Detrimental interactions of hypoxia and complement MASP-1 in endothelial cells as a model for atherosclerosis-related diseases.

Both hypoxia and the complement lectin pathway (CLP) are involved in atherosclerosis and atherosclerosis-related stroke and acute myocardial infarction (AMI). We have previously shown that mannose-binding lectin-associated serine protease-1 (MASP-1), the most abundant enzyme of CLP, induces an inflammatory phenotype of endothelial cells (ECs) by cleaving protease activated receptors (PARs). In the absence of data, we aimed to investigate whether hypoxia and MASP-1 interact at the level of ECs, to better understand their role in atherosclerosis-related diseases. Hypoxia attenuated the wound healing ability of ECs, increased ICAM-1 and decreased ICAM-2 expression and upregulated PAR2 gene expression. Hypoxia and MASP-1 increased GROα and IL-8 production, and endothelial permeability without potentiating each other's effects, whereas they cooperatively disrupted vascular network integrity, activated the Ca2+, CREB and NFκB signaling pathways, and upregulated the expression of E-selectin, a crucial adhesion molecule in neutrophil homing. VCAM-1 expression was not influenced either by hypoxia, or by MASP-1. In summary, hypoxia potentiates the effect of MASP-1 on ECs, at least partially by increasing PAR expression, resulting in interaction at several levels, which may altogether exacerbate stroke and AMI progression. Our findings suggest that MASP-1 is a potential drug target in the acute phase of atherosclerosis-related diseases.

Complement MASP-1 Modifies Endothelial Wound Healing.

Endothelial wound-healing processes are fundamental for the maintenance and restoration of the circulatory system and are greatly affected by the factors present in the blood. We have previously shown that the complement protein mannan-binding lectin-associated serine protease-1 (MASP-1) induces the proinflammatory activation of endothelial cells and is able to cooperate with other proinflammatory activators. Our aim was to investigate the combined effect of mechanical wounding and MASP-1 on endothelial cells. Transcriptomic analysis showed that MASP-1 alters the expression of wound-healing-related and angiogenesis-related genes. Both wounding and MASP-1 induced Ca2+ mobilization when applied individually. However, MASP-1-induced Ca2+ mobilization was inhibited when the treatment was preceded by wounding. Mechanical wounding promoted CREB phosphorylation, and the presence of MASP-1 enhanced this effect. Wounding induced ICAM-1 and VCAM-1 expression on endothelial cells, and MASP-1 pretreatment further increased VCAM-1 levels. MASP-1 played a role in the subsequent stages of angiogenesis, facilitating the breakdown of the endothelial capillary network on Matrigel®. Our findings extend our general understanding of endothelial wound healing and highlight the importance of complement MASP-1 activation in wound-healing processes.

The Lectin Pathway of the Complement System-Activation, Regulation, Disease Connections and Interplay with Other (Proteolytic) Systems.

The complement system is the other major proteolytic cascade in the blood of vertebrates besides the coagulation-fibrinolytic system. Among the three main activation routes of complement, the lectin pathway (LP) has been discovered the latest, and it is still the subject of intense research. Mannose-binding lectin (MBL), other collectins, and ficolins are collectively termed as the pattern recognition molecules (PRMs) of the LP, and they are responsible for targeting LP activation to molecular patterns, e.g., on bacteria. MBL-associated serine proteases (MASPs) are the effectors, while MBL-associated proteins (MAps) have regulatory functions. Two serine protease components, MASP-1 and MASP-2, trigger the LP activation, while the third component, MASP-3, is involved in the function of the alternative pathway (AP) of complement. Besides their functions within the complement system, certain LP components have secondary ("moonlighting") functions, e.g., in embryonic development. They also contribute to blood coagulation, and some might have tumor suppressing roles. Uncontrolled complement activation can contribute to the progression of many diseases (e.g., stroke, kidney diseases, thrombotic complications, and COVID-19). In most cases, the lectin pathway has also been implicated. In this review, we summarize the history of the lectin pathway, introduce their components, describe its activation and regulation, its roles within the complement cascade, its connections to blood coagulation, and its direct cellular effects. Special emphasis is placed on disease connections and the non-canonical functions of LP components.