The C5a/C5a receptor 1 axis controls tissue neovascularization through CXCL4 release from platelets

Area of Science:

• Immunology
• Vascular Biology
• Hematology

Background:

• Platelets play a role in tissue repair and neovascularization.
• The specific molecular mechanisms by which platelets regulate vessel formation remain largely unknown.

Purpose of the Study:

• To investigate the role of complement anaphylatoxin C5a-mediated activation of C5a receptor 1 (C5aR1) on platelets in regulating tissue neovascularization.
• To elucidate the underlying molecular mechanisms and identify key effector molecules involved in this process.

Main Methods:

• Utilized C5aR1 knockout (C5ar1-/-) mice and platelet-specific C5aR1 deletion models.
• Assessed endothelial cell functions (migration, tube formation) in vitro.
• Analyzed vascularization parameters (collateralization, capillarization, pericyte coverage) in vivo.
• Investigated the release of CXC chemokine ligand 4 (CXCL4) from platelets.

Main Results:

• C5aR1 activation on platelets inhibits endothelial cell migration and tube formation, thereby negatively regulating neovascularization.
• Vascularization was significantly increased in C5ar1-/- mice and mice with platelet-specific C5aR1 deletion.
• C5a induced preferential release of the antiangiogenic factor CXCL4 from platelets.
• Blocking the C5aR1-CXCL4 axis reversed the antiangiogenic effect of platelets.

Conclusions:

• Identified a novel mechanism where C5a/C5aR1 axis activation in platelets controls tissue neovascularization.
• Platelet-derived CXCL4, induced by C5a/C5aR1 signaling, acts as a key antiangiogenic effector molecule.
• This pathway represents a potential therapeutic target for modulating neovascularization in various conditions.