Divisional history and hematopoietic stem cell function during homeostasis.

Area of Science:

• Hematology
• Stem Cell Biology
• Cellular Dynamics

Background:

• Hematopoietic stem cells (HSCs) are crucial for blood cell production.
• Understanding HSC behavior during homeostasis is vital for regenerative medicine.
• The role of cell division history in HSC function remains incompletely understood.

Purpose of the Study:

• To investigate the homeostatic behavior of hematopoietic stem and progenitor cells (HSPCs) based on their division history.
• To determine if cell-surface phenotype or temporal quiescence is a better indicator of HSC function.
• To explore the consequences of HSCs exiting dormancy.

Main Methods:

• Utilized an HSPC-specific GFP label-retaining system to track cell division history.
• Assessed repopulating potential and functional activities of HSCs after transplantation.
• Phenotypically characterized dormant HSPCs and compared their stem cell activity.

Main Results:

• Homeostatic HSCs lose repopulating potential after limited cell divisions.
• Exiting dormancy and accumulating divisions leads to loss of G0 return ability and quiescent HSC functions.
• Dormant HSPCs, phenotypically resembling multipotent progenitors, exhibit robust stem cell activity.
• Phenotype is a less reliable indicator of function than temporal quiescence.

Conclusions:

• Temporal quiescence is a more critical determinant of HSC function than cell-surface phenotype.
• Once homeostatic HSCs leave dormancy, they exhibit phenotypic self-renewal but lose actual self-renewal activity, leading to functional extinction.
• These findings challenge the universal definition of self-renewal as a characteristic of homeostatic HSCs, contrasting it with stress-induced self-renewal.