Kcnq2/Kv7.2 controls the threshold and bihemispheric symmetry of cortical spreading depolarization

Abstract

Spreading depolarization (SD) is a slowly propagating wave of massive cellular depolarization associated with acute brain injury and migraine aura. Genetic studies link molecular defects in enhanced cytoplasmic Ca2+ flux, glial Na+-K+ ATPase, and interneuronal Na+ current with SD susceptibility, emphasizing the important roles of synaptic activity and extracellular ionic homeostasis in determining SD threshold. In contrast, gene mutations in ion channels that shape intrinsic membrane excitability are frequently associated with epilepsy susceptibility. It is not well known whether epileptogenic mutations in voltage-gated potassium channels that regulate membrane repolarization also modify SD threshold and generation pattern. Here we report that the Kcnq2/Kv7.2 potassium channel subunit, frequently mutated in developmental epilepsy, is an SD modulatory gene with significant control over seizure-SD transition threshold, bilateral cortical expression, and temporal susceptibility. Chronic DC-band cortical EEG recording from awake conditional Kcnq2 deletion mice (Emx2cre/+::Kcnq2flox/flox) revealed spontaneous cortical seizures and SD. In contrast to a related potassium channel deficient model, Kv1.1 KO mice, spontaneous cortical SDs in Kcnq2 cKO mice are tightly coupled to the terminal phase of seizures, arise bilaterally, and are observed predominantly during the dark phase. Administration of the nonselective Kv7.2 inhibitor XE991 to Kv1.1 KO mice reproduced the Kcnq2 cKO-like SD phenotype (tight seizure coupling and bilateral symmetry) in these mice, indicating that Kv7.2 currents directly and actively modulate SD properties. In vitro brain slice studies confirmed that Kcnq2/Kv7.2 depletion or pharmacological inhibition intrinsically lowers the cortical SD threshold, whereas pharmacological activators elevate the threshold to multiple depolarizing and hypometabolic SD triggers. Together these results identify Kcnq2/Kv7.2 as a distinctive SD regulatory gene, and point to SD as a potentially significant pathophysiological component of KCNQ2-linked epileptic encephalopathy syndromes. Our results also implicate KCNQ2/Kv7.2 channel activation as an adjunctive therapeutic target to inhibit SD incidence.

Loss of KCNQ2 or KCNQ3 Leads to Multifocal Time-Varying Activity in the Neonatal ForebrainEx Vivo

“…Although the calcium activity was robust in CA3, we noticed that the LFPs were typically smaller or absent in slices from Pyr:Kcnq2 mice. This result could be attributed to several reasons, such as electrode placement, increased GABAergic receptor activity (see below), the higher tendency of Kcnq2 -null excitatory neurons to show spreading depression and persistent depolarization leading to sodium channel inactivation ( Aiba and Noebels, 2021 ), or a combination of these mechanisms. We did not pursue this question further.…”

“…Together, these data suggest that loss of KCNQ2 channels drives LF activity through a mechanism that is independent of fast synaptic transmission. Thus, in the absence of rapid synaptic transmission, slices from Pyr:Kcnq2 mice can still generate large hypersynchronous events, likely because of sodium channel-driven depolarization of Kcnq2 -null excitatory neurons and a large build-up and diffusion of potassium ( Aiba and Noebels, 2021 ).…”

A hyperthermic seizure unleashes a surge of spreading depolarizations inScn1adeficient mice

“…We also detected a stereotyped delay in postictal SD onset, almost always one minute after seizure termination. This is in contrast to the Kcnq2 conditional KO mouse in which most SDs were generated even before seizure activity fully terminated 7 . This result highlights the distinct SD regulatory mechanisms between epilepsy models with specific circuit defects.…”

“…We characterized SD incidence of Scn1a deficient (Scn1a +/RX ) and WT mice using a DC-band chronic EEG recording method reported in our previous study 7 . In the study cohorts, we recorded a total of seventeen Scn1a +/RX (7 males, 10 females) and eleven littermate WT mice (5 males and 6 females).…”

“…Due to their excitatory nature, SD events are detected in association with seizures or epileptic discharges in both experimental and clinical settings 6,7 Such “peri-ictal” SD events have been considered as a candidate mechanism contributing to epilepsy comorbidities such as peri-ictal migraine headache and immobility 8 . However, understanding of SD incidence in epilepsy is extremely limited.…”