Table 3.
Methods for Assessing HSC Aging
| HSC feature | Effect of age | Method of measurement | Advantage | Limitation |
|---|---|---|---|---|
| Pool size | Expanded with age [1] | Flow cytometry-based analyses of BM populations | Quantitative | Does not reflect functionality |
| Repopulation capacity | Decreased with age [1] | Flow cytometry-based analyses of multilineage blood and BM chimerism after transplantation | Quantitative; reflects function; clinically relevant | Dependent on transplantation method (i.e., lethal vs sub-lethal irradiation, purified HSCs vs whole BM, competitive vs noncompetitive setting, etc.); similar effects observed on regenerative and inflammatory stresses; readout takes months |
| Lineage potential | Lymphoid deficiency with age [1] | Flow cytometry-based analyses of lymphoid and myeloid blood and BM populations | Quantitative; reflects function; clinically relevant | Dependent on engraftment efficiency; HSC exhaustion can also result in improved lymphomyeloid ratio since lymphoid cells have longer turnover time than myeloid cells; similar effects observed on regenerative and inflammatory stress; readout takes months |
| Replication stress | Increased with age [7,15,145] | Tracking division kinetics in culture; immunofluorescence-based visualization of γH2A.x and fibrillarin colocalization | Purified HSCs; scalable; quantitative, molecular feature | Dependent on cell cycle status |
| DNA damage | Increased with age [1] | Immunofluorescence-based γH2A.x staining; alkaline COMET assays | Purified HSCs; scalable; quantitative, molecular feature | Unclear how it relates to functionality |
| Cell polarity | Loss of polarity with age [15,17,70,189]. | Immunofluorescence-based visualization of Cdc42 and β-actin | Purified HSCs; scalable; quantitative, molecular feature | Unclear how it relates to functionality |
| Surface marker | Increased expression with age [54,102,190] | Flow cytometry-based analyses of CD150 and CD41 levels in BM populations | Quantitative | Unclear how it relates to functionality; CD41 is also upregulated in inflammatory conditions and CD150 on HSC activation |
| Cell cycle status | Loss of quiescence with age [7,147] | Flow cytometry-based cell cycle analyses; BrdU/EdU incorporation assays | Quantitative | Unclear how it relates to functionality; influenced by inflammation |