Medizinische Universität Graz - Research portal
Selected Publication:
Pasterk, L.
The impact of advanced oxidized protein products on platelets and platelet-endothelial crosstalk
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Graz Medical University; 2016. pp.
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- Authors Med Uni Graz:
- Advisor:
- Marsche Gunther
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- Abstract:
- The multifaceted role of platelets was underestimated for a long time, but now their important role in inflammation as well as their contribution in all stages of atherosclerosis is more frequently perceived and investigated. Platelets are involved in inflammation by releasing their pro-coagulant and proinflammatory granule content at the site of inflammation and actively participate by directly interacting with endothelial cells and/or neutrophils. By doing so, platelets are able to trigger cell activation or amplify activation dependent cell functions. Individuals with increased platelet reactivity are at a higher potential risk for thrombosis which can lead to complete vessel occlusion and severe outcomes such as myocardial infarction and stroke. Several inflammatory diseases are associated with high levels of oxidative stress and increased platelet functionality. Moreover, there is a direct link between inflammatory diseases and high prevalence of thrombotic events. During inflammation, activated neutrophils release myeloperoxidase (MPO), the only enzyme that is able to form the oxidant hypochlorous acid (HOCl). Of note, albumin which is the most abundant protein in the vasculature, is the primary target of HOCl, with limited damage to other materials. HOCl-modified albumin was shown to present the major fraction of advanced protein products (AOPPs), which accumulate in several inflammatory diseases, such as renal disease, and are markers for oxidative stress and inflammation. Whether AOPPs contribute to coagulation abnormalities which are frequently seen in uremic patients, has not been elucidated so far. In our study we could show a novel role for AOPPs as potent activators of platelet function. In the present study we revealed several AOPPs mediated changes on platelets, such as an increase in platelet adhesion molecules (P-selectin, phosphatidylserine and cluster of differentiation 40 ligand (CD40L) as a result of platelet granule release and protein integration in the outer platelet membrane. Since AOPPs induced platelet aggregation and P-selectin surface expression could be considerably reduced when interfering with cluster of differentiation 36 (CD36) receptor binding, we can clearly argue that CD36 is the main platelet receptor facilitating the interactions between platelets and AOPPs. In this thesis project we elucidated that platelets upon AOPPs exposure were activated via a signalling cascade involving phospholipase C (PLC), phosphokinase C (PKC) and Calcium (Ca2+) mobilisation as well as production of intracellular reactive oxygen species (ROS). By acting on platelets, AOPPs induce platelet-endothelial interactions as indicated by increased platelet adhesion to cultured human coronary artery endothelial cells (HCAECs) and, of note, endothelial tissue factor (TF) expression results from this cell-cell crosstalk. Moreover, results obtained with in vitro modified AOPPs could be translated in a physiological relevant context, as AOPPs isolated from sera of uremic patients enhanced platelet aggregation dependent on their levels of oxidative modifications in a CD36 dependent manner. In our study cohort of end stage renal disease patients on hemodialysis, AOPPs and serum TF levels were significantly increased. Notably, a significant correlation of AOPPs and serum TF was found, suggesting that platelets link oxidative stress and a prothrombotic phenotype. Our results provide clear evidence that AOPPs formed in conditions underlying chronic oxidative stress can contribute to increased platelet reactivity. The resulting procoagulant phenotype on endothelial cells might contribute to the coagulation abnormalities in uremia and other inflammatory diseases. Our findings reveal previously unknown pro-thrombotic activities of oxidized albumin.