USP40 alleviates atherosclerosis by stabilizing SIRT1 to suppress endothelial apoptosis and NLRP3 inflammasome activation.

Atherosclerosis (AS) is a chronic inflammatory vascular disease driven by endothelial dysfunction, and dysregulated ubiquitination has emerged as an important pathogenic mechanism. Although deubiquitinating enzymes (DUBs) are key regulators of protein homeostasis, the role of USP40 in AS remains unknown. Here, we defined the function and mechanism of USP40 in cellular and animal models of AS. USP40 expression was reduced in the aortic endothelium of atherosclerotic mice and in ox-LDL-treated human umbilical vein endothelial cells (HUVECs). In Western diet-fed ApoE-/- mice, AAV9-mediated USP40 overexpression markedly reduced aortic plaque burden, lipid accumulation, collagen deposition, and macrophage infiltration without altering circulating lipid levels. Conversely, USP40 knockdown aggravated ox-LDL-induced endothelial apoptosis and NLRP3 inflammasome activation. Mechanistically, USP40 interacted with SIRT1 and stabilized it by removing K48-linked polyubiquitin chains, thereby preventing proteasomal degradation. SIRT1 depletion substantially reversed the anti-apoptotic and anti-inflammatory effects of USP40. These findings reveal a previously unrecognized USP40/SIRT1 axis that protects the endothelium and limits atherosclerosis, highlighting USP40 as a potential therapeutic target for AS.