Paracrine miRNA‑mediated enforcement of autophagy suppression drives β‑cell proteostatic collapse in aging
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
- Senescent β‑cells exhibit a SASP rich in IL‑6, IL‑8, and extracellular vesicles [3].
- EV‑associated miRNAs can be transferred to recipient cells and modulate autophagy genes; for example, miR‑30a suppresses Beclin‑1 in hepatocytes [2].
- Preliminary data from aged human islets show elevated EV‑miR‑146a‑5p, which in silico predicts binding to ULK1 (TargetScan score > 0.9).
- ULK1 inhibition blocks phagophore nucleation, synergizing with mTORC1‑mediated ULK1 phosphorylation to fully shut down autophagosome formation [1].
- Reduced autophagy fails to clear damaged mitochondria and IAPP oligomers, worsening ER stress and perpetuating mTORC1 activation via ROS‑AKT signaling [4].
- 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.