Non-genomic effects of the Pregnane X Receptor negatively regulate platelet functions, thrombosis and haemostasis

Abstract

The pregnane X receptor (PXR) is a nuclear receptor (NR), involved in the detoxification of xenobiotic compounds. Recently, its presence was reported in the human vasculature and its ligands were proposed to exhibit anti-atherosclerotic effects. Since platelets contribute towards the development of atherosclerosis and possess numerous NRs, we investigated the expression of PXR in platelets along with the ability of its ligands to modulate platelet activation. The expression of PXR in human platelets was confirmed using immunoprecipitation analysis. Treatment with PXR ligands was found to inhibit platelet functions stimulated by a range of agonists, with platelet aggregation, granule secretion, adhesion and spreading on fibrinogen all attenuated along with a reduction in thrombus formation (both in vitro and in vivo). The effects of PXR ligands were observed in a species-specific manner, and the human-specific ligand, SR12813, was observed to attenuate thrombus formation in vivo in humanised PXR transgenic mice. PXR ligand-mediated inhibition of platelet function was found to be associated with the inhibition of Src-family kinases (SFKs). This study identifies acute, non-genomic regulatory effects of PXR ligands on platelet function and thrombus formation. In combination with the emerging anti-atherosclerotic properties of PXR ligands, these anti-thrombotic effects may provide additional cardio-protective benefits.

Src-family Protein Tyrosine Kinases: A promising target for treating Cardiovascular Diseases

“…In other organizations, the total levels and the activation levels of specific SFK members were also important for regulating apoptotic activity 28 . Flora et al reported that down-regulation of SFKs activity negatively regulated platelet functions, thrombosis, and haemostasis 29 . All in all, SFKs are the key to regulating the life activities of the body of every aspect.…”

An adaptable analysis workflow for characterization of platelet spreading and morphology

“…Testing platelet function in response to genetic mutations, gene knockouts, and pharmacological agents is a valuable and widely used assay in platelet research [1][2][3][4][5][6][7][8]. In these studies, the analysis of platelet spreading, either by the calculation of adhesion levels, spread surface areas or morphological categorization, is used as a measure of platelet function.…”

Structural, functional, and mechanistic insights uncover the fundamental role of orphan connexin-62 in platelets

“…The preparation of washed platelets, immunoblotting, immunofluorescence, and platelet functional assays such as aggregation, dense granule secretion, fibrinogen binding, P-selectin exposure, calcium mobilization, clot retraction, platelet spreading, thrombus formation, and tail bleeding were performed as described previously. 26,27,[30][31][32] Detailed descriptions of reagents and these methods are provided in supplemental Methods (available on the Blood Web site).…”