co-signalling molecule Creb Binding Protein. We show that IL- 1 β time dependently suppressed both TLX and it co-signalling molecule HDAC5. This study establishes a time-course of IL- 1 β -induced changes on both an inflammatory signalling mediator and a regulator of neurogenesis in hippocampal NSCs in vitro, and proposes therapeutic target points that may be exploited to mitigate the negative effects of IL- 1 β on hippocampal neurogenesis and associated cognitive and psychiatric functions.

NLRP3 Inflammasome: Key Mediator of Neuroinflammation in Murine Japanese Encephalitis

BackgroundJapanese Encephalitis virus (JEV) is a common cause of acute and epidemic viral encephalitis. JEV infection is associated with microglial activation resulting in the production of pro-inflammatory cytokines including Interleukin-1 β (IL-1β) and Interleukin-18 (IL-18). The Pattern Recognition Receptors (PRRs) and the underlying mechanism by which microglia identify the viral particle leading to the production of these cytokines is unknown.Methodology/Principal FindingsFor our studies, we have used murine model of JEV infection as well as BV-2 mouse microglia cell line. In this study, we have identified a signalling pathway which leads to the activation of caspase-1 as the key enzyme responsible for the maturation of both IL-1β and IL-18 in NACHT, LRR and PYD domains-containing protein-3 (NLRP3) dependent manner. Depletion of NLRP3 results in the reduction of caspase-1 activity and subsequent production of these cytokines.Conclusion/SignificanceOur results identify a mechanism mediated by Reactive Oxygen Species (ROS) production and potassium efflux as the two danger signals that link JEV infection to caspase-1 activation resulting in subsequent IL-1β and IL-18 maturation.

Adhesion to fibronectin regulates interleukin-1 beta expression in microglial cells

The extracellular matrix (ECM) of the central nervous system (CNS) is rapidly degraded following acute brain injury, leading to inflammation and neuronal death. Under these conditions, the pro-inflammatory cytokine interleukin-1β (IL-1β) is primarily produced by microglial cells and is a key mediator of neuroinflammation, but whether the ECM regulates microglial IL-1 synthesis after CNS injury remains unknown. This study aimed to investigate whether cell attachment to ECM molecules modulated IL-1β production in activated microglia in vitro. We found adhesion to fibronectin, fibrillin-1 and laminin promoted microglial cell adhesion and spreading, potentiated by bacterial lipopolysaccharide (LPS) treatment. Adhesion to fibronectin (but not fibrillin-1 or laminin) regulated IL-1β expression via a cell density-dependent mechanism, whereby fibronectin-induced cell proliferation resulted in less IL-1β being produced. These data suggest an important regulatory mechanism of IL-1 production, associated with microglial migration and proliferation, driven by ECM degradation and/or synthesis in an injured brain.

Differential effects of interleukin-1 alpha and beta on interleukin-6 and chemokine synthesis in neurones

Interleukin (IL)-1 is a key mediator of neuroinflammation via actions of two agonists IL-1α and β that bind to the IL-1 type I receptor (IL-1RI), and are thought to trigger identical responses. However, evidence suggests that IL-1α and β may have differential actions in the central nervous system (CNS). The objective of this study was to test the hypothesis that IL-1α and β differentially regulate the expression of IL-6 and chemokines KC, IP-10 and MCP-1 in primary neurones. Here we demonstrate that, whilst IL-1β induced significant synthesis of IL-6 in neurones, IL-1α had no effect. In contrast, IL-1α and β induced strong synthesis and constitutive release of chemokines KC, IP-10 and MCP-1 from neurones, and these responses were IL-1RI-dependent. Whilst IL-1β-induced IL-6 synthesis was dependent on the nSMase/Src kinase signalling cascade, specific inhibitors of nSMase (3-OMS) and Src kinase (PP2) failed to inhibit IL-1α- and IL-1β-induced chemokines synthesis, suggesting the existence of alternative signalling pathway(s) in neurones.

Plasma Interleukin-8 as a Potential Predictor of Mortality in Adult Patients with Severe Traumatic Brain Injury

Because of complex pathophysiology and severe consequences, traumatic brain injuries (TBI) are an important medical problem. Pathophysiology of TBI includes local and systemic stress response, in which interleukin-8 (IL-8) is considered as a key mediator of neuroinflammation. However, prognostic relevance of IL-8 measurement in adult patients with severe TBI is not certain. Therefore, IL-8 was determined in blood samples from central venous and jugular bulb catheter and in cerebrospinal fluid of twenty patients with isolated TBI at admission to Intensive Care Unit. None of the patients had history of stroke, dementia, autoimmune diseases, acute infection or medication with anti-inflammatory drugs. Ten patients died due to traumatic brain injury, while the other ten recovered well. While there was no significant difference of IL-8 levels in cerebrospinal fluid between survivors and nonsurvivors, central venous plasma level of IL-8 was significantly lower in survivors (71.00 +/- 14.17 pg/ml), than in nonsurvivors (111.26 +/- 16.9 pg/ml). Receiver Operating Characteristic (ROC) analysis revealed significant prognostic value for IL-8 in the blood as well as for the age of patients, Glasgow Coma Scale (GCS) and Acute Physiologic and Chronic Health Evaluation (APACHE II). These findings suggest that the central venous plasma values of IL-8 at admission might be an early predictive marker in patients with severe TBI, comparative to standard clinical prognostic markers such as APACHE II and GCS.

IL-8 is a key mediator of neuroinflammation in severe traumatic brain injuries.

The subjects were 22 patients with severe head injury. The average age was 45 +/- 18.3 years. There were 13 survivors and 9 fatalities. Samples of peripheral blood and cerebrospinal fluid (CSF) were taken four times, at the time of admission and at 24, 72, and 168 hours later. IL-6: For the survivor group, peripheral blood levels were 181, 105, 37, and 26 pg/ml, respectively (median values). CSF levels were 5376, 3565, 328, and 764 pg/ml, respectively. For the fatality group, peripheral blood levels were 102, 176, 873, and 3059 pg/ml, respectively, whereas CSF levels were 15241, 97384, 548225, and 366500 pg/ml, respectively. IL-8: For the survivor group, peripheral blood levels were 36, 15, 15, and 15 pg/ml, respectively, whereas CSF levels were 23736, 4074, 355, and 1509 pg/ml, respectively. For the fatality group, peripheral blood levels were 21, 28, 43, and 77 pg/mL, respectively, whereas CSF levels were 29003, 8906, 5852, and 8220 pg/ml, respectively. IL-6 and IL-8 levels were significantly higher after 72 hours in the fatality group. The fact that CSF IL-8 was 1000 times that in the peripheral blood at the time of admission, and decreased thereafter, indicates that IL-8 is a key mediator of neuroinflammation.