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In Vivo Amelioration of Age-Associated Hallmarks by Partial Reprogramming

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In Vivo Amelioration of Age-Associated Hallmarks by Partial Reprogramming

Ocampo A et al. (Izpisua Belmonte JC, senior author) · Cell 167(7): 1719–1733.e12 · 2016 · DOI: 10.1016/j.cell.2016.11.052

TL;DR

The foundational in-vivo partial reprogramming study. Used a doxycycline-inducible 4-factor (OSKM: OCT4, SOX2, KLF4, c-MYC) transgenic mouse system to show that cyclic, short-pulse OSKM expression can ameliorate aging phenotypes and extend lifespan in a Hutchinson-Gilford Progeria Syndrome model (LAKI mice; Lmna G609G knockin), and can improve tissue regeneration (muscle, pancreatic beta-cells) and glucose homeostasis in normally aged wild-type mice. Critically demonstrated that cyclic dosing avoids tumorigenesis — the key safety breakthrough enabling the in-vivo partial reprogramming paradigm. This paper predates Lu 2020 (OSK retinal) and Yang 2023 (ICE system) and established the conceptual and experimental foundation for in-vivo epigenetic rejuvenation as a research program.

903 citations as of 2026-05-07; citation_percentile = 100; FWCI = 34.8 (OpenAlex).

Background and rationale

Full Yamanaka reprogramming (sustained OSKM expression) erases differentiated cell identity to generate iPSCs — which carry high teratoma risk and are not clinically tractable for whole-organism aging reversal. Ocampo et al. tested whether brief, cyclic OSKM expression could capture the epigenetic-resetting benefit of reprogramming without driving cells to pluripotency. The conceptual bet: epigenetic aging is a contributor to loss of cellular function, and transient TF pulses might reset methylation state while leaving cell-type identity intact.

The paper builds on partial-reprogramming as a process and represents the in-vivo proof-of-concept for in-vivo-partial-reprogramming-therapy.

Experimental systems

System 1 — LAKI progeria model (primary lifespan experiment)

Mouse model: LAKI mice carry a Lmna G609G knockin mutation (homozygous: G609G/G609G) that produces progerin — a truncated, toxic form of lamin A — recapitulating key features of Hutchinson-Gilford Progeria Syndrome (progeria). These mice exhibit accelerated phenotypes including growth retardation, lipodystrophy, cardiovascular defects, and shortened lifespan on a C57BL/6 background. The LAKI model is a progeroid model, not a model of normal aging. needs-human-replication

4F transgene: A doxycycline-inducible OSKM system was incorporated into the LAKI background (“LAKI 4F” mice). Controls: LAKI mice without the 4F transgene.

Cyclic dosing: 2 days doxycycline (Dox) ON / 5 days Dox OFF (weekly cycle). Cyclic dosing in single-copy 4F mice produced no teratomas or cancer (see Safety section); teratomas appeared only in two-copy (gene-dosage-doubled) mice under cyclic dosing. Continuous dox in single-copy 4F mice caused rapid mortality within 4 days without reaching the stage of tumor development.

Group sizes (lifespan study):

  • LAKI −Dox (control): n = 20
  • LAKI +Dox (cyclic): n = 13
  • LAKI 4F −Dox (transgenic, no induction): n = 18
  • LAKI 4F +Dox cyclic (treated): n = 15

System 2 — Wild-type aged mice (functional improvement)

Mice: 12-month-old wild-type C57BL/6J mice (aged but not progeroid). Two functional assays:

  1. Metabolic disease recovery: Streptozotocin (STZ, 30 mg/kg, 5 daily injections)-induced beta-cell ablation → glucose tolerance testing (GTT) 2 weeks after STZ. n = 6/group (−Dox n = 6; +Dox n = 6; Figure 7B legend). Pancreatic islet histology at 2 weeks post-STZ: n not specified per group for histology endpoint.
  2. Muscle injury recovery: Cardiotoxin (CTX, 10 µM, 50 µL intramuscular)-induced injury to tibialis anterior (TA) → histological assessment of regeneration (fiber cross-sectional area, centralized nuclei) 10 days post-injury. Fiber CSA and central nuclei: n = 4/group (Figure 7G); Pax7+ satellite cell counts: n = 4/group (Figure 7H).

