Interference with glutamate antiporter system x c - enables post-hypoxic long-term potentiation in hippocampus

• Published in: Experimental physiology 2024-09, Vol.109 (9), p.1572-1592
• Main Authors: Heit, Bradley S, Chu, Alex, McRay, Alyssa, Richmond, Janet E, Heckman, Charles J, Larson, John
• Format: Article
• Language: English
• Subjects: Amino Acid Transport System y+ - metabolism; Animals; Glutamic Acid - metabolism; Hippocampus - metabolism; Hypoxia - metabolism; Hypoxia - physiopathology; Long-Term Potentiation - physiology; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Receptors, N-Methyl-D-Aspartate - metabolism; Synaptic Transmission - physiology
• ISSN: 0958-0670; 1469-445X
• DOI: 10.1113/EP092045

Our group previously showed that genetic or pharmacological inhibition of the cystine/glutamate antiporter, system x , mitigates excitotoxicity after anoxia by increasing latency to anoxic depolarization, thus attenuating the ischaemic core. Hypoxia, however, which prevails in the ischaemic penumbra, is a condition where neurotransmission is altered, but excitotoxicity is not triggered. The present study employed mild hypoxia to further probe ischaemia-induced changes in neuronal responsiveness from wild-type and xCT KO (xCT ) mice. Synaptic transmission was monitored in hippocampal slices from both genotypes before, during and after a hypoxic episode. Although wild-type and xCT slices showed equal suppression of synaptic transmission during hypoxia, mutant slices exhibited a persistent potentiation upon re-oxygenation, an effect we termed 'post-hypoxic long-term potentiation (LTP)'. Blocking synaptic suppression during hypoxia by antagonizing adenosine A receptors did not preclude post-hypoxic LTP. Further examination of the induction and expression mechanisms of this plasticity revealed that post-hypoxic LTP was driven by NMDA receptor activation, as well as increased calcium influx, with no change in paired-pulse facilitation. Hence, the observed phenomenon engaged similar mechanisms as classical LTP. This was a remarkable finding as theta-burst stimulation-induced LTP was equivalent between genotypes. Importantly, post-hypoxic LTP was generated in wild-type slices pretreated with system x inhibitor, S-4-carboxyphenylglycine, thereby confirming the antiporter's role in this phenomenon. Collectively, these data indicate that system x interference enables neuroplasticity in response to mild hypoxia, and, together with its regulation of cellular damage in the ischaemic core, suggest a role for the antiporter in post-ischaemic recovery of the penumbra.