Increased Sirt1 secreted from visceral white adipose tissue is associated with improved glucose tolerance in obese Nrf2-deficient mice.

ABSTRACT

Obesity is associated with metabolic dysregulation characterized by insulin resistance and glucose intolerance. Nuclear factor E2-related factor (Nrf2) is a critical regulator of the stress response and Nrf2-deficient mice (Nrf2-/-) are protected against high fat diet (HFD)-induced metabolic derangement. We searched for factors that could underline this favorable phenotype and found that Nrf2-/- mice exhibit higher circulating levels of sirtuin 1 (Sirt1), a key player in cellular homeostasis and energy metabolism, compared to wild-type mice. Increased Sirt1 levels in Nrf2-/- mice were found not only in animals under standard diet but also following HFD. Interestingly, we report here that the visceral adipose tissue (eWAT) is the sole source of increased Sirt1 protein in plasma. eWAT and other fat depots displayed enhanced adipocytes lipolysis, increased fatty acid oxidation and glycolysis, suggesting autocrine and endocrine actions of Sirt1 in this model. We further demonstrate that removal of eWAT completely abolishes the increase in circulating Sirt1 and that this procedure suppresses the beneficial effect of Nrf2 deficiency on glucose tolerance, but not insulin sensitivity, following a HFD regime. Thus, in contrast to many other stressful conditions where Nrf2 deficiency exacerbates damage, our study indicates that up-regulation of Sirt1 levels specifically in the visceral adipose tissue of Nrf2-/- mice is a key adaptive mechanism that mitigates glucose intolerance induced by nutritional stress.