Abstract 376: Erythrocyte Microparticles Can Induce Kidney Vaso-Occlusions in Sickle Cell Disease

Abstract

Background— Patients with sickle cell disease suffer from painful vaso-occlusive crises. These crises are associated with disseminated vaso-occlusions, raised levels of circulating erythrocyte microparticles as well as thrombospondin-1 (TSP1). Microparticules (MP) are submicron membrane vesicles shed by compromised or activated cells. We hypothesized that TSP1 mediates the shedding of erythrocyte MP and participates in vaso-occlusions. Methods and Results— We injected TSP1 to transgenic SAD mice with sickle cell disease, sensitive to renal vaso-occlusions. We characterized circulating MP by FACS after phosphatidylserine labeling. TSP1 injection strongly stimulated MP levels (+260%) and initiated renal vaso-occlusions within 5 minutes, without impacting systemic parameters (heart rate, cardiac output). This was consistent with increased local vascular resistance. In vitro, TSP1 triggered a rapid conversion of purified erythrocytes into echinocytes carrying long and apparently fragile spicules. This was followed by MP shedding. These modifications of erythrocyte phenotype and MP shedding were recapitulated by peptides derived from TSP1 carboxyterminus. We purified the MP shed by erythrocytes in vitro, and administered them back into SAD mice. Erythrocyte MP triggered immediate renal vaso-occlusions, similar to those induced by TSP1. In vitro, purified erythrocyte MP triggered the production of radical oxygen species by endothelial monolayers, favored erythrocyte adhesion to them and induced endothelial apoptosis. Purified erythrocyte MP also compromised acetylcholine-dependent vasodilation in perfused microvessels. These effects of MP were inhibited by saturating surface phosphatidylserine with annexin-V, or with inhibitors of endothelial ROS production. Conclusions— We conclude that TSP1 can trigger the production of microparticles by erythrocytes in sickle cell disease. Second, our data reveal that erythrocyte MP can induce endothelial injury, and this mechanism facilitates the occurrence of vaso-occlusive crises in mice. Therefore, our work supports a novel concept that toxic erythrocyte microparticles constitute a direct connection between sickle cell anemia and vascular disease.