TITLE: CROSS-TALK BETWEEN HAEMOSTASIS AND INFLAMMATION:
C-TERMINAL THROMBOSPONDIN-1 (TSP-1) PEPTIDE ACTIVATES PLATELETS, MONOCYTES AND PMNL

AUTHORS: Kerstin Jurk, PhD, Hugo Van Aken, MD, PhD, Beate E. Kehrel, PhD
AFFILIATION: Klinik und Poliklinik für Anaesthesiologie und Operative Intensivmedizin, Universitaet Muenster, Muenster, Germany.

INTRODUCTION: Thrombospondins are a family of secreted glycoproteins that regulate cell adhesion, migration, inflammation and platelet aggregation. TSP-1 is the most abundant a-granule protein in human platelets. The integrin- associated protein (IAP, CD47) is a receptor for the carboxyl- terminal cell binding domain of TSP-1. In this study we investigate the role of TSP-1 binding to CD47 in haemostasis and inflammation.
METHODS: A peptide with the amino acid sequence RFYVVMWK (TSP-1 peptide), aequivalent to the TSP-1 binding domain to CD47, was synthetized. The dose-dependent expression of CD11b (MAC-1 integrin), a protein necessary for leukocytes to exit the vasculature and for migration into infected/ damaged tissue, MRP8/14 (early inflammation marker) on monocytes, CD62P (P-selectin) expression on platelets and fibrinogen binding to platelets, PMNL and monocytes, as well as platelet-leukocyte association was studied with gelfiltered platelets and elutriation-isolated PMNL and monocytes using flowcytometrical methods.
RESULTS: RFYVVMWK activated platelets and leukocytes; it induced platelet-fibrinogen binding and aggregation in a dose dependent manner. Additionally it induced the secretion of the platelet a-granules, demonstrated by expression of CD62P on platelets and TSP-1 binding to the surface of activated platelets. It induced in a dose dependent manner CD11b expression on monocytes and the binding of fibrinogen to the surface of activated monocytes and PMNL as well as MRP8/14 expression on monocytes. RFYVVMWK-activated leukocytes associated not only with activated but also with quiescent platelets.
CONCLUSIONS: Our findings support the hypothesis that haemostasis and inflammation are tightly interwoven processes. Thrombospondin-1 from activated platelets accelerates platelet activation processes and induces leukocyte activation processes.