Thesis defense Bart van den Eshof: PARadigms of vascular signalingNews
On 14 November 2018 Bart van den Eshof will defend his thesis at Utrecht University. In his thesis he provides an overview of communication networks in endothelial cells, which may contribute to a better understanding of the interplay of coagulation factors, platelets and the vessel wall. This may prompt future investigations to identify key targets for therapeutic intervention.
The inside of all blood vessels is lined with a tight network of specialized endothelial cells that form a semipermeable barrier between blood and underlying tissues. By virtue of their strategic position at the interface between blood and tissue, endothelial cells are constantly exposed to blood cells, proteins and other blood components. To sense their environment, endothelial cells are equipped with a wide range of transmembrane receptors that convert information from the extracellular environment into intracellular signaling pathways. To better understand the swift adaptive endothelial response it is crucial to map these communication networks.
To cover the rapid and reversible post-translational modifications a system-wide analysis of cellular signaling networks is required. Therefore, during his PhD-research Bart van den Eshof investigated endothelial signaling pathways, with particular emphasis on coagulation, using an unbiased quantitative mass spectrometry approach.
Thrombin is the key serine protease of the coagulation cascade and its predominant receptor is protease-activated receptor 1 (PAR1). Bart’s data demonstrate that thrombin dynamically regulates a plethora of phosphorylation events, including actin cytoskeleton and cell junctions signaling. Next, he shows that thrombin-induced phosphoregulation is mediated exclusively through PAR1. In addition, he shows that PAR1 inhibitors vorapaxar and parmodulin-2 demonstrate distinct antagonistic properties and that only canonical PAR1 cleavage by thrombin, and not by other proteases, generates a tethered ligand that potently induces early signaling.
These data provide mechanistic inside into the activation and inhibition of PAR1-mediated signaling in endothelial cells. To dissect diverging and converging signaling pathways, Bart analyzed the communication networks initiated by histamine and other members of the PAR family (PAR1,2,3,4). His data show that PAR1 and PAR2 induce similar phosphoregulation of proteins involved in Gαq- and the MAPK pathway. In contrast, they differentially regulate proteins related to clathrin-mediated endocytosis. Thrombin and histamine induce highly similar phosphoregulation, while they differentially phosphorylate proteins related to the Gα12/13 pathway.
Furthermore, Bart assessed phosphoproteomic regulation in endothelial cells induced by platelet proteins and compared it to vascular endothelial growth factor (VEGF)-mediated phosphoregulation. These data show that platelet release and lysate induced highly similar signal transduction and that their effect is not primarily driven by VEGF. In parallel, he used a proteomics approach to compare cord blood platelets with adult peripheral blood platelets and shows that their protein abundance is highly similar, while limited differences are related to proteins involved in mitochondrial energy metabolism. Finally, he performed an integrated analysis of all phosphoproteomic analyses to reveal unique signaling signatures and core activation pathways.
Taken together, this thesis provides a unique overview of communication networks in endothelial cells, which may contribute to a better understanding of the interplay of coagulation factors, platelets and the vessel wall and may prompt future investigations to identify key targets for therapeutic intervention.
Promotores: Prof K Mertens, PhD and prof AB Meijer, PhD. Copromotor: M van den Biggelaar, PhD