Uncoupling of Inflammation and Insulin Resistance by NF-κB in Transgenic Mice through Elevated Energy Expenditure
2009; Elsevier BV; Volume: 285; Issue: 7 Linguagem: Inglês
10.1074/jbc.m109.068007
ISSN1083-351X
AutoresTianyi Tang, Jin Zhang, Jun Yin, Jarosław Staszkiewicz, Barbara Gawrońska‐Kozak, Dae Young Jung, Hwi Jin Ko, Helena Ong, Jason K. Kim, Randy Mynatt, Roy J. Martin, Michael J. Keenan, Zhan‐Guo Gao, Jianping Ye,
Tópico(s)NF-κB Signaling Pathways
ResumoTo study the metabolic activity of NF-κB, we investigated phenotypes of two different mouse models with elevated NF-κB activities. The transcriptional activity of NF-κB is enhanced either by overexpression of NF-κB p65 (RelA) in aP2-p65 mice or inactivation of NF-κB p50 (NF-κB1) through gene knock-out. In these models, energy expenditure was elevated in day and night time without a change in locomotion. The mice were resistant to adulthood obesity and diet-induced obesity without reduction in food intake. The adipose tissue growth and adipogenesis were inhibited by the elevated NF-κB activity. Peroxisome proliferator-activator receptor γ expression was reduced by NF-κB at the transcriptional level. The two models exhibited elevated inflammatory cytokines (tumor necrosis factor-α and interleukin-6) in adipose tissue and serum. However, insulin sensitivity was not reduced by the inflammation in the mice on a chow diet. On a high fat diet, the mice were protected from insulin resistance. The glucose infusion rate was increased more than 30% in the hyperinsulinemic-euglycemic clamp test. Our data suggest that the transcription factor NF-κB promotes energy expenditure and inhibits adipose tissue growth. The two effects lead to prevention of adulthood obesity and dietary obesity. The energy expenditure may lead to disassociation of inflammation with insulin resistance. The study indicates that inflammation may prevent insulin resistance by eliminating lipid accumulation. To study the metabolic activity of NF-κB, we investigated phenotypes of two different mouse models with elevated NF-κB activities. The transcriptional activity of NF-κB is enhanced either by overexpression of NF-κB p65 (RelA) in aP2-p65 mice or inactivation of NF-κB p50 (NF-κB1) through gene knock-out. In these models, energy expenditure was elevated in day and night time without a change in locomotion. The mice were resistant to adulthood obesity and diet-induced obesity without reduction in food intake. The adipose tissue growth and adipogenesis were inhibited by the elevated NF-κB activity. Peroxisome proliferator-activator receptor γ expression was reduced by NF-κB at the transcriptional level. The two models exhibited elevated inflammatory cytokines (tumor necrosis factor-α and interleukin-6) in adipose tissue and serum. However, insulin sensitivity was not reduced by the inflammation in the mice on a chow diet. On a high fat diet, the mice were protected from insulin resistance. The glucose infusion rate was increased more than 30% in the hyperinsulinemic-euglycemic clamp test. Our data suggest that the transcription factor NF-κB promotes energy expenditure and inhibits adipose tissue growth. The two effects lead to prevention of adulthood obesity and dietary obesity. The energy expenditure may lead to disassociation of inflammation with insulin resistance. The study indicates that inflammation may prevent