Hypothesis

Age‑related mitochondrial dysfunction in adrenal cortical progenitor cells triggers zona reticularis senescence, leading to selective loss of DHEA(S) synthesis while sparing 11‑oxygenated androgen production.

Mechanistic Rationale

1. Mitochondrial ROS and senescence – Aging increases mitochondrial superoxide in the adrenal cortex, particularly in the zona reticularis where CYP17A1 activity generates electrophilic intermediates that can exacerbate oxidative stress【https://pmc.ncbi.nlm.nih.gov/articles/PMC10410302/】. Persistent ROS activates p16^INK4a^ and p21^Cip1^ pathways, driving a senescent phenotype that reduces progenitor proliferation and CYP17A1 transcription.

2. IL‑1β–mediated CYP17A1 suppression – Senescent zona reticularis cells secrete IL‑1β and other SASP factors. IL‑1β signaling through its receptor on neighboring progenitor cells suppresses CYP17A1 expression via NF‑κB‑dependent transcriptional repression, thereby lowering DHEA(S) output【https://pmc.ncbi.nlm.nih.gov/articles/PMC6741703/】. Importantly, the enzymes for 11‑oxygenated androgen synthesis (HSD3B2, SULT2A1) are less sensitive to IL‑1β, explaining their relative preservation.

3. Sex‑specific modulation – Androgen signaling in males promotes a pro‑inflammatory macrophage phenotype (M1) that amplifies IL‑1β release, accelerating zona reticularis senescence; estrogen in females favors an M2 phenotype that limits SASP, accounting for the more pronounced adrenal atrophy observed in older males【https://pmc.ncbi.nlm.nih.gov/articles/PMC10410302/】.

4. Feedback loop with cortisol – Declining DHEA removes its inhibitory effect on ACTH secretion, contributing to mild ACTH rise that drives zona fasciculata hyperplasia and sustains elevated basal cortisol despite impaired glucocorticoid receptor feedback【https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2019.00054/full】.

Testable Predictions

• Prediction 1: In aged mice, isolated zona reticularis progenitors will show higher mitochondrial ROS, increased p16^INK4a^ expression, and lower CYP17A1 mRNA compared with young counterparts; treatment with mito‑targeted antioxidant (MitoQ) will restore CYP17A1 and DHEA(S) secretion ex vivo.
• Prediction 2: Blocking IL‑1β signaling (using anakinra or IL‑1R knockout) in aged adrenal explants will rescue CYP17A1 activity and DHEA(S) production without affecting aldosterone or corticosterone synthesis.
• Prediction 3: Male mice will exhibit greater IL‑1β‑positive senescent cells in the zona reticularis than females; gonadectomy of males will reduce this disparity, while ovariectomy of females will increase it.
• Prediction 4: Chronic low‑dose ACTH administration in young mice will mimic the aged phenotype (zona fasciculata expansion, zona reticularis thinning) only when combined with mito‑ROS inducer (e.g., antimycin A), indicating that ACTH‑driven hyperplasia requires oxidative stress to suppress the reticularis.

Potential Confounders and Alternatives

• Vascular rarefaction could independently limit oxygen/nutrient delivery to the zona reticularis, contributing to senescence; however, if mitochondrial ROS is the primary driver, improving perfusion without reducing ROS will not rescue DHEA(S) output.
• Systemic inflammation may elevate IL‑1β globally; adrenal‑specific IL‑1R knockout will help dissect local versus systemic effects.
• Changes in ACTH pulsatility or circadian timing could alter zona reticularis function; measuring ACTH pulses alongside mitochondrial markers will clarify hierarchy.

By targeting mitochondrial ROS and IL‑1β signaling, this hypothesis offers a mechanistic link between adrenal cortical senescence, the adrenopause phenotype, and the sex‑biased progression of HPA axis dysregulation in aging.