Abstract 2112: Immortal DNA Strand and Human Cardiac Stem Cell Renewal
Based on the immortal DNA strand theory, we tested the hypothesis that non-random chromatid segregation during human cardiac progenitor cell (hCPC) division generates a daughter stem cell which retains the properties of the mother cell and a daughter cell that forms a committed progeny. In contrast, random DNA strand segregation during hCPC division would not have a similar effect. To determine whether hCPCs divide by non-random and/or random segregation of chromatids, we employed clonal assay of BrdU tagged hCPCs. This analysis was done in 5 samples of human myocardium. Undifferentiated cells obtained from each sample/patient were exposed to BrdU until nearly 100% hCPCs became BrdU-positive. Subsequently, BrdU-labeled hCPCs were plated at limiting dilution to generate single cell derived clones. According to the random chromatid segregation model of hCPC division, all clonal cells were expected to be BrdU-positive and the signal for the halogenated nucleotide was anticipated to be progressively attenuated with each round of cell replication. Conversely, according to the non-random chromatid segregation model of hCPC division, only the originally committed daughter cell was presumed to retain BrdU while the other clonal cells were projected to be BrdU-negative. Of the 402 clones obtained so far, 377 were characterized by BrdU-labeling of all clonal cells and 25 by BrdU-labeling of a single hCPC. Thus, hCPCs appear to consist of two subsets of progenitors which divide by non-random and random segregation of chromatids. These observations support the notion that a subset of ~6% of hCPCs divide by asymmetric distribution of chromatids. This small group of cells carried the original DNA templates. Conversely, 94% of hCPCs contained only newly synthesized DNA. The clones generated by hCPCs with the old DNA were significantly larger and were composed of clonal cells which were all p16INK4a-negative and expressed IGF-1 receptors. Conversely, some of the clones formed by hCPCs with the new DNA were very small and at times the clonal cells were uniformly p16INK4a-positive and lacked IGF-1 receptors. Collectively, our findings suggest that in the decompensated heart a small subset of hCPCs with exceptional growth reserve divide by non-random chromatid segregation.