A Pathway Involving Farnesoid X Receptor and Small Heterodimer Partner Positively Regulates Hepatic Sirtuin 1 Levels via MicroRNA-34a Inhibition

Abstract

Sirtuin 1 (SIRT1) is a NAD-dependent deacetylase that is critically involved in diverse cellular processes including metabolic disease, cancer, and possibly aging. Despite extensive studies on SIRT1 function, how SIRT1 levels are regulated remains relatively unknown. Here, we report that the nuclear bile acid receptor farnesoid X receptor (FXR) inhibits microRNA-34a (miR-34a) in the liver, which results in a positive regulation of SIRT1 levels. Activation of FXR by the synthetic agonist GW4064 decreases hepatic miR-34a levels in normal mice, and consistently, hepatic miR-34a levels are elevated in FXR-null mice. FXR induces expression of small heterodimer partner (SHP), an orphan nuclear receptor and transcriptional corepressor, which in turn results in repression of p53, a key activator of the miR-34a gene, by inhibiting p53 occupancy at the promoter. MiR-34a decreased SIRT1 levels by binding to the 3′-untranslated region of SIRT1 mRNA, and adenovirus-mediated overexpression of miR-34a substantially decreased SIRT1 protein levels in mouse liver. Remarkably, miR-34a levels were elevated, and SIRT1 protein levels were reduced in diet-induced obese mice, and FXR activation in these mice reversed the miR-34a and SIRT1 levels, indicating an intriguing link among FXR activation, decreased miR-34a, and subsequently, increased SIRT1 levels. Our study demonstrates an unexpected role of the FXR/SHP pathway in controlling SIRT1 levels via miR-34a inhibition and that elevated miR-34a levels in obese mice contribute to decreased SIRT1 levels. Manipulation of this regulatory network may be useful for treating diseases of aging, such as metabolic disease and cancer. Sirtuin 1 (SIRT1) is a NAD-dependent deacetylase that is critically involved in diverse cellular processes including metabolic disease, cancer, and possibly aging. Despite extensive studies on SIRT1 function, how SIRT1 levels are regulated remains relatively unknown. Here, we report that the nuclear bile acid receptor farnesoid X receptor (FXR) inhibits microRNA-34a (miR-34a) in the liver, which results in a positive regulation of SIRT1 levels. Activation of FXR by the synthetic agonist GW4064 decreases hepatic miR-34a levels in normal mice, and consistently, hepatic miR-34a levels are elevated in FXR-null mice. FXR induces expression of small heterodimer partner (SHP), an orphan nuclear receptor and transcriptional corepressor, which in turn results in repression of p53, a key activator of the miR-34a gene, by inhibiting p53 occupancy at the promoter. MiR-34a decreased SIRT1 levels by binding to the 3′-untranslated region of SIRT1 mRNA, and adenovirus-mediated overexpression of miR-34a substantially decreased SIRT1 protein levels in mouse liver. Remarkably, miR-34a levels were elevated, and SIRT1 protein levels were reduced in diet-induced obese mice, and FXR activation in these mice reversed the miR-34a and SIRT1 levels, indicating an intriguing link among FXR activation, decreased miR-34a, and subsequently, increased SIRT1 levels. Our study demonstrates an unexpected role of the FXR/SHP pathway in controlling SIRT1 levels via miR-34a inhibition and that elevated miR-34a levels in obese mice contribute to decreased SIRT1 levels. Manipulation of this regulatory network may be