Salvianolic Acid B Suppresses ER Stress-Induced NLRP3 Inflammasome and Pyroptosis via AMPK/FoxO4 and Syndecan-4/Rac1 Signal Pathways in Human Endothelial Progenitor Cells

Abstract

Increasing evidence demonstrates that uncontrolled endoplasmic reticulum (ER) stress responses can activate the inflammasome, which often leads to endothelial dysfunction that underlies the pathogenesis of chronic inflammatory diseases such as atherosclerosis. Salvianolic acid B (SalB), a bioactive compound isolated from Radix Salviae, has been reported to exert anti-oxidative and anti-inflammatory activities in various types of cells. However, the effect of SalB on ER stress-related inflammasome and endothelial dysfunction has not been studied. In the present study, we demonstrated that SalB substantially abrogated ER stress-induced cell death and reduction in capillary tube formation that was linked to declined intracellular reactive oxygen species (ROS) levels, restored mitochondrial membrane potential (MMP), and increased expression of HO-1 and SOD2 in bone marrow-derived endothelial progenitor cells (BM-EPCs). Inhibition of ER stress by CHOP or caspase-4 siRNA transfection attenuated the protective effect of SalB. Furthermore, SalB alleviates ER stress-mediated pyroptotic cell death via suppression of TXNIP/NLRP3 inflammasome activation, as evidenced by decrease in cleavage of caspase-1 and downstream mature interleukin (IL)-1β and IL-18 secretion. Furthermore, our results provide mechanistic evidence that modulation of AMPK/FoxO4/KLF2 and Syndecan-4/Rac1/ATF2 signaling pathways by SalB significantly protected BM-EPCs against cell injury caused by ER stress via reduction of intracellular ROS levels and NLRP3-dependent pyroptosis. In summary, our findings identify that ER stress-induced mitochondrial ROS release and NLRP3 assembly in BM-EPCs, while SalB inhibit NLRP3 inflammasome-mediated pyroptotic cell death via regulating novel AMPK/FoxO4/KLF2 and Syndecan-4/Rac1/ATF2 signaling pathways. These findings suggest SalB to be a potential new agent with applications in the fields of atherosclerotic heart disease. Funding Information: The project was supported by grants from the National Natural Science Foundation of China (No. 81503281), Natural Science Foundation of Guangdong Province (No. 2021A1515011257), Science and Technology Planning Project of Guangzhou (No. 201904010109), Joint Funds of Natural Science Foundation of Guangdong Province (No. 2020B1515120094), and the Talent Grant of Sun Yat-sen University (No. 18ykpy11). Declaration of Interests: The authors declare that there is no conflict of interest to reveal. Ethics Approval Statement: Informed consent for bone marrow collection was obtained from healthy volunteers. All procedures were performed in accordance with the guidance and approval of the local institutional review board (approval no. 2016[130]).