Ion channels and transporters mediate the transport of charged ions across hydrophobic lipid membranes. In immune cells, divalent cations such as calcium, magnesium, and zinc have important roles as ...second messengers to regulate intracellular signaling pathways. By contrast, monovalent cations such as sodium and potassium mainly regulate the membrane potential, which indirectly controls the influx of calcium and immune cell signaling. Studies investigating human patients with mutations in ion channels and transporters, analysis of gene-targeted mice, or pharmacological experiments with ion channel inhibitors have revealed important roles of ionic signals in lymphocyte development and in innate and adaptive immune responses. We here review the mechanisms underlying the function of ion channels and transporters in lymphocytes and innate immune cells and discuss their roles in lymphocyte development, adaptive and innate immune responses, and autoimmunity, as well as recent efforts to develop pharmacological inhibitors of ion channels for immunomodulatory therapy.
Ion channels play fundamental roles in both excitable and non-excitable tissues and therefore constitute attractive drug targets for myriad neurological, cardiovascular and metabolic diseases as well ...as for cancer and immunomodulation. However, achieving selectivity for specific ion channel subtypes with small-molecule drugs has been challenging, and there currently is a growing trend to target ion channels with biologics. One approach is to improve the pharmacokinetics of existing or novel venom-derived peptides. In parallel, after initial studies with polyclonal antibodies demonstrated the technical feasibility of inhibiting channel function with antibodies, multiple preclinical programmes are now using the full spectrum of available technologies to generate conventional monoclonal and engineered antibodies or nanobodies against extracellular loops of ion channels. After a summary of the current state of ion channel drug discovery, this Review discusses recent developments using the purinergic receptor channel P2X purinoceptor 7 (P2X7), the voltage-gated potassium channel K
1.3 and the voltage-gated sodium channel Na
1.7 as examples of targeting ion channels with biologics.
The three small-conductance calcium-activated potassium (K
Ca
2) channels and the related intermediate-conductance K
Ca
3.1 channel are voltage-independent K
+
channels that mediate calcium-induced ...membrane hyperpolarization. When intracellular calcium increases in the channel vicinity, it calcifies the flexible N lobe of the channel-bound calmodulin, which then swings over to the S4-S5 linker and opens the channel. K
Ca
2 and K
Ca
3.1 channels are highly druggable and offer multiple binding sites for venom peptides and small-molecule blockers as well as for positive- and negative-gating modulators. In this review, we briefly summarize the physiological role of K
Ca
channels and then discuss the pharmacophores and the mechanism of action of the most commonly used peptidic and small-molecule K
Ca
2 and K
Ca
3.1 modulators. Finally, we describe the progress that has been made in advancing K
Ca
3.1 blockers and K
Ca
2.2 negative- and positive-gating modulators toward the clinic for neurological and cardiovascular diseases and discuss the remaining challenges.
Potassium channel modulators and their properties in treating both neurological and autoimmune diseases are discussed. These chemicals also may act as anti-inflammatory drugs.
Microglia show a rich repertoire of activation patterns regulated by a complex ensemble of surface ion channels, receptors, and transporters. We and others have investigated whether microglia vary ...their K+ channel expression as a means to achieve functional diversity. However, most of the prior studies were conducted using in vitro models such as BV2 cells, primary microglia, or brain slices in culture, which may not accurately reflect microglia physiology in adult individuals. Here we employed an in vivo mouse model of selective innate immune activation by intracerebroventricular injection of lipopolysaccharides (ICV‐LPS) to determine the role of the voltage‐gated Kv1.3 channel in LPS‐induced M1‐like microglial activation. Using microglia acutely isolated from adult brains, we detected Kv1.3 and Kir2.1 currents, and found that ICV‐LPS increased the current density and RNA expression of Kv1.3 but did not affect those of Kir2.1. Genetic knockout of Kv1.3 abolished LPS‐induced microglial activation exemplified by Iba‐1 immunoreactivity and expression of pro‐inflammatory mediators such as IL‐1β, TNF‐α, IL‐6, and iNOS. Moreover, Kv1.3 knockout mitigated the LPS‐induced impairment of hippocampal long‐term potentiation (hLTP), suggesting that Kv1.3 activity regulates pro‐inflammatory microglial neurotoxicity. Pharmacological intervention using PAP‐1, a small molecule that selectively blocks homotetrameric Kv1.3 channels, achieved anti‐inflammatory and hLTP‐recovery effects similar to Kv1.3 knockout. We conclude that Kv1.3 is required for microglial M1‐like pro‐inflammatory activation in vivo. A significant implication of our in vivo data is that Kv1.3 blockers could be therapeutic candidates for neurological diseases where microglia‐mediated neurotoxicity is implicated in the pathogenesis.
Main Points
This in vivo study of the role of Kv1.3 in microglial activation shows that Kv1.3 is required for microglial M1‐like pro‐inflammatory activation and neurotoxicity.