useful for treating diseases of aging, such as metabolic disease and cancer. IntroductionThe NAD+-dependent Sirtuin 1 (SIRT1) 3The abbreviations used are: SIRT1Sirtuin 1PGC-1αperoxisome proliferator-activated receptor γ coactivator αFXRfarnesoid X receptorSHPsmall heterodimer partnermiRmicroRNA3′-UTR3′-untranslated regionHNF-4hepatic nuclear factor 4qRT-PCRreverse transcription-quantitative PCRAdadenovirusChIPchromatin immunoprecipitationGSTglutathione S-transferaseCoIPcoimmunoprecipitationsiRNAsmall interfering RNAlucluciferaseWDwestern style diet. deacetylase plays a critical role in cellular metabolism, the stress response, and possibly aging, by modulating the activity of its target proteins via protein deacetylation (1Rodgers J.T. Lerin C. Haas W. Gygi S.P. Spiegelman B.M. Puigserver P. Nature. 2005; 434: 113-118Crossref PubMed Scopus (2524) Google Scholar, 2Motta M.C. Divecha N. Lemieux M. Kamel C. Chen D. Gu W. Bultsma Y. McBurney M. Guarente L. Cell. 2004; 116: 551-563Abstract Full Text Full Text PDF PubMed Scopus (1184) Google Scholar, 3Luo J. Nikolaev A.Y. Imai S. Chen D. Su F. Shiloh A. Guarente L. Gu W. Cell. 2001; 107: 137-148Abstract Full Text Full Text PDF PubMed Scopus (1873) Google Scholar, 4Guarente L. Cold Spring Harb. Symp. Quant. Biol. 2007; 72: 483-488Crossref PubMed Scopus (285) Google Scholar). Recent studies demonstrate that SIRT1 plays an important role in maintaining metabolic homeostasis in response to hormonal and nutritional fluctuations by modulating the activity of PGC-1α, a master metabolic regulator (5Rodgers J.T. Puigserver P. Proc. Natl. Acad. Sci. U.S.A. 2007; 104: 12861-12866Crossref PubMed Scopus (444) Google Scholar, 6Rodgers J.T. Lerin C. Gerhart-Hines Z. Puigserver P. FEBS Lett. 2008; 582: 46-53Crossref PubMed Scopus (490) Google Scholar). During nutritional deprivation, SIRT1 promotes fat mobilization and suppresses adipogenesis and regulates hepatic glucose and lipid metabolism by activating key metabolic regulators, including PGC-1α (5Rodgers J.T. Puigserver P. Proc. Natl. Acad. Sci. U.S.A. 2007; 104: 12861-12866Crossref PubMed Scopus (444) Google Scholar, 6Rodgers J.T. Lerin C. Gerhart-Hines Z. Puigserver P. FEBS Lett. 2008; 582: 46-53Crossref PubMed Scopus (490) Google Scholar). Activation of SIRT1 by natural or synthetic SIRT1 activators reduced acetylation levels of PGC-1α and protected against diet-induced obesity and insulin resistance by promoting mitochondrial function (7Lagouge M. Argmann C. Gerhart-Hines Z. Meziane H. Lerin C. Daussin F. Messadeq N. Milne J. Lambert P. Elliott P. Geny B. Laakso M. Puigserver P. Auwerx J. Cell. 2006; 127: 1109-1122Abstract Full Text Full Text PDF PubMed Scopus (3267) Google Scholar, 8Baur J.A. Pearson K.J. Price N.L. Jamieson H.A. Lerin C. Kalra A. Prabhu V.V. Allard J.S. Lopez-Lluch G. Lewis K. Pistell P.J. Poosala S. Becker K.G. Boss O. Gwinn D. Wang M. Ramaswamy S. Fishbein K.W. Spencer R.G. Lakatta E.G. Le Couteur D. Shaw R.J. Navas P. Puigserver P. Ingram D.K. de Cabo R. Sinclair D.A. Nature. 2006; 444: 337-342Crossref PubMed Scopus (3619) Google Scholar, 9Feige J.N. Lagouge M. Canto C. Strehle A. Houten S.M. Milne J.C. Lambert P.D. Mataki C. Elliott P.J. Auwerx J. Cell Metab. 2008; 8: 347-358Abstract Full Text Full Text PDF PubMed Scopus (608) Google Scholar). SIRT1 levels are dynamically regulated in response to fasting and feeding under physiological conditions but markedly reduced in diet-induced obese mice (10Coste A. Louet J.F. Lagouge M. Lerin C. Antal M.C. Meziane H. Schoonjans K. Puigserver P. O'Malley B.W. Auwerx J. