Complement activation by apoptotic endothelial cells following hypoxia/reoxygenation.

Area of Science:

• Endothelial cell biology
• Immunology
• Inflammation research

Background:

• Reperfusion of ischemic tissue causes inflammation and injury.
• Complement activation on the endothelium contributes to this inflammatory process.

Purpose of the Study:

• Investigate complement activation mechanisms on reoxygenated hypoxic endothelial cells.
• Model complement activation on endothelium in reperfused ischemic tissue.

Main Methods:

• Used hypoxic human umbilical vein endothelial cells (HUVEC) and reoxygenation.
• Assessed apoptosis using Annexin V and hypodiploid nuclei staining.
• Analyzed complement activation via C3 deposition and C1 binding.

Main Results:

• Reoxygenated HUVEC activated the classical complement pathway, leading to C3 deposition.
• Apoptotic HUVEC directly activated complement in the absence of antibodies.
• Complement activation was linked to phosphatidylserine exposure on apoptotic cells.
• Caspase inhibition during reoxygenation abolished complement activation.

Conclusions:

• Oxidative stress during reoxygenation induces endothelial cell apoptosis.
• Apoptotic endothelial cells initiate classical complement pathway activation.
• Endothelial complement activation may drive inflammation and facilitate tissue repair.