Selective overexpression of human SIRT1 in adipose tissue enhances energy homeostasis and prevents the deterioration of insulin sensitivity with ageing in mice

SIRT1, a longevity regulator and NAD(+)-dependent deacetylase, plays a critical role in promoting metabolic fitness associated with calorie restriction and healthy ageing. Using a tissue-specific transgenic approach, the present study demonstrates that over-expression of human SIRT1 selectively in adipose tissue of mice prevents ageing-induced deterioration of insulin sensitivity and ectopic lipid distribution, reduces whole body fat mass and enhances locomotor activity. During ageing, the water-soluble vitamin biotin is progressively accumulated in adipose tissue. Over-expression of SIRT1 alleviates ageing-associated biotin accumulation and reduces the amount of biotinylated proteins, including acetyl CoA carboxylase, a major reservoir of biotin in adipose tissues. Chronic biotin supplementation increases adipose biotin contents and abolishes adipose SIRT1-mediated beneficial effects on insulin sensitivity, lipid metabolism and locomotor activity. Biochemical, spectrometric and chromatographic analysis revealed that biotin and its metabolites act as competitive inhibitors of SIRT1-mediated deacetylation. In summary, these results demonstrate that adipose SIRT1 is a key player in maintaining systemic energy homeostasis and insulin sensitivity; enhancing its activity solely in adipose tissue can prevent ageing-associated metabolic disorders.

Lipocalin-2 deficiency prevents endothelial dysfunction associated with dietary obesity: role of cytochrome P450 2C inhibition

BACKGROUND AND PURPOSE

Lipocalin-2 is a pro-inflammatory adipokine up-regulated in obese human subjects and animal models. Its circulating levels are positively correlated with the unfavourable lipid profiles, elevated blood pressure and insulin resistance index. Augmented lipocalin-2 has been found in patients with cardiovascular abnormalities.The present study was designed to investigate the role of lipocalin-2 in regulating endothelial function and vascular reactivity.

EXPERIMENTAL APPROACH

Wild-type and lipocalin-2 knockout (Lcn2-KO) mice were fed with either a standard chow or a high-fat diet. Blood pressures and endothelium-dependent relaxations/contractions were monitored at 2 week intervals.

RESULTS

Systolic blood pressure was elevated by high-fat diet in wild-type mice but not in Lcn2-KO mice. Endothelial dysfunction, reflected by the impaired endothelium-dependent relaxations to insulin and augmented endothelium-dependent contractions to ACh, was induced by high-fat diet in wild-type mice. In contrast, Lcn2-KO mice were largely protected from the deterioration of endothelial function caused by dietary challenges. The eNOS dimer/monomer ratio, NO bioavailability, basal and insulin-stimulated PKB/eNOS phosphorylation responses were higher in aortae of Lcn2-KO mice. Administration of lipocalin-2 attenuated endothelium-dependent relaxations to insulin and promoted endothelium-dependent contractions to ACh. It induced eNOS uncoupling and elevated COX expression in the arteries. Treatment with sulphaphenazole, a selective inhibitor of cytochrome P450 2C9, improved endothelial function in wild-type mice and blocked the effects of lipocalin-2 on both endothelium-dependent relaxations to insulin and endothelium-dependent contractions to ACh, as well as eNOS uncoupling.

CONCLUSIONS

Lipocalin-2, by modulating cytochrome P450 2C9 activity, is critically involved in diet-induced endothelial dysfunction.