Serum MASP-1 in complex with MBL activates endothelial cells

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• The complement system is crucial for inflammation.
• Mannose-binding lectin (MBL) and associated serine proteases (MASPs) form initiation complexes in the lectin pathway.
• Endothelial cells are key players in inflammatory responses.

Purpose of the Study:

• To investigate the role of MBL-MASP complexes in activating endothelial cells.
• To determine which specific MASP proteases are responsible for endothelial cell activation.
• To elucidate the mechanism by which MASP-1 activates endothelial cells.

Main Methods:

• Utilized cultured human umbilical vein endothelial cells (HUVECs).
• Employed recombinant catalytic fragments and N-terminal domains of MASP-1, MASP-2, and MASP-3.
• Tested a stable zymogen mutant form of MASP-1.
• Assessed Ca(2+) signaling in HUVECs as a measure of activation.

Main Results:

• MBL-MASP complexes, specifically MASP-1, elicit Ca(2+) signaling in HUVECs.
• Recombinant catalytic fragments of MASP-2 and MASP-3, as well as non-enzymatic domains of MASP-1 and MASP-2, did not activate HUVECs.
• The proteolytic activity of MASP-1 is essential for endothelial cell activation.
• MASP-1 can directly activate endothelial cells, independent of lectin pathway activation.

Conclusions:

• MASP-1 is the sole component of MBL-MASP complexes capable of triggering endothelial cell activation.
• The proteolytic activity of MASP-1 is critical for its function in endothelial cell stimulation.
• MASP-1 plays a pivotal role in the early stages of innate immune responses by activating endothelial cells.