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 17187-17192Crossref PubMed Scopus (153) Google Scholar). However, the molecular basis by which SIRT1 levels are regulated under normal conditions and why they are substantially reduced in metabolic disease states remains largely unknown.The nuclear receptor, farnesoid X receptor (FXR), is the primary biosensor for endogenous bile acids and regulates expression of numerous genes involved in lipid and glucose metabolism (11Zhang Y. Lee F.Y. Barrera G. Lee H. Vales C. Gonzalez F.J. Willson T.M. Edwards P.A. Proc. Natl. Acad. Sci. U.S.A. 2006; 103: 1006-1011Crossref PubMed Scopus (696) Google Scholar, 12Sinal C.J. Tohkin M. Miyata M. Ward J.M. Lambert G. Gonzalez F.J. Cell. 2000; 102: 731-744Abstract Full Text Full Text PDF PubMed Scopus (1378) Google Scholar, 13Lee F.Y. Lee H. Hubbert M.L. Edwards P.A. Zhang Y. Trends Biochem. Sci. 2006; 31: 572-580Abstract Full Text Full Text PDF PubMed Scopus (274) Google Scholar, 14Fiorucci S. Rizzo G. Donini A. Distrutti E. Santucci L. Trends Mol. Med. 2007; 13: 298-309Abstract Full Text Full Text PDF PubMed Scopus (175) Google Scholar, 15Cariou B. Staels B. Trends Pharmacol. Sci. 2007; 28: 236-243Abstract Full Text Full Text PDF PubMed Scopus (118) Google Scholar). FXR indirectly inhibits its metabolic target genes by inducing the expression of small heterodimer partner (SHP), an orphan nuclear receptor and transcriptional corepressor (16Lu T.T. Makishima M. Repa J.J. Schoonjans K. Kerr T.A. Auwerx J. Mangelsdorf D.J. Mol. Cell. 2000; 6: 507-515Abstract Full Text Full Text PDF PubMed Scopus (1208) Google Scholar, 17Goodwin B. Jones S.A. Price R.R. Watson M.A. McKee D.D. Moore L.B. Galardi C. Wilson J.G. Lewis M.C. Roth M.E. Maloney P.R. Willson T.M. Kliewer S.A. Mol Cell. 2000; 6: 517-526Abstract Full Text Full Text PDF PubMed Scopus (1471) Google Scholar). It is well established that the FXR/SHP pathway plays an important role in maintaining bile acid and cholesterol levels by inhibiting the transcription of cholesterol cytochrome P450 7A1 hydroxylase, a key enzyme in hepatic bile acid biosynthesis (16Lu T.T. Makishima M. Repa J.J. Schoonjans K. Kerr T.A. Auwerx J. Mangelsdorf D.J. Mol. Cell. 2000; 6: 507-515Abstract Full Text Full Text PDF PubMed Scopus (1208) Google Scholar, 17Goodwin B. Jones S.A. Price R.R. Watson M.A. McKee D.D. Moore L.B. Galardi C. Wilson J.G. Lewis M.C. Roth M.E. Maloney P.R. Willson T.M. Kliewer S.A. Mol Cell. 2000; 6: 517-526Abstract Full Text Full Text PDF PubMed Scopus (1471) Google Scholar), and has been also shown to regulate fatty acid metabolism (18Watanabe M. Houten S.M. Wang L. Moschetta A. Mangelsdorf D.J. Heyman R.A. Moore D.D. Auwerx J. J. Clin. Invest. 2004; 113: 1408-1418Crossref PubMed Scopus (939) Google Scholar). Interestingly, FXR activation by the synthetic agonist, GW4064, or hepatic overexpression of constitutively active FXR using adenoviral delivery significantly improved hyperglycemia and hyperlipidemia in diabetic obese db/db mice (11Zhang Y. Lee F.Y. Barrera G. Lee H. Vales C. Gonzalez F.J. Willson T.M. Edwards P.A. Proc. Natl. Acad. Sci. U.S.A. 2006; 103: 1006-1011Crossref PubMed Scopus (696) Google Scholar). Although both SIRT1 and FXR are critical for hepatic metabolism and activation of both proteins