Hypothesis

Senescent immune cells, particularly neutrophil-derived extracellular traps (NETs) and exhausted CD8+ T cells, accumulate in the aging adrenal cortex and directly provoke zona reticularis vascular rarefaction. This immune‑mediated microvascular injury reduces oxygen and nutrient supply to DHEA‑producing cells, accelerating adrenopause independently of intrinsic glucocorticoid dysregulation.

Mechanistic Basis

• NETosis and pericyte loss – Aging neutrophils exhibit heightened NET release [4]. NET components (histones, neutrophil elastase) degrade pericyte‑derived basement membrane proteins, causing capillary dropout in the zona reticularis where pericytes regulate angiocrine support for steroidogenesis.
• T‑cell derived IFNγ – Senescent CD8+ T cells increase IFNγ secretion with age [1]. IFNγ suppresses steroidogenic acute regulatory (StAR) expression and CYP17A1 activity in zona reticularis fibroblasts, lowering DHEA synthesis.
• Paracrine amplification – Lost pericytes reduce secretion of angiocrine factors such as IGF2 and PDGFB that normally sustain zona reticularis cell survival; their decline creates a feed‑forward loop of stromal atrophy and further immune infiltration.

Testable Predictions

1. In aged mice, pharmacological inhibition of NETosis (e.g., with PAD4 inhibitor GSK484) will preserve adrenal capillary density, maintain zona reticularis thickness, and elevate circulating DHEA‑S compared with untreated controls.
2. Genetic depletion of senescent CD8+ T cells (using p16‑3MR transgenic model) will reduce adrenal IFNγ levels, restore StAR expression, and attenuate the age‑related drop in DHEA without altering HPA axis cortisol rhythms.
3. Adrenal‑specific overexpression of pericyte‑protective angiocrine IGF2 will rescue DHEA production in the presence of high NET burden, indicating that vascular support is the critical downstream effector.

Experimental Approach

• Animal models – Use 24‑month‑old C57BL/6 mice; treat subgroups with PAD4 inhibitor, administer p16‑3MR‑induced senolytic clearance, or deliver adrenal‑targeted IGF2 via AAV9.
• Readouts – Quantify adrenal capillary density (CD31 immunostaining), pericyte coverage (NG2+/PDGFRβ+), zona reticularis thickness (histomorphometry), serum DHEA‑S (ELISA), adrenal IFNγ and NET markers (MPO‑DNA complexes), and StAR/CYP17A1 mRNA (qPCR).
• Controls – Include young (3‑month) mice, vehicle‑treated aged mice, and groups receiving irrelevant IgG or scrambled siRNA.
• Statistical plan – Power analysis targeting 80% power to detect a 25% change in DHEA‑S (α=0.05); ANOVA with post‑hoc Tukey.

Falsifiability

If NET inhibition or senescent T‑cell clearance fails to improve adrenal vasculature or DHEA levels despite confirming target engagement, the hypothesis that immune senescence directly drives adrenopause would be refuted, pointing to alternative non‑immune mechanisms.