Senescence and functional failure in hematopoietic stem cells.

Maintaining normal function of hematopoietic stem cells (HSCs) is critical to blood coagulation, oxygen transportation, and host defense against infection. A potential cause of HSC dysfunction is senescence, in which HSCs and progenitor cells suffer from proliferative arrest. Studies on humans and various animal models have indicated that HSCs can become senescent, showing a significant decline in functional ability with increasing age. There are genetic elements mapped to specific chromosomal sites that regulate HSC senescence. These elements may differ among species, strains, and even individuals. HSC senescence and related pathological effects may not be obvious during normal lifetime under most circumstances since individual primitive HSC clones can function long-term to produce progeny that sustain life-long mature blood cell production. Shortening of telomeres at the chromosomal ends could contribute to HSC senescence, especially when HSCs are stressed under certain pathological conditions. Future studies should define the molecular elements that are important in the regulation of HSC senescence.