Association between cigarette smoke exposure and immunoproteasome suppression in vascular endothelial cells

Introduction The immunoproteasome is integral to endothelial redox homeostasis and protein quality control; however, its modulation by cigarette smoke remains unclear. We investigated whether cigarette smoke extract (CSE) suppresses immunoproteasome expression and promotes oxidative and inflammatory activation in vascular endothelial cells (VECs). Methods Mouse VECs were exposed to 1.0% CSE for 16 h or treated with the β5i-selective inhibitor ONX-0914 (0.5–1.0 μM, 24–36 h). mRNA expression levels of proteasome subunits, NADPH oxidase 4 (NOX4), and inflammatory mediators were assessed by quantitative PCR. Proteasomal activity and intracellular reactive oxygen species (ROS) were quantified using luminescent assays. β5i expression in small pulmonary arterioles (≤0.5 mm) from smokers (n = 10) and nonsmokers (n = 10) was analyzed by immunohistochemistry. Results CSE significantly suppressed immunoproteasome expression, reducing β5i mRNA by 66% ± 4% ( p = 0.0037) and decreasing proteasomal activity. Treatment with ONX-0914 increased intracellular ROS and upregulated NOX4 and inflammatory mediators, including monocyte chemoattractant protein-1 (approximately 6- to 7-fold at 0.5 μM for 36 h). Reduced endothelial β5i expression was more frequent in smokers than in nonsmokers. Discussion Cigarette smoke-associated β5i suppression is linked to endothelial oxidative stress and inflammation, suggesting a potential mechanism underlying smoking-related vascular dysfunction.