Endoplasmic reticulum stress increases inflammatory cytokines in an epilepsy mouse model Gabrg2^+/Q390X knockin: A link between genetic and acquired epilepsy?

Abstract

Objective: Neuroinflammation is a major theme in epilepsy, which has been characterized in acquired epilepsy but is poorly understood in genetic epilepsy. γ-Aminobutyric acid type A receptor subunit gene mutations are significant causes of epilepsy, and we have studied the pathophysiology directly resulting from defective receptor channels. Here, we determined the proinflammatory factors in a genetic mouse model, the Gabrg2 +/Q390X knockin (KI). We have identified increased cytokines in multiple brain regions of the KI mouse throughout different developmental stages and propose that accumulation of the trafficking-deficient mutant protein may increase neuroinflammation, which would be a novel mechanism for genetic epilepsy. Methods: We used enzyme-linked immunosorbent assay, immunoprecipitation, nuclei purification, immunoblot, immunohistochemistry, and confocal microscopy to characterize increased neuroinflammation and its potential causes in a Gabrg2 +/Q390X KI mouse and a Gabrg2 +/knockout (KO) mouse, each associated with a different epilepsy syndrome with different severities. Results: We found that proinflammatory cytokines such as tumor necrosis factor alpha, interleukin 1-beta (IL-1β), and IL-6 were increased in the KI mice but not in the KO mice. A major underlying basis for the discrepancy in cytokine expression between the two mouse models is likely chronic mutant protein accumulation and endoplasmic reticulum (ER) stress. The presence of mutant protein dampened cytokine induction upon further cellular stimulation or external stress such as elevated temperature. Pharmacological induction of ER stress upregulated cytokine expression in the wild-type and KO but not in the KI mice. The increased cytokine expression was independent of seizure occurrence, because it was upregulated in both mice and cultured neurons. Significance: Together, these data demonstrate a novel pathophysiology for genetic epilepsy, increased neuroinflammation, which is a common mechanism for acquired 2302 | SHEN Et al.

Epileptic Mechanisms Shared by Alzheimer’s Disease: Viewed via the Unique Lens of Genetic Epilepsy

“…Additionally, the Gabrg2 +/Q390X mice had increased mortality and impaired cognition compared to the Gabrg2 +/− mouse with a loss-of-function mutation in the same protein that did not cause ER stress [60,78]. Importantly, we identified increased neuroinflammation in the Gabrg2 +/Q390X mice but not in the Gabrg2 +/− mouse without ER stress [79]. The loss-of-function model has only mild epilepsy with normal cognition.…”

“…The study on Gabrg2 +/Q390X mice implicates that mutant protein accumulation may exist from the beginning of life, although the protein aggregates will not emerge until later in life [30]. Importantly, increased neuroinflammation due to ER-retained mutant protein was observed in knockin mouse pups carrying the GABRG2(Q390X) mutation, suggesting that underlying changes occur long before any symptom emerges [79]. The efficacy of memantine in epilepsy and cognitive improvement with GRIN2A mutations does a good job of explaining why the blockade of NMDA receptors is beneficial for AD.…”

“…In Gabrg2 +/Q390X epilepsy mouse models, the existence of the mutant protein that is aggregation prone with slow degradation promotes a mild infrequent absence to a much severe epilepsy phenotype of DS with increased seizure severity and cognitive impairment [60]. We recently identified that the mutant protein caused increased ER stress in the Gabrg2 +/Q390X mouse and caused increased neuroinflammation, as evidenced by inflammatory cytokines such as tumor necrosis factor (TNF) alpha, interleukin 1-beta, and interleukin 6 in the newborn pups [79]. Given that neuroinflammation is an established patho-mechanism of AD [87,88] and TBI [89], this thus provides a direct link between GE and AD as well as TBI, a risk factor for both epilepsy and AD.…”

Inflammation-related genes and immune infiltration landscape identified in kainite-induced temporal lobe epilepsy based on integrated bioinformatics analysis

“…Besides, expression of Icam1 was significantly up-regulated in the hippocampi with hippocampal sclerosis ( Nakahara et al, 2010 ). Interleukin-6 (Il6) is a prototypical proinflammatory cytokine for maintaining homeostasis, and animal experiments showed the involvement of cytokines in epilepsy ( Shen et al, 2020 ). The previous report has revealed that an increased level of IL6 was observed in cerebrospinal fluid and serum from patients with epilepsy ( Peltola et al, 1998 ; Tao et al, 2020 ).…”

A new identified COL4A2 mutation contributes to astrocyte activation by activating JAK/STAT signaling in epilepsy

“…Recent studies reported that neuroinflammation is the pathological signature of central nervous system diseases including epilepsy (Galan, 2021;Devinsky et al, 2013;Vezzani et al, 2013). Proinflammatory cytokines such as tumor necrosis factor alpha, interleukin 1-beta (IL-1β), and IL-6 were increased in the Gabrg2 +/Q390X knockin mice, providing the first link of neuroinflammation between genetic epilepsy associated with an ion channel gene mutation and acquired epilepsy (Shen et al, 2020). Astrocytes are characteristic glial cells responsible for nutrition support, blood-brain barrier formation, extracellular ion equilibrium, and synaptic plasticity (Karve et al, 2016;Araki et al, 2021).…”