Synapse development is regulated by microglial THIK-1 K ⁺ channels

Abstract

Microglia are the resident immune cells of the central nervous system. They constantly survey the brain parenchyma for redundant synapses, debris, or dying cells, which they remove through phagocytosis. Microglial ramification, motility, and cytokine release are regulated by tonically active THIK-1 K+ channels on the microglial plasma membrane. Here, we examined whether these channels also play a role in phagocytosis. Using pharmacological blockers and THIK-1 knockout (KO) mice, we found that a lack of THIK-1 activity approximately halved both microglial phagocytosis and marker levels for the lysosomes that degrade phagocytically removed material. These changes may reflect a decrease of intracellular [Ca2+]i activity, which was observed when THIK-1 activity was reduced, since buffering [Ca2+]i reduced phagocytosis. Less phagocytosis is expected to result in impaired pruning of synapses. In the hippocampus, mice lacking THIK-1 expression had an increased number of anatomically and electrophysiologically defined glutamatergic synapses during development. This resulted from an increased number of presynaptic terminals, caused by impaired removal by THIK-1 KO microglia. The dependence of synapse number on THIK-1 K+ channels, which control microglial surveillance and phagocytic ability, implies that changes in the THIK-1 expression level in disease states may contribute to altering neural circuit function.

Characterisation of C101248: A novel selective THIK-1 channel inhibitor for the modulation of microglial NLRP3-inflammasome

“…Electrophysiological studies show that THIK-1 is an outwardly rectifying channel with a very small single-channel conductance (∼5 pS at +100 mV) and short open time duration (<0.5 ms) ( Kang et al, 2014 ). THIK-1 controls key microglial function across the spectrum including surveillance, ramification, phagocytosis and membrane voltage ( Izquierdo et al, 2021 ; Madry et al, 2018a , 2018b ). Importantly, blockade of THIK-1 also suppresses NLRP3-dependent release of proinflammatory IL-1β in the rodent brain ( Madry et al, 2018b ) and in cultured macrophages and microglia ( Drinkall et al, 2022 ).…”

Lipid accumulation induced by APOE4 impairs microglial surveillance of neuronal-network activity

“…After 4 weeks of differentiation from iPS-derived primitive hematopoietic progenitors, iMGLs in culture exhibited ramified morphology, stained positive for microglial specific-markers such as IBA1 and P2RY12, and displayed mature electrophysiological properties typical of ex vivo microglia in culture via whole cell patchclamp analysis (Figure 1B and Supplemental Figure 1A-E). Additionally, immunostaining of iMGLs revealed the expression of canonical ion channels P2X1 and THIK-1, critical regulators of microglial homeostasis (Figure 1B) (Izquierdo et al, 2021;Koizumi et al, 2013;Madry et al, 2018). We also detected expression of the voltage-gated potassium channel KCNE3, and the voltage-gated calcium channel CACNA2D4, in addition to the metabotropic glutamate receptor, GLUR7 (Figure 1B).…”

Microglia‐dependent remodeling of neuronal circuits

“…Additionally, the activity of microglial THIK‐1 has been shown to function as a potassium sensor when in close proximity to both axons and synapses and may function as a readout for neuronal membrane activity (Madry et al, 2018; Ronzano et al, 2021). Indeed, abrogation or inhibition of THIK‐1 leads to an increase in synaptic density because of defective microglia pruning (Izquierdo et al, 2021).…”