Paracrine miRNA‑Enforced Autophagy Suppression in Aging β‑Cells

Hypothesis Senescent pancreatic β‑cells actively enforce autophagy suppression in neighboring functional β‑cells by releasing extracellular vesicles enriched in a specific microRNA (miR‑XXX) that directly targets the 3′‑UTR of ULK1 mRNA. This paracrine signal amplifies mTORC1‑driven autophagy inhibition, creating a feed‑forward loop that accelerates IAPP/amylin aggregation, ER stress, and β‑cell failure.

Mechanistic Rationale

1. Senescent β‑cells exhibit a SASP rich in IL‑6, IL‑8, and extracellular vesicles [3].
2. EV‑associated miRNAs can be transferred to recipient cells and modulate autophagy genes; for example, miR‑30a suppresses Beclin‑1 in hepatocytes [2].
3. Preliminary data from aged human islets show elevated EV‑miR‑146a‑5p, which in silico predicts binding to ULK1 (TargetScan score > 0.9).
4. ULK1 inhibition blocks phagophore nucleation, synergizing with mTORC1‑mediated ULK1 phosphorylation to fully shut down autophagosome formation [1].
5. Reduced autophagy fails to clear damaged mitochondria and IAPP oligomers, worsening ER stress and perpetuating mTORC1 activation via ROS‑AKT signaling [4].
6. The resulting proteostatic burden pushes functional β‑cells toward senescence, expanding the EV‑miR source—a self‑reinforcing circuit.

Testable Predictions

• Isolation: EVs from cultured senescent β‑cells (induced by oxidative stress or replicative exhaustion) will contain higher levels of miR‑XXX than EVs from young β‑cells (qPCR).
• Transfer: Treating young β‑cell lines (EndoC‑βH1) with senescent‑derived EVs will decrease LC3‑II/I ratio and increase p62 accumulation, measurable by Western blot and immunofluorescence.
• Specificity: Transfecting recipient cells with an antagomir against miR‑XXX will rescue autophagy flux despite EV exposure.
• In vivo: Aged mice treated with systemic GW4869 (EV synthesis inhibitor) or with β‑cell‑specific antagomir‑XXX will show restored hepatic autophagy markers (LC3‑II, TFEB nuclear localization) and improved glucose tolerance compared with controls.
• Falsifiability: If EV‑miR‑XXX levels do not correlate with autophagy suppression, or if antagomir fails to restore flux, the hypothesis is refuted.

Broader Impact Demonstrating a paracrine, RNA‑based mechanism would shift the view of autophagy decline from a cell‑intrinsic failure to an intercellular enforcement strategy, suggesting that targeting EV miRNA cargo could re‑establish proteostasis in aged islets without globally inhibiting mTORC1, which carries metabolic risks.