Abstract 16933: Asymmetric Chromatid Segregation is Independent of Asymmetric Cell Division in Human Cardiac Stem Cells
The controversy concerning the growth reserve of the adult heart has not been resolved, and questions are raised about the actual existence of cardiac stem cells (CSCs) and their function. Importantly, the notion that CSCs reside, live, and die within the heart requires the characterization of the pattern of stem cell division. Understanding stem cell self-renewal has been complicated by a theory suggesting that stem cells cosegregate the original DNA template in consecutive divisions so that the daughter cell that inherits the old DNA retains stem cell features, while the daughter cell that acquires the new DNA undergoes lineage commitment. Symmetric and asymmetric chromatid segregation (SCS vs. ACS) during mitosis was determined by a clonal assay of human CSCs (hCSCs) pre-labeled with BrdU. Collectively, 2,725 clones were obtained; 203 clones were characterized by BrdU-labeling of a single hCSC, indicating that 7% of founder hCSCs divided by ACS. To exclude that the BrdU-positive hCSC had reached growth arrest early in the formation of the clone, 40 clones, each containing one BrdU-positive hCSC, were stained for the aging-associated protein p16INK4a. In these clones, BrdU-positive and BrdU-negative cells did not express p16INK4a, excluding the occurrence of replicative senescence. Moreover, ∼50% of the BrdU-positive hCSCs expressed Ki67, indicating that they were indeed cycling cells. To determine whether ACS is coupled with asymmetric cell division, leading to the formation of one stem cell and one committed cell, hCSCs were exposed to a BrdU-pulse followed by a chase-period, during which hCSCs traversed one cell cycle in the absence of the thymidine analog. BrdU incorporation in anaphase/telophase nuclei was determined together with the uniform or non-uniform partitioning of α-adaptin, which identifies symmetric and asymmetric hCSC division, respectively. In ∼6% of mitotic cells, BrdU was restricted to one set of chromosomes but α-adaptin was evenly distributed indicating that ACS was coupled with symmetric stem cell division. In conclusion, our results provide evidence that the human heart possesses a pool of hCSCs that, during division, undergo ACS, generating two daughter stem cells, which retain the old and new DNA, respectively.
- © 2012 by American Heart Association, Inc.