Impaired hematopoietic stem cell functioning after serial transplantation and during normal aging

Area of Science:

• Gerontology
• Stem Cell Biology
• Hematopoiesis

Background:

• Adult somatic stem cells are crucial for tissue repair and exhibit self-renewal.
• Stem cell pool reduction during aging is observed in short-lived DBA/2 (D2) mice but not long-lived C57BL/6 (B6) mice.
• This suggests a genetically determined 'mitotic clock' limits stem cell function and potentially organismal aging.

Purpose of the Study:

• To investigate the intrinsic, genetically controlled limitations on stem cell self-renewal and expansion potential.
• To compare the serial transplantation capacity of hematopoietic stem cells (HSCs) between short-lived D2 and long-lived B6 mice.
• To explore the role of stem cell aging in tissue reconstitution and graft acceptance.

Main Methods:

• Serial transplantation of unfractionated bone marrow (BM) or purified Lin(-)Sca-1(+)c-kit(+) (LSK) cells from D2 and B6 mice into lethally irradiated recipients.
• Quantification of stem cell activity and population doublings across serial transplants.
• Assessment of graft acceptance in non-conditioned recipients and aged mice.

Main Results:

• Serial transplantation significantly reduced stem cell activity in both mouse strains.
• B6 mice exhibited approximately 30 population doublings, while D2 mice showed only approximately 20, a 1,000-fold difference in expansion potential.
• Recipients of serially transplanted BM cells accepted fresh grafts without conditioning, and young BM cells engrafted aged mice.

Conclusions:

• An intrinsic, genetically programmed mechanism limits hematopoietic stem cell (HSC) proliferation and function during aging.
• This 'mitotic clock' in HSCs contributes to the aging process and reduced tissue regenerative capacity.
• Stem cell aging is a critical factor in organismal lifespan and health.