Role of Sirt1 as a Regulator of Autophagy

Sirt1, a NAD+-dependent deacetylase, has been implicated in cellular processes, including cell survival, metabolism, and adaptation to cellular stress. Autophagy plays an important role in the maintenance of intracellular homeostasis by removing protein aggregates and damaged organelles. Nutrient-sensing pathways include the mammalian target of rapamycin (mTOR), AMP-activated kinase (AMPK), and Sirt1 pathways and regulate autophagy machinery depending on nutrient status. Sirt1 may induce autophagy directly by deacetylating autophagy-related genes (Atg) 5 and 7 and LC3. In addition, Sirt1 deacetylates FOXOs and modulates the expression of autophagy regulatory molecules. Sirt1-deacetylated FOXO1 stimulates the expression of Rab7, a small GTPase that is a crucial factor in the maturation of autophagosomes and endosomes. Sirt1 also deacetylates FOXO3, leading to activation of its transcriptional activity and subsequent Bnip3-mediated autophagy. Furthermore, nutrient-sensing pathways interact with each other, and Sirt1 may indirectly induce autophagy via the activation of AMPK and inhibition of the mTOR pathway. Thus, Sirt1 regulates autophagy machinery through multiple mechanisms.