title: Tubular injury in a rat model of type 2 diabetes is prevented by metformin: a possible role of HIF-1α expression and oxygen metabolism.
abstract: OBJECTIVE
  Chronic hypoxia has been recognized as a key regulator in renal tubulointerstitial fibrosis, as seen in diabetic nephropathy, which is associated with the activation of hypoxia-inducible factor (HIF)-1α. We assess here the effects of the biguanide, metformin, on the expression of HIF-1α in diabetic nephropathy using renal proximal tubular cells and type 2 diabetic rats.
  
  
  METHODS
  We explored the effects of metformin on the expression of HIF-1α using human renal proximal tubular epithelial cells (HRPTECs). Male Zucker diabetic fatty (ZDF; Gmi-fa/fa) rats were treated from 9 to 39 weeks with metformin (250 mg ⋅ kg(-1) ⋅ day(-1)) or insulin.
  
  
  RESULTS
  Metformin inhibited hypoxia-induced HIF-1α accumulation and the expression of HIF-1-targeted genes in HRPTECs. Although metformin activated the downstream pathways of AMP-activated protein kinase (AMPK), neither the AMPK activator, AICAR, nor the mTOR inhibitor, rapamycin, suppressed hypoxia-induced HIF-1α expression. In addition, knockdown of AMPK-α did not abolish the inhibitory effects of metformin on HIF-1α expression. The proteasome inhibitor, MG-132, completely eradicated the suppression of hypoxia-induced HIF-1α accumulation by metformin. The inhibitors of mitochondrial respiration similarly suppressed hypoxia-induced HIF-1α expression. Metformin significantly decreased ATP production and oxygen consumption rates, which subsequently led to increased cellular oxygen tension. Finally, metformin, but not insulin, attenuated tubular HIF-1α expression and pimonidazole staining and ameliorated tubular injury in ZDF rats.
  
  
  CONCLUSIONS
  Our data suggest that hypoxia-induced HIF-1α accumulation in diabetic nephropathy could be suppressed by the antidiabetes drug, metformin, through the repression of oxygen consumption.
authors.affiliation: Division of Metabolism and Biosystemic Science, Department of Medicine, Asahikawa Medical University, Asahikawa, Japan. taka0716@asahikawa-med.ac.jp
authors.forename: Yumi
authors.initials: Y
authors.lastname: Takiyama
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Harumi
authors.forename: Jun
authors.initials: J
authors.lastname: Watanabe
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Fujita
authors.forename: Jun
authors.initials: J
authors.lastname: Honjo
authors.forename: Norihiko
authors.initials: N
authors.lastname: Shimizu
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Makino
authors.forename: Masakazu
authors.initials: M
authors.lastname: Haneda
mesh_terms: D000263:Adenylate Kinase / Q000235:genetics / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D002460:Cell Line; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D003928:Diabetic Nephropathies / Q000235:genetics / Q000378:metabolism / Q000517:prevention & control*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D007150:Immunohistochemistry; D007328:Insulin / Q000494:pharmacology / Q000627:therapeutic use; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D007976:Leupeptins / Q000494:pharmacology; D008297:Male; D008687:Metformin / Q000494:pharmacology / Q000627:therapeutic use*; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011924:Rats, Zucker; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
chemical_list: D015853:Cysteine Proteinase Inhibitors; C497444:Hif1a protein, rat; D007004:Hypoglycemic Agents; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007328:Insulin; D007976:Leupeptins; D008687:Metformin; D000263:Adenylate Kinase; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde