ASS1 Promotes Atherosclerotic Inflammation Through the NLRP3/IL-33/ST2 Axis in Ox-LDL-Induced Foam Cells

Background: Atherosclerosis is a chronic inflammatory disease characterized by lipid-driven immune dysregulation. Argininosuccinate synthase 1 (ASS1) has been implicated in macrophage inflammation, yet its precise mechanistic role in foam cell-mediated vascular injury during atherosclerosis remains unclear. This study investigates whether ASS1 promotes disease progression via the NLRP3/IL-33/ST2 axis.

Methods: An in vitro foam cell model was established using phorbol 12-myristate 13-acetate (PMA)-differentiated U937 macrophages treated with oxidized low-density lipoprotein (ox-LDL). The role of ASS1 was assessed via knockdown (si-ASS1) and overexpression (ASS1 overexpression) plasmids. Co-culture systems with human umbilical vein endothelial cells (HUVECs) and human aortic vascular smooth muscle cells (HAVSMCs) were used to evaluate endothelial Apoptosis and VSMC proliferation/migration. In vivo, atherosclerosis was induced in Apolipoprotein E‑deficient (apoE)-deficient mice via a 12-week high-fat diet, and ASS1 expression was modulated using AAV9 vectors. Molecular analyses included ROS detection, enzyme-linked immunosorbent assay (ELISA), qPCR, western blot, and immunofluorescence. Plaque burden was assessed via Oil Red O staining.

Results: Ox-LDL treatment significantly upregulated ASS1 expression in U937-derived foam cells. ASS1 overexpression enhanced intracellular ROS production, NLRP3 inflammasome activation, STAT3 phosphorylation, and IL-33 secretion. These effects were reversed by ASS1 knockdown. Rescue experiments demonstrated that STAT3 is required for ASS1-mediated NLRP3 activation and IL-33 upregulation. ASS1 altered IL-33 receptor ST2 signaling by increasing the soluble decoy isoform (sST2) and decreasing the membrane-bound signaling isoform (ST2L). In co-culture, ASS1-overexpressing foam cells promoted HUVEC Apoptosis (via mitochondrial pathway) and HAVSMC proliferation, migration, and dedifferentiation. NLRP3 overexpression alone mimicked the pro-inflammatory effects of ASS1 and reversed the anti-inflammatory effects of ASS1 knockdown. In vivo, ASS1 knockdown in apoE^-/- mice reduced plaque lipid deposition, serum levels of IL-33 and IL-1β, and vascular expression of NLRP3 and p-STAT3, while ASS1 overexpression exacerbated these parameters.

Conclusions: ASS1 drives atherosclerosis by activating the STAT3/NLRP3 inflammasome axis, shifting the IL-33/ST2 balance toward a pro-inflammatory state, and amplifying foam cell-mediated endothelial injury and smooth muscle cell dysfunction. Targeting ASS1 may offer a novel therapeutic strategy for inflammatory vascular disease.

ASS1; IL-33; NLRP3 inflammasome; ST2; atherosclerosis; endothelial cells; foam cells; vascular smooth muscle cells.