RESEARCH ARTICLES Enhanced prereceptor glucocorticoid metabolism and lipogenesis impair insulin signaling in the liver of fructose-fed rats Ana Vasiljević a , Nataša Veličković a, ⁎, Biljana Bursać a , Ana Djordjevic a , Danijela Vojnović Milutinović a , Nataša Nestorović b , Gordana Matić a a Department of Biochemistry, Institute for Biological Research “Siniša Stanković,” University of Belgrade, 11000 Belgrade, Serbia b Department of Cytology, Institute for Biological Research “Siniša Stanković,” University of Belgrade, 11000 Belgrade, Serbia Received 13 November 2012; received in revised form 18 February 2013; accepted 1 April 2013 Abstract Overconsumption of fructose, as a highly lipogenic sugar, may profoundly affect hepatic metabolism and has been associated with many components of the metabolic syndrome, particularly with insulin resistance and Type 2 diabetes. In this study, we proposed that high fructose diet may enhance lipogenesis and decrease insulin sensitivity in the liver through dysregulation of glucocorticoid signaling. Therefore, we examined the effects of long-term consumption of 10% fructose solution on triglyceridemia, liver histology and intracellular corticosterone level, as well as on 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) and hexose-6-phosphate dehydrogenase (H6PDH) mRNA and protein levels in the rat liver. Glucocorticoid action was assessed by glucocorticoid receptor (GR) expression and intracellular redistribution. We also analyzed the expression of enzymes involved in gluconeogenesis and lipogenesis, phosphoenolpyruvate carboxykinase (PEPCK) and lipin-1. The results have shown that fructose-rich diet led to increase in 11βHSD1 and H6PDH protein levels, while hepatic corticosterone concentration remained unchanged. Concomitantly, GR was increasingly accumulated in the cytoplasm, whereas its nuclear level was unchanged and accompanied by diminished PEPCK mRNA level. Elevation of lipin-1 in the liver microsomes suggested that fructose diet led to an increase in lipogenesis and consequently to hypertriglyceridemia. The observed increase of insulin receptor supstrate-1 phosphorylation on Ser 307 represents a hallmark of impaired insulin signaling in the liver of fructose-fed rat and probably is a consequence of the alterations in 11βHSD1 and lipin-1 levels. Overall, our findings suggest that fructose-rich diet may perturb hepatic prereceptor glucocorticoid metabolism and lipogenesis, resulting in hypertriglyceridemia and attenuated hepatic insulin sensitivity. © 2013 Elsevier Inc. All rights reserved. Keywords: 11βHSD1; Glucocorticoids; Lipogenesis; Fructose; Liver 1. Introduction High caloric intake is in the focus of research in recent years due to its apparent association with growing metabolic disorders, especially obesity and Type 2 diabetes mellitus [1]. Increased consumption of fructose, a highly lipogenic sugar, can trigger a cascade of events originating in the liver and adipose tissue that lead to hyperglycemia, dyslipidemia, hepatic steatosis and insulin resistance [2]. Fructose-fed rat have therefore been utilized as a model for studying various aspects of metabolic syndrome [3], including gluconeogenesis [4], de novo lipogenesis [5] and chronic low-grade inflammation [6]. Many studies have shown that glucocorticoid hormones play a fundamental role in pathogenesis of diet-induced metabolic syn- drome [7] and in development of obesity and insulin resistance [8]. Although glucocorticoid secretion is mainly determined by activity of the hypothalamic-pituitary-adrenal axis, there is evidence suggesting that elevated intracellular glucocorticoid concentrations may better predict the promotion and maintenance of obesity than circulating hormone levels [9,10]. Intracellular level of these hormones is crucially dependent on the microsomal enzyme 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1), which acts primarily as an oxidoreductase and catalyses the production of active glucocorticoids [corticosterone (CORT) in rats] from inactive 11-keto steroids (11- dehydrocorticosterone). The pool of cofactor nicotinamide adenine dinucleotide phosphate (NADPH) that drives the oxidoreductase reaction of 11βHSD1 is thought to be generated by hexose-6- phosphate-dehydrogenase (H6PDH), a microsomal enzyme coloca- lized in the lumen of endoplasmic reticulum (ER) with 11βHSD1 [11]. Many studies have suggested that tissue-specific dysregulation of 11βHSD1 contributes to the pathogenesis of obesity, hypertension and insulin resistance [12]. However, a link between prereceptor glucocorticoid metabolism and metabolic disturbances induced by high fructose consumption is still missing. At the molecular level, CORT acts by binding to glucocorticoid receptor (GR), a ligand-activated transcription factor. After ligand binding, GR translocates from the cytoplasm to the nucleus and mediates glucocorticoid-regulated transcription of numerous genes [13]. The important metabolic role of glucocorticoids includes Available online at www.sciencedirect.com ScienceDirect Journal of Nutritional Biochemistry 24 (2013) 1790 – 1797 ⁎ Corresponding author. Tel.: +381 11 207 83 18; fax: +381 11 276 14 33. E-mail address: nvelickovic@ibiss.bg.ac.rs (N. Veličković). 0955-2863/$ - see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jnutbio.2013.04.001