Hydrogen sulfide mitigates ox‑LDL‑induced NLRP3/caspase‑1/GSDMD dependent macrophage pyroptosis by S‑sulfhydrating caspase‑1

Abstract

Macrophage pyroptosis mediates vascular inflammation and atherosclerosis (AS). Hydrogen sulfide (H 2 S) exerts a protective role in preventing inflammation and AS. However, its molecular mechanisms of regulating the pyroptosis signaling pathway and inhibiting macrophage pyroptosis remain unexplored. The present study aimed to determine whether H 2 S mitigates macrophage pyroptosis by downregulating the pyroptosis signaling pathway and S-sulfhydrating caspase-1 under the stimulation of oxidized low-density lipoprotein (ox-LDL), a pro-atherosclerotic factor. Macrophages derived from THP-1 monocytes were pre-treated using exogenous H 2 S donors sodium hydrosulfide (NaHS) and D,L-propargylglycine (PAG), a pharmacological inhibitor of endogenous H 2 S-producing enzymes, alone or in combination. Subsequently, cells were stimulated with ox-LDL or the desulfhydration reagent dithiothreitol (DTT) in the presence or absence of NaHS and/or PAG. Following treatment, the levels of H 2 S in THP-1 derived macrophages were measured by a methylene blue colorimetric assay. The pyroptotic phenotype of THP-1 cells was observed and evaluated by light microscopy, Hoechst 33342/propidium iodide fluorescent staining and lactate dehydrogenase (LDH) release assay. Caspase-1 activity in THP-1 cells was assayed by caspase-1 activity assay kit. Immunofluorescence staining was used to assess the accumulation of active caspase-1. Western blotting and ELISA were performed to determine the expression of pyroptosis-specific markers (NLRP3, pro-caspase-1, caspase-1, GSDMD and GSDMD-N) in cells and the secretion of pyroptosis-related cytokines [interleukin (IL)-1β and IL-18] in the cell-free media, respectively. The S-sulfhydration of pro-caspase-1 in cells was assessed using a biotin switch assay. ox-LDL significantly induced macrophage pyroptosis by activating the pyroptosis signaling pathway. Inhibition of endogenous H 2 S synthesis by PAG augmented the pro-pyroptotic effects of ox-LDL. Conversely, exogenous H 2 S (NaHS) ameliorated ox-LDL-and ox-LDL + PAG-induced macrophage pyroptosis by suppressing the activation of the pyroptosis signaling pathway. Mechanistically, ox-LDL and the DTT increased caspase-1 activity and downstream events (IL-1β and IL-18 secretion) of the caspase-1-dependent pyroptosis pathway by reducing S-sulfhydration of pro-caspase-1. Conversely, NaHS increased S-sulfhydration of pro-caspase-1, reducing caspase-1 activity and caspase-1-dependent macrophage pyroptosis. The present study demonstrated the molecular mechanism by which H 2 S ameliorates macrophage pyroptosis by suppressing the pyroptosis signaling pathway and S-sulfhydration of pro-caspase-1, thereby suppressing the generation of active caspase-1 and activity of caspase-1.