Age Related Changes in Hoechst 33342 Efflux Dynamics and Side Population Phenotype in Murine Bone Marrow.
Bibliographic record
Abstract
Abstract The mechanisms underlying the aging of the hematopoietic stem cell (HSC) compartment remain poorly understood. The ATP-binding cassette cell surface transport protein, ABCG2, has been identified as the transporter responsible for Hoechst 33342 (Hst) efflux in primitive stem cells and its expression is associated with the side population (SP) phenotype in both murine and human bone marrow (BM). ABCG2 expression and Hst efflux activity is highest in those cells with the greatest repopulating potential and is progressively downregulated during differentiation. The substrate profile of ABCG2, which includes a number of antineoplastic drugs, protoporphyrin IX and the chlorophyll breakdown product pheophorbide, suggest that ABCG2 transporters may function to protect stem cells from cytotoxic insults, a function which may be of great importance in stem cell maintenance. Amongst laboratory mice, the C57BL/6 strain is the longest lived and appears to accumulate HSC’s with age as assessed by both phenotype and colony forming assays. While the phenotypic features of the SP profile have been well characterized in both humans and young mice, little is known of the Hst efflux dynamics or phenotype of the SP profile in old and very old C57BL/6 mice. In order to further characterize the SP profile in old mice, whole BM was extracted from the femurs, tibiae, pelvis and thoracolumbar vertebral bodies of young (9–13 week) and old (95–108 week) C57BL/6 (Ly5.1) mice. Cells were stained with 5μg/ml Hst followed by staining with a combination of CD45.1 FITC, Sca1 PE, c-kit APC, CD34 FITC, biotinylated CD34 and lineage markers and strep PE-Texas Red. In addition, serial sampling of Hst incubated cells was performed to assess Hst efflux activity at 20 mins incubation through to 100mins. Six-color flow analysis was performed on a FACS Vantage™ (BD) cytometer and data analyzed using FlowJo™ software. Results show a marked increase in cells with an SP phenotype in old vs young mice (mean±SD 1.85%±0.88 vs 0.15%±0.09) which were more highly enriched for CD34-Sca1+ckit+ (22.2%±8.65 vs 8.89%±6.7) cells. Subdividing the SP profile into four regions (R1 to R4) from highest to lowest Hst efflux activity revealed that in old mice, SP cells with the highest Hst efflux activity were almost exclusively of a CD34-Sca1+ckit+ phenotype (82.3%±14.0 vs 11.5%±7.8), with a decreasing proportion of these cells represented throughout the remaining SP tail, though a significant proportion of cells within R4 remain CD34-Sca1+ckit+ (15.3%±7.83 vs 4.19±3.01). Similar patterns have been observed in both whole and lineage depleted BM. In addition, BM cells from old C57BL/6 mice show prolonged Hst efflux activity with an increase in cells in the SP gate at 100 mins (1.51%±0.50 vs 0.10%±0.06). We conclude that in old C57Bl/6 mice, cells accumulate which have the capacity to efflux Hst in agreement with previous reports of an increase in HSC number with age in this mouse strain.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".