Abstract 1426: Endothelial Microparticles Interact With Endothelial Progenitor Cells -Influence On Mobilization, Apoptosis, And Cell Migration
Background: Endothelial cell (EC) apoptosis is a marker of endothelial dysfunction, which itself is one of the earliest pathophysiological correlates of atherosclerosis and strongly associated with an impaired cardiovascular prognosis. EC apoptosis is quantified using flow-cytometry based enumeration of circulating endothelial microparticles (EMP) within peripheral blood. Bone marrow-derived endothelial progenitor cells (EPC) are an important cellular risk predictor. The vasculoprotective action of EPC seem to be mediated by an enhanced reendothelialization process after EC damage. We postulate that apoptotic EC interact with circulating EPC via EMP.
Methods and Results EMP were obtained from human coronary arterial EC (HCAEC) after serum starvation or TNF-alpha activation and isolated using ultracentrifugation. Flow cytometric analyses revealed that EMP were positive for annexin V, CD31, CD49e, CD51, CD51/61, CXCR2, and CXCR4. Cell culture experiments demonstrated that fluorescent-labelled EMP were incorporated by cultivated HCAEC. Co-cultivation of peripheral mononuclear cells with EMP lead to an enhanced conversion of mononuclear cells into acDi-LDL/lectin positive EPC-like cells. Co-cultivation of EPC with EMP prevented TNF-alpha induced cell apoptosis, and migration of EPC was enhanced in response to EMP. Finally, we measured EPC liberation from bone marrow into peripheral blood in C57bl6 mice. Treatment of mice with EMP enhanced the number of circulating sca-1/flk-1 positive EPC within peripheral blood compared to vehicle treated mice. The number of circulating EMP and CD34+/KDR+ EPC were determined in 40 patients with coronary artery disease using flow cytometry. The number of colony forming unit-endothelial cells (CFU-EC) in vitro was determined as a marker for the clonogenic potential of formerly circulating EPC. The number of circulating EMP correlated with EPC function (p<0.001, r=0.601).
Conclusion EMP and circulating EPC interact in rodents and humans. EMP influence conversion, migration, and apoptosis of EPC in vitro. EMP mobilize EPC in vivo after i.v. treatment of wildtype mice with EMP. We speculate that the described interaction of EMP with EPC enhance the homing process of EPC within the area of EC damage.