Regulation of Kir4.1 expression in astrocytes and astrocytic tumors: a role for interleukin-1 beta

<p>Abstract</p> <p>Objective</p> <p>Decreased expression of inwardly rectifying potassium (Kir) channels in astrocytes and glioma cells may contribute to impaired K⁺ buffering and increased propensity for seizures. Here, we evaluated the potential effect of inflammatory molecules, such as interleukin-1β (IL-1β) on Kir4.1 mRNA and protein expression.</p> <p>Methods</p> <p>We investigated Kir4.1 (Kcnj10) and IL-1β mRNA expression in the temporal cortex in a rat model of temporal lobe epilepsy 24 h and 1 week after induction of status epilepticus (SE), using real-time PCR and western blot analysis. The U373 glioblastoma cell line and human fetal astrocytes were used to study the regulation of Kir4.1 expression in response to pro-inflammatory cytokines. Expression of Kir4.1 protein was also evaluated by means of immunohistochemistry in surgical specimens of patients with astrocytic tumors (<it>n</it> = 64), comparing the expression in tumor patients with (<it>n</it> = 38) and without epilepsy (<it>n</it> = 26).</p> <p>Results</p> <p>Twenty-four hours after onset of SE, Kir4.1 mRNA and protein were significantly down-regulated in temporal cortex of epileptic rats. This decrease in expression was followed by a return to control level at 1 week after SE. The transient downregulation of Kir4.1 corresponded to the time of prominent upregulation of IL-1β mRNA. Expression of Kir4.1 mRNA and protein in glial cells in culture was downregulated after exposure to IL-1β. Evaluation of Kir4.1 in tumor specimens showed a significantly lower Kir4.1 expression in the specimens of patients with epilepsy compared to patients without epilepsy. This paralleled the increased presence of activated microglial cells, as well as the increased expression of IL-1β and the cytoplasmic translocation of high mobility group box 1 (HMGB1).</p> <p>Conclusions</p> <p>Taken together, these findings indicate that alterations in expression of Kir4.1 occurring in epilepsy-associated lesions are possibly influenced by the local inflammatory environment and in particular by the inflammatory cytokine IL-1β.</p

Defective microglial development in the hippocampus of Cx3cr1 deficient mice

Microglial cells participate in brain development and influence neuronal loss and synaptic maturation. Fractalkine is an important neuronal chemokine whose expression increases during development and that can influence microglia function via the fractalkine receptor, CX3CR1. Mice lacking Cx3cr1 show a variety of neuronal defects thought to be the result of deficient microglia function. Activation of CX3CR1 is important for the proper migration of microglia to sites of injury and into the brain during development. However, little is known about how fractalkine modulates microglial properties during development. Here we examined microglial morphology, response to ATP, and K(+) current properties in acute brain slices from Cx3cr1 knockout mice across postnatal hippocampal development. We found that fractalkine signaling is necessary for the development of several morphological and physiological features of microglia. Specifically, we found that the occurrence of an outward rectifying K(+) current, typical of activated microglia, that peaked during the second and third postnatal week, was reduced in Cx3cr1 knockout mice. Fractalkine signaling also influenced microglial morphology and ability to extend processes in response to ATP following its focal application to the slice. Our results reveal the developmental profile of several morphological and physiological properties of microglia and demonstrate that these processes are modulated by fractalkine signaling

Astrocyte immune responses in epilepsy

Astrocytes, the major glial cell type of the central nervous system (CNS), are known to play a major role in the regulation of the immune/inflammatory response in several human CNS diseases. In epilepsy-associated pathologies, the presence of astrogliosis has stimulated extensive research focused on the role of reactive astrocytes in the pathophysiological processes that underlie the development of epilepsy. In brain tissue from patients with epilepsy, astrocytes undergo significant changes in their physiological properties, including the activation of inflammatory pathways. Accumulating experimental evidence suggests that proinflammatory molecules can alter glio-neuronal communications contributing to the generation of seizures and seizure-related neuronal damage. In particular, both in vitro and in vivo data point to the role of astrocytes as both major source and target of epileptogenic inflammatory signaling. In this context, understanding the astroglial inflammatory response occurring in epileptic brain tissue may provide new strategies for targeting astrocyte-mediated epileptogenesis. This article reviews current evidence regarding the role of astrocytes in the regulation of the innate immune responses in epilepsy. Both clinical observations in drug-resistant human epilepsies and experimental findings in clinically relevant models will be discussed and elaborated, highlighting specific inflammatory pathways (such as interleukin-1 beta/toll-like receptor 4) that could be potential targets for antiepileptic, disease-modifying therapeutic strategies. (c) 2012 Wiley Periodicals, In

The inflammatory molecules IL-1\u3b2 and HMGB1 can rapidly enhance focal seizure generation in a brain slice model of temporal lobe epilepsy

