Mast cell-derived exosomes activate endothelial cells to secrete plasminogen activator inhibitor type 1

Abstract

Objective - Previous studies supported the contribution of exosomes to an acellular mode of communication, leading to intercellular transfer of molecules. In this study we provide evidence that mast cell-derived exosomes induce plasminogen activator inhibitor type 1 (PAI-1) expression in endothelial cells, detectable at the level of PAI-1 mRNA and protein synthesis. The stimulating effect was also measured at the level of PAI-1 promoter activity. Methods and Results - To identify components responsible for this activity, exosome proteins were separated by 2-dimensional PAGE, and protein spots were identified by microsequencing using electrospray (IS1-Q-TOF-Micromass) spectrometer. Components of 3 independent systems that can be involved in activation of endothelial cells, namely the prothrombinase complex, tumor necrosis factor-α, and angiotensinogen precursors were identified. Procoagulant activity of exosomes was confirmed by a thrombin generation assay using a specific chromogenic substrate. Because the potential of mast cell-derived exosomes to induce PAI-1 expression was completely abolished by hirudin, thrombin generated on exosomes seems to be responsible for this activity. Conclusions - It can be concluded that mast cell-derived exosomes via significant upregulation of PAI-1 secretion from endothelial cells may provide feedback between the characteristically increased PAI-1 levels and procoagulant states, both observed in diverse syndromes manifesting as endothelial cell dysfunction. © 2005 American Heart Association, Inc.