RXR Ligands Negatively Regulate Thrombosis and Hemostasis.

Area of Science:

• Hematology
• Molecular Biology
• Pharmacology

Background:

• Platelets express retinoid X receptors (RXRα and RXRβ).
• RXR ligands inhibit platelet responses to ADP and thromboxane A2.
• The broader impact of RXR ligands on platelet function and their mechanisms remain unclear.

Purpose of the Study:

• To investigate the effects of RXR ligands on platelet function stimulated by collagen receptor (GPVI) agonists and thrombin.
• To elucidate the underlying mechanisms of RXR-mediated regulation of platelet responses.
• To assess the in vitro and in vivo impact of RXR ligands on thrombus formation.

Main Methods:

• Assessed platelet aggregation, granule secretion, integrin activation, calcium mobilization, and integrin αIIbβ3 signaling.
• Evaluated thrombus formation in vitro and thrombosis/hemostasis in vivo.
• Measured protein kinase A activation via VASP S157 phosphorylation.

Main Results:

• RXR ligands attenuated platelet responses to GPVI agonists and thrombin.
• RXR ligands inhibited integrin αIIbβ3 outside-in signaling.
• 9-cis-retinoic acid impaired in vitro and in vivo thrombus formation, thrombosis, and hemostasis.
• RXR ligands stimulated protein kinase A activation in a cAMP and NF-κB dependent manner.

Conclusions:

• RXR plays a significant negative regulatory role in platelet function and thrombus formation.
• RXR ligands upregulate protein kinase A, a known inhibitor of platelet activity.
• This mechanism provides a potential explanation for the cardioprotective effects of RXR ligands in vivo.