Platelets link coagulation and complement in regulating murine placental vascular development
Arno Smid1, Lisa Schumann1, Olga Oleshko2
1Institute of Clinical Biochemistry, Hannover Medical School, Hannover, Germany.
The Journal of Clinical Investigation
|July 23, 2026
Summary
Placental microthrombi (PMTs) are crucial for regulating maternal blood flow during early pregnancy. Their formation involves platelets and complement, and their absence causes bleeding, while dysregulation leads to placental failure.
Area of Science:
- Reproductive biology
- Immunology
- Hematology
Background:
- Maternal blood flow regulation is critical for early placental development.
- Placental microthrombi (PMTs) are identified as key structures in this process.
- PMTs involve platelets, coagulation, and complement systems.
Purpose of the Study:
- To investigate the role of platelet activation via protease-activated receptor 4 (PAR4) in PMT formation.
- To determine the contribution of complement activation to placental thrombosis and bleeding.
- To elucidate the interplay between coagulation and complement in placental vascular development.
Main Methods:
- Utilized PAR4-deficient and C3-deficient mouse models.
- Examined CMP-sialic acid synthase-deficient (Cmas-/-) mice with dysregulated complement activation.
- Assessed placental development, implantation site bleeding, and thromboinflammation.
Main Results:
- PAR4 deficiency abolished PMTs and led to implantation site bleeding.
- C3 deficiency increased bleeding, indicating complement's role in placental thrombosis.
- Dysregulated complement in Cmas-/- mice caused thrombosis and failed placental development.
- Platelet activation via PAR4 localized complement activation to trophoblast surfaces, coupling coagulation and complement.
- Maternal platelet depletion mitigated thromboinflammation in Cmas-/- pregnancies, restoring placental growth.
Conclusions:
- Platelets, coagulation, and complement cooperate critically in establishing maternal placental blood flow.
- Successful pregnancy necessitates balanced activation and regulation of these systems to prevent pathological thrombosis.
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