Hypothesis

Chronic low‑grade IFN‑I signaling reprograms tissue‑resident macrophages through sustained PI3K‑AKT activation and Foxo1 inhibition, shifting them toward a glycolytic, HIF‑1α‑driven state that amplifies the SASP via NLRP3 inflammasome activation and creates a self‑reinforcing IFN‑I/SASP loop that drives inflammaging.

Mechanistic Rationale

1. In γ/δ T cells, tonic IFN‑I downregulates Foxo1 via PI3K‑AKT, expanding IL‑17‑producing subsets 1.
2. Similar PI3K‑AKT‑Foxo1 signaling controls macrophage metabolism; Foxo1 loss promotes HIF‑1α stabilization and glycolytic shift, which is known to prime NLRP3 inflammasome activity.
3. Active NLRP3 releases IL‑1β and caspase‑1‑processed gasdermin D, prompting NF‑κB‑dependent transcription of SASP cytokines (IL‑6, IL‑8, S100A8/A9) and IFN‑β, thereby feeding back onto IFNAR in an autocrine fashion.
4. This loop explains the observed STAT3 bias in monocytes and CD4⁺ T cells 2, as SASP‑derived IFN‑I favors STAT3 activation while inducing SOCS3‑mediated STAT1 suppression.
5. The metabolic shift also links to progeroid phenotypes 3 and accounts for the paradox of heightened IFN‑I tone with reduced antiviral responsiveness via chronic STING overstimulation 4.

Testable Predictions

• Blocking IFNAR specifically in macrophages (e.g., using LysM‑Cre‑Ifnar1 floxed mice) will reduce HIF‑1α target genes, NLRP3 inflammasome activation, and SASP secretion in aged tissues.
• Genetic deletion of Foxo1 in macrophages will phenocopy the aged SASP profile even in young mice, whereas macrophage‑specific Foxo1 overexpression will suppress SASP despite systemic IFN‑I elevation.
• Pharmacologic inhibition of PI3K‑AKT (e.g., with a selective AKT inhibitor) in aged mice will normalize STAT3/STAT1 balance in monocytes and improve viral clearance without abolishing baseline IFN‑I tone.
• In humans, ex vivo treatment of peripheral blood monocytes from older donors with an IFNAR antagonist will decrease phospho‑S6 (PI3K‑AKT readout) and HIF‑1α, correlating with reduced IL‑1β and S100A8/A9 production.

Experimental Approach

• Generate macrophage‑specific Ifnar1 and Foxo1 conditional KO mice; assess aging‑related phenotypes (frailty index, tissue histology, serum SASP cytokines) and challenge with influenza virus to measure antiviral immunity.
• Perform flow cytometry and phospho‑flow on sorted macrophages from young vs. old mice to quantify p‑AKT, Foxo1 nuclear exclusion, HIF‑1α, and cleaved caspase‑1.
• Use Seahorse glycolysis assays to link IFN‑I tone to metabolic reprogramming.
• In parallel, collect monocytes from a longitudinal cohort of healthy adults (ages 20‑80); treat ex vivo with anti‑IFNAR2 antibody and measure changes in p‑STAT1/STAT3, SOCS3, and SASP mediators by multiplex ELISA and RNA‑seq.
• Computational modeling: integrate phospho‑proteomics, transcriptomics, and metabolomics data to simulate the IFN‑I→PI3K‑AKT→Foxo1→HIF‑1α→NLRP3→SASP→IFN‑I circuit and predict intervention points.

If validated, this hypothesis would reposition macrophage‑intrinsic PI3K‑AKT‑Foxo1 signaling as a central node linking interferonopathy to inflammaging, offering a tractable target for breaking the IFN‑I/SASP feedback loop while preserving host defense.