Novel Identified complement regulatory functions of Thrombospondin-1: Mechanisms, physiological relevance and potential for therapeutic applications

• Applicant: Dr. Karsten Häffner
• Subject Area: Pediatric and Adolescent Medicine ; Nephrology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 504543994

Within the last years it has become more and more evident that the complement system is a major player in the pathomachnisms not only in primary complement mediated disorders. These insights have already lead to the development of new therapeutic strategies in some diseases. Recently many studies have emerged which also demonstrate a strong relationship between the coagulation, immune and complement system in vascular diseases like hemolytic uremic syndrome, thrombotic thrombocytopenic purpura and antineutrophil cytoplasmatic antibody-associated vasculitis. These diseases often affect children or adolescents and the lack of efficient therapeutic options can lead to serious life-long impairments in these young patients. Despite huge advances in the field there are still a lot of unknown factors which drive complement dysregulation. A complement regulatory role has been described for Thrombospondin-5 in rheumatoid arthritis. Here we hypothesize that another member of this protein family, Thrombospondin-1 (TSP-1), is involved in regulating complement activity at sites of endothelial impairment. First experiments performed in our lab demonstrate that TSP-1 is able to inhibit the alternative pathway strongly, even in the absence of factor H, the most important regulator of the complement system. To further determine the TSP-1 influences on each complement pathway we will use specific ELISAs. In following in vitro experiments we will analyze TSP-1 as well as fragments thereof to precisely identify the domains and mechanisms involved in complement inhibition for each step of the complement cascade. These findings will be confirmed in vivo in factor H knockout mice, showing complement overactivation. These findings will be confirmed in vivo in factor H knockout mice, showing complement overactivation.Considering that TSP-1 is a main component of the alpha-granula in platelets and involved in inflammation, wound healing as well as thrombosis, we believe that the protein acts as a bridge between thrombocytes, the extracellular matrix, the coagulation and the complement system, further fine-tuning physiological responses at sites of injury. To gain a deeper understanding of the physiological relevance of the complement regulatory role of TSP-1 we will employ a microfluidic system capable of mimicking the endothelium during thrombosis and vasculitis. We will incubate the cells with platelets, force degranulation and determine TSP-1 localization and complement activity. Furthermore, we will add additional TSP-1 to whole blood and study its influence on NET formation, complement activation and endothelial injury. Taken together we think that the clarification of the role of TSP-1 in complement regulation might help to better understand the pathophysiological mechanisms between endothelium, coagulation and complement and pave the way for new treatment options for the affected patients.

• DFG Programme: Research Grants