Hydrogen sulfide induced neuronal cell death occurs via glutamate receptor and is associated with calpain activation and lysosomal rupture in mouse primary cortical neurons

Hydrogen sulfide (H2S) is a cytotoxic gas recently proposed as a novel neuromodulator. Endogenous levels of H2S in the brain range between 50 and 160 ¦ÌM and perturbed H2S synthesis has been reported in the brains from stroke, Alzheimer's disease and Down syndrome patients. Recently, in immature non-glutamate receptor expressing mouse cortical neurons H2S was shown to inhibit cell death exhibited by high concentrations of glutamate whereas H2S was not cytotoxic. Due to the reported role of H2S in facilitating LTP through NMDA receptors we examined the effects of H2S on glutamate receptor functioning using mature cortical neurons expressing functional glutamate receptor subtypes. Addition of 100 ¦ÌM glutamate exhibited extensive cell death which was exacerbated by co-incubation with ¡Ü200 ¦ÌM of the H2S donor sodium hydrosulfide (NaHS). At <200 ¦ÌM NaHS induced apoptosis whereas >200 ¦ÌM NaHS induced necrosis. Cell death was inhibited by pharmacological glutamate receptor antagonists MK801 and APV (NMDA receptor antagonists), and CNQX (kainate and AMPA receptor antagonist) but not kynurenate (broad spectrum glutamate receptor antagonist), GYKI52466 (more selective AMPA receptor antagonist) and CYZ (AMPA receptor potentiator). Although markers of apoptosis were observed, we did not detect caspase activation either by Western blotting or fluorescence assays and caspase inhibitors did not prevent cell death. Rather, H2S induced calpain activation and lysosomal membrane destabilization; processes inhibited by preferential antagonists of NMDA and kainate receptors. These data suggest that H2S induced neuronal death through ionotropic glutamate receptors, which recruits apoptosis to ensure cellular demise and employs calpains and lysosomal rupture. This study provides novel insights into cell death observed in neurodegenerative diseases involving glutamate receptor activation and perturbed H2S synthesis.