Background

Research shows that gut‑derived exosomes carry pro‑inflammatory cargo to the brain, accelerating neurodegeneration[1]. Conversely, hypothalamic neural stem cells secrete exosomal miRNAs that regulate systemic aging speed[2], yet downstream trafficking of brain‑derived exosomes to the gut remains poorly documented. Gut enteroendocrine cells modulate organismal aging through nutrient‑dependent neuropeptide F secretion[4], offering a plausible target for central vesicular signals.

Hypothesis

We hypothesize that aging‑associated changes in hypothalamic exosome composition—specifically a loss of miR‑29b‑3p and gain of miR‑34a‑5p—are selectively packaged into vesicles that travel via the vagus nerve to the gut. There, these miRNAs repress enteroendocrine neuropeptide F transcription and disrupt epithelial tight‑junction proteins, leading to reduced gut barrier integrity, dysbiotic shifts, and systemic inflammation that drives aging.

Predictions

• Loss‑of‑function: Conditional deletion of Rab27a (exosome release machinery) in hypothalamic neurons will increase circulating miR‑29b‑3p, decrease miR‑34a‑5p in gut tissue, elevate neuropeptide F expression, improve barrier function, and extend lifespan even in mice fed a high‑fat diet.
• Gain‑of‑function: Direct intestinal delivery of synthetic miR‑34a‑5p‑loaded exosomes from old hypothalami will suppress neuropeptide F, increase permeability, provoke microbiota dysbiosis, and shorten lifespan in young recipients.
• Correlational: Aged mice will show a reciprocal shift in hypothalamic exosome miRNA cargo (↓miR‑29b‑3p, ↑miR‑34a‑5p) that predicts the magnitude of gut neuropeptide F decline and microbiome alteration.

Experimental Approach

1. Cell‑specific exosome labeling: Cross Rab27a^fl/fl mice with Sim1‑CreERT2 to inducibly block exosome release in hypothalamic nuclei; validate label transfer using Cre‑dependent CD63‑GFP reporter and track GFP+ vesicles in gut via confocal microscopy.
2. miRNA profiling: Isolate exosomes from hypothalamus and gut lumen of young (3 mo) and old (24 mo) mice; perform small‑RNA sequencing to identify age‑altered miRNAs.
3. Functional rescue: Treat aged Rab27a‑deficient mice with antagomiR‑34a‑5p or agomiR‑29b‑3p via oral gavage; assess neuropeptide F levels (qPCR, ELISA), gut permeability (FITC‑dextran assay), 16S rRNA microbiome sequencing, and survival curves.
4. Loss‑of‑gut test: Vagotomy in young mice receiving old‑hypothalamus exosomes will block miRNA transfer and prevent gut phenotype, confirming vagal dependence.

Potential Outcomes

• If predictions hold, the data will establish a brain‑to‑gut exosome axis that sets intestinal homeostasis and modulates longevity.
• Failure to observe miRNA shifts or lifespan changes would falsify the hypothesis, suggesting that circulating factors other than exosomes mediate any brain‑gut influence.

Implications

A validated descending exosome route would reframe longevity strategies: targeting hypothalamic vesicle production or gut miRNA receptors could complement microbiome‑centric approaches, offering a bottom‑up intervention stack that corrects the central driver of gut aging rather than merely treating symptoms.