Hypothesis

Aged stem cells accumulate altered nuclear lamina interactions that tether super-enhancer regions to the nuclear periphery, leading to local chromatin compaction and accessibility loss despite gaining broad H3K4me3 domains at promoters. This peripheral sequestration uncouples enhancer-promoter looping, causing lineage‑inappropriate transcription and functional decline.

Mechanistic Rationale

• Loss of H4K16ac epipolarity reduces the electrostatic barrier that keeps chromatin away from lamin-associated domains (LADs), allowing H3K4me3‑broadened promoters to drift toward the periphery.
• Simultaneously, age‑related decline in TET activity increases 5mC at super-enhancers, strengthening their affinity for LAD‑binding proteins such as LBR and lamin A/C.
• Pioneer factor occupancy (e.g., SOX9) at super-enhancers becomes unstable, further favoring peripheral anchoring over transcriptional condensate formation.
• The resulting mislocalization explains the bidirectional accessibility shifts observed in neural stem cells: quiescent cells retain peripheral tethering (low accessibility), whereas activated cells attempt to loop enhancers but are restrained by excessive integrin‑mediated adhesions that reinforce nuclear stiffness and peripheral chromatin retention.

Testable Predictions

1. In young stem cells, super‑enhancer loci show low Lamin B1 ChIP‑signal; in aged cells, the same loci gain Lamin B1 occupancy correlating with reduced ATAC‑seq signal.
2. Acute depletion of lamin A/C (using siRNA or CRISPRi) in aged HSCs will reduce peripheral super‑enhancer tethering, increase ATAC‑seq accessibility at lineage‑specific enhancers, and restore competitive repopulation without altering global H3K4me3 breadth.
3. Overexpressing a membrane‑tethered H4K16ac mimic (e.g., H4K16ac‑GFP‑CAAX) in aged NSCs will decrease peripheral chromatin binding, attenuate aberrant adhesion gene accessibility, and rescue migration after ROCK inhibition.
4. Pharmacological disruption of LINC complexes (e.g., with SUN1/KASH domain peptides) will phenocopy lamin A/C loss, alleviating accessibility erosion in both HSCs and NSCs.

Experimental Approach

• Perform DamID or CUT&RUN for Lamin B1 and LBR in FACS‑sorted young vs. old HSCs and NSCs; intersect peaks with ATAC‑seq and H3K4me3 broad domains.
• Use lentiviral shRNA to knock down LMNA in aged mouse HSCs; assay competitive transplantation, ATAC‑seq, and H3K4me3 ChIP‑seq.
• Express H4K16ac‑CAAX in aged NSCs via AAV; measure adhesion gene ATAC‑seq, traction force microscopy, and migration in vitro after ROCKi treatment.
• Treat aged stem cell cultures with SUN1‑derived dominant‑negative peptide; assess changes in super‑enhancer H3K27ac, RNA‑pol II occupancy, and functional readouts (colony formation, neurosphere formation).

If lamin‑mediated peripheral tethering drives the accessibility paradox, reducing lamina‑chromatin interactions should normalize enhancer activity and stem‑cell function without erasing the age‑associated H3K4me3 broadening. Conversely, if accessibility changes persist despite lamina disruption, the hypothesis would be falsified, pointing to alternative mechanisms such as phase‑separation defects or metabolite‑driven chromatin changes.