Platelets beyond the vasculature – extra-vascular mechanisms and function

• Applicant: Dr. Leo Nicolai
• Subject Area: Cell Biology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 512460086

Platelets are key effectors in thrombosis and hemostasis, but recent years have greatly expanded our knowledge on the role of these cells beyond classical clot formation – platelet seem to be at the nexus of host defense and possess important immune-modulatory function in health and disease. Insights into these non-canonical platelet functions hold promise for (1) improving existing antiplatelet therapies and (2) extending pharmacological targeting of platelets to inflammation. We have recently shown that platelet actively migrate along intravascular endothelium and follow substrate gradients to identify sites of vascular injury and pathogen invasion in a process termed haptotaxis. In addition, we have observed extravascular platelets in the context of inflammation and tissue injury. This aspect of platelet function as well as their behavior after leaving the vascular bed remains largely unexplored. We hypothesize that the extravascular environment might also promote platelet spreading and migration. Our preliminary data identify extravascular platelets with motile behavior after vascular injury. In addition, we observe reduced wound healing in mice with migration-deficient platelets. Regarding the mechanism of migration, our preliminary screening experiments identify GPIIbIIIa dependent outside-in signaling via Src-Galpha13 as crucial for mechanosensing and ensuing Arp2/3 dependent lamellipodia formation. We want to pursue this further by exploring the molecular cascade involved in regulation of extravascular migration (Aim 1). This will be addressed using innovative in vitro assays and readouts. Also, we want to use intravital imaging, in vitro modeling and genetic/pharmacological intervention to extend our understanding of platelet effector function in the extravascular space (Aim 2). Extravascular platelet function and behavior and interaction with the microenvironment will be assessed by intravital imaging in a murine mesenterium and ear skin imaging model. Lastly, we want to investigate the effect of extravasated platelets and extravascular motility on tissue regeneration by assessing cutaneous wound healing (Aim 3). In this context, we will study platelet recruitment, extravasation and migration.

• DFG Programme: Research Grants