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

Abstract

ObjectiveDecreased 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.MethodsWe 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 (n = 64), comparing the expression in tumor patients with (n = 38) and without epilepsy (n = 26).ResultsTwenty-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).ConclusionsTaken 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.

Role of Astrocytes in Epilepsy

“…No changes in astrocytic Kir currents were found in a kainate model of epilepsy (Takahashi et al 2010). Recently, down-regulation of Kir4.1 mRNA and protein has been reported in the context of epilepsy and inflammation, possibly mediated by the proinflammatory cytokine interleukin (IL)-1β (Zurolo et al 2012), whereas another study reported enhanced Kir4.1 expression in a rat pilocarpine model (Nagao et al 2013). Unfortunately, functional consequences of these changes have not been assessed in the latter two studies.…”

Epilepsy Related to Developmental Tumors and Malformations of Cortical Development

“…Furthermore, the low expression of several potassium channel genes observed in GG suggests a disturbed ion homeostasis and transport that could represent an additional potential mechanism leading to increased excitability in GNT [57]. Interestingly, evaluation of the inward-rectifying potassium channel on astrocytes Kir4.1 in tumor specimens showed a significantly lower Kir4.1 expression in the specimens of patients with epilepsy compared to patients without epilepsy [70]. Over the last decade, an increasing number of observations support the role of inflammation in the pathophysiology of human epilepsy (for reviews see [71][72][73][74] ; Fig.…”

“…Accordingly, the activation of these pathways has been shown to play a pivotal role in seizure precipitation and recurrence using a post-translational mechanism independent of transcriptional activation nuclear factor kappa-B and involving the rapid activation of Src kinases and phosphorylation of the NMDA-NR2B receptors [177][178][179]. IL-1β may also regulate the expression of inward-rectifying potassium channels on astrocytes (such as Kir4.1), influencing the potassium buffering, which could represent an additional mechanism contributing to neuronal hyperexcitability and seizure development [70].…”

Astroglial NMDA receptors inhibit expression of Kir4.1 channels in glutamate-overexposed astrocytes in vitro and in the brain of rats with acute liver failure

“…Cultured astrocytes were shown to swell following Kir4.1 silencing with siRNA (Obara- Michlewska et al, 2011) and also when Kir4.1 expression decreased following oxygen and glucose deprivation (Benesova et al, 2012). Animal model studies have suggested that decreased Kir4.1 mRNA and/or protein content in the brain contributes to the pathogenesis of various CNS disorders, including epilepsy (Stewart et al, 2010;Zurolo et al, 2012), ischaemia (Pivonkova et al, 2010), amyotrophic lateral sclerosis (Bataveljić et al, 2012;Kaiser et al, 2006), congenital hyperammonaemia (Lichter-Konecki et al, 2008) and hepatic encephalopathy (HE) associated with acute toxic liver failure (ALF) (Obara- Michlewska et al, 2011). However, the mechanism underlying pathological loss of Kir4.1 channels is unknown.…”