Background: Microglia and CNS-infiltrating macrophages (CNS MPs) perform opposing deleterious pro-inflammatory and protective functions in ischemic stroke. Kv1.3 channels regulate pro-inflammatory microglial functions and are promising therapeutic targets to curb neuroinflammation. Since Kv1.3 channel expression in CNS MPs following ischemic stroke is unknown, we characterized Kv1.3 expression in CNS MPs at different times following ischemic stroke.
Methods: In the 30-min transient middle cerebral artery occlusion (MCAO) mouse model, we performed flow cytometric assays of cell surface Kv1.3 expression (fluorescent labeled Kv1.3 blocking peptide ShK-F6CA) and phycoerythrin-microsphere phagocytosis on acutely isolated CNS MPs from ipsi- and contralateral hemispheres (including sham surgery controls) at 30 min, 24h, 48h, 72h and 7d time points. Among CD11b+ CNS MPs, resting microglia (CD45lowLy6clow), activated microglia (C45highLy6clow) and infiltrating macrophages (CD45highLy6chigh) were monitored. By quantitative PCR, we measured Kv1.3, Kir2.1 potassium channel and COX2 gene expression in CD11b+ CNS MPs.
Results: After 48h following MCAO, proportions of activated microglia and infiltrating macrophages were increased ipsilaterally. Kv1.3 channels were highly expressed in CD45highLy6clow activated microglia at baseline but significantly declined after 48 hours ipsilaterally with same trend contralaterally. Kv1.3 mRNA in CNS MPs also showed an overall decreasing trend ipsilateral to MCAO. No changes in phagocytic properties were observed following MCAO.
Conclusions: Despite increased proportions of activated microglia and infiltrating macrophages, a precipitous downregulation of Kv1.3 channel expression occurs in CD45high activated microglia after 48 hours following transient cerebral ischemia in mice. Early microglial Kv1.3 channel blockade effects on neuroinflammation following ischemic stroke need to be determined.