Hypothesis

Age‑related atrophy of the adrenal zona reticularis lowers circulating DHEA‑S, which diminishes sigma‑1 receptor–driven astrocytic aquaporin‑4 (AQP4) translocation to perivascular endfeet, thereby impairing glymphatic influx during slow‑wave sleep. Restoring physiologic night‑time DHEA‑S levels will reactivate AQP4‑dependent CSF flow, rescue the brain’s nocturnal "autopsy," and interrupt the maladaptive HPA‑axis feedback loop.

Mechanistic Rationale

DHEA functions as an endogenous agonist of the sigma‑1 receptor (1). Sigma‑1 activation in astrocytes triggers ER calcium release, promoting AQP4 phosphorylation and its enrichment at vascular endfeet (2). In aged animals, zona reticularis loss reduces DHEA‑S, decreasing sigma‑1 tone and causing AQP4 mislocalization, a state linked to reduced glymphatic influx (3). The resulting accumulation of metabolic waste and inflammatory mediators amplifies neuroinflammation, which blunts glucocorticoid feedback, flattens corticosterone rhythms, and further suppresses slow‑wave sleep (4,5). This creates a self‑reinforcing cycle that accelerates neuroendocrine aging.

Predictions & Experimental Design

Baseline characterization – Cohorts of young (3‑month) and aged (18‑month) C57BL/6 mice will be monitored for serum DHEA‑S, corticosterone diurnal rhythm (via tail‑tip sampling), EEG‑defined slow‑wave sleep proportion, DTI‑ALPS index as a glymphatic proxy, and perivascular AQP4 distribution (immunofluorescence). Aged mice are expected to show reduced DHEA‑S, flattened corticosterone, decreased SW sleep, lower ALPS scores, and diffuse AQP4 staining.

Intervention – Aged mice will receive subcutaneous DHEA‑S pellets delivering a physiologic night‑time peak (≈5 µg/h) for 4 weeks. Controls include vehicle‑treated aged mice and a DHEA‑S + sigma‑1 antagonist (BD‑1063, 10 mg/kg i.p. daily) group to test pathway specificity.

Outcome measures – After treatment:

1. Serum DHEA‑S restored to young‑adult range.
2. Increased SW sleep duration and density (EEG spectral analysis).
3. Elevated DTI‑ALPS index indicating enhanced glymphatic flux.
4. Rescue of perivascular AQP4 polarization (quantified by membrane‑to‑cytosol fluorescence ratio).
5. Re‑emergence of robust corticosterone rhythm (higher morning peak, lower nadir).
6. Reduced hippocampal IL‑6, TNF‑α, and amyloid‑β load (ELISA/immunohistochemistry).

Statistical comparisons will use two‑way ANOVA with post‑hoc Tukey tests; n = 10 per group provides 80 % power to detect a 20 % change in ALPS index (α = 0.05).

Potential Outcomes

Supportive result – DHEA‑S treatment normalizes SW sleep, improves ALPS index, restores AQP4 polarization, and reestablishes corticosterone amplitude; the sigma‑1 antagonist abolishes these improvements, confirming receptor mediation.

Falsifying result – DHEA‑S elevates SW sleep but fails to alter glymphatic metrics, AQP4 localization, or HPA rhythm, indicating that adrenal steroid effects on sleep architecture are independent of glymphatic clearance, or that additional downstream mechanisms are required for the predicted rescue.