P24 Cystathionine-γ-lyase/hydrogen sulfide system maintains cellular redox homeostasis via glutathione recycling

Abstract

Cystathionine-γ-lyase (CSE) is one of the major enzymatic pathways which responsible for endogenous hydrogen sulfide (H2S) production, particularly in liver, kidney, intestine and smooth muscle tissues. Several previous studies have elucidated that CSE/H2S system plays a crucial role in oxidative biology. In this study, we demonstrated that silencing of CSE protein expression using RNAi or inhibition of CSE activity using inhibitor propargylglycine (PAG) sensitized human hepatocellular carcinoma HepG2, human embryonic kidney cell HEK293 and normal human lung fibroblast IMR90 to hydrogen peroxide (H2O2)-induced cell death. The enhanced H2O2 sensitivity was contributed by an increased oxidative stress experienced by cells upon CSE deficient. CSE knock down or PAG administration significantly increased several oxidative markers in all the three cell lines. We further evaluated that the increase of oxidative stress was due to lack of CSE catalytic activity to produce H2S by using site-directed mutated CSE [1] . Catalytic null CSE mutants did not produce H2S in in vitro enzymatic assays and resulted in similar or higher production of oxidative markers as compared to CSE knock down. On the other hand, catalytic enhanced CSE mutant which produced significantly higher H2S resulted in a reduction of oxidative markers. Furthermore, using exogenous H2S, we showed that H2S exhibited anti-oxidative property via increasing endogenous glutathione level and promoting glutathione recycling. This study provides evidences that CSE/H2S system regulates cellular redox homeostasis and highlights the important involvement of H2S in cellular anti-oxidative defence, particularly in maintenance of glutathione level.