Identification of cardiac stem cells with FLK1, CD31, and VE-cadherin expression during embryonic stem cell differentiation

We evaluated the expression of the FLK1, one of the lateral mesoderim early markers where cardiogenesis occurs, to characterize and isolate cardiac stem/progenitor cells from ES cells. Dissociated cells from embryoid bodies (EBs) on day 3, 4, or 5 were collected into two subpopulations with or without FLK1 expression and coculture on OP9 stromal cells was continued to examine whether contracting colonies came out or not. FLK1(+) cells from EBs at days 3 and 4 formed spontaneous contracting colonies more efficiently than FLK1(-) cells on the same days, but not at day 5. Most contracting cardiac colonies derived from FLK1 cells mainly on day 4 were detected on endothelial cells along with hematopoietic cells. Further characterization of cells with these capabilities into three lineages revealed the FLK1(+) CD31-VE-cadherin phenotype. Our findings indicate that FLK1(+) cells, especially FLK1(+) CD31(-)VE-cadherin(-) cells, could act as cardiohemangioblasts to form cardiac cells as well as endothelial cells and hematopoietic cells.