Contribution of cysteine aminotransferase and mercaptopyruvate sulfurtransferase to hydrogen sulfide production in peripheral neurons

Hydrogen sulfide (H₂S) is a gaseous neuromodulator produced from L‐cysteine. H₂S is generated by three distinct enzymatic pathways mediated by cystathionine γ‐lyase (CSE), cystathionine β‐synthase (CBS), and mercaptopyruvate sulfurtransferase (MPST) coupled with cysteine aminotransferase (CAT). This study investigated the relative contributions of these three pathways to H₂S production in PC12 cells (rat pheochromocytoma‐derived cells) and the rat dorsal root ganglion. CBS, CAT, and MPST, but not CSE, were expressed in the cells and tissues, and appreciable amounts of H₂S were produced from L‐cysteine in the presence of α‐ketoglutarate, together with dithiothreitol. The production of H₂S was inhibited by a CAT inhibitor (aminooxyacetic acid), competitive CAT substrates (L‐aspartate and oxaloacetate), and RNA interference (RNAi) against MPST. Immunocytochemistry revealed a mitochondrial localization of MPST in PC12 cells and dorsal root ganglion neurons, and the amount of H₂S produced by CAT/MPST at pH 8.0, a physiological mitochondrial matrix pH, was comparable to that produced by CSE and CBS in the liver and the brain, respectively. Furthermore, H₂S production was markedly increased by alkalization. These results indicate that CAT and MPST are primarily responsible for H₂S production in peripheral neurons, and that the regulation of mitochondrial metabolism may influence neuronal H₂S generation.