Background: Pyroptosis, an inflammatory cell death, is involved in the progression of atherosclerosis. Pyroptosis in endothelial cells (ECs) and its underlying mechanisms in atherosclerosis are poorly understood. Here, we investigated the role of a caspase-4/5-NF-κB pathway in pyroptosis in palmitic acid (PA)-stimulated ECs and EVs as players in pyroptosis. Methods: Human umbilical vein endothelial cells (HUVECs) were cultured in an endothelial cell medium, treated with Ox-LDL, PA, caspase-4/5 inhibitor, NF-κB inhibitor, and sEV release inhibitor for 24 h, respectively. The cytotoxicity of PA was determined using an MTT assay, cell migration using a scratch-wound-healing assay, cell morphology using bright field microscopy, and lipid deposition using oil red O staining. The mRNA and protein expression of GSDM-D, CASP4, CASP5, NF-κB, NLRP3, IL-1β, and IL-18 were determined with RT-PCR and Western blot. Immunofluorescence was used to determine NLRP3 and ICAM-1 expressions. Extracellular vesicles (EVs) were isolated using an exosome isolation kit and were characterized by Western blot and scanning electron microscopy. Results: PA stimulation significantly changed the morphology of the HUVECs characterized by cell swelling, plasma membrane rupture, and increased LDH release, which are features of pyroptosis. PA significantly increased lipid accumulation and reduced cell migration. PA also triggered inflammation and endothelial dysfunction, as evidenced by NLRP3 activation, upregulation of ICAM-1 (endothelial activation marker), and pyroptotic markers (NLRP3, GSDM-D, IL-1β, IL-18). Inhibition of caspase-4/5 (Ac-FLTD-CMK) and NF-κB (trifluoroacetate salt (TFA)) resulted in a significant reduction in LDH release and expression of caspase-4/5, NF-κB, and gasdermin D (GSDM-D) in PA-treated HUVECs. Furthermore, GW4869, an exosome release inhibitor, markedly reduced LDH release in PA-stimulated HUVECs. EVs derived from PA-treated HUVECs exacerbated pyroptosis, as indicated by significantly increased LDH release and augmented expression of GSDM-D, NF-κB. Conclusions: The present study revealed that inflammatory, non-canonical caspase-4/5-NF-κB signaling may be one of the crucial mechanistic pathways associated with pyroptosis in ECs, and pyroptotic EVs facilitated pyroptosis in normal ECs during atherosclerosis.

Evogliptin, an anti-diabetic drug had positive impact on various cardiovascular events including inflammation and vascular calcification (VC), an active process driven by vascular smooth muscle cell (VSMC) phenotypic transition. Sphingolipids such as ceramide (CER) mediates inflammation and VC in the vascular tissue. We investigated whether evogliptin ameliorate phenotypic transition and pyroptosis in VSMCs as underlying cause of VC. In cultured VSMCs, isolated from the aorta of (C57/BL6) mouse, we observed more severe calcification with prior treatment of CER in P _i -treated VSMCs as detected by Alizarin Red Staining. Prior CER- stimulation led to a marked upregulation of osteogenic markers such as RUNX2, OPN, BMP2 and decreased contractile markers SM22-α and α- SMA in P _i -treated VSMCs as compared to control cells. In addition, increased expression of pyroptotic markers such as NLRP3, GSDM-D, IL-1 β , IL-18, and LDH release was observed with prior treatment of CER in P _i -treated VSMCs as compared to control cells. Furthermore, MCC950 (NLRP3 inhibitor), disulfiram (GSDM-D inhibitor) and evogliptin significantly downregulated osteogenic and pyroptotic markers including LDH release in both P _i ‐induced only and CER + P _i -treated VSMCs. Moreover, GW4869 (SMase inhibitor) and evogliptin significantly reduced SMase activity in sphingomyelin (SM)-induced VSMCs as compared to both P _i and SM only-treated groups. Also, the cleavage efficiency of GSDM-D was high in P _i and CER + P _i groups which was reduced with prior treatment of evogliptin. Hence, our data demonstrate that evogliptin alleviates VC by blocking phenotypic transition and associated pyroptosis via modulation of NLRP3/GSDM-D mediated pathway in CER-induced VSMCs.