While others have reported that fetal liver contains a population of endothelial progenitors based on expression of cell surface markers or culture assays, this is the first proof of a CD31+Sca1+ progenitor by demonstrating highly efficient in vivo angiogenesis and a direct connection to the host vasculature. We have developed a novel isolation method based on collagenase digestion and culture on a fetal liver-derived feeder layer and demonstrate that the feeder cells or their supernatants are required for endothelial progenitor survival and proliferation. Proteogenomic profiling of the endothelial progenitors and the feeder cells was done with tandem mass spectrometry proteomics using MudPIT and gene transcript expression profiling using high density DNA microarrays. This approach identified a number of gene transcripts, proteins and candidate growth factor pathways that are likely to be involved in endothelial progenitor growth, differentiation and angiogenesis.
