Hypothesis

Age‑related decline in central cholinergic efferent vagal output from the dorsal motor nucleus of the vagus (DMV) and hypothalamus reduces acetylcholine release in the gut wall, leading to progressive loss of intestinal stem cell (ISC) regenerative capacity and accelerated systemic aging.

Mechanistic Basis

The C. elegans data show that nervous‑system‑to‑gut acetylcholine signaling via STR‑2 neurons directly modulates DAF‑16/FOXO activity and intestinal lipid metabolism to set lifespan [[https://elifesciences.org/reviewed-preprints/97829|Brain‑to‑gut ACh signaling extends C. elegans lifespan]]. In mammals, the DMV supplies the primary vagal efferent cholinergic tone to the myenteric plexus and enteroendocrine cells. Recent work demonstrates that age‑related autonomic dysfunction amplifies inflammaging through afferent cytokine sensing [[https://pmc.ncbi.nlm.nih.gov/articles/PMC12806315/|Autonomic dysfunction and inflammaging]]. However, no study has linked central epigenetic noise accumulation in DMV or hypothalamic nuclei to reduced vagal efferent firing and consequent gut pathology.

We propose that age‑associated increase in transcriptional noise at loci governing cholinergic neurotransmission (e.g., Chat, Vacht) blunts DMV neuron excitability. This diminishes acetylcholine release onto intestinal muscarinic receptors (M3) on enteroendocrine L‑cells, decreasing secretion of peptide YY and glucagon‑like peptide‑1. Lower peptide signaling reduces downstream cAMP/PKA activity in ISCs, weakening Wnt/β‑catenin driven proliferation [[https://pmc.ncbi.nlm.nih.gov/articles/PMC2818053/|Enteroendocrine regulation of ISCs]]. Concurrently, reduced vagal cholinergic input lowers intestinal alkaline phosphatase activity, allowing luminal LPS to trigger TLR4‑mediated NF‑κB activation in ISCs, promoting senescence [[https://www.aging-us.com/article/102074/text|Vagal tone and gut barrier]]. The combined effect is ISC exhaustion, barrier leak, and heightened systemic inflammation.

Predictions

1. Aged mice will show decreased Chat expression and reduced c‑Fos activation in DMV neurons after vagal stimulation compared with young mice.
2. Chemogenetic activation of DMV‑vagal efferent neurons in aged mice will restore intestinal acetylcholine levels, increase ISC markers (Lgr5, Ki67), and improve barrier function (FITC‑dextran assay).
3. Restoration of vagal efferent tone will extend median lifespan by ~15% and delay onset of age‑related frailty indices.
4. Selective inhibition of DMV cholinergic output in young mice will phenocopy gut aging signatures (ISC loss, elevated LPS‑binding protein) within 4 weeks.

Experimental Approach

• Use Chat‑Cre mice crossed with AAV‑DIO‑hM3Dq (Gq‑DREADD) to selectively excite DMV vagal efferents. Administer CNO in young (3 mo) and aged (20 mo) cohorts.
• Measure intestinal acetylcholine via microdialysis, enteroendocrine hormone ELISA, ISC proliferation (immunofluorescence for Lgr5/Ki67), barrier permeability, and serum LPS‑binding protein.
• Perform RNA‑seq on isolated ISCs to assess Wnt, FOXO, and senescence pathways.
• Monitor survival and frailty (grip strength, gait speed) over 12 months.
• Include controls: AAV‑DIO‑mCherry, peripheral vagal afferent stimulation, and muscarinic antagonist (atropine) to confirm cholinergic specificity.

Potential Pitfalls and Alternatives

If DMV activation does not rescue ISC function, the deficit may lie downstream in intestinal cholinergic receptor expression or in non‑neuronal sources of acetylcholine (e.g., epithelial ChAT). Conversely, if peripheral afferent stimulation yields similar benefits, the hypothesis would need revision to incorporate bidirectional loops. Nonetheless, a positive result would reframe the gut‑brain axis as a top‑down driver of aging and justify therapeutic strategies targeting central vagal efferent circuits.