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Published online July 3, 2008
Diabetes 57:2626-2636, 2008
DOI: 10.2337/db07-1579
© 2008 by the American Diabetes Association
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Mechanism of Oxidative DNA Damage in Diabetes

Tuberin Inactivation and Downregulation of DNA Repair Enzyme 8-Oxo-7,8-Dihydro-2'-Deoxyguanosine-DNA Glycosylase

Simona Simone1,2, Yves Gorin1, Chakradhar Velagapudi1, Hanna E. Abboud1,3, and Samy L. Habib1,3

1 George O'Brien Kidney Research Center, Department of Medicine, Division of Nephrology, University of Texas Health Science Center, San Antonio, Texas
2 Department of Emergency and Transplantation, University of Bari, Policlinico, Bari, Italy
3 South Texas Veterans Healthcare System, Geriatric Research, Education, and Clinical Center, San Antonio, Texas

Corresponding author: Samy L. Habib, habib{at}uthscsa.edu

OBJECTIVE—To investigate potential mechanisms of oxidative DNA damage in a rat model of type 1 diabetes and in murine proximal tubular epithelial cells and primary culture of rat proximal tubular epithelial cells.

RESEARCH DESIGN AND METHODS—Phosphorylation of Akt and tuberin, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) levels, and 8-oxoG-DNA glycosylase (OGG1) expression were measured in kidney cortical tissue of control and type 1 diabetic animals and in proximal tubular cells incubated with normal or high glucose.

RESULTS—In the renal cortex of diabetic rats, the increase in Akt phosphorylation is associated with enhanced phosphorylation of tuberin, decreased OGG1 protein expression, and 8-oxodG accumulation. Exposure of proximal tubular epithelial cells to high glucose causes a rapid increase in reactive oxygen species (ROS) generation that correlates with the increase in Akt and tuberin phosphorylation. High glucose also resulted in downregulation of OGG1 protein expression, paralleling its effect on Akt and tuberin. Inhibition of phosphatidylinositol 3-kinase/Akt significantly reduced high glucose–induced tuberin phosphorylation and restored OGG1 expression. Hydrogen peroxide stimulates Akt and tuberin phosphorylation and decreases OGG1 protein expression. The antioxidant N-acetylcysteine significantly inhibited ROS generation, Akt/protein kinase B, and tuberin phosphorylation and resulted in deceased 8-oxodG accumulation and upregulation of OGG1 protein expression.

CONCLUSIONS—Hyperglycemia in type 1 diabetes and treatment of proximal tubular epithelial cells with high glucose leads to phosphorylation/inactivation of tuberin and downregulation of OGG1 via a redox-dependent activation of Akt in renal tubular epithelial cells. This signaling cascade provides a mechanism of oxidative stress–mediated DNA damage in diabetes.


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