Epilepsy is a neurological disorder characterized by a hyperexcitable brain tissue and unpredictable seizures, i.e., aberrant firing discharges in large neuronal populations. It is well established that proinflammatory cytokines, in addition to their canonical involvement in the immune response, have a crucial role in the mechanism of seizure generation. The purpose of the present study was to investigate the role of interleukin-1\u3b2 (IL-1\u3b2) and high mobility group B1 (HMGB1) in the generation of seizure-like discharges using two models of focal epilepsy in a rat entorhinal cortex slice preparation. Seizure like-discharges were evoked by either slice perfusion with low Mg(2+) and picrotoxin or with a double NMDA local stimulation in the presence of the proconvulsant 4-amino-pyridine. The effects of IL-1\u3b2 or HMGB1 were evaluated by monitoring seizure discharge generation through laser scanning microscope imaging of Ca(2+) signals from neurons and astrocytes. In the picrotoxin model, we revealed that both cytokines increased the mean frequency of spontaneous ictal-like discharges, whereas only IL-1\u3b2 reduced the latency and prolonged the duration of the first ictal-like event. In the second model, a single NMDA pulse, per se ineffective, became successful when it was performed after IL-\u3b2 or HMGB1 local applications. These findings demonstrate that both IL-1\u3b2 and HMGB1 can rapidly lower focal ictal event threshold and strengthen the possibility that targeting these inflammatory pathways may represent an effective therapeutic strategy to prevent seizures

Defective microglial development in the hippocampus of Cx3cr1 deficient mice

Microglial cells participate in brain development and influence neuronal loss and synaptic maturation. Fractalkine is an important neuronal chemokine whose expression increases during development and that can influence microglia function via the fractalkine receptor, CX3CR1. Mice lacking Cx3cr1 show a variety of neuronal defects thought to be the result of deficient microglia function. Activation of CX3CR1 is important for the proper migration of microglia to sites of injury and into the brain during development. However, little is known about how fractalkine modulates microglial properties during development. Here we examined microglial morphology, response to ATP, and K+ current properties in acute brain slices from Cx3cr1 knockout mice across postnatal hippocampal development. We found that fractalkine signaling is necessary for the development of several morphological and physiological features of microglia. Specifically, we found that the occurrence of an outward rectifying K+ current, typical of activated microglia, that peaked during the second and third postnatal week, was reduced in Cx3cr1 knockout mice. Fractalkine signaling also influenced microglial morphology and ability to extend processes in response to ATP following its focal application to the slice. Our results reveal the developmental profile of several morphological and physiological properties of microglia and demonstrate that these processes are modulated by fractalkine signalin

Expression levels of the miR-146a targets (IRAK-1, IRAK-2 and TRAF-6) after transfection with anti-miR-146a LNA or miR-146a mimic.

<p>(<b>A–C</b>) Quantitative real-time PCR of IRAK-1 (A), IRAK-2 (B) and TRAF-6 (C) expression 24 hours after exposure to IL-1β in U373 glioblastoma cell line transfected with LNA-antimiR-146a (25 nM) or miR-146a mimic (pre-mir-146a, 50 nM). (<b>D</b>) Quantitative real-time PCR of IRAK-1, 24 hours after exposure to IL-1β in cultured human astrocytes transfected with LNA anti-miR-146a (50 nM) or miR-146a mimic (pre-mir-146a, 50 nM). Data are expressed relative to the levels in unstimulated cells and are mean ± SEM from two separate experiments performed in triplicate (<b>E</b>) IRAK-1 protein expression 24 hours after exposure to IL-1β in glial cells transfected with LNA anti-miR-146a (50 nM) or miR-146a mimic (pre-mir-146a, 50 nM); Representative immunoblot (1 control; 2, IL-1β; 3, IL-1β + LNA-antimiR-146a; 4, IL-1β + LNA-antimiR-146a scramble; 5, IL-1β + mimic; 6, IL-1β + mimic scramble) and optical density measurements. Data are expressed relative to the levels in unstimulated cells and are mean ± SEM from two separate experiments (*p<0.05, compared to control; **p<0.05, LNA or mimic transfected cells stimulated with IL-1β compared to IL-1β alone).</p

Effect of anti-miR-146a LNA or miR-146a mimic upon IL-1β-induced release of inflammatory molecules.

<p>(<b>A</b>) Cytokine release 24 hours after exposure to IL-1β in U373 cells transfected with LNA-antimiR-146a (50 nM) or miR-146a mimic (miR-146a mimic, 50 nM). Data are expressed relative to unstimulated control cells (mean ± SEM from three separate experiments). In comparison with IL-1ß alone, cultures stimulated with IL-1ß and transfected with LNA-anti miR-146a exhibited significant increase of IL-6 and IP-10 release, whereas transfection of glial cells with miR-146a mimic significantly decreased the levels of IL-6, IL-8, G-CSF, IFN-γ, IP-10, MIP-1β, and TNF-α (* p<0.05). LNA-anti miR-146a and miR-146a mimic alone did not significantly affect the levels of cytokines in the culture medium, compared to non treated cells.</p

Effect of anti-miR-146a LNA or miR-146a mimic upon IL-1β-induced IL-6 and COX-2 mRNA.

<p>Quantitative real-time PCR of IL-6 (A–B) and Cox-2 (C–D). (<b>A–B</b>) IL-6 mRNA levels, 24 hours after exposure to IL-1β in U373 cells (A) and cultured human astrocytes (B) transfected with LNA-antimiR-146a (50 nM) or miR-146a mimic (pre-mir-146a, 50 nM). (<b>C–D</b>) COX-2 mRNA levels, 24 hours after exposure to IL-1β in U373 cells (C) and cultured human astrocytes (D) transfected with LNA-antimiR-146a (50 nM) or miR-146a mimic (pre-mir-146a, 50 nM). Data are expressed relative to the levels in unstimulated cells and are mean ± SEM from two separate experiments performed in triplicate (*p<0.05 compared to control; **p<0.05, LNA or mimic transfected cells stimulated with IL-1β compared to IL-1β alone).</p