AUTHOR=Zhang Da , Wang Xiuli , Tian Xiaoyu , Zhang Lulu , Yang Guosheng , Tao Yinghong , Liang Chen , Li Kun , Yu Xiaoqi , Tang Xinjing , Tang Chaoshu , Zhou Jing , Kong Wei , Du Junbao , Huang Yaqian , Jin Hongfang 

TITLE=The Increased Endogenous Sulfur Dioxide Acts as a Compensatory Mechanism for the Downregulated Endogenous Hydrogen Sulfide Pathway in the Endothelial Cell Inflammation

JOURNAL=Frontiers in Immunology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2018.00882

DOI=10.3389/fimmu.2018.00882

ISSN=1664-3224

ABSTRACT=<p>Endogenous hydrogen sulfide (H<sub>2</sub>S) and sulfur dioxide (SO<sub>2</sub>) are regarded as important regulators to control endothelial cell function and protect endothelial cell against various injuries. In our present study, we aimed to investigate the effect of endogenous H<sub>2</sub>S on the SO<sub>2</sub> generation in the endothelial cells and explore its significance in the endothelial inflammation <italic>in vitro</italic> and <italic>in vivo</italic>. The human umbilical vein endothelial cell (HUVEC) line (EA.hy926), primary HUVECs, primary rat pulmonary artery endothelial cells (RPAECs), and purified aspartate aminotransferase (AAT) protein from pig heart were used for <italic>in vitro</italic> experiments. A rat model of monocrotaline (MCT)-induced pulmonary vascular inflammation was used for <italic>in vivo</italic> experiments. We found that endogenous H<sub>2</sub>S deficiency caused by cystathionine-γ-lyase (CSE) knockdown increased endogenous SO<sub>2</sub> level in endothelial cells and enhanced the enzymatic activity of AAT, a major SO<sub>2</sub> synthesis enzyme, without affecting the expressions of AAT1 and AAT2. While H<sub>2</sub>S donor could reverse the CSE knockdown-induced increase in the endogenous SO<sub>2</sub> level and AAT activity. Moreover, H<sub>2</sub>S donor directly inhibited the activity of purified AAT protein, which was reversed by a thiol reductant DTT. Mechanistically, H<sub>2</sub>S donor sulfhydrated the purified AAT1/2 protein and rescued the decrease in the sulfhydration of AAT1/2 protein in the CSE knockdown endothelial cells. Furthermore, an AAT inhibitor <sc>l</sc>-aspartate-β-hydroxamate (HDX), which blocked the upregulation of endogenous SO<sub>2</sub>/AAT generation induced by CSE knockdown, aggravated CSE knockdown-activated nuclear factor-κB pathway in the endothelial cells and its downstream inflammatory factors including ICAM-1, TNF-α, and IL-6. In <italic>in vivo</italic> experiment, H<sub>2</sub>S donor restored the deficiency of endogenous H<sub>2</sub>S production induced by MCT, and reversed the upregulation of endogenous SO<sub>2</sub>/AAT pathway <italic>via</italic> sulfhydrating AAT1 and AAT2. In accordance with the results of the <italic>in vitro</italic> experiment, HDX exacerbated the pulmonary vascular inflammation induced by the broken endogenous H<sub>2</sub>S production in MCT-treated rat. In conclusion, for the first time, the present study showed that H<sub>2</sub>S inhibited endogenous SO<sub>2</sub> generation by inactivating AAT <italic>via</italic> the sulfhydration of AAT1/2; and the increased endogenous SO<sub>2</sub> generation might play a compensatory role when H<sub>2</sub>S/CSE pathway was downregulated, thereby exerting protective effects in endothelial inflammatory responses <italic>in vitro</italic> and <italic>in vivo</italic>.</p>