The Ponzo Effect
Endothelial Progenitor Cells Appear on the Horizon
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Can cell-based therapies be used to treat cardiovascular diseases that result from injury, inflammation, and the wear and tear of aging and cellular senescence? This is the premise of regenerative medicine. This emerging field has developed from advances in our understanding of cellular and molecular mechanisms contributing to cardiovascular disease in the post–“response to injury” era and, more directly, from the recent explosion of interest in stem cell biology and cellular plasticity. The field of stem cell biology has made enormous advances in recent years, with one example being the identification of adult multipotential progenitor cells capable of contributing to a variety of tissues (including endothelium and muscle).1 The recent demonstration that bone marrow–derived precursor cells can differentiate to cardiac myocytes and can improve cardiac function after myocardial infarction in animal models2 contradicts several decades of dogma about the nature of heart muscle lineage commitment and raises the (as yet unfulfilled) promise of regenerative therapies for myocardial infarction and heart failure. In parallel, regenerative medicine has set its sights on vessel wall events—in particular, atherosclerosis and angiogenesis—as additional targets for cell-based therapies. In this issue of Circulation, Szmitko et al3 concisely describe what is known about endothelial progenitor cells (EPCs) as potential tools in the setting of vascular disease. At the same time, it is worthwhile to consider what is not known about vascular progenitor cells and where the field must head if regenerative medicine is to achieve clinical applicability.
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What Are EPCs?
To address this question, it is first necessary to understand the general definition of progenitor cells and their antecedents, stem cells. In simple terms, stem cells are small populations of cells in adults that retain the ability to regenerate multiple cell types or lineages within a tissue or organ. However, the operational definition …