Mobilization of very small embryonic-like stem cells in acute coronary syndromes and stroke.

The bone marrow (BM) niche contains small heterogenous populations of cells which may contribute to cardiac and endothelial repair, including committed lineages [endothelial progenitor cells (EPCs), multipotent mesenchymal stromal cells (MSCs) and more primitive very small embryonic-like cells (VSELs) expressing pluripotent stem cell (PSC) markers (Oct-4, Nanog, SSEA-1)]. VSELs are present in BM, peripheral blood and some solid organs in mice and were recently identified in peripheral blood in patients with acute coronary syndromes and stroke. VSELs can be expanded in vitro and differentiated into cells from all three germ layers. This population of cells displays the morphology of primitive PSC (small size, open type chromatin, large nucleus, narrow rim of cytoplasm) and express PSC markers. The isolation of human VSELs is based on their size and presence of several surface markers (CXCR4, CD133, CD34) and lack of markers of hematopoietic lineage (lin, CD45). In acute myocardial infarction and ischemic stroke VSELs are rapidly mobilized into peripheral blood, and express increased levels of PSC markers as well as early cardiac (GATA-4, Nkx2.5/Csx), neural (GFAP, nestin, beta-III-tubulin, Olig1, Olig2, Sox2, Musashi) and endothelial lineage markers (VE-cadherin, von Willebrand factor). The number of VSELs mobilized in acute myocardial infarction is inversely correlated with left ventricular ejection fraction and the release of cardiac necrosis markers. Mobilization of these cells is also reduced in patients with diabetes and in the elderly. BM-derived VSELs were expanded and after cardiogenic pre-differentiation injected intramyocardially in mice models of myocardial infarction leading to improved left ventricular contractility. VSELs are probably progeny of epiblast cells which migrated to the BM and developing organs during embryonic development. The cells are present in a quiescent state in the adult BM and solid organs and might serve as a reserve pool of resident stem cells. VSELs are promising candidates for further pre-clinical and clinical studies on cellular cardiovascular therapy.