insulin resistance by eliminating lipid accumulation. IntroductionThe IKKβ 2The abbreviations used are: IKKβ (IKK2)IκBα kinase 2NF-κBnuclear factor κBWATwhite adipose tissueHFDhigh fat diet (58% of calories in fat)IκBαinhibitor κB αp50 (NF-κB1)NF-κB p50 subunitp65 (RelA)NF-κB p65 subunitTNF-αtumor necrosis factor αKOknock-outDAPI4′,6-diamidino-2-phenylindolePPARperoxisome proliferator-activator receptorITTinsulin tolerance testGTTglucose tolerance testRTreverse transcriptionILinterleukinWTwild typeTgtransgenicMEFmouse embryo fibroblast./NF-κB signaling pathway plays an important role in the control of inflammation, apoptosis, carcinogenesis, and oxidative stress (1Hayden M.S. Ghosh S. Cell. 2008; 132: 344-362Abstract Full Text Full Text PDF PubMed Scopus (3438) Google Scholar). In this pathway, the serine kinase IKKβ (IKK2) activates the transcription factor NF-κB through phosphorylation of NF-κB inhibitor (IκBα). In obesity research, the metabolic activity of IKKβ was tested in the control of insulin sensitivity (2Yuan M. Konstantopoulos N. Lee J. Hansen L. Li Z.W. Karin M. Shoelson S.E. Science. 2001; 293: 1673-1677Crossref PubMed Scopus (1614) Google Scholar, 3Cai D. Yuan M. Frantz D.F. Melendez P.A. Hansen L. Lee J. Shoelson S.E. Nat. Med. 2005; 11: 183-190Crossref PubMed Scopus (1763) Google Scholar, 4Arkan M.C. Hevener A.L. Greten F.R. Maeda S. Li Z.W. Long J.M. Wynshaw-Boris A. Poli G. Olefsky J. Karin M. Nat. Med. 2005; 11: 191-198Crossref PubMed Scopus (1461) Google Scholar) or food intake in transgenic mice (5Zhang X. Zhang G. Zhang H. Karin M. Bai H. Cai D. Cell. 2008; 135: 61-73Abstract Full Text Full Text PDF PubMed Scopus (1029) Google Scholar). In these studies, the IKKβ activity was modified either globally or tissue-specifically in several major tissues/organs, such as the liver (3Cai D. Yuan M. Frantz D.F. Melendez P.A. Hansen L. Lee J. Shoelson S.E. Nat. Med. 2005; 11: 183-190Crossref PubMed Scopus (1763) Google Scholar, 4Arkan M.C. Hevener A.L. Greten F.R. Maeda S. Li Z.W. Long J.M. Wynshaw-Boris A. Poli G. Olefsky J. Karin M. Nat. Med. 2005; 11: 191-198Crossref PubMed Scopus (1461) Google Scholar), skeletal muscle (6Cai D. Frantz J.D. Tawa Jr., N.E. Melendez P.A. Oh B.C. Lidov H.G. Hasselgren P.O. Frontera W.R. Lee J. Glass D.J. Shoelson S.E. Cell. 2004; 119: 285-298Abstract Full Text Full Text PDF PubMed Scopus (1060) Google Scholar), and brain (5Zhang X. Zhang G. Zhang H. Karin M. Bai H. Cai D. Cell. 2008; 135: 61-73Abstract Full Text Full Text PDF PubMed Scopus (1029) Google Scholar). In these studies, the role of IKKβ in the regulation of energy expenditure and adipose tissue growth was not examined. Although IKKβ and NF-κB activities are parallel in most cases, their activities are not identical (7Perkins N.D. Nat. Rev. Mol. Cell Biol. 2007; 8: 49-62Crossref PubMed Scopus (1901) Google Scholar). IKKβ has NF-κB-independent activities (7Perkins N.D. Nat. Rev. Mol. Cell Biol. 2007; 8: 49-62Crossref PubMed Scopus (1901) Google Scholar, 8Zhang J. Gao Z. Yin J. Quon M.J. Ye J. J. Biol. Chem. 2008; 283: 35375-35382Abstract Full Text Full Text PDF PubMed Scopus (215) Google Scholar). We investigated the metabolic activity of NF-κB using the NF-κB transgenic mice in the current study.NF-κB activation is associated with energy expenditure in cachexia (9Strasser F. Curr. Opin. Support Palliat. Care. 2007; 1: 