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Hydrogen sulfide (H2S) is a novel gasotransmitter and acts as a multifunctional regulator in various cellular functions. Past studies have demonstrated a significant role of H2S and its generating enzyme cystathionine gamma-lyase (CSE) in the cardiovascular system. Lipopolysaccharide (LPS), a major pathogenic factor, is known to initiate the inflammatory immune response. The cross talk between LPS-induced inflammation and the CSE/H2S system in vascular cells has not yet been elucidated in detail. Here we showed that LPS decreased CSE mRNA and protein expression in human endothelial cells and blocked H2S production in mouse aorta tissues. Transfection of the cells with TLR4-specific siRNA knockdown TLR4 mRNA expression and abolished the inhibitory role of LPS on CSE expression. Higher dose of LPS (100 μg/ml) decreased cell viability, which was reversed by exogenously applied H2S at physiologically relevant concentration (30 μM). Lower dose of LPS (10 μg/ml) had no effect on cell viability, but significantly induced inflammation gene expressions and cytokines secretion and stimulated cell hyper-permeability. H2S treatment prevented LPS-induced inflammation and hyper-permeability. Lower VE-cadherin expression in LPS-incubated cells would contribute to cell hyper-permeability, which was reversed by H2S co-incubation. In addition, H2S treatment blocked LPS-induced NFκB transactivation. We further validated that LPS-induced hyper-permeability was reversed by CSE overexpression but further deteriorated by CRISPR/Cas9-mediated knockout of CSE. In vivo, deficiency of CSE sensitized the mice to LPS-induced inflammation in vascular tissues. Take together, these data suggest that CSE/H2S system protects LPS-induced inflammation and cell hyper-permeability by blocking NFκB transactivation.LPS decreases CSE expression in endothelial cells.CSE/H2S system reverses LPS-induced inflammation and cell hyper-permeability.H2S blocks LPS-induced NFκB transactivation.Deficiency of CSE sensitizes the mice to LPS-induced inflammation.