Redox proteomics workflow to unveil extracellular targets of oxidation in vascular endothelial cells.

Redox regulation has emerged as a key process in cellular signaling. The role of extracellular cell surface redox-sensitive proteins in redox regulation and intracellular communication has been supported by secretion of oxidoreductases that modulate thiol-disulfide switches. Despite these advances, redox-sensitive targets on the cell surface remain little explored. We established a comprehensive redox proteomic workflow using plasma membrane impermeable thiol labeling where we identified 1159 cell surface and extracellular proteins susceptible to oxidation. Treatment with diamide or urate hydroperoxide (HOOU) resulted in 377 and 12 differentially abundant redox-modulated proteins compared to control. Such proteins represent chaperones, adhesion molecules, vesicle-associated proteins, channels, receptors, cytoskeleton, and others, which may play a relevant role in several signaling pathway. Eleven oxidoreductases were redox-modulated by diamide, including members of the protein disulfide isomerase (PDI), peroxiredoxin (PRDX), and quiescin sulfhydryl oxidase (QSOX) families, with a particular focus on PDI TMX3 (TMX3), which provides the first evidence of its secretion in endothelial cells. In conclusion, our findings not only revealed potential redox-sensitive targets on the cell surface but also offer a useful tool for future investigations aiming to analyze redox regulation in the extracellular environment across diverse biological contexts. SIGNIFICANCE: Redox signaling at the cell surface is emerging as a crucial regulator of vascular function, emphasizing its role in cardiovascular disease. However, the extracellular redox proteome remains underexplored because of the complexity of the method. We developed a reproducible workflow combining differential thiol labeling and mass spectrometry to systematically map oxidized extracellular proteins in endothelial cells exposed to oxidants. Hundreds of proteins were identified as redox-sensitive targets. Key functional groups included molecular chaperones, adhesion molecules, vesicle-associated proteins, channels, receptors, and cytoskeleton. This work reveals novel insights into extracellular redox regulation, expands the repertoire of known redox-sensitive proteins, and establishes a versatile platform to investigate redox dynamics at cell surface both in vascular biology and other pathophysiological contexts.