title: Action of metformin on the insulin-signaling pathway and on glucose transport in human granulosa cells.
abstract: BACKGROUND
  Hyperinsulinemia in polycystic ovary syndrome is widely treated with the insulin sensitizer metformin, which, in addition to its systemic effects, directly affects the ovarian insulin-stimulated steroidogenesis pathway.
  
  
  OBJECTIVE
  Our aim was to investigate the interaction of metformin with the other insulin-stimulated ovarian pathway, namely that leading to glucose uptake.
  
  
  METHODS
  Human granulosa-luteal cells were cultured with metformin (10(-7) M), insulin (10 ng/ml) or metformin and insulin (met + ins) combined. Insulin receptor (IR) involvement was assessed by culture with an (anti)-insulin receptor (IR) antibody.
  
  
  METHODS
  The effect of metformin on insulin-receptor substrate proteins 1 and 2 (IRS-1 and -2) mRNA and protein expression was determined. The KGN granulosa-cell line was used to investigate the effect of insulin and metformin on Akt activation and glucose transporter-4 (Glut-4) expression. Glut-4 translocation from the cytosol to the membrane was determined in cytoplasmic and membrane-enriched fractions of protein lysates.
  
  
  RESULTS
  IRS-1 mRNA and protein increased with all treatments. In contrast, basal IRS-2 mRNA levels were barely detectable, but transcription was up-regulated by metformin. The anti-IR antibody reduced treatment-stimulated IRS-1 to basal levels and IRS-2 expression to an even greater extent than IRS-1, showing greater dependence on the IR than IRS-1. Metformin in the presence of insulin activated Akt and this was dependent on phosphoinositide-3 kinase, as was translocation of Glut-4 to the membrane. Metformin was able to substantially enhance the insulin-stimulated translocation of Glut-4 transporters from the cytosol to the membrane.
  
  
  CONCLUSIONS
  This net increase in Glut-4 transporters in the plasma membrane has the potential to increase glucose uptake and metabolism by granulosa cells of the insulin-resistant polycystic ovary, thereby facilitating follicle growth.
authors.affiliation: Division of Basic Medical Sciences, St. George's University of London, Cranmer Terrace, Tooting, London, SW17 0RE United Kingdom. srice@sgul.ac.uk
authors.forename: Suman
authors.initials: S
authors.lastname: Rice
authors.forename: Laura Jane
authors.initials: LJ
authors.lastname: Pellatt
authors.forename: Stacey Joanna
authors.initials: SJ
authors.lastname: Bryan
authors.forename: Saffron Ann
authors.initials: SA
authors.lastname: Whitehead
authors.forename: Helen Diane
authors.initials: HD
authors.lastname: Mason
mesh_terms: D001693:Biological Transport, Active / Q000187:drug effects; D015153:Blotting, Western; D002460:Cell Line; D004789:Enzyme Activation; D005260:Female; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D008687:Metformin / Q000494:pharmacology*; D051058:Oncogene Protein v-akt / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D021381:Protein Transport; D012313:RNA / Q000096:biosynthesis / Q000302:isolation & purification; D011956:Receptors, Cell Surface / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D011956:Receptors, Cell Surface; D012313:RNA; D008687:Metformin; D019869:Phosphatidylinositol 3-Kinases; D051058:Oncogene Protein v-akt; D005947:Glucose