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Pro-inflammatory cytokines and adipose tissue

Published online by Cambridge University Press:  05 March 2007

Simon W. Coppack*
Affiliation:
Academic Medical Unit, St Bartholomew's and The Royal London School of Medicine, Whitechapel, London E1 1BB, UK
*
Corresponding Author: Dr Simon Coppack, fax +44 207 377 7636, email [email protected]
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Abstract

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Cytokines appear to be major regulators of adipose tissue metabolism. Therapeutic modulation of cytokine systems offers the possibility of major changes in adipose tissue behaviour. Cytokines within adipose tissue originate from adipocyte, preadipocyte and other cell types. mRNA expression studies show that adipocytes can synthesise both tumour necrosis factor a (TNF-a) and several interleukins (IL), notably IL-1b and IL-6. Other adipocyte products with ‘immunological’ actions include complement system products and macrophage colony-stimulating factor. Cytokine secretion within adipocytes appears similar to that of other cells. There is general agreement that circulating TNF-a and IL-6 concentrations are mildly elevated in obesity. Most studies suggest increased TNF-a mRNA expression or secretion in vitro in adipose tissue from obese subjects. The factors regulating cytokine release within adipose tissue appear to include usual ‘inflammatory‘ stimuli such as lipopolysaccaride, but also the size of the fat cells per se and catecholamines. There is conflicting data about whether insulin and cortisol regulate TNF-a. The effects of cytokines within adipose tissue include some actions that might be characterised as metabolic. TNF-a and IL-6 inhibit lipoprotein lipase, and TNF-a additionally stimulates hormone-sensitive lipase and induces uncoupling protein expression. TNF-a also down regulates insulin-stimulated glucose uptake via effects on glucose transporter 4, insulin receptor autophosphorylation and insulin receptor substrate-1. All these effects will tend to reduce lipid accumulation within adipose tissue. Other effects appear more ‘trophic’, and include the induction of apoptosis, regulation of cell size and induction of de-differentiation (the latter involving reduced peroxisome proliferator-activated receptor g). Cytokines are important stimulators and repressors of other cytokines. In addition, cytokines appear to modulate other regulatory systems. Examples of the latter include effects on leptin secretion (probably stimulation followed by inhibition) and reduction of b3-adrenoceptor expression. There seems to be no clear agreement as to which cytokines derived from adipose tissue act as remote regulators, i.e. hormones. Leptin, which is structurally a cytokine, is also a hormone. IL-6 appears to be released systemically by adipose tissue, but TNF-a is probably not. Both leptin and IL-6 appear to act on the hypothalamus, IL-6 acts on the liver, while leptin may have actions on the pancreas. The importance of the immune system in whole-body energy balance provides a rationale for the links between cytokines and adipose tissue. It seems clear that TNF-a is a powerful autocrine and paracrine regulator of adipose tissue. Other cytokines, notably leptin, and possibly IL-6, have lesser actions on adipose tissue. These cytokines act as hormones, reporting the state of adipose tissue stores throughout the body.

