BACKGROUND: Exposure to chronic psychological stress is a risk factor for metabolic cardiovascular disease. Given the important role of lysosomal CTSS (cathepsin S) in human pathobiology, we examined the role of CTSS in stress-related thrombosis, focusing on inflammation, oxidative stress, and apoptosis. METHODS: Six-week-old wild-type mice (CTSS+/+) and CTSS-deficient mice (CTSS-/-) randomly assigned to nonstress and 2-week immobilization stress groups underwent iron chloride3 (FeCl3)-induced carotid thrombosis surgery for morphological and biochemical studies. RESULTS: On day 14 poststress/surgery, stress had increased the lengths and weights of thrombi in the CTSS+/+ mice, plus harmful changes in the levels of PAI-1 (plasminogen activation inhibitor-1), ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 13 motifs), and vWF (von Willebrand factor) and arterial tissue CTSS expression. Compared to the nonstressed CTSS+/+ mice, the stressed CTSS-/- mice had decreased levels of PAI-1, vWF, TNF (tumor necrosis factor)-α, interleukin-1ß, toll-like receptor-4, cleaved-caspase 3, cytochrome c, p16INK4A, gp91phox, p22phox, ICAM-1 (intercellular adhesion molecule-1), MCP-1 (monocyte chemoattractant protein-1), MyD88 (myeloid differentiation primary response 88), and MMP (matrix metalloproteinase)-2/-9 and increased levels of ADAMTS13, SOD (superoxide dismutase)-1/-2, eNOS (endothelial NO synthase), p-Akt (phospho-protein kinase B), Bcl-2 (B-cell lymphoma-2), p-GSK3α/ß (phospho-glycogen synthase kinases alpha and beta), and p-Erk1/2 (phospho-extracellular signal-regulated kinase 1 and 2) mRNAs and/or proteins. CTSS deletion also reduced the arterial thrombus area and endothelial loss. A pharmacological inhibition of CTSS exerted a vasculoprotective action. In vitro, CTSS silencing and overexpression, respectively, reduced and increased the stressed serum and oxidative stress-induced apoptosis of human umbilical vein endothelial cells, and they altered apoptosis-related proteins. CONCLUSIONS: CTSS inhibition appeared to improve the stress-related thrombosis in mice that underwent FeCl3-induction surgery, possibly by reducing vascular inflammation, oxidative stress, and apoptosis. CTSS could thus become a candidate therapeutic target for chronic psychological stress-related thrombotic events in metabolic cardiovascular disease.