Angiotensin II-driven TGF-β1 increases platelet PAR4 expression enhancing thrombotic risk in hypertension

Hypertensive patients exhibit heightened susceptibility to pro-thrombotic state, elevating their cardiovascular event risk. G protein-coupled receptors (GPCRs) serve as central mediators of platelet function; however, the mechanisms through which GPCRs contribute to platelet hyperreactivity remain unclear. This study explores protease-activated receptor 4 (PAR4) on platelet hyperactivation in hypertension.

Platelet GPCR expression from 150 hypertensive patients, spontaneously hypertensive rats (SHRs), and L-NAME-induced hypertensive mice were analysed using RNA-seq and flow cytometry. In vivo and ex vivo thrombosis model, and in vitro platelet functional studies assessed PAR4 overexpression on platelet activation and confirmed by using PAR4-deficient mice. Megakaryocytes and transforming growth factor beta 1 (TGF-β1)-deficient mice were employed to investigate transcriptional regulation of PAR4.

PAR4 expression was elevated in platelets from hypertensive patients and positively correlated with integrin αⅡbβ3 activation and P-selectin exposure, a finding validated in SHRs and hypertensive mice. PAR4 overexpression potentiated thrombin- and AYPGKF-induced platelet activation via Gq and G12/13 signalling of PAR4 but not SFLLRN-induced platelet activation of PAR1, driving arterial thrombus formation. Mechanistic studies using TGF-β1-deficient mice identified TGF-β1 activated transcription factor Smad2, enabling its binding to the PAR4 promoter and PAR4 transcription upregulation. Angiotensin Ⅱ initiated TGF-β1/Smad2 signalling, and valsartan, an angiotensin Ⅱ receptor blocker (ARB), reduced PAR4 expression to attenuate thrombus formation in hypertension.

Angiotensin Ⅱ-driven TGF-β1 upregulates platelet PAR4 transcription to enhance platelet activation in hypertension. Valsartan reverses platelet PAR4 overexpression to inhibit thrombus formation, revealing a new pleiotropic antithrombotic pharmacological mechanism of ARBs in hypertension.