Regulation of System x_c⁻Activity and Expression in Astrocytes by Interleukin‐1β

Abstract

We recently demonstrated that interleukin-1β (IL-1β) increases system xc− (cystine/glutamate antiporter) activity in mixed cortical cell cultures, resulting in an increase in hypoxic neuronal injury when glutamate clearance is impaired. Herein, we demonstrate that neurons, astrocytes and microglia all express system xc− subunits (xCT, 4F2hc, RBAT) and are capable of cystine import. However, IL-1β stimulation increases mRNA for xCT— the light chain that confers substrate specificity— in astrocytes only; an effect blocked by the transcriptional inhibitor actinomycin D. Additionally, only astrocytes show an increase in cystine uptake following IL-1β exposure; an effect associated with a change in xCT protein. The increase in cystine uptake that follows IL-1β is lacking in astrocytes derived from mice harboring a mutation in Slc7a11 (sut gene), which encodes for xCT, and in wild-type astrocytes treated with the protein synthesis inhibitor cycloheximide. IL-1β does not regulate the light chain of the amino acid transporter, LAT2, or the expression and function of astrocytic excitatory amino acid transporters (EAATs), demonstrating some target selectivity. Finally, the enhanced neuronal vulnerability to hypoxia that followed IL-1β treatment in our mixed culture system was not observed in chimeric cultures consisting of wild-type neurons plated on top of sut astrocytes. Nor was it observed in wild-type cultures treated with a system xc− inhibitor or an NMDA receptor antagonist. Overall, our data demonstrate that IL-1β selectively regulates system xc− activity in astrocytes and that this change is specifically responsible for the deleterious, excitotoxic effects of IL-1β found under hypoxic conditions.

DCPIB, the Proposed Selective Blocker of Volume-Regulated Anion Channels, Inhibits Several Glutamate Transport Pathways in Glial Cells

“…Astrocytes were preloaded with D-[ 14 C] cystine as a radiotracer according to the technique proposed by Jackman et al (2010) with several modifications. Rates of the L-[ 14 C] cystine uptake were determined in Na 1 -free LiCl medium to suppress activity of Na 1 -dependent amino acid transporters, which was additionally supplemented with the g-glutamyl transpeptidase inhibitor 0.5 mM acivicin.…”

Astrogliosis

“…In the healthy CNS, astrocytes (1) maintain the extracellular homeostasis of K þ , water, pH, and transmitter uptake (Halassa and Haydon 2010;Jin et al 2013), (2) may modulate synaptic activity directly via release of "gliotransmitters" (Volterra and Meldolesi 2005;Halassa and Haydon 2010;Hamilton and Attwell 2010;Henneberger et al 2010), and (3) take part in the formation and pruning of synapses (Chung et al 2013;Clarke and Barres 2013). Functional changes undergone by reactive astrocytes in response to specific molecular triggers can impact neurons via (1) down-regulation of glutamine synthase associated with reduced inhibitory synaptic currents in local neurons (Ortinski et al 2010), (2) increased expression of xCT (Slc7a11), a cysteine-glutamate transporter associated with increased glutamate signaling, seizures, and excitotoxicity (Jackman et al 2010;Buckingham et al 2011), and (3) changes in the expression of multiple GPCRs and G proteins and calcium signaling evoked by their ligands (Hamby et al 2012). There is increasing evidence for astrocyte participation in complex behaviors including sleep (Halassa and Haydon 2010), pain (Hansen and Malcangio 2013), mood, depression (Halassa and Haydon 2010; Paradise et al 2012;Czeh and Di Benedetto 2013;Martin et al 2013), and certain childhood behavioral disorders with altered synapse development (Stephan et al 2012;Clarke and Barres 2013).…”

Inflammation, Glutamate, and Glia: A Trio of Trouble in Mood Disorders

“…Inflammatory cytokines including TNF and LPS administration upregulate the xC-system and induce glutamate release from cultured and primary microglia (Figuera-Losada et al, 2014;Mesci et al, 2015;Piani and Fontana, 1994). Similarly, IL-1β has been implicated in increasing the xC-system expression on the surface of astrocytes (but not on microglia or macrophages)-an effect that is mediated through the activation of nuclear factor kappa B (NF-kB) signaling (Jackman et al, 2010). LPSinduced activation of TLR3 and 4 increases surface expression of the xC-system and thus co-administration of LPS and the xC-system stimulator cystine can potentially lead to enhanced glutamate toxicity (Kigerl et al, 2012).…”