IL-4 type 1 receptor signaling up-regulates KCNN4 expression, and increases the KCa3.1 current and its contribution to migration of alternative-activated microglia

Abstract

The Ca2+-activated K+ channel, KCa3.1 (KCNN4/IK1/SK4), contributes to “classical,” pro-inflammatory activation of microglia, and KCa3.1 blockers have improved the outcome in several rodent models of CNS damage. For instance, blocking KCa3.1 with TRAM-34 rescued retinal ganglion neurons after optic nerve damage in vivo and, reduced p38 MAP kinase activation, production of reactive oxygen and nitrogen species, and neurotoxicity by microglia in vitro. In pursuing the therapeutic potential of KCa3.1 blockers, it is crucial to assess KCa3.1 contributions to other microglial functions and activation states, especially the IL-4-induced “alternative” activation state that can counteract pro-inflammatory states. We recently found that IL-4 increases microglia migration – a crucial function in the healthy and damaged CNS – and that KCa3.1 contributes to P2Y2 receptor-stimulated migration. Here, we discovered that KCa3.1 is greatly increased in alternative-activated rat microglia and then contributes to an enhanced migratory capacity. IL-4 up-regulated KCNN4 mRNA (by 6 h) and greatly increased the KCa3.1 current by 1 day, and this required de novo protein synthesis. The increase in current was sustained for at least 6 days. IL-4 increased microglial migration and this was reversed by blocking KCa3.1 with TRAM-34. A panel of inhibitors of signal-transduction mediators was used to analyze contributions of IL-4-related signaling pathways. Induction of KCNN4 mRNA and KCa3.1 current was mediated specifically through IL-4 binding to the type I receptor and, surprisingly, it required JAK3, Ras/MEK/ERK signaling and the transcription factor, activator protein-1, rather than JAK2, STAT6, or phosphatidylinositol 3-kinase.The same receptor subtype and pathway were required for the enhanced KCa3.1-dependent migration. In providing the first direct signaling link between an IL-4 receptor, expression and roles of an ion channel, this study also highlights the potential importance of KCa3.1 in alternative-activated microglia.

Influence of IL13 on Periostin Secretion by Synoviocytes in Osteoarthritis

“…IL13 mediates its effects by interacting with a complex receptor system comprising of IL4Rα and two IL13 binding proteins, IL13Rα1 and IL13Rα2. However, unlike IL4, IL13 does not appear to be important in the initial differentiation of cluster of differentiation 4 (CD4) T-naive T-cells into TH2 cells, because there are no functional IL13 receptors on human Tcells (33)(34)(35). Rather, IL13 is related to fibrosis of tissue in various chronic types of inflammation because IL13Rs are expressed on endothelial cells, fibroblasts, and smooth muscle cells.…”

Protective and Toxic Neuroinflammation in Amyotrophic Lateral Sclerosis

“…Multiple mechanisms can lead to motor neuron injury, which funnel into a final pathway or noncell-autonomous toxicity and neuroinflammation leading to motor neuron death [59][60][61][62][63]. In contrast, M2 produce high levels of antiinflammatory cytokines and neurotrophic factors including IL-4, IL-10, and insulin-like growth factor (IGF)-1 in addition other neruoprotection signals such as CD200 and fractalkine [51,60,[64][65][66][67][68].…”

Role of KCa3.1 Channels in Macrophage Polarization and Its Relevance in Atherosclerotic Plaque Instability

“…Moreover, recent studies have indicated that expression of KCCN4, the gene that encodes the KCa3.1 channel, is upregulated in IL-4-treated human macrophages. 17,24 However, the expression pattern of KCa3.1 channels and their role in modulating the balance of macrophage phenotypes are still not well defined. Using the whole-cell patch clamp recording method and Western blot assays, we demonstrated increased KCa3.1 levels in IFN-γ and LPS-treated macrophages, as well as in IL-4-treated macrophages, though the increase was significantly larger in the IFN-γ and LPS-induced M1 macrophages.…”

“…16 However, in advanced atherosclerotic lesions, the role of KCa3.1 in the pathogenesis of plaque instability and its underlying mechanisms are unknown. A recent study reported that IL-4 stimulation increases KCa3.1 current in microglia, 17 which suggests that KCa3.1 may be involved in the polarization of macrophages and atherosclerotic plaque disruption. In this study, we pharmacologically modulated KCa3.1 activity and examined how this altered macrophage phenotype and determined its effect on plaque stability.…”