improves metabolic outcomes (7Lagouge M. Argmann C. Gerhart-Hines Z. Meziane H. Lerin C. Daussin F. Messadeq N. Milne J. Lambert P. Elliott P. Geny B. Laakso M. Puigserver P. Auwerx J. Cell. 2006; 127: 1109-1122Abstract Full Text Full Text PDF PubMed Scopus (3267) Google Scholar, 8Baur J.A. Pearson K.J. Price N.L. Jamieson H.A. Lerin C. Kalra A. Prabhu V.V. Allard J.S. Lopez-Lluch G. Lewis K. Pistell P.J. Poosala S. Becker K.G. Boss O. Gwinn D. Wang M. Ramaswamy S. Fishbein K.W. Spencer R.G. Lakatta E.G. Le Couteur D. Shaw R.J. Navas P. Puigserver P. Ingram D.K. de Cabo R. Sinclair D.A. Nature. 2006; 444: 337-342Crossref PubMed Scopus (3619) Google Scholar, 11Zhang Y. Lee F.Y. Barrera G. Lee H. Vales C. Gonzalez F.J. Willson T.M. Edwards P.A. Proc. Natl. Acad. Sci. U.S.A. 2006; 103: 1006-1011Crossref PubMed Scopus (696) Google Scholar), it remains largely unknown whether the expression and activity of these two proteins are coordinately regulated.MicroRNAs (miRs) are recently discovered small (21–23-nucleotide) noncoding RNAs that inhibit translation and/or destabilize target mRNAs by binding to their 3′-untranslated regions (3′-UTRs) with partial base pairing (19Hobert O. Science. 2008; 319: 1785-1786Crossref PubMed Scopus (706) Google Scholar). MiRs play important roles in cellular metabolism under normal and metabolic stress conditions (20Esau C. Davis S. Murray S.F. Yu X.X. Pandey S.K. Pear M. Watts L. Booten S.L. Graham M. McKay R. A. S. S. S. Cell Metab. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar, E. L.B. J.A. J. Science. 2007; PubMed Scopus Google Scholar), and expression of has been in such as and metabolic (20Esau C. Davis S. Murray S.F. Yu X.X. Pandey S.K. Pear M. Watts L. Booten S.L. Graham M. McKay R. A. S. S. S. Cell Metab. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar, E. L.B. J.A. J. Science. 2007; PubMed Scopus Google Scholar, M. M. C.J. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: PubMed Scopus Google Scholar, K. M. Lee G. M. M. C.J. M.A. A. J.T. Mol. Cell. 2007; Full Text Full Text PDF PubMed Scopus Google Scholar). Here, we that the FXR/SHP regulatory pathway inhibits expression of miR-34a, which results in a positive regulation of hepatic SIRT1 levels under physiological this regulatory network is in diet-induced obese mice, in elevated miR-34a levels and reduced SIRT1 levels in the in the of the molecular basis by which SIRT1 levels are regulated under normal conditions and why they are substantially reduced in metabolic disease states remains Our at in an by that the FXR/SHP pathway plays a role in controlling hepatic SIRT1 levels via miR-34a inhibition and that elevated miR-34a levels in obese mice contribute to decreased SIRT1 protein in in normal mice, hepatic miR-34a levels are regulated via a pathway the nuclear bile acid receptor FXR and an orphan nuclear receptor and transcription corepressor Activation of FXR inhibits the expression of hepatic miR-34a the of suppresses transcription of the miR-34a by inhibiting the occupancy of p53, the key activator of the miR-34a in diet-induced obese mice, the FXR/SHP pathway is that miR-34a levels are elevated, which to reduced SIRT1 protein levels. Remarkably, activation of FXR in these obese mice by with GW4064 for SIRT1 levels and decreases miR-34a levels. Edwards and (11Zhang Y. Lee F.Y. Barrera G. Lee H. Vales C. Gonzalez F.J. Willson T.M. Edwards P.A. Proc. Natl. Acad. Sci. U.S.A. 