Type
Symposium on ‘New perspectives on adipose tissue function’
Copyright
Copyright © The Nutrition Society 2001

References

Bastard, J-P, Jarde, C, Bruckert, E, Blondy, P, Capeau, J, Laville, M, Vidal, H & Hainque, B (2000) Elevated levels of interleukin 6 are reduced in serum and subcutaneous adipose tissue of obese women after weight loss. Journal of Clinical Endocrinology and Metabolism 85, 33383342.Google ScholarPubMed
Berkowitz, DE, Brown, D, Lee, KM, Emala, C, Palmer, D, An, Y & Breslow, M (1998) Endotoxin-induced alteration in the expression of leptin and b3-adrenergic receptor in adipose tissue. American Journal of Physiology 274, E992E997.Google Scholar
Beutler, B, Krochin, N, Milsark, I, Leudke, C & Cerami, A (1986) Control of cachexin (tumor necrosis factor) synthesis: mechanisms of endotoxin resistance. Science 232, 977979.CrossRefGoogle Scholar
Crawford, EK, Ensor, JE, Kalvakolanu, I & Hasday, JD (1997) The role of 3ç poly(A) tail metabolism in tumor necrosis factor-alpha regulation. Journal of Biological Chemistry 272, 2112021127.CrossRefGoogle Scholar
Fawcett, RL, Waechter, AS, Williams, LB, Zhang, P, Louie, R, Jones, R, Inman, M, Huse, J & Considine, RV (2000) Tumor necrosis factor-a inhibits leptin production in subcutaneous and omental adipocytes from morbidly obese humans. Journal of Clinical Endocrinology and Metabolism 85, 530535.Google Scholar
Feingold, KR & Grunfeld, C (1992) Role of cytokines in inducing hyperlipidemia. Diabetes 41, Suppl. 2, 97101.CrossRefGoogle ScholarPubMed
Feingold, KR, Staprans, I, Memon, RA, Moser, AH, Shigenaga, JK, Doerrler, W, Dinarello, CA & Grunfeld, C (1992) Endotoxin rapidly induces changes in lipid metabolism that produce hypertriglyceridemia: low doses stimulate hepatic triglyceride production while high doses inhibit clearance. Journal of Lipid Research 33, 17651776.CrossRefGoogle ScholarPubMed
Fried, SK, Bunkin, DA & Greenberg, AS (1998) Omental and subcutaneous adipose tissues of obese subjects release interleukin-6: depot differences and regulation by glucocorticoid. Journal of Clinical Endocrinology and Metabolism 83, 847850.Google Scholar
Fried, SK & Zechner, R (1989) Cachectin/tumor necrosis factor decreases human adipose tissue lipoprotein lipase mRNA levels, synthesis, and activity. Journal of Lipid Research 30, 19171923.CrossRefGoogle ScholarPubMed
Friedman, JM (2000) Obesity in the new millennium. Nature 404, 632634.Google Scholar
Gearing, A, Beckett, P, Christodoulou, M, Churchill, M, Clements, J, Davidson, AH, Drummond, AH, Galloway, WA, Gilbert, R, Gordon, JL, Leber, TM, Mangan, M, Miller, K, Nayee, P, Owen, K, Patel, S, Thomas, W, Wells, G, Wood, LM & Woolley, K (1994) Processing of tumor necrosis factor-a precursor by metalloproteinases. Nature 370, 555557.Google Scholar
Greenberg, AS, Nordan, RP, McIntosh, J, Calvo, JC, Scow, RO & Jablons, D (1992) Interleukin 6 reduces lipoprotein lipase activity in adipose tissue of mice in vivo and in 3T3-L 1 adipocytes: a possible role for interleukin 6 in cancer cachexia. Cancer Research 52, 41134116.Google Scholar
Grunfeld, C, Zhao, J, Fuller, J, Pollack, A, Moser, A, Friedman, JE & Feingold, KR (1996) Endotoxin and cytokines induce expression of leptin, the ob gene product, in hamsters. Journal of Clinical Investigation 97, 21522157.Google Scholar
Hardardottir, I, Grunfeld, C & Feingold, KR (1994) Effects of endotoxin and cytokines on lipid metabolism. Current Opinion in Lipidology 5, 207215.Google Scholar
Hauner, H, Bender, M, Haastert, B & Hube, F (1998) Plasma concentrations of soluble TNF-alpha receptors in obese patients. International Journal of Obesity and Related Metabolic Disorders 22, 12391243.Google Scholar
