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

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.

Versatility of the complement system in neuroinflammation, neurodegeneration and brain homeostasis

“…It has been demonstrated that MASP-1 induces p38- mitogen-activated protein kinases (MAPK) activation, NFkappaB signaling and Ca 2+ mobilization in HUVECs, inducing IL-6 and IL-8 production (Jani et al, 2014) as well as E-selectin expression (Dobó et al, 2014). MASP-1, like thrombin, also activates endothelial cells directly by cleaving the protease activated receptors (PARs; Megyeri et al, 2009). Other complement components have been demonstrated to interact with endothelial cells and promote vascular toxicity.…”

15 Kallikrein-related Peptidases (KLKs), Proteinase-mediated Signaling and Proteinase-activated Receptors (PARs)

“…We now suggest that crosstalk of coagulation enzymes with other proteolytic cascades, like those of the complement (Oikonomopoulou et al, 2012) and the KLK system (Blaber et al, 2010), can similarly play an amplification role to activate PAR signaling. In particular, the cross-relationship between the MASP-1 complement proteinase and endothelium-dependent PAR4 signaling supports this hypothesis (Megyeri et al, 2009). This kind of 'proteolytic cascade'-driven PAR signaling is likely to play a role not only in the inflammatory response, but also in the setting of tumorigenesis, as outlined in the following sections.…”

Is complement a culprit in infection-induced forms of haemolytic uraemic syndrome?

“…All three complement pathways have been implicated in EC activation (Heinen et al 2007;Megyeri et al 2009;Zhang et al 2007). The products of the terminal complement pathway (C5a and C5b-9) have direct effects on ECs.…”