Glutamate as a co-agonist for acid-sensing ion channels to aggravate ischemic brain damage
Glutamate is traditionally viewed as the first messenger to activate N-methyl-D-aspartate receptors (NMDARs) and downstream cell death pathways in stroke, but unsuccessful clinical trials with NMDAR antagonists implicate the engagement of other NMDAR-independent mechanisms. Here we show that glutamate and its structural analogs, in-cluding NMDAR antagonist L-AP5 (or APV), robustly potentiated currents mediated by acid-sensing ion channels (ASICs) which are known for driving acidosis-induced neurotox-icity in stroke. Glutamate increased the proton affinity and open probability of ASICs, ag-gravating ischemic neurotoxicity in both in vitro and in vivo models. Site-directed mutagen-esis and structure-based in silico molecular docking and simulations uncovered a novel glu-tamate binding cavity in the extracellular domain of ASIC1a. Computational drug screen-ing of NMDAR competitive antagonist analogs identified a small molecule, LK-2, that binds to this cavity and abolishes glutamate-dependent potentiation of ASIC currents but spares NMDARs, providing strong neuroprotection efficacy comparable to that in ASIC1a or other cation ion channel knockout mouse models. We conclude that glutamate serves as the first messenger for ASICs to exacerbate neurotoxicity, and that selective blockage of glutamate binding sites on ASICs without affecting NMDARs may be of strategic im-portance for developing effective stroke therapeutics devoid of the psychotic side effects of NMDAR antagonists.