Hauner, H, Petruschke, T, Russ, M & Eckel, J (1995) Effects of tumour necrosis factor alpha (TNF) on glucose transport and lipid metabolism of newly-differentiated human fat cells in cell culture. Diabetologia 38, 764771.CrossRefGoogle ScholarPubMed
Hotamisligil, GS, (1999) The role of TNFa and TNF receptors in obesity and insulin resistance. Journal of Internal Medicine 245, 621625.CrossRefGoogle ScholarPubMed
Hotamisligil, GS, Arner, P, Atkinson, RL & Spiegelman, BM (1997) Differential regulation of the p80 tumor necrosis factor receptor in human obesity and insulin resistance. Diabetes 46, 451455.CrossRefGoogle ScholarPubMed
Hotamisligil, GS, Arner, P, Caro, JF, Atkinson, RL & Spiegelman, BM (1995) Increased adipose tissue expression of tumor necrosis factor-a in human obesity and insulin resistance. Journal of Clinical Investigation 95, 24092415.Google Scholar
Hotamisligil, GS, Budavari, A, Murray, D & Spiegelman, BM (1994) Reduced tyrosine kinase activity of the insulin receptor in obesity-diabetes. Central role of tumor necrosis factor-alpha. Journal of Clinical Investigation 94, 15431549.CrossRefGoogle ScholarPubMed
Hotamisligil, GS, Johnson, RS, Distel, RJ, Ellis, R, Papaioannou, VE & Spiegelman, BM (1996a) Uncoupling of obesity from insulin resistance through a targetted mutation in aP2, the adipocyte fatty acid binding protein. Science 274, 13771379.Google Scholar
Hotamisligil, GS, Peraldi, P, Budavari, A, Ellis, R, White, MF & Spiegelman, BM (1996b) IRS-1-mediated inhibition of insulin receptor tyrosine kinase activity in TNF-α-and obesity-induced insulin resistance. Science 271, 665668.CrossRefGoogle ScholarPubMed
Hotamisligil, GS, Shargill, NS & Spiegelman, BM (1993) Adipose expression of tumor necrosis factor-α: direct role in obesity-linked insulin resistance. Science 259, 8791.CrossRefGoogle ScholarPubMed
Hube, F, Birgel, M, Lee, Y-M, & Hauner, H (1999a) Expression pattern of tumour necrosis factor receptors in subcutaneous and omental human adipose tissue: role of obesity and non-insulin dependent diabetes mellitus. European Journal of Clinical Investigation 29, 672678.Google Scholar
Hube, F & Hauner, H (1999) The role of TNF-α in human adipose tissue: prevention of weight gain at the expense of insulin resistance. Hormone and Metabolic Research 31, 626631.Google Scholar
Hube, F, Lee, Y-M, Rohrig, K & Hauner, H (1999b) The phosphodiesterase inhibitor IBMX suppresses TNF-α expression in human adipocyte precursor cells: a possible explanation for its adipogenic effect. Hormone and Metabolic Research 31, 359362.CrossRefGoogle Scholar
Jain, RG, Meredith, MJ & Pekala, PH (1998) Tumor necrosis factor-alpha mediated activation of signal transduction cascades and transcription factors in 3T3-L1 adipocytes. Advances in Enzyme Regulation 38, 333347.CrossRefGoogle ScholarPubMed
Jain, RG, Phelps, KD & Pekala, PH (1999) Tumor necrosis factor-alpha initiated signal transduction in 3T3-L1 adipocytes. Journal of Cell Physiology 179, 5866.3.0.CO;2-1>CrossRefGoogle ScholarPubMed
Jones, JH & Kennedy, RI (1993) Cytokines and hypothalamic-pituitary function. Cytokine 5, 531538.Google Scholar
Jones, TH (1994) Interleukin-6 an endocrine cytokine. Clinical Endocrinology 40, 703713.CrossRefGoogle ScholarPubMed
Kanety, H, Hemi, R, Papa, MZ & Karasik, A (1996) Sphingomyelinase and ceramide suppress insulin-induced tyrosine phosphorylation of the insulin receptor substrate-1. Journal of Biological Chemistry 271, 98959897.Google Scholar
Kawakami, M, Pekala, PH, Lane, DM & Cerami, A (1982) Lipoprotein lipase suppression in 3T3-L1 cells by an endotoxin-induced mediator from exudate cells. Proceedings of the National Academy of Sciences USA 79, 912916.CrossRefGoogle ScholarPubMed