Selective Kv1.3 blockers could be therapeutic candidates for neurological diseases in which neurotoxic microglial activation is implicated.
Microglia are highly plastic cells that can assume different phenotypes in response to microenvironmental signals. Lipopolysaccharide (LPS) and interferon‐γ (IFN‐γ) promote differentiation into ...classically activated M1‐like microglia, which produce high levels of pro‐inflammatory cytokines and nitric oxide and are thought to contribute to neurological damage in ischemic stroke and Alzheimer's disease. IL‐4 in contrast induces a phenotype associated with anti‐inflammatory effects and tissue repair. We here investigated whether these microglia subsets vary in their K+ channel expression by differentiating neonatal mouse microglia into M(LPS) and M(IL‐4) microglia and studying their K+ channel expression by whole‐cell patch‐clamp, quantitative PCR and immunohistochemistry. We identified three major types of K+ channels based on their biophysical and pharmacological fingerprints: a use‐dependent, outwardly rectifying current sensitive to the KV1.3 blockers PAP‐1 and ShK‐186, an inwardly rectifying Ba2+‐sensitive Kir2.1 current, and a Ca2+‐activated, TRAM‐34‐sensitive KCa3.1 current. Both KV1.3 and KCa3.1 blockers inhibited pro‐inflammatory cytokine production and iNOS and COX2 expression demonstrating that KV1.3 and KCa3.1 play important roles in microglia activation. Following differentiation with LPS or a combination of LPS and IFN‐γ microglia exhibited high KV1.3 current densities (∼50 pA/pF at 40 mV) and virtually no KCa3.1 and Kir currents, while microglia differentiated with IL‐4 exhibited large Kir2.1 currents (∼ 10 pA/pF at −120 mV). KCa3.1 currents were generally low but moderately increased following stimulation with IFN‐γ or ATP (∼10 pS/pF). This differential K+ channel expression pattern suggests that KV1.3 and KCa3.1 inhibitors could be used to inhibit detrimental neuroinflammatory microglia functions. GLIA 2016;65:106–121
Main Points
Microglia subtypes differ significantly in the expression of three potassium channels (Kir2.1, KV1.3 and KCa3.1).
KV1.3 and KCa3.1 blockers could be used to inhibit detrimental neuroinflammatory microglia functions.
A subset of potassium channels is regulated primarily by changes in the cytoplasmic concentration of ions, including calcium, sodium, chloride, and protons. The eight members of this subfamily were ...originally all designated as calcium-activated channels. More recent studies have clarified the gating mechanisms for these channels and have documented that not all members are sensitive to calcium. This article describes the molecular relationships between these channels and provides an introduction to their functional properties. It also introduces a new nomenclature that differentiates between calcium- and sodium-activated potassium channels.
Microglia‐mediated inflammation exerts adverse effects in ischemic stroke and in neurodegenerative disorders such as Alzheimer's disease (AD). Expression of the voltage‐gated potassium channel Kv1.3 ...is required for microglia activation. Both genetic deletion and pharmacological inhibition of Kv1.3 are effective in reducing microglia activation and the associated inflammatory responses, as well as in improving neurological outcomes in animal models of AD and ischemic stroke. Here we sought to elucidate the molecular mechanisms underlying the therapeutic effects of Kv1.3 inhibition, which remain incompletely understood. Using a combination of whole‐cell voltage‐clamp electrophysiology and quantitative PCR (qPCR), we first characterized a stimulus‐dependent differential expression pattern for Kv1.3 and P2X4, a major ATP‐gated cationic channel, both in vitro and in vivo. We then demonstrated by whole‐cell current‐clamp experiments that Kv1.3 channels contribute not only to setting the resting membrane potential but also play an important role in counteracting excessive membrane potential changes evoked by depolarizing current injections. Similarly, the presence of Kv1.3 channels renders microglia more resistant to depolarization produced by ATP‐mediated P2X4 receptor activation. Inhibiting Kv1.3 channels with ShK‐223 completely nullified the ability of Kv1.3 to normalize membrane potential changes, resulting in excessive depolarization and reduced calcium transients through P2X4 receptors. Our report thus links Kv1.3 function to P2X4 receptor‐mediated signaling as one of the underlying mechanisms by which Kv1.3 blockade reduces microglia‐mediated inflammation. While we could confirm previously reported differences between males and females in microglial P2X4 expression, microglial Kv1.3 expression exhibited no gender differences in vitro or in vivo.
Main Points
The voltage‐gated K+ channel Kv1.3 regulates microglial membrane potential.
Inhibition of Kv1.3 depolarizes microglia and reduces calcium entry mediated by P2X4 receptors by dissipating the electrochemical driving force for calcium.
Main Points
The voltage‐gated K+ channel Kv1.3 regulates microglial membrane potential.
Inhibition of Kv1.3 depolarizes microglia and reduces calcium entry mediated by P2X4 receptors by dissipating the electrochemical driving force for calcium.
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