Chromatin insulation loss drives age‑associated enhancer hijacking and inflammation in stem cells

Aged stem cells show eroded chromatin insulation, manifest as loss of TAD boundaries and ectopic super‑enhancer activity that drives inflammatory gene programs rather than lineage‑specific transcription. This decay mirrors a failure of insulator proteins such as CTCF and cohesin to maintain genomic architecture, not the execution of a conserved aging program. We hypothesize that reinforcing insulator binding at the flanks of tissue‑specific super‑enhancers restores proper enhancer‑promoter looping, silences maladaptive interferon‑stimulated genes, and rescues regenerative capacity without invoking a programmed death mechanism.

Mechanism

In young mesenchymal and muscle stem cells, CTCF occupies convergent sites at TAD borders, blocking aberrant enhancer contact with promoters of immune genes. With age, CTCF occupancy drops and cohesin loading frays; it's as if the genome loses its fence. This permits super‑enhancers destined for ECM remodeling to contact interferon‑stimulated loci, producing the chronic inflammatory signature observed across tissues Multi‑tissue analysis reveals widespread upregulation of immune and interferon response pathways with age, accompanied by chromatin remodeling at endogenous retroviral sequences. Restoring CTCF levels or stabilizing cohesin should re‑establish boundary strength, sequester super‑enhancers to their native targets, and dampen NF‑κB/IRF signaling.

Testable predictions

we're expecting the following outcomes

1. Forced expression of CTCF (or a cohesin‑loading factor such as NIPBL) in aged murine MSCs and MuSCs will:
   • increase insulation score at formerly weakened TAD borders (Hi‑C),
   • reduce H3K27ac accumulation at non‑myogenic super‑enhancers,
   • lower expression of IFN‑stimulated genes (e.g., Ifit1, Isg15),
   • improve colony‑forming efficiency and myogenic differentiation in vitro.
2. Acute degradation of CTCF in young stem cells using an auxin‑inducible degron will recapitulate age‑associated TAD loss, ectopic super‑enhancer activity, and heightened interferon response within 72 h, echoing the Hi‑C weakening seen after YY1 depletion from super‑enhancers and promoters in aged MSCs YY1 depletion from super‑enhancers and promoters in aged MSCs leads to weakened Hi‑C contacts, and YY1 knockdown in young cells recapitulates age‑associated expression changes.
3. Comparative genomics of long‑lived versus short‑lived mammalian species will reveal stronger conservation of CTCF motifs flanking super‑enhancers in the former, correlating with basal lower interferon tone, consistent with the observation that muscle stem cells exhibit 938‑1,491 differential TADs between young and old/geriatric mice, with approximately 38% showing loss of insulation Muscle stem cells exhibit 938‑1,491 differential TADs between young and old/geriatric mice, with approximately 38% showing loss of insulation.
4. Pharmacological inhibition of bromodomain proteins (e.g., BET inhibitors) will not suppress the age‑related interferon signature if CTCF loss is upstream, indicating that the phenotype stems from architectural collapse rather than enhancer activity per se.

Falsification

If enhancing CTCF fails to restore TAD insulation, does not diminish ectopic super‑enhancer marks, and does not improve regenerative readouts, then the hypothesis that insulator loss drives age‑associated enhancer hijacking is invalid. Conversely, if CTCF augmentation rescues phenotypes without altering global DNA methylation or telomere length, it supports the view that aging phenotypes arise from secondary architectural decay rather than a primary death program.