Human vascular smooth muscle cells express functionally active endothelial cell protein C receptor

Area of Science:

• Vascular biology
• Endothelial cell biology
• Signaling pathways

Background:

• Endothelial cell protein C receptor (EPCR) regulates anticoagulation and signals to endothelial cells.
• Activated protein C (APC) has known signaling roles independent of its anticoagulant function.
• The presence and function of EPCR in vascular smooth muscle cells (SMCs) are not well understood.

Purpose of the Study:

• To investigate the expression and functionality of EPCR in vascular smooth muscle cells (SMCs).
• To determine if APC can signal through EPCR in SMCs and modulate their responses.
• To explore the potential role of EPCR-APC signaling in vascular injury.

Main Methods:

• Detection of EPCR protein and mRNA in SMCs using flow cytometry, Western blotting, and quantitative RT-PCR.
• Analysis of intracellular signaling pathways (calcium transients, ERK-1/2 phosphorylation) in APC-stimulated SMCs.
• Assessment of SMC proliferation using [(3)H]-thymidine incorporation and investigation of EPCR-mediated signaling with antibodies.

Main Results:

• EPCR protein and mRNA were detected in SMCs, indicating EPCR expression.
• APC stimulation of SMCs induced intracellular calcium transients and ERK-1/2 phosphorylation.
• APC-induced signaling was dependent on EPCR binding and protease-activated receptor-1 (PAR-1) cleavage.
• APC promoted SMC proliferation, an effect enhanced by thrombin.
• EPCR was found in SMCs within human carotid artery plaques.

Conclusions:

• Vascular smooth muscle cells express functionally active EPCR.
• EPCR-bound APC can modulate SMC signaling, including mitogenic responses via PAR-1.
• EPCR-APC signaling in SMCs may play a role in the response to vascular injury.