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p53 mutant mice that display early ageing-associated phenotypes

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p53 mutant mice that display early ageing-associated phenotypes

TL;DR

Two independent transgenic mouse lines with augmented p53 activity — the serendipitously-derived p53+/m allele (a C-terminal-fragment-producing chimeric truncation) and the previously-described pL53 transgenic (a temperature-sensitive Ala135Val mutant) — both showed enhanced cancer resistance but accelerated aging phenotypes. Foundational evidence for the antagonistic pleiotropy of p53 in aging: tumor-suppressive activity carries a tissue-aging cost. The paper hypothesizes that the underlying mechanism is accelerated stem-cell exhaustion driven by enhanced p53-dependent senescence/arrest in progenitor compartments.

Design

  • Subjects: mixed inbred C57BL/6 × 129/Sv background (chimeras backcrossed two generations into B6 — not pure B6, important for strain-effect interpretation).
  • Genotype groups and n’s:
    • p53+/m: n=35
    • p53+/+ (WT): n=56
    • p53+/-: n=217
    • p53-/-: n=72
    • p53-/m: n=34
    • pL53 transgenic (separate line): n=66
  • m-allele structure: deletion of p53 exons 1–6 plus ≥20 kb of upstream sequence; produces a chimeric mRNA with a 55-bp leader of unknown origin spliced into exon 7. Encodes a ~24K C-terminal p53 fragment that augments wild-type p53 activity (in vitro: enhances p53 protein stability and ~2.3× p21 promoter transactivation when co-expressed with WT p53).
  • pL53 line: ~20 copies of a transgene carrying the Ala135Val temperature-sensitive p53 mutation (Lavigueur et al. 1989). Independent line, similar augmented-p53-activity model.
  • Endpoints: lifespan, tumor incidence and type (Table 1), age-associated phenotypes assessed at 24 months for p53+/m, 16–20 months for pL53 (Table 2), wound healing, hair regrowth, 5-FU haematopoietic recovery.

Key results

Tumor resistance and lifespan (p53+/m)

  • <6% tumor incidence in p53+/m mice (0 of 35 had life-threatening tumors; 2 of 35 had small localized lung lesions on histopath) vs >45% in p53+/+ littermates.
  • Median lifespan 96 weeks (p53+/m) vs 118 weeks (p53+/+) — paper reports as 23% reduction in median lifespan.
  • Maximum lifespan 136 weeks (p53+/m) vs 164 weeks (p53+/+).
  • Survival-curve comparison: P < 0.0001.

Wild-type p53 dependence

  • p53-/m mice (m allele on a p53-null background) showed only slight tumor delay vs p53-/- and similar maximal lifespan (9–10 months). The m allele’s tumor-suppressive activity requires functional WT p53.
  • Body weight reduced at 18–24 months (vs WT reduction not until 30 months).
  • Spleen, liver, kidney mass 25–40% reduced at 24 months.
  • Quadriceps muscle mass: WT mass was ~2.5× p53+/m mass at 22–24 months.
  • Pronounced lordokyphosis and osteoporosis (whole-body X-ray; reduced cortical and trabecular bone in tibia).
  • Pronounced lymphoid atrophy (reduced spleen white pulp).
  • Greatly reduced subcutaneous adipose, dermal thickness, hair regrowth.
  • Retarded wound healing.
  • Reduced anaesthetic stress tolerance — old p53+/m mice died at standard Avertin doses.
  • Reduced 5-FU haematopoietic recovery (significantly slower WBC repopulation, P=0.02).

Phenotypes NOT observed

  • No differences in lung, heart, brain, intestinal histology, hair greying, alopecia, joint disease, cataracts, blood chemistry, or male fecundity.

Internal replication via pL53 line

  • pL53 mice showed similar but milder phenotypes — sparse fur, lordokyphosis, reduced hair regrowth, reduced subcutaneous adipose (P=0.001), delayed wound healing (P=0.05). Two genetically distinct augmented-p53-activity models converge on the same accelerated-aging phenotype.

Mechanism (p53 response)

  • Kidney cells from p53+/m showed sustained p53 protein levels at 24 h post-irradiation (vs decay in p53+/-).
  • p53+/m MEFs showed elevated basal and post-irradiation p21 expression.
  • p53+/m MEFs were 2–4× more resistant to ras+myc transformation than WT.

Extrapolation to humans

DimensionStatusNotes
Pathway conserved in humans?yesTP53 highly conserved; ~85% mouse/human identity; same target genes
Phenotype conserved in humans?partialLi-Fraumeni patients (loss-of-function p53) get cancer early, supporting one half of the trade-off; no human equivalent of hyperactive p53 to test the converse. The paper notes that age-related reductions in body, liver, spleen, and kidney mass in humans (after age 60) parallel the p53+/m phenotype, but causation cannot be inferred.
Replicated in humans?noGenetic constraint — cannot deliberately engineer hyperactive p53 in humans

needs-human-replication — Direct evidence that elevated p53 activity accelerates human aging is observational and weak.

Limitations

  • Mixed C57BL/6 × 129/Sv background — strain-specific aging effects not fully controlled.
  • The m-allele deletion extends ≥20 kb upstream of p53 and could affect haploinsufficiency of an upstream gene (Efnb3 region). Authors acknowledge but argue against this based on the pL53 internal replication.
  • The m-allele protein product was demonstrated by in vitro translation but could not be directly detected in p53+/m mouse tissues — the mechanism is inferred from indirect activity assays, not direct protein measurement in vivo.
  • Whether accelerated aging is caused by enhanced senescence/apoptosis or is a downstream consequence of stem-cell-pool depletion (themselves caused by the same activity) is not separable in this model.

Independent replication (later work)

  • Maier et al. 2004 (Genes Dev; doi:10.1101/gad.1162404) — p44 short-isoform-overexpressing mice show similar accelerated aging. Different molecular intervention from Tyner 2002, same conceptual finding. Not yet a studies/ page in this wiki; cite by DOI for now.

See also

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