title: Metformin opposes impaired AMPK and SIRT1 function and deleterious changes in core clock protein expression in white adipose tissue of genetically-obese db/db mice.
abstract: OBJECTIVE
  AMPK activates SIRT1 in liver and skeletal muscle. Impaired circadian function is associated with development of obesity. SIRT1 regulates circadian function and is suppressed in white adipose tissue (WAT) of obese patients. We examined the potential role of AMPK and SIRT1 in regulation of circadian components in WAT of obese db/db mice and in mice fed a high-fat diet (HFD), and investigated whether metformin-mediated activation of AMPK opposed any deleterious changes in the WAT clock mechanism.
  
  
  METHODS
  db/+ and db/db mice were administered metformin (250 mg/kg/day; 7 days). Separately, mice were fed HFD for 16-weeks. 3T3-L1 adipocytes were incubated with metformin, EX527 or FK866, inhibitors of SIRT1 and NAMPT, respectively. Gene and protein expression were measured by qRT-PCR and immunoblotting.
  
  
  RESULTS
  AMPK activity, NAMPT expression and SIRT1 expression were decreased in WAT of db/db and HFD mice, in association with suppressed expression of the core circadian components CLOCK and BMAL1. Expression of Pparγ and the adipogenic repressors Irf3 and Irf4 were also suppressed. Metformin increased AMPK activity in WAT of db/db mice and in metformin-treated adipocytes, with increased NAMPT, SIRT1 and circadian component expression. Metformin-mediated induction of Clock mRNA in adipocytes was blocked by inhibition of NAMPT and SIRT1.
  
  
  CONCLUSIONS
  Decreased AMPK-SIRT1 signalling in db/db and HFD mice impacts WAT circadian function causing dysregulated lipid regulation, favouring an obese phenotype. Metformin mediates a phenotypic shift away from lipid accretion through AMPK-NAMPT-SIRT1 mediated changes in clock components, supporting chronotherapeutic treatment approaches for obesity.
authors: Centre for Diabetes, Blizard Institute, Bart's and the London School of Medicine and Dentistry, Queen Mary University of London, London, UK.
authors: P W
authors: PW
authors: Caton
authors: J
authors: J
authors: Kieswich
authors: M M
authors: MM
authors: Yaqoob
authors: M J
authors: MJ
authors: Holness
authors: M C
authors: MC
authors: Sugden
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D052436:Adipose Tissue, White / Q000187:drug effects / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D001786:Blood Glucose / Q000187:drug effects; D056926:CLOCK Proteins / Q000378:metabolism*; D016207:Cytokines; D059305:Diet, High-Fat; D004195:Disease Models, Animal; D005786:Gene Expression Regulation; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D054409:Nicotinamide Phosphoribosyltransferase; D009765:Obesity / Q000097:blood / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D056564:Sirtuin 1 / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D016207:Cytokines; D007004:Hypoglycemic Agents; D008687:Metformin; D056926:CLOCK Proteins; C538944:Clock protein, mouse; D054409:Nicotinamide Phosphoribosyltransferase; C495867:nicotinamide phosphoribosyltransferase, mouse; D055372:AMP-Activated Protein Kinases; C470545:Sirt1 protein, mouse; D056564:Sirtuin 1