P48 Cystathionine gamma lyase mediates its anti-inflammatory and cytoprotective functions through protein sulfhydration

Cystathionine gamma lyase (CSE) also known as γ -cystathionase, is a key enzyme in the transsulfuration pathway leading to the synthesis of glutathione, the major antioxidant in the cell. CSE converts cystathionine to cysteine, the availability of which is the rate limiting step in glutathione biosynthesis. In addition, CSE utilizes cysteine to generate hydrogen sulfide (H 2 S), which is one of the three gasotransmitters, the other two being nitric oxide and carbon monoxide. H 2 S plays an important role in diverse signaling pathways. One of the mechanisms by which H 2 S signals is via the formation of a persulfide (-SSH) bond at reactive Cys residues, a process designated sulfhydration. Using a modified biotin switch assay, we have shown that sulfhydration of target proteins such as cyclooxygenase 2 (COX2) and nuclear factor κ B (NF- κ B) modulates their activity thereby regulating prosurvival and inflammatory responses. Using CSE knockout mice we show that H 2 S functions as an anti-inflammatory and antioxidant molecule in vivo . Depletion of CSE led to a decrease in levels of glutathione and increase in oxidative stress as revealed by protein carbonylation, lipid peroxidation and DNA damage detection assays. Primary hepatocytes and mouse embryo fibroblasts isolated from CSE knockout mice had higher levels of reactive oxygen species and exhibited a higher susceptibility to oxidants such as hydrogen peroxide. Our studies reveal an important role for CSE in the maintenance of redox homeostasis in the cell.