Sirtuin 1 (SIRT1) is an NAD+dependent class III histone deacetylase. It is a member of the sirtuin family of proteins, homologous to the yeast Sir2 protein. SIRT1 modulates intracellular activities through transcription regulation and functions in several separate cellular functions. SIRT1 deacetylates and inactivates tumor suppressor protein p53, a process regulated by Hypermethylated in Cancer 1 (HIC1) protein to allow cells to bypass apoptosis and survive DNA damage. The level of SIRT1 is significantly elevated in mouse and human prostate cancer. SIRT1 promotes vascular relaxation by activating endothelial nitric oxide synthase. SIRT1 also protects against microglia-dependent amyloid-beta toxicity through inhibiting NF-kappa b signaling.