Restoring Neuroprotective Tryptophan Metabolism via Targeted Probiotic Engineering

**Background and Rationale** The gut-brain axis has emerged as a critical bidirectional communication pathway in neurodegeneration, with mounting evidence demonstrating that intestinal microbiota composition significantly influences central nervous system health. Tryptophan, an essential amino acid obtained through diet, serves as a precursor for multiple bioactive metabolites with opposing neurological effects. Under healthy conditions, tryptophan is metabolized along three primary pathways: t...