312-316Crossref PubMed Google Scholar, 10Tisdale M.J. J. Natl. Cancer Inst. 1997; 89: 1763-1773Crossref PubMed Scopus (421) Google Scholar). However, the cause/effect relationship has not been tested for NF-κB/energy expenditure in transgenic models. NF-κB is a transcription factor that regulates expression of a broad spectrum of genes. Its activity is found in many types of cells, including adipocytes and macrophages (1Hayden M.S. Ghosh S. Cell. 2008; 132: 344-362Abstract Full Text Full Text PDF PubMed Scopus (3438) Google Scholar, 11Shoelson S.E. Lee J. Goldfine A.B. J. Clin. Invest. 2006; 116: 1793-1801Crossref PubMed Scopus (82) Google Scholar). The common form of NF-κB contains two subunits: p65 (RelA) and p50 (NF-κB1). p65 contains the transactivation domain and mediates transcriptional activation of target genes. p50 usually inhibits the transcriptional activity of p65 (12Schmitz M.L. Baeuerle P.A. EMBO J. 1991; 10: 3805-3817Crossref PubMed Scopus (664) Google Scholar), and the inhibition disappears in the p50-KO mice (13Bohuslav J. Kravchenko V.V. Parry G.C. Erlich J.H. Gerondakis S. Mackman N. Ulevitch R.J. J. Clin. Invest. 1998; 102: 1645-1652Crossref PubMed Scopus (241) Google Scholar). Expression of NF-κB target genes (TNF-α, interferon-γ, inducible nitric-oxide synthase, etc.) is increased in p50-KO mice (13Bohuslav J. Kravchenko V.V. Parry G.C. Erlich J.H. Gerondakis S. Mackman N. Ulevitch R.J. J. Clin. Invest. 1998; 102: 1645-1652Crossref PubMed Scopus (241) Google Scholar, 14Gadjeva M. Tomczak M.F. Zhang M. Wang Y.Y. Dull K. Rogers A.B. Erdman S.E. Fox J.G. Carroll M. Horwitz B.H. J. Immunol. 2004; 173: 5786-5793Crossref PubMed Scopus (74) Google Scholar, 15Gao Z. Yin J. Zhang J. He Q. McGuinness O.P. Ye J. J. Biol. Chem. 2009; 284: 18368-18376Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar). NF-κB activity is increased by either p65 overexpression or p50 knock-out. In the current study, the NF-κB activity is enhanced in these approaches in two lines of transgenic mice (aP2-p65 mice and p50-KO mice).In cellular models, NF-κB was shown to inhibit the differentiation and function of adipocytes in the signaling pathway of TNF-α (16Ruan H. Hacohen N. Golub T.R. Van Parijs L. Lodish H.F. Diabetes. 2002; 51: 1319-1336Crossref PubMed Scopus (418) Google Scholar, 17Ruan H. Pownall H.J. Lodish H.F. J. Biol. Chem. 2003; 278: 28181-28192Abstract Full Text Full Text PDF PubMed Scopus (157) Google Scholar). The molecular mechanism is related to inhibition of PPARγ activity by NF-κB. There are several molecular models for the inhibition (18Ye J. Biochem. Biophys. Res. Commun. 2008; 374: 405-408Crossref PubMed Scopus (132) Google Scholar, 19Guilherme A. Virbasius J.V. Puri V. Czech M.P. Nat. Rev. Mol. Cell Biol. 2008; 9: 367-377Crossref PubMed Scopus (1562) Google Scholar). These include suppression of PPARγ in mRNA expression (16Ruan H. Hacohen N. Golub T.R. Van Parijs L. Lodish H.F. Diabetes. 2002; 51: 1319-1336Crossref PubMed Scopus (418) Google Scholar, 20Zhang B. Berger J. Hu E. Szalkowski D. White-Carrington S. Spiegelman B.M. Moller D.E. Mol. Endocrinol. 