Hypothesis

Chronic brain‑derived neuropeptide Y (NPY) signaling via vagal efferents suppresses intestinal epithelial mTORC1 activity, thereby enhancing autophagy and reshaping the gut microbiota to promote systemic longevity.

Mechanistic Rationale

et al. note that most longevity work treats the gut→brain axis as the dominant causal direction, yet brain‑to‑gut signaling remains mechanistically underexplored [1]. NPY is a well‑characterized hypothalamic peptide released during stress and energy‑balance regulation, and vagal efferents convey NPY to the gut wall [2]. In intestinal epithelial cells, NPY binds Y1 receptors that inhibit mTORC1 through upstream activation of TSC2, a pathway shown to stimulate autophagy in multiple tissues [3]. Enhanced autophagy in gut epithelium can improve barrier integrity, reduce inflammaging, and alter mucosal niches that favor beneficial microbial taxa [4]. Conversely, impaired gut autophagy drives dysbiosis and systemic inflammation, accelerating aging phenotypes [5]. Thus, brain NPY may set a basal autophagic tone in the gut that overrides cell‑autonomous aging cues.

Testable Predictions

1. Elevating central NPY (via hypothalamic overexpression or pharmacological agonism) will increase LC3‑II/I ratios and p62 degradation specifically in intestinal epithelial cells of aged mice.
2. Vagotomy will abolish the NPY‑induced autophagy boost in the gut, confirming efferent dependence.
3. Mice with sustained central NPY elevation will exhibit a shift toward higher relative abundance of butyrate‑producing taxa (e.g., Faecalibaculum spp.) and reduced circulating LPS‑binding protein.
4. The longevity benefit of central NPY elevation will be lost in gut‑specific autophagy‑deficient mice (Atg5^fl/fl;Vil‑Cre).

Experimental Design

• Model: C57BL/6J mice, 20 months old; groups: (a) control virus, (b) hypothalamic NPY‑overexpressing AAV, (c) NPY‑AAV + subdiaphragmatic vagotomy, (d) NPY‑AAV + gut‑specific Atg5 knockout.
• Readouts (at 3 mo post‑treatment): western blot of LC3‑II/I and p62 from isolated intestinal epithelia; 16S rRNA sequencing of fecal microbiota; serum cytokines (IL‑6, TNF‑α); grip strength, frailty index, and survival monitoring.
• Controls: sham virus, sham vagotomy, and littermate wild‑type counterparts.

Potential Outcomes and Falsifiability

If central NPY elevates gut autophagy independently of vagal input, we would see increased LC3‑II/I in groups (a) and (b) but not (c). A lack of autophagy change in (b) would falsify the hypothesis that brain NPY acts via vagal efferents. If gut‑specific Atg5 deletion abolishes the microbiota shift and longevity extension seen in (b), it confirms that intestinal autophagy is necessary downstream of brain NPY. Conversely, if Atg5‑deficient mice still show lifespan extension, the hypothesis would be falsified, indicating that brain NPY influences longevity through gut‑independent mechanisms.