Note: Wild-type aged mice did not undergo a lifespan study in this paper. The aged WT experiments demonstrated improved recovery from acute injury/disease, not baseline lifespan extension in normally aged animals. long-term-unknown

Key results

Cyclic OSKM extends lifespan and ameliorates hallmarks in LAKI progeria mice

LAKI 4F mice under cyclic doxycycline administration showed significantly extended survival compared to LAKI controls (log-rank [Mantel-Cox] test, p < 0.0001). The paper does not state a lifespan extension percentage explicitly in the text — it reports “a dramatic increase in median and maximal lifespan” with the result shown in Figure 4B survival curves only. Reading from Figure 4B, median survival of LAKI 4F −Dox is approximately 18 weeks and LAKI 4F +Dox approximately 24 weeks, yielding a visual estimate of ~33% median lifespan extension; this figure is widely cited in secondary literature but is a curve-read, not a number stated in the paper 1. needs-replication

Accompanying hallmark amelioration in LAKI 4F + cyclic Dox:

  • Improved body weight maintenance (LAKI mice lose weight rapidly with age)
  • Improved cardiovascular function (ECG parameters; n=4/group)
  • Reduced expression of aging-associated markers in skin and other tissues
  • Improved transcriptomic signatures toward a younger state

Tissue regeneration improved in wild-type aged mice

In 12-month-old WT C57BL/6J mice, cyclic OSKM expression improved:

  • Glucose homeostasis recovery post-STZ: faster normalization of blood glucose in OSKM-expressing mice vs. controls following pancreatic beta-cell ablation; interpreted as improved regenerative capacity of remaining beta-cell progenitors or improved metabolic adaptation.
  • Muscle regeneration post-cardiotoxin: larger cross-sectional area of regenerating muscle fibers and more pronounced regeneration histology in OSKM mice vs. controls after tibialis anterior injury.
DimensionStatus
Pathway conserved in humans?partial (OSKM are human TFs; epigenetic drift mechanisms conserved; LAKI progeria model uses human LMNA mutation)
Phenotype conserved in humans?unknown (no human partial reprogramming data; progeria model not normal aging)
Replicated in humans?no

needs-human-replication needs-replication — single-lab (Belmonte group); progeria model vs. normal aging; no independent replication of the lifespan claim at the same scale.

Critical methodological insight: cyclic dosing avoids tumorigenesis

This is the safety finding that unlocked the in-vivo reprogramming paradigm:

The paper describes two distinct failure modes tested in mice carrying the 4F cassette:

  • Continuous doxycycline in single-copy 4F mice: caused rapid significant weight loss and high mortality within 4 days (Figure 3A, 3B; −Dox n = 11; +Dox n = 26) due to dedifferentiation of cells in vital organs. Teratomas are not specifically reported for this arm — mice died of organ failure before tumor development could be assessed.
  • Cyclic doxycycline (2 days ON / 5 days OFF) in mice carrying two copies of both the OSKM polycistron and the rtTA cassette: after 8 weeks of cyclic administration, teratoma formation was observed in the liver, kidney, and pancreas (Figure 3E, 3F). Teratomas contained ectoderm, mesoderm, and endoderm tissue — confirming full pluripotency induction in vivo.
  • Cyclic doxycycline in single-copy 4F mice (the main experimental protocol): no teratomas or signs of dysplasia or cancer reported. No signs of pluripotency were detected in any organ analyzed after 35 cycles.

This establishes the principle that the window between “epigenetic rejuvenation” and “full reprogramming → tumor” depends on OSKM gene dosage and pulse scheduling — the key safety insight enabling subsequent work (Browder 2022, Yang 2023). The main LAKI 4F experiments used single-copy mice. The precise mechanistic reason why single-copy cyclic dosing avoids pluripotency while achieving epigenetic effects is not fully characterized. dose-response-unclear

Molecular context

Ocampo et al. reported changes in H3K9me3 and H3K27me3 histone marks and gene expression programs consistent with partial reversal of aging-associated epigenetic drift — the central mechanistic claim. The paper does not characterize TET demethylase involvement (that finding came from Lu 2020, which showed TET1/TET2 are required for OSK-mediated axon regeneration) 2.

The partial-reprogramming process page (verified 2026-05-04) provides a detailed mechanistic synthesis integrating Ocampo 2016 with Lu 2020 and Yang 2023.

Significance for the wiki

This paper is the founding primary source for:

  • partial-reprogramming (verified process page) — Ocampo 2016 is the first of three key citations in § Two main experimental strategies.
  • in-vivo-partial-reprogramming-therapy (verified intervention page) — Ocampo 2016 establishes the in-vivo concept that the intervention page translates toward clinical development.
  • information-theory-of-aging — Ocampo 2016 is consistent evidence that epigenetic changes are reversible in vivo, supporting the information-theory hypothesis, though the paper does not itself invoke that framing.
  • progeria (verified) — the LAKI/HGPS model used here is described in detail on the progeria page; Ocampo 2016 is cited as proof that genetic HGPS phenotypes are partially reversed by OSKM.

