Influence of the platelet-derived DAMP HMGB1 on thrombosis and inflammation

• Applicant: Professor Dr. Meinrad Paul Gawaz, since 2/2017
• Subject Area: Cardiology, Angiology
• Term: from 2015 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 190538538

High-mobility group box 1 (HMGB1) is a "damage associated molecular pattern" molecule (DAMP), which plays a central role in tissue damage and sterile inflammation. Platelets also express and, upon platelet activation, release HMGB1, thereby potentially affecting tissue repair and regeneration as well as immunological processes. The influence of platelet-derived HMGB1 on such cellular functions is poorly understood. We have previously shown that platelets inhibit recruitment of mesenchymal stem cells (MSC) to apoptotic cardiac myocytes and fibroblasts through HMGB1/toll-like receptor (TLR)-4 interaction, which may have implications on the outcome of myocardial damage (Vogel et al., JBC, 2014). Apoptotic, but not necrotic cell death, constitutes a key stimulus for the recruitment of MSC to damaged tissue and tumor cells - a tropism that is mediated via hepatocyte groth factor (HGF) (Vogel et al., BBRC, 2010; Vogel et al., CMLS, 2013) and regulated by platelet-derived HMGB1 through down-regulation of HGF receptor MET (Vogel et al., JBC, 2014). Further, platelets induce migration and survival of monocytes by binding of HMGB1 to RAGE (receptor of advanced glycation end products) and TLR-4 (unpublished). In monocyte-platelet aggregates, HMGB1-driven anti-apoptotic effects could be detected, as well. Moreover, we have identified an HMGB1-induced prothrombotic and proaggregatory effect for platelets, which was mediated via cGKI, a cGMP-dependent protein kinase. The purpose of this project is to investigate the role of HMGB1 for platelet function as well as identify HMGB1-mediated interactions of platelets with monocytes. In addition to cell biolocical approaches, we will perform ex vivo and in vivo studies with RAGE, TLR-4, MyD88, and cGKI knockout mice. The specific contribution of platelet-derived HMGB1 will be assessed by using recently generated mice with a platelet-specific HMGB1 defect (PF4-Cre; HMGB1-flox/flox). In models such as Fe(III)-chlorideinduced thrombosis or intestinal ischemia, infiltrating monocytes and platelets will be detected with intravital microscopy in the respective regions by using CX3CR1-eGFP/+ reporter mice or ROSA-mT/mG mice. In in vivo models of ischemic stroke and myocardial infarction, the relevance of plateletderived HMGB1 for these diseases will finally be determined. In prospective patient cohorts, we will measure platelet surface expression and release of HMGB1 and evaluate its role for coronary heart disease and stroke, in order to define patient subgroups that show a particularly high response to new therapeutic approaches.

• DFG Programme: Clinical Research Units
• Subproject of: KFO 274: Platelets - Molecular Mechanisms and Translational Implications
• Participating Person: Dr. Dominik Rath
• Ehemaliger Antragsteller: Dr. Sebastian Vogel, until 2/2017