Differential Responses of Visceral and Subcutaneous Fat Depots to Nutrients Francine H. Einstein, 1 Gil Atzmon, 2 Xiao-man Yang, 2 Xiao-Hui Ma, 2 Marielisa Rincon, 3 Eric Rudin, 2 Radhika Muzumdar, 2,3 and Nir Barzilai 2 Increased visceral adiposity is a pivotal component of the metabolic syndrome. Differential gene expression patterns of fat-derived peptides (FDPs) in visceral fat and subcutaneous fat have been characterized in the fasting state. Here we examined whether delivery of nutrients differentially affects the expression of FDPs in visceral fat versus subcutaneous fat (in the fed state). We increased the rate of glucose flux into adi- pose tissue of normal rats (n  16) by hyperglycemia or hyperinsulinemia using the clamp technique. Glucose uptake was associated with increased expression of FDPs, including resistin (5-fold), adiponectin (2- fold), leptin (15-fold), plasminogen activating inhibi- tor-1 (10-fold), and angiotensinogen (4-fold) in visceral fat, but markedly less in subcutaneous fat. Cytokine expression de-rived mainly from vascular/ stromal/macrophage components of adipose tissue was less dramatically increased. Infusion of glucosamine amplified the results obtained by increasing glucose uptake into adipose tissue, suggesting that flux through the hexosamine biosynthetic pathway may serve as a mechanism for “nutrient sensing.” Nutrient-dependent expression of FDPs in visceral fat was also associated with increased plasma levels of several FDPs. Because a biologic sensing pathway can dynamically couple daily food intake to abnormal plasma levels of important FDPs, we challenge the practice of obtaining plasma levels after fasting to assess risk factors for metabolic syndrome. Diabetes 54:672– 678, 2005 I ncreased adiposity is a risk factor for insulin resis- tance, type 2 diabetes, and coronary artery disease (1–3). Increased visceral fat is associated with and may account for the changes in peripheral and hepatic insulin sensitivity seen with obesity (4 – 6). In rodent and human experiments, removal of subcutaneous fat did not result in improvement of insulin action, sup- porting the hypothesis that visceral fat may be metaboli- cally more active (7,8). We previously demonstrated a causal relationship between visceral fat and insulin resis- tance by surgical removal of visceral fat from both old and young rats and further demonstrated an improvement in both peripheral and hepatic insulin resistance as well as an improvement in expression of several fat-derived peptides (FDPs) (9,10). Previous studies have attempted to explain the physio- logic differences between visceral fat and subcutaneous fat in humans by examining variability in gene expression in simultaneously obtained adipose tissue biopsies in the fasting state (11,12). We previously demonstrated these differences using expression array showing that 20% of the genes expressed differed by at least twofold in one depot relative to the other (13). In this experiment, we evaluated gene expression and plasma levels of FDPs in response to nutrients. Although changes in glucoregulatory hormones have been docu- mented after glucose tolerance tests and food boluses, nutrients may have a more complex and prolonged action affecting gene transcription, secretion, and ultimately plas- ma levels. For example, plasma levels of the FDP leptin are increased throughout the day, and its levels are max- imal at 2 A.M. (14), an effect that is linked to food intake and not a diurnal variation (15). This line of investigation is important because plasma levels of these surrogate markers of risk are proportional to fat depot size. In the central obesity typical of the metabolic syndrome, visceral fat accounts for up to 27% of total fat volume in obese humans (16), making an understanding of its regulation significant. The hexosamine biosynthetic pathway (HBP) has a major role in directing hexose phosphates and glutamine to glycosylation and synthesis glycoproteins. Because the HBP accounts for only a small percentage (1–3%) of the glucose metabolized in myocytes, adipocytes, and other cells, it is hypothesized to be an ideal candidate for a cellular nutrient sensor, responding to energy availability and mediating different metabolic effects (17). Hypergly- cemia or hyperinsulinemia, by increasing the flux through the HBP, can lead to insulin resistance and glycosylation of transcription factors such as Sp1 (17–19). Sp1 is an important transcription factor that can modulate expres- sion of FDPs, particularly those involved in insulin action and the metabolic syndrome (20). Leptin gene expression in adipose and muscle tissues is increased during en- From the 1 Department of Obstetrics and Gynecology and Women’s Health, Albert Einstein College of Medicine, Bronx, New York; the 2 Department of Medicine, Diabetes Research and Training Center, Institute for Aging Re- search, Albert Einstein College of Medicine, Bronx, New York; and the 3 Department of Pediatrics, Albert Einstein College of Medicine, Bronx, New York. Address correspondence and reprint requests to Nir Barzilai, MD, Institute for Aging Research, Belfer Bldg. #701, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461. E-mail: barzilai@aecom.yu.edu. Received for publication 5 August 2004 and accepted in revised form 18 November 2004. F.H.E. and G.A. contributed equally to this work. FDP, fat-derived peptide; GAPDH, glyceraldehyde-3-phosphate dehydroge- nase; HBP, hexosamine biosynthetic pathway; IL, interleukin; PAI-1, plasmin- ogen activating inhibitor-1; TNF-, tumor necrosis factor-. © 2005 by the American Diabetes Association. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 672 DIABETES, VOL. 54, MARCH 2005