Abstract
Stem/progenitor cells from multiple tissues have been isolated based on enhanced activity of cytosolic aldehyde dehydrogenase (ALDH) enzyme. ALDH activity has emerged as a reliable marker for stem/progenitor cells, such that ALDH(bright/high) cells from multiple tissues have been shown to possess enhanced stemness properties (self-renewal and multipotency). So far though, not much is known about ALDH activity in specific fetal organs. In this study, we sought to analyze the presence and activity of the ALDH enzyme in the stem cell antigen-1-positive (Sca-1+) cells of fetal human heart. Biochemical assays showed that a subpopulation of Sca-1+ cells (15%) possess significantly high ALDH1 activity. This subpopulation showed increased expression of self-renewal markers compared to the ALDH(low) fraction. The ALDH(high) fraction also exhibited significant increase in proliferation and pro-survival gene expression. In addition, only the ALDH(high) and not the ALDH(low) fraction could give rise to all the cell types of the original population, demonstrating multipotency. ALDH(high) cells showed increased resistance against aldehyde challenge compared to ALDH(low) cells. These results indicate that ALDH(high) subpopulation of the cultured human fetal cells has enhanced self-renewal, multipotency, high proliferation, and survival, indicating that this might represent a primitive stem cell population within the fetal human heart.