title: Metformin modulates hyperglycaemia-induced endothelial senescence and apoptosis through SIRT1.
abstract: OBJECTIVE
  Endothelial dysfunction can be detected at an early stage in the development of diabetes-related microvascular disease and is associated with accelerated endothelial senescence and ageing. Hyperglycaemia-induced oxidative stress is a major contributing factor to the development of endothelial dysfunction. Clinical data indicate that the hypoglycaemic agent, metformin, has an endothelial protective action; however, its molecular and cellular mechanisms remain elusive. In the present study, we have investigated the protective effect of metformin during hyperglycaemia-induced senescence in mouse microvascular endothelial cells (MMECs).
  
  
  METHODS
  MMECs were cultured in normal glucose (11 mM) and high glucose (HG; 40 mM) in the presence and absence of metformin (50 μM) for 72 h. The expression of sirtuin-1 (SIRT1) and senescence/apoptosis-associated markers was determined by immunoblotting and immunocyto techniques. SIRT1 expression was inhibited with appropriate siRNA.
  
  
  RESULTS
  Exposure of MMECs to HG significantly reduced SIRT1 protein expression, increased forkhead box O1 (FoxO-1) and p53 acetylation, increased p21 and decreased Bcl2 expression. In addition, senescence-associated β-galactosidase activity in MMECs was increased in HG. Treatment with metformin attenuated the HG-induced reduction of SIRT1 expression, modulated the SIRT1 downstream targets FoxO-1 and p53/p21, and protected endothelial cells from HG-induced premature senescence. However, following gene knockdown of SIRT1 the effects of metformin were lost.
  
  
  CONCLUSIONS
  HG-induced down-regulation of SIRT1 played a crucial role in diabetes-induced endothelial senescence. Furthermore, the protective effect of metformin against HG-induced endothelial dysfunction was partly due to its effects on SIRT1 expression and/or activity.
authors.affiliation: Department of Pharmacology, Weill Cornell Medical College in Qatar, Doha, Qatar.
authors.forename: Gnanapragasam
authors.initials: G
authors.lastname: Arunachalam
authors.forename: Samson Mathews
authors.initials: SM
authors.lastname: Samuel
authors.forename: Isra
authors.initials: I
authors.lastname: Marei
authors.forename: Hong
authors.initials: H
authors.lastname: Ding
authors.forename: Chris R
authors.initials: CR
authors.lastname: Triggle
mesh_terms: D000107:Acetylation; D000263:Adenylate Kinase / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002196:Capillaries / Q000166:cytology / Q000187:drug effects; D016922:Cellular Senescence / Q000187:drug effects*; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects*; D005455:Fluorescent Antibody Technique; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000378:metabolism; D020868:Gene Silencing; D006943:Hyperglycemia / Q000503:physiopathology*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D056564:Sirtuin 1 / Q000235:genetics / Q000502:physiology*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C467200:Foxo1 protein, mouse; D007004:Hypoglycemic Agents; D017382:Reactive Oxygen Species; D008687:Metformin; D000263:Adenylate Kinase; D001616:beta-Galactosidase; C470545:Sirt1 protein, mouse; D056564:Sirtuin 1
keywords: FoxO-1; endothelial dysfunction; forkhead box O1 transcription factor; hyperglycaemia; metformin; microvascular endothelial cells; reactive oxygen species; sirtuin1; vascular senescence