Stem cells: the building blocks to repair the injured heart

Myocardial infarction is the major cause of death in western countries due to impaired function of the heart, which is the result of cardiomyocyte death and fibrotic scar formation. The endogenous regenerative capacity of the heart is unable to replenish this significant loss of tissue and conventional medical management cannot correct the underlying defects in cardiac muscle cell number. Recently, tremendous effort is being put into the development of cell transplantation protocol for heart repair, which has been put forward as an alternative therapy to reduce cell damage, cardiomyocyte death and improve tissue contraction. Unfortunately the ideal stem cell population for heart repair has not been identified to date, but several characteristics are defined which the ideal population should have namely, reduce cell damage, reduce cardiomyocyte death, induce differentiation into cardiomyocytes and endothelial cells, and improve tissue contraction. It is unclear whether this will be possible in one optimal population. Therefore the research focus is shifting towards improving the characteristics of the stem cell populations that are identified to date. In this review, we will give an overview of the different stem/progenitor cell populations and their application in cardiac repair and discuss current knowledge on issues like differentiation capacity, paracrine secretion profile, genetic modification of progenitor cells and their influence on cardiac remodeling.