Hypothesis

Rejuvenating the brain‑to‑gut arm of the vagus nerve—specifically the cholinergic efferents originating in the dorsal motor nucleus (DMV)—will remodel the aged intestinal microenvironment sufficiently to reverse microbiome‑driven aging, thereby extending healthspan without direct microbiome manipulation.

Mechanistic Rationale

Age‑related decline in vagal efferent activity reduces acetylcholine release into the gut wall, weakening the cholinergic anti‑inflammatory pathway and allowing luminal TNF‑α and bile‑acid dysregulation to favor pathogenic taxa such as Parabacteroides goldsteinii【https://pmc.ncbi.nlm.nih.gov/articles/PMC12515389/】. Restoring vagal firing boosts mucosal acetylcholine, which activates α7‑nicotinic receptors on intestinal macrophages and enteric neurons, suppressing NF‑κB signaling and increasing IL‑10 production. This creates a more anaerobic, slightly acidic lumen that promotes mucin‑degrading symbionts like Akkermansia muciniphila and enhances secondary bile‑acid conversion, both linked to longevity【https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2018.02091/full】. Additionally, vagal afferent feedback to the nucleus tractus solitarius normalizes enteroendocrine neuropeptide F secretion, further stabilizing gut‑brain homeostasis【https://doi.org/10.1101/2024.06.26.600832】.

Testable Predictions

1. Neuronal rejuvenation → increased vagal tone – Targeted expression of OSK factors or intermittent fasting‑induced SIRT1 activation in DMV neurons of 24‑month‑old mice will raise vagal firing rates (in vivo electrophysiology) and intestinal acetylcholine levels (microdialysis) by ≥30% compared with aged controls.
2. Microbiome rejuvenation – Fecal 16S rRNA sequencing will show a significant shift toward a youth‑like composition: ↑Akkermansia (≥2‑fold), ↓Parabacteroides goldsteinii (≥50% reduction), and restored microbial diversity (Shannon index) matching 3‑month‑old donors.
3. Healthspan transfer – Microbiota transplants from OSK‑treated aged donors into germ‑free aged recipients will recapitulate ≥15% increase in median lifespan and improved hippocampal‑dependent memory (Morris water maze) without further neuronal manipulation.
4. Necessity of vagal efferents – Pharmacological blockade with peripheral atropine or subdiaphragmatic vagotomy in OSK‑treated mice will abolish the microbiome shifts and longevity benefits, confirming efferent dependence.
5. Sufficiency of vagal activation – Chemogenetic (hM3Dq) activation of DMV neurons in aged mice, without OSK, will reproduce the microbiome and cognitive improvements, demonstrating that enhanced vagal output alone is sufficient.

Potential Challenges

• Achieving neuron‑specific OSK expression without off‑target effects in surrounding brainstem nuclei may require refined viral vectors or Cre‑driver lines.
• Chronic vagal stimulation could provoke maladaptive cardiovascular responses; dose‑response studies are needed to balance gut benefits with systemic safety.
• Microbiome variability across facilities may obscure effect sizes; using littermate controls and standardized housing will be critical.

If these predictions hold, the hypothesis would invert the prevailing gut‑centric longevity paradigm, establishing that rejuvenated central autonomic output can drive peripheral microbial youth, and that a bottom‑up intervention stack—vagal neurorejuvenation followed by microbiome‑friendly diet or prebiotics—could be more effective than microbiome‑first approaches alone.