1996; 10: 1457-1466Crossref PubMed Scopus (308) Google Scholar), DNA binding activity (21Suzawa M. Takada I. Yanagisawa J. Ohtake F. Ogawa S. Yamauchi T. Kadowaki T. Takeuchi Y. Shibuya H. Gotoh Y. Matsumoto K. Kato S. Nat. Cell Biol. 2003; 5: 224-230Crossref PubMed Scopus (256) Google Scholar), and interaction with transcriptional coactivators (22Gao Z. He Q. Peng B. Chiao P.J. Ye J. J. Biol. Chem. 2006; 281: 4540-4547Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar). It is not clear which mechanism plays a major role in the physiological conditions. In this study, we addressed this issue by examining PPARγ activity in the adipose tissue of aP2-p65 mice and p50-KO mice. Our results suggest that an increase in the NF-κB activity leads to transcriptional inhibition of PPARγ expression. This negative regulation may be responsible for the inhibition of adipocyte differentiation and suppression of adipose tissue growth in the transgenic mice. The transgenic mice exhibited an increase in energy expenditure and resistance to diet-induced obesity.DISCUSSIONThe current study was designed to understand the molecular mechanism of inflammation in the pathogenesis of insulin resistance. The role of NF-κB in insulin resistance was indicated by the phenotypes of IKKβ transgenic mice and the activities of TNF-α (2Yuan M. Konstantopoulos N. Lee J. Hansen L. Li Z.W. Karin M. Shoelson S.E. Science. 2001; 293: 1673-1677Crossref PubMed Scopus (1614) Google Scholar, 3Cai D. Yuan M. Frantz D.F. Melendez P.A. Hansen L. Lee J. Shoelson S.E. Nat. Med. 2005; 11: 183-190Crossref PubMed Scopus (1763) Google Scholar, 4Arkan M.C. Hevener A.L. Greten F.R. Maeda S. Li Z.W. Long J.M. Wynshaw-Boris A. Poli G. Olefsky J. Karin M. Nat. Med. 2005; 11: 191-198Crossref PubMed Scopus (1461) Google Scholar, 22Gao Z. He Q. Peng B. Chiao P.J. Ye J. J. Biol. Chem. 2006; 281: 4540-4547Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar, 32Gao Z. Hwang D. Bataille F. Lefevre M. York D. Quon M.J. Ye J. J. Biol. Chem. 2002; 277: 48115-48121Abstract Full Text Full Text PDF PubMed Scopus (585) Google Scholar). These studies suggest that NF-κB may inhibit insulin sensitivity by induction of inflammatory cytokines or through inhibition of PPARγ activity (11Shoelson S.E. Lee J. Goldfine A.B. J. Clin. Invest. 2006; 116: 1793-1801Crossref PubMed Scopus (82) Google Scholar, 18Ye J. Biochem. Biophys. Res. Commun. 2008; 374: 405-408Crossref PubMed Scopus (132) Google Scholar). However, the NF-κB activity has never been directly examined in animals using the NF-κB transgenic approach. In the current study, this issue is addressed in two lines of NF-κB transgenic mice, in which the transcriptional activity of NF-κB is increased by different mechanisms. The two models share the same metabolic phenotypes in energy expenditure, insulin sensitivity, and resistance to obesity. The phenotypes of aP2-p65 mice suggest that NF-κB activity in adipose tissue is important in the regulation of metabolism.In the two models, inflammation was observed in adipose tissue with elevated macrophage infiltration and expression of inflammatory cytokines (TNF-α, IL-1, IL-6, and mcp-1). The systemic inflammation is indicated by elevated proteins for TNF-α and IL-6 in the serum (15Gao Z. Yin J. Zhang J. He Q. McGuinness O.P. Ye J. J. Biol. Chem. 2009; 284: 18368-18376Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar). The inflammation is a result of increased NF-κB activity from overexpression of the p65 subunit (aP2-p65) or deletion of the p50 subunit (p50-KO) (12Schmitz M.L. Baeuerle P.A. EMBO J. 1991; 10: 3805-3817Crossref PubMed Scopus (664) Google Scholar). Although NF-κB p65 activity is increased in microphages in the p65 transgenic mice, we did not observe elevated p65 expression in liver. This might be a result of the dilution of Kuffer's cells by hepatocytes. Macrophages produce much more proinflammatory cytokines (especially TNF-α and IL-1) than adipocytes (33Fain J.N. Bahouth S.W. Madan A.K. Int. J. Obes. Relat. Metab. Disord. 