Tissue-specific regulation of SIRT1 by calorie restriction

Abstract

Calorie restriction (CR) has been reported to increase SIRT1 protein levels in mice, rats, and humans, and elevated activity of SIRT1 orthologs extends life span in yeast, worms, and flies. In this study, we challenge the paradigm that CR induces SIRT1 activity in all tissues by showing that activity of this sirtuin in the liver is, in fact, reduced by CR and activated by a high-caloric diet. We demonstrate this change both by assaying levels of SIRT1 and its small molecule regulators, NAD and NADH, as well as assessing phenotypes of a liver-specific SIRT1 knockout mouse on various diets. Our findings suggest that designing CR mimetics that target SIRT1 to provide uniform systemic benefits may be more complex than currently imagined.

Figure 1.

Differential regulation of SIRT1 in the tissues of CR mice. (A) The expression of SIRT1 is upregulated in the muscle and WAT but downregulated in the liver of CR mice. The expression of SIRT1 in the liver, muscle, and WAT of mice fed ad libtum or calorie restricted was determined by Western blotting with the anti-SIRT1 antibody. Tubulin was used as a loading control. (B) The NAD/NADH ratio is increased in the muscle and WAT but decreased in the liver of CR mice. Note that levels of both NAD and NADH are increased in WAT by CR. The NAD and NADH concentrations in the liver, muscle, and WAT of wild-type and SIRT1 knockout mice fed ad libitum or calorie restricted are expressed as nanomole per gram of tissue.

Figure 2.

SIRT1 liver-specific knockout mice have no overt phenotype when fed a chow diet. (A) SIRT1 is specifically knocked out in the livers of SIRT1 LKO mice. Expression of SIRT1 in the liver, the muscle, and the WAT was detected by Western blotting with an anti-SIRT1 antibody. Actin was used as a loading control. (B–F) Body weight, liver weight, blood glucose, and insulin levels (fed and fasted), and glucose tolerance were compared between wild-type and SIRT1 LKO mice on a chow diet.

Figure 3.

SIRT1 LKO mice are protected from physiological decline when fed a high-fat diet. (A–G) Body weight gain over time, WAT weight, liver weight, blood glucose, and insulin levels (both fed and fasted) and glucose tolerance were compared between wild-type and LKO mice on a high-fat diet. (H) Expression of ABCA1, FAS, and SREBP1c were compared between wild-type and LKO mice fed a high-fat diet or a CR diet by QRT–PCR. (I) Expression of SREBP1c was compared between wild-type and LKO mice fed a high-fed diet by Western blotting. Statistics was calculated by Student’s t-test. (*) P < 0.05; (**) P < 0.01.

Figure 4.

SIRT1 LKO mice respond to CR normally. (A–F) Body weight, WAT weight, liver weight, blood glucose levels, insulin levels, and glucose tolerance were compared between wild-type and LKO mice on a CR diet. (G) Expression of PGC-1α, PEPCK, and G6P were compared between wild-type and LKO mice fed a high-fat diet or a CR diet by QRT–PCR.