Abstract 3422: Asymmetric Division of Human Cardiac Progenitor Cells Involves Immortal DNA Strand Cosegregation

The objective of this study was to determine whether asymmetric division of human cardiac progenitor cells (hCPCs) occurs by: random DNA template segregation; selective retention of the old template DNA strand; or a combination of both processes. Myocardial samples were enzymatically dissociated and hCPCs were sorted for the stem cell antigen c-kit. During in vitro expansion, hCPCs were exposed to BrdU for 36 hours to reach a 90% degree of labeling. BrdU-tagged hCPCs were plated at limiting dilution to obtain single cell-derived clones. Sixty clones comprising 10 –125 c-kit-positive hCPCs developed in 7–10 days. In four cases, one single BrdU-bright hCPC was identified while the remaining clonogenic cells were negative for the halogenated nucleotide. In these clones, the number of BrdU-negative hCPCs was 25, 85, 95, and 111. Conversely, in 56 clones hCPCs were uniformly labeled and showed very low levels of BrdU. In a second group of experiments, hCPCs in late-anaphase initial-telophase were identified and the distribution of BrdU in the two clusters of chromosomes was analyzed. In 5% of mitotic cells, three-dimensional reconstruction by confocal microscopy documented that BrdU-labeling was restricted at one pole only of the dividing hCPCs. PCNA which is highly expressed in newly synthesized DNA was restricted to the BrdU-negative chromosomes. In a third set of studies, hCPCs were loaded with quantum dots, cultured for 36 hours in the presence of BrdU and examined 96 hours later. Quantum dots are progressively diluted by cell division independently from the modality of DNA template segregation. Thus, hCPCs with minimal levels of quantum dots and bright BrdU localization were interpreted as replicating cells which retained the old DNA strand. By this approach, 5% hCPCs displayed these two critical properties. The uneven distribution of the cell fate determinants Numb and α-adaptin confirmed that hCPCs underwent asymmetric division. In conclusion, these data support the hypothesis that immortal DNA strand cosegregation participates in asymmetric kinetics of hCPCs although random-segregation of DNA template is the prevailing mechanism of hCPC growth.