AOC3 (amine oxidase copper containing 3), also known as vascular adhesion protein-1 (VAP-1), is a multifunctional cell-surface enzyme with primary amine oxidase activity 1. AOC3 catalyzes the oxidation of primary amines to produce ammonium, formaldehyde, methylglyoxal, and hydrogen peroxide 1. The protein is primarily expressed by endothelial cells, smooth muscle cells (SMCs), adipocytes, and pericytes 1, and serves as a marker distinguishing myofibroblasts from activated fibroblasts 2. AOC3 regulates immune cell extravasation and leukocyte-endothelial cell adhesion through both enzymatic and adhesive mechanisms 13. In disease contexts, AOC3 contributes significantly to pulmonary fibrosis development by promoting pathogenic leukocyte accumulation and myofibroblast differentiation; AOC3-deficient mice showed 30-50% reduction in fibrosis 3. Similarly, AOC3 knockout increased atherosclerotic plaque formation through vascular smooth muscle cell dedifferentiation and T-cell recruitment 4. In colorectal cancer, AOC3 serves as a cancer-associated fibroblast (CAF) activation marker, with expression downregulated by TGF-β1 treatment 5. AOC3 expression is transcriptionally regulated by myocardin-related transcription factors (MRTFs) and serum response factor in SMCs 6. Additionally, zinc-α2-glycoprotein acts as an allosteric inhibitor of AOC3 7. AOC3 dysregulation has been identified in triple-negative breast cancer metabolic pathways 8.