The effects of different dietary interventions and ageing on DNA methylation levels of SIRT1 in the brain of mammary tumour mouse model

Sirtuin 1 (SIRT1) is a NAD+-dependent deacetylase that maintains cell homeostasis by playing an important role in cellular processes, such as gene transcription, stress reaction and apoptosis. Dietary interventions such as calorie restriction (CR) modulates SIRT1 activity and that leads to increment in healthspan and lifespan in many organisms. The preservation of brain functions that decline with ageing is positively impacted by SIRT1. The aim of this study was understanding the biological link between DNA methylation of Sirt1 and effects of different types of dietary interventions and a causal role of ageing in mice brain. To investigate Sirt1 gene methylation due to ageing and CR, 10 weeks old female C57BL/6 mice were fed ad libitum (AL), with chronic calorie restriction (CCR) (15% CR ) or intermittent calorie restriction (ICR) (three weeks of AL followed by one week 60% CR in a cyclic manner). Pyrosequencing was performed to examine the methylation levels of Sirt1 from brain homogenates and understand the underlying mechanisms of CCR and ICR in relation to ageing at the genomic level. Western-blot was used to determine protein expression levels whereas RT-PCR was used to determine Sirt1 mRNA levels. We could not find any significant difference in expression and DNA methylation levels of Sirt1 with ageing. Also, the diet-associated mRNA and protein expression levels and DNA methylation changes of Sirt1 were not obtained. A significant negative correlation was observed between DNA methylation levels and mRNA/protein expression of Sirt1. In addition, a statistically significant positive correlation was found between protein expression and mRNA expression. These findings indicate that decrease of SIRT1 by ageing might be regulated at the proteomic levels or with other epigenetic mechanisms. DNA methylation has a regulative effect on Sirt1 expression regardless of diet and age.