https://www.cell.com/cell-reports/fulltext/S2211-1247(25)00650-3
Gpt5
Here’s a structured analysis of the Cell Reports article “Comparative analysis of mouse strains for in vivo induction of reprogramming factors” (Picó et al., 2025):
Summary
- Background: Forced expression of Yamanaka factors (Oct4, Sox2, Klf4, c-Myc, or OSKM) in vivo can reverse age-associated phenotypes. However, continuous induction often causes toxicity (loss of cell identity, organ dysfunction, premature death). Partial/cyclic protocols mitigate this but fail to achieve full rejuvenation in wild-type mice.
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Methods:
- Compared four existing whole-body OSKM-inducible mouse strains with OSKM cassettes at different genomic loci.
- Conducted transcriptomic (RNA-seq) and phenotypic analysis across multiple tissues.
- Tested effects of copy number, transactivators, and doxycycline dose.
- Developed next-generation mouse strains to restrict OSKM to certain tissues or cell populations (e.g., avoiding liver/intestine, targeting non-dividing cells).
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Findings:
- OSKM expression patterns differ by strain and cassette locus.
- Expression alters transcriptomes across tissues, often suppressing mature cell identity signatures and activating inflammatory pathways.
- High expression levels remain toxic even outside liver/intestine.
- Cassette copy number affects OSKM levels and survival.
- New “chimeric” strains (Ki67 Cre, CAG Cre) reduced toxicity, preserved body weight, and extended survival relative to whole-body reprogrammable strains.
- These strains showed reduced OSKM in liver/intestine but maintained expression in other tissues like kidney, enabling safer reprogramming.
Novelty
- Systematic cross-strain comparison of OSKM induction in vivo — clarifies how genomic insertion site, cassette order, and copy number affect expression and outcomes.
- Transcriptome-wide atlas of in vivo reprogramming across multiple tissues — highlights conserved responses (loss of cell-type identity, immune activation).
- Identification of liver/intestine as critical toxicity bottlenecks — confirms prior findings and extends them by testing different promoters and copy numbers.
- Generation of “next-generation” mouse models (Ki67 Cre, CAG Cre) that avoid ubiquitous OSKM expression — achieving longer survival with reduced organ dysfunction.
- Provides a toolbox of reprogrammable strains for the community, aiming at safer organismal rejuvenation strategies.
Critique
Strengths
- Comprehensive, side-by-side comparison of multiple reprogrammable strains.
- Integrates survival, physiology, and transcriptomics — giving mechanistic insights.
- Pragmatic: instead of only reporting toxicity, the authors engineer improved models.
- Valuable resource: cryopreserved mouse lines and RNA-seq data are made publicly available.
Limitations
- Age of mice: all experiments conducted in 2-month-old animals (young adults); unclear if results generalize to aged cohorts where rejuvenation would matter most.
- Short follow-up: focus is on survival and acute transcriptomic effects; long-term rejuvenation or healthspan outcomes are not demonstrated.
- Epigenetics underexplored: authors acknowledge lack of analysis of methylation/epigenetic clocks, which are critical for aging studies.
- Expression variability: while liver/intestine toxicity is addressed, other tissues/organs that might limit safety were not fully mapped.
- Therapeutic relevance: human translation is still remote; results are tool-building rather than demonstration of organismal rejuvenation.
Overall Evaluation
This study is a methodological advance rather than a rejuvenation breakthrough. It provides a comparative atlas and improved mouse models that reduce toxicity from whole-body OSKM induction, which is a significant step for the field. The novelty lies in systematically dissecting strain differences and engineering safer reprogrammable lines. However, the work stops short of proving actual rejuvenation or lifespan extension — future studies in aged cohorts and with epigenetic markers are needed.