Hypothesis In aged tissues that exhibit intact basal interferon‑stimulated genes (ISGs) but fail to mount inducible IFNβ/IFNλ1 production upon viral mimic stimulation (e.g., postmenopausal ectocervical fibroblasts), the defect stems from epigenetic silencing of the IFN promoters rather than receptor desensitization or SOCS‑mediated feedback. Specifically, age‑associated up‑regulation of the histone methyltransferase EZH2 leads to increased H3K27me3 at the IFNB1 and IFNL1 promoters, rendering them refractory to transcription factor binding (IRF3/IRF7, NF‑κB) while leaving downstream JAK‑STAT signaling and basal ISG expression intact. Conversely, tissues that show chronic JAK‑STAT hyperactivation (aged tendon stem cells) or downstream pSTAT hyporesponsiveness (cardiovascular immune cells) retain accessible IFN promoters but are governed by distinct mechanisms—SOCS overexpression or receptor-level tachyphylaxis. This model predicts a tissue‑specific epigenetic layer that can be pharmacologically reversed by EZH2 inhibition, restoring inducible IFN responses without exacerbating chronic pathway activation elsewhere.

Testable Predictions

1. Chromatin state – ChIP‑seq or CUT&RUN for H3K27me3 and EZH2 will show significant enrichment at the IFNB1 and IFNL1 promoters in aged ectocervical fibroblasts compared with young controls, but not in aged tendon stem cells or cardiovascular immune cells where promoter accessibility remains unchanged.
2. Transcription factor binding – Concurrently, IRF3/IRF7 and p65 occupancy at these promoters will be markedly reduced in the same fibroblast population despite normal cytosolic activation and nuclear translocation upon poly(I:C) stimulation.
3. Functional rescue – Treatment of aged fibroblasts with a selective EZH2 inhibitor (e.g., GSK126) will decrease H3K27me3 at IFN promoters, restore IRF3/IRF7 binding, and rescue inducible IFNβ/IFNλ1 secretion and downstream ISG induction to levels comparable with young cells, without affecting basal ISG expression.
4. Specificity – The same EZH2 inhibition will not further augment JAK‑STAT signaling in aged tendon stem cells (where chronic activation is driven by EGFR/IL6ST) nor exacerbate pSTAT hyporesponsiveness in cardiovascular immune cells, indicating that the epigenetic block is upstream and tissue‑restricted.
5. SOCS levels – Quantitative PCR or western blot will reveal no significant increase in SOCS1/3 mRNA or protein in the ectocervical fibroblasts, distinguishing this mechanism from SOCS‑mediated feedback.

Experimental Design

• Obtain primary ectocervical fibroblasts from young (≤30 y) and postmenopausal (>55 y) donors.
• Stimulate with poly(I:C) (1 µg/mL, 6 h) ± EZH2 inhibitor (GSK126, 1 µM).
• Measure: (a) IFNB1/IFNL1 mRNA by RT‑qPCR; (b) secreted IFNβ/IFNλ1 by ELISA; (c) ISG expression (MX1, OAS1) by RT‑qPCR; (d) H3K27me3 and EZH2 occupancy at IFN promoters by CUT&RUN; (e) IRF3/IRF7 and p65 chromatin occupancy; (f) SOCS1/3 expression.
• Parallel assays in aged tendon stem cells and cardiovascular immune cells will confirm that EZH2 inhibition does not alter their respective phenotypes.

Falsifiability If aged ectocervical fibroblasts show no increase in H3K27me3 at IFN promoters, or if EZH2 inhibition fails to restore inducible IFN production despite reducing the mark, the hypothesis is refuted. Conversely, a successful rescue would support the model that epigenetic silencing, rather than receptor exhaustion, underlies the loss of inducible interferon responses in specific aged tissues.