Hypothesis

IL‑5‑primed eosinophils release extracellular vesicles (EVs) enriched in miR‑124 that are taken up by adipose tissue macrophages, suppressing NF‑κB signaling and driving an anti‑inflammatory M2‑like phenotype. This pathway explains how systemic eosinophil loss with age leads to heightened WAT inflammation and offers a tractable lever for rejuvenation.

Mechanistic Rationale

• Eosinophil activation by IL‑5 engages PI3K/ERK/p38 pathways, known to regulate EV biogenesis and cargo sorting (3).
• miR‑124 is a master regulator of macrophage polarization; its overexpression inhibits NF‑κB and promotes IL‑10 secretion, whereas its loss skews macrophages toward a pro‑inflammatory state.
• Recent work shows eosinophil‑derived EVs can deliver functional RNAs to neighboring cells in asthma models, suggesting a conserved cross‑talk mechanism.
• In aged mice, declining adipose tissue eosinophils (ATEs) reduce EV‑mediated miR‑124 transfer, tipping the macrophage balance toward inflammation, which then amplifies CCL11, IL‑6, and adipocyte hypertrophy (1).

Testable Predictions

1. EV Isolation – EVs isolated from IL‑5‑treated eosinophils (or from young mouse blood) will contain higher miR‑124 levels than EVs from untreated or aged eosinophils.
2. Macrophage Reprogramming – Co‑culture of bone‑marrow‑derived macrophages with eosinophil‑derived EVs will decrease p65 NF‑κB phosphorylation and increase Arg1/CD206 expression; this effect will be blocked by an miR‑124 antagomir.
3. In Vivo Rescue – Systemic injection of eosinophil‑derived EVs into aged mice will raise ATE:macrophage ratios, lower WAT IL‑6/IL-1β/CCL2, and improve glucose tolerance, whereas EVs from miR‑124‑deficient eosinophils will fail to do so.
4. Specificity – Depleting eosinophils (using anti‑Siglec‑F antibody) in young mice will recapitulate the aged adipose inflammatory profile, an effect reversible by EV transfer.

Experimental Approach

• Generate eosinophil‑specific Dicer or miR‑124 knockout mice (using eosinophil‑cre) to test cell‑autonomous requirement.
• Label eosinophil‑derived EVs with fluorescent dyes (e.g., PKH67) and track uptake by adipose macrophages via flow cytometry and confocal microscopy.
• Perform RNA‑seq on macrophage phenotypes after EV treatment to confirm NF‑κB pathway suppression.
• Metabolic readouts: glucose tolerance test, insulin tolerance test, indirect calorimetry.

Potential Outcomes & Falsifiability

• If eosinophil‑derived EVs do not transfer miR‑124 or fail to alter macrophage phenotype, the hypothesis is falsified.
• If miR‑124 inhibition abolishes the EV effect but eosinophil numbers remain unchanged, it confirms the mechanistic link.
• Conversely, if EV transfer improves metabolic health without altering macrophage polarization, alternative mechanisms must be considered.

This hypothesis integrates IL‑5 signaling, eosinophil heterogeneity, and intercellular RNA transfer to propose a concrete, testable axis linking eosinophil loss to age‑related adipose inflammation and offers a novel therapeutic avenue—eosinophil‑EV or miR‑124 mimetics—to restore homeostatic macrophage function in aging.