Aging of hematopoietic stem cells is regulated by the stem cell niche.

Adult stem cells provide the basis for regeneration of aging tissue. Their dual ability for self-renewal and multilineage differentiation is controlled by direct interaction with a specific microenvironment -- the so called "stem cell niche". Hematopoietic stem cells (HSC) reside in the bone marrow. It is still under debate if HSC can rejuvenate infinitively or if they do not possess "true" self-renewal and undergo replicative senescence such as any other somatic cell. Furthermore, the question arises to what extent age-related changes in HSC are due to intrinsic factors or regulated by external stimuli. There is growing evidence, that the stem cell niche is most important for the regulation of cellular aging in adult stem cells. It is the stem cell niche that (i) maintains HSC in a quiescent state that reduces DNA damage as well as replicative senescence, (ii) protects from radicals and toxic compounds, (iii) regulates cell intrinsic signal cascades and (iv) modulates gene expression and epigenetic modifications in HSC. Thus, the interplay with the stem cell niche controls HSC function including the aging process of the hematopoiesis.