2006; 103: 1006-1011Crossref PubMed Scopus (696) Google that of diabetic obese db/db mice with GW4064 for improved metabolic by glucose and lipid levels. with these an intriguing link among FXR activation, decreased miR-34a levels, increased hepatic SIRT1 levels, and metabolic studies demonstrate that FXR regulates hepatic SIRT1 levels miR-34a Interestingly, SIRT1 may regulate hepatic FXR as PGC-1α shown to FXR activity in the regulation of metabolism fasting by expression of the FXR and also by FXR Y. C.J. Gonzalez F.J. Edwards P.A. 2004; PubMed Scopus Google Scholar). SIRT1 and PGC-1α activity (1Rodgers J.T. Lerin C. Haas W. Gygi S.P. Spiegelman B.M. Puigserver P. Nature. 2005; 434: 113-118Crossref PubMed Scopus (2524) Google Scholar, 6Rodgers J.T. Lerin C. Gerhart-Hines Z. Puigserver P. FEBS Lett. 2008; 582: 46-53Crossref PubMed Scopus (490) Google Scholar), SIRT1 FXR activity via of PGC-1α we recently that SIRT1 FXR by deacetylation of FXR Z. B. J. S. D. S. Cell Metab. Full Text Full Text PDF PubMed Scopus Google Scholar). FXR acetylation inhibits its by inhibiting of FXR with and binding Z. B. J. S. D. S. Cell Metab. Full Text Full Text PDF PubMed Scopus Google Scholar). Although FXR acetylation is dynamically by and FXR acetylation levels are elevated in mice and diet-induced obese mice Z. B. J. S. D. S. Cell Metab. Full Text Full Text PDF PubMed Scopus Google Scholar). with that an intriguing positive regulatory FXR and SIRT1 is in in normal obese mice, the FXR/SHP may be of elevated FXR acetylation levels, which results in elevated miR-34a with important roles of FXR in miR-34a and SIRT1 protein levels, levels were elevated, and SIRT1 protein levels are substantially decreased in FXR-null mice. However, it is and why activation of the nuclear bile acid receptor which the to levels of bile regulates which hepatic fasting this results of of the of regulatory in hepatic metabolism, but it may also an to the of feeding and Staels and D. B. F. N. A. Gonzalez F.J. J.C. F. Staels B. J. Biol. 2005; Full Text Full Text PDF PubMed Scopus (175) Google Scholar, B. K. D. A. E. J.C. Gonzalez F.J. F. Staels B. FEBS Lett. 2005; PubMed Scopus Google that FXR plays an important role in the feeding to fasting and were markedly in FXR-null mice. with these Auwerx and (10Coste A. Louet J.F. Lagouge M. Lerin C. Antal M.C. Meziane H. Schoonjans K. Puigserver P. O'Malley B.W. Auwerx J. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 17187-17192Crossref PubMed Scopus (153) Google that SIRT1 levels are dynamically regulated under fasting and feeding in normal mice. SIRT1 levels were increased fasting but expression in the in normal mice (10Coste A. Louet J.F. Lagouge M. Lerin C. Antal M.C. Meziane H. Schoonjans K. Puigserver P. O'Malley B.W. Auwerx J. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 17187-17192Crossref PubMed Scopus (153) Google Scholar). that under normal FXR dynamically regulates metabolic in response to fasting and feeding and FXR feeding contribute to of levels of hepatic SIRT1 via miR-34a which for an to the fasting this regulatory network is in metabolic disease in constitutively elevated miR-34a levels and reduced SIRT1 levels in the studies demonstrate that SIRT1 and inhibits p53 which results in decreased expression of miR-34a J. Nikolaev A.Y. Imai S. Chen D. Su F. Shiloh A. Guarente L. Gu W. Cell. 2001; 107: 137-148Abstract Full Text Full Text PDF PubMed Scopus (1873) Google Scholar, M. M. C.J. