Tgfb increases platelet PAR4 expression to exacerbate thrombotic risk in hypertension

Background Hypertensive patients are highly susceptible to developing a pro-thrombotic state, which substantially elevates their cardiovascular risk. Although platelet activation is pivotal in thrombosis, its precise contribution to thrombotic events in hypertension remains largely unclear. Objectives This study aims to elucidate the underlying mechanisms of platelet hyperactivation for the higher prevalence of thrombotic complications in hypertension. Methods Platelets from healthy volunteers, hypertensive patients, Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHRs), as well as wild-type and L-NAME induced hypertensive mice were utilized. We employed RNA-seq, RT-PCR, flow cytometry, Western blot, immunofluorescence, in vitro platelet functional studies, in vivo FeCl3-induced thrombosis models, and ex vivo microfluidic whole - blood perfusion assays to evaluate the changes in platelet and PAR4 expression. Moreover, megakaryocyte cultures and platelet-specific TGF-β knockout mouse models were used to systematically investigate the regulatory role of the TGF-β/smad2 pathway in PAR4 receptor expression. Results Comparative analysis of platelets from 50 hypertensive patients versus normotensive controls demonstrated 2.3-fold elevated PAR4 expression (Western blot, p<0.01), corroborated in spontaneous hypertensive rats (SHRs) and L-NAME-induced hypertensive mice. Functional characterization revealed PAR4 hyperactivation potentiates thrombin signaling via amplified Gq/G12/13 pathways, driving exacerbated aggregation responses (AUC +58%, p<0.001), αIIbβ3 activation (PAC-1 binding +142%), and accelerated thrombus formation under arterial shear (-44% adhesion area, microfluidic assay). Mechanistic interrogation through megakaryocyte cultures and platelet-specific TGF-β knockout models identified TGF-β/Smad2 signaling as the transcriptional regulator of PAR4 upregulation. Angiotensin II was shown to activate platelet AT1Rs, initiating a signaling cascade that amplifies TGF-β/Smad2 activity and subsequent PAR4 overexpression. Valsartan, an AT1 receptor blocker, effectively suppresses PAR4 expression, thereby inhibiting platelet activation and thrombus formation in hypertensive patients Conclusions These findings highlight that hypertensive patients have significantly elevated platelet PAR4 expression which leads to platelet hyperactivity, while providing mechanistic justification for repurposing AT1R antagonists to concurrently address thrombotic risk. The identified AT1R/TGF-β/Smad2 axis offers a precision therapeutic target, enabling antiplatelets without exacerbating bleeding risks inherent to conventional antiplatelet regimens.