Characterization of the molecular basis of labile heme as a prothrombotic modulator under hemolytic conditions

• Applicant: Professorin Dr. Marie-Therese Hopp
• Subject Area: Biochemistry
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 507218303

The metalloporphyrin heme is a coordination complex of an iron ion incorporated in a porphyrin ring system, which is widely distributed in the body as an essential part of hemoproteins, especially the oxygen-transport protein hemoglobin. An unbalanced heme homeostasis leads to the release of heme, whose clearance is usually regulated by several proteins including hemopexin. Increased intravascular heme levels, however, have been associated with prothrombotic, cytotoxic, proinflammatory, and complement-activating effects, which characterize the harmful complications observed in patients suffering from hemolytic disorders, such as sickle cell disease and transfusion-related hemolysis. Considering the high prevalence of thrombosis and the associated mortality it is surprising that the mechanistic link between labile heme and prothrombotic effects is not yet completely elucidated on the molecular level. Concerning the most relevant proteins in this context, namely the components of the blood coagulation system, distinct proteins, among them factor VIII, activated protein C, and fibrinogen, have been identified as heme-binding or even heme-regulated proteins, while others (thrombin, FXIIIa) do not bind heme. Many questions regarding a potential interaction of heme with most of the coagulation factors are still open. This proposal thus aims at the elucidation of the transient interaction of heme with the coagulation factor FVIII and von Willebrand factor by means of biophysical (e.g., UV/Vis, SPR) and structural analysis (rRaman) methods. In addition, biochemical and hematological functional assays as well as cellular approaches with high physiological relevance (e.g., platelet/endothelial cell function analysis) will be performed. The results obtained will be incorporated into the mechanistic knowledge graph HemeKG to crosslink the already known effects and to unravel so far unknown aspects of heme’s coagulation-modulating effects. In conclusion, the procoagulant effects of heme will be targeted on different levels, i.e. the molecular, biochemical, bioinformatic, and cellular level applying a variety of spectroscopic methods and functional assays. This will allow for a more detailed characterization of heme’s prothrombotic nature and provide new perspectives for the treatment of hemolysis-associated thrombosis.

• DFG Programme: Research Grants