Enhanced fracture repair in p21−/− mice is mediated through increased callus mineralization
Bibliographic record
Abstract
Fracture healing is a complex, multi-phase process involving mesenchymal progenitor cell (MPC) recruitment, chondrogenesis, osteogenesis and bone remodelling. The cyclin-dependent kinase inhibitor p21 is known to regulate cell cycle progression and has been implicated in tissue regeneration. Here, we investigated the role of p21 in endochondral fracture repair using a transverse tibial fracture model in physiologically normal mice. Prx1CreERT2-GFP;R26RTdtomato mice on C57BL/6 and p21 −/− backgrounds enabled lineage tracing of MPCs. Longitudinal in vivo micro-CT, histological analysis, tissue cytometry and mechanical testing were used to assess callus formation, cellular composition, and mechanical integrity. Our results demonstrate that p21 −/− mice exhibit enhanced bone regeneration, with significantly higher bone mineral density (BMD) and bone volume fraction (BV/TV) in the fracture callus at 2 and 4 weeks post-fracture (wpf). Histology revealed increased Prx1 + cell recruitment, along with greater expression of chondrogenic (Sox9) and osteogenic (BSP) markers in p21 −/− mice at 2wpf. Biomechanical testing showed that despite similar strength, p21 −/− calluses had reduced toughness, suggesting altered matrix remodelling. Collectively, our findings highlight p21 as a negative regulator of bone regeneration, likely through modulation of MPC recruitment and differentiation. Together, these data suggest therapeutic targeting of p21 may enhance fracture healing and counteract osteoporosis in terms of bone remodelling and repair.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.003 | 0.001 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.003 | 0.003 |
| Insufficient payload (model declined to judge) | 0.008 | 0.002 |
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".