Activity-dependent endoplasmic reticulum Ca ²⁺ uptake depends on Kv2.1-mediated endoplasmic reticulum/plasma membrane junctions to promote synaptic transmission

Abstract

The endoplasmic reticulum (ER) forms a continuous and dynamic network throughout a neuron, extending from dendrites to axon terminals, and axonal ER dysfunction is implicated in several neurological disorders. In addition, tight junctions between the ER and plasma membrane (PM) are formed by several molecules including Kv2 channels, but the cellular functions of many ER-PM junctions remain unknown. Recently, dynamic Ca 2+ uptake into the ER during electrical activity was shown to play an essential role in synaptic transmission. Our experiments demonstrate that Kv2.1 channels are necessary for enabling ER Ca 2+ uptake during electrical activity, as knockdown (KD) of Kv2.1 rendered both the somatic and axonal ER unable to accumulate Ca 2+ during electrical stimulation. Moreover, our experiments demonstrate that the loss of Kv2.1 in the axon impairs synaptic vesicle fusion during stimulation via a mechanism unrelated to voltage. Thus, our data demonstrate that a nonconducting role of Kv2.1 exists through its binding to the ER protein VAMP-associated protein (VAP), which couples ER Ca 2+ uptake with electrical activity. Our results further suggest that Kv2.1 has a critical function in neuronal cell biology for Ca 2+ handling independent of voltage and reveals a critical pathway for maintaining ER lumen Ca 2+ levels and efficient neurotransmitter release. Taken together, these findings reveal an essential nonclassical role for both Kv2.1 and the ER-PM junctions in synaptic transmission.

Distinct cellular expression and subcellular localization of Kv2 voltage‐gated K+ channel subtypes in dorsal root ganglion neurons conserved between mice and humans

“…In central neurons, Kv2 clusters localize to the soma, proximal dendrites, and axon initial segment (Lim et al., 2000; Scannevin et al., 1996; Trimmer, 1991). At clusters, Kv2 channels organize protein signaling complexes and endoplasmic reticulum–plasma membrane junctions (Johnson et al., 2018; Kirmiz et al., 2018; Panzera et al., 2022; Vierra et al., 2021). To determine whether Kv2 channels in DRG neurons form clusters similar to central neurons, we compared en face z ‐projections of Kv2 clusters in DRG neurons and ventral horn neurons in the same spinal cord section (Figure 7).…”

“…Further studies could investigate if Kv2 clusters are localized to extracellular structures in the DRG. Kv2.2 has been identified in juxtaparanodes but not paranodes of axons in the osseous spiral lamina of the cochlea (Kim & Rutherford, 2016), and previous work has also identified that Kv2.1 channels are necessary for enabling ER Ca2+ uptake during electrical activity in both the soma and axon (Panzera et al., 2022). To our knowledge, Kv2.2 immunofluorescence has not been previously reported in distal axons in the brain, spinal cord, or DRG.…”

Neuronal FOS reports synchronized activity of presynaptic neurons

“…A candidate mechanism for integrating periodic mGlu activation involves the endoplasmic reticulum (ER). Recently identified mechanisms that link electrical activity with calcium accumulation in the ER ( 34 ) suggest that the ER could act as a cellular memory of past electrical activity. In this scenario, the magnitude of mGlu-mediated release events would be a function of past activity in that neuron.…”

Increased KV2.1 Channel Clustering Underlies the Reduction of Delayed Rectifier K+ Currents in Hippocampal Neurons of the Tg2576 Alzheimer’s Disease Mouse

“…In particular, it has recently been shown that K V 2.1 clustering at neuronal ER-PM junctions promotes the clustering of PM L-type Ca 2+ channels and their coupling to ryanodine receptor ER Ca 2+ release channels [ 74 ], hence allowing the generation of localized Ca 2+ release events. Moreover, the fact that K V 2.1 clusters induce the formation of -and localize at- ER-PM junctions confers to K V 2.1 the ability not only to trigger a structural remodeling of the ER but also to affect neuronal Ca 2+ handling by modulating ER Ca 2+ uptake [ 75 ]. Of note, we have recently reported about the occurrence of an ER Ca 2+ remodeling in the Tg2576 primary neurons.…”