Search

Reactive oxygen species (ROS) production has recently been established as an essential contributor in the pathogenesis of obesity-associated insulin resistance. The FoxO1 pathway plays a role not only in nutrient sensing but also in regulating ROS production. We exposed adipocytes in free fatty acids (FFA) and demonstrated that FoxO1 protein levels decrease in a dose-dependent manner. The FoxO1 downregulation correlated with an increase in the production of ROS and a proinflammatory adipokine pattern characterized by a decrease in adiponectin and an increase in IL-6, plasminogen activator inhibitor-l, and monocyte chemotactic protein-1 mRNA expression levels. Similarly, a decrease in FoxO1 protein levels was seen in adipocytes of db/db mice compared with controls. Treatment with the sirtuin agonist resveratrol, which translocates FoxOl to the nucleus, increased FoxO1 protein levels in adipocytes exposed to FFA. This correlated with a decrease in the generation of ROS and a partial reversal of the proinflammatory adipokine pattern. Together these results indicate that the insulin-resistant adipocyte produced by the exposure to a high concentration of fatty acids is characterized by decreased levels of FoxOl. These data also suggest that modulation of the Sirtl/FoxO1 pathway is a potentially useful therapeutic target for the obesity-induced dysfunctional adipocyte. inflammatory cytokines; insulin resistance; fatty acids doi:10.1152/ajpendo.00629.2006.

Reactive oxygen species (ROS) production has recently been established as an essential contributor in the pathogenesis of obesity-associated insulin resistance. The FoxO1 pathway plays a role not only in nutrient sensing but also in regulating ROS production. We exposed adipocytes to free fatty acids (FFA) and demonstrated that FoxO1 protein levels decrease in a dose-dependent manner. The FoxO1 downregulation correlated with an increase in the production of ROS and a proinflammatory adipokine pattern characterized by a decrease in adiponectin and an increase in IL-6, plasminogen activator inhibitor-1, and monocyte chemotactic protein-1 mRNA expression levels. Similarly, a decrease in FoxO1 protein levels was seen in adipocytes of db/db mice compared with controls. Treatment with the sirtuin agonist resveratrol, which translocates FoxO1 to the nucleus, increased FoxO1 protein levels in adipocytes exposed to FFA. This correlated with a decrease in the generation of ROS and a partial reversal of the proinflammatory adipokine pattern. Together these results indicate that the insulin-resistant adipocyte produced by the exposure to a high concentration of fatty acids is characterized by decreased levels of FoxO1. These data also suggest that modulation of the Sirt1/FoxO1 pathway is a potentially useful therapeutic target for the obesity-induced dysfunctional adipocyte. [ABSTRACT FROM AUTHOR]

1-acylglycerol-3-phosphate-O-acyltransferase 1 (AGPAT1) is a ubiquitously expressed enzyme that catalyzes the formation of phosphatidic acid from lysophosphatidic acid. In turn, phosphatidic acid has been shown to increase mTOR activity, which is known to impair insulin signaling. This study was designed to determine whether AGPAT1 interacts with mTOR to alter insulin signaling. Overexpression of AGPAT1 in C2C12 cells and 3T3 preadipocytes increased the phosphorylation of p70S6K1 at Thr389; a downstream marker of mTOR activation. Importantly, increased p70S6K1 phosphorylation was accompanied by a decrease in the overall abundance of IRS-1 protein. There was also a decrease in the phosphorylation of Akt in AGPAT1 overexpressing cells. These effects were enhanced by the addition of fatty acids to the media. In humans, an overnight lipid infusion reduced insulin sensitivity and their skeletal muscle showed a 1.6-fold increase in AGPAT1 mRNA (p<0.05; n=7). Similarly, in liver samples from insulin resistant human subjects with NAFLD (non alcoholic fatty liver disease) there was an increase in AGPAT1 mRNA levels, which directly correlated with BMI (p<0.05). Overall these data indicate that AGPAT1 overexpression can lead to mTOR activation, which results in a down regulation of insulin signaling. The increase in AGPAT1 levels in human subjects with insulin resistance suggests that AGPAT1 may play a role in the development of insulin resistance. [ABSTRACT FROM AUTHOR]

Mass spectrometry technology has enabled significant advances in detailing the alterations of the lipidome in response to pathological conditions or experimental manipulations. Lipids comprise a wide range of compounds with functions that include structural, intracellular signaling, trafficking, and storage. Characterization of lipid species has evolved significantly over recent years due to the progress made in the area of mass spectrometry. This chapter details the methods used for the analysis of lipids tailored to the intrinsic characteristics of adipose tissue. Particular attention is given to the analysis of triglycerides, diacylglycerols, and phospholipid., (© 2014 Elsevier Inc. All rights reserved.)