Kern, PA, Saghizadeh, M, Ong, JM, Bosch, RJ, Deem, R & Simsolo, RB (1995) The expression of tumor necrosis factor in human adipose tissue. Regulation by obesity, weight loss, and relationship to lipoprotein lipase. Journal of Clinical Investigation 95, 21112119.CrossRefGoogle ScholarPubMed
Kirchgessner, TG, Uysal, KT, Weisbrock, SM, Marino, MW & Hotamisligil, GS (1997) Tumor necrosis factor-a contributes to obesity-related hyperleptinemia by regulating leptin release from adipocytes. Journal of Clinical Investigation 100, 27772782.CrossRefGoogle Scholar
Lawrence, VJ & Coppack, SW (2000) The endocrine function of the fat cell – regulation by the sympathetic nervous system. Hormone and Metabolic Research 32, 453467.Google Scholar
Ledgerwood, EC, Prins, JB, Bright, NA, Johnson, DR, Wolfreys, K, Pober, JS, O'Rahilly, S & Bradley, JR (1998) Tumor necrosis factor is delivered to mitochondria where a tumor necrosis factor-binding protein is localised. Laboratory Investigation 78, 15831589.Google Scholar
Liu, LS, Spelleken, M, Rohrig, K, Hauner, H & Eckel, J (1998) Tumour necrosis factor-alpha acutely inhibits insulin signaling in human adipocytes: implication of the p80 tumor necrosis factor receptor. Diabetes 47, 515522.CrossRefGoogle ScholarPubMed
McDermott, MF (2001) TNF and TNFR biology in health and disease. Cellular and Molecular Biology (In the Press).Google Scholar
Mattacks, CA & Pond, CM (1999) Interactions of noradrenalin and tumour necrosis factor a, interleukin 4 and interleukin 6 in the control of lipolysis from adipocytes around lymph nodes. Cytokine 11, 334346.Google Scholar
Mohamed-Ali, V, Goodrick, SJ, Bulmer, K, Holley, JMP, Yudkin, JS & Coppack, SW (1999) Production of soluble tumor necrosis factor receptors by human subcutaneous adipose tissue in vivo. American Journal of Physiology 277, E971E975.Google Scholar
Mohamed-Ali, V, Goodrick, SJ, Rawesh, A, Miles, JM, Katz, DR, Yudkin, JS, Klein, S & Coppack, SW (1997) Subcutaneous adipose tissue secretes interleukin-6 but not tumour necrosis factor-a in vivo. Journal of Clinical Endocrinology and Metabolism 82, 41964200.Google Scholar
Mohamed-Ali, V, Pinkney, JH & Coppack, SW (1998) Adipose tissue as an endocrine and paracrine organ. International Journal of Obesity and Related Metabolic Disorders 22, 11451158.CrossRefGoogle ScholarPubMed
Montague, CT, Prins, JB, Sanders, L, Zhang, J, Sewter, CP, Digby, J, Byrne, CD & O'Rahilly, S (1998) Depot-related gene expression in human subcutaneous and omental adipocytes. Diabetes 47, 13841391.Google Scholar
Morin, CL, Eckel, RH, Marcel, T & Pagliassotti, MJ (1997a) High fat diets elevate adipose tissue-derived tumor necrosis factor-alpha activity. Endocrinology 138, 46654671.Google Scholar
Morin, CL, Pagliassotti, MJ, Windmiller, D & Eckel, RH (1997b) Adipose tissue-derived tumor necrosis factor-alpha activity is elevated in older rats. Journal of Gerontology 52, B190B195.Google Scholar
Mullberg, J, Durie, FH, Otten-Evans, C, Alderson, MR, Rose-John, S, Cosman, D, Black, RA & Mohler, KM (1995) A metalloproteinase inhibitor blocks shedding of the IL-6 receptor and the p60 tumor necrosis factor receptor. Journal of Immunology 155, 51985205.Google Scholar
Niesler, CU, Siddle, K & Prins, JB (1998) Human preadipocytes display a depot-specific susceptibility to apoptosis. Diabetes 47, 13651368.Google Scholar
Niesler, CU, Urso, B, Prins, JB & Siddle, K (2000) IGF-1 inhibits apoptosis induced by serum withdrawal, but potentiates TNF-α-induced apoptosis in 3T3-L1 adipocytes. Journal of Endocrinology 167, 165174.Google Scholar
Nisoli, E, Briscini, L, Giordano, A, Tonello, C, Weisbrock, SM, Uysal, KT, Cinti, S, Carruba, MO & Hotamisligil, GS (2000a) Tumor necrosis factor a mediates apoptosis of brown adipocytes and defective brown adipocyte function in obesity. Proceedings of the National Academy of Sciences USA 97, 80338038.CrossRefGoogle ScholarPubMed
