SIK3 and Wnk converge on Fray to regulate glial K+ buffering and seizure susceptibility

Abstract

Glial cells play a critical role in maintaining homeostatic ion concentration gradients. Salt-inducible kinase 3 (SIK3) regulates a gene expression program that controls K+ buffering in glia, and upregulation of this pathway suppresses seizure behavior in the eag, Shaker hyperexcitability mutant. Here we show that boosting the glial SIK3 K+ buffering pathway suppresses seizures in three additional molecularly diverse hyperexcitable mutants, highlighting the therapeutic potential of upregulating glial K+ buffering. We then explore additional mechanisms regulating glial K+ buffering. Fray, a transcriptional target of the SIK3 K+ buffering program, is a kinase that promotes K+ uptake by activating the Na+/K+/Cl- co-transporter, Ncc69. We show that the Wnk kinase phosphorylates Fray in Drosophila glia and that this activity is required to promote K+ buffering. This identifies Fray as a convergence point between the SIK3-dependent transcriptional program and Wnk-dependent post-translational regulation. Bypassing both regulatory mechanisms via overexpression of a constitutively active Fray in glia is sufficient to robustly suppress seizure behavior in multiple Drosophila models of hyperexcitability. Finally, we identify cortex glia as a critical cell type for regulation of seizure susceptibility, as boosting K+ buffering via expression of activated Fray exclusively in these cells is sufficient to suppress seizure behavior. These findings highlight Fray as a key convergence point for distinct K+ buffering regulatory mechanisms and cortex glia as an important locus for control of neuronal excitability.

Astrocyte-neuron circuits in epilepsy

“…In line with this premise, optogenetic activation of astrocytes suppresses seizures in a Na + /K + -ATPase dependent manner following cortical kainic acid injection and in a model of focal cortical dysplasia in rats ( Zhao et al, 2022 ). Similarly, bolstering K + buffering suppresses seizures in the well characterized ‘Shaker’ Drosophila line ( Li et al, 2021 ; Lones and DiAntonio, 2023 ).…”

Blocking salt‐inducible kinases with YKL‐06‐061 prevents PTZ‐induced seizures in mice

“…In addition, we cannot exclude the role of SIK2 and SIK3 in the development of seizure behavior. Boosting the glial SIK3 K + buffering pathway suppresses seizures (Lones & DiAntonio, 2023 ) and YKL‐06‐061 is a pan‐inhibitor of SIK1, SIK2, and SIK3 (Mujahid et al., 2017 ); a more selective SIK1 inhibitor or knockdown of SIK1 needs to be evaluated in detail in future studies.…”