Hypothesis

Chronic low‑level type I interferon (IFN‑I) signaling does more than remodel mature immune cells; it directly reprograms hematopoietic stem and progenitor cells (HSPCs) to fuel extramedullary myelopoiesis, a key source of inflammaging.

Mechanistic insight

We propose that tonic IFN‑I activates STAT1/STAT2‑IRF9 complexes in HSPCs, which induce the transcription factor Zeb2. Zeb2 then binds and represses the Foxo1 locus, mirroring the IFN‑I‑Foxo1 axis described in γδ T cells. Loss of Foxo1 removes its restraint on mTORC1 signaling, shifting HSPC metabolism toward aerobic glycolysis and increasing mitochondrial ROS. Elevated ROS leaks mitochondrial DNA into the cytosol, reigniting cGAS‑STING signaling and producing more IFN‑I—a feed‑forward loop [2]. Simultaneously, Zeb2 drives a myeloid‑biased transcriptional program, promoting expansion of Ly‑6C⁻ monocytes that seed the spleen and liver.

Testable predictions

• Ifnar1 deletion specifically in HSPCs will reduce Zeb2 induction, preserve Foxo1 activity, and lower extramedullary myeloid output in aged mice.
• Pharmacologic JAK inhibition will decrease downstream ISG expression but will not break the cGAS‑STING‑ROS loop unless ROS is scavenged.
• Overexpressing Zeb2 in young HSPCs will recapitulate the aged myeloid bias and increase spleen hematopoiesis even without elevated IFN‑I.
• Inhibiting mitochondrial ROS (e.g., with MitoQ) will diminish cGAS‑STING activation and break the feed‑forward loop, reducing inflammaging markers.

Experimental approach

1. Generate Vav‑Cre‑Ifnar1^fl/fl mice and aged controls; assess spleen myeloid cells, Foxo1 protein, Zeb2 mRNA, and serum IL‑6/TNF.
2. Treat aged wild‑type mice with a JAK inhibitor (ruxolitinib) versus a MitoQ analog; compare pSTAT1, mitochondrial ROS (MitoSOX), and cGAS activation (phospho‑TBK1).
3. Transplant young HSPCs transduced with Zeb2‑overexpressing vector into irradiated recipients; track chimerism and myeloid lineage bias.
4. Perform single‑cell ATAC‑seq and RNA‑seq on sorted HSPCs to map chromatin changes at the Foxo1 and Zeb2 loci.

Falsifiability

If IFN‑I signaling in HSPCs is dispensable for age‑associated myeloid skewing, then HSPC‑specific Ifnar1 loss will not alter Foxo1 levels, Zeb2 expression, or extramedullary hematopoiesis compared with controls. Likewise, if Zeb2 is not downstream of IFN‑I, its overexpression will not rescue the myeloid phenotype in Ifnar1‑deficient HSPCs.

This hypothesis links the IFN‑I‑Foxo1 axis to a metabolic‑ROS‑cGAS‑STING circuit, offering a unified mechanism that connects interferonopathy with IL‑6/TNF‑driven inflammaging and points to combined JAK inhibition plus mitochondrial antioxidant therapy as a potential strategy.