Nisoli, E, Carruba, MO, Tonello, C, Macor, C, Federspil, G & Vettor, R (2000b) Induction of fatty acid translocase/CD36, peroxisome proliferator-activated receptor-γ2, leptin, uncoupling proteins 2 and 3, and tumor necrosis factor-α gene expression in human sub-cutaneous fat by lipid infusion. Diabetes 49, 319324.CrossRefGoogle Scholar
Ofei, F, Hurel, S, Newkirk, J, Sopwith, M & Taylor, R (1996) Effects of an engineered human anti-TNF-α antibody (CDP571) on insulin sensitivity and glycemic control in patients with NIDDM. Diabetes 45, 881885.CrossRefGoogle ScholarPubMed
Ogawa, H, Nielsen, S & Kawakami, M (1989) Cachetin/tumor necrosis factor and interleukin-1 show different modes of combined effect on lipoprotein lipase and intracellular lipolysis. Biochimica et Biophysica Acta 1003, 131135.CrossRefGoogle Scholar
Papanicolaou, DA, Wilder, RL, Manolagas, SC & Chrousos, GP (1998) The pathophysiologic roles of interleukin-6 in human disease. Annals of Internal Medicine 128, 127137.Google Scholar
Pekala, PH, Kawakami, M, Angus, CW, Lane, MD & Cerami, A (1983) Selective inhibition of synthesis of enzymes for de novo fatty acid biosynthesis by an endotoxin-induced mediator from exudate cells. Proceedings of the National Academy of Sciences USA 80, 27432747.Google Scholar
Peraldi, P, Hotamisligil, GS, Buurman, WA, White, MF & Spiegelman, BM (1997a) Tumor necrosis factor (TNF)-α inhibits insulin signalling through stimulation of the p55 TNF receptor and activation of sphingomyelinase. Journal of Biological Chemistry 271, 1301813022.Google Scholar
Peraldi, P, Xu, M & Spiegelman, BM (1997b) Thiazolidinediones block tumor necrosis factor-α-induced inhibition of insulin signaling. Journal of Clinical Investigation 100, 18631869.CrossRefGoogle ScholarPubMed
Petruschke, T & Hauner, H (1993) Tumor necrosis factor-alpha prevents the differentiation of human adipocyte precursor cells and causes delipidation of newly developed fat cells. Journal of Clinical Endocrinology and Metabolism 76, 742747.Google ScholarPubMed
Plata-Salaman, CR (2000) Central nervous system mechanisms contributing to the cachexia-anorexia syndrome. Nutrition 16, 10091012.CrossRefGoogle Scholar
Pond, CM (1999) Physiological specialisation of adipose tissue. Progress in Lipid Research 38, 225248.Google Scholar
Pond, CM (2001) Long-term changes in adipose tissue in human disease. Proceedings of the Nutrition Society 60, 365374.Google Scholar
Prins, JB, Niesler, CU, Winterford, CM, Bright, NA, Siddle, K, O'Rahilly, S, Walker, NI & Cameron, DP (1997) Tumor necrosis factor-a induces apoptosis of human adipose cells. Diabetes 46, 19391944.CrossRefGoogle Scholar
Prins, JB & O'Rahilly, S (1997) Regulation of adipose cell number in man. Clinical Science 92, 311.Google Scholar
Purohit, A, Ghilchik, MW, Duncan, L, Wang, DY, Singh, A, Walker, MM & Reed, MJ (1995) Aromatase activity and interleukin-6 production by normal and malignant breast tissues. Journal of Clinical Endocrinology and Metabolism 80, 30523058.Google Scholar
Qi, C & Pekala, PH (2000) Tumor necrois factor-α-induced insulin resistance in adipocytes. Proceedings of the Society for Experimental Biology and Medicine 223, 128135.Google Scholar
Rothwell, NJ (1994) CNS regulation of thermogenesis. Critical Reviews in Neurobiology 8, 110.Google Scholar
Saleh, J, Summers, LKM, Cianflone, K, Fielding, BA, Sniderman, AD & Frayn, KN (1998) Coordinated release of acylation stimulating protein (ASP) and triacylglycerol clearance by human adipose tissue in vivo in the postprandial period. Journal of Lipid Research 39, 884891.Google Scholar