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: PubMed Scopus Google Scholar, M. C.J. Cell 8: PubMed Scopus Google Scholar, L. de E. Z. Y. W. L. J. D. Chen C. M.A. Nature. 2007; PubMed Scopus Google Scholar). with this regulatory we also that overexpression of SIRT1 in of diet-induced obese mice using of substantially decreased hepatic miR-34a levels for 1 with which also decreased miR-34a levels in obese mice indirectly SIRT1 by protein activation S. K. B. Y. F. K. M. R.A. M. J. Biol. 2008; Full Text Full Text PDF PubMed Scopus Google Scholar, C. Gerhart-Hines Z. J.N. Lagouge M. L. Milne J.C. Elliott P.J. Puigserver P. Auwerx J. Nature. PubMed Scopus Google Scholar), the that is in a be However, the SIRT1 expression with the the of the regulatory miR-34a and SIRT1 in in which SIRT1 inhibits expression of its miR-34a, SIRT1 are as important cellular critically involved in diverse including metabolic and (19Hobert O. Science. 2008; 319: 1785-1786Crossref PubMed Scopus (706) Google Scholar, L. de E. Z. Y. W. L. J. D. Chen C. M.A. Nature. 2007; PubMed Scopus Google Scholar). of genes are to be regulated by and elevated levels of been in diverse conditions (20Esau C. Davis S. Murray S.F. Yu X.X. Pandey S.K. Pear M. Watts L. Booten S.L. Graham M. McKay R. A. S. S. S. Cell Metab. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar, E. L.B. J.A. J. Science. 2007; PubMed Scopus Google Scholar). Recent in studies that may by in disease conditions (20Esau C. Davis S. Murray S.F. Yu X.X. Pandey S.K. Pear M. Watts L. Booten S.L. Graham M. McKay R. A. S. S. S. Cell Metab. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar, J. S. R. K.G. J. M. M. 2007; PubMed Scopus Google Scholar). It be important to whether of elevated miR-34a in obese mouse using hepatic SIRT1 levels and metabolic outcomes in these mice. of SIRT1 levels by of the may a target for treating such as metabolic and cancer, in which SIRT1 plays an important IntroductionThe NAD+-dependent Sirtuin 1 (SIRT1) 3The abbreviations used are: SIRT1Sirtuin 1PGC-1αperoxisome proliferator-activated receptor γ coactivator αFXRfarnesoid X receptorSHPsmall heterodimer partnermiRmicroRNA3′-UTR3′-untranslated regionHNF-4hepatic nuclear factor 4qRT-PCRreverse transcription-quantitative PCRAdadenovirusChIPchromatin immunoprecipitationGSTglutathione S-transferaseCoIPcoimmunoprecipitationsiRNAsmall interfering RNAlucluciferaseWDwestern style diet. deacetylase plays a critical role in cellular metabolism, the stress response, and possibly aging, by modulating the activity of its target proteins via protein deacetylation (1Rodgers J.T. Lerin C. Haas W. Gygi S.P. Spiegelman B.M. Puigserver P. Nature. 2005; 434: 113-118Crossref PubMed Scopus (2524) Google Scholar, 2Motta M.C. Divecha N. Lemieux M. Kamel C. Chen D. Gu W. Bultsma Y. McBurney M. Guarente L. Cell. 2004; 116: 551-563Abstract Full Text Full Text PDF PubMed Scopus (1184) Google Scholar, 3Luo J. Nikolaev A.Y. Imai S. Chen D. Su F. Shiloh A. Guarente L. Gu W. Cell. 2001; 107: 137-148Abstract Full Text Full Text PDF PubMed Scopus (1873) Google Scholar, 4Guarente L. Cold Spring Harb. Symp. Quant. Biol. 2007; 72: 483-488Crossref PubMed Scopus (285) Google Scholar). Recent studies demonstrate that SIRT1 plays an important role in maintaining metabolic homeostasis in response to hormonal and nutritional fluctuations by modulating the activity of PGC-1α, a