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.

RESEARCH DESIGN AND 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: Yumi Takiyama, Tatsuo Harumi, Jun Watanabe, Yukihiro Fujita, Jun Honjo, Norihiko Shimizu, Yuichi Makino, Masakazu Haneda
• Journal: Diabetes (Diabetes) Vol. 60 Issue 3 Pg. 981-92 (Mar 2011) ISSN: 1939-327X [Electronic] United States
• PMID: 21282369 (Publication Type: Journal Article)

Chemical References

• Cysteine Proteinase Inhibitors
• Hif1a protein, rat
• Hypoglycemic Agents
• Hypoxia-Inducible Factor 1, alpha Subunit
• Insulin
• Leupeptins
• Metformin
• Adenylate Kinase
• benzyloxycarbonylleucyl-leucyl-leucine aldehyde

Topics

• Adenylate Kinase (genetics, metabolism)
• Analysis of Variance
• Animals
• Cell Line
• Cysteine Proteinase Inhibitors (pharmacology)
• Diabetes Mellitus, Type 2 (drug therapy, genetics, metabolism)
• Diabetic Nephropathies (genetics, metabolism, prevention & control)
• Epithelial Cells (drug effects, metabolism)
• Humans
• Hypoglycemic Agents (pharmacology, therapeutic use)
• Hypoxia-Inducible Factor 1, alpha Subunit (genetics, metabolism)
• Immunohistochemistry
• Insulin (pharmacology, therapeutic use)
• Kidney Tubules, Proximal (drug effects, metabolism)
• Leupeptins (pharmacology)
• Male
• Metformin (pharmacology, therapeutic use)
• Oxygen Consumption (drug effects, physiology)
• Rats
• Rats, Zucker
• Reverse Transcriptase Polymerase Chain Reaction
• Signal Transduction (drug effects, physiology)