Hydrogen Sulfide (H₂S)/Polysulfides (H₂S_n) Signalling and TRPA1 Channels Modification on Sulfur Metabolism

Hydrogen sulfide (H₂S) and polysulfides (H₂S_n, n ≥ 2) produced by enzymes play a role as signalling molecules regulating neurotransmission, vascular tone, cytoprotection, inflammation, oxygen sensing, and energy formation. H₂S_n, which have additional sulfur atoms to H₂S, and other S-sulfurated molecules such as cysteine persulfide and S-sulfurated cysteine residues of proteins, are produced by enzymes including 3-mercaptopyruvate sulfurtransferase (3MST). H₂S_n are also generated by the chemical interaction of H₂S with NO, or to a lesser extent with H₂O₂. S-sulfuration (S-sulfhydration) has been proposed as a mode of action of H₂S and H₂S_n to regulate the activity of target molecules. Recently, we found that H₂S/H₂S₂ regulate the release of neurotransmitters, such as GABA, glutamate, and D-serine, a co-agonist of N-methyl-D-aspartate (NMDA) receptors. H₂S facilitates the induction of hippocampal long-term potentiation, a synaptic model of memory formation, by enhancing the activity of NMDA receptors, while H₂S₂ achieves this by activating transient receptor potential ankyrin 1 (TRPA1) channels in astrocytes, potentially leading to the activation of nearby neurons. The recent findings show the other aspects of TRPA1 channels-that is, the regulation of the levels of sulfur-containing molecules and their metabolizing enzymes. Disturbance of the signalling by H₂S/H₂S_n has been demonstrated to be involved in various diseases, including cognitive and psychiatric diseases. The physiological and pathophysiological roles of these molecules will be discussed.