title: Metformin reduces hepatic expression of SIRT3, the mitochondrial deacetylase controlling energy metabolism.
abstract: Metformin inhibits ATP production in mitochondria and this may be involved in the anti-hyperglycemic effects of the drug. Sirtuin 3 (SIRT3) is a mitochondrial protein deacetylase that regulates the function of the electron transport chain and maintains basal ATP yield. We hypothesized that metformin treatment could diminish mitochondrial ATP production through downregulation of SIRT3 expression. Glucagon and cAMP induced SIRT3 mRNA in mouse primary hepatocytes. Metformin prevented SIRT3 induction by glucagon. Moreover, metformin downregulated constitutive expression of SIRT3 in primary hepatocytes and in the liver in vivo. Estrogen related receptor alpha (ERRα) mediates regulation of Sirt3 gene by peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). ERRα mRNA expression was regulated in a similar manner as SIRT3 mRNA by glucagon, cAMP and metformin. However, a higher metformin concentration was required for downregulation of ERRα than SIRT3. ERRα siRNA attenuated PGC-1α mediated induction of SIRT3, but did not affect constitutive expression. Overexpression of the constitutively active form of AMP-activated protein kinase (AMPK) induced SIRT3 mRNA, indicating that the SIRT3 downregulation by metformin is not mediated by AMPK. Metformin reduced the hepatocyte ATP level. This effect was partially counteracted by SIRT3 overexpression. Furthermore, metformin decreased mitochondrial SIRT3 protein levels and this was associated with enhanced acetylation of several mitochondrial proteins. However, metformin increased mitochondrial mass in hepatocytes. Altogether, our results indicate that metformin attenuates mitochondrial expression of SIRT3 and suggest that this mechanism is involved in regulation of energy metabolism by metformin in the liver and may contribute to the therapeutic action of metformin.
authors.affiliation: Department of Pharmacology and Toxicology, Institute of Biomedicine, University of Oulu, Oulu, Finland.
authors.forename: Marcin
authors.initials: M
authors.lastname: Buler
authors.forename: Sanna-Mari
authors.initials: SM
authors.lastname: Aatsinki
authors.forename: Valerio
authors.initials: V
authors.lastname: Izzi
authors.forename: Jukka
authors.initials: J
authors.lastname: Hakkola
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D017931:DNA Primers / Q000235:genetics; D004272:DNA, Mitochondrial / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects*; D005260:Female; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000187:drug effects*; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D008856:Microscopy, Fluorescence; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D011960:Receptors, Estrogen / Q000378:metabolism; D056566:Sirtuin 3 / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors; D000097983:ERRalpha Estrogen-Related Receptor
chemical_list: D000255:Adenosine Triphosphate; D017931:DNA Primers; D004272:DNA, Mitochondrial; D008687:Metformin; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D034741:RNA, Small Interfering; D011960:Receptors, Estrogen; D056566:Sirtuin 3; D015534:Trans-Activators; D014157:Transcription Factors; D000097983:ERRalpha Estrogen-Related Receptor; C485290:Ppargc1a protein, mouse; C525046:Sirt3 protein, mouse