Microparticles From Ischemic Muscle Promotes Postnatal Vasculogenesis

Abstract

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-μm 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 CD 144+ ). 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-1β–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.