Hypothesis

Aging‑induced glucocorticoid excess overwhelms zona reticularis proteostasis, prompting the selective aggregation of the androgen‑synthetic enzyme CYP17A1 into insoluble, amyloid‑like deposits. This sequestration reduces misfolded‑protein toxicity while preserving cortisol‑synthetic capacity, thereby manifesting as the observed DHEA decline (adrenopause) despite maintained corticosterone output.

Mechanistic Basis

• Chronic cortisol elevation increases oxidative stress and alters lipid microenvironment in zona reticularis, destabilizing CYP17A1, a cytochrome P450 enzyme reliant on NADPH‑cytochrome P450 reductase and heme incorporation.
• Age‑related decline in HSP70/HSP90 chaperone activity (see [4]) limits refolding capacity, shifting the equilibrium toward nucleation of CYP17A1 monomers.
• Aggregated CYP17A1 adopts a cross‑β sheet conformation that is thermodynamically stable, effectively sequestering damaged enzyme and preventing proteotoxic gain‑of‑function interactions.
• Because cortisol‑synthetic enzymes (CYP21A2, CYP11B1) are more stably associated with lipid droplets and possess higher intrinsic stability, they remain largely soluble, preserving glucocorticoid output.
• The resulting drop in functional CYP17A1 diminishes 17,20‑lyase activity, lowering DHEA/DHEA‑S synthesis while cortisol production continues, mirroring the non‑linear rise in cortisol/DHEAS ratio with age ([2]).

Testable Predictions

1. Biochemical fractionation of young vs. aged rat adrenal glands will show a higher proportion of insoluble, SDS‑resistant CYP17A1 in the zona reticularis fraction, detectable by western blot of the pellet fraction.
2. Immunohistochemistry with conformation‑specific amyloid antibodies (e.g., anti‑A11) will co‑localize with CYP17A1 in aged zona reticularis but not in zona fasciculata.
3. Pharmacological inhibition of aggregation using a known amyloid‑blocker (e.g., epigallocatechin‑gallate) administered to middle‑aged mice will increase soluble CYP17A1, elevate circulating DHEA‑S, and reduce the cortisol/DHEAS ratio without suppressing basal cortisol.
4. Genetic overexpression of HSP70 specifically in the zona reticularis (using a Cyp11b2‑Cre driver) will attenuate CYP17A1 aggregation, preserve DHEA output, and improve stress‑termination kinetics in aged animals.
5. Conversely, forced expression of aggregation‑prone CYP17A1 mutants in young adrenal cells will recapitulate the aged phenotype: reduced DHEA secretion, unchanged cortisol, and increased markers of proteostatic stress.

Potential Implications

If protein aggregation serves as a deliberate containment mechanism for steroidogenic enzymes, therapeutic strategies aimed at dissolving aggregates may inadvertently exacerbate proteotoxic stress or disrupt adrenal zonation. Instead, modulating chaperone networks or enhancing selective autophagy of aggregates could restore adrenal androgen output while preserving glucocorticoid homeostasis. This reframes adrenopause not as simple enzyme loss but as a proteostatic adaptation with trade‑offs that become maladaptive when aggregate clearance fails.