Provided herein are methods and compositions for modulating the activity of sirtuin deacetylase protein family members； p53 activity； apoptosis； lifespan and sensitivity to stress of cells and organisms. Exemplary methods comprise contacting a cell with an activating compound, such as a flavone, stilbene, flavanone, isoflavone, catechin, chalcone, tannin or anthocyanidin； or an inhibitory compound, such as a sphingolipid, e.g., sphingosine. Also disclosed herein are methods for treating, preventing or diagnosing a disease associated with neuronal cell death, e.g., a neurodegenerative disease.
