Angiogenic Microvascular Endothelial Cells Release Microparticles Rich in Tissue Factor That Promotes Postischemic Collateral Vessel Formation

Objective-Therapeutic angiogenesis is a promising strategy for treating ischemia. Our previous work showed that endogenous endothelial tissue factor (TF) expression induces intracrine signaling and switches-on angiogenesis in microvascular endothelial cells (mECs). We have hypothesized that activated mECs could exert a further paracrine regulation through the release of TF-rich microvascular endothelial microparticles (mEMPs) and induce neovascularization of ischemic tissues. Approach and Results-Here, we describe for the first time that activated mECs are able to induce reparative neovascularization in ischemic zones by releasing TF-rich microparticles. We show in vitro and in vivo that mEMPs released by both wildtype and TF-upregulated-mECs induce angiogenesis and collateral vessel formation, whereas TF-poor mEMPs derived from TF-silenced mECs are not able to trigger angiogenesis. Isolated TF-bearing mEMPs delivered to nonperfused adductor muscles in a murine hindlimb ischemia model enhance collateral flow and capillary formation evidenced by MRI. TF-bearing mEMPs increase angiogenesis operating via paracrine regulation of neighboring endothelial cells, signaling through the 1-integrin pathway Rac1-ERK1/2-ETS1 and triggering CCL2 (chemokine [C-C motif] ligand 2) production to form new and competent mature neovessels. Conclusions-These findings demonstrate that TF-rich mEMPs released by microvascular endothelial cells can overcome the consequences of arterial occlusion and tissue ischemia by promoting postischemic neovascularization and tissue reperfusion.