Hypothesis

Chronic type I interferon (IFN-I) signaling in the aged microenvironment directly represses the transcription factor Foxo1 in hematopoietic stem cells (HSCs), forcing a myeloid‑biased differentiation program that contributes to inflammaging; pharmacological or genetic activation of the NRF2 antioxidant pathway in HSCs restores Foxo1 expression, rebalances lymphoid‑myeloid output, and mitigates age‑related immune dysregulation.

Mechanistic Basis

Recent work shows that tonic IFN‑I downregulates Foxo1 in innate‑like Ly‑6C⁻ CD44ʰⁱ γ/δ T cells, expanding IL‑17‑producing populations and linking IFN‑I to Foxo1 loss in lymphoid cells [1]. Parallel studies reveal that persistent IFN-I signaling represses NRF2, shifting macrophages toward aerobic glycolysis and driving oxidative stress [3]. Foxo1 is a known regulator of HSC quiescence, self-renewal, and lymphoid priming; its inhibition pushes HSCs toward myeloid fate [5]. We propose that IFN-I-mediated NRF2 suppression creates a redox-sensitive circuit: elevated reactive oxygen species (ROS) activate stress-responsive kinases (e.g., p38 MAPK) that phosphorylate Foxo1, promoting its nuclear export and proteasomal degradation. Loss of Foxo1 diminishes transcription of lymphoid-biased genes (e.g., Il7r, Bcl11a) and lifts repression of myeloid-determinants (Pu.1, C/ebpα), thereby skewing output.

NRF2 activation, conversely, restores redox homeostasis, reduces ROS-dependent Foxo1 inhibition, and may directly upregulate Foxo1 transcription via antioxidant response elements (ARE) in its promoter [6]. Thus, NRF2 agonists could break the IFN-I→ROS→Foxo1 suppression loop, rescuing lymphoid potential without globally blocking IFN-I antiviral defenses.

Predictions & Experimental Design

1. Foxo1 levels in aged HSCs – Flow cytometry and intracellular staining will show reduced Foxo1 protein in Lin⁻Sca1⁺cKit⁺ (LSK) cells from 24‑month-old mice compared with 3-month-old controls; this reduction will correlate with serum IFN-β levels (measured by ELISA).
2. IFN-I dependence – Treating aged mice with anti-IFNAR1 antibody for 2 weeks will restore Foxo1 in LSK cells and increase the lymphoid-to-myeloid ratio in blood and bone marrow; IFNAR1-deficient aged mice will retain youthful Foxo1 expression.
3. ROS mediation – Aged HSCs will exhibit higher MitoSOX fluorescence; NAC (N-acetylcysteine) treatment will partially rescue Foxo1, implicating ROS as an intermediate.
4. NRF2 rescue – Administration of the NRF2 activator dimethyl fumarate (DMF) or genetic overexpression of Nrf2 in Vav-Cre-driven HSCs will restore Foxo1, enhance B- and T-cell output, and reduce myeloid expansion (Gr-1⁺Mac-1⁺ cells) in aged mice.
5. Functional readout – Competitive bone-marrow transplantation assays will demonstrate that NRF2-activated aged HSCs confer superior lymphoid reconstitution compared with untreated aged HSCs, without compromising pathogen clearance after LCMV infection (viral titers measured at day 8).
6. Human relevance – Cord blood and peripheral blood CD34⁺ cells from young (<30 y) and old (>65 y) donors will be cultured with recombinant IFN-α; Foxo1 expression will be assessed by qPCR and western blot, and NRF2 activation (via sulforaphane) will be tested for its ability to counteract IFN-induced Foxo1 loss.

Potential Implications

If validated, this hypothesis positions the IFN-I–NRF2–Foxo1 axis as a controllable node that links inflammaging-associated myeloid skewing to stem-cell intrinsic regulation. It suggests that transient NRF2 activation—already clinically approved for conditions such as psoriasis and multiple sclerosis—could rejuvenate hematopoietic output in the elderly, improving vaccine responsiveness and reducing inflammaging-driven pathology while preserving essential IFN-I antiviral functions. Conversely, failure to rescue Foxo1 despite NRF2 activation would falsify the model and redirect focus toward alternative IFN-I effectors (e.g., STAT1-dependent epigenetic modifiers) in HSC aging.