2004; 28: 616-622Crossref PubMed Scopus (157) Google Scholar).Induction of energy metabolism by NF-κB is an intriguing observation. This activity is responsible for the prevention of adulthood obesity and dietary obesity in the two models. The mechanism of energy expenditure involves the inflammatory cytokines, such as TNF-α, IL-1, and IL-6, whose levels are positively associated with energy expenditure (10Tisdale M.J. J. Natl. Cancer Inst. 1997; 89: 1763-1773Crossref PubMed Scopus (421) Google Scholar). In transgenic mice with deficiency in these cytokines or their receptors, the body weight gain is enhanced in mouse models for TNF-α (34Pamir N. McMillen T.S. Kaiyala K.J. Schwartz M.W. LeBoeuf R.C. 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Bell M. Hultgren O. Horn M. Ahrén B. Enerback S. Ohlsson C. Wallenius V. Jansson J.O. Diabetes. 2006; 55: 1205-1213Crossref PubMed Scopus (134) Google Scholar). The cytokines may act in the central nervous system to regulate energy balance (36Wallenius V. Wallenius K. Ahrén B. Rudling M. Carlsten H. Dickson S.L. Ohlsson C. Jansson J.O. Nat. Med. 2002; 8: 75-79Crossref PubMed Scopus (991) Google Scholar, 41Anforth H.R. Bluthe R.M. Bristow A. Hopkins S. Lenczowski M.J. Luheshi G. Lundkvist J. Michaud B. Mistry Y. Van Dam A.M. Zhen C. Dantzer R. Poole S. Rothwell N.J. Tilders F.J. Wollman E.E. Eur. Cytokine Netw. 1998; 9: 279-288PubMed Google Scholar, 42Luheshi G.N. Gardner J.D. Rushforth D.A. Loudon A.S. Rothwell N.J. Proc. Natl. Acad. Sci. U.S.A. 1999; 96: 7047-7052Crossref PubMed Scopus (320) Google Scholar, 43Klir J.J. Roth J. Szelényi Z. McClellan J.L. Kluger M.J. Am. J. Physiol. 1993; 265: R512-R517PubMed Google Scholar, 44Luheshi G.N. Ann. N.Y. Acad. Sci. 1998; 856: 83-89Crossref PubMed Scopus (125) Google Scholar). They may target the hypothalamus (43Klir J.J. Roth J. Szelényi Z. McClellan J.L. Kluger M.J. Am. J. Physiol. 1993; 265: R512-R517PubMed Google Scholar, 44Luheshi G.N. Ann. N.Y. Acad. Sci. 1998; 856: 83-89Crossref PubMed Scopus (125) Google Scholar). In the peripheral tissues, TNF-α and IL-1 enhance mitochondrial function through activation of PGC-1α by phosphorylation (45Puigserver P. Rhee J. Lin J. Wu Z. Yoon J.C. Zhang C.Y. Krauss S. Mootha V.K. Lowell B.B. Spiegelman B.M. Mol. Cell. 2001; 8: 971-982Abstract Full Text Full Text PDF PubMed Scopus (596) Google Scholar). The increased energy expenditure may reflect the combined activities of multiple cytokines in our models because their expression was induced by NF-κB. Our data suggest that NF-κB is a powerful transcription factor in the induction of energy metabolism. It may be a target for drug intervention of energy metabolism (46von Haehling S. Genth-Zotz S. Anker S.D. Volk H.D. Int. J. Cardiol. 2002; 85: 173-183Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar, 47Guttridge D.C. Mayo M.W. Madrid L.V. Wang C.Y. Baldwin Jr., A.S. Science. 