Abstract 16477: Revascularization After Ischemia is Mediated by Clonally Expanding Endothelial Cells and is Impaired by Aging

Vascularization is critical to maintain organ function. Outgrowth and clonal expansion of endothelial cells (ECs) has been documented in vitro , however, the contribution of clonally expanding ECs to physiological versus ischemia-induced vessel growth is unknown. We analyzed the contribution of EC expansion to postnatal retina angiogenesis and ischemia-induced neovascularization after acute myocardial infarction (AMI) as well as hindlimb ischemia (HLI) using so-called Confetti mice that were crossed with the tamoxifen-inducible VE-cadherin Cre-deleter line (CDH5CreERT2/+;Rosa26Confetti/+) for genetic tracing of clonally expanding endothelial cells. Tamoxifen was injected to induce CFP-, GFP-, RFP- and YFP-fluorescent proteins in endothelial cells. In postnatal retina angiogenesis, we observed stochastic EC expansion, resulting in random distribution of fluorescence labeled EC in most sections (less than 10% of sections showed clonal expansion, n=60 sections of 8 mice). However, in pathological angiogenesis during retinopathy of prematurity (ROP) clonally expanded endothelial cells were enriched in 69% of sections (p 9 sections in each group). In aged mice that were subjected to HLI, less clonal expansion events were observed and only 11% of sections showed clonal expansion (p