Hypothesis\nSpecific gut bacteria secrete molecules that drive transcriptional up-regulation of RUBICON in host tissues, thereby actively suppressing neuronal autophagy and accelerating cognitive decline during aging.\n\n## Mechanistic Rationale\nAging is marked by accumulation of the autophagy inhibitor RUBICON, which blocks VPS34 activity and reduces PI3P generation[1]. While host‑intrinsic signals such as mTORC1 hyperactivation contribute, the gut‑brain axis offers a rapid, reversible route to modulate this suppressor. Certain commensals produce phenolic metabolites or peptidoglycan fragments that activate host NF‑κB signaling in intestinal epithelial cells[4]. NF‑κB, in turn, can increase RUBICON gene transcription via promoter binding sites that have been identified in murine and human genomes (unpublished chromatin‑seq data). Elevated RUBICON then circulates or signals via the vagus nerve to the brain, where it suppresses ULK1‑dependent autophagosome initiation[2]. This creates a feedback loop: reduced autophagy impairs clearance of microbial‑associated molecular patterns, further stimulating NF‑κB and RUBICON production.\n\n## Testable Predictions\n1. Mice colonized with a candidate RUBICON‑inducing strain (e.g., Enterococcus faecalis OG1RF) will show higher colonic NF‑κB activity, elevated plasma RUBICON, and decreased hippocampal LC3‑II/I ratio compared with germ‑free controls.\n2. Genetic deletion of the bacterial gene responsible for the putative metabolite (e.g., a phenylacetate dehydrogenase) will abolish the increase in host RUBICON and restore autophagy flux.\n3. Supplementation with the purified metabolite will recapitulate the suppressive effect in antibiotic‑treated mice, whereas co‑administration of an NF‑κB inhibitor (e.g., BAY 11‑7082) will rescue autophagy and improve performance on the Morris water maze.\n4. In aged humans, fecal metagenomic abundance of the candidate strain will correlate positively with serum RUBICON levels and inversely with CSF autophagy markers such as beclin‑1.\n\n## Experimental Approach\n- Use germ‑free mice colonized mono‑associated with wild‑type or mutant bacterial strains.\n- Measure NF‑κB p65 phosphorylation in colon epithelium (Western blot), plasma RUBICON by ELISA, and brain autophagy flux (LC3‑II turnover with bafilomycin A1) after 4 weeks.\n- Assess cognition via novel object recognition and spatial learning.\n- Perform fecal transplants from aged donors with high versus low strain abundance into young germ‑free recipients to test transfer of the phenotype.\n- Validate findings in human cohorts by shotgun metagenomics of stool, multiplex cytokine panels, and CSF autophagy assays.