master metabolic regulator (5Rodgers J.T. Puigserver P. Proc. Natl. Acad. Sci. U.S.A. 2007; 104: 12861-12866Crossref PubMed Scopus (444) Google Scholar, 6Rodgers J.T. Lerin C. Gerhart-Hines Z. Puigserver P. FEBS Lett. 2008; 582: 46-53Crossref PubMed Scopus (490) Google Scholar). During nutritional deprivation, SIRT1 promotes fat mobilization and suppresses adipogenesis and regulates hepatic glucose and lipid metabolism by activating key metabolic regulators, including PGC-1α (5Rodgers J.T. Puigserver P. Proc. Natl. Acad. Sci. U.S.A. 2007; 104: 12861-12866Crossref PubMed Scopus (444) Google Scholar, 6Rodgers J.T. Lerin C. Gerhart-Hines Z. Puigserver P. FEBS Lett. 2008; 582: 46-53Crossref PubMed Scopus (490) Google Scholar). Activation of SIRT1 by natural or synthetic SIRT1 activators reduced acetylation levels of PGC-1α and protected against diet-induced obesity and insulin resistance by promoting mitochondrial function (7Lagouge M. Argmann C. Gerhart-Hines Z. Meziane H. Lerin C. Daussin F. Messadeq N. Milne J. Lambert P. Elliott P. Geny B. Laakso M. Puigserver P. Auwerx J. Cell. 2006; 127: 1109-1122Abstract Full Text Full Text PDF PubMed Scopus (3267) Google Scholar, 8Baur J.A. Pearson K.J. Price N.L. Jamieson H.A. Lerin C. Kalra A. Prabhu V.V. Allard J.S. Lopez-Lluch G. Lewis K. Pistell P.J. Poosala S. Becker K.G. Boss O. Gwinn D. Wang M. Ramaswamy S. Fishbein K.W. Spencer R.G. Lakatta E.G. Le Couteur D. Shaw R.J. Navas P. Puigserver P. Ingram D.K. de Cabo R. Sinclair D.A. Nature. 2006; 444: 337-342Crossref PubMed Scopus (3619) Google Scholar, 9Feige J.N. Lagouge M. Canto C. Strehle A. Houten S.M. Milne J.C. Lambert P.D. Mataki C. Elliott P.J. Auwerx J. Cell Metab. 2008; 8: 347-358Abstract Full Text Full Text PDF PubMed Scopus (608) Google Scholar). SIRT1 levels are dynamically regulated in response to fasting and feeding under physiological conditions but markedly reduced in diet-induced obese mice (10Coste A. Louet J.F. Lagouge M. Lerin C. Antal M.C. Meziane H. Schoonjans K. Puigserver P. O'Malley B.W. Auwerx J. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 17187-17192Crossref PubMed Scopus (153) Google Scholar). However, the molecular basis by which SIRT1 levels are regulated under normal conditions and why they are substantially reduced in metabolic disease states remains largely unknown.The nuclear receptor, farnesoid X receptor (FXR), is the primary biosensor for endogenous bile acids and regulates expression of numerous genes involved in lipid and glucose metabolism (11Zhang Y. Lee F.Y. Barrera G. Lee H. Vales C. Gonzalez F.J. Willson T.M. Edwards P.A. Proc. Natl. Acad. Sci. U.S.A. 2006; 103: 1006-1011Crossref PubMed Scopus (696) Google Scholar, 12Sinal C.J. Tohkin M. Miyata M. Ward J.M. Lambert G. Gonzalez F.J. Cell. 2000; 102: 731-744Abstract Full Text Full Text PDF PubMed Scopus (1378) Google Scholar, 13Lee F.Y. Lee H. Hubbert M.L. Edwards P.A. Zhang Y. Trends Biochem. Sci. 2006; 31: 572-580Abstract Full Text Full Text PDF PubMed Scopus (274) Google Scholar, 14Fiorucci S. Rizzo G. Donini A. Distrutti E. Santucci L. Trends Mol. Med. 2007; 13: 298-309Abstract Full Text Full Text PDF PubMed Scopus (175) Google Scholar, 15Cariou B. Staels B. Trends Pharmacol. Sci. 2007; 28: 236-243Abstract Full Text Full Text PDF PubMed Scopus (118) Google Scholar). FXR indirectly inhibits its metabolic target genes by inducing the expression of small heterodimer partner (SHP), an