Hematopoietic stem cells and aging.

Hematopoiesis is a process by which a single cell--called a hematopoietic stem cell (HSC)--has the proliferative potential to give rise to all of the major lineages of blood and immune cells. Stem cells can undergo both symmetric division, which results in two copies of the parent stem cell, and asymmetric division, which results in self-renewal of the parent stem cell as well as production of a daughter cell that is capable of differentiating along a specific lineage. A number of different elements of HSC replication change with age, even though these transformations do not appear to result in hematopoietic deficiencies under normal circumstances. In this Perspective, the author discusses these age-related alterations.