Microparticles From Ischemic Muscle Promotes Postnatal Vasculogenesis

Background-We hypothesized that microparticles (MPs) released after ischemia are endogenous signals leading to postischemic vasculogenesis. Methods and Results-MPs from mice ischemic hind-limb muscle were detected by electron microscopy 48 hours after unilateral femoral artery ligation as vesicles of 0.1- to 1-mu m diameter. After isolation by sequential centrifugation, flow cytometry analyses showed that the annexin V+ MP concentration was 3.5-fold higher in ischemic calves than control muscles (1392 +/- 406 versus 394 +/- 180 annexin V+ MPs per 1 mg; P < 0.001) and came mainly from endothelial cells (71% of MPs are CD144+). MPs isolated from ischemic muscles induced more potent in vitro bone marrow-mononuclear cell (BM-MNC) differentiation into cells with endothelial phenotype than those isolated from control muscles. MPs isolated from atherosclerotic plaques were ineffective, whereas those isolated from apoptotic or interleukin-1 beta-activated endothelial cells also promoted BM-MNC differentiation. Interestingly, MPs from ischemic muscles produced more reactive oxygen species and expressed significantly higher levels of NADPH oxidase p47 (6-fold; P < 0.05) and p67 subunits (16-fold; P < 0.001) than controls, whereas gp91 subunit expression was unchanged. BM-MNC differentiation was reduced by 2-fold with MPs isolated from gp91-deficient animals compared with wild-type mice (P < 0.05). MP effects on postischemic revascularization were then examined in an ischemic hind-limb model. MPs isolated from ischemic muscles were injected into ischemic legs in parallel with venous injection of BM-MNCs. MPs increased the proangiogenic effect of BM-MNC transplantation, and this effect was blunted by gp91 deficiency. In parallel, BM-MNC proangiogenic potential also was reduced in ABCA1 knockout mice with impaired vesiculation. Conclusion-MPs produced during tissue ischemia stimulate progenitor cell differentiation and subsequently promote postnatal neovascularization. (Circulation. 2009; 119:2808-2817.)