Ferroptosis‑Senolytic Priming Mitigates SASP‑Driven Immune Exhaustion via Lipid‑Peroxidation‑Dependent NRF2 Activation

Ferroptosis‑based senolytics not only eliminate senescent cells but also generate oxidized lipid mediators that activate NRF2 in surrounding immune cells, thereby dampening SASP‑driven chronic inflammation and restoring endogenous T‑helper‑cell clearance of senescent debris.

Mechanistic Rationale

Senescent cells accumulate labile iron and polyunsaturated fatty acids, making them prone to ferroptosis when exposed to lipid‑peroxidation inducers such as naturally occurring PUFA‑derived compounds Ferroptosis‑based senolytics. The resulting lipid‑peroxidation products include specific oxidized phospholipids (e.g., POVPC, PGPC) that can act as electrophilic signaling molecules. These molecules modify KEAP1 cysteines, leading to NRF2 stabilization and transcription of antioxidant genes in neighboring macrophages and T cells. NRF2 activation has been shown to suppress NF‑κB‑dependent SASP components such as IL‑6 and TNF‑α SASP regulation via mitochondrial dysfunction. Moreover, NRF2‑driven expression of HO‑1 and SOD2 promotes a macrophage phenotype skewed toward tissue repair and enhances the capacity of CD4+ T helper cells to recognize and clear senescent cells via increased perforin/granzyme release T‑cell‑mediated senescent cell clearance.

Experimental Design

1. Model – Use aged mice with experimentally induced osteoarthritis (OA) in the knee joint, a setting where ferroptosis senolytics have shown efficacy Local clearance reduces cartilage degeneration.
2. Groups – (a) Vehicle control; (b) Ferroptosis senolytic (e.g., PUFA‑derived lipoxin analog); (c) Ferroptosis senolytic + NRF2 inhibitor (ML385); (d) NRF2 inhibitor alone.
3. Treatment – Intra‑articular injection twice weekly for 4 weeks.
4. Readouts –
   • Joint histology (OARSI score) and cartilage thickness (µCT).
   • SASP cytokine levels in synovial fluid (ELISA for IL‑6, TNF‑α, IL‑1β).
   • Flow cytometry of synovial infiltrates: senescent cell frequency (p16^INK4a^+), NRF2 nuclear translocation in F4/80^+ macrophages and CD4^+ T cells, activation markers (CD69, granzyme B).
   • T‑helper‑cell cytotoxic assay ex vivo: co‑culture sorted CD4^+ T cells with senescent synovial fibroblasts, measure senescent cell death (SA‑β‑gal loss).
   • Lipid‑peroxidation product quantification (LC‑MS for POVPC/PGPC) in synovial fluid.
5. Statistical analysis – ANOVA with post‑hoc Tukey; n≥8 per group for power.

Expected Outcomes and Falsifiability

If the hypothesis is correct, group (b) will show reduced SASP cytokines, increased NRF2 activity in immune cells, enhanced T‑helper‑cell‑mediated senescent cell clearance, and improved cartilage preservation compared with control. Adding the NRF2 inhibitor (group c) should abolish these benefits, returning SASP levels, immune phenotype, and cartilage protection to values indistinguishable from vehicle (group a). Group d alone should not worsen outcomes but will block any NRF2‑dependent protective signal.

A falsifying result would be: ferroptosis senolytic reduces senescent cell burden and improves cartilage without increasing NRF2 activation in immune cells, or NRF2 inhibition fails to diminish the senolytic’s anti‑SASP and tissue‑protective effects. Either outcome would indicate that the proposed lipid‑mediated NRF2 pathway is not essential for the observed benefits, prompting alternative mechanisms (e.g., direct immunomodulation by ferroptotic DAMPs).

This hypothesis integrates ferroptotic lipid signaling with NRF2‑dependent immune reprogramming, offering a testable bridge between senolytic clearance and senomorphic SASP modulation.