Limitations

  • Progeroid model, not normal aging. The lifespan extension result is in LAKI Lmna-G609G mice. HGPS is caused by a dominant toxic-gain-of-function lamin A truncation (progerin) that causes nuclear dysfunction. Whether OSKM-mediated epigenetic reversal has the same effect magnitude in the much more complex landscape of normal aging is unknown. The WT experiments showed functional improvement in injury recovery but not lifespan extension.
  • Small group sizes. Lifespan study: n=15 (treated) vs n=18 (untransgenic Dox-treated control). Standard for a Mouse study of this era, but underpowered for definitive survival curve conclusions.
  • c-Myc inclusion (oncogenic risk). All experiments used full OSKM (c-Myc included). c-Myc is a proto-oncogene; its inclusion increases tumorigenesis risk beyond OSK alone. Subsequent work (Lu 2020, Yang 2023) moved to c-Myc-omitting OSK for this reason.
  • Single lab. Belmonte group (Salk Institute); not independently replicated at the same scale. The subsequent Browder 2022 systemic OSKM study (independent group) used normally aged rather than progeroid mice and did not claim lifespan extension as a primary endpoint.
  • Mechanism incompletely resolved. The paper reports epigenetic marker changes and functional outcomes; the precise CpG loci and TF-binding sequences responsible for the rejuvenating effect were not characterized at single-base resolution in 2016.
  • Teratoma definition of “safe” is copy-number- and protocol-specific. The cyclic 2d-on/5d-off protocol in single-copy 4F mice reported no teratomas or dysplasia in any organ after 35 cycles. However, the same cyclic protocol in two-copy (4F/4F; rtTA/rtTA) mice produced teratomas at 8 weeks. The safe dosing window therefore depends on OSKM gene copy number, is likely tissue- and age-specific, and long-term safety monitoring beyond the study period was not performed.

needs-human-replication — no human equivalent data exists
needs-replication — single lab; progeria-model; not yet replicated in normally aged mice lifespan study by an independent group
long-term-unknown — long-term safety of cyclic OSKM (including carcinogenesis risk over years) uncharacterized
dose-response-unclear — the molecular boundary between “rejuvenating pulse” and “dedifferentiation toward pluripotency” is not precisely mapped

EntityRelationship
partial-reprogramming (verified)Process page: mechanistic synthesis of Ocampo 2016 + Lu 2020 + Yang 2023; this study page is the primary citation for the Belmonte cyclic-OSKM experiments
in-vivo-partial-reprogramming-therapy (verified)Intervention page: Ocampo 2016 is the foundational in-vivo proof-of-concept; all clinical-development framing on that page rests on this result
epigenetic-alterationsHallmark targeted: OSKM expression reverses aging-associated histone and methylation marks
stem-cell-exhaustionHallmark addressed: improved regenerative capacity in aged muscle and pancreatic tissue
oct4Core OSKM TF; required for the partial reprogramming effect
sox2Core OSKM TF
klf4Core OSKM TF
c-mycFourth OSKM factor; included here (unlike Lu 2020 / Yang 2023 OSK protocols); oncogenic risk
progeria (verified)LAKI Lmna-G609G mouse = HGPS model; Ocampo 2016 used this model for lifespan study
lmnaGene encoding lamin A; G609G knockin in LAKI mice produces progerin; stub — no wiki page yet
hutchinson-gilford-progeria-syndromeSynonym for progeria; verify resolution via progeria.md aliases
information-theory-of-agingOcampo 2016 is consistent with the epigenetic-information-loss causal hypothesis; cited as supportive but indirect evidence
mus-musculusAll experiments conducted in mouse
lu-2020-osk-vision-restorationFollow-on landmark; used OSK (not OSKM) in retinal ganglion cells; identified TET1/TET2 requirement
yang-2023-epigenetic-information-lossICE system; Yang 2023 represents the systemic extension of what Ocampo 2016 initiated

Footnotes

Footnotes

  1. Primary source: Ocampo A et al. · Cell 167(7):1719–1733.e12 · 2016 · doi:10.1016/j.cell.2016.11.052 · in-vivo (dox-inducible OSKM) · n=66 total (LAKI lifespan study: LAKI −Dox n=20, LAKI +Dox n=13, LAKI 4F −Dox n=18, LAKI 4F +Dox n=15) · log-rank (Mantel-Cox) p<0.0001 · model: LAKI Lmna-G609G/C57BL/6 + aged WT C57BL/6J. Note: lifespan extension ~33% is a visual estimate from Figure 4B survival curves; the paper does not state this percentage in the text. Verified against primary source PDF 2026-05-07. ↩

  2. lu-2020-osk-vision-restoration · in-vivo (Tet-Off AAV2 dual-vector; intravitreal) · model: Mus musculus C57BL6/J (optic nerve crush + glaucoma models; 1–20 month old) · doi:10.1038/s41586-020-2975-4 · local PDF available · 771 citations; FWCI=113 · TET1/TET2 required (TET3 not); OSK without c-Myc; established TET-demethylase mechanistic requirement absent from Ocampo 2016 ↩

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