Hypothesis

Neuronal base excision repair (BER) failure in the dorsal motor nucleus of the vagus (DMV) occurs before measurable gut barrier loss and drives age‑related gut‑brain axis dysregulation.

Mechanistic Rationale

Aging reduces OGG1 activity, increasing 8‑oxoguanine lesions in neuronal DNA [1]. When APE1‑mediated excision is insufficient, AP sites accumulate, triggering p53‑dependent apoptosis or senescence in autonomic neurons [2]. The DMV houses cholinergic premotor neurons that generate vagal efferent tone; loss of these cells diminishes acetylcholine release onto celiac ganglion‑splenic nerve circuits, weakening the cholinergic anti‑inflammatory pathway [3]. Consequently, macrophage‑derived TNF and IL‑1β rise, increasing intestinal epithelial tight‑junction permeability and altering mucus secretion. Structural decay of vagal afferents (Nissl loss, lipofuscin, dystrophic terminals) further compromises feedback from the gut to the brainstem [4], creating a feed‑forward loop where brain‑originating BER deficit amplifies gut inflammation, which then secondarily damages enteric neurons.

Testable Predictions

1. In middle‑aged mice, DMV neuronal APE1 activity will decline significantly before any rise in fecal LPS or serum zonulin.
2. Chemogenetic inhibition of DMV cholinergic output will reproduce gut barrier defects even when OGG1/APE1 levels are normal.
3. Viral‑mediated APE1 overexpression restricted to DMV neurons will preserve vagal efferent firing, lower circulating cytokines, and prevent gut permeability increase in aged animals.
4. Selective vagal afferent transection will not prevent the early gut phenotype if DMV BER is impaired, confirming efferent dominance.

Experimental Design

• Use OGG1‑reporter and APE1‑activity assay on laser‑captured DMV neurons from mice at 6, 12, 18 months; parallel measurement of serum LPS, zonulin, and colonic claudin‑1 staining.
• Apply DREADDs (hM4Di) to DMV choline acetyltransferase‑positive cells; assess gut permeability after CNO treatment in young mice.
• Deliver AAV9‑Syn‑APE1‑GFP via fourth‑ventricle injection to target DMV; confirm expression and evaluate vagal efferent electrophysiology, cytokine panel, and FITC‑dextran gut leak assay in 18‑month mice.
• Perform subdiaphragmatic vagotomy to isolate afferent contribution; compare gut outcomes with DMV‑specific APE1 rescue.

If DMV BER loss precedes and predicts gut dysfunction, and its restoration rescues the gut phenotype, the hypothesis is supported. Conversely, if gut barrier failure appears first or DMV APE1 manipulation does not alter gut measures, the brain‑first model is falsified.