The brain sets the tempo of gut aging through efferent vagal signaling that remodels enteric glia and reprograms intestinal stem cell (ISC) epigenetics. Chronic hypothalamic inflammation, exemplified by elevated CRH release from the paraventricular nucleus, increases vagal efferent tone to the gut. Acetylcholine released from vagal terminals acts on α7 nicotinic receptors on enteric glia, triggering STAT3 phosphorylation and downstream DNA methyltransferase activity. This epigenetic shift silences key ISC niche genes such as Lgr5 and Ascl2, reducing proliferative capacity and barrier repair. Consequently, dysbiosis and increased permeability arise not as primary gut defects but as downstream consequences of brain‑derived signaling.

Testable predictions:

1. Chemogenetic activation of hypothalamic CRH neurons in young mice will accelerate age‑related ISC decline, markers of epithelial thinning, and microbial translocation within 8 weeks.
2. Optogenetic inhibition of vagal efferents during CRH neuron activation will prevent ISC epigenetic changes and preserve gut barrier integrity despite hypothalamic inflammation.
3. Selective deletion of the α7 nicotinic acetylcholine receptor in enteric glia will block CRH‑induced STAT3 activation and rescue ISC function, even with sustained hypothalamic inflammation.

Experimental approach: Use AAV‑DIO‑hM3Dq to stimulate CRH‑PVN neurons in male mice, combined with gut‑specific retrograde tracing to confirm vagal efferent engagement. Measure ISC proliferation (EdU incorporation), Lgr5‑GFP reporter activity, and colonic methylation arrays at 4, 8, and 12 weeks. Parallel cohorts receive vagal efferent optogenetic silencing (eNpHR3.0) or glial α7nAChR knockout. Falsifiability: If CRH‑driven hypothalamic activation fails to alter ISC epigenetics or barrier function, or if vagal efferent blockade does not rescue the phenotype, the hypothesis is refuted. This framework shifts focus from top‑down microbiome‑centric models to a bottom‑up circuit‑level mechanism where brain‑derived signals set the gut’s aging trajectory.