Hypothesis

Sleep orchestrates an active triage that not only clears metabolic waste but also licenses epigenetic resetting of neural chromatin; disrupted sleep blocks this licensing, leaving aging‑associated marks that impair the fidelity of induced pluripotent stem cell (iPSC) reprogramming.

Mechanistic Basis

During NREM sleep, neuronal slow‑wave bursts drive extracellular norepinephrine oscillations that expand the interstitial space ~60% and power glymphatic influx [2]. This convective flux carries not only soluble proteins like β‑amyloid but also nucleosomal particles and histone‑modifying enzymes released from active synapses. We propose that the glymphatic stream preferentially extracts repressive chromatin complexes (e.g., HDAC2‑containing NuRD, PRC2) from peri‑synaptic niches, thereby lowering local histone deacetylation and H3K27me3 levels. The resulting chromatin openness permits sleep‑dependent recruitment of TET enzymes and histone acetyltransferases that erase age‑related DNA methylation and acetylation marks, a process that cannot occur when norepinephrine troughs are absent during wakefulness or sleep deprivation.

Consequently, sleep loss sustains a high‑norepinephrine tone that suppresses glymphatic inflow, traps repressive marks, and locks neurons into a DNA‑damage‑response state (elevated CHEK2, NBN) that mirrors the senescence‑associated secretory phenotype observed in aged adults [1]. These retained epigenetic lesions impede the epigenetic remodeling required for efficient iPSC reprogramming, leading to incomplete resetting and aberrant lineage priming.

Predictions and Experimental Design

1. Enhanced glymphatic flow improves reprogramming – Mice receiving auditory slow‑wave stimulation (0.5 Hz) during NREM sleep to boost glymphatic influx will yield fibroblasts‑derived iPSCs with higher pluripotency marker expression (OCT4, NANOG) and lower residual methylation at age‑associated CpGs compared to unstimulated controls.
2. Blocking norepinephrine abrogates the effect – Pharmacological inhibition of β‑adrenergic receptors (propranolol) during sleep will prevent the stimulation‑induced increase in reprogramming efficiency and maintain high levels of H3K27me3 at pluripotency gene promoters.
3. Sleep deprivation retains repressive marks – Neurons isolated from sleep‑deprived mice will show elevated HDAC2 chromatin occupancy and reduced TET activity, correlating with lower reprogramming yield and increased expression of SASP factors (IL‑6, TNF).

Experiments: isolate cortical neurons after (a) normal sleep, (b) sleep deprivation, (c) sleep deprivation + slow‑wave stimulation, (d) sleep deprivation + stimulation + propranolol. Perform ATAC‑seq, ChIP‑seq for H3K27me3/HDAC2, and quantitative reprogramming assays (colonies‑forming efficiency, pluripotency score).

Potential Outcomes and Falsifiability

• If slow‑wave stimulation raises iPSC efficiency and this rise is blocked by propranolol, the hypothesis gains support: sleep‑driven glymphatic flow, via norepinephrine dynamics, gates epigenetic resetting.
• If stimulation fails to improve reprogramming despite verified glymphatic enhancement (measured by CSF‑ISF tracer flux), or if propranolol does not diminish the effect, the causal link between sleep‑phase molecular programs and epigenetic resetting is refuted.
• If sleep deprivation does not alter repressive chromatin marks or reprogramming outcomes, the proposed epigenetic surveillance role of sleep would be falsified, implying that observed aging effects stem from unrelated pathways.

This framework directly ties the "autopsy" metaphor to a tangible, manipulable molecular cascade, offering a clear path to test whether sleep’s nightly verdict decides not just what debris is cleared, but which epigenetic states are permitted to persist.