Calorie restriction on insulin resistance and expression of SIRT1 and SIRT4 in rats.

The sirtuin proteins are nicotinamide adenine dinucleotide dependent deacetylases and adenosine diphosphate (ADP)-ribosyl transferases associated with metabolic balance and lifespan extension. Sirtuin 1 (SIRT1) and sirtuin 4 (SIRT4) have been reported to regulate insulin secretion, but their association with the development of insulin resistance and nonalcoholic fatty liver disease remain undefined. The aim of this study was to determine the expression of SIRT1 and SIRT4 in the liver and pancreas of rats fed with different diets and analyze the association of these proteins with insulin resistance and nonalcoholic fatty liver disease. Male Sprague-Dawley rats were randomly divided into the following 4 diet treatment groups: normal control (NC), calorie restriction (CR), high-fat (HFa), and high-fructose (HFr), and these groups were maintained for 12 weeks. Blood biochemical analysis and histopathology indicated that HFa and HFr groups were insulin resistant and developed nonalcoholic fatty livers. SIRT1 was present in the nucleus and cytoplasm of the pancreatic beta-cells, while SIRT4 was located in the cytoplasm. Treatment with the CR diet increased the expression of SIRT1 in both the pancreas and liver, while treatment with the HFa and HFr diets caused a decrease. SIRT4 was upregulated in the liver of rats treated with the HFa diet, but did not change with the CR diet treatment. These data suggest that SIRT1 and SIRT4 were both involved in the development of insulin resistance and nonalcoholic fatty liver disease.