Hydrogen sulfide (H₂S) has been recognized as a smooth muscle relaxant. Cystathionine γ-lyase, which is localized to smooth muscle, is thought to be the major H₂S-producing enzyme in the thoracic aorta. Here we show that 3-mercaptopyruvate sulfurtransferase (3MST) and cysteine aminotransferase (CAT) are localized to vascular endothelium in the thoracic aorta and produce H₂S. Both 3MST and CAT were localized to endothelium. Lysates of vascular endothelial cells produced H₂S from cysteine and α-ketoglutarate. The present study provides a new insight into the production and release of H₂S as a smooth muscle relaxant from vascular endothelium.

Accumulating evidence shows that hydrogen sulfide (H ₂ S) has a variety of physiological functions. H ₂ S is produced from cysteine by 3 sulfurtransferases. H ₂ S, in turn, generates polysulfides, the functions of which are not well understood. H ₂ S induces Ca ²⁺ influx in astrocytes, a type of glia. However, the receptor that mediates the response has not been identified. Here, we have shown that polysulfides induce Ca ²⁺ influx by activating transient receptor potential (TRP)A1 channels in rat astrocytes (EC ₅₀ 91 nM, Hill coefficient value 1.77±0.26) and that the maximum response was induced at 0.5 μM, which is 1/320 of the concentration of H ₂ S required to achieve a response of similar magnitude (160 μM, EC ₅₀ 116 μM). TRPA1‐selective agonists, allyl isothiocyanate and cinnamaldehyde, induced Ca ²⁺ influx, and responses to polysulfides were suppressed by TRPA1‐selective inhibitors, HC‐030031 and AP‐18, as well as by siRNAs selective to TRPA1. The present study suggests that polysulfides are possible H ₂ S‐derived signaling molecules that stimulate TRP channels in the brain.—Kimura, Y., Mikami, Y., Osumi, K., Tsugane, M., Oka, J., Kimura, H. Polysulfides are possible H ₂ S‐derived signaling molecules in rat brain. FASEB J. 27, 2451–2457 (2013). www.fasebj.org

H₂S (hydrogen sulfide) has recently been recognized as a signalling molecule as well as a cytoprotectant. We recently demonstrated that 3MST (3-mercaptopyruvate sulfurtransferase) produces H₂S from 3MP (3-mercaptopyruvate). Although a reducing substance is required for an intermediate persulfide at the active site of 3MST to release H₂S, the substance has not been identified. In the present study we show that Trx (thioredoxin) and DHLA (dihydrolipoic acid) associate with 3MST to release H₂S. Other reducing substances, such as NADPH, NADH, GSH, cysteine and CoA, did not have any effect on the reaction. We also show that 3MST produces H₂S from thiosulfate. The present study provides a new insight into a mechanism for the production of H₂S by 3MST.

Hydrogen sulfide (H₂S) has recently been recognized as a signaling molecule as well as a cytoprotectant. Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) are well-known as H₂S-producing enzymes. We recently demonstrated that 3-mercaptopyruvate sulfurtransferase (3MST) along with cysteine aminotransferase (CAT) produces H₂S in the brain and in vascular endothelium. However, the cellular distribution and regulation of these enzymes are not well understood. Here we show that 3MST and CAT are localized to retinal neurons and that the production of H₂S is regulated by Ca²⁺; H₂S, in turn, regulates Ca²⁺ influx into photoreceptor cells by activating vacuolar type H⁺-ATPase (V-ATPase). We also show that H₂S protects retinal neurons from light-induced degeneration. The excessive levels of light exposure deteriorated photoreceptor cells and increased the number of TUNEL- and 8-hydroxy-2′-deoxyguanosine (8-OHdG)-positive cells. Degeneration was greatly suppressed in the retina of mice administered with NaHS, a donor of H₂S. The present study provides a new insight into the regulation of H₂S production and the modulation of the retinal transmission by H₂S. It also shows a cytoprotective effect of H₂S on retinal neurons and provides a basis for the therapeutic target for retinal degeneration.