2000; 289: 2363-2366Crossref PubMed Scopus (748) Google Scholar).Inhibition of adipose tissue growth may also contribute to the energy expenditure in the two models. PPARγ expression was inhibited by NF-κB, and the inhibition was observed at the transcriptional level in our study. The inhibition was observed in the PPARγ gene promoter, and a NF-κB response element was found within the 1–2 kb region from the transcription start site. Given the master activity of PPARγ in adipocytes, the suppression may be the molecular mechanism of adipose tissue deficiency in the aP2-p65 mice and p50-KO mice. The inhibition may promote energy expenditure by stimulating lipid oxidation because lipid accumulation is inhibited in adipose tissue. The fat-specific PPARγ knock-out mice (PPARγ adipose-KO) exhibited a similar increase in energy expenditure (48Jones J.R. Barrick C. Kim K.A. Lindner J. Blondeau B. Fujimoto Y. Shiota M. Kesterson R.A. Kahn B.B. Magnuson M.A. Proc. Natl. Acad. Sci. U.S.A. 2005; 102: 6207-6212Crossref PubMed Scopus (386) Google Scholar). Insulin sensitivity is also protected in the PPARγ adipose-KO mice (48Jones J.R. Barrick C. Kim K.A. Lindner J. Blondeau B. Fujimoto Y. Shiota M. Kesterson R.A. Kahn B.B. Magnuson M.A. Proc. Natl. Acad. Sci. U.S.A. 2005; 102: 6207-6212Crossref PubMed Scopus (386) Google Scholar). This phenotype may be related to an increase in the NF-κB activity because PPARγ suppresses the transcriptional activity of NF-κB (49Pascual G. Fong A.L. Ogawa S. Gamliel A. Li A.C. Perissi V. Rose D.W. Willson T.M. Rosenfeld M.G. Glass C.K. Nature. 2005; 437: 759-763Crossref PubMed Scopus (1012) Google Scholar). However, this possibility needs to be tested in the PPARγ adipose-KO mice.The current study suggests that inflammation may have two different activities in the regulation of metabolism. The first is inhibition of insulin sensitivity (negative effect), as suggested by many studies of low grade inflammation. The second is induction of energy expenditure (positive effect), as indicated by current and other reports (34Pamir N. McMillen T.S. Kaiyala K.J. Schwartz M.W. LeBoeuf R.C. Endocrinology. 2009; 150: 4124-4134Crossref PubMed Scopus (63) Google Scholar, 35Chida D. Osaka T. Hashimoto O. Iwakura Y. Diabetes. 2006; 55: 971-977Crossref PubMed Scopus (74) Google Scholar, 36Wallenius V. Wallenius K. Ahrén B. Rudling M. Carlsten H. Dickson S.L. Ohlsson C. Jansson J.O. Nat. Med. 2002; 8: 75-79Crossref PubMed Scopus (991) Google Scholar, 37Xu H. Hirosumi J. Uysal K.T. Guler A.D. Hotamisligil G.S. Endocrinology. 2002; 143: 1502-1511Crossref PubMed Scopus (77) Google Scholar, 38Matsuki T. Horai R. Sudo K. Iwakura Y. J. Exp. Med. 2003; 198: 877-888Crossref PubMed Scopus (175) Google Scholar, 39Somm E. Henrichot E. Pernin A. Juge-Aubry C.E. Muzzin P. Dayer J.M. Nicklin M.J. Meier C.A. Diabetes. 2005; 54: 3503-3509Crossref PubMed Scopus (92) Google Scholar, 40García M.C. Wernstedt I. Berndtsson A. Enge M. Bell M. Hultgren O. Horn M. Ahrén B. Enerback S. Ohlsson C. Wallenius V. Jansson J.O. Diabetes. 