Sarraf, P, Frederich, RC, Turner, EM, Ma, G, Jaskowiak, NT, Rivet, DJ 3rd, Flier, JS, Lowell, BB, Fraker, DL & Alexander, HR (1997) Multiple cytokines and acute inflammation raise mouse leptin levels: potential role in inflammatory anorexia. Journal of Experimental Medicine 185, 171175.Google Scholar
Sethi, JK, Xu, H, Uysal, KT, Wiesbrock, SM, Scheja, L & Hotamisligil, GS (2000) Characterisation of receptor-specific TNFalpha functions in adipocyte cell lines lacking type 1 and 2 TNF receptors. FEBS Letters 469, 7782.Google Scholar
Sewter, CP, Digby, JE, Blows, F, Prins, JB & O'Rahilly, S (1999) Regulation of tumour necrosis factor-alpha release from human adipose tissue in vitro. Journal of Endocrinology 163, 3338.CrossRefGoogle ScholarPubMed
Stephens, JM, Butts, MD & Pekala, PH (1992) Regulation of transcription factor mRNA accumulation during 3T3-L1 preadipocyte differentiation by tumor necrosis factor-alpha. Journal of Molecular Endocrinology 9, 6172.Google Scholar
Stephens, JM & Pekala, PH (1991) Transcriptional regression of the GLUT4 and C/EBP genes in 3T3-L1 adipocytes by tumor necrosis factor-alpha. Journal of Biological Chemistry 266, 2183921845.Google Scholar
Strassmann, G, Fong, M, Windsor, S & Neta, R (1993) The role of interleukin-6 in lipopolysaccharide-induced weight loss, hypoglycemia and fibrinogen production in vivo. Cytokine 5, 285290.Google Scholar
Strosberg, AD & Pietri-Rouxel, F (1996) Function and regulation of the beta3-adrenoceptor. Trends in Pharmacological Science 17, 373381.CrossRefGoogle Scholar
Sumida, M, Shiosaka, T, Nagar, A, Isshikimasuda, M, Okuda, H & Hamada, M (1997) Suppressive effect of tumor necrosis factor-a on adipogenic cell differentiation and on gene expression of hormone-sensitive lipase. Journal of Clinical Biochemistry and Nutrition 22, 111.Google Scholar
Szalkowski, D, White-Carrington, S, Berger, J & Zhang, B (1995) Antidiabetic thiazolidinediones block the inhibitory effect of tumour necrosis factor-α on differentiation, insulin-stimulated glucose uptake, and gene expression in 3T3-L1 cells. Endocrinology 136, 14741481.Google Scholar
Torti, FM, Torti, SV, Larrick, JW & Ringold, GM (1989) Modulation of adipocyte differentiation by tumor necrosis factor and transforming growth factor. Journal of Cell Biology 108, 11051113.Google Scholar
Uysal, KT, Wiesbrock, SM & Hotamisligil, GS (1998) Functional analysis of tumor necrosis factor (TNF) receptors in TNF-alpha-mediated insulin resistance in genetic obesity. Endocrinology 139, 48324838.Google Scholar
Uysal, KT, Wiesbrock, SM, Marino, MW & Hotamisligil, GS (1997) Protection from obesity-induced insulin resistance in mice lacking TNF-α function. Nature 389, 610614.Google Scholar
Van der Poll, T, Romijn, JA, Endert, E, Borm, JJ, B¨ller, HR & Sauerwein, HP (1991) TNF mimics the metabolic response of acute infections in healthy humans. American Journal of Physiology 261, E457E465.Google Scholar
Ventre, J, Doebber, T, Wu, M, MacNaul, K, Stevens, K, Pasparakis, M, Kollias, G & Moller, DE (1997) Targeted disruption of the tumour necrosis factor-alpha gene: metabolic consequences in obese and nonobese mice. Diabetes 46, 15261531.Google Scholar
Yudkin, JS, Kumari, M, Humphries, SE & Mohamed-Ali, V (2000) Inflammation, obesity, stress and coronary heart disease: is interleukin-6 the link? Atherosclerosis 148, 209214.Google Scholar
Zhang, B, Berger, J, Hu, E, Szalkowski, D, White-Carrington, S, Spiegelman, BM & Moller, DE (1996) Negative regulation of peroxisome proliferator-activated receptor-g gene expression contributes to the antiadipogenic effects of tumor necrosis factor-α. Molecular Endocrinology 10, 14571466.Google Scholar
Zhang, Y, Proenca, R, Maffei, M, Barone, M, Leopold, L & Friedman, JM (1994) Positional cloning of the mouse obese gene and its human homologue. Nature 372, 425432 (published erratum appears in Nature 374, 479).Google Scholar