The phosphorylation status of T522 modulates tissue-specific functions of SIRT1 in energy metabolism in mice

The goal of this project is to understand how the phosphorylation status of T522 at SIRT1, the most conserved mammalian NAD+-dependent protein deacetylase, regulates its activity and function in vivo. We have previously reported that SIRT1 can be phosphorylated and activated by two anti-apoptotic members of the dual specificity tyrosine phosphorylation-regulated kinase (DYRK), DYRK1A and DYRK3, in response to acute environmental stresses. However, whether this modification is involved in regulation of SIRT1 activity remains elusive. To assess the physiological impacts of the phosphorylation of T522 on SIRT1, we generated SIRT1 T522 phosphorylation mimic (T522E mutation, or TEKI) and dephosphorylation mimic (T522A mutation, or TAKI) knock-in mouse models. Our current findings indicated that TAKI mice but not TEKI mice displayed impaired hepatic fatty acid oxidation and developed hepatic steatosis after high-fat diet feeding. To understand the molecular mechanisms underlying this phenotype, we examined the hepatic transcriptomes of SIRT1 WT, TAKI and TEKI mice after 5-month high-fat diet feeding by microarray analysis. 5 WT, 5 TAKI, and 3 TEKI mice were fed with a western-style high-fat diet for 5 months. Their hepatic total RNA was isolated using the Qiagen RNeasy mini-kit, and gene expression profiles were analyzed using Agilent Whole Mouse Genome 4x44 multiplex format oligo arrays (014868) (Agilent Technologies, Santa Clara, CA), following the Agilent 1-color microarray-based gene expression analysis protocol.