SIRT1 regulates Dishevelled proteins and promotes transient and constitutive Wnt signaling.

Sirtuin 1 (SIRT1) is a class III histone deacetylase that deacetylates histone and nonhistone proteins to regulate gene transcription and protein function. Because SIRT1 regulates very diverse responses such as apoptosis, insulin sensitivity, autophagy, differentiation, and stem cell pluripotency, it has been a challenge to reconcile how it orchestrates such pleiotropic effects. Here we show that SIRT1 serves as an important regulator of Wnt signaling. We demonstrate that SIRT1 loss of function leads to a significant decrease in the levels of all three Dishevelled (Dvl) proteins. Furthermore, we demonstrate that SIRT1 and Dvl proteins complex in vivo and that inhibition of SIRT1 leads to changes in gene expression of Wnt target genes. Finally, we demonstrate that Wnt-stimulated cell migration is inhibited by a SIRT1 inhibitor. Because the three mammalian Dvl proteins serve as key messengers for as many as 19 Wnt ligands, SIRT1-mediated regulation of Dvl proteins may explain the diverse physiological responses observed in different cellular contexts. Previously, SIRT1 had only been shown to mediate the epigenetic silencing of Wnt antagonists. In contrast, here we report that SIRT1 regulates Dvl protein levels and Wnt signaling in several cellular contexts. These findings demonstrate that SIRT1 is a regulator of transient and constitutive Wnt signaling.

The role of sirtuin proteins in obesity.

Although the progressive metabolic changes associated with obesity are complex, it is well-recognized that obesity is a risk factor for the development of insulin resistance and type 2 diabetes. Because both obesity and type 2 diabetes are associated with insulin resistance, there is significant interest in defining the mechanistic basis for insulin resistance. Recent studies involving SIRT1, the most intensely studied sirtuin family member, have shown that it regulates many metabolic adaptations linked with obesity. SIRT1 has been shown to regulate the expression of adipokines, repress the activity of factors required for maturation of fat cells, regulate insulin secretion, modulate plasma glucose levels and insulin sensitivity and alter mitochondrial capacity. Moreover, some investigators have suggested that altering SIRT1 activity may be a promising new therapy for type 2 diabetes. In this review we focus on the role of sirtuins in obesity with particular emphasis on the contribution of SIRT1.