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. 2021 Mar 5:12:613105.
doi: 10.3389/fphar.2021.613105. eCollection 2021.

Effects of Interleukin-1β in Glycinergic Transmission at the Central Amygdala

Affiliations

Effects of Interleukin-1β in Glycinergic Transmission at the Central Amygdala

Jocelyn Solorza et al. Front Pharmacol. .

Abstract

Interleukin-1β (IL-1β) is an important cytokine that modulates peripheral and central pain sensitization at the spinal level. Among its effects, it increases spinal cord excitability by reducing inhibitory Glycinergic and GABAergic neurotransmission. In the brain, IL-1β is released by glial cells in regions associated with pain processing during neuropathic pain. It also has important roles in neuroinflammation and in regulating NMDA receptor activity required for learning and memory. The modulation of glycine-mediated inhibitory activity via IL-1β may play a critical role in the perception of different levels of pain. The central nucleus of the amygdala (CeA) participates in receiving and processing pain information. Interestingly, this nucleus is enriched in the regulatory auxiliary glycine receptor (GlyR) β subunit (βGlyR); however, no studies have evaluated the effect of IL-1β on glycinergic neurotransmission in the brain. Hence, we hypothesized that IL-1β may modulate GlyR-mediated inhibitory activity via interactions with the βGlyR subunit. Our results show that the application of IL-1β (10 ng/ml) to CeA brain slices has a biphasic effect; transiently increases and then reduces sIPSC amplitude of CeA glycinergic currents. Additionally, we performed molecular docking, site-directed mutagenesis, and whole-cell voltage-clamp electrophysiological experiments in HEK cells transfected with GlyRs containing different GlyR subunits. These data indicate that IL-1β modulates GlyR activity by establishing hydrogen bonds with at least one key amino acid residue located in the back of the loop C at the ECD domain of the βGlyR subunit. The present results suggest that IL-1β in the CeA controls glycinergic neurotransmission, possibly via interactions with the βGlyR subunit. This effect could be relevant for understanding how IL-1β released by glia modulates central processing of pain, learning and memory, and is involved in neuroinflammation.

Keywords: auxiliary subunit; beta subunit; central amygdala (CeA); glycine receptors; interleukin-1β; neuroimmune communication.

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Conflict of interest statement

The authors hui declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Glycinergic sIPSCs are modulated by IL-1β in CeA neurons of rat. (A) Representative synaptic sIPSC glycinergic currents in the presence of CNQX (10 μM), APV (50 μM), picrotoxin (50 µM), bicuculline (10 μM), clamped at +20 mV, 5 and 15 min after incubation with IL-1β. (B) Upper: Event distribution histograms of sIPSCs amplitudes before (black bars) and after IL-1β application (gray bars). Below: table with summarized analysis and statistics of distribution histograms (C) Cumulative probability histogram of amplitude in CeA neurons before (black line), 5 min (gray line) and 15 min (discontinuous line) after incubation with IL-1β. (D) Graphical representation of the mean ± SEM (n = 4 rats, 13 cells) of glycinergic sIPSC currents parameters: amplitude (pA), frequency (Hz) and decay time (ms). One-way ANOVA and Bonferroni post-hoc test (*p < 0.05 and ***p < 0.001).
FIGURE 2
FIGURE 2
Molecular model of heteropentameric 2α1:3β GlyRs and identification of the residues which putatively interact with IL-1β. αGlyR, βGlyR subunits and IL-1β are represented in green, yellow and grey, respectively.
FIGURE 3
FIGURE 3
Sequence Alignment of complete Human ECD domains of α(1–3) and βGlyR subunits. Red arrow indicates the location of the residue (Y240) that was mutated in the βGlyR subunit.
FIGURE 4
FIGURE 4
The effects of IL-1β are mediated by interaction with auxiliary βGlyR. (A) Representative glycine-activated currents of α1β wild type and α1βY240Α after the perfusion of glycine (black line) + IL-1β (red line). (B): Graphical representation of effects of glycine or glycine + IL-1β in homo and heteropentameric GlyRs. (C) Graphical representation of dose-response curve. Glycine activated currents at different glycine concentrations (10–1,000 μM) were normalized to a percentage of the maximal response to the application of glycine 1,000 μM in HEK293T cells transfected with different subunits of GlyRs. Data are presented as mean ± SEM.

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