orphan nuclear receptor and transcriptional corepressor (16Lu T.T. Makishima M. Repa J.J. Schoonjans K. Kerr T.A. Auwerx J. Mangelsdorf D.J. Mol. Cell. 2000; 6: 507-515Abstract Full Text Full Text PDF PubMed Scopus (1208) Google Scholar, 17Goodwin B. Jones S.A. Price R.R. Watson M.A. McKee D.D. Moore L.B. Galardi C. Wilson J.G. Lewis M.C. Roth M.E. Maloney P.R. Willson T.M. Kliewer S.A. Mol Cell. 2000; 6: 517-526Abstract Full Text Full Text PDF PubMed Scopus (1471) Google Scholar). It is well established that the FXR/SHP pathway plays an important role in maintaining bile acid and cholesterol levels by inhibiting the transcription of cholesterol cytochrome P450 7A1 hydroxylase, a key enzyme in hepatic bile acid biosynthesis (16Lu T.T. Makishima M. Repa J.J. Schoonjans K. Kerr T.A. Auwerx J. Mangelsdorf D.J. Mol. Cell. 2000; 6: 507-515Abstract Full Text Full Text PDF PubMed Scopus (1208) Google Scholar, 17Goodwin B. Jones S.A. Price R.R. Watson M.A. McKee D.D. Moore L.B. Galardi C. Wilson J.G. Lewis M.C. Roth M.E. Maloney P.R. Willson T.M. Kliewer S.A. Mol Cell. 2000; 6: 517-526Abstract Full Text Full Text PDF PubMed Scopus (1471) Google Scholar), and has been also shown to regulate fatty acid metabolism (18Watanabe M. Houten S.M. Wang L. Moschetta A. Mangelsdorf D.J. Heyman R.A. Moore D.D. Auwerx J. J. Clin. Invest. 2004; 113: 1408-1418Crossref PubMed Scopus (939) Google Scholar). Interestingly, FXR activation by the synthetic agonist, GW4064, or hepatic overexpression of constitutively active FXR using adenoviral delivery significantly improved hyperglycemia and hyperlipidemia in diabetic obese db/db mice (11Zhang Y. Lee F.Y. Barrera G. Lee H. Vales C. Gonzalez F.J. Willson T.M. Edwards P.A. Proc. Natl. Acad. Sci. U.S.A. 2006; 103: 1006-1011Crossref PubMed Scopus (696) Google Scholar). Although both SIRT1 and FXR are critical for hepatic metabolism and activation of both proteins improves metabolic outcomes (7Lagouge M. Argmann C. Gerhart-Hines Z. Meziane H. Lerin C. Daussin F. Messadeq N. Milne J. Lambert P. Elliott P. Geny B. Laakso M. Puigserver P. Auwerx J. Cell. 2006; 127: 1109-1122Abstract Full Text Full Text PDF PubMed Scopus (3267) Google Scholar, 8Baur J.A. Pearson K.J. Price N.L. Jamieson H.A. Lerin C. Kalra A. Prabhu V.V. Allard J.S. Lopez-Lluch G. Lewis K. Pistell P.J. Poosala S. Becker K.G. Boss O. Gwinn D. Wang M. Ramaswamy S. Fishbein K.W. Spencer R.G. Lakatta E.G. Le Couteur D. Shaw R.J. Navas P. Puigserver P. Ingram D.K. de Cabo R. Sinclair D.A. Nature. 2006; 444: 337-342Crossref PubMed Scopus (3619) Google Scholar, 11Zhang Y. Lee F.Y. Barrera G. Lee H. Vales C. Gonzalez F.J. Willson T.M. Edwards P.A. Proc. Natl. Acad. Sci. U.S.A. 2006; 103: 1006-1011Crossref PubMed Scopus (696) Google Scholar), it remains largely unknown whether the expression and activity of these two proteins are coordinately regulated.MicroRNAs (miRs) are recently discovered small (21–23-nucleotide) noncoding RNAs that inhibit translation and/or destabilize target mRNAs by binding to their 3′-untranslated regions (3′-UTRs) with partial base pairing (19Hobert O. Science. 2008; 319: 1785-1786Crossref PubMed Scopus (706) Google Scholar). MiRs play important roles in cellular metabolism under normal and metabolic stress conditions (20Esau C. Davis S. Murray S.F. Yu X.X. Pandey S.K. Pear M. Watts L. Booten S.L. Graham M. McKay R. A. S. S. S. 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