Complement Protease MASP-1 Activates Human Endothelial Cells: PAR4 Activation Is a Link between Complement and Endothelial Function

• DOI: 10.4049/jimmunol.0900879
• Publication Date: 2009-08-11T01:06:32Z
• Authors: Márton Megyeri; Veronika Makó; László Beinrohr; Zoltán Doleschall; Zoltán Prohászka; László Cervenak; Péter Závodszky; Péter Gál
• Keywords: Intracellular Fluid; 0301 basic medicine; 0303 health sciences; MAP Kinase Signaling System; Hydrolysis; NF-kappa B; Membrane Proteins; Complement System Proteins; p38 Mitogen-Activated Protein Kinases; Cell Line; Enzyme Activation; 03 medical and health sciences; Mannose-Binding Protein-Associated Serine Proteases; Humans; Receptors, Thrombin; Calcium Signaling; Endothelium, Vascular; Inflammation Mediators

Abstract Activation of the complement system can induce and enhance inflammatory reaction. Mannose-binding lectin-associated serine protease-1 (MASP-1) is an abundant protease of the complement lectin pathway; however, its physiological function is unclear. In this study, we demonstrate for the first time that MASP-1 is able to activate Ca2+ signaling, NF-κB, and p38 MAPK pathways in cultured HUVECs. Activation was initiated by MASP-1 only; the related protease, MASP-2, had no such effect. The phenomenon was dependent on the proteolytic activity of MASP-1, suggesting modulation of endothelial cell function through a protease-activated receptor (PAR). Using synthetic peptide substrates representing the protease-sensitive regions of PARs, we were able to demonstrate that PAR4 is a target of MASP-1. The presence of functionally active PAR4 in HUVECs was demonstrated using PAR4 agonist peptide and mRNA quantification. Finally, we showed that the amount of membrane-bound intact PAR4 decreases after MASP-1 treatment. All of these results provide a novel link between the regulation of endothelial cell function and complement system activation, and they suggest that MASP-1-induced PAR4 activation could contribute to the development of the inflammatory reaction.