The Microglial K+ Channels Kv1.3 and KCa3.1 as Potential Therapeutic Targets for Ischemic Stroke

Abstract

Activated microglia significantly contribute to the secondary inflammatory damage in ischemic stroke and therefore constitute attractive targets for post-infarct intervention. Microglia express the voltage-gated Kv1.3 and the calcium-activated KCa3.1 channels, both of which have been reported to be involved in microglia mediated neuronal killing, oxidative burst and inflammatory cytokine production. However, most of these experiments have been performed with cultured neonatal microglia and it has always been questioned whether these cultures accurately reflect the K+ channel expression of activated microglia in adult brain. Following intrahippocampal LPS injection or middle cerebral artery occlusion (MCAO) with 7 days of reperfusion we observed Kv1.3 and KCa3.1 immunoreactivity on activated microglia in mouse brain. In both conditions we further detected currents exhibiting the biophysical and pharmacological properties of Kv1.3 and KCa3.1 on microglia immediately following isolated with CD11b-magnetic beads. Channel expression was significantly higher than on microglia isolated from control brains. We next investigated the effect of genetic deletion and pharmacological blockade of KCa3.1 on the reperfusion injury following ischemic stroke using reversible MCAO as a model. KCa3.1-/- mice and wild-type mice treated with the KCa3.1 blocker TRAM-34 exhibited significantly smaller infarct areas and improved neuronal survival and motor coordination in neurological deficit test on day-7 after MCAO. Kv1.3 blockade with PAP-1 exhibited similar beneficial effects in wild-type mice but did not further reduce infarct area or improve neurological deficit in KCa3.1-/- mice. In male Wistar rats combined blockade of both Kv1.3 and KCa3.1 with PAP-1 and TRAM-34 also did not further reduce infarct area compared to treatment with either TRAM-34 or PAP-1 alone suggesting that blockade of one microglial K+ channel is sufficient to improve outcomes in ischemic stroke.Supported by RO1 GM076063 from the National Institute of Health.