Tryptophan metabolism: entering the field of aging and age-related pathologies

Aging is an important risk factor for many debilitating diseases, including cancer and neurodegeneration. In model organisms, interfering with metabolic signaling pathways, including the insulin/insulin-like growth factor (IGF) 1 (IIS) and TOR pathways, can protect against age-related pathologies and increase lifespan. Recent studies in multiple organisms have implicated tryptophan metabolism as a powerful regulator of age-related diseases and lifespan. Its high conservation throughout evolution has enabled studies that begin to dissect the contribution of individual enzymes and metabolites. Here, we focus on the emerging view of tryptophan metabolism as a pathway that integrates environmental and metabolic signals to regulate animal biology and health.