Natriuretic peptides ANP and BNP potentiate thrombosis via their receptor NPRA

Abstract: Platelets play essential roles in hemostasis and thrombosis. At sites of vascular injury, exposure of platelets to soluble agonists or subendothelial adhesive proteins triggers platelet activation, leading to thrombus formation. Natriuretic peptides (NPs), the B-type natriuretic peptide (BNP) and an inactive N-terminal fragment of the prohormone (NT-proBNP), have been established as biomarkers in heart failure, coronary heart disease and pulmonary hypertension. High concentrations of plasma ANP and BNP are closely associated with risks for thrombotic diseases such as myocardial infarction (AMI) in acute coronary syndromes (ACS) and cardioembolic stroke. BNP is also a predictor of adverse outcomes in patients with ACS/AMI. However, despite the well-recognized correlation, it is unknown whether increased plasma levels of ANP and BNP impact platelets and are causal for thrombotic diseases. The main effects of ANP and BNP are mediated through their receptor, the natriuretic peptide receptor-A (NPRA), a membrane-bound guanylyl cyclase that generates the important second messenger cGMP. In platelets, cGMP is believed to be synthesized predominantly by soluble guanylyl cyclase (sGC), which is a receptor for nitric oxide (NO). We have now obtained compelling preliminary data that human platelets express functional NPRA. Our previously published work suggests a stimulatory role of the cGMP-dependent kinase in platelet activation and thrombosis. Therefore, we hypothesize that NPs promote platelet activation through the NPRA/cGMP/PKG pathway. We further hypothesize that ANP and BNP are not only biomarkers for the cardiovascular diseases but also contribute to the pathogenesis of thrombus formation in these diseases. To test this hypothesis, we propose the following specific aims: Aim 1 will investigate the NPs/NPRA platelet axis and its potential to promote platelet activation and thrombosis. Aim 2 will identify a role of a novel PKG isoform, PKG II, in NP-promoted platelet activation, and in thrombosis and hemostasis in vivo. In summary, the information gained from this proposal will provide important mechanistic insights into the molecular mechanisms that ANP and BNP promote thrombosis and hence expand the knowledge base upon which novel antithrombotic therapeutic targets can be developed.