Regulation of System xc- Activity and Expression in Astrocytes by Interleukin-1β: Implications for Hypoxic Neuronal Injury

We recently demonstrated that interleukin-1 beta (IL-1 beta) increases system x(c)(-) (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 x(c)(-) subunits (xCT, 4F2hc, RBAT) and are capable of cystine import. However, IL-1 beta 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-1 beta exposure; an effect associated with a change in xCT protein. The increase in cystine uptake that follows IL-1 beta 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-1 beta 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-1 beta 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 x(c)(-) inhibitor or an NMDA receptor antagonist. Overall, our data demonstrate that IL-1 beta selectively regulates system x(c)(-) activity in astrocytes and that this change is specifically responsible for the deleterious, excitotoxic effects of IL-1 beta found under hypoxic conditions. (C) 2010 Wiley-Liss, Inc.