Complex formation with pentraxin-2 regulates factor X plasma levels and macrophage interactions

Area of Science:

• Biochemistry
• Immunology
• Hematology

Background:

• Scavenger receptor class A member I (SR-AI) acts as a receptor for coagulation factor X (FX), creating an FX reservoir on macrophages.
• The interaction between FX and SR-AI influences macrophage function and coagulation processes.

Purpose of the Study:

• To identify additional proteins involved in the FX/SR-AI complex.
• To elucidate the role of pentraxin-2 (PTX2) in the FX/SR-AI interaction and its impact on protein stability and plasma levels.

Main Methods:

• Immunoprecipitation experiments to detect protein complexes in plasma.
• Binding studies to quantify interactions between FX, SR-AI, and PTX2.
• Short hairpin RNA (shRNA)-mediated knockdown of PTX2 in mice.
• Analysis of FX and PTX2 levels in SR-AI-deficient mice and human plasma samples.

Main Results:

• Pentraxin-2 (PTX2) is identified as a third component of the FX/SR-AI complex.
• PTX2 and FX are essential for preventing each other's internalization by SR-AI.
• FX and PTX2 circulate as a complex in plasma, involving the FX activation peptide.
• PTX2 and FX levels are interdependent in mice and humans, with reduced levels observed in SR-AI-deficient mice and patients with FX deficiency.

Conclusions:

• PTX2 is a novel binding partner for FX, and together they prevent SR-AI-mediated macrophage uptake.
• The interdependent plasma levels of FX and PTX2 have clinical relevance, particularly concerning PTX2-targeted therapies for systemic amyloidosis.