2006; 55: 1205-1213Crossref PubMed Scopus (134) Google Scholar). Our study indicates that energy expenditure may antagonize insulin resistance by eliminating lipid accumulation through elevated lipid oxidation, which prevents lipotoxicity in the pathogenesis of insulin resistance. In both aP2-p65 mice and p50-KO mice (15Gao Z. Yin J. Zhang J. He Q. McGuinness O.P. Ye J. J. Biol. Chem. 2009; 284: 18368-18376Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar), insulin sensitivity was examined by the hyperinsulinemic-euglycemic clamp. The systemic insulin sensitivity was enhanced in both models, as indicated by the glucose infusion rate. In terms of tissue specificity, insulin sensitivity was dramatically enhanced in liver and fat but not in the skeletal muscle, suggesting the importance of the two organs in inflammation action. The muscle data suggest that the skeletal muscle is not sensitive to inflammation on insulin sensitivity. In our models, the positive effect of inflammation overrides the negative effect of inflammation, leading to an increase in insulin sensitivity. The energy expenditure represents a new aspect of inflammation that was not reported in the IKKβ transgenic studies (2Yuan M. Konstantopoulos N. Lee J. Hansen L. Li Z.W. Karin M. Shoelson S.E. Science. 2001; 293: 1673-1677Crossref PubMed Scopus (1614) Google Scholar, 3Cai D. Yuan M. Frantz D.F. Melendez P.A. Hansen L. Lee J. Shoelson S.E. Nat. Med. 2005; 11: 183-190Crossref PubMed Scopus (1763) Google Scholar, 4Arkan M.C. Hevener A.L. Greten F.R. Maeda S. Li Z.W. Long J.M. Wynshaw-Boris A. Poli G. Olefsky J. Karin M. Nat. Med. 2005; 11: 191-198Crossref PubMed Scopus (1461) Google Scholar).In summary, the current study suggests that elevated inflammation from NF-κB has a significant activity in the induction of energy expenditure. The enhanced energy expenditure prevented diet-induced obesity and insulin resistance in the aP2-p65 and p50-KO mice. The energy expenditure may be a result of up-regulated expression of NF-κB target genes and inhibition of lipid accumulation. The energy expenditure may be a key mechanism for the disassociation of inflammation with insulin resistance. IntroductionThe IKKβ 2The abbreviations used are: IKKβ (IKK2)IκBα kinase 2NF-κBnuclear factor κBWATwhite adipose tissueHFDhigh fat diet (58% of calories in fat)IκBαinhibitor κB αp50 (NF-κB1)NF-κB p50 subunitp65 (RelA)NF-κB p65 subunitTNF-αtumor necrosis factor αKOknock-outDAPI4′,6-diamidino-2-phenylindolePPARperoxisome proliferator-activator receptorITTinsulin tolerance testGTTglucose tolerance testRTreverse transcriptionILinterleukinWTwild typeTgtransgenicMEFmouse embryo fibroblast./NF-κB signaling pathway plays an important role in the control of inflammation, apoptosis, carcinogenesis, and oxidative stress (1Hayden M.S. Ghosh S. Cell. 2008; 132: 344-362Abstract Full Text Full Text PDF PubMed Scopus (3438) Google Scholar). In this pathway, the serine kinase IKKβ (IKK2) activates the transcription factor NF-κB through phosphorylation of NF-κB inhibitor (IκBα). In obesity research, the metabolic activity of IKKβ was tested in the control of insulin sensitivity (2Yuan M. Konstantopoulos N. Lee J. Hansen L. Li Z.W. Karin M. Shoelson S.E. Science. 2001; 293: 1673-1677Crossref PubMed Scopus (1614) Google Scholar, 3Cai D. Yuan M. Frantz D.F. Melendez P.A. Hansen L. Lee J. Shoelson S.E. Nat. Med. 2005; 11: 183-190Crossref PubMed Scopus (1763) Google Scholar, 4Arkan M.C. Hevener A.L. Greten F.R. Maeda S. Li Z.W. Long J.M. Wynshaw-Boris A. Poli G. Olefsky J. Karin M. Nat. Med. 2005; 11: 191-198Crossref PubMed Scopus (1461) Google Scholar) or food intake in transgenic mice (5Zhang X. Zhang G. Zhang H. Karin M. Bai H. Cai D. Cell. 2008; 135: 61-73Abstract Full Text Full Text PDF PubMed Scopus (1029) Google Scholar). In these studies, the IKKβ activity was modified either globally or tissue-specifically in several major tissues/organs, such as the liver (3Cai D. Yuan M. Frantz D.F. Melendez P.A. Hansen L. Lee J. Shoelson S.E. Nat. Med. 2005; 11: 183-190Crossref PubMed Scopus (1763) Google Scholar, 4Arkan M.C. Hevener A.L. Greten F.R. Maeda S. Li Z.W. Long J.M. Wynshaw-Boris A. Poli G. Olefsky J. Karin M. Nat. Med. 2005; 11: 191-198Crossref PubMed Scopus (1461) Google Scholar), skeletal muscle (6Cai D. Frantz J.D. Tawa Jr., N.E. Melendez P.A. Oh B.C. Lidov H.G. Hasselgren P.O. Frontera W.R. Lee J. Glass D.J. Shoelson S.E. Cell. 2004; 119: 285-298Abstract Full Text Full Text PDF PubMed Scopus (1060) Google Scholar), and brain (5Zhang X. Zhang G. Zhang H. Karin M. Bai H. Cai D. Cell. 2008; 135: 61-73Abstract Full Text Full Text PDF PubMed Scopus (1029) Google Scholar). In these studies, the role of IKKβ in the regulation of energy expenditure and adipose tissue growth was not examined. Although IKKβ and NF-κB activities are parallel in most cases, their activities are not identical (7Perkins N.D. Nat. Rev. Mol. Cell Biol. 2007; 8: 49-62Crossref PubMed Scopus (1901) Google Scholar). IKKβ has NF-κB-independent activities (7Perkins N.D. Nat. Rev. Mol. Cell Biol. 2007; 8: 49-62Crossref PubMed Scopus (1901) Google Scholar, 8Zhang J. Gao Z. Yin J. Quon M.J. Ye J. J. Biol. Chem. 2008; 283: 35375-35382Abstract Full Text Full Text PDF PubMed Scopus (215) Google Scholar). We investigated the metabolic activity of NF-κB using the NF-κB transgenic mice in the current study.NF-κB activation is associated with energy expenditure in cachexia (9Strasser F. Curr. Opin. Support Palliat. Care. 2007; 1: 312-316Crossref PubMed Google Scholar, 10Tisdale M.J. J. Natl. Cancer Inst. 1997; 89: 1763-1773Crossref PubMed Scopus (421) Google Scholar). However, the cause/effect relationship has not been tested for NF-κB/energy expenditure in transgenic models. NF-κB is a transcription factor that regulates expression of a broad spectrum of genes. Its activity is found in many types of cells, including adipocytes and macrophages (1Hayden M.S. Ghosh S. Cell. 2008; 132: 344-362Abstract Full Text Full Text PDF PubMed Scopus (3438) Google Scholar, 11Shoelson S.E. Lee J. Goldfine A.B. J. Clin. 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There are several molecular models for the inhibition (18Ye J. Biochem. Biophys. Res. Commun. 2008; 374: 405-408Crossref PubMed Scopus (132) Google Scholar, 19Guilherme A. Virbasius J.V. Puri V. Czech M.P. Nat. Rev. Mol. Cell Biol. 2008; 9: 367-377Crossref PubMed Scopus (1562) Google Scholar). These include suppression of PPARγ in mRNA expression (16Ruan H. Hacohen N. Golub T.R. Van Parijs L. Lodish H.F. Diabetes. 2002; 51: 1319-1336Crossref PubMed Scopus (418) Google Scholar, 20Zhang B. Berger J. Hu E. Szalkowski D. White-Carrington S. Spiegelman B.M. Moller D.E. Mol. Endocrinol. 1996; 10: 1457-1466Crossref PubMed Scopus (308) Google Scholar), DNA binding activity (21Suzawa M. Takada I. Yanagisawa J. Ohtake F. Ogawa S. Yamauchi T. Kadowaki T. Takeuchi Y. Shibuya H. Gotoh Y. Matsumoto K. Kato S. Nat. Cell Biol. 2003; 5: 224-230Crossref PubMed Scopus (256) Google Scholar), and interaction with transcriptional coactivators (22Gao Z. He Q. Peng B. Chiao P.J. Ye J. J. Biol. 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