Emodin reprograms the senescent immune secretome via EGFR/STAT3 inhibition to enhance immunosurveillance and attenuate inflammaging without requiring senolytic clearance

Mechanistic Rationale

Emodin’s well‑documented inhibition of EGFR/MAPK signaling suppresses M1 macrophage polarization and lowers IL-1β, IL-6, and TNF-α production [1]. In parallel, EGFR blockade diminishes STAT3 phosphorylation, a shift that has been linked to reduced NF‑κB‑driven transcription of classic SASP factors and increased activity of non‑canonical NF‑κB pathways that favor IL-10 and TGF‑β release [2]

We propose that this dual attenuation of pro‑inflammatory signaling and activation of anti‑inflammatory programs rewires the secretome of senescent immune cells. Rather than eliminating p16⁺ lymphocytes or macrophages, emodin tilts their secretory profile toward a reparative state characterized by elevated IL-10, TGF-β, and upregulated phagocytic receptors such as MerTK and Axl. This 'SASP switch' would improve the ability of aged immune cells to recognize and clear senescent parenchymal cells, thereby lowering tissue‑level inflammaging while leaving the senescent immune compartment numerically unchanged.

Testable Predictions

1. In vivo cytokine profile – Chronic emodin treatment in aged mice will reduce circulating IL-6, TNF-α, and IL-1β levels without a significant decrease in the frequency of p16⁺ CD4⁺ T cells, CD8⁺ T cells, or F4/80⁺ macrophages in spleen, blood, or liver.
2. Enhanced phagocytic capacity – Bone‑marrow‑derived macrophages isolated from emodin‑treated aged mice will show higher MerTK and Axl mRNA and protein expression, and will exhibit increased uptake of fluorescently labeled senescent fibroblasts in vitro compared with macrophages from vehicle‑treated controls.
3. Myeloid‑EGFR dependence – Myeloid‑specific EGFR knockout mice will fail to show the emodin‑induced improvements in frailty index, grip strength, or hippocampal‑dependent memory, despite identical drug exposure, indicating that EGFR signaling in myeloid cells is necessary for the hypothesized secretome reprogramming.

Experimental Approach

• In vivo pharmacology: Administer emodin (30 mg/kg/day, oral) to 20‑month‑old C57BL/6 mice for 12 weeks. Collect serum for multiplex cytokine analysis (IL-6, TNF-α, IL-1β, IL-10, TGF-β) and isolate immune organs for flow cytometry (p16‑Int‑GFP reporter or p16 immunostaining) to quantify senescent immune subsets.
• Ex vivo phagocytosis assay: Differentiate bone marrow to macrophages, treat with emodin (10 µM) for 24 h, then co‑culture with senescent MEFs labeled with CFSE and a p21‑driven mCherry reporter. Measure phagocytic index by flow cytometry and confocal microscopy.
• Genetic validation: Generate LysM‑Cre;EGFR^fl/fl mice. Treat with emodin as above and assess the same phenotypic readouts. Lack of benefit in the knockout cohort would support the myeloid‑EGFR dependence.

If emodin’s anti‑aging actions stem from secretome reprogramming rather than senolysis, we would observe a dissociation between inflammatory biomarker improvement and senescent immune cell burden, coupled with enhanced phagocytic capacity that is lost when EGFR is removed from myeloid lineages. This framework directly challenges the assumption that immune‑targeted geroprotectors must eliminate senescent immune cells to be effective, and it shifts the focus toward modulating the quality